Simulation study of chemo‐mechanical impacts of CO2 injection in morrow b sandstone reservoir

This study investigates the impacts of geomechanical and geochemical changes on carbon storage in a partially depleted oil reservoir, using results from four different coupled simulation models. Models were used to examine the relative importance of storage mechanisms, and how changing reservoir parameters might affect these mechanisms through time. The study uses data from a Morrowan sandstone reservoir in the Farnsworth Unit (FWU), Ochiltree County, Texas which is currently undergoing CO2 enhanced oil recovery (EOR). Partially depleted oil reservoirs such as the FWU offer attractive carbon utilization and/or storage targets because of existing infrastructure and economic benefits from incremental oil recovery as well as tax credits. However, prediction of storage capacity or long‐term fluid migration in these fields can be difficult because of the wide variation in formation fluids and operational histories that may have undergone. CO2 injection can cause complex geomechanical and geochemical responses in a reservoir as a result of interplay between dynamic changes in pore pressure, reservoir temperature, fluid composition, and interactions between formation fluids, CO2, and reservoir rock. Thus, multiple coupled numerical simulation models must be developed and used to more precisely understand what CO2 storage mechanisms are most significant, as well as the long‐term fate of the stored CO2. Our study used results from hydrodynamic, coupled hydro‐geomechanical, coupled hydro‐geochemical, and coupled hydro‐geomechanical‐geochemical models to examine how changes in geomechanical and geochemical properties can impact the injectivity or storage capacity of CO2. Models simulated historical field operations and then forward‐modeled a water‐alternate‐gas (WAG) operation for 20 years, followed by a 1000‐year post‐injection monitoring. The work demonstrates that in this specific reservoir, geomechanical impacts appear to be more significant than any geochemical processes, which showed minimal impact on reservoir properties. Furthermore, these simulation scenarios corroborated other studies showing more than 90% of CO2 injected are being stored and will remain stored in the reservoir. The study was able to draw on a rich set of data from this currently operational project for the work. Because the Morrow is a widespread oil‐bearing reservoir in the midcontinent of the United States and is fairly typical of many sandstone reservoirs elsewhere, the study has significance beyond the boundaries of our field area. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd.