Durability of oilwell cement in CO2-rich environments

Abstract

The anthropogenic emissions of carbon dioxide (CO2) into the atmosphere is considered as one of the main reasons for global warming. The injection of CO2 into underground formations is an immediate to mid-term option to decrease the level of this gas in the atmosphere. Depleted oil and gas reservoirs are among the best candidates for the carbon capture and storage projects (CCS). The reason for this is based on the well-characterised structure of these type of underground formations through the different periods of their life. One of the most concerned problems associated with CCS projects is CO2 leakage through well cements. Oilwell cements exposed to CO2-bearing fluids undergo geomechanical and geochemical changes which may endanger their integrity. This paper aims at providing a framework to predict the lifespan of a cement exposed to CO2-bearing fluid using numerical modelling based on coupling geochemical and geomechanical processes. The main processes of the radial compaction and the radial cracking are investigated. It was shown that the radial cracking process leads to a definite lifespan of the cement matrix after being exposed to CO2-bearing fluids, while the radial compaction process can increase the durability of the cement matrix. Generally, this process becomes more effective with increasing the radial stress on the cement sheath from the surrounding rocks.