Application of a new reduced‐complexity assessment tool to estimate CO₂ and brine leakage from reservoir and above‐zone monitoring interval (AZMI) through an abandoned well under geologic carbon storage conditions

This study employs a combination of detailed simulations and reduced‐complexity models in the Well Leakage Analysis Tool (WLAT), developed by the National Risk Assessment Partnership (NRAP), US Department of Energy, to investigate how the rates of CO 2 and brine leakage through an abandoned well under geologic CO 2 storage conditions are affected by various factors. The factors considered in this study include depth of well penetration into the storage system, location relative to the point of injection, and effective permeability of the abandoned well. Location is the primary factor used to identify high‐ and low‐risk abandoned wells. For the typical CO 2 injection scenario considered in this study, the potential impact of CO 2 and brine leakage through an abandoned well is very low if the abandoned well is 6.2 km or further away from the CO 2 injector. Due to the buoyancy of CO 2 relative to formation brine, wells intersecting (i.e., accepting flow from) the top of the above‐zone monitoring interval (AZMI), which is the interval immediately above the seal, have a higher chance to become a pathway for CO 2 than wells intersecting the bottom of the AZMI. If the permeability of an abandoned well is 10 −14 m 2 or less, the risk of CO 2 and brine leakage through the well becomes very low. Due to the combined effect of pressure increase and buoyancy, the CO 2 leakage rate is higher than brine leakage rate within the CO 2 plume extent. Specific values reported in this study are site‐specific results and cannot be regarded as general findings.