超临界CO2-H2O流体对煤渗流孔隙结构的影响
Influence of supercritical CO2-H2O fluid on seepage pore structure of coals
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摘要: 深部煤层封存CO2过程中超临界CO2（SCCO2）对含水煤层渗流孔隙结构的改变很大程度上决定了CH4的采收率；为此，基于SCCO2地球化学反应装置，模拟了温度45 ℃、压力12 MPa下含水比例较低的SCCO2-H2O混合流体（质量比SCCO2∶H2O =10∶1）与不同煤阶煤（长焰煤、气煤和无烟煤）的相互作用；通过压汞法研究了煤渗流孔隙对SCCO2-H2O的响应，采用热力学分形模型探讨了SCCO2-H2O对渗流孔隙非均质性的影响。结果表明：SCCO2-H2O作用增加了所有煤样的孔隙度和孔体积，造成渗透率增加，但不同煤阶煤的渗流孔隙对SCCO2-H2O的响应表现出差异性；SCCO2-H2O作用后，长焰煤渗流孔体积显著增加，气煤中孔含量明显增大，无烟煤中-大孔体积略微升高；煤样渗流孔体积的增加可归因于矿物的化学反应和溶解迁移、水分的散失和吸附溶胀，其中矿物含量及其分布很大程度上决定了流体作用后不同煤阶煤渗流孔隙结构的变化特征；SCCO2-H2O作用降低了渗流孔隙的非均质性，造成孔隙结构趋于简单，孔隙连通性增强，渗透性提升。Abstract: In the process of CO2 storage in deep coal seam, the change of seepage pore structure in water-bearing coal seam by supercritical CO2 （SCCO2） greatly determines the recovery of CH4. Thus, the interaction of SCCO2-H2O mixture fluid with low water rate （mass ratio of SCCO2∶H2O =10∶1） with three rank coals （long flame coal, gas coal and anthracite） was simulated on a SCCO2 geo-reaction system under conditions of temperature of 45 ℃ and pressure of 12 MPa. Mercury intrusion method was used to address the response of seepage pore distribution to SCCO2-H2O exposure, and the influence of SCCO2-H2O on seepage pore heterogeneity of coal samples was discussed based on thermodynamic fractal model. The results show that SCCO2-H2O exposure causes an increase in porosity and pore volume of all coal samples. As a result, the permeability of coals increases. Nevertheless, the response of seepage pores to SCCO2-H2O varies with coal rank. After SCCO2-H2O exposure, the seepage pore volume of long flame coal shows a remarkable increase, the meso-porosity of gas coal rapidly increases, while slight increase in macropore and mesopore is found for anthracite. The increase in seepage pore volume of coal samples can be attributed to the chemical reaction, dissolution and mobilization of mineral matters, water loss, and sorption swelling. The content and distribution of mineral matters greatly determine the change in seepage pore structure of various rank coals. SCCO2-H2O interaction degrades the seepage pore heterogeneity of coal samples and thus smoothen pore structure, improve pore connectivity and increase permeability.
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Keywords:
- coalbed methane /
- supercritical CO2 /
- mercury intrusion method /
- pore structure /
- seepage pore
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