Stratigraphically controlled gas production from Abo red beds (Permian), east-central New Mexico
Authors: Broadhead Ronald F. 
Published: July 2023

Red-bed sandstones of the Abo Formation (Permian: Wolfcampian to Leonardian) currently produce natural gas from the Pecos Slope Abo field in northern Chaves County, New Mexico. The Pecos Slope Abo field is located on the Northwest shelf of the Permian Basin. Production currently comes from an approximately 700 mi2 area. The Abo has been designated a "tight gas sand," thus Abo gas can be sold for as much as $5.41 per MCF (thousand ftJ), $2.60 more than the regulated ceiling price of gas produced from formations not designated as tight. The tight-sand designation greatly stimulated drilling, and more than 350 wells have been drilled since field discovery in 1977. Because of low permeability, wells must be artificially fractured to obtain economic production. Initial calculated open flow rises from a few tens of MCFGPD (thousand ft3 of gas per day) before fracturing to an average of approximately 2,200 MCFGPD after fracturing. The Abo red beds are subdivided vertically into three informal lithologic units on the Northwest shelf of the Permian Basin: a lower unit of "granite wash," a middle unit of mudstone, and an upper unit of interbedded sandstone and mudstone. The lower unit of "granite wash" is more than 800 ft (244 m) thick in some places and is composed of interbedded, coarse-grained arkosic sandstones and arkosic conglomerates. This unit rings Abo-age uplifts of Precambrian granitic basement and intertongues basinward with marine limestones of the Hueco Formation. The middle unit is approximately 100 ft (30 m) thick and conformably overlies the clastic facies of the lower unit or the Hueco limestone facies. The middle unit is composed of calcareous, sparsely fossiliferous, argillaceous mudstone and minor fine-grained sandstone. It is a shallow-marine shelf deposit. The upper unit is approximately 600 ft (183 m) thick and is composed of interbedded mudstones and lenticular sandstones. It conformably overlies the middle unit and is disconformably overlain by the dolostones, anhydrites, and fine-grained sandstones of the Yeso Formation (Permian-Leonardian). The upper unit intertongues southward with lagoonal dolostones; a shelf-margin reef facies lies south of the lagoonal dolostones. Sandstone lenses are generally 10ft (3m) to 20ft (6 m) thick. Sandstones are very fine grained, arkosic, and hematitic. The upper unit was deposited as a fluvial-deltaic system which prograded southward over the marine mudstones of the middle unit. Gas is produced from sandstones of the upper unit. Primary porosity has been reduced by compaction to values near zero and is present mostly as submicroscopic pores. The average in situ matrix permeability of Abo sandstones is only 0.0067 millidarcies. Such small amounts of matrix porosity and permeability probably do not contribute greatly to production. The Abo wells tap a gas-filled natural fracture system, and mudstones seal the fractured sandstone reservoirs. Because fluvial-deltaic deposits extend almost 100 mi (160 km) north of present production, the area underlain by potential Abo sandstone reservoirs is at least five times greater than the area that is currently productive.