页岩气超临界等温吸附模型及储量计算优化

Improved shale gas supercritical isothermal adsorption model and the calculation method of geologic reserve

页岩吸附能力研究对评价页岩气资源潜力具有重要意义.论文基于单分子层吸附模型和吸附势理论,建立了考虑页岩微孔、中(大)孔在高压条件下的吸附机理差异的超临界等温吸附模型,构建了微孔滞留率对地质储量影响的gas-in-place(GIP)计算公式,并进行了实例分析.研究结果表明:Dubibin-Astakhov(DA)方程应用于研究页岩微孔吸附机理需要结合吸附势特征曲线进行修正,模型中的虚拟饱和蒸汽压采用改进的Dubinin公式,并采用逐渐增大k值的方法求取最优k值,使得吸附特征能不随温度变化;将微孔吸附气含量部分地计入地质储量,对地质储量GIP公式进行修正,微孔吸附量通过建立的DA-Langmuir等温吸附模型直接获得.该方法考虑了页岩吸附机理,计算结果更加符合实际;改进的储量计算模型表明,微孔吸附气滞留率对浅层页岩气地质储量影响较大,随埋深增加,微孔吸附气滞留率对地质储量影响减小.

Shale adsorption performance is of great significance for evaluating the potential of shale gas resources.The supercritical isothermal adsorption model based on adsorption potential theory and monolayer adsorption theory was established,with the consideration of the adsorption mechanism for shale micropores,mesopores and macropores under high pressure.The calculation for gas-in-place(GIP)which can reflect the influence of microporous adsorption retention rate was derived,and then field case analysis was carried out.Results show that the Dubibin-Astakhov(DA)equation needs to be corrected by combining the adsorption characteristic curve in order to be applied in adsorption mechanism study,and the kvalue needs to be increased gradually to obtain the optimal value so that the adsorption characteristic energy3閩can be free from the influence of temperature.The microporous adsorption capacity is considered in part in the geological reserves(GIP)calculation as an improvement.Meanwhile,the micro-porous adsorption capacity can be accessed through the established DA-Langmuir isotherm adsorption model directly.This method considers the shale adsorption mechanism,which can improve the accuracy of the calculation.The improved GIP calculation model shows that the adsorbed gas retention rate of micropores has a great influence on the shallow geological reserve,and less influence on the geological reserve with the increase of the depth.