Fully coupled thermal-hydro-mechanical model of pore pressure propagation around borehole with dynamic mudcake growth

Abstract

Pore pressure is a significant parameter in drilling engineering. A better understanding of near-wellbore pore pressure propagation by taking into account the thermal-hydro-mechanical coupling process and dynamic mudcake growth is beneficial for wellbore stability analysis, formation testing while drilling and well logging while drilling. To reveal the pore pressure evolution mechanism, a new fully coupled thermal-hydro-mechanical model of pore pressure propagation around a borehole with dynamic mudcake growth is proposed. A comparison with the conventional approach suggests that neglecting the dynamic mudcake effect or the coupling effect can overestimate the pore pressure in the vicinity of borehole. The variation process of pore pressure can be divided into four stages, and the coupling effect weakens as time progresses. Compared with the Young's modulus of the rock, formation porosity, and temperature difference, the near-wellbore pore pressure is more sensitive to the overbalanced pressure, in situ stresses, formation permeability, and the Poisson's ratio of the rock. The near-wellbore pore pressure disturbance in formations with a low permeability and high in situ stress is more significant; therefore, to consider the effects of thermo-hydro-mechanical coupling and dynamic mudcake growth in deep and ultra-deep well drilling is required.