低渗煤层瓦斯非达西渗流特征研究
发布时间：2018-08-19 10:41
【摘要】：煤层瓦斯是威胁矿井安全生产的主要灾害之一,其抽采效率在很大程度上取决于渗流特性。长期的低渗透油气藏开发实践表明,流体在低渗多孔介质中的流动为带有启动压力梯度的低速非达西渗流。但是,现行瓦斯抽采技术大多遵循线性渗流理论,往往忽略了低渗煤层内存在的低速非线性渗流及扩散现象,导致抽采难易程度评价及抽采工艺选择出现偏差。针对不同煤体结构煤层,如何快速、准确地评价其抽采难易程度以及选择适宜的抽采工艺,以实现瓦斯高效抽采,是亟待解决的问题。而解决该问题的前提及关键,在于对瓦斯在不同煤体结构煤层内流动状态的把握。为此本文就低渗煤层瓦斯非达西渗流特征展开研究。基于煤样孔隙结构分析结果,实验探讨了启动压力梯度与渗透率的关系;采用启动压力梯度测试系统,以采自不同煤矿的具有不同煤体结构的煤样为对象,分别研究了围压、气体性质、含水率对启动压力梯度的影响。研究表明:(1)渗透率与启动压力梯度之间呈负指数关系;(2)不同破坏类型煤体之间启动压力梯度存在较大差异,表现为Ⅰ类煤和Ⅳ类煤的启动压力梯度最大。Ⅱ类煤的启动压力梯度最小。Ⅲ类煤的启动压力梯度介于中间;(3)对于每一类煤,围压越大启动压力梯度越大,同时围压较低时四类煤启动压力梯度值差异较大,围压较高时,四类煤启动压力梯度值逐渐接近;(4)对于Ⅰ类煤的每一个煤芯,三种气体渗流时启动压力梯度的关系为:氮气甲烷二氧化碳;(5)对于每一类煤,含水率在1%~7%范围内时,随着含水率增加,启动压力梯度逐渐增大。基于变形控制方程与气固耦合渗流方程,借助COMSOL-Multiphysics软件探讨了围压、不同气体、进气压力对启动压力梯度的影响,数值模拟结果表明:(1)在一定范围内随着围压增大,启动压力梯度逐渐增大。(2)不考虑吸附作用时,三种气体渗流时启动压力梯度的关系为:氮气甲烷二氧化碳。考虑吸附作用时,三种气体渗流时启动压力梯度的关系为:二氧化碳甲烷氮气。造成这种现象的原因是吸附作用影响了试件的应力敏感系数,导致试件的强度发生改变。(3)在试件参考线L1和参考点B上,进气压力越大,试件下部出气口流量越大,渗透性越强,启动压力梯度越小。基于GSI煤体分类体系,对采自沙曲煤矿的具有不同煤体结构的煤样进行了定量表征,探讨了GSI与启动压力梯度的关系;在此基础上,初步提出了基于启动压力梯度的低渗煤层瓦斯流态判识方法。研究表明:对于沙曲煤矿而言:当GSI=46.58时,λ=0,瓦斯流态为线性渗流;当GSI46.58时,λ=0.00189(46.58-GSI)1.49665,λ随GSI的减小而增大;当GSI46.58时,λ=0.00189(GSI-46.58)1.50559,λ随GSI的增大而增大;对于GSI≠46.58时,若Δp/L≥λ,瓦斯流态为低速非线性渗流;若Δp/Lλ,瓦斯流态为扩散。
[Abstract]:Coal seam gas is one of the main disasters threatening mine safety production, and its extraction efficiency depends on seepage characteristics to a great extent. The long term practice of developing low permeability reservoirs shows that the flow of fluid in low permeability porous media is low speed non Darcy seepage with starting pressure gradient. However, most of the current gas drainage techniques follow the linear seepage theory and often ignore the phenomenon of low speed nonlinear seepage and diffusion in low permeability coal seams, which leads to the deviation of the evaluation of drainage difficulty and the selection of extraction technology. It is an urgent problem how to quickly and accurately evaluate the difficulty and ease of drainage and how to select the appropriate extraction technology to realize the high efficiency of gas extraction in different coal structure coal seams. The premise and key to solve this problem is to grasp the flow state of gas in coal seam with different coal structure. Therefore, the characteristics of gas non Darcy seepage in low permeability coal seam are studied in this paper. Based on the results of pore structure analysis of coal samples, the relationship between starting pressure gradient and permeability is discussed experimentally, and the confining pressure of coal samples with different coal body structure is studied by using starting pressure gradient test system. The effect of gas properties and moisture content on the starting pressure gradient. The results show that: (1) there is a negative exponential relationship between permeability and starting pressure gradient, and (2) there are great differences in starting pressure gradient between different failure types of coal. The starting pressure gradient of type 鈪，
本文编号：2191423
[Abstract]:Coal seam gas is one of the main disasters threatening mine safety production, and its extraction efficiency depends on seepage characteristics to a great extent. The long term practice of developing low permeability reservoirs shows that the flow of fluid in low permeability porous media is low speed non Darcy seepage with starting pressure gradient. However, most of the current gas drainage techniques follow the linear seepage theory and often ignore the phenomenon of low speed nonlinear seepage and diffusion in low permeability coal seams, which leads to the deviation of the evaluation of drainage difficulty and the selection of extraction technology. It is an urgent problem how to quickly and accurately evaluate the difficulty and ease of drainage and how to select the appropriate extraction technology to realize the high efficiency of gas extraction in different coal structure coal seams. The premise and key to solve this problem is to grasp the flow state of gas in coal seam with different coal structure. Therefore, the characteristics of gas non Darcy seepage in low permeability coal seam are studied in this paper. Based on the results of pore structure analysis of coal samples, the relationship between starting pressure gradient and permeability is discussed experimentally, and the confining pressure of coal samples with different coal body structure is studied by using starting pressure gradient test system. The effect of gas properties and moisture content on the starting pressure gradient. The results show that: (1) there is a negative exponential relationship between permeability and starting pressure gradient, and (2) there are great differences in starting pressure gradient between different failure types of coal. The starting pressure gradient of type 鈪，
本文编号：2191423
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