Self‐healing of cement fractures under dynamic flow of CO₂‐rich brine

Abstract

Fractures and defects in wellbore cement can lead to increased possibilities of CO 2 leakage from abandoned wells during geological carbon sequestration. To investigate the physicochemical response of defective wellbore cement to CO 2 -rich brine, we carried out a reactive flow-through experiment using an artificially fractured cement sample at a length of 224.8 mm. A brine solution with dissolved CO 2 at a pH of approximately 3.9 was injected through the sample at a constant rate of 0.0083 cm 3 /s. Surface optical profilometry analysis and 3-D X-ray microtomography imaging confirmed fracture closure and selfhealing behavior consistent with the measured permeability decrease. Visual inspection of the reacted fracture surface showed the development of reactive patterns mapping the flow velocity field inside the fracture, as well as restricted flow toward the sample outlet. The postexperiment permeability of the core sample was measured at half of its initial permeability. A reactive transport model was developed with parameters derived from the experiment to further examine property evolution of fractured cement under dynamic flow of CO 2 -rich brine. Sensitivity analysis showed that residence time and the size of initial fracture aperture are the key factors controlling the tendency to self-healing or fracture opening behavior and therefore determine the long-term integrity of the wellbore cement. Longer residence time and small apertures promote mineral precipitation, fracture closure, and therefore flow restriction. This work also suggests a narrow threshold separating the fracture opening and self-sealing behavior.

Reaction-driven casing expansion: potential for wellbore leakage mitigation

“…However, even this limited expansion could still be effective, particularly in remedying leakage of CO 2 -bearing fluids. For CO 2 -rich fluids, it may be sufficient to reduce the aperture of fractures and debonding defects only to the point where reactive transport leads to self-sealing behaviour [17,20,53,130], rather than completely closing interfacial flaws by purely mechanical means. Yet, it would not be trivial to expand conventional casing strings by even 1-2% using the pull-through mandrel methods that are now being applied to expandable wellbore casing tubes.…”

Validation of Self‐Healing Properties of Construction Materials through Nondestructive and Minimal Invasive Testing

“…Another construction material for which the self‐healing performance has been studied by high resolution synchrotron CT, is the annular cement and the cement plugs of wellbores . The use of depleted oil and gas reservoirs for capture and storage of CO 2 is considered as one of the promising solutions to reduce global emission of greenhouse gasses but first the potential problem of CO 2 leakage through the fractured cement needs to be addressed.…”

Micro-CT Characterization of Wellbore Cement Degradation in SO42-–Bearing Brine under Geological CO2 Storage Environment

“…While under the condition that the fracture width is large and the hydraulic residence time is short, the hydraulic condition is not conducive to the deposition of calcium carbonate, because the high-velocity water flow washes away calcium carbonate precipitants. As a result, calcium carbonate precipitants fail to fill in the fracture and the self-healing mechanism does not work [19,20]. Field studies have also looked at the self-healing effects of fractured channels.…”