Underpressured reservoir - the other part of the story

Conference · Fri Jul 01 04:00:00 EDT 1988 · AAPG (Am. Assoc. Pet. Geol.) Bull.; (United States)

OSTI ID:6371902

Spencer, C W

The significance of underpressured reservoirs has been somewhat neglected because underpressuring is difficult to detect. Oil and gas reservoirs with abnormally high or abnormally low pressures are present in many basins in the US and worldwide. The above-normal (overpressured) reservoirs are generally deep (> 10,000 ft or 3050 m), commonly gas bearing, and, in onshore basins in the US, usually occur in low-permeability (tight) reservoir-rock sequences. Reservoirs with below-normal pressures are mostly shallow (< 6000 ft or 1830 m), usually contain gas and/or oil, and occur in both tight and permeable (conventional) reservoirs. Abnormally low reservoir pressures can be caused by gaseous diffusion and gas shrinkage in reservoirs that have been uplifted or otherwise cooled. Recharge of these low-pressure reservoirs by meteoric water does not occur rapidly enough to repressure the reservoirs to a normal, hydrostatic pressure. Underpressuring can occur regionally as a result of reservoir water drainage to a low-elevation discharge area. Examples of underpressuring can be found in Rocky Mountain oil- and gas-bearing sandstone and carbonate reservoirs that range in age from the Tertiary to early Paleozoic. Abnormally low reservoir pressure can cause exploration and completion problems. The most serious problem is that deep mud and mud filtrate invasion complicates well-log identification of hydrocarbon saturation. Also, underpressured gas-bearing reservoirs typically yield poor or no shows during drilling, even where mud-logging equipment is used. Drill-stem tests (DSTs) are frequently inconclusive because of deep fracture and/or matrix invasion by mud and mud filtrate. A better understanding of their unique characteristics is needed in order to increase discovery rates.

• Research Organization: Geological Survey, Denver, CO (USA)
• OSTI ID: 6371902
• Report Number(s): CONF-8808223-
• Conference Information: Journal Name: AAPG (Am. Assoc. Pet. Geol.) Bull.; (United States) Journal Volume: 72:7
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020300* -- Petroleum-- Drilling &amp; Production
EXPLORATION
GEOLOGIC DEPOSITS
MINERAL RESOURCES
PETROLEUM DEPOSITS
RESERVOIR PRESSURE
RESERVOIR ROCK
RESOURCES
ROCKS
SANDSTONES
SEDIMENTARY ROCKS
WELL COMPLETION