Thermally Induced Pore Pressure Build Up in Saturated Porous Low Permeable Formation

Abstract

Heating a saturated low permeable geological formation induces pore pressure build-up, so-called thermal pressurization, due to the difference in thermal dilation of the solid skeleton and the pore water. The excess pore pressure generally leads to a decrease in the effective stress and can provoke thermally hydraulic fracturing or shear failure. This paper aims at deriving an explicit solution of the pore pressure increase as a linear function of the temperature variation and total mean stress variation in the framework of linear poroelasticity under undrained conditions. The thermal pressurization coefficient is deduced and then under the condition of constant total stress, which is a function of the difference between the thermal expansion coefficients of the pore water and the porous medium, porosity, bulk moduli of water, porous medium, and solid phase. The finite element solution is used to show the accuracy of mathematical development. The presence of this solution allows evaluation of the effect of temperature-dependent thermal expansion coefficient and temperature and pressure-dependent bulk modulus of water. An equivalence between thermo-poro-elastic and thermo-elastic problems is established. This equivalence allows determining the pore pressure from a thermo-mechanical simulation. Moreover, the undrained dilation coefficient and undrained bulk modulus are also derived from this analysis.