Basement structure, lithology and permeability at Kawerau and Ohaaki geothermal fields, New Zealand

Wood, C. P.; Brathwaite, Robert L.; Rosenberg, M. D.

doi:10.1016/s0375-6505(01)00003-7

Cited by 62 publications

(51 citation statements)

References 17 publications

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“…2 Ma (Wilson et al, 1995). Lavas, ignimbrites and volcanic-derived sediments, collectively referred to as "volcaniclastic" rocks in this study, unconformably overlie Mesozoic greywacke and argillite rocks, collectively grouped as Torlesse composite terrane (Mortimer, 1995;Wood et al, 2001;Figs. 3, 4).…”

Section: Stratigraphy and Structurementioning

confidence: 99%

“…Ohaaki is situated in the eastern TVZ and is one of five fields where greywacke basement has been encountered, the others being Kawerau, Rotokawa, Ngatamariki and Tauhara (Wood et al, 2001;Bignall et al, 2010;Chambefort et al, 2014). Low permeability and porosity measurements obtained in greywacke rocks suggests that permeability in the basement greywacke is mostly secondary in origin and due to structures such as faults and fractures (Wood et al, 2001;Bertrand et al, 2012;Wallis et al, 2012;McNamara et al, 2014).…”

Section: Stratigraphy and Structurementioning

confidence: 99%

“…Low permeability and porosity measurements obtained in greywacke rocks suggests that permeability in the basement greywacke is mostly secondary in origin and due to structures such as faults and fractures (Wood et al, 2001;Bertrand et al, 2012;Wallis et al, 2012;McNamara et al, 2014).…”

Section: Stratigraphy and Structurementioning

confidence: 99%

“…In 1995, deep exploration drilling was resumed with the aim to assess the potential for production from the greywacke that underlies much of the resource. Although limited permeability was found in greywacke (Wood et al, 2001), a much more detailed picture of greywacke geometry emerged. In 2007, additional deep wells were drilled showing that the productive reservoir extended down to at least 2500 m at the western margin of the field.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Ohaaki geothermal system: Refinement of a conceptual reservoir model

Mroczek

Milicich

Bixley³

et al. 2016

Geothermics

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Section: Stratigraphy and Structurementioning

confidence: 99%

Section: Stratigraphy and Structurementioning

confidence: 99%

Section: Stratigraphy and Structurementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Ohaaki geothermal system: Refinement of a conceptual reservoir model

Mroczek

Milicich

Bixley³

et al. 2016

Geothermics

View full text Add to dashboard Cite

“…Paragenetic alteration mineral relationships (i.e., episodic veining and wall rock interrelationships) are also much better preserved in drill core samples. While previous studies have acknowledged potential geochemical and preservation bias in drill cutting samples relative to drill core samples (Kristmannsdóttir, 1982;Wood, 1996;Solum et al, 2006), few studies have quantitatively evaluated the significance of this bias and the implications for geochemical studies.…”

Section: Q14mentioning

confidence: 99%

Geochemical bias in drill cutting samples versus drill core samples returned from the Reykjanes Geothermal System, Iceland

Fowler

Zierenberg

2016

Geothermics

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a b s t r a c tThe wholerock major and trace element composition of drill cutting samples are compared to drill core samples from adjacent depths in the seawater recharged Reykjanes geothermal system in Iceland. The first appearance of alteration minerals and lithologies in drill cutting samples is a useful tool for interpreting broad subsurface characteristics. However, use of drill cutting samples for determining igneous affinity and elemental exchanges during hydrothermal alteration is problematic. Samples recovered from immediately above and below the cored intervals in wells RN-17B and RN-30 demonstrate that drillcutting samples are biased towards preservation of least altered primary igneous minerals and more resistant alteration minerals, including albite, quartz, and epidote, with preferential loss of finer-grained and less resistant minerals including chlorite and actinolite. This selective recovery obscures elemental exchanges resulting from hydrothermal alteration processes. For some elements, compositional variations (enrichments and depletions) measured from 9.5 m of core exceeds that observed in ∼3000 m of cutting analyses. Concentration ratios of hydrothermally immobile elements including Zr, Nb, V, Y, HREE, Hf, Ta and Th in deep (>2245 m) spot drill core samples record bimodal, trace element-enriched and trace element-depleted precursor compositions similar to subaerial Reykjanes Peninsula basalts. The same elements in nearly 3000 m of drill cutting samples from well RN-17 overwhelmingly reflect the more common trace element-enriched igneous precursor, demonstrating that mixing of drill cutting samples obscures details of their igneous affinity. A new and different drill rig was used to deepen well RN-17 below 2266 m in a sidetrack hole (RN-17ST), which resulted in a change in drilling conditions, accompanied with an increased well deviation angle from ∼0• to ∼4• . Wholerock geochemical results for drill cutting samples from RN-17ST are homogenous for virtually every element; suggesting the change in drilling conditions resulted in extreme mixing of the drill cuttings. Anomalously high concentrations of Cu, Ni, Cr and Ta in some drill cutting samples likely reflects contamination of drill cutting samples by metal alloys used in drill bits and drill collars or more resistant spinel and sulfide phases.

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Heterogeneity of structure and stress in the Rotokawa Geothermal Field, New Zealand

et al. 2015

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Geometric characterization of a geothermal reservoir's structures, and their relation to stress field orientation, is vital for resource development. Subsurface structure and stress field orientations of the Rotokawa Geothermal Field, New Zealand, have been studied, for the first time, using observations obtained from analysis of three acoustic borehole televiewer logs. While an overall NE-SW fracture strike exists, heterogeneity in fracture dip orientation is evident. Dominant dip direction changes from well to well due to proximity to variously oriented, graben-bounding faults. Fracture orientation heterogeneity also occurs within individual wells, where fractures clusters within certain depth intervals have antithetic dip directions to the well's dominant fracture dip direction. These patterns are consistent with expected antithetic faulting in extensional environments. A general S Hmax orientation of NE-SW is determined from induced features on borehole walls. However, numerous localized azimuthal variations from this trend are evident, constituting stress field orientation heterogeneity. These variations are attributed to slip on fracture planes evidenced by changes in the azimuth of drilling-induced tensile fractures either side of a natural fracture. Correlation of observed fracture properties and patterns to well permeability indicators reveal that fractures play a role in fluid flow in the Rotokawa geothermal reservoir. Permeable zones commonly contain wide aperture fractures and high fracture densities which have a dominant NE-SW strike orientation and NW dip direction. Studies of this kind, which show strong interdependency of structure and stress field properties, are essential to understand fluid flow in geothermal reservoirs where structural permeability dominates.

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Basement structure, lithology and permeability at Kawerau and Ohaaki geothermal fields, New Zealand

Cited by 62 publications

References 17 publications

Ohaaki geothermal system: Refinement of a conceptual reservoir model

Ohaaki geothermal system: Refinement of a conceptual reservoir model

Geochemical bias in drill cutting samples versus drill core samples returned from the Reykjanes Geothermal System, Iceland

Heterogeneity of structure and stress in the Rotokawa Geothermal Field, New Zealand

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