低频波动采油对径向储层初始渗流的影响

Influence of low-frequency vibration oil recovery on the initial flow of radial reservoir

分析低频波动作用下饱和单相渗流流体径向孔隙介质的物性变化,可揭示低频波动采油对井筒附近具有变化压力梯度的实际储层渗流的影响。通过构建低频波动对径向储层初始渗流影响的弹性波传播控制方程,考虑弹性波与井筒周围初始时刻流动方向的一致性,采用映射网格与边界层加密进行物理模型网格划分,以削弱弹性波边界虚假反射;通过COMSOL系统有限元模拟,对比波动耦合渗流和Biot流动、初始径向渗流的物性特征,以与半解析解的差异,说明数值模拟揭示低频波动影响下储层物性参数周期性变化的有效性。研究结果表明:波动耦合渗流不等于初始径向渗流与Biot流动的简单叠加;震源位于注入井时,低频波动对径向渗流场具有明显的降压、增速和增孔作用,越靠近注入井,效果越明显;研究区基础参数条件下,局部最大压降达40%,距离井筒中心10 m范围内相对流速明显增加;低渗透率、高孔隙度时低频波动对渗流的促进作用更为明显。

After physical property change of radial pore medium saturated by single phase fluid was analyzed under low-frequency vibration,influence of low-frequency vibration oil recovery on the actual reservoir flow with various pressure gradients near the wellbore may be known. The control equations for elastic wave propagating were established,which shows the influence of the low-frequency vibration on the initial flow of the radial reservoir. Considering the consistency of directions of elastic wave and initial Darcy flow around the wellbore,physical model meshing was made according to the mapped meshing and boundary mesh refinement to weaken the boundary spurious reflection. By comparing coupled vibration flow with Biot flow and initial radial flow based on finite element simulation of COMSOL system,it is demonstrated that the numerical simulation can reveal the effectiveness of periodic changes of reservoir physical property under the influence of the low-frequency vibration according to the difference in semi-analytical solution. The research results present that the coupled vibration flow is not simply equal to the sum of Biot flow and initial radial flow. The low-frequency vibration has obvious function of increasing the seepage velocity and permeability and decreasing the injection pressure in the radial flow field when the vibration source is in the injection well;the effect is more obvious near the injection well. The local maximum pressure decrease ratio reaches 40%,and the action range with significant velocity increase is 10 m to the center of wellbore. The effect is more obvious at lower permeability and higher porosity.