High temperature instruments and methods developed for supercritical geothermal reservoir characterisation and exploitation—The HiTI project

Ásmundsson, R.; Pézard, Philippe; Sanjuan, Bernard; Henninges, Jan; Deltombe, Jean-Luc; Halladay, Nigel; Lebert, François; Gadalia, Alain; Millot, Romain; Gibert, Benoit; Violay, Marie; Reinsch, Thomas; Naisse, Jean-Marc; Massiot, Cécile; Azaïs, Pierre; Mainprice, David; Karytsas, Constantine; Johnston, Colin

doi:10.1016/j.geothermics.2013.07.008

Cited by 30 publications

(8 citation statements)

References 11 publications

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“…The three boreholes heads are located within an area of 1 km 2 ; the depth intervals, and number of fractures identified in each well, are detailed in Table . The BHTV logs were acquired with an ABI‐85, a high‐temperature logging tool able to operate at up to 300°C [ Ásmundsson et al , ]. The boreholes intersect several lithologies; here we focus on the andesitic formations which form the main part of the deep reservoir [ McNamara et al , ].…”

Section: Datamentioning

confidence: 99%

Statistical methods of fracture characterization using acoustic borehole televiewer log interpretation

et al. 2017

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Acoustic borehole televiewer (BHTV) logs provide measurements of fracture attributes (orientations, thickness, and spacing) at depth. Orientation, censoring, and truncation sampling biases similar to those described for one‐dimensional outcrop scanlines, and other logging or drilling artifacts specific to BHTV logs, can affect the interpretation of fracture attributes from BHTV logs. K‐means, fuzzy K‐means, and agglomerative clustering methods provide transparent means of separating fracture groups on the basis of their orientation. Fracture spacing is calculated for each of these fracture sets. Maximum likelihood estimation using truncated distributions permits the fitting of several probability distributions to the fracture attribute data sets within truncation limits, which can then be extrapolated over the entire range where they naturally occur. Akaike Information Criterion (AIC) and Schwartz Bayesian Criterion (SBC) statistical information criteria rank the distributions by how well they fit the data. We demonstrate these attribute analysis methods with a data set derived from three BHTV logs acquired from the high‐temperature Rotokawa geothermal field, New Zealand. Varying BHTV log quality reduces the number of input data points, but careful selection of the quality levels where fractures are deemed fully sampled increases the reliability of the analysis. Spacing data analysis comprising up to 300 data points and spanning three orders of magnitude can be approximated similarly well (similar AIC rankings) with several distributions. Several clustering configurations and probability distributions can often characterize the data at similar levels of statistical criteria. Thus, several scenarios should be considered when using BHTV log data to constrain numerical fracture models.

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Section: Datamentioning

confidence: 99%

Statistical methods of fracture characterization using acoustic borehole televiewer log interpretation

et al. 2017

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“…Basalt is a major rock type of the crust, and its mechanical properties exert significant influence over many tectonic and volcanic processes. A systematic investigation of basalt deformation and failure mode is therefore of fundamental importance not only for understanding the dynamics of volcanic systems but also for other applications related to engineering geology [Jiang et al, 2014], geothermal systems [Ásmundsson et al, 2014;Fowler et al, 2015;Pope et al, 2015], reservoirs in volcanic environments [Wu et al, 2006;Ólvasdóttir et al, 2015], and CO 2 sequestration [Matter et al, 2009;Khatiwada et al, 2012]. Numerous studies have been conducted on the elastic and transport properties of basalts, and how they evolve with hydrostatic loading [Vinciguerra et al, 2005;Adelinet et al, 2010;Fortin et al, 2010] and cyclic uniaxial compression [Heap et al, 2009].…”

Section: Introductionmentioning

confidence: 99%

Micromechanics of brittle faulting and cataclastic flow in Mount Etna basalt

et al. 2016

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Understanding how the strength of volcanic rocks varies with stress state, pressure, and microstructural attributes is fundamental to understanding the dynamics and tectonics of a volcanic system and also very important in applications such as geothermics or reservoir management in volcanic environments. In this study we investigated the micromechanics of deformation and failure in basalt, focusing on samples from Mount Etna. We performed 65 uniaxial and triaxial compression experiments on nominally dry and water‐saturated samples covering a porosity range between 5 and 16%, at effective pressures up to 200 MPa. Dilatancy and brittle faulting were observed in all samples with porosity of 5%. Water‐saturated samples were found to be significantly weaker than comparable dry samples. Shear‐enhanced compaction was observed at effective pressures as low as 80 MPa in samples of 8% porosity. Microstructural data revealed the complex interplay of microcracks, pores, and phenocrysts on dilatant failure and inelastic compaction in basalt. The micromechanics of brittle failure is controlled by wing crack propagation under triaxial compression and by pore‐emanated cracking under uniaxial compression especially in the more porous samples. The mechanism of inelastic compaction in basalt is cataclastic pore‐collapse in agreement with a recent dual‐porosity model.

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“…The dependence of permeability on the temperature‐dependent mechanical rock properties controls how fast and to what temperatures the circulating fluids can extract heat. There are some economic uses of hydrothermal circulation, as, for example, geothermal power [e.g., Palmason , ; Asmundsson et al ., ] and mining ore deposits in extinct fluid pathways [ Nelson and Giles , ; Mills and Elderfield , ]. Our current understanding of hydrothermal circulation around the BDT at mid‐ocean ridge has been aided by geophysical observations.…”

Section: Introductionmentioning

confidence: 99%

Brittle versus ductile deformation as the main control of the deep fluid circulation in oceanic crust

Violay

Gibert

Mainprice

et al. 2015

Geophysical Research Letters

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The brittle to ductile transition may strongly influence hydraulic properties of rocks at the depth and temperature ranges that hydrothermal fluids circulate. To examine this transition in the context of the oceanic crust, we conducted a series of deformation experiments on a natural basalt sample at in situ oceanic crust conditions. Dilatancy was measured during deformation. The method consisted in monitoring the volume of pore fluid that flows into or out of the sample at constant pore pressure. Mechanical and microstructural observations at experimental constant strain rate of 10−5 s−1 indicated that the basalt was brittle and dilatant up to 800°C. At higher temperature, the deformation mode became macroscopically ductile and samples compacted. These observations have important implications on heat transfer and fluid migration in oceanic crust.

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High temperature instruments and methods developed for supercritical geothermal reservoir characterisation and exploitation—The HiTI project

Cited by 30 publications

References 11 publications

Statistical methods of fracture characterization using acoustic borehole televiewer log interpretation

Statistical methods of fracture characterization using acoustic borehole televiewer log interpretation

Micromechanics of brittle faulting and cataclastic flow in Mount Etna basalt

Brittle versus ductile deformation as the main control of the deep fluid circulation in oceanic crust

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