PETROLEUM SYSTEMS IN SUPERIMPOSED CONTINENTAL BASINS: A CASE FROM THE JUNGGAR BASIN, NW CHINA

The Junggar Basin in the Northwest China is a typical petroliferous superimposed continental basin, filled with 15 km sedimentary strata from the Carboniferous to Quaternary. To date, more than 30 oilfields and over 400 oil and gas pools have been discovered in the basin. It contains six sets of source rocks and is characterized by very complex processes of petroleum migration and accumulation. How to determine the petroleum system in a petroliferous superimposed basin? Taking the Junggar Basin as an example, we firstly documented the oil source of various types of crude oils discovered in the basin, and then classified the petroleum within the entire basin based on the tectonic-structural configurations, and the distribution area of the multiple sets of overlapping hydrocarbon kitchens and their corresponding oil and gas accumulations in the basin. The Carboniferous is a set of marine-continental transitional facies source rocks, and is mainly distributed in the eastern region of the basin. The Permian, Triassic lacustrine source rocks and the Jurassic coal-bearing source rocks are widely distributed in the basin. The Cretaceous and Paleogene lacustrine source rocks are mainly distributed in the southern region. Six groups of crude oils have been discovered in the Junggar Basin, corresponding to the source rocks developed at the Carboniferous, Permian, Triassic, Jurassic, Cretaceous and Paleogene. The oil and gas derived from the Carboniferous source kitchen are mainly distributed in the Dinan uplift to the Wucaiwan sag; the oil and gas derived from the Permian source kitchen are widely distributed, mainly in the northwestern, central and eastern areas; the oils derived from the Triassic source kitchen are limited to the eastern area; the oil and gas derived from the Jurassic source kitchen are mainly distributed in the eastern and the southern regions; the oils derived from the Cretaceous source kitchen are mainly distributed in the middle of the southern Junggar Basin; the oils derived from the Paleogene source kitchen are confined to the western part of the Southern Junggar. The Junggar Basin comprises five petroleum systems, i.e. the Western, Central, Eastern, Southern and Ulungu petroleum systems, and 15 sub-petroleum systems based on the structural configuration of the basin and the relationships between source kitchens of different geological ages and their corresponding oil and gas pools.