页岩气储层纳米级孔隙中气体的质量传输机理及流态实验

An experimental study on the mass transfer mechanism and the flow regime of gas in nano-scale pores of shale gas reservoirs

为了探究页岩气储层纳米级孔隙中气体的质量传输方式、机理、气体流态,以及页岩表观渗透率的合理表示方法,首先基于前人的研究成果,从微观和宏观的角度综合分析了页岩纳米孔隙中气体的质量传输机理;然后通过开展致密页岩中气体渗流实验,对纳米孔隙中气体的真实流态进行了分析,讨论了孔隙尺寸、压力等参数对页岩渗透率的影响;进而对不同页岩表观渗透率模型进行了比较,探讨了其合理的表示方法。研究结果表明:(1)页岩纳米孔隙中游离气质量传输方式主要为滑脱流、努森扩散及斐克扩散,吸附气质量传输方式主要为表面扩散,气体流态为滑脱流或过渡流,不存在连续流,并且孔隙越小、压力越低,滑脱流越弱,努森扩散越强;(2)在相同的实验条件下,Darcy渗透率最低,B-K表观渗透率和Civan表观渗透率非常接近,Klinkenberg表观渗透率居中,APF表观渗透率与Wu表观渗透率最高且出现了曲线交替;(3)在Wu表观渗透率中,滑脱流在滑脱区和过渡区都是气体质量主要的传输方式;(4)在APF表观渗透率中,滑脱流是滑脱区气体质量主要的传输方式,而努森扩散则是过渡区气体质量主要的传输方式。

In order to explore the mass transfer mode and mechanism and the flow regime of gas in nano-scale pores of shale gas reservoirs and to develop a method for expressing the apparent permeability of shale reasonably,it is necessary to comprehensively analyze the mass transfer mechanism of gas in nano-scale pores of shale gas reservoirs from microscopic and macroscopic perspectives based on previous research results.After gas seepage in tight shale was experimentally studied,the real flow regime of gas in nano-scale pores was analyzed,and the effects of pore size,pressure and other parameters on shale permeability were discussed.Finally,the reasonable expression method of apparent permeability was discussed by comparing different apparent permeability models.And the following research results were obtained.First,the mass transfer mode of free gas in nano-scale pores of shale gas reservoirs is mainly slippage flow,Knudsen diffusion and Fick diffusion,and that of adsorbed gas is mainly surface diffusion.The flow regime of gas is slippage flow or transitional flow without continuous flow.Besides,the smaller the pores and the lower the pressure,the weaker the slippage flow and the stronger the Knudsen diffusion.Second,under the same experimental conditions,the Darcy permeability is the lowest,the Klinkenberg apparent permeability is the medium,and both APF and Wu apparent permeability are the highest.Their curves of APF and Wu apparent permeability alternate.The Beskok–Karniadakis(B–K)apparent permeability and the Civan apparent permeability are very close.Third,in the model of Wu apparent permeability,the slippage flow is the main mass transfer mode of gas in the slippage and transition zones.Fourth,in the model of APF apparent permeability,the slippage flow is the main mass transfer mode of gas in the slippage zone while Knudsen diffusion is the main mass transfer mode in the transition zone.