3D CSEM acquisition and inversion for appraisal of deepwater gas field Available to Purchase

We present the application of 3D Controlled-Source Electromagnetics (CSEM) to appraisal of gas discoveries, focusing on how the data were acquired and inverted to achieve the survey objectives. The motivation for acquiring the CSEM data was to distinguish high from low gas saturation in undrilled reservoir segments, which is a significant subsurface risk when working with seismic DHIs alone. The project took advantage of recent innovations in CSEM acquisition and imaging: A high-power, deep-towed source emitting an electric current of 7000 A and TTI 3D Gauss-Newton inversion. We also applied a new method for reducing the impact of metallic well casing on the inversion result, which constitutes an interpretation challenge for the drilled reservoirs segments. We describe the acquisition parameters and explain our inversion approach. The resulting resistivity models over the discoveries clearly demonstrate that resistivity from CSEM can reduce the saturation uncertainty in the undrilled reservoir segments. Both unconstrained and constrained inversion results are presented, and uncertainties discussed.