Monitoring CO2 sequestration with electromagnetics in the presence of steel-cased wells

Injecting and storing CO2 in sedimentary reservoirs is an attractive avenue for removing CO2 from the atmosphere. Monitoring the injection of CO2 is important for improving engineering of the operation as well as for identifying potential issues, such as CO2 migrating out of the reservoir into near-surface aquifers. This can occur if a caprock is fractured, or if migration pathways, such as along old wellbores, provide a trajectory for CO2 to get out of the storage reservoir. For monitoring, electromagnetic (EM) data provides complementary information to other data types that are typically collected (e.g. seismic, well-logs, pumping data, etc.). EM data are sensitive to variations in electrical conductivity and are impacted by pore fluids (e.g. brine vs. CO2). A particular challenge that we will address is developing methods for handling the impacts of steel-cased wells on EM data. Steel is highly conductive and magnetic, so it distorts EM responses and can make interpretation of the data challenging. However, this large conductivity is advantageous because it helps channel currents to depth, where we are interested in monitoring. We have developed numerical models in SimPEG that use cylindrical meshes and allow us to simulate conductive, magnetic wells. In this presentation, we use these numerical simulations to investigate the feasibility of monitoring injection of CO2 into sedimentary reservoirs and under what circumstances we can detect the migration of CO2 within, and out of, the reservoir.