In 2008 Contact Energy undertook a comprehensive research program investigating subsidence anomalies located within the Wairakei-Tauhara geothermal system. About 4 km of continuous core from 13 boreholes in the vicinity of the four known subsidence bowls was logged and preserved. The core underwent geotechnical analysis (including compressibility measurements) and petrology tests (XRD, smectite abundance, SEM). Down-hole reservoir measurements (pressure, temperature, permeability) were conducted on all 13 boreholes including staged injectivity tests, completion tests, heating runs and chemistry sampling.

This paper presents an overview of the work undertaken and a summary of the results including:
• Improved understanding of the processes that cause subsidence.
• Detailed information on the shallow aquifer characteristics and how these relate to changes in the deep high temperature reservoir.
• How interpreted feed zones correlate to the core and other measurements made during drilling.
• 3D subsidence modelling using measured rock properties obtained from the core to model historical and predict future subsidence.

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