Diagenesis of nonmarine rocks and gas entrapment in northern Green River basin, Wyoming

Conference · Tue Mar 01 04:00:00 EST 1983 · Am. Assoc. Pet. Geol., Bull.; (United States)

OSTI ID:6183545

Dickinson, W W; Gautier, D L

More than 5000 m (16,404 ft) of Upper Cretaceous and Tertiary nonmarine rocks have accumulated in the northern Green River basin. Isotopic, petrographic, and mineralogic studies of cores from seven wells reveal that an intricate sequence of diagenetic events has acted upon mineralogically immature sediments to produce the observed low permeabilities. Gas accumulates in sandstones because it is generated from humic matter at a rate that exceeds its ability to escape. In the central part of the basin, normal hydrostatic pressures exist down to about 2500 m (8200 ft). Sandstone porosities in this zone range from 10 to 15% and permeabilities usually exceed 10 md. At depths of about 3500 m (11,483 ft), overpressuring and gas accumulation are associated with sandstones that have average porosities of about 7% and in-situ permeabilities of approximately 0.005 md. This transition is not marked by a depositional boundary. Porosity reduction, which is assumed to be paralleled by permeability loss, proceeds by some combination of three principal processes: (1) precipitation of calcite or silica cements early in the burial history; (2) porosity loss through grain deformation and compaction; and (3) the filling and coating of residual and secondary pores by illite, chlorite, microcrystalline quartz, or ferroan carbonates. Zones of conventional reservoir porosity and permeability have not been recognized in areas of overpressuring and gas accumulation, nor are they to be expected. Because the gas is diagenetically entrapped, the search for economic accumulations should, paradoxically, be limited to sandstones of low porosity and permeability.

• Research Organization: Geological Survey, Denver, CO
• OSTI ID: 6183545
• Report Number(s): CONF-8304200-
• Conference Information: Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Journal Volume: 67:3
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020200* -- Petroleum-- Reserves
Geology
& Exploration
DIAGENESIS
ENERGY SYSTEMS
FEDERAL REGION VIII
GEOLOGIC DEPOSITS
GEOLOGIC STRUCTURES
GEOLOGIC TRAPS
GEOPRESSURED SYSTEMS
MINERAL RESOURCES
NATURAL GAS DEPOSITS
NORTH AMERICA
PERMEABILITY
POROSITY
RESOURCES
ROCKS
SEDIMENTARY BASINS
SEDIMENTARY ROCKS
USA
WYOMING