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AAPG Bulletin

Abstract


Volume: 39 (1955)

Issue: 2. (February)

First Page: 155

Last Page: 188

Title: Little Beaver Field, Colorado, a Stratigraphic, Structural, and Sedimentation Problem

Author(s): George H. Fentress (2)

Abstract:

The Little Beaver field of the Denver-Julesberg basin is in Washington and Adams counties of northeastern Colorado. It was discovered by promotional means without the aid of the seismograph or surface work. Subsurface control was too sparse to be an aid. Snowden and Tucker drilled the discovery well in September, 1950, and development followed around this well. Minor quantities of oil were tested in the "D" sand although the well was a gas completion in the "J" sand. Slow and discouraging exploitation followed until late spring of 1952. By August 1, 1954, eighty-five oil wells and nine gas wells had been completed in the two sand members. From 87 of these wells, 4,314,153 barrels of oil had been produced by August 1, 1954. On January 1, 1954, this became the largest field in the basin and the second largest in Colorado. The Adena field has since become the second largest in the state.

The "D" and "J" sands are members within the Dakota group of Cretaceous age and are alphabetically designated in order to avoid controversy over names. The "D" is the first Dakota sand unit and is productive on the east side of the field. The "J" is the second Dakota sand unit, generally thought to be the Muddy sand, and is productive on the west.

Oil, gas, and permeable sands are found in a sand-bar type of stratigraphic trap on a prominent nose or terrace-type feature where little or no reversal has been noted. The saturated "D" sand ranges from 6 to 46 feet within the maximum "D" thickness of 71 feet. The saturated "J" sand ranges from 2 to 24 feet in what is called a first member development. There are minor quantities of gas in a second member.

The "D" sand productive area covers about 1,850 acres and the "J" oil and gas productive area about 1,300 acres, some of which is yet untested. A moderate recovery figure is 300 barrels of oil per acre-foot and 700 MCF of gas per acre-foot. These figures are close to 30 per cent of total oil in place. Water is at this time a negligible item but apparently constitutes a minor drive. The "J" sand has a gas-cap drive but the major driving mechanism is gas in solution in both sand reservoirs.

The intense activity which this field instigated has netted several very important discoveries in the area.

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