An Engineering Study of the Hawkins (Woodbine) Field

Abstract

This engineering study describes the modeling techniques used to develop a 189 million bbl additional recovery program. One of the most significant results of the study is the indicated one-third higher recovery efficiency of gas-drivel/gravity-drainage as compared with water drive for this reservoir. Introduction The Hawkins (Woodbine) field was unitized Jan. 1, 1975, following a reservoir study that showed that a gas injection project would increase oil recovery by an estimated 189 million bbl. This additional oil recovery would result from preventing future gas-cap shrinkage and from replacing a moderately efficient water-displacement mechanism with highly efficient gas-drive/gravity-drainage.Field performance indicated that gas displacement accompanied by gravity drainage will recover about one-third more of the remaining oil column than possible using water displacement. This observed difference in recovery efficiency was verified by simple mathematical models, core data, and finite-difference reservoir simulators. Field Description The Hawkins (Woodbine) field produced more than 530 million bbl of oil from discovery in 1940 through 1974. The field, located in the Woodbine basin of Texas, shares a common aquifer with East Texas, Van, Neches, and other Woodbine fields. It is located about 100 miles east of Dallas, as Fig. 1 shows. The Hawkins field produces 112,000 BOPD, and had 510 active producers at the end of 1974. Production is from the Woodbine formation of Upper Cretaceous Production is from the Woodbine formation of Upper Cretaceous age. The Woodbine formation is divided into upper, Lewisville sands and lower, Dexter sands. The Dexter sands, thicker and more permeable than the Lewisville sands, contain about 80 percent of permeable than the Lewisville sands, contain about 80 percent of the field's oil reserve.The field is divided into two segments by a major north-south fault. The western segment contains about 80 percent of the field's oil reserve. A unique property of the Hawkins field is an asphalt zone that underlies the oil column in the western segment. Early reservoir studies indicated that the aquifer pressure near the Hawkins field had been drawn down at time of discovery by withdrawals from other fields in the Woodbine basin, particularly the East Texas field. Pressure-interference effects in the Woodbine basin have been studied extensively; this basin provides a classic example of pressure interference over a wide area. Reservoir Properties The first step in the engineering study was determination of reservoir properties.Fig. 2, a composite log showing the Lewisville and Dexter sand members, is fundamental to understanding reservoir rock properties. The Lewisville sands are lenticular, and the total properties. The Lewisville sands are lenticular, and the total Lewisville section averages 70-percent shale. The Dexter sands are massive and continuous, and the total section is about 70-percent sand. Table 1 shows the average sand properties obtained from analyzing 35,900 ft of conventional cores from 193 wells in the field. JPT P. 123