Abstract
The poroelastodynamic failure of a wellbore due to periodic loading during drilling is an unsolved problem. The conventional poroelastic method to calculate the stress distribution around wellbore is for static loading cases and cannot be used for short-time dynamic-loading cases which result in wave propagation in the formation. This paper formulates a poroelastodynamic model to characterize dynamic stress and pressure wave due to periodic loadings and to analyze the transient failure of the suddenly drilled wellbore in a non-hydrostatic stress field. The fully coupled poroelastodynamic model was developed based on the equations of motion, fluid flow and constitutive equations to reflect stress and pressure waves that resulted from a periodic stress perturbation at the wellbore surface. The model was analytically solved by means of field expansions of the solutions, by performing a Laplace transform as well as some special techniques. Simulation results show that the pressure and stress responses inside the formation resemble a damped oscillator where the amplitude decays as the distance to wellbore increases. Especially the potential shear failure zone around the wellbore was computed and plotted. Influences of poroelastic parameters, in-situ stress and periodic load parameters on the shear failure responses were analyzed in a detailed parametric study, and the results provide fundamental insights into wellbore stability maintenance in different reservoirs.
Highlights
Wellbore instability can cause many substantial problems during drilling, such as stuck pipe and lost circulation
The poroelastodynamic model is developed basedinondetail, Biot’sand theory, we show that the pressure and stress responses inside the formation resemble a damped oscillator present a novel solution to the model
Results presented in this paper provide fundamental insights into wellbore instability in different reservoirs, and suggestions are made on maintaining wellbore stability
Summary
Wellbore instability can cause many substantial problems during drilling, such as stuck pipe and lost circulation. The wellbore is embedded into a formation that is characterized by non-hydrostatic been addressed horizontal stresses In this far-field paper, we consider poroelastodynamic failure of a wellbore dueon to Biot’s periodic loading we present a novel solution to the model. It and is noteworthy that the periodic stress perturbation at the surface are analyzed in detail, the results show thatpore the pressureand reaches peak at inside a certain and location, the conventional poroelastic theory pressure stressits responses thetime formation resemblewhile a damped oscillator where the amplitude alwaysasfails to discover this phenomenon to the that lack the of pore consideration of solid-fluid decays the distance to wellbore increases. Results presented in this paper provide fundamental insights into wellbore instability in different reservoirs, and suggestions are made on maintaining wellbore stability
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