Characteristics Of Marine Petroleum Conduit Systems In The Middle Part Of Western Sichuan Depression,China

By using logging,high precision 3D seismic data and surface outcrops,the effect of marine conduit systems on petroleum migration and accumulation is studied in the middle part of western Sichuan depression.(1)The research shows that the marine unconformity surface conduit systems in the middle part of western Sichuan depression mainly exist at the top of the Upper Sinian Dengying Formation,the Permian bottom in Caledonian period,the top of the Middle Permian in Dongwu movement,and in some regions of the top of the Middle Triassic Leikoupo Formation.The study considers that the unconformity dissolving holes in the top of the Dengying Formation,Caledonian unconformity filling and matching Features,development characteristics of micro-cracks in unconformity on top of Maokou Formation,and local distributing characteristics and corrosion characteristics of unconformity on Leikoupo Formation.Among them,there is a coincident area of Sinian unconformity and Caledonian unconformity in the southern part of the middle Sichuan depression,where the lateral migration of oil and gas is the strongest on the unconformity surface of the area,which is the long-distance lateral direction of oil and gas in the study area.The most favorable areas for migration were followed by the unconformity surface of Dengying Formation,the top unconformity surface of Maokou Formation and the top unconformity surface of Leikoupo Formation.Unconformity surface conduit systems are responsible for the lateral migration of petroleum.The natural gas is mainly transported along the unconformity surface to the high structure.(2)Due to the lateral compressive stress of longmen mountain,the thrust fault and reverse thrust fault were developed in the middle section of western sichuan depression,to north east-south west.A triangular tectonic belt is formed between the thrust fault and reverse thrust fault,which is a favorable oil and gas exploration area.A multistage fracture occurs in a depression.The guankou-dayi fault and zhangming-pengzhou fault are two major faults.Most of the oil and gas are transported from these two faults.The development and combination mode of multistage fracture construct the three-dimensional network fault transmission system.Fault conduit systems are developed in Permian strata,Leikoupo Formation and the Upper Sinian Dengying Formation.According to the research,there is a lateral fault in the attachment of the Shibantan,and it goes to the north west-south east direction.The existence of tectonic transition zone may separate the cognac structure from Pengzhou structure and yazi structure in the north east.The accumulation model of cognac may have certain independence.The fault conduit systems controlled the longitudinal migration of petroleum.The fault transmission system causes the oil and gas to be transported upward along the fault.In the position of the Pengzhou tectonic,the existence of deep faults directly communicates the source rocks and reservoirs,oil and gas can move vertically from deep to shallow reservoirs along faults,and the presence of stepped faults in the yazi river can be indirect.Source rocks are associated with reservoirs.The fault transport system makes it possible to transport gas in the long-distance longitudinal direction,and its presence makes it possible to move the underlying hydrocarbons up and down the fault.(3)There are many high-quality reservoirs in western sichuan depression.Due to lithological constraints,oil and gas are transported in the reservoir with high permeability and large pore size.Based on the results of exploration and the development of reservoir,it is believed that the oil and gas in the reservoir are transported to the high structure in the direction of jinma-yazi river tectonic belt,xiaoquan-xinchang tectonic belt and deyang-guanghan slope belt.(4)Through analysing the tectonic evolution history of the Sichuan Basin,the structure of Pengzhou tectonic accumulation process was anatomized.It was considered that the impact of gypsum salt rock of the Jialingjiang Formation and Leikoupo Formation of the Middle-Lower Triassic was not affected by the early large faults,and that within the Leikoupo Formation the late charging of natural gas has caused the discovery of asphalt in the Leikoupo Formation.By making balanced geologic profiles,it is believed that the current gas reservoir formed in the Leikoupo Formation of the Middle Triassic is developed during the Early Cretaceous,and the fault transport system develops.The Leikoupo Formation starts to communicate with the underlying strata and the gas along the fault breaks from the deep move it upwards and adjust it laterally along the unconformity in the layer to the construction high point.The deep-formed paleo-reservoir reservoirs are transported along the fault uplift to the appropriate reservoirs under the action of the fault transport systems,and are laterally transported and aggregated along major unconformities to form secondary reservoirs.The formation of the Leikoupo Formation gas pool in Pengzhou may fall into this category.