Complexity Assembly Mechanism In The Pore Structure And Its Effects On The Physical Properties Of CBM Reservoir

The coal-bed pore structure determines its reservoir and transportation properties.Clarifying the control mechanism of pore structure is the basis for realizing the efficient development and utilization of resources,which has important theoretical value and practical significance.A large number of studies show that the coal reservoir matrix is a extremely complex fractal porous medium,and often shows the characteristics of complex particle morphology,random spatial distribution and fractal scale structure.Their spatial composition affects the coal reservoir physical properties seriously,such as porosity,hydraulic tortuosity,permeability and pore diameter distribution,and they control the occurrence and migration behavior of oil and gas resources.Therefore,Quantifing the characterization of fractal pore structure in coal reservoir is the key to realize the evaluation of productivity.The purpose of this study is to effectively characterize the micro features of coal matrix in pore structure.Therefore,we selected the coal reservoir in Wuxiang South block of Qinshui Basin as the research objrct to analyse the geographical location,stratigraphic and coal reservoir characteristics,development and types of pore structure in the study area systematically.Selecting the coal reservoir of 3#and 15#as samples for the experiment of Mercury injection,and then analysis the data of the pore diameter and porosity,permeability,hydraulic tortuosity,found that real Wu Xiang study blocks of coal-bed is isotropic,anisotropic,heterogeneous,scale difference and the statistical characteristics,such as coarse coal burst for subsequent fractal characterization of pore structure characterization of the basis and the model validation.The classical scale quantity relationship is often used to describe the scale invariant attribute of fractal pore structure in coal reservoir.Although this method quantifies the fractal behavior,it does not clarify the definition of fractal behavior.Therefore,the paper based on fractal topology theory calibrates two kinds of complex types of fractal pore structure in coal reservoir porous media,that is,the original complexity caused by describing the original configurations such as pore diameter distribution,connectivity and geometric morphology,and the behavioral complexity dominated by the scale invariant attribute.Among them,the scaling lacunarity P（P_x,P_y）and scaling coverage F of fractal topology are the basis of quantitative description of behavior complexity.On this basis,this paper realizes the equivalent representation of the original complexity elements with the help of the four parameter random growth algorithm,realizes the scale invariant definition of self similarity and self affine attributes by using the fractal topology theory,and then constructs the mathematical framework for the quantitative representation of the fractal pore structure model of porous media in arbitrary coal reservoir,Combined with the actual coal sample porosity data in Wuxiang research block,the simulation reconstruction is carried out to verify the correctness of the equivalent representation of the model proposed in this paper.The paper starting with the fractal topological parameters of original complexity and behavioral complexity,systematically analyzes the control and influence on the characteristics of fractal pore structure,that is,the parameters of cdd,M,N andεinfluence the degree of fracture,random distribution and boundary roughness of the affected pore structure belong to the original complexity;The scale structure characteristics such as self similarity and self affine controlled by behavior parameters P,F,P_x,P_y,H_xyare controlled by behavior complexity,while the anisotropy of pore structure is the result of the coupling of original and behavior complexity.Based on the above research results,we combined with the LBM method to simulate the flow field of the constructed model,and analyze the influence trend and restrictions of the modeling parameters on the physical parameters such as fluid permeability and hydraulic tortuosity of the matrix pore structure.The analysis results show that different parameter controls different morphological characteristics which have different variation laws on their physical parameters.Then discussed the controlling factors of fractal pore structure anisotropy and the pore-permeability relationship of its characteristics.It is found that it appears exponentially with the change of anisotropy parameters.Based on the research datas of Wuxiang research block,relying on the fractal pore complexity assembly,this paper adopts the optimized QSGS algorithm to control the generation of micro fractal pore structure of coal reservoir porous media by changing the original and behavior complexity parameters,and finally constructs the complex types and assembly mechanism framework of coal reservoir matrix in fractal pore model,The fractal pore structure which breaks through the shackle of the same solid size,can accurately represent the scale invariant attribute characteristics of porous media and has controllable porosity is constructed,the quantitative characterization of the physical characteristics such as anisotropy,fragmentation degree and boundary roughness of reservoir microstructure is realized,and the influence mechanism between the characteristics of pore structure and the law of seepage physical parameters is explored.This article consists of 53 figures and 18 tables,and there are 93 references supporting it.