Transport Mechanisms Within Thermally-Shocked Region of an Enhanced Geothermal System (EGS)

摘要

There is a consensus regarding the beneficial effects of thermally induced cracks in an EGS reservoir. Thermally induced cracks have proven to aid reservoir performance, hydrologically and thermally by lowering the flow impedance and increasing heat exchange surface area respectively. The commonly-practiced engineering approach neglects the benefits of the thermal cracks by excluding them from reservoir simulation. By ignoring the existence of thermally induced cracks, progress towards understanding the mechanism and extent of their contribution is hindered. This paper investigates the transport mechanism within a thermally-shocked region of the EGS reservoir to address the thermal crack contribution in a reservoir's performance. A porous medium with different length scales is recommended to simulate heat and mass transport within the thermally fractured region. The role of diffusion and convection in both heat and mass transport for the generated porous medium is discussed. The analysis shows that depending upon the degree of fragmentation of the thermally-fractured region, transport mechanisms will be different. A numerical example shows that for porous media, the heat and mass transport mechanisms change when the pore's length scale changes. The finding challenges the accepted notion that heat and mass transport are analogous on varying scales.