页岩纳米孔隙气体流动的滑脱效应

Slippage effect of shale gas flow in nanoscale pores

页岩具有超低基质渗透率及纳米尺度的孔喉结构,天然气在页岩纳米孔隙中的流动不再遵循达西定律,受到较常规储层更加显著的滑脱效应影响,研究页岩纳米孔隙气体流动的滑脱效应,对于指导页岩气的压裂设计、产能预测、气藏数值模拟等都具有重要的意义。为此,在文献调研的基础上,分析对比了目前页岩中气体流动的多尺度流动规律,并着重分析了评价滑脱效应对气体在页岩中流动的影响规律,以及气体解吸对于页岩纳米孔隙滑脱效应的影响。结果表明:Klinkenberg方程无法准确地描述页岩的滑脱效应,孔隙尺寸越小,滑脱效应对于气体流动影响越大,且页岩受到滑脱效应影响的压力范围更大,这不仅仅局限于低压范围内,如果在页岩气产能预测与气藏数值模拟过程中,不考虑滑脱效应将会带来更大的计算偏差;有机质孔隙表面的气体吸附、解吸会改变气体的流动通道,对纳米孔隙中气体滑脱效应存在重要的影响;最后指出,多尺度流动效应和基于孔喉分布的应力—温度—流动耦合模型是页岩气储层渗流机理的下一步研究方向。

Gas shale contains a nanoscale pore-throat structure with ultra-matrix permeability. Shale gas flow in nanoscale pores no longer follows the Darey＇s Law but is subject to a more significant slippage effect compared to conventional reservoirs. It is great significant in the guidance of shale gas fracturing design, production forecast, numerical simulation to study the slippage effect of shale gas flow in nanoscale pores. On the basis of the literature research, we analyzed and compared the multiseale flow in gas shales, fo cusing on the analysis and assessment of the influencing law of the slippage effect on gas flow in shales and the impact of gas desorption on the slippage effect of nanoscale pores in shales. The results showed that： the Klinkenberg equation can not accurately describe the shale slippage effect; the smaller the pore size is, the greater the impact of slippage effect on gas flow in shales and the wider the pressure range of shale subject to slippage effect, which is not limited to the low-pressure range. If the slippage effect is not considered, there will be a greater calculating deviation in shales gas production forecast and shale gas reservoir simulation. The gas adsorption and desorption of organic pore surface will change gas flow channel, exerting a significant impact on the slippage effect of gas in nanoscale pores. Finally it is pointed out that the next research on shale gas reservoir percolation mechanism will be the multiscale flow effect and stress-temperature-flow coupling model based on pore throat distribution.