Sub-surface geology and velocity structure of the Krafla high temperature geothermal field, Iceland: Integrated ditch cuttings, wireline and zero offset vertical seismic profile analysis

John M. Millett*, Sverre Planke, Felix Kästner, Anett Blischke, Gylfi Páll Hersir, Sæunn Halldórsdóttir, Ólafur G. Flóvenz, Sigurveig Árnadóttir, Helga M. Helgadóttir, Sergey Vakulenko, Sergey Buryak, Ögmundur Erlendsson, Rüdiger Giese, Jehanne P. Cavailhes, Dougal A. Jerram, Ásgrímur Guðmundsson, Egill Júlíusson

*Corresponding author for this work

Research output: Contribution to journalArticle

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Abstract

The Krafla geothermal area in northern Iceland comprises one of the best studied examples of a high temperature geothermal field associated with an active volcanic rift zone. Of key importance to improved resource exploration and development in volcanic areas such as Krafla, is the interpretation and understanding of the subsurface geology. Within this study we present results from an integrated analysis of the downhole volcanic stratigraphy from the K-18 borehole within the Krafla caldera based on combined wireline, ditch cuttings, and zero-offset VSP (vertical seismic profile) analyses. This study presents the first published sonic log velocity data from a high temperature geothermal borehole in Iceland and clearly demonstrates the importance of borehole velocity data for improving volcanic facies interpretations. The shallow subsurface geology of the K-18 site from c. 0–380 m comprises an inter-layered sequence of sub-aerial basaltic lavas, hyaloclastites and tuffaceous lithologies of both felsic and basic composition, which are progressively replaced by basaltic sheet intrusions with increasing depth. An interval of variably basic to more evolved mixed tuffaceous facies is identified based on cuttings analysis, gamma and sonic velocities between c. 790–1120 m depth. Discrete high sonic Vp units cut the lower c. 100 m of this interval and are interpreted as either sheet intrusions or lava interiors. At c. 1800 m, a sharp increase in P-wave velocity from c. 4.5 to c. 5.5 km/s, represents the transition from a mixed lava and sheet intrusion dominated sequence, into a dense basic intrusion forming the local basement that persists to the bottom of the borehole at c. 2215 m. Reduced travel time analysis of processed zero-offset VSP results reveal good correspondence with the major stratigraphic boundaries in the borehole, supporting the potential for VSP studies to robustly characterize complex volcanic stratigraphy in high temperature geothermal fields. Finally, the application of percentage-based ditch cuttings analyses methods for volcanic facies analysis in geothermal boreholes is tested and assessed to have future potential.

Original languageEnglish
JournalJournal of Volcanology and Geothermal Research
Early online date30 Mar 2018
DOIs
Publication statusE-pub ahead of print - 30 Mar 2018

Fingerprint

ditches
vertical seismic profile
Geothermal fields
Iceland
Geology
geology
boreholes
Boreholes
velocity structure
volcanology
borehole
intrusion
profiles
Stratigraphy
stratigraphy
lava
Temperature
stratigraphic boundary
intervals
facies analysis

Keywords

  • Geothermal
  • Iceland
  • IMAGE
  • Krafla
  • Sonic velocity
  • VSP

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

Cite this

Sub-surface geology and velocity structure of the Krafla high temperature geothermal field, Iceland : Integrated ditch cuttings, wireline and zero offset vertical seismic profile analysis. / Millett, John M.; Planke, Sverre; Kästner, Felix; Blischke, Anett; Hersir, Gylfi Páll; Halldórsdóttir, Sæunn; Flóvenz, Ólafur G.; Árnadóttir, Sigurveig; Helgadóttir, Helga M.; Vakulenko, Sergey; Buryak, Sergey; Erlendsson, Ögmundur; Giese, Rüdiger; Cavailhes, Jehanne P.; Jerram, Dougal A.; Guðmundsson, Ásgrímur; Júlíusson, Egill.

In: Journal of Volcanology and Geothermal Research, 30.03.2018.

Research output: Contribution to journalArticle

Millett, JM, Planke, S, Kästner, F, Blischke, A, Hersir, GP, Halldórsdóttir, S, Flóvenz, ÓG, Árnadóttir, S, Helgadóttir, HM, Vakulenko, S, Buryak, S, Erlendsson, Ö, Giese, R, Cavailhes, JP, Jerram, DA, Guðmundsson, Á & Júlíusson, E 2018, 'Sub-surface geology and velocity structure of the Krafla high temperature geothermal field, Iceland: Integrated ditch cuttings, wireline and zero offset vertical seismic profile analysis', Journal of Volcanology and Geothermal Research. https://doi.org/10.1016/j.jvolgeores.2018.03.024
Millett, John M. ; Planke, Sverre ; Kästner, Felix ; Blischke, Anett ; Hersir, Gylfi Páll ; Halldórsdóttir, Sæunn ; Flóvenz, Ólafur G. ; Árnadóttir, Sigurveig ; Helgadóttir, Helga M. ; Vakulenko, Sergey ; Buryak, Sergey ; Erlendsson, Ögmundur ; Giese, Rüdiger ; Cavailhes, Jehanne P. ; Jerram, Dougal A. ; Guðmundsson, Ásgrímur ; Júlíusson, Egill. / Sub-surface geology and velocity structure of the Krafla high temperature geothermal field, Iceland : Integrated ditch cuttings, wireline and zero offset vertical seismic profile analysis. In: Journal of Volcanology and Geothermal Research. 2018.
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abstract = "The Krafla geothermal area in northern Iceland comprises one of the best studied examples of a high temperature geothermal field associated with an active volcanic rift zone. Of key importance to improved resource exploration and development in volcanic areas such as Krafla, is the interpretation and understanding of the subsurface geology. Within this study we present results from an integrated analysis of the downhole volcanic stratigraphy from the K-18 borehole within the Krafla caldera based on combined wireline, ditch cuttings, and zero-offset VSP (vertical seismic profile) analyses. This study presents the first published sonic log velocity data from a high temperature geothermal borehole in Iceland and clearly demonstrates the importance of borehole velocity data for improving volcanic facies interpretations. The shallow subsurface geology of the K-18 site from c. 0–380 m comprises an inter-layered sequence of sub-aerial basaltic lavas, hyaloclastites and tuffaceous lithologies of both felsic and basic composition, which are progressively replaced by basaltic sheet intrusions with increasing depth. An interval of variably basic to more evolved mixed tuffaceous facies is identified based on cuttings analysis, gamma and sonic velocities between c. 790–1120 m depth. Discrete high sonic Vp units cut the lower c. 100 m of this interval and are interpreted as either sheet intrusions or lava interiors. At c. 1800 m, a sharp increase in P-wave velocity from c. 4.5 to c. 5.5 km/s, represents the transition from a mixed lava and sheet intrusion dominated sequence, into a dense basic intrusion forming the local basement that persists to the bottom of the borehole at c. 2215 m. Reduced travel time analysis of processed zero-offset VSP results reveal good correspondence with the major stratigraphic boundaries in the borehole, supporting the potential for VSP studies to robustly characterize complex volcanic stratigraphy in high temperature geothermal fields. Finally, the application of percentage-based ditch cuttings analyses methods for volcanic facies analysis in geothermal boreholes is tested and assessed to have future potential.",
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author = "Millett, {John M.} and Sverre Planke and Felix K{\"a}stner and Anett Blischke and Hersir, {Gylfi P{\'a}ll} and S{\ae}unn Halld{\'o}rsd{\'o}ttir and Fl{\'o}venz, {{\'O}lafur G.} and Sigurveig {\'A}rnad{\'o}ttir and Helgad{\'o}ttir, {Helga M.} and Sergey Vakulenko and Sergey Buryak and {\"O}gmundur Erlendsson and R{\"u}diger Giese and Cavailhes, {Jehanne P.} and Jerram, {Dougal A.} and {\'A}sgr{\'i}mur Gu{\dh}mundsson and Egill J{\'u}l{\'i}usson",
note = "The research leading to these results has received funding from the European Community's Seventh Framework Programme under grant agreement No. 608553 (Project IMAGE). The VMAPP project run by VBPR, DougalEARTH Ltd. and TGS also contributed funding to the borehole characterization of the K-18 borehole. Landsvirkun is acknowledged for their effort and assistance in this work and in particular for allowing the use of the data from well K-18. We further acknowledge the support from the Research Council of Norway through its Centres of Excellence funding scheme, project 22372 (SP and DAJ).",
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T1 - Sub-surface geology and velocity structure of the Krafla high temperature geothermal field, Iceland

T2 - Integrated ditch cuttings, wireline and zero offset vertical seismic profile analysis

AU - Millett, John M.

AU - Planke, Sverre

AU - Kästner, Felix

AU - Blischke, Anett

AU - Hersir, Gylfi Páll

AU - Halldórsdóttir, Sæunn

AU - Flóvenz, Ólafur G.

AU - Árnadóttir, Sigurveig

AU - Helgadóttir, Helga M.

AU - Vakulenko, Sergey

AU - Buryak, Sergey

AU - Erlendsson, Ögmundur

AU - Giese, Rüdiger

AU - Cavailhes, Jehanne P.

AU - Jerram, Dougal A.

AU - Guðmundsson, Ásgrímur

AU - Júlíusson, Egill

N1 - The research leading to these results has received funding from the European Community's Seventh Framework Programme under grant agreement No. 608553 (Project IMAGE). The VMAPP project run by VBPR, DougalEARTH Ltd. and TGS also contributed funding to the borehole characterization of the K-18 borehole. Landsvirkun is acknowledged for their effort and assistance in this work and in particular for allowing the use of the data from well K-18. We further acknowledge the support from the Research Council of Norway through its Centres of Excellence funding scheme, project 22372 (SP and DAJ).

PY - 2018/3/30

Y1 - 2018/3/30

N2 - The Krafla geothermal area in northern Iceland comprises one of the best studied examples of a high temperature geothermal field associated with an active volcanic rift zone. Of key importance to improved resource exploration and development in volcanic areas such as Krafla, is the interpretation and understanding of the subsurface geology. Within this study we present results from an integrated analysis of the downhole volcanic stratigraphy from the K-18 borehole within the Krafla caldera based on combined wireline, ditch cuttings, and zero-offset VSP (vertical seismic profile) analyses. This study presents the first published sonic log velocity data from a high temperature geothermal borehole in Iceland and clearly demonstrates the importance of borehole velocity data for improving volcanic facies interpretations. The shallow subsurface geology of the K-18 site from c. 0–380 m comprises an inter-layered sequence of sub-aerial basaltic lavas, hyaloclastites and tuffaceous lithologies of both felsic and basic composition, which are progressively replaced by basaltic sheet intrusions with increasing depth. An interval of variably basic to more evolved mixed tuffaceous facies is identified based on cuttings analysis, gamma and sonic velocities between c. 790–1120 m depth. Discrete high sonic Vp units cut the lower c. 100 m of this interval and are interpreted as either sheet intrusions or lava interiors. At c. 1800 m, a sharp increase in P-wave velocity from c. 4.5 to c. 5.5 km/s, represents the transition from a mixed lava and sheet intrusion dominated sequence, into a dense basic intrusion forming the local basement that persists to the bottom of the borehole at c. 2215 m. Reduced travel time analysis of processed zero-offset VSP results reveal good correspondence with the major stratigraphic boundaries in the borehole, supporting the potential for VSP studies to robustly characterize complex volcanic stratigraphy in high temperature geothermal fields. Finally, the application of percentage-based ditch cuttings analyses methods for volcanic facies analysis in geothermal boreholes is tested and assessed to have future potential.

AB - The Krafla geothermal area in northern Iceland comprises one of the best studied examples of a high temperature geothermal field associated with an active volcanic rift zone. Of key importance to improved resource exploration and development in volcanic areas such as Krafla, is the interpretation and understanding of the subsurface geology. Within this study we present results from an integrated analysis of the downhole volcanic stratigraphy from the K-18 borehole within the Krafla caldera based on combined wireline, ditch cuttings, and zero-offset VSP (vertical seismic profile) analyses. This study presents the first published sonic log velocity data from a high temperature geothermal borehole in Iceland and clearly demonstrates the importance of borehole velocity data for improving volcanic facies interpretations. The shallow subsurface geology of the K-18 site from c. 0–380 m comprises an inter-layered sequence of sub-aerial basaltic lavas, hyaloclastites and tuffaceous lithologies of both felsic and basic composition, which are progressively replaced by basaltic sheet intrusions with increasing depth. An interval of variably basic to more evolved mixed tuffaceous facies is identified based on cuttings analysis, gamma and sonic velocities between c. 790–1120 m depth. Discrete high sonic Vp units cut the lower c. 100 m of this interval and are interpreted as either sheet intrusions or lava interiors. At c. 1800 m, a sharp increase in P-wave velocity from c. 4.5 to c. 5.5 km/s, represents the transition from a mixed lava and sheet intrusion dominated sequence, into a dense basic intrusion forming the local basement that persists to the bottom of the borehole at c. 2215 m. Reduced travel time analysis of processed zero-offset VSP results reveal good correspondence with the major stratigraphic boundaries in the borehole, supporting the potential for VSP studies to robustly characterize complex volcanic stratigraphy in high temperature geothermal fields. Finally, the application of percentage-based ditch cuttings analyses methods for volcanic facies analysis in geothermal boreholes is tested and assessed to have future potential.

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KW - IMAGE

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KW - Sonic velocity

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