Changes In Fluid Properties Research Articles

Sedimentary processes and patterns in deposits corresponding to freshwater lake-facies of hyperpycnal flow – An experimental study based on flume depositional simulations

Abstract The article establishes a depositional model for lacustrine hyperpycnal flow by examining dynamics, transport factors, and laminae formation. The results show that several typical experimental phenomena such as fluid front mixing, double flow division, underwater leap, water skiing, and “new head” can be observed in the flume experiment. Based on the experimental observation of the flow process, three modes of transport of hyperpycnal flow in freshwater lake basins are summarized: bottom-bed loading, suspended loading, and uplift loading. Further, the change of fluid properties in hyperpycnal flow is summarized in three stages: a high-concentration stage, a low-concentration stage, and an uplifting stage. There are two main factors affecting the long-range transport of hyperpycnal flow: (1) the concentration difference between the head deposits and the ambient water body and (2) shear force of turbulence in the upper part of hyperpycnal flow. The simulation experiments of hyperpycnites laminae show that the laminae change from continuous to intermittent with the increase of the transportation distance. It is clear that the mode of transport of the hyperpycnal flow has a controlling effect on the degree of development of the laminae. Eventually, a depositional model of lake-facies hyperpycnal flow under experimental conditions was constructed.

Modifying the Effects around the Well can have an Impact on the Drilling Process

Environmental changes around a well can significantly affect the drilling process. This paper examines the effects of flow rate, bottomhole pressure, sheet permeability, viscosity, pressure gradient and well radius on the drilling process. It is shown that the energy-dynamic instability of the sheet’s near-shiva space, a highly active region in the formation, leads to changes in reservoir rock and fluid properties during the drilling process. These changes include physicochemical transformations such as deposition of asphaltenes, paraffins, and resins, as well as swelling of clay particles, which can disrupt reservoir physical properties and affect hydrocarbon flow. In addition, completion and production techniques and the chemistry of drilling and pressure fluids are particularly critical for low-permeability reservoirs. In this paper, the concept of skin effect is also introduced to assess the impact of process fluids on the bottomhole region, and a new assessment model is proposed. The results of the study are important for improving drilling technology and optimising reservoir development.

Multi-scale nonlinear reservoir flow simulation based on digital core reconstruction

During the exploitation of oil and gas reservoirs, changes in reservoir physical or fluid properties will lead to alterations in formation seepage capacity, subsequently impacting the productivity of oil and gas wells. Therefore, it is crucial to evaluate the variations in reservoir physical and fluid properties as well as their influence on oil and gas well productivity during reservoir exploitation.It employs a descriptive approach to investigate cross-scale (i.e., micro-scale → small-scale → large-scale) fluid seepage phenomena in water flooding. By leveraging digital core reconstruction technology and focusing on micro-pore network simulation, it establishes an analytical framework for studying cross-scale seepage fields, facilitating the exploration of the micro-seepage mechanism that governs non-homogeneous water flooding's impact on liquid production capacity within a reservoir. Integrating constraints from micro-pore network simulation and small-scale core displacement test data, while considering macro-heterogeneity near wellbore areas as flow unit divisions and superposition bases within large-scale reservoirs, it reveals the nonlinear flow characteristics of changes in liquid production capacity in water-flooding oil reservoirs based on microscopic digital core analysis. This approach aligns with findings from small-scale core testing and sweep coefficient correction while also addressing the non-uniform distribution characteristics of physical parameters within large-scale reservoirs.By integrating permeability field characteristics at three levels, this approach optimizes its technical advantages in describing dynamic permeability fields at each level, thereby facilitating precise prediction of water drive oil development effects.

Thermo-Hydro-mechanical coupling analysis of geothermal reservoirs: optimizing extraction capacities by revealing influential factors

Abstract Extraction of high-temperature geothermal resources from reservoirs is a challenge due to the complex interactions between temperature, permeability, and stress fields. Variations in physical fields are critical to thermal reservoir engineering. In this study, the coupling mechanism between temperature, permeability, and stress fields is systematically explored using theoretical analyses and numerical simulations, by utilizing the three-field coupling model. This study models the changes in porosity and permeability evolution during geothermal extraction, emphasizing the importance of the coupling term. The effects of pressure differences between injection and production wells, reservoir temperature variations, and fluid property changes on the temperature distribution and output thermal power within the geothermal reservoir were modeled and analyzed. The results reveal the significant effect of pressure differences between wells, and show that the geothermal extraction capacity of supercritical carbon dioxide (SC-CO2) is 1.83 times higher than that of water. Based on the statistical characteristics of the distribution pattern of natural fractures within the geothermal reservoir, the study simulated the distribution of natural fractures and developed a coupled THM model containing natural fractures. The results show that increasing the porosity of hydraulic and natural fractures can effectively increase the geothermal production capacity, especially the increase in the porosity of natural fractures is significant. These findings provide a key theoretical basis for understanding the THM coupling mechanism during geothermal extraction, and provide substantial support for optimizing the development and utilization of geothermal resources.

Impact of wall slip and jump in the heat transmission enhancement of copper-alumina/water hybrid nanofluid due to a stretched cylinder

The early jump in wall temperature and partial slip all along transfer on thermal energy in hybrid nanofluid was studied simultaneously. In addition, the flow characteristics and heat transfer performances on alumina–copper/water ( A l 2 O 3 − Cu / H 2 O ) hybrid nanofluid through the stretching cylinder were examined below the effect on thermal radiation and Lorentz magnetic forces. This Roseland’s flux model was working on the effect on thermal radiations. Denoting fundamental equations was traced over constructing numerical model results about temperature and velocity distributions although considering variable internal energy and fluid property change. The numerical algorithm bvp4c technique was utilised to obtain convergent solutions. The effect on impending parameters of temperature and velocity distributions was investigated over a graphical illustration. It was noticedthat wall momentum diffused with nanofluid quickly to its dispersion on hybrid nanofluid by the existence of the partial slip. The thermal behaviour of the hybrid mono-nanofluid was higher than that of the nanofluid. Moreover, hybrid particles advance the thermal behaviour of the employing fluid.

Grasping the behavior of magnetorheological fluids in gradient pinch mode via microscopic imaging

Magnetorheological (MR) fluids are suspensions of micrometer-sized ferromagnetic particles in a carrier fluid, which react to magnetic fields. The fluids can be operated in several fundamental modes. Contrary to the other modes, the rheology and microstructure formation of the MR fluid in the gradient pinch mode have been studied to a far lesser extent. The magnetic field distribution in the flow channel is intentionally made non-uniform. It is hypothesized that the Venturi-like contraction is achieved via fluid property changes, leading to a unique behavior and the presence of a pseudo-orifice. The main goal is to investigate the presence of the Venturi-like contraction effect in the fluid by means of optical imaging and hydraulic measurements. To accomplish the goal, a unique test rig has been developed including a fluorescence microscope and MR valve prototype. The Venturi-like contraction hypothesis was confirmed. The results indicate that the effective flow channel size decreases by 92% at the maximum magnetic flux applied. This has a direct impact on the flow characteristics of the MR valve. The variation of the pressure–flow rate curve slope with magnetic field was demonstrated. The results provide valuable information for understanding the rheology and microstructure formation mechanism in MR fluids in the pinch mode.

Operando Identification of Temperature-Dependent Pore-Scale Gas Saturations in PEM Water Electrolyzers

Polymer electrolyte membrane (PEM) water electrolysis is a promising solution for the chemical storage of intermittent renewable energy in the form of clean hydrogen (1). For the widespread adoption of this technology, the efficiency of PEM electrolyzers must be improved through informed material design and tailored operating conditions to compete with incumbent carbon-emitting technologies (2). A main source of inefficiency is related to mass transport losses, where oxygen gas, a by-product of the anode reaction, accumulates in the anode porous transport layer (PTL) and hinders reactant liquid water delivery to reaction sites (3). Although extensive studies have explored this two-phase flow phenomenon, the consideration of operating temperature on gas accumulation in the PTL adds further complexity. A duality in temperature effects has been reported in the literature where increasing the operating temperature may encourage gas coverage which obstructs liquid water transport, but it may also enhance liquid water delivery due to favorable fluid property changes in viscosity and surface tension (4). Efforts have been made previously to reconcile these competing observations using 2D visualization methods (5), however a closer investigation using 3D visualization techniques will provide valuable pore-scale insights in the comprehensive understanding of the impact of operating temperature on gas transport in the PTL, and subsequently mass transport losses in the PEM electrolyzer.In this work, we employed operando X-ray computed tomography (CT) to visualize three-dimensional (3D) pore-scale gas saturations in the PTL at various industrially relevant operating conditions. Specifically, a custom in-house electrolyzer was imaged with synchrotron CT at five different temperatures (40°C, 50°C, 60°C, 70°C, 80°C) and current densities ranging from 0.5 A/cm² to 4.0 A/cm² with 0.5 A/cm² incremental steps. Electrochemical impedance spectroscopy and Tafel measurements were also acquired to characterize the relationship between gas distributions and corresponding mass transport overpotentials. Considering X-ray transparency, a model PTL made of carbon fibers was used to achieve sufficient contrast to quantify water and gas in the obtained images. Using precise volume registration and subtraction methods, pore-scale gas distributions in the PTL were quantified to reveal changes in bubble accumulation and coverage area at different operating temperatures and over operation time. The novel insights from this work will aid in our understanding of the complex relationship between operating temperature and multiphase flow phenomena in the PTL, which is vital for tailoring operating conditions of PEM electrolyzers to curtail the costs of green hydrogen production.

Numerical simulation study of enhanced geothermal system modification and heat mining performance under cyclic injection

Enhanced geothermal systems (EGS) involve complex thermal–hydraulic-mechanical (THM) coupling. The reservoir's permeability evolution and heat extraction characteristics under cyclic variable pressure injection conditions are unknown. In this paper, a THM model that considered the dynamic changes of rock matrix and fluid properties was developed based on the theory of local heat balance. The THM coupling model investigated the effects of the number of fractures, initial permeability of fractures (kf), maximum injection pressure (P), frequency (td), and working fluid on the heat recovery performance of the EGS under cyclic injection for 20 years. Finally, the sensitivity of each parameter was discussed. When the number of fractures increased from 100 to 200, the temperature of the reservoir decreased by 68.5 K, and the cumulative heat energy extracted increased by 6.6 × 1014 J. With the increase of the initial permeability of the fractures, the irregularities in the temperature and permeability fields of the reservoir were significantly enhanced. When the maximum injection pressure increased from 34 MPa to 40 MPa, the permeability ratio of the reservoir increased by about 13.45 %, and the cumulative extracted thermal energy increased by 3.5 × 1014 J. The frequency of cyclic injection increased from 5 d to 45 d, the production temperature decreased by 26.78 K, and the permeability ratio of the reservoir and the cumulative extracted thermal energy increased. The low-temperature range of CO2-EGS is significantly larger than that of H2O-EGS, and the reservoir temperature decreases faster. The permeability of CO2-EGS increases by 29.32 %, and the cumulative thermal energy extraction increases by 17.5 × 1014 J compared with H2O-EGS. Parameter sensitivities were found for cyclic injection. Factors affecting production temperature and reservoir permeability in that order: P > td > kf. Injection frequency had a slightly greater impression on cumulative extracted thermal energy than injection pressure.

Fluid phase behavior in multi-scale shale reservoirs with nano-confinement effect

Shale reservoirs are featured by widely distributed micro-scale fractures and nano-scale pores. The phase behavior of reservoir fluids in these complex environments remains uncertain. Hence, an efficient model is developed to investigate the fluid phase behavior in multi-scale shale reservoirs based on a pore-size-dependent equation of state. The porous space is discretized into specific sizes of nanopores and fractures regions. Phase equilibrium calculations for pure components, binary mixtures and multi-component shale oils show that adsorption and critical properties shifts display opposite effects on a fluid distribution, and the shifts in the critical properties are the main reason for more lighter components present in nanopores. The nano-confinement effect enhances the ability of CO2 to enter nanopores. An innovative multi-scale model of partial equilibrium is developed to explore changes in fluid properties during pressure depletion. The results reveal that gas appears in the fracture region, while the confined fluids within nanopores are always kept in the oil phase. Lighter components within nanopores are rapidly released as pressure drops. However, the content of heavier components within nanopores gradually decreases if the pressure stabilizes for a while, meaning that a slow pressure drop is more conducive to the recovery of shale oil from nanopores.

Numerical simulation on JAG-type corrugated plate flow heat transfer characteristics considering physical property changes and shell heat transfer

This research considers the combined effects of changes in fluid properties and shell heat transfer. The realizable k-epsilon turbulence model combined with the enhanced wall function is used to numerically simulate the flow and heat transfer characteristics of a new plate-shell heat exchanger plate side, which was verified to be accurate in combination with previous research results. Focus was placed on the analysis concerning the flow heat transfer characteristics for different corrugation depths at different inlet velocities. It was found that increasing the corrugation depth can make the fluid distribution tends to be uniform heat transfer performance increases, but the increase in velocity will have the opposite effect on the heat transfer performance. Furthermore, field synergy theory reveals the synergistic distribution regularities of the velocity field with the temperature field and pressure field. Consecutive vortex structures are formed along the grooves, and the flow in the core region of the corrugated channels is similar to the heat flow, reducing the synergistic ability among the three fields makes the heat transfer less effective. These findings contribute to understanding heat transfer in similar scenarios, especially in energy engineering and thermal management.

Investigation on mixed thermalelstohydrodynamic lubrication behavior of slipper/swash plate interface in water hydraulic axial piston pump

To reveal the thermal-fluid-structure interaction characteristics of water-lubricated slipper/swash plate interface, a transient mixed thermoelstohydrodynamic (MTEHD) lubrication model incorporating asperity contact, elastic deformation, heat transfer and viscosity temperature effect is originally presented. The change in fluid properties caused by cavitation is considered for solution the piston chamber pressure. Distributions of pressure, temperature, deformation and tilting state of slipper simulated by MTEHD show strong reasonableness. Effect of operating and structural parameters on energy consumption characteristics calculated by MTEHD and hydrodynamic lubrication is contrastively analyzed. The results show that energy consumption is different in delivery and suction stroke due to different degrees of MTEHD effects and transient contact. Besides, the optimal dimension for the width of studied sealing surface is determined.

Dynamics of Drop Formation in the Presence of Interfacial Mass Transfer.

The dynamics of drop formation have been investigated in the presence of interfacial mass transfer through controlled flow visualization experiments. The mixtures of n-hexane (solvent) and acetone (solute) were used as a dispersed phase, having different initial compositions varying over a broad range. Drops were formed at the submerged position in the continuous phase (water) at the same operating flow conditions. The unsteady force balance model is developed to analyze the implications of the simultaneously occurring interfacial transfer of the solute on the formation dynamics in real time, and predictions are validated with experimental results. Based on initial compositions, the analysis of the transient drop shape shows a sharp transition in the drop formation regime. At lower initial solute concentrations, i.e., ϕ0 < 0.2, axisymmetric drop formation occurs and the interfacial solute transfer has negligible effects on the formation dynamics. Over an intermediate range of solute concentrations, i.e., 0.2 < ϕ0 < 0.5, Marangoni instability is triggered along the evolving interface, and therefore, the interface deformations and contractions occur during the drop formation. At ϕ0 = 0.5, the drop takes highly nonaxisymmetric shapes and remains away from equilibrium until its detachment from an orifice. For ϕ0 > 0.5, the spontaneous ejection of plumes of the solute results in the rapid generation of multiple droplets of smaller size. This work shows that higher solute concentration gradients not only lead to faster solute transport but also induce strong interfacial instability simultaneously. Thus, the coupled effects of transient change in composition and fluid properties govern the drop size and its formation time in such systems under non-equilibrium.

The Mineral Chemistry of Magnetite and Its Constraints on Ore-Forming Mechanism in the Sandaozhuang Skarn-Type W-Mo Deposit in East Qinling, China

The Sandaozhuang super-large W-Mo deposit is located in the southern margin of the North China Craton, within the well-known East Qinling Mo mineralization belt, and is one of the typical skarn-type W-Mo deposits in China. Based on EMPA and LA-ICP-MS analyses, major and trace elements were presented, and the mineral chemistry of magnetite at various mineralization stages was discussed. Combining field observations, petrography, and geochemical characteristics, the magnetite at the Sandaozhuang deposit can be classified into three types, namely early-magmatic-stage high-temperature magnetite (Mag1), potassic-alteration-stage magnetite (Mag2), and retrograde-alteration-stage magnetite (Mag3). The Mag1 and Mag2 magnetites primarily occurred in granites in association with potassium (K) feldspar and biotite, whereas Mag3 is associated with metallic sulfide minerals that occurred mainly in vein-like structures in skarn. The three magnetites Mag1, Mag2, and Mag3 can be distinguished as having magmatic, magmatic–hydrothermal transition, and hydrothermal origins, respectively. All three types of magnetite exhibit a depletion of high-field-strength elements (HFSEs) such as Zr, Hf, Nb, Ta, and Ti, and large-ion lithophile elements (LILEs) including Rb, K, Ba, and Sr, compared to the mean continental crust composition. Conversely, they are enriched in elements such as Sn, Mo, V, Cr, Zn, and Ga. Mag3 showed no significant depletion of Co, Ni, Cu, and Bi, indicating that the influence of coexisting sulfides on the composition of magnetite at the Sandaozhuang deposit is limited. There are systematic variations in major and trace elements from Mag1 to Mag3, which exhibited similar patterns in trace element spider and rare earth element diagrams, and Y/Ho ratio, indicating a consistent source for the three types of magnetite. The changes in V and Cr contents and (Ti + V) vs. (Al + Mn) diagram of magnetite at the Sandaozhuang deposit reflected the evolution of ore-forming fluids with an initial increase in oxygen fugacity and a subsequent decrease, as well as a gradual decrease in temperature during skarn mineralization. The early high-temperature and high-oxygen-fugacity magmatic fluids became W and Mo enriched by hydrothermal fluid interaction. The rapid change in fluid properties during the retrograde alteration stage led to the precipitation of scheelite and molybdenite.

Non-Galilean Taylor–Culick law governs sheet dynamics in unsteady fragmentation

We present the results of a combined experimental and theoretical investigation of sheet evolution, expansion and retraction, under unsteady fragmentation upon drop impact on a surface of comparable size to that of the drop. We quantify and model the effect of the continuous time-varying – unsteady – shedding of droplets from the sheet via its bounding rim. We present and validate especially developed advanced image processing algorithms that quantify, with high accuracy, the key quantities involved in such unsteady fragmentation, from sheet, to rim, to ligaments, to droplet properties. With these high precision measurements, we show the important effect of continuous unsteady droplet shedding on the sheet dynamics. We combine experiments and theory to derive and validate governing equations of the sheet that incorporate such continuous shedding – associated with continuous loss of momentum and mass – from unsteady fragmentation. Combining this theory with the universal unsteady rim dynamics discovered in Wang et al. (Phys. Rev. Lett., vol. 120, 2018, 204503), we show that the governing equation of the sheet can be reduced to a continuous-shedding, non-Galilean Taylor–Culick law, from which we deduce new analytical expressions for the time evolution of the sheet radius. We show the robustness of the predictions to changes of fluid properties, including surface tension and moderate fluid viscosity and elasticity, including use of physiological mucosalivary fluid. We also reconcile prior literature's inconsistent experimental results on the sheet dynamics upon drop impact.

A fluid identification method for caved-fracture reservoirs based on the stacking model

It is difficult to identify the fluid properties with one single logging curve in a caved-fracture reservoir due to multi-stage tectonism, diagenetic evolution, rapid lithology change, developed fractures, and significant heterogeneity. Therefore, a stack generalization-based method is proposed for improving fluid identification accuracy. First, a traditional method with cross-plots is adopted by coring and logging data, but it is found that the identification effect of the caved-fracture reservoir fluid is poor. Second, based on the cross-plot, a correlation analysis is conducted to select sensitive logging parameters such as resistivity, compensated neutron, density, acoustic, and total hydrocarbon, which reflect changes in fluid properties, as feature vectors for the identification of fluid types in caved-fracture reservoirs. Third, support vector machine, k-nearest neighbor algorithm, decision tree, and stochastic gradient descent classification are selected as the base learners. 80% of the data sample points and the remaining 20% are selected as training and test samples for building the stacking models to verify the prediction accuracy of the model. Finally, a fully connected neural network is used as a meta-learner to control the final output. The experimental results show that the prediction accuracy of the stack generalization method can reach 88%. Compared with the cross-plot and single machine learning discriminant model, the fluid identification method based on the stack generalization model has a better effect and can improve the fluid identification effect of caved-fracture reservoirs in the study area.

A Review of the Complex Flow and Heat Transfer Characteristics in Microchannels.

Continuously improving heat transfer efficiency is one of the important goals in the field of energy. Compact heat exchangers characterized by microscale flow and heat transfer have successfully provided solutions for this purpose. However, as the characteristic scale of the channels decreases, the flow and heat transfer characteristics may differ from those at the conventional scale. When considering the influence of scale effects and changes in special fluid properties, the flow and heat transfer process becomes more complex. The conclusions of the relevant studies have not been unified, and there are even disagreements on some aspects. Therefore, further research is needed to obtain a sufficient understanding of flow structure and heat transfer mechanisms in microchannels. This article systematically reviews the research about microscale flow and heat transfer, focusing on the flow and heat transfer mechanisms in microchannels, which is elaborated in the following two perspectives: one is the microscale single-phase flow and heat transfer that only considers the influence of scale effects, the other is the special heat transfer phenomena brought about by the coupling of microscale flow with special fluids (fluid with phase change (pseudophase change)). The microscale flow and heat transfer mechanisms under the influence of multiple factors, including scale effects (such as rarefaction, surface roughness, axial heat conduction, and compressibility) and special fluids, are investigated, which can meet the specific needs for the design of various microscale heat exchangers.

Opportunities and challenges of nanotechnology in enhanced oil recovery: An overview

Primary objective of this review includes advantages and challenges associated with implementation of nanotechnology in EOR (enhanced oil recovery). Nanotechnology refers to science which deals in dimensions of nanoscale (1–100 nm). Nanotechnology is an important technique due to their small size. Small size of particles offers high surface area which makes nanotechnology as one of the candidates for EOR technique. Also, nanoparticles result in change in fluid and formation properties which ultimately leads to increased production. Wettability alteration, increase in structural disjoint pressure and reduction in interfacial tension are some of the factors that are being contributed by Nanoparticles for enhanced oil recovery. Apart from these advantages there are some drawbacks associated with the techniques. Mass scale production of Nanoparticles, stability of Nanoparticles is some of the tedious and unresolved task that require immediate attention. Thus, the review focusses on advantages and challenges discussed in brief occurring in implementation of nanotechnology in EOR.

Cooling-induced permeability enhancement for networks of microfractures in superhot geothermal environments

Recent researches have proposed the use of enhanced geothermal system reservoirs consisting of dense networks of microfractures, created by hydraulic and/or thermal fracturing in superhot/supercritical geothermal environments, because of their suitability for thermal energy harvesting. During fracturing and energy extraction, the fracture networks are exposed to cooling due to the injection of cold fluid into the reservoirs. Previous studies showed such cooling enhanced reservoir permeability in conventional geothermal environments. However, the cooling may result in a higher risk of seismicity, owing to decreased normal stress on the fractures. Nevertheless, it is unclear whether cooling-induced permeability enhancement and a higher risk of seismicity occurs within networks of microfractures which consist of numerous interconnected microfractures at various orientations to the in situ triaxial stress. Thus, no dominant fractures have the possibility to cause permeability enhancement/induced seismicity. In this study, results are presented for borehole cooling experiments on a dense network of microfractures in granite, at 400 °C, under true triaxial stress. Permeability and acoustic emissions were measured with decreases in borehole temperature (up to ~ 90 °C). Results showed that permeability increased with increasing temperature drop at relatively low stress levels (15 and 20 MPa). The permeability enhancement occurred without intensive failure, and was reversible. However, permeability was almost constant at a higher stress level (65 MPa). Results showed that permeability enhancement required a thermal stress equivalent to the mean stress, so that the normal stress was reduced to near-zero, for a considerable amount of the microfractures. Additionally, the permeability of dense microfracture networks can be increased by cooling primarily through thermo-elastic deformation (without intensive failure), which may be useful to compensate for the reduction in injectivity due to cooling-induced fluid property changes.

Enrichment mechanism of REE in rhyolite and its relationship with uranium mineralization in the Dazhou uranium ore-field, Southeast China

The Dazhou rhyolites in the Gan-Hang Belt host uranium deposits and show high rare earth element (REE) concentrations. However, the occurrence, source, and enrichment process of REE and its association with uranium mineralization in rhyolite remain unclear. In this study, fresh and altered rhyolites were selected, and the petrography, elemental and isotope geochemistry were investigated to explore the genetic mechanism of REE-rich rhyolites and its relationship with uranium mineralization. Based on the alteration and mineral paragenesis, the Dazhou rhyolites can be classified into four types: fresh rhyolite (Fr-rhyolite), hematitic rhyolite (Hem-rhyolite), clayified rhyolite (Cla-rhyolite), and hydromica rhyolite (Hyd-rhyolite). The altered rhyolites share similar average εNd(t) values with the fresh rhyolites (Fr-rhyolites = −5.8, Hem-rhyolites = −6.1, Hyd-rhyolites = −6.2), indicating their same REE sources, that means there are no external REE input for the REE-enriched altered rhyolites. In the Fr-rhyolites, the REE contents (average 341 ppm) and high field strength element (HFSE) contents increase with a decrease in the Al2O3/TiO2 ratio, indicating that magmatic crystallization differentiation leads to the initial enrichment of both REE and HFSE. In the altered rhyolites, the REE concentrations (average 655 ppm, 1045 ppm, 999 ppm for Hem-rhyolites, Cla-rhyolites, Hyd-rhyolites, respectively) are elevated compared to those in the Fr-rhyolites, indicating a significant hydrothermal enrichment for the REE. Mineralogical and petrographic studies have shown that REE are mainly hosted in parisite and monazite; therefore, the ore-forming fluid should be enriched in CO32– and F−. During the hydrothermal alteration, hematitization occurred early, followed by clayization and hydromicazation in the late stage, recording a fluid property change from an early higher-temperature, oxidizing fluid to a late lower-temperature, more reducing and acidic fluid. The early-stage fluid was responsible for the REE migration, while the decrease of temperature led to a decrease in the stability of the REE-complex that promote the precipitation of REE minerals. Combined with previous studies, REE mineralization has similar mineralization age and alteration characteristics to uranium mineralization in the Dazhou uranium ore-field, indicating the two mineralization types have derived from the same source and activated, migrated, and precipitated under the same mineralization event. The factors that controlled the precipitation of REE and uranium ore minerals are different, with the former mainly controlled by temperature, whereas the latter controlled by redox conditions.

Towards an engineering tool for the prediction of running ductile fractures in CO2 pipelines

A prerequisite for the deployment of CO2 capture and storage (CCS) is to establish a large network of high-pressure transport pipelines. It is then vital to assess new and existing pipeline designs for running ductile fracture (RDF). RDF is a phenomenon in which a defect develops into a crack propagating along the pipeline, sustained by the pressure forces from the escaping fluid. The most common engineering method for RDF, the Battelle two-curve method (BTCM), was originally developed for natural gas (NG) and has proved non-conservative for CO2. In this work we examine the BTCM in the light of available RDF experiments with CO2-rich mixtures. We present an improved material curve, in which the change in fluid properties when replacing NG with CO2 results in a new effective toughness correlation. Furthermore, we present an improved method for calculating the crack-tip pressure. This delayed homogeneous equilibrium model (D-HEM) accounts for the non-equilibrium thermodynamics due to the rapid depressurization, resulting in boiling pressures below the saturation pressure. Together, the adaptation of the material and fluid treatment yields improved results, and is a step towards a viable engineering tool for the prediction of RDF in CO2 pipelines.