Introduction

Fullerton Field is located in northwestern Andrews County, Tex., and produces primarily from the lower Clearfork zone, an early Permian dolomite formation. The anticlinal structure has closure on two domes with the major axis of the structure extending in a general north-south direction. The commercial extent of the reservoir is determined by porosity pinch outs which do not follow the structural contours. The developed area of the North Dome covers 21,400 acres and is drilled on 40-acre spacing. The South Dome has a developed area of 3,700 acres and is also drilled on 40-acre spacing.

The field had an original static BHP of 2,980 psi, and the crude oil bubble point was 2,370 psi with 1,160 cu ft of gas per bbl being in solution. Early in the producing life of the field it was obvious that the solution gas drive mechanism would be relatively inefficient and the operators began to study the various means of unitizing and entering into a secondary recovery program.

Gas Injection Operations

In February. 1954, 24,040 surface acres of the field were unitized in order to instigate secondary recovery operations. Four months after unitization 16wells were converted to gas injection[See Fig. 1], and gas injection operations were initiated with a volume of approximately 21 MMcf/day or 30 per cent of the total gas production being returned to the reservoir. In September, 1956, four additional wells were converted to gas injection, and the injection volume was increased to 25 MMcf/day.

Fullerton Field operates under a limiting 2,000 cu ft/bbl gas-oil ratio. Gas which is returned to the reservoir is utilized in removing production penalties to the maximum of 66 bbl of oil per producing day per well. One of the immediate benefits of gas injection is to increase current allowable by production penalty removals.

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