Investigation of the inhibition characteristics of different polyamines under several temperature and shale contamination conditions in drilling fluids

Abstract

Drilling fluid, which can be also called drilling mud, which is necessary to use for successful drilling, perform many functions in oil drilling, and can be composed of a mixture of many chemical additives. Drilling fluids are used in oil drilling operations for hydrostatic pressure, cutting removal from well and suspending them at static conditions, cooling lubrication of drilling equipment, and shale inhibition. Shale inhibition is an important function of oil drilling mud to provide well stability. Clay is one of the most common minerals which is found in shale formations. The smectite group (montmorillonite, also known as bentonite), which is the most common clay mineral, shows a very high swelling effect with hydration when it encounters water or water-based mud. While shales are known to make up 75% of the drilled formations, clay inhibition is a significant parameter to ensure borehole stability during drilling operations. Therefore, clay inhibitor additives are necessary, especially drilling shaly formations. In the face of the high cost, high toxicity, and adverse effects of conventional clay inhibitors on drilling mud, organic amine groups polyamines have been used as an alternative clay inhibitor in recent years in terms of their effectiveness in reducing shale hydration, low toxic effects on the environment, biodegradability, original extractions from plants, resistance to thermal stability and ability to easy expand of these properties. In the face of the high cost, high toxicity, and adverse effects of conventional clay inhibitors on drilling mud, organic amine groups polyamines have been used as an alternative clay inhibitor in recent years in terms of their effectiveness in reducing shale hydration, low toxic effects on the environment, biodegradability, original extractions from plants, resistance to thermal stability and ability to easy expand of these properties. According to these advantages of polyamines, to have an idea about their performance in deep and high temperature well conditions, studies are still being carried out on their resistance at high temperatures. So, the thermal stability of clay inhibition is a subject that is open to improvement for these polyamine additives. In this study, it is aimed to determine the clay inhibition properties of the mud samples for the increasing temperature parameter on the muds prepared with different bentonite amounts and different polyamine amounts. The study is carried out on three polyamine products with different pH values, which are coded as PA1 (pH=7.5-8.0), PA2 (pH=8.0-8.5), and PA3 (pH=9.8-10.2). To determine and compare whether these polyamine products show clay inhibition properties, CP (commercial product) shale inhibitor product is also tested as a reference product. In addition, mud samples are prepared and tested without any polyamine products, 0% polyamine case, just with fresh water and bentonite. This is necessary to see and compare the effect of the polyamine product when used. The mud samples prepared for the study are mixed under laboratory conditions, with the specified amount of bentonite, 20 g, 40 g, 60 g, and 80 g, and the determined amount of polyamine, 0%, 1%, 2%, 3%, and 4% as volume. After preparing the mud samples, they are aged in a hot roller oven for 16 hours at the specified aging temperatures, 77 °F, 150 °F, 200 °F, 250 °F, and 330 °F. After the aging procedure is done, rheological measurements, 600 RPM, 300 RPM, 200 RPM, 100 RPM, 60 RPM, 30 RPM, 6 RPM, 3 RPM dial reading, 10-second, 1-minute, and 10-minute gel strength, and capillary suction time tests are performed to observe and compare the clay hydration and swelling effect. When the results are examined, it is determined that each of the products PA1, PA2, PA3, and CP provided clay inhibition with preventing the swelling, while the product with the best clay inhibition performance is PA1. PA2 and CP polyamine products give closer shale inhibition results, and they have the second best performance after PA1. PA3 shows less clay inhibition performance compared to the other tested polyamine products, PA1, PA2, and CP. The percentage of polyamine to be used varies depending on the aging temperature and the amounts of bentonite, but the use of 2% polyamine has been found to have an optimistic use value in most cases, especially for 40 gr to 60 gr bentonite amounts. For lower bentonite amount, such as 40 g or less, 1% polyamine concentration is enough for drilling mud to provide inhibition of clay with prevent swelling. For higher bentonite amounts, such as 80 gr or more, at least 3% to 4% polyamine concentration is required to prevent clay swelling. Also, this study shows that polyamine products mostly provide thermal stability according to the increased aging temperature in terms of clay inhibition. Especially high amounts of polyamine, such as 3% to 4%, the concentration at mud creates stable shale inhibition properties against the high temperature. 2% or less polyamine concentration has also stable clay inhibition against the temperature at low bentonite amounts. Moreover, while most of polymer has bacterial degradation problems at high temperature well condition, polyamines cannot show any bacterial biodegradation at a high aging temperature, i.e., 300 °F temperature. So, polyamine does not require any biocide additive which is used in case of bacterial biodegradation. In conclusion, polyamine is an additive that has high shale inhibition against the increased bentonite. Proper polyamine amount can prevent even high bentonite amounts. Also, the polyamine is a more environmentally-friendly, efficient, and less costly shale inhibitor mud additive compared to the traditional ones.