RECONSTRUCTION AND FRACTAL ANALYSIS FOR THREE DIMENSIONAL FRACTURE NETWORK OF LONGMAXI SHALE
LAN Hengxing1,2, WU Yuming1, LI Quanwen1,3, CHEN Junhui1,3, ZHAO Xiaoxia1,3
1. Institute of Geographic Sciences and Natural Resources Research, CAS, Beijing 100101;
2. School of Geological Engineering and Geomatics, Chang'an University, Chang'an 710054;
3. University of Chinese Academy of Sciences, Beijing 100049
Recent studies were based on the small samples which were as big as core samples to get the fracture propagation features. However, the small samples had many limitations. For example, continuous fracture propagation characteristics were difficult to get, which means it was a tough work to analyze the relationship between in-situ stress and fracture distribution. Hence, fracture propagation characteristics were gathered from a 2m×3m×0.7m samples from Shizhu County, Chongqin. The sample was cut into several cubic samples whose lengths of the sides were 30cm. At the same time, every surface of the cubic sample is numbered. Then the fracture distribution characteristics on each surface of the samples is obtained. The 3D fracture network is rebuilt according to the surface number. The fracture network shows the obvious rules that there are more fractures on the surface in the principle stress direction in contrast to other directions. The fractures on the surface perpendicular to the principle stress are 62°to the principle stress direction. Research on the fractal dimension proves that fractures on the different surfaces conform to the fractal dimension feature, which indicates that fractures' structure in small scale and big scale have similar regularity. In addition, fracture density and fractal dimension number in the maximum principle stress direction are bigger than other directions, which means fracture network structure is more complex. And fracture network structure in the surface perpendicular to the principle stress is less complex than that in the minimum horizontal stress direction. There are more bedding fractures in the horizontal stress direction while more shear fractures in the vertical direction, which are-62°to the minimum horizontal principle stress direction.