Reactive transport of CO2-saturated water in a cement fracture: Application to wellbore leakage during geologic CO2 storage

• Sealing is a function of initial leak path size, dissolved CO2 concentration, and residence time.
• Presence of amorphous zeolite prevents self-enhancing behavior.
• Secondary precipitation of calcite causes self-sealing behavior.

Time dependence of fluid flux up a leaky well has significant implications for the feasibility of geologic CO2 storage. We present laboratory experiments that study various boundary conditions, fluid fluxes, and residence times to understand the range of behavior in fractured cement cores. Carbonic acid progressively reacts with cement by dissolving phases which neutralize the acid and liberate calcium ions. This dissolution does not increase the aperture of the fracture, due to the formation of an amorphous silicate residue. Where aqueous calcium concentration and pH are sufficiently high calcium carbonates become insoluble and precipitate in the open fracture. When the driving force for fluid flux is a constant pressure differential precipitation leads to a progressive reduction in fluid flux and the development of self-limiting behavior. With sufficient residence time precipitation leads to sealing of the leaky well.

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