Abstract
<jats:title>Abstract</jats:title> <jats:p>Heat exchange and energy extraction from a naturally fractured reservoirs (NFR) are important processes for EGS design. Cold water is circulated from a wellbore and carries warmer water up to the surface. Depending on the circulation velocity and temperature out to the surface, different extraction efficiency may be achieved. Such an efficiency also depends on the depth, formation temperature and its gradient, both hydraulic and thermal properties of the solid skeleton and fluid, thus a model coupling the energy transfer from an injecting tubing, annulus and into/from a NFR must be established. A semi-analytical solution is obtained for convective-conductive energy transfer between tubing, annulus and fissured NFR, the temperature perturbation, induced fluid pressure and stresses can be calculated in vicinity of a wellbore. These induced THM responses at a wellbore and inside the formation are also of great interest to EOR recovery, CO2 sequestration, and drilling process in HP/HT environment, when fluids are injected and then circulated or produced. A wellbore system including tubing and annulus is coupled to a dual-porosity reservoir model to simulate heat extraction or adsorption via a wellbore from a NFR in this paper. We conclude that a coupled wellbore-reservoir system with conductive-convective heat transfer is important for wellbore integrity evaluation and design in heat energy extraction, CH4 injection/production and CO2 sequestration in NFR so that the determination of injectivity, storage capacity and safety factors may be evaluated.</jats:p>