Surface Geochemical Exploration in Southwestern King and Southern Dickens Counties, Texas—A Review and Prognosis
Gary K. Rice
Surface, or near-surface, geochemical exploration has played an important role in oil discoveries in southwestern King and southern Dickens Counties in northwest Texas on the Eastern Shelf of the Midland Basin. This report reviews the role of geochemical exploration during the last 20+ years, why geochemical exploration has been important in this geographical area, and the future outlook.
Near-surface geochemical exploration takes advantage of nearly vertical petroleum gas migration from reservoir depths to the surface. Although vertical migration techniques have been maligned by some (Davidson 1994), 70 years of perseverance and scientific advances produced valuable exploration technologies. Below the water table vertical migration involves a separate gas phase and upward movement due to buoyancy through fractures in rocks overlying the reservoir. Vertical gas migration can be modeled using well known mass transport principals described by Darcy’s law (Arp, 1992; Klusman and Saeed, 1996). Vertical migration rates and surface concentrations calculated by the models have been verified by field measurements (Rice, et al, 2002).
The subject area, as with most of the Eastern Shelf of the Midland Basin, is well suited for surface geochemistry. Flat stratigraphy, infrequent faults, and limited stacked reservoirs are ideal conditions for imaging reservoirs using gas migration data. Since the most ubiquitous reservoir, Tannehill Sandstone (lower Permian) is thin, often narrow, and not well imaged in seismic data, alternate exploration techniques are necessary. Surface geochemistry is the main technique used with subsurface geology for finding Tannehill Sandstone and other reservoirs in the area.
Although seismic data may not image stratigraphic traps or thin reservoirs, stratigraphic traps in this area may have a structural component that can be detected using seismic data. Where available, seismic data is also part of the integration mix. Subsurface geology, geochemical exploration, and seismic data have been successfully integrated in some cases.
While surface geochemistry can help refine reservoir locations, we have to collect data in the right areas. A geological understanding of the depositional environment resulting in predicted sand deposits has been the key to exploration success. Published reports about Navigator field (Cannon, et al, 2001), Wages Dreamfield and Grantham field (Rice, et al, 2006) illustrate the exploration challenges in finding and developing these reservoirs. The presentation includes an up-to-date report of fields discovered with and without surface geochemistry, including reservoirs in Tannehill Sandstone, Stockwether Limestone, and Croton Limestone.
AAPG Search and Discover Article #90065©2007 AAPG Southwest Section Meeting, Wichita Falls, Texas