考虑多因素的页岩气吸附模型——以川东南五峰组—龙马溪组页岩为例

甲烷在页岩中的吸附同时受页岩本体物理性质和外部储存条件的综合影响,为了建立考虑多种因素影响的页岩气吸附模型,以川东南五峰组—龙马溪组页岩为例,开展了不同总有机碳含量(TOC含量)的页岩在多个不同温度、不同含水率下对甲烷的吸附实验,采用Langmuir吸附模型对吸附数据进行了拟合,分析了饱和吸附量及Langmuir压力分别与温度、TOC含量及含水率的定量关系,最终建立了考虑温度、压力、TOC含量及含水率综合影响的多因素页岩气吸附模型,并通过与实测吸附数据对比验证了该模型的准确性。结果表明:Langmuir模型能很好的拟合五峰组—龙马溪组页岩在不同特定条件下的吸附数据,拟合精度较高,决定系数R²介于0.972 8～0.998 2。饱和吸附量与TOC含量呈正线性相关,与温度及含水率呈线性负相关。Langmuir压力与TOC含量呈线性负相关,与温度及含水率呈线性正相关。30℃下TOC含量为4.17%的页岩干样吸附量比TOC含量为2.95%的页岩干样吸附量高约39%。当温度由30℃增至80℃时,TOC含量为4.17%的页岩干样其饱和吸附量降低约30.6%。对于TOC含量为3...

An adsorption model with multiple factors for shale gas:Taking the Wufeng Formation-Longmaxi Formation shale in southeast Sichuan as an example

The adsorption of methane on shale is simultaneously affected by the physical properties of shale and external storage conditions.To establish a shale gas adsorption model that takes into account the influence of multiple factors,the Wufeng Formation-Longmaxi Formation shale in southeastern Sichuan is used to carry out the experiments on the adsorption of methane on shale with different total organic contents(TOC)at different temperatures and different water contents.The Langmuir model is used to fit the adsorption data and the quantitative relationship between saturated adsorption capacity,Langmuir pressure and temperature,TOC,water content are analyzed,and finally,the multi-factors adsorption model which considering the comprehensive effects of temperature,TOC,and water content is established,also the accuracy of the model is verified by comparing with the measured adsorption data.The results show that the Langmuir model can fit the adsorption data of Wufeng Formation-Longmaxi Formation shale well with high fitting accuracy,the coefficient R² is between 0.9728 and 0.9982.The saturated adsorption capacity has a positive linear correlation with TOC and a negative linear correlation with temperature and water content.In contrast,Langmuir pressure has a negative linear correlation with TOC and a positive linear correlation with temperature and water content.The adsorption capacity of dry shale with TOC of 4.17%is about 39%higher than that of dry shale with TOC of 2.95%at 30℃.The adsorption capacity of dry shale with a TOC of 4.17%decreases by 30.6%when the temperature increases from 30℃to 80℃.For the shale with TOC of 3.66%,when the water content increases from 0 to 4.2%,the saturated adsorption capacity of the wet sample decreases by 23.1 and 11.6%at 30℃and 60℃,respectively.The established adsorption model which based on the Langmuir model and considering the effects of multiple factors can calculate the adsorption capacity of shale with different TOC at different temperatures and different water contents accurately.From comparing with 2 sets of experimental data,the relative error in the entire experimental pressure range is less than 6%,and the average errors are2.48%and 3.67%,respectively.The proposed model has been verified to have good applicability to different shales by using adsorption data of different shales in other literature.