致密油藏注气后储层渗流特征参数动态反演方法

Dynamic inversion method of percolation characteristic parameters after gas injection in tight reservoirs

致密油藏在气驱开发过程中,通常由于气窜导致开发效果变差甚至停产。针对致密储层注气后储层渗流特征参数尚无成熟的理论求解方法的问题,从渗流力学原理出发,利用Stone模型建立油、气、水三相饱和度与相对渗透率的表征函数。分析开发动态参数和储层渗流特征参数与相对渗透率的函数关系,建立饱和度-含水率-气油比关系图版。借助该图版,实现由开发动态参数反演出储层渗流特征参数的目的。开发动态参数包括含水率和气油比;储层渗流特征参数包括地下混合液流度、储层平均渗透率和气窜通道平均渗透率等。应用该方法对实际气窜井组进行储层渗流特征参数动态反演,结果表明:反演结果与实际单井气窜特征和生产动态变化特征吻合;气窜井生产期间内的储层平均渗透率远小于未气窜井;气窜程度越高,则气窜通道平均渗透率越大,所处层位存在明显裂缝或窜流通道。

In the process of gas flooding development of tight reservoirs,gas channeling usually leads to poor development performance or even shutdown. There was no mature theoretical method to calculate the percolation characteristic parameters after gas injection in the tight reservoirs. Based on the principle of percolation mechanics,the characterization functions between oil-gas-water three-phase saturations and relative permeability are established by using the Stone model. By analyzing the function relation among the dynamic parameters,the percolation characteristics parameters and relative permeability,the saturation-water cut-gas-oil ratio(GOR)relation charts are established. With the help of these charts,the percolation characteristic parameters are reversed by using dynamic development parameters. The dynamic development parameters include water cut and GOR,and the percolation characteristic parameters include the fluidity of underground mixed fluid,average reservoir permeability and average permeability of gas channeling channel. This method is applied to perform the dynamic reversion of reservoir percolation characteristics parameter in the well group with gas channeling. The results show that the inversion results are consistent with the characteristics of single-well gas channeling and production dynamic behavior. The average permeability of gas channeling wells during production is much lower than that of wells without gas channeling. The higher the degree of gas channeling is,the greater the average permeability of gas channeling channel will become,which indicates that there are obvious fractures or gas channeling channels in the layer.