Validaing a Borehole Seismic Survey in Complex Geology

A rig-source VSP was acquired in the Gulf of Mexico (GOM) using both seismicVISION While Drilling (SVWD) and wireline VSP measurements. After a bit run, a time mistie was noted on the SVWD data. Strong ocean currents caused the rig to rotate during the bit run. After the well was complete, a wireline VSP was recorded. The rig rotated during the wireline acquisition. The same time mistie was observed. 3D ray-trace modeling was used to confirm that the strongly dipping salt structure caused a large time mistie for a very small change in source position. The possibility of rig-rotation needs to be accounted for in pre-survey design even for rig-source VSPs.