Rapid Interpretation of CSEM Reconnaissance Data

Summary A new method called Quasi-3D Resistivity Mapping (Q3DRM) has been developed for rapid interpretation of controlled-source electromagnetic (CSEM) reconnaissance data. Q3DRM is based on scaled resistivity profiles generated from single or multi-frequency 1D inversion of amplitude and/or phase measurements from online, inline electric fields (Ex). Application of Q3DRM to model and actual grid-style reconnaissance surveys is shown. Results show that the method recovers the shallowest and largest reservoirs. Reservoir non-detections are due to combinations of reservoir size, depth, resistivity contrast, and survey density. 3D modeling also shows that incorporating phase measurements increases reservoir detectability and stability of the results. Although Q3DRM has limited sensitivity and accuracy due to assumptions and data limitations, it can be applied rapidly to CSEM surveys, even when very little is previously known about subsurface resistivities. This technique allows real-time detection of resistive anomalies during coarse-grid reconnaissance surveys for subsequent finer-grid surveying during the same vessel deployment. Q3DRM results also provide useful starting models for more detailed 3D interpretation and for full 3D imaging.