Title: Image-based modelling of rock non-linear deformation under low-stress levels Show Chinese title

Title: 基于图像的岩石低应力水平下的非线性变形建模

Abstract: Rock geophysical properties are widely reported to exhibit non-linear behaviours under low-stress conditions (below 10-20 MPa) before transitioning to the linear elastic stage, primarily due to the closure of microcracks and grain interfaces. Image-based modelling of rock deformation struggles to effectively characterise the microcrack closure effect because of the partial-volume effect, where image voxels are larger than microcracks and contain both pore and solid phases. This study presents a novel method to simulate non-linear rock deformation under elevated stress conditions. The method reconstructs digital rock models by treating partial-volume voxels as transitional phases that incorporate microcracks. By assigning intermediate elastic moduli and assuming that the pore portion within each partial-volume voxel deforms before the remaining solid content, the method employs the finite element method to simulate rock deformation and calculate the porosity of the deformed model. The method is tested on two Bentheimer sandstone models, and the results demonstrate its ability to predict the non-linear changes in porosity and elastic properties as the effective stress increases. This work provides a new pathway for image-based modelling of non-linear rock deformation considering the microcrack closure effect, offering valuable insights into the complex mechanical behaviour of rocks under confinement. Show Chinese abstract

Abstract: 岩石的地球物理性质在低应力条件（低于10-20 MPa）下通常表现出非线性行为，随后过渡到线性弹性阶段，这主要是由于微裂隙和颗粒界面的闭合。基于图像的岩石变形建模难以有效表征微裂隙闭合效应，这是由于部分体积效应，其中图像体素大于微裂隙，并包含孔隙和固体相。本研究提出了一种新方法，在高应力条件下模拟非线性岩石变形。该方法通过将部分体积体素视为过渡相来重建数字岩石模型，这些过渡相包含微裂隙。通过赋予中间弹性模量，并假设每个部分体积体素内的孔隙部分在剩余固体内容物之前发生变形，该方法采用有限元法模拟岩石变形并计算变形模型的孔隙度。该方法在两个Bentheimer砂岩模型上进行了测试，结果表明其能够预测有效应力增加时孔隙度和弹性性质的非线性变化。这项工作为考虑微裂隙闭合效应的基于图像的非线性岩石变形建模提供了一条新途径，为岩石在约束下的复杂力学行为提供了有价值的见解。