Integral equation-based wellbore preconditioner for 3D electromagnetic response modeling

ABSTRACT Modeling subsurface controlled-source electromagnetic (CSEM) responses using the finite-element (FE) method is challenging in the presence of highly conductive wellbore casing. The very large conductivity contrast between the casing and the host formation leads to increased computation time and potentially unstable solutions. We address this difficulty by preconditioning an FE solver with an integral equation (IE) primary solution that captures the CSEM response of a realistic-sized steel wellbore casing. Our hybrid IE-FE approach determines the primary field using 2D IE forward modeling and then interpolates the IE-computed solution onto the nodes. Then, using an existing FE simulator, we solve for the secondary electric and magnetic fields. This approach removes the need for an ultrafine FE mesh around the wellbore, thereby improving the FE solution stability while greatly reducing the FE computation time. Our method is illustrated by modeling the CSEM responses of idealized fluid-bearing zones.