瓦斯压力和应力对裂隙影响下的渗透率模型研究
Study on permeability model under the influence of gas pressure and stress on fracture
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摘要: 煤层的渗透率演化对研究矿井瓦斯抽采、煤层气开采及钻孔优化布置起到至关重要的作用。为了研究瓦斯压力-裂隙及应力-裂隙耦合作用对煤岩渗透率演化模型的影响，基于应变，探讨了瓦斯压力和应力作用对煤体裂隙变形和渗透率的影响，构建了基于瓦斯压力-裂隙及应力-裂隙耦合的煤体渗透率理论模型，并结合前人的试验数据，对建立的基于瓦斯压力-裂隙及应力-裂隙耦合的煤体渗透率模型进行了对比验证。研究结果表明：①将煤体的结构单元体简化为立方体模型，分别分析了瓦斯压力引起的裂隙变形与煤体基质吸附变形引起的裂隙变形对煤体渗透率的影响；基于煤岩裂隙宽度与渗透率的关系，推导了瓦斯压力-裂隙耦合作用下煤体的渗透率模型。②侧向应力对裂隙变形的影响与煤体吸附所引起的内膨胀变形相似，均通过改变煤体骨架向裂隙内部膨胀来影响煤体裂隙的变形；通过试验数据验证了侧向应力和法向应力对煤体渗透率的影响机理相同，构建了三向应力-裂隙耦合作用下煤体的渗透率模型。③结合前人的试验数据，进行了全局优化非线性拟合，与基于有效应力的模型相比，所构建的模型与试验数据吻合度较好，验证了所建立模型的可靠性，并发现裂隙对法向应力的敏感性远大于侧向应力。Abstract: The permeability evolution of coal seam plays an important role in the study of mine gas drainage, coalbed methane extraction and drilling optimization layout. In order to study the influence of gas-fracture and stress-fracture coupling on the evolution model of coal and rock permeability, this paper discussed the influence of gas and stress on coal fracture deformation and permeability based on the perspective of strain.The theoretical models of coal permeability based on gas-fracture and stress-fracture coupling were established. Combined with the previous experimental data, the coal permeability models based on gas-fracture and stress-fracture coupling were compared and verified. The results of the study are as follows: ①The structural unit of coal body is simplified as a cube model, and the influence of fracture deformation caused by gas pressure and coal matrix adsorption deformation on coal permeability is analyzed. Based on the relationship between coal fracture opening and permeability, the permeability model of coal under gas-fracture coupling is deduced. ②The influence of lateral stress on fracture deformation is similar to the internal expansion deformation caused by coal adsorption, both of which affect the deformation of coal cracks by changing the coal skeleton expansion into the fracture; the experimental data verify that the influence mechanism of lateral stress and normal stress on coal permeability is the same, and the coal permeability model under three-dimensional stress-fracture coupling is constructed. ③Combined with the previous experimental data, the global optimization of nonlinear fitting is performed. Compared with the model based on effective stress, the model constructed in this paper is in good agreement with the experimental data, which verifies the reliability of the model established in this paper. It is found that the sensitivity of fractures to normal stress is much greater than that of lateral stress.
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Keywords:
- coal and rock /
- gas /
- three dimensional stress /
- fracture /
- permeability model
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