New Vitrinite Reflectance Data for the Wind River Basin, Wyoming.

摘要

The Wind River Basin is a large Laramide (Late Cretaceous through Eocene) structural and sedimentary basin that encompasses about 7,400 square miles in central Wyoming. The basin is bounded by the Washakie Range and Owl Creek and southern Bighorn Mountains on the north, the Casper arch on the east and northeast, and the Granite Mountains on the south, and Wind River Range on the west. Important conventional and unconventional oil and gas resources have been discovered and produced from reservoirs ranging in age from Mississippian through Tertiary (Fox and Dolton, 1989; De Bruin, 1993; Johnson and others, 1996, 2007). In recent years, advances and success in horizontal drilling and multistage fracture stimulation have led to an increase in exploration and completion of wells in marine shales in other Rocky Mountain Laramide basins that were traditionally considered hydrocarbon source rocks. Important parameters that control hydrocarbon production from these shales include: reservoir thickness, amount and type of organic matter, and thermal maturity (Milici, 1993; Curtis, 2002). The purpose of this report is to present new vitrinite reflectance data collected mainly from Cretaceous marine shales in the Wind River Basin to better characterize their thermal maturity and hydrocarbon potential. These new data supplement previously published data by Johnson and others (1991), Barker and Crysdale (1993), Katz and Liro (1993), Nuccio and others (1993), Pawlewicz (1993), Nuccio and others (1996), and Finn and others (2006). Ninety-nine samples from Cretaceous and Tertiary strata were collected from well cuttings stored at the U.S. Geological Survey Core Research Center in Lakewood, Colorado. All samples were analyzed for vitrinite reflectance to determine levels of thermal maturation. Preparation of samples for reflectance analysis required (1) crushing the larger pieces into 0.25- to 1-millimeter pieces, (2) casting the pieces with epoxy in pre-cut and drilled plugs, and (3) curing the samples overnight. Subsequently, a four-step grinding and polishing process was implemented that included sanding with progressively finer sandpaper (60 to 600 grit) followed by a two-step polishing process (0.3 and 0.05 micron). Vitrinite reflectance measurements were determined at 500 X magnification using plane-polarized incident white light and a 546-nanometer monochromatic filter in immersion oil.