AN INTEGRATED APPROACH TO GEOLOGICAL AND FLUID FLOW MODELLING: FROM A 3D GEOLOGICAL MODEL TO TOUGH2

Abstract

Various attempts have been made to understand geothermal fluid circulation in the Taupo Volcanic Zone (TVZ), focusing on the locations of the convective plumes over which the active geothermal systems lie. Additional studies have considered the effects of permeability and fault structures on convection through investigation of generic circulation models. These studies usually overlook the geological complexity of an area by simplifying the permeability models to two units consisting of undifferentiated volcanic layers, overlying the TVZ greywacke basement, therefore missing any variability in the rock properties of the different volcanic strata. A 3D Leapfrog Geothermal geological model is built to be incorporated into a TOUGH2 reservoir model to represent more realistic geology and hence permeability input data into the simulation.
This paper presents a 3D geological model through the central TVZ, extending from Waiotapu in the north to Ngatamariki in the south. The model will be used to create a TOUGH2 reservoir model of this area that investigates structural controls and recharge effects on fluid flow on a regional scale. The geology and structure of the area has been simplified to reflect the end use in a TOUGH2 flow model. The geology units have been simplified into hydrogeological groups based on similar age and groundwater flow characteristics (e.g., pore and fracture permeability, porosity). The fault structures used in the model have also been simplified to focus on large-scale faults (e.g., Paeroa Fault, Reporoa Caldera collapse fault) or those with significant fluid pathways (e.g. Ngapuru Fault, major upflow zones and associated springs). A combination of borehole data, surface geology and structures were used to generate representative geological formations at depth.