Mitigating Shale Drilling Problems through Comprehensive Understanding of Shale Formations

Abstract

Abstract In order to develop an inhibitive water-based mud capable of mitigating the adverse effects of shale-mud interactions, it is important to characterize the shale sample in terms of its geological structure, mineralogical composition, reactivity potential, etc. Further, the shale-mud interactions should be studied through a series of experimental tests such as swelling, dispersion and inhibition durability. This paper presents the results of characterization and testing of one of the studied shale samples with X-ray diffraction, micro-CT, ultrasonic rock mechanics testing, capillary suction time and cation exchange capacity. The paper also shows how petrophysics data of shale formations can be utilized to improve and optimize drilling practices in order to achieve the ultimate goal of enhanced wellbore stability. Depending on clay content, different shale formations have different responses when exposed to drilling fluids. It is therefore very important to characterize the shale formation to develop the appropriate drilling fluid. The tested shale sample was found to be a silica-rich shale with a small percentage of clay minerals, mainly kaolinite. Characterization scheme included also Micro-CT where the images revealed the heterogeniety and fractures in the internal matrix. Dynamic elastic moduli were determined using ultrasonic rock mechanics testing. A cation exchange capacity (CEC) value of 2.5 meq and capillary suction time (CST) value of 42.6 seconds indicated low tendency of the shale rock to both swelling and dispersion.