Coupled Thermo-poro-mechanical Effects on Borehole Stability

Abstract

A new model and numerical scheme are developed to study the effects of poro-elasticity and thermo-elasticity on borehole stability. The poro-thermo-mechanical model integrates the effects of both thermal and hydraulic diffusion in determining the effects of the drilling fluid and mud weight on the borehole system. Thermal diffusion into shale formations occurs quicker than hydraulic diffusion, thereby dominating pore pressure changes during early time. The thermal differential can affect shale stability in two ways:The differential-driven thermal diffusion induces additional pore pressure that adds to the poro-elastic stress change near wellbore.The thermal differential directly induces a change in rock stresses. Previous publications have adequately investigated and addressed the second of the two issues. The current work attempts to model and assess the impact of the first mechanism. In the model, thermal diffusion is coupled with hydraulic diffusion to obtain the pore pressure distribution reflecting the cumulative impact. The generated poro-elastic and thermo-elastic stresses are obtained by solving equilibrium equations utilizing superposition. A field case is included in this paper and shown that the thermo-elasticity adversely would affect the borehole stability. Introduction Over the past 20 years a large number of studies have been dedicated to understanding thermal impact on borehole stability. Detournay and Cheng [1] developed the poro-elastic, transient and plane-strain analytical solution for an isothermal case. Wang and Papamichos [2] extended the model for the non-isothermal condition by uncoupling the temperature and the thermally induced pore pressure. Xuli [3] developed a fully coupled thermo-poro-elasto-plastic model. The above methods employed a finite element model in achieving the solution. Yu, M.J. and Sharma, M [4], [5] incorporated the chemical effect in the decoupled thermo-poro-elastic model and applied an analytical solution. Both the numerical finite element and analytical methods have their disadvantages. The field equations are difficult to solve within the finite element framework. On the other hand, the analytical method is unstable and slow. In this paper, a new numerical model based on finite difference method is developed to simulate the stress changes during drilling of an inclined wellbore subjected to an anisotropic stress field and a non-isothermal condition. Poro-elastic, thermal poro-elastic, thermo-elastic stresses are evaluated and their effect on borehole stability is addressed in a field case.

The Effects of Geomechanics on the WAG Injection Model

“…The change in porosity and permeability leads to the change in all results in the case of without geomechanics (as changes in different phases saturations, pressures, front movement, and production after injection) 8) .…”

2D Numerical Simulation of Improving Wellbore Stability in Shale Using Nanoparticles Based Drilling Fluid

“…Yu et al [35] introduced a chemical-mechanical wellbore instability model for shales that accounted for solute diffusion and found that the onset of instability depended not only on water activity, but also on the properties of the solutes. Zhai et al [36] developed a poro-thermo-mechanical model that integrated the effects of both thermal and hydraulic diffusion to determine the effects of drilling fluid and mud weight on the wellbore system. They found that the pressure differential effect was dominant in high mobility formation while thermal effect was important for low mobility formation.…”