3D poro-elasto-plastic modeling of breakouts in deviated wells

Abstract

Borehole breakouts are stress-induced enlargements of the wellbore cross-section. Predicting wellbore breakouts is important for the success of any drilling operation; however, accurate prediction of breakouts in deviated wells can be a technically challenging task. Misalignment between wellbore trajectory and field principal stress orientation along with the strong coupling between fluid flow, stresses and plasticity are some of the factors that makes breakouts in deviates well more challenging. This paper discusses a 3D poro-elasto-plastic numerical modeling approach for breakouts in deviated wells. Dynamic mudcake buildup on the wellbore wall is also incorporated into the numerical model, enabling quantitative analysis of the mudcake effect on the borehole breakout. The influences of well trajectory, fluid seepage between wellbore and formation pores, plastic strain softening of the rock, and dynamic mudcake buildup on the breakout are highlighted and analyzed using numerical examples. The results indicate that the breakout shape of deviated wells is largely dependent on well inclination while its volume can be reduced by mitigating fluid seepage through mudcake buildup. The proposed finite-element modeling approach in this study confirms the need to consider the coupling among these factors when predicting wellbore breakouts in complex geological and drilling conditions.