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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 64 (1980)

Issue: 5. (May)

First Page: 714

Last Page: 714

Title: Oil and Gas Potential of San Luis Basin, South-Central Colorado: ABSTRACT

Author(s): R. R. Gries

Article Type: Meeting abstract

Abstract:

Are there major oil and gas traps in the San Luis basin? Gas and oil seeps have been reported and used at ranches in this basin since the late 1800s. Despite the presence of porous and permeable sandstones, thick widespread clays for seals, and hydrocarbons, only 15 oil and gas tests have been drilled in 2,500 sq mi (4,023 sq km), most before 1955.

Recent seismic work has helped delineate the structure and stratigraphy of the eastern half of the basin where gas occurs in all water wells. A high on the Precambrian basement surface dominates the center of the basin with sediments faulted and dipping down to the east to a depth of about 20,000 ft (6,096 m) adjacent to the Sangre de Cristo Mountains. The basin fill is Tertiary clastic and volcanic rocks that can be divided into four units using seismic work, well samples, and palynology. The uppermost unit, the Alamosa Formation (Pliocene-Pleistocene), is green lacustrine clay and sandstone. The underlying Santa Fe Formation (Miocene-Pliocene) is red fluvial-lacustrine clay and sandstone with a few thin volcanic flows. An unnamed unit (middle Paleocene to Eocene) is angularly unconf rmable with the overlying Santa Fe and similar in lithology. The oldest unnamed unit consists of thick volcanic flows interbedded with volcaniclastics and claystones and is also unconformable with the overlying unit.

Potential trapping mechanisms are major sedimentary-rock pinch-outs and truncations in the unnamed unconformable units as well as in channels in the overlying fluvial sandstones. Porous volcanic rocks and sandstones on the fault blocks, fault traps, and structural closures are also possible traps in the oldest unit. The paucity of drilling and the presence of traps and hydrocarbons make the outlook optimistic for this basin.

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Copyright 1997 American Association of Petroleum Geologists