Fluid Filtration Research Articles

Functional analysis of multi-scale fractures within a single fracture cluster in multi-horizontal wells

Defining the fracture function at each scale in the reservoir helps to analyze and optimize the thermal recovery properties of the reservoir. This study aims to reveal the functionalities of fractures at different scales by simulating one single fracture cluster coupled in multi-scale fractures. The geometric layout and parameter characteristics of the main fractures, branch fractures, and micro-fracture domain are investigated to speculate on their functions and influence on heat extraction performance. The results display that the main fractures and micro-fracture domain serve as the predominant channel for fluid flow. The branch fractures exert control over the flow transition from the main fractures to the micro-fracture domain, thereby influencing the generation of preferential flow. Micro-fracture domain is the primary way of fluid filtration loss. When the thickness of micro-fracture domain increased from 0 m to 20 m, the production flow rate increased from 2 kg/s to 4.2 kg/s, and the water loss ratio increased from 1 % to 4.9 %. However, expanding the micro-fracture domain can significantly enhance production flow rate and heat recovery rate at the expense of increased water loss ratio. Notably, preferential-flow-induced thermal breakthrough will not occur prematurely in this process. The permeability of branch fractures exerts the most substantial influence on the overall heat extraction, owing to its greatest impact on reservoir lifespan. These findings would provide valuable insights for optimizing fracturing morphology in multi-horizontal wells.

Liquidate the collector in deformed oil modeling of non-isothermal flow in a horizontal well

In the article, an effective approximate solution to the determination of the flow formula in a horizontal well during non-isothermal percolation of fluid in the reservoir deformable layers is provided. The analysis of the conducted reports showed that in this case, the conclusions made in the literature regarding the non-isothermal filtration process are valid even when determining the ratio of the flow rate of the horizontal well to the flow rate of the vertical well. It was determined that the flow rate of a horizontal well in a deformed formation is less than the flow rate of a well from a non-deforming formation drainage at the same pressure drop.

Forecasting the Remaining Useful Life of Filters in Nuclear Power Plants

To function effectively, nuclear power plants rely on the effective filtration of air, water, and process fluids, examples of which include inlet sea water, reactor coolant, plant drinking water, and moderator purification. Filtration assets degrade over time, which impairs their filtering performance and reduces the flow rate. Being able to determine the remaining useful life (RUL) of a filter could result in benefits, particularly when moving from a time-based to a condition-based maintenance strategy that would optimize the filter replacement procedure and reduce early replacement of filters that are still fit for purpose. For many filter applications, a time-based strategy is sufficient. For strategically important assets, such as fueling machines, there are benefits to be gained from the development of predictive maintenance strategies. In this paper, we propose a predictive condition-based strategy using differential pressure data as a proxy for filter health. The key objective in this work was the creation of a model that could predict a filter asset RUL. The differential pressure for 7 to 14 days is predicted by a heuristic-based regression model of the history of each filter. This approach has been demonstrated using a civil nuclear generation application but could be applied to wider applications. While this model is still undergoing on-site evaluation, it has been estimated that there will be an operationally significant lifetime cost reduction.

A MATLAB approach for developing digital rock models of heterogeneous limestones for reactive transport modeling

Porosity is a key parameter controlling the physico-chemical behavior of porous rocks. Digital rock physics offers a unique technique for imaging the inherently heterogeneous rock microstructure at fine spatial resolutions and its computational reconstruction, through which a better understanding and prediction of the rock behavior can be achieved. In this study, we propose a simple but accurate method to build a 3D porosity map of centimeter-scale carbonate rock cores from X-ray Micro Computed Tomography (XMCT) imaging data. The method consists of 3 main steps: i) decomposition of 3D volumetric XMCT data into sub-volumes, ii) processing of equidistributed 2D cross-section images in each sub-volume and iii) 2D slice-by-slice calculation of porosity and its assembly to reconstruct a 3D continuum porosity map over the whole core domain using a MATLAB code. The proposed approach significantly conserves the required memory to manipulate large image datasets. The digitized porosity representations are used to build 3D permeability maps of the cores by applying an explicit permeability-porosity relationship. The permeability maps are used as input for numerical simulation of the rock response to the percolation of reactive fluids through which the general validity of the approach is verified. The developed digital rock model paves the way for an improved understanding of reactive transport in carbonate rocks.

Formation mechanisms of Fe-dominated versus Fe polymetallic deposits in the West Tianshan, NW China: A magnetite perspective

The West Tianshan in the Central Asian Orogenic Belt is one of important Fe belts in China, where many submarine volcanogenic iron-oxide deposits constitute the Awulale metallogenic belt. The Dunde deposit is a Fe-Zn-Au deposit, whereas Chagangnuoer, Zhibo, and Beizhan are Fe-dominated deposits. To examine the factors controlling the formation of Fe polymetallic deposits, the texture and chemical composition of magnetite from the Dunde deposit were studied in detail and compared with those of other deposits in the same belt. The Dunde deposit magnetite can be divided into Mag-1, Mag-2, and Mag-3, which correspond to stages of retrograde, sulfide, and carbonate stages, respectively. They have experienced oxy-exsolution and coupled dissolution and reprecipitation (CDR), forming multiple generations of magnetite. The exsolution of gahnite in Mag-1 and 10 times higher Zr, Hf, Sc, Ta, Nb, Mn, and Zn contents in the all stages of magnetite than those of Fe-dominated deposits, indicating the Dunde magnetite was crystallized from high-temperature, high-salinity, Fe-Zn-rich fluids. The similar chalcophile element contents in host volcanic rocks between Dunde and other deposits indicate host volcanic rocks are not the reason for Zn enrichment in Dunde. The higher Mg + Mn and Si + Al contents in Dunde magnetite than magnetite of other deposits indicate stronger fluid-rock interaction. Extensive CDR texture in Mag-1 and Mag-2 and lower Zn in secondary magnetite indicate that Zn leached from Zn-rich magnetite may have also contributed to the formation of sphalerite in sulfide stage. Our study has demonstrated that high-temperature, high-salinity, Fe- and Zn-rich primary fluids, a higher degree of fluid-rock interaction, and repeated fluid infiltration are key factors controlling the formation of Fe-Zn polymetallic deposits, such as the Dunde deposit in West Tianshan.

Modelling of Multicomponent Fluid Flow in Deforming and Reacting Porous Rock

We propose a coupled hydro-chemo-mechanical model and its 1D numerical implementation. We demonstrate its application to model filtration of a multicomponent fluid in deforming and reacting host rocks, considering changes in the densities, phase proportions and chemical compositions of coexisting phases. We presented 1D numerical implementation on the example of soapstone formation from serpentinite during H₂O-СО2 fluid filtration with low concentration of СО2 coupled with viscous deformation of mineral matrix, considering MgO-SiO2-H₂O-СО2 system. The numerical results show porosity wave propagation by viscous (de)compaction mechanism accompanied with the formation of an elongated zone with higher filtration properties. After the formation of such a channel, the formation and propagation of reaction fronts occurs associated with the transformation of the mineral composition of the original rock. During H2O-CO2 fluid filtration, starting from 1 weight percent of dissolved CO2, carbonization of hydrated serpentinite starts, specifically antigorite transforms to magnesite and talc.

Genesis of high-Al chromitites from Xiaosuihe peridotite (Central Jilin Province, NE China): Implication for initial subduction of the Paleo-Asian ocean

This study presents whole-rock major- and trace-element data of serpentinites and mineral geochemistry of chromite/spinel from both serpentinites and associated podiform chromitites from the Xiaosuihe region in central Jilin Province, NE China, aimed to elucidate the genesis of serpentinites and podiform chromitites. The serpentinites exhibit low Al2O3/SiO2 ratios (0.01–0.02) and high Mg# (0.90–0.91), indicating their derivation from the fore-arc mantle wedge and protolith as harzburgite. Chromitite ores with semi-massive to disseminated textures occur as small pods. The chromite/spinel (Chr) present in both the podiform chromitite and serpentinite can be categorized into four distinct microstructural groups: (1) partially altered chromite, characterized by high-Al primary cores (Cr# = 0.44–0.49), surrounded by high-Cr porous rims; (2) porous chromite, featuring abundant pores enriched in Cr and Fe and depleted in Mg and Al, filled with chlorite; (3) zoned chromite consisting of high-Al cores surrounded by non-porous rims of Cr-magnetite (Cr-mag); and (4) homogeneous chromite, which is non-porous ferritchromite (Fe-Chr). The high-Al primary cores of the partly altered chromite are depleted in Cr but enriched in Mg, exhibiting MORB-like tholeiitic affinities. In contrast, the altered Chr displays low Mg# [Mg/(Mg + Fe2+)] along with elevated Cr# [Cr/(Cr + Al)] and Fe# [Fe3+/(Cr + Al + Fe3+)] values. Based on the above results, the high-Al cores of chromite within the chromitite originally formed through melt/fluid-rock interaction within the forearc mantle wedge. During the exhumation and post-magmatic processes, the reaction between high-Al Chr and olivine resulted in chlorite formation alongside secondary Chr enriched in Fe2+ and Cr content. Subsequently, the infiltration of hydrous fluid led to the development of Fe3+-rich Chr or Cr-mag along grain boundaries or fractures within the original chromite during the retrograde process. The Xiaosuihe serpentinized harzburgites, along with associated chromitites, represent the composition of peridotite in the forearc mantle wedge that could have formed during the initial subduction of an oceanic island arc abutting the northern North China Craton during the Cambrian. Subsequently, these rocks underwent retrograde metamorphism from amphibolite (eclogite) to greenschist facies during their exhumation.

Ultrasound-derived rates of muscle wasting in the intensive care unit and in the post-intensive care ward for patients with critical illness: Post hoc analysis of an international, multicentre randomised controlled trial of early rehabilitation

Background and aimsMuscle wasting results in weakness for patients with critical illness. We aim to explore ultrasound-derived rates of change in skeletal muscle in the intensive care unit (ICU) and following discharge to the post-ICU ward. DesignPost hoc analysis of a multicentre randomised controlled trial of functional–electrical stimulated cycling, recumbent cycling, and usual care delivered in intensive care. MethodParticipants underwent ultrasound assessment of rectus femoris at ICU admission, weekly in the ICU, upon awakening, ICU discharge, and hospital discharge. The primary outcome was rate of change in rectus femoris cross-sectional area (ΔRFCSA) in mm2/day in the ICU (enrolment to ICU discharge) and in the post-ICU ward (ICU discharge to hospital discharge). Secondary outcomes included rate of change in echo intensity (ΔEI), standard deviation of echo intensity (ΔEISD), and the intervention effect on ultrasound measures. Echo intensity is a quantitative assessment of muscle quality. Elevated echo intensity may indicate fluid infiltration, adipose tissue, and reduced muscle quality. Results154 participants were included (mean age: 58 ± 15 years, 34% female). Rectus femoris cross-sectional area declined in the ICU (−4 mm2/day [95% confidence interval {CI}: −9 to 1]) and declined further in the ward (−9 mm2/day [95% CI: −14 to −3]) with a mean difference between ICU and ward of −5 mm2/day ([95% CI: −2, to 11]; p = 0.1396). There was a nonsignificant difference in ΔEI between in-ICU and the post-ICU ward of 1.2 ([95% CI: −0.1 to 2.6]; p = 0.0755), a statistically significant difference in ΔEISD between in-ICU and in the post-ICU ward of 1.0 ([95% CI, 0.5 to 1.5]; p = 0.0003), and no difference in rate of change in rectus femoris cross-sectional area between groups in intensive care (p = 0.411) or at hospital discharge (p = 0.1309). ConclusionsMuscle wasting occurs in critical illness throughout the hospital admission. The average rate of loss in muscle cross-sectional area does not slow after ICU discharge, even with active rehabilitation.

Hydrocarbon fluid evolution and accumulation process in ultradeep reservoirs of the northern Fuman Oilfield, Tarim Basin

Marine deep Ordovician reservoirs are significantly controlled by strike-slip fault zones, which govern reservoir fluid evolution during various activity periods. Such fluid evolution elucidates the process underpinning ultra-deep oil and gas accumulation and delineates the pivotal role of strike-slip fault zones in hydrocarbon aggregation. This method can improve the understanding of the mechanism of hydrocarbon accumulation in deep to ultradeep carbonate rocks. The findings indicate that the Ordovician reservoirs in the northern thrust fault zone of the Fuman Oilfield predominantly exhibit two stages of calcite vein formation. The distribution patterns of rare earth elements and Sr isotope characteristics suggest that both stages of vein formation were sourced from Middle to Lower Ordovician marine strata, with no evidence of oxidizing fluid infiltration. This indicates that late-stage oil and gas charging in deep-ultradeep formations has good sealing properties. In these calcite veins, early-, middle-, and late-stage fluid inclusions were primarily entrapped. By examining the development of primary oil inclusions and combining the U‒Pb isotope data of host minerals, this study confirms the occurrence of three stages of oil and gas charging in the deep Ordovician strata of the northern thrust fault zone in the Fuman Oilfield. These stages correspond to approximately 459 ± 7.2 Ma (mid-Caledonian), 348 ± 18 Ma (early Permian), and 268 Ma (late Permian). The key accumulation period of oil and gas reservoirs in the study area is the middle and late Caledonian, and there is a good correspondence between oil and gas charging and fault activity.

Stacking of Distributed Dynamic Strain Reveals Link Between Seismic Velocity Changes and the 2020 Unrest in Reykjanes

AbstractIn this study, we measure seismic velocity variations during two cycles of crustal inflation and deflation in 2020 on the Reykjanes peninsula (SW Iceland) by applying coda wave interferometry to ambient noise recorded by distributed dynamic strain sensing (also called DAS). We present a new workflow based on spatial stacking of raw data prior to cross‐correlation which substantially improves the spatial coherency and the time resolution of measurements. Using this approach, a strong correlation between velocity changes and ground deformation (in the vertical and horizontal direction) is revealed. Our findings may be related to the infiltration of volcanic fluids at shallow depths, even though the concurrent presence of various processes complicates the reliable attribution of observations to specific geological phenomena. Our work demonstrates how the spatial resolution of DAS can be exploited to enhance existing methodologies and overcome limitations inherent in conventional seismological data sets.

Brittle initiation of dissolution–precipitation creep in plagioclase-rich rocks: insights from the Bergen arcs, Norway

The initiation of ductile shear zones commonly occurs spatially associated with fluid-rock reactions along brittle precursors. In many cases the relative timing of fracturing, fluid infiltration, reaction, and recrystallisation is unclear, making it difficult to disentangle mechanisms of shear zone initiation from subsequent deformation and recrystallisation. Here we present the study of the transition from a dry plagioclase-diopside-garnet-scapolite host granulite-facies lithology to (1) a low strain amphibolite-facies rock, and (2) a transition from low strain to high strain amphibolite-facies lithologies. Hydration of the granulite-facies precursor at amphibolite-facies conditions produces an assemblage comprised dominantly of plagioclase-amphibole-zoisite-clinozoisite-kyanite-scapolite-quartz. Detailed study of plagioclase chemistry and microstructures across these two transitions using Electron Backscatter Diffraction (EBSD) and Wavelength Dispersive Spectrometry (WDS) allows us to assess the degree of coupling between deformation and fluid-rock reaction across the outcrop. Plagioclase behaves dominantly in a brittle manner at the hydration interface and so the initial weakening of the rock is attributed to grain size reduction caused by fracture damage and fluid infiltration at amphibolite-facies conditions. Extensive fracturing-induced grain size reduction locally increases permeability and allows for continuing plagioclase and secondary mineral growth during shear. Based on plagioclase microstructures, such as, an inherited but dispersed crystallographic preferred orientation (CPO), truncation of chemical zoning, and the dominance of fine (5–150 µm), slightly elongate, polygonal grains we conclude that deformation is dominantly facilitated by dissolution–precipitation creep assisted by grain boundary sliding in the shear zone.

The Role of Aquaporin 4 in Lacrimal Gland Ductal Fluid Secretion in Mice.

Earlier reports highlighted the predominant presence of aquaporin 4 (AQP4) in the duct cells of rabbit lacrimal glands (LGs). Whereas significant alterations in AQP4 mRNA levels have been observed in experimental dry eye and during pregnancy, the impact of AQP4 in LG ductal fluid production remains unclear. In our recent work, the role of AQP4 in LG ductal fluid secretion was investigated utilizing wild type (WT) and AQP4 knock out (KO) mice. Tear production was assessed in both WT and KO animals. Immunostaining was used to identify AQP4 protein. Duct segments were harvested from LGs of WT and KO mice. Fluid secretion and filtration permeability (Pf) were quantified using video-microscopy. Ductal tear production, elicited by a cell-permeable cAMP analogue (8-bromo cAMP), carbachol, vasoactive intestinal peptide (VIP), and phenylephrine (PHE), were assessed in both WT and KO ducts. A higher expression of AQP4 protein was noted in the duct cells from WT mice when compared to acinar cells. Pf did not show notable alterations between WT and AQP4 KO ducts. Carbachol elicited comparable secretory responses in ducts from both WT and KO animals. However, 8-bromo cAMP, VIP, and PHE stimulation resulted in decreased secretion in ducts from AQP4 KO LGs. Our findings underscore the functional relevance of AQP4 in the fluid production of mouse LG ducts. AQP4 seems to play different roles in fluid secretions elicited by different secretagogues. Specifically, cAMP-mediated, and adrenergic agonist-related secretions were reduced in AQP4 KO ducts.

Polytopal discontinuous Galerkin discretization of brain multiphysics flow dynamics

A comprehensive mathematical model of the multiphysics flow of blood and Cerebrospinal Fluid (CSF) in the brain can be expressed as the coupling of a poromechanics system and Stokes' equations: the first describes fluids filtration through the cerebral tissue and the tissue's elastic response, while the latter models the flow of the CSF in the brain ventricles. This model describes the functioning of the brain's waste clearance mechanism, which has been recently discovered to play an essential role in the progress of neurodegenerative diseases. To model the interactions between different scales in the porous medium, we propose a physically consistent coupling between Multi-compartment Poroelasticity (MPE) equations and Stokes' equations. In this work, we introduce a numerical scheme for the discretization of such coupled MPE-Stokes system, employing a high-order discontinuous Galerkin method on polytopal grids to efficiently account for the geometric complexity of the domain. We analyze the stability and convergence of the space semidiscretized formulation, we prove a-priori error estimates, and we present a temporal discretization based on a combination of Newmark's β-method for the elastic wave equation and the θ-method for the other equations of the model. Numerical simulations carried out on test cases with manufactured solutions validate the theoretical error estimates. We also present numerical results on a two-dimensional slice of a patient-specific brain geometry reconstructed from diagnostic images, to test in practice the advantages of the proposed approach.

Seismicity Migration and the Upper Crustal Structure in the Xinfengjiang Reservoir

Abstract After the impoundment of the Xinfengjiang Reservoir (XFJR) in Guangdong, China, numerous earthquakes occurred in the area, including a magnitude 6.1 event in 1962. Analysis of historical earthquakes indicates that M ≥ 4 earthquakes began occurring in the northwestern XFJR in 2012, and seismicity has gradually migrated from the southeastern to the northwestern reservoir (NWR). However, the mechanisms governing the migration of seismicity and the current upper-crustal structure beneath the reservoir area remain unclear. In our study, we conducted tomographic imaging by combining waveform data from short-period and permanent stations to construct a 3D velocity model. Our high-resolution velocity models revealed a horizontal fractured zone at ∼5 km depth that extends from the southeastern to northwestern XFJR, and a steep fault that extends to about 9 km depth. These two fractured zones may interact with each other, allowing for fluid infiltration and contributing to earthquake triggering via pore pressure diffusion in the XFJR areas. Furthermore, the calculation of Coulomb stress changes indicated that microearthquakes in the southeastern XFJR may contribute to the seismicity in the NWR. However, the influences of M ≥ 4 earthquakes in the northwestern XFJR on subsequent M ≥ 4 earthquakes in the southeastern XFJR vary differently. Our results provide crucial insights for understanding the migration of microearthquakes in the XFJR area.

Boundary Value Problems for a Model Hyperbolic Equation of the Third Order with Non-local Conditions of the First Kind

Considers nonlocal problems of the first kind for a model third-order hyperbolic equation. The main goal of the article is to prove the solvability of nonlocal problems of the first kind for a model third-order hyperbolic equation. Using the Riemann function method, the problem is reduced to Volterra integral equations of the second kind. Using the method of integral equations, the existence of a unique solution to nonlocal problems of the first kind is proven. The resulting solution to nonlocal problems of the first kind makes it possible to describe the process of moisture transfer in soils, heat transfer in a heterogeneous medium, and fluid filtration in porous media.

Fluid–Melt–Rock Interaction during the Transition from Magmatism to HT-UHT-Granulite- and Amphibolite-Facies Metamorphism in the Ediacaran Adrar–Suttuf Metamafic Complex, NW Margin of the West African Craton (Southern Morocco)

Abstract Underplated mafic intrusions ponded at the base of the lower continental crust in extensional settings can experience ultra-high-temperature (UHT) granulite-facies metamorphism during tens of My due to slow cooling rates. These intrusions are also the source of heat and carbonic fluids for regional high-temperature (HT) granulite-facies metamorphism in the continental crust. This work analyses the fluid–melt–rock interaction processes that occurred during the magmatic to HT-UHT-granulite- and amphibolite-facies metamorphic evolution of high-grade mafic rocks from the Eastern Ediacaran Adrar–Suttuf Metamafic Complex (EASMC) of the Oulad Dlim Massif (West African Craton Margin, Southern Morocco). P–T conditions were determined using Ti-in-amphibole thermometry, two-pyroxene and amphibole–plagioclase thermobarometry, and phase diagram calculations. The thermobarometric study reveals the presence of tectonically juxtaposed lower- and mid-crustal blocks in EASMC that experienced decompression-cooling paths from, respectively, UHT and HT granulite-facies conditions at ca. 1.2 ± 0.28 GPa and 975 ± 50°C, and ca. 0.82 ± 0.15 GPa and 894 ± 50°C, to amphibole-facies conditions at ca. 0.28 ± 0.28 GPa and 787 ± 45°C (precision reported for the calibrations at 1 s level). An age for the magmatic to UHT granulite-facies metamorphic transition of 604 Ma was constrained from published SHRIMP Th–U–Pb zircon ages of the igneous protoliths. An amphibole 40Ar–39Ar cooling age of 499 ± 8 Ma (precision at 2 s level) was obtained for the lower-crustal blocks. Amphibole 40Ar–39Ar closure temperatures of 520–555°C were obtained for an age range of 604–499 Ma and an average constant cooling rate of 4.2°C/My, suggesting that the lower-crustal blocks cooled down to the greenschist–amphibolite facies transition in ca. 100 My. During the high-temperature stage, interstitial hydrous melts assisted textural maturation of the rock matrix and caused incongruent dissolution melting of olivine and pyroxenes, and, probably, development of An-rich spikes at the grain rims of plagioclase, and local segregation of pargasite into veins. Subsequent infiltration of reactive hydrous metamorphic fluids along mineral grain boundaries during cooling down to amphibolite-facies conditions promoted mineral replacements by coupled dissolution-precipitation mechanisms and metasomatism. Ubiquitous dolomite grains, with, in some cases, evidence for significant textural maturation, appear in the granoblastic aggregates of the high-grade mafic rocks. However, calculated phase relationships reveal that dolomite could not coexist with H2O–CO2 fluids at HT-UHT granulite- and low-medium P amphibolite-facies conditions. Therefore, it is proposed that it may have been generated from another CO2-bearing phase, such as an immiscible carbonatitic melt exsolved from the parental mafic magma, and preserved during cooling due to the prevalence of fluid-absent conditions in the granoblastic matrix containing dolomite. The lower-crustal mafic intrusions from EASMC can represent an example of a source of heat for granulitisation of the mid crust, but a sink for carbon due to the apparent stability of dolomite under fluid-absent conditions.

Turbulent flow characteristics over rough permeable and impermeable gravel-bed stream- an experimental study

Abstract The study aims to presents flow heterogeneity over rough permeable and impermeable gravel-bed stream. The rough permeable stream is prepared by laying multiple layers of gravel, whereas its impermeable counterpart is presented by a resin-casted gravel-bed. In general, a common approach can be found in literature to mimic an impermeable bed by laying single layer of gravels, therefore some results are compared with single layer gravel-bed stream keeping the hydraulic conditions same. An acoustic Doppler velocimeter was used for flow measurements whereas; double averaging (DA) methodology was adopted for data analysis. The larger flow penetration depth and intense flow mixing in permeable gravel-bed infer sufficient impetus for organized flow turbulence and damping of DA Reynolds shear stresses whereas; the wall-blocking in resin-casted gravel-bed prevents fluid infiltration which leads to follow the linear stress profile away from the crest level. The damping of DA Reynolds shear stress (RSS) is compensated by enhanced DA form-induced shear stress (FISS). The results are further analysed under the light of the energy budget to characterize the mass-momentum exchange as it penetrates the subsurface layers. The energy budget indicates negative pressure energy diffusion rates corroborating gain in turbulence production in the permeable gravel-bed stream.

The role of hydrothermal processes and the formation of the J-M reef and associated rocks of olivine-bearing zone I of the Stillwater Complex, Montana

AbstractSeveral lines of evidence, including hydrous melt inclusions and unusually Cl-rich apatite, have been used to suggest that the reappearance of olivine and PGE-sulfide of the J-M Reef in the Stillwater Complex, Montana, is due to fluid infiltration and hydration melting. This study builds upon the hydration melting model using the programs MELTS and PELE with Stillwater bulk rock compositions for the original protolith. Cl-bearing phases are not modeled by MELTS and thus simple oxide mixtures of either a pure H2O or a H2O + Na2O “faux brine” are added to norite, gabbronorite, and melanorite protoliths at 1050 °C at 2 kbar pressure, conditions for which the nominally “dry” protolith is > 95% solid. Incongruent hydration melting results in up to 37% olivine produced in the melanorite. The olivine Fo content is a function of the partial melt retained on cooling, and ranges between 76 and 86, overlapping the natural range of olivine compositions observed in the rocks. Modeling with the PELE program, which includes a silicate liquid Cl component, sulfur species, and a more complex C-O–H-S fluid, suggests that, for CO2-rich fluids, fluid metal concentrations on the order of 25 ppm Pt, 75 ppm Pd, 0.03 wt.% Cu, and 0.20 wt.% Ni at a fluid/rock mass ratio of ~ 0.25 are needed to account for the observed ore grades. Sulfide and ore metals are readily remobilized for more H2O-rich fluids, consistent with heterogeneous distribution of sulfide and regionally variable ore grades.

Altered spinels act as a mirror of multi-episodic fluid metasomatism in the forearc mantle: An example from the Minhe ophiolite in Qilian Orogen, NW China

Forearc mantle peridotites commonly undergo complex melt/fluid metasomatism, which inevitably has a considerable influence on their geochemical compositions at the whole-rock scale. Serpentinites predominantly comprise the Minhe ophiolite, which is a fragment of the Proto-Tethys Ocean that outcrops in the Qilian Orogen in NW China. These serpentinites contain zoned spinels that vary compositionally from the centers to the margins, with a spinel core overgrown by ferritchromite layer and magnetite at the outermost rim. The mineral chemistry of the spinel cores (i.e., Cr#, Mg#, Cr2O3, and Al2O3) suggests that the protolith of the serpentinites was an oceanic mantle remnant in a forearc setting. Moreover, the ferritchromite exhibited increases in Fe, Mn, Sc, and Ni contents and decreases in Mg, Cr, Al, V, Zn, and Ga contents. Considering the linear correlation among elements (e.g., Co, Ni, and Zn) and the absence of mineral inclusions, the ferritchromite likely formed through ionic substitutions induced by slab fluids. The magnetite was enriched in Cr, Ni, V, Zn, Co, and Cu, but did not have a magmatic origin owing to low V concentrations. All evidence indicates that the peridotites underwent at least two episodes of fluidic metasomatism in the subduction zone. During early slab subduction, aqueous fluids released from the dehydration of the subducted slab directly serpentinized the forearc mantle peridotites, thereby altering the olivine and orthopyroxene to lizardite/chrysotile. During this process, certain mobile elements (e.g., Fe, Ni, and Mn) in the fluids and/or olivine serpentinization were incorporated into existing spinels, favoring ferritchromite growth. The second fluidic episode was dependent on prograde metamorphism at greater depths in the subduction channel, which not only produced antigorite via the recrystallization of lizardite and chrysotile, but also drove the fluids towards a more oxidizing state, thereby facilitating the growth of Cr-magnetites. Subsolidus re-equilibration controlled by fluid infiltration further promoted the inter-diffusion of elements (e.g., Cr, V, Co, Ni, Cu, and Zn) in the zoned spinels.

Numerical Solution of the Inverse Problem of Non-stationary Filtration of Bingham Non-Newtonian Fluid to a Horizontal Well

Numerical Solution of the Inverse Problem of Non-stationary Filtration of Bingham Non-Newtonian Fluid to a Horizontal Well