Abstract

It is hypothesized here that fractures in the basement can be tracked at the surface by lineaments seen on satellite imagery in the Val Verde Basin. Experience in other basins around the world teaches that, although such basement fractures may be buried by a thick Paleozoic section and hidden beneath the Ouachita Thrust, plus several hundred feet of flat-lying Cretaceous carbonates, they may show up at the surface as intermittent but persistent lineaments running across the basin on the Cretaceous carbonates. Interpretation of regional magnetic data confirms the spatial coincidence of regional suprabasement and intra-basement structural elements with observed surface lineaments. It is suggested that basement-induced fractures extend upward into the overlying Ellenberger carbonates and have become the loci of hydrothermal dolomitization in the Ellenberger, with a resulting increase of permeability and potential for commercial gas accumulations. Local structural high elements may also form along such fractures.

Two such lineament trends appear to bear a close correlation with the Puckett-Grey Ranch and Brown-Bassett gas fields, each of which holds over one TCF of gas in Ellenberger carbonates. Interpretation of regional magnetic data adds weight to this correlation.

The hypothesis is based on the interpretation of two adjacent Landsat images covering the area from the Marathon Uplift to east of the Devils River, and regional magnetic and gravity compilations.

Risks in exploring for Ellenberger gas in this basin include the drilling depths and carbon dioxide content of the gas, both of which increase southward. Operational problems include the difficulty of obtaining useful seismic data through the high-velocity Cretaceous carbonates that blanket the area. Hence this play has high risk and high costs, but the potential reward is great.