基于孔隙结构分形特征的水锁损害预测新方法

A new method for the prediction of water-locking damage based on the fractal feature of pore structures

水锁损害是致密砂岩气藏最主要的损害类型,损害一旦发生则难以完全解除,会严重影响气藏的发现、评价和开发,因此,对储层水锁损害程度进行准确的预测极为重要。运用泡压法测试得到了储层岩石的连通喉道对渗流能力的分布,反映了不同含水饱和度下的渗流特征;在此基础上,建立了包含多种水锁损害控制因素的孔隙分形维数计算方法;最终建立起了基于孔隙结构分形特征的水锁损害预测模型,便可容易地计算不同含水饱和度下的渗透率损害率。应用该模型对四川盆地西部上三叠统须家河组岩心的水锁损害进行了预测,结果显示:对于该类储层,只要保证直径大于1μm的喉道连通,返排压差高于0.3MPa,就能保证水锁损害率低于30%。由此表明新方法能够更准确地反映水锁损害程度。

Water locking is the main damage to tight sandstone gas reservoirs,which,once occurred,would be very difficult to unlock completely and make it very hard to discover,evaluate and exploit the reservoirs,so it is extremely important to predict its damage level.In view of this,the bubble pressure method was used to test the seepage distribution of the connected throats in reservoir rocks,reflecting the varied seepage characteristics of the rocks at different levels of water saturation.On this basis,a fractal dimension calculation method was then developed with multiple controlling factors of water locking damage taken into account;and thus a prediction model was built according to the fractal feature of pore structures,which was in favor of calculating permeability and damage degree at different levels of water saturation.This model was used to predict the water locking damage of core samples from the Xujiahe Formation in West Sichuan Basin.In this case,the prediction results showed that the water-locking damage degree will be lower than 30%if the throats are larger than 1 μ m in diameter and the pressure drop in the flow back of fluids is higher than 0.3 MPa.In conclusion,this method can accurately reflect the water-locking damage degree.