正交裂缝网络单相流动实验和数值模拟

Experimental Study and Numerical Simulation of Single-Phase Flow in Orthogonal Fracture Network

为了研究正交裂缝网络模型中单相流体渗流运动特征,利用缝洞介质物理模拟实验装置进行了一系列单相流动实验.根据实验数据拟合得到了临界速度的经验关系式,给出了用临界速度确定破坏油田井壁线性规律时极限产量的方法,基于等效思路用有限元方法对非线性渗流进行了数值模拟.研究表明:低渗流速度下裂缝网络模型中渗流服从线性渗流规律,随着渗流速度不断增大,渗流曲线向压力梯度轴弯曲,呈现非线性渗流特征;渗透率与垂直裂缝密度的对数成线性关系;临界速度随垂直裂缝数增加而增大;非线性渗流的数值模拟结果与实验数据拟合较好,相对误差小于4.93%.流体在井底附近地带运动时能产生使线性渗流规律受到破坏的强惯性阻力.

In order to investigate the characteristics of single-phase flow in orthogonal fracture network models,a series of single-phase flow experiments were conducted using a fractured vuggy media experimental setup.The empirical formula for critical velocity was obtained by fitting the experimental data.The method to determine limit capacity by critical velocity was proposed when linear law is destroyed on wellface.Based on equivalent idea,the nonlinear flow in fractured network model was simulated using a finite element method.The results show that the fluid flow follows Darcy law when velocity is slow.With the increasing of velocity,the flow curves bend to pressure gradient axis and fluid flow presents nonlinear characteristics.The permeability and logarithm of vertical fracture density show linear relationship.The critical velocity increases with the increasing of number of vertical fracture.Numerical simulation results are consistent with experimental data under the nonlinear flow conditions with relative error less than 4.93%.A strong mass force which can destroy linear flow law may happen when fluid flows near the bottom-hole area.