Experimental study about the gas slip flow in Longmaxi shales from the southern Sichuan Basin
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摘要: 针对页岩储层气体滑脱效应特征及其影响机制不清问题，选取四川盆地长宁地区志留系龙马溪组页岩样品，开展了低温氮气吸附孔隙结构表征实验，并利用非稳态脉冲衰竭方法测量了不同围压下氦气、氮气在页岩岩心上的气体渗透率，分析了平均孔隙压力、气体类型、围压对滑脱效应的影响，建立了滑脱因子的预测关系式。结果表明：压力低于2.5 MPa时，页岩气体滑脱效应不能忽略。由于“分子筛效应”的影响，页岩克氏渗透率与测试流体介质类型有关，以氦气为流动介质测试得到的克氏渗透率大于以氮气为流动介质的测试结果。滑脱效应与气体类型有关，龙马溪组页岩的氦气滑脱因子约为氮气滑脱因子的1.7倍。利用滑脱因子计算得到围压为10~40 MPa时，氦气在页岩上的有效渗流孔径为113~166 nm，氮气的有效渗流孔径为66~99 nm，均远大于液氮吸附法测试的平均孔径。建立了龙马溪组页岩气体滑脱因子与克氏渗透率的幂函数关系，为页岩气流动模型的建立提供了基础。Abstract: In order to clarify the gas slip flow effect and its influencing mechanism of shale gas reservoirs, low-temperature nitrogen adsorption measurements were performed on the Silurian Longmaxi Formation shales from the Sichuan Basin. Pore structure characteristics of shales were described based on nitrogen adsorption-desorption isotherms. Non-steady state gas flow experiments on gas shales were carried out to obtain the apparent permeability coefficients of helium and nitrogen. The effects of pore pressure, gas types, confining pressure on gas slippage were discussed. Results show that gas slippage cannot be neglected when the pore pressure is less than 2.5 MPa. The Klinkenberg corrected permeability coefficients of shales are gas-dependent due to the "molecular sieving effect". The Klinkenberg corrected permeability of helium on shales is larger than that of using nitrogen. Gas slippage factors are also related to gas types. Helium slippage factor of shales is about 1.7 times of nitrogen slippage factor. The effective transport pore diameter of helium on shales with the confining pressure being 10-40 MPa ranges from 113 to 166 nm, while that of nitrogen is between 66 and 99 nm. These values are significantly larger than that derived from low-temperature nitrogen adsorption. A power function is utilized to fit the gas slippage factor and permeability of shales and can be used to predict gas flow in shales.
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Key words:
- shale /
- slippage effect /
- permeability /
- transport pore diameter /
- Sichuan Basin
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图 1 龙马溪组页岩低温液氮吸附-解吸等温线(a)及BJH氮气吸附法孔径分布曲线(b)
Figure 1. Low temperature nitrogen adsorption-desorption isotherms of the Longmaxi Formation shale(a), and pore size distribution of the Longmaxi Formation shale using BJH method (b)
图 2 非稳态脉冲渗透率测试装置图
Figure 2. Schematic representation of the non-steady pulse decay permeability setup
图 3 龙马溪组页岩非稳态气测渗透率示意图
a.上、下游压力变化曲线；b.上、下游压差随时间的半对数关系
Figure 3. Sketch of experimental non-steady gas permeability measurements on the Longmaxi Formation shale
图 4 不同围压(Pc)下龙马溪组页岩平均孔隙压力倒数与氦气渗透率(a)、氮气渗透率(b)的关系
Figure 4. Relationship between the reciprocal average pore pressure and helium apparent permeability (a) and nitrogen apparent permeability (b) of the Longmaxi Formation shale at different confining pressures
图 5 不同孔隙压力下滑脱效应对气测渗透率的影响(围压30 MPa)
Figure 5. Function of slip effect on gas permeability at different pore pressures(confining pressure 30 MPa)
图 6 龙马溪组页岩氦气和氮气有效渗流孔径随围压的变化
Figure 6. Function of equivalent seepage pore diameter of helium and nitrogen on the Longmaxi Formation shale with confining pressures
图 7 不同围压下龙马溪组页岩气体克氏渗透率与滑脱因子的幂函数关系
Figure 7. Power function between Klinkenberg-corrected permeability and slip factors of the Longmaxi Formation shale at different confining pressures
表 1 龙马溪组页岩氦气和氮气测试的克氏渗透率、滑脱因子和等效渗流孔径
Table 1. Klinkenberg-corrected permeability of helium and nitrogen, slip factors and equivalent seepage pore diameter
围压
Pc/MPa氦气 氮气 克氏渗透率/
10-6 μm2滑脱因子/
MPa渗流孔径①/
nm克氏渗透率/
10-6 μm2滑脱因子/
MPa渗流孔径①/
nm10 0.40 0.43 166 0.31 0.24 99 20 0.29 0.50 141 0.25 0.29 83 30 0.23 0.56 127 0.22 0.33 74 40 0.20 0.63 113 0.19 0.37 66 注：①为等效渗流孔径，是根据滑脱因子的表达式(3)转换得到 
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