Effect of Supercritical CO2 on the Poroelastic Characteristics of Poorly Cemented Sandstone Reservoirs During Depletion and Injection

Abstract

While there is continuing interest in geologic CO2 storage, experimental studies on poroelastic characteristics of reservoir rocks during depletion and subsequent CO2 injection are scarce. Rock stiffness, confining stress, and pore pressure control the poroelastic response of saturated rocks. Also, the stress and pore pressure evolution during injection is a key parameter to understanding operations thresholds for CO2 storage projects. As depleted fields in the Gulf of Mexico have been identified as strong candidates for CO2 storage projects, it is important to understand if the poroelastic characteristics from such fields have been altered due to depletion. Among rock properties, Young’s modulus (E), bulk modulus (Kb) and Biot coefficient (α) are of particular importance. In this study, the poroelastic deformation of a core from the West Delta field in the Gulf of Mexico is characterized experimentally and the impacts of supercritical CO2 (scCO2) on the specimen are investigated. The experimental program simulated reservoir stress changes due to production-induced depletion and scCO2 injection through cycling both the confining pressure (Cp) and pore pressure (Pp). We measured the deviatoric stress, volumetric strain, derived the corresponding Young’s (E), bulk moduli (Kb) and Biot coefficient (α). The results show that the effect of scCO2 on E is more significant at greater confining pressures during the injection phase than depletion at a constant simple effective stress. Interaction of scCO2 with clay minerals caused rock frame dehydration and led to an increase in E. The bulk modulus increased with increasing the confining pressure at a given Pp and decreased with Pp at a certain Cp. α rose with Pp during both depletion and injection phases. Interaction with scCO2 limited the variation of α and the effect of Pp and Cp on α decreased in significance during the depletion phase. Longer interaction time with scCO2 increased α from 10-25% at different Pp values compared to argon during the injection stage. However, the influence of effective stress in reducing the α weakened.