Overpressured reservoirs in Rocky Mountain region

Conference · Mon Aug 01 04:00:00 EDT 1983 · Am. Assoc. Pet. Geol., Bull.; (United States)

OSTI ID:6525453

Spencer, C W

Overpressured oil and gas reservoirs in the Rocky Mountain region are more widespread than generally recognized. Reservoir pressure gradients in excess of 0.5 psi/ft (> 11.3 kPa/m) are considered overpressured. However, most overpressured reservoirs have pressure gradient greater than 0.6 psi/ft (> 13.6 kPa/m). Although a variety of conditions can cause ovepressuring, most high pressures in the region are interpreted to be caused by the active generation of oil and gas in sequences that still contain organic matter capable of yielding thermally generated hydrocarbons. Rocks with above normal pressure in Rocky Mountain basins range in age from Late Devonian to Tertiary and are commonly associated with low-permeability (tight) reservoirs. Most overpressured reservoirs occur in Cretaceous and Tertiary sandstone sequences. Overpressuring is not common in rocks older than Cretaceous except in very organic-rich sequences, probably because lean source beds that have been heated over a long period of time are no longer capable of yielding enough hydrocarbons to maintain abnormal pressure. Statistically, nearly all overpressured reservoirs and source rocks have temperatures of about 200/sup 0/F (93/sup 0/C) or higher. In addition, available data indicate that hydrocarbon-related overpressuring does not usually occur if vitrinite reflectance values are < R/sub 1/ = 0.5% in oil-prone sequences or < R/sub 1/ = 0.7% in gas-prone sequences. Hydrocarbons expelled into widespread, high-permeability reservoirs probably migrate owing to hydrodynamic flow and buoyancy. These reservoirs usually have normal pressures.

• Research Organization: Geological Survey, Denver, CO
• OSTI ID: 6525453
• Report Number(s): CONF-8309274-
• Conference Information: Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Journal Volume: 67:8
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020200* -- Petroleum-- Reserves
Geology
&amp; Exploration
03 NATURAL GAS
030200 -- Natural Gas-- Reserves
Geology
&amp; Exploration
FEDERAL REGION VIII
GEOLOGIC DEPOSITS
MINERAL RESOURCES
NATURAL GAS DEPOSITS
NORTH AMERICA
ORIGIN
PERMEABILITY
PETROLEUM DEPOSITS
PRESSURE GRADIENTS
RESERVOIR ROCK
RESOURCES
TEMPERATURE EFFECTS
USA