Reservoir Barrier and Polymer Waterflood, Northeast Hallsville Crane Unit

As a result of field-wide polymer injection, recovery in this unit exceeded by 40 percent the estimated recovery for an ordinary waterflood, and at an average cost of just 33 cents per barrel.

Introduction

The Northeast Hallsville Crane unit operated by Hunt Oil Co. was one of the first field-wide applications of a polymer flood. Since this field is well along in the final stages of be flood project, it has been possible to look at the effects of polymer injection and draw some conclusions about the use of these chemicals. The original purpose of polymer use in this project was to create a viscous barrier between the oil zone and a large associated gas cap. However, flood response from nearby producers as a result of the barrier placement was encouraging enough to extend the use of polymers to the central area of the oil zone, where early water breakthrough had been experienced. Early results from these attempts at using polymers to improve waterflood recovery were favorable. Ultimately a total of 313,000 lb of polymer was injected into 10 of the 15 unit injectors. Polymer injection into the Northeast Hallsville Crane unit generally has been both technically and economically successful. Certainly, the effectiveness of the reservoir barrier has been well established. As for improvement of oil recoveries by mobility control, it was found that higher polymer amounts resulted in higher oil recoveries over the range of polymer treatments used. Substantially better results were achieved in areas where there was no water injection prior to the polymer slug injection. prior to the polymer slug injection. Development History

The Northeast Hallsville Crane unit is about 3 miles northwest of the town of Marshall in Harrison County, Tex. Unit production is from the Crane zone of the middle Pettit formation, a thin oolitic limestone pay at a depth of about 6,900 ft. The map in Fig. 1 pay at a depth of about 6,900 ft. The map in Fig. 1 shows the location and areal extent of the Crane porosity development and its relation to the large porosity development and its relation to the large associated Woodlawn gas field. The Crane pay in this area was first discovered in 1950 as a gas producing reservoir in the Woodlawn portion of the field. Oil production was established portion of the field. Oil production was established in the Northeast Hallsville field in 1956 as the reservoir was developed to the west. Reservoir lists had been essentially defined by early 1960 after 42 wells had been drilled. Primary oil production peaked in March, 1959, at 42,500 bbl/month. Early withdrawals from the gas zone had caused migration of oil into the gas cap by the time of the oil zone development. As a result, the gas-oil contact was not found as a clearly defined structural level but was established as a broad transition zone between approximately 6,300 and 6,400 ft subsea. The extreme volatility of the crude oil also contributed to the lack of a clearly defined gas-oil contact.

JPT

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