Gas Injection Performance Review of the LL-370 Reservoir in the Bolivar Coastal Field, Venezuela

The Conservation Plant Tia Juana No.1 began pressure maintenance operations of the LL–370 area of the Bolivar Coastal field in Oct., 1954. Gas is being returned to the B–6 Eocene sandstone via seven injection wells. During the first two years of operations, the average injection rate has been 133.9 MMcf/D. This represents a small excess of gas injected over hydrocarbon volume withdrawals. In the third quarter of 1956, average production was 77,583 BOPD, with a producing gas-oil ratio of 876 cu ft/bbl. Fifty-nine wells were classified as producers. Production characteristics of the LL–370 area under pressure maintenance have been very satisfactory and superior to predicted behavior. There has been no evidence of excessive gas channelling. The vertical segregation of oil and gas in the reservoir continues to play an important part in the production mechanism. As a result, required high-gas shutoffs in up dip areas continue to be successful with the isolation of upper high-gas saturated zones by squeeze cementing and the return of the lower portion of the sandstone to low gas-oil ratio production. The average reservoir production decline is nil, with the production decline of individual wells balanced by production increases in others. Not only will this project result in a much greater recovery of oil from the reservoir, but also a huge quantity of gas is being conserved for the future. Geology and General Reservoir Characteristics The LL–370 area is located in Lake Maracaibo 7 miles from the community of Tia Juana which is on the northeast shoreline of the lake. The oil-bearing formation consists of a truncated monocline of Eocene sandstone called the B–6. The total surface area covers 11,048 acres and is subdivided into four reservoirs by faults, which are only partial pressure barriers. The area is bounded by major faulting to the northeast and southwest, the Miocene-Eocene unconformity to the west at the top of the formation, and a water leg to the southeast. Additional Eocene productive units overlie and underlie the B–6, but these are isolated by extensive shale barriers and only local communication probably exists.