A Tailor-Made Water-Injection System Saves Money in the LL-5 Flank Water Flood at Lake Maracaibo
Authors: Moore Harry J. 
Published: December 2007

One of the world's largest flank water floods will begin operation at the end of 1961. A specially designed system will inject 320,000 BWPD into the aquifer of the large LL–5 reservoir underlying Lake Maracaibo in Venezuela. The design of the injection system was significantly influenced by results of an injectivity test conducted in 1960. The number of injection wells of the original 1959 flood proposal was reduced from 12 to 8, and the central plant with its costly submarine distribution lines was eliminated. Approximately $4 million in capital investment and over $1 million/year in operating costs were saved.

Introduction

Creole Petroleum Corp. has directed a great amount of engineering and capital investment toward supplementing recovery from its major reservoirs underlying Lake Maracaibo in Venezuela. Because of conservation considerations, until recent years emphasis had been placed almost entirely on pressure maintenance by injection of gas that otherwise would have been flared. Compressor plants and systems capable of injecting over 750 MMcf of gas/D have been installed in the lake, and nine major reservoirs capable of efficiently producing 400,000 BOPD are receiving pressure maintenance from them. Although all the gas that can be economically gathered is now being compressed and injected, there still remain many additional reservoirs for which supplemental recovery would be attractive. By 1959, laboratory investigation and reservoir study had concluded that flank water injection also could serve as an effective means of supplemental recovery for at least one of these the LL–5 reservoir. Until that time, however, no water-injection system had been developed which could be adapted to the unique circumstance of a large flank flood on Lake Maracaibo. The degree of treating that the lake water would require was an unknown, as were the injection-well rates and pressures that might be possible. In 1959, Creole set out to determine exactly what would be required for a large flank water flood for the LL–5 reservoir. Extensive injectivity and equipment testing were carried out, and in 1960 the design of a special system was completed for full-scale injection of water into the LL–5 aquifer.

The LL–5 Reservoir

Fig. 1 is a location map showing the position of the LL–5 reservoir in the Bolivar Coastal fields that lie along the eastern shore of Lake Maracaibo. The LL–5 was discovered in 1938. It is a large, monoclinal, stratigraphic trap which forms part of a Miocene fault block. The surface area covers approximately 25,000 acres, and the average section and net- sand thicknesses are 255 and 95 ft, respectively. The areal boundaries, illustrated by Fig. 2, consist of a major fault on the east, a shale-out of the sands to the northwest and a mobile oil-water contact on the southwest. The reservoir dips 2.7 to the southwest from a subsea sand top depth of 2,700 ft in the updip portion to 4,350 ft at the oil-water contact. During 1961, the LL–5 reservoir has been capable of an efficient producing rate of 180,000 BOPD, or about 20 per cent of Creole's total Western Div. potential for medium and light crudes of API gravity above 220. It is a significant factor in production planning, therefore, and has been the subject of several reservoir studies. These have concluded that the optimum operating program for the LL–5 would be to inject a minimum of 300,000 BWPD along the flank of the reservoir, while injecting gas at the crest at a rate of 100 MMcf/D.

JPT

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