Controlled Source Electro Magnetic:The concept of using...

Controlled Source Electro Magnetic:

The concept of using resistivity measurements for large-scale offshore exploration was first mooted by academics more than 35 years ago. Commercial applications emerged in the late 1990s, and since the turn of the century several hundred seabed electromagnetic surveys have been conducted worldwide. Sea bed logging can make a significant contribution to how the industry finds hydrocarbons by enabling additional analytical data to be considered, including the ranking of already existing prospects, before further resources are committed to exploration which can be valuable given the high cost of drilling deepwater wells.

The primary application of CSEM is the identification and characterization of units that are more resistive than the surrounding rocks. Typically, a potential reservoir is identified with seismic data, and CSEM can then be used to analyse its resistivity. The technique seeks to detect the potential resistivity contrast between oil or gas-saturated rocks, and those with significant water content. The transformation from resistivity to geology, and finally pore fluid content, is an interpretive process that requires careful interpretation and integration of the CSEM data with seismic data, and, where available, local well control.

Shell has extensive experience worldwide of this technique, and is one of the largest users of CSEM, having undertaken more than 120 surveys.