2D inversion of ultradeep electromagnetic logging measurements for look-ahead applications

Abstract

Knowing formation ahead of the drill bit can help with hydrocarbon exploration and production, especially for low-angle and vertical wells. The advent of electromagnetic look-ahead technology makes it possible to interrogate formations tens of feet ahead of the drill bit. The formation can be very complex, such as fault and unconformity. However, existing approaches to recover the formation rely primarily on the 1D forward solver, which presumes that the formation is layered and transversely isotropic. For complicated formation, it will give rise to incorrect resistivity distribution. As a consequence, we have investigated and implemented a 2D pixel-based inversion algorithm to interpret the measurements for complex scenarios. We conduct a sensitivity study to illustrate the differences between look-ahead applications and look-around applications. To improve the look-ahead ability, we propose an effective technique to incorporate the prior information. In addition, we develop several examples to demonstrate the performance of the 2D inversion algorithm. It is found that using prior information as a reference model in the objective function enhances inversion performance significantly, and the proposed method can reasonably reconstruct some complex structures.