基于分形理论的致密气藏束缚水饱和度计算模型研究

摘要

The theoretical calculation method of irreducible water saturation of tight sandstone gas reservoir is established by using fractal theory.According to the capillary bundle model based on fractal characteristics of capillary size distribution and tortuosity and considering the existence form of two kinds of irreducible water in capillary and film,the irreducible water saturation calculation model is established with the consideration of the pore distribution, temperature and driving pressure conditions.Compared with NMR method,the calculation method is credible.It can be used to calculate irreducible water saturation of different cores under different temperature and pressure difference.The results of sensitivity analysis show that the higher the temperature,the larger the pressure difference,the lower the irreducible water saturation is.Under the same driving pressure condition,the irreducible water satura-tion at high temperature can be reduced by up to 1 5 .3% compared with that at normal tem-perature.Under the same temperature condition,the driving pressure increases 1 MPa,and the irreducible water saturation can be reduced by up to 14.1%.%运用分形理论建立了致密砂岩气藏束缚水饱和度的理论计算方法．根据毛管束模型，基于毛管大小分布和迂曲度所具有的分形特征，系统考虑毛细管和薄膜两种束缚水存在形式，建立了考虑孔隙分布和温度、压差等条件的束缚水饱和度计算模型，与所对应的核磁共振法实验测试结果相比，新方法的计算结果精度高，可用于计算致密砂岩在不同温度、压差条件下的束缚水饱和度．敏感性分析结果表明，温度越高，压差越大，岩心束缚水饱和度越低，相同驱替压差条件下高温与常温相比，束缚水饱和度最多可降低15．3％，相同温度条件下驱替压差升高1 MPa，束缚水饱和度最多可降低14．1％．