Abstract

Reconnaissance, soil background-normalized radiometric surveys covering large portions of the Austin Chalk play provide generalized favorable areas for further investigation. Typical of the better favorable areas are linear anomalies that are a few thousand feet wide and a mile or more long. They are aligned along the northeasterly-trending set of regional fractures that are clearly discernible on aerial photographs.

Gridded soil gas surveys of the favorable radiometric areas generally reveal fracture trace-aligned trends of low-to-moderate soil gas concentrations. Higher concentrations often occur peripheral to the low-to-moderate trends.

Seismic lines shot at right angles to the northeasterly-trending fractures are processed to provide pseudo-velocity, color sections that show well-defined fracture zones of porosity in the Austin Chalk. Well log data from horizontal boreholes show a direct correlation between the surface geochemical data and the fractures identified by the logs. It can be inferred that the utilization of these seismic, surface-geochemical and photogeological methods makes it possible to predict the presence of hydrocarbon-bearing, vertical fracture reservoirs in the Austin Chalk.