Boscán Field
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The Boscán Oil Field is located 40 km southwest of Maracaibo, Venezuela and covers an area of about 660 square kilometers. The field produces a 10.5 degree API gravity crude oil from the Eocene Misoa Formation locally called the Boscán Formation. The field was discovered in 1946 with drilling of the Zulia 7F-1 well (renamed BN-257) which tested 730 barrels of oil per day (BOPD). This well encountered reservoir section very close to the Boscán bounding fault at about 5900 feet (1777 m) measured depth (MD). Production began in 1947.
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[edit] Stratigraphy
The stratigraphic section at Boscán Field consists of sands and shales of Oligocene and Eocene ages deposited in a fluvial-deltaic depositional setting. The Oligocene sediments are commonly non-oil bearing and are dominantly shaley. The Eocene sands are part of the Misoa Formation and form the producing reservoir section locally known as the Boscán Formation.
[edit] Structure
The Boscán structure is a southwest-dipping monocline (flat, tilting surface) which contains oil over a very large depth range from 4500 feet (1355 m) to 9500 feet (2861 m) below sea level. The reservoir is broken by a series of minor normal faults which do not apparently compartmentalize the oil in the reservoir.
[edit] Trapping Mechanism
The productive section in the field is associated with a regional unconformity between the Oligocene Icotea Formation and the older Eocene sandstones. Shales and other tight formations in the Icotea Formation provide the trap preventing vertical migration. On the east side of the field a large strike-slip fault provides additional trapping of oil, preventing it from moving laterally to the east.
[edit] Production
Boscán Field has produced over 1 billion barrels of oil. There have been a total of 680 oil wells drilled in the field with 525 active wells as of December, 2004. The reservoir drive is a combination of weak aquifer drive on the south flank, solution gas expansion, and gravity drainage. As a result of the weak aquifer support, the field is pressure-depleted over large areas where there has been considerable fluid volume extracted.
