基于CGAL的岩石裂隙面三维重构方法研究

Research on 3D reconstruction method of rock fracture surface based on CGAL

水力压裂后裂隙的几何学特征决定了裂隙岩体强度、变形行为及渗流特性。为进一步定量分析剪应力–注水压力耦合作用下砂岩裂隙面表面粗糙度、隙宽、产状和分形特征等,提出一种基于计算几何算法库(computational geometry algorithms library,CGAL)的裂隙面三维重构方法。结合水力压裂试验后含裂隙试件CT扫描图像的灰度分布特征,优化了其预处理方法以保证三维重构的准确性,采用Delaunay细化方法重构了试验后含裂隙试件,并用随机抽样一致算法检测试件表面,实现了自动校正倾斜、统一空间位置,最终通过裁切可单独提取裂隙面,并通过裂缝沟通体积、裂缝沟通面积和分形维数对其进行了量化表征。结果表明,基于CGAL三维重构后的裂隙模型可再现砂岩试样在剪应力–注水压力耦合作用下内部裂隙的发育特征,为岩石裂隙面几何特征的量化表征及裂隙面渗流特性数值模拟研究提供了基础。

The geometric characteristics of the fracture after hydraulic fracturing determine the strength,deformation behavior and seepage characteristics of the fractured rock mass.In order to further quantitatively analyze the surface roughness,fracture aperture,occurrence and fractal characteristics of sandstone fracture surfaces under the coupling of shear stress and water injection pressure,a method for 3D reconstruction of fracture surface based on the computational geometry algorithms library(CGAL)was proposed.Combined with the grayscale distribution of CT images of fractured specimens,preprocessing method was optimized to ensure the accuracy of the 3D reconstruction.The Delaunay refinement algorithm was used to reconstruct surfaces of fractured specimens.Surface planes of specimens were detected employing random sampling consistent algorithm,which helped to realize automatic tilt correction and coordinate setting.Finally,the fracture surface could be extracted by cropping.It is quantitatively characterized by calculating the fracture communication volume,fracture communication area and fractal dimension.The results show that based on the 3D model of fractures,the development of fracture systems in sandstone specimens under the coupling of shear stress and water injection pressure can be reproduced,which provides a foundation for the geometric quantitative characterization of fracture surface and numerical simulation of fracture surface seepage behavior.