The geomechanics of Shenhua carbon dioxide capture and storage (CCS) demonstration project in Ordos Basin, China

Carbon dioxide (CO2) capture and storage (CCS) is considered widely as one of promising options for CO2 emissions reduction, especially for those countries with coal-dominant energy mix like China. Injecting and storing a huge volume of CO2 in deep formations are likely to cause a series of geomechanical issues, including ground surface uplift, damage of caprock integrity, and fault reactivation. The Shenhua CCS demonstration project in Ordos Basin, China, is the first and the largest full-chain saline aquifer storage project of CO2 in Asia. The injection started in 2010 and ended in 2015, during which totally 0.3 million tonnes (Mt) CO2 was injected. The project is unique in which CO2 was injected into 18 sandstone formations simultaneously and the overlying coal seams will be mined after the injection stopped in 2015. Hence, intense geomechanical studies and monitoring works have been conducted in recent years, including possible damage resulting from the temperature difference between injected CO2 and formations, injection induced stress and deformation change, potential failure mode and safety factor, interaction between coal mining and CO2 geological storage, determination of injection pressure limit, and surface monitoring by the interferometric synthetic aperture radar (InSAR) technology. In this paper, we first described the background and its geological conditions of the Shenhua CCS demonstration project. Then, we gave an introduction to the coupled thermo-hydro-mechano-chemical (THMC) processes in CO2 geological storage, and mapped the key geomechanical issues into the THMC processes accordingly. Next, we proposed a generalized geomechanical research flowchart for CO2 geological storage projects. After that, we addressed and discussed some typical geomechanical issues, including design of injection pressure limit, CO2 injection induced near-field damage, and interaction between CO2 geological storage and coal mining, in the Shenhua CCS demonstration project. Finally, we concluded some insights to this CCS project.