3D borehole geophone orientation study, central Alberta

Peter Gagliardi and Don C. Lawton

ABSTRACT

Geophone orientation azimuths were found analytically from 3D and 2D walkaway VSP data acquired near Lousana, Alberta. The 3D dataset was divided based on source-well azimuth into bins with centers trending 0°-180°, 45°-225°, 90°-270° and 135°-315°; the standard deviation in orientation azimuth was found to be 5.24 using all azimuths, and 1.28°, 0.66°, 1.07° and 2.77° respectively when binned. The 2D dataset consisted of three lines; the standard deviation for this survey was 1.73° for all lines, 1.87° for the east line, 0.71° for the southeast line and 1.81° for the south line. In both cases, the mean angle calculated for each receiver did not appear to have any dependence on source-well azimuth, suggesting flat, isotropic geology near the well. Removal of sources nearer than 300 m (approximately 1/3 of the geophone depth) significantly improved the scatter in the 2D walkaway, but had little effect on the 3D walkaway. Finally, the orientation angles for the 3D walkaway analysis were also calculated using a linear regression analysis of trace hodograms. Results showed that mean angles calculated using this method differed from the analytic method by less than 1° on average, but that the analytic method produced less scatter.

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