利用COMSOL软件模拟低渗油田非线性渗流规律

Simulation on the non-linear seepage law of low-permeability oilfields with COMSOL software

非线性渗流规律表现为流体低速流动时渗流速度与压力梯度关系曲线不为直线且不过原点,即当压力梯度较小时,流体渗流速度可能为0。储层渗透率越小,非线性渗流特征越明显。为了清楚认识低渗油田非线性渗流规律及其对油田生产的影响,在描述低速非线性渗流规律的连续模型基础上,推导出单相不可压缩流体稳定渗流微分方程,同时利用在流体力学等领域广泛应用的COMSOL软件模拟低渗油田正方形反九点井网流体渗流规律。COMSOL软件模拟结果清楚展示出正方形反九点直井井网、压裂井网流线及等势线分布的差异以及压裂时压力波及面积随裂缝长度和裂缝与井排夹角变化的规律。模拟结果表明非线性渗流时,等势线分布不再呈圆形;直井压裂后,压力波及面积明显增加,裂缝长度、裂缝与井排夹角都会影响压力波及面积。

The non-linear seepage law is shown by the fact that, when lfuid lfows at a low rate, the seeping rate is not in a straight line with the relation curve of pressure gradient and is not through the original point, that is, when the pressure gradient is relatively small, the lfuid seeping rate may be zero. The smaller the permeability of a reservoir is, the more obvious the non-linear seepage feature is. In order to understand the law of non-linear seepage in low-permeability oilifelds and its effect on oilifeld production, a single-phase uncompressible lfuid stable seepage differential equation was inferred based on the continuous model which described the low-rate non-linear seepage law. Meanwhile, the COMSOL software which is widely used in lfuid mechanics was used to simulate the square inverted nine-spot pattern seepage law of low permeability oilifelds. The COMSOL simulation result clearly shows the difference in distribution of lfow lines of square inverted nine-spot vertical well pattern and fracturing pattern as well as equipotential line and the law of changes of pressure affected area with fracture length and the angle between the fracture and well array during fracturing. The simulation result shows that, under non-linear seepage, the equipotential line is not circularly distributed. After a straight well is fractured, the pressure affected area increases apparently. The fracture length and the angle between the fracture and well array both will affect the pressure affected area.