Structural interpretation using PS seismic on the Kvitebjørn Field in the North Sea

Abstract

Seismic data from an ocean-bottom cable (OBC) survey are based on a different acquisition method than conventional/streamer seismic data. When acquiring the OBC data, the receivers are placed on the sea floor instead of near the sea surface. This allows PS (converted shear) seismic to be recorded in addition to pressure data (PZ). PZ data are equivalent to PP data from streamer seismic. Because the PS data have different information and travel paths from PZ, they should in theory not give exactly the same image as the pressure data. The OBC data set acquired on the Statoil-operated Kvitebjørn Field is a good example of this. In these data, it is obvious that the PS seismic image of the Jurassic target is significantly different from the PZ image. Figure 1 shows the PP, PZ, and PS seismic from the same line going through a proven gas well. The top reservoir is on a trough (green marker) on the PP and PZ seismic. Comparison of the reservoir section with the same interval on the time-aligned PS data reveals a completely different reflection pattern. The question that often arises in a case like this is: can the PS seismic can be trusted? Even if the answer is yes, a big question remains: do they add any valuable information about the field?