Test of Reservoir Simulation Models for the Broadlands Geothermal Field Using Repeat Gravity Measurements

Abstract

A powerful and independent method of testing 3-D numerical reservoir simulation models using repeat gravity measurements is demonstrated. The models predict changes in vapour saturation with time, and hence changes in density, and therefore changes in gravity. By comparing the measured gravity differences with those calculated for the simulation model the models can be tested. A test suggests that, for a 3-D simulation model of the Broadlands Geothermal Field, changes in vapour saturation within the Ohaaki area are overestimated, and their lateral extent is under-estimated, during the drawdown test in 1967-1971. The upper part of the production zone may be shallower, thinner, have greater porosity, and extend further than considered in the model.