Examining the processes that control diffuse flow in seafloor hydrothermal systems can provide insight into what is happening below the seafloor at mid-ocean ridges. The diffuse flow could be either entrained seafloor fluids mixed with hot, upwelling fluids, or diffuse flow could be driven by sidewall heating across some low permeability barrier. This barrier would separate the diffuse flow fluids from the high temperature fluids, effectively preventing mixing. Three parameters were manipulated through a numerical model based on the single-pass model, and the fluid and heat flow results analyzed and compared to observed hydrothermal systems. These three parameters are depth of the extrusive layer at the top of the system, the permeability of the extrusive layer, and the existence of a low permeability barrier separating the high-temperature output from the induced diffuse flow.

Hydrothermal circulation through the seafloor on the mid-ocean ridge flanks is responsible for globally significant fluid, heat and chemical fluxes between the ocean and the oceanic crust. This dissertation investigates the locations of fluid ingress and egress, fluid flow paths within the crust, and the hydrology of the crust. Based on a global compilation of sediment interstitial water chemistry and models of interstitial water chemical transport and reaction, it is found that <10% of the ridge flank hydrothermal fluid flux passes through marine sediments globally. This requires that the large majority of hydrothermal fluid enters and leaves the crust through exposed basement outcropping through the sediment (“outcrops”). A probabilistic model of basement topography and sedimentation was used to quantify the distribution of seafloor outcrops globally, estimating that outcrops are, on average, a few kilometres apart on young crust, increasing to tens of kilometres apart as the crust ages. A model in which fluid travels laterally within the crustal aquifer for kilometres to tens of kilometres between discrete outcrops (“outcrop-to-outcrop flow”) is consistent with the global heat flow data. This finding supports the proposition that outcrop-to-outcrop flow is the dominant mode of ridge flank hydrothermal circulation globally. An alternative model of ridge flank hydrothermal circulation in which fluid circulation occurs by local convection within isolated outcrops is also possible, and is probably the dominant mode of circulation in crust younger than 3-5 Myrs old, on average, where there is insufficient sediment cover to support the lateral pressure gradients required by outcrop-to-outcrop flow. Estimated crystallization temperatures of carbonate minerals in the crust suggest that, at some locations in the aquifer, local convective mixing may be restricted (i.e., the aquifer is poorly mixed), whereas the carbonate data for other locations cannot distinguish between a well mixed and a poorly mixed aquifer. A poorly mixed aquifer requires that vertical permeability is 1.5 - 2.5 orders of magnitude lower than horizontal permeability. This permeability anisotropy may arise from interlaying of different lithological units within the upper crust. / Graduate / 0388 / 0547 / brocka@uvic.ca

Hydrothermal circulation through the seafloor on the mid-ocean ridge flanks is responsible for globally significant fluid, heat and chemical fluxes between the ocean and the oceanic crust. This dissertation investigates the locations of fluid ingress and egress, fluid flow paths within the crust, and the hydrology of the crust. Based on a global compilation of sediment interstitial water chemistry and models of interstitial water chemical transport and reaction, it is found that <10% of the ridge flank hydrothermal fluid flux passes through marine sediments globally. This requires that the large majority of hydrothermal fluid enters and leaves the crust through exposed basement outcropping through the sediment (“outcrops”). A probabilistic model of basement topography and sedimentation was used to quantify the distribution of seafloor outcrops globally, estimating that outcrops are, on average, a few kilometres apart on young crust, increasing to tens of kilometres apart as the crust ages. A model in which fluid travels laterally within the crustal aquifer for kilometres to tens of kilometres between discrete outcrops (“outcrop-to-outcrop flow”) is consistent with the global heat flow data. This finding supports the proposition that outcrop-to-outcrop flow is the dominant mode of ridge flank hydrothermal circulation globally. An alternative model of ridge flank hydrothermal circulation in which fluid circulation occurs by local convection within isolated outcrops is also possible, and is probably the dominant mode of circulation in crust younger than 3-5 Myrs old, on average, where there is insufficient sediment cover to support the lateral pressure gradients required by outcrop-to-outcrop flow. Estimated crystallization temperatures of carbonate minerals in the crust suggest that, at some locations in the aquifer, local convective mixing may be restricted (i.e., the aquifer is poorly mixed), whereas the carbonate data for other locations cannot distinguish between a well mixed and a poorly mixed aquifer. A poorly mixed aquifer requires that vertical permeability is 1.5 - 2.5 orders of magnitude lower than horizontal permeability. This permeability anisotropy may arise from interlaying of different lithological units within the upper crust. / Graduate / 0388 / 0547 / brocka@uvic.ca

Esta tese trata do desenvolvimento de um modelo de otimização para planejamento da operação de sistemas hidrotérmicos de produção de energia elétrica, chamado SolverSIN. São abordados ao longo do texto os seguintes itens: a estruturação do problema de planejamento da operação hidrotérmica, o reservatório equivalente de energia potencial, o balanço hidroenergético, o balanço de energia e o balanço de intercâmbios entre sistemas de produção de energia. O modelo foi testado e avaliado no Sistema Interligado Nacional de Energia Elétrica (SIN), o sistema hidrotérmico brasileiro, um dos mais complexos do mundo. Foi feita a caracterização da operação histórica do SIN para determinação das funções de perdas e das funções de custo térmico, fundamentais para viabilizar o equacionamento proposto. O modelo \"SolverSIN\" foi escrito em duas linguagens computacionais, um em Planilha eletrônica e outro em linguagem GAMS. A principal contribuição desse modelo é dar suporte à tomada de decisão operacional, envolvendo sistemas hidrotérmicos com eficiência, transparência e precisão. A eficiência do modelo está associada à proposta metodológica, baseada no balanço de energia entre fontes de produção de energia elétrica e as equações de balanço hidroenergético aplicadas aos reservatórios equivalentes de energia potencial. A otimização é feita empregandose a Programação Não Linear (PNL) com utilização das rotinas SNOPT, CONOPT e MINOS. A transparência do modelo é também uma propriedade muito importante, isso fica evidente com processamento do SolverSIN, pois ele permite ao decisor observar claramente o comportamento das variáveis envolvidas no processamento, tanto em situações de simulação, como nas de otimização. A propriedade da precisão é essencial e ela fica evidente com as aplicações apresentadas. Os resultados obtidos demonstram que o equacionamento proposto é adequado para emprego no planejamento da operação de sistemas hidrotérmicos. O SolverSIN é um modelo viável para emprego no planejamento operacional em tempo real de qualquer sistema hidrotérmico. / This thesis treats of development of an optimization model for operation planning of hydrothermal systems for electrical energy production. Discus the problem structure of hydrothermal operation planning, the potential energy equivalent reservoir, the hydro energetic balance, the energy balance and the interchange balance between energy production systems. An optimization model for operation planning is presented and is discussed a case study application with the Brazilian Electrical System. The characterization of historical operation of Brazilian System is done for lose functions determination, needed for the optimization model proposed. Thermal function coasts are also defined. The model entitled \"SolverSIN\" is presented in electronic sheet (Excel) version or GAMS program and is done applications with result analysis. The main contribution of this model is decision maker support on operational hydrothermal systems with efficiency, transparency and precision. The model efficiency is associated with methodological proposal, based on energy balance of electrical sources and hydro energetic balance equations applied to potential energy equivalent reservoir. The optimization process is solved by Non Linear Programming (NLP) with commercial solvers SNOPT, CONOPT and MINOS, with reliable on international technical community. The model transparency is also a property very important. The SolverSIN model runs allow that the decision maker clearly observe the involved variables, either on simulation, or optimization. The precision property is essential and gives evidence with presented applications. The results show that the SolverSIN model is proper for any hydrothermal systems operation planning.

Esta tese trata do desenvolvimento de um modelo de otimização para planejamento da operação de sistemas hidrotérmicos de produção de energia elétrica, chamado SolverSIN. São abordados ao longo do texto os seguintes itens: a estruturação do problema de planejamento da operação hidrotérmica, o reservatório equivalente de energia potencial, o balanço hidroenergético, o balanço de energia e o balanço de intercâmbios entre sistemas de produção de energia. O modelo foi testado e avaliado no Sistema Interligado Nacional de Energia Elétrica (SIN), o sistema hidrotérmico brasileiro, um dos mais complexos do mundo. Foi feita a caracterização da operação histórica do SIN para determinação das funções de perdas e das funções de custo térmico, fundamentais para viabilizar o equacionamento proposto. O modelo \"SolverSIN\" foi escrito em duas linguagens computacionais, um em Planilha eletrônica e outro em linguagem GAMS. A principal contribuição desse modelo é dar suporte à tomada de decisão operacional, envolvendo sistemas hidrotérmicos com eficiência, transparência e precisão. A eficiência do modelo está associada à proposta metodológica, baseada no balanço de energia entre fontes de produção de energia elétrica e as equações de balanço hidroenergético aplicadas aos reservatórios equivalentes de energia potencial. A otimização é feita empregandose a Programação Não Linear (PNL) com utilização das rotinas SNOPT, CONOPT e MINOS. A transparência do modelo é também uma propriedade muito importante, isso fica evidente com processamento do SolverSIN, pois ele permite ao decisor observar claramente o comportamento das variáveis envolvidas no processamento, tanto em situações de simulação, como nas de otimização. A propriedade da precisão é essencial e ela fica evidente com as aplicações apresentadas. Os resultados obtidos demonstram que o equacionamento proposto é adequado para emprego no planejamento da operação de sistemas hidrotérmicos. O SolverSIN é um modelo viável para emprego no planejamento operacional em tempo real de qualquer sistema hidrotérmico. / This thesis treats of development of an optimization model for operation planning of hydrothermal systems for electrical energy production. Discus the problem structure of hydrothermal operation planning, the potential energy equivalent reservoir, the hydro energetic balance, the energy balance and the interchange balance between energy production systems. An optimization model for operation planning is presented and is discussed a case study application with the Brazilian Electrical System. The characterization of historical operation of Brazilian System is done for lose functions determination, needed for the optimization model proposed. Thermal function coasts are also defined. The model entitled \"SolverSIN\" is presented in electronic sheet (Excel) version or GAMS program and is done applications with result analysis. The main contribution of this model is decision maker support on operational hydrothermal systems with efficiency, transparency and precision. The model efficiency is associated with methodological proposal, based on energy balance of electrical sources and hydro energetic balance equations applied to potential energy equivalent reservoir. The optimization process is solved by Non Linear Programming (NLP) with commercial solvers SNOPT, CONOPT and MINOS, with reliable on international technical community. The model transparency is also a property very important. The SolverSIN model runs allow that the decision maker clearly observe the involved variables, either on simulation, or optimization. The precision property is essential and gives evidence with presented applications. The results show that the SolverSIN model is proper for any hydrothermal systems operation planning.

While several lines of evidence strongly hint at the biological importance of impact-induced hydrothermal systems during the impact cataclysm at ~3.9 Ga, these systems are not well understood. There is unambiguous evidence of hydrothermal activity at many terrestrial craters, but the available samples represent a very limited number of crater diameters and locations within the crater. Therefore, computer models are crucial for learning how impact-induced hydrothermal systems work, how long they last, and whether they provide suitable environments for thermophilic microorganisms. This dissertation presents detailed simulations of hydrothermal activity at the terrestrial craters Chicxulub and Sudbury, as well as at range of crater sizes on early Mars. A well-established computer code HYDROTHERM was used. The models for terrestrial craters were constrained by seismic, magnetic, and gravity surveys, as well as petrological, mineralogical, and chemical analyses of samples (by others).Sudbury crater is ~180 km in diameter, and 1.85 Ga. Simulation results indicate that a hydrothermal system at Sudbury crater remained active for several hundred thousand to several million years, depending on assumed permeability, and produced habitable volumes of up to ~20,000 km^3.Chicxulub crater is also ~180-km in diameter, but only 65 Ma. The lifetime of the hydrothermal system ranges from 1.5 Ma to 2.3 Ma depending on assumed permeability. The temperatures and fluxes observed in the model are consistent with alteration patterns observed by others in borehole samples.Another set of simulations modeled post-impact cooling of hypothetical craters with diameters of 30, 100, and 180 km in an early Martian environment. System lifetimes, averaged for all permeability cases examined, were 67,000 years for the 30-km crater, 290,000 years for the 100-km crater, and 380,000 for the 180-km crater. Also, an ap-proximation of the thermal evolution of a Hellas-sized basin (~2000 km) suggests poten-tial for hydrothermal activity for ~10 Myr after the impact. The habitable volume reached a maximum of ~6,000 km^3 in the 180-km crater model.Possible morphological and mineralogical signs of hydrothermal activity in Martian craters were observed, both in this work and by others. These observations, while by no means definitive, are generally consistent with model predictions.

Eocene magmatism in the Great Basin is spatially and temporally associated with major gold mineralization and with the early stages of the westward retreat of magmatism from its eastern-most advance. The Battle Mountain Mining District in north-central Nevada is one of the more prominent areas of Eocene intrusive activity and Au-(Cu) mineralization. The district hosts Jurassic dikes, three centers of Cretaceous magmatism, as well as the major magmatic event of the late Eocene. This study, however, focuses on the youngest of the three events and looks in depth at the Eocene igneous centers across the district and their associated hydrothermal alteration and mineralization. The major areas of late Eocene magmatism and hydrothermal activity are at Elder Creek in the north, Copper Basin in the east, and Copper Canyon in the south, along with the smaller occurrences and deposits such as Buffalo Valley, Modoc, Long Peak, and Timber Canyon. New U-Pb ages on zircons were determined for 38 igneous rocks from around the district. These ages along with the 67 previously published U-Pb, Ar-Ar, and K-Ar ages were used to constrain the timing of emplacement of all of the igneous centers of Eocene age to a contracted period beginning around 42 Ma and ending between 39 and 38 Ma. The internal consistency in the resulting U-Pb ages requires that many of the previous dates in the district, especially the K-Ar ages, should be viewed with caution. Inherited cores were found in the zircons from 37 of the 38 samples analyzed in this study. This includes both abundant Jurassic and Cretaceous cores that are likely derived from older igneous rocks in the subsurface, as well as abundant cores of other ages that resemble but do not fully match the reported detrital zircon populations of the allochthonous sedimentary rocks from the Roberts Mountains and Golconda allochthons. Populations of zircons that are not known from surficial exposures imply that other rocks may be present at depth provided the some of the inherited zircons to the magmas. To better characterize the Eocene magmas, intrusive rocks were analyzed for major and selected trace elements, and their constituent minerals were analyzed by electron microprobe. Rock compositions are broadly calc-alkaline, metaluminous to weakly peraluminous, and range from quartz monzodiorites to high-silica rhyolites, with the majority of the rocks being granodiorites. Based on their titanite + magnetite ± ilmenite mineralogy and the compositions of biotite and hornblende, the igneous rocks are relatively oxidized with average ΔNNO values of +1.16 at 500 bars, +1.74 at 1000 bars and +2.29 at 2000 bars. Aluminum-in-hornblende with plagioclase thermobarometry on mineral rims indicates that the magmas were emplaced in the upper 5 km of the crust. Data from certain phenocryst interiors and from porphyritic dike swarms, however, reflects higher equilibration pressures and may indicate the position of an underlying source at a depth of 10-15 km. Overall these data characterize the Eocene magmatic system over ~10 km vertical extent. Hydrogen isotopic evidence suggests a minimum of two major fluids sources in these hydrothermal systems to explain the origin of the diverse mineralization and alteration in the district. The Na-Ca(-K) types of alteration, which are observed in many parts of the district, suggest there is a large influx of external saline fluids that contained isotopically heavy hydrogen in all of the major Eocene deposits. The range of δD values for all actinolite samples associated with the Na-Ca(-K) types is from -19‰ to -59‰. These values represent a significant shift from the δD values of hydrous minerals in the magmas and in the associated potassic alteration where the range of δD values for biotite is from -35‰ to -82‰, for amphiboles it is from -55‰ to -92‰, and for secondary biotite is from -34‰ to -90‰. The values for unaltered igneous hornblende and biotite are akin to those of magmatic water, whereas the heavier isotopic compositions from actinolite plot in the fields of either basinal brines or metamorphic fluids. In contrast, the sulfur isotopic compositions from these systems are surprisingly homogeneous across the district. Alteration assemblages characterized by petrographic and electron microprobe studies. Alteration of siliciclastic and igneous rocks includes: potassic, sericitic, sodic-calcic, calcic, and potassic-calcic alteration. Two types of skarn occur in the district. Fortitude-type skarns replace carbonate rocks and consist of hedenbergite + diopside + andradite + pyrrhotite with Au+Cu, mineralization whereas Labrador-type, potassic-calcic and calcic-ferric alteration and skarns replace feldspathic, silicic, and carbonate rocks, respectively, and consist of andradite + diopside + hematite + magnetite with Au+Cu mineralization. Taken together, the volume and distribution of these assemblages, along with fluid inclusion data, hydrogen isotope compositions, and petrologic considerations indicate two fluid sources: magmatic fluids generated potassic, sericitic, and Fortitude-type skarns, and moderately saline, non-magmatic fluids produced Na-Ca(-K) alteration mineral assemblages and Labrador-type skarns. Those features inferred to be magmatic-hydrothermal are restricted in their extent and related to particular intrusive phases, whereas the Na-Ca(-K) alteration features typically extend over several kilometers and are not correlated with any particular intrusive phase. Observations within the Battle Mountain district and regionally indicate that a variety of fluids – magmatic and non-magmatic – played significant roles in Eocene intrusion-centered hydrothermal systems. Consequently both fluid types need to be considered in interpreting Cenozoic metallogeny in the northern Great Basin.

Hydrothermal systems associated with oceanic spreading centers account for a quarter of Earth's total heat flux and one third of the heat flux through the ocean floor. Circulation of seawater through these systems alters both the crust and the circulating fluid, impacting global geochemical cycles. The warm vent fluids rich in nutrients support a wide variety of unique biological communities. Thus, understanding hydrothermal processes at oceanic spreading centers is important to provide insight into thermal and biogeochemical processes. In this dissertation I present the results of numerical modeling efforts for mid-ocean ridge hydrothermal systems. In the three manuscripts presented, permeability emerges as a key controlling factor for hydrothermal venting. In the first manuscript, I use 2-D numerical models to find that the distribution of permeability in the crust controls fluid velocity as well as the amount of mixing between hot hydrothermal fluids and cold seawater. This, in turn, effects the temperature and composition of fluids emerging on the surface. For the second manuscript, I construct single-pass 1-D models to show that a sudden increase in permeability caused due to magmatic or seismic events in the seafloor causes a sharp rise in the fluid output of the system. This, in conjunction with steep thermal gradients close to the surface, results in a rapid increase of venting temperatures. In the third manuscript, I develop a particle tracking model to study fluid trajectories in the subsurface. The results show that permeability distribution in the subsurface governs fluid paths and consequently, the residence time of fluids in the crust. Based on the work presented in this document, I conclude that permeability distribution, both local and field scale, exerts a major control on hydrothermal circulation in the subsurface and on the temperature and composition of venting fluids on the surface. / Ph. D.

A expansão da oferta energética frente à crescente demanda se mostra como um grande desafio para o país nas últimas décadas, tanto que para estimular os investimentos privados na área de geração de energia elétrica, o poder executivo, em 2003, iniciou as discussões de forma a apresentar seus objetivos e os pré-requisitos para alcançá-los e que mais tarde viria a se transformar na reforma do modelo institucional, introduzida no ano de 2004. Um dos marcos da reforma promovida são os leilões de compra de energia elétrica, tanto de geração existente, quanto de empreendimentos novos, sendo que a modalidades de contratação da energia pode ser por quantidade e por disponibilidade. Na modalidade de contratação por quantidade, o gerador vender um determinado montante de energia a um preço e deverá entregá-la ao comprador independentemente do seu montante de geração verificada em cada período. Na modalidade de contratação de energia por disponibilidade, o empreendedor é remunerado pelo investimento incorrido para construção e manutenção da usina, sendo ressarcido pelos compradores do contrato no custo de operação da usina incorrido, em caso de despacho da geração pelo operador do sistema elétrico. A contratação por disponibilidade é aplicada aos empreendimentos termelétricos e eólicos, cujos combustíveis podem ser desde os ventos e resíduos agrícolas de baixo custo, até óleo combustível derivado de petróleo com um alto custo e suscetível às oscilações de preço no mercado internacional. Esse custo assumido pelo comprador é um dos principais pontos de discussão desse trabalho, uma vez que por ocasião do leilão esse custo é ainda uma mera estimativa intrinsecamente relacionada com a operação eletro-energética do sistema elétrico brasileiro. Além disso, será introduzida a discussão sobre o impacto do custo da energia contratada por disponibilidade na tarifa dos consumidores, como resultado do próprio leilão associado à estratégia de cada distribuidora para contratação de seu mercado. / Electric energy supply of the fast growing demand in Brazil has been a challenge for the country in the last fifteen years. In order to stimulate power generation investments, a new institutional power sector model was introduced in 2004. This model introduced the obligation of the energy requirements acquisition by Distribution Utilities (DISCO) only through energy auctions from old and new power plants. New power plants energy auctions can be performed in two different ways: energy and capacity contracts. In the energy contracts, the energy amount is guaranteed by the seller, frequently in the case of hydro power plants. On the other hand, in the capacity arrangements the seller requires a fee, which results from the bidding process, as well as a charge defined to recover maintenance and fuel costs of thermal power plants, if the plant were requested to dispatch. Thermal power plants are dispatched by the Independent System Operator (ISO) using hydrothermal system optimization model. However, fuel costs are paid by DISCOs and will be passed-through to the end customers tariffs. The main focus of this work, is the economical and financial risks of capacity arrangement and the impact in the captive customers tariffs.

Este trabalho apresenta o desenvolvimento de um Sistema de Suporte a Decisão (SSD) para o planejamento operacional de sistemas hidrotérmicos de grande porte formados por um conjunto de usinas hidrelétricas e termelétricas, operados para geração e atendimento a demandas de energia elétrica. São consideradas também outras fontes de geração de energia, a expansão do sistema, transposições, usos múltiplos da água e restrições ambientais. O SSD integra um banco de dados com informações sobre o sistema hidrotérmico, uma interface gráfica para facilitar a edição dos dados e visualização dos resultados e os modelos de simulação e otimização. Os modelos do SSD chamado HIDROTERM baseiam-se na programação não linear (PNL). Nas diversas aplicações feitas do SSD com dados do Sistema Interligado Nacional (SIN), formado por 4 subsistemas e 128 usinas hidrelétricas ativas, foram obtidos resultados bastante satisfatórios demonstrando diversos avanços em relação ao modelo SISOPT de Barros et al. (2003), com destaque para a velocidade de processamento, o porte de sistemas aos quais o modelo pode ser aplicado e a representação bem mais completa do sistema hidrotérmico. Além do planejamento da operação do sistema hidrotérmico, o SSD pode ser aplicado também para diagnósticos do sistema existente, análises de impacto de mudanças em regras operacionais e de usos múltiplos da água, planejamento e avaliação de alternativas de expansão. / This paper presents the development of a Decision Support System (DSS) for the operational planning of large-scale hydrothermal systems formed by a series of hydroelectric and thermoelectric power plants, operated for the production and service demands for energy. Other sources of energy production, the expansion of the system, water transfers, multiple uses of water and environmental constraints are also considered. The DSS integrates a database with information of the hydrothermal system, a graphical interface to facilitate the editing of the data and display the results and the simulation and optimization models. The models of the called DSS HIDROTERM are based on the non-linear programming (NLP). In several applications made with the DSS with data for the Brazilian Hydrothermal System, formed by 4 subsystems and 128 active hydroelectric plants, very satisfactory results were obtained demonstrating various advances in relation to the model SISOPT from Barros et al. (2003), with emphasis on the processing speed, the size of systems to which the model can be applied and in a much more complete representation of the hydrothermal system. In addition to the planning of the operation of the hydrothermal system, the DSS can be applied also to the existing system diagnoses, analyses the impact of changes in operating rules and of multiple uses of water, planning and evaluation of expansion alternatives.