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Abstract: Oil Geochemistry Study; Blocks III and IV Bachaquero Field, Lake Maracaibo, Venezuela

Brooks A. Patterson, Helena Gamero De Villarroel, Luis Rondon

Blocks III and IV Bachaquero Field, located on the east side of Lake Maracaibo, comprise an area of 40 square kilometers. In 1956 the discovery well penetrated oil saturated sands in a south dipping homoclinal structure. In 1958 production reached a maximum of 245,000 barrels per day of moderate gravity oil from three Miocene age Lagunillas Formation sands, designated as L, M, and N.

The Bachaquero Field has experienced production problems including high gas-oil ratios from M and N sands to the north, high water cuts in all three sands to the south, and low production rates in the southeast. In addition, the vertical and lateral continuity of the oil pools are unknown. High resolution gas chromatography and analysis of biological markers was employed in order to resolve the continuity of the oil pools, determine genetic origin of the oils, and shed light on erratic production.

Oil in the L sands are vertically discontinuous from oil in the M+N sands. The two oil pools appear laterally continuous within the study area, indicating absence of fault barriers. Well VLD 311, open to both L and M sands, produces a mix of oils, but with a strong contribution from the M sand.

Bachaquero Field reservoirs were charged with oil from two different facies of the Upper Cretaceous La Luna or perhaps from La Luna and Colon source rocks as the stratigraphically younger L sands contain less mature oil with a stronger terrigenous imprint than oil the M and N sands.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela