Search Results (153)

Residual oil saturation in reservoirs is primarily influenced by viscous and capillary forces, with interfacial tension (IFT) being a critical factor in fluid distribution due to capillary pressure. Adjusting IFT is essential for enhancing oil recovery, particularly in waterflooding, which is the most common secondary recovery technique after primary production. The salinity of injected water directly affects the IFT between crude oil and brine, making it a crucial factor in optimizing recovery. However, limited studies have examined IFT using live oil samples under actual reservoir conditions. In this study, a high-pressure, high-temperature (HPHT) drop shape analyzer was used to measure the IFT between live oil and brine under reservoir conditions. Five live oil samples and two sodium chloride (NaCl) brine concentrations (30,000 and 100,000 ppm) were tested at a reservoir temperature of 180 °F. Measurements were conducted above the bubble points of the oils, replicating undersaturated reservoir conditions. The results revealed that the impact of pressure on IFT was more complex than that of salinity. IFT generally decreased with increasing pressure but showed mixed behavior across different samples. Conversely, IFT consistently increased with higher salinity. These findings enhance the understanding of IFT behavior under reservoir conditions, supporting improved reservoir simulations and oil recovery strategies. Full article

This study investigates pegmatites with exceptionally rare mineralogical and chemical signatures, hosted by the 1.8 Ga peralkaline albite-enriched granite, which corresponds to the renowned Madeira Sn-Nb-Ta-F (REE, Th, U) deposit in Pitinga, Brazil. Four distinct pegmatite types are identified: border pegmatites, pegmatitic albite-enriched granite, miarolitic pegmatite, and pegmatite veins. The host rock itself has served as the source for the fluids that gave rise to all these pegmatites. Their mineral assemblages mirror the rare-metal-rich paragenesis of the host rock, including pyrochlore, cassiterite, riebeckite, polylithionite, zircon, thorite, xenotime, gagarinite-(Y), genthelvite, and cryolite. These pegmatites formed at the same crustal level as the host granite and record a progressive magmatic–hydrothermal evolution driven by various physicochemical processes, including tectonic decompressing, extreme fractionation, melt–melt immiscibility, and internal fluid exsolution. Border pegmatites crystallized early from a F-poor, K-Ca-Sr-Zr-Y-HREE-rich fluid exsolved during solidification of the pluton’s border and were emplaced in contraction fractures between the pluton and country rocks. Continued crystallization toward the pluton’s core produced a highly fractionated melt enriched in Sn, Nb, Ta, Rb, HREE, U, Th, and other HFSE, forming pegmatitic albite-enriched granite within centimetric fractures. A subsequent pressure quench—likely induced by reverse faulting—triggered the separation of a supercritical melt, further enriched in rare metals, which migrated into fractures and cavities to form amphibole-rich pegmatite veins and miarolitic pegmatites. A key process in this evolution was melt–melt immiscibility, which led to the partitioning of alkalis between two phases: a K-F-rich aluminosilicate melt (low in H₂O), enriched in Y, Li, Be, and Zn; and a Na-F-rich aqueous melt (low in SiO₂). These immiscible melts crystallized polylithionite-rich and cryolite-rich pegmatite veins, respectively. The magmatic–hydrothermal transition occurred independently in each pegmatite body upon H₂O saturation, with the hydrothermal fluid composition controlled by the local degree of melt fractionation. These highly F-rich exsolved fluids caused intense autometasomatic alteration and secondary mineralization. The exceptional F content (up to 35 wt.% F in pegmatite veins), played a central role in concentrating strategic and critical metals such as Nb, Ta, REEs (notably HREE), Li, and Be. These findings establish the Madeira system as a reference for rare-metal magmatic–hydrothermal evolution in peralkaline granites. Full article

The Cuyu gold deposit in central Jilin Province in Northeast China is located in the eastern segment of the northern margin of the North China Craton (NCC), as well as the eastern segment of the Xing’an–Mongolian Orogenic Belt (XMOB). Gold ore-bodies are controlled by NW-trending faults and mainly occur in late Hercynian granodiorite. The mineralization process in the Cuyu deposit can be divided into three stages: quartz + coarse grained arsenopyrite + pyrite (stage I), quartz + sericite + pyrite + arsenopyrite + electrum + chalcopyrite + sphalerite (stage II), and quartz + calcite ± pyrite (stage III). Stage II is the most important for gold mineralization. We conducted analyses including petrography, microthermometry, laser Raman spectroscopy of fluid inclusions, and H–O–S–Pb isotopic analysis to elucidate the mineralization processes in the Cuyu deposit. Five types of primary fluid inclusions (FIs) are present in the hydrothermal quartz and calcite grains of the ore: liquid-rich two-phase aqueous fluid inclusions (L-type), vapor-rich two-phase aqueous fluid inclusions (V-type), CO₂-bearing two- or three-phase inclusions (C1-type), CO₂-rich two- or three-phase inclusions (C2-type), and pure CO₂ mono-phase inclusions (C3-type). From stages I to III, the fluid inclusion assemblages changed from L-, C2-, and C3-types to L-, V-, C1-, C2-, and C3-types and, finally, to L-types only. The corresponding homogenization temperatures for stages I to III were 242–326 °C, 202–298 °C, and 106–188 °C, and the salinities were 4.69–9.73, 1.63–7.30, and 1.39–3.53 wt.% NaCl equiv., respectively. The ore-forming fluid system evolved from a NaCl-H₂O-CO₂ ± CH₄ ± H₂S fluid system in stage I and II with immiscible characteristics to a homogeneous NaC-H₂O fluid system in stage III. Microthermometric data for stages I to III show a decreasing trend in homogenization temperatures and salinities. The mineral assemblages, fluid inclusions, and H–O–S–Pb isotopes indicate that the initial ore-forming fluids of stage I were exsolved from diorite porphyrite and characterized by a high temperature and low salinity. The addition of meteoric water in large quantities led to decreases in temperature and pressure, resulting in a NaCl-H₂O-CO₂ ± CH₄ ± H₂S fluid system with significant immiscibility in stage II, facilitating the deposition of gold and associated polymetallic sulfides. The Cuyu gold deposit has a similar ore genesis to those of gold deposits in the Jiapigou–Haigou gold belt (JHGB) of southeastern Jilin Province indicating potential for gold prospecting in the northwest-trending seam of the JHGB. Full article

Miniaturization and reliable, real-time, non-invasive monitoring are essential for investigating microfluidic processes in Lab-on-a-Chip (LoC) systems. Progress in this field is driven by three complementary approaches: analytical modeling, computational fluid dynamics (CFD) simulations, and experimental validation techniques. In this study, we present an on-chip experimental method for estimating the slug-flow velocity in microchannels through in situ optical monitoring. Slug flow involving two immiscible fluids was investigated under both liquid–liquid and gas–liquid conditions via an extensive experimental campaign. The measured velocities were used to determine the slug length and key dimensionless parameters, including the Reynolds number and Capillary number. A comparison with analytical models and CFD simulations revealed significant discrepancies, particularly in gas–liquid flows. These differences are mainly attributed to factors such as gas compressibility, pressure fluctuations, the presence of a liquid film, and leakage flows, all of which substantially affect flow dynamics. Notably, the percentage error in liquid–liquid flows was lower than that in gas–liquid flows, largely due to the incompressibility assumption inherent in the model. The high-frequency monitoring capability of the proposed method enables in situ mapping of evolving multiphase structures, offering valuable insights into slug-flow dynamics and transient phenomena that are often difficult to capture using conventional measurement techniques. Full article

The lattice Boltzmann method (LBM) is widely applied to model the pore-scale two-phase flow of immiscible fluids through porous media, and one common variant of the LBM is the color gradient method (CGM). However, in the literature, many competing algorithms have been proposed for accomplishing different steps in the CGM. Therefore, this paper is the first in a series that aims to critically review and evaluate different algorithms and methodologies that have been proposed for use in the CGM. Specifically, in this paper, we (1) provide a brief introduction to the LBM and CGM that enables and facilitates consideration of more sophisticated topics subsequently; (2) compare three methods for modeling the behavior of fluids of moderately different viscosities; (3) compare two methods for calculating the color gradient; and (4) compare two methods for modeling external forces or accelerations acting upon the fluids of interest. These topics are selected for the first paper in the series because proper selection of these algorithms is necessary and sufficient to perform two common “benchmark” simulations, namely bubble tests and layered Poiseuille flow. Future papers in the series will build upon these topics, considering more challenging conditions or phenomena. By systematically reviewing key aspects, features, capabilities, and limitations of the CGM, this series of papers will extend our collective ability to apply the method to a variety of important fluid flow problems in geosciences and engineering. Full article

The evolution of droplets during the printing process is modeled using the volume of fluid (VOF) method, which involves solving the Navier–Stokes and continuity equations for incompressible flow with multiple immiscible phases on a finite volume grid. An indicator function tracks the interfaces and calculates surface tension forces. A grid independence study confirmed the convergence and efficacy of the solutions. The computational model agreed well with experimental data, accurately capturing the impact, spreading, and recoiling of droplets on a solid surface. Additionally, the model validated the interaction of droplets with hydrophilic and hydrophobic surfaces for both constant and dynamic contact angles. Key non-dimensional numbers (Re, We, Oh) were considered to study the interplay of forces during droplet impact on a solid surface. The final print quality is influenced by droplet dynamics, governed by body forces (surface tension, gravity), contact angle, dissipative forces due to motion, and material properties. Computational studies provide insights into the overall process performance and final print quality under various process conditions and material properties. Full article

The Hammam–Zriba F–Ba (Zn–Pb) stratabound deposit is located within the Zaghouan Fluorite Province (ZFP), which is the most important mineral sub-province in NE Tunisia, with several CaF₂ deposits occurring mainly along the Zaghouan Fault and corresponding to an F-rich MVT mineral system developed along the unconformity surface between the uppermost Jurassic limestones and the late Cretaceous layers. Petrographic analysis, microthermometry, and Raman spectroscopy applied to fluid inclusions in fluorite revealed various types of inclusions containing brines, oil, CO₂, and CH₄ along with solid phases such as evenkite, graphite, kerogen and bitumen. Microthermometric data indicate homogenization temperatures ranging from 85 °C to 145 ± 5 °C and salinities of 13–22 wt.% NaCl equivalent. This study supports a model of heterogeneous trapping, where saline basinal brines, oil, and gases were simultaneously trapped within fluorite, which indicates fluid immiscibility. The Raman analysis identified previously undetected organic compounds, including the first documented occurrence of evenkite, a mineral hydrocarbon, co-genetically trapped with graphite. The identification of evenkite and graphite in fluid inclusions offers new insights into the composition of hydrocarbon-bearing fluids within the MVT deposits in Tunisia, contributing to an understanding of the mineralogical characteristics of these deposits. The identified hydrocarbons correspond to three oil families. Family I (aliphatic compounds) is attributed to the lower-Eocene Bou-Dabbous Formation, family II (aromatic compounds) is attributed to the Albian Fahdene Formation and the Cenomanian–Turonian Bahloul Formation, and family III is considered as a mixture of aliphatic and aromatic compounds generated by the three sources. The presence of graphite in fluid inclusions could suggest the involvement of a thermal effect from deep-seated sources through the reservoir to the site of fluorite precipitation. These findings suggest that the fluorite mineral system might have been linked with the interaction of multi-reservoir fluids, potentially linked to the neighboring petroleum system in northeastern Tunisia during the Miocene. This study aims to investigate the composition of fluid inclusions in fluorite from the Hammam–Zriba F–Ba (Zn–Pb) deposit, with a particular focus on the plausible sources of hydrocarbons and their implications for the genetic relationship between the mineralizing system and petroleum reservoirs. Full article

Stabilizing micron-sized particles in low-viscosity polymer dispersions is challenging when density differences are present. This study demonstrates that graphite particles in aqueous polyurethane dispersions can be efficiently prevented from sedimentation using the capillary suspension concept. Capillary suspensions are solid/liquid/liquid systems and the capillary forces inferred from adding a second immiscible fluid can lead to drastic changes in texture and flow. Here, both spherical and flake-shaped graphite particles were used as fillers, with octanol as the secondary liquid. At low graphite concentrations, octanol increases the low-shear viscosity significantly attributed to the formation of loose particle aggregates immobilizing part of the continuous phase. Above a critical graphite concentration, capillary forces induce a self-assembling, percolating particle network, leading to a sharp yield stress increase (>100 Pa). The corresponding percolating particle network efficiently suppresses sedimentation; for the system including 28 vol% spherical particles, a shelf life of at least six months was achieved. Capillary forces do not affect the high-shear viscosity of suspensions; here, a hydrophobically modified polyether thickener can be used. Transfer of the stabilization concept presented here to other high-density particles like silver or metal oxides suspended in other polymer dispersions is straightforward and is applicable in various fields like flexible printed electronics. Full article

To understand the fluid evolution of Permian pegmatites, three pegmatite fields of the Austroalpine basement units located in the Rappold Complex at St. Radegund, the Millstatt Complex, and the Polinik Complex were investigated. To achieve this goal, fluid inclusions trapped in the magmatic accessories of garnet, tourmaline, spodumene, and beryl were studied using host mineral chemistry combined with fluid inclusion microthermometry and Raman spectrometry. Taking into account the previous work by the authors on pegmatite fields in the Koralpe and Texel Mountains, Permian fluid was determined to have evolved from two stages: Stage 1 is characterized by the homogeneous entrapment of two cogenetic immiscible fluid assemblages, a CO₂-N₂ ± CH₄-rich and a low-saline H₂O-rich fluid. Both fluids are restricted to inclusions in the early-magmatic-garnet-core domains of the Koralpe Mountains. Stage 2 is linked with the CO₂-N₂-CH₄-H₂O-NaCl-CaCl₂ ± MgCl₂ fluid preserved as an inclusion in all the pegmatite accessories of the KWNS. It represents the mechanical mixture of the stage 1 fluid caused by compositional changes along the solvus, which is typical for a hydrothermal vein environment process. Increasing X_CH4±N2 proportions from the eastern toward the western pegmatite fields of the KWNS results in a tectonic model that includes magmatic redox-controlled fluid flow along deep crustal normal faults during the anatexis of metasediments in Permian asymmetric graben structures. Because of a high number of solids within the inclusions as well as their irregular shapes, post-entrapment modifications have caused density changes that have to be considered with caution. However, the conditions in the range of 6–8 kbar at >670 °C for stage 1 and ca. 4 kbar at <670 °C for stage 2 represent the best approximations to explain the uprise of a two-stage Permian fluid associated with accessory mineral crystallization in close relation to fractionating melt. Full article

The Jiaojia gold deposit in the Jiaodong Peninsula, located in the northwestern part of the Jiaodong gold province in eastern China, has a gold reserve of over 300 t. Gold mineralization in Jiaojia deposit occurred in three stages: (1) The Pyrite–Quartz–Sericite Stage (Stage I) developed primary minerals that included quartz, sericite, and a small amount of anhedral pyrite, appearing as disseminations within milky quartz and foliated sericite. (2) The Quartz–Pyrite Stage (Stage II) developed quartz that appears smoky gray and pyrite that appears with a euhedral cubic morphology, with crystal faces oriented in a longitudinal pattern. Native gold occurs as fracture filling in pyrite. (3) The Quartz–Polymetallic Sulfides Stage (Stage III) developed polymetallic sulfides, including pyrite, chalcopyrite, galena, sphalerite, and magnetite. Native gold filled the pyrite fractures and was enclosed within the pyrite. (4) The Quartz–Carbonate Stage (Stage IV) developed the main minerals of quartz and carbonate, with scattered occurrences of pyrite. In situ geochemical analysis of pyrite, the main gold-carrying mineral from mineralization Stages I to III in the Jiaojia gold deposit, was conducted, including major element, trace element, and sulfur isotope analyses. The δ³⁴S values of Jiaojia pyrite range from 4.5 to 8.0‰. Pyrite in Stage I (Py I) has δ³⁴S values ranging from 4.5 to 7.4‰, with an average of 6.4‰. Pyrite in the Stage II (Py II) has δ³⁴S values ranging from 5.9 to 8.0‰, with an average of 6.8‰. Pyrite in Stage III (Py III) has δ³⁴S values ranging from 6.4 to 7.9‰, with an average of 7.4‰. Combined with the C-D-O-He isotopes, the ore-forming fluids of the Jiaojia gold deposit likely originated from subducted oceanic plate-related metasomatized mantle. The Co/Ni ratios of Jiaojia pyrite range from 0.50 to 1.47 in Stage I, 0.27 to 1.69 in Stage II, and 0.58 to 295 in Stage III. The Cu/Au ratios in the Jiaojia pyrite in all mineralization stages were >1. These geochemical features imply that the ore-forming fluids of the Jiaojia gold deposit were in a medium- to low-temperature reducing environment, with temperatures gradually decreasing from ore Stages I to III. The increase in Co and As in the pyrite of Stage III implies that gold precipitation resulted from fluid immiscibility caused by a decrease in pressure and temperature and an increase in the oxygen fugacity of the ore-forming fluid. Full article

It is possible to formulate an immiscible and incompressible two-phase flow in porous media in a mathematical framework resembling thermodynamics based on the Jaynes generalization of statistical mechanics. We review this approach and discuss the meaning of the emergent variables that appear, agiture, flow derivative, and flow pressure, which are conjugate to the configurational entropy, the saturation, and the porosity, respectively. We conjecture that the agiture, the temperature-like variable, is directly related to the pressure gradient. This has as a consequence that the configurational entropy, a measure of how the fluids are distributed within the porous media and the accompanying velocity field, and the differential mobility of the fluids are related. We also develop elements of another version of the thermodynamics-like formalism where fractional flow rather than saturation is the control variable, since this is typically the natural control variable in experiments. Full article

The Langcun W-Mo deposit, located in the Zhejiang Province of South China, is a medium-sized porphyry deposit. The ore bodies mainly occur in aplite, granite porphyry, and the contact zone with hornfels of the Nanhua System. Four stages of mineralization are recognized in the Langcun deposit, including the quartz–K-feldspar stage (stage I), quartz–sericite–molybdenite stage (stage II), quartz–chlorite–pyrite stage (stage III), and calcite stage (stage IV). Stages I and II are the main ore-forming stages for wolframite and molybdenite. The petrographic and microthermometric results show that four types of fluid inclusions exist in the Langcun W-Mo deposit, including two-phase liquid-rich fluid inclusions (type LV), three-phase CO₂-rich fluid inclusions (type LC), pure CO₂ fluid inclusions (type C), vapor H₂O inclusions (type V), and multi-phase inclusions with daughter minerals (type LDV). In stage I, the fluid inclusion assemblage is LDV + LV + V, and the LDV and LV fluid inclusions have similar homogenization temperatures (281–387 °C), indicating a boiling fluid inclusions association. In stage II, the fluid inclusion assemblage is LC + C, indicating immiscibility between CO₂ and aqueous fluids. The homogenization temperatures of type LC are in the range of 228–342 °C, and the salinities are in the range of 2.77–5.14 wt.% NaCl equiv. The fluid inclusions in stages III and IV are type LV, with homogenization temperatures in the ranges of 224–275 °C and 200–225 °C, respectively, and salinities in the ranges of 1.74 to 4.96 wt.% NaCl equiv and 1.06 to 3.39 wt.% NaCl equiv, respectively. Hydrogen and oxygen isotopic results indicate that the ore-forming fluids mainly come from magmatic water in the early stage and may have received an input of meteoric water in the late stage, which results in the decrease in the temperature and salinity of ore-forming fluid. Early W-Mo precipitation was induced by CO₂ escape because of decompression, and fluid mixing resulted in Mo precipitation in the later stage. Full article

Miscible gas flooding improves oil displacement through mass exchange between oil and gas phases. It is one of the most efficient enhanced oil recovery methods for intermediate density oil reservoirs. In this work, analytical solutions for saturation, concentration and pressure are derived for oil displacement by a partially miscible gas injection at a constant rate. The mathematical model considers two-phase, three-component fluid flow in a one-dimensional homogeneous reservoir initially saturated by a single oil phase. Phase saturations and component concentrations are described by a $2\times 2$ hyperbolic system of partial differential equations, which is solved by the method of characteristics. Once this Goursat–Riemann problem is solved, the pressure drop between two points in the porous media is obtained by the integration of Darcy’s law. The solution of this problem may present three different fluid regions depending on the rock–fluid parameters: a single-phase gas region near the injection point, followed by a two-phase region where mass transfer takes place and a single-phase oil region. We considered the single-phase gas and the two-phase gas/oil regions as incompressible, while the single-phase oil region may be incompressible or slightly compressible. The solutions derived in this work are applied for a specific set of rock and fluid properties. For this data set, the two-phase region displays rarefaction waves, shock waves and constant states. The pressure behavior depends on the physical model (incompressible, compressible and finite or infinite porous media). In all cases, the injection pressure is the result of the sum of two terms: one represents the effect of the mobility contrast between phases and the other represents the single-phase oil solution. The solutions obtained in this work are compared to an equivalent immiscible solution, which shows that the miscible displacement is more efficient. Full article

The volume of fluid (VoF) method is widely used in multiphase flow simulations to track and locate the interface between two immiscible fluids. The relative volume fraction in each cell is used to recover the interface properties (i.e., normal, location, and curvature). Accurate computation of the local interface curvature is essential for evaluation of the surface tension force at the interface. However, this interface reconstruction step is a major bottleneck of the VoF method due to its high computational cost and low accuracy on unstructured grids. Recent attempts to apply data-driven approaches to this problem have outperformed conventional methods in many test cases. However, these machine learning-based methods are restricted to computations on structured grids. In this work, we propose a machine learning-enhanced VoF method based on graph neural networks (GNNs) to accelerate interface reconstruction on general unstructured meshes. We first develop a methodology for generating a synthetic dataset based on paraboloid surfaces discretized on unstructured meshes to obtain a dataset akin to the configurations encountered in industrial settings. We then train an optimized GNN architecture on this dataset. Our approach is validated using analytical solutions and comparisons with conventional methods in the OpenFOAM framework on a canonical test. We present promising results for the efficiency of GNN-based approaches for interface reconstruction in multiphase flow simulations in the industrial context. Full article

Pore-scale remediation investigation of oil-contaminated soil is important in several environmental and industrial applications, such as quick responses to sudden accidents. This work aims to investigate the oil pollutant removal process and optimize the oil-contaminated soil remediation performance at the pore scale to find the underlying mechanisms for oil removal from soil. The conservative forms of the phase-field model and the non-Newtonian power-law fluid model are employed to track the moving interface between two immiscible phases, and oil pollutant flushing removal process from soil pores is investigated. The effects of viscosity, interfacial tension, wettability, and flushing velocity on pore-scale oil pollutant removal regularity are explored. Then, the oil pollutant removal effects of two flushing agents (surfactant system and surfactant–polymer system) are compared using an oil content prediction curve based on UV-Visible transmittance. The results show that the optimal removal efficiency is obtained for a weak water-wetting system with a contact angle of 60° due to the stronger two-phase fluid interaction, deeper penetration, and more effective entrainment flow. On the basis of the dimensionless analysis, a relatively larger flushing velocity, resulting in a higher capillary number (Ca) in a certain range, can achieve rapid and efficient oil removal. In addition, an appropriately low interfacial tension, rather than ultra-low interfacial intension, contributes to strengthening the oil removal behavior. A reasonably high viscosity ratio (M) with a weak water-wetting state plays synergetic roles in the process of oil removal from the contaminated soil. In addition, the flushing agent combined with a surfactant and polymer can remarkably enhance the oil removal efficiency compared to the sole use of the surfactant, achieving a 2.5-fold increase in oil removal efficiency. This work provides new insights into the often-overlooked roles of the pore scale in fluid dynamics behind the remediation of oil-contaminated soil via flushing agent injection, which is of fundamental importance to the development of effective response strategies for soil contamination. Full article