Is natural convection within an aquifer a critical phenomenon in deep borehole heat exchangers' efficiency?

Abstract

Deep borehole heat exchangers (BHEs) can be utilised effectively for geothermal (heat) extraction from up to a few kilometres below the subsurface using the conventional closed U-loop or coaxial configurations. These systems take advantage of the high enthalpy energy in the deeper ground without relying on fracture flow extraction/injection, hence avoiding the complexity and uncertainty of hydraulic fracturing to enhance the permeability of deep aquifers. Despite the recent theoretical advancement in deep BHE systems, recent studies mainly assume conductive heat transfer in the ground, neglecting the effects of groundwater and heat convection (natural or forced) on the system's thermal capac..