The Palo Duro Basin is a broad structural low in the southern Texas Panhandle that formed as a result of nearly continuous Pennsylvanian and Permian subsidence. True complexity of this basin is unknown because of the sparsity of structural information. However, surface and subsurface studies, including examinations of outcrop, well log, and seismic reflection data, indicate that structures within and adjoining the basin consist primarily of small, fault-bounded, isolated, positive basement areas and poorly defined subbasins.

Successful development of low-permeability-sandstone gas reservoirs depends on an understandingof their natural fracture patterns and on predictions of the orientation of horizontal stresses.This report describes the preliminary results of fracture analysis of the Lower Cretaceous TravisPeak Formation, a tabular sandstone and shale unit approximately 2,000 ft (610 m) thick thatproduces gas from low-permeability (less than 1 md) sandstone in much of East Texas. Depth to thetop of the formation ranges between 5,900 and 9,500 ft (1,798 and 2,895 m) in the study area.

The State-owned submerged lands of Texas encompass almost 6,000 mi2 (15,540 km2). They lie below waters of the bay-estuary-lagoon system and the Gulf of Mexico and extend 10.3 mi (16.6 km) seaward from the Gulf shoreline (fig. 1). The importance of these lands and their resources to resident flora and fauna as well as to people is well known and documented; more than one-third of the state's population is concentrated within an area of the Coastal Zone that is only about one-sixteenth of the state's land area.

Four clastic depositional sequences compose the lower part of the Triassic Dockum Formation in the Palo Duro Basin. Each sequence consists of a basal interbedded mudstone and interbedded siltstone succession overlain by an upper succession of sandstone containing minor conglomerate, siltstone, and mudstone beds. Regional cross sections indicate that the lower parts of sequences typically thicken basinward, whereas the upper sandy partsnbecome more discontinuous basinward and upsection.

This study is a product of ongoing Bureau of Economic Geology investigations, by means of geologic and petrophysical modeling, into the nature of reservoir compartmentalization or heterogeneity. The model has been designed to provide a basis for subsequent infill drilling in the reservoirs in question along trends of greatest geologic potential, rather than according to geometrically defined well spacings.The Lower Ordovician Ellenburger Group was the site of the investigations from which more than 10,000 ft (3,050 m) of core from 63 wells was logged.