The Development of a Leak Remediation Technology for Potential Non- Wellbore Related Leaks from CO2 Storage Sites.

Abstract In order to reduce global atmospheric greenhouse gas emissions, many pilot-scale and commercial-scale Carbon Capture and Storage (CCS) projects are under development or are operating commercially. There are two main recognized potential leakage mechanisms which may allow CO 2 to leak out of the intended storage complex, migrate into overlying aquifers and eventually seep back to the near-surface and atmosphere, with potentially negative impacts upon natural resources and/or the environment. The primary potential leakage pathway is via wellbores, which may provide a direct connection between the storage formation and the surface. Should a well integrity related leak occur, established remediation techniques may be employed to mitigate and/or remediate further leakage. A second potential leakage pathway includes fluid migration through geological faults, fractures and high permeability zones within a caprock. Not only is it more difficult to constrain and characterize these leaks, there is currently no routine method available to intercept and repair solution leakage via such pathways. This experimental study was conducted to assess the injection of chemical solutions capable of physically and chemically interacting with a CO 2 - containing brine to form a geochemically stable blocking agent capable of preventing further fluid leakage. A number of potential blocking agents were evaluated, and experiments were carried out under quasi formation conditions ( i.e. elevated pressure and temperature) using a combination of simulated 2D caprock micromodels and 3D geological porous medium core floods. Experiments succeeded in determining the behaviour of the blocking agent, CO 2 saturated brine behaviour, reaction front location, the concentration and amount of blocking agent required and an indicative timescale for remediation. Using experimental parameters as bounding conditions, numerical simulations using PetraSim (TOUGH2 and TOUGHReact) were used to assess the upscaling requirements of the blocking process in preparation for large-scale laboratory tests and a field demonstration.