Shale strength characterization based on the multi-scale homogenization theory
Han Qiang1,2, Qu Zhan1,2, Ye Zhengyin3
1. College of Petroleum Engineering, Xi’an Shiyou University, Shaanxi Xi’an 710065, China;
2. Shaanxi Key Laboratory of Well Stability and Fluid & Rock Mechanics in Oil and Gas Reservoirs, Shaanxi Xi’an 710065, China;
3. School of Aeronautics, Northwest Polytechnical University, Shaanxi Xi’an 710072, China
Shale strength is a basic technical parameter required for shale oil and gas development. At present, macroscopic laboratory test and logging interpretation have problems with sample preparation and discontinuous interpretation of parameters. To effectively evaluate shale multi-scale strength, the micro/meso-strength homogenization Π function models of shale were established based on the principle of maximum plastic dissipation energy and the theory of microscopic porous media. The basic mechanical properties of pure clay minerals were evaluated by shale micromechanical test. Meanwhile, the numerical simulation of shale micro/meso-mechanical test was performed. Micro/meso scale hardness-strength model was solved by dimensional analysis. The results demonstrate that the clay packing density has a significant influence on strength at a micro scale. Under the influence of non-clay inclusions, the ratio of hardness and internal cohesion coefficient is positively correlated to friction coefficient at a meso scale. According to the shale meso-mechanical test, the prediction of shale macro strength parameters was performed based on model solutions. The normalized comparison analysis was conducted considering the common lab results as conventional true value. The results show that the normalized mean value of the friction angle is 1.12, and that of the cohesion is 1.21.The established system on shale strength characterization can provide basis for effectively solving oil and gas development.
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2019, Vol. 40 
