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Barrington, New Zealand

Kokhanenko P.,University of Canterbury | Brown K.,GEOKEM | Jermy M.,University of Canterbury
Proceedings of the 19th Australasian Fluid Mechanics Conference, AFMC 2014 | Year: 2014

Silica scaling is a highly undesirable process accompanying the extraction of geothermal energy. The mechanisms of transport and attachment of silica nanoparticles governing this process remain poorly understood. The comparative analysis of the existing experimental and theoretical data suggested the theory underestimates the convective transport of the particles on to a rough wall. The proposed hypothesis of specific inertial deposition of the nanoparticles onto roughness elements (not accounted in the current theory) was tested. The analytical solution of the corresponding mass transfer problem showed that this additional transport is significant enough to explain observed anomalies of the silica scaling process and, therefore, must be accounted in future numerical simulations. Source


Simmons S.F.,University of Utah | Brown K.L.,GEOKEM | Tutolo B.M.,University of Minnesota | Tutolo B.M.,University of Oxford
Economic Geology | Year: 2016

In order to analyze the concentrations of Ag, As, Au, Cd, Cu, Hg, Mn, Mo, Ni, Pb, Se, Sb, Te, Tl, W, and Zn in deep hydrothermal chloride waters at 195° to 320°C, and in shallow boiled chloride waters at 160° to 230°C, we sampled wells drilled to 3-km depth in geothermal systems of the North Island, New Zealand. Six of the systems are located in a segment of volcanic arc in the central Taupo Volcanic Zone, and the seventh system is associated with an intraplate mafic (felsic) volcanic center. The concentrations of metals range widely from 0.1 to>1,000 μg/kg with a large degree of intersystem variability. Some of the largest contrasts in Au, Ag, Pb, and Te concentrations are observed in the two nearest systems, Rotokawa and Wairakei, which are only 10 km apart. The correlations between metals are poor, except for Ag-Au-Pb-Te, and As-Sb. The correlations between metals, Cl, and H2S are also poor, with the exception of Rotokawa where the highest concentrations of Ag, Au, Cu, and Te correlate with the highest concentration of aqueous H2S. Speciation calculations indicate that the dominant aqueous species of Ag, Au, Cu, Pb, and Zn involve HS- complexes. The calculations also show that the states of saturation range from undersaturated conditions for acanthite, arsenopyrite, and gold to oversaturated conditions for chalcopyrite, sphalerite, and tellurides. Notably, the Au-and Ag-transporting capacities of the deep chloride waters are much larger than the measured aqueous concentrations. These results suggest that fluid-mineral equilibria and the concentrations of ligands exert weak influence on metal concentrations at the temperatures and depths of sampling. The complex trends in hydrothermal metal concentrations strongly suggest that the deep-seated sources of metals, comprising magmatic intrusions, deep country rock, and their related fluids, limit the hydrothermal supplies of metals. Between the geothermal systems, hydrothermal fluxes of Ag (6-8,000 kg/y), Au (0.9-66 kg/y), Cu (30-23,500 kg/y), and Te (2-10,400 kg/y) are variable. The highest concentrations and fluxes of Ag, Au, and Te in Rotokawa and Mokai are attributed to direct fluid inputs from intrusions of andesitic and basaltic magmas, respectively. Compared to their deep counterparts, boiled chloride waters are strongly depleted in Ag, Au, Cd, Cu, Pb, and Te, because these metals deposit in sharp response to gas loss and cooling in the well. By comparison, the As, Mn, Mo, Ni, Sb, Tl, and Zn concentrations are measurably less depleted in boiled waters, making them available to form metal anomalies at shallow depths and in the peripheral parts of the epithermal environment. Periods of strong metal flux through the geothermal system combined with deep boiling favor epithermal ore formation and the development of large precious metal deposits. However, even moderate metal fluxes can produce Au and Ag mineralization as long as the duration of focused fluid flow and boiling can be sustained. There is no evidence that the compositions of deep magmatic intrusions, mafic or intermediate, limit the ore-forming potential of a geothermal system. © 2016 Society of Economic Geologists, Inc. Source


Muller L.,Ecolab | Brown K.,GEOKEM | Robinson R.,Top Energy
Transactions - Geothermal Resources Council | Year: 2014

With global warming now accepted by most scientific communities and governments, there has been increasing focus and funding for development of reliable, alternative, low carbon emit-ting, energy sources. Of these wind and solar have seen the largest increases in capacity even though geothermal energy offers many benefits over both. Improving the efficiency of geothermal energy conversion is paramount to the successful utilisation of nonstandard resources, such as low enthalpy reserves and enhanced geothermal systems (EGS or Hot Rock Technology). For many geothermal systems, energy recovery is sacrificed to prevent scale formation in heat recovery equipment. For some systems effective chemical or mechanical solutions have been de-veloped that extend the ability to recover energy beyond that which is possible without additives. For other systems, in particular those with arsenic and antimony sulphide, no such chemical treatments were available with remedial cleaning of heat exchangers the only option. While the chemical cleaning is successful, the process does mean taking the plant off-line, taking the plant off line loss of production, producing a hazardous waste and potentially exposes personnel to undesirable hazards. This paper identifies situations where the application of specially developed polymers have been used to reduce operating and maintenance costs arising from antimony sulphide deposition, including prevention of deposition in heat exchangers and online removal of deposits from reinjection wells. These examples have provided a high return on investment for the sites involved. The paper discusses the chemical challenges and potential solutions to these deposits and proposes development work to achieve online deposit prevention and removal. Copyright © (2014) by the Geothermal Resources Council. Source


Hannington M.,Leibniz Institute of Marine Science | Hannington M.,University of Ottawa | Hardardottir V.,ISOR | Garbe-Schonberg D.,University of Kiel | Brown K.L.,GEOKEM
Nature Geoscience | Year: 2016

The origins of high-grade hydrothermal ore deposits are debated, but active geothermal systems provide important clues to their formation. The highest concentrations of gold are found in geothermal systems with direct links to island arc magmatism. Yet, similar concentrations have also been found in the absence of any input from arc magmas, for example, in the Reykjanes geothermal field, Iceland. Here we analyse brine samples taken from deep wells at Reykjanes and find that gold concentrations in the reservoir zone have increased over the past seven years from an average of 3 ppb to 14 ppb. The metal concentrations greatly exceed the maximum solubility of gold in the reservoir under saturated conditions and are now nearly two orders of magnitude higher than in mid-ocean ridge black smoker fluids - the direct analogues of Reykjanes deep liquids. We suggest that ongoing extraction of brine, the resulting pressure drop, and increased boiling have caused gold to drop out of solution and become trapped in the reservoir as a colloidal suspension. This process may explain how the stock of metal in the reservoirs of fossil geothermal systems could have increased over time and thus become available for the formation of gold-rich ore deposits. © 2016 Macmillan Publishers Limited. All rights reserved. Source


Lichti K.A.,Quest Integrity NZL Ltd. | Brown K.L.,GEOKEM
NACE - International Corrosion Conference Series | Year: 2013

The risk of voluminous silica scaling limits many geothermal energy plants to steam and brine separation temperatures above the saturation limit for silica in the separated brine. The impact of these limits are compounded in the face of demand for secondary heat extraction using binary plant that can significantly increase energy efficiency from geothermal fluids. Options for additional energy extraction include (i) increase in pH to increase the solubility limit for silica and (ii) decrease in pH to delay the time for onset of polymerization reactions for colloidal silica sufficient to allow reinjection to a reservoir where elevated temperature will lower the silica saturation index. These two scale-control methods can have significant impact on localized corrosion in chloride rich brines. Conditions for scale control and the risk of corrosion can both be modeled theoretically to predict ideal conditions for enhanced energy production with minimal risk of corrosion. However, prudent operators can benefit from confirmation testing of scaling and corrosion risks using a pilot plant that mimics planned operating conditions. Repeated testing of the thermodynamic models will improve the developed model prediction capabilities. Source

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