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Petroleum Systems in the Junggar Basin, a Complex Multicycle Basin in Northwest China

Tianguang Xu1, Dengfa He2, and Yun Huang3
1 IHS Energy, Houston, TX
2 Research Institute of Petroleum Explorarion and Development, Beijing, China
3 PetroChina - Xinjiang, Urumqi, China

The Junggar basin, a complex multicycle basin, is located at the junction of the Kazakstan, Siberia, and Tarim blocks. The basin originated as a foreland unit during the Late Carboniferous-Permian, followed by an intercontinental subsidence stage from the Triassic to Cretaceous under the control of the Indosinian and Yanshanian orogenies. Since the Early Tertiary, the basin has entered into another foreland stage with the influence of the Himalayan orogeny.

The complex multicycle tectonic events led to the formation of multiple pods of thermally mature marine and non-marine source rocks. These source rocks were deposited during the Carboniferous, Permian, Jurassic, and Tertiary, respectively, and underwent different thermal maturations. Reservoirs in the basin are widespread through the stratigraphic column, ranging in age from the Carboniferous to Tertiary. Most oils are discovered in the Permian, Triassic, and Jurassic successions; while most gases are trapped in the Jurassic, Permian, and Tertiary successions. Reservoirs rocks are dominated by coarse-grained sandstones. The most significant regional seals are the Upper Triassic and Lower Jurassic mudstones. Traps are related to structural styles, stratigraphic variations, and unconformities.

Multiple source-reservoir-seal associations define the multiple petroleum systems, including the Carboniferous – Carboniferous, Permian – Permian/Triassic/Jurassic, Jurassic – Jurassic/Cretaceous, and Paleogene – Neogene petroleum systems. These petroleum systems overlap and communicate each other, especially in the northwestern and central parts of the basin, and are characterized by multiple source pods charging the same reservoir and one single source pod charging multiple reservoirs. Most hydrocarbon accumulations in the basin are attributed to multiple petroleum systems. However, geochemical studies indicate that the Permian – Permian/Triassic/Jurassic Petroleum System is responsible for the most hydrocarbon accumulations in the basin.