Geochemical Characterization of Neoproterozoic Heavy Oil from Rajasthan, India: Implications for Future Exploration of Hydrocarbons

The discovery of heavy oil in the Bikaner-Nagaur basin of Rajasthan in western India in reservoirs of Neoproterozoic age during the early nineties was one of the most significant events in the history of oil and gas exploration in India. Recently, discovery of heavy oil in the Punam Structure in the same basin has reconfirmed the hydrocarbon potential of the basin and has regenerated tremendous interest in exploration activities. Another significant factor that enhances exploration interest and hydrocarbon prospectivity of this basin relates to the fact that the Indian Mesoproterozoic and Neoproterozoic sedimentary basins share similar tectonic settings and depositional environments as their producing counterparts elsewhere (Oman, China, Siberian Platform, North Africa, Australia and so on). In this study, geochemical characterization of the heavy oil from Punam-X has been carried out for determining the source, maturity and extent of biodegradation using established biomarker ratios. Organic geochemical studies on the heavy oil from Punam-X indicate that the oil was generated in an anoxic hypersaline environment from marine clastic source rock. The oil is found to be generated from early mature source rock. Gas chromatograph analysis of the oil shows that it has also undergone some degree of biodegradation. Various similarities have been found between the Punam-X oil and other heavy oils of similar age found in Oman, Pakistan and in the adjoining areas in the Bikaner-Nagaur basin.