A unique Austin Chalk reservoir, Van field, Van Zandt County, Texas

Conference · Sat Sep 01 00:00:00 EDT 1990 · AAPG Bulletin (American Association of Petroleum Geologists); (USA)

OSTI ID:6130015

Lowe, J T ^[1]

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1. Unocal Corp., Houston, TX (USA)

Significant shallow oil production from the Austin Chalk was established in the Van field, Van Zandt County, in East Texas in the late 1980s. The Van field structure is a complexly faulted domal anticline created by salt intrusion. The Woodbine sands, which underlie the Austin Chalk, have been and continue to be the predominant reservoir rocks in the field. Evidence indicates that faults provided vertical conduits for migration of Woodbine oil into the Austin Chalk where it was trapped along the structural crest. The most prolific Austin Chalk production is on the upthrown side of the main field fault, as is the Woodbine. The Austin Chalk is a soft, white to light gray limestone composed mostly of coccoliths with some pelecypods. Unlike the Austin Chalk in the Giddings and Pearsall fields, the chalk at Van was not as deeply buried and therefore did not become brittle and susceptible to tensional or cryptic fracturing. The shallow burial in the Van field was also important in that it allowed the chalk to retain primary microporosity. The production comes entirely from this primary porosity. In addition to the structural position and underlying oil source from the Woodbine, the depositional environment and associated lithofacies are also keys to the reservoir quality in the Van field as demonstrated by cores from the upthrown and downthrown (less productive) sides of the main field fault. It appears that at the time of Austin Chalk deposition, the main field fault was active and caused the upthrown side to be a structural high and a more agreeable environment for benthonic organisms such as pelecypods and worms. The resulting bioturbation enhanced the reservoir's permeability enough to allow migration and entrapment of the oil. Future success in exploration for analogous Austin Chalk reservoirs will require the combination of a favorable environment of deposition, a nearby Woodbine oil source, and a faulted trap that will provide the conduit for migration.

• OSTI ID: 6130015
• Report Number(s): CONF-9010204-; CODEN: AABUD
• Journal Information: AAPG Bulletin (American Association of Petroleum Geologists); (USA), Vol. 74:9; Conference: Gulf Coast Association of Geological Societies and Gulf Coast Section of SEPM (Society of Economics, Paleontologists, and Mineralogist) meeting, Lafayette, LA (USA), 17-19 Oct 1990; ISSN 0149-1423
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
58 GEOSCIENCES
OIL FIELDS
ORIGIN
RESERVOIR ROCK
TEXAS
ANTICLINES
CLAYS
DEPOSITION
DRILL CORES
EXPLORATION
GEOLOGIC FAULTS
GEOLOGIC FORMATIONS
LIMESTONE
MIGRATION
PERMEABILITY
POROSITY
PRODUCTION
CARBONATE ROCKS
FEDERAL REGION VI
GEOLOGIC DEPOSITS
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
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PETROLEUM DEPOSITS
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020200* - Petroleum- Reserves
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& Exploration
580000 - Geosciences