两相低速非达西渗流模型及相对渗透率曲线求取方法

Calculation of two-phase relative permeability curves based on a low-velocity non-Darcy flow model

流体在特低渗透-致密油藏中的渗流规律不符合达西定律,传统计算两相相对渗透率曲线的JBN方法并不适用。为了解决此类低速非达西渗流实验数据的处理问题,得到更为准确的相对渗透率曲线,在考虑两相渗流拟启动压力梯度的基础上,统计得到经验关系式,可计算不同空气渗透率岩样任意含水率下的拟启动压力梯度。依据低渗透岩样两相稳定流实验结果,提出两相流过程中不同相的拟启动压力梯度相等的假设,建立两相低速非达西渗流模型,基于该模型得出求取两相非达西渗流相对渗透率曲线的方法。应用大庆油田岩样实验数据,对比JBN方法和所提出的新方法,结果表明考虑两相渗流拟启动压力梯度的影响后,油相和水相相对渗透率都有明显变化。

The fluid flow in ultra-low permeability-tight oil reservoirs does not conform to Darcy’s law,which cannot be determined by the conventional Johnson,Bossler,and Naumann(JBN)method for calculating two-phase relative permeability curves.Considering the pseudo threshold pressure gradient of two-phase flow,the empirical relation was obtained through statistics for processing the experimental data of low-velocity non-Darcy flow and acquiring more accurate relative permeability curves.This empirical relation was employed to calculate the pseudo threshold pressure gradient at any water cut of rock samples with different air permeability.According to the experimental results of two-phase steady flow in low-permeability rock samples,a hypothesis was proposed,in which the pseudo threshold pressure gradients of different phases in the two-phase flow were equal,and a two-phase low-velocity non-Darcy flow model was constructed.Based on this model,a method was developed to obtain the relative permeability curves of two-phase non-Darcy flow.The proposed method were compared with the JBN method by using the experimental data of the rock samples from Daqing Oilfield.The results demonstrate that the relative permeability of the oil phase and the water phase changes significantly after considering the influence from the pseudo threshold pressure gradient of the two-phase flow.