Convective heat transfer of water flow in intersected rock fractures for enhanced geothermal extraction

Numerous intersected rock fractures constitute the fracture network in enhanced geothermal systems. The complicated convective heat transfer behavior in intersected fractures is critical to the heat recovery in fractured geothermal reservoirs. A series of three-dimensional intersected fracture models is constructed to perform the flow-through heat transfer simulations. The geometry effects of dead-end fractures (DEFs) on the heat transfer are evaluated in terms of intersected angles, apertures, lengths, and the connectivity. The results indicate that annular streamlines appear in the rough DEF and cause an ellipse distribution of the cold front. Compared to plate DEFs, the fluid flow in the rough DEF enhances the heat transfer. Both the increment of outlet water temperature ΔT_out and the ratio of heat production Q_r present the largest at the intersected angle of 90° while decline with the decrease of the intersected angle between the main flow fracture (MFF) and the DEFs. The extension of the length of intersected DEFs is beneficial to heat production while enhancing its aperture is not needed. Solely increasing the number of intersected DEFs induces a little increase of heat extraction, and more significant heat production can be obtained through connecting these DEFs with the MFF forming the flow network.