High Porosity Regions Research Articles

Harnessing the power of machine learning for the optimization of CO2 sequestration in saline aquifers: Applied on the tensleep formation at teapot dome in Wyoming

The sequestration of carbon dioxide in deep saline aquifers offers a highly promising approach to mitigate CO2 emissions resulting from the fossil fuels industry. The practicality of this solution is mostly dependent upon the CO2 trapping efficiency, which governs the capacity of the aquifer for CO2 storage. Generally, the compositional reservoir simulation is employed to evaluate the trapping efficiency, but is computationally expensive, particularly when adjusting parameters necessitates hundreds of simulations. In this paper, A machine learning (ML) proxy model was used to address these difficulties for fast evaluation and optimization of the residual and dissolution trapping mechanisms in the Tensleep sandstone formation in the Teapot Dome Field, located in Wyoming, USA. The initial CO2 storage capacity of the aquifer was calculated to be 17.7 thousand tons. In the simulation model, several injection wells were placed in the high porosity regions and CO2 injection was simulated over duration of 10 years, followed by a 90-year post-injection period. The injection rates were optimized to maximize the overall trapping efficiency, which takes into account both residual and solubility indices. In order to construct a dataset for machine learning-based proxy models, the Latin hypercube sampling technique was adopted to generate 100 simulation runs that varied operating constraints: maximum injection rate, maximum injection pressure, and number of injection wells. The Radial Basis Function-Artificial Neural Network (RBF-ANN) was specifically trained to accurately determine the most appropriate injection rates by identifying complex and non-linear correlations within the data. The total CO2 trapping effectiveness by the RBF-ANN model was enhanced from 75% to 83%, accompanied by an insignificant increase in the leakage index from 0.64% to 1.3%. The results indicated that machine learning proxy modeling offers a rapid and accurate approach to optimize the storage of CO2 in saline aquifers. Through the reduction of CO2 emissions, this method significantly improves the viability of large-scale sequestration projects, so making a valuable contribution to climate change mitigation.

In-plane compressive properties and failure mechanisms of gradient Cf/ZrB2–SiC composites in high-temperature environment

The gradient Cf/ZrB2–SiC composites can exert the dual advantages of low-density and excellent heat resistance, but which have the complex mechanical properties due to the inhomogeneous geometry characteristics. The in-plane compressive behavior and failure analysis can examine the material integrity and the effect of inhomogeneous characteristics. The in-plane compressive elastic modulus distribution is expressed mathematically by using the superficial elastic modulus, back elastic modulus, and the gradient pore distribution. The superficial elastic modulus and the gradient pore distribution of the gradient materials were characterized by nanoindentation test and Micro-CT statistics. The back of the gradient materials is the porosity needled C/C composites without introducing ZrB2–SiC matrix, whose elastic modulus can be referenced from our previous work. The in-plane compressive experiments of the gradient materials in the high-temperature environment were also conducted to study the failure mechanisms. The strength of the gradient materials is further revealed by the temperature-dependent properties of carbon fibers and thermal residual stress release. The results indicate the gradient structure can effectively eliminate the delamination damage, but the high temperature drastically weakens the ability of needled fibers suppressing delamination damage in the high-porosity region of the gradient materials. This study can be helpful to the material design and evaluation of mechanical properties for the gradient Cf/ZrB2–SiC composites.

Straight fiber bundles with non-uniform porosity: Shell-side hydrodynamics and mass transfer in cross flow

This study explores fully developed shell-side hydrodynamics and mass transfer past straight fiber bundles with non-uniform porosity in cross-flow. Simplified geometries made up by checkerboard arrays of alternately high and low porosity regions are considered. Simulations are performed for two domain sizes: a small geometry (26 fibers) and a large geometry (104 fibers). In the small geometry, the Darcy friction coefficient (fT) exhibits hydraulic isotropy at low transverse flow Reynolds numbers (ReT) but becomes dependent on the flow attack angle (θ) at higher ReT. In the large geometry, this dependency is observed at lower ReT. A non-uniform porosity reduces fT at almost all ReT and θ in the small geometry, with the large geometry exhibiting a more complex behavior. Regarding mass transfer, up to ReT≈1-10 (depending on θ), a non-uniform porosity leads to lower Sherwood numbers compared to regular square arrays. However, at higher ReT, it enhances mass transfer.

Quantifying Spatiotemporal Heterogeneity within Fuel Cells Using Simultaneous Neutron and X-Ray Tomography (NeXT)

Heterogeneity within electrochemical devices, such as fuel cells, influences their performance and durability in ways that are not fully understood. 4-dimensional (4-D; 3 spatial dimensions and time) operando visualization techniques such as X-ray (1-2) and neutron (3) tomography are powerful tools to probe heterogeneity within operating electrochemical devices in high spatiotemporal resolution. Combining neutron and X-ray tomography (NeXT) (3-4) simultaneously offers unique advantages over single-modality methods, especially in terms of enhanced contrast between materials. There is a significant opportunity to utilize NeXT to characterize and quantify heterogeneity within electrochemical devices during cell operation. In this study, we utilize quantitative NeXT to identify spatiotemporal heterogeneity in the morphology of the membrane electrode assembly (MEA) and water distribution within the porous layers and the membrane. A custom interfacial tracking algorithm is utilized to accurately characterize 4-D morphology and boundaries of cell components. Heterogeneity is found to depend upon location with respect to cell components and operating conditions (such as current density and inlet relative humidity). Variations in the MEA morphology is dominated by variations in membrane morphology, whereby variations of up to 80 μm is observed in membrane thickness for N117 membranes (Chemours, USA). We find that the interface between the gas diffusion layer and the enclosing gasket is a high porosity region that accumulates liquid water during cell operation, and this liquid accumulation leads to high membrane hydration and membrane swelling near the interface. With this study, we demonstrate the viability of quantitative NeXT to characterize operando heterogeneity within multi-component electrochemical devices, taking us a step closer towards rational control and design of inherent heterogeneity within these devices.

The effect of X-ray computed tomography scan parameters on porosity assessment of carbon fibre reinfored plastics laminates

Combinations of X-ray Computed Tomography (XCT) scan times, from 30 s to 60 min, and voxel sizes, from 6 to 50 µm, were investigated for their effect on the porosity measurements of a unidirectional carbon fibre epoxy composite volume. The sample had a total void volume of around 2%, which is typical of the tolerance expected in the aerospace industry. The volume contained localised voids that create sub-volumes with representative high (5%) and low (1%) porosity regions. The ability to detect small-size voids in the lower porosity regions decreased as the voxel size increased. Scan resolutions above 25 µm resulted in a coarser segmentation and overestimation of the porosity due to the presence of partial volume effects. Scan times shorter than 2 min resulted in noisy images, requiring aggressive filtering that affected the segmentation of voids. Porosity segmentation was performed by thresholding and Deep Learning methods. Deep Learning segmentation was found to recognise noise better, providing more consistent and cleaner segmented data than thresholding. To capture micro-voids that contribute to porosity levels at the typical aerospace tolerance of 2%, scan parameters with a voxel size equal to or smaller than 25 µm, scan times of 2 to 8 min, and deep learning segmentation were found to be the most promising. These shorter scan times can be used to increase the productivity of CT scanning for porosity or observing time-resolved events. The data provided here contributes to the body of knowledge studying X-ray hardware settings and optimising image segmentation.

Micro-CT in the mechanical properties and energy absorption of closed-cell aluminium foam

In situ loading experiments of closed-cell aluminium foam with densities of 0.217 g/cm3, 0.347 g/cm3, 0.414 g/cm3 and 0.588 g/cm3 prepared from industrial pure aluminium 1060 and titanium hydroxide TiH2 foaming agent were carried out by micro-CT. The pore structure parameters such as porosity, pore size distribution and sphericity of aluminium foams with different densities were analyzed, and the effects of pore structure parameters on mechanical properties and energy absorption were investigated to reveal the differences in mechanical characterization of aluminium foams with different densities. The results show that: the collapse of aluminium foam pores in the in-situ loading experiments starts from the high porosity region; aluminium foam with high density has low porosity, small pores and good sphericity; the stress-strain curve of aluminium foam with high density is located above and the elastic modulus is large; the energy absorption capacity is related to the density of aluminium foam, and the energy absorption capacity is large with high density, but the energy absorption efficiency is mainly related to whether the structure is uniform or not.

Modeling and thermodynamic analysis of the hydration and germination of triticale seeds

We investigated the hydration and germination of triticale seeds to improve process efficiency and product quality. The grains were hydrated in a water bath at 20–50 °C for 15 h. Temperatures of 20 °C–30 °C and process times as of 660 min provided the best hydration rates without hindering the germination capacity of the seeds. Throughout processing, we monitored the moisture uptake and volumetric expansion of the samples by gravimetric methods. A tracer pigment added to the hydration water and the images obtained with scaning electron microscopy elucidated the mechanisms of moisture uptake throughout the grains. The water penetrated the grain primarily through the micropyle, a region of high porosity. The mass transfer (diffusion coefficient) and thermodynamic properties (enthalpy, entropy, and Gibbs free energy) indicated the process is non-spontaneous and endothermic. Such piece of information is helpful in equipment design. We also proposed mathematical models, based on Fick's Law of Diffusion, that predict the moisture content of cereal seeds hydrated at 20–50 °C for up to 15 h with great accuracy (P ≤ 3.36% and RMSE≤1.54%).

TiO2-CuO heterojunction nanoparticles synthesized by green chemistry supported on beach sand granules: Optical, morphological and structural characterization

This research has studied the optical, morphological/textural and structural properties of pulverized TiO2-CuO heterostructures and their immobilization on chemically purified beach sand granules to evaluate the potential of these materials for wastewater treatment. The preparation of TiO2-CuO heterojunctions was developed by the ultrasound-assisted wet impregnation method in the presence of PEG-400. For this methodology, the TiO2 and CuO nanoparticles were first synthesized by green chemistry using Moringa (Moringa Oleifera) leaves aqueous extract and an ultrasound bath. Then, the metal oxide nanoparticles were calcinated and immobilized on etched sand granules via immersion in a coating suspension. All materials were characterized by UV–Vis DRS, photoluminescence (PL), SEM-EDS, HRTEM-SAED, BET area, Raman spectroscopy, XRD and XPS. Optical characterization revealed that the CuO incorporation favors light adsorption in the visible spectrum and reduces the band gap energy from 3.14 to 1.28 eV. Morphological studies showed that the pulverized materials are agglomerated with an affinity for the high porosity regions of the beach sand granules. Also, TiO2-CuO heterojunctions exhibited a broader size distribution (15.81 ± 7.45 nm) than pure TiO2 nanoparticles (10.38 ± 1.24 nm). The structural analysis confirmed that the pure TiO2 and CuO nanoparticles are formed exclusively in the anatase and tenorite phases. At the same time, the heterostructures’ process preparation favors the partial transition from CuO to Cu2O. Finally, the purified sand support is mainly based on α-Quartz (trigonal); the as-prepared material is a potentially versatile and reusable candidate for pollutant photodegradation under UV or visible light sources.

Hydrodynamics and mass transfer in straight fiber bundles with non-uniform porosity

The present study investigates the effects of non-uniformity in a bundle’s porosity by considering a model channel made up of “dense” (low porosity) and “loose” (high porosity) regions. In a first, simplified, approach these regions are treated as non-interacting porous media and previously obtained computational results are used for the Darcy permeability and the Sherwood number. In a second, and more complete, approach 3-D CFD simulations are conducted for a checkerboard arrangement of alternately “dense” and “loose” regions with square-arrayed fibers, accounting for entry effects and for interactions between regions. Non-uniformity causes a significant increase of the permeability and a strong reduction of the Sherwood number. These effects are larger, approaching those obtained for non-interacting regions, if the regions’ length scale is large. The attainment of fully developed conditions is greatly shifted forward in non-uniform bundles and the mass transfer development length may largely exceed the physical length of most hollow-fiber devices.

Mega‐Depressions on the Cocos Ridge: Links Between Volcanism, Faults, Hydrothermal Circulation, and Dissolution

AbstractHigh‐resolution bathymetry and three‐dimensional seismic data along the Cocos Ridge reveal a 245 km2 field of ∼1–4 km in diameter seafloor depressions. The seafloor depressions are part of a two‐tiered honeycomb pattern. The lower‐tier depressions have steep faults that truncate strata with chaotic internal reflections consistent with sediment collapse into the depression. These extend into a lens shaped interval just above igneous basement. Overlying these depressions is a second broader set with rough seafloor morphology with gently dipping boundaries defined by pinch‐out stratigraphic patterns. Drilling results indicate that the lens‐shaped zones that host the deeper depressions represent anomalous regions of high porosity, low velocity, and low density within calcareous rich sediment. Analysis of nannofossils from IODP Site U1414 suggests the collapse structures formed during the late Miocene, whereas the younger shallower depressions likely formed between the early Pliocene and the Pliocene‐Pleistocene boundary. Geochemical and petrological analysis at Site U1414 suggests that hydrothermal circulation during the late Miocene led to carbonate dissolution and collapse. Following collapse, focused fluid‐flow and bottom current scouring resulted in formation of the overlying set of depressions and a honeycomb seafloor morphology. Similar sets of depressions along the Carnegie Ridge to the south support the hypothesis that two‐tiered depressions formed in response to processes that occurred broadly across the Panama Basin between the late Miocene and the Pliocene‐Pleistocene transition. Geochemical results at Site U1414, combined with geophysical data, suggest this two‐tiered system of depressions currently guides ongoing fluid outflow.

Graphene oxide-reinforced thin shells for high-performance, lightweight cement composites

Lightweight cement composites have been proposed in the literature, fabricated by controlling the cement coating onto 3D-printed polymer scaffolds to form submillimeter thin-shell structures. In this study, we adopted graphene oxide (GO) to reinforce the thin-shell structures and modify the weak interface between polymer scaffold and cement paste to produce high-performance, lightweight cement composites. The results indicated the thickness of thin shells was maintained constant for different GO dosages by controlling the workability of cement paste. GO significantly reduced high-porosity regions between the cement matrix and polymer scaffold, along with the microstructure refinement of the cement matrix and promoted the formation of low-density calcium-silicate-hydrates (from 50% to up to 66%). The GO shows a much higher reinforcing efficiency than traditional bulk cement, where the composites' compressive strength and specific energy absorption were increased significantly by up to 91% and 78%, respectively, with 0.01 wt% dosage. Compared with traditional lightweight concrete, the compressive strength of the GO-reinforced composites was increased by up to 20-fold. This study promoted understanding of the reinforcing mechanism of GO in thin-shell structures and demonstrated the effectiveness of GO for enhancing the performance of novel lightweight cementitious composites with a wide range of applications for load-bearing, energy absorption, decoration, and thermal insulation.

Nanostructure of serpentinisation products: Importance for water transport and low-temperature alteration

The hydration of mantle rocks occurs at mid-ocean ridges, in subduction zones and in ophiolites where it strongly modifies the properties of the oceanic lithosphere. The nanostructure of the reaction products is poorly constrained, but it is very important, as it controls fluid transport during solid volume increase, and it influences phase reactivity during further fluid/rock interaction at low temperature. We image contacts between olivine and its hydration products at the nanoscale, in a dunite collected during the Oman Drilling Project that underwent nearly isochemical serpentinisation and solid volume increase. Olivine first reacts to form a ∼100 nm thick coating composed of a brucite/serpentine mixture, suggesting isochemical serpentinisation at this scale too. Lizardite columns ∼1 μm wide replace this mixture at its margin. The columns are embedded in a brucite-rich assemblage containing a high density of nanopores that may favour fluid transport during reaction. We interpret these observations as a nanometre-scale, two-step process. Fluid pathways are formed rather than clogged by reaction products thanks to mass transfer at a scale limited to less than 100 nm. The preservation of the fluid pathways during solid volume increase explains the observed high extents of reaction. The presence of brucite in high porosity regions may explain its preferential reaction during low temperature fluid/rock interaction.

Porosity detection and localization during composite cure inside an autoclave using ultrasonic inspection

Composite materials offer unique benefits in aerospace applications such as increased strength-to-weight ratio and improved fatigue properties. They are increasingly being used in major commercial aircraft programs. However, current processing methods can lead to defects in composite parts, which must be detected using post-manufacturing inspection methods. Porosity (i.e., pores, voids) is a critical defect from the cure process that is detrimental to performance of the composite part. It is therefore necessary to understand and eliminate the formation of porosity defects. At NASA Langley Research Center, an in-situ cure monitoring system was developed to detect porosity defects as they form in real-time inside an autoclave. A capability to directly detect and localize porosity within a composite during cure did not exist before.This study is focused on an elevated-temperature ultrasonic inspection system to detect porosity defects in composites during autoclave cure. The ultrasonic inspection system operated inside an autoclave within an enclosure cooled by intermittent liquid nitrogen (LN2) injections. A high-temperature, 2.25 MHz, transducer transmitted ultrasonic waves through the tool plate and into the composite part and measured the amplitude and time of flight of the reflected waves with a 1 mm × 1 mm step size/areal resolution. Porosity was observed via the ultrasonic reflections, which experienced increased attenuation in regions of high porosity. Distinct regions of increased porosity were present due to uneven pressure across the panel, which was driven by an intentional misfit between the flat caul plate and the tapered composite panel with ply drops. The results were validated by post-cure ultrasonic inspection and micrographs. The in-situ inspection system was able to successfully provide porosity detection and localization in the tapered ply-drop panel. The successful results indicate the promise of this system for future implementation in the manufacturing of composite structures for aerospace applications.

Silicic conduits as supersized tuffisites: Clastogenic influences on shifting eruption styles at Cordón Caulle volcano (Chile)

Understanding the processes that drive explosive-effusive transitions during large silicic eruptions is crucial to hazard mitigation. Conduit models usually treat magma ascent and degassing as a gradual, unidirectional progression from bubble nucleation through magmatic fragmentation. However, there is growing evidence for the importance of bi-directional clastogenic processes that sinter fragmented materials into coherent clastogenic magmas. Bombs that were ejected immediately before the first emergence of lava in the 2011–2012 eruption at Cordón Caulle volcano (Chile) are texturally heterogeneous composite assemblages of welded pyroclastic material. Although diverse in density and appearance, SEM and X-ray tomographic analysis show them all to have been formed by multi-generational viscous sintering of fine ash. Sintering created discrete clasts ranging from obsidian to pumice and formed a pervasive clast-supporting matrix that assembled these clasts into a conduit-sealing plug. An evaluation of sintering timescales reveals texturally disparate bomb components to represent only minutes of difference in residence time within the conduit. Permeability modelling indicates that the plug was an effective conduit seal, with outgassing potential—even from high-porosity regions—being limited by the inability of gas to flow across tendrils of densely sintered inter-clast matrix. Contrary to traditional perspectives, declining expressions of explosivity at the surface need not be preceded or accompanied by a decline in fragmentation efficiency. Instead, they result from tips in balance between the opposing processes of fragmentation and sintering that occur in countless cycles within volcanic conduits. These processes may be particularly enhanced at silicic fissure volcanoes, which have laterally extensive subsurface plumbing systems that require complex magma ascent pathways. The textures investigated here reveal the processes occurring within silicic fissures to be phenomenologically identical to those that have been inferred to occur in tuffisite veins: silicic conduits are essentially supersized examples of edifice-penetrating tuffisites.

Elemental Mapping of Entire Thick Film Electrodes By Laser-Induced Breakdown Spectroscopy

Next generation lithium-ion batteries require new research and development in the field of high energy / high power materials and concepts regarding cell design and electrode architectures. Particularly for automotive applications, the identification and control of degradation processes are main issues for maintaining long cell life-time and high safety standards. One promising approach for the visualization of elemental composition in lithium-based battery systems is the appliance of laser-induced breakdown spectroscopy (LIBS), which enables a rapid screening of materials, e.g., entire electrodes. So far, this diagnostic approach is being used for semi-quantitative investigation of battery components. However, at KIT, a full-quantitative analysis was developed for characterizing the lithium distribution and concentration as function of state-of-charge. From technical point of view, recording of three-dimensional (3D) elemental profiles, verification of material stoichiometry or even a quality controlled analysis during continuous roll-to-roll production can be easily performed under standard ambient conditions. In this work, we will focus on establishing LIBS for quantitative chemical mapping of entire electrodes after electrochemical cycling. Electrodes with variation in local porosity and tortuosity have been prepared by mechanical loading, while fs-laser radiation was applied for the development of 3D electrode architectures. First of all, on anode side, an increased tortuosity was realized by separator defects, consciously placed in coin cells during cell assembly. Simply saying, the separator sheet was blocked on selected regions in order to investigate post-mortem the possible emergence of local lithium plating. Secondly, compression molding was locally performed for studying lithium distribution in cathodes showing a sudden change in porosity. Two types of geometrical arrangements were applied for the formation of low and high porosity regions. Briefly, non-uniformities in porosity and tortuosity affect the electrochemical performance, especially at charging and discharging currents equal or above 1C. In an early stage of electrochemical cycling, a significant drop in specific capacity could be observed for both types of electrodes. Yielded from quantitative LIBS data, an enhanced local lithium concentration could be detected at the electrode surface, located in the neighborhood of separator defects (for anodes) and at the interface between low and high porosity regions (for cathodes). In contrast, fs-laser generated micro-pillars provide new pathways for Li+-ions, leading to a tremendous boost in diffusion kinetics. Thus, an enhanced specific capacity was observed for cells with laser-structured electrodes during high power conditions. Chemically proven by LIBS, a slight enrichment of intercalated lithium could be detected along the contour of each laser-generated micro-pillar, which indicates that laser-structuring can fulfill the requirements for next generation batteries, providing both, a contemporaneous high energy- and power density on battery-level. In summary, a full screening of entire electrodes achieved from post-mortem LIBS studies will be presented, based on influencing factors such as porosity, tortuosity, and laser-assisted surface modification.

In Situ Investigation of Chemomechanical Effects in Thiophosphate Solid Electrolytes

Summary Solid-state batteries can suffer from catastrophic failure at high current densities due to solid electrolyte fracture, interface decomposition, or lithium filament growth. Failure is linked to chemomechanical material transformations that can manifest during electrochemical cycling. We systematically investigate how solid electrolyte microstructure and interfacial decomposition (e.g., interphase) affect failure mechanisms in lithium thiophosphates (Li3PS4, LPS) electrolytes. Kinetically metastable interphases are engineered with iodine doping, and microstructural control is achieved using milling and annealing processing techniques. In situ transmission electron microscopy reveals iodine diffusion to the interphase, and upon electrochemical cycling, pores are formed in the interphase region. In situ synchrotron tomography reveals that interphase pore formation drives edge fracture events, which are the origin of through-plane fracture failure. Fractures in thiophosphate electrolytes actively grow toward regions of higher porosity and are affected by heterogeneity in microstructure (e.g., porosity factor). This work provides fundamental design guidelines for high-performance solid-state batteries.

Predicting final stage sintering grain growth affected by porosity

Grain growth has a definitive impact on the quality of transparent sintered materials in areas such as ballistics, biomaterials, jewelry, etc. Controlling the sintering trajectory at the precise moment of final stage sintering is one of the main sintering challenges for obtaining high-performance, fully-dense nano-ceramics. However, the final stage of sintering involves a very complex coupling between the rate of porosity elimination/grain growth and transition mechanisms. This complexity makes predicting the sintering trajectory very difficult, and most transparent material production escapes this problem by using expensive high-pressure methods such as hot isostatic pressing (HIP). In the quest for a pressureless transparent material process, this paper addresses the challenge of predicting grain growth in the transition domain from the grain growth onset (in a high porosity region) to full density for MgAl2O4 spinel. We present a comprehensive modeling approach linking theoretical models such as Zhao & Harmer's and Olevsky's equations to accurately predict the complex grain growth transition region of final stage sintering. This modeling approach opens up the possibility for numerical exploration of microstructure development via underlying kinetics experimental identification.

Radial Variations in Axial Velocity Affect Supercritical CO2 Extraction of Lipids from Pre-pressed Oilseeds

Packed beds of spherical particles in a cylindrical vessel have a high porosity region next to the vessel wall that allows preferential fluid flow. Consequently, there are radial variations in porosity (e) and superficial fluid velocity (U) that depend on the vessel-to-particle diameter ratio (D/dp) and the flow regime of the fluid. This work ascertained if these radial variations affected SuperCritical (SC) CO2 extraction curves of oil from pre-pressed seeds at 40 °C and 28 MPa, as compared with the commonly adopted plug flow condition. It focused specifically on comparing extraction curves as a function of the controlling mass transfer mechanism (characterized by the dimensionless Biot number, Bi) and D/dp ratio. A predictive model was adopted to describe the SC-CO2 extraction of oil from sheared seeds comparing plug flow with radial variations in superficial CO2 velocity, U(r), from literature correlations. Selected independent variables included the initial oil content of the substrate (132.7 ≤ Co ≤ 397.2 g/kg), dp (1 or 2 mm), U (1–4 mm/s), and vessel volume (0.038–495 L). Co markedly affected the effective diffusivity of the oil (0.780 ≤ De ≤ 6.24 × 10−10 m2/s), whereas dp and U moderately affected the film mass transfer coefficient (2.44 ≤ kf ≤ 7.40 × 10−5 m/s). Radial variations in superficial CO2 velocity decreased extraction rates, with differences between extraction curves when considering plug flow or adopting U(r) diminishing as Bi increased for D/dp = 20, or as D/dp increased for Bi = 18. Bi increased by increasing U and kf, or decreasing Co and De, whereas D/dp increased by increasing vessel volume. The radial variations in porosity in a packed bed and associated changes in superficial CO2 velocity may have a more pronounced negative impact in laboratory or pilot plant extraction vessels (small D) than industrial vessels (large D), mainly when extracting small particles and applying large superficial CO2 velocities. A proxy for the SC-CO2 extraction of oil from pre-pressed seeds in an industrial extraction vessel (495-L capacity, D/dp = 270) would be plug flow using the porosity, and superficial CO2 velocity predicted for the axis of the extraction vessel (eo and Uo, respectively). Literature correlations predict a value of eo slightly less than e, and value of Uo slightly less than U. The remainder of the CO2 bypassing the vessel along a high porosity region near the vessel wall, containing a small fraction of the loaded substrate.

Using PC clinker as aggregate-enhancing concrete properties by improving ITZ microstructure

The interfacial transition zone (ITZ) in a concrete microstructure is a region of high porosity and low binding materials at the interface of cement paste and aggregate that causes significant reduction in compressive and flexural strengths and considerable increase in permeability of the concrete. Extensive research activities have been devoted to reduction of the ITZ, to avoid its negative effects on concrete properties. This research introduces reactive aggregate concrete (RAC), formed by partial replacement of natural aggregate with Portland cement (PC) clinker of the same size as a reactive aggregate in the concrete mix to reduce the ITZ and improve the concrete properties. After determining the optimum replacement level based on 28 and 60 d compressive strengths, the developed RAC was characterised by measuring its workability, setting time, compressive and flexural strengths, for varying age, water absorption, open-pore volume and chloride penetration depth. Microstructural studies of the ITZ were also performed using scanning electron microscopy. In all measurements, normal concrete was also considered for comparison purposes. The results confirm 121% and 33% enhancement in 7 and 90 d compressive strengths accompanied with 53, 19 and 22·4% reductions in 28 d chloride penetration depth, open-pore volume and water absorption, respectively.

An integrated approach for carbonate reservoir characterization: a case study from the Linguado Field, Campos Basin

Abstract The main reservoirs in the Linguado Field are grainstone and packstone carbonates composed of oolites, oncolites, pelloids, and rare bioclasts, of the Quissama Formation (Albian-age) and coquinas of the Coqueiros Formation (Aptian-age). Within Quissama Formation, facies have high porosity variations and their 3D characterization is of utter importance to allow for a better location of the wells. The objective of this study was a volumetric characterization of Quissama Formation by means of an adapted classical workflow composed of well-seismic tie, seismic preconditioning, seismic interpretation, seismic inversion, petrophysical properties estimation, and porosity geostatistical modeling. Seismic inversion results allowed the interpretation of a horizon to separate the carbonate platform in an upper zone, with low acoustic impedance, from a lower zone, with high acoustic impedance. Finally, behavioral knowledge of acoustic impedance and the porosity distribution within the Albian carbonate platform helped to better characterize the distribution of carbonaceous facies allowing the confirmation that commercial wells were drilled in low acoustic impedance and high porosity regions. It was also possible to confirm that a well, declared as noncommercial, was drilled in a poor reservoir region with high acoustic impedance and low porosity and identified other locations that were not yet drilled but could represent potential targets.