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ZAMORA, LUCAS G., and OSWALDO E. GALLANGO, Intevep, Caracas, Venezuela

ABSTRACT: Heavy and Extra Heavy Hydrocarbons in Venezuela

Most of Venezuela's giant accumulations of heavier than 22 degrees API hydrocarbons, are located in the more stable flanks of the Maracaibo and Eastern Venezuela basins, at depths shallower than 2400 meters. The reservoir rocks are unconsolidated fluviodeltaic Neogene sands, transgressive over large regional pre-Oligocene unconformities. There are also large volumes accumulated along the mountainous and more active flanks, either in Neogene alluvial sediments or in Cretaceous and older fractured rocks. These accumulations, located near present day erosion surfaces, are subjected to meteoric water influx.

Extensive research carried out by the affiliates of Petroleos de Venezuela, S.A., and other institutions during the past ten years, has shown that the main cause of degradation is the action of microorganisms brought in by meteoric water influx and, to less extent, the washing of lighter hydrocarbon fractions by either connate or meteoric water. These studies have also shown that most of the heavy and extra-heavy hydrocarbons are the result of biodegradation of low maturity crudes generated from Cretaceous rocks, rich in marine organic matter, which started its generation during the Paleogene.

The heavy and extra-heavy hydrocarbons, bitumen included, so far discovered in Venezuela, add up to 1.5 x 1012 bbl in place. This figure includes proved, probable and possible volumes, and the expectancy of additional hydrocarbons of this kind to be discovered yet is of 0.1 x 1012 bbl in place.

AAPG Search and Discovery Article #90988©1993 AAPG/SVG International Congress and Exhibition, Caracas, Venezuela, March 14-17, 1993.