Fast marine CSEM inversion in the CMP domain using analytical derivatives

Abstract

Utilization of the marine controlled-source electromagnetic method (mCSEM) as a means to reduce risks in the exploration of hydrocarbons has been gradually growing; however, the interpretation of the rendered data is still a challenge for the oil industry. This 1D inversion method is an alternative to the high computational costs of 2D and 3D inversions, as well as their complex implementations and the lack of information provided by anomaly profiles and maps. This method uses a set of algorithms to compose an mCSEM inversion workflow, which inverts data in the common midpoint (CMP) domain as a set of 1D models that correspond to their respective CMP cells. Moreover, these 1D models are laterally constrained so as to provide a georesistivity section with geological meaning. In addition, the presented analytical derivatives of the electromagnetic field responses for 1D models with respect to their resistivities, apart from making the 1D inversion an order of magnitude faster, the expressions developed in this study can be used to clarify some aspects of the electromagnetic methods in stratified medium. This workflow was applied to simulated and field data, wherein geoelectrical sections with resistive bodies at the correct positions and well-estimated background resistivities were recovered in only a few minutes. These results demonstrate the value of this routine as a useful tool for mCSEM data interpretation.