Coupled Thermoporomechanical Effects on Borehole Stability

Presented at: SPE Annual Technical Conference and Exhibition, New Orleans, Louisiana, October 2009.


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.