A Strain Rate Dependent Constitutive Model for the Lower Silurian Longmaxi Formation Shale in the Fuling Gas Field of the Sichuan Basin,China
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The research was financially supported by the China Scholarship Council project, the National Natural Science Foundation of China (grants No. 51574218, 41688103, 51678171, 51608139, U1704243 and 51709113), the Guangdong Science and Technology Department (grant No. 2015B020238014), the Guangzhou Science Technology and Innovation Commission (grant No. 201604016021), the High-level Talent Research Launch Project (grant No. 950318066), the Shandong Provincial Natural Science Foundation, China (grants No. ZR2017PD001 and ZR2018BD013) and the Science Foundation of Chinese Academy of Geological Sciences (grant No. JYYWF20181201).

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    Abstract:

    Shale, as a kind of brittle rock, often exhibits different nonlinear stress-strain behavior, failure and time-dependent behavior under different strain rates. To capture these features, this work conducted triaxial compression tests under axial strain rates ranging from 5×10?6 s?1 to 1×10?3 s?1. The results show that both elastic modulus and peak strength have a positive correlation relationship with strain rates. These strain rate-dependent mechanical behaviors of shale are originated from damage growth, which is described by a damage parameter. When axial strain is the same, the damage parameter is positively correlated with strain rate. When strain rate is the same, with an increase of axial strain, the damage parameter decreases firstly from an initial value (about 0.1 to 0.2), soon reaches its minimum (about 0.1), and then increases to an asymptotic value of 0.8. Based on the experimental results, taking yield stress as the cut-off point and considering damage variable evolution, a new measure of micro-mechanical strength is proposed. Based on the Lemaitre’s equivalent strain assumption and the new measure of micro-mechanical strength, a statistical strain-rate dependent damage constitutive model for shale that couples physically meaningful model parameters was established. Numerical back-calculations of these triaxial compression tests results demonstrate the ability of the model to reproduce the primary features of the strain rate dependent mechanical behavior of shale.

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HOU Zhenkun, LI Xianwen, ZHANG Yanming, LIANG Huqing, GUO Ying, CHENG Hanlie, GAO Ruchao.2019. A Strain Rate Dependent Constitutive Model for the Lower Silurian Longmaxi Formation Shale in the Fuling Gas Field of the Sichuan Basin, China[J]. Acta Geologica Sinica(),93(4):972-981

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History
  • Received:August 01,2018
  • Revised:December 20,2018
  • Adopted:
  • Online: August 20,2019
  • Published: