高压条件下页岩对CH4、CO2气体吸附特征及其在二元混合气体中应用:以四川盆地焦石坝地区龙马溪组页岩为例

Adsorption characteristics of CH4 and CO2 on shale and its application to binary mixture adsorption under high-pressure conditions: A case study of the Longmaxi Formation shale in Jiaoshiba area of Sichuan Basin

为了解高压条件下页岩对甲烷(CH4)、二氧化碳(CO2)及二元混合气体吸附行为,以四川盆地焦石坝地区下志留统龙马溪组页岩样品为研究对象,通过重量法等温吸附实验,研究了不同温度压力条件下CH4、CO2在页岩中的吸附行为。实验表明,在0.01~50 MPa,40~100℃条件下,页岩对CH4、CO2过剩吸附量随压力增大而增加,直至达到最大值,然后随压力增大而减小;绝对吸附量随压力增大而增加,在40~43 MPa之后,吸附量趋于稳定。在高压条件下,页岩对CO2吸附量大于CH4,约为其5倍。利用CH4、CO2单一气体Langmuir吸附量和Langmuir压力,通过扩展的(Extended)Langmuir模型进行拟合,对不同比例CH4/CO2二元混合气体吸附量进行模拟预测,研究表明,二元气体总吸附量随混合气中CO2比例增大而增加。在高压条件下,Langmuir过剩吸附模型能较好地拟合CH4、CO2在页岩中的吸附,扩展的Langmuir过剩吸附模型也能较好地拟合二元混合气体在页岩中的吸附。

This work investigates the adsorption characteristics of CH4,CO2,and binary mixtures on shale at high pressures.The adsorption capacity of CH4 and CO2 on shale was measured by the gravimetric isothermal adsorption method,using SCES006 shale from the Lower Silurian layers of the Sichuan Basin at different pressures and temperatures.The adsorption capacity of binary mixtures was studied through an extended Langmuir model.Results show that the excess adsorption increases with increasing pressure,reaches a maximum value,and then decreases for both CH4 and CO2 when pressure is lower than 50 MPa and temperature is between 40℃and 100℃.The absolute adsorption increases with increasing pressure,and reaches a stable value for pressures ranging from 40 to 43 MPa.At high-pressure conditions,the adsorption amount of CO2 is about five times greater than that of CH4.The adsorption capacities of binary mixtures of CO2 and CH4 with different proportions of shale samples were modeled through an extended Langmuir model by utilizing the dates of Langmuir adsorption,amounts,and Langmuir pressures of CH4 and CO2 single components.Results reveal that total adsorption capacity increases with increasing CO2 content in the mixed gases.At high pressure,the adsorption capacity of CH4 and CO2 on shale can be better fitted by a Langmuir excess adsorption model,and the adsorption capacity of binary mixtures of CO2 and CH4 on shale could be fitted by the extended Langmuir excess adsorption model.