A Fully Coupled Thermoporoelastic Model for Drilling in Geological Formations

Abstract

Coupled processes in geological formations impact drilling and borehole stability. The coupling of the matrix deformation, and fluid and heat diffusions results in a time dependent response in the formation. A general theory of thermoporoelasticity is developed that fully couples the three processes: mechanical, hydraulic, and thermal in rocks saturated by a compressible and thermally expansible fluid. A finite element model is developed for the fully coupled processes consisting of: thermoporoelastic deformation, hydraulic conduction, thermal osmosis, heat conduction, pressure thermal effect, and the interconvertibility of mechanical and thermal energy. The model is used to analyze the problem of a wellbore subjected to hydrostatic and non hydrostatic in situ stress fields. The results indicate that heating induces an increase in the pore pressure, while cooling induces a decrease in the pore pressure. The total radial and tangential stresses are more compressive in the case of heating and less compressive in the case of cooling relative to the isothermal case. It is also shown that the lower the permeability/fluid viscosity ratio, the larger the thermal loading effect on the pore pressure changes and that full coupling is important for modeling tight formations