摘要
页岩富含纳米孔,且吸附气占总气量可高达85%,因此页岩气表面扩散对气体传输具有重要的作用.页岩气藏压力高,页岩表面能量非均质性强,吸附气非等温解吸附等,均加剧了吸附气表面扩散模拟的复杂性.基于低压条件下推导的Hwang模型,考虑高压条件下吸附气覆盖度的影响,建立了页岩吸附气表面扩散模型.同时,该模型还考虑了页岩表面能量非均质性、等量吸附热和非等温解吸附对表面扩散的影响.研究表明:1)表面扩散系数随压力的增大而增大,随温度的升高而增大,随表面活化能的减小而增大,随气体分子量的减小而增大;2)黏性流动、努森扩散和表面扩散对气体传输的贡献是此消彼长的,主要受孔隙尺度和压力的控制;3)表面扩散在微孔(半径<2 nm)中,对气体传输贡献大,可高达92.95%;在宏孔(半径>50 nm)中,贡献低于4.39%,可忽略;在介孔(2<半径<50 nm)中,表面扩散的贡献介于微孔和宏孔之间.
Surface diffusion plays a key role in gas mass transfer of shale reservoirs, due to the majority of gas is adsorbed gas in shale reservoirs with abundant nanopores of organic matter, up to 85%. The surface diffusion simulation is very complex as a result of high reservoir pressure, nanopore wall energy heterogeneity and non-isothermal desorption of adsorbed gas in shale reservoirs. In this paper, a new model of surface diffusion for adsorbed gas in shale reservoirs is established, which is based on Hwang model derived under low pressure, and considers the effect of adsorbed gas coverage under high pressure. In addition, new model also considers the effects of nanopore wall energy heterogeneity, isosteric sorption heat and adsorbed gas non-isothermal desorption on surface diffusion. Results show that： l） the surface diffusion coefficient increases with pressure, temperature, decreasing activation energy and decreasing gas molecular weight; 2） contributions of viscous flow, Knudsen diffusion and surface diffusion to gas mass transfer are varying while the development of shale reservoirs, which is mainly controlled by nanopore-scale and gas pressure; 3） in micropores （nanopore radius 〈2 nm）, the contribution of surface diffusion to the gas mass transfer is dominant, up to 92.95%; in macroporous （nanopore radius〉 50 nm）, less than 4.39%, can be ignored; in mesoporous （2 〈nanopore radius 〈50 nm）, the contribution between micropores and macropores.
出处
《中国科学：技术科学》
EI
CSCD
北大核心
2015年第5期525-540,共16页
Scientia Sinica(Technologica)
基金
国家自然科学基金重大项目(批准号:51490654)
国家自然科学基金(批准号:51374222)
国家科技重大专项(编号:2011ZX05030-005-04)资助项目
关键词
页岩气
吸附
解吸附
表面扩散
纳米孔
shale gas reservoirs, adsorption, desorption, surface diffusion, nanopores
