Variable Porosity Research Articles

Microwave dielectric properties, Raman spectra and sintering behavior of novel low loss La7Nb3W4O30 ceramics with rhombohedral structure

This study introduced a novel low-loss tungstate ceramic, La7Nb3W4O30 (LNWO), synthesized using the solid-state techniques. The structural analysis of the La7Nb3W4O30 ceramic material, utilizing X-ray diffraction (XRD) patterns and followed by detailed structural refinement, validated its rhombohedral structure. Transmission electron microscopy (TEM) was utilized to confirm the ordered layer arrangement characteristic of the rhombohedral structure. The internal structure was characterized by scanning electron microscopy (SEM), with the sample's relative density reaching 97.5 %. The correlation between the full width at half maximum (FWHM) of the Raman matrix at 901 cm−1 corresponding to the symmetric bending mode vibrations of WO5 and the Q × f value was discussed. Furthermore, the main factors affecting the dielectric constant, including density, bond valence, secondary phases, and variations in porosity, were analyzed. Encouragingly, the ceramic showed significant microwave dielectric properties when it was sintered at 1425 °C (εr = 23.68, Q × f = 26,687 GHz (f = 7.2 GHz), τf = −35.2 ppm/°C).

Mesoscopic investigation of the matrix pores and ITZ effects on the mechanical properties of seawater sea-sand coral aggregate concrete

In this study, the matrix pores and ITZ effects on the mechanical properties of seawater sea-sand coral aggregate concrete (SSCAC) were investigated via the meso-element equivalent method. The effective modulus and strength of aggregate and matrix in SSCAC at different scale level were derived via the Voigt model and Mori-Tanaka method. A three-step equivalence process was established to consider the influence of the matrix pores. The surface permeability zone for coral aggregate was proposed to explain the strength enhanced effect of the interface transition zone (ITZ) in SSCAC. A comparisons study was carried out to analyze the difference between SSCAC and ordinary Portland concrete about the stress-strain relationships, failure patterns, and failure mechanisms. Finally, the impact of porosity variations on the mechanical properties development of SSCAC have been investigated, which indicate that the compressive and splitting tensile strengths of SSCAC present distinct three-stage variations with respect to porosity. A sensitive range of ITZ effect was proposed to reveal that as porosity within 7%–18%, the variation of porosity can influence the ratio of splitting tensile strength to compressive strength of SSCAC remarkably. To ensure optimal performance in both splitting tensile strength and compressive strength, it is recommended to maintain the porosity of SSCAC within the range of 5%–10%.

Quantification of hydrogen depletion and mineral reactivity in underground hydrogen storage reservoirs

The utilisation of renewable energy has surged over the past decades due to shifts in climate patterns and the diminishing reserves of fossil fuels. Among the renewables, hydrogen energy has emerged as a promising clean energy carrier in recent years. In the hydrogen industry, storage faces a notable hurdle due to the relatively low density of hydrogen gas (0.0813 kg/m³ at 25 °C and 1 atm) and its lower storage density (7–27 kg/m³ at 25 °C and 100–400 atm). As a potential remedy, underground hydrogen storage emerges as a viable option, even though it is not without its challenges. Among these challenges, a prominent one involves the diversity in the composition and physical properties of the reservoir due to the influence of both biological and geo-chemical reactions. In this study, an extensive modelling effort was undertaken to gain insights into the impact of both bio and geo-chemical reactions, variations in porosity, hydrogen depletion, and the effects of diffusion across various levels of salinity, pressure, and temperature. Diverse Water/Rock ratios, distinct minerals, and residual gases were also considered. The modelled conditions encompassing mineral properties and parameters led to a cumulative hydrogen loss of 8.38% over a century. From this, 2.31% was identified due to the reactivity in reservoir rock and 6.07% due to the aqueous diffusion to cap rock and its reactivity. Among these reactions, carbonate dissolution emerged as the most noteworthy, resulting in considerable hydrogen loss contingent upon the presence of methanogenesis bacteria. As per the modelled scenario, porosity was reduced in reservoir rock by 0.41%, and in carbonate cap rock, it was increased by 56%, which could increase the hydrogen leakage. Also, methane (CH4) exhibited the most favourable characteristics as a cushion gas due to its lower reactivity. However, it's crucial to acknowledge that these figures could significantly fluctuate based on variations in mineral composition, bacterial populations and their growth, and the prevailing subsurface conditions. These modelled findings can serve as a valuable tool for comprehending the mechanisms of hydrogen loss and mineral reactivity within a given underground system.

Sol-gel derived silicate-phosphate glass SiO2–P2O5–CaO–TiO2: The effect of titanium isopropoxide on porosity and thermomechanical stability

Despite of several decades lasting extensive research of bioactive and bioresorbable glasses the systematic parametrization and determination of the key factors affecting porosity and thermomechanical characteristics still remains challenging. Here, we present silica-phosphate glasses, with the composition 70SiO2–20P2O5–(10-x)CaO–xTiO2 (mol%; x = 0, 2.5, 5, and 7.5), prepared by sol-gel method and reinforced by titanium dioxide via titanium isopropoxide (TTIP) incorporation which demonstrated tunable variation of porosity from micro-to macro-region and superb mechanical integrity during the calcination process. The presence of 7.5 mol% TiO2 promotes dimensional stability up to 1000 °C as investigated by thermomechanical analysis. The XRD showed the dominant presence of silicon phosphate [Si(P2O7)], titanium phosphate [Ti(P2O7)] and calcium phosphates [β-Ca(P2O6) and γ- Ca2(P2O7)]. The effect of TiO2 doping on the multiscale morphology and porosity was investigated by means of SEM, MIP, μCT, N2 adsorption and USAXS/SAXS. Increasing TiO2 content leads to the formation of open porosity up to 70 vol% and drives the formation of a refined interconnected macroporosity of 2–30 μm. In contrast, mesoporosity with a dominance of 3–6 nm pores decreases in all samples with increasing TiO2 content. USAXS/SAXS revealed an increase in primary particle size with increasing TiO2 content which is in good agreement with the nitrogen physisorption analysis showing that microporosity decreases with increasing TiO2 content.

New correlations to estimate the rough fracture permeability using computational fluid dynamics simulation

In fractured reservoirs, the fracture network provides the main path for fluid flow. Appropriate estimation of the fracture permeability influences the precise prediction of the reservoir’s future performance. Commonly, for a known geometry of natural or induced fracture, the permeability is estimated by applying local cubic law. One major drawback of this approach is that the fracture surface roughness, which has a significant effect on fracture permeability, is not considered. Moreover, the knowledge about the impact of fracture surface roughness on fracture permeability is not currently sufficient. In this research, the fluid flow in fractures with rough-walled surfaces was studied using computational fluid dynamics. For this purpose, the fluid flow through fractures was simulated by applying appropriate roughness for fracture walls. Furthermore, two correlations, based on response surface methodology and power-law models, were proposed to predict fracture permeability as a function of four independent variables (surface roughness, fracture aperture, angle, and porosity). The results of the two presented correlations were validated, and the statistical analysis indicates that both models are appropriate to predict fracture permeability. The findings of this study will be of great assistance with understanding and characterization of the fluid flow in rough fractures and can be used in future works.

Practical considerations for using petrophysics and geoelectrical methods on clay rich landslides

Understanding the geological and hydrological conditions present within an unstable slope is crucial for assessing the likelihood of failure. Recently, geoelectrical characterization and monitoring of landslides has become increasingly prevalent in this context, due to the spatial sensitivity of electrical methods to critical hydro-mechanical parameters. We explore a situational relationship between resistivity and matric potential (or negative pore pressure), which is a key parameter in estimating the resistance to shear in geological materials, and gravimetric moisture content (GMC). We have chosen a well-characterized active landslide instrumented with geoelectrical monitoring technology, the Hollin Hill Landslide Observatory, situated in Lias rocks in the southern Howardian Hills, United Kingdom. We report on petrophysical relationships between porosity, GMC, electrical resistivity, and matric potential. We trial the application of these petrophysical relationships to inverted resistivity images. Ground model development is achieved through a mixture of clustering resistivity distributions and analysis of surface movements. Our findings show the shrink swell properties of clay result in a variable porosity, which is problematic for applying classic petrophysical relationships documented in the literature. Moreover, directly translating resistivity distributions into matric potential has additional challenges. Nonetheless, volumetric imaging of resistivity suggest that low shear strengths are concentrated downslope of a rotational backscarp. We infer that an accumulation of moisture drives the development of a slip surface at depth, which subsequently manifests in failure at the ground surface. We conclude that the time-lapse resistivity images alone could not be used to infer the pore pressure conditions present within the slope without development of the petrophysical relationships shown here. Therefore, we suggest that the results have practical implications for landslide monitoring with geophysical methods.

Time-dependent model for two-phase flow in ultra-high water-cut reservoirs: Time-varying permeability and relative permeability

For the ultra-high water-cut reservoirs, after long-term water injection exploitation, the physical properties of the reservoir change and the heterogeneity of the reservoir becomes increasingly severe, which further aggravates the spatial difference of the flow field. In this study, the displacement experiments were employed to investigate the variations in core permeability, porosity, and relative permeability after a large amount of water injection. A relative permeability endpoint model was proposed by utilizing the alternating conditional expectation (ACE) transformation to describe the variation in relative permeability based on the experimental data. Based on the time dependent models for permeability and relative permeability, the traditional oil-water two-phase model was improved and discretized using the mimetic finite difference method (MFD). The two cases were launched to confirm the validation of the proposed model. The impact of time-varying physical features on reservoir production performance was studied in a real water flooding reservoir. The experimental results indicate that the overall relative permeability curve shifts to the right as water injection increases. This shift corresponds to a transition towards a more hydrophilic wettability and a decrease in residual oil saturation. The endpoint model demonstrates excellent accuracy and can be applied to time-varying simulations of reservoir physics. The impact of variations in permeability and relative permeability on the reservoir production performance yields two distinct outcomes. The time-varying permeability of the reservoir results in intensified water channeling and poor development effects. On the other hand, the time-varying relative permeability enhances the oil phase seepage capacity, facilitating oil displacement. The comprehensive time-varying behavior is the result of the combined influence of these two parameters, which closely resemble the actual conditions observed in oil field exploitation. The time-varying simulation technique of reservoir physical properties proposed in this paper can continuously and stably characterize the dynamic changes of reservoir physical properties during water drive development. This approach ensures the reliability of the simulation results regarding residual oil distribution.

Heat transfer analysis of ternary hybrid nanofluid through variable characteristic porous medium: Non-similar approach

This paper aims at developing non-similar solutions for heat transfer augmentation in ternary hybrid nanofluids. Nanofluid is composed of three distinct (Silver, Copper, Aluminum oxide) nanosize particles while water is considered as a base fluid. Darcy–Forchheimer expression with variable porosity and permeability is adopted. Joule heating and viscous dissipations are also considered. Non-similar approach is utilized. Numerical solutions are computed by bvp4c solver of MATLAB. Graphical illustrations for flow and thermal fields behavior are provided. Comparative results are obtained for ternary hybrid nanofluid and nanoliquid. Physical quantities such as skin drag coefficient and Nusselt number are computed and interpreted. Our results reveal that rate of heat transfer augments substantially for Ag/water nanofluid in comparison to other classes of nanofluid.

Achieving high-strength porous tungsten with wide porosity range via selective dissolution W-Ti-Fe precursor

Porous tungsten with wide porosity variation is considered a candidate for high-energy X-ray flash radiography. This work combines tape casting and dealloying to selectively dissolve a W-Ti-Fe precursor, achieving high-strength porous tungsten with a wide porosity range. The PVB exists on the surface of particles in the form of an amorphous carbon film after pyrolysis, providing conditions for the W-Fe-C interface reaction. The porosity of porous tungsten is 50.7–80.4%. The compressive strengths of porous tungsten with porosity of 50.7% and 80.4% are 221.9 MPa and 10.6 MPa, respectively. The dissolution of the Ti located in the ligament can enhance the porosity of porous tungsten. The coating composed of the solid solution formed at the interface of W and Ti during heat treatment and Fe3W3C can enhance the ligament strength. This work provides a theoretical reference for preparing porous tungsten with a wide porosity range and high performance.

An enhancement in the petrophysical evaluation in a vuggy carbonate gas reservoir by integrating the core data and empirical methods, Zagros basin, south of Iran

The presence of vuggy pore types poses challenges in accurately assessing effective porosity. This study focuses on the significant scientific issue of improving petrophysical evaluation in vuggy carbonate gas reservoirs. The Kangan Formation is one of the main gas reservoir formations in the southern Zagros region, Iran. The main objective of the current research is to distinguish and exclude the influence of vuggy pore types from effective porosity in the reservoir pay zones of the Kangan reservoir.In the current research, a combination of full suite logs, image logs, core analysis, and thin section studies was employed. The image logs illustrate that vuggy porosity is abundant in the Kangan Formation and these results are confirmed by the available core thin sections, specifically in Zone Kangan_B; Additionally, the cross plots of compressional velocity versus bulk density and total porosity, as a part of rock physics study, indicate the characteristics of the vuggy reservoir. Two methods are utilized to quantify vuggy porosity. The first method, the Velocity Deviation Log (VDL) approach, identifies various available pore types, especially vugs. The second method is a newly proposed approach that can exclude vuggy porosity from the computed effective porosity. In this novel approach, a variable porosity exponent (m) is derived by adopting the Lucia equation to exclude vuggy porosity from the effective porosity computations. Thus, petrophysical evaluation can be implemented based on the constant and variable “m”. Comparing both petrophysical results, it is evident that the amounts of effective porosity and water saturation are modified in the vuggy-bearing intervals. Applying the proposed approach will improve the accuracy of petrophysical properties and lead to the proper calculation of the hydrocarbon volume in the carbonate reservoir rocks containing isolated vugs, particularly in gas-bearing reservoirs where conventional logs are affected by gas contents.

A new method for investigating the impact of temperature on in-situ reservoir properties using high-temperature AFM

Accurately evaluating the influence of temperature variations is crucial for geothermal engineering. Existing conventional testing methods are limited in providing detailed characterizations of reservoir micro properties at high temperatures. This study employed variable-temperature AFM testing techniques to examine sandstone and limestone under in-situ temperatures (25-200°C). The study analyzed the mechanisms behind the temperature effects on rock properties and established theoretical models for porosity and permeability variations with elevated temperatures based on these mechanisms. The research revealed that sandstone and limestone exhibit similar temperature effects at high temperatures. The pore fractal dimension of sandstone and limestone does not change with temperature change. As the temperature increases, sandstone and limestone experience mean roughness (Ra) and porosity reductions. The impact of high temperature was more pronounced on sandstone compared to limestone, with sandstone showing a decrease of 2.8 % and 0.59 % in mean roughness (Ra) and AFM porosity, respectively, from 25 °C to 200 °C, while limestone exhibited reductions of 1.4 % and 0.085 %, respectively. With increasing temperature, sandstone transformed some pores with equivalent diameters of 1-2.5 μm to pores smaller than 1μm, while limestone did not show significant changes in pore structure. The temperature effects on sandstone and limestone were attributed to mineral expansion. Sandstone contains a higher proportion of minerals with a high coefficient of thermal expansion, such as quartz. In contrast, limestone primarily comprises minerals with lower thermal expansion coefficients, such as calcite, resulting in a more significant temperature impact on sandstone than on limestone. The theoretical models based on the mechanisms for porosity and permeability at high temperatures exhibited good predictive performance for sandstone and are more suitable for reservoirs predominantly composed of minerals with high coefficients of thermal expansion. The variation of porosity and permeability at high temperatures have different impacts on geothermal reservoirs. Temperature effects on porosity and permeability should be considered in geothermal engineering.

Influence of Spatter on Porosity, Microstructure, and Corrosion of Additively Manufactured Stainless Steel Printed Using Different Island Size

Specimens of 316 L stainless steel were printed using laser powder bed fusion (LPBF), a popular metal additive manufacturing (AM) technique, with varying island sizes. Not many researchers have considered the impact of spatter while optimizing LPBF printing parameters. In this research, the influence of spatter was considered while also investigating the effect of varied island size on the microstructure, surface roughness, microhardness, and corrosion resistance of LPBF-316 L. No correlation was observed between surface roughness or microhardness and minor variations in island size. However, a correlation was drawn between varied island sizes and porosity in LPBF-316 L. The specimens associated with larger island sizes showed significantly enhanced corrosion resistance due to fewer manufacturing defects and reduced porosity, attributed to the minimal influence of the spatter. Based on analysis, the LPBF parameters were revised, which lead to superior corrosion resistance of LPBF-316 L, attributed to high density and reduced porosity.

Mechanical properties of native and decellularized reproductive tissues: insights for tissue engineering strategies

Understanding the mechanical properties and porosity of reproductive tissues is vital for regenerative medicine and tissue engineering. This study investigated the changes in Young's modulus (YM), storage modulus (E′), loss modulus (Eʺ), and porosity of native and decellularized bovine reproductive tissues during the estrous cycle. Testis tunica albuginea had significantly higher YM, E′, and Eʺ than the inner testis, indicating greater stiffness and viscoelasticity. Endometrium showed no distinct differences in YM, E′, or Eʺ across the estrous cycle or between horns. Ovaries exhibited significant variations in YM, E′, Eʺ, and porosity, with higher YM and E′ in the ipsilateral cortex and medulla during the luteal phase. Decellularized ovarian tissues displayed increased porosity. The oviduct displayed no significant differences in YM or E′ in the isthmus, but the contralateral ampulla had reduced YM and E′ in the luteal phase. These findings offer valuable insights into the dynamic mechanical properties and porosity of reproductive tissues, facilitating the development of biomimetic scaffolds for tissue engineering applications.

Time-lapse 3D Micro-tomography of Calcite Column Experiments to Study pH-Dependent Dynamic Dissolution Processes

We investigated the spatiotemporal evolution of calcite dissolution processes using time-lapse high-resolution X-ray CT imaging of live column experiments and real-time data logging of effluent pH and TDS. We evaluated the sensitivity of three pH solutions (7, 5, and 4) to dissolution processes. The results showed spatial variations in dissolution associated with spatial variation in porosity and pore sizes, manifesting as spatial heterogeneity in the dissolution pattern. Dissolution was dominant in larger pores compared to smaller ones. The magnitude of this uneven spatial dissolution exceeded the overall dissolution. However, the total porosity increased linearly over the time of dissolution experiments, with the slope dependent on the pH of the injected solution. Surface area decreased linearly during dissolution, and the decrease in surface area was also found to depend linearly on the increase in total porosity. The temporal evolution of pH-dependent reaction rates demonstrated a decreasing trend that followed a power-law behavior. The time to reach the steady reaction rate, which was evaluated from changes in calcite volume, appeared to be significantly later than the time at which the tracer reached its asymptote. The reaction rate at these two distinct times could differ by an order of magnitude. We emphasize the use of the steady state in mineral volume changes method to determine representative reaction rates in porous media, the significance of which emerges due to the coupling of hydrodynamic and reactive transport processes originating at the pore scale.

Quantitative Analysis of Diagenesis Control on the Spatial Heterogeneity of Sarvak Carbonate Formation, the Dezful Embayment of Zagros Basin, Western Iran

Summary The heterogeneity indices in conventional carbonate reservoirs are usually influenced by various diagenetic processes. The main aim of this study is to build 3D geological models of the diagenetic and heterogeneity indices addressing the role of diagenesis on spatial heterogeneity variations in the Sarvak carbonate reservoir of an Iranian oil field situated in the Dezful Embayment in the Zagros Basin. Vertical heterogeneity has been discussed in many studies, but the literature is limited on the 3D geological modeling of heterogeneity and providing spatial heterogeneity maps. In this study, we determined the main diagenetic parameters influencing the reservoir heterogeneity and constructed 3D geological models for evaluating the spatial heterogeneity. A couple of heterogeneity indices including the coefficients of variation (CVs) of porosity and permeability, Lorenz coefficient, and Dykstra-Parsons coefficient in cored intervals along with some diagenetic parameters were calculated and modeled. This study shows that lateral heterogeneity is mappable and correlatable with different diagenetic overprints along with shale volume, which controls the reservoir quality and spatial heterogeneity. It also indicates that lateral trends of the heterogeneity indices in different zones of the studied reservoir are influenced by other diagenetic parameters such as secondary porosity (SPI), dolomitization, cementation, and velocity deviation log (VDL, as a diagenetic index). Different diagenetic parameters control reservoir heterogeneity in each zone by decreasing or increasing the degree of the heterogeneity, some of which have dual constructive or destructive effects on heterogeneity indices. Moreover, the results show that the effect of shale volume on reservoir heterogeneity is significant, especially when the amount of the shale volume is notable.

Measurement of precision and quality characteristics of lattice structures in metal-based additive manufacturing using computer tomography analysis

Additive manufacturing, especially lattice structure fabrication, has garnered interest for its potential in high-precision aerospace and medical applications. Due to porosity and dimensional variation, obtaining mechanical characteristics and accuracy remains a research priority. This study addresses the current knowledge gap by providing a comprehensive methodology for the qualitative evaluation of cellular structures in additive manufacturing, focusing on the critical parameters of relative density, dimensional deviations, and porosity characteristics. The research utilizes advanced μCT analysis to investigate the impact of these factors on the overall quality and functionality of printed objects, particularly in metallic lattice structures fabricated using Laser Powder Bed Fusion (LPBF) technology. The cell structures were constructed using MS1 tool steel as the material base. An extensive investigation was carried out on a diverse array of lattice configurations, including Body-Centered Cubic (BCC), Diamond, Fluorite, Kelvin, Schwarz, and Fischer – Koch. It was observed that discrepancies between actual and designed relative densities in structures such as BCC, Diamond, and Kelvin indicate densification attributable to the manufacturing process, particularly in smaller cell structures. Furthermore, global porosity analysis demonstrated a clear relationship between increased density and reduced porosity. Optimal manufacturing conditions for minimizing defects and enhancing the precision and quality of additive manufactured metallic lattice structures were identified as a cell size of 3 mm and a 50 % relative density.

An Experimental Investigation of Interaction between CO2 Solution and Rock under Reservoir Conditions in the Jimsar Shale Oil Formation

Chemical sequestration is one important manner of CCUS. The injection of CO2 into an oil reservoir can not only sequestrate CO2 but also raise the oil recovery factor. The performance of chemical sequestration of CO2 depends on the interaction between CO2 solution and reservoir rock. In this paper, we have conducted three different scales of experiments, e.g., microscopic scale, core scale, and time scale, to fully investigate the interaction and resultant variation to mineral content, microscopic structure, porosity, and permeability under reservoir conditions (i.e., reservoir temperature of 90 °C) in Jimusar shale oil formation. The microscopic-scale experiment applied SEM and hyperspectral scanning to obtain microscopic pore throat structure and element distribution before and after soaking the rock in CO2 solution. The core-scale experiment employed XRD to evaluate mineral content variation caused by CO2 solution. Core flooding experiments were conducted to evaluate porosity and permeability variation caused by the dissolution of CO2 solution into the core samples. The third type of experiment was employed to investigate the effect of time sequence on the dissolution, in which the time ranged from 1 day to 14 days continuously. The experimental results indicate that, under Jimsar reservoir conditions, CO2 solution exhibits a relatively robust dissolution capability, causing significant alterations to the properties of the core samples. Specifically, the CO2 solution effectively dissolves carbonate upon contact. Calcite is the primary target for dissolution, followed by dolomite. In the presence of sufficient CO2, complete dissolution of all carbonates is achievable. On a microscopic scale, dissolution primarily occurs in the calcium-rich areas, leaving other regions unaffected. The typical pore size resulting from CO2 solution-induced dissolution ranges from several to dozens of micrometers. This dissolution process significantly enhances both porosity and permeability. For Jimsar shale core samples, porosity experienced an increase of over 20%, and permeability nearly doubled. Under Jimsar reservoir conditions at 90 °C, CO2 solution can consume all carbonates present in core samples within 8 days. The increase in porosity and permeability is rapid during the initial days and stabilizes around the 6th day. These research findings establish a theoretical foundation for CO2 chemical sequestration.

Enhanced heat flow assessment in Gulf of Hammamet and Pelagian Sea: Temperature corrections and conductivity adjustments

This study proposes new corrections of formation temperatures combined to correction of formation conductivities to reconstruct the heat flow map of the Gulf of Hammamet-Pelagian Sea, Eastern Tunisia. For that, a new linear Cross-Plot temperature correction approach, based on Bottom Hole Temperatures (BHT) and Drill Stem Temperatures (DST) of 63 drilled boreholes, was applied. In addition, and as temperature is transmitted from the substratum to the top of a stratigraphic column owing to the thermal conductivity, the latter was investigated according to a high appraisal of ±5 m and taking into account porosity variation with depth. The produced corrected thermal conductivity and geothermal gradient allowed to calculate the corrected heat flow in the Gulf of Hammamet – Pelagian Sea. Results show that the corrected geothermal gradient varies between 23 °C/Km and 58 °C/Km with a regional mean of about 39 °C/Km. The corrected heat flow rises from 49.5 to 119 mW/m2 with a regional mean of about 68 mW/m2. Variation of heat flow is dependent of the geodynamic evolution of the area where high heat flows follow folding structures and relatively low heat flows follow major trending faults. The major variations are E-W, N-S and NW-SE in direction following the major structural trends.

Hydromechanical simulation of a carbonate petroleum reservoir using pseudo-coupling

In the domain of petroleum reservoir management, numerical flow simulation stands as the primary tool for prediction and control. Traditionally, rock compressibility has been the key geomechanical parameter, often applied as a single, unchanging value across the entire reservoir model throughout the simulation. This study introduces a novel methodology that enhances reservoir simulation accuracy by incorporating rock mechanical behavior through a pseudo-coupling approach, without increasing computational costs. This approach empowers reservoir engineers to consider rock hydromechanical behavior in daily reservoir studies.The pseudo-coupling updates both porosity and permeability based on tables that correlate pore pressure to porosity and permeability multipliers, thereby replacing the conventional reliance on compressibility. It begins with reservoir-rock samples selection guided by lithological composition, followed by mechanical and hydromechanical laboratory tests, and numerical adjustments with ABAQUS stress analysis software. The resulting mechanical parameters serve for generating pseudo-coupling tables tailored to each facies.Validation experiments comparing pseudo-coupling simulations with conventional and fully coupled models reveal convergence in porosity and permeability variations with pore pressure between both coupled approaches. Extensive assessments further compare pseudo-coupling simulations against conventional reservoir simulations using a synthetic model based on a carbonate post-salt reservoir, denoted as Field B. The pseudo-coupling approach emerges as a more robust model capable of discerning preferential flow paths, all while maintaining computational efficiency. Moreover, these preferential flow paths were also predicted by the reservoir team responsible for the field development, but through a trial-and-error procedure to match production history, whilst the pseudo-coupling predicted it based on rock mechanical behavior.In this way, the proposed methodology enables an enhancement in the accuracy and efficiency of petroleum reservoir management by considering geomechanical effects, without incurring any additional computational costs when compared to conventional reservoir simulation.

Density structure of Kīlauea volcano: implications for magma storage and transport

SUMMARY A Bayesian linear regression to determine the bias in the Nafe–Drake relationship between compressional velocity and density provides an improved model for the density structure of Kīlauea volcano, Hawaiʻi. In previous work, we combined the results of seismic tomography with the Nafe–Drake relationship between compressional velocity and density to explain the large values of gravity disturbances overlying the summits and rift zones of the island's volcanoes. These results were used to determine mechanisms for gravitational instability of the island flanks. Here, we use laboratory measurements of the relationship of velocity and density for a wide range of Hawaiʻi island rocks as a prior in a Bayesian regression, with seismic tomography, to refine the 3-D density structure for Kīlauea volcano. This refined structure shows dense bodies (3220 kg m−3) between 5 and 8 km below sea level that underly regions of magma storage, found from geodetic and geophysical studies, beneath the summit and East Rift Zone of Kīlauea volcano. Above these bodies, density isosurfaces surround and cradle sources of pressure change determined from geodetic models, both at the summit and along the East Rift Zone. Continued subsidence of the summit following the 2018 eruption is aligned with a bowl-shaped density structure, formed primarily by density isosurfaces between 2800 and 2900 kg m−3 at 4–6 km depth. These surfaces underly the ∼3 km depth at which dyke injection initiates, are largely aseismic, and from their density values are inferred to contain high concentrations of olivine. Taken together, these density structures are consistent with an olivine-rich mush with variable porosity that increases in density with depth and provides a mechanism to form olivine cumulates both at the summit and along the rift zones. This structural framework for Kīlauea volcano is consistent with melt and mush transport occurring over a large range of depths to accommodate the growth and spreading of the volcano.