Major blanket-geometry, low-permeability gas sandstones in Texas include the Cotton Valley sandstone, the Travis Peak Formation, the Cleveland formation, and the Olmos Formation. The Cotton Valley (Upper Jurassic) and the Travis Peak (Lower Cretaceous) are widespread, sand-rich units within the East Texas basin that contain marginal marine deltaic, barrier-strandplain, and fan-delta facies. Gas production from the Cotton Valley is more extensively developed than from the Travis Peak, in part because today’s hydraulic fracturing technology was either developed or improved during completion of Cotton Valley tight gas reservoirs.
The Pennsylvanian Cleveland sandstone of the Anadarko basin is in a mixed gas and oil to somewhat gas-prone province wherein the Cleveland produces gas from thin, distal deltaic facies or prodelta sediments reworked by shelf processes. Clay is abundant in the fine to very fine sandstone of the Cleveland. The Upper Cretaceous Olmos Formation contains gas within broadly lenticular delta-front deposits of the Maverick basin. The Olmos contains fine-grained to very-finegrained silty sandstones within massive shales.
In 1980 tight gas sandstones accounted for 28% of gas wells completed in the 5,000- to 15,000-ft-depth range in Texas. Most of the completions in blanket-geometry hydropressured sandstones were within the formations reviewed herein.
Figures & Tables
Geology of Tight Gas Reservoirs
Tight gas reservoirs occur in low-permeability, gas-bearing formations that are present to some extent in all gas-producing basins worldwide. This is the first volume to bring together data on tight reservoirs for a variety of basins and different geologic settings. The papers in this volume discuss characteristics of some of the most significant tight gas areas in the United States; however, these data are equally applicable to many other recognized and unrecognized tight gas provinces in other nations. In general, tight reservoirs in the United States are grouped into tight gas sandstones and eastern Devonian shales. The Devonian shale sequences are dominantly marine shale but include some siltstone and sandstone. Tight gas sandstone formations of other than Devonian age are present throughout the United States and consist primarily of fluvial and marine sandstones and siltstones. In addition, gas also occurs in low-permeability marine carbonate reservoirs. The 14 papers in this volume cover such topics as: coal-bed methane and tight gas sands interrelationships; gas-bearing shales in the Appalachian basin; exploration and development of hydrocarbons from low-permeability chalks; and geologic characterization of low-permeability gas reservoirs.