Geophysical characterization of the near-surface at Priddis, Alberta
J. Helen Isaac, Lei Zhi, Malcolm B. Bertram, Donald C. Lawton, Laurence R. Bentley
We integrated well data with seismic reflection and refraction data and electrical resistivity data acquired at the same time as the refraction data on the University of Calgary lands at Priddis, Alberta, in 2012. The purpose was to derive a model of the near-surface so that we might predict the lithology to be encountered in wells that were planned to be drilled in the autumn of 2013 for the installation of a permanent downhole seismic recording and monitoring system.
There is a good match between the velocity model derived from the refraction survey, the interpretation of reflectors on the reflection data, the existing Rothney test well lithology and the electrical resistivity inversion. A sandstone penetrated between 65 m and 90 m in the Rothney observation test well was predicted to be encountered updip between about 25 m and 50 m in Well 1, drilled in October, 2013. Well 1 turned out to have three sandstones within this interval: at 23-28 m, 31-37 m and 46-50 m. A major resistive unit, interpreted to be a sandstone, correlates to strong reflectors on the reflection seismic data and a relatively high velocity on the seismic refraction data. We predicted that the top of this unit would be encountered at about 95 m depth in Well 1. Our predictions turned out to be accurate as Well 1 penetrated a sandstone from 91-102 m. A hard shale with sandstone ledges was penetrated at 124 m in Well 1 and slowed the drilling of the well. It projects onto the observation well deeper than the total depth. It correlates to a high amplitude reflection on the seismic data.