Geological characteristics and distribution of global primary hydrocarbon accumulations of Precambrian-Lower Cambrian

Abstract

In recent years, primary hydrocarbon accumulations of Precambrian-Lower Cambrian have caused an increasing attention in the oil and gas explorations worldwide. The Eastern Siberian Basin in Russia, the Oman Basin in the Middle East, and the Sichuan Basin in China are endowed with the richest oil and gas reserves in the Precambrian-Lower Cambrian primary hydrocarbon accumulations. This study takes these three basins as examples to systematical and comprehensively document the geological characteristics and distribution of the global Precambrian-Lower Cambrian primary hydrocarbon accumulations through a large amount of data analysis and statistics, to provide insights for further breakthroughs of oil and gas explorations in ancient stratigraphic successions of sedimentary basins. The global proven and controlled reserves of Precambrian-Lower Cambrian primary hydrocarbon accumulations have reached 30.09×109 boe (4.12×108 t), of which 84.2% are distributed in the Eastern Siberian Basin, while the Oman Basin and the Sichuan Basin account for 8.9% and 6.5%, respectively. The source rocks are dominated by marine mudstones, shales and carbonate rocks, which are generally immature to over-mature and mostly distribute in low structural parts. Carbonate rocks and clastic rocks are important types of reservoir rocks. Early dolomitization, superficial leaching and hydrocarbons injection are important mechanisms for the development of ancient carbonate reservoirs. Most of the hydrocarbons in deep and ultra-deep ancient strata are stored in carbonate rocks. At the same time, the extensively developed high-quality regional caprocks are the key to preserving abundant hydrocarbons. Three types of accumulation models, self-generating and self-preserving, reservoirs adjacent to source rocks, and reservoirs isolated to source rocks, constitute the main models of Precambrian-Lower Cambrian primary hydrocarbon accumulations.

Keywords

• hydrocarbon accumulation model
• precambrian-lower cambrian
• eastern siberian basin
• oman basin
• sichuan basin