Geology and Reservoir Characteristics of Tight Gas Sandstones in Travis Peak Formation, Chapel Hill Field, East Texas
Robert J. Finley, Shirley P. Dutton
Chapel Hill and adjacent Chapel Hill North and Northeast fields produce gas, oil, and condensate from the upper Travis Peak Formation on a north-south elongate anticlinal structure in Smith County, Texas. In 1985, 12.8 bcf of gas and 1.1 million bbl of liquids were recovered from gross perforated intervals mostly 100 to 200 ft thick within the 300 to 350-ft upper delta fringe facies of the formation. The Travis Peak at Chapel Hill is a quartzarenite to subarkose with abundant quartz overgrowths (15 to 20%), and minor ankerite and dolomite (< 3%) and authigenic clay minerals (< 3%). Where present, reservoir bitumen typically amounts to 5% of rock volume and occludes porosity. Porosity ranges from 2 to 17%; permeability, which ranges from < 0.001 to 99 md, averages < 0.05 md and is highly variable vertically. Hydraulic fracture treatments are required for economic production rates.
The Lower Cretaceous Travis Peak in the eastern East Texas basin consists of regressive fluvial-deltaic facies overlain by marginal marine delta fringe facies. Productive upper delta fringe sandstones at Chapel Hill are interpreted as distal edges of lower delta plain to bay, tidal flat, and distributary channel deposits. Individual sandstones show highly variable thickness and mud content that are reflected in gamma ray log character. The sequence is sand rich with no shale barriers to contain hydraulic fractures, and reservoir quality of sandstones is dependent, in part, on amounts of admixed silt and clay and the degree of bioturbation. Thin (4 ft), areally limited mudstones and muddy carbonates 80 ft below the top of the Travis Peak indicate local marine transgression. High sandst ne percent trends show northwest to north-northwest sediment input directions consistent with regional patterns. Core and log data can be used to recognize repetitive sandstone types, but hydraulic fracturing precludes relating these types to hydrocarbon productivity.
AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.