基于纳米压痕的非均质性页岩基质力学尺度效应研究

页岩基质力学精细表征是我国页岩气大规模高效开发的前提，目前学者普遍采用宏观力学实验开展页岩力学变形与破坏机理研究，忽略了矿物成分及微观结构强非均质性的影响。鉴于此，本项目将通过分子动力学模拟、压痕试验、三维有限元数值仿真和理论分析等手段开展非均质性页岩基质微观力学特性及其尺度效应研究。构建页岩基质矿物纳米压痕的分子动力学模型，揭示页岩矿物颗粒变形机制，建立纳观尺度基质矿物弹塑性力学本构关系。开展页岩基质靶向微、纳米压痕实验，验证基质矿物力学本构关系，分析非均质性页岩微观力学特性的主控因素。基于页岩数字岩芯和纳观力学本构关系建立三维有限元数值仿真模型，实现跨尺度压痕实验反演分析，提出基于页岩基质矿物组织结构非均质性特征和微观力学参数的力学多尺度升级模型，探明页岩基质力学特性尺寸依赖演化规律。研究结果能够揭示非均质页岩基质的力学变形机制，为页岩气储层精细评价提供理论依据。

The fine characterization of shale matrix mechanics is the premise of large-scale and efficient development of shale gas in China. At present, scholars generally study the mechanism of deformation and failure of shale mechanics by using micromechanics experiments, ignoring the influence of strong heterogeneity of mineral composition and microstructure. This project aims to study on the micromechanical properties and mechanical scale effect of heterogeneous shale matrix by means of molecular dynamics simulation, indentation test, three-dimensional finite element method and theoretical analysis. Molecular dynamics model of polycrystalline shale minerals of nano-indentation experiments is constructed to explain the deformation mechanism of shale mineral particles and to establish the elastic-plastic mechanical constitutive relationship of nano-scale matrix minerals. Then targeting micro and nano indentation experiments of shale matrix are conducted to verify the mechanical constitutive relationship, and the main controlling factors of micro-mechanical properties of heterogeneous shale are analyzed. Three-dimensional finite element model is built based on the digital core of shale sample and the established constitutive relationship, realizing the across-scale inversion analysis of indentation experiments. Based on the heterogeneity of the mineral composition and microstructure of shale matrtix and the microscopic mechanical parameters, a multi-scale upgrade model of mechanical properties of shale matrix is proposed to reveal the scale-dependent evolution law of mechanical properties of shale matrix. The results help to reveal the deformation mechanism of heterogeneous shale matrix, and provides a theoretical basis for the fine characterization of shale gas reservoirs.