Systematic Feasibility Assessment of Geomechanical Risks for CO2 Injection and Long-Term Storage Incorporating Rock Properties Degradation and Thermal Effects

ABSTRACT: As part of carbon capture and storage feasibility assessment, geomechanical risk analysis is conducted in field of interest to determine maximum injection pressure and associated geomechanical risks during injection and long-term storage. The objective of the study is to evaluate the feasibility of injecting and storing CO2 in the field by assessing CO2 containment and leakage risks, in particular "showstoppers", for decision-making on progressing to comprehensive coupled geomechanical study and mature the field as a CO2 storage site. Using the rock mechanical properties from calibrated 1D geomechanical models as input, caprock integrity analysis is conducted and maximum injection pressure is determined to ensure the caprock does not experience tensile and 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 they remain stable with reduction in maximum injection pressure, if required. Rock properties degradation due to CO2-rock interaction and thermal effects on geomechanical containment risks are incorporated by using rock properties degradation and thermal properties database of the area and estimated temperature changes in the reservoir and caprock. Upon finalization of the maximum injection pressure, reservoir expansion and surface uplift are conducted to determine the maximum uplift. The methodology has been applied to one of the CO2 storage candidates located in offshore Peninsular Malaysia. Changes of minimum horizontal stress at caprock during reservoir pressure increase were calculated to determine the injection pressure that will cause tensile or shear failure. Fault stability analyses were conducted on all the faults intersecting the formations of interest by using the rock strength and stress properties from the nearest well to the faults, and the faults were found to remain stable. Finally, reservoir expansion for each of the formations of interest was calculated and used as part of the input for seabed uplift analysis. Low seabed uplift was determined at the end of injection and will not affect the surface facility integrity. 1. INTRODUCTION One of the best alternative methods of produced carbon dioxide (CO2) disposal to meet net zero carbon emission is CO2 capture and geological storage. With more countries committed to the reduction of greenhouse gas emission following their ratification of the Paris Climate Agreement, there has been increasing global interest in the geological storage (Baklid et al., 1996, Bissell et al., 2011, Mustafa et al., 2021 and Tewari et al., 2022). However, there are numerous geomechanical challenges and risks associated with CO2 injection and storage in depleted reservoirs, saline aquifers and dry geological structures that are required to be addressed. The key challenges include maintaining the seal integrity throughout the injection operation and storage life. The pressure and temperature changes will give rise to changes in stresses and pose risks to fault re-activation and breach of caprock integrity. These processes and mechanisms can be complex and need to be modelled simultaneously as they inter-relate between them (Tan et al., 2022 and Chidambaram et al., 2023). A comprehensive assessment of the geomechanical-related risks to manage CO2 containment and mitigate leakage risks requires a coupled geomechanical study (Masoudi et al., 2011, Masoudi et al., 2013, Chidambaram et al., 2021 and Mustafa et al., 2022). However, it is resource intensive and time-consuming which are not warranted for preliminary feasibility assessment of potential CO2 geological storage site. An analytical approach based on 1D geomechanical models may be implemented instead which is solely for preliminary assessement of the risks. The goal is to identify any "showstoppers" from geomechanical perespective that will make the geological structure to be not viable as CO2 storage site (Musa at al., 2023 and Tan et al., 2024).