Abstract
Driven by concerns for safe storage of CO2, substantial effort has been directed on wellbore integrity simulations over the last decade. Since large scale demonstrations of CO2 storage are planned for the near-future, numerical tools predicting wellbore integrity at field scale are essential to capture the processes of potential leakage and assist in designing leakage mitigation measures. Following this need, we developed a field-scale wellbore model incorporating (1) a de-bonded interface between cement and rock, (2) buoyancy/pressure driven (microannulus) flow of brine and CO2, (3) CO2 diffusion and reactivity with cement and (4) chemical cement-rock interaction. The model is aimed at predicting leakage through the microannulus and specifically at assessing methods for CO2 leakage remediation. The simulations show that for a low enough initial leakage rate, CO2 leakage is self-limiting due to natural sealing of the microannulus by mineral precipitation. With a high leakage rate, CO2 leakage results in progressive cement leaching. In case of sustained leakage, a CO2 reactive solution can be injected in the microannulus to induce calcite precipitation and block the leak path. The simulations showed full clogging of the leak path and increased sealing with time after remediation, indicating the robustness of the leakage remediation by mineral precipitation.
Highlights
Large scale geological storage of CO2 can significantly reduce CO2 emissions and limit global warming [1]
Flow of supercritical CO2 and brine along the initially water-saturated microannulus; Diffusion of dissolved CO2 into the caprock; Diffusion of dissolved CO2 into impermeable cement and reactions of dissolved CO2 and cement; Leakage into the aquifer overlying the caprock; Injection of a CO2 -reactive solution in the microannulus leak path to promote clogging by calcite formation; In this paper, we report on microannulus leakage, the intentional clogging process for leakage remediation, and the post-clogging phase to assess the sustainability of the clogging procedure
CO2 to migrate to aquifers or to the are known to preventing leak due to oil, microannuli formed by processes migrate to aquifers or to the surface, wells are known to leak due to microannuli formed by processes such as cement shrinkage or pressure and temperature fluctuations [2,5]
Summary
Large scale geological storage of CO2 can significantly reduce CO2 emissions and limit global warming [1]. Geological reservoirs are selected for the physical containment of CO2 which guarantees permanent storage in the subsurface. CO2 injection wells (and possibly old oil and gas wells) penetrating the reservoirs and the caprocks above can compromise the integrity of the storage complex. Wells have a primary structural seal of casing and annular cement (between the casing and the geological formation) and a cement plug when abandoned. Despite these seals, many oil and gas wells leak during their operational lifetime or after abandonment through leakage pathways formed by cement shrinkage or pressure and temperature fluctuations [1]. If annular cement is placed properly, the most likely leak path for CO2 is along the well through fractures in the cement or microannuli between the cement and the casing or adjacent rock [2,3,4,5]
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