Refined Classification Of The Material Composition Of The Early Cambrain Black Shale In Guizhou And Its Control On Reservoir Physical Properties

The thesis takes the black shale of the Lower Cambrian formations in Guizhou Province as the research objects,adopts literature research,field survey and sampling,indoor test analysis and theoretical summary as research process,takes the material content characteristics of the shale,reservoir physical properties and the control relationship between them as the core scientific contents,systematically collects and organizes the basic geological data in the study area,and carries out field survey and sampling and experimental testing work,and comprehensively studies the refined material content of the shale and reservoir physical properties,and obtains the following understanding.1.Using elemental geochemistry,we identified the sedimentary provenance of the shales in the study area,and concluded that their provenance is mainly characterized by felsic provenance,passive continental margin tectonics,and moderate-to-strong chemical weathering,with slight differences in the Sandu Outcrop,which may also be influenced by the volcanic island arc.The samples of each outcrop were affected by different degrees of K-metamorphism and considered seawater as their main source of K,which was enriched/entered into the shale through volcanic ash halmyrolysis.Based on organic geochemistry,the organic matter of the shales in the study area is the type I kerogen;its thermal maturity _RmcR_o value reaches the over-maturity stage with the refined laser Raman method for calculating thermal maturity in this thesis;its TOC content generally reaches the standard of favorable formation.The analysis of the elemental state using electron probe during the study showed a good correlation between carbon peak position and thermal maturity.Based on XRD test,the mineral composition of the shale in the target section is mainly quartz,clay minerals,feldspar,and a small amount of dolomite,pyroxene,pyrite,barite,etc.The shale rock-phases were studied accordingly,and seven major categories and nineteen subcategories of shale rock-phases were classified.2.Based on optical microscopy,a detailed observation and description of the microlithological characteristics of the shales was conducted.The calcareous material is relatively little developed,mostly irregular particles or lenticular clumps,superimposed with siliceous clumps,with strong partial cementation;the silica material observation focuses on the identification of quartz in shale,and was classified into clastic quartz,biogenic quartz and its intermediate void-filling quartz,quartz veins,etc.,among which clastic quartz is dominant and the rest is relatively less,and it was believed that quartz veins and large granular quartz shells both with fibrous internal structure were formed during the stratigraphic uplift;organic materials were generally developed and morphologically diverse,and special morphological structures were occasionally seen,such as fossils with membrane structures,spherical asphalt combined with sedimentary organic matter,etc.Fine material observation is beneficial for shale lithological variability.We analyzed and summarized the misjudgments/misconceptions caused by the obscuring effect of dropped blocks and opaque minerals in the process of shale observation with optical microscope,and propose the integrated use of reflected light and transmitted light to reduce misjudgments.3.The shale material content was（semi-）quantitatively calculated using an image processing method with a simplified adjustment based on a lithological classification scheme:organic matter+silt-sized/clay-sized quartz+mineral types.The average organic matter content in 1 cm³ unit volume sample was 0.13 g;and the average total quartz content was 1.05 g,with an average clay-sized quartz content of 0.64 g.The results were combined with geochemical tests to mainly analyze the origins of the organic matter and quartz of the shales:the paleoproductivity of the shales in the study area is comparable to that of the international standard data Post-Archean Australian Shale（PAAS）,and the paleoproductivity is higher only in the Heishapo Outcrop;the organic matter enrichment in the Changyanggou Outcrop is controlled by paleoproductivity,the organic matter enrichment in the Heishapo Outcrop is controlled by paleoproductivity and water redox conditions,the organic matter enrichment in the Nangao Outcrop is controlled by paleoproductivity/water redox conditions/migrated organic matter enrichment resulted by hydrothermal action,and the organic matter enrichment in the Sandu Outcrop is lower and the abundance is controlled by water redox conditions.The study area is generally indirectly influenced by hydrothermal action to varying degrees,resulting in a general enrichment of Ba in the shale,and a large amount of free Si is imported into the shale together with it.It was also suggested that in the Changyanggou and Nangao Outcrops,the indirect hydrothermal action was relatively strong and hydrothermal fluids may be the main cause of clay-sized quartz,while in the Hesshapo and Sandu outcrops,the indirect hydrothermal action is relatively weak and biological may be the main cause of clay-sized quartz.4.Using brittleness index,uniaxial compression method/experiment,the results show that the shale in the study area has good brittleness and compressibility;the compressive strength of the parallel laminae（cylindrical specimens）is lower than that of the vertical laminae,and the elastic modulus in the parallel laminae direction is greater than that in the vertical laminae direction.The compressive strength and elastic modulus of shale are controlled by the combination of grain and matrix.Based on this,it was suggested that the internal mechanical structure of shale can be reduced to a particle-centered"strong cemented group"and matrix.It was also suggested that the excess of grain/clay-sized quartz in the shale leads to the occurrence of"excess cementation",which results in a higher compressive strength between laminations than in the vertical laminate direction,and presumably also leading to the development of vertical laminations in the siliceous rocks trapped in the shale5.With mercury injection/liquid nitrogen experiments,the pore development is better in the shale rock-phases with higher content of both clay-sized quartz and silt-sized quartz,while the shale rock-phases with higher content of clay mineral are the second best.The effect of silt-sized/clay-sized quartz on pore development is opposite,with the former promoting pore development,while the latter exhibiting inhibition.Good correlation between the material content or combinations and the degree of pore development/pore morphology among samples from the same section and the same rock-phase,which is thought to be due to the similar sedimentary-burial-diagenesis background of such samples,and also indicates the influence of sedimentary-burial-diagenesis on the pore development of shales.6.In the process of pressure testing permeability of the target shale,there are differences in the characteristics of sample permeability between parallel laminae direction（cylindrical plugs drilled in parallel laminae direction）,with vertical laminae direction（cylindrical plugs drilled in vertical laminae direction）.The permeability of shale is controlled by matrix and grain,i.e.,the increase of matrix/reduction of grain leads to decrease of permeability and increase of decay coefficient.And,the shale rock-phase plays a controlling role in it.The high or low content of clay mineral in shale affects the control of permeability by particles,e.g.,the development of parallel-layer permeability in shale with high clay content is inhibited by particles,while the development of parallel-layer permeability in shale with low clay content is promoted by particles.Different rock-phases have different dominant permeability directions,e.g.,argillaceous quartz siliceous shale is dominated by lateral permeability,siliceous shale A and mixed shale by vertical permeability.And the dominant permeability directions transfer from each other with the change of shale material content.The research results of the thesis are of positive significance in the development of shale petrology and the control of shale material content on physical property development,enriching the theory of differential shale gas enrichment and,at the same time,being of practical value to the exploration and development of shale gas.This thesis contains 113 figures,11 tables,6 attached tables,and 399 references.