Constraining mechanical and permeability properties of the Krafla geothermal reservoir, North-East Iceland

• Main Author: Eggertsson, GH
• Other Authors: Lavallee, Yan, Kendrick, Jackie E
• Format: Thesis
• Language: English
• Published: 2019
• Subjects: Krafla; Iceland
• Online Access: http://livrepository.liverpool.ac.uk/3060931/; http://livrepository.liverpool.ac.uk/3060931/1/201128440_May2019.pdf

Krafla volcano, located in North-East Iceland, holds an active hydrothermal system, that has been exploited for geothermal energy since 1978. Today it is exploited by Landsvirkjun National Power Company of Iceland and the system is generating ~60 MWe from ~18 wells, tapping into fluids at 200-300°C. But as the geothermal industry is heading into a new era, with aims to drill further and reach the roots of geothermal reservoirs, sourcing higher enthalpy (possibly supercritical) fluids, understanding the physical properties rocks at these conditions is vital. In relation to this, the first well of the Icelandic Deep Drilling Project (IDDP) was drilled in Krafla in 2009. Drilling was terminated at a depth of 2.1 km, when the drill string penetrated a rhyolitic magma body, which could not be bypassed despite attempts to side-track the well. This pioneering effort demonstrated that the area close to magma had great energy potential, even though the well did not reach its initial target of 4-5 km depth. In this thesis, I have employed laboratory experiments to describe the physical behaviour of reservoir rocks at Krafla under different conditions. During two field surveys in 2015 and 2016, and information gathered from drilling of geothermal wells, six main rock types were identified and sampled [and their porosities (i.e., storage capacities) where determined]: three groups of basalts (a lava with 10 to 27 % porosity, a basalt dyke with 31-36% porosity, and a porous lava with 34 to 60 % porosity), hyaloclastites (<35-45% porosity), obsidians (0-5% porosity), ignimbrites (13-18% porosity), and intrusive felsite’s and micro-gabbro’s (9-16% porosity). Samples are primarily from surface exposures, but selected samples of hyaloclastite core were sampled from cores drilled within the Krafla caldera. The permeability properties of both intact and fractured reservoir rocks were investigated using a hydrostatic cell, simulating stress conditions extant in the geothermal reservoir. The impact of thermal stimulation and ...