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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 55 (1971)

Issue: 2. (February)

First Page: 352

Last Page: 352

Title: Reservoir Analysis, Pennsylvanian Tensleep Formation, Little Buffalo Basin, Wyoming: ABSTRACT

Author(s): J. A. McCaleb, W. R. Emmett, K. W. Beaver

Article Type: Meeting abstract

Abstract:

The Little Buffalo Basin field, in northwestern Wyoming on the southwest side of the Big Horn basin, is a north-south asymmetric anticline 3½ mi long, 1½ mi wide, with about 1,000 ft of structural closure. Oil was discovered in 1943 in the Pennsylvanian Tensleep. Cumulative production has been over 30 million bbl of oil from the 1,500 acres. Reservoir energy is from an active water drive from the north-northwest. A core study of the Tensleep revealed that extensive crossbedding, permeability variation, and fracture orientation influence oil recovery from this reservoir.

The Tensleep sandstone and dolomite gradationally overlie the Amsden Formation carbonates and shales, and average 275 ft in thickness. There is a general increase in average grain size of the Tensleep sandstone progressing upward in the section and also an increasing amount of crossbedding and poor sorting. Deposition occurred in relatively high-energy transporting currents in a shallow water, nearshore, and/or deltaic marine environment. Nonmarine channeling and sanddunes also occur in the upper part of the section. Pore-filling cements of carbonate, silica, anhydrite, and clay particles are generally due to 2 factors: (1) primary deposition of carbonate and clay with dissolution of these and other minerals during fluvial channeling and erosion in Late Pennsylvanian-Early Permian, an (2) redeposition of these minerals in open pore spaces and fractures by downward-percolating groundwater.

As a direct result of this reservoir study, well spacing has been reduced from 40 to 20 acres by drilling 30 new wells in certain areas of the field that would not otherwise have been efficiently depleted. These additional wells have accelerated production from 3,000 b/d to a new peak rate of 9,400 b/d and have increased ultimate oil recovery.

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Copyright 1997 American Association of Petroleum Geologists