Effect of long-term pore pressure evolution on the integrity of cement plugs of abandoned oil wells in CCS sites

Abstract

In the context of Carbon Capture Storage (CCS) in abandoned hydrocarbon reservoirs, a preliminary study of the effects of pore pressure evolution on the integrity of oil-well cement seals is performed. A 2D cross-section of the sealed oil-well system (caprock-external cement sheath-steel casing-cement plug) is analysed along its service-life (injection/production activities and abandonment) using the Finite Element Method with zero-thickness interface elements to represent potential cracks. In particular, these elements are pre-inserted in the analysis in between the contacts of caprock-external cement sheath, external cement sheath-casing and casing-cement plug. The results presented show that, depending on the initial state and range of pressure evolution, the different interfaces considered may open or close in a non-trivial manner during the pressure return process. This seems to indicate the importance of considering carefully the pressure return process and subsequent effective stresses evolution in abandoned reservoirs recycled to CCS, in order to avoid that new cracks in well cement seals may lead to potential CO2 leakage in the storage site.