页岩中基于孔隙度和有机碳含量的甲烷吸附量计算

Calculation of methane adsorption in shale based on porosity and organic carbon content

关键词:  龙马溪组  等温吸附  甲烷  高压

Key words:  Longmaxi formation  isothermal adsorption  methane  high pressure

摘要:

根据四川盆地页岩气勘探开发经验,页岩气在地下的赋存状态为吸附态和游离态,以及少量溶解态,其中游离态的含量可达20%~85%。因此,研究地层高压条件下页岩中甲烷吸附特征对页岩储层的准确评价以及储量预测具有重要意义。以四川地区页岩气储层为对象进行等温吸附实验,分析实验结果后发现,甲烷在页岩孔隙中随压力增加其吸附量逐渐增加,但吸附量的增加率呈逐渐下降的特性。通过分析常用吸附量计算模型,发现甲烷在页岩中的吸附量受孔隙度和有机碳含量的影响。通过与实验结果的拟合,引入由孔隙度与有机碳含量决定的计算因数,进而得到新的等温吸附量计算方法,平均相对误差为8%左右。该研究对简化页岩吸附量计算方法,准确预测页岩层储量具有重要意义。 

Abstract:

According to the exploration and development experience of shale gas in Sichuan basin, the occurrence states of shale gas are adsorption state and free state, as well as a small amount of dissolve state, in which the content of free state can reach 20%-85%. Therefore, the study of methane adsorption characteristics in shale under high pressure has a great significance to accurate evaluation of shale reservoir and reserves prediction. In this paper, the shale gas reservoir in Sichuan area is taken as an example for isothermal adsorption experiment. After analyzing the experimental results, it is found that the adsorption capacity of methane increase with the increase of pressure in shale pores, but the increase rate of adsorption capacity decrease gradually. It is found that the adsorption capacity of methane in shale is affected by porosity and organic carbon content through analyzing the commonly used calculation model of adsorption capacity. Through the fitting of experimental results, introducing the calculation factors determined by porosity and organic carbon content, a new calculation method of isotherm adsorption capacity is obtained with an average relative error of 8%. It has a great significance to simplify the calculation method of shale adsorption and accurately predict shale reserves.