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Using a geology-based assessment methodology, the U.S. Geological Survey estimated undiscovered, technically recoverable mean resources of 8.5 billion barrels of oil and 66 trillion cubic feet of gas in continuous accumulations in the Upper Cretaceous Eagle Ford Group and associated Cenomanian-Turonian strata in onshore lands of the U.S. Gulf Coast region, Texas.

Palaeogene dolostones from the sub-surface of Florida are ideal for the study of dolomite maturation because they record the early stages of a secondary dolomite overprint without destruction by later diagenetic overprints. Two distinct dolomite textures occur in the dolostones of the Upper Eocene Ocala and Lower Oligocene Suwannee limestones in west-central Florida: a porous and permeable sucrosic dolomite and a less porous and relatively impermeable indurated non-sucrosic dolomite. In both textures, the initial matrix dolomite is dully luminescent, whereas the secondary overprint is dominantly luminescent cement in the Suwannee and only neomorphic luminescent dolomite in the Ocala. The abundance of luminescent dolomite ranges from 2% to 38%, which translates to 1AE6 km 3 of material in the Suwannee and 13AE5 km 3 in the Ocala. Extrapolated trace-element contents (Sr and Na) and d 18 O values for the matrix and luminescent end-members indicate a marine origin for the matrix dolomite in both units, and a freshwater-seawater mixingzone origin for the secondary luminescent dolomites. The d 18 O values indicate that a saline, middle mixing-zone environment overprinted the Suwannee but a more dilute mixing zone affected the Ocala. Fluid-fluid mixing models constrained by modern Floridan aquifer hydrochemistry and extrapolated 87 Sr/ 86 Sr values of the luminescent phases indicate that the mixing zones operated during the Late Miocene to Pliocene in the Ocala and affected the Suwannee in the Pliocene. The luminescent Suwannee mixing-zone cement reduced porosity up to threefold and permeability up to 100-fold, which converted many sucrosic dolomites to indurated dolomites. By contrast, the neomorphic luminescent Ocala dolomite did not have an appreciable impact on the maturations. Although freshwater-seawater mixing zones were not the sites of the initial dolomitization, the mixing-zone environment did dramatically overprint and mature the regionally widespread dolomites of the Ocala and Suwannee limestones. This maturation occurred shortly after formation of the proto-Floridan aquifer; the timing suggests the matrix dolomites were 'ripe' for alteration and that the only prerequisite for mixingzone dolomite is pre-existing dolomite substrates to reduce kinetic barriers. In contrast to recent claims, the results of this study demonstrate that mixing zones can be effective in forming regionally significant amounts of secondary dolomite and influencing the petrophysical maturation of dolomite bodies.

No abstract

Using a geology-based assessment methodology, the U.S. Geological Survey estimated mean undiscovered volumes of 7.4 billion barrels of oil, 6.7 trillion cubic feet of associated/dissolved natural gas, and 0.53 billion barrels of natural gas liquids in the Bakken and Three Forks Formations in the Williston Basin Province of Montana, North Dakota, and South Dakota. is defined by the postulated maximum extent of petroleum fluids within the Bakken and Three Forks Formations. The Devonian and Mississippian Bakken Formation consists of four members in ascending order: (1) the Pronghorn Member (formerly known as "Sanish sand") (LeFever and others, 2011), (2) lower shale member, (3) middle member, and (4) upper shale member. The sandstones and siltstones of the Pronghorn Member represent the first transgressive unit of the Bakken Formation and are limited in extent. The maximum thickness of the Pronghorn is 58 feet (LeFever and others, 2011). The upper and lower shale members are the primary source rocks for the Bakken TPS, with present-day total organic carbon (TOC) values from <1 weight percent to 35 weight percent (Lillis, 2013). The shale members are present in parts of Montana and North Dakota and extend into the Canadian provinces of Saskatchewan and Manitoba, though the Canadian provinces were not assessed. The lower shale member reaches a maximum thickness of 56 feet along the east flank of the Nesson anticline (fig. 1). The middle member of the Figure 1. Map showing the Williston Basin Province, Bakken Total Petroleum System (TPS), and the Bakken Formation Assessment Units (AUs). Major structural features are also shown. Inset map shows location of the Bakken TPS (pink).

Using a geology-based assessment methodology, the U.S. Geological Survey assessed undiscovered, technically recoverable continuous mean resources of 46.3 billion barrels of oil and 281 trillion cubic feet of gas in the Wolfcamp shale and Bone Spring Formation of the Delaware Basin in the Permian Basin Province, southeast New Mexico and west Texas.

Using a geology-based assessment methodology, the U.S. Geological Survey assessed technically recoverable mean resources of 20 billion barrels of oil and 16 trillion cubic feet of gas in the Wolfcamp shale in the Midland Basin part of the Permian Basin Province, Texas.

Extending and building on a geology-based assessment of undiscovered, technically recoverable petroleum resources in the Bakken and Three Forks Formations of the Williston Basin Province in Montana and North Dakota, the U.S. Geological Survey has estimated the water and proppant demands and water-production volumes associated with possible future development of those petroleum resources. The water and proppant assessment results are presented here, along with related drilling information and relevant water budget volumes for the region.