Depositional environment of downdip Yegua (Eocene) sandstones, Jackson County, Texas
Yegua sandstones at a depth of 8300-8580 ft (2530-2615 m) were partly cored in the Arco Jansky 1 dry hole. Total thickness of the sandstone section is approximately 240 ft (73 m). The sandstones are enclosed in thick marine shales and are about 20 mi (32 km) downdip from thicker and more abundant sandstones in the Yegua Formation. The section is similar to reservoirs recently discovered in the area at the Toro Grande (1984), Lost Bridge (1984), and El Torito (1985) fields. The sandstones are fine to very fine grained and occur in thin beds that are 0.5-9 ft (0.15-2.7 m) thick. Sedimentary structures within the beds range from a lower massive division to a laminated or rippled upper division. Grain size within beds fines upward from 0.18 mm at the base to 0.05 mm at the top. The sandstones are interpreted to be turbidites of the AB type that were deposited within channels. The sandstones contain an average of 50% quartz and are classified as volcanic-arenites to feldspathic litharenites. Carbonate cement ranges from 0 to 27%. Average porosity is 29% and permeabilities are in the range of 60-1600 md in the clean sandstones. Much of the porosity is secondary and is the result of the dissolution of cements, volcanic rock fragments, and feldspar grains. Yegua sandstones produce gas and condensate at nearby Toro Grande field on a gentle, faulted anticline. The local trend of reservoir sandstones may be controlled in part by faulting that was contemporaneous with deposition.
- Research Organization:
- Texas A and M Univ., College Station
- OSTI ID:
- 5907482
- Report Number(s):
- CONF-8710198-
- Journal Information:
- AAPG (Am. Assoc. Pet. Geol.) Bull.; (United States), Journal Name: AAPG (Am. Assoc. Pet. Geol.) Bull.; (United States) Vol. 71:9; ISSN AABUD
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
020200* -- Petroleum-- Reserves
Geology
& Exploration
ALLUVIAL DEPOSITS
ANTICLINES
CENOZOIC ERA
DEPOSITION
FEDERAL REGION VI
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC FORMATIONS
GEOLOGIC STRUCTURES
GEOLOGIC TRAPS
MINERAL RESOURCES
NATURAL GAS DEPOSITS
NORTH AMERICA
PETROLEUM DEPOSITS
POROSITY
RESERVOIR ROCK
RESOURCES
ROCKS
SANDSTONES
SEDIMENTARY ROCKS
TERTIARY PERIOD
TEXAS
USA