Full‐azimuth, anisotropic 3D EM inversion applied to a low‐resistivity pay reservoir with well control

Abstract

We demonstrate advances in 3D EM inversion-based subsurface imaging on a challenging target in a mature area of the Gulf of Mexico. These advances include the use of the anisotropic (v , h) cube as well as a data weight scheme which permits inversion of all azimuthal data in the 3D grid. Our inversion is based on a quasi-Newton optimization algorithm with approximate calculation of the Hessian matrix and a finite-difference time-domain forward modeler. Its capability to resolve small targets of lowresistivity pay in complex geology is confirmed by the case example presented here. A proven hydrocarbon find (¡ < 5 ¢ m versus background, 2 km x 2 km) is compared with well and seismic data. There is a significant improvement in resolution over previous inversions using isotropic 3Dinversion, however, due to the acquisition in deep water and lack of substantial anisotropy, the target was identified in both cases.