Chemo-poroelastic analysis of pore pressure and stress distribution around a wellbore in swelling shale: effect of undrained response and horizontal permeability anisotropy

Abstract

The aim of this paper is to study the effect of undrained response and horizontal permeability anisotropy on transient changes in pore pressure and stress state of surrounding area to wellbores drilled in swelling shales. For this purpose a finite element model of coupled chemo-hydro-mechanical processes is developed and used. Super convergent patch recovery method is employed to accurately evaluate time dependent stress tensor. From the results of this study it was found that at any time and radial position around the wellbore, change in pore pressure, thus effective stress, depends on horizontal permeability anisotropy, which influences three main contributing processes namely hydraulic flow, chemical effect and undrained response. It was also revealed that at a given time after shale is exposed to the mud, maximum change in pore pressure, thus in effective stress, can take place at different radial distances from the wellbore along different directions due to permeability anisotropy.