Parametric study on the integrity of wellbores in CO2 storage sites

Abstract

Carbon capture and storage is considered as an amelioration technique to address the increasing level of carbon dioxide in the atmosphere. Depleted oil and gas reservoirs are potential candidates for the long sequestration of the captured carbon dioxide. The huge number of drilled oil and gas wells in these hydrocarbon reservoirs around the world, however, pose a threat to the integrity of geological CO2 storage projects. These wells are direct connections to the Earth’s surface and even when capped, any defects in their structure can become high leakage pathways. To predict the consequences of this possible loss, a model was developed and introduced by the authors based on coupling the geochemical and geomechanical alterations benefitting from a plastic-damage model. This model simulates the alteration of the rock-cement-casing assemblage in abandoned wells for carbon storage sites. In this paper, a parametric study has been established to investigate the wellbore integrity at various conditions found underground. The results show that separation at the cement-casing interfaces is highly probable in injection wells. The abandoned wells will maintain their integrity within the first thousand years after exposure to CO2-bearing fluids. Our observations suggest that the compaction of the cement-rock interfacial transition zone helps the cement sheath maintain its integrity for a longer period of time.