The evolution law of pore characteristics and pore bulk modulus for overpressured coal-bearing formation in Yuwang Minefield
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摘要: 煤及煤层气开发中的异常高压现象会对资源开发带来危险，从而威胁到人员和财产的安全。本文选取云南雨汪煤矿的6个煤样，联合CT扫描技术和低温液氮吸附实验方法，分析测试得到超压煤样孔隙半径、孔喉半径、孔容-孔径微分分布的孔隙特征参数；基于Gassmann模型的机理，推导了不同围压条件下的干燥及饱和超压煤样孔隙体积模量。结果表明：雨汪煤矿超压地层煤样孔隙率偏大，可达到10 %，孔隙形状主要为球形和柱体，孔隙大小以介孔为主。干燥煤样的纵横波速度随围压的施加呈非线性增加。饱和煤样孔隙体积模量随围压的增加而变大，围压相同时，孔隙体积模量在水饱和度大于90 % 时迅速增加。Abstract: The abnormal high pressure in coal and coalbed methane exploitation will bring danger to exploitation, thus threatening the safety of personnel and property.Six coal samples collected from Yuwang colliery in Yunnan province were analyzed by CT scanning and low-temperature liquid nitrogen adsorption experiment.Analysis reveals the characteristic parameters of pore radius, pore throat radius and pore volume-pore diameter differential distribution of overpressured coal samples.Meanwhile, the pore bulk modulus of overpressured coal samples under different confining pressures is derived based on the mechanism of the Gassmann model.The results show that the porosity of Yuwang colliery overpressured stratum can reach 10 %, and the mesoporous pore shape is mainly spherical and cylindrical.The shear wave velocity of dry coal samples increases nonlinearly with confining pressure.The pore bulk modulus of saturated coal sample remains proportional to confining pressure, but increases rapidly when the water saturation exceeds 90 % with the same confining pressure.
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Key words:
- coal /
- abnormal high pressure /
- porosity /
- pore feature /
- pore volume modulus
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图 1 压力与埋藏深度关系示意图
Figure 1. Schematic diagram of the relationship between pressure and burial depth
图 6 超压煤样等温吸脱附曲线
Figure 6. Isothermal adsorption and desorption curves of overpressured coal samples
图 7 孔容-孔径微分分布曲线
Figure 7. Differential distribution curve of pore volume-pore diameter
图 9 不同围压下煤样的纵横波速度曲线
Figure 9. P-wave and S-wave velocity curves of coal samples under different confining pressures
图 10 干岩石孔隙体积模量随围压变化曲线
Figure 10. Variation curve of dry rock pore bulk modulus with confining pressure
表 1 地层压力分类标准
Table 1. Formation pressure classification standard
编号 压力分类 压力梯度/(kPa·m-1) 压力系数 1 负压 < 9.6 < 0.96 2 常压 9.6~15.0 0.96~1.50 3 超压 15.0~17.3 1.50~1.73 4 强超压 >17.3 >1.73 
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表 2 超压煤岩孔隙率测试结果
Table 2. Overpressure coal rock porosity test result data
编号 S1-2 S1-3 S2-1 S3-1 S4-1 S4-2 平均 孔隙率/% 10.55 16.11 7.27 9.18 10.09 10.22 10.57
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表 3 组成超压煤岩矿物质量分数
Table 3. Composition of overpressure coal and rock mineral mass fraction
% 煤样编号 铵云母 高岭石 锐钛矿 铁白云石 S1-2 48.5 48.2 0.9 2.4 S1-3 46.3 50.6 1.7 1.4 S2-1 49.7 46.9 0.8 2.6 S3-1 40.7 49.5 0.7 9.1 S4-1 45.8 46.5 5.4 2.3 S4-2 44.1 52.7 1.3 1.9 均值 45.85 49.07 1.8 3.28
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表 4 超压煤岩中的矿物密度和体积模量
Table 4. Density and bulk modulus of minerals in overpressure coal and rock
组成矿物 铵云母 高岭石 锐钛矿 铁白云石 体积模量/GPa 58.5 1.5 217.1 94.9 密度/(g·cm-3) 2.7 1.6 4.3 2.9
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表 5 组成超压煤岩矿物体积分数
Table 5. The volume fraction of minerals that make up the overpressure coal rock
矿物成分 铵云母 高岭石 锐钛矿 铁白云石 体积分数 0.342 0.627 0.008 0.023
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表 6 煤样工业成分分析结果
Table 6. Industrial composition analysis results of coal samples
% 样品编号 灰分 有机质 S1-2 13.3 86.7 S1-3 21.67 78.33 S2-1 14.28 85.72 S3-1 26.75 73.25 S4-1 15.06 84.94 S4-2 20.05 79.95 均值 18.52 81.48
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表 7 不同围压条件下Kdry值
Table 7. Kdry value under different confining pressure conditions
GPa 围压/MPa 0 5 10 15 20 S1-2 3.539 3.897 4.092 4.281 4.342 S2-1 3.863 4.178 4.379 4.556 4.631 S4-1 3.731 3.984 4.223 4.371 4.446 S4-2 3.597 3.931 4.119 4.311 4.401
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表 8 不同围压条件下的干岩石孔隙体积模量Kφ值
Table 8. Dry rock pore bulk modulus Kφ value under different confining pressure conditions
GPa 围压/MPa 0 5 10 15 20 S1-2 0.885 1.131 1.301 1.500 1.420 S2-1 1.104 1.386 1.621 1.875 2.031 S4-1 1.008 1.203 1.434 1.611 1.652 S4-2 0.920 1.219 1.327 1.536 1.473
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表 9 样品Ksat随含水饱和度的变化
Table 9. Change of Ksat of sample with water saturation
GPa 样品编号 含水饱和度/% 围压/MPa 样品编号 含水饱和度/% 围压/MPa 0 5 10 15 20 0 5 10 15 20 S1-2 0 3.573 3.922 4.113 4.298 4.358 S4-1 0 3.760 4.007 4.241 4.387 4.460 10 3.576 3.924 4.115 4.300 4.360 10 3.763 4.009 4.243 4.388 4.461 20 3.581 3.928 4.118 4.302 4.362 20 3.767 4.013 4.245 4.391 4.463 30 3.586 3.932 4.121 4.305 4.364 30 3.771 4.016 4.248 4.393 4.465 40 3.594 3.938 4.126 4.309 4.368 40 3.778 4.022 4.252 4.397 4.469 50 3.605 3.946 4.133 4.315 4.374 50 3.788 4.030 4.259 4.402 4.474 60 3.620 3.957 4.142 4.322 4.381 60 3.800 4.040 4.267 4.409 4.480 70 3.646 3.976 4.159 4.336 4.393 70 3.823 4.057 4.281 4.421 4.491 80 3.696 4.014 4.190 4.362 4.418 80 3.866 4.092 4.309 4.445 4.513 90 3.827 4.114 4.275 4.432 4.484 90 3.980 4.185 4.383 4.509 4.572 100 5.398 5.429 5.450 5.472 5.480 100 5.414 5.438 5.465 5.484 5.494 S2-1 0 3.889 4.197 4.395 4.568 4.642 S4-2 0 3.629 3.955 4.139 4.328 4.416 10 3.891 4.199 4.396 4.570 4.643 10 3.632 3.958 4.141 4.329 4.417 20 3.895 4.201 4.398 4.571 4.645 20 3.637 3.961 4.144 4.332 4.420 30 3.899 4.204 4.401 4.573 4.646 30 3.641 3.965 4.147 4.334 4.422 40 3.905 4.209 4.405 4.576 4.649 40 3.649 3.971 4.152 4.338 4.426 50 3.914 4.215 4.410 4.581 4.653 50 3.660 3.979 4.159 4.344 4.431 60 3.925 4.224 4.417 4.586 4.658 60 3.674 3.990 4.168 4.351 4.437 70 3.945 4.239 4.429 4.596 4.667 70 3.699 4.008 4.184 4.364 4.449 80 3.984 4.268 4.452 4.615 4.684 80 3.747 4.045 4.215 4.390 4.472 90 4.087 4.346 4.516 4.667 4.732 90 3.873 4.142 4.297 4.458 4.534 100 5.426 5.460 5.485 5.511 5.523 100 5.402 5.433 5.453 5.476 5.488
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