The Travis Peak (Hosston) Formation: Geologic Framework, Core Studies, and Engineering Field Analysis

The Travis Peak Formation constitutes a 1,000- to 5,000-ft-thick elastic wedge that formed two major depocenters as it spread across a shallow, carbonate-supported shelf along the north flank of the Gulf Coast Basin. The depocenters, which developed in the northern part of the East Texas Basin and in northeast Louisiana, consisted of high-constructive delta complexes dominated by fluvial-deltaic facies. A delta-fringe facies tract, including tidal flat, distributary channel, bay, and nearshore shallow marine shelf facies, formed around the margins of the elastic wedge. These marginal-marine deposits within the upper Travis Peak constitute the most important productive facies of the formation within a nine-county area of research emphasis in the East Texas Basin. Three sandstone types within the upper Travis Peak have been defined from sedimentologic properties observed in core and have been interpreted as channel and sandy tidal flat deposits. Sandstones in the Travis Peak were found to be mineralogically mature, with detrital quartz constituting 89 to 99 percent of the framework constituents. Low permeability and occlusion of porosity is primarily due to quartz overgrowths, which average 21 percent of clean sandstones. Within six Travis Peak gas fields in the eastern East Texas Basin, reservoir engineering studies show that porosity ranges from 8 to 11 percent and water saturation ranges from 28 to 44 percent within intervals of net pay. Permeability-thickness product is low in the southern part of the study area and increases toward the center and northern parts. Upper limits of permeability for 157 wells range from 0.074 md (median value) to 0.084 md (thickness-weighted average). These data are derived largely from well tests that postdate fracture treatment; therefore, pre-frac in situ values are expected to be lower. Within Chapel Hill field, reservoir sandstone types with greatest lateral continuity were deposited as sandy tidal flats, including associated channel sandstones. Where channel patterns are evident, as indicated by the thickest net sandstone, their trend is northwest. Lower energy tidal flat deposition is characterized by increased mud content of sandstones, and local marine transgression resulted in deposition of mudstone and muddy limestone.