Enrichment Mechanism Of Fuling Shale Gas Under The Joint Control Of Sedimentary Diagenesis And Tectonism

The formation and evolution of marine shale gas in South China is highly complex.Ordovician Silurian is a very important geological turning period in geological history.A series of sedimentary geological events occurred,such as hernantian glaciation,global sea level change,volcanic eruption and underflow activity.Compared with North America,shale gas accumulation in Fuling area has the characteristics of complex sedimentary background,long evolution history,high thermal maturity of organic matter and strong structural transformation.The development practice of Fuling shale gas field shows that the gas bearing capacity of different shale layers in Wufeng Longmaxi formation is different,and the output of shale gas wells in different structural units varies greatly.Therefore,the research on the main controlling factors of shale gas enrichment under complex geological background is a major scientific problem faced by shale gas exploration and development.In previous studies,there is a lack of clear understanding of the joint control mechanism of sedimentation,diagenesis and tectonism on shale gas enrichment.At the same time,there are some basic problems in the process of shale gas formation,such as the lithofacies composition and reservoir differences in the isochronal framework under the influence of sedimentary geological events,The formation and evolution mechanism of different types of pores in shale and the qualitative and quantitative analysis of shale gas preservation mechanism under different geological conditions are also lack of in-depth discussion.On the basis of seismic,drilling,outcrop and a large number of laboratory tests,the shale of Wufeng Longmaxi formation in Fuling shale gas field is taken as the research object.Under the guidance of sedimentology,sequence stratigraphy,rock mineralogy and unconventional geology,the vertical heterogeneity and main controlling factors of organic rich shale facies are identified,The lithofacies genesis and sedimentary process(controlled by multiple geological processes and controlling factors)under different paleoceanographic conditions are analyzed;The evolution path of micro nano pores in highly mature shale is reconstructed,and the types of organic-inorganic synergistic diagenesis and its influence mechanism on pore development are revealed;The evaluation index system of Fuling shale gas preservation conditions is established,and the qualitative and quantitative comprehensive evaluation of Fuling shale gas preservation conditions is carried out;Finally,deepen the research on the comprehensive matching effect of hydrocarbon generation,reservoir formation and preservation,reveal the differential enrichment mechanism of Fuling shale gas in the whole process of sedimentation,burial diagenesis and structural uplift transformation,and establish a typical reservoir forming model of shale gas in Fuling area.The main understanding of this study is as follows:(1)Based on the data of drilling,whole rock X-ray diffraction,high-pressure mercury injection and argon ion polishing scanning electron microscope,the shale facies of the first member of the Wufeng Longmaxi formation is divided,and the different development characteristics of reservoir quality in different lithofacies are identified.Through the horizontal comparison of geochemical elements,it is revealed that volcanic events,underflow events and terrigenous clastic supply are the main factors controlling the vertical development of shale The dynamic evolution process of shale deposition in the first member of Wufeng Longmaxi formation is established by the main sedimentary geological events of heterogeneity.(2)Taking the limited space hydrocarbon generation and expulsion simulation experiment as the main line,the pore morphology characterization,pore physical property measurement,rock and mineral identification and other technical means are integrated to reconstruct the pore formation evolution process of marine shale of high mature Longmaxi formation,clarify the different evolution paths of different types of pore development,clarify the organic-inorganic synergistic diagenesis types and different diagenesis stages of shale,and reveal the characteristics of shale Mechanism of diagenesis on formation and evolution of shale pores/(3)Based on the detailed anatomy of structural deformation characteristics in the study area,combined with the geological characteristics of shale gas reservoir formation,the differences of shale gas reservoir formation conditions under different geological conditions are compared,the control of tectonic action on the differences of shale gas reservoir formation conditions is clarified,the comprehensive evaluation method and identification index system of shale gas reservoir formation and preservation conditions are preliminarily established,the favorable preservation units of shale gas are divided,and different geological conditions are clarified Preservation mechanism of shale gas under different conditions.(4)Based on the above research contents,this paper systematically expounds the sedimentary diagenesis process from two aspects: the vertical difference of shale rich organic matter under the coupling control of volcanic events,underflow events and terrigenous input events during the shale deposition period,the development degree of shale pores under different diagenesis in the shale burial depth stage,and the plane difference of shale gas preservation conditions changed by structural transformation during the formation uplift-According to the enrichment mechanism of Fuling shale gas under the control of structural coupling,different reservoir forming modes of typical blocks in the study area are divided...