Polarity consistent geophone rotation analysis by inversion: Penn West 3D VSP

Robert James Ferguson

The Rig-source VSP/ Offset VSP/ Walkaway VSP of Penn West Petroleum Ltd is used to demonstrate a new geophone rotation analysis. This survey employs non-gimballed geophones in a deviated well-bore and so the orientation of all three components is required for proper wavefield separation. Three walkaway VSP source lines are recorded in a total of 45 geophone levels downhole. Data are gathered according to common receiver and first break energy is analyzed based on the new method. So that absolute measurements can be made for each receiver level, each three component recording is rotated such that all sources for a common receiver reside vertically above that receiver and then first-break analysis is used to point one of the geophone components at the source location. Within each common receiver gather very good agreement is found between sources for the dip between the geophone component and the source location and that good agreement is found for the azimuth of the two remaining components.