ABSTRACT

Geothermal energy resources in HDR becomes increasingly attractive due to both environmental and economic reasons. Increasing energy efficiency, hydraulic fracturing has been proposed, which has been extensively applied in petroleum engineering. Both the mechanical response and hydraulic flow coupled to the thermal effects are of great interests in these processes. Transient semi-analytical solutions for temperature and pore pressure and effective stress field near a circular borehole subjected to a non-isothermal constant flow are presented. The solutions couple conductive heat transfer with Darcy fluid flow in a poroelastic medium. They are applicable in low permeability porous media such as heavy oil reservoirs, HDR or shales, where conduction dominates the heat transfer process but a convective heat transfer must be considered for high permeability formations such as sandstones and fractured media where energy transport carried by hydraulic flow velocity can be dominating. Solutions presented show separately the effects of thermal perturbation and fluid flow on fluid pressures and effective stress development. It will be shown that a substantial thermal induced compressive stress may be generated near a borehole, which may prevent a fracture from initiating on the wellbore wall when wellbore temperature is high, whereas enhance a fracturing process when a cooler wellbore fluid in injected. Failure to incorporate such an effect may lead to serious error in designing a Enhanced Geothermal System (EGS) and hydraulic fracture predictions.

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