Köpük reolojisi üzerine deneysel çalışmalar

Abstract

COz ile petrol Üretimini artırma yönteminin önemli bir sorunu gazın petrole göre daha düşük olan akmazlığı ve yoğunluğu nedeniyle rezervuarda kanallaşma ve yerçekimi ile ayrışmasıdır. Bu sorunu çözmek için kullanılan yöntemlerden biri gaz ile birlikte yüzey aktifleyici madde çözeltisini rezervuara enjekte ederek yeraltında köpük oluşturmaktır. Köpüğün gazın öteleme etkinliğini artırması da en önemli özelliğinin, gaza oranla çok yüksek olan akmazlığı olduğu belirlenmiştir. Bu nedenle rezervuar koşullarında köpük ak mazi iğinin ve genel olarak reolojisinin tanımlanmasının uygulama acısından önemi büyüktür. Bunu yapabilmenin iyi bir yolu ise deneysel araştırmalardır. Bu çalışmada kılcal tüplerde köpüğün reolojisi incelenmiş ve çeşitli faktörlerin köpük akmazlığı m nasıl etkilediği belirlenmiştir. öte yandan bu bilgileri gözenekli ortam için yorumlayabilmek amacıyla sınırlı sayıda da olsa gözenekli ortamda mobilite deneyleri yapılmıştır. Kılcal tüp deneyleri köpüğün psödoplastlk akis davranışı gösterdiği hakkındaki bilgileri güçlendirmiştir. Köpüğün akis debisinin kılcal tüplerde köpüğün akmazlığı m etkilediği ve bunun köpüklerin dokusunda meydana gelen değişime bağlı olduğu belirlenmiştir ; köpük debisi C köpük akısının hızı D artıkça köpüğü oluşturan baloncukların çapı küçülmekte ve köpük stabiliteleri de artmaktadır. Diğer taraftan köpüğü oluşturmak için kullanılan gaz fazının da köpüğün akmazlığı acısından son derece önemli olduğu ortaya çıkmaktadır. COe ile oluşturulan köpük hava ile oluşturulan köpüklere oranla aynı koşullarda daha d üs tik akmazlık değerleri göstermiştir. Uygulama acısından son derece önemli olan bu bilginin CO2 'nin sıvı içinde yüksek çözünebilirliğine bağlı olarak hızlanan gaz difüzyonunun köpüğün stabllitesine olumsuz katkısının sonucu oluştuğu düşünülmektedir. Deneylerde elde edilen diğer önemli bulgu da Çözelti tuzluluğunun köpük akmazlığına olumlu etkisidir. Belirli değere kadar artan tuzlulukla köpük akmazlığının arttığı gözlenmiştir.

In recent years there has been an increased interest in CO2 injection to increase oil recovery- Depending upon the COz efficiency in displacing oil and the availibility of CO2. The most significant problem of CO2 displacement is the high mobility and low density of gas, thus causing CO2 to be channelled and seperated by gravity. The method of injecting water and gas subsequently into the reservoir is generally not a solution, because water is more mobile than oil. The most important feature of foam which causes oil production to increase is its viscosity. Its proven that foam viscosity is higher its components, gas and weater. Therefore, it can displace oil better and decreases the amount of oil stored reservoir. To be aware of foam viscosity it should to be investigated. It is important to know how foams rheology gets affected by reservoir conditions and various application parameters. A good way to find out about it is to conduct laboratory works. The goal of this study is to investigate experimentally the rheology and flow behavire through permeable media and capillary tubes. In this study, a laboratory investigation conducted on the rhology of foam in capillary tubes and its flow in the porous medium taking into consideration the probability of oil displacement in Turkey by the use of foam. This investigation has presented interesting results in the point of possibile applications in the oil reservoirs of Turkey. The effect of salinity and gas phase on the foam viscosity, is particularly significant when the salinity of reservoir water of oil fields in Turkey is taken into accont. VI The experimental set up used in the investigation has been designed to inject a certain gas and surfactant solution into the core in order to form foam. Capillary tubes» cyl indi rical porous medium model, vertical and areal sweep efficiency models can be located on the experiment apparatus in respect of experiment type. In the Theological evaluation of the experiments carried out in capillary tubes Rabinawitsch-Mooney equation has been applied due to its simplicity on finding the shear rate on the well of the capillar tubes. In this method the assumptions are as follows 1. Steady state flow 2. Time independent flow 3. No shear on tube wall 4. Laminar flow 5. Isothemal flow 6. Flow in straight tubes Rheological Evaluation For 90 quality foam and 5 different diameters and 6 flow rates shear stress vs. shear rate plots took us to two Important results when the gas phase is air. Shear stress and shear rate curves identify pseudo plastic flow and flow rate increases with increasing shear stress. It is obvious that O. 42-0. 45 slope of lines also shows the same thing. As it is known, slope less than one identifies pseudoplastic flow. Although shear stres - shear rate lines for experiment el data seem to be parallel on logarrithmic plot in contrast their slope decreases from high flow to low flow rate. It can be seen on logarithmic plot that apparent viscosity is dependent to the tube diameters also. This is ture especially for wider diameters tubes CD=0.53 and D"0. 453 this connection will be discussed in the fifth section in more detail. flow rate and when shear rate is approaching to one hundread l/'s, lines are approaching together as well. This case shows that flow becomes Newtonian while the flow rate is 4 ml/min. and the slope of T«y line as 0.44, for 2 ml/min. slope is 0. 72. This circumstance shows that the flow appr ouches to Newtonian. The negative effect VII When the quality gets higher, the viscosity of foam increases and the diameters of bubbles widen, water amount in unit volume falls and foam stability gets better. These factors lessen the mobility of foam and increase the shear resistance. Additionaly, the type of gas has a very important affect on viscosity. The Effect of Gas Type The difference between air foam viscosity and CO2 foam viscosity is an important conclusion of the experiments in cappilary tubes. For low quality, the viscosity of foam formed with air is two times and for high quality, three times more than CQz foams. The difference of air and CO2 is very important in respect of field application. Because CO2 is generally used in displacment proccesses in contrast to this circumstance. Equation that supplies static C yar 11 anma) time of constant diameter bubble has been derived from Fick def us Ion formula. The Effect of Surfactant Concentration When the concantr ati on of surface active agent in solution for 90 quality foam made from air and CO2 is up to 3C 0. 5, viscosity increases fast. Thereafter, that raise stop for CO2 foam, but it continues to raise slowly to the maximum consantration ÎS 2 of experiment for air foam. These conclution support the results of other investigations on critical misel concentration. The Effect of Salinity Apparent viscosity which Increases with saltiness for air - foam falls in % 5, becomes maximum in X 8 and falls again in fi IO saltiness value. For CO2 foames, the apparent viscosity is maximum when concentration is 9£ A. vm Porous Medium Experiments The flow of the foam in acappilary tube gives important information about its r neology. In this experiments flow of foam was observed while it is directed into the capillary tubes without deforming its texture. However the flow of the foam in porous media is quite different in this case, it is observed that occurance of foam is a process which is continuously renewed. It is supposed that, by depending on environmental conditions, foam bubbles disappear and new foam bubbles occur or the same foam bubbles proceed while they were changing their shapes. To search for this case several experiments have been done on cylindric. The real goal of foam displacment has been considered and support! v affects of foam on areal and vertical sweeping efficiency have also been experienced with same models Just like being done in capillary tube experiments. Mobility Experiments Using Cylindirical Models The experiment in this section were conducted in cylindirical models contained glass beads the the features of which were presented in Chapter A in detail. During the applications of the experiments, entering pressure and production have always been noted and the moment that foam reaches the outlet end is supposed as arrival time. It has been measured that permeability is 28 D and porosity is 0. 38. The Effect of Flow Rate Considering the effect of flow rate on foam texture and subsequently on the foam flow in capillary tubes, its effect in porous media was studied. Three different flow rates, 3 m/'day, A. 5 m/'day and Sm/'day there had been no significant change in the mobility of X 90 quality air -made foam during different values of flow rates. This result is very astounding when it is compered to effect of flow rate in capillary tubes. This proves that the flow in permeable zone is different from the flow in a pipe. In the permeable zone, there have been shape modifications of bubbles or when old bubbles disappear, new bubbles occur. Therefore, the entrance shape of foam into the permeable zone has no Importance for flow because they will change. IX The Effect of Foam Quality For three different quality air made foam flow foil wing results had been founded. 60 quality foam 5 MF 90 quality foam İO MF 95 quality foam 12 MF As can be seen in above measurements mobility factor increases with increasing quality. The aim of using foam as a displacment agent is to provide low mobility factor and the importance of the quality of foam in capillary tubes is more considerable than that of the exoeriments conducted in porous media. The Effect of Concentration Concantratlon between X 0. 1 and X 0. 3 cause a small MF difference. After X 0. 3, MF raises with increasing concentration. This is the most important difference between experiments carried out in permeable zone and in cappilary tube. In the foam making C agent!) solut ins prepared by refined water, viscosity slightly changes after X 0. 5 approximate concentration value. But in permeable zone experiments, mobility increases very fast by X 1.2 concentration value. The raise in MF from that value to X 2, increase is slow. Such a change of MF with the surfactant concentration is matched with some previous work results as well as capillary tube experiments. The Effect of COb Another serial of experiment had been held out by using CO2 as the gas phase and by considering the significant affect of CO2 on foam viscosity. For the solutions that have different salinity values, arrival times which were observed in X 0. 5 surfactant concentration experiments have been shown in chapter five. The affect of salinity on foam stability and viscosity in cappillary tubes had been seen as an extraordinary increase in the value of 7. 5-1 0 X. Viscosity had droped for X İO salinity in cappilary tube but for the same salinity, mobility had a high performance. The stabilization looks like in foam has a complete blokage crystalization. X of COz on foam stability causes the incident. In low flow rates, foam Partially separates into liquid and gas phases during the flow in the tube. It is very difficult to say about flow features from llneei - axis shear strees - shear rate graph curves. However, the curves generally have pseudoplastic behaviour. When the gas phase is air, viscosity decrease for low shear rates depends heavily upon diameter and flow rate. When we compare the results of experiments to the others done for air, we can notice a significant difference such as low viscosity values for the same shear stresses. Another shear evaluation method by David - Marsden has been developed to include compressibility of foam. In this method, from the slopes of the lines in Q-r graphs shear parameter ft has been determined. Foam Flow Rate and Capillary Tube Diameter When air is used as the gas phase, the flow rate of 90 quality foam changes. When the flow rate increases, viscosity increases rationally. Changes this affection becomes more clear by getting smaller diameters of the foam bubbles. This was seen in microscopic experiments. For example, in maximum flow rate 5.15 ml/'min, di mater of bubbles is 0. 9 + 0. 2 mm, while in minimum flow rate 2.5 ml/'min, it is 3 t 0.5 mm. Static stability exprement of the same foams have different result. In maximum flow rate, half ing time is 15 «tin. CFor 100 ml) and in minimum flow rate, it drops to 7.5 min. The reason for the dropping in static stability is because of the decreasing of the foam bubbles density. But that is not a complete reason. Bulk foam made from many bubbles in cappillary tubes or subsequent single bubbles separated by liquid films have an important affect on apperant viscosity. The reasons are ; 1. Small diameter 2. Increasing capillary pressure of the bubbles and 3. Surface stress gr adi ant. The Effect of Quality The quality values of air 80 and more, foam's apprent viscosity continuously increases. This happens slower in CO2 foams.