Bulk Permeability Research Articles

Numerical investigation on the sensitivity of endplate design and gas diffusion material models in quantifying localized interface and bulk electrical resistance

A localized non-intuitive relationship between electrical interface contact resistance and bulk properties such as bulk electrical resistance and permeability in the fuel cell gas diffusion layer (GDL) is reported. A numerical method is adopted to investigate contact pressure and hence the interface contact resistance at the interfaces of bipolar plate (BPP)|GDL and GDL|Polymer electrolyte membrane (PEM). The results are observed to be sensitive to GDL material models as well as endplate designs. This means, endplates designed to improve the electrical contact resistance or contact pressure at the BPP|GDL interface may not necessarily assure an improvement in bulk properties, in fact, it is observed in this study that these properties are inversely related. Further, a differential deformation in GDL along with consolidation effect is predicted with compressible version of hyperelastic material model. More importantly, it is revealed that the selection of material models plays a significant role in the deformation behaviour of the GDLs irrespective of the clamping design adopted.

Understanding the permeability of burrow-related gas reservoirs through integrated laboratory techniques

This study integrates results from petrographic investigations, spot permeability measurements, computed tomography (CT) scans, and core water flooding experiments to investigate the potential correlation between the spot permeability and the bulk permeability of burrow-related reservoirs. These results are obtained from samples collected from Thalassinoides-bearing strata of the upper Jurassic Hanifa Formation, central Saudi Arabia, and provide insights to select the appropriate permeability values that represent the bulk permeability of burrow-related reservoirs. The petrographic results show a mud-dominated matrix with isolated moldic pores and grain-dominated Thalassinoides passive fills with substantial interparticle pores and minor moldic and interskeletal pores. The spot permeability of the passive fills of the Thalassinoides network ranges from 6 mD to 628 mD, whereas the spot permeability of the matrix surrounding the Thalassinoides network ranges from 0.1 mD to 5 mD. These results indicate that the passive fills of the Thalassinoides network, which is fully represented in the CT scans of the 9.75-cm diameter core, are substantially permeable compared to the tight matrix, and suggest a dual-porosity system in the studied strata. The bulk permeabilities estimated from the harmonic, arithmetic, and geometric means vary considerably (0.7 mD, 28.9 mD, and 1.8 mD, respectively). The CT scan observations of the investigated core suggest a low to moderate bioturbation intensity (mean = 15.8% ± 6.2%), while the core water flooding results suggest that the bulk permeability of the core is 17.3 mD. Previous research has indicated that harmonic and geometric means should be considered the best estimates for bulk permeability at low bioturbation intensities in Thalassinoides-related reservoirs. Nevertheless, the core water flooding results are close to the arithmetic mean, indicating that after establishing burrow connectivity, the fluid flow behavior is similar to that in a continuous parallel permeability domain, irrespective of bioturbation intensity. Therefore, this study suggests that the burrow connectivity should be considered in bulk permeability estimation when linking such estimation to bioturbation intensity.

Laboratory assessment on factors controlling the acoustic properties of carbonates: A case study from Bombay offshore

Carbonates are known to have a heterogeneous, complicated pore structure, characterized by textural variations. This complex nature of carbonates makes it challenging to establish correlations to interpret petrophysical properties from acoustic properties. The present study focuses on investigating various parameters that influence carbonates by integrating parameters estimated from laboratory based measurements along with digital image analysis (DIA) technique, to capture the heterogeneity in pore architecture. A generalized rock physics model for carbonates of Bombay offshore basin has been developed based on compressional wave velocity (Vp) measured at laboratory conditions using ultrasonic measurement techniques. Our study maximizes the use of information obtained from the laboratory analysis that is usually constrained by accurate geological details. For this purpose, we measured Vp of carbonate core plugs using transducers of 54 kHz frequency by utilizing the through transmission technique. The parameters investigated at the laboratory include bulk density, porosity, permeability, mineral content, pore size and pore aspect ratio. Statistical analysis was performed using single as well as multiple parameter function. Mineral content was correlated with Vp and porosity. Bulk Density and porosity showed greater correlation with Vp as single parameter function while pore size showed poor correlation. A combination of bulk density, porosity and mode pore size was able to explain more than 83% of the deviation of Vp. It was observed that the predictability of Vp increases when it is modeled as a multi-parameter function of bulk density, porosity and pore size. The effectiveness of the velocity model improved when Vp was modeled as a function of these investigated parameters collectively rather than in isolation. Thus, an integrated study such as multi-regression analysis would help to present a more realistic picture that affect the relations between petrophysical, mineralogical and acoustic properties. Furthermore, while considering different saturation conditions, our study suggest that porosity and mineral composition have an effect on Vp, while effect of porosity is more prominent. We observed approximate 50% decrease in Vp values when porosity varied from 2 to 40% for different saturation conditions. Hence, the results potentially allow the interpretation of different petrophysical properties from acoustic data and thereby help in connecting geology and seismology.

Petrophysical and mechanical rock property database of the Los Humeros and Acoculco geothermal fields (Mexico)

Abstract. Petrophysical and mechanical rock properties are key parameters for the characterization of the deep subsurface in different disciplines such as geothermal heat extraction, petroleum reservoir engineering or mining. They are commonly used for the interpretation of geophysical data and the parameterization of numerical models and thus are the basis for economic reservoir assessment. However, detailed information regarding petrophysical and mechanical rock properties for each relevant target horizon is often scarce, inconsistent or distributed over multiple publications. Therefore, subsurface models are often populated with generalized or assumed values resulting in high uncertainties. Furthermore, diagenetic, metamorphic and hydrothermal processes significantly affect the physiochemical and mechanical properties often leading to high geological variability. A sound understanding of the controlling factors is needed to identify statistical and causal relationships between the properties as a basis for a profound reservoir assessment and modeling. Within the scope of the GEMex project (EU H2020, grant agreement no. 727550), which aims to develop new transferable exploration and exploitation approaches for enhanced and super-hot unconventional geothermal systems, a new workflow was applied to overcome the gap of knowledge of the reservoir properties. Two caldera complexes located in the northeastern Trans-Mexican Volcanic Belt – the Acoculco and Los Humeros caldera – were selected as demonstration sites. The workflow starts with outcrop analog and reservoir core sample studies in order to define and characterize the properties of all key units from the basement to the cap rock as well as their mineralogy and geochemistry. This allows the identification of geological heterogeneities on different scales (outcrop analysis, representative rock samples, thin sections and chemical analysis) enabling a profound reservoir property prediction. More than 300 rock samples were taken from representative outcrops inside the Los Humeros and Acoculco calderas and the surrounding areas and from exhumed “fossil systems” in Las Minas and Zacatlán. Additionally, 66 core samples from 16 wells of the Los Humeros geothermal field and 8 core samples from well EAC1 of the Acoculco geothermal field were collected. Samples were analyzed for particle and bulk density, porosity, permeability, thermal conductivity, thermal diffusivity, and heat capacity, as well as ultrasonic wave velocities, magnetic susceptibility and electric resistivity. Afterwards, destructive rock mechanical tests (point load tests, uniaxial and triaxial tests) were conducted to determine tensile strength, uniaxial compressive strength, Young's modulus, Poisson's ratio, the bulk modulus, the shear modulus, fracture toughness, cohesion and the friction angle. In addition, X-ray diffraction (XRD) and X-ray fluorescence (XRF) analyses were performed on 137 samples to provide information about the mineral assemblage, bulk geochemistry and the intensity of hydrothermal alteration. An extensive rock property database was created (Weydt et al., 2020; https://doi.org/10.25534/tudatalib-201.10), comprising 34 parameters determined on more than 2160 plugs. More than 31 000 data entries were compiled covering volcanic, sedimentary, metamorphic and igneous rocks from different ages (Jurassic to Holocene), thus facilitating a wide field of applications regarding resource assessment, modeling and statistical analyses.

Geomechanical and flow implications with continued bioconversion of coal to methane: Experiments and modeling

Microbial conversion of coal to methane is a promising technology during transition of coal-based energy from conventional coal mining to natural gas recovery from coal. Significant research advances have been made towards engineering ideal microbial communities and nutrients for bio-stimulation of coal. However, actual field applications require geomechanical and flow behavior characterization of coal during the bioconversion process as well as gas production over the life of the created “biogenic gas reservoirs”. This study presents the results of an experimental investigation to estimate gas/methane production using bioconversion of coal and analyses of variations in bulk modulus, strain and permeability. Bulk modulus of coal demonstrated time-dependent behavior with continued bioconversion of solid coal. The phenomenon was modeled using mass balancing in a closed environment and the logistic equation based biogenic gas production with time. The modeled gas production and changes in modulus of coal showed excellent agreement with the corresponding experimental results. Next, numerical simulation of biogenic conversion of coal in a constant stress in-situ condition, replicating the Huff ‘n Puff method under field conditions, was carried out. The results showed that bioconversion can lead to decrease in effective stress, increase in permeability and decrease in the modulus of coal with time. Repeated recharge of coal with nutrients and recovering the produced gas, that is, sequential cycles of Huff n’ Puff, showed further increase in permeability and decrease in coal strength, potentially leading to coal failure in-situ, further increasing the permeability, thus enhancing the prospect of field application of the technology.

Tutorial: Maximizing Value From Mudlogs–Integrated Approach to Determine Net Pay

In the current business environment, operators are increasingly striving to reduce logging expenses when possible while maintaining safety of the drilling operations. Mudlogging has been remarkably successful through the oil industry downturn due to the value of information derived from the analysis as well as the relatively low cost. Information about the lithology and fluid content of the borehole during drilling is important for drilling optimization and qualitative petrophysical assessment. This tutorial takes mudlogs a step further to quantify net pay and estimate reserves in low-permeability reservoirs where traditional log analysis is challenging. Methods will be described for estimating gas-in-mud based on characterized gas measurement systems and obtaining bulk volume of gas per volume of rock drilled. Corrections are discussed for mud gas systems based on their mechanical operating parameters of mud flow into the gas extractor, gas sample suction rate out of the gas extractor, recirculated gas, and estimated gas extraction efficiencies. Applying these corrections yields normalized bulk gas volume and gas-oil ratio (GOR), which is calibrated with the petrophysical assessment from wireline logs and PVT samples. Finally, correlations between bulk hydrocarbon volume and permeability are used to estimate volumetrics. Case studies presented show that the calibrated mudlogs can be used for quantitative assessment of bulk volume of hydrocarbons in high-angle/horizontal wells where conveying wireline logs might be challenging. Pay flags computed from the mudlog interpretation can be used to guide completion decisions. Additionally, GOR estimates derived from mudlogs can be used for fluid typing and optimizing the fluid sampling program in deepwater development wells. Results presented clearly show that mudlogs can provide continuous, real-time, and quantitative petrophysical assessments.

The effects of reed fly ash modified bitumen on the volumetric and mechanical properties of open grade friction course mixtures

The global use of open grade friction course (OGFC) asphalt pavements began in 1950, though this practice has gained further interest over time, especially for high-speed high-volume roads, due to the material’s excellent characteristics in terms of skid resistance, drainage control, and noise reduction. Unfortunately, the porous structure of this type of mixture results in other problems related to mechanical and durability properties, despite extensive studies being conducted to overcome such problems using virgin modifiers such as polymers or fibres. Recently, the concept of using recycled and by-product materials as stabilising additives for asphalt binders and mixtures has became more popular, both in order to reduce the construction costs and to increase pavement service life, as well as preserving natural resources and reducing the environmental impact of construction. This study investigates the effect of using one such by-product material, reed fly ash (RFA), as a modifier for asphalt binder and to examine the performance of the resulting OGFC asphalt mixture. The effect of RFA on the OGFC mixture performance is examined in terms of volumetric (bulk density, air voids, porosity and permeability) and mechanical (indirect tensile strength (ITS), skid resistance, and Cantabro abrasion loss (CL)) properties. The results indicate that adding RFA to asphalt binder has a positive influence on mixture performance. In terms of volumetric measures, it leads to increases in air voids, porosity, and permeability of about 17%, 37%, and 102%, respectively at 18% RFA, while the bulk density is reduced as RFA dosage increases. Simultaneously, mechanical properties are increased, with ITS and skid resistance increased by about 10% and >25%; respectively at 18% RFA. However, the resistance to abrasion was enhanced only at lower dosages of RFA (6% RFA), by about 36%. Nevertheless, the use of RFA at optimal percentages appears to offer a sustainable approach to stabilising asphalt binder for OGFC mixtures.

Local Weather Conditions Create Structural Differences between Shallow Firn Columns at Summit, Greenland and WAIS Divide, Antarctica

Understanding how physical characteristics of polar firn vary with depth assists in interpreting paleoclimate records and predicting meltwater infiltration and storage in the firn column. Spatial heterogeneities in firn structure arise from variable surface climate conditions that create differences in firn grain growth and packing arrangements. Commonly, estimates of how these properties change with depth are made by modeling profiles using long-term estimates of air temperature and accumulation rate. Here, we compare surface meteorology and firn density and permeability in the depth range of 3.5–11 m of the firn column from cores collected at Summit, Greenland and WAIS Divide, Antarctica, two sites with the same average accumulation rate and mean annual air temperature. We show that firn at WAIS Divide is consistently denser than firn at Summit. However, the difference in bulk permeability of the two profiles is less statistically significant. We argue that differences in local weather conditions, such as mean summer temperatures, daily temperature variations, and yearly wind speeds, create the density discrepancies. Our results are consistent with previous results showing density is not a good indicator of firn permeability within the shallow firn column. Future modeling efforts should account for these weather variables when estimating firn structure with depth.

Potential overlooked bioturbated reservoir zones in the shallow marine strata of the Hanifa Formation in central Saudi Arabia

A comprehensive study including sedimentological, ichnological, petrographic and petrophysical investigations and geostatistical modeling of the late Kimmeridgian bioturbated strata of the upper Hanifa Formation suggests that the grain-dominated burrow fills of these strata enhance the stratum porosity and permeability by creating permeable pathways in the otherwise tight mud-dominated unit. The bioturbation patterns in these strata reveal a boxwork pattern organized as a horizontal network and vertical shafts. These shafts exhibit circular to elliptical cross-sections with the long axis ranging from 0.39 to 1.65 cm that intersects at angles of 60°, 90°, and 120°. This pattern suggests the domination of Thalassinoides ichnotaxa in the studied strata. The Thalassinoides, with a bioturbation intensity ranging from 10% to 40%, contain passive fills that are characterized by coarse-grained (the majority of the grain sizes is > 0.5 mm) carbonates with a packstone texture consisting of skeletal, coated and peloidal grains. These passive fills have a porosity (a mean (μ) of 7% ± 2%) and permeability (μ of 82 ± 98 mD) substantially higher than the matrix porosity (μ of 1.5% ± 0.5%) and permeability (μ of 0.6 ± 0.6 mD). Multipoint statistics (MPS) models suggest that the Thalassinoides in these strata generated connected porous and permeable pathways even at a low bioturbation intensity (~10%). The MPS models also indicate that the bulk permeability of these strata increases with the bioturbation intensity and reaching up to 204 mD for models with a 40% bioturbation intensity. The similarity of these results to those published for well-studied ichnofossil-hosted tight gas reservoirs suggests that the mud-dominated units of the upper Hanifa Formation could form potential flow zones. Interestingly, however, these strata are overlooked as subsurface reservoirs, probably because of the limitations of downhole logging tools and the lack of integrated, comprehensive investigations. This study provides an illustrative example of shallow marine strata in which mud-dominated sediments could be flow units because of the impact of burrows. Hence, understanding the bioturbation trends in these strata could be beneficial for the prediction of the reservoir quality of similar strata elsewhere.

Investigations on the suitability of banana peel powder as an alternative additive in synthetic green sand moulding system

ABSTRACT An experimental study focused on the determination of mechanical properties of synthetic green sand system using Nagavali river sand by adding banana peel powder as an additive. Compression strength, shear strength, mould hardness bulk density and permeability are the various properties found in the laboratory following standard testing procedures. Sand aggregate is prepared by mixing the bentonite as binder and banana peel powder as an additive to the silica sand in various amounts. Encouraging results in terms of strength and hardness are obtained by testing the standard sand samples. In fact, the properties exhibited are almost similar to the values obtained by addition of 2% dextrin as an additive to the sand aggregate. Since the banana peel powder can be easily prepared which is most economical in terms of cost compared with dextrin, that can be an alternative additive in preparing the sand moulds to obtain adequate strength and hardness.

The Effect of Mineral Dissolution on the Effective Stress Law for Permeability in a Tight Sandstone

AbstractWe present flow‐through experiments to delineate the processes involved in permeability changes driven by effective stress variations and mineral cement dissolution in porous rocks. CO2‐enriched brine is injected continuously into a tight sandstone under in situ reservoir conditions for 455 hrs. Due to the dolomite cement dissolution, the bulk permeability of the sandstone specimen significantly increases, and two dissolution passages are identified near the fluid inlet by X‐ray CT imaging. Prereaction and postreaction examinations of the effective stress law for permeability suggest that after reaction, the bulk permeability is more sensitive to pore pressure changes and less sensitive to effective stress changes. These observations are corroborated by Scanning Electron Microscopy and X‐ray CT observations. This study deepens our understanding of the effect of mineral dissolution on the effective stress law for permeability, with implications for characterizing subsurface mass and energy transport, particularly during fluid injection/production into/from geologic reservoirs.

Evaluation of water repellency in bentonite filled polypropylene composites via physical and mechanical methods

With the advent of polymeric materials having dimensional stability, outdoor applications for polymer composites are increasing expeditiously. The employment of durable material in wet environments is the most effective means of water repellency. Silane modification was applied to bentonite clay for the donation of hydrophobicity on its surface. Surface functionalities of powder surfaces were confirmed by FTIR-ATR spectroscopy and SEM techniques. Polypropylene composities involving pristine and modified bentonite powders were produced in bulk and film forms at three different loading ratios. Water permeability of bulk and film samples was evaluated via water absorption test. In addition to water uptake values, optical microscopy was utilized in order to visualize the structural deterioration of composite samples after water immersion. Mechanical behaviours of composite materials before and after water absorption test were reported in order to analyze the effect of water aging. Based on the findings, in-depth discussions were performed by comparison with basic models postulated regarding migration of water molecules into polymer structure.

A new modification of nanocomposite membrane permeation models: Consideration of sorption effects

Permeation models were modified to determine the permeability of C3H8, CH4 and H2 gases through the silica/PDMS nanocomposite membrane accurately. The average absolute relative error (AARE %) of permeation models is about 10–15% for low-sorbing gases of CH4 and H2 and approximately 30% for high-sorbing gas of C3H8. Furthermore, the gas solubility around the nanoparticles in the polymeric matrix is more than in the polymeric bulk due to sorption effects around the nanoparticles. Therefore, a new interface region is assumed to consider the sorption effects as a function of nanoparticle volume fraction and polymeric bulk permeability in the permeation models by genetic algorithm. It was found that the best-modified model for C3H8 and H2 is Lewis–Nielsen and for CH4 is Bruggeman. Finally, the AARE values were obtained less than 5% for C3H8 and less than 2% for CH4 and H2 that were in a good agreement with experimental data.

Fracture-Induced Permeability in Whitby Mudstone.

Shale host rock and containment potential are largely determined by the connected pore network in the rock, and the connection between the pore network and the naturally present or mechanically induced fracture network together determines the total bulk permeability. Pore connectivity in shales is poorly understood because most of the porosity is present in sub-micrometer-sized pores that are connected through nanometer-sized pore throats. We have used a number of different techniques to investigate the microstructure and permeability of Early Jurassic shales from the UK (Whitby Mudstone), under intact and fractured conditions. Whitby Mudstone is a clay matrix-rich rock (50–70%), with different mineralogical layers on the sub-millimeter scale and very low natural permeability (10–19 to 10–22 m2), representative of many gas shales and caprocks present in Europe. Artificial fracturing of this shale increases its permeability by 2–5 orders of magnitude at low confining pressure (5 MPa). At high confining pressures (30 MPa), permeability changes were more sensitive to the measuring direction with respect to the bedding orientation. Given the distinct lack of well-defined damage zones, most of the permeability increase is controlled by fracture permeability, which is sensitive to the coupled hydro-chemo-mechanical response of the fractures to fluids.

Lattice-Boltzmann computation of hydraulic pore-to-pore conductance in packed beds of uniform spheres

This paper presents a study on pore conductance in packed beds of uniform spheres. Fluid flow through the packed beds is simulated by a parallel Lattice-Boltzmann (LB) model. To facilitate a pore-level analysis, the void spaces within beds are divided into interconnected pore elements, and the flow fields in each pore element are reconstructed from the LB-simulated results. By this way, the flow structures are effectively identified in pores regardless of their complicated shapes. The reconstructed pore-flow data are employed to determine the hydraulic pore-to-pore conductance, which is used in pore network model to calculate bulk permeability. Results show that as bed porosity increases, the hydraulic pore-to-pore conductance presents a transition from one-peak distribution to wide distribution. Furthermore, a new model based on the LB reconstructed pore radius is proposed, which provides predictions of permeability much closer to the Carman-Kozeny predictions compared to the previous literature predictions based on the use of hydraulic and equivalent radii and/or geometric correction functions employed in the Hagen-Poiseuille expression for fluid flow in cylindrical tubes.

Interactive roles of geometrical distribution and geomechanical deformation of fracture networks in fluid flow through fractured geological media

In this study, the combined effects of geometrical distribution and geomechanical deformation of fracture networks on fluid flow through fractured geological media are investigated numerically. We consider a finite-sized model domain in which the geometry of fracture systems follows a power-law length scaling. The geomechanical response of the fractured rock is simulated using a hybrid finite-discrete element model, which can capture the deformation of intact rocks, the interaction of matrix blocks, the displacement of discrete fractures and the propagation of new cracks. Under far-field stress loading, the locally variable stress distribution in the fractured rock leads to a stress-dependent variable aperture field controlled by compression-induced closure and shear-induced dilatancy of rough fractures. The equivalent permeability of the deformed fractured rock is calculated by solving for the fracture-matrix flow considering the cubic relationship between fracture aperture and flow rate at each local fracture segment. We report that the geometrical connectivity of fracture networks plays a critical role in the hydromechanical processes in fractured rocks. A well-connected fracture system under a high stress ratio condition exhibits intense frictional sliding and large fracture dilation/opening, leading to greater rock mass permeability. However, a disconnected fracture network accommodates much less fracture shearing and opening, and has much lower bulk permeability. We further propose an analytical solution for the relationship between the equivalent permeability of fractured rocks and the connectivity metric (i.e. percolation parameter) of fracture networks, which yields an excellent match to the numerical results. We infer that fluid flow through a well-connected system is governed by traversing channels (forming an “in parallel” architecture) and thus equivalent permeability is sensitive to stress loading (due to stress-dependent fracture permeability), whilst fluid flow through a disconnected system is more ruled by matrix (linking isolated clusters “in series”) and has much less stress dependency.

Magmatic and tectonic segmentation of the intermediate-spreading Costa Rica Rift—a fine balance between magma supply rate, faulting and hydrothermal circulation

SUMMARY 3-D tomographic modelling of wide-angle seismic data, recorded at the intermediate-spreading Costa Rica Rift, has revealed a P-wave seismic velocity anomaly low located beneath a small overlapping spreading centre that forms a non-transform discontinuity at the ridge axis. This low velocity zone displays a maximum velocity anomaly relative to the ‘background’ ridge axis crustal structure of ∼0.5 km s−1, has lateral dimensions of ∼10 × 5 km, and extends to depths ≥2.5 km below the seabed, placing it within layer 2 of the oceanic crust. We interpret these observations as representing increased fracturing under enhanced tectonic stress associated with the opening of the overlapping spreading centre, that results in higher upper crustal bulk porosity and permeability. Evidence for ongoing magmatic accretion at the Costa Rica Rift ridge axis takes the form of an axial magma lens beneath the western ridge segment, and observations of hydrothermal plume activity and microearthquakes support the presence of an active fluid circulation system. We propose that fracture pathways associated with the low velocity zone may provide the system through which hydrothermal fluids circulate. These fluids cause rapid cooling of the adjacent ridge axis and any magma accumulations which may be present. The Costa Rica Rift exists at a tipping point between episodic phases of magmatic and tectonically enhanced spreading. The characteristics inherited from each spreading mode have been preserved in the crustal morphology off-axis for the past 7 Myr. Using potential field data, we contextualize our seismic observations of the axial ridge structure at the whole segment scale, and find that the proposed balance between magmatic and tectonically dominated spreading processes observed off-axis may also be apparent along-axis, and that the current larger-scale magma supply system at the Costa Rica Rift may be relatively weak. Based on all available geophysical observations, we suggest a model for the inter-relationships between magmatism, faulting and fluid circulation at the Costa Rica Rift across a range of scales, which may also be influenced by large lithosphere scale structural and/or thermal heterogeneity.

Multidisciplinary database of permeability of fault zones and surrounding protolith rocks at world-wide sites

Brittle faults and fault zones are important fluid flow conduits through the upper part of Earth’s crust that are involved in many well-known phenomena (e.g. earthquakes, thermal water and gas transport, or water leakage to underground tunnels). The permeability property, or the ability of porous materials to conduct water and gas, is one of the key parameters required in understanding and predicting fluid flow. Although close to a thousand studies have been done, and permeability tested in parts of fault zones, a sytematic summary and database is lacking. This data descriptor is for a multi-disciplinary world-wide compilation and review of bulk and matrix permeability of fault zones: 410 datasets, 521 reviewed sites, 379 locations, >10000 publications searched. The review covers studies of faulting processes, geothermal engineering, radioactive waste repositories, groundwater resources, petroleum reservoirs, and underground engineering projects. The objectives are to stimulate the cross-disciplinary data sharing and communication about fault zone hydrogeology, document the biases and strategies for testing of fault zones, and provide the basic statistics of permeability values for models that require these parameters.

One-dimensional stacking miniaturized low-frequency metamaterial bulk for near-field applications

Metamaterials (MTMs) are very promising in engineering applications because they can be used to easily manipulate the spatial and temporal distributions of electromagnetic fields and waves. Nevertheless, studies on MTMs have been directed primarily toward high-frequency electromagnetics and optics. Consequently, the development and applications for MTMs in low-frequency electromagnetics still face some bottleneck problems and challenges. For example, deteriorated resonance strength and large unit dimensions are inevitable for low-frequency MTM unit cells. Moreover, the existing analytical, computational, and experimental methodologies for MTMs are not applicable for low-frequency cases. To address these problems, one-dimensional compact stacking miniaturized MTM bulk in the kHz frequency band, which is the lowest resonance frequency for passive MTMs reported to date in the literature, is proposed and fabricated. This work develops a miniaturized and high performance low-frequency MTM unit cell using a unit topology that consists of two spiral structures connected with a via and a lumped chip capacitor. A numerical model is proposed for performance simulations of the MTM unit cell, and a quality factor equivalence-based method is introduced. An experimental–numerical methodology is developed to extract the complex permeability of the MTM bulk. Comprehensive numerical computations and experimental studies significantly impact the investigation of the extraordinary performance of MTM-based near-field electromagnetic devices. Both numerical and experimental results have confirmed the feasibility and applicability of the presented work, which reveals the extraordinary physical properties of novel MTM-based electromagnetic devices.

Fabrication and performance of SiO2–based electromagnetic wave penetrating foamed ceramics with dense surface

SiO2–based foamed ceramics with good comprehensive performance of electromagnetic wave penetration, thermal insulation and water resistance were fabricated from a powder mixture including quartz, calcium carbonate, talc and Si3N4 by a direct foaming method. The sintering temperature and the Si3N4 content in the mixture are two key factors affecting the microstructure, phase composition and performance of the foamed ceramics. Owing to its porous internal structure with high total porosity of 89% and dense surface with few small pores, the foamed ceramic fabricated by sintering at 1200 °C from the mixture containing 18 wt% Si3N4, which shows a bulk density, permittivity and permeability as low as 0.31 g/cm3, 2.16+j0.007 and 1+j0 respectively, closed porosity as high as 87%, and relatively high compressive strength of 6.1 MPa, is an excellent electromagnetic wave penetrating material possessing good performance of thermal insulation and water resistance.