Reservoir Characteristics And Pore Evolution Simulation Research Of Longmaxi Formation Shale In Chengkou Area,Northeastern Chongqing

The reservoir characteristics of Longmaxi Formation in northeast chongqing are yet to be further studied,and the evolution mode and control mechanism of reservoir pores need to be explained urgently.This paper took the shale of Longmaxi Formation in well C1,miaoba and tianba profiles in chengkou area of northeast chongqing as the research object.Relevant test experiments were used to analize the reservoir characteristics such as mineral composition,organic geochemistry,pore structure.Combined with thermal simulation experiment to study the shale pore evolution process and diagenesis,the diagenetic-pore evolution model was established and the controlling factors of pore development were analyzed.?1?The reservoir material composition characteristics of the Longmaxi Formation shale in the study area were described.It mainly develops carbonaceous?mud?shale,carbonaceous siliceous shale,silty shale,argillaceous siltstone,mudstone,and porphyrite.The main mineral components are quartz?land-based detrital quartz,biogenic quartz and diagenetic quartz?and clay minerals?illite,imon mixed mineral?,and minor minerals are feldspar?potassium,sodium feldspar?,carbonate Rock?more dolomite,less calcite?,pyrite.The main organic matter type is saprolite I kerogen with a small amount of humus-soil type II₁ kerogen with an average organic carbon content of 3.7%.The average vitrinite reflectance is 1.52%,which is in the early stage of maturity-over-maturation and has certain hydrocarbon generation potential.?2?The developmental characteristics of shale reservoir pores were clarified.Based on the pore fractal feature,a new pore partitioning scheme for adsorption pores?less than 3.5 nm?,adsorption-diffusion pores?3.5 nm to7.5 nm?,diffusion pores?7.5 to 50.4 nm?,and percolation pores?greater than 50.4 nm?was proposed.?3?The high-quality reservoirs of the Longmaxi Formation were identified by using multiple indicators for the C1 well.The vertical heterogeneity of the reservoirs was analyzed,and the differences of shale reservoirs in different areas of the study area were compared.?4?The variation characteristics and pore evolution of shale material composition under thermal simulation conditions were described.Pore evolution showed different characteristics in the three stages of immature-mature maturity?R_o<1%?,mature mid-high maturity?R_o between 1.0%².0%?and early maturity?R_o>2.0%?.?5?It is determined that the shale reservoir in the study area is in the Mid-stage diagenesis B to late-stage diagenesis.Diagenetic-pore evolution model was established and the control mechanism of pore development was revealed.Structure-burial,sedimentary environment,material composition,diagenesis directly or indirectly control pore development,and brittle minerals and grapholite also have an important impact on reservoir pore development.