Field-Scale Experiments in Underground Gasification of Coal at Gorgas, Al.

Field-scale experiments were conducted at Gorgas, Al, from 1951 to 1954. Three reaction paths were formed by electrolinking-carbonization, using electrode spacing's of 150, 152, and 155 feet. The coal along these reaction paths was gasified, using air, oxygen, and steam separately or in various combinations. At the conclusion of operation, a drilling survey was conducted to determine the location and approximate area of the reaction zones. The Upper Jurassic Smackover Formation is found in an arcuate belt in the subsurface from south Texas to panhandle Florida. The Smackover is the most prolific hydrocarbon-producing formation in Alabama and is an important hydrocarbon reservoir from Florida to Texas. In this report Smackover hydrocarbon reservoirs in southwest Alabama are described. Also, the nine enhanced- and improved-recovery projects that have been undertaken in the Smackover of Alabama are evaluated. The report concludes with recommendations about potential future enhanced- and improved-recovery projects in Smackover reservoirs in Alabama and an estimate of the potential volume of liquid hydrocarbons recoverable by enhanced- and improved-recovery methods from the Smackover of Alabama. The Smackover was deposited on a carbonate ramp, similar to that of the present-day Persian Gulf, in much of the Gulf-Coast region. However, in southwest Alabama,  smackover strata were deposited in four interconnected basins: the eastern part of the Mississippi interior salt basin, the Manila embayment (which contains two separate depocenters), the Conecuh embayment, and a basinal area south of the Baldwin high. The distribution of facies was more closely controlled by local paleotopography than by southerly regional dip, as would have been the case in an unmodified ramp setting. High-energy facies were deposited in nearshore areas rimming exposed paleohighs and near the updip limit of Smackover deposition; lower energy strata were deposited in basin centers. Based on ammonites recovered from the lower portion of the unit, the Smackover has been assigned a late Oxfordian age. The Smackover ranges up to more than 550 feet thick in the study area. Basal Smackover strata in Alabama contain laminar and domal stromatolites; these deposits probably formed in shallow water during the early stages of marine transgression. Middle Smackover strata are dominated by lime mudstone and pelletal or fossiliferous lime wackestone. These strata were deposited at and near the time of maximum transgression, and during and after a period of rapidly increasing water depth. Middle-Smackover lime mudstone is typically laminated and organic rich. Upper Smackover strata were laid down during a relative sea-level stillstand. Progradational strata of the upper Smackover are dominated by ovoid grainstone and diverse peritidal carbonates on the flanks of the paleohighs and by pelletal and oncoidal packstone and grainstone in the centers of the depositional basins. The Smackover locally contains substantial amounts of siliciclastic material, particularly near the Conecuh ridge and its associated small paleohighs (e.g., Barnett, North Wallers Creek, Uriah, Vocation, and Burnt Corn Creek fields) and in the Manila embayment. Diagenesis of Smackover reservoirs was dominated by the effects of (1) early cementation, (2) leaching of calcium carbonate allochems, and (3) dolomitization, both mimetic and nonmimetic. The Smackover Formation is overlain in southwest Alabama by the Buckner Anhydrite Member of the Haynesville Formation, whose basal portion is dominated by subaqueous evaporites in depositional basins, and by peritidal and supratidal evaporitic and siliciclastic strata on the flanks and crests of paleohighs. As of December 1990, the Smackover had produced oil, condensate and/or natural gas from 73 established fields in Alabama. At that time, cumulative production from Smackover reservoirs in Alabama totaled over 113 million barrels (MMB) of oil (including Norphlet oil production at South Womack Hill field and minor amounts from a few other fields, which are not reported separately), 145 MMB of condensate (including Norphlet condensate production at Hatter's Pond field, which is not reported separately), and 1.12 trillion cubic feet (TCF) of natural gas. Smackover hydrocarbon traps in southwest Alabama can be characterized as structural or combination structural and stratigraphic traps. Many structural traps result from halokinesis of the Louann Salt, but basement-cored anticlinal traps are locally common. The Buckner Anhydrite Member of the Haynesville Formation commonly forms the seal. Combination traps generally involve porosity or permeability pinch-outs occurring on regional dip, on halokinetically generated anticlines or structural noses, or on basement-related anticlines or faulted anticlines. Most Smackover reservoirs originated as nearshore-marine carbonate sediments with minor admixtures of noncarbonate material. Some of these reservoirs preserve abundant evidence of their environment of deposition. Others have been highly altered and their origins are unclear.

Tags: kmd