Revised Experimental Approaches To Address Shale Drilling Challenges

Abstract

Abstract Shale drilling problems are major sources of non-productive time in drilling operations. The use of water-based drilling fluids to drill shale formations can cause wellbore stability problems such as swelling, dispersion and heaving as a result of the reaction of water with clay minerals. Consequently, wellbore instability problems can be triggered and stuck pipe problems can be encountered due to tight spots or higher solids loading in the wellbore. Therefore, it is essential to have the required techniques to assess the shale samples and their adsorption and swelling potential in order to be proactive and mitigate the scope of shale drilling problems. Initial moisture content is one of the factors controlling the swelling behaviour of shales. Correlating the ultimate swelling percentage to moisture content and other parameters can help in predicting the swelling potential and mitigating any associated problems. It was found that swelling potential increases for shale/clay samples with higher moisture content. Furthermore, evaluation of the long-term inhibition potential of shale inhibitors is necessary to mitigate time dependent borehole instability problems. Due to the presence of some unique geological conditions as in the case of a loss circulation zone overlaid with a shale formation, sometimes there is a need to replace a high cost inhibitive mud with a low cost non-inhibitive mud to drill the next formation. If the original inhibition provided by the inhibitive drilling fluid to the shale rock does not last long enough to drill the loss circulation zone, the previously drilled shale formation starts reacting again with the non-inhibitive drilling fluid leading to various drilling problems. Hence, there is a need for isolation of the reactive shale zone by a casing string before drilling ahead. Inhibitive muds with long-term inhibition potential may eliminate the need of a protective casing for the previously drilled shale formation. Two shale inhibitors were tested: potassium chloride and polyamins. The results showed the superior performance of the polyamines as long-term shale inhibitors compared to potassium chloride especially with shale samples of high kaolinite content.