A NOVEL CONCEPT FOR LONG-TERM CO2 SEALING BY INTENTIONAL SALT CLOGGING

ABSTRACT
Well abandonment after CO2 storage demands a mitigation strategy for CO2 leakage along the wellbore. We propose forming a salt seal around the wellbore after CO2 has been injected into a depleted gas field, preventing possible CO2 transport to the surface. The placed salt plug will protect the wellbore material from contact with supercritical CO2 and acid brine. We propose the concept of brine-alternating CO2 injection for intentional salt clogging of the reservoir. Injec-tion of CO2 will evaporate water from previ-ously injected brine, causing salt precipitation. The formation of a dryout zone is a known process occurring during CO2 injection in saline aquifers or depleted gas fields that leads to unintentional clogging and possibly injectivity issues.
Modeling is performed with TOUGH2, simu-lating injection of brine and subsequently CO2. Our model is based on the K12-B depleted gas field, using the elevated pressure conditions of a CO2-filled storage reservoir. The model results indicate that injecting multiple cycles of brine and CO2 could be used for controlled precipita-tion of salt in the reservoir. The injection proce-dure results in a 40 cm thick salt bank around the well, with the precipitated salt reducing the porosity from 10 to 8% at the location of maxi-mum salt precipitation. This porosity decrease causes complete permeability impairment. We conclude that brine-alternating CO2 injection could pose an effective method for intentional salt-clogging of the near-wellbore area.