Extensional tectonic influence on lower and upper cretaceous stratigraphy and reservoirs, southern Powder River basin, Wyoming
The southern Powder River basin has been influenced significantly by an extensional system affecting Lower Cretaceous, Upper Cretaceous and Tertiary units. The system is composed of small throw, nearly vertical normal faults which are identified in the Cretaceous marine shales and that we believe are basement derived. Resultant fractures were present at erosional/depositional surfaces, both marine and nonmarine, that, in part, controlled erosion and subsequent deposition of Lower and Upper Cretaceous rocks. The normal faults also affected coal deposition in the Tertiary, now exposed at the surface. The erosion and resultant deposition formed extensive stratigraphic traps in Cretaceous units in both conventional and unconventional reservoirs. These reservoirs are interbedded with mature source rocks that have generated and expelled large amounts of hydrocarbons. Resulting overpressuring in the Fall River through the Niobrara formations has kept fractures open and has preserved primary porosity in the reservoirs. The normal faults offset thin sandstone reservoirs forming permeability barriers. Associated fractures may have provided vertical pathways for organic acids that assisted development of secondary porosity in Upper Cretaceous sandstones. These normal...faults and fractures provide significant potential for the use of horizontal drilling techniques to evaluate fractured, overpressured conventional and unconventional reservoirs.
- OSTI ID:
- 6180581
- Journal Information:
- Mountain Geologist; (United States), Vol. 30:2; ISSN 0027-254X
- Country of Publication:
- United States
- Language:
- English
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01 COAL, LIGNITE, AND PEAT
58 GEOSCIENCES
POWDER RIVER BASIN
PETROLEUM GEOLOGY
CRETACEOUS PERIOD
FRACTURED RESERVOIRS
GEOLOGIC FAULTS
GEOLOGIC TRAPS
OIL FIELDS
POROSITY
SANDSTONES
SHALES
STRATIGRAPHY
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020200* - Petroleum- Reserves
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580000 - Geosciences