İSTANBUL TECHNICAL UNIVERSITY  INSTITUTE OF SCIENCE AND TECHNOLOGY DETERMINATION OF RESERVOIR ROCK WETTABILITY BY THIN LAYER WICKING APPROACH MSc. Thesis by Fatma Bahar ÖZTORUN, B.S. Department: PETROLEUM AND NATURAL GAS ENGINEERING Programme: PETROLEUM AND NATURAL GAS ENGINEERING JUNE 2006 İSTANBUL TECHNICAL UNIVERSITY  INSTITUTE OF SCIENCE AND TECHNOLOGY DETERMINATION OF RESERVOIR ROCK WETTABILITY BY THIN LAYER WICKING APPROACH MSc. Thesis by Fatma Bahar ÖZTORUN, B.S. Department: PETROLEUM AND NATURAL GAS ENGINEERING Programme: PETROLEUM AND NATURAL GAS ENGINEERING Supervisor : Assistant Pr of. Dr. H. Özgür YILDIZ Co-advisor : Assoc. Prof. Dr. Ayhan Ali S İRKECİ Member of jury : Prof. Dr. Mustafa ONUR Member of jury : Assistant Prof. Dr. Şenol YAMANLAR Member of jury : Prof. Dr. Mehmet Sabri ÇEL İK JUNE 2006 ii ACKNOWLEDGEMENTS I would like to express my deep thanks to my supervisor Assistant Prof. Dr. H. Özgür Yıldız, for his advice, encouragement, kindness, patience, and thoughtfulness throughout the research and also in my academic life. I am profoundly indebted to my co-advisor Assoc. Prof. Dr. Ayhan A. Sirkeci for his steady support and motivation in writing this thesis. I am also thankful to my committee member Prof. Dr. Mehmet Sabri Çelik for his valuable advices and his warm support in this work. Special thanks are also due to my other committee members, Prof. Dr. Mustafa Onur and Assistant Prof. Dr. Şenol Yamanlar for their advice, suggestions, and valuable comments. Thanks to my office-mate Melih Gökmen and Rüstem Tajibaev who contributed greatly in accomplishing the experimental part of this project. Especially, I would like to express my gratitude to Mustafa Çınar, for his support during the experiments, and to Fatih Can for his motivating discussion on the subject. I would like to thank all the faculty members and my colleagues in the Department of Petroleum and Natural Gas Engineering at Istanbul Technical University for their assistances in every possible way. My heartfelt thanks to my family who have been of constant support, courage, and love all through my life. Finally, this thesis is dedicated to my parents and my beloved fiancé Can K. Hoşgör. June 2006 Fatma Bahar Öztorun iii TABLE OF CONTENTS LIST OF TABLES vi LIST OF FIGURES vii LIST OF SYMBOLS AND ABBREVATIONS x ÖZET xii SUMMARY xiii 1. INTRODUCTION 1 2. LITERATURE REVIEW 6 2 . 1 . Interf a c i a l Tensio n 6 2.2. Contact Angle 6 2.2.1. Contac t angle mea sur e me n t in liquid s 9 2.2.2. Contac t angle on hetero ge n e ou s surfa c e s - Cassi e ’ s equat i o n 10 2.2.3. Limita t i o n s of contac t angle measur e me n t s 10 2.2.3.1. Hysteresis 10 2.2.3.2. Spreading pressure 11 2.3. Theory of wetting 12 2.3.1. Types of wetting 16 2.3.1.1. Adhesive wetting-the Young- Dupré equa tion 16 2.3.1.2 . Equili br i u m and non-eq u i l i br i u m work of adhesi o n - work of 56 spreading 17 2.3.1.3. Imme rsion 18 2.4. Capillary pressure 19 2.4.1. Capillar y rise and Washburn equation 20 2.4.2. Thin Layer Wickin g 22 2.5. Surfac e Free Energy 23 2.5.1. Zisma n metho d (Crit i c a l surface tension) 25 2.5.2. Fowkes method (Geome t r i c mean) 25 2.5.3. Wu method (Harmo n i c mean) 26 2.5.4. Van Oss (Acid Base) method 26 2.2.3.1. Oss-Chaudary-Good equation 26 iv 3. EXPERIMENTAL 29 3 . 1 . Materia l s 29 3.1.1. Solid samples 29 3.1.2. Liquids 30 3.2. Pre-studies 32 3.2.1. Prepar a t i o n of powdere d sample s 32 3.2.2. Surfac e tensio n me asur e me n t s 32 2.3.3. Liquid viscos i t y measur e me n t s 34 3.3. Equipment 36 3.3.1. Glass slide 36 3.3.2. Wicking apparatus 36 3.3.3. Stopwatch 37 3.3.4. Goniome t e r 38 3.4. Procedure 38 3.4.1. Contac t angle mea sur e me n t s on powdere d surfac e 38 3.4.1.1. Preparat i o n of coated sample 38 3.4.1.2. Wicking experime n t 39 3.4.1.3. Determin a t i o n of effectiv e pore radius 40 3.4.1.4 . Contact angle measure me n t 41 3.4.2. Contac t angle mea sur e me n t s on flat surface 41 3.4.2.1 . Goniome t r i c me asure me n t s 41 3.4.3. Determi n a t i o n of the surface energy comp one n t s 42 3.5. The procedur e for calculat i o n 43 3.5.1. Contact angle calculations 43 3.5.1.1. Vapor-li q u i d- s o l i d interfac e 43 3.5.1.2. Liquid-l i q u i d - s o l i d interfac e 47 3.5.1.3. Alterna t i v e determi n a t i o n of r* and its effect on contact angle measureme n t s 48 3.5.2. Surfac e free energy calcul a t i ons 49 4. EVALUATION OF EXPERIMENTAL RESULTS 52 4 . 1 . The result s of Thin Layer Wickin g experi me n t s 52 4.1.1. The results for quartz 52 4.1.2. The results for glass 54 2.2.3. The results for Berea sandston e 56 2.3.1. The results for Benthei m sandsto n e 58 v 2.4.1. The results for calcite 60 2.4.2. The results for carbona t e rock sample 536 62 2.5.1. The results for carbona t e rock sample 703 64 4.2. The compori s o n of the standar d liquid s 66 4.3. The result s of the surfac e free energy compo n e n t s 67 5. CONCLUSIONS 68 6. RECOMMENDATIONS 69 REFERENCES 70 APPENDIX 74 CIRRICULUM VITAE 77 vi LIST OF TABLES Page Number Table 3.1. P hys i c a l prop er t i e s of dis t i ll ed wate r and 2%Na Cl sol uti on ………… 30 Table 3.2. Th e prop ert ie s of hydro ca r bon s ………… …… …… …… …… …… … 30 Table 3.3. P r o p e r t i e s of chemi ca l s used in the exper i men t s ………… …… …… .. 31 Table 3.4. Val ues of surface tension compo nen ts (in mJ/m 2 ) and the viscos i t i e s (in poi se) of the liqui ds used in wickin g experi me nt s ……………… . 31 Table 3.5. Th e vi sc osi ty range s ………… …… …… …… …… …… …… …… … . 35 Table 3.6. Re su l t s of goni o me t r i c meas u r e me n t s …………… …… …… …… …… 4 2 Table 3.7. Th e surfa ce free ener g y comp o n ent s of calc i te and glass ………… … . 4 3 Table 3.8. Co mpo si ti on of Berea sand ston e at 400 o C ………… …… …… …… … 4 3 Table 3.9. Dist ance vs time record ed during the wick ing expe rime nt for dodecane 4 3 Table 3.10 . D i s t a n c e vs time recor d ed durin g th e wick i n g expe r i me n t for wate r … 44 Table 3.11 . Th e calc ul ated cont act angle val ue s of test liqu ids ………………… . .. 4 6 Table 3.12 . Th in layer wickin g results for apolar li qui ds …………………...….… 48 Table 3.13 . Th e conta ct ang le val ues wit h respec t to apol ar li qui ds and dode ca ne .. 4 9 Table 3.14 . Th e surfa ce tens i o n s and cos θ v al u e s of liqu i d s …………… …… … . . 50 Table 4.1. Th e calc ul ated cont act angle val ue s of test liqu ids for quart z ……….. 54 Table 4.2. Th e calc ul ated cont act angle val ue s of liqu id-liquid - soli d interface for quar t z …………… …… …… …… …… …… …… …… …… …… . . 54 Table 4.3. Th e calc ul ated cont act angle val ue s of test liqu ids for glass ……..….. 56 Table 4.4. Th e calc ul ated cont act angle val ue s of liqu id-liquid - soli d interface for glas s …………… …… …… …… …… …… …… …… …… …… … 56 Table 4.5. Th e calc ul ated cont act angle val ue s of test liqu ids for Bere a ……… . .. 5 8 Table 4.6. Th e calc ul ated cont act angle val ue s of liqu id-liquid - soli d interface for Bere a …………… …… …… …… …… …… …… …… …… …… .. 58 Table 4.7. Th e calcul ated cont act angle val ues of test liqu ids for Bent hei m …… . 6 0 Table 4.8. Th e calc ul ated cont act angle val ue s of liqu id-liquid - soli d interface for Bent h e i m ………… …… …… …… …… …… …… …… …… …… . 60 Table 4.9. Th e calc ul ated cont act angle val ue s of test liqu ids for cal ci te …...… .. 62 vii Table 4.10 . Th e calc ul ated cont act angle val ue s of liqu id-liquid - soli d interface for cal cite ………… …… …… …… …… …… …… …… …… …… … . 62 Table 4.11 . Th e calc ul ated cont act angle val ue s of test liqu ids for carb ona te rock 536 ………………………… …………………………………… 64 Table 4.12 . Th e calc ul ated cont act angle val ue s of liqu id-liquid - soli d interface for carb o n a te rock 536 …………… …… …… …… …… …… …… … . 64 Table 4.13 . Th e calc ul ated cont act angle val ue s of test liqu ids for carb ona te rock 703 ………………………… …………………………………… 66 Table 4.14 . Th e calc ul ated cont act angle val ue s of liqu id-liquid - soli d interface for carb o n a te rock 703 …………… …… …… …… …… …… …… … . 66 Table 4.15 . Th e surfa ce free ener g y comp o n ent s of calc i te and glass ………… … . 6 7 Table A.1 Wic k i n g time versus l2 For Quar t z samp l e …………… …… …… … . 76 Table A.2 Wi cki ng time versus l 2 For Glas s samp l e ……………… …… …… . 7 6 Table A.3 Wi cki ng time versus l 2 For Berea sands t o n e sampl e …………… … . 7 6 Table A.4 Wi cki ng time versus l 2 For Benthei m sandsto n e sample ………… .. 7 6 Table A.5 Wicki ng time versus l 2 For Calc it e sampl e …………… …… …… … 76 Table A.6 Wi cki ng time versus l 2 For Carbon at e rock sample 536 ………… .. 7 7 Table A.7 Wi cki ng time versus l 2 For Carbon at e rock sample 703 ………… .. 7 7 Table A.8 Wi cki ng time versus l 2 For Crud e oil …………… …… …… …… … 7 7 vii i LIST OF FIGURES Page Number Figure 1.1 : D e g r e e s of wettabi l i t y . ……..…………….……………….……… .... 2 F i g u r e 1.2 : Schema ti c di ag ram of wat er- wet and oil-wet rock …… ..…….…… ... 3 F i g u r e 2.1 : Sol id - li qui d-vapor interface .… ..… ...… ………….………………….. 7 F i g u r e 2.2 : Di splacemen t of a tri pl e li ne aroun d it s equi lib r ium posi ti on that all ows deriva ti on of the Youn g equ at ion …...……………………… . 8 F i g u r e 2.3 : Il lu st rati ons of advan ci ng and receedi ng con tact angl es ………… .... 11 F i g u r e 2.4 : Sc he ma ti c repre s ent ation of wet te d rock s ………… …… …… …… .. 13 F i g u r e 2.5 : Capi ll ar y pressur e vs. saturati on curve s ………… …… …… …… ... . 15 F i g u r e 2.6 : Ad hesi ona l wet ti ng ………… …… …… …… …… …… …… …… … . 16 F i g u r e 2.7 : S p r e a d i n g wetti n g …………… …… …… …… …… …… …… …… .. . 1 7 F i g u r e 2.8 : Immer s iona l wett ing ………… …… …… …… …… ..… …… .… …… 18 F i g u r e 2.9 : Cont act angle of par tiall y im mer se d soli d …………… …… …… … . 19 F i g u r e 2.10 : Capi ll ar y with the cons t ant circul ar cross-sect ion ………………….. 21 F i g u r e 2.11 : S c h e ma t i c represent at i o n of the contact angl e formed bet ween a liq uid dr op and soli d surfac e ………… …… …… …… …… … . .… . 28 F i g u r e 3.1 : K S V Sig ma 701 tensi o me t e r …………… …… …… …… …… …… . . 33 F i g u r e 3.2 : Du Nou y ring and its interact ion with the liquid …………………… 34 F i g u r e 3.3 : Sur face tensi on measurement pr ocess wi th Du Nou y ring met hod …. 34 F i g u r e 3.4 : C a n n o n Fensk e visc o si me t e r …………… …… …… …… …… …… .. 35 F i g u r e 3.5 : S c h e ma t i c wick i n g appa r a t u s …………… …… …… …… …… … . . .. . . 37 F i g u r e 3.6 : B a s i c eleme nt s of a gonio me t e r …………… …… …… …… …… … . . 38 F i g u r e 3.7 : Pre pa r at io n of coa te d slides ………… …… …… …… …… …… …… 39 F i g u r e 3.8 : Schema ti c Representation of Thi n Layer Wi cki ng experime nt …… .. 40 F i g u r e 3.9 : Wi cki ng experime nt of Berea sa mpl e wit h dodeca n e ……………… 44 F i g u r e 3.10 : Wi cki ng experime nt of Berea sa mpl e wit h wat er ………… …… … . .. 45 F i g u r e 3.11 : T h e results of wicking experi men t s for dodecane , di stille d wa t e r , bri ne and ker o se ne on Bere a samp l e … … …… …… …… …… .. 46 F i g u r e 3.12 : The results of wickin g exp eri ment s for mineral oil and cr ude oil 47 ix F i g u r e 3.13 : Determin at ion of effect ive pore radi us fro m apol a r liq uid s ………. .. 48 F i g u r e 3.14 : Thi n layer wi cki ng expe rime nt for br o monapth alene and eth ylene g lyc ol on calc it e samp le …… …… …… …… …… …… …… …… … . .. 50 F i g u r e 4.1 : T h e results of wicking experi men t s for dodecane , di stille d w a t e r , brin e and kero s e ne on quar tz ………… …… …… …… … … . .. . 53 F i g u r e 4.2 : The results of wickin g exp eri ment s for mineral oil on quar tz ……… 53 F i g u r e 4.3 : T h e results of wicking experi men t s for dodecane , di stille d wa te r, brine and kero se ne on gla s s ………… …… …… …… …… … . . 55 F i g u r e 4.4 : The results of wickin g exp eri ment s for mineral oil on glass ………... 55 F i g u r e 4.5 : T h e results of wicking experi me nt s for dodecane, di stilled wa te r, brine and kero se ne on Ber ea ………… …… …… …… …… … . 57 F i g u r e 4.6 : The results of wickin g exp eri ment s for mineral oil on Berea …… ..... 57 F i g u r e 4.7 : T h e results of wicking experi men t s for dodecane , di stille d wa t e r , bri ne and ker o se ne on Ben t he im …………… …… …… …… .. . 59 F i g u r e 4.8 : The results of wickin g exp eri ment s for mineral oil on Bent heim …... 59 F i g u r e 4.9 : T h e results of wicking experi men t s for dodecane , di stille d w a t e r , brin e and kero se ne on calc i t e …………… …… …… …… …… 61 F i g u r e 4.10 : The results of wickin g exp eri ment s for mineral oil on cal cite ……… 61 F i g u r e 4.11 : T h e results of wicking experi men t s for dodecane , di stille d w a t e r , brine and kero se ne on carbon at e rock 536 …………………... 63 F i g u r e 4.12 : The results of wickin g exp eri ment s for mineral oil on car bonate r o c k 536 …………… …… …… …… …… …… …… …… …… …… .. . 6 3 F i g u r e 4.13 : T h e results of wicking experi men t s for dodecane , di stille d w a t e r , brine and kero sene on ca rbon at e rock 703 ………………….... 65 F i g u r e 4.14 : The results of wickin g exp eri ment s for mineral oil on car bonate r o c k 703 …………… …… …… …… …… …… …… …… …… …… .. . 6 5 x LIST OF SYMBOLS AND ABBREVIATIONS A : Cross sect io n a l area, cm 2 d 5 0 : Aver a g e par ti cl e siz e , μm d t : Change in time, s dV : Change in volume , cm 3 f : Propor tio ns of the surface occupi ed by mat er ials, unit less F : Force, dyne F : Helmho lt z fre e energ y of the syst em, Joule F s : Surfac e free ener g y of the syst e m, dyne/ cm g : Gravit at i o n al accel e r a tio n , cm/s 2 G : Gibbs free energy per unit area , Joul e l : Heigh t of the wet ti ng fron t, cm lT : Total length of the capi llary, cm l1, l2 : Respec t i ve leng t h of the liqu i d colu mn s, cm L : Length , cm ΔP : Press u r e di ffe r en ce acro s s the liqu i d - v a p o r inter f a c e in a capil la r y , dyne / c m 2 ΔPc : Capi llary pr essure, dyne/ cm 2 ΔPe : External pressure , dyne/ cm 2 ΔPh : Hydrost a t i c pressur e , dyne/ cm 2 r : Radi us of a capil lary, cm r* : Effect iv e radi us, cm s : Surfa c e of soli d, cm 2 S : Spreadi ng coeffici e n t , dyne/cm t : Time, s T : Temp era tu r e, Kel vin v : Lamina r stati on a r y fl ow, cm/s W : Work, Joule Ze : Depression of the liquid in the cap il lary, cm δz : Small line ar displ ac eme nt, cm iΓ : Adsorpt i o n of the element i in mole s per uni t area , mol es /c m 2 iμ : Chemical potential of the element, Joule eΠ : Spreadi ng pressure, dyne/cm LW Sγ : Lifshi tz van der Waals compo nen ts of the surface ten sion, dyne/cm AB Sγ : Acid-Base compo nen ts of the surface tension, dyne/cm Sγ + : Surface ten sion of elect r on accep tor component s, dyn e/cm Sγ − : Surface ten sion of elect r on donor comp on ent, dyne/cm γ : Surface tensio n, dyne/cm xi Lγ : Surface tensio n of the liq uid , dyne/cm 12 LL γ : Int er facial tensi on between two immi sci ble liquid s L 1 and L 2 , dyne/cm LVγ : Liqu id-v ap or surface ten si on, dyne/ cm Sγ : Surface tensio n of the soli d, dyne/ cm LSγ : Sol id-liq uid sur face tens i on, dyne/cm 1LS γ : Surface tensio n bet wee n the liqui d L 1 and a soli d, dyne/cm 2SL γ : Surface tensio n bet wee n the liqui d L 2 and a soli d, dyne/cm VSγ : Sol id-vapor surface ten s ion, dyne/cm µ : Viscosit y, cp µ1 , µ2 : Visc os it ies of two immi s ci bl e li qui ds , cp ρ : Densi ty of the liqui d, g/cm 3 θ : Cont a ct ang l e , o θ12 : The cont ac t angle on a liqui d- l i q u id - s o l i d interfa c e , o xii REZERVUAR KAYAÇ ISLATIMLILI ĞININ İNCE TABAKA YÜKSELME YÖNTEMİYLE ÖLÇÜLMES İ ÖZET Bu yüksek lisans laboratuar çal ışmasında, minerolojik olarak heterojen kompozisyona sahip gözenekli madde ile temas halinde olan iki karışmayan akışkanın katı yüzeyi ile oluşturacakları kontak (temas) aç ısının ölçülebilirli ği araştırılmıştır. Bu araştırmada, kontak aç ılarının dinamik hesaplanmasında kullanılan Washburn denklemi ve bu denklemin ince tabaka kılcal yükselme (thin layer wicking approach) yöntemine olan uygulaması aç ıklanmıştır. Bu deneysel çal ışmada, öğütülerek toz haline getirimiş numune “powder” olarak çe şitli kumtaşı ve kireçta şı kayaç örnekleri ile bu kayaçlar ı oluşturan temel saf mineraller (kuvars ve kalsit) kullan ılmıştır. Çalışmada yükselme sıvısı olarak saf su, ağırlıkça %2’ lik NaCl tuzlu su çözeltisi, gazya ğı, mineral oil ve ham petrol kullanılmış ve bunların numunenin katı yüzeyinde oluşturdukları temas aç ıları ölçülmü ştür. Bu araştırma projesinde, öğütülmüş mineraller (powder) üzerinde uygulanan ince tabaka kılcal yükselme tekniğinin heterojen yapıdaki kayaçlar ın temas aç ılarının bulunmasında uygulanabilirliği ve ıslatımlılık ile temas aç ısı arasındaki ilişki araştırılmış ve sonuçlar ı verilmiştir. xii i DETERMINATION OF RESERVOIR ROCK WETTABILITY BY THIN LAYER WICKING APPROACH ABSTRACT The present graduate research st udy is an atte mp t to invest i ga t e the possibi l i t y of contac t angl e det er mi na tio n of two immi s ci ble flui ds in cont a ct wit h the solid sur fa c e of a porous material wi th heteroge neous min eralo gical compos i tio n. Applicatio n of the Wash burn equ at ion for dyn amic measurement of con tact angle and the met hod of Thi n Layer Wickin g were descri b e d . Experi me n t s were con duc t e d on the powder e d sampl es of different sand st one and limest o n e rock sampl es and also thei r represe n t at iv e pure mi ner al s such as quartz and cal ci te , respec t i vel y. In this st udy, dist il l e d wa ter, 2% NaCl br ine, kerosene , mi neral oil, and crude oil are used as a wick ing li qui d, an d cont act angles wi th respec t to the soli d sampl e’ s surfa ce were meas u r e d . Appl i c abi l i ty of the “Thin Layer Wi cking Tech niq ue” for contact angl e determinati on of the he terog eneous rock samp les and the relati on betwee n the wett ab il i t y and the contac t angle were discus se d . 1 1. INTRODUCTION “Oil recovery from porous sedimentary rock s depends mainly on the overall efficiency with which oil is displaced by some other fluid. Interfacial phenomena in porous rocks lie at the heart of oil recovery because they determine the fraction of oil that moves from the swept region toward a producing well. Detailed studies of displacement efficiency from the pore spaces, commonly referred as microscopic displacement efficiency, were first reported over 70 years ago. Microscopi c displacement efficiency is determined by the interactions of rock pore geometry and interface boundary conditions. These interactions constitute what is known as reservoir wettability” (Morrow, 1991). Fluid distribution in porous media is affected not only by the forces at fluid/fluid interfaces but by the forces at fluid/soli d interfaces (Green and Willhite, 1998). Wettability is an important phenomenon that controls the distribution, location, and flow of fluids in a reservoir. It has a strong influence on core analyses, such as dispersion, capillary pressure, waterflood behavior, relative permeability, tertiary recovery, irreducible water and oil saturation and electrical properties (Anderson, 1986). The wettability of a rock is related to the affinity of its surface for water and oil. For general definition, wettability is the relative preference of a solid surface to be coated by a certain fluid in a system (Morrow, 1991 ). Reservoir rocks have complicated pore structure and mineral composition, therefore measured wettability is the average wetting ability of the various minerals forming the rock surface. In the past, petroleum reservoirs were considered to be strong water wet. Because before the migration of oil into the reservoir, it was thought that pore space was occupied with formation water. But in the beginning of 1940’s it was seen that oil can wet the surface of sandstone (Bartell and Miller, 1928) and silica (Benner and Bartell, 1942). There are several methods for wettability measurements but mostly Amott, USBM (United States Bureau of Mines) and contact angle methods are preferred in the petroleum industry. 2 The first two methods can be used to measure average wettability of a rock where regular shaped cores are available. In addition, when pure fluids and artificial cores are used, contact angle is the best wettability measurement method (Anderson, 1986). The contact angle measures the wetting tendency of a liquid on a solid surface when another immiscible liquid is present (Hunter, 1987 ). If a small drop of a liquid is placed on a uniform, perfectly flat, solid surface, a contact angle is formed at the junction between three phases. If the contact angle is less than 90 o, liquid wets the solid surface and it is greater than 90 o, the drop rounds up and does not wet the surface. Additionally, the solid is said to have neutral or intermediate wettability if the contact angle is about 90 o. When the oil-water-rock system is considered, the system is defined as water wet if θ is between 0o and 60o to 75 o, the system is defined as oil wet if θ is between 180 o and 105 o to 120 o, in Figure 1.1 (Anderson, 1986). Some researchers use accurate boundaries for the separation of wettability types. For instance, Treiber et al. have chosen cut-off values of 75 o and 105 o whereas Morrow has chosen 62o to 133 o or Chilingar and Yen use 80 o to 100 o (Morrow, 1991). Fi gure 1.1 : Degrees of Wettability (Morrow, 1990) a) Completely water wet b) Strongly water wet c) Water wet d) Oil wet e) Strongly oil wet f) Completely oil wet The terms intermediate (Marsden and Nikida s, 1962), fractional (Fatt and Klikoff, 1959 ; Iwankow, 1960) or heterogeneous (Browns a nd Fatt, 1956), mixed (Salathiel, 1973) and 3 speckled (Morrow et al., 1986) were introduced to indicate types of wetting conditions which are not simply either strongly water-wet or oil-wet (Jadhunandan, 1990; Gökmen, 2003). If the rock is strongly hydrophilic, the initial water wets the solid surface and occupies the small pores. If the rock is strongly oleophilic, the oil wets the solid surface and initial water is placed in the middle of the large pores as shown in Figure 1.2 (Cuiec, 1991). Figur e 1.2 : Schematic Diagram of Water-Wet and Oil-Wet Rock (Morrow, 1991) Contact angle defines the wetting behavior of solids or it can be said that it is a measure of surface hydrophobicity. As the contact angle increases, solid surface becomes more hydrophobic. Furthermore, it is also used to find the surface free energy of a solid. Surface energy components of solids are acknowledged as the key to realize the mechanism of surface-based phenomena. The energy of solid surfaces helps to predict most surface properties such as wetting, adsorption and adhesion. Therefore there is a strong relationship between wettability and measurements of contact angle and surface free energy components. A finite measurable contact angle can be obtained if γL is greater than γS and if γ L is less than γS liquid spreads and wets the solid completely. Solids having higher surface free energies exhibit lower values of water contact angles that direct water wet surfaces (Y ıldırım, 2001; Giese and van Oss, 2002). The elastic and viscous restraints of the bulk phase disable direct measurements of the surface tension components ( LW S S S, ,γ γ γ+ − ) and necessitate indirect meth ods (Schultz and Narin, 1992). Especially, contact angle measurements are utilized for determining the surface free 4 energy values of solids by measuring contact angles with at least three different liquids of which two must be polar and H-bonding (van Oss et al., 1988 ). In some cases achieving a reproducible contact angle with direct contact angle measurements is not easy. For instance, contamination of the droplet by adsorption of impurities from the gas phase yields reduction of θ. Surface roughness can change θ value; when θ is smaller than 90 o roughness causes lessening, and when θ is greater than 90 o roughness causes increasing in θ value. Also hysteresis can be seen in contact angle measurements and creates differentiation between advancing and receding contact angle values (Rosen, 1989). The measurement of contact angle on flat surfaces is useless when large samples of solid or flat and polished solid surfaces are unavailable. Pore geometry, surface roughness and adsorbility of porous surfaces prevent the direct measurements of contact angles. Also polishing the surface of solids causes atomic rearrangements and provides creation of new surfaces. Moreover, in contact angle visualization reservoir is modeled with pure and single mineral which limits the investigation of mineralogically heterogeneous rock system (Wolfram, 2002; Morrow, 1991), and flat, smooth and polished surface does not wholly represent the naturally porous surface of the rocks composed of several different minerals (Y ıldız, 1998). In this situation, quantifying the wetting characteristics of solid surfaces with a capillary rise in a bed of particles is a better approach when contact angles cannot be directly measured. As a consequence, when the powdered form of a single mineral crystal or rock containing many different components exist, capillary rise and thin layer wicking methods are available for estimating the contact angle. A liquid may penetrate spontaneously into a porous media by capillary forces. This process is referred to as wicking .Washburn (1921) formulated the rate of penetration of a liquid into a porous medium or powdered material. According to Washburn (1921), the distance penetrated by a liquid flowing under capillary pressure alone into a horizontal capillary is equal to r cos t 2 γ θ μ . In the 1980s Van Oss developed Thin Layer Wicking method for measuring the contact angles of all minerals, even with irregularly shaped, such as nonswelling clays, talc, dolomite, limestone, calcite, silicates and the cuboids 5 hematite (Karagüzel et al., 2005). In this me thod, a thin layer of powdered solid sample is deposited on glass slide. This facilitates penetration of the liquid into the layer and a sharp visible progressing contact angle line can be seen. Using the wicking results, wetting contact angle can be calculated with the Washburn equation; 2 L cos 2 t r γ θ l μ = ( 1.1 ) Where, l is the height of the column of liquid has reached by capillary rise in time t, r is the average radius of the pores of the porous medium, θ is the contact angle, γ L is the surface tension and µ is the viscosity of the liquid. θ and r are the unknowns of the equations. In order to find these values, a low energy liquid that wets the surface completely is used, in this situation θ will be 0o and r can be found. Contact angles of studied liquids can then be calculated (van Oss, 1994). The Amott test and the USBM test are the most commonly used methods of quantifying wettability based on oil/brine/rock displacement behavior (Cuiec, 1990). Both depend on capillary pressure and microscopic displacement efficiency (Morrow, 1990). The serious weakness for USBM method is that the test does not recognize systems that achieve residual oil saturation by spontaneous imbibition (Ma et.al, 1994 ). In other words, the method does not recognize very strongly water wet or very strongly oil wet systems. On the other hand, the Amott test demonstrates the effect of displacement by capillary forces due to water or oil imbibition over total displacement forces of capillary and viscous together (Y ıldız and Gökmen, 2001). A weakness of the Amott test is its failure to distinguish between important degrees of strong water-wetness (Morrow, 1990). This was the reason that in this study, application of the Washburn equation for dynamic determination of contact angle and the method of Thin Layer Wicking were described in order to qualitatively characterize wettabil ity of porous material with heterogeneous mineralogical composition such as sandstones and carbonates. The primary objective of the present study was to determine wettability of a rock composed of many different mineral constituents by applying Thin Layer Wicking approach. 6 2. LITERATURE REVIEW 2.1 Interfacia l Tensi on When two immiscible phases exist together, interface is the boundary formed between the phases. Interfaces can be classified according to state (solid, liquid or gaseous) of two adjacent phases. When a liquid is in contact with a gas, another immiscible fluid, or a solid, intermolecular attraction within the liquid is unbalanced at the interface. This excess energy exists at any interface. If one of the phases is the gas phase, the measurement is called surface tension, and if the interphase of two liquids is investigated, the measurement is called interfacial tension. It can be quantified as the force acting normal to the interface per unit length (force/unit length, mN/m). According to Defay and Prigogine (1966), interfacial tension is defined in terms of energy; i i iσ=G μ− ∑Γ ( 2.1 ) G is the Gibbs free energy per unit area; iΓ is the adsorption of the element i in moles per unit area; and iμ is the chemical potential of the element. Thus, the interfacial tension is equal to the free surface energy per unit area, G , if the system is in physical- chemical equilibrium, that is i i iΓ μ∑ =0 (Francisca et al., 2003). 2 . 2 Contact Angle The intersection region of solid-liquid, solid-fluid, and liquid-fluid is called the contact line where the contact angle is formed. The contact angle is an angle between the tangent to the liquid-fluid interface and the solid interface. Two contact angles can be defined; the intrinsic contact angle, θ, is the angle at a very short distance from the solid 7 and the apparent contact angle, θ a , that is measured at the macroscopic level (Marmur, 1992). In 1805, Thomas Young suggested treating the contact angle of a liquid as the result of the mechanical equilibrium of a drop resting on a plane solid surface under the action of three surface tensions; γ L V at the interface of the liquid and vapor phases, γS L at the interface of the solid and the liquid, and γ S V at the interface of the solid and vapor. (Zisman, 1944). In the presence of a vapo r phase, if a non-reactive liquid does not wholly coat the solid surface, which is plane, undeformable, perfectly smooth and chemically homogeneous, the liquid surface will intersect the solid surface at a “contact angle” θ. The basic Young equation defines the contact angle as following form illustrated in Figure 2.1. SV SL LV cos γ γθ γ −= ( 2 . 2 ) Fi gure 2.1 : Solid-Liquid-Vapor Interface This equation can be derived by calculatin g the difference of the surface free energy Fs of the system caused by a small displacement δ z of the S / L/ V contact (triple line, T L ) line under the assumptions given in Figure 2.2. The total length of T L is constant throughout its displacement, the radius r of the T L region is larger than the range of the atomic (or molecular) interactions in the system but must be smaller than the characteristic dimension of the liquid and inside the region of radius r , the intersection of the L / V 8 surface with the plane of figure is a straight line, the variation of interfacial free energy per unit length of T L , resulting from a small linear displacement δz of T L is: F s ( z + δ z ) – F s ( z ) = δ F s = ( γ S L – γ S V ) δ z + cos( θ ) γL V δ z ( 2 . 3 ) The equilibrium condition d( δ F s ) / d( δ z ) = 0 forms the classical equation of Young (Eustathopoulos et al., 1999 ). Fi gure 2.2 : Displacement of a Triple Line Around its Equilibrium Position That Allows Derivation of the Young Equation (Eustathopoulos et al., 1999 ). Another approach established by Dupré demonstrates the relation between the reversible work of adhesion of liquid and solid, W A, γSV and γSL : W A = γ S V + γ L V - γ S L ( 2 . 4 ) This expression shows that the reversible work of separating the liquid and solid phases should be equal to the change in the free energy of the system. According to Sumner (1937), the Young equation can also be derived thermodynamically for the ideal plane solid surface on condition that the system is in thermal and mechanical equilibrium so γ S L , γ S V and γ L V are defined as follows: 9 SL SL SV LV F ( . ) A F ( . ) A F ( . ) A İ İ İ T, μ S V T, μ LV T, μ γ γ γ ⎛ ⎞∂= ⎜ ⎟∂⎝ ⎠ ⎛ ⎞∂= ⎜ ⎟∂⎝ ⎠ ⎛ ⎞∂= ⎜ ⎟∂⎝ ⎠ 2 5 2 6 2 7 Here; F is the Helmholtz free energy of the system, A , is the area of the interfaces, T is the temperature and μi is the potential of each component in the phases. Surface wettability and hydrophobicity, surface free energy and its components, surface adsorption and heterogeneity can be determined by the contact angle estimations. The contact angle can be given in two forms; Stat ic and Dynamic. After a drop of a liquid place over a solid surface, all phases (solid, li quid, and gas) try to reach their equilibrium position, as soon as the three phase line is not moving any longer; the static contact angle is achieved. On the other hand, while the liquid is spreading over the solid and the three phase line is in controlled motion, the contact angle changes continuously with time and dynamic contact angle can be measured. 2.2.1 Contact Angle Measurements in Liqui ds Young’s equation can be used to find contact angles of a drop of a liquid, L on a solid, S, immersed in a different liquid. If the tw o liquids are immiscible, then we can define the following equation; cos 2 1 2 1 1SL L L SL SL = +γ γ θ γ ( 2 . 8 ) where, 1LS γ , 2SL γ , and 12 LL γ are solid surface interfacial energies for a given liquid and the interfacial tension between two immiscible liquids, respectively, and θ S L ı is a contact angle (van Oss 1994 ; Adamson 1990). Here, the difference of solid interfacial energies on the left hand side of above equation is called adhesion tension and is usually referred as the difference between the solid surface interfacial tensions of non-wetting and wetting phases. If adhesion tensions of both liquids measured in one vapor environment 10 are known, the contact angle on liquid-liquid-solid interface then can be easily calculated (Tacibayev, 2005), ( ) ( ) ( )SL SL S SL S SL 12 L L L L γ - γ γ - γ γ - γ cos θ γ γ −= = 12 1 2 2 1 2 1 12 21 LL LL γ cos θγcos θγ 21 −= ( 2. 9 ) 2 . 2 . 2 Contact Angle on Heterog e n e o u s Surfaces - Cassie’s Equation In 1948, Cassie gave a formula for contact angles on solid surfaces composed of different materials; A 1 2cos cos cos1 2f f= +θ θ θ ( 2 . 1 0 ) θA aggregates contact angle measured on the heterogeneous surface. f’ s are the proportions of the surface occupied by materials and 11 2f f+ = . θ 1 and θ2 are the contact angles found on solid surface only consisting of material 1 and 2 respectively (Giese et al., 2002; van Oss, 1994 ). 2.2.3 Limitatio ns of Contact Angle Measurement s 2.2.3.1 Hysteresi s In contact angle measurements an important problem, which is called hysteresis, occurs. In reality, solid surfaces are non-ideal and don’t satisfy the conditions of Young’s equation to be valid, thus a liquid drop on a surface can have many different stable contact angle (Anderson, 1986). The angle me asured just after a drop of liquid has advanced on the solid surface is called advancing angle ( θ A ), and the angle measured just after arrest of a liquid drop is called receding angle ( θ R ) shown in Figure 2.3 (Schultz and Narin, 1992). The difference betwee n the maximum (advancing) and minimum (receding) contact angle values is ca lled the contact angle hysteresis. 11 Fi gure 2.3 : Illustrations of Advancing and Receding Contact Angles According to Adamson (1990), there are thre e main reasons for hysteresis. First one, which raises the hysteresis, is the contamination of liquid or solid surface. Second, hysteresis effects are associated with rough surfaces. The surface roughness causes many metastable states of the drop to be formed with different contact angles and the macroscopically and microscopically observed contact angles will not be the same. The third cause is the surface immobility on a macromolecular scale. The contact angle cannot reach its equilibrium value becaus e surface immobility creates hysteresis by resisting the fluid motion (Anderson, 1986). There is another very important phenomenon in hysteresis called the surface heterogeneity and it is tried to be avoided by measuring the angle on a single mineral crystal, where as a core contains many different constituents. Also for wetting of polymers, Schultz and Nardin’s (1992) experiments shows that hysteresis are related with the polar character of the polymer surface and reorientation of polar groups on the surface in contact with a polar liquid such as water. Timmons and Zisman (1966) informed that an apparent penetration of water molecules into a surface could cause a significant contact angle hysteresis. 2 . 2 . 3 . 2 Spreadin g Pressur e In Young’s equation, svγ is assumed to be to equal to 0sγ . First one describes the surface of a solid in equilibrium with the vapor of a liquid and the latter, 0 sγ , a solid in equilibrium with its own vapor . Consequently, in some cases they have distinction caused by adsorption. The adsorption of the vapors of the wetting liquid onto the solid surface can reduce the surface energy of the solid (Hiemenz and Rajagopalan, 1997). This is defined by spreading pressure, 0e s svΠ = −γ γ , having the dimensions of an 12 energy per unit area or a force per unit length (Hunter, 1993). This term should be added to Young’s equation; L S SL ecos = − + Πγ θ γ γ ( 2.11) However, under non-spreading conditions there is no need to add imaginary equilibrium spreading pressure. This can be neglected based on the results of wicking and thin layer wicking that state with non spreading liquids (i.e. γ L > γS and cos θ < 1 ) neither spreading nor pre-wetting takes place, as evidenced by a strongly negative slope of plots of µ l2/t vs. γL (van Oss, 1994). 2.3 Theory of Wetting On the basis of thermodynamic wetting can be defined by the physicochemical reaction caused by intermolecular forces of attraction. Wettability represents the energy lost by the system during the wetting of a solid by a liquid. This can be shown with m T,P G ( ) s ∂= − ∂γ (2.12) where, G is the free Gibbs energy, T is the temperature, P is the pressure and s is the surface of the solid. If T,P( G / s) 0∂ ∂ < , the reaction is spontaneous and wettability is positive (Morrow, 1991 ). Wettability is defined as the tendency of one fluid to spread on or adhere to a solid surface in the presence of other immiscible fluids seen in Figure 2.4 (Anderson, 1986). According to Adamson (1990), wetting indica tes that the contact angle between a liquid and a solid surface is zero or so close to zero that the liquid spreads over the solid easily. Young described the contact angle as: γ L cos θ = γS - γSL ( 2 .1 3 ) The reversible free energy of adhesion ∆GSL of the liquid on the solid (also called solid- liquid interfacial free energy) was given by Dupré (1869) as: 13 ∆GSL = γSL - γS – γL ( 2 . 1 4 ) by combining Young’s and Dupré’s equation, Harkins & Feldman’s spreading coefficient that determines the ability of the liquid to wet a solid can be found. S = ∆GLL - ∆GSL ( 2.1 5) ∆GLL is the free energy of cohesion of the liquid and equals to -2 γ L , then; S = γS – γ L - γSL ( 2 . 1 6 ) S = – γ L (1- cos θ) (2.17 ) For nonspreading condition S ≤ 0 and for spreading condition S > 0 referring that the liquid wets the solid surface (Zisman, 1944). The difference between the work of adhesion and the work of cohesion (W A-W C) gives the spreading coefficient, where W C is equal to 2 γLV . A positive spreading coefficient is necessary for a liquid to spread on a solid surface seen in Figure 2.6. Therefore, wettability can be estimated from calculating the surface tension of the solid or solid-liquid interfacial free energy and from measurements of the contact angle (Michel et al., 2001). Fi gure 2.4: Schematic representation of wetted rocks (Gökmen, 2003) a) wettability of a rock b) oil-wet c)water-wet rock 14 There appear many different methods for wettability measurements. They are divided into two; quantitative methods: contac t angles, Amott (imbibition and forced displacement) and USBM wettability method; qualitative methods: imbibition rates, microscope examination, flotation, glass slide method, relative permeability curves, capillarimetric method, displacement capillary pressure, reservoir logs, nuclear magnetic resonance, and dye adsorption (Adamson, 1986). The Amott test (Amott, 1959) and the USBM test (Donaldson et al., 1969) are the most commonly used methods of quantifying wettability based on oil/brine/rock displacement behavior (Cuiec, 1990). Both depend on cap illary pressure and microscopic displacement efficiency. The Amott test for characterizing wettability is based on imbibition and forced displacement. The main principle of this method is that the wetting fluid generally imbibes spontaneously into the core, displacing the non-wetting one (Anderson, 1986). Method consists of two parts after establishing the S wi . The first part is spontaneous imbibition in water followed by forced displacement by water. The second part is a test for spontaneous imbibition in oil at a residual oil saturation followed by forced displacement by oil (Y ıldız and Gökmen, 2001). The test results are expressed with Amott wettability indices. The ratio of the spontaneous increase in water saturation the total increase is the wettability index to water, Iw. The ratio of oil imbibed spontaneously to the total displacement of oil give the wettability index to oil, Io. The difference between Iw and Io gives the Amott-Harvey wettability index (Morrow and Mason, 2001; Zhou et al., 1996). The imbibition can take several hours to more than 2 months to complete. If the imbibition is stopped after a short period of time underestimation of Io and Iw can be occurred. Also the main weakness of the Amott test is that it is insensitive near neutral wettability (Anderson, 1986). More over, it is failure to distinguish between important degrees of strong water-wetness (Morrow, 1990). US Bureau of Mines (USBM) has developed a quantitative method for determining the average wettability of porous media that contains brine and crude oil by using capillary pressure curves determined with a centrifuge (Donaldson et al., 1969). This method is based on correlation between the degree of wetting and the areas under the capillary- pressure curves as seen in the Figure 2.5 (Robin, 2001). 15 a) Water Wet b) Oil Wet Fi gure 2. 5 : Capillary Pressure vs. Saturation Curves (Robin, 2001) A1 and A2 are the areas under the capillary pressure versus saturation curves obtained during oil and brine drives respectively (And erson, 1986). These areas are representative of the energy needed to inject either fluid in the porous medium. When A 1 >A 2 the solids are preferentially water-wet, on the other hand, when A2>A 1 the solids are preferentially oil-wet. The main advantage over the Amott test is its sensitivity near neutral wettability (Anderson, 1986). The serious weakness for US BM method is that the test does not recognize systems that achieve residual oil saturation by spontaneous imbibition8 . In other words, the method does not recognize the very strongly water wet or very strongly oil wet systems (Ma et. al, 1994 ; Y ıldız and Gökmen, 2001). In addition, USBM test cannot determine whether a system has fractional or mixed wettability while Amott sometimes sensitive. Furthermore; USBM ha s a minor disadvantage, sample must be spun in centrifuge so it can be measured on plug size samples (Anderson, 1986). 16 2.3.1. Types of Wetting Osterhuf (1930) has given three types of wetting: 2.3.1.1. Adhesi ve wetti ng-the Young- Dupré equati on Fi gure 2.6 : Adhesional Wetting (Rosen, 1989) In adhesional wetting in Figure 2.6, a liquid that is not in touch with a substrate makes contact with that substrate and adheres to it. When the solid surface is lowered towards the liquid until contact is established, the chan ge of interfacial free energy of the system, or the work gained, is given by: -W Ao = γSL – ( γSV -γLV ) ( 2 . 1 8 ) Here -W Ao equals to work of adhesion of the liquid phase on the solid. So Young-Dupré equation is; 0 a LV W cos 1θ = −γ ( 2 . 1 9 ) In this equation, cohesion forces create γLV and adhesion forces create W Ao (Eustathopoulos et al., 1999). The difference between the work of adhesion and cohesion equals to spreading coefficient S L/S; a C S V S L L V L V L / S S V S L L V W W 2 ( . ) S ( . ) − = − + − = − − 2 2 0 2 2 1 γ γ γ γ γ γ γ 17 When these works are equal we get: SV SL LV LV LV LV 2 ( . ) (cos 1) 2 ( . ) − + = + = 2 2 2 2 2 3 γ γ γ γ γ θ γ Here, if θ= 0 then cos θ=1 and S L/S = 0. Therefore, if Wa >Wc the liquid spreads over the substrate to form a thin film (Rosen, 1989). Th e driving force of this kind of wetting is simply expressed as; SV LV SLγ γ γ+ − = 0. 2.3.1.2 Equil ibrium and non-equil ibrium wo rk of adhesion - work of sprea d i n g F i g u re 2.7 : Spreading Wetting (Rosen, 1989 ) When a liquid in contact with a substrate spr eads over and displaces another fluid, this is called spreading wetting seen in Figure 2.7 (Rosen, 1989). Surface energy reduction ( ∆γSV ) occurs when there is adsorption of liquid vapors on the solid surface. γSV and W a are denoted (P sat) and W a(P sat) when the solid surface is in equilibrium with a saturated vapor of the liquid at a partial pressure of Psat. SV SV sat SV sat a a sat SV sat LV SV sat (P ) (P ) ( . ) W W (P ) (P ) (1 cos ) (P ) ( . ) γ = γ + Δγ = + Δγ = γ + θ + Δγ 0 0 2 24 2 25 18 Formation of a continuous liquid film on a solid surface causes the change in the interfacial energy of the system. This can be represented with the work of spreading, W s(P sat) (Eustathopoulos et al., 1999) ; s sat LV SL SV sat LV satW (P ) (P ) 2 Wa (P )= γ + γ + γ = γ − (2.26) To summarize, the driving force is equal to SV SL LV( )γ γ γ− + and this is named as spreading coefficient SL/S . If spreading coefficient is positive liquid will spread over the substrate, and if it is negative, spreading cannot occur spontaneously. 2.3.1.3 Im mersi on Figure 2.8 : Immersional Wetting (Rosen ,1989) In immersional wetting in Figure 2.8, substrat e which is not in contact with a liquid is immersed by the liquid totally. The drivi ng force of this wetting phenomenon is the quantity of; SV LVγ γ− (Rosen, 1989). Work of immersion, W i, defines the surface energy change when a S/V surface of unit area is replaced by a S/L interface of equal area by immersion of a solid in a liquid. 2( )SL SV e γ - γ Z r ρg = (2.27) Where Z e is the depression of the liquid in the capillary, r is the internal radius of capillary. The thermodynamic quantity ( γS L – γ S V ) is the work of immersion that 19 describes any infiltration process of liquids into porous media (Eustathopoulos et al., 1999). Figure 2.9 : Contact Angle of Partially Immersed Solid (Rosen, 1998 ) The depth of immersion of the solid on the wetting liquid can be found by the contact angle, when the contact angle decreases, the dept of immersion increases (Figure 2.9). Therefore, immersion is complete when θ = 0 o. 2.4 Capil la ry Pressure If two immiscible fluids are in contact in a porous medium, a meniscus is formed between these two fluids. The pressure difference between wetting and nonwetting phase across the interface is the capillary pressure (Yildiz, 1 998). Along with force balances, capillary pressure can be defined: x 2 2 nw w 2 nw w nw w , c nw w F 0 ( . ) P ( ) (2 ) P ( ) (2 ) 0 ( . ) (P P ) 2 ) ( . ) 2 ) P P ( . ) r 2 cos P P P ( . ) r nw,s w,s nw,s w,s nw,s w,s w n w r γ r r γ r r r( γ γ ( γ γ γ θ = π − π − π + π = π − = π − −− = = − = ∑ 2 28 2 29 2 30 2 31 2 32 G 20 where, Pnw and Pw are pressure difference across the nonwetting and wetting phase respectively, r is the radius of the capillary, w , sγ is the surface tension of wetting phase (dyne/cm), n w , sγ is the surface tension of nonwetting phase (dyne/cm), and w , n wγ is the interfacial surface tension of wetting/nonwe tting phase (dyne/cm). According to this equation, capillary pressure is associated wi th interfacial tension, capillary radius and which defines the relative wettability characteristics of the fluids on solid surface. The phase that has lower capillary pressure will preferentially wet the porous medium (Green and Willhite, 1998). 2.4.1 Capil lary Rise and Washburn Equati on When a powdered solid is in interest, the mechanism of the wetting is related with the capillary rise phenomenon (Adamson, 1990). The difference between the solid-air and solid-liquid interfacial energies is the driving force (adhesion tension) for a liquid into a powder bed in a capillary. There occurs a pressure difference across the curved liquid- vapor interface and this difference is given in terms of interfacial energies by; 2 P S S L ( γ - γ ) r Δ = ( 2.3 3) The Young equation (2.13) can be utilized, if the liquid’s co ntact angle on the solid is larger than zero, consequently pressure difference at the interface boundary can be defined as the liquid surface tension and contact angle; L2( cos )P r Δ = γ θ ( 2.3 4) The voluminal laminar stationary flow, ΦV , of incompressible uniform viscous liquid through a capillary with the constant circular cross-section can be modelled as in the following Figure 2.10. and flow rate is calculated from Hagen-Poiseuille equation: 21 Fi gure 2.10: Capillary With the Constant Circular Cross-Section 8 8 4 4 2 v s d V π r d P π r Δ P Φ = = υ π r = ( - ) = d t μ d z μ L (2.35) here, dV is the volume of the liquid that penetrates through cross section of a capillar in time dt , and equals to πr 2 dl . Thus we can write the expression for the velocity under laminar conditions: 8 2dl r Δ P = d t μl (2.36) substituting pressure difference that was given in equati on (2.34) into above equation: 4 dl r γ c o s θ = d t μl (2.37) and integrating this equation with the initial condition of l=0 at t=0; we obtain the Washburn equation. cos 2 2 rl t= γ θμ (2.38) where r is the average radius of the capillary, γ is the surface tension and µ is the viscosity of the liquid. The γcosθ/2 µ term is defined as the coefficient of penetrance or the penetrativity of the liquid and measures the penetrating degree of a liquid (Washburn, 1921; Y ıldırım, 2001). 22 The Washburn Equation can be used to calc ulate contact angle of powders or porous solids. Capillary rise velocity of a liquid in capillary tube filled with packed solid powder provides determination of the contact angle value of that imbibing liquid (Giese et al., 2002; Y ıldırım, 2001). This equation assumes that the liquid penetrates into a capillary filled with air or vapor having negligible viscosity (Marmur, 1992). 2.4.2 Thin Layer Wicking The capillary rise method is limited due to the requirement of well-packed columns of monodisperse particles. Instead of capillary rise technique, Van Oss has developed an alternative method for determining the contact angles of powdered solids (Van Oss, 1994; Y ıldırım,2001). This method, which was firs t suggested by Chaudhury, is known as Thin Layer Wicking and it also depends on Washburn equation (Giese et al., 2002). When powdered particles are in question it is hard to define their radius. If they are treated as a bundle of capillaries with varying radii, it can then be found a representative r value which is called effective radius, r * . For the determination of r* , we have to use completely wetting non-polar liquids havi ng low energy. In such a case, it can considered that cosθ in Washburn equation equals to 1. With these approaches, the wicking experiment is accomplished by preparing an aqueous suspension of powder and spreading it over a microscope slide. After drying the sample, coated glass slide is immersed into the liquid. The velocity of the liquid is measured in terms of the length, l, is traveled by a liquid in time, t . First experiment should be done with a spreading n-alkane liquid (standard liquid) in order to find r* . The plot of l2 versus t gives a straight line with a slope that is needed in modified Washburn equation (2.39) : 22 μ l r* γ t = (2.39) If a second wicking experiment with the liquid in question (test liquid) is applied, the advancing contact angle value of powdered solid can be calculated with the Washburn equation by the help of r* : 23 1cos ( ) 22 μ l r* γ t −=θ (2.40) The main advantage of the TLW method is, its suitability for polydispersed suspensions of irregularly shaped particles (Y ıldırım, 2001). Semi flat shaped particles do not create homogeneous settlement in capillary tube. On the other hand, they do more homogeneous packing during thin layer settling over glass slide because they settle their large surface and form homogeneous bed of powder. This enables the reproducibility and repetability of the test results (Karagüzel, 2005). 2.5 Surfa ce Free Energy The surface free energy of solids is a characteristic parameter in determination of the surface properties like wetting, spreading, adhesion, and adsorption. Surface free energy is defined as the work required increasing th e area of substance by one unit area. It is quantified in terms of the forces acting on a unit length at the solid-liquid interface. It is also referred as the surface tension of the solid because the units’ force/length and energy/area are the same (N/m), but the phys ical functions are different. According to Adam (1956), the surface tension is numerical ly equivalent to the surface energy for all pure liquid and nonstressed pure solid surfaces. Solid surfaces are divided into high and low energy surfaces. Solids that have high specific surface free energy have high energy surfaces. Their atoms are held together by the chemical bonds; therefore large input of en ergy is needed to fracture these solids. These energies are ranging from 1000 to 4000 mJ/m 2. On the contrary, solids that have low specific surface free energies have low energy surfaces, and their molecules are held by physical forces, especially van der Waals. The free energy of these surfaces are smaller than 100 mJ/m 2 (Schrader, 1992). According to Fowkes (1972), the surface tension of non-polar liquid or the surface free energy of non-polar solid are composed of; d i p h ad eπγ γ γ γ γ γ γ γ= + + + + + + (2.41) 24 where, γ is the surface free energy of solids and indexes are referred to dispersion, induced dipole-dipole, dipole-dipole, hydrogen bonding, π bonding, electrostatic, acceptor-donor interaction, respectively. Basically, this equation can be written with dispersion and nondispersion components; d nγ γ γ= + (2.42) According to van Oss and co-workers, dispersion, induction and polarization terms can be combined into the Lifshitz van der Waals components, LW d i pγ γ γ γ= + + ( 2 . 4 3 ) so the total surface free energy of solid and liquid surface tension equals to; LW ABγ γ γ= + ( 2 . 4 4 ) where, AB 2γ γ γ+ −= and γ + is the nonadditive part of the solid surface free energy resulting from electron acceptor interactions whereas γ – results from electron donor interactions (Janczuk et al.,1998). A solid phase is very different from a liqui d phase because of the absence of surface mobility. For this reason, as in the case for a liquid phase, surface tension of a solid phase cannot be measured directly. Therefore, several different approaches have been used to measure solid surface energy, including direct force measurement, contact angle, sedimentation of particles, solidification front interactions with particles, film flotation, gradient theory, the Lifshitz theory of van der Waals forces, and theory of molecular interactions. Among these techniques, contact angle approach is the simplest one (Kwok et al., 2000). Besides, for the measurement of surface energy of powdered solids it is the most appropriate method. There are four basic approaches for evaluation of contact angles and they all depend on the Young’s equation, L S SLcosγ θ γ γ= − , that describes the wetting of solid surface with a liquid (Karagüzel, 2005). 25 2.5.1 Zism an Method (Criti cal Surfa ce Tension) Zisman et al. (1950) characterized the low surface energy surface by establishing a linear relationship between cosθ of non-polar liquids an d their surface tension, γ LV . If cosθ is plotted against γ LV , a curve that can be extrapolated to cosθ = 1 is formed. The extrapolated value is called the critical surface tension of the solid and can be used to characterize the solid surface. It is the highest value of the surface tension of a liquid which will completely wet the solid surface (Giese et al., 2002; Schultz and Nardin, 1992). The energy of the solid surface can be calculated from the slope (m) of the line using the following formula (Karagüzel, 2005); L Sc os 1 m ( )θ γ γ= − − (2.4 5) 2.5.2 Fo wk es Method (Geometric Mean) Fowkes theory is based on two assumptions; a. Surface energies are additive : γ = γd + γp + … b. Geometric mean is used for the work of adhesion for each type of energy: d d d p p p 12 1 2 12 1 2W 2 , W 2γ γ γ γ= = (2.46) This method examines the solid energy by dividing it into two components. Geometric mean approach combines the dispersive ( γd) and polar ( γp) components with the Young equation; d d p p L L S L S(1 cos ) 2( )+ = +γ θ γ γ γ γ ( 2 . 4 7 ) Owens and Wendt (1969) rearranged the equation; p p dLL S Sd d L L (1 cos ) ( ) γγ θ γ γγ γ + = + (2.48) 26 When the graph of p d L L/γ γ versus dL L(1 cos )γ θ γ+ is plotted, the slope will be p Sγ and dSγ is the intercept. Then the total free surface energy is equal to d p S S Sγ γ γ= + . 2.5.3 Wu Method (Harmoni c Mean) Wu (1971 ) has claimed that the harmonic mean is better suited for low energy surfaces, such as polymer. In this method, harmonic means of polar and dispersive energy components are being used. Contact angle is found using the two liquids with known values of γd and γp. The values are put into the following equation, and two equations are solved for d Sγ and pSγ (Karagüzel, 2005); d d d d d dL S L S L s sd d L L (1 cos ) 4 γ γ γ γθ γ γ γγ γ ⎛ ⎞+ = + + +⎜ ⎟⎝ ⎠ (2.49) 2.5.4 Van Oss (Acid Base) Method In this approach, contact angles against at least three liquids with known values of dispersive ( γ d ), acid ( γ + ) and base ( γ - ) components are measured and put into the following equation: d d L S L S L S L0.5(1 cos ) θ γ γ γ γ γ γ γ− + + −+ = + + (2.50) and the total surface energy of the solid is; d AB S S S= +γ γ γ (2.51 ) AB S S S2 + −=γ γ γ (2.52) 2.5.4.1 Oss-Chauda ry-Good Equatio n OCG equation represents a ther modynamic approach to determining the values of the surface free energy components of solids and provides the calculation of surface free energies of powdered minerals with the help of contact angle values. From the studies of Fowkes et.al and Van Oss et.al, the surface free energy of a phase i can be written as; 27 LW AB i i iγ γ γ= + (2.53) LW iγ is the non-polar components of surface free energy, while the ABiγ is the polar(acid- base) components and it conforms to the equation AB 2γ γ γ+ −= where γ + and γ - are the non additive parts of the liquid surface te nsion or solid surface free energy resulting from electron acceptor and electron donor interactions (Y ıldırım, 2001). Interaction between solid-liquid is explained with the following equation: LW AB SL SL SLG G GΔ = Δ + Δ (2.54) for LW bonds Fowkes has proposed; LW LW LW SL S LG 2 γ γΔ = − (2.55) and for acid-base interactions Van-Oss has proposed; AB SL S L S LG 2 2γ γ γ γ+ − − +Δ = − − (2.56) If we combine these three equations we get, LW LW SL S L S L S LG 2 2 2γ γ γ γ γ γ+ − − +Δ = − − − (2.57) Dupré expressed the variation in free energy associated with the solid liquid interaction with the following relation: SL SL S LG γ γ γΔ = − − (2.58) Substituting equation 2.58 into 2.57 LW LW SL S L S L S L S L2( )γ γ γ γ γ γ γ γ γ+ − − += + − + + (2.59) work of adhesion or Gibbs free energy of interaction can be related to the interfacial energies through Young’s equation; L S SLcosγ θ γ γ= − (2.60) 28 by combining this equation with the Young’s equation we get; LW LW L S L S L S L(cos 1) 2( )γ θ γ γ γ γ γ γ+ − − ++ = + + (2.61) This is known as Van Oss- Chaudary-Good equa tion and characterizes a solid surface in terms of its surface free energy components as shown in Figure 2.11. (van Oss, 1994). Figur e 2.11 : Schematic Representation of the Contact Angle Formed Between a Liquid Drop and Solid Surface (Y ıldırım, 2001) For finding the value of γs, contact angle determination with three or more liquids which at least two must be polar should be done. If the contact angle of apolar liquid is measured, this equation is reduced to; LW LW L S L(cos 1) 2γ θ γ γ+ = ( 2 . 6 2 ) Because Lγ + and Lγ − are zero and LWLγ = Lγ so LWSγ can be determined. Contact angles gained from polar liquids provide Sγ + and Sγ − by solving a set of simultaneous Young’s equations. When are known, the surface tension of the solid, Sγ , can be calculated from; LW S S S S2( )γ γ γ γ− += + (2.63) Furthermore, solid-liquid interfacial energy ca n be determined by the following formula; L W LW - + + - S L S L S L S L S Lγ = γ + γ - 2( γ γ + γ γ + γ γ ) ( 2 . 6 4 ) 29 3. EXPERIMENTAL In this part of the thesis, the experiments conducted for the determination of the contact angles of various rocks samples will be explained. The solid and liquid samples, the preparations of samples for the experiments, the equipment used in the experiments and the procedure of the experiments will be explained. 3.1 Materials 3.1.1 Solid Samples In this study, samples of quartz, calcite, glass, Berea and Bentheim sandstones and carbonate rocks are used. Quartz (SiO2, Silicon dioxide) and calcite (CaCO3, Calcium carbonate) are the most common minerals in the face of the earth. Quartz and calcite are pure and single minerals whereas; sandstone and carbonate rocks contain many different constituents. However, sandstone is composed predominantly of quartz and carbonate rock is composed primarily of calcite mineral. Sandstone may also contain detritic feldspar and zircon, grona, topaz, colombite, tantalite, andalucite, magnetite, ilmenite, rutile, monazite, casiterite, gold and platinum. Calcite and carbonate rocks are the sedimentary rocks formed by chemical precipitation; moreover calcite is the most stable carbonate mineral (Kumbasar & Aykol, 1993). Sandstones, having porosity value of about 21% and 23% respectively, are from Berea and Bentheim formations. Both sandstones and carbonate rocks are used for core analysis in Petroleum and Natural Gas Engineering Department’s laboratories in ITU. Pure quartz and calcite samples are provided from the Department of Mining Engineering. In addition to this, soda-lime glass was used in the experiment to see if its wettability behavior was similar to that of quartz mineral. For thin layer wicking experiments, samples had to be crushed and then ground to powder size below 38 µm. Average sizes (d50) and size distribution of powder particles were analyzed with Fritsch 30 Analysette 22 Compact Particle Size Analyzer that uses laser light scattering method for analyzing. 3.1.2 Liquids In this study, distilled water, brine, kerosene, mineral oil and crude oil are used as the test liquids and heptane, octane, decane and dodecane are used as the standard liquids. Distilled water and %2 NaCl solution are used as water phase. Distilled water is produced by the help of the water purification system. Brine is prepared with weight/volume proportion method (Ucko, 1982). In this method, solution is prepared according to the total volume. The amount of solid in the solution can be found using the formula given below: amount of solid w / v (100 ml solution) (volume of the solvent)= (3.1) Thus, 2 gr of NaCl is mixed with 100 ml distilled water in order to get 2% NaCl solution. Physical properties of distilled water and prepared brine are given in Table 3.1. Table 3.1 : Physical Properties of Distilled Water and 2%NaCl Solution Aqueous Phase ρ, g/ cm3 at 20oC µ, cp at 20oC γ, dyne/cm at 21oC Distilled Water 1 1.0136 72.3 %2 NaCl 1.0241 1.0701 72.6 Kerosene, mineral oil and crude oil are used as oil phase. Refined kerosene has been provided from İzmit Tüpraş Refinery. A highly refined colorless white mineral oil is from Millers Oils Ltd. Brighouse, England and crude oil is supplied from Ozan Sungurlu field. The properties of refined oils and crude oil used in the wicking experiments are given in the Table 3.2. 31 Table 3.2 : The Properties of Oil Oil Phase ρ, g/ cm3 at 20oC µ, cp at 20oC γ, dyne/cm at 21oC Kerosene 0.800 1.3528 25.43 Mineral Oil 0.860 22.31 33.91 Crude Oil 0.919 27.00 10.47 To find effective pore radius, nonpolar alkanes which do not react with rock minerals were used. Thin layer wicking experiments were first conducted with apolar liquids heptane, octane, decane, and dodecane. Then, in estimation of effective pore radius of powder bed dodecane was chosen as the standard liquid. In addition to this, for the calculation of surface free energy components contact angle measurements were also conducted using polar ethylene glycol and apolar 1-bromonaphthelene and distilled water. These apolar and polar liquids were from Merck Company and provided by Surface Chemistry Laboratory located at the Department of Mining Engineering in ITU. Properties of chemicals used in the experiments are given in Table 3.3. (Karagüzel, 2005) and values of surface tension components and the viscosities of the liquids are given in the Table 3.4 (van Oss, 1994; Asmatalu 2001). Each liquid was put in a glass container and stored in dark and cool place. Table 3.3 : Properties of Chemicals Used in the Experiments (Karagüzel, 2005) Chemical's Name Formula Molecular Weight (g/ml) Purety, % Producer Sodium Chloride NaCl 58.44 99 Merck Heptane C7H16 100.21 >99 Merck Octane C8H18 114.23 >99 Merck Decane C10H22 142.29 >99 Merck Dodecane C12H26 170.34 >99 Merck Bromonapthalene C10H7Br 207.08 >99 Merck Ethylene Glycol HOCH2CH2OH 62.07 >99 Merck 32 Table 3.4 : Values of Surface Tension Components (in mJ/m2) and Viscosities (in poise) of The Liquids used in Wicking Experiments (Van Oss, 1994; Asmatalu 2001) Liquids µ Heptane 20.3 20.30 0 0 0.0 0.00409 Octane 21.6 21.60 0 0 0.0 0.00542 Decane 23.8 23.80 0 0 0.0 0.00907 Dodecane 25.4 25.35 0 0 0.0 0.01493 Bromonapthalene 44.4 44.40 0 0 0.0 0.04890 Etylene Glycol 48.0 29.00 19 1.92 47.0 0.19900 Water 72.8 21.80 51 25.5 25.5 0.01000 3.2. Pre-studies 3.2.1 Preparation of Powdered Samples For thin layer wicking experiments, all solid samples had to be crushed to the size of sand particles and then ground to the size of powder. Samples were crushed with a hand- held hammer then sand-sized particles were ground using a mechanical agate mill. After that powdered samples were screened through a 38 µm mesh sieve. Over screen particles were ground until all material was below 38 µm. 3.2.2 Surface Tension Measurements Surface tension measurements were achieved with the KSV Sigma 701 Tensiometer (Figure 3.1), which is a modular high performance PC controlled piece of equipment. It measures force on a sample being pulled through a fluid/fluid interface so surface or interfacial tension can be measured. There are two parts to the tensiometer. The measuring unit consists of a plastic lifting stage and a balance connected to a small wire hook for hanging samples. The tensiometer is controlled via a computer running windows operating system. Lγ LWLγ ABLγ L⊕γ L−γ 33 Figure 3.1: KSV Sigma 701 Tensiometer In the experiments, a probe is hung on a balance and brought into a contact with the liquid interface tested. The forces experienced by the balance as the probe interacts with the surface of the liquid can be used to calculate surface tension. Two types of probes are commonly used, du Nouy Ring and the Wilhelmy Plate. In this study, du Nouy ring method was employed. It had been preferred for comparison purposes because many literatures have been obtained with the ring method. Furthermore, the wetted length of the ring exceeds that of the plate by a factor of 3. This leads a higher force on the balance and accordingly to a better accuracy. The figure of the du Nouy ring is given Figure 3.2. Figure 3.2 : Du Nouy Ring and its Interaction With The Liquid 34 The du nouy ring method utilizes the interaction of ring with the surface being tested. The ring was submerged below the interface and subsequently raised upwards. As the ring is moved upwards it raises a meniscus of the liquid. Eventually, the meniscus is torn from the ring and returned to its original position. The volume and thus the force exerted of the meniscus passes through a maximum value and begin to diminish prior to the actual tearing event. The process is shown in Figure 3.3. The calculation of the surface tension by this technique is based on the measurement of this maximum force. Figure 3.3 : Surface Tension Measurement Process With Du Nouy Ring Method When the surface investigated was the interface of two immiscible liquids, interfacial tension measurements were conducted. This time, the denser liquid was poured into the sample vessel before the lighter liquid. Du Nouy ring was immersed into the lighter fluid until the ring was a few mm above the interface between the two immiscible liquids. Then measurements started and the ring submerged into the denser liquid and then rose through the lighter liquid. This action helped to measurement of interfacial tension. 3.2.3 Liquid Viscosity Measurements Cannon Fenske Routine type viscometers (Figure 3.4) for transparent liquids were used for viscosity measurements. The Cannon glass viscometers let one to determine 35 viscosities using ASTM testing methods. The viscosity instruments were chosen according to the recommended viscosity ranges. The viscosity ranges are given in Table 3.5. According to this table, the viscosities of distilled water, kerosene, dodecane, and 2% NaCl solution were measured with size 50 and mineral oil was measured with size 100. Table 3. 5 : The Viscosity Ranges of Cannon Fenske Viscometers Size Approx. viscometer constant, cSt/s Range centistokes 25 0.002 0.5 to 2 50 0.004 0.8 to 4 75 0.008 1.6 to 8 100 0.015 3 to 15 150 0.035 7 to 35 200 0.1 20 to 100 Prior to the experiments, all glass parts were washed and rinsed with distilled water. Then, they were filled with chromic acid and allowed to stand for 2 days to remove any organic deposits or contaminations. After that they were washed with distilled water and then put into the oven to dry. Experiments were carried at in a constant temperature bath to measure viscosities of each liquid sample at different temperatures. The instrument was filled with the sample and put into the water bath. All the measurements were conducted after equilibrium time of approximately 15 minutes. Figure 3.4 : Cannon Fenske Viscometer 36 In order to calculate kinematic viscosity in mm2/s (cSt), efflux time in seconds was multiplied by the viscometer constant. The constant values at 40oC and 100oC were given, thus constants at other temperatures were obtained by interpolation. The viscosity in mPa.s (cP) can be obtained by the multiplication of the kinematic viscosity with the density in grams per milliliter. 3.3 Equipment The main equipments used in the thin layer wicking experiments and contact angle measurements on flat surface will be given in this section. These are glass slides, wicking apparatus, stopwatch and goniometer. 3.3.1 Glass Slides Wicking procedure was applied to the powdered sample layer spread over a glass slide. ISO Lab cut edged microscope slides, manufactured from high-optical grade soda-lime glass, were used in the experiments. The glass slides were chosen because glass has high surface energy and this will not impede the liquid adsorption into the powder (Chen, 1999). Slides were 26×76 mm in size and had 25.4 mm thickness. In each experiment approximately 35 slides were utilized with each powdered sample. On the one face of the glass slide, a scale with increments of 5 mm was marked for the observation of wetting front penetration. The cleanness of the slides was very important because any contamination on the glass surface could alter the adhesion of a powder layer and affect capillary rise. For this reason, each slide was thoroughly washed with detergent and rinsed with distilled water before coating process. Then they were kept in an oven 110oC to achieve dry coated surfaces. 3.3.2 Wicking Apparatus Coated glass slides were lowered into the beaker filled with wetting liquid by the wicking apparatus. The glass beakers used in the wicking experiments were thoroughly cleaned to avoid any contamination of wetting liquid. The wicking apparatus consists of adjustable stand, rotating handle, and fastener to which a coating sample is attached. Adjustable stand was controlled by the handle which is needed to lower and pull the 37 sample back (Tacibayev, 2004). The apparatus is described in Figure 3.5. Numbers represent; rotating handle (1), adjustable stand (2), hook (3) , fastener(4) , glass slide(5), glass container (6), wetting liquid (7), respectively. Figure 3.5 : Schematic Wicking Apparatus (Tajibaev, 2004) 3.3.3 Stopwatch Digital stopwatch was used to detect the speed of propagation of the wetting front by recording the time needed for a liquid to travel a length of each increment on the scale. Time was recorded when the wetting front reached to the first 5 mm line till the 5th line was wetted by the liquid. The t = 0 value is unknown because of the uncertainty of the time, when the liquid begins to wick through the powder film, but this is not a problem because the ratio is desired value which is the slope of the straight line and independent of the t = 0 value (Giese and van Oss, 2002). 38 3.3.4 Goniometer It is an image based instrument that makes axisymmetrical drop shape analysis (ADSA) of liquid droplets on a flat surface. It is used to measure contact angle of a test liquid placed on a flat solid surface by using the sessile drop technique. The basic elements of a goniometer include a light source, sample stage, lens, and image capture. Contact angle can be evaluated directly by measuring the angle formed between the solid and the tangent to the drop surface. The Figure 3.6 shows the basic elements of a goniometer. Figure 3.6 : Basic Elements of a Goniometer 3.4 Procedure 3.4.1 Contact Angle Measurements on Powdered Surface The thin layer wicking method was used in order to determine the contact angles of the powdered samples. This technique covers the deposition of powdered sample on the glass slides and determination of the contact angles of the powder using the Washburn equation. 3.4.1.1 Preparation of the coated sample Aqueous suspension of fine mineral particles was transferred on to clean glass microscope slides with a pipette and then water was evaporated leaving uniform thin layer of mineral powder. The concentration of powder in the water which gave the desired thickness and uniformity of film was investigated and decided to use 4% solids ratio suspensions. However, according to Holysz (1998), the measured contact angle values are independent from the thickness of the layer. He has studied different 39 thickness of layers and proved that even up to 2 mm thick, good liquid penetration values were obtained. This is important because thin layer were prepared from the deposited layer of less controlled thicknesses. Figure 3.7 : Preparation of Coated Slides (Tajibaev, 2004) To prepare the coated slides for wicking, the following procedure was applied illustrated in Figure 3.7. Four grams of sample was dispersed in 100 ml of distilled water and agitated by a magnetic stirrer to keep the particles in suspension. During stirring, aliquots of 3 ml were withdrawn with a pipette and spread equally over clean glass slide. In order to get uniform layer of coating, the suspension was accurately dispersed drop by drop on the glass surface from one end to another until the whole surface was covered with suspension. After water was evaporated at the room temperature for 24 hours, the coated slides were dried in an oven at 110oC for 1 hour to remove any residual water remaining within pores. The residual water can dilute the wicking liquids and change their surface tensions and viscosities; this may cause a change in of the capillary rise pattern (Karagüzel et al., 2005). This procedure was applied to obtain, a uniform thin layer of powdered sample adhering to the surface of the glass. 3.4.1.2 Wicking experiment Wicking experiments were performed by immersing the slides vertically into 5 mm depth of wicking liquids in a beaker. Prior to immersion tests, the glass slide was kept inside a closed container for about 1 hour, to allow the powder to come in to contact with the vapor of the wicking liquid for equalizing the spreading pressure (Yıldırım, 40 2001). Once the equilibrium was attained, the slide was immersed into the liquid and at this instant; the stopwatch was started to measure the time at which the liquid front reaches each of the marks on the slide. The rise of the liquid up to 2 cm from the liquid entry level was observed. About 35 slides were prepared for each sample and each measurement was repeated at least 3 times. The average wicking times for each sample were given in Appendix A. The schematic description of thin layer wicking experiment is given in Figure 3.8. Figure 3.8 : Schematic Representation of Thin Layer Wicking Experiment (Tajibaev,2004) 3.4.1.3 Determination of effective pore radius The value of r* in Washburn equation which is the pore size characteristics of a powder bed was determined using completely wetting liquids (non-polar) having low energy. In Wu and Nancollas’s paper (1999), it was stated that using spreading liquids like n- alkanes, θ remains exactly equal to zero in Washburn equation, so that cosθ =1, as a result of the formation of precursor film. By the elimination of contact angle value, effective pore radius can be obtained. Experiments were conducted with heptane, octane, decane and dodecane owing to their low surface tension and non-polarity. It was observed that experiments conducted with heptane and octane gave smaller value of r*. Holysz (1998) explained the reason for the smaller r* value with the partially evaporation of these hydrocarbons from the surface during the penetration process. Taking r* constant, a liquid that yielded the highest value 41 of r*cosθ was considered to be a standard liquid. In this case, also taking into account volatility and viscosity best results were obtained with dodecane. Therefore, dodecane was chosen as the standard liquid to be used in wicking experiment to find r*. 3.4.1.4 Contact angle measurement During the wicking experiment conducted with the standard liquid, the travel distance (l2) was recorded as a function of time (t). The plot of l2 versus t formed a straight line. Because the standard liquid completely wets the surface, cosθ equals to 1. So r*, which is the radius of a capillary tube that would wick a given liquid at the same rate as the powder would, can be easily calculated. After the mean pore radii determination, the same wetting tests were performed with test liquid. In these tests, again linear plots of l2 versus t were determined. Therefore, the contact angle values of test liquids were calculated from the slopes and obtained r* values by the help of the Washburn equation. 3.4.2 Contact Angle Measurements on Flat Surface Contact angles of polished solid samples may be measured using sessile drop method. This time, the experiments conducted on flat solid surface and the results of thin layer wicking method are compared with goniometric measurements. 3.4.2.1 Goniometric measurements The contact angle measurements were conducted on polished surfaces of quartz, calcite and glass slide employing sessile drop technique. In this method, a small drop of liquid was placed on the surface of a polished sample with a syringe and the contact angle was measured using a goniometer. The static angle formed between the liquid drop and flat solid surface was read from the scale of the goniometer with the help of a microscope. These experiments were performed for distilled water, brine, kerosene, dodecane and mineral oil on glass slide, polished quartz and calcite mineral surfaces. The measured values are given in Table 3.6. These results were compared with contact angle values obtained from thin layer wicking method. 42 Table 3.6 : Results of Goniometric Measurements Liquids θο, on Glass Slide θο, on Polished Quartz θο, on Polished Calcite Distilled Water 10 30 75 Brine 10 35 70 Dodecane 0 0 16 Kerosene 0 0 10 Mineral Oil 0 0 12 3.4.3 Determination of the Surface Energy Components Oss-Chaudary-Good equation characterizes a solid surface in terms of its surface free energy components. The values of γ LW, ⊕ Lγ and −Sγ for a solid can be derived from the contact angle values obtained by the thin layer wicking method, provided that the surface tension properties of the liquid are known. To determine these values, three wicking tests were conducted with polar water and ethylene glycol and apolar bromonapthalene using the same experimental procedure. ⊕ Lγ and −Sγ values of bromonapthalene are zero so LWSγ was easily determined from the contact angle measurement. As LWSγ was estimated, the values of ⊕ Lγ and −Sγ were determined from the contact angle measurements conducted with water and ethylene glycol. Water has the largest value of the Lewis acid parameter. Since the ⊕ Lγ interacts with the −Sγ , a large ⊕ Lγ value ensures that the product of ⊕Lγ −Sγ will be large yielding a well determined value of − Sγ . Other polar liquids have low and similar ⊕Lγ values that create difficulties in finding a unique and reliable value of − Sγ . Therefore, water must be one of the liquids in energy calculations (Giese and van Oss, 2002). Once the three surface tensions are obtained, the surface tension of the solid, γ s, can be determined. It should be pointed out that by test liquids, it is not possible to determine the whole surface free energy of a substance but only to estimate certain components of the surface free energy, usually those which are present in the test liquids (Karagüzel et al. 2005). The thin layer wicking experiments were also performed to determine the surface energy components of calcite and glass samples with polar distilled water and ethylene glycol and apolar bromonapthalene. By the help of their cosθ values and known parameters of liquids, the surface free energy components were calculated and tabulated in Table 3. 43 Table 3.7 : The Surface Free Energy Components of Calcite and Glass Samples Calcite 36.61 29.17 7.44 0.68 20.36 4.57 Glass 49.54 21.48 28.06 7.08 27.80 -1.56 3.5 The Procedure for Calculations 3.5.1 Contact Angle Calculations The composition of Berea sandstone that was used in sample calculations is given Table3.8. Table 3.8 : Composition of Berea Sandstone (Ma & Morrow, 1991) Mineral % Quartz 78.5 Rock fragments 8.6 Dolomite 2.5 Calcium oxide 0 Untwinned feldspar 5.3 Microline feldspar 0.7 Chert 1.6 Kaolinite 2.8 Total solids 100 Porosity (%) 18.3 3.5.1.1 Vapor-liquid-solid interface For the calculation of contact angle formed between air-water-solid surface two wicking experiments were done. To determine effective radius, wicking experiments were conducted by dodecane with at least on three coated slides. Test results are shown in Table 3.9. Table 3.9 : Distance against Wicking Time For Dodecane Wicking Time, seconds Distance, l, cm l2, cm2 t1, s t2, s t3, s 0.5 0.25 7 6 10 1 1 36 34 38 1.5 2.25 75 74 84 2 4 135 127 157 Sγ LWSγ AB Sγ S⊕γ S−γ SLγ 44 The given data was plotted on the graph in order to obtain the slopes of ( tl /2 ) for dodecane and to calculate r* in Figure 3.9. 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0 50 100 150 200 Time, s l2 , cm 2 do1 do2 do3 Figure 3.9 : Wicking Experiment of Berea Sample with Dodecane The average slope value for dodecane was found as 0.02876. ( )2 dl /t = . Equation (2.39), was used for the calculations of effective pore radius. In calculations, 25.38 dyne / cmLγ = and 0.015454 Poiseµ = (at 20oC) for dodecane were used. 52 0.015454 0.02876 3.503 10 (cm) 25.38 2 * 2µ l r = γ t − × = = × To determine contact angle of water the wicking experiments were conducted using water making at least three repetitions, and the results are given in Table 3.10. Table 3.10 : Distance against Wicking Experiment Time for Water Wicking Time, seconds Distance, l, cm l2, cm2 t1, s t2, s t3, s 0.5 0.25 8 7 6 1 1 17 17 20 1.5 2.25 36 34 36 2 4 55 54 60 45 The given data were plotted on the graph in order to obtain the slopes of tl /2 for water. The average slope of the graph (Fig.3.10) plotted by these data was found as ( ) 0.07952 w l /t = . 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0 10 20 30 40 50 60 70 Time, s l2 , cm 2 dw1 dw2 dw3 Figure 3.10 : Wicking Experiment of Berea Sample with Water The contact angle of distilled water was calculated using Equation (2.40). In these equations, the values of 72.3 dyne / cmLγ = and 0.010136 Poiseµ = (at 20oC) for distilled water were used. 5 2 2 0.010136 0.0795 0.636 3.503 10 72.3 2 * µ l cosθ= r γ t − × = = × × ( )2 0.636 51 2 -1 -1 * η lθ=cos =cos r γ t   =   Thus, the value of the contact angle of distilled water with respect to the particles’ surface for the Berea sandstone sample was determined as 51o. 46 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0 50 100 150 Time, s l2 , cm 2 dodecane distilled water brine kerosene Figure 3.11 : The Results of Wicking Experiments for Dodecane, Distilled Water, Brine and Kerosene on Berea Sample Contact angles of 2% NaCl solution, kerosene, mineral oil and crude oil on this sample were calculated in the same manner. The slopes of these liquids are given in Figure 3.11 and Figure 3.12. According to these results, the calculated contact angle values are given in Table 3.11. Table 3.11 : The Calculated Contact Angle Values of Test Liquids on Berea Sample θ o Distilled Water 51 2% NaCl solution 50 Kerosene 25 Mineral Oil 45 Crude Oil 70 47 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0 500 1000 1500 2000 2500 Time, s l2 , cm 2 mineral oil crude oil Figure 3.12 : The Results of Wicking Experiments for Mineral Oil and Crude Oil on Berea 3.5.1.2 Liquid-liquid-solid interface To estimate the contact angle formed on the distilled water-kerosene-solid interface, Equation (2.9) was used. Contact angles of distilled water dwθ and kerosene kθ on Berea sandstone powdered samples were calculated as 51o and 25o, respectively. The interfacial tension between distilled water and kerosene dw-kγ is 43.5 dyne/cm. Surface tensions of distilled water, dwγ , and kerosene, kγ , are 72.3 dyne/cm and 25.43 dyne/cm, respectively. ( ) ( ) ( ) 72.3 cos 51 25.43 cos 25 0.5278 43.5 52.78 58 (2.9)dw dw k kdw-k dw-k -1 dw-k γ cosθ -γ cosθ cosθ = γ θ cos × − × = = = = 48 Thus, the contact angle value of distilled water/ kerosene/ Berea sandstone sample was determined as 58o. 3.5.1.3 Alternative determination of the r* and its effect on contact angle measurements In this part, the thin layer wicking experiments are performed with heptane, octane, decane and dodecane. The test results are given in Table 3.12 and the effective pore radius is determined as r*= 0.0008 from the slope of 2Lγ -2µl /t graph in Figure 3.13. Table 3.12 : Thin Layer Wicking Results for Apolar Liquids Liquids γ (dyne/cm) 2*µ*l2 / t Heptane 20.3 0.00060 Octane 21.6 0.00071 Decane 23.8 0.00076 Dodecane 25.38 0.00103 y = 8E-05x - 0.001 R2 = 0.8828 0.00000 0.00020 0.00040 0.00060 0.00080 0.00100 0.00120 0 5 10 15 20 25 30 surface tension, dyne/cm 2* µ* l2 / t Figure 3.13 : Determination of Effective Pore Radius from Apolar Liquids 49 The contact angles of the Berea sandstone are calculated with the Washburn equation by using the slope r* = 0.00008 in Figure 3.13. The calculated contact angle values and are given in Table 3.13. When these results are compared with the results determined from using only dodecane as the standard liquid presented in Table 3.12 and 3.13, it can be observed that dodecane is found to be the most suitable alkane to be used as a standard liquid for effective pore radius measurements in Thin Layer Wicking experiments. Table 3.13 : The Contact Angle Values With respect to Apolar Liquids and Dodecane With Apolar Liquids With Only Dodecane θo θo Distilled Water 72 51 Brine 75 50 Kerosene 65 25 Mineral Oil 70 45 Crude Oil 80 70 3.5.2 Surface Free Energy Calculations Solid surface free energy can be calculated from the summation of the Lifshitz van der Walls and acid-base interactions from the liquids that have known surface tensions. Here, the powdered calcite sample’s free surface energy is calculated from the contact angles of water, bromonapthelene and ethylene glycol found with the thin layer wicking experiments. The Thin Layer Wicking measurements for bromanapthalene and ethylene glycol are shown in the Figure 3.14. By using these l2/t values in Washburn equation, the cosθ values of bromonapthalene and ethylene glycol are found 0.621 and 0.668, respectively. Also the cosθ of distilled water is found 0.423. The necessary values of liquids that are used in these calculations are given in Table 3.14. 50 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0 2000 4000 6000 8000 10000 12000 Time, s l2 , cm 2 ethylene glychol bromonapthalene Figure 3.14 : Thin Layer Wicking Experiment for Bromonapthalene and Ethylene Glycol on Calcite Sample Table 3.14 : The Surface Tensions and cosθ Values of Liquids on Calcite Liquids Cos θ Bromonapthalene 44.4 44.40 0 0 0.0 0.621 Ethylene Glycol 48.0 29.00 19 1.92 47.0 0.668 Distilled Water 72.8 21.80 51 25.5 25.5 0.423 For the calculation of the Lifshitz van der Walls energy bromanapthalene is used because it has no acid-base interaction. For this reason Oss-Chaudary-Good equation (Eq.2.61) becomes Equation 2.61 ; LW LW L S L LW L S LW 2 S (1 cos ) 2( ) (1 0.621) 2( 44.4) 29.17 mJ / m + γ = γ γ + γ = γ γ = θ Lγ LWLγ ABLγ L⊕γ L−γ 51 After that, solid surface’s energy components and solid surface free energy can be calculated from the polar liquids; distilled water and ethylene glycol using again the OCG equation (Eq.2.61). The calculations for distilled water are given below: LW LW L S L S L S L S S S S (1 cos ) 2( ) (1 0.4234)72.3 2( 29.17 21.8 25.5 25.5) 26.23 5.05 5.05 − + + − − + − + + γ = γ γ + γ γ + γ γ + = × + γ + γ = γ + γ θ There appears an equation having two unknowns. Furthermore, same equation is used for ethylene glycol and another equation having two unknowns is obtained. LW LW L S L S L S L S S S S (1 cos ) 2( ) (1 0.668)48 2( 29.17 29 1.92 47) 10.95 1.39 6.86 − + + − − + − + + γ = γ γ + γ γ + γ γ + = × + γ + γ = γ + γ θ When we solve these two equations simultaneously we can find S −γ = 20.36 mJ/m2 and S +γ = 0.68 mJ/m2. Acid-base interaction energy can be calculated with Equation (2.52). AB S S S AB S AB 2 S 2 2 20.36 0.68 7.44 mJ / m + −γ = γ γ γ = × γ = Then calcite surface free energy is the summation of ABSγ and LWSγ (Eq. 2.63). LW AB 2 S S S 29.17 7.44 36.61mJ / mγ = γ + γ = + = Lastly, calcite-water interfacial energy can be determined by Equation (2.64) ; LW LW SL S L S L S L S L SL 2 SL 2( ) 36.61 72.3 2( 29.17 21.8 20.36 25.5 0.68 25.5) 4.57 mJ / m − + + −γ = γ + γ − γ γ + γ γ + γ γ γ = + − × + × + × γ = 52 4. EVALUATION OF EXPERIMENTAL RESULTS In this section, the results of Thin Layer Wicking experiments conducted on quartz, glass, Berea and Bentheim sandstones, calcite and carbonate rocks using standard (dodecane) and test liquids (distilled water, brine, kerosene, mineral oil, and crude oil) will be evaluated. The comparison of apolar standard liquids (heptane, octane, decane, and dodecane) which were used to find average pore radius will be given. Furthermore, the surface free energy calculations for calcite and glass samples due to distilled water, obtained by the help of Thin Layer Wicking results conducted with polar bromanapthalene and apolar ethleyene glycol will be compared. 4.1 The Results of Thin Layer Wicking Experiments 4.1.1 The Results For Quartz The results of Thin Layer Wicking Experiments with respect to dodecane and test liquids - distilled water, brine, kerosene, mineral oil - for quartz mineral are given in Figures 4.1 and 4.2. The result of mineral oil has to be given in another plot because of longer wicking time in comparison to the other liquids due to mineral oil’s lower wicking tendency. It can be seen that distilled water and brine give similar wicking rate like dodecane and kerosene do. 53 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0 50 100 150 200 Time, s l2 , cm 2 dodecane distilled water brine kerosene Figure 4.1 : The Results of Wicking Experiments for Dodecane, Distilled Water, Brine and Kerosene on Quartz 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0 500 1000 1500 2000 Time, s l2 , cm 2 mineral oil Figure 4.2 : The Results of Wicking Experiments for Mineral Oil on Quartz 54 The calculated contact angle values according to test liquid/air/quartz system are given in Table 4.1. Consistent with the results of goniometer, the distilled water and brine has low contact angle values but mineral oil has lower value showing higher spreading tendency. Kerosene shows complete spreading over quartz mineral. Besides, the calculated contact angle values according to liquid/liquid phase/quartz system are given in Table 4.2. From these results, it can be concluded that quartz mineral is strongly water wet according to the cut-off values cited in the literature (Morrow, 1991). Table 4.1 : The Calculated Contact Angle Values of Test Liquids for Quartz Liquids θo Distilled Water 26 Brine 26 Kerosene 0 Mineral Oil 15 Table 4.2 : The Calculated Contact Angle Values of Liquid-Liquid- Quartz Liquids θo Distilled Water - Kerosene 24 Brine - Kerosene 13 Distilled Water- Mineral Oil 47 Brine - Mineral Oil 32 4.1.2 The Results For Glass The results of Thin Layer Wicking Experiments conducted using dodecane and test liquids - distilled water, brine, kerosene - for glass are given in Figure 4.3 Also, the results for mineral oil is given in Figure 4.4. It can be seen that distilled water and brine give similar wetting tendencies. 55 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0 10 20 30 40 50 60 Time, s l2 , cm 2 dodecane distilled water brine kerosene Figure 4.3 : The Results of Wicking Experiments for Dodecane, Distilled Water, Brine and Kerosene on Glass 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0 100 200 300 400 500 600 700 Time, s l2 , cm 2 mineral oil Figure 4.4 : The Results of Wicking Experiments for Mineral Oil on Glass 56 The calculated contact angle values according to test liquid/air/glass system are given in Table 4.3. Consistent with the results of goniometer, kerosene and mineral oil has lower value showing higher spreading tendency than the distilled water and brine. Besides, the calculated contact angle values according to liquid /liquid/ glass system are given in Table 4.4. From these results, it can be concluded that glass used in this study is water wet according to the cut-off values cited in the literature (Morrow, 1991). Table 4.3 : The Calculated Contact Angle Values of Test Liquids for Glass Liquids θo Distilled Water 45 Brine 48 Kerosene 6 Mineral Oil 5 Table 4.4 : The Calculated Contact Angle Values of Liquid-Liquid-Solid Interface for Glass Liquids θo Distilled Water - Kerosene 53 Brine - Kerosene 56 Distilled Water- Mineral Oil 68 Brine - Mineral Oil 68 4.1.4 The Results For Berea Sandstone The results of Thin Layer Wicking Experiments carried out with dodecane and test liquids - distilled water, brine, kerosene - for Berea sandstone are given in Figure 4.5 Furthermore; the results for mineral oil and crude oil are given in Figure 4.6. It can be seen that distilled water and brine give similar wetting tendencies. In addition mineral oil and crude oil have higher wicking properties. 57 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0 50 100 150 Time, s l2 , cm 2 dodecane distilled water brine kerosene Figure 4.5 : The Results of Wicking Experiments for Dodecane, Distilled Water, Brine and Kerosene on Berea 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0 500 1000 1500 2000 2500 Time, s l2 , cm 2 mineral oil crude oil Figure 4.6 : The Results of Wicking Experiments for Mineral Oil and Crude Oil on Berea 58 The calculated contact angle values according to test liquid/ air / Berea system are given in Table 4.5. The thin layer wicking experiment was also performed for mineral oil and crude oil and it can be seen that crude oil gives the highest contact angle value. Besides, the calculated contact angle values according to liquid/ liquid/ Berea system are given in Table 4.6. From these results, it can be concluded that Berea sandstone used in this study is water wet according to the cut-off values cited in the literature (Morrow, 1991). Table 4.5 : The Calculated Contact Angle Values of Test Liquids for Berea Liquids θo Distilled Water 51 Brine 50 Kerosene 25 Mineral Oil 45 Crude Oil 70 Table 4.6 : The Calculated Contact Angle Values of Liquid-Liquid-Solid Interface for Berea Liquids θo Distilled Water - Kerosene 58 Brine - Kerosene 55 Distilled Water- Mineral Oil 65 Brine - Mineral Oil 68 4.1.4 The Results For Bentheim Sandstone The results of Thin Layer Wicking Experiments employing dodecane and test liquids - distilled water, brine, kerosene - for Bentheim sandstone are given in Figure 4.7 It can be seen that wicking behaviors of dodecane and kerosene differ from distilled water and brine. Also, the results for mineral oil is given in Figure 4.8. 59 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0 200 400 600 800 Time, s l2 , cm 2 dodecane distilled water brine kerosene Figure 4.7 : The Results of Wicking Experiments for Dodecane, Distilled Water, Brine and Kerosene on Bentheim 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0 2000 4000 6000 8000 10000 12000 Time, s l2 , cm 2 mineral oil Figure 4.8 : The Results of Wicking Experiments for Mineral Oil on Bentheim 60 The calculated contact angle values for test liquid/air /Bentheim system are given in Table 4.7. Kerosene has lower contact angle value which represent higher wetting ability. Also mineral oil has lower contact angle values than aqueous phases. Furthermore, the calculated contact angle values in the case of aqueous phase/ oil phase/Bentheim system are given in Table 4.8. From these results, it can be concluded that Bentheim sandstone has intermediate wetting according to the cut-off values cited in the literature (Morrow, 1991). Table 4.7 : The Calculated Contact Angle Values of Test Liquids for Bentheim Liquids θo Distilled Water 62 Brine 64 Kerosene 9 Mineral Oil 34 Table 4.8 : The Calculated Contact Angle Values of Liquid-Liquid-Solid Interface for Bentheim Liquids θo Distilled Water - Kerosene 79 Brine - Kerosene 81 Distilled Water- Mineral Oil 83 Brine - Mineral Oil 85 4.1.5 The Results For Calcite The results of Thin Layer Wicking Experiments using dodecane and test liquids - distilled water, brine, kerosene - for calcite mineral are given in Figure 4.9, and the results for mineral oil and crude oil are given in Figure 4.10. It can be seen that distilled water and brine have similar wetting tendencies, while mineral oil and crude oil have higher wicking properties. Mineral oil and crude oil have longer wicking time due to their higher wicking properties. 61 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0 100 200 300 400 Time, s l2 , cm 2 dodecane distilled water brine kerosene Figure 4.9 : The Results of Wicking Experiments for Dodecane, Distilled Water, Brine and Kerosene on Calcite 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0 2000 4000 6000 8000 Time, s l2 , cm 2 mineral oil crude oil Figure 4.10 : The Results of Wicking Experiments for Mineral Oil and Crude Oil on Calcite 62 The calculated contact angle values according to test liquid/ air /calcite system are given in Table 4.9. Kerosene has zero contact angle value which represents complete wetting. Also mineral oil has lower contact angle values than aqueous phases. In addition, crude oil has the highest contact angle value. Furthermore, the calculated contact angle values for aqueous phase/ oil phase/ calcite system are given in Table 4.10. From these results, it can be concluded that calcite mineral used in this study has intermediate wetting according to the cut-off values cited in the literature (Morrow, 1991). Table 4.9 : The Calculated Contact Angle Values of Test Liquids for Calcite Liquids θo Distilled Water 67 Brine 65 Kerosene 0 Mineral Oil 32 Crude Oil 71 Table 4.10 : The Calculated Contact Angle Values of Liquid-Liquid-Solid Interface for Calcite Liquids θo Distilled Water - Kerosene 87 Brine - Kerosene 82 Distilled Water- Mineral Oil 81 Brine - Mineral Oil 78 4.1.6 The Results For Carbonate Rock – Sample 536 The results of Thin Layer Wicking Experiments in the case of dodecane and test liquids - distilled water, brine, kerosene - for carbonate rock, (sample 536), are given in Figure 4.11. and the results for mineral oil and crude oil are given in Figure 4.12. It can be seen that the four liquids have similar wetting tendencies. In addition, crude oil has a very long wicking time. 63 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0 200 400 600 800 1000 1200 Time, s l2 , cm 2 dodecane distilled water brine kerosene Figure 4.11 : The Results of Wicking Experiments for Dodecane, Distilled Water, Brine and Kerosene on Carbonate Rock 536 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0 2000 4000 6000 8000 10000 12000 14000 Time, s l2 , cm 2 mineral oil crude oil Figure 4.12 : The Results of Wicking Experiments for Mineral Oil and Crude Oil on Carbonate Rock 536 64 The calculated contact angle values according to test liquid/air/carbonate system are given in Table 4.11. Mineral oil has zero contact angle value which represents complete wetting. While kerosene has lower contact angle values than aqueous phases. In addition, crude oil has the highest contact angle value. Furthermore, the calculated contact angle values according to aqueous phase/oil phase/carbonate system are given in Table 4.12. From these results, it can be concluded that carbonate rock used in this study is oil wet according to the cut-off values cited in the literature (Morrow, 1991). Table 4.11 : The Calculated Contact Angle Values of Test Liquids for Carbonate Rock 536 Liquids θo Distilled Water 76 Brine 78 Kerosene 32 Mineral Oil 0 Crude Oil 81 Table 4.12 : The Calculated Contact Angle Values of Liquid-Liquid-Solid Interface for Carbonate Rock 536 Liquids θo Distilled Water - Kerosene 96 Brine - Kerosene 99 Distilled Water- Mineral Oil 121 Brine - Mineral Oil 134 4.1.7 The Results For Carbonate Rock - Sample703 The results of Thin Layer Wicking Experiments with respect to dodecane and test liquids - distilled water, brine, and kerosene - for carbonate rock (sample 703) are given in Figure 4.13 Furthermore; the results for mineral oil and crude oil are given in Figure 4.14. It can be seen that the four liquids display similar wetting tendencies. In addition, crude oil has high wicking inclination. 65 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0 200 400 600 800 1000 1200 Time, s l2 , cm 2 dodecane distilled water brine kerosene Figure 4.13 : The Results of Wicking Experiments for Dodecane, Distilled Water, Brine and Kerosene on Carbonate Rock 703 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0 5000 10000 15000 20000 25000 Time, s l2 , cm 2 mineral oil crude oil Figure 4.14 : The Results of Wicking Experiments for Mineral Oil and Crude Oil on Carbonate Rock 703 66 The calculated contact angle values according to test liquid/air/carbonate system are given in Table 4.13. Kerosene and mineral oil have lower contact angle values than aqueous phases. In addition, crude oil has highest contact angle value. Furthermore, the calculated contact angle values according to aqueous phase/oil phase/carbonate system are given in Table 4.14. From these results, it can be concluded that carbonate rock used in this study is oil wet according to the cut-off values cited in the literature (Morrow, 1991). Table 4.13 : The Calculated Contact Angle Values of Test Liquids for Carbonate Rock 703 Liquids θo Distilled Water 76 Brine 74 Kerosene 24 Mineral Oil 36 Crude Oil 81 Table 4.14 : The Calculated Contact Angle Values of Liquid-Liquid-Solid Interface for Carbonate Rock 703 Liquids θo Distilled Water - Kerosene 98 Brine - Kerosene 95 Distilled Water- Mineral Oil 103 Brine - Mineral Oil 106 4.2 The Comparison of the Standard Liquids Experiments were conducted with heptane, octane, decane, and dodecane due to their low surface tension and apolarity. Taking into account volatility and viscosity, dodecane that gives the highest value of r*cosθ was selected as the standard liquid, and all calculations were performed with its r* value. It has been observed that there was a rapid evaporation of octane and heptane from the surface during the penetration process. This can negatively affect the penetration rate and cause erroneous values of r*. Therefore the effect of evaporation should be handled seriously if octane and heptane 67 wanted to be used in wicking experiments. It was also observed that calculations of contact angles with respect to dodecane gave better results than calculations of contact angles with respect to apolar liquids. This deduction can be seen in Table 3.13. 4.3 The Results of Surface Free Energy Components The calculated surface free energy components of calcite and glass were given in Table 4.15. According to Karaguzel (2005), when hydrophobicity increases the Lifshitz van der Waals interaction energy increases, because it replaces the place of acid-base energy components. From Table 4.15, it can be seen that calcite has a higher LWSγ value and lower ABSγ value than glass. This proves that calcite is more hydrophobic than glass. Moreover, the results show that calcite has higher solid-liquid interfacial tension than glass which means that calcite needs more energy to form unit solid-liquid interface. This also leads to a more hydrophobic surface. The conclusion that calcite is more hydrophobic than glass is in well agreement with the result obtained with contact angle calculations using thin layer wicking method. Table 4.15 : The Surface Free Energy Components of Calcite and Glass Samples Calcite 36.61 29.17 7.44 0.68 20.36 4.57 Glass 49.54 21.48 28.06 7.08 27.80 -1.56 Sγ LWSγ AB Sγ S⊕γ S−γ SLγ 68 5. CONCLUSIONS The appl icat ion of the Wash bur n equati on is a very usefu l approa ch to qua nti fy the wett abi l i t y of a porous core sample wit h hete rogeneous mi ner al ogi ca l composi ti on avai la bl e in powde r ed form. Powd ered sampl e of quartz mi neral was pr ove d to be more wat er - w e t than powde r e d sampl e of ca lc ite min era l. Furthe rmore ; the con ta ct angl e values of car bona te s are close r to that of calci t e whil e the cont a ct angl e valu es of Berea and Bent hei m sand st one and gro und gl ass are closer to that of quart z. This stu dy is the first Thi n Layer Wick in g st udy in Petroleum and Natu ral Gas Engi neeri ng fi el d and it can be a leadi ng surv ey to attempt new investig at ions in this subj ect. The con tact angle values obtained fro m Thin Layer Wicki ng Experime nt s and the goniometri c result s are found to be in good agreemen t wit h the lit eratu re. Speci fic to the mineral and rock sampl es used in thi s st udy, quartz mi ner al is found to be str ongl y water wet whereas the san dston e samp les and glass are fou nd t o be water wet accordi ng to the cut off val ues ci ted in the literature. Speci fi c to the miner a l and rock sampl e s used in thi s stud y, the calcit e mi ne r al is fou nd to be int er me dia te wate r wet and the car b ona t es are foun d to be oil wet accordi ng to the cut off values ci te d in the lite ratur e. The surface free energ y val ues of calci te and glass are in good agr eement wi th the valu es fou nd in the liter at ure . Acc ordi ng to the calcul at ed surfa ce fr ee ene rgy compo n en ts cal ci te is pro ved to be more hydroph obi c than gl ass. This con cl usio n fi ts wit h the resul ts obta i n e d from cont a ct angl e calcu l atio n s by using Thi n Layer Wi cki ng techni que. Dodecane is fou nd to be the most suit able al kan e to be used as a standard liq uid for effe ct ive pore radi us measur emen ts in Thin Lay er Wicki ng experi men ts. 69 6. RECOMMENDATIONS Thin Layer Wic ki ng Metho d has been pro ve d to pro vid e cl earl y acce pta bl e and consisten t resul ts of advanci ng contact angles measured on the powd ered sampl es. The importance of int er facial tension and viscos i ti es of stan dard and test liqui ds on Thi n Layer Wicki ng experime nts should be wel l unde rstoo d and the effects of temperature and humid it y shoul d not be igno red . Extr eme care should be appli ed when handling the sampl es to not let any pur it ies mi x into the powder sampl e s . Also, all equipme n t s especi al ly glass slid e should be clea ned thorou gly . The direct inh al at ion of alkanes sho uld be avoi ded due to their hazardo us vap or therefor e through out the each exper imen t the laborator y shoul d be well vent il at ed. The relati ons hi p of wet ta bi li ty wit h sur fa c e free ener g y can be furt h e r inve s t i ga t e d . For future st udi e s , the relati o n betwe e n the contact angl es measur ed us i ng Thi n Layer Wicki ng Met hod, and the val ues of wet tabili ty measu r ed by other met hod s used in petroleum indu st ry (e.g . Capil lary ri se) is of special interest. Spon taneous imbib it ion can be studied wit h the same rock sampl e s and a corre la t i o n can be for med between powder wickin g and spontane o u s imbi bit i o n . Alterat ion of wet tabi lity by changi ng brine comp osit ion and rock typ e and usi ng di fferen t type of cru de oil fro m different for mati ons, fur thermore the effect of the temperat u r e on the contact angle can also be stu died by Thin Lay er Wicki ng Tech niq ue. 70 REFERENCES Adam, N.K., 1956., P h y s i c a l C h e m i s try , Oxford University Press, London. Adamson, A.W., 1990. P h y s i c al C h e m i s try of S urfaces , John Wiley & Sons, Inc., Los Angeles, California. Amott, E., 1959. 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WICKING TIME VERSUS L2 FOR SAMPLES 75 Table A.1 : Wickin g Time versus l 2 For Quartz Sa mple Wicking Time for Test Liquids, (t, seconds) Distance, l, cm l 2 , cm 2 Dode cane D. water Brine Kerosene Mineral oil 0,5 0,25 10 6 6 10 48 1 1 40 16 16,5 46 310 1,5 2,25 106 34 35 101 960 2 4 184 59 63 190 1740 Table A.2 : Wickin g Time versus l 2 For Glass Sampl e Wicking Time for Test Liquids, (t, seconds) Distance, l, cm l 2 , cm 2 Dode cane D. water Brine Kerosene Mineral oil 0,5 0,25 4 2 3 3 17 1 1 12 6 6 9 128 1,5 2,25 27 11 11 18 285 2 4 52 19 21 35 575 Table A.3 : Wickin g Time versus l 2 For Berea Sandst o n e Sample Wicking Time for Test Liquids, (t, seconds) Distance, l, cm l 2 , cm 2 Dode cane D. water Brine Kerosene Mineral oil 0,5 0,25 8 7 4 7 65 1 1 36 17 15 28 385 1,5 2,25 78 34 30 68 960 2 4 140 54 54 120 1680 Table A.4 : Wickin g Time versus l 2 For Benthei m Sandsto n e Sample Wicking Time for Test Liquids, (t, seconds) Distance, l, cm l 2 , cm 2 Dode cane D. water Brine Kerosene Mineral oil 0,5 0,25 31 16 17 26 390 1 1 161 79 84 153 1920 1,5 2,25 382 175 205 358 4980 2 4 738 355 405 660 9600 Table A.5 : Wickin g Time versus l 2 For Calcit e Sa mple Wicking Time for Test Liquids, (t, seconds) Distance, l, cm l 2 , cm 2 Dode cane D. water Brine Kerosene Mineral oil 0,5 0,25 20 16 13 20 183 1 1 85 48 52 78 985 1,5 2,25 191 110 103 168 2740 2 4 336 205 198 295 5700 76 Table A.6 : Wickin g Time versus l 2 For Carbonat e Rock Sample 536 Wicking Time for Test Liquids, (t, seconds) Distance, l, cm l 2 , cm 2 Dode cane D. water Brine Kerosene Mineral oil 0,5 0,25 30 23 25 20 165 1 1 184 135 151 160 1860 1,5 2,25 463 365 455 480 3624 2 4 933 860 1050 9 1 5 7250 Table A.7 : Wickin g Time versus l 2 For Carbonat e Rock Sample 703 Wicking Time for Test Liquids, (t, seconds) Distance, l, cm l 2 , cm 2 Dode cane D. water Brine Kerosene Mineral oil 0,5 0,25 37 31 32 38 285 1 1 203 184 170 210 2260 1,5 2,25 552 495 420 565 6900 2 4 1059 1005 930 1020 13500 Table A.8 : Wickin g Time versus l 2 For Crude Oil Wicking Results for Crude Oil Distance, l, cm l 2 , cm 2 Berea Calcit e Carbonat e - 53 6 Carbonat e - 70 3 0 , 2 5 0,06   36  0,5 0,25 82 400 775 1240 0,75 0,56   3060  1 1,00 465 1800 6720 9000 1,25 1,56   11700  1,5 2,25 1119 3615  20700 2 4,00 2220 7272   77 CURRICULUM VITAE Fatma Bahar Öztorun was born in 1981, İstanbul. She graduated from Petroleum and Natural Gas Engineering programme at Istanbul Technical University in 2003. She is still taking her master programme in Petroleum and Natural Gas Engineering at ITU. She has been a research assistant in the same department since February 2005.