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Reservoir Geology
of the Giant Heavy Oil Boscan Field,
Vela, Mariano L.1, Eduardo A. Naranjo2 (1)
ChevronTexaco, Maracaibo, Venezuela
(2) PDVSA,
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.