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Geology and Hydrocarbon Production, Sweetwater Field, Fisher and Nolan Counties, Texas

J. L. Mergele, J. A. Breyer

The Sweetwater "Canyon Sand" field lies along the boundary of Fisher and Nolan Counties, north of Sweetwater, Texas. The field was discovered in 1955 when oil was found in Pennsylvanian sandstone in a well testing a structural anomaly in the Lower Ordovician Ellenburger Group. More than 4 million bbl of crude oil and 750 mmcf of gas have been produced from the field. The oil is trapped by the updip pinch-out of Pennsylvanian sandstone. The field is still in production, and yielded 58,486 bbl/year of oil from 1972 to 1981.

The field occurs in a sandstone complex at the base of the slope separating the Eastern shelf from the deeper parts of the Midland basin. The complex consists of four sandstone units. The lowest unit, unit D, covers 4 mi2 (10 km2) and averages 8 ft (2.4 m) in thickness. There is no production from this unit. Unit C occurs above and locally in contact with unit D. It covers 9 mi2(23 km2) and averages 37 ft (11 m) in thickness. A downslope extension of this sandstone connects unit C with Hollins field to the southwest. Most production in Sweetwater field is from this unit. Units A and B occur at the same stratigraphic level, above and in contact with unit C, but separate from each other. Together units A and B cover 8.5 mi2 (22 km2). Both units have been productive. Lobe complexes similar to the Sweetwater field complex occur above and below the producing interval.

AAPG Search and Discovery Article #91037©1987 AAPG Southwest Section, Dallas, Texas, March 22-24, 1987.