摘要
针对弹塑性储层,基于线弹性理论假设的传统起裂模型已不再适用,需要研究基于非线性本构方程的起裂模型。基于岩石非线性本构方程,运用塑性全量理论,建立了弹塑性地层井周应力场模型;结合"井壁"应力场模型和弹塑性岩石破坏准则,建立了弹塑性地层的起裂压力预测模型。结果表明:岩石产生塑性屈服,"井眼"应力集中效应会减弱,"周向张应力会减小",甚至无法产生。屈服后的起裂压力比线弹性理论预测值大,起裂模式存在拉张和剪切两种方式,剪切起裂存在破坏角。屈服后,幂硬化指数小于等于0.5的岩石只可能产生剪切起裂;幂硬化指数大于0.5的岩石,屈服应力、幂硬化指数、内摩擦角和凝聚力越小,越容易产生剪切起裂,反之越容易产生拉张起裂。
Since traditional hydraulic fracturing initiation models are primarily based on linear elastic theory, they are not applicable for the elastoplastic reservoirs. Therefore, it is necessary to explore a new initiation model on the basis of the nonlinear constitutive equation. Considering the total deformation theory of plasticity, a model is established for the stress field around a well. Furthermore, an elastoplastic hydraulic fracturing initiation model is proposed according to the stress distribution model and failure criteria of elastoplastic rock. The results show that once the rock is yielded, the effect of stress concentration around the wellbore is greatly weakened and the circumferential tensile stress decreases and even disappears. The initiation pressure is higher than that predicted by the linear-elastic theory. There are two types of fracturing initiation modes including tensile and shear failures, and the shear failure is characterized by a failure angle. When the hardening index of rock is not greater than 0.5, only shear failure takes place. However, when the hardening index is greater than 0.5, the shear failure tends to happen more frequently when the values of yield stress, hardening index, internal friction angle and cohesion are small; on the contrary the tensile failure occurs.
出处
《岩土力学》
EI
CAS
CSCD
北大核心
2015年第9期2494-2500,2509,共8页
Rock and Soil Mechanics
基金
国家自然科学基金项目(No.51374178)
国家科技重大专项项目(No.2011ZX05002-004-007HZ)
关键词
弹塑性地层
非线性本构方程
塑性全量理论
井周应力场
起裂模式
起裂压力
elastoplastic formation
nonlinear constitutive equation
total deformation theory of plasticity
stress field around wellbore
initiation mode
initiation pressure
