陆相页岩有机质-黏土矿物复合孔隙体系中多组分烃类-水混合物赋存的分子模拟

Molecular simulations of a multicomponent hydrocarbon-water mixture in the organic matter-clay mineral composite pore system of lacustrine shales： A case study of the Da’anzhai Member of the Jurassic Ziliujing Formation， Sichuan Basin

任文希 曾小军 王光付 郭建春 刘彧轩

Wenxi REN Xiaojun ZENG Guangfu WANG Jianchun GUO Yuxuan LIU

针对四川盆地侏罗系陆相页岩气烃类组成多样的特点，建立了干酪根狭缝孔、伊利石狭缝孔和复合孔组成的有机质-黏土矿物复合孔隙体系分子模型。通过分子动力学模拟，研究了湿气在复合孔隙体系中的微观赋存特征及其影响因素。研究发现：①压力较低时，烃类分子会优先占据复合孔中靠近干酪根壁面的孔隙空间；而在高压条件下，分子数增加，较重的烃类分子会优先占据复合孔中靠近干酪根壁面的孔隙空间，使得轻质烃类只能在伊利石壁面处赋存。②在相同压力条件下，孔径越大，孔隙空间越大，可以容纳的烃类分子越多。③高压条件下水分子之间相互作用增强，并在氢键作用下聚集成团，团状水簇可赋存在干酪根表面，或游离于复合孔中，或形成水膜附着于伊利石表面。④有机质-黏土矿物复合孔隙体系中的有机质孔隙、复合孔和黏土矿物孔隙均对烃类赋存有贡献。相对于有机质孔隙，复合孔和黏土矿物孔隙能够容纳更多烃类分子，且以轻质烃类为主，含气性和可动性更好。

Given the diverse hydrocarbon compositions of the Jurassic lacustrine shale gas in the Sichuan Basin， we develop a molecular model for the organic matter-clay mineral composite pore system composed of kerogen and illite slit pores and composite pores. Using molecular dynamics simulations， we explore the microscopic occurrence characteristics of wet gas in the composite pore system and the influential factors related. The results indicate that at lower pressures， hydrocarbon molecules preferentially occupy space near kerogen walls within the composite pores， while the number of hydrocarbon molecules increases under high-pressure conditions， and the heavier hydrocarbon molecules are preferentially concentrated in space near kerogen walls within the composite pores， leaving lighter hydrocarbons to be confined to the illite walls. Under the same pressure conditions， a larger pore diameter meaning larger pore space， can accommodate more hydrocarbon molecules. Under high-pressure conditions， interactions between water molecules get enhanced， forming clusters due to hydrogen bonding. These water clusters can be found on the surface of the kerogen， or free in the composite pores， or develop into a water film on the surface of illite. The organic matter pores， composite pores， and clay mineral pores in the organic matter-clay mineral composite pore system all contribute to the occurrence of hydrocarbons. Compared to organic matter pores， the latter two pore types can accommodate a greater number of hydrocarbon molecules dominated by lighter ones， characterized by higher gas content and better mobility.

10.11743/ogg20250121