Geomechanical Risk Analysis for Feasibility Assessment and Evaluation of CO2 Injection and Long-Term Storage

Abstract

Abstract One of the efforts to reduce the impact of climate change is by reducing carbon dioxide (CO2) emission through carbon capture and storage (CCS) operation. As part of CCS feasibility study, geomechanical risk analysis is conducted on the field of interest to determine maximum injection pressure as well as the associated geomechanical risks during injection and long-term storage. In geomechanical risk analysis, first fully calibrated and validated 1D geomechanical models are developed from the available log data of the wells in the field of interest. Using the rock mechanical properties as input, caprock integrity analysis is conducted and maximum injection pressure is determined to ensure the caprock does not experience tensile or shear failure during CO2 injection. If there are faults penetrating the caprock and reservoir of interest, fault stability analysis is conducted on the faults to ensure the faults remain stable. Finally, reservoir expansion and seabed uplift analyses are conducted to determine the maximum seabed uplift. This methodology has been applied to one of the CO2 storage site candidates located in offshore Peninsular Malaysia. 1D geomechanical models for the wells in the field are constructed and calibrated with pore pressure and stress measurement data. Wellbore stability analysis was conducted and validated with drilling experience and caliper log. Rock mechanical properties and stress data were extracted at formation of interest for caprock integrity analysis. Changes of minimum horizontal stress at caprock due to reservoir pressure increase due to CO2 injection was calculated to determine the injection pressure that will cause tensile or shear failure. Safety factor is applied to the pressure for final maximum injection pressure in the formation. Fault stability analysis was conducted on all the faults intersecting the formations of interest using the rock strength properties and stress data from the 1D geomechanical model of the nearest well to the fault. Normal and shear stresses plotted in the shear stress-normal stress plot for pre- and post-injection showed that all the faults remain stable. Finally, reservoir expansion was calculated and used as part of the input for seabed uplift analysis. Low seabed uplift was determined at the end of injection, and it will not impact the surface facility integrity.