四川盆地志留系页岩CH_4和CO_2吸附特征

Adsorption characteristics of CH_4 and CO_2 on Silurian shale in Sichuan Basin

页岩气是一种非常具有开发潜力的非常规天然气能源。选取四川宜宾地区志留系龙马溪组页岩,对总有机碳、黏土矿物含量和镜质体反射率等储层性质进行表征,通过场发射扫描电子显微镜和低温氮气吸附-解吸方法对页岩的孔隙结构进行分析。从孔隙结构表征发现,页岩中有大量的孔隙发育,并且大多数孔隙的尺寸在100 nm以下,微孔对总比表面积的贡献最大,中孔对孔体积做出了较大贡献。对页岩样品分别进行了CH_4和CO_2单组分气体的等温吸附实验,分析了影响页岩吸附气体能力的因素,考察了页岩样品CO_2/CH_4的选择性。结果表明,页岩对CO_2的吸附量要远大于对CH_4的吸附量;有机质含量TOC和孔隙结构对页岩的吸附有很大影响,呈正相关;温度越高,页岩对气体的吸附能力越差;单位压力变化对吸附的影响随着压力的增高而下降,逐渐趋于平缓;在竞争吸附中,页岩对CO_2有更高的选择性。

The basic reservoir physical parameters of Silurian shale samples in Sichuan Basin including total organic carbon, clay mineral content and vitrinite reflectance were represented. Pore structure was characterized by field emission scanning electron microscope and low temperature nitrogen adsorption methods. Based on these characterizations, shale samples have well-developed pore structure, with micropores predominantly comprising the pore structure. It is also found that the micropore is the major contributor to the overall specific surface area, whereas most of the pore volume is occupied by mesopores. The adsorption capacity of pure methane and carbon dioxide were performed using a setup of the manometric method. The factors affecting the adsorption capacity of shale gas were investigated, and the selectivity of CO2/CH4 adsorption on shale samples was studied. The results show that the adsorption capacity of CO2 on shale is higher than that of CH4. TOC and pore structure have a great influence on shale adsorption, which is positively correlated. Meantime, a high temperature is unfavorable to shale gas adsorption and the influence of unit pressure on the adsorption decreases with the increase of pressure. In the study of competitive adsorption, shale has higher selectivity to CO2.