中文摘要：

页岩具有复杂的物理化学特性,在页岩中钻井将导致页岩和钻井液之间产生复杂的物理化学耦合作用（如：液体、离子、热等的传输扩散、热渗作用、电渗作用、化学渗滤作用、离子交换、膨胀压力的产生等）,这将深刻地改变井壁围岩的孔隙压力和应力的分布,从而影响井壁稳定性。该文将在有关文献的基础上,针对具有化学活性的页岩,首先提出一组瞬态的流、固、热、化学四场耦合方程组（包括固体变形、能量传输、流体流动、溶质离子扩散等四个相互耦合过程）试图来考虑它们之间复杂的物理化学耦合关系;然后以COMSOL（基于偏微分方程组的多物理过程模拟工具）作为平台,着重分析钻井过程中的流固热化学耦合作用过程,讨论井壁温度发生突然降低、钻井液与岩层液体之间存在离子浓度差的条件下,井壁附近围岩的孔隙水压力、应力、温度、溶质离子浓度的变化过程,为井壁稳定分析提出更为准确的应力分布。计算结果反映了热-化学耦合作用对井壁围岩应力有重要影响。

英文摘要：

The evolution of borehole stresses and borehole stability in chemically active shales is profoundly affected by their complex physical and chemical interactions with drilling fluids （e.g. hydraulic flow, diffusion of ions, heat transport, thermo-osmosis, electro-osmosis, chemo-osmosis, ion exchange, and changes in swelling pressure）. In this paper, a coupled porochemothermoelastic model for chemically active rocks is presented to evaluate these complex intricate links and their impact on the evolution of borehole stresses and pore pressure, which incorporates cross-coupled fluid flow equation, energy conservation equation, ion diffusion equation and mechanical equilibrium equation with many cross-coupling terms. A 2-D coupled porochemothermoelastic example of drilling in shales is solved by using a COMSOL-based simulator, which is the first engineering tool that performs partial differential equation-based multiphysics modelling in an interactive environment. The evolutions ofborehole stresses, pore pressure, temperature and solute concentration in the vicinity of the borehole due to cooling and the difference of ion concentration between formulation fluid and drilling mud are presented to demonstrate the significant thermo-chemical effects on stress and pore pressure distributions.