| Title | A 3-D GEOLOGICAL MODEL OF THE ROTORUA GEOTHERMAL FIELD |
|---|---|
| Authors | S. Alcaraz, J. Barber |
| Year | 2015 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Rotorua Geothermal Field, 3-D visualisation, Geological modelling, Leapfrog Geothermal |
| Abstract | A 3-D geological model of the Rotorua Geothermal Field and surrounding area is built to better understand and visualise the geological setting of the field and provide a platform for future data integration to illustrate and model the geothermal reservoir behaviour and response to utilisation. Representative formations and faults are modelled using 3-D modelling and visualisation software Leapfrog Geothermal. The Rotorua Geothermal Field covers an area of ~18 km2 in the southern part of the Rotorua caldera, which formed during the eruption of the Mamaku Plateau Formation ~240,000 years ago. Pre-caldera domes surround the caldera and old ignimbrites outcrop to the south and west, although the exact nature, extent and thickness of deposits below the Mamaku Plateau Formation are unconstrained. Effusive eruptions followed the Rotorua caldera collapse, and rhyolitic dome complexes formed in the south-west of the caldera. A lake formed within the depression and an interlayered series of primary and re-sedimented tephra, alluvium and lacustrine sediments then covered the ignimbrite. Faults are inferred throughout the field. The Rotorua caldera is located north-west of the Taupo Fault Belt rift and active faults are mapped south and north-east of the caldera rim, while the structures within the caldera have been buried under young sedimentary and volcaniclastic layers. Lineaments and alignment of thermal features are used to infer the location of several faults within the caldera. There is little geological evidence at depth to confirm the existence of most of these faults, although more than 1300 boreholes have been drilled in the area. Most wells are shallow (< 150 m drilled depth) and reliable geological data is scarce. Complimentary geophysical surveys (seismic, gravity, MT) are therefore used as indicators of the likely geological structures at greater depth. |