Abstract

The distribution of sediments in the Permian Basin during Guadalupian time was strongly influenced by the presence of topography associated with deep-seated structures. Although topographic expression of early to middle Pennsylvanian tectonism was greatly reduced by the late Permian, recurrent movement/flexuring of the structural elements, differential compaction and erosion associated with sea level lowstands was expressed as variations in sand isopach and reservoir distribution patterns in the Queen, Seven Rivers and Yates age reservoirs. Sands migrating across the Midland Basin and Central Basin Platform were forced to follow a tortuous path through low-relief topographic features.

Present day dune sands of the Pecos Dune Field Complex are thickest in abandoned drainages cut into the western margin of the escarpment and thin to absent on the High Plains. This is the model for Queen sand migration across the Central Basin Platform.

As many of the deep structures on the platform are parallel or sub-parallel to the platform axis, both fluvial and eolian sands would pass through the saddles between structural elements. As the sands approached the western margin of the platform they would have been deflected to the northwest, parallel to the Pennsylvanian structural trend.

An understanding of the influence of structurally associated topography on reservoir distribution is critical to successful reservoir characterization, exploitation and exploration of the reservoir sands. Many of the shallow reservoirs are not associated with the largest of the productive deep structures, but with smaller, less prominent features. Small changes in the depositional topography can result is significant variations in reservoir distribution. Residence time in a subaqueous reducing environment is also necessary for reservoir development. Timing of the development of topography in space and time varies from area to area on the platform.

Examples of the influence of paleotopography are seen in the fluvial Queen sands at Concho Bluff and Concho Bluff North Fields, which were deposited in depressions above the relict upper Grayburg-age Midland Basin, Queen sands reservoir distribution in the Monahans area which was influenced by topographic expression related to relic Pennsylvanian age structures, and other Queen gas production on the Central Basin Platform.