页岩储层基质气体扩散能力评价新方法

A new method for gas diffusivity evaluation in matrix rocks of shale reservoir

为了更好地评价页岩气在储层基质岩块中的流动能力,以便准确地预测页岩气水平井产量变化规律,以Fick第一定律为基础,依据物质平衡方程,建立了考虑在压差引起浓度差的作用下气体广义扩散能力评价模型,并提出了页岩气体扩散速率系数和扩散效率计算方法。在此基础上,设计了相应的页岩气体扩散能力评价实验装置和实验流程,通过在不同实验条件下的气体扩散实验,获得了随时间变化的气体累积扩散量,利用实验数据计算获得了页岩气体扩散系数、扩散速率系数、扩散效率及流动系数,进而对页岩扩散能力的影响因素进行分析。研究结果表明,页岩基质中的气体主要以广义扩散的方式为压裂裂缝中气体流动提供重要补充;页岩渗透率决定着页岩气体扩散能力大小,渗透率越大,扩散能力越强,而孔隙度与页岩扩散能力相关性小。

To better evaluate the flow ability of shale gas in the matrix rock of reservoirs and accurately predict the yield variation laws of shale-gas horizontal well,based on the Fick’s first law and material balance equation,the general gas diffusivity evaluation model was established in consideration of the gas concentration difference induced by pressure difference;the diffusion rate coefficient and diffusion efficiency of shale gas were proposed.On this basis,the corresponding experimental apparatus and flow were designed for shale gas diffusivity evaluation.Meanwhile,the cumulative gas diffusion amount changing over time was obtained through gas diffusion experiments under different conditions.Shale gas diffusion coefficient,diffusion rate coefficient,diffusion efficiency and flow coefficient were obtained using experimental data,so as to analyze the influence factors of shale gas diffusivity.The research results indicate that the gas in shale gas matrix provide important supplies for gas flow in fracturing fissures by means of general diffusion.The magnitude of shale gas diffusivity is determined by shale permeability.The greater the permeability is,the higher the diffusivity will be.The porosity has a small correlation with shale gas diffusivity.