粗糙割理中煤层气运移规律及排采井间的干扰方式

发布时间：2018-02-04 13:15

本文关键词： 煤储层格子Boltzmann方法非匹配裂隙分形裂-渗关系　出处：《河南理工大学》2015年硕士论文　论文类型：学位论文

【摘要】：鉴于当前全国范围内频繁的瓦斯爆炸事故、严重的环境污染等重大问题,作为一种新型洁净能源,煤层气(CBM)的开发利用就成为了一项重大而又意义深远的工作。但因煤岩介质是一种二元孔隙结构,其中割理/裂隙端面几何及基质孔隙结构均异常复杂,表现出分形特征。而割理/裂隙网络作为煤层气运移的主要通道,其几何形貌对流体的运移的影响显著。因此探明粗糙割理中流体的运移控制机理是实现煤层气开采潜能科学评估及开采工艺优化设计的基本前提,具有重要的理论意义及实用价值。然而,现场数据、常规的实验测试手段及经验关系式往往是基于宏观层面的统计结果,内蕴平稳、连续假设且受精度和环境的影响明显,不利于煤层气运移规律的发掘。因此要从机理层面理解煤层气的运移过程,必须从孔隙尺度出发,在探明微观几何的控制作用和方式后,才能科学地推演复杂孔隙结构的输运属性。近来,随着计算机技术的快速发展及分形理论的日趋成熟,两者耦合的分析模式已成为当前探索煤层气运移规律的重要手段和有效方法。结合煤层气开采潜能评估这一难点问题,本文采用基于动理论的格子Boltzmann技术体系,于孔隙尺度下着重研究了粗糙割理中煤层气运移规律。具体包括:(1)依据割理端面几何的自仿射分形属性,系统分析了割理粗糙复合形貌空间下煤层气的运移规律,并依据其作用方式及强度,提出了三重效应的裂-渗关系模型,即局部粗糙效应、流体内部作用以及流-固间的效用,对应的物性参数分别为局部粗糙度因子、水文弯曲度及大尺度下裂隙端面曲折率。其中水文弯曲度及端面曲折率表现出尺度不变特征,而局部粗糙度因子具有长程平稳的特点。基于以上研究给出了单粗糙割理中煤层气运移的分形裂-渗方程。(2)结合割理端面自仿射分形属性及端面间的长程相关而短程非匹配的事实,提出了一种构建自然割理的算法。在此基础上,系统分析了非匹配自仿射粗糙割理复合形貌空间下煤层气运移规律,具体特征如下:沿割理走向,剖面流速的分布为偏正态分布而非泊肃叶方程所描述的抛物线模型;自仿射非匹配割理空间中开度分布为一周期性的波状起伏分布,该分布特征会增加割理流的水文弯曲度,进而削弱割理空间的渗透性能;非匹配程度越高,曲折流效应越明显,并呈单调递增趋势。(3)依据割理网络的空间构型,于孔隙尺度下模拟了基于垂直井的煤层气排采过程,并分析了排采井间的干扰模式,结果表明:井间距离及储层压力均对煤层气的排采有一定的影响,趋势为:井间距离同井口位置处煤层气的流速之间呈单调递增趋势,同时针对当前实验模型来说,当井间距离为7.65时,排采井之间的相互影响最小;储层压力同流速之间也呈单调递增趋势。因此,适当增大井间距离及储层压力有利于煤层气的排采。
[Abstract]:In view of the current frequent gas explosion accidents, serious environmental pollution and other major problems, as a new clean energy. The exploitation and utilization of CBM (coalbed methane) has become an important and far-reaching work, but the coal-rock medium is a binary pore structure. The geometry of cleat / fissure end surface and pore structure of matrix are all very complex, showing fractal characteristics, and cleat / fissure network is the main channel of coalbed methane migration. The geometric morphology has a significant effect on the fluid migration. Therefore, it is the basic premise of realizing the scientific evaluation of coal-bed methane exploitation potential and the optimization design of mining process to find out the control mechanism of fluid migration in rough cleat. It has important theoretical significance and practical value. However, the field data, conventional experimental test methods and empirical relations are often based on the statistical results at the macro level, and the implication is stable. The continuity hypothesis is obviously affected by precision and environment, which is not conducive to the discovery of the migration law of CBM. Therefore, to understand the migration process of CBM from the mechanism level, we must proceed from the pore scale. The transport properties of complex pore structures can be deduced scientifically only after the control function and mode of microscopic geometry are proved. Recently, with the rapid development of computer technology and the maturation of fractal theory. The coupled analysis model has become an important means and an effective method to explore the migration law of coalbed methane (CBM). In this paper, the lattice Boltzmann technology system based on dynamic theory is adopted. The migration law of coalbed gas in rough cleavage is studied at pore scale, including: 1) according to the self-affine fractal properties of the surface geometry of the cleat. The migration law of coalbed methane in the cleat and rough composite morphology space is analyzed systematically. According to its action mode and strength, the cleft permeability relation model of triple effect, namely local roughness effect, is put forward. The local roughness factor is the corresponding physical parameters of the internal interaction of the fluid and the effectiveness of the fluid-solid. The hydrological bending degree and the fracture end surface zigzag rate at large scale, in which the hydrological bending degree and the end surface zigzag rate show the invariant characteristics of the scale. The local roughness factor is stable in long range. Based on the above research, the fractal fracture-permeability equation of coalbed methane migration in single rough cleat is given. Combining the self-affine fractal properties of cleats and the facts of long range correlation and short range mismatch between facets. An algorithm for constructing natural cleats is proposed. On this basis, the migration law of coalbed gas in the composite topography space of mismatched self-affine rough cleats is systematically analyzed. The specific characteristics are as follows: along the cleat direction. The profile velocity distribution is a partial normal distribution rather than a parabola model described by the Poisson equation. The opening distribution in the self-affine mismatched cleat space is a periodic wave-like undulating distribution, which will increase the hydrological curvature of the cleat flow and weaken the permeability of the cleat space. The higher the mismatch degree, the more obvious the zigzag flow effect, and the monotone increasing trend. (3) according to the spatial configuration of the cleat network, the coal bed methane production process based on vertical well is simulated in pore scale. The interference mode between production wells is analyzed. The results show that the distance between wells and reservoir pressure have some influence on the coal bed methane production. The trend is as follows: the velocity of coalbed methane at the same well head position is increasing monotonously. At the same time, according to the current experimental model, when the distance between wells is 7.65, the interaction between the drainage and production wells is the least. There is also a monotone increasing trend between reservoir pressure and flow velocity. Therefore, proper increase of inter-well distance and reservoir pressure is beneficial to the expulsion and production of coalbed methane.
【学位授予单位】：河南理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TD712

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