摘要
错综复杂的裂隙网络为煤层气渗流提供了主要通道,其结构特征显著影响着煤层气产能。针对现有煤层气渗流模型未考虑裂隙网络连通性这一不足,基于拓扑图论分析了煤岩裂隙网络的连通性,推导了裂隙分支长度的幂律关系表达式。结合分形几何,在经典立方定律的基础上构建了考虑裂隙网络结构特征的渗透率模型,模型表明裂隙网络渗透率是分形维数、裂隙率、迂曲度分形维数、比例系数、连通性、最大裂隙分支长度、方位角、倾角以及特征长度的函数。开展了真三轴应力条件下煤岩裂隙网络渗流试验,分析了真三轴应力条件下煤岩裂隙网络渗透率演化规律;试验结果表明:随着主应力σ_(1)、σ_(2)和σ_(3)的升高,煤岩中的裂隙逐渐被压缩,气体的渗流通道变窄,裂隙网络渗透率随着主应力σ_(1)、σ_(2)和σ_(3)的升高均呈现出了负指数降低的趋势。从试验规律和结果出发,将构建的煤岩裂隙网络分形渗透率模型和S&D模型(Shi-Durucan)相结合,建立了真三轴应力条件下煤岩裂隙网络渗透率计算模型,并通过试验数据验证了模型的有效性,获得的渗透率变化趋势与加载3个主应力的过程相吻合,能够体现出三向应力的变化对渗透率的影响趋势,相比S&D模型更能反映煤岩裂隙网络渗透率的各向异性特征。
The complex fracture network provides the main channel for coalbed methane seepage,and its structural characteristics significantly affect the productivity of coalbed methane.In view of the lack of fracture network connectivity in existing coalbed methane seepage models,based on topological graph theory,the connectivity characteristics of fracture network were analyzed,and the expression of power law relation of fracture branch length was derived.Combined with fractal geometry,a permeability model considering fracture network structure characteristics was established on the basis of classical cubic law.The model shows that the permeability of fracture network is a function of fractal dimension,porosity,tortuosity fractal dimension,scale coefficient,connectivity,maximum fracture branch length,azimuth angle,dip angle and feature length.The permeability evolution of fracture network under true triaxial stress was analyzed.The results show that with the increase of the principal stressesσ_(1),σ_(2) andσ_(3),the fractures in coal are gradually compressed and the gas seepage channel becomes narrow. The permeability of fracture network shows a negative exponential decrease with the in-crease of the principal stresses σ_(1), σ_(2) and σ_(3). Based on the experimental rules and results, the fracture network fractal per-meability model and S&D model (Shi-Durucan) were combined to establish the fracture network permeability calculation model under true triaxial stress. The effectiveness of the model was verified by the experimental data. The obtained per-meability variation trend is consistent with the process of loading the three principal stresses, which can reflect the influ-ence trend of the change of three-way stress on the permeability. Compared with the S&D model, it can better reflect the anisotropy characteristics of the permeability of the fracture network.
作者
罗亚飞
朱永建
黄飞
夏彬伟
LUO Yafei;ZHU Yongjian;HUANG Fei;XIA Binwei(Work Safety Key Lab on Prevention and Control of Gas and Roof Disasters for Southern Coal Mines,Hunan University of Science and Technology,Xiangtan411201,China;School of Resource,Environment and Safety Engineering,Hunan University of Science and Technology,Xiangtan411201,China;State Key Laboratory of Coal Mine Disaster Dynamics and Control,Chongqing University,Chongqing 400044,China)
出处
《煤炭学报》
EI
CAS
CSCD
北大核心
2024年第8期3561-3570,共10页
Journal of China Coal Society
基金
国家自然科学基金资助项目(52274198,52304214)
湖南省自然科学基金青年基金资助项目(2023JJ40287)。
关键词
裂隙网络
渗透率
拓扑连通性
真三轴
煤层气
fracture network
permeability
topological connectivity
true three-dimensional
coal bed methane
