Cleat network dominates the migration of coalbed methane in coal reservoirs,therefore,to identify its permeability is vital for quantitative estimate productivity of coal reservoirs.Compared with experimental test, the numerical method has such features as high repeatability and not being affected by the environment,test precision and human factors.It has become an effective method for description of the reservoir microstructure and excavation of fluid migration laws.In this paper,combined with self-affine property of surface geometries and spatial configuration of cleats,an algorithm representing cleat networks is developed based on the Weier-strass-Mandelbrot ( W-M) function The fluid flow in cleat network was simulated at pore scale by Lattice Boltz-mann method ( LBM) and its permeability was calculated correspondingly.The results show that without butt cleats,the permeability of cleat networks follows the triple-effect fractal fracture-permeability model.After butt cleats being introduced,the Hurst exponent,the aperture of butt cleats and face cleats all affect the permeabili-ty of reservoir.The permeability increases with the increases of Hurst exponent and the aperture of butt cleats. However,the permeability of coal reservoir is dominated by spatial configuration and surface geometries of face cleats when the aperture of butt cleats is smaller than that of face cleats.%煤储层中割理网络主宰着煤层气的运移,查明其渗透性能对储层产能的定量评估具有重要意义.相对试验测试而言,数值方法不受环境、测试精度以及人为因素影响且重复性高,现已成为储层微观结构精细描述以及流体运移规律探讨的有效手段.为此,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,提出了一种基于Weierstrass-Mandelbrot( W-M)函数的割理网络构建方法.在此基础上,采用格子波尔兹曼方法( LBM) ,于孔隙尺度再现了割理网络中流体运移过程并定量分析了其渗透性能.结果表明:无端割理情况下储层渗透率满足三重效应分形裂-渗关系;引入端割理后,Hurst指数、面割理和端割理开度共同影响储层渗透性能,具体表现为渗透率随Hurst指数及割理开度的增加而增大.但当端割理开度小于面割理开度时,煤储层渗透率主要受控于面割理的空间构型及其复合几何形貌.
展开▼
