考虑岩石弹塑性变形的井周应力场计算模型研究

针对煤岩、页岩等岩石具有弹塑性这一特性，考虑岩石非线性硬化与软化变形，并耦合工作液渗滤作用，沿井筒径向方向将地层分为塑性软化、塑性硬化和弹性区，根据弹性区与塑性区交界处应力连续的特点，建立了耦合工作液渗滤和岩石非线性硬化与软化变形的井壁应力场模型。分析表明，塑性区大小与井眼流体压力、泊松比和地层初始孔隙流体压力呈正相关关系，与岩石强度呈负相关关系。与弹性状态相比，岩石塑性变形降低了井眼应力集中效应，岩石塑性变形对井周径向应力影响较小，但会使井周周向应力增加。

A Study on Calculation Model of Stress Field Around Wells Considering Rock Elastic-plastic Deformation

Aiming at the elastic-plastic characteristics of coal, shale and other rocks, a calculation method for stress field of elastic-plastic formation is established, which divide the formation into the plastic softening, the plastic hardening and the elastic zone along the radial direction. In this new model the nonlinear hardening and softening deformation of rock and the percolation effect of the working fluid are considered. The analysis shows that the plastic zone range is positively correlated with the borehole fluid pressure, Poisson's ratio and the initial pore fluid pressure, and is inversely related to the strength of the rock. Compared with the elastic state, the plastic deformation of rock decreases the stress concentration effect, and the plastic deformation of the rock has a little influence on the radial stress of the formation while it can increase the circumferential stress of the formation.