低渗透油藏气水相对渗透率计算方法研究

和常规油气藏不同，致密气藏中流体的渗流并不符合经典的达西定律，而是同时存在着动态启动压力梯度和应力敏感效应。常规的JBN方法计算相对渗透率时并没有将这两者考虑在内，势必造成计算的误差。在分析致密气藏特殊渗流机理的基础上，建立了考虑动态启动压力梯度和应力敏感效应的致密气藏两相渗流计算方法并进行了实例验证。结果表明，在考虑动态启动压力梯度和应力敏感性的情况下，气、水两相的渗流能力均有明显下降，其中水相相对渗透率降低速度加快，而气相相对渗透率上升速度有所减缓，等渗点相对渗透率降低，岩芯的残余水饱和度升高。不同孔隙压力下的相对渗透率实验结果表明，随着孔隙流体压力的下降，动态启动压力梯度和应力敏感性对于渗流的影响越来越显著，这两种因素在内的新方法得到的相对渗透率曲线和传统的JBN方法得到的曲线差异也越来越明显。新方法计算得到的相对渗透率曲线更能准确的表征致密储层流体的渗流形态。

Study on Calculation Method of Relative Permeability of Gas and Water in Low Permeable Oil Storage

Different from conventional reservoirs, fluid percolation in tight reservoirs does not conform to the classic Darcy's law, but has both dynamic starting pressure gradient and stress sensitive effect. The JBN method don't take these two factors into account when calculating relative permeability, which is bound to cause calculation errors. The seepage mechanism of tight gas reservoir was analyze, then a two phase seepage calculation method was built and verified considering the dynamic threshold pressure gradient and stress effect. The results show that when consider the dynamic threshold pressure gradient and stress effect, the seepage ability of gas and water phase both decrease obviously, and the decrease degree of water is bigger than the gas phase. The isotonic point of relative permeability decreases and the residue water saturation increases in rock sample. With the decline of pore pressure, the effect of dynamic threshold pressure gradient and stress becomes more and more significant. The new relative permeability curves calculated by the new method is more different with the curves calculated by the JBN method. The new method can describe the seepage of fluid in tight formation more accuracy.