Intentional salt clogging: a novel concept for long‐term CO 2 sealing

Well abandonment in the context of CO 2 storage operations demands a mitigation strategy for CO 2 leakage along the wellbore. To prevent possible CO 2 transport toward the surface and to protect the wellbore material from contact with acid brine, we propose forming a salt seal around the wellbore at reservoir level, after CO 2 injection into a depleted gas field. The mechanism of water evaporation into dry gas and subsequent salting‐out of the dissolved halite is a well‐known issue in hydrocarbon production. We propose alternating injection of brine and CO 2 to facilitate intentional salt clogging of the reservoir. Salt clogging was studied with TOUGH2, simu‐lating multiple cycles of brine and CO 2 injection. We developed two near‐well reservoir models – a homogeneous 2D model and a more complex heterogeneous 2D model – using certain characteristics of the K12‐B depleted gas field. The homogeneous 2D model yields a 50‐cm thick salt bank around the well and complete permeability impairment after eight cycles of brine‐CO 2 injection. Addition of vertical permeability heterogeneities causes variation in the lateral extent of salt precipitation and hence vertical discontinuities in the salt bank. A carefully designed injection strategy – with more injection cycles and lower injection rates – improves the vertical sealing. Predictions of the amount of required clogging for effective sealing would benefit from more accurate porosity‐permeability relationships and insights in the long‐term stability of the salt bank regarding re‐dissolution. We conclude that alternating brine‐CO 2 injection could be a promising method for intentional salt‐clogging of the near‐wellbore area. © 2013 Society of Chemical Industry and John Wiley & Sons, Ltd