The Barnett Shale in southeastern New Mexico: distribution, thickness, and source rock characterization

Abstract

Basinal dark-gray to black marine shales in the New Mexico part of the Permian Basin that have been traditionally correlated as the Barnett Shale (Upper Mississippian) are late Mississippian to Morrowan (Early Pennsylvanian) in age. The Upper Mississippian Barnett Shale in the south correlates northward with Chesterian and Meramecian strata on the Mississippian shelf. The shelf strata in the north are dominated by marine limestones; tongues of Barnett shales extend northward onto the shelf where they intertongue with the shelf limestones. The overlying Morrowan (Lower Pennsylvanian) shales grade northward into a sandy facies consisting of interbedded dark-gray to black shales and lenticular sandstones. That part of the Upper Mississippian -Lower Pennsylvanian shale sequence that is correlated as the Barnett Shale consists of 200 to 350 ft of dark-gray to black shale with minor thin sandstones and minor thin limestones throughout most of its extent in the New Mexico part of the Permian Basin. The overlying Morrowan (Lower Pennsylvanian) shales are subdivided into two stratal units, the lower Morrow shale and the upper Morrow shale. The lower Morrow shale consists of 200 to 350 ft of dark-gray to black marine shales and minor thin sandstones. The upper morrow shale consists of 100 to 800 ft dark-gray to black marine shales and minor thin sandstones.The Barnett Shale contains mature, organic-rich petroleum source rocks. Total Organic Carbon (TOC) content ranges from 0.85 to 4.9 percent in the New Mexico part of the Permian Basin. The kerogen population is dominantly gas prone but also appears to contain oil-prone types. The Barnett Shale is thermally mature throughout its extent in the New Mexico part of the Permian Basin. A northwest-southeast trending fairway for Barnett shale gas exploration extends throughout the western portion of the New Mexico part of the Permian Basin. This fairway is defined by the most thermally mature source rocks with TOC contents greater than 2 percent.Exploratory drilling for shale gas has not yet taken place in the New Mexico part of the Permian Basin.The lower and upper Morrow shales contain sufficient TOC to be considered source rocks in southeastern New Mexico and are thermally mature. The Morrow shales are less thermally mature than the deeper, underlying Barnett Shale.