Tectonic Evolution And Hydrocarbon Accumulation In Yili Basin,Northwest China

The formations of Yili Basin after the middle Permian basin, hydrocarbon generation and accumulation systems and the transformation systems of the basin, as well as the dynamic process of the conversion relationship between them in different period, is the main line of the project. With the theory of Plate Tectonics and Petroleum Systems theory, combining the geological, geochemical, geophysical and other multi-disciplinary research thought, using organic geochemistry analysis, simulation and other means, hierarchically step by step to carry out the research on the relationship between Ili basin tectonic evolution and oil and gas reservoirs.Yili Basin is a composite stacked intermountain basin, clamping in Tianshan Orogenic belt in Central Asia. The regional tectonic evolution of the Yili Basin is the background and framework of the formation and development of Yili Basin. The evolution of the Tianshan orogenic belt directly influence and control of the tectonic evolution of the study area, based on previous studies, based on existing geological and geophysical data, we can divide the formation and evolution of the regional tectonic into six tectonic stage:the Proterozoic supercontinent cracking and flattening, the Neoproterozoic Rodinia supercontinent formation and breakup, early Paleozoic formation and disappearance of the early ancient Tianshan ocean stage, late early-Paleozoic the ancient Junggar ocean formation with the closing stage, late Paleozoic continental within the rifting phase, Mesozoic the thrust displacement and Cenozoic basin formation stage.Re-sort the basin strata, determining the basement of Yili Basin is the Sinian strata, then successively followed by the Carboniferous rift-type volcanic and marine carbonate formation, Permian continental volcanic combination and clastic rocks formation, Triassic rivers and lakes deposition and Jurassic fluvio-lacustrine coal-bearing strata, generally absent lower Cretaceous strata, then covered river alluvial fan deposits in Cenozoic.Before early Paleozoic, Yili Basin was a part of the ancient continent of Xinjiang, then Yili Basin became a stand-alone unit, collided with the Junggar block and the Tarim plate one after another in early Late-Paleozoic. From Carboniferous continental rift basin to the Cenozoic intermountain basin, Yili Basin experienced the Permian Depression-stretching period, Triassic atrophy and Jurassic extension stage, the Cretaceous basin uplift and erosion phase, and shrinking in Cretaceous. Yili Basin was a "therma"l basin during Carboniferous-Permian, became a cold basin the Triassic, the modern basin superimposed multiple tectonic movements is strongly deformed, the transformation is very serious.After comprehensive analysis the typical Carboniferous-Jurassic geological section and single well hydrocarbon source rock types in Yili Basin, we evaluate the abundance of organic matter, the type of organic matter, organic matter maturity. This paper argue that the source rock in carbonate rocks of Carboniferous Akeshake formation belong to poor hydrocarbon source rock, the type of organic matter is mainly Ⅲ and in the mature stage; mudstone from the Upper Permian Tamqisayi formation is moderate good hydrocarbon source rock, the type of organic matter is type Ⅲ, in over-mature to mature stage; the mudstone in the upper Triassic Xiaoquangou group (T2-3xq) is in the middle-good source rocks, with organic matter type Ⅲ1but in immature to low-mature stage; Lower Jurassic coal measure strata-Shuixigou Group Badaowan (J1b) formation, its lithology change, and the mudstone and coal is uneven distributed in the Yili Basin, belong to poor hydrocarbon source rocks, organic matter type is Ⅲ and in immature to Low-mature stage.Using the well sonic logs of Well Ning3, this project estimates about400m thickness of erosion today, and about1600m denudation strata during Early Cretaceous. With BasinMod, we reconstruct the burial and thermal history of the Well Ning3, the results show that from280Ma (Late Permian) to144Ma (Early Cretaceous), sedimentation/deposition rate are relatively large, Yili Basin deposition of a stratigraphic thickness of about1500m during this period. From144Ma to130Ma significant hiatus, during130-96Ma (Early Cretaceous), Yili Basin uplift, denudated nearly1600m sedimentary strata; from Late Cretaceous began Ili basin re-accept the deposition, the Ili basin deposition rate increased slowly during65-6Ma, from6-2.5Ma, Yili Basin uplifted again, erosion about400m.The simulation results show that, the Permian Tamuqisayi Formation is the main hydrocarbon source rocks in the basin, this formation came into the oil threshold in Early Triassic (240Ma), reached the peak of oil generation in the Middle Jurassic (180Ma), basically ended the oil generation in Early Cretaceous(140Ma), started the gas generation at the early Jurassic (200Ma), stepped into gas generation peak early Cretaceous (140Ma) and the gas generation was over in the late Early Cretaceous(120Ma). This formation is mainly in high maturation stage.By analyzing the tectonic effetct on the hydrocarbon accumulation mode in the basin, we can draw the following views:Hercynian and Indosinian traps were formed meanwhile the Permian hydrocarbon is migrating and accumulating, which is likely to converge or converged over Permian hydrocarbon, but the the Yanshan and Himalayan movement destroyed these traps seriously. However, Yanshanian and Himalayan traps laged in the first stage of migration and accumulation of the Permian hydrocarbon, they are all poor traps without oil or gas, but under the right conditions, can form the secondary reservoir.