Mark Pawlewicz1 and Mitchell Henry2
1 U.S. Geological Survey, Lakewood, CO
2 U.S. Geological Survey, Denver, CO
Burial history models for boreholes in the Delaware and Midland basins, and the Central Basin Platform of the Permian Basin, west Texas and southeast New Mexico, calibrated using vitrinite reflectance (Ro), provide a means to evaluate the burial and thermal history of the most significant petroleum province in the United States.
Results indicate that the earliest petroleum generation began in Late Pennsylvanian time for the Woodford Shale in the northern Delaware basin and in Early to Late Permian time for other areas in the region. An exception is along the north margin of the Midland basin, where the Woodford Shale is just in the early stages of petroleum generation. Only four of six wells achieved temperatures high enough to generate gas; the earliest maturation conditions (1.2 %Ro) for gas generation exist in the Permian Simpson Group strata in south-central Midland basin.
The modeling indicates: (1) in the Delaware basin, the Woodford Shale, Barnett Shale, Wolfcampian strata, Bone Spring Limestone, and Delaware Mountain Group are in the oil window, and all but the Delaware Group are within the gas window; (2) for the Midland basin, Simpson Group, Woodford Shale, Barnett Shale, Wolfcampian strata, and Spraberry Formation achieved the oil window, and also the gas window except for the Spraberry; (3) for the east margin of the Central Basin Platform, the Simpson Group, Woodford Shale, Barnett Shale, and Wolfcampian strata are within the oil and gas windows, whereas the Clear Fork Group is only in the oil window; (4) on the west margin of the Central Basin Platform, all formations have passed into the gas window.