Ngatamariki Geothermal Field, New Zealand: Geology, geophysics, chemistry and conceptual model

Chambefort, Isabelle; Buscarlet, Etienne; Wallis, Irene C.; Sewell, Steven; Wilmarth, Maxwell

doi:10.1016/j.geothermics.2015.07.011

Cited by 38 publications

(54 citation statements)

References 22 publications

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“…Bottomhole temperatures for the northern injection wells reach ∼280 • C, and production well NM07 reaches almost 290 • C. In contrast, the maximum temperatures in the southern injection zone reach only ∼260 • C and are located away from the main upflow in the field (between NM07 and NM08/09; Chambefort et al, 2016). While these temperatures could be interpreted to be near the brittle-ductile transition for quartz-bearing rock (e.g., Scholz, 1988), this is unlikely given that seismicity at the nearby (and lithologically similar) Rotokawa geothermal field occurs in host rock with measured temperatures in excess of 330 • C .…”

Section: Event Locationmentioning

confidence: 99%

“…However, these injections also offer valuable insight into seismogenesis, which may help to better manage future injection-induced seismic hazard. Prior to our study period, which extends from June 2012 to the end of 2015, the development of the Ngatamariki resource had been limited to resource exploration in the 1980s followed by the drilling of three deep exploration wells (NM05, NM06, and NM07 to ∼3-km depth) in the 2000s (Chambefort et al, 2016). Prior to our study period, which extends from June 2012 to the end of 2015, the development of the Ngatamariki resource had been limited to resource exploration in the 1980s followed by the drilling of three deep exploration wells (NM05, NM06, and NM07 to ∼3-km depth) in the 2000s (Chambefort et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

“…While most case studies have addressed low-temperature, high-permeability reservoirs such as the Arbuckle group in Oklahoma (e.g., Langenbruch & Zoback, 2016) or medium-temperature, low-permeability reservoirs targeted at EGS sites (e.g., Deichmann & Giardini, 2009;Evans et al, 2005), here we present a case of induced seismicity related to injection operations in the high-temperature, The Ngatamariki geothermal field in the central Taupō Volcanic Zone of New Zealand is a convenient place to study induced seismicity. Prior to our study period, which extends from June 2012 to the end of 2015, the development of the Ngatamariki resource had been limited to resource exploration in the 1980s followed by the drilling of three deep exploration wells (NM05, NM06, and NM07 to ∼3-km depth) in the 2000s (Chambefort et al, 2016). The start of injection operations in 2012 represented the first large-scale fluid injection into the undisturbed, high-temperature (∼280 • C) Ngatamariki reservoir (Bignall, 2009).…”

Section: Introductionmentioning

confidence: 99%

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Seismic Response to Injection Well Stimulation in a High‐Temperature, High‐Permeability Reservoir

Hopp

Sewell

Mroczek

et al. 2019

Geochem Geophys Geosyst

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Fluid injection into the Earth's crust can induce seismic events that cause damage to local infrastructure but also offer valuable insight into seismogenesis. The factors that influence the magnitude, location, and number of induced events remain poorly understood but include injection flow rate and pressure as well as reservoir temperature and permeability. The relationship between injection parameters and injection‐induced seismicity in high‐temperature, high‐permeability reservoirs has not been extensively studied. Here we focus on the Ngatamariki geothermal field in the central Taupō Volcanic Zone, New Zealand, where three stimulation/injection tests have occurred since 2012. We present a catalog of seismicity from 2012 to 2015 created using a matched‐filter detection technique. We analyze the stress state in the reservoir during the injection tests from first motion‐derived focal mechanisms, yielding an average direction of maximum horizontal compressive stress (SHmax) consistent with the regional NE‐SW trend. However, there is significant variation in the direction of maximum compressive stress (σ1), which may reflect geological differences between wells. We use the ratio of injection flow rate to overpressure, referred to as injectivity index, as a proxy for near‐well permeability and compare changes in injectivity index to spatiotemporal characteristics of seismicity accompanying each test. Observed increases in injectivity index are generally poorly correlated with seismicity, suggesting that the locations of microearthquakes are not coincident with the zone of stimulation (i.e., increased permeability). Our findings augment a growing body of work suggesting that aseismic opening or slip, rather than seismic shear, is the active process driving well stimulation in many environments.

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Section: Event Locationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Seismic Response to Injection Well Stimulation in a High‐Temperature, High‐Permeability Reservoir

Hopp

Sewell

Mroczek

et al. 2019

Geochem Geophys Geosyst

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“…The Ngatamariki Geothermal Field is located in the southern part of the highly productive, in terms of volcanic and geothermal output, central TVZ (Figure ) with an installed electrical capacity of 82 MW (Chambefort et al, ). In this region, the TVZ is characterized by a series of rift basins developed through a metasedimentary graywacke basement that records a 2‐Ma evolution from andesitic arc volcanism (ca.…”

Section: Geological Setting and Sample Descriptionmentioning

confidence: 99%

Mineral Alteration and Fracture Influence on the Elastic Properties of Volcaniclastic Rocks

et al. 2019

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In geothermal environments, the physical properties of rocks, such as porosity and alteration, are highly variable and control the reservoir's elastic and hydraulic properties. Elastic wave velocity in volcaniclastic rocks and their relation to fractures, pore shapes, and mineral alteration is mostly unknown. We measure ultrasonic P and S wave speeds on volcanic rocks from the Ngatamariki Geothermal Reservoir, New Zealand. Data clustering of wave speed versus porosity and density allow us to classify lithotypes of variable propylitic and phyllic mineral alteration. Wave speeds increase first due to porosity reduction as a result of mineral alteration and welding and, second, due to the high elasticity of alteration minerals (epidote, chlorite, and carbonates). We model the rock porosity as composed of equant pores and oblate-spheroidal microfractures following an elastic effective medium model. For our samples, microfracture porosities range from 4% in the volcaniclastic tuffs to less than 1% in the ignimbrites, which we validate with pycnometer porosity data under effective pressure. We quantify that within one geological volcaniclastic formation, wave speeds vary up to 47% due to rock alteration and welding, while the effect of microfractures and changes in effective stress on wave speeds is secondary (up to 11%) but not negligible. From the experimental and numerical results we show that equant pores remain open at reservoir conditions (2,000 m) and can retain considerable porosity (10%). Our analysis has implications for microfracture and pore network characterization in geothermal reservoirs, in particular, in vapor-dominated systems where matrix porosity and permeability play a role.

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“…However, well networks are seldom where we need them and are predominately placed in well-developed areas, where well-exposed outcrops needed for structural geology measurements are sparse (Ball et al 2010;Bense et al 2013). Some studies integrate surface and subsurface data sets to study fault zone hydrogeology, such as geothermal studies (Revil et al 2015;Chambefort et al 2016;McNamara et al 2016;Mroczek et al 2016).…”

Section: Introductionmentioning

confidence: 99%

Complexity of hydrogeologic regime around an ancient low‐angle thrust fault revealed by multidisciplinary field study

et al. 2016

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Co‐located and integrated observation of the surface and subsurface is necessary to characterize fault zone hydrogeology. The spectacular cliff‐face exposure of the Champlain Thrust fault at Lone Rock Point, Vermont, and a nearby well‐field site provides the opportunity for co‐located structural and hydrogeologic field observations. We mapped the prominent structural features of the Champlain Thrust fault and discrete groundwater seeps in outcrop, and also drilled through the fault near the outcrop and determined aquifer parameters from aquifer pumping tests. In outcrop, the fault core thickness varies on the meter scale, splays out into multiple strands, and is offset by a minor normal fault. Groundwater seeps are prevalent in the heavily fractured footwall, but limited in the fault core and hanging wall, suggesting that at the cliff face the water table is generally near the fault core and groundwater flow in the hanging wall is limited. Enrichment of more soluble minerals in cemented fault rock associated with older strands of the fault system may play an important role in localizing karst features in the hanging wall. At the well‐field site, the Champlain Thrust fault is offset significantly by a high‐angle normal fault, the water table is near the surface, and aquifer pumping tests reveal a complex hydrogeologic system, with karst and steep fractures as strong hydraulic conduits in the hanging wall and fault core. The most salient features of the fault zone hydrogeology in the surface and subsurface data are different, but can be integrated into a preliminary conceptual model. Together, the surface and subsurface methods underscore and emphasize the complexity and heterogeneity of the hydrogeology of this low‐angle sedimentary fault.

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Ngatamariki Geothermal Field, New Zealand: Geology, geophysics, chemistry and conceptual model

Cited by 38 publications

References 22 publications

Seismic Response to Injection Well Stimulation in a High‐Temperature, High‐Permeability Reservoir

Seismic Response to Injection Well Stimulation in a High‐Temperature, High‐Permeability Reservoir

Mineral Alteration and Fracture Influence on the Elastic Properties of Volcaniclastic Rocks

Complexity of hydrogeologic regime around an ancient low‐angle thrust fault revealed by multidisciplinary field study

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