CONDUCTIVE HEAT-FLOW AND THERMALLY-INDUCED FLUID-FLOW AROUND A WELL BORE IN A POROELASTIC MEDIUM

Transient analytical solutions for temperature and pore pressure chang es near a circular borehole under instantaneous temperature and fluid pressure changes inside the borehole are presented. The solutions coup le conductive heat transfer with Darcy fluid flow, and a borehole unde r a nonhydrostatic far-field stress state is simulated. The heat condu ction equation is decoupled from the coupled system of isothermal gove rning equations, and the complete solution is obtained by superimposin g this decoupled solution on the isothermal one. The solution is there fore applicable to low-permeability media, where heat transfer is domi nated by conduction only. Both cold and warm injection processes are s tudied, and the applications to hydraulic fracture initiation and ther mally induced fluid flow are discussed. Taking Westerly granite as an example, it is concluded that the maximum thermally induced pore press ure inside the rock formation can be 30% higher than the isothermal po re pressure, with a borehole temperature and fluid pressure change rat io (Delta T/Delta p) = 1 degrees C/MPa. It is emphasized that the ther mally induced pore pressure change can be significant inside a low-per meability porous medium, and a coupled solution must be obtained to ad dress the mechanical, hydraulic, and thermal responses appropriately.