A fluid-solid-chemistry coupling model for shale wellbore stability

Abstract

A fluid-solid-chemistry coupling model is built considering fluid flow and ion transmission induced by shale-drilling fluid system electrochemical potential osmosis, nonlinearity of flow and solute diffusion in shale-drilling fluid system, and solid deformation resulted from fluid flow and ion transmission. The model is used to compute the time-varying pore pressure, stress and damage index in formations around the wellbore of a well. The result shows that the pore pressure and stress are lower without consideration of the diffusion potential induced by ion selective character of shale membrane. The linear model overestimates the pore pressure and stress fields around the sidewall. The damage index reveals that collapse first occurs in formations near the wellbore, the caving pressure increases and changes obviously with time, the fracture pressure reduces but doesn't change significantly with time, and the drilling fluid density window narrows down with time. Key words: shale, chemical potential, electric potential, pore pressure, rock stress, wellbore damage