DeMoss Flood Handles Early Water-Breakthrough Problem

The DeMoss field located in Archer County, Tex., 7 miles southeast of Archer City, is being water flooded under a unitized program (Fig. 1). The correct name for the unit is "Strawn (Basal) Sand Reservoir Unit"; however, for brevity and convenience it will be called the DeMoss flood in this paper. The purpose of this report is twofoldit is a case history of waterflood operation, andit shows how the profit and ultimate oil recovery were increased by the use of equipment designed to handle large volumes of fluid. Two features,very high vertical permeability andhigh horizontal-permeability variation in portions of the pay zone, are believed largely responsible for early and excessive water breakthrough during waterflood operations. The possibility that this solution to the problem of excessive water production in water floods could be instrumental in the development and production of waterflood reserves, which otherwise may be uneconomical, has been an added stimulus in the preparation of the paper. Primary Development and Production History The discovery well, A.J. DeMoss No. 1 (Unit Well No. 3–1) was completed in Nov., 1949, in open hole from 3,598 to 3,608 ft, flowing 302 BOPD and no water. Rapid development on 10-acre spacing followed, resulting in 27 producers by June, 1950 (Fig 2). General completion practice was to drill a few feet into the pay section with rotary tools, run electric logs, set and cement either 5 - or 7 in. production casing in a lime cap over-laying the pay zone. The wells were then swabbed-in on a flowing status. Very few of the wells had the entire pay zone penetrated by the wellbore. Production by solution-gas drive first began to decline in Nov., 1950; consequently, small hydraulic-fracture treatments were applied to a majority of the wells during Jan., 1951. Primary production peaked at 35,674 bbl of oil in April, 1951, as a result of the frac jobs; then, it declined to a low of 3,150 bbl of oil by Jan., 1957 (Fig. 3). Primary recovery to Jan. 1957, was 1,101,039 STB. An investigation of records revealed that the A.J. DeMoss No. 14 (Unit Well No. 3–14) probably produced 35 per cent of the accumulated, total primary recovery. This high one-well recovery figure is a result of a mildly active water-intrusion in this area acting on this well only. During the primary life of the field, the water encroached updip toward this well, thus sweeping a reservoir area greater than the normal well location. This will logically explain the very high recovery figure for the well.