Tannehill Tribulations and Triumphs

Gary K. Rice¹, David Mowrey², and Greg King^3
1 GeoFrontiers Corporation, Rowlett, TX
² Hollis R. Sullivan, Inc, Wichita Falls, TX
³ Salida Exploration LLC, Abilene, TX

Tannehill sandstone (Permian) fluvial/deltaic oil reservoirs on the Eastern Shelf of the Midland Basin in northwest Texas, USA are challenging exploration targets. The narrow, thin channel sandstone sections are poorly imaged on seismic data. In addition, many areas with Tannehill sandstone contain no producible petroleum.

Near-surface geochemical technology advanced sufficiently during its 70 years of emergence to become the principal method integrated with subsurface geology for Tannehill exploration and development. The following case histories chronicle the difficulties and the successes.

Wages Dreamfield (Tannehill) in King County was discovered by the third author. After the field was developed, five producing wells were surrounded by dry holes. Surface geochemical results were questionable because a dry hole was in a high gas concentration pattern. However, geochemical interpretation integrated with subsurface geology recognized a slight eastern (up-dip) lateral migration and successfully predicted a narrow channel between two dry holes. This interpretation led to additional wells that would not have been drilled otherwise.

Grantham (Tannehill) field in Dickens County was discovered by the second author. The prospect originated from subsurface mapping focusing on a 1959 dry hole, which had been unsuccessfully re-entered. Regional mapping suggested a prospect with structural gain and improved sand development to the east. Geochemical data indicated significant microseepage over the prospective area and was one of the primary tools during development of a 10-well field in a 4500-foot deep channel only 1000-1500 feet wide and more than 5000 feet long. In this case, geochemical data closely mapped the narrow reservoir.