Computer Modelling of Heat and Mass Flow in Steaming Ground at Karapiti Thermal Area, New Zealand

Heat and mass transfer in steaming ground have been modeled using the TOUGH2 geothermal simulator and the results compared with field data collected by Bromley and Hochstein (2001). They measured temperatures at several sites over periods of 4 to 7 days at the soil surface, and depths of 0.01 m, 0.05 m, 0.10 m, 0.15 m, and 0.20 m. Soil porosities and saturations were also measured. These data sets were processed to extract four key sub-sets of data that were then used to calibrate a TOUGH2 model for each site. Two of these data sets are the steady state temperature and gas saturation versus depth; and the other two involve parameters of the variation with depth of the transient, approximately sinusoidal, diurnal temperature, namely, amplitude decay and phase shift. Calibration of the TOUGH2 models provides information about soil properties and heat and mass flows at each site. Model calibration also indicates a suitable range of parameters for the van Genuchten-Mualem relative permeability and van Genuchten capillary functions (Mualem, 1976; van Genuchten, 1980).