Chemo-poroelastic Coupling Method for Wellbore Stability Analysis in Shale Gas Formation with Weakness Planes

Due to the fact that the shale formations are usually featured by rich in clay mineral and well-developed bedding planes, which makes it strong water-sensitive and strength-anisotropic. Once the mass transfer of mud filtrate occurs around the borehole of the shale formation, the reaction between the shale and drilling mud causes shale to swell, weaken, and eventually fall/collapse into the wellbore. This study aimed to develop a coupled chemo-poroelastic model to accurately predict the wellbore collapse. The impacts of the chemo-poroelastic coupling, the anisotropic and weakened strength are integrated in this model. Based on the chemo-poroelastic method, the characteristics and evolution laws of failure zones around a wellbore have been simulated. The results show that the wellbore stability is time-dependent due to the influence of the chemo-poroelastic coupling and the weakened strength, the anisotropic and weakened strength have a more significant influence than the chemo-poroelastic coupling. Thus, the anisotropic and weakened strength should be involved in the analysis of wellbore stability for shale gas wells.