Investigating the exploration potential for 3D CSEM using a calibration survey over the Troll Field

We demonstrate the ability of the controlled source electromagnetic (CSEM) technique to reveal hydrocarbon reservoirs by reinvestigating the North Sea Troll field with a 3D acquisition grid. Unlike previous applications of 2D CSEM surveys over this field, which have shown a large electromagnetic response over the gas province, the focus in this study is on the thinner and smaller oil reservoir. A weak but consistent anomaly enables detection and delineation of the oil zone and reduces the ambiguity associated with traditional 2D lines. This holds true even for a sparse receiver grid where the target is located between the receiver and source lines. The 3D data show the extent of the oil zone and that it is matched to the top reservoir structural high as well as north-south aligned faults. Variation in magnitude of the anomaly is qualitatively in good correlation with resistivity logs at the well locations. This suggests that 3D CSEM data pave the way for exploration use because of its superiority over 2D data in terms of reduced sensitivity to survey layouts.