一种煤层气藏相渗的获得方法及曲线形态讨论

煤层气的相渗曲线通常采用气–水两相驱替实验获得,实验认为煤岩割理的两相流动区域较小,且临界流动含水饱和度较高。然而,煤层中的流体运移是一种耦合基质解吸和割理两相流动的过程。基质中解吸出的气体汇聚在割理后,与水相共同参与流动,并非简单的单向驱替过程,这导致生产过程中气驱波及效率远好于实验得到的结果。为获得煤层中的相渗规律,本文建立考虑基质解吸作用的煤层气流动拟稳态产能模型,通过联立煤层气的物质平衡方程,获得一种基于生产历史的煤层气–水相渗曲线的反演方法。同时,研究分析实验得到与反演得到的相渗曲线之间的差异,认为差异主要源于实验室单向驱替过程中较小的波及系数。最后,研究通过数值模拟分析两种相渗曲线对产气动态的影响。

An approximation of the relative permeability and discussion on curve shapes in coalbed methane reservoirs

In coalbed methane(CBM) reservoirs,relative permeability curves are commonly obtained using gas-water displacement experiment,and it is commonly concluded that the 2-phase flow area is very narrow and that the critical water saturation is extremely high according to experimental results. However,the fluid flow in coal is a complex process of coupled desorption from matrix and 2-phase flow in cleats. The process that gas desorbs from matrix,enters cleats and displaces water is different from one-direction gas displacement in laboratory,which leads to that the sweeping efficiency in production process is higher than that in experiment. To obtain the appropriate relative permeability in coal,a CBM productivity model was established in pseudo-steady state considering the desorption effect in matrix. Combining the material balance equation,an inversion method of the relative permeability curve in CBM reservoirs was proposed based on production history. The difference between relative permeability curves obtained from experiment and the developed method was discussed,and it is pointed out that the difference contributes to the low sweeping efficiency in experiment. Finally,the effects of two types of relative permeability curves were illustrated using numerical simulation method.