Modelling of temperature conditions near the bottom of well IDDP-1 in Krafla, Northeast Iceland

Axelsson, Guðni; Egilson, Þorsteinn; Gylfadóttir, Sigríður Sif

doi:10.1016/j.geothermics.2013.05.003

Cited by 32 publications

(16 citation statements)

References 8 publications

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“…Drastic permeability increase during cooling of jointing bodies (Fig. 7b ) may also explain why the aureoles of shallow magma bodies serendipitously encountered by geothermal drilling 33 , 34 have very steep temperature gradients over short distances of a few tens of metres 35 , 36 . Drilling of these magmatic aureoles has been characterised by strong loss in drilling fluid circulation 37 ; the results here suggest that efficient cooling by injection of fluids at ~80 °C in a magmatic aureole at ca.…”

Section: Discussionmentioning

confidence: 99%

Disclosing the temperature of columnar jointing in lavas

et al. 2018

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Columnar joints form by cracking during cooling-induced contraction of lava, allowing hydrothermal fluid circulation. A lack of direct observations of their formation has led to ambiguity about the temperature window of jointing and its impact on fluid flow. Here we develop a novel thermo-mechanical experiment to disclose the temperature of columnar jointing in lavas. Using basalts from Eyjafjallajökull volcano (Iceland) we show that contraction during cooling induces stress build-up below the solidus temperature (980 °C), resulting in localised macroscopic failure between 890 and 840 °C. This temperature window for incipient columnar jointing is supported by modelling informed by mechanical testing and thermal expansivity measurements. We demonstrate that columnar jointing takes place well within the solid state of volcanic rocks, and is followed by a nonlinear increase in system permeability of <9 orders of magnitude during cooling. Columnar jointing may promote advective cooling in magmatic-hydrothermal environments and fluid loss during geothermal drilling and thermal stimulation.

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Section: Discussionmentioning

confidence: 99%

Disclosing the temperature of columnar jointing in lavas

et al. 2018

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“…Geothermal reservoir temperatures exceed 300°C at depths as shallow as 2 km(Figure 4). While models might still be speculative, because of the limited data available, the models byAxelsson et al (2014) show that a magmatic intrusion could have been emplaced in the vicinity of the IDDP-1 well 25-35 years ago, and the size of it would depend on the distance to the well. No direct contact with the magma was needed to explain relatively high steam temperatures at the well.…”

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confidence: 99%

Resistivity characterization of the Krafla and Hengill geothermal fields through 3D MT inverse modeling

et al. 2015

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Krafla and Hengill volcanic complexes, located 300 km apart, are both known as hightemperature geothermal systems located within neo-volcanic zones of Iceland. This paper demonstrates the utilization of three-dimensional (3D) magnetotelluric (MT) inversions from three different inverse modeling algorithms, which leads to characterizing the electrical resistivity structure of geothermal reservoirs with a much greater level of confidence in accuracy and resolution than if a single algorithm was employed in the data interpretation. These are the first 3D MT inversions of a Krafla MT dataset. The inverted model of electrical resistivity is a classic example of a high-temperature hydrothermal system, with a highly resistive near-surface layer, identified as unaltered porous basalt, overlying a low resistivity cap corresponding to the smectite-zeolite zone. This layer is in turn underlain by a more resistive zone, identified as the epidote-chlorite zone, also called the resistive core, which is often associated with production of geothermal fluids. The electrical structure in the upper 1-2 km does not correlate with lithology but with alteration mineralogy. At the location of the IDDP-1 well, which encountered magma at 2.1 km depth, the resistivity image shows high resistivity, most likely due to the epidote-chlorite geology and/or the presence of deeper supercritical fluids. Two km northwest of the well, however, an intrusive low-resistivity feature is imaged rising from depth, and a plausible interpretation is that of a magma intrusion. One possible explanation for the magma encounter at the IDDP-1 well is the existence of pathways or fissures connected to the magma chamber and intersected by the well. The MT response to these magma pathways is not discernible in the data, perhaps because this magma volume is below the threshold of resolvability. The electrical resistivity structure of the Hengill geothermal area also reveals characteristic features of a high temperature geothermal system with two low-resistivity layers. The nature of the uppermost low-3 resistivity layer and the increasing resistivity below it is attributed to hydrothermal mineral alteration, while the nature of the deep low-resistivity layer, centered over the northeast, is not yet well understood. The geothermal system in the northeast area appears to be shallower than the system manifested in the southwest. 3D MT inversions of Krafla and Hengill data sets show that knowledge of the subsurface electrical resistivity contributes substantially to a better understanding of complex geothermal systems.

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“…Our models explain the conditions encountered in the IDDP-1 well as the natural result of drilling into a shallow magmatic intrusion hosted in basaltic rock, even though the 900 °C hot magma itself was rhyolitic 15 . The measured reservoir conditions 13 ( Fig. 3 , yellow star) lie directly on the p – h ascent path of a system with a 2-km deep intrusion in rocks with T BDT of 550 °C and an intermediate permeability of 10 −15 m 2 , values which are appropriate for the Krafla system 21 26 .…”

Section: Discussionmentioning

confidence: 99%

“…Thermodynamic considerations indicate that supercritical geothermal resources may be very favourable for power production 8 and their theoretical response to production has been studied by numerical modelling 9 . In 2009–2012, an exploratory well drilled by the Iceland Deep Drilling Project (IDDP) penetrated a magma body at 2.1 km depth in the Krafla volcanic system and tapped an overlying reservoir of supercritical water at a temperature of 450 °C and enthalpy of 3.2 MJ kg −1 , capable of generating 35 MW electricity from a single well 10 11 12 13 14 . In spite of studies of the magma 15 , well testing 14 and modelling 13 , the thermo-hydraulic nature of the reservoir at Krafla has remained enigmatic.…”

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confidence: 99%

“… 23 ). This definition avoids the distinction between ‘superheated' (fluid pressure below the critical pressure) and ‘supercritical' (above the critical pressure) resources, which was previously used in the analysis of the IDDP-1 well 12 13 but is arbitrary as supercritical fluid properties vary gradually across the critical isobar. Rather, our definition allows analyzing the full continuum of supercritical resource conditions including the development of economically attractive resources at subcritical pressures such as IDDP-1.…”

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confidence: 99%

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Geologic controls on supercritical geothermal resources above magmatic intrusions

2015

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A new and economically attractive type of geothermal resource was recently discovered in the Krafla volcanic system, Iceland, consisting of supercritical water at 450 °C immediately above a 2-km deep magma body. Although utilizing such supercritical resources could multiply power production from geothermal wells, the abundance, location and size of similar resources are undefined. Here we present the first numerical simulations of supercritical geothermal resource formation, showing that they are an integral part of magma-driven geothermal systems. Potentially exploitable resources form in rocks with a brittle–ductile transition temperature higher than 450 °C, such as basalt. Water temperatures and enthalpies can exceed 400 °C and 3 MJ kg−1, depending on host rock permeability. Conventional high-enthalpy resources result from mixing of ascending supercritical and cooler surrounding water. Our models reproduce the measured thermal conditions of the resource discovered at Krafla. Similar resources may be widespread below conventional high-enthalpy geothermal systems.

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Modelling of temperature conditions near the bottom of well IDDP-1 in Krafla, Northeast Iceland

Cited by 32 publications

References 8 publications

Disclosing the temperature of columnar jointing in lavas

Disclosing the temperature of columnar jointing in lavas

Resistivity characterization of the Krafla and Hengill geothermal fields through 3D MT inverse modeling

Geologic controls on supercritical geothermal resources above magmatic intrusions

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