Tectonic Features Of The Northern Margin In Kashi Depression And Controls Of Hydrocarbon Accumulation

The northern margin of the Kashi Depression is our study area which is commonly influenced by the Southwestern Tianshan,West Kunlun and Talas-Ferghana strike-slip faults.There are complex tectonic deformations with great potential for hydrocarbon exploration.But limited by the quality of data,no more oil field has been discovered.Based on geological and geophysical data,study area was divided into four structural segments in this paper: the Kelatuo,Artushi,Talanghe and Bapan.More reasonable structural models are established to analyze their geometric structure and characteristics of tectonic evolution.Meanwhile,petroleum geological conditions and reservoirs are analyzed to study pattrens of hydrocarbon accumulation.And the possible differences about oil source in Kelatuo and Artushi are discussed from tectonic point of view.Through our research,following understanding has been achieved:(1)The structural of each segment have similarities,both are mainly controlled by three faults,namely,the Piedmont Fault F1,Artushi North Fault F2,and Deep Blind Thrust F3.Fault F2 in shallow layer is relatively gentle in Kelatuo and Atushi segment,and tectonics are mainly developed on the upper block of F2,which are propagation fold in the front of Fault F2.The layers of Kelatuo area are monocline with high angles,however,strata of core and the wings on Artushi anticline are complete.The occurrence of Fault F2 in Talanghe segment becomes high and steep,,located in the footwall of F2.The formation of Kashi anticline is similar to Talanghe anticline,which is back-thrusting structure caused by shallow detachment fault,so they are both belong to the Southwestern Tianshan thrust system.The strike of surface anticline in Bapan segment is offset with that of Talanghe anticline,and the formation are more superposed vertically.(2)Tectonic evolution since the Neogene can be divided into three stages.From the beginning of the Neogene to the end of the Miocene,major faults F1 and F2 cut through the basement,and there are a series of secondary faults such as F3.The whole Pliocene is a intensive stage,F1 and F2 active sharply,and secondary faults such as F3 are no longer alive due to overlying Neogene strata.From Quaternary to now,system has weakened F1 and F2,and the upper fault block of F2 develops regulation faults,forming current folds associated with faults.F3 continues to move leading stress to shallow layers,forming slip anticlines controlled by back thrusts.(3)There are two sets of source rocks,Carboniferous carbonate rocks and Jurassic coal series strata.If oil source does have differences between the Akemomu gases reservoir and hydrocarbon in Kelatuo area,that is,gas source rock of the former is Carboniferous,and the latter is Jurassic.From the tectonic point of view,oil and gas generated from Carboniferous in Kelatuo area is laterally lost due to property and hydrocarbon concentration of the overlying Jurassic,while gases generated from Carboniferous in Akemomu area rise to the unconformity plane and directly enter the Kezilesu Formation because of lack of Jurassic system.