The Study on Shale Wellbore Stability with Coupled Mechanical–Chemical Processes in Wushi Oilfield

Abstract

Wellbore instability (WI) is a challenge in the drilling process, which often causes complex accidents. Measures should be taken to prevent WI in low-strength formation. It is crucial in wellbore engineering to ensure wellbore stability. In fact, WI was solved with large sources of lost time and trouble cost. However, at present, the mechanism of the instability of the shale borehole wall is unclear. To study the shale WI in Wushi Oilfield, the rock mechanics parameters of rocks were tested according to the actual situation of the oilfield. Experimental results were helpful to determine parameters for numerical simulation. A mechanical–chemical coupling model of shale wellbore was established. The numerical simulation results indicated that there was stress concentration around the wellbore wall. The effects of rock elastic modulus, cohesive force, deviation angle, azimuth, drilling fluid density, and hydration time on the stability of the shale borehole were analyzed. The numerical simulation results could provide a reference for on-site drilling optimization.