Laboratory insights into the geomechanical response of North Sea reservoir and cap rocks to CO2 injection

Summary The Norwegian Continental Shelf is an emerging host for full-scale carbon capture and storage (CCS). To ensure safe operation and reservoir storage conformance, CCS requires accurate evaluation of the geomechanical response of reservoir and cap rocks to CO2 injection. During injection of CO2, increasing pore pressure and decreasing temperature lead to stress changes within and around the reservoir. Here, we investigate in the laboratory the mechanical response of North Sea reservoir and cap rocks to stress changes expected due to CO2 injection. We performed multi-stage triaxial tests on select samples of North Sea reservoir sandstones and cap rocks, simulating stress paths relevant to CO2 injection, and while measuring stress and strain, ultrasonic wave velocities, and monitoring laboratory-scale microseismicity. Mechanical parameters determined during the test campaign were used to constrain models predicting reservoir response to CO2 injection, and are compared with the experimentally determined failure criteria of both intact and fractured reservoir and cap rocks. We show that for the selected lithologies, the combined pore pressure and temperature changes—which vary with depth, lithology, and distance from the well—can significantly affect the in situ stress field and must be accounted for to correctly predict the reservoir response to CO2 injection.