Numerical simulations to assess thermal potential at Tauranga low-temperature geothermal system, New Zealand

Tauranga low-temperature geothermal system (New Zealand) has been used for the last 40 years for direct uses including space heating, bathing and greenhouses. Warm-water springs in the area are between 22 and 39 A degrees C, with well temperatures up to 67 A degrees C at 750 m depth. A heat and fluid flow model of the system is used to determine reservoir properties and assess thermal potential. The model covers 130 km by 70 km to 2 km depth, and was calibrated against temperatures measured in 17 wells. Modelling shows that to maintain the observed primarily conductive heat flow regime, bulk permeability is a parts per thousand currency sign2.5 x 10(-14) m(2) in sedimentary cover and a parts per thousand currency sign1 x 10(-16) m(2) in the underlying volcanic rocks. The preferred model (R (2) = 0.9) corresponds to thermal conductivities of 1.25 and 1.8 W/m(2) for sedimentary and volcanic rocks, respectively, and maximum heat flux of 350 mW/m(2). The total surface heat flow is 258 MW over 2,200 km(2). Heat flux is highest under Tauranga City, which may be related to inferred geology. Model simulations give insights into rock properties and the dynamics of heat flow in this low-temperature geothermal system, and provide a basis to estimate the effects of extracting hot fluid.