Modelling a Novel Scheme of Mining Geothermal Energy from Hot Dry Rocks

On the basis of a conceptual model for an Excavation based Enhanced Geothermal System (EGS-E), which proposed to extract heat from Hot Dry Rock at depth through dominantly adopting shaft, roadways, and caved rock failure techniques but not depending on either wellbore drilling or fracturing stimulation, a novel extensive version of heat extraction is proposed in this paper. Considering its mechanical stability issues, the new scheme contains two fields apart away: the ones are near-field by piping flow to touch the tunnel wall; the others are far-field through filling and driving fluid within the voids of collapsed rock. The former is represented as a tunnel unit being installed hollow linear, which can extract and produce heat precisely according to structural design and accurate operative prediction. The latter is represented as interconnective fissures being induced by stope excavation due to gravitational weight and unloading of a deep-buried squeeze. The EGS-E uses a two-stage heat exchange system of "fluid-rock" and "fluid-fluid." Then, a 3D transient thermal-hydraulic model is established to demonstrate the heat extraction performance. The temperature field and accumulated heat energy are investigated. The modeling work provides a tentative workflow to simulate an EGS-E system and, most probably for the first time, demonstrated that the deep underground Hot Dry Rock heat mining turns out to be preliminarily studied in a quantitative way.