An Update on the Modelling of the Ohaaki Geothermal System

Authors: E Clearwater, MJ O'Sullivan, K Brockbank
Keywords: Ohaaki, Geothermal, modelling, TOUGH2, Leapfrog Geothermal
Conference: New Zealand Geothermal Workshop Session: Reservoir Modelling
Year: 2011 Language: English
Geo Location:
Abstract: Since the Ohaaki power station was commissioned in 1988, a series of large three-dimensional numerical models of the Ohaaki geothermal system have been developed at the University of Auckland in collaboration with Contact Energy and its predecessors. Over the course of 2010 and 2011 the model has been reviewed and re-calibrated in order to improve the match between measured data and model results. This was part of an ongoing effort to represent the Ohaaki system more accurately, so that the model can be used to better predict the future behaviour of the resource.

Updates of the model grid include horizontal refinement and deepening of the model. During the calibration process some adjustments were made to the deep up flow of very hot water and CO2 at the base of the model. Also some adjustments were made to permeabilities and porosities, including the use of the LEAPFROG software to make the rock type assignment in our reservoir model better match the geological model developed by Contact Energy and GNS Science.

Natural state simulations were used to compare the model results to the temperature data for the pre-exploitation state of the reservoir. Then production history simulations were carried out and pressure, temperature, CO2 flow and enthalpy data were compared to model results, using data from the well testing period, the recovery period and the production period. Overall, a significant improvement in the model match has been made compared to the previous (2006) model.
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