川南长宁地区五峰组—龙马溪组页岩气评价新方法

为了准确评价川南长宁地区五峰组—龙马溪组海相页岩气的含气量,将页岩气分成吸附气和游离气单独进行计算再求和,以等温吸附实验数据为基础,提出并构建了基于微孔充填理论和D-A(Dubibin-Astakhov)方程相结合的吸附气量评价模型,模型中的可变参数微孔最大吸附量V₀、与吸附体系对气体的亲和力有关的常数B、与吸附体系表面非均质性相关的参数t的计算中均考虑了影响吸附气量的关键参数,如地层压力、总有机碳(TOC)含量和孔隙度等;以含气饱和度法为基础,结合吸附态甲烷对孔隙体积的影响,构建了对游离气量进行定量校正的评价模型。结果表明:新建立的吸附气与游离气含量评价模型在研究区页岩含气量评价中具有良好的应用效果,计算的含气量与实测数据相关系数超过0.90。该研究成果为页岩气资源潜力评价和"甜点"预测提供了依据。

New method of shale gas evaluation of Wufeng-Longmaxi Formation in Changning area,southern Sichuan Basin

In order to evaluate the gas content of marine shale of Wufeng-Longmaxi Formation in Changning area,southern Sichuan Basin,the shale gas was divided into adsorbed gas and free gas and then calculated separately. Based on isothermal adsorption experimental data,a new adsorbed gas volume evaluation model was proposed and constructed based on micropore filling theory and D-A(Dubibin-Astakhov) equation. The key parameters affecting the adsorbed gas volume, such as formation pressure,total organic carbon(TOC) content and porosity, were taken into account in the calculation of the variable parameter V₀ which is the maximum micropore adsorption capacity,the constant B related to the affinity of the adsorption system for gas,and the parameter t related to the surface heterogeneity of the adsorption system. Based on the gas saturation method and combined with the effect of adsorbed methane on pore volume,an evaluation model for quantitative correction of free gas volume was established. The results show that the newly established evaluation model of adsorbed gas and free gas volume has a good application effect in the evaluation of shale gas content in the study area,and the correlation coefficient between the calculated gas content and measured data is more than 0.90. The research results provide a basis for shale gas resource potential evaluation and sweet spot prediction.