Characteristics and Genesis of Heavy Oil in Orinoco Heavy Oil Belt in East Venezuela Basin

Abstract

This paper focuses on the features and genesis of Orinoco heavy oil in the East Venezuela Basin based on geochemical data and geologic evolution of this heavy oil belt. In accordance with crude oil composition and properties, heavy oil in the north gradually changes into extra-heavy oil in the south. Orinoco heavy oil is the product of secondary hydrocarbon generation, especially bacteria degradation, which was active in the proper temperature conditions caused by sustained, slow, small subsidence since the Cenozoic Era at this slope zone. As a result, crude oil experienced sustained biodegradation in the process of southward long-distance migration and accumulation along the slope. The flushed zones with meteoric water in the northern belt provided abundant inorganic nutrients for microorganisms, which accelerated bacteria metabolism and crude degradation. Thus, low API occurs locally against a background of high API in the north of the heavy oil belt. In addition to microbial degradation, the increase in viscosity was also related to water washing. Multi-phase crude accumulation gave rise to complicated, nonhomogeneous crude oil properties. Our study may provide useful information for heavy oil exploration and development in relevant prospects.