In order to develop a better understanding of the property, microstructure evolution and thermal history of FSW Inconel 718's, the strain, strain rate and thermal cycles need to be determined. In order to estimate the strain field of a deformed body, a displacement function needs to be determined. A 3D deformation model was developed to determine the displacement coefficients. A rectangular box created in this model deforms following a linear displacement function. Three orthogonal planes cut this deformed box, which leads to three deformed planes. The shape parameters (L, H, θ¹ and θ²) on the three orthogonal planes can be expressed as the functions of displacement coefficients. Although the displacement coefficients can not be expressed in the forms of the shape parameters symbolically, a numerical solution can be found using numerical optimization methods. The shape parameters were obtained by assuming the displacement coefficients (three cases). Then, the numerical optimization was carried out to determine the displacement coefficients. The solved displacement coefficients are the same as the assumed ones, which shows that this inverse problem can be solved, and this model is robust to determine the displacement function numerically. This model was used to estimate the strain and strain rate at the boundary of the nugget zone of Friction Stir Welding (FSW) Inconel 718. A numerical/experimental methodology was developed to estimate the thermal history in the stir zone of FSW Inconel 718.The thermocouple experiment was conducted to measure the thermal cycles in Heat Affected Zone (HAZ). Using the measured temperature in HAZ and a numerical model, the peak temperature (1039 ºC) and cooling rate (58.18 ºC/s) were determined. The microstructure in different regions was characterized and co-related with the thermal cycles. In order to understand the microstructure evolution in the stir zone, the strain rate (12.612 s-1) was estimated using the mathematical model as mentioned above. According to the estimated thermal history and strain rate, the assumption that the dynamic recrystallizaiton occurred during FSW was made. The grain size in the nugget zone affects the hardness. The relationship among the microstructure, mechanical properties, and thermal cycles was discussed.

Additive manufacturing (AM) is a process of creating objects from 3D model data by adding layers of material. AM technologies present several advantages compared to traditional manufacturing technologies, such as producing less material waste and being capable of producing parts with greater geometric complexity. However, deficiencies in the printing process due to high process uncertainty can affect the microstructural properties of a fabricated part leading to defects. In metal AM, previous studies have linked defects in parts with melt pool temperature fluctuations, with the size of the melt pool and the scan pattern being key factors associated with part defects. Thus being able to adjust certain process parameters during a part's fabrication, and knowing when to adjust these parameters, is critical to producing reliable parts. To know when to effectively adjust these parameters it is necessary to have models that can both identify when a defect has occurred and forecast the behavior of the process to identify if a defect will occur. This study focuses on the development of accurate forecasting models of the melt pool temperature distribution. Researchers at Mississippi State University have collected in-situ pyrometer data of a direct laser deposition process which captures the temperature distribution of the melt pool. The high-dimensionality and noise of the data pose unique challenges in developing accurate forecasting models. To overcome these challenges, a tensor decomposition modeling framework is developed that can actively learn and adapt to new data. The framework is evaluated on two datasets which demonstrates its ability to generate accurate forecasts and adjust to new data.

Many geologic processes occur in association with hydrothermal fluids and some of these fluids are eventually trapped as fluid inclusions in minerals formed during the process. Fluid inclusions provide valuable information on the pressure, temperature and fluid composition (PTX) of the environment of formation, hence understanding PTX properties of the fluid inclusions is required. The most important step of a fluid inclusion study is the identification of Fluid Inclusion Assemblages (FIA) that represent the finest (shortest time duration) geologic event that can be constrained using fluid inclusions. Homogenization temperature data obtained from fluid inclusions is often used to reconstruct temperature history of a geologic event. The precision with which fluid inclusions constrain the temperatures of geologic events depends on the precision with which the temperature of a fluid inclusion assemblage can be determined. Synthetic fluid inclusions trapped in the one-fluid-phase field are formed at a known and relatively constant temperature. However, microthermometry of synthetic fluid inclusions often reveals Th variations of about ± 1- 4 degrees Centigrade, or one order of magnitude larger than the precision of the measurement for an individual inclusion. The same range in Th was observed in well-constrained natural FIAs where the inclusions are assumed to have been trapped at the same time. The observed small variations are the result of the effect of the fluid inclusion size on the bubble collapsing temperature. As inclusions are heated the vapor bubble is getting smaller until the pressure difference between the pressure of the vapor and the confining pressure reaches a critical value and the bubble collapses. It was observed that smaller inclusions reach critical bubble radius and critical pressure differences at lower temperatures than larger inclusions within the same FIA. Homogenization temperature (Th) variations depend on many factors that vary within different geological environments. In order to determine minimum and acceptable Th ranges fro FIAs formed in different environments we investigated several geologic environments including sedimentary, metamorphic, and magmatic hydrothermal environments. The observed minimum Th ranges range from 1-4 degrees Centigrade and acceptable Th range from 5-25 degrees Centigrade. The variations are mostly caused by the fluid inclusion size, natural temperature and pressure fluctuations during the formation of an FIA and reequilibration after trapping. Fluid inclusions containing H₂O-CO₂-NaCl are common in many geologic environments and knowing the salinity of these inclusions is important to interpret PVTX properties of the fluids. A technique that combines Raman spectroscopy and microthermometry of individual inclusions was developed to determine the salinity of these inclusions. In order to determine the salinity, the pressure and temperature within the inclusion must be known. The pressure within the inclusions is determined using the splitting in the Fermi diad of the Raman spectra of the CO₂ at the clathrate melting temperature. Applying the technique with to synthetic fluid inclusions with known salinity suggests that the technique is valid and useable to determine salinity of H₂O-CO₂-NaCl fluid inclusions with unknown salinity. / Ph. D.

This thesis demonstrates that geological setting, depositional facies, open system flux of hot basinal brines and descending of shallow waters have a strong impact on the distribution of the diagenetic alterations within continental and paralic/shallow marine sandstones which in turn control the quality and heterogeneities of the reservoirs. Geological setting controls the mineralogical and textural maturity of sandstone, whereas depositional facies control the pore water chemistry (marine, brackish or meteoric), sedimentary texture and sand body geometry. Eogenetic alterations in the fluvial deposits are dominated by precipitation of infiltrated clays, kaolinitization of detrital silicates, whereas the shallow marine deposits are dominated by precipitation of early calcite and kaolinite. Conversely mesogenetic alterations are dominated by clay minerals transformation, quartz overgrowths and Ferroan- carbonates, barite and anhydrite. Flux of hot basinal brines is evidenced by precipitation of mesogenetic minerals that lack of internal sources (e.g. barite, anhydrite and ferroan carbonate cements), which is evidenced by: (1) restricted occurrence of these minerals in downthrown blocks. (2) The high fluid inclusion homogenization temperatures (Th) of quartz overgrowths (Th &gt; 110-139°C), and carbonate cements (T &gt; 80-140°C), which also have light δ18OV-PDB(-17.6‰ to -6.7‰). Flux of hot basinal brines is further evidenced by occurrence of saddle Fe-dolomite along stylolites. Fluid inclusion microthermometry further revealed a dramatic shift in pore- water chemistry from NaCl dominated brines during precipitation of quartz overgrowths to NaCl-CaCl2 dominated brines during cementation by Fe-dolomite. Presence of mixed brine (NaCl+CaCl2) systems in the fluid inclusions suggests flux of descending waters, which have circulated in the overlying carbonate-evaporite successions. The restricted occurrence of oil- filled inclusion to quartz overgrowths and methane to Fe-carbonate cements suggest migration of oil during precipitation by quartz and migration of methane during precipitation by Fe- carbonate cements. The extensive mesogenetic cements in the down thrown blocks is attributed to flux of basinal brines along deep seated faults, i.e. open system diagenesis. Integration of fluid inclusion microthermometry, isotopes, Raman spectrometry and thermal tectonic evolution of basins are essential techniques for unraveling the evolution of basinal fluids, cementation conditions and relative timing of hydrocarbons migration. / <p>Errata: Felaktigt disputationsdatum på spikbladet.</p>

Diagenetic and structural aspects of tight gas sandstones must be addressed concurrently in order to fully understand low-permeability sandstones and to better predict their reservoir quality attributes that arise from a combination of pore-scale and fracture distribution characteristics. This dissertation focuses on aspects of rock evolution that are germane to concurrent structural and diagenetic evolution, such as loading and thermal history, rock mechanical property evolution, and fracture timing. I tested the hypothesis that the cement precipitation step, governed by thermal exposure and grain surface attributes, governs how sandstone attributes evolve using observations from the Late Cretaceous Williams Fork sandstones from the Piceance Basin, Colorado. My research shows that essential information for predicting and understanding fracture patterns in sandstone can be obtained by unraveling cement precipitation (diagenetic) history. Fractures depend on the mechanical properties existing during fracture growth. I show that key rock mechanical properties (subcritical crack index, Young's modulus and Poisson's ratio), petrophysical behavior, and reservoir quality depend in a systematic way on time-temperature history and the intrinsic grain surface attributes of these sandstones. I classified the Williams Fork lithofacies petrographically and correlated those with log responses to create a model that can be used to predict reservoir quality and diagenesis directly from well logs. I determined rock mechanical characteristics by measuring the subcritical crack index (SCI), a mechanical property that influences fracture distribution characteristics, and by examining log-derived bulk mechanical properties. To quantify the influence of quartz cementation on the SCI and to determine the range of SCI values for sandstone of given framework composition at different diagenetic stages, I measured SCI on Williams Fork core samples and their outcrop equivalents. Diagenetic modeling is applied to determine the sandstone characteristics during fracturing. / text

A new apatite (U-Th)/He (AHe) dataset from subvertical transects collected in the Teton and Gallatin Ranges in the Teton-Yellowstone region provides insight for the slip history and length of the Teton fault. Along the northernmost segment of the Teton fault, inverse thermal history modeling of AHe data from Eagles Rest Peak yield a ~9 Ma age for onset of fault slip. This age supports previous interpretations that Mount Moran may be the true center of the Teton fault. This refined interpretation coupled with lengthdisplacement fault scaling analysis and previous estimates of total fault displacement (~6 km) indicates that the Teton fault may extend 50-90 km north of Mount Moran. However, this new data precludes the possibility that the Teton and East Gallatin faults represent the same structure. Yet, because these systems share a similar structure trend and initial slip ages (13 Ma and 16 Ma, respectively), they may still be related at a larger scale. To the south, the Teewinot transect yields the oldest onset age of ~32 Ma, however a >500 m vertical data gap in this transect leads us to cautiously interpret the results of this model, particularly as this age conflicts with four other transects along-strike.

The Northern Carnarvon Basin is the richest petroleum province in Australia. About 50 gas/condensate and oil fields, associated mainly with Jurassic source rocks, have been discovered in the sub-basins and on the Rankin Platform since 1964. The basin is located at the southern end of the North West Shelf of Australia. It can be mainly subdivided into the Exmouth, Barrow, Dampier and Beagle Sub-basins, the Rankin Platform and Exmouth Plateau. The sub-basins are rift-related grabens and half-grabens developed during the Jurassic to the earliest Cretaceous and contain over 10 kilometres of Mesozoic and Cainozoic sedimentary rocks, among which are several thousand meters of Jurassic rocks. The formations of the Jurassic and the lower part of the Barrow Group of Early Cretaceous age in the sub-basins of the Northern Carnarvon Basin were found to be overpressured with excess pressures of 5-29 MPa at depths of 2900-3600 m indicated by repeat formation tests (RFTs) and drill stem tests (DSTs). The characteristics of organic matter, thermal history and thermal maturity, pressure seal and overpressure evolution in the sub-basins are crucial to a proper understanding of the nature and dynamic processes of hydrocarbon generation and migration in the basin. Based on organic geochemical data, the important source rocks in the basin are Jurassic organic-rich fine-grained rocks including the Murat Siltstone, the rift-related Athol Formation and Dingo Claystone. The Mungaroo Formation of the Middle-Upper Triassic contains gas-generating source rocks. These formations recognised to be organic rich based on 1256 values of the total organic carbon content (TOC, %) from 17 wells. Average TOC values (calculated from samples with TOC < 15 %) are about 2.19 % in the Mungaroo Formation, about 2.09 % in the Murat Siltstone and about 1.74 % in the Athol Formation and Dingo Claystone. / Data from kerogen element analysis, Rock-Eval pyrolysis, visual kerogen composition and some biomarkers have been used to evaluate the kerogen type in the basin. It appears that type III kerogen is the dominant organic-matter type in the Triassic and Jurassic source rocks, while the Dingo Claystone may contain some oil-prone organic matter. The vitrinite reflectance (Ro) data in some wells of the Northern Carnarvon Basin are anomalously low. As a major thermal maturity indicator, the anomalously low Ro data seriously hinder the assessment of thermal maturity in the basin. This study differs from other studies in that it has paid more attention to Rock-Eval Tmax data. Therefore, problems affecting Tmax data in evaluating thermal maturity were investigated. A case study of contaminated Rock-Eval data in Bambra-2 and thermal modelling using Tmax data in 16 wells from different tectonic subdivisions were carried out. The major problems for using Tmax data were found to be contamination by drilling-mud additives, natural bitumen and suppression due to hydrogen index (HI) > 150 in some wells. Although the data reveal uncertainties and there is about ±3-10 % error for thermal modelling by using the proposed relationship of Ro and Tmax, the "reliable" Tmax data are found to be important, and useful to assess thermal maturity and reduce the influence of unexpectedly low Ro data. / This study analyzed the characteristics of deep overpressured zones and top pressure seals, in detail, in 7 wells based on the observed fluid pressure data and petrophysical data. The deep overpressured system (depth greater than 2650-3000 m) in the Jurassic formations and the lower part of the Barrow Group is shown by the measured fluid pressure data including RFTs, DSTs and mud weights. The highly overpressured Jurassic fine-grained rocks also exhibit well-log responses of high sonic transit times and low formation resistivities. The deep overpressured zone, however, may not necessarily be caused by anomalously high porosities due to undercompaction. The porosities in the deep overpressured Jurassic rocks may be significantly less than the well-log derived porosities, which may indicate that the sonic-log and resistivity-log also directly respond to the overpressuring in the deep overpressured fine-grained rocks of the sub-basins. Based on the profiles of fluid pressure and well-log data in 5 wells of the Barrow Sub-basin, a top pressure seal was interpreted to be consistent with the transitional pressure zone in the Barrow Sub-basin. This top pressure seal was observed to consist of a rock layer of 60-80 % claystone and siltstone. The depths of the rock layer range from 2650 m to 3300 m with thicknesses of 300-500 m and temperatures of 110-135 °C. Based on the well-log data, measured porosity and sandstone diagenesis, the rock layer seems to be well compacted and cemented with a porosity range of about 2-5 % and calculated permeabilities of about 10-19 to 10-22 M2. / This study performed thermal history and maturity modelling in 14 wells using the BasinMod 1D software. It was found that the thermal maturity data in 4 wells are consistent with the maturity curves predicted by the rifting heat flow history associated with the tectonic regime of this basin. The maximum heat flows during the rift event of the Jurassic and earliest Cretaceous possibly ranged from 60-70 mW/m2 along the sub-basins and 70-80 mW/m2 on the southern and central Exmouth Plateau. This study also carried out two case studies of thermal maturity and thermal modelling within the deep overpressured system in the Barrow and Bambra wells of the Barrow Sub-basin. These case studies were aimed at understanding whether overpressure has a determinable influence on thermal maturation in this region. It was found that there is no evidence for overpressure-related retardation of thermal maturity in the deep overpressured system, based on the measured maturity, biomarker maturity parameters and 1D thermal modelling. Therefore, based on the data analysed, overpressure is an insignificant factor in thermal maturity and h hydrocarbon generation in this basin. / Three seismic lines in the Exmouth, Barrow and Dampier Sub-basins were selected and converted to depth cross-sections, and then 2D geological models were created for overpressure evolution modelling. A major object of these 2D geological models was to define the critical faults. A top pressure seal was also detected based on the 2D model of the Barrow Sub-basin. Two-dimensional overpressure modelling was performed using the BasinMod 2D software. The mathematical 2D model takes into consideration compaction, fluid thermal expansion, pressure produced by hydrocarbon generation and quartz cementation. The sealed overpressured conditions can be modelled with fault sealing, bottom pressure seal (permeabilities of 10-23 to 10-25 M2 ) and top pressure seal (permeabilities of 10-19 to 10-22 m2). The modelling supports the development of a top pressure seal with quartz cementation. The 2D modelling suggests the rapid sedimentation rates can cause compaction disequilibrium in the fine-grained rocks, which may be a mechanism for overpressure generation during the Jurassic to the Early Cretaceous. The data suggest that the present-day deep overpressure is not associated with the porosity anomaly due to compaction disequilibrium and that compaction may be much less important than recurrent pressure charges because most of the porosity in the Jurassic source rocks has been lost through compaction and deposition rates have been very slow since the beginning of the Cainozoic. / Three simple 1D models were developed and applied to estimate how rapidly the overpressure dissipates. The results suggest that the present day overpressure would be almost dissipated after 2 million years with a pressure seal with an average permeability of 10-22 M2 (10-7 md). On the basis of numerous accumulations of oil and gas to be expelled from the overpressured Jurassic source rocks in the basin and the pressure seal modelling, it seems that the top pressure seal with permeabilities of 10-19 to 10-22 M2 (10-4 to 10-7 md) is not enough to retain the deep overpressure for tens of millions of years without pressure recharging. Only if the permeabilities were 10-23 m2 (10-8 md) or less, would a long-lived overpressured system be preserved. This study suggests that hydrocarbon generation, especially gas generation and thermal expansion, within sealed conditions of low-permeability is a likely major cause for maintaining the deep overpressure over the past tens of millions of years. Keywords: Thermal history; Deep overpressure; Type III kerogen; Rock-Eval Tmax; Thermal maturity; Palaeoheatflow modelling; Pressure seal; 2D deep overpressure modelling; Pressure behaviour modelling; Overpressure generation; Northern Carnarvon Basin.

L'objectif général de cette thèse de doctorat est de caractériser les propriétés de membranes PFSA de type Nafion N115 et Nafion NRE212 en termes de sorption d'eau, de propriétés de transport et de propriétés mécaniques, sur une large gamme de conditions expérimentales. Nous avons réalisé de très nombreuses mesures afin de comparer les résultats avec les données de la littérature, souvent dispersées. Des protocoles simples et reproductibles nous ont permis de mesurer les propriétés des membranes et d'étudier l'influence de certains paramètres sur leur variation. Les échantillons ont par exemple été séchés à différentes températures et nous avons étudié l'effet de ce prétraitement thermique sur la capacité de sorption, les propriétés de transport et les propriétés mécaniques. Les membranes Nafion ont également été exposées à une température modérée (60°C - 80°C) et à une humidité relative constante (RH = 0.3 à 0.95) pendant plusieurs semaines, conditions à l'origine d'un phénomène dit de "vieillissement hygrothermique" qui affecte leur capacité de sorption et leur conductivité protonique. De tels effets ont été observés mais ils se sont révélés réversibles et sans conséquences notables en terme de performances une fois les membranes utilisées en pile à combustible. Nos résultats peuvent être utilisés dans des études impliquant le transport et la gestion de l'eau dans les piles à combustible ainsi que leur durabilité, en particulier pour de la simulation numérique ou de la modélisation. Plus fondamentalement, ils peuvent aider à comprendre la thermodynamique de sorption et les phénomènes de transport dans les membranes PFSA / The overall aim of this PhD thesis was to characterize the properties of commercial Nafion N115 and Nafion NRE212 membranes in term of water sorption, transport, and mechanical properties over a wide range of experimental conditions. Because of the high dispersion of the data in the literature, our primary objective was to gather a comprehensive set of experimental measurements and to compare them with published results. Simple and reproducible protocols allowed us to measure the membrane properties over a wide range of experimental conditions and to study the influence of certain parameters on their evolution. For example, the samples were heat-treated at different temperatures and the effect of thermal history on water sorption, transport and mechanical properties was investigated. Nafion membranes were also exposed to moderate temperature (60°C - 80°C) and constant relative humidity (RH = 0.3 to 0.95) for long periods of time, which is known to cause a so-called ?hygrothermal aging? resulting in a decrease in their sorption capacity and proton conductivity. Such effects were observed but they appeared to be reversible and without noticeable consequences in term of fuel cell performance. Our experimental results can be used in studies involving water transport, water management and durability of fuel cells, especially for numerical simulation or modelling. More fundamentally, they can help understanding the thermodynamics of sorption and transport phenomena in PFSA membranes

Dans l’étude de la diagenèse des formations silico-clastiques ou carbonatées, il est souvent difficile de contraindre la température et l’âge des différents épisodes de cimentation ou de recristallisation. Le premier objectif de ce travail de thèse était de tester le potentiel de deux outils isotopiques récents (le géothermomètre des « clumpedisotopes » Δ47 et le géochronomètre U-Pb par analyse ponctuelle sur lame mince) dans le cadre de l’étude de la diagenèse des carbonates. Le deuxième objectif était de préciser l’histoire diagénétique, thermique, ethydrogéologique des réservoirs carbonatés du bassin de Paris. Pour atteindre ces deux objectifs, nous avons étudié des ciments de calcite et dolomite collectés dans les calcaires du Jurassique Moyen du dépocentre du bassin de Paris. La bonne caractérisation pétrographique et sédimentologique de ces échantillons, et le couplage entre les géothermomètres Δ47 et inclusions fluides, nous ont permis d’accéder à plusieurs informations de premier ordre. Premièrement, nous montrons que le Δ47 permet de reconstruire simultanément et précisément la température de formation des ciments diagénétiques dans la gamme 60-100°C (avec une précision de ~3-5°C) et la composition isotopique en oxygène des fluides (δ18Owater) à partir desquels ces ciments ont précipités (avec une précision de ~ 1‰). Deuxièmement, nous présentons une amélioration des connaissances de l’histoire thermique et des périodes de paléo-circulation des fluides à l’échelle régionale dans le bassin de Paris. Notamment, le croisement du géothermomètre Δ47 avec la méthode de datation U-Pb nous a permis pour la première fois de poser des contraintes thermo-chronologiques absolues sur l’ensemble des phases de circulations de fluides étudiées. Plus largement, ce couplage Δ47 /(U-Pb) inédit dévoile un champ d’application nouveau en thermo-chronologie de basse température (10-100°C). Nous anticipons que ce travail initie de nombreuses applications pour l’étude des histoires thermiques des bassins sédimentaires, via l’analyse de la diagenèse des carbonates / Diagenesis studies of both siliciclastic and carbonate rock units face the difficulty of constraining the temperature and age of the successive episodes of mineral crystallization. The first objective of this PhD work was to test the potential of two recent isotopic tools (the "clumped isotopes" Æ47 geothermometer and the laser ablation U-Pb geochronometer ) to integrate conventional carbonate diagenesis studies. The second objective was to reconstruct the diagenetic, thermal, and hydrogeological histories of the Middle Jurassic carbonate reservoirs of the Paris Basin. To achieve these goals, we studied calcite and dolomite cements mostly collected in the basin subsurface (exploration cores). The good petrographical and sedimentological characterization of the studied samples, together with the analysis of fluid inclusions and ?47 thermometry for determining the temperature and the chemical and isotopic compositions of the mineralizing fluids, allowed us to reach several first-order information. First, we show that Æ47 allows to simultaneously and precisely reconstruct the formation temperature of diagenetic cements in the range 60-100 ¡C (with an accuracy of ~ 3-5 ¡C) and the oxygen isotopic composition of the parent fluids (d18Owater) with a precision of ~ 1 ä. Secondly, this work improves our knowledge on the thermal history and past fluid-flows occurring at the basin scale. In particular, the coupling of the Æ47 thermometer with the U-Pb chronometer permitted for the first time to set absolute thermo-chronological constraints on every fluid-flow episodes investigated. More broadly, this unprecedented Æ47/(U-Pb) coupling reveals a new field of application in the low-temperature thermo-chronology field (10-100 ¡C). We anticipate that this pioneer thermo-chronological approach will induce many future applications in the study of sedimentary basins via carbonate diagenesis studies

En général, le métabolisme des poissons est estimé à des valeurs de température constantes, mais les effets de fluctuations journalières de température similaires à celles retrouvées en milieu naturel semblent peu connus. Les objectifs du présent mémoire sont de quantifier les effets de la température moyenne d’acclimatation et d’évaluer les effets de l’historique thermique des individus, sur les réponses métaboliques de tacons de saumon Atlantique (Salmo salar) aux fluctuations journalières de la température. Des tacons provenant de deux rivières, une fraîche et une chaude, ont été acclimatés à un maximum de quatre régimes thermiques (constant 15 °C ou 20 °C, fluctuant 15 °C ± 2.5 °C ou 20 °C ± 2.5 °C) et leur taux métabolique standard estimés par respirométrie par débit-intermittent. Les fluctuations journalières de température (15 °C ± 2.5 °C) près de l’optimum thermique pour cette espèce (16 °C) n’affectent pas le taux métabolique standard. À l’opposé, les fluctuations journalières de température plus chaudes (20 °C ± 2.5 °C) augmentent de 35.4% le taux métabolique standard des tacons de la rivière plus chaude, mais pas ceux des poissons de la rivière fraîche. Ainsi, la température moyenne à laquelle sont acclimatés les poissons peut affecter leur réponse métabolique aux fluctuations journalières de température, mais cette réponse peut varier entre populations provenant de rivières présentant des régimes thermiques différents. Enfin, grâce aux données de métabolisme précédemment estimées, un modèle de métabolisme standard a été développé pour des tacons de saumon Atlantique soumis à des fluctuations journalières de température. / Usually, fish metabolism is evaluated under constant values of temperature, but the effects of daily temperature fluctuations similar to those found in natural environment on metabolism seems to be much less understood. The goals of this study are to quantify the effects of the mean acclimation temperature and to assess the effects of the thermal history on the metabolic response of Atlantic salmon (Salmo salar) parr to daily fluctuations of water temperature. Atlantic salmon parr originating from two rivers, one cool and one relatively warm, were acclimated to up to four thermal regimes (constant 15 °C or 20 °C, daily fluctuating 15 °C ± 2.5 °C or 20 °C ± 2.5 °C) and their standard metabolic rate was estimated using intermittent-flow respirometry. Daily temperature fluctuations (15 °C ± 2.5 °C) near this species’ thermal optimum (16 °C) do not influence standard metabolic rate. In contrast, daily fluctuations of higher temperature (20 °C ± 2.5 °C) do increase standard metabolic rate by 35.4% for fish from the warmer river, but not for fish from the cooler river. Therefore, the mean temperature to which fish are acclimated may affect their responses to daily fluctuations of water temperature, but this response may vary between populations originating from rivers having different thermal regimes. Using standard metabolic rates previously estimated, a standard metabolic rate model was developed for Atlantic salmon parr exposed to daily fluctuations of temperature.