Comparison of the impact of moisture on methane adsorption and nanoporosity for over mature shales and their kerogens
Comparison of the impact of moisture on methane adsorption and nanoporosity for over mature shales and their kerogens
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DOI：
10.1016/j.coal.2021.103705
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发表时间：
2021-02-13
影响因子：
5.6
通讯作者：
Snape, Colin E.
中科院分区：
文献类型：
--
作者：
Li, Wei;Stevens, Lee A.;Snape, Colin E.
在储层条件下，页岩中的水分对气体吸附和纳米孔隙度有不利影响，也可能影响干酪根对甲烷吸附能力的贡献。以四川盆地南部五峰组—龙马溪组两组过成熟页岩为研究对象，采用高压甲烷吸附、低压氮（N-2）和二氧化碳（CO2）吸附等方法，在干燥条件下、95%相对湿度条件下对脱矿分离出的页岩干酪根进行了研究。干酪根浓缩物占68？97%和50% ？干燥和95% rh时，页岩的甲烷吸附量分别为64%。孤立干酪根对甲烷的吸附量大于页岩有机质，因为其吸附等温线较浅，表明页岩中没有明显的大微孔和小介孔。在95% R.H.时，干酪根和页岩的甲烷吸附能力降低了46-72%，而在95% R.H.时，干酪根的表面积和孔隙体积分别减少了81%和48-59%，页岩的表面积和孔隙体积分别减少了98-99%。水可以阻塞大多数小于1.3 nm的微孔，减少了微孔体积，阻塞了连接较大孔隙的微孔颈，大大减少了可用于气体输送的孔隙。与甲烷吸附能力相比，SA和孔隙体积的比例损失更大，这可能是由于低压N-2分析中-196℃结冰所致。如果不考虑游离甲烷和吸附甲烷的水分，则将总气态（GIP）高估了36？45%为页岩气。
Moisture in shales under reservoir conditions adversely affects gas adsorption and nanoporosity and is also likely to impact on the contribution that kerogen makes to the methane adsorption capacity. To investigate these phenomena, two over mature shales from the Wufeng-Longmaxi Formation, south of the Sichuan basin, and their kerogens isolated by demineralisation were investigated dry and at 95% relative humidity (R.H.) by high-pressure methane adsorption, and low-pressure nitrogen (N-2) and carbon dioxide (CO2) sorption. The kerogen concentrates account for 68?97% and 50?64% of the methane adsorption capacities for the shales dry and at 95% R.H. respectively. However, the isolated kerogens could adsorb more methane than the organic matter in the shales because their shallower adsorption isotherms indicate large micropores and small mesopores not evident for the shales. Methane adsorption capacities of the kerogens and shales reduced by 46-72% at 95% R.H. This compares with the reductions in surface area (SA) and pore volume of 81% and 48-59%, respectively, for the kerogens and 98-99% for both SA and pore volume of the shales at 95% R.H. Water can block most micropores less than 1.3 nm reducing the micropores volume and blocking the micropore necks connecting the larger pores, and vastly reducing accessible pores for gas transport. The greater proportional losses in SA and pore volume compared to the methane adsorption capacities is probably due to ice forming at -196 degrees C in the low-pressure N-2 analysis. Failure to take moisture into account for free and adsorbed methane overestimates the total gas in place (GIP) by 36?45% for the shales investigated.