Petroleum Geology of Carter Sandstone (Upper Mississippian), Black Warrior Basin, Alabama

Abstract

The presence of combination petroleum traps makes the Black Warrior basin of northwestern Alabama an attractive area for continued hydrocarbon exploration. More than 1,500 wells have been drilled, and more than 90 separate petroleum pools have been discovered. The primary hydrocarbon reservoirs are Upper Mississippian sandstones. The Carter sandstone is the most productive petroleum reservoir in the basin, having yielded more than 1.195 million bbl (1.9 × 105 m3) of oil and 141 bcf (4.0 × 109 m3) of natural gas. Productivity of the Carter sandstone is directly related to its environment of deposition. The Carter accumulated within a high constructive elongate to lobate delta, which prograded into the basin from the northwest to the southeast. Carter bar-finger and distal-bar lithofacies constitute the primary hydrocarbon reservoirs. Parkwood prodelta and interdistributary bay and Floyd marine-shelf shales are excellent source rocks, containing amorphous and herbaceous kerogen. Primary porosity in the Carter sandstone has been reduced by quartz overgrowths and calcite cementation. Dissolution porosity results from the leaching of carbonate allochems, calcite cement, and/or matrix. Petroleum traps in the Carter sandstone in central Fayette and Lamar Counties, Alabama, are primarily stratigraphic and combination (structural-stratigraphic) traps. Structural closures associated with normal faults and stratigraphic pinch-outs of the Carter constitute the chief trapping mechanisms. Considerable lateral and vertical lithologic variability is present in the Carter sandstone, and no apparent regional porosity and permeability trends have been recognized in the basin. The potential is excellent for future development of hydrocarbon reservoirs in the Upper Mississippian Carter sandstone. Frontier regions south and east of the known productive limits of the Black Warrior basin are ideal areas for continued exploration.