Insights into the shallow intrusion of rhyolite from field, textures, and drilling the IDDP-1 magma well, Krafla, Iceland.

• Main Author: Saubin, Elodie
• Format: Other/Unknown Material
• Language: English
• Published: University of Canterbury 2020
• Subjects: Krafla; New Zealand; Iceland
• Online Access: https://hdl.handle.net/10092/100164; https://doi.org/10.26021/7767

This thesis focusses on shallow intrusions of rhyolite, in the context of heat resources for geothermal development. Rhyolite is the dominant sub-surface magma type at the roots of some of the most vigorous geothermal systems worldwide, including Krafla, in Iceland, and the Taupo Volcanic Zone, in New Zealand. Supercritical fluids located in deeper and hotter environments than those conventionally extracted provide more efficient energy production and greater power output. As potential reservoir, the margins of magma chambers constitute an enticing new target. The Iceland Deep Drilling Project consortium accidentally drilled magma in 2009 at Krafla, at 2 km depth. This IDDP-1 well was the hottest geothermal well worldwide, with high productive capability (35 MWe). Based on this experience, a new consortium, the Krafla Magma Testbed (KMT), aims to drill back into this magma body for geothermal exploration, creation of research opportunities and monitoring. Improved scientific knowledge of the targeted reservoir is critical to the success of the project, and is the topic of this thesis. The main objectives of this work are (1) to characterize rock properties at the margins of shallow rhyolite intrusions, specifically around the active Krafla rhyolite magma body, (2) to constrain the size and structure of this intrusion, and (3) to better understand magma response to drilling. Results are obtained via four complementary approaches: Firstly, fossil rhyolite intrusions in Iceland are used as a macro-scale analogy of rock properties around active intrusions. Four field case studies are compared to investigate the host rock response to intrusion, with field measurement of rock strength, permeability and fracture density, as well as textural and lithological information on the intrusions. Secondly, chilled margins thickness and the extent of impacted host rocks of a further 14 intrusions that emplaced at <1 km depth and are <1 km thick are compared to a numerical model of heat transfer by thermal diffusion. ...