3D inversion of controlled source electromagnetic data with steel casings

Steel casings in oil and gas development have the potential to enhance controlled source electromagnetic (CSEM) responses, particularly in detecting subtle changes in reservoir properties. A method is proposed to map the 3D distribution of injected fluid during hydraulic fracturing, incorporating the effects of steel casings. Edge conductivity, a parameter combining intrinsic conductivity and the cross-sectional area of the casing, is introduced into the conductivity model. By aligning edge conductivities with mesh edges and integrating them into a finite volume framework, casing effects are captured without requiring complex mesh refinements. The algorithm is validated through cylindrical mesh simulations and forward modeling using a line current transmitter. For inversion, an objective function combining data misfit and model smoothness constraints is optimized with the Gauss-Newton method. Synthetic scenarios with horizontally drilled wells and top-casing sources demonstrate the ability to recover fluid trajectories and detect asymmetric fluid distributions. Additionally, the method can assess casing integrity by estimating edge conductivities where the casing is present. Integrating steel casing data into CSEM modeling enhances reservoir characterization and supports decision-making in oil and gas exploration and CO₂ sequestration.