Deep Shale Reservoir Characteristics Of Wufeng-Longmaxi Formation In Luzhou Block

Sichuan Basin is rich in deep shale gas resources,which has broad exploration space and development prospects.The research on the characteristics of deep shale reservoirs has important theoretical and practical significance for the commercial development of shale gas.Taking the deep shale of Wufeng-Longmaxi Formation in Luzhou block in the south of Sichuan Basin as the research object,this paper studies the characteristics of organic geochemistry,mineral composition and pore structure of deep shale gas reservoir by using the research methods of data investigation,field investigation,experimental test,logging analysis and theoretical analysis.By comparing and analyzing the differences between deep and medium-shallow shale reservoirs,this paper expounds the particularity of deep shale reservoir and its main controlling factors,which provides a basis for the exploration of deep shale gas reservoirs in China.The following are the main results:(1)The type of organic matter in deep shale of Wufeng-Longmaxi Frormation in Luzhou block is mainly type I kerogen,the degree of thermal evolution reaches the high-over mature stage.The content of organic carbon is between 1.84% and 5.73%,and the 1-3 layers are the sections with the highest organic carbon content,with an average value of 4.98%.The mineral composition of shale is complex,mainly including quartz,carbonate rock minerals,clay minerals,feldspar and barite.Clay minerals are mainly illite.The reservoir has high brittleness index,showing good brittleness and compressibility,which is conducive to the formation of natural fractures and later fracturing transformation.(2)Both organic pores and inorganic pores are highly developed.The sizes of organic pores are different,ranging from a few nanometers to hundreds of nanometers.With the increase of buried depth,organic pores change from regular elliptic pores to slit pores.Inorganic pores are complex and irregular in shape,and are most developed in Wufeng Formation.The development level of micro fractures is high,mainly structural micro fractures.The pore structure parameters first decrease and then increase with the increase of buried depth.The pore volume and specific surface area at the top of Wufeng Formation are higher than those of other small layers.Pores are mainly distributed at 0～2 nm,3～5 nm and 10～50 nm.Micropores and mesopores dominate the contribution to pores,while macropores have the lowest contribution.Pore development is mainly affected by factors such as formation buried depth,organic matter and mineral development.(3)The logging curve shows the response characteristics of high natural gamma,high acoustic time difference,high resistivity,high uranium content and relatively low density,low neutron and low uranium free gamma.Combined with the variation characteristics of logging curves in different layers and the logging calculation results of reservoir parameters,it is judged that layer 3-1 is a high-quality shale gas reservoir section,and the comprehensive quality of Wufeng Formation is similar to that of layer 4,second only to that of layer 1-3.Both middle-shallow layers and deep shale have the response characteristics of high natural gamma,high uranium,high acoustic moveout,low compensated neutron and low compensated density,but the curve shape changes of acoustic moveout,density and resistivity of deep shale reservoir are more complex.(4)Compared with the middle and shallow layers,the material composition of deep shale gas reservoir has the characteristics of high organic carbon content,high quartz,low feldspar,high pyrite and low clay minerals,indicating that the deep shale reservoir has better organic geochemical conditions and mineral composition conditions.The pores of deep shale reservoir are characterized by inorganic pore development,low porosity,high degree of mesoporous development and poor degree of macropore development.The deep layer is mainly mesoporous,and the development degree of macropores is very poor.Sedimentary environment,mineral development,reservoir burial depth are the main factors for the differences between deep and medium shallow shale reservoirs.This thesis has 49 figures,18 tables,169 References.