The thermoporoelastic coupling analysis of wellbore stability in shale formation under supercritical CO2 drilling conditions

Supercritical carbon dioxide (ScCO₂) drilling can effectively protect shale formation from hydration damage and improve drilling rate comparing to conventional drilling technology. The wellbore stability of shale formation is one considerable issue under ScCO₂ drilling conditions. In this study, the numerical simulations are performed to calculate collapse cycling time of shale formation under ScCO₂ drilling conditions based on thermoporoelastic coupling model. The results show that comparing to water seepage condition, the variation of formation temperature is larger, pore pressure and stress are lower for ScCO₂ seepage condition without adsorption effect, the comparison between water and ScCO₂ seepage conditions verifies the thermoporoelastic coupling model. For ScCO₂ drilling conditions, if adsorption‒induced strain is ignored, the risk of wellbore collapse will be slightly underestimated comparing to the results with adsorption effect. When adsorption‒enhanced elastic modulus is ignored, the risk of wellbore collapse will be significantly underestimated comparing to the results with adsorption effect. The wellbore collapse may occur with the increasing well depth for ScCO₂ drilling conditions. This study can provide the theoretical guidance for exploiting shale reservoirs using ScCO₂.