Marine and nonmarine gas-bearing rocks in Upper Cretaceous Neslen and Blackhawk Formation, eastern Uinta basin, Utah: sedimentology, diagenesis, and source rock potential

Conference · Fri Aug 01 04:00:00 EDT 1986 · Am. Assoc. Pet. Geol., Bull.; (United States)

OSTI ID:7040228

Pitman, J K; Franczyk, K J; Anders, D E

The Upper Cretaceous nonmarine Neslen Formation and marginal-marine Blackhawk Formation in the eastern Uinta basin, Utah, contain large amounts of thermogenic gas that were generated in place from interbedded humic-rich source rocks. Distribution of source and reservoir rocks in these units is controlled by the depositional environments. The Blackhawk, composed of laterally extensive sandstone and locally interbedded carbonaceous siltstone and minor coal, reflects deposition in nearshore and backshore marine environments. Potential reservoir sequences in the Neslen and Blackhawk are composed dominantly of monocrystalline quartz and sedimentary lithic fragments, principally chert. Alteration in these rocks included the mechanical compaction of unstable framework grains, the precipitation of minor quartz overgrowths, and the formation of barite, dolomite, and ankerite as pore fill and replacement minerals. The growth of authigenic illite, illite-smectite, and minor chlorite and kaolinite followed the dissolution of chemically unstable detrital grains. Porosity and permeability in these units typically are low, from 2 to 10% and 1 md, respectively. Most of the porosity is attributed to partial to complete dissolution of fossiliferous chert grains and to the decomposition of lithic fragments and matrix. Natural fractures, partly cemented with carbonate, barite, and kaolinite, occur locally. Source rock analyses and reconstructed burial profiles indicate that peak hydrocarbon generation in the Neslen and Blackhawk occurred about 20 Ma at maximum burial depth and temperature. Hydrocarbon generation decreased during the late Tertiary due to widespread cooling that occurred in response to regional uplift and erosion associated with the development of the Colorado Plateau.

• Research Organization: Geological Survey, Reston, VA
• OSTI ID: 7040228
• Report Number(s): CONF-8609129-
• Conference Information: Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Journal Volume: 70:8
• Country of Publication: United States
• Language: English

Related Subjects

03 NATURAL GAS
030200* -- Natural Gas-- Reserves
Geology
& Exploration
CLAYS
COAL DEPOSITS
COAL SEAMS
CRETACEOUS PERIOD
DIAGENESIS
FEDERAL REGION VIII
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC FORMATIONS
MESOZOIC ERA
MINERAL RESOURCES
NATURAL GAS DEPOSITS
NORTH AMERICA
RESOURCES
ROCKS
SANDSTONES
SEDIMENTARY ROCKS
SEDIMENTATION
SILTSTONES
SOURCE ROCKS
UINTA BASIN
USA
UTAH