Geological Structure and Its Controls on Giant Oil and Gas Fields in Kuqa Depression,Tarim Basin:A Clue from New Shot Seismic Data

The Kuqa depression of Tarim basin formed on the pre-Late Permian Paleozoic folded basement and has undergone the evolution of foreland basin in Late Permian to Triassic,extensional sag basin in Jurassic to Paleogene,and rejuvenated foreland basin in Neogene to Quaternary,respectively.The weak intervals in the basement,the Jurassic coal beds,and the gypsum and salt or mud intervals of Paleogene Kumgrim Formation in the west and the Neogene Jidik Formation in the east have contributed as a whole to detaching shallowly upward from the north to the south.The detachment and the surface which dips shallowly basin-ward,constitute a typical tectonic wedge.The internal structure of the thrust wedge is characterized by the stratification in vertical,zonation horizontally,and segmentation in longitude.The N-W trending Awat-Karayuergun fault and the N-E trending Kuqa fault divide the Kuqa depression into three segments as Wushi sag,Baicheng sag,and Yangxia sag from west to east.The characters of structural layers have controlled largely the regional development of the effective source rocks in Triassic to Jurassic and the occurrence of reservoir-cap rock associations.The structural deformation with a stratification character has decided upon the formation of sub-salt imbricate structures with the thrust faults as the pathways for oil and gas.The combination of fault-related folds and the accordingly imbricate structures have resulted in the occurrence of such composite oil and gas zones or plays.For example,each fault-related folds in the Dabei-Kelasu structural belts has accumulated oil and gas separately,and then they combined together to form a larger composite gas plays.This kind of phenomenon has at present been proven partly by the Dabei gas play,the sub-Kelasu gas play and the Kelasu gas play.The tear faults or the transfer faults have controlled the enrichment in oil and gas in different blocks or segments.The Kuqa depression is a favorable area for oil and gas to accumulate.Thus,it is a promising area for petroleum exploration.However,the geological structures have played a great role in the zonation of different types of oil and gas fields in the area at present.