页岩气储层粘土矿物孔隙特征及其甲烷吸附作用

Pore Characteristics and Methane Adsorption of Clay Minerals in Shale Gas Reservoir

粘土矿物是页岩的主要组成矿物,与页岩气的赋存和富集密切相关。粘土矿物因其特殊的晶体结构,在晶层之间、矿物内部以及矿物颗粒之间形成了不同类型的孔隙,这些孔隙的大小、形貌和比表面积决定着粘土矿物的甲烷吸附能力。为此,本文综述了粘土矿物的孔隙结构以及孔隙中的水和有机质对甲烷吸附性的影响,指出不同类型的粘土矿物孔隙发育与形貌特征存在差异,蒙脱石中多发育圆形、狭缝状的微孔且总比表面积最大,导致蒙脱石在所有粘土矿物中的甲烷吸附量最大;伊利石与高岭石中多发育中孔与大孔,吸附甲烷的能力低于蒙脱石。粘土矿物孔隙中的水与有机质显著影响到甲烷的吸附能力,水分子会占据孔隙表面,降低了甲烷的吸附能力,但可溶有机质对粘土矿物甲烷吸附能力的具体影响目前尚不明了。同时,根据页岩气勘探需求指出了本方向某些有待深入探讨的问题。

The clay minerals are the main constituent minerals of the shale. It＇ s closely related with the occurrence and enrichment of shale gas. Because of its special crystal structure, clay minerals formed different types of pores between the crystal layers, in the internal mineral and between the mineral particles. The pore size, morphology and the specific surface area determine the methane adsorption capacity of the clay minerals. This paper reviews the occurrence of methane adsorption and various influence factors, such as pore structure, the water and organic matter in the pore. Different types of clay minerals are different in pore development and morphology. The round and slit micropores are most frequently found in smectite clay, which has the biggest total surface area and methane adsorption capacity. The mesoporous and macroporous are most developed in illite and kaolinite with the methane adsorption capacity belowing montmorillonite. Water and organic matters present in the pore of the clay minerals will also affect the methane adsorption capacity. Generally believed that water molecules will occupy the surface of pore, and resulting in a decrease of methane adsorption capacity of clay minerals. However, the specific effects of the soluble organic matter to the methane adsorption capacity of clay minerals are not clear yet. Finally, this paper indicates some of the issues to be explored in depth according to the needs of shale gas exploration.