Mathematical Modelling of Heat and Mass Transport in Deep Geothermal Reservoirs

Abstract

Current mathematical modelling of deep geothermal processes in New Zealand include generic supercritical chemical research, single field pluton!hot plate modelling. and conceptual multi-field modelling. This paper concentrates on a conceptual model of Taupo Volcanic Zone, (TVZ), New Zealand, emphasising the implications of the findings of recent GPS and micro-seismic studies in TVZ on models of processes transporting mass, heat and chemicals. We argue that in addition to the well established process of groundwater convection extracting heat and chemicals by interacting with magmatic-like intrusives under TVZ, that two other processes may be important. Firstly, the existence of a ductile layer between about 7 to 15 km depth will produce a region of "enhanced conduction" in which very high conductive fluxes of energy arise from a temperature distribution which varies exponentially with depth. Secondly, water may transport up through the ductile layer, episodically, as a result of extensional processes in the ductile region. Heat transfer in the TVZ of about 4200 MW may be made up from about 1300 MW from the cooling of intrusives in the brittle region in the upper 7 km; of about an additional 2300 MW of conducted heat entering the brittle region from the ductile region; and about an additional 600 MW of episodic water transport through the ductile region.