动边界复合油藏低速非达西渗流试井分析

WELL TEST ANALYSIS OF LOW VELOCITY AND NON-DARCY FLOW IN COMPOSITE RESERVOIR WITH DYNAMIC BOUNDARY

低渗透油气藏中常出现低速非达西渗流现象。各种增产措施的实施,使得该类油气藏的近井与远井区域的岩石和流体的性质有很大不同,因此,可以把低渗透油藏的渗流区域看作复合油藏。充分考虑启动压力梯度与动边界的影响,建立了均质复合油藏低速非达西渗流试井的数学模型,进行数值求解,并绘制了有界油藏定压条件下的典型曲线,得到了动边界的传播规律。研究结果表明:非达西流的存在,使得压力导数双对数曲线中的内区、外区径向流段不再是水平线,而是逐步开始上翘;动边界传播初期,动边界位置RD与无因次时间tD有较好的线性关系;动边界传播中后期,R3D与tD有较好的线性关系。

Low velocity and non-Darcy flow exists in low-permeability reservoirs near the wellbore.Various kindsof stimulation treatments make the physical properties of the formation and fluid surrounding and far away fromthe well different.Thus the vadose area of low permeability reservoir can be divided into two zones:near wellborezone and distant wellbore zone,which make it a composite reservoir.Based on the low velocity and non-Darcy flowtheory,a well testing model is established in composite reservoir with full consideration on the effect of thresholdpressure gradient and dynamic boundary,and it is solved by numerical discrete method.Then the characteristiccurve and the propagated rule of the dynamic boundary of the model are gained and analyzed.The results show thatthe pressure derivative in log-log well test plot in distant wellbore zone and near wellbore zone does not stay level,but goes upward gradually.At early stage of dynamic boundary propagate,the situation of dynamic boundary RDand the dimension time tD have a good linear relationship.In middle and late stage,R3D and tD have a good linearrelationship.