泥岩流-固-化耦合模型参数的蒙特卡洛估计

泥岩流-固-化耦合模型的研究与应用是正确认识泥岩井壁失稳机制的根本途径之一。化学线弹性本构方程实现了渗流、化学场作用下泥岩变形的表征，而泥岩中渗流及溶质扩散则分别满足Speigler-Kedem 模型和Fick第一定律。简化应用了泥岩的流-固-化耦合模型（包括泥岩力学平衡方程、泥岩孔隙流体及溶质质量守恒方程），基于商业有限元软件Comsol Multiphysics，使用有限单元法求解了正向方程，并依据最小二乘准则，应用蒙特卡洛随机搜索方法，根据泥岩渗流、溶质扩散及泥岩单向扩散侧向约束膨胀实验数据，反演求解了模型参数（包括泥岩渗透率、膜效率、溶质扩散系数及膨胀系数）。理论拟合曲线与实验数据结果非常吻合，说明简化后的泥岩流-固-化耦合模型能够有效描述多场耦合环境中泥岩的性质，所建立的模型参数求解方法准确可靠，为流-固-化耦合模型在井壁稳定研究中的推广应用奠定了基础。

Monte Carlo estimation on the parameters of shale chemo-poro-mechanical coupling model

The research and application of shale chemo-poro-mechanical coupling model is one of fundamental approaches to correctly understand the shale borehole instability mechanism. The shale deformation with pore fluid flowing and solute diffusion can be characterized using the chemical linear-elastic constitutive equation, while the pore fluid flowing and solute diffusion of shale satisfy the Speigler-Kedem model and the Fick First Law, respectively. The shale chemo-poro-mechanical coupling model is simplified and applied in this study, including shale mechanical equilibrium equation as well as pore fluid and solute mass balance equations. Based on the commercial finite element software Comsol Multiphysics, the forward equation is solved using the finite element method. According to the least squares criterion as well as the pore pressure transmission, solute diffusion, shale one dimensional swelling experimental data, Monte Carlo randomly search method was used to retrieve the model parameters, including shale permeability, membrane efficiency, solute diffusion coefficient and swelling coefficient. The theoretical fitting curve is well consistent with experimental data, indicating that the simplified shale chemo-poro-mechanical coupling model can effectively describe the shale properties under multi-field coupling environment. The established model parameter solution method is accurate and reliable, laying a basis for the promotion and application of chemo-poro-mechanical coupling model in the research of wellbore stability.