Model-Based Decision Making to Manage Production in the Western Compartment at Rotokawa

Abstract

This paper documents how Mercury NZ Limited used a model-based approach to refine the reservoir management strategy at the Rotokawa geothermal field. We describe the data analysis required to refine our conceptual understanding of the reservoir and how this conceptual model was implemented as a numerical model of a sector in the field known as the Western Compartment. We detail how the diverse datasets from geology, reservoir engineering, geophysics and geochemistry were included to constrain the numerical model forecasts. Tools developed in-house at Mercury were used to run scenarios where changes in surface operations were fed back to the reservoir via a coupled wellbore simulator. Well enthalpies, deliverability curves and decline rates from this coupled numerical model forecast were passed into a decision analysis model using key financial variables. The outcome of this multi-system modelling was a refinement to the reservoir management strategy, namely a reduction in take from the Western Compartment and the decision to locate future make-up production outside of the Compartment.