Downhole seismic source

Abstract

A prototype model of a downhole controlled seismic source has been built and field tested. This instrument is a swept‐frequency, penumatically powered seismic source that operates in the 10 to 100 Hz range. This particular version is a vertical‐dipole source and generates vertically polarized shear waves. The instrument is an improved version of a downhole monofrequency source first tested in the crust of Kilauea Lava Lake, Hawaii, in 1981. The present prototype source was field tested recently at the Chevron Oil Field Research facility in La Habra, California. Data from this test, combined with calculations for a full‐scale instrument, indicate that considerable amounts of energy can be coupled into the ground with this type of downhole source. Signals from these prototype sources are easily detectable at distances of 150 m or more. A larger version of the source is currently being designed and fabricated for use in 0.20 m diameter holes, and it will theoretically have a range 30 times greater than the current prototype model. This new seismic source has applications in scientific studies related to the Continental Scientific Drilling Program. The source also has applications in locating magma bodies for the Magma Energy Program and in evaluating oil reservoirs.