Study Of Digital 3D Reconstruction Method And Macroscopic-microscopic Failure Behaviors For Sandstone

Digital rock analysis-numerical simulation methods are currently the most popular method to study the petro-physical,hydraulic,mechanical and thermal properties of rocks,the failure process of rocks and the fluid flow behaviors in microstructures of rocks during various engineering projects involved in rocks,such as the stability and strength analysis of geotechnical structures,the failure process of rocks during the rock blasting and the exploration of shale-gas and oil energy resources.The main advantages of the digital rock analysis-numerical simulation methods are the fast determination of the physical and hydraulic properties of rocks(e.gs.,porosity and permeability),the quantitative understanding of the effects of pore-scale variables on the mechanical,hydraulic and thermal properties of rocks and the intuitive investigation of the fluids(e.gs.,shale-gas and oil)evolutions in microstructures of rocks,which are helpful to various practical engineering.This paper aims at proposing a digital microstructural analysis framework,combined with the rock digital sample(RDS),to predict the common physical and hydraulic properties of rocks,and to study the macroscopic-microscopic failure process of rocks based on the comprehensive theories of rock mechanics,fluid mechanics,digital image processing and computing mechanics.Uniaxial compression and triaxial compression tests combined with X-ray CT imaging are applied to capture the damage information in the sandstone samples.The digital color difference segmentation(DCDS)algorithm is proposed to segment the crack,pore and grain phases in rocks,and the pore-scale variables are defined to estimate the common physical and hydraulic properties of rocks.The three-dimensional(3D)coupled reconstruction algorithm of the multiple-point geostatistical(MPS)algorithm and the marching cube(MC)algorithm is proposed to reconstruct the microstructures of rock samples.Based on the reconstructed rock digital samples of sandstone,the failure mechanism of sandstone samples subjected to the uniaxial and triaxial compression are studied.The effects of pore-scale variables on the mechanical,hydraulic and thermal properties of sandstone sample are studied.The main contents and conclusions are drawn as follows:(1)Obtaining the experimental dataset and X-ray CT image dataset of sandstone samples subjected to uniaxial compression and triaxial compression with X-ray CT imaging based on the SIEMENS-SOMATOM scope X-ray CT scanner and the Rock600-50 HT PLUS rock measurement systems.(2)The digital color difference segmentation(DCDS)algorithm is proposed to accurately segment the crack,pore and solid matrix phases determined by the crack and pore segmentation thresholds based on the digital color difference image of rocks.The microstructures with true spatial geometries and topologies are extracted and reminded as enough as possible.(3)The coupled 3D reconstruction algorithm of the MPS and MC algorithms is proposed to reconstruct the pore-solid microstructure models and crack-pore-solid microstructure models,in which the pore-scale variables of the true microstructure models and reconstructed microstructure models are compared to validate the accuracy of the proposed method.(4)The rock parameter computing theory framework,based on the reconstructed RDS,is proposed to predict the common mechanical properties,hydraulic properties and thermal properties of rocks such as the porosity,permeability,specific surface,tortuosity,and thermal conductivity.(5)The pore-scale variables are defined to quantitatively describe the microstructural characteristics of sandstone samples,and the initiation,propagation and connection behaviors of cracks in sandstones samples are studied by the X-ray CT imaging and digital 3D reconstruction methods,in which the failure process and damage mechanism of rocks subjected to uniaxial compression and triaxial compression are experimentally studied.(6)With the help of the RDS of sandstone,the failure process and damage mechanism of sandstone are numerically studied based on the digital numerical simulations of RDS,in which the failure process of sandstone samples subjected to uniaxial and triaxial compression are studied in details,and the effects of pore-scale variables on the cracking behaviors of sandstone samples are analyzed.