Effect of Pore Pressure on Seepage Characteristics of Coal and Rock at Different Temperatures
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摘要: 在深部煤层瓦斯抽采过程中，地温较高且孔隙压力逐渐降低，而目前综合考虑温度和孔隙压力对煤岩渗透特性耦合作用的研究较少.利用自主研发的出口端压力可调的三轴渗流装置，以贵州矿区原煤试件为研究对象，进行不同温度下改变孔隙压力的渗流试验，并建立了考虑温度的渗透率匹配模型.研究表明，煤岩渗透率随孔隙压力增大按指数函数减小；煤岩渗透率随压差的增大而减小，随温度的升高而降低，在不同的温度状态下，渗透率的下降速率和变化幅度有所不同.在模拟瓦斯开发的物理试验中，压差应尽量小，减少其误差，为建立不同边界条件的渗透率模型提供帮助；随温度的升高，温度突变系数呈增大的趋势；随孔隙压力的增大，温度突变系数呈减小的趋势.温度突变系数在整个阶段不为常数，且割理压缩系数可变，这两个特征更能真实地匹配模型，反映瓦斯的开发过程.Abstract: The ground temperature is higher and the pore pressure gradually decreases in the process of gas extraction in deep coal seams, however there are few studies on the coupling effect of temperature and pore pressure on the permeability of coal. Seepage experiments on the raw coal from Guizhou mining area are carried out by the self-developed triaxial seepage equipment with an adjustable outlet pressure to study the influence of pore pressure and temperature on the permeability. A permeability matching model with temperature effect is also developed in this study. An exponential relationship between the permeability and pore pressure is found and presented. The results show that the permeability decreases with increasing pore pressure, and it decreases as the differential pressure increases. Also, the permeability of coal seam decreases with increased temperature, and the decreasing rate and magnitude of permeability are different under different temperatures. Therefore, the differential pressure should be as small as possible to reduce the error and help develop the permeability model with different boundary conditions in the physical simulation experiments of coalbed methane (CBM) extraction. As the temperature increases, the mutation coefficient of temperature increases. While, the mutation coefficient of temperature decreases as pore pressure increases. It has been found these two characteristics that the mutation coefficient of temperature is not a constant in the whole stage and the realistic model matching with a variable cleat compressibility coefficient can reflect the development process of CBM.
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Key words:
- coal and rock /
- permeability /
- pore pressure /
- effective stress /
- temperature /
- differential pressure
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图 2 出口端正压的三轴渗流装置原理
Fig. 2. The sketch of traixial seepage device with positive pressure at outlet
图 4 不同温度状态下煤岩渗透率与孔隙压力变化关系
a.压差Δp=0.1 MPa；b.压差Δp=0.3 MPa；c.压差Δp=0.5 MPa
Fig. 4. Relationship between permeability and pore pressure of coal under different temperature
图 5 不同压差状态下煤岩渗透率与孔隙压力变化关系
Fig. 5. Variation relationship between pore pressure and permeability of coal under different pressure difference
a.T=30 ℃; b.T=50 ℃; c.T=70 ℃
图 6 不同温度状态下温度突变系数与孔隙压力变化关系
Fig. 6. The relationship between temperature mutation coefficient and pore pressure at different temperatures
a.Δp=0.1 MPa; b.Δp=0.3 MPa; c.Δp=0.5 MPa
表 1 林华9号煤层原煤基本力学参数
Table 1. Basic mechanical parameters of raw coal in No.9 coal seam of Lin Hua
围压(MPa) 与层理面关系 σc(MPa) E(MPa) ν 3.0 ⊥ 38.28 1 905.04 0.125 9 // 39.55 2 114.45 0.114 5 
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表 2 煤岩数据匹配的模型参数
Table 2. Model parameters of coal about data matching
△p(MPa) T(℃) cf0(MPa-1) a(MPa-1) 0.1 30 -0.006 4 4.002 0 50 -0.004 2 3.994 2 70 -0.006 4 4.004 3 0.3 30 -0.006 2 4.002 1 50 -0.006 1 3.995 1 70 -0.007 5 4.023 5 0.5 30 -0.006 8 4.018 8 50 -0.008 4 3.995 1 70 -0.006 3 4.399 7
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表 3 不同温度条件下的弹性模量
Table 3. Values of elastic modulus under different temperature conditions
温度(℃) 25 30 50 70 弹性模量(MPa) 181.46 178.88 168.72 160.00
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