Rock Mechanical Characterization of Shale-Drilling Fluid Interactions to Mitigate Borehole Instability Problems

Borehole instability is one of the biggest problems faced by the oil and gas industry when drilling shale formations, mudrocks, marl, or a combination of them using water-based muds.The physio-chemical interaction of water-based drilling muds and the rock formations along with their micro and macro scale mechanical degradation are some of the root causes for instantaneous and time dependent borehole instability problems. Though there are comprehensive studies of physio-chemical aspect of shale-drilling fluid interactions, only a few studies are available, that describe the rock mechanical aspect of shale-drilling fluid interactions. Hence, there is a need for a compressive study of the rock-mechanical aspect of shale-drilling mud interactions. This R&D will concentrate on the testing and evaluation of the geo-mechanical aspect of shale-drilling fluid interactions by conducting rock mechanical testing of original shale cores, water saturated shale cores and two water-based muds saturated shale cores for comparative assessment of the rock-fluid interactions effect on the mechanical properties of reactive shales/mudocks.This paper describes the rock mechanical diagnostic signatures of rock-fluid interactions that were related to instantaneous and time dependent borehole instability problems. This study will provide a tool for field's engineers to predict the nature of the borehole instability problems and provide appropriate technical guidelines to the mud engineers and drilling fluid consultants to reduce the probability and the likelihood of creating instantaneous and time dependent borehole instability problems.