Since January 1978 Maraven is conducting the M-6 Steam Drive Project in Tia Juana, one of the Bolivar Coast Heavy Oil Reservoirs near Lake Maracaibo. The project is carried out on a semi-open seven- spot well configuration, using the existing 231-m grid and comprises at present 21 injectors and 130 producers. The project area is 7, 4 Km2, depth 1800 ft ss, and originally contained 525 million bbl of 13 degr. API Crude. The recovery by primary depletion, enhanced by steam soak, was 22 pct. STOIIP at the start of steam drive.

Steam is supplied by a plant with a nominal capacity of 10,000 t/d of saturated, dry steam at 1000 psig. Lake Maracaibo water softened by ion-exchange is used as feed water and natural gas as fuel.

Following a build-up period of 6 months the steam injection rate has ranged between 6000 and 8500 t/d, averaging 7400 t/d up to end 1981, at well head pressures of around 500 psig. The oil production increased from a pre—project level of 8000 b/d to 18,000-23,000 b/d since early 1980, accompanied by an increase in water production from 4000 up to 40,000 b/d. Cumulative performance data for the period Jan. 1978-Dec. 1981 are: steam injected 10.2 million tons, oil produced 23.7 million bbl, extra oil produced 15.9 million bbl and water produced 33.0 million bbl. Corresponding main project parameters are: cumulative oil production 4.5% STOIIP, of which 3% STOIIP is extra, oil/steam ratio 2.3 bbl/ton, extra-oil/steam ratio 1.6 bbl/ton.

Although these figures show that the overall performance has been very satisfactory so far, individual well performances indicate an irregular flow distribution, both areally and vertically, duo to the heterogeneous nature of the reservoir. Corrective measures taken so far are selective recompletion of producers where steam breaks through and adjustments to the well pattern. Results from this policy have been favorable during the second half of 1981, the oil production rate reaching a high of 23,000 b/d in December.

Selective recompletion of the injectors on the lower sands which do not take steam at present is under consideration.

It is expected that by continuous adjustment of the project policy to the performance as it develops under the given conditions, it will be possible to recovery 20% STOIIP of extra oil at an oil/steam ratio of 2 bbl/ton. In later stages when additional information has become available the merits of increasing the recovery by injecting more steam and/or interspacing will be investigated.

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