【作者】 李辉；

【导师】 金毅；

【作者基本信息】 河南理工大学 ， 地质资源与地质工程， 2018， 硕士

【摘要】 煤储层中的割理网络作为流体运移的主要通道,深刻影响煤层气的运移与产出,因此,割理网络输运属性定量评估对于储层产能预测和煤层气开采具有重要的意义。大量证据表明煤储层自然裂隙具有分形特征,使用分形理论来表征其复杂几何形貌是一种行之有效的研究手段。基于以上认识,本文聚焦于割理网络模型的表征及其传质过程的孔隙尺度模拟。在割理网络表征及其渗流扩散行为方面主要开展了如下四个方面的研究:(1)单割理自仿射几何定量表征及新Weierstrass-Mandelbrot函数的发展Weierstrass-Mandelbrot(W-M)随机分形函数常用来表征自然裂隙端面几何形貌,据新近分形拓扑理论,H(Hurst指数)与_fD(分形维数)之间并非_fD≈d-H(d为欧几里得维数)的关系,而是_fD=d(1+H),于是修正了W-M函数及其结构函数。(2)煤储层割理网络的构建利用修正的W-M函数,结合自然裂隙端面几何自仿射属性和煤储层割理空间构型及分布,实现了割理网络自仿射属性表征,发展了一种自仿射粗糙割理网络构建方法。(3)孔隙尺度下割理网络流体运移过程的LBM模拟及渗透性能分析采用格子Boltzmann方法(LBM)于孔隙尺度下模拟了流体运移过程并计算了其渗透性能。对比分析表明无端割理情况下储层渗透率满足三重效应分形裂-渗关系。端割理的引入会增强储层的渗透性能。Hurst指数、面割理和端割理开度均能引起割理网络整体渗流特征的改变。具体表现为渗透率随Hurst指数及面割理的开度增加而增大,而与端割理具有小开度下影响权重高,大开度下影响权重小的特点,且该权重值与端、面割理开度的比值具有一定的幂率关系。同时,在查明它们之间的差异性贡献后,建立了煤储层割理网络影响下的经验渗透率模型。(4)割理网络中对流-扩散过程的模拟及输运属性分析结合Taylor-Airs方程,理论解析并建立了弯曲裂隙中对流-扩散过程中弥散系数的预测模型,采用新的LBM程序模拟并初步验证了其有效性。进而在割理网络表征模型中模拟对流-扩散过程,初步分析了端、面割理开度及弯曲度对割理网络中对流-扩散行为的影响,发现割理网络中对流-扩散行为主要受控于与宏观流方向一致的面割理。本次主要研究了割理网络的渗流特征及其对流-扩散行为,以期为今后研究煤层气运移及割理网络等复杂介质物质输运问题提供理论基础。更多还原

【Abstract】 As the main channel of fluid transport,cleat network in coal reservoir affects transport and output of coalbed methane deeply.Therefore,the quantitative assessment of the transport properties of cleat networks is of great significance to predict reservoir productivity and exploit coalbed methane.A large amount of evidence indicates that natural fractures in coal reservoirs have fractal features.Using fractal theory to characterize complex geometries is an effective research method.Based on the above understanding,this paper focuses on the representation of the cleat model and the pore-scale simulation of the mass transfer process.The following four aspects are mainly studied in the characterization of cleat networks and the flow-diffusion process:(1)Quantitative characterization of single cleat self-affine geometry and development of new Weierstrass-Mandelbrot functionThe Weierstrass-Mandelbrot(W-M)random fractal function is often used to characterize the natural fracture surface geometry.But according to the new fractal topography theory,the relationship between H(Hurst exponent)andD_f(fractal dimension)is notD_f≈d-H(d Victoria Euclid dimension)but_fD=d(1+H).Thus the W-M function and its structure function was fixed.(2)Construction of coal reservoir cleavage networkCombining the geometric self-affine properties of the natural fracture face and the configuration and distribution of the cleat space in coal reservoir,the characterization of self-affine networks was achieved by using the new W-M function and a method to construct the cleat network model was developed,which can realize the quantitative characterization of self-affine rough cleat networks.(3)LBM simulation and permeability analysis of fluid flow in cleat network with pore scaleThe Lattice Boltzmann Method(LBM)was used to simulate the fluid transport process at the pore scale and calculate its permeability.The comparative analysis showed that the reservoir permeability satisfies the triple-effect fracture-permeability model without butt cleat.The introduction of butt cleat will enhance the permeability of the reservoir.Hurst exponent,the aperture of face cleat and butt cleat can all cause the change of seepage characteristics of the whole cleat network.More details,the permeability will increase when the Hurst exponent and the aperture of butt cleats increase,vice versa,while the butt cleat had the characteristics of high influence weight in small aperture and small influence weight in large aperture.And there was a power-law relationship between the ratio of the face cleat aperture and the weight value.At the same time,after ascertaining the differential contributions between them,an empirical permeability model under the influence of coal cleat network were established.(4)Simulation of advection-diffusion process and analysis of transport properties in cleat networkBased on the Taylor-Airs equations,the prediction model of the dispersion coefficient in the advection-diffusion process in tortuous fractures was analyzed and established.The new LBM program was used to simulate and verify the effectiveness of the new dispersion equation.Then simulated the advection-diffusion process in the cleat network characterization model,and analyzed the influence of the aperture of butt cleat and face cleat,the tortuosity on the advection-diffusion behavior in the cleat network.It was found that the advection-diffusion behavior in the cleat network was mainly dominated by the face cleat which direction was same as macroscopic flow.This paper mainly studied the seepage characteristics and the advection-diffusion behavior of cleat networks so as to provide a theoretical basis for the future study on the migration of coal-bed methane or mass transport of complex medium such as cleat networks.更多还原