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| Poroelastodynamic response of a wellbore during unloading in a formation under non-hydrostatic in-situ stresses |
| XIA Yang，WEN Hao，JIN Yan，CHEN Mian，LU Yunhu |
| (State Key Laboratory of Petroleum Resource and Engineering，China University of Petroleum(Beijing)，Beijing 102249，China) |
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Abstract 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.
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2018, Vol. 37 
