非均匀应力场中井筒卸载过程井壁围岩孔隙弹性动力响应机制  

Poroelastodynamic response of a wellbore during unloading in a formation under non-hydrostatic in-situ stresses

作　　者：夏阳[1] 文豪 金衍[1] 陈勉[1] 卢运虎[1] XIAYang, WEN Hao, JINYan, CHENMian, LUYunhu(State Key Laboratory of Petroleum Resource and Engineering, China University of Petroleum（Beijing）, Beijing 102249, China)

机构地区：[1]中国石油大学(北京)油气资源与工程国家重点实验室,北京102249

出　　处：《岩石力学与工程学报》2018年第5期1115-1125,共11页Chinese Journal of Rock Mechanics and Engineering

基　　金：国家自然科学基金杰出青年基金项目(51325402);国家自然科学基金重大项目(51234006)~~

摘　　要：传统井壁稳定理论没有考虑流体和固体的惯性作用,无法解释井筒受力变化下井壁失稳的本质。为了分析井筒卸载过程中井周应力场瞬态演化过程,揭示井壁围岩孔隙弹性动力响应机制,基于Biot饱和多孔介质弹性动力学理论,综合考虑孔隙流体、固体颗粒的压缩性及惯性、黏滞耦合作用,建立多孔弹性地层非均匀地应力场中表征井筒卸载过程井壁围岩动力响应的数学模型,通过对模型进行分解,采用Laplace变换和位移变换法,得到非轴对称井周应力解析解,分析井筒卸载过程井周应力场瞬时波动现象。研究表明:固体和流体的惯性作用导致井筒卸载早期井周孔隙压力与应力场产生波动,该现象传统理论无法揭示;井筒卸载过程中卸载速率越大,孔隙压力与应力的波动峰值越大;卸载后的井底压力越高,径向应力波动峰值越大,环向应力波动峰值越小。建立的模型为动载条件下井壁稳定力学分析提供了理论基础,并对认识钻井过程井下复杂事故具有重要工程意义。Traditional theories of wellbore stability have not considered the inertial effects of solid-fluid system and are not suitable for studying the wellbore stability under dynamic loads. In order to analyze the transient variation of the stress field near wellbore and to reveal the poroelastodynamic mechanism during the unloading process,this paper presents a mathematical model based on Biot′s theory of poroelastodynamics to characterize the dynamic behavior of a wellbore in a poroelastic formation subjected to a non-hydrostatic stress field by considering the compressibility of pore fluid and solid grains,the inertial effect and the coupled viscous effect. Through the techniques of mode decomposition,Laplace transform and displacement transform,the analytical solutions of stress components and pore pressure are obtained. The transient behavior of the stress field during the wellbore unloading is analyzed. The results show the importance of the inertial effects of the solid-fluid system,which produces a wave-diffusion behavior in the early times. The higher the unloading rate,the larger the peak of pore pressure and stress. The wellbore pressure has nearly no effect on the peak pore pressure. On the other hand,the higher the wellbore pressure,the larger the peak radial stress and the smaller the peak hoop stress.

关 键 词：岩石力学 饱和多孔介质 非均匀地应力 卸载 动力响应 井壁稳定 

分 类 号：TU45[建筑科学—岩土工程]