Anisotropic permeability and fluid dispersion in pervasively fractured lavas, Rotokawa Geothermal System, New Zealand.

2021 ◽  
Author(s):  
Warwick Kissling ◽  
Cecile Massiot
Keyword(s):  
Fluid Flow ◽  
New Zealand ◽  
Geothermal Field ◽  
Geothermal System ◽  
Geothermal Systems ◽  
Fracture Density ◽  
Tracer Transport ◽  
Fracture Models ◽  
Flow Through ◽  
Permeability Anisotropy

<p>Geothermal provides nearly 20% of New Zealand’s electricity as well as increasing opportunities for direct use. In New Zealand’s ~20 high temperature geothermal systems, fluids flow dominantly through fractured rocks with low matrix permeability. It is important to understand the nature of these fracture systems, and how fluids flow through them, so that the geothermal systems may be more efficiently and sustainably used. Here we present fluid flow calculations in several distinct discrete fracture models, each of which is broadly consistent with the fracture density and high dip magnitude angle distributions directly observed in borehole image logs at the Rotokawa Geothermal Field (>300°C, 175 MWe installed capacity). This reservoir is hosted in fractured andesites. In general, fractures are steeply dipping, and the reservoir is known to be compartmentalized.</p><p>Our new code describes fluid flow through large numbers (e.g., thousands) of stochastic fracture networks to provide statistical distributions of permeability, permeability anisotropy and fluid dispersion at reservoir scale (e.g., 1 km<sup>2</sup>). Calculations can be based on both the cubic flow law for smooth-walled fractures and the Forchheimer flow model, which includes an additional term to describe the nonlinear drag (i.e. friction) in real fractures caused by surface roughness of the fracture walls.</p><p>Models with fracture density consistent with borehole observations show pervasive connectivity at reservoir scales, with fluid flow (hence permeability) and tracer transport predominantly along the mean fracture orientation. As the fracture density is varied, we find a linear relationship between permeability which holds above a well-defined percolation threshold. Permeability anisotropy is in general high (~10 to 15), because of the steeply dipping fractures. As fracture density decreases, mean anisotropy decreases while its variability increases. Significant dispersion of fluid occurs as it is transported through the reservoir. These fracture models will inform more traditional continuum models of fractured geothermal reservoirs hosted in volcanic rocks, to provide a better description of fluid flow within reservoirs and aid the responsible and sustainable use of that resource in the future.</p>

Heat transfer estimation through a high-temperature geothermal field in New Zealand quantified by multi-channel data modelling

2021 ◽  
Author(s):  
Alberto Ardid ◽  
Rosalind Archer ◽  
David Dempsey
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
High Temperature ◽  
New Zealand ◽  
Geothermal Field ◽  
Heat Fluxes ◽  
Geothermal System ◽  
Geothermal Systems ◽  
Total Heat Flow ◽  
Sustainable Resource Management

<p>In high-temperature geothermal systems, understanding heat transfer helps conceptualize the whole system as well as estimating the resource size. To obtain the fullest picture, it is necessary to integrate different types of data, e.g., surface electromagnetic surveys, wellbore lithology, geochemistry, and temperature logs. This can be achieved through joint modelling. Here, we quantify the spatial distribution of heat transfer through the hydrothermally-altered, impermeable smectite layer that has developed atop the Wairākei-Tauhara geothermal system, New Zealand. Our approach involves first constraining 1D magnetotelluric (MT) inversion models with methylene blue analysis (MeB, an indicator of conductive smectite clay) and mapping these onto temperature and lithology data from geothermal wells. Then, one-dimensional models of heat transfer are fitted to well temperature logs to estimate heat flux variations across the field. We use our integrated method to estimate the average heat flux through the clay cap (2.2 W/m2) and total heat flow (380 ± 21 MW) of the Wairākei-Tauhara geothermal field. This approach models multiple datasets for estimating heat fluxes and could be applied in geothermal provinces around the world with implications for sustainable resource management and our understanding of magmatic systems.</p>

scholarly journals Tectonic Evolution of the Southern Negros Geothermal Field and Implications for the Development of Fractured Geothermal Systems

Geofluids ◽  
2018 ◽  
Vol 2018 ◽  
pp. 1-20 ◽  
Author(s):  
Loraine R. Pastoriza ◽  
Robert E. Holdsworth ◽  
Kenneth J. W. McCaffrey ◽  
Edward Dempsey
Keyword(s):  
Fluid Flow ◽  
Structural Evolution ◽  
Geothermal Field ◽  
Geothermal System ◽  
Geothermal Systems ◽  
Fracture Permeability ◽  
Fault Rock ◽  
Stress Regime ◽  
Permeability Characteristics ◽  
Geothermal Fluids

Fluid flow pathway characterisation is critical to geothermal exploration and exploitation. In fractured geothermal reservoirs, it requires a good understanding of the structural evolution together with the fracture distribution and fluid flow properties. A fieldwork-based approach has been used to evaluate the potential fracture permeability characteristics of a typical high-temperature geothermal reservoir in the Southern Negros Geothermal Field, Philippines. This is a liquid-dominated resource hosted in the andesitic Quaternary Cuernos de Negros Volcano, Negros Island. Fieldwork reveals two main fracture groups based on fault rock characteristics, alteration type, relative age of deformation, and associated thermal manifestation, with the youngest fractures mainly related to the development of the current geothermal system. Fault kinematics, cross-cutting relationships, and palaeostress analysis suggest at least two distinct deformation events under changing stress fields since probably the Pliocene. We propose that this deformation history was influenced by the development of the Cuernos de Negros Volcano and the northward propagation of a major neotectonic structure located to the northwest, the Yupisan Fault. A combined slip and dilation tendency analysis of the mapped faults indicates that NW-SE structures should be particularly promising drilling targets under the inferred current stress regime, consistent with drilling results. However, existing boreholes also suggest that NE–SW structures can act as effective channels for geothermal fluids. Our observations suggest that these features were initiated as the dominant features in the older kinematic system and have then been reactivated at the present day.

scholarly journals The Hydrothermal Alteration of the Cordón de Inacaliri Volcanic Complex in the Framework of the Hidden Geothermal Systems within the Pabelloncito Graben (Northern Chile)

Minerals ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1279
Author(s):  
Santiago Nicolás Maza ◽  
Gilda Collo ◽  
Diego Morata ◽  
Carolina Cuña-Rodriguez ◽  
Marco Taussi ◽  
...  
Keyword(s):  
Hydrothermal Alteration ◽  
Geothermal Field ◽  
Geothermal System ◽  
Volcanic Complex ◽  
Geothermal Systems ◽  
Acid Sulfate ◽  
Alteration Zones ◽  
Geological Processes ◽  
Freshwater Bodies ◽  
Hydrothermal Alteration Zones

Detailed mineralogical analyses in areas with surface hydrothermal alteration zones associated with recent volcanism (<1 Ma) in the Central Andean Volcanic Zone could provide key information to unravel the presence of hidden geothermal systems. In the Cordón de Inacaliri Volcanic Complex, a geothermal field with an estimated potential of ~1.08 MWe·km−2 has been recently discovered. In this work, we focus on the hydrothermal alteration zones and discharge products of this area, with the aim to reconstruct the geological processes responsible for the space-time evolution leading to the geothermal records. We identified (1) discharge products associated with acid fluids that could be related to: (i) acid-sulfate alteration with alunite + kaolinite + opal CT + anatase, indicating the presence of a steam-heated blanket with massive fine-grained silica (opal-CT), likely accumulated in mud pots where the intersection of the paleowater table with the surface occurred; (ii) argillic alteration with kaolinite + hematite + halloysite + smectite + I/S + illite in the surrounding of the acid-sulfate alteration; and (2) discharge products associated with neutral-alkaline fluids such as: (i) discontinuous pinnacle-like silica and silica deposits with laterally developed coarse stratification which, together with remaining microorganisms, emphasize a sinter deposit associated with alkaline/freshwater/brackish alkaline-chlorine water bodies and laterally associated with (ii) calcite + aragonite deriving from bicarbonate waters. The scarce presence of relics of sinter deposits, with high degree crystallinity phases and diatom remnants, in addition to alunite + kaolinite + opal CT + anatase assemblages, is consistent with a superimposition of a steam-heated environment to a previous sinter deposit. These characters are also a distinguishing feature of paleosurface deposits associated with the geothermal system of the Cordón de Inacaliri Volcanic Complex. The presence of diatoms in heated freshwater bodies at 5100 m a.s.l. in the Atacama Desert environment could be related with the last documented deglaciation in the area (~20–10 ka), an important factor in the recharge of the hidden geothermal systems of the Pabelloncito graben.

Precious Metals in Modern Hydrothermal Solutions and Implications for the Formation of Epithermal Ore Deposits

SEG Discovery ◽  
2008 ◽  
pp. 1-12
Author(s):  
Stuart F. Simmons ◽  
Kevin L. Brown
Keyword(s):  
New Zealand ◽  
Precious Metals ◽  
Ore Deposits ◽  
Taupo Volcanic Zone ◽  
Geothermal System ◽  
Hydrothermal Solutions ◽  
Geothermal Systems ◽  
Gold Silver ◽  
Wide Range ◽  
Time Required

ABSTRACT We determined the concentrations of gold, silver, arsenic, antimony, and mercury in deep hydrothermal solutions (~1 km depth, 200° to &gt;300°C) from active geothermal systems in the Taupo Volcanic Zone, New Zealand, and Ladolam, Lihir Island, Papua New Guinea. The wide range of concentrations in the New Zealand systems and the stable isotope signatures at Ladolam confırm that magmas are an important source of high concentrations of gold and silver in hydrothermal solutions. The Rotokawa geothermal system in New Zealand has the highest hydrothermal fluxes of gold (~30–100 kg/yr) and silver (~5000–11,000 kg/yr), which, if they remained constant, could match the metal inventories of the largest ore deposits in the world in &lt;50,000 years. This relatively short time span is comparable to the amount of time required to account for the known gold resource in ores at Ladolam, which has a slightly lower gold flux (~25 kg/yr). The fact that a giant gold deposit exists at Ladolam, rather than at Rotokawa, demonstrates the importance of fluid focusing and effıcient metal deposition in the formation of epithermal gold and silver ore deposits.

Cinnabar, livingstonite, stibnite and pyrite in Pliocene silica sinter from Northland, New Zealand

2004 ◽  
Vol 68 (1) ◽  
pp. 191-198 ◽  
Author(s):  
W. A. Hampton ◽  
G. P. White ◽  
P. W. O. Hoskin ◽  
P. R. L. Browne ◽  
K. A. Rodgers
Keyword(s):  
New Zealand ◽  
Liquid Phase ◽  
Trace Element ◽  
Electron Microprobe ◽  
Fractured Rocks ◽  
Geothermal Field ◽  
Geothermal System ◽  
Sulphide Mineralization ◽  
Fracture Sealing ◽  
Periodic Changes

AbstractSilica sinter masses in the southern portion of the Pliocene Puhipuhi geothermal field of Northland, New Zealand, have recrystallized to microcrystalline quartz and moganite but many primary depositional fabrics of the sinters can still be recognized. Finely disseminated cinnabar, acicular stibnite, pyrite framboids and minor livingstonite are distributed through both massive sinter and stromatolitic fabrics with sulphide mineralization extending from fractured rocks about former spring vents into less disturbed sinter layers. The deposition of sulphides in the sinters is part of a continuum of mineralization resulting from the former hydrothermal regime and which extends to depth in the extinct geothermal system. Periodic changes in the hydrology, such as repeated fracturing following fracture sealing facilitated episodic sulphide deposition. Mercury is considered to have travelled in the liquid phase with antimony and precipitated directly as cinnabar. Remobilization of the sulphides, along with the recrystallization of the sinter masses, have produced complex textural relations. The multifaceted paragenesis of the sulphides is reflected in the range of their minor and trace element compositions revealed by electron microprobe analyses.

Geothermal manifestations in the Tyrrhenian area: the role of faults in channelling superhot geothermal fluids

2021 ◽  
Author(s):  
Martina Zucchi
Keyword(s):  
Fluid Flow ◽  
Fault Zones ◽  
Ore Deposits ◽  
Contact Metamorphism ◽  
Normal Faults ◽  
Geothermal System ◽  
Low Permeability ◽  
Geothermal Systems ◽  
Rock Interaction ◽  
Geothermal Fluids

&lt;div&gt; &lt;p&gt;&lt;span&gt;Extensional tectonics and related magmatism affecting continental crust can favour the development of geothermal systems. Granitoids intruded in the upper crust represent the main expression of magmatism; they are strictly controlled by brittle structures during their emplacement and exhumation. The cooling of the magmatic bodies produce a thermal perturbation in the hosting rocks resulting in thermo-metamorphic aureoles of several meter thick, usually characterised by valuable ore deposits. After the emplacement and during the cooling stage such granitoids can promote the geothermal fluids circulation mainly through the fault zones. In case of favourable geological and structural conditions, geothermal fluids can be stored in geological traps (reservoirs), generally represented by rock volumes with sufficient permeability for storing a significant amount of fluid. Traps are confined, at the top, by rocks characterised by low, or very low permeability, referred to as the cap rocks of a geothermal system. Several studies are addressed to the study of fluid migration through the permeable rock volumes, whereas few papers are dealing with fluid flow and fluid-rock interaction within the cap rocks. &lt;/span&gt;&lt;/p&gt; &lt;/div&gt;&lt;div&gt; &lt;p&gt;&lt;span&gt;In this presentation, an example of fault-controlled geothermal fluid within low permeability rocks is presented. The study area is located in the south-eastern side of Elba Island (Tuscan Archipelago, Italy), where a succession made up of shale, marl and limestone (Argille a Palombini Fm, early Cretaceous) was affected by contact metamorphism related to the Porto Azzurro monzogranite, which produced different mineral assemblages, depending on the involved lithotypes. These metamorphic rocks were dissected by high-angle normal faults that channelled superhot geothermal fluids. Fluid inclusions analyses on hydrothermal quartz and calcite suggest that at least three paleo-geothermal fluids permeated through the fault zones, at a maximum P of about 0.8 kbar. The results reveal how brittle deformation induces fluid flow in rocks characterised by very low permeability and allow the characterisation of the paleo-geothermal fluids in terms of salinity and P-T trapping conditions. &lt;/span&gt;&lt;/p&gt; &lt;/div&gt;

scholarly journals Aspects of the Chronology, Structure and Thermal History of the Kawerau Geothermal Field

2021 ◽  
Author(s):  
◽  
Sarah Dawn Milicich
Keyword(s):  
New Zealand ◽  
Hydrothermal Alteration ◽  
Electrical Power ◽  
Geothermal Field ◽  
Geothermal System ◽  
Hydrothermal Conditions ◽  
Geothermal Resources ◽  
Textural Characteristic ◽  
Structural Framework ◽  
Geological Conditions

<p>The development and management of high-temperature geothermal resources for electrical power generation requires accurate knowledge of the local geological conditions, particularly where they impact on the hydrology of the resource. This study is an integrated programme of work designed to develop new perspectives on the geological and structural framework of the Kawerau geothermal resource as a sound basis for field management. Although the geological approaches and techniques utilised in this study have previously been used, their application to an integrated study of a geothermal system in New Zealand has not been previously undertaken.  Correlating volcanic and sedimentary stratigraphy in geothermal areas in New Zealand can be challenging due to similarities in lithology and the destruction of distinctive chemical, mineralogical and textural characteristic by hydrothermal alteration. A means to overcoming these issues is to utilise dating to correlate the stratigraphy. Zircons are resistant to the effects of typical hydrothermal conditions and were dated using SIMS techniques (SHRIMP-RG) to retrieve U–Pb ages on zircons. These age data were then used to correlate units across the field, in part aided by correlations to material that had previously been dated from fresh rock by ⁴⁰Ar/³⁹Ar techniques, and used to redefine the stratigraphic framework for the area. [...]  Although previously inferred to be a long–lived system, the modern Kawerau Geothermal Field is a Holocene entity reflecting the rejuvenation of magmatic heat flux associated with Putauaki volcano superimposed on an area of multiple reactivated fault structures, sporadic magmatism and variable rates of subsidence. This study documents past patterns of fluid flow, temperatures and chemistry, and inferred permeability within the field. Using textural relationships in selected samples, the relative timing and patterns of hydrothermal alteration, and fluid flows can be established. These textural relationships are then calibrated against fluid inclusion palaeotemperature measurements and isotope data and related to temperatures and compositions of past fluids. Short–lived heat sources beneath the field resulted from local magma intrusions, and are responsible for the 0.36 Ma and 0.138 Ma rhyolites and Holocene eruptive activity of Putauaki andesite–dacite volcano. The Putauaki activity is inferred to be responsible for the thermal and alteration characteristics of the modern system.</p>

THREE-DIMENSIONAL SIMULATION OF FLUID FLOW THROUGH A DISCRETE FRACTURE AND MATRIX

2021 ◽  
Author(s):  
Kunwar Mrityunjai Sharma ◽  
Tariq Anwar Ansari
Keyword(s):  
Fluid Flow ◽  
Oil And Gas ◽  
Flow Behavior ◽  
Gas Production ◽  
Geothermal System ◽  
Porous Rocks ◽  
Permeability Model ◽  
Matrix Block ◽  
The Matrix ◽  
Flow Through

The study of fluid flow mechanics in fractured porous rocks is crucial in the area of oil and gas production industries, enhanced geothermal system (EGS), CO2 sequestration, disposal of nuclear waste in deep geological repositories (DGR), etc. There are usually two types of flows in fractured rockmass setting. The dominant flow occurs through the fractures whereas there is also a slow movement of fluid through the matrix block. The fluid movement between fracture and matrix is often continuous across the fracture. The present study focuses on the development of a numerical model which can simulate the flow behavior through fracture and matrix simultaneously, which is also known as dual permeability model. To simulate this problem, a 3D model is built in COMSOL Multiphysics 4.3a where a cylindrical geometry is made, and a fracture is defined parallel to the axis of the geometry. The asperity of the fracture is defined by a variable ‘a’ which varies along the x-axis, in such a way that increases the value of ‘a’ alters the geometry of fracture and increases the roughness of fracture. Darcy flow physics is used to simulate the situation with known parameters like porosity, permeability, storage coefficient, etc. Pressure is applied as a boundary condition at two ends of the geometry which acts as driving force for fluid to flow through the block. The influence of fracture asperity on the flow behavior is examined by doing the parametric study and the study shows the decrement in the velocity magnitude with an increase in asperity. The formation of dual flow velocity regime, one along the defined fracture and the other along with the matrix, indicates the efficiency of the developed dual-porosity and permeability model.

scholarly journals Anisotropy as an indicator for reservoir changes: example from the Rotokawa and Ngatamariki geothermal fields, New Zealand

2019 ◽  
Vol 220 (1) ◽  
pp. 1-17 ◽  
Author(s):  
Stefan Mroczek ◽  
Martha K Savage ◽  
Chet Hopp ◽  
Steven M Sewell
Keyword(s):  
New Zealand ◽  
Shear Wave ◽  
Fluid Pressure ◽  
Geothermal Field ◽  
Taupo Volcanic Zone ◽  
Fracture Density ◽  
Splitting Technique ◽  
Geothermal Fluids ◽  
Geothermal Fields ◽  
Field Production

SUMMARY We investigate the relation between geothermal field production and fracture density and orientation in the Ngatamariki and Rotokawa geothermal fields, located in the Taupo Volcanic Zone, New Zealand using shear wave splitting (SWS). We determine the SWS parameters for 17 702 microseismic events across 38 stations spanning close to 4 yr from 2012 to 2015. We compare the strength of anisotropy to changes in field production and injection. We also compare the orientation of the anisotropy to in situ and regional measurements of maximum horizontal stress orientation. ($S_{\mathrm{ H}_{\mathrm{ max}}}$). Due to the volume of unique events (approximately 160 000), shear wave phases are picked automatically. We carry out automatic SWS measurements using the Multiple Filter Automatic Splitting Technique (MFAST). The SWS measurements are interpreted in the context of stress aligned microcracks. Outside both fields and within Ngatamariki, fast polarizations align with the NE–SW regional orientation of $S_{\mathrm{ H}_{\max}}$. Within Rotokawa a greater complexity is observed, with polarizations tending toward N–S. We observe increases in per cent anisotropy coinciding with the start of production/injection in Ngatamariki and then a later correlated drop in per cent anisotropy and vP/vS ratios in southern Ngatamariki as injection is shifted to the north. This relationship is consistent with pore fluid pressure within the reservoir being affected by local changes in production and injection of geothermal fluids causing cracks to open and close in response.

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