基于3D打印透明微细孔隙模型的多孔介质渗流规律

Pore seepage law based on 3D printed micro-pore model

多孔介质渗流规律研究是油、气、水资源开采及水害防治的基础性工作,物理模型试验是开展此研究的重要手段。基于真实砂层试样CT图片,经剪切、二值化处理、矢量边界提取、建模等步骤,构建了二维孔隙模型;采用高精度光固型3D打印机,选用刚性光敏材料,制备了透明微细孔隙试验模型。构建了包括注水系统、压力监测系统、观测系统、孔隙模型及管路的试验系统,开展了12个注水流量梯度、4个不同渗流方向的渗流模型试验,实现了对孔隙渗流过程的可视化观测及注水压力的高密度实时监测,从微观角度研究了多孔介质渗流规律。研究发现:①在多孔介质渗流过程中分流及汇流持续发生,试验模型不同位置孔隙渗流的活跃性差异较大;②随着水力梯度的增大,达西定律计算的渗透系数整体呈下降趋势,在低水力梯度条件下,同一模型平面90°改变注入方向时,渗透系数差异较大;水力梯度越大,水力梯度与渗透系数呈现相关性越强的幂函数关系;③渗流速度与水力梯度呈高度相关的二次函数关系,渗流速度越高相关性越强,符合Forchheimr型非线性渗流公式,同一模型平面90°改变注入方向时,水力梯度差异较大,呈现明显的各向异性特征;④孔隙试验模型渗流为“层流+紊流”的混合流,随着渗流速度的增加,紊流惯性力对水力梯度的贡献占比增大,其主要与孔隙介质中孔隙及喉道结构特征有关。

The study of porous media seepage law is the basis for oil,gas and water resources exploitation and water disaster prevention while a physical model test is an important means to carry out the research on it.Based on the CT image of real sand sample,through the steps of shearing→binarization→boundary extraction→modeling,a two-dimensional pore model was constructed.Using a high-precision light-solid 3D printer and rigid photosensitive material,a transparent fine pore test model was constructed.With a test platform including water injection system,pressure monitoring system,observation system,pore test model and pipeline,12 injection water flow gradients and 4 seepage directions were tested for seepage model,which realized the observation of pore seepage process and high-density real-time monitoring of water injection pressure.The study found that①in the process of porous media seepage,diversion and confluence continue to occur.The experiment model has a large difference in the active degree of pore seepage at different positions;②the relationship between hydraulic gradient and permeability coefficient is a power function,and the larger the hydraulic gradient,the stronger the correlation;③the relationship between seepage velocity and hydraulic gradient is a highly correlated quadratic function.When the plane changes the injection direction at 90°,the hydraulic gradient varies greatly,showing obvious anisotropic characteristics;and④the porous model is a mixed flow of“laminar flow+turbulent flow”,with the increase of seepage velocity,the proportion of turbulent flow in hydraulic gradient increases,which is mainly related to the characteristics of pore structure.