Three-dimensional inversion of controlled source electromagnetic data with steel casings

ABSTRACT 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. To map the 3D distribution of injected fluid during hydraulic fracturing, a method was proposed that incorporates the effects of such casings. We introduced an edge conductivity parameter, which combines intrinsic conductivity and the cross-sectional area of the casing, into the conductivity model. By aligning these edge conductivities with mesh edges within a finite volume framework, casing effects were captured without complex mesh refinements. The algorithm was 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 was optimized with the Gauss-Newton method. Synthetic scenarios involving horizontally drilled wells and top-casing sources demonstrated the method's ability to recover fluid trajectories and detect asymmetric fluid distributions. Additionally, the method proved effective in assessing casing integrity by estimating edge conductivities. This work shows that integrating steel casing data into CSEM modeling enhances reservoir characterization and supports decision-making in oil and gas exploration and CO₂ sequestration.