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Reservoir Geology of the Giant Heavy Oil Boscan Field, Maracaibo Basin, Venezuela


Vela, Mariano L.1, Eduardo A. Naranjo2 (1) ChevronTexaco, Maracaibo, Venezuela (2) PDVSA, Maracaibo, Venezuela


The Boscán Field is a giant heavy oil field located on land 45 km SW of Maracaibo, Venezuela. It was discovered by Richmond Exploration Co. in 1947. Over the 58-year-life of the field, 797 wells have been drilled with 522 of them currently active. Field dimensions are 20 km by 35 km and depth to top of the reservoir ranges from 4500 to 9200 feet subsea. The reservoir is predominantly the Eocene Misoa Formation consisting primarily of channels and bars in a tidal-dominated depositional environment. Reservoir net sand to gross thick­ness ratio is 70-80%, sand porosity is 10-26% and sand permeability 100-5000 md. Oil gravity is 9.5-12oAPI and viscosity 130 cp to 500 cp depending on temperature related to reservoir depth. The field is a combination of stratigraphic-structural trap -monoclinal with southern dip and a strike-slip “Boscan” fault to the east-. OOIP is estimated to be between 25 and 35 billion bbl of oil, current production is 113,000 BOPD, and a cumulative produc­tion 1.2 billion bbl of oil.

The field is dominantly on primary depletion, but there have been several IOR field tri­als, and produced water has been re-injected into different parts of the reservoir since 1963. Recently, ChevronTexaco and PDVSA began a managed water injection pilot project testing for enhanced oil recovery with pressure maintenance. Production data suggests that the oil decline rate is arrested as a result of water injection.

A 440 square kilometer 3D seismic survey completed over the northern half of the field in 2000 has greatly assisted the understanding of the structure, stratigraphy, reservoir con­nectivity and drilling potential in the field. The interpretation of the seismic data has permit­ted to successfully predict and drill vertical and highly deviated wells with high productivity in difficult areas of the field.