Rapid imaging approach for marine controlled-source electromagnetic with deployed transmission system

Abstract

The marine controlled-source electromagnetic (MCSEM) method is widely used in gas hydrate exploration. For the deployed transmission system of MCSEM, it is equipped with two groups of orthogonal transmission antennas to obtain more comprehensive information. The mainstream processing method involves using a single rotated field component for conventional 2D inversion to obtain the resistivity model. However, data preprocessing and inversion speed are relatively slow, making it difficult to quickly or nearly real-time identify gas hydrate anomalous areas. In order to leverage the benefits of multi-component data and obtain a potential real-time imaging method for the future, we have developed a rapid imaging technique for the deployed transmission system to obtain apparent resistivity pseudosections. The current and electromagnetic field data in different directions are replaced by rotational invariants, and an approximate formula is derived based on the half-space formula and test corrections. This formula maps the apparent resistivity and field data. Results from model tests demonstrate that the apparent resistivity pseudosections can qualitatively identify reservoirs, particularly in the lateral range. In 2015, the South China Sea gas hydrate exploration project acquired data using the deployed transmission system. The pseudosections reveal that the rapid imaging method can directly detect resistivity anomalies and serve as an approximate and effective display method for deployed transmission system of MCSEM, thanks to its simplicity, efficiency, and low computational cost.