| Marine deposits refer to a series of sedimentary processes resulting from marine dynamics in marine environments.The marine sedimentary strata are usually rich in organic structures and rich in oil and gas resources.The Sichuan basin is one of the typical marine sedimentary basins in China and also one of the important petroliferous basins.In this paper,the marine sedimentary strata in the middle of West Sichuan Depression in Sichuan basin are chosen as the object of study.Based on the analysis of field data,core observation,indoor slice observation,interpretation of seismic data,logging and other comparative data,the geological characteristics of oil and gas accumulation are systematically analyzed,and the main controlling factors of hydrocarbon accumulation are summarized,and favorable areas are predicted,so as to provide references for oil and gas exploration of marine sedimentary strata in China.The main findings and understandings are as follows:(1)Leikoupo Formation has two main source rocks of Permian and Leikoupo Formation.There are four main reservoirs in the study area,they are tidal flat facies type dolomite reservoir,karst dolomite reservoir associated with unconformity,granulated facies dolomite reservoir(platform margin beach and platform beach),and gypsum dolomite facies dolomite as a potential reservoir.Main controlling factors of reservoir are reef facies and dolomitization,quasi co dissolution,early exposure erosion and late burial and hydrothermal karstification.The main development of three cover are T2l gypsum rock cover,T3m+T3t shale cap rock and J-K shale area cap rock.The combination of source rock and reservoir is divided into two types,they are Xinchang type and Pengzhou 1 well type.(2)Since the Indosinian,the western Sichuan Depression has been subjected to multi-stage compressional slipping from west to east,middle slip surfaces are not well developed,the tectonic deformation concentrated in Piedmont basin,deformation is not strong,the southern two detachment layers were developed,forming a multilayer structure of vertical superimposed deformation,in the northern part of the basement,the slippage effect is obvious,the multi period tectonic superposition occurs,and the structural deformation is transferred to the basin in the basement.The piedmont zone mainly develops extrusion type hydrocarbon source detachment fault.The depression zone is divided into two sets of fault systems in the deep and shallow strata,which are bounded by the middle and lower Triassic gypsum salt rock detachment layers.The middle part of the Western Sichuan Basin is divided into 3 deformation zones,which are the deformation zone and the deformation zone,according to the regional difference(structural style)and the formation mechanism of the tectonic deformation.The balanced section and the top surface of the 3D ray paleoburial depth reconstruction results show that mainly experienced three stages of tectonic evolution in West Sichuan depression:Indosinian formed the prototype,Yanshan transformation,the Himalayan period,to further strengthen the stereotypes.(3)There are 3 types of traps in the middle part of the Western Sichuan Basin,which are structural,lithologic and structural lithologic complex.31 local structures and 17 third lithology were discovered and implemented.(4)There are two periods of oil and gas filling in the history of the geological evolution of the Likoupo Formation in the study area.The filling periods are Late Triassic(220-210 Ma)and Middle-Late Jurassic(170-150 Ma).The transport system is mainly unconformity,fracture and fracture,and the configuration relationship with the source rock is "breaking blanket".According to the formation and evolution characteristics of fluid dynamic field,the dynamic migration and accumulation process of oil and gas in Leikoupo formation in the study area was analyzed.During the middle and late Indosinian and late Yanshanian,the migration of oil and gas from the center of the southwest depression to the east slope.The oil and gas in the middle and late Yanshan orogeny also migrated to the northwest uplift zone.The Himalayan Longmenshan-Xiushui-west of the Bo-Yang fault zone is infiltrated by atmospheric water,and the direction of hydrocarbon migration in the depression is about the same as in the middle and late Yanshan.(5)Leikoupo Formation in Sichuan is divided into two types,including self generation and self storage,self generation and upper storage-self generation and self storage.The gas reservoirs in the study area are divided into five types,including structural lithologic gas reservoir in upper fourth of Leikoupo Formation,structural gas reservoir in third of Leikoupo Formation,lithologic structural gas reservoir in upper fourth of Leikoupo Formation,lithologic gas reservoir in slope,stratigraphic unconformity lithologic gas reservoir in upper fourth of Leikoupo Formation of the slope.(6)The main controlling factors of oil and gas enrichment in the Likoupo Formation in western Sichuan are identified.?The inherited paleo uplift is the long term migration and accumulation of oil and gas.?Dissolved porous dolomite reservoir,tectonic lithologic and stratigraphic lithologic trap is the gas enrichment area and the important reason for the development of the "lower upper reservoir" type gas reservoir.?The development of the deep fracture which connects hydrocarbon source is the main reason for the accumulation of gas in the Leikoupo Formation.?The main reason for the difference in the gas accumulation and development of self generating and self storing reservoir is whether the inside fracture which connects the third-Leikoupo Formation development.? The development of Leikoupo hydrocarbon source rock is the reason why gas is more accumulated in Yuantong-Ande sag other than Wenxing-Mianyang slope zone.(7)Jinma yazihe_Anxian southern uplift zone,Dayi tectonic zone,Xinchang West Zone and Ma Jing tectonic belt is the favorable area in the middle of Leikoupo Formation in natural gas exploration. |
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