The Controlling Effect Of Lithologic Factors On The Fracturing Of Fine-grained Sedimentary Rocks

With the decline of domestic oil and gas production,oil and gas supply is becoming increasingly scarce.So the development of unconventional resources research,especially shale oil and gas,is essential to alleviate the crisis of resources.For China's vast territory,pulveryte of the lacustrine basin developed multiple stages,large thickness,abundant reserves of shale gas resources.However,the technology of shale gas exploration and development in China is not yet mature,and fracturing evaluation is one of the problems to be solved urgently.This thesis mainly makes use of the lacustrine fine sedimentary rocks to evaluate of the fracturing property of the Mesozoic and Cenozoic erathem.The samples of Mesozoic erathem are collected from the Jiaolai Basin and Fuxin basin,and the samples of Cenozoic erathem are collected from Huangxian basin,Jiyang depression,Wutu basin,Fushun basin and Huadian basin.Carbonate minerals content of the fine-grained sedimentary rocks of Mesozoic erathem is generally high,which is mainly composed of calcareous or dolomitic fine sedimentary rocks,kerogen for type II and III.The Cenozoic fine-grained sedimentary rocks has lower diagenesis intensity,the higher TOC content,and better kerogen type,which is mainly composed of type I.According to the composition and diagenetic characteristics of fine-grained sedimentary rocks,and combining the structures and structural parameters obtained by image analysis,the sdudy use them to compare with those parameters of conventional triaxial and fracture toughnes.For the components,felsic minerals,carbonate minerals and other authigenic minerals such as pyrite are the major brittle minerals in fine-grained sedimentary rocks.Under the condition of similar diagenesis,the more content they have,the stronger the fracture of fine-grained sedimentary rocks is.However,when a mineral is low,fracability is often affected by another mineral,so that their correlation is not strong.The higher the clay mineral content is,the lower the brittleness of fine-grained sedimentary rocks is,and the worse the toughness is.However,there are also large differences in the control effect of different clay mineral compone nts on crushability.The higher the content of total organic carbon of fine grained sedimentary rocks,the stronger the plasticity of rock,the more unfavorable to rock fracturing.For the structure,the increase of the quantity of fine sediment rock particles can enhance the brittleness and the fracturing property of the rock.Generally,there is a weak positive correlation between the average particle size of the particles and the fractalability.The more uniform distribution of particles on the whole is,the higher the rock strength is,the better the fracturing is.The better the vertical differentiation of particles is,the more easily plastic flow mudstone and silty sand in the process of fracturing is,and more easily reduced the fracturing property of the rock is.For the tectonics,the smaller the layer thickness of the fine-grained sedimentary rock is,the more the layer are,the more the weak structural plane have,the worse the brittleness and fracturing property of rock are,the smaller the frac ture toughness is.The thick layer makes a main control role to the the fine-grained sedimentary rocks with large difference in lamellar thickness in the fracturing process,the increase of layer thickness difference is conducive to enhancing the brittleness of fine-grained sedimentary rocks and fracturing property,and fracture toughness is also enhanced.Fine grained sedimentary rock with poor layers continuity are mainly argillaceous siltstone and siltstone,which has high rock strength and good fracturing property.However,fine grained sedimentary rock with good layers continuity are mainly mud shale and shale,which has low rock strength and bad fracturing property.In addition,the fracture toughness of fine-grained sedimentary rocks is mainly controlled by the structural planes between the layers,but the continuity of the layers is not significant.For the diagenesis,with the enhancement of diagenesis,the compaction,cementing and conversion from unstable minerals to stabilize minerals are also enhanced.The more the compactness is,the higher the brittleness,fracture toughness and fracturing properties of the fine sedimentary rocks are.According to the characteristics of various aspects of lithologic factors,analyzing the main control factors of fine-grained sedimentary rocks by using correlation analysis method can draw a conclusion: The maximum control effect of the fine grained sedimentary rock is the diagenesis intensity,followed by the quantity of particles.At the same time,the overall distribution of particles uniformity,the continuity of the layers,the content of quartz and the variance of the density of the layers also have an important influence on the index of the fracturing.