Slaughter Estate Unit Tertiary Pilot Performance
Authors: Rowe Hunter G. , York Derryl S. , Ader Joseph C. 
Published: December 2007

Amoco Production Co. began in the early 1970's to work toward a reservoir test of the CO2 miscible displacement process in the Slaughter Estate Unit (SEU). Because of difficulties in obtaining a reliable pure CO2 source, a feed gas stream to the Slaughter gasoline plant sulfur recovery unit was chosen as the solvent injection source. This solvent gas stream consisted of approximately 72% CO2 and 28% hydrogen sulfide. Laboratory tests demonstrated that the displacement process using this acid gas as a solvent was the same as when pure CO2 was used.

Six pilot injection wells and two pilot producers were drilled in 1972 in a portion of the SEU (Slaughter field) that had not been waterflooded. Waterflooding was begun in 1972 and a peak secondary oil rate of 407 BOPD (64.7 m/d oil) was observed in June 1973. By mid-1976 most of the secondary oil had been produced, a secondary decline rate was well established, and the WOR had increased significantly.

Alternate solvent Gas and water injection, for favorable areal sweep, was initiated in Aug. 1976, and the first tertiary oil production was observed in Oct. 1977 when oil production from the two pilot producers increased from 22 to 29 BOPD (3.5 to 4.6 m/d oil). Peak tertiary production was 152 BOPD (24.2 m/d oil) in Feb. 1979. Through July 1981 the pilot was still producing about 70 BOPD (11.1 m /d oil) and cumulative incremental tertiary oil production was 95,680 STB (15 212 stock-tank m ), which represents 14.9% original oil in place (OOIP).

A total of 26% hydrocarbon pore volume (HCPV) Solvent gas was injected into the pilot area through Oct. 1979. In Nov. 1979 nitrogen chase gas injection was initiated; an interruption in the pilot's nitrogen supply in April 1980 forced a temporary change to residue chase gas injection until Dec. 1980 when nitrogen injection was resumed. Current plans call for the injection of 29.6% HCPV chase gas into the pilot area.

The SEU tertiary pilot was conducted so that both secondary and tertiary recovery factors could be delineated clearly by actually measuring oil in the tank. Performance data from this pilot conclusively show that alternate CO2 -water will move tertiary oil in significant quantities in this and similar west Texas reservoirs.

Introduction

The SEU CO2 pilot is one of several miscible gas improved oil-recovery projects operated by Amoco Production Co. in the Permian basin of west Texas. It is located in Hockley County. approximately 30 miles (48 km) west of Lubbock, as shown in Fig. 1. The SEU boundary and relative location of the pilot are shown in Fig. 2.

In the late 1960's, waterflooding operations in the SEU had been under way for approximately 6 years and oil production in the unit was continuing to increase. However, because the SEU represented a significant resource base, planning for potential tertiary recovery operations was initiated at an early date. This planning resulted in the 1972 drilling of a 12-acre (48 600-m ) double five-spot pilot in a non water flooded area of the unit, designed to test the CO2 miscible displacement process by obtaining oil-in-the-tank performance data.

Because unit waterflooding operations were in their early stages, it was felt that secondary and tertiary operations for the pilot should be conducted in separate phases. Waterflood performance data would provide an indication of ultimate secondary recovery and also establish high water saturation conditions that would be a severe test of the recovery efficiency of CO2 flooding. Performance data under these conditions would indicate clearly the additional tertiary oil that could be recovered and also would provide data to determine the volume of CO2 required to recover this incremental oil.

JPT

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