An Experimental Study of Shale-Drilling Fluid Interactions to Enhance Long-Term Shale Inhibition

Abstract

Abstract The objective of this paper is to discuss shale-fluid interactions while drilling clay-rich shale formations. Shale swelling, dispersion and sloughing are frequently encountered problems that may lead to excessive non-productive time. Comprehensive understanding of the behavior of the shale sample helps in mitigating shale drilling problems. To understand the behavior of a shale sample when exposed to fluids, different types of characterization tests have been conducted starting with mineralogy identification using X-ray diffraction, X-ray fluorescence and also the conventional swelling tests. It went further to study the organic carbon content using thermogravimetric analysis. After carrying out X-ray diffraction and thermogravimetric analyses on two shale samples to determine clay content and organic carbon content, a series of swelling tests were conducted using different types of non-inhibitive and inhibitive fluids. Linear shale swelling results are represented as the percentage of volume expansion as a function of swelling time while shale. Results showed high variance among shale inhibitors in terms of the ability to inhibit shale particles for prolonged time intervals This paper provides a review of various factors that influence shale-drilling fluid interactions Due to the presence of some unique conditions, such as loss circulation, sometimes there is a need to use a low cost non-inhibitive mud instead of a high cost inhibitive mud to drill the next formation after the shale section. If the durability of original inhibition is not long enough to ensure smooth drilling of the the second zone, the previously drilled inhibited shale formation starts reacting again with the non-inhibitive drilling fluid. Hence, the reactive shale zone needs to be isolated by a casing string before drilling ahead. However, if inhibitive muds with long-term inhibition potential such as 24 hours or more are available, multiple formations including the shale formation can be drilled and cased in one hole section.