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Both straight and curved carbon fibers are widely used in various commercial gas diffusion layer (GDL) fabrications. The effect of the different carbon fiber curvatures on two-phase flow dynamics within the cathode GDLs of proton exchange membrane fuel cells remains unclear. In this study, we investigate liquid transport in three types of GDLs with varying fiber curvatures using the two-phase volume of fluid simulations in OpenFOAM. For the first time, a rod periodic surface model is combined with a layer-by-layer fiber stacking strategy, to stochastically reconstruct GDL structures while incorporating crucial parameters from physical (experimental) GDLs. A grid independence study and model validation are conducted. Following pore network analysis of pore size distribution and connectivity, we study the time-varying GDL total and local water saturation and capillary pressure. Despite maintaining similar layer and bulk porosity, increased fiber curvature enhances pore connectivity but raises water saturation and capillary pressure, increasing the risk of flooding. Additionally, droplets in gas channels with straight-fiber GDLs are larger and have slower movement than those in curved-fiber GDLs. Fiber curvature inversely affects drainage capacity in GDLs and connected channels. With comparable water saturation and capillary pressure, curved-fiber GDLs exhibit lower discrepancies, suggesting improved uniformity in water distribution. [Display omitted] • Curved and straight fiber GDLs are reconstructed with similar bulk and layer porosity. • Increasing fiber curvature enhances pore connectivity and pore quantity. • GDL water saturation and capillary pressure increase with an increased fiber curvature. • Increasing the amount of small pores results in stronger water spreading within GDLs. • Detached droplets in GCs have smaller sizes and longer liquid bridge when using curved-fiber GDLs. [ABSTRACT FROM AUTHOR]

Liquid water within the cathode Gas Diffusion Layer (GDL) and Gas Channel (GC) of Proton Exchange Membrane Fuel Cells (PEMFCs) is strongly coupled to gas transport properties, thereby affecting the electrochemical conversion rates. In this study, the GDL and GC regions are utilized as the simulation domain, which differs from previous studies that only focused on any one of them. A Volume of Fluid (VOF) method is adopted to numerically investigate the two-phase flow (gas and liquid) behavior, e.g., water transport pattern evolution, water coverage ratio as well as local and total water saturation. To obtain GDL geometries, an in-house geometry-based method is developed for GDL reconstruction. Furthermore, to study the effect of GDL carbon fiber diameter, the same procedure is used to reconstruct three GDL structures by varying the carbon fiber diameter but keeping the porosity and geometric dimensions constant. The wall wettability is introduced with static contact angles at carbon fiber surfaces and channel walls. The results show that the GDL fiber microstructure has a significant impact on the two-phase flow patterns in the cathode field. Different stages of two-phase flow pattern evolution in both cathode domains are observed. The liquid water in the GDL experiences water invasion, spreading, and rising, followed by the droplet breakthrough in the GDL/GC interface. In the GC, the water droplets randomly experience accumulation, combination, attachment, and detachment. Due to the difference in surface wettability, the water coverage of the GDL/GC interface is smaller than that of the channel side and top walls. It is also found that the water saturation inside the GDL stabilizes after the water breakthrough, while local water saturation at the interface keeps irregular oscillations. Last but not the least, a water saturation balance requirement between the GDL and GC is observed. In terms of varying fiber diameter, a larger fiber diameter would result in less water saturation in the GDL but more water in the GC, in addition to faster water movement throughout the total domain. Effect of GDL fiber diameter on water behavior in PEMFC gas channel and gas diffusion layer, varying the fiber diameter: 10 μm (case A), 15 μm (case B), and 20 μm (case C). [Display omitted] • Two-phase flow VOF simulation in a "T-shape" PEMFC cathode. • GDL reconstruction using an in-house geometry-based method. • Dynamic liquid water transport behavior in the GDL and GC. • Effect of GDL fiber diameter on water transport in the GDL and GC. • Finding a water saturation balance requirement between the GDL and GC. [ABSTRACT FROM AUTHOR]

The objective of the present paper is to study numerically the hydro-mechanical behaviour of concrete targets subjected to a rigid projectile, with special attention to the influence of water saturation. An elastoplastic model, encompassing two primary plastic mechanisms (shear and pore collapse), is improved to capture the influence of water saturation. The adopted model is implemented in the finite element code Abaqus/Explicit and validated by simulating two dynamic compression tests at the material point level and two penetration tests at the structure level. Not only a strong influence of water saturation on both volumetric and deviatoric behaviours of concrete is observed at material point level, but also the time-evolutions of projectile velocity, projectile deceleration and penetration depth in concrete targets are also satisfactorily reproduced by the numerical simulations. After that, a series of parametric studies are performed to understand the influence of water saturation on the penetration performance of concrete. It is found that with the presence of pore water, penetration resistance of concrete increases with decreasing water saturation, indicating a higher projectile deceleration and lower penetration depth obtained in saturated targets. Numerical modelling and analysis will enhance our understanding of the vulnerability of concrete infrastructures subjected to near-field detonations or impacts. • Fully coupled hydro-mechanical behaviour of concrete target subjected to a rigid projectile is analysed. • Water saturation of concrete target has an important impact on the penetration behaviour of projectile. • Concrete target with lower saturation degree exhibits higher penetration resistance. [ABSTRACT FROM AUTHOR]

Continuous wave (CW) laser irradiation induces temperature changes in various phases within porous media, accompanied by phase change and gas transport. Water saturation is a crucial factor influencing this context's moisture and heat transfer process. This paper addresses this issue by establishing a theoretical model for CW laser irradiation on unsaturated porous media. Through experiments and simulations, it studies the effects of different water saturations on heat and mass transfer under laser irradiation. The results indicate that the critical depth reflects the influence of water saturation under laser irradiation on the distribution of solid-phase temperature in both time and space dimensions. Specifically, an increase in water saturation enhances the uniformity of solid-phase temperature distribution, while the gas temperature exhibits a similar distribution pattern. For mass transfer processes, it increases the evaporation rate and Darcy velocity of porous media within the effective range of laser irradiation. Lower water saturation facilitates phase change processes and accelerates gas transport rates. Importantly, this trend remains consistent even with the emergence of dry-saturation zones. Additionally, the decrease in water saturation has a coupled promoting effect on gas temperature and mass transfer processes. Lowering water saturation can increase gas temperature and consequently enhance mass transfer processes. Simultaneously, enhancing mass transfer processes benefits heat exchange between the two phases. In the four sets of experiments, the conformity of the surface temperature rise curves obtained from experiments and simulations is good, indicating that the model can accurately reflect the temperature rise patterns of sand particles. In summary, this work provides valuable research results on the effects of different water saturations on laser irradiation-induced temperature rise, phase change, and gas and moisture transport within porous media. It lays a specific theoretical foundation for laser soil remediation technology. [ABSTRACT FROM AUTHOR]

Coal reservoirs commonly exhibit the coexistence of gas and water, wherein the distribution of water plays a crucial role in influencing methane storage and transportation. The presence of water affects methane adsorption, and models predicting adsorbed methane that do not account for water conditions can introduce errors, posing challenges in meeting practical production needs. In this study, through a series of centrifugation experiments and nuclear magnetic resonance (NMR) adsorption experiments, the distribution characteristics of bound water and movable water in reservoirs and their influence on multiphase methane were assessed. The results indicate that under water-bearing conditions, there exists specific methane in the adsorption space, exhibiting properties similar to free methane. In terms of the relaxation characteristics, the presence of water affects both the peak area and morphology of the T 2 spectra of multiphase methane. Based on the NMR response characteristics of adsorbed methane at different water saturations, we proposed and established a theoretical model for predicting the content and density of adsorbed methane under varying water saturations. Additionally, utilizing two-dimensional NMR technology, a simple identification spectrum for multiphase methane was established. The study suggests that the presence of water delays the time of adsorption equilibrium for methane. At low water saturations, water primarily inhibits the adsorption rate of methane. However, with increasing pressure and water saturation, water predominantly suppresses the adsorption capacity of methane. At low water saturations, the bound water has a significant effect on adsorbed methane. Conversely, as water saturations increase, movable water gradually occupies adsorption sites with weaker adsorption potential. It is worth noting that with an increase in water saturation, the content of adsorbed methane decreases, but the adsorption phase density may not necessarily decrease. These research findings provide new insights into the interaction mechanisms between water and methane in water-bearing coal reservoirs. • There exists specific methane in the adsorption space at water-bearing conditions. • As Water saturation increases, adsorption phase density not necessarily decrease. • The density of adsorbed water (1.1 g/cm3) may exceed that of liquid water. • A 2D NMR spectrum of adsorbed methane and free methane has been established. [ABSTRACT FROM AUTHOR]

[Display omitted] • A database is generated using 3D multiphase CFD simulations. • Six surrogate models are produced to predict the resistance and water saturation. • Every model has proven to be accurate at predicting resistance. • Ensemble models have better performance at predicting water saturation. • It is suggested that CatBoost be combined with "3D + 1D" for flooding prediction. In the simulation of proton exchange membrane fuel cells, a "3D + 1D" model combines a detailed 3D domain with a simplified 1D domain. The "3D + 1D" method accurately simulates flooding by considering the resistance to oxygen transfer and water saturation in porous media adjacent to the flow field. This study proposes an efficient model compatible with "3D + 1D." The model should be able to swiftly and accurately predict the resistance and water saturation under various flow fields, GDL porosities, and operating conditions. To this end, a multiphase 3D computational fluid dynamics model generates a data set. The data set comprises anticipated variations. A comparative investigation of six regression methods has been presented. The methods are based on Response Surface Methodology (RSM), Artificial Neural Networks (ANN), and four ensemble machine learning methods, named Random Forest (RF), XGBoost, Lightgbm, and CatBoost. Genetic algorithm optimization tunes hyperparameters. It has been found that every model has proven to be accurate at predicting resistance. With an R2 of 0.9899, CatBoost has the best performance, while RSM presents the simplest regression employed to formulate the resistance. In the context of predicting water saturation, ensemble machine-learning models have demonstrated better performance than RSM and ANN models. CatBoost performs the best with an R2 of 0.983 in predicting water saturation. It is recommended that CatBoost and the "3D + 1D" method be integrated to achieve an accurate prediction of flooding. [ABSTRACT FROM AUTHOR]

• Water saturation effects on CO 2 hydrate saturation during CO 2 injection is assessed. • Influence of water memory on the kinetics of CO 2 hydrate is investigated. • Hydrate volume/density during hydrate formation is estimated using medical CT scan. Injection of high-pressure CO 2 into depleted gas reservoirs can lead to low temperatures promoting formation of hydrate in the near wellbore area resulting in reduced injection rates. The design of effective mitigation methods requires an understanding of the impact of crucial parameters on the formation and dissociation of CO 2 hydrate within the porous medium under flowing conditions. This study investigates the influence of water saturation (ranging from 20 % to 40 %) on the saturation and kinetics of CO 2 hydrate during continuous CO 2 injection. The experiments were conducted under a medical X-ray computed tomography (CT) to monitor the dynamics of hydrate growth inside the core and to calculate the hydrate saturation profile. The experimental data reveal increase in CO 2 hydrate saturation with increasing water saturation levels. The extent of permeability reduction is strongly dependent on the initial water saturation: beyond a certain water saturation the core is fully blocked. For water saturations representative of the depleted gas fields, although the amount of generated hydrate is not sufficient to fully block the CO 2 flow path, a significant reduction in permeability (approximately 80 %) is measured. It is also observed that the volume of water + hydrate phases increases during hydrate formation, indicating a lower-than-water density for CO 2 hydrate. Having a history of hydrate at the same water saturation leads to an increase in CO 2 consumption compared to the primary formation of hydrate, confirming the existence of the water memory effect in porous media. [ABSTRACT FROM AUTHOR]

Understanding the mechanical and failure behavior of rock subjected to dynamic shear load is essential for the scientific design and safe operation of rock engineering. To understand the coupled effect of water and strain rate on the mechanical and failure behavior of sandstone, direct shear tests with constant normal pressure were conducted on sandstone specimens under different water saturations with shear strain rate ranging from 10−5 s−1 to 10−2 s−1. The acoustic emission (AE) and scanning electron microscope (SEM) techniques were applied to analyze shear behavior and reveal failure mechanism under different loading conditions. Results show that at a given strain rate shear strength decreases with increasing water saturation, while it increases with strain rate when the water saturation remains constant. Meanwhile, the water-saturated specimens are more sensitive to strain rate effect than dry specimens, which is mainly the result of the Stefan effect. Both water and strain rate affect AE activity and fracturing of the specimens during shearing process. AE activity was more intense and lasted longer at low water saturation condition. With increasing strain rate, the peak AE counts decreased, yet the peak cumulative energy of AE events increased. The SEM analysis reveals that the development of microcracks is fuller under the conditions of low water saturations and high strain rates. The microcrack network and fracture surfaces are more complicated at lower water saturation, while microcracks are wider and the fracture surfaces are smoother under higher strain rate shearing. The findings of this study contribute to a better understanding of mechanical and failure behavior of sandstone material under the coupled effect of water saturation and dynamic disturbance. • Failure behaviors were characterized by acoustic emission counts, b -value, rising angle and average frequency. • Failure mechanism was revealed by characterizing microstructure features of fracture surfaces using SEM. • The shear strength of sandstone is weakened by water, while the strain rate effect enhances it. • Microcracks developed more extensively under low water saturation and high strain rates. [ABSTRACT FROM AUTHOR]

Water management is a critical issue for achieving the optimum performance of proton exchange membrane fuel cells (PEMFC) since water flooding limits the flow of reactants to catalyst zones and produces electrode regions with higher electric resistance. We used a 3D non-isothermal multiphase model of a single PEMFC to investigate the liquid water saturation distribution at the cathode side. We used an open-source toolbox to solve finite volume method calculations and implement an effective diffusion model based on fiber layers. A parametric study of the condensation rate and saturation at 0.4, 0.2, and 0.1 V illustrates the distribution of liquid water saturation and the flooding zones across the electrode components. The comparison shows that the flooding zones are located at the land ribs. Also, increased water saturation and higher oxygen consumption produce a reactant restriction in the porous media and impact the global performance of the fuel cell. [Display omitted] [ABSTRACT FROM AUTHOR]

Predicting the cutter consumption rate of mechanical excavators using the Cerchar abrasivity index (CAI) results is possible. However, changing operational parameters in the field may cause differences between the estimated cutter consumption rate based on CAI test results and the real cutter consumption rate observed in the field. One of the essential parameters in the field that affects the cutter consumption rate is the increase in the water content of the excavated rocks. In theory, an increase in the water content of rocks is expected to reduce their abrasivity. In addition, the prediction of cutter consumption rate is based solely on CAI test results conducted on dry surfaces. However, especially during the excavation of low-strength clay-rich rocks, the excavated rock material can adhere to the cutters and block them, leading to a higher cutter consumption rate than initially predicted. This study aims to analyze the rock-pin interaction in CAI tests conducted on wet surfaces of clay-rich rocks and investigate the effect of water saturation on CAI at different scratch lengths. CAI tests were conducted on dry and wet surfaces of 20 clay-rich rocks with low strength at 10, 30, 50, and 70 mm scratch lengths, respectively. The relationships between the CAI test results obtained on dry and saturated rock surfaces were statistically analyzed for each scratch length. A positive linear correlation was found between CAI values obtained on dry (CAI Dry) and saturated surfaces (CAI Sat) at each scratch length. The percentage variations in CAI values at each scratch length were analyzed in detail. It was found that 90 % of samples have higher CAI Dry than CAI Sat at 10 mm scratch length. However, it was observed that as the scratch length increased, the relationship between the CAI values obtained in dry and saturated conditions changed, and the proportion of samples with CAI Dry higher than CAI Sat decreased to 65 %, 55 %, and 25 % at scratch lengths of 30 mm, 50 mm, and 70 mm, respectively. In CAI tests conducted on saturated surfaces, it was observed that the excavated rock material adhered to the test pins, and as the scratch length increased, the increase in CAI Sat values was considered to be due to this situation. This study revealed the importance of considering the adhesion potential of rocks to cutters at water-saturated conditions for the accurate prediction of cutter consumption in the excavation of clay-rich rocks. • A problem encountered during the excavations in the field was investigated through the approximately 800 CAI tests. • The effect of rock materials adhering to the test pin on CAI was investigated. • Standard CAI test results may be inadequate for predicting cutter consumption in water-saturated clay-rich rocks. • To estimate an accurate cutter consumption rate, the adhesion potential of clay-rich rocks has to be considered. [ABSTRACT FROM AUTHOR]

This study presents indirect methods of source rocks characterization by integrating geochemical data with well logs and seismic inversion results. Well logs and seismic data are commonly more available than scarce geochemical data in oil and gas fields. Combining high vertical resolution well logs with high lateral resolution seismic data generates some enhanced geochemical data on inter-well spaces where no well is drilled. Acoustic impedance was obtained and utilized for the TOC prediction and source rock detection because of its good correlation with geological parameters such as the lithology and fluid contents. A cross-plot of log-derived water saturation versus acoustic impedance successfully differentiates source from non-source rocks based on geological variations of lithology, porosity, formations density, and the TOC content. The impact of the TOC content on acoustic properties was elaborated in the next step. Acoustic impedance is obtained as the most important seismic attribute for the TOC prediction. Well logs and seismic data are integrated to predict the TOC logs from seismic data. First, seismic data were inverted to obtain the acoustic impedance. Then, the produced acoustic impedance was used as a seismic attribute for the TOC prediction. The outcome is used to illustrate and follow the TOC variation to distinguish source rocks in the oil and gas fields. The study is carried out in the Cretaceous succession in three hydrocarbon fields in the central part of the Persian Gulf to observe the TOC variations in the Albian-aged Kazhdumi Formation. • Fusion of geochemical, petrophysical and seismic data for source rock characterization • A rock physics template based on acoustic impedance versus water saturation cross-plot for source rock detection • Inversion of post-stack seismic data to acoustic impedance and total organic carbon • Taking the advantage of high vertical resolution of well logs and high horizontal resolution of seismic data for source rock mapping • A fast, cost-effective and robust method for source rock mapping [ABSTRACT FROM AUTHOR]

Frost heave of rocks is a significant challenge in cold regions, posing threats to geotechnical engineering and causing geo-disasters. This study presented a novel micro frost heave model based on Discontinuous Deformation Analysis (DDA) to investigate the mechanism of frost damage in porous rock, with a specific focus on the coupling effect of pore characteristics and water saturation. First, pore ice was divided into three categories based on capillary mechanics, and they were treated differently in DDA according to their characteristics. Then, the developed model was validated by comparing numerical simulation with the physical experimental results of the parallel-sided slot model. Subsequently, simulations were conducted to analyze frost heave strain, pore damage, and the uniaxial compressive strength (UCS) of the frozen sandstone samples at varying water saturations. Finally, the microscopic mechanisms underlying UCS characteristics, such as the peak strength and the critical saturation, were discussed in detail. This research offered a novel and simple model for investigating the micro-mechanisms of the mechanical behavior of frozen rock. [ABSTRACT FROM AUTHOR]

Surfactant-modified clay minerals, organoclays, are well-studied and used commercially for removing contaminants from water. Nevertheless, dry organoclay properties are typically used to understand and predict contaminant sorption. In this work, the effects of water saturation on two properties important to contaminant sorption were examined: organoclay interlayer space and surfactant alkyl tail conformational ordering. Montmorillonite was modified to 0.25–3.0 CEC using three surfactants: hexadecyltrimethylammonium (HDTMA), hexadecylpyridinium (HDPy), and hexadecyltrimethylphosphonium (HDTMP). At low surfactant-loadings (< 1 CEC and < 15% f OC), water saturation expanded the maximum organoclay interlayer by 4–8 Å, depending on the surfactant and its loading but had little effect on surfactant tail conformational ordering. At low surfactant loadings, water saturation likely promotes contaminant sorption relative to expectations based on dry organoclay properties, particularly for larger contaminants, due to a relaxation of the physical constraints of the interlayer. At higher surfactant loadings, HDTMA and HDTMP organoclays showed relatively small effects of water saturation, but effects were significant for HDPy organoclays. The maximum interlayer space of the HDPy organoclay at 20.7% f OC expanded 3-fold (+22.3 Å) upon hydration, which is attributed to a substantial rearrangement of the pyridinium headgroup. All HDPy organoclays with f OC > 20% experienced a notable increase in the alkyl tail conformational ordering upon hydration, becoming fully solid-like, even as negligible interlayer expansion occurred at the highest loadings. At high HDPy-loading water saturation would likely restrict sorption of contaminants relative to what might be expected based on dry properties, due to the energetic barrier of cavity formation in the more solid-like interlayer phase. This work provides evidence from three types of organoclays that water-saturated organoclay properties can differ substantially from those of dry organoclays. Characterization of organoclays under water-saturated conditions that are relevant to contaminant sorption will facilitate our understanding and improvement of organoclay performance. [Display omitted] • HDTMA, HDTMP, and HDPy organoclays were produced at surfactant loadings of 1–3 CEC. • Water saturation of organoclays substantially altered properties relevant to contaminant sorption. • At low surfactant loadings, water saturation expanded the organoclay interlayer space by 4–8 Å. • Water saturation reoriented HDPy in the 21% f OC organoclay, nearly tripling the interlayer space. • At high loadings, saturation increased HDPy alkyl tail conformation to fully solid-like. [ABSTRACT FROM AUTHOR]

• The thermo-hydro-mechanical flow (THM) model of water-bearing coal seam is established. • Coal seam water can hinder gas migration, thus reducing CH 4 production and CO 2 /N 2 storage. • Different migration rates of CO 2 and N 2 lead to different breakthrough times of CO 2 /N 2 -ECBM. • The injection ratio of mixed gases (CO 2 , N 2)will impact parameter of coal seam, including reservoir permeability, CH 4 production, and CO 2 /N 2 storage capacity. • CO 2 displacement mainly utilizes competitive adsorption characteristics, while N 2 displacement utilizes "high-speed scouring" effect and " dredging, expanding " effect on fractures. Gas injection to increase coalbed methane production is an effective energy saving and emission reduction technology, with triple benefits of clean energy production, environmental protection and safety production. In this paper, a coupled thermo-hydro-mechanical flow (THM) model is developed, the effects of different injected gases on ECBM are considered, the effect of initial water saturation on CO 2 /N 2 -ECBM is quantified using the control variable method. Exploring changes in storage and production during the injection gas mixture enhanced CBM recovery (GM-ECBM). The results show that: The breakthrough time of CO 2 injection was much later than N 2 injection. The higher the initial water saturation, the lower the CH 4 production and gas storage. CO 2 injection will reduce the permeability of coal seam and damage it, while N 2 injection can effectively restore the permeability. The higher the initial water saturation, the slower the permeability decrease during CO 2 -ECBM and the slower the permeability increase during N 2 -ECBM. Increasing the N 2 injection concentration before the N 2 breakthrough time can promote CH 4 production, and increasing the CO 2 injection concentration near the N 2 breakthrough time will delay the N 2 breakthrough time and provide more time for CH 4 to migration in the pore space, which will increase the CH 4 production. When injecting gas mixture into water-bearing coal seam, the higher the initial water saturation, the slower the coal seam permeability increases when N 2 is disturbed, and the slower the coal seam permeability decreases when CO 2 and N 2 are co-disturbed, while both production and storage will decrease. [ABSTRACT FROM AUTHOR]

• The mechanical properties and microstructure of the interface between polyurethane mortar and concrete were tested. • The roughness has the greatest influence on the interface, followed by curing temperature and then water saturation. • The shear strength and splitting tensile strength have a good linear relationship under the influence of all factors. • Microscopic tests show that the polyurethane mortar body structure loosens gradually as the curing temperature decreases. As a repair material, polyurethane mortar has excellent mechanical properties. The aim of this study is to explore the mechanical properties and microstructure of the interface between polyurethane mortar and concrete. The effects of curing temperature (−20 °C, −10 °C, 0 °C, 10 °C, 20 °C), water saturation of concrete (0 %, 30 %, 70 %, 100 %) and roughness (0, 1.5, 3.0, 4.5, 6.0 mm) on the bonding interface strength (shear strength and splitting tensile strength) were investigated through shear and splitting tests. The microstructure of the bonded interface was analysed by scanning electron microscopy at different curing temperatures and water saturation of the concrete, and an interfacial bonding mechanism was proposed. The results of the study show that the strength of the bonded interface increases gradually as the curing temperature rises. At the same curing temperature, the strength of the bonded interface decreases with increasing water saturation of the concrete and is essentially linear. The rate of strength loss of high-water-saturation specimens increases gradually as the temperature rises. When the temperature is positive, the interfacial bond strength increases and then decreases with increasing roughness, and a critical value (4.5 mm) of roughness exists that makes the bond strength reach a maximum. At negative temperatures, the interfacial bond strength increases with increasing roughness. The grey correlation analysis shows that roughness has the greatest influence on the interfacial bonding performance, followed by curing temperature and then water saturation. The interfacial shear strength and splitting tensile strength have a good linear relationship under the influence of all factors. Microscopic tests show that the polyurethane mortar body structure loosens gradually as the curing temperature decreases. As the water saturation of the concrete increases, the interface width between the polyurethane mortar and concrete shows an overall tendency to increase. [ABSTRACT FROM AUTHOR]

Abstract To investigate the effect of the application of complex resistivity logging in sand-shale reservoirs, measurements of complex resistivity are performed on core plugs obtained from artificial clear sand samples and shaly sand samples with different clay types and contents in a frequency range of 40 Hz to 15 MHz. This paper discusses the relationship between the complex resistivity values of samples and their porosity, water saturation, salinity, ion type, clay content, and temperature using the Cole-Cole model to fit complex resistivity curves and obtain the model parameters R0 and τ, which represent the resistivity at zero frequency and the time constant respectively. The results show that τ has the same trend as R0 i.e., it decrease as porosity, water saturation, salinity, clay content and temperature increase. Based on the Archie model and Waxman-Smith model, the saturation evaluation model of τ is built. This study also extracts the slope of the real part of complex resistivity and explores the correlation between the slope and permeability. A model of slope can be used to predict permeability, and the model parameters are different for clear sand samples and different shaly sand samples. This study provides strong support for studies of the rock complex resistivity mechanism and the application of complex resistivity logging in oil and gas evaluation. Highlights • Complex resistivity measurements of artificial clear and shaly sands are conducted in a frequency range from 40Hz to 15MHz. • The effect of frequency, porosity, water saturation, salinity, ion type, clay content, and temperature are discussed. • A model for predicting saturation with the time constant of the Cole-Cole model is built. • A model for predicting permeability with the slope of the real part of complex resistivity is verified and developed. [ABSTRACT FROM AUTHOR]

Water saturation conditions in the rock masses around underground openings vary with place and time. For the long-term stability assessment of underground structures, it is essential to understand the effect of water on the time-dependent behavior of rocks. In this study, the effects of water saturation on the loading-rate dependence of strength, which is one of the time-dependent characteristics of rocks, were investigated both theoretically and via experiments. First, the effects of loading rate and water saturation on rock strength and its variability were clarified by means of a theory that is based on both stochastic and rate processes. Next, alternating loading-rate tests were conducted on Sanjome andesite using uniaxial compression testing under various water saturation conditions. The test results showed that the rock strength increases with a decrease in water saturation and that an increase in strength accompanied by a tenfold increase in loading rate is almost constant under various water saturation conditions. All of the test results were consistently explained by our theory of the dependence of rock strength and its variability under different loading rates and water saturation conditions. It was also found that the dependence of strength on the loading rate is equivalent to that on the water saturation, and that the strength obtained from a test could be converted to one under an arbitrary loading rate and water saturation condition. In addition, we proposed a constitutive equation based on these theoretical and experimental results that could reproduce the loading-rate dependence of stress-strain curves under various water saturation conditions using a single set of constants. • Alternating loading-rate tests were conducted under various water saturation conditions. • An increase in strength with a tenfold increase in loading rate was independent of water saturation. • The theory consistently explained all the test results of strength and its variability. • The proposed equation could reproduce the test results using a single set of constants. [ABSTRACT FROM AUTHOR]

Abstract Estimation of petrophysical parameters is an important issue of any reservoirs. Porosity, volume of shale and water saturation has been evaluated for reservoirs of Upper Assam basin, located in northeastern India from well log and seismic data. Absolute acoustic impedance (AAI) and relative acoustic impedance (RAI) are generated from model based inversion of 2-D post-stack seismic data. The top of geological formation, sand reservoirs, shale layers and discontinuities at faults are detected in RAI section under the study area. Tipam Sandstone (TS) and Barail Arenaceous Sandstone (BAS) are the main reservoirs, delineated from the logs of available wells and RAI section. Porosity section is obtained using porosity wavelet and porosity reflectivity from post-stack seismic data. Two multilayered feed forward neural network (MLFN) models are created with inputs: AAI, porosity, density and shear impedance and outputs: volume of shale and water saturation with single hidden layer. The estimated average porosity in TS and BAS reservoir varies from 30% to 36% and 18% to 30% respectively. The volume of shale and water saturation ranges from 10% to 30% and 20% to 60% in TS reservoir and 28% to 30% and 23% to 55% in BAS reservoir respectively. Graphical abstract Image 1 Highlights • Relative acoustic impedance inversion delineate reservoir tops. • Porosity section is generated using porosity wavelet technique. • Neural Network model development for Volume of Shale mapping. • Neural Network Model development for Water saturation prediction. • Estimation of Petrophysical parameters in reservoirs, Upper Assam Basin. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Ability of SFM to simulate the ionic solutions flooding experiments. • S wirr has a strong effect on oil recovery during brine flooding stage. • Low salinity brine is preferred in recovery process during brine flooding stage. • High salinity ionic solution is preferred during ionic solution flooding. • IL tested gives promising results at harsh conditions of salinity and pressure. Abstract Surfactant flooding is one of the important methods applied in chemical enhanced oil recovery (CEOR). Toxicity, high cost, and degradation at harsh conditions are the main issues that face companies during surfactant flooding process. Ionic liquids (ILs), known as liquid organic salts at ambient condition, have been suggested as alternative chemicals due to their superiority over the conventional surfactants. In this paper, we report simulation of core flooding experiments conducted using ionic liquid (Ammoeng 102) on Berea sandstone core samples to study efficiency of the IL on oil recovery. The core flooding experiments were published elsewhere (BinDahbag et al., 2014, 2015). The experiments were simulated using surfactant flood model (SFM), accessible in CMG STARS software. The measured oil recovery and pressure drop were utilized to history match the core flood experiments. First scenario was simulated by injecting 20 wt% salinity brine (83% sodium chloride, NaCl, and 17% calcium chloride, CaCl 2) into a core sample initially saturated with 26% irreducible water saturation (S wirr) of the same brine to recover 43% of the original oil in place (OOIP) followed by the ionic solution flooding to recover more than 5% of the OOIP. To study the effect of S wirr on oil recovery using ionic solution, the second scenario was simulated similar to the first one in terms of the injected liquids and sequence except the irreducible water saturation (34% compared to 26%). About 38% of the OOIP was produced during brine flooding whereas more than 6% of the OOIP oil was recovered during ionic solution flooding. To study the effect of brine salinity on oil recovery, a third scenario similar to first one except salinity of brine (10% instead of 20 wt%) was simulated. The result for the third scenario shows recovery of 53% of the OOIP throughout brine flooding followed by 2% incremental recovery during the ionic solution flooding. The results demonstrate that the effect of irreducible water saturation is important during brine flooding stage; however, it is insignificant during ionic solution flooding stage for the runs conducted in this study. In addition, low salinity brine flooding results in higher oil recovery, however, ionic solution flooding was more efficient at higher salinity environment. Simulation of all scenarios showed an acceptable agreement between the experimental and simulation oil recoveries. However, the simulation pressure drops were not matched with the experiments. This may be possible by including the well parameters into the sensitivity analysis. Nevertheless, this has not been conducted in order to isolate the impact of well parameters on the estimated relative permeability parameters. [ABSTRACT FROM AUTHOR]

Abstract Kaolinite clay fines are prevalent in sandstone porous media and it has great impacts on permeability and well productivity decline. High temperature sandstone formations detach the fines from the pore surface and migrate along with the permeating fluid. At some point the fine particles are strained in the pore throats, which leading to permeability damage and well productivity decline. To the best of our knowledge this phenomenon is not well explored in the high temperature carbonate media. Since most of the world's oil reserves are held in carbonate media and its worth to explore the formation damage, especially due to fines migration during higher reservoir temperature at these formations composed of carbonate minerals. Hence, this paper presents laboratory modeling of kaolinite fines colloidal flow in high temperature porous carbonate media during saline water injection. In this paper, we have conducted three sets of coreflood experiments in the temperature ranges of 100 °C 150 °C, and 200 °C. Kaolinite suspension water has been injected into the porous limestone core at these temperature regimes to investigate the possibility of permeability and injectivity deterioration. The main experimental results showed there is an increase in water saturation and heat transfer rates. Concentration of fines surges with increasing PVI and permeability declines with increasing time. Pressure elevates with enhancing PVI, but it plummets after some time. Significantly, the water discharge rate declines for increasing suspension injection and on the other side, for fresh water injection, the rate of water discharge rises steadily. Furthermore, the electrical and thermal conductivities of effluent kaolinite colloid were higher. Moreover, experimental model were tested against statistical based optimizational model, response surface methodology (RSM). These results revealed good agreement and, hence, this paper has explicated the importance of kaolinite clay fines suspension transport in high temperature carbonate reservoirs. Highlights • Kaolinite fines suspension flow was examined in high temperature limestone rock. • A linear increase in water saturation was observed at high temperatures. • High heat transfer and enthalpy rates were achieved. • Permeability and pressure decline was noted at high temperatures. • Kaolinite fines suspension flow caused an injectivity decline. [ABSTRACT FROM AUTHOR]

Abstract In this work, the effects of water saturation and particle size on methane hydrate formation and dissociation in a fixed bed of silica sand were investigated. The experiments were carried out at 277.15 K with the initial pressure fixed at 8 MPa. Three water saturations (50%, 70%, and 90%) and two particle sizes (0.18-0.25 mm and 0.3-0.9 mm) of silica sand were used. The results indicated that water conversion to methane hydrates increased with the decrease of water saturation. 70% was found to be an optimum water saturation due to the largest hydrate amount and the highest gas uptake obtained using the small particle size of silica sand (0.18-0.25 mm). In addition, hydrate formation rate and gas uptake obtained using small particle size of silica sand were larger, and gas recovery and hydrate dissociation rate were higher in the dissociation experiments using the small particle size of silica sand. Therefore, the medium water saturation (70%) and small particle size (0.18-0.25 mm) are favorable for methane hydrate formation and dissociation in the fixed bed of silica sand. [ABSTRACT FROM AUTHOR]

Abstract To understand combined effects of water saturation and loading rate on the fracture behavior of rock materials, dynamic notched semi-circular bending (NSCB) tests were conducted on dry and saturated sandstone specimens under a wide range of loading rates using a modified split Hopkinson pressure bar (SHPB) setup. Test results revealed that, the dynamic fracture initiation, propagation toughness and crack propagation velocity of saturated specimen were apparently lower than that of dry ones at the same loading rate. The above parameters increased with the increase of loading rate. Compared with the dry specimen, the saturated specimen owned a higher rate dependency of the dynamic fracture initiation, propagation toughness and a lower rate dependency of crack propagation velocity. Moreover, dual effects of water on the fracture behavior under different loading rates were discussed. It is believed that the different rate dependencies of fracture behaviors between dry and saturated specimens was governed by the combined weakening and enhancing effects of water. A micro-mechanical model was further developed to explain the experimental results based on the duality of water and linear elastic fracture mechanics (LEFM). [ABSTRACT FROM AUTHOR]

Abstract Displacement pressure difference and initial water saturation are two key factors of evaluating water phase trapping (WPT) damage under a given reservoir situation. Requiring a high displacement pressure to drive liquid through a tight rock, the conventional method has difficulty in measuring very small liquid flow rates. Besides, it exists a strongly advantageous flow path selectivity phenomenon, causing a situation that the water existing in those thinner pores cannot be moved effectively. As a result, the irreducible water saturation is high after oil displacing water, thus leading to an overestimated oil permeability damage from WPT. This paper would have presented a high back pressure displacement method (HBPD) for the establishment of initial water saturation and measurement of liquid permeability of core samples from tight oil reservoirs. Then the damage of WPT using this new method was compared with the results obtained by the conventional method. According to the reservoir fluid flow situation, pore pressure and downstream pressure were simulated by the operation of back pressure. Results showed that an average initial water saturation (S wi) of 46.2% was established by the conventional method. However, the S wi established with the use of this new method was only 29.9%, which was consistent with the results from sealed core data of the reservoir. The oil permeability damage derived from water phase trapping was estimated as an average of 37.0% with the conventional method while that of 21.8% by the new method respectively. The conventional method overestimated the damage of water phase trapping at 41.4%. Our research appears to have an insight into analyzing oil-water flow behaviors and investigating the reservoir forming process of tight oil reservoirs. Highlights • A new evaluation method on water phase trapping damage in tight oil reservoirs is proposed. • A back pressure is exerted at the outlet of cores to investigate the oil-water flow behaviors. • Water that exists in those thinner pores can be displaced effectively under the effect of back pressure. [ABSTRACT FROM AUTHOR]

Bakken Petroleum System (BPS) is composed of both conventional and unconventional units, which exhibits significant variations in lithology, rock texture, clay content, total organic carbon, accompanied by high connate water salinity, presence of disseminated pyrite grains, and low values of porosity. These petrophysical attributes of the BPS lead to inconsistency in the oil-in-place estimates for those obtained from Electromagnetic (EM) induction log, Nuclear Magnetic Resonance (NMR) log, dielectric dispersion log measured by Array Dielectric Tool (ADT), and Dean-Stark core measurements. For purposes of improved hydrocarbon saturation estimation and petrophysical characterization in the BPS, a joint-inversion-based interpretation was performed on dispersive electrical conductivity and dielectric permittivity measurements at 4 dielectric-log-acquisition frequencies and 1 induction resistivity acquired at 20 kHz. This analysis was performed across a 350-ft depth interval in one of the science wells intersecting the BPS. Three geo-electromagnetic mixing models, namely Complex Refractive Index model, Stroud-Milton-De model, and Waxman Smits model are integrated and coupled to the inversion scheme to simultaneously estimate water saturation, formation brine conductivity, cementation exponent and saturation exponent in BPS. Water saturation estimates obtained using the proposed interpretation method were compared against those obtained from NMR log, Dean-Stark core measurements and service company’s dielectric inversion. In Middle Bakken from depth XX720 to XX750 ft, our estimates of water saturation are in better agreement with those estimated by service company’s mineral inversion method and service company’s dielectric interpretation as compared to those obtained from NMR interpretation and Dean Stark core measurement. Water saturation and formation brine conductivity estimates in Middle Bakken are in the ranges of 0.5–1 and 25–45 S/m, respectively. Inversion-derived brine conductivity and saturation exponent estimates are most uncertain in Lodgepole and Three Forks 2 formations, which exhibit a wide range of pore size distribution. Average relative errors in matching the 1 induction resistivity and 8 dielectric dispersion logs using the inversion-derived estimates are 33% and 20%, respectively, in the 350-ft depth interval of BPS. The proposed inversion achieves high certainty for the estimates when the formation has low clay content, low electrical anisotropy, and high porosity. [ABSTRACT FROM AUTHOR]

Abstract Pellet/powder bentonite mixture is one of the candidate materials for sealing plugs in deep geological high-level radioactive waste disposal. This note presents an investigation on the structure changes of this mixture occurring during the saturation process by means of X-ray computed micro-tomography. The test was performed in an infiltration column (60 mm in inner diameter and 120 mm in height). Water was supplied to the two ends of the column and the changes of the sample morphology were observed during a period of 100 days of hydration. Digital Volume Correlation (DVC) technique was used to determine the vertical displacement field of the bentonite powder. A pressure transducer was used to measure the axial swelling pressure during the hydration. The results show that the initial distribution of powder in the inter-pellet pores was not homogeneous; the powder filled almost completely the pores in the zones close to the two ends while air-filled inter-pellet voids were observed in the middle of the column specimen. When water started to infiltrate inside the specimen from both ends, the pellets and the powder grains started to swell (because of the swelling properties of smectite, the principal mineral of bentonite) and filled the voids. That induced at the same time increase of swelling pressure and downward movement of powder grains. The results allowed a better understanding on the hydro-mechanical couplings, at the pellet scale, in the pellet/powder bentonite mixture upon wetting. Highlights • 3D observation of pellet/powder bentonite mixture upon wetting • The initial structure of the mixture is heterogeneous and granular • Hydration creates a homogeneous material in a column of 120 mm length after 100 days of hydration from both ends. • The bentonite powder grains tend to move downward during the first day of hydration when the bentonite pellets are rearranged due to their wetting-induced swelling. [ABSTRACT FROM AUTHOR]

Abstract Calculating hydrocarbon in place is one of the most important aspects to be considered in reservoir evaluation. Carbonate rocks with high heterogeneity, exhibit significant changes in petrophysical and lithological properties. Archie's exponents (m and a) are basic parameters for saturation calculations. Uncertainties in obtaining these exponents lead to considerable errors in the saturation assessment. In this study, various pore and rock typing methods were carried out on a Permian–Triassic carbonate reservoir in the central Persian Gulf, Iran. The used methods include pore typing, pore facies classification, velocity deviation log, reservoir quality index, Winland R35, Pittman R35 and ranges of core permeability. Archie's exponents were obtained for different classes based on extracted data from petrographical studies, conventional core analysis and wire line log data. Results showed that determination of rock types based on pore typing has the greatest effect on the precise determination of Archie's exponents. On the other hand, the most unreliable results were related to the velocity deviation log. Pore types directly control the connectivity of the fluid pathways and so have the most important effect. Combining pore types in various groups such as velocity deviation or pore facies classification, reduce the measurement accuracy of Archie's exponents and resulted water saturation. Finally, it can be concluded that, in addition to the high impact of pore type on the accuracy of the obtained exponents, the permeability and pore throat radius are less effective in determining the Archie's exponents. Graphical abstract Image 1 Highlights • Archie's exponents in Kangan and Dalan formations in Iran considered for the first time. • Various rock and pore typing methods used for considering the effect of heterogeneity. • Pore typing is the best method for classifying the reservoir rocks according to their m and a exponents. • Increasing heterogeneity decrease the accuracy of water saturation calculation in carbonate reservoirs. • Reducing accuracy from pore type to pore facies and velocity-deviation log demonstrate the effect of heterogeneity. [ABSTRACT FROM AUTHOR]

Permeability is an important parameter for describing the transport properties of gas shales. This study investigates the effects of water saturation on stress-dependent permeability and the slip factor of Carboniferous shales in the Qaidam Basin, China. To analyze correlations between water saturation, effective stress, helium permeability, and slip factor, helium permeability of 12 shale samples with different water saturation at pore pressures up to 6.89 MPa and effective stresses up to 27.58 MPa at 25 °C is measured. Subsequently, shale characteristics, including mineral composition, total organic carbon (TOC) content, thermal maturity, vitrinite reflectance, and pore structure distribution (PSD; pore volume and type), are determined. The analyses reveal a consistent (exponential) relation between apparent effective gas permeability (at 6.89 MPa) and effective stress. The apparent effective helium permeability (at 4.13 MPa) decreases exponentially with increasing water saturation, particularly in shale samples with a high intrinsic permeability. The critical water saturation value of shale is 30%–40%. Two different modes of gas–water two-phase flow are observed. When water saturation is ∼30%, helium permeability decreases sharply and gas–water flow in the shale samples appear as channel flow. However, when water saturation is >40%, helium permeability slowly decreases, gas–water flow in the shale samples appear as funicular flow, gas and water simultaneously flow in all capillaries, and thin films of structured water on mineral surfaces reduce the pore-throat diameter. Thus, increased water films in narrow flow paths increase the gas slippage effect. Furthermore, the slip factor initially decreased with increasing water saturation before increasing. Helium permeability exhibits a negative correlation with TOC and clay contents and a positive correlation with quartz content. The micropores and mesopores in samples with high clay content and TOC are favorable to gas adsorption but not to gas transport. Permeability measurements of humidity oven–dried samples reveal a power–law relation between the gas slip factor and Klinkenberg-corrected permeability; the slope of the resulting curve (−0.29) is lower than that obtained for low-permeability gas sands. This study provides practical information for further studies of shale gas migration and the gas slippage effect in certain gas–water flows. [ABSTRACT FROM AUTHOR]

From research and field development, the threshold pressure gradient (TPG) in tight formations is required before the fluid starts to flow. This paper addresses the different factors that affect the TPG in tight sandstone gas reservoirs with high water saturation. First and foremost, the petrophysical properties were obtained through the following tests: X ray diffraction, scanning electron microscope and nuclear magnetic resonance using cores from Sulige gas field in China. Secondly, the TPG experimental investigations were performed using air bubble method, and a TPG correlation was obtained considering the influences of permeability, connate water and movable water. Finally, a gas production model was established with the TPG, slip and diffusion effects taken into account, and its applications were discussed using actual reservoir parameters. The results showed that the cores have plenty of clay minerals and high connate water saturation. Besides, the throat radii from NMR mainly are distributed between 0.0004 and 0.1 µm, with a few between 0.1 and 0.4 µm. The clay depositions decrease the pore and throat diameters, which result in Jamin effect. The experimental results showed that the TPG exists at the connate water saturation, and increase exponentially with either an increase in dimensionless water saturation or decrease in permeability. The IPR curves showed the TPG effect on gas production is very serious i.e. production loss degree decreases especially at high bottom hole pressure, and the production loss degree decreases as the bottom hole pressure decreases. The greater the water saturation or the smaller the permeability, the greater the production loss degree. In addition, the TPG affects the intercept of the abscissa of the flow curve, and the slope of the curve decreases as water saturation increases. [ABSTRACT FROM AUTHOR]

Gas slippage phenomenon in single phase gas flow conditions has been extensively investigated. However, only a few researchers have focused on gas slippage in gas/water two-phase flow conditions. Unfortunately, initial water saturation always exists in tight gas reservoirs, and its impact on gas slippage and flow capacity should not be neglected. In this work, gas slippage for single phase and two-phase flows in tight rocks were experimentally investigated, and our results directly demonstrated that gas slip factors increase with an increase in water saturation. But interestingly, the measured values were significantly higher than those predicted by the Klinkenberg idealized model. This finding indicated that the heterogeneous pore-network structure could largely affect the gas/water distribution characteristics, e.g., leading to ‘water blocking’ or ‘gas trapping’ inside actual samples, which further influenced the two-phase gas slippage behaviors. Thus, a heterogeneity coefficient χ was proposed to correct the deviation between actual cases and the Klinkenberg’s ideal model ( χ  = 0.5 is for the ideal case, and χ ranges from 0.5 to 2.0 for actual tight sandstones), and thus the two-phase gas slippage for actual tight rocks could be well characterized. Besides, the impact of two-phase gas slippage on the relative gas permeability also needs to be paid more attention. Without a correction of gas slippage, the relative permeability for gas flow in a high-pressure reservoir condition would be overestimated, and this error could be up to 20% for our studied samples. Our present work illustrates a better understanding on how water saturation affects gas slippage in a two-phase flow condition, and paves a path for a more accurate evaluation of the gas flow capacity in actual reservoir systems. [ABSTRACT FROM AUTHOR]

This paper provides quantitative experimental data that demonstrate the impact of changing partial water saturation on the static elastic and strength (UCS) properties of gas shales from two different unconventional plays. To achieve this goal, a testing set-up and experimental methodology based on the control of total suction were specifically developed. Two core samples from different unconventional shale gas reservoirs were tested. The obtained results clearly show a significant dependence of the Young's modulus on total suction, where a non-linear decrease of stiffness higher than 50% can be observed when suction is reduced during a wetting process. On the other hand, the Poisson's ratio is not highly influenced by different saturation states; it can be considered constant for suction values greater than 10 MPa. A significant impact on the uniaxial compressive strength was also observed, where a 20% decrease of this strength parameter was measured when gas shales are conditioned to lower suction value. To include the observed behavior of gas shales in elastic constitutive model, an empirical relationship to express the dependence of Young's modulus on suction is proposed. Besides a better understanding of the behavior of gas shales during the drilling procedures and hydraulic fracturing phase, the findings of this study are also of great relevance to understand the impact that exposure of core samples to non-controlled air humidity may have on the results of laboratory tests. [ABSTRACT FROM AUTHOR]

Water saturation ( S w ) and hydrocarbon saturation ( S hc = 1 - S w ) estimates in hydrocarbon-bearing formations are generally derived from Dean-Stark core measurements, NMR log, and electromagnetic (EM) logs, such as induction log, galvanic resistivity (laterolog), or dielectric dispersion logs. In-situ estimation of hydrocarbon saturation in conventional reservoirs primarily rely on the deep-sensing or high-resolution EM logs. However, in the hydrocarbon-bearing shale formations, hydrocarbon saturation estimates obtained from EM logs tend to be unreliable. Conventional EM-log-interpretation models tend to break down for shale formations because they neglect the interfacial polarization effects and the dispersive behavior of EM properties of such geomaterials. This can be addressed by jointly processing the subsurface galvanic resistivity, induction, propagation and dielectric dispersion logs using an integrated model that accounts for the interfacial polarization mechanisms. One galvanic resistivity (laterolog) and dielectric dispersion logs, comprising 4 conductivity and 4 dielectric permittivity logs measured at four distinct frequencies, were acquired in a 520-feet depth interval of a well drilled in the upper Wolfcamp shale formation. We implement a novel log interpretation technique for the improved estimation of water saturation ( S w ), brine conductivity ( C w ), textural index/cementation exponent ( m ), and saturation exponent ( n ) in the upper Wolfcamp shale. Log processing was performed with an integrated mechanistic model, which combines Complex Refractive Index (CRI) model to analyze the conductivity and permittivity logs acquired at 1 GHz, Stroud-Milton-De (SMD) model to analyze the 3 conductivity dispersion and 3 permittivity dispersion logs in the frequency range of 10 MHz to 0.3 GHz, and Waxman-Smits (WS) model to analyze the deep galvanic resistivity log (RLA5) measured by the EM laterolog tool at 1 kHz. In the upper Wolfcamp shale, estimates derived from the joint inversion were robust in the presence of pyrite, low water saturation, and low porosity as compared to estimates from the inversion of only four-frequency dielectric dispersion logs. Formation brine conductivity and saturation-exponent estimates are more reliable compared to water saturation and cementation exponent estimates. Water saturation estimates obtained using the proposed methodology are compared against those obtained using multi-mineral inversion and those derived using CRIM model. Average relative errors in fitting the 1 laterolog resistivity and 8 dielectric dispersion logs using the estimates obtained from the proposed method are 10% and 20%, respectively, and their extreme values are 55% and 60%, respectively, in the 520-ft depth interval of the upper Wolfcamp shale formation. [ABSTRACT FROM AUTHOR]

The present study applied Lattice Boltzmann method (LBM) for examining the transport of liquid water in a GDL carbonic paper of polymer electrolyte membrane (PEM) fuel cells. The stochastic method is used for GDL carbonic paper reconstruction. In order to study the behavior of liquid water, different simulations are carried out on the reconstructed GDL. While removing from the GDL of a PEM fuel cell, the dynamics of liquid water is simulated by LBM in this study. The effects that the wettability of GDL imposes on the removal process and liquid water distribution are investigated. In addition, the dynamic behaviors and the saturation process of the liquid water in GDL in a steady state and a transient mode are also explored. The effects of surface wettability on the effective clusters in GDL, merging of different clusters and the loops developed by the fingers are investigated. Moreover, the effects of mixed wettability on the liquid water dynamic behavior and liquid water saturation within the GDL are studied in detail. The results show that the best location for insertion of the hydrophilic layer inside the GDL is near the GDL-GC interface. In this case, the time required for liquid water to reach the GDL/GC interface is reduced about 17% than purely hydrophobic GDL. A decrease of 18.7% in the steady-state saturation level is also observed by insertion of hydrophilic layer; therefore, use of hydrophilic layer near GDL-GC interface is more effective than increasing the contact angle of GDL-fibers. Different validation studies are also reported to show the accuracy of the model. [ABSTRACT FROM AUTHOR]

This paper discusses the relationship among capillary pressure ( P C ), nuclear magnetic transverse relaxation time ( T 2 ) and resistivity index ( I ). The three parameters are related to the geometry of pore structure. We use the fractal concept to describe the relationship between T 2 and I .In addition, a new T 2 -I model is established. 8 Cores from tight sandstone reservoir in China are selected to do experiments. The results reveal that the cores have continuous fractal dimension characteristics. Additionally, the fractal dimensions appear great differences in the different pore radius scales. Therefore, a piece-wise fitting method is adopted. We divided the pores into macropore, mesopore and micropore. Through the verification, our T 2 -I model and piece-wise fitting method are feasible. An application example is also provided in this paper. Based on our researches, we adopt NMR logging data to obtain dynamic parameters of Archie’s formula b and n for calculating water saturation in Tight Sandstone Reservoir. The comparison between our method and normal method demonstrated that our model is much better at matching the core water saturation. [ABSTRACT FROM AUTHOR]

Understanding wave propagation across rock joints is of great importance in rock engineering, petroleum engineering, and other geophysical applications. Previous studies have shown that wave behaviours across filled rock joints are highly affected by the properties of filling materials. However, how clay minerals and water saturation of the infilling affect wave attributes across filled rock joints is still poorly understood. In this study, ultrasonic tests were conducted on kaolinite- and bentonite-filled rock joints to investigate the roles of clay minerals and the water saturation of infillings on elastic P-wave behaviours across individual filled rock joints. The test results show that the infilling's water saturation and mineralogical compositions have combined effects on P-wave signatures of single rock joints filled with clayey soils. Particularly, for the kaolinite-filled rock joint, P-wave velocity and attenuation first increase and then slightly decline with the increasing water saturation. By contrast, for the bentonite-filled rock joint, an increase in water saturation causes gradual decreases in velocity and attenuation. The integrated interpretation of the experimental results indicates that the difference in heterogeneity saturation due to clay hydration is the first-order reason for the discrepancies in saturation-dependent P-wave attributes between kaolinite- and bentonite-filled rock joints. The findings of this study can help further understand wave propagation and attenuation across rock joints filled with fluid-saturated clayey soils. [ABSTRACT FROM AUTHOR]

The evaluation of effective and relative gas permeability is critical for modeling hydrocarbon recovery from low-permeability (unconventional) reservoirs, and for evaluating the potential for clean energy pathways such as carbon capture and sequestration and hydrogen storage in subsurface. Nevertheless, due to the low flow rates and long experimental times associated with low-permeability (nanodarcy/microdarcy range) sample testing, measuring relative permeability through conventional techniques is technically challenging, time-consuming, and expensive. Additionally, and importantly, none of the routine laboratory techniques for measuring relative permeability can mimic the boundary conditions under which wells are produced from, or injected into, in the field. For the first time, effective and relative gas permeability of partially-saturated low-permeability sedimentary rocks were investigated using state-of-the-art core analysis techniques based on rate-transient analysis (RTA). Conventional and new straight-line analysis methods, commonly applied to production data in the field, were used to estimate effective gas permeability of core plugs under variable stress conditions and water saturations. Five low-permeability siltstone and organic/clay-rich samples, differing in mineralogy, porosity, and pore size distribution, were analyzed for proof-of-concept testing. The observed flow regimes consist of transient linear flow followed by boundary-dominated flow regimes, as previously reported for field data. Satisfactory correlation (average coefficient of variation less than 7%) between permeability estimates using different RTA techniques demonstrates the applicability of this method for effective and relative permeability assessment of partially-saturated ultra-tight reservoirs (down to less than 1.0∙10−5 md). Importantly, test times after the initiation of the production phase, were on the order of minutes, which is significantly shorter than those commonly achievable using conventional techniques (e.g., hours using pulse-decay gas permeability testing). Effective gas permeability (from 1.5∙10−3 to 7.5∙10−6 md), and slip factor (from 715 to −286 psia−1), decreased with increasing water saturation (0–53%), reflecting the lower contribution of slip flow to gas transport. Effective gas permeability decreased with increasing effective stress (500–4000 psia), likely due to reduced effective (transport) pore throat size and increased tortuosity. The reduction of slip factor and the observed stress dependency with water saturation is attributed to the channel flow mechanism. • Effective gas permeability of core plugs was estimated using RTAPK methods under varying stress and water saturation. • Five low-permeability samples with different mineralogy and porosity were tested using RTAPK for proof-of-concept. • RTAPK method was demostated to be effective for assessing permeability in partially-saturated ultra-tight reservoirs. • RTAPK testing takes minutes, significantly shorter than conventional methods for effective permeability measuement. [ABSTRACT FROM AUTHOR]

In this study, we developed a relationship for Uniaxial Compressive Strength (UCS) based on total formation porosity, bulk density and water saturation using Genetic Programming (GP). The numerical values of these parameters, which offered rock UCS, were obtained by analyzing various logs including sonic, neutron, gamma ray and electric logs. The elastic moduli were calculated by analyzing compressional and shear sonic logs and using mathematical correlations. The rock UCS was then analytically calculated using the empirical Wang and Plumb correlations (Plumb R.A. 1994). In order to predict UCS of the formation rock using the GP technique, approximately 5000 data points associated with 3 different wells in one of the Iranian oil fields were collected and analyzed. The data points associated with one of the wells were used to structure the GP model after being calibrated with some UCS data derived from core analysis while the other two sets of the data points were employed to test the accuracy of model's predictions. The predicted UCS values using GP model were consistent and in very good agreement with the corresponding values calculated analytically using well log data. [ABSTRACT FROM AUTHOR]

A major drawback of old resistivity tools is the poor vertical resolution and estimation of hydrocarbon when applying water saturation (S w ) from historical resistivity method. In this study, we have provided an alternative method called saturation height function to estimate hydrocarbon in some clastic reservoirs in the Niger Delta. The saturation height function was derived from pseudo capillary pressure curves generated using modern wells with complete log data. Our method was based on the determination of rock type from log derived porosity-permeability relationship, supported by volume of shale for its classification into different zones. Leverette-J functions were derived for each rock type. Our results show good correlation between S w from resistivity based method and S w from pseudo capillary pressure curves in wells with modern log data. The resistivity based model overestimates S w in some wells while S w from the pseudo capillary pressure curves validates and predicts more accurate S w . In addition, the result of S w from pseudo capillary pressure curves replaces that of resistivity based model in a well where the resistivity equipment failed. The plot of hydrocarbon pore volume (HCPV) from J-function against HCPV from Archie shows that wells with high HCPV have high sand qualities and vice versa. This was further used to predict the geometry of stratigraphic units. The model presented here freshly addresses the gap in the estimation of S w and is applicable to reservoirs of similar rock type in other frontier basins worldwide. [ABSTRACT FROM AUTHOR]

Internal structure of coalbed methane (CBM) reservoirs can be evaluated through ultrasonic measurements. The compressional wave that propagates in a fractured coal reservoir may indicate the internal coal structure and fluid characteristics. The P-wave propagation was proposed to study the relations between petrophysical parameters (including water saturation, fractures, porosity and permeability) of coals and the P-wave velocity (V p ), using a KON-NM-4A ultrasonic velocity meter. In this study, the relations between V p s and water saturations were established: Type I is mainly controlled by capillary of developed seepage pores. The controlling factors on Type II and Type III are internal homogeneity of pores/fractures and developed micro-fractures, respectively. Micro-fractures density linearly correlates with the V p due to the fracture volume and dispersion of P-wave; and micro-fractures of types C and D have a priority in V p . For dry coals, no clear relation exists between porosity, permeability and the V p . However, as for water-saturated coals, the correlation coefficients of porosity, permeability and V p are slightly improved. The V p of saturated coals could be predicted with the equation of V p -saturated = 1.4952V p -dry–26.742 m/s. The relation between petrophysical parameters of coals and V p under various water saturations can be used to evaluate the internal structure in fractured coals. Therefore, these relations have significant implications for coalbed methane (CBM) exploration. [ABSTRACT FROM AUTHOR]

The road to understanding the frequency dispersion (relaxation) of permittivity and resistivity in tight rocks remains relatively uncharted. Our team from Da'anzhai Group, Jurassic formation, Sichuan Basin carried out practical research to explore this phenomenon. The research was conducted under laboratory conditions for a selection of low frequencies, with ranges between 0.1 Hz to 1 kHz. Our research has shown that, although both the permittivity and resistivity decrease as the frequency increases, the two individual metrics display different behaviours when compared with each other. While the degree of resistivity variation is minimal, to the point that it is redundant, the permittivity, on the other hand, demonstrates something that is scientifically noteworthy. Permittivity has a distinctive dispersion degree across the entire sample of frequencies and the difference between the minimum and maximum frequencies is several orders of magnitude. An additional, and unexpected, learning from our research is that the level of frequency dispersion increases as the water saturation and concentration increases. In this paper, a collection of equations has been formulated to describe this relationship. These equations particularly shed light on the areas of rock porosity and saturation. They also show that the degree of frequency dispersion of permittivity or resistivity can be used as a function of water saturation and concentration. Two new variables are introduced here, D R and D C , to demonstrate the relaxation law quantitatively. In our practical research, we have characterised the relationship between the saturation and concentration with dielectric relaxation, using three different concentrations of D R and D C and five different saturations of NaCl solution. In difference to conventional Archie's multiple experimental parameters, we have established a new formula to derive the saturation from Rp and Cp, or from D R and D C directly. Two important frequencies were also further investigated for Cp dispersion: first is the critical frequency, which marks the dispersion speed change from steep phase to steady phase, and second is the zero-frequency, which marks the dispersion when it approaches zero. All tight rocks were measured under the same conditions, with the results displaying the same pattern of variations. The results have led us to believe that Cp's frequency dispersion at low-frequencies provides a new methodology to characterise tight rocks. [ABSTRACT FROM AUTHOR]

Shaly sandstone reservoirs have complex pore systems with ultra-low to low interparticle permeability and low to moderate porosity. This has leaded to development of several models to calculate water saturation in shaly sandstone reservoirs using different approaches, assumptions and certain range of conditions for application. This practical study has used actual well logging data from two different fields of South Texas and North Sea to evaluate and compare the most popular five shaly sandstone models for calculating water saturation. A systematic approach is presented for identification of shale distribution for selection of suitable model. Furthermore, sensitivity analysis of tortuosity coefficient (a), cementation exponent (m) and water saturation exponent (n) is achieved to investigate their effects on computed values of water saturations using different models. The results indicated that identification of shale distribution is necessary and improper utilization of shaly sandstone models results in drastically erroneous values of water saturation. Therefore, shale distribution in the South Texas field is identified to be mainly laminated with few of structural ones while distribution is dispersed in the North Sea field. The results also showed that the increase of shale volume decreases water saturation calculated for all popular models. In addition, the increase of tortuosity coefficient and/or cementation exponent (m) causes overestimation of water saturation while the increase of saturation exponent (n) results in an underestimation values. The application of the attained results of this study will have real improvement in selection and application of the appropriate shaly model. This provides more accuracy and real improvement in formation evaluation, reserve estimation, reservoir characterization, and consequently in reservoir simulation. [ABSTRACT FROM AUTHOR]

Accurate estimation of permeability is essential in reservoir characterization and in determining fluid flow in porous media which greatly assists optimize the production of a field. Some of the permeability prediction techniques such as Porosity-Permeability transforms and recently artificial intelligence and neural networks are encouraging but still show moderate to good match to core data. This could be due to limitation to homogenous media while the knowledge about geology and heterogeneity is indirectly related or absent. The use of geological information from core description as in Lithofacies which includes digenetic information show a link to permeability when categorized into rock types exposed to similar depositional environment. The objective of this paper is to develop a robust combined workflow integrating geology and petrophysics and wireline logs in an extremely heterogeneous carbonate reservoir to accurately predict permeability. Permeability prediction is carried out using pattern recognition algorithm called multi-resolution graph-based clustering (MRGC). We will bench mark the prediction results with hard data from core and well test analysis. As a result, we showed how much better improvements are achieved in the permeability prediction when geology is integrated within the analysis. Finally, we use the predicted permeability as an input parameter in J-function and correct for uncertainties in saturation calculation produced by wireline logs using the classical Archie equation. Eventually, high level of confidence in hydrocarbon volumes estimation is reached when robust permeability and saturation height functions are estimated in presence of important geological details that are petrophysically meaningful. [ABSTRACT FROM AUTHOR]

This work uses neutron radiography to examine the through-plane liquid water distribution of an operating polymer electrolyte membrane fuel cell (PEMFC) with a Sigracet SGL 25BC, a 235 μm thick, 2D straight fiber Gas Diffusion Layer (GDL). This work is performed for interdigitated flow fields at several cross flow rates, and a parallel flow field for comparison. The effect on pressure drop, effective permeability and liquid water saturation is determined. These results are compared to the previously studied Sigracet SGL 10BC, a 420 μm thick, 3D “spaghetti” fiber GDL, for comparable cross flow rates. The SGL 25BC has a higher permeability than the SGL 10BC. The 25BC has a relatively constant saturation within the GDL, from 8% to 10%, which is higher than the 10BC saturation level, between 4 and 8%. This may indicate that 2D GDLs may be better suited to low pumping power situations, while 3D GDLs may be better suited to low liquid water situations. [ABSTRACT FROM AUTHOR]

Pore geometry is one of the main factors that may lead Archie's equation inaccurate in low and middle porosity sandstone formations. In order to build a robust relationship between the formation resistivity factor and the porosity for the low and middle porosity sandstone formations, we presented a pore-throat model (PT model) that considered the effect of pore geometry. The PT model is an effective medium model that treats the pore space as a series of a spherical pore and two throats. The spherical pore can be described by the pore radius, and the throat can be described by the ratio of the pore radius over the throat radius (the pore-throat radius ratio) and the tortuosity. We collected seventy-two core plugs from the typical low and middle porosity sandstone formation in the Ordos Basin in China, having porosity ranging from about 3–20%. Forty-seven of the samples with low clay content were chosen for laboratory resistivity measurements to validate the PT model. The core experiments and the application to the well logging interpretation indicated that the PT model provides a more convincing formation resistivity factor, while the formation resistivity factor calculated using Archie's equation is larger than that measured in the lab, especially when the porosity is relatively low. The tortuosity used in the PT model was calculated by a theoretical method and verified by a thin section analysis method. The PT model enhances the understanding of the effects of the pore geometry on the relationship of the formation resistivity factor and the porosity. [ABSTRACT FROM AUTHOR]

The thermal conductivity of porous media is crucial for many geological and engineering projects. Although the thermal conductivity at low temperatures is often overlooked, it is of great significance to calculate the amount of heat that the ice sheet absorbs from the Earth. In this study, the thermal conductivity of dry and water-saturated sandstone was measured in the temperature range of 193 to 373 K using a transient hot wire method. All samples were collected from East China, with a sample porosity distribution of 5 to 13%. The effects of temperature, water saturation and phase transition of fluid in the pores were investigated. The results indicate that the thermal conductivity decreases with an increase in temperature and that the decrease is steeper when the temperature is below 273 K. Moreover, it is found that the thermal conductivity of the saturated sandstone is larger than that of the dry sandstone. With an increase in porosity, the thermal conductivity significantly increases in saturated sandstone but remains almost the same or even decreases in dry sandstones. Finally, it is revealed that the effect of phase transformation on the thermal conductivity is significant. When the water in pores becomes ice, the thermal conductivity increases significantly and increases further as the temperature decreases. [ABSTRACT FROM AUTHOR]

Accurate determination of cementation factor (m) has a significant role in the petrophysical characterization of underground reservoirs. For clean sandstones, the application of this parameter in Archie's Equation provides a basic framework for estimating water saturation. However, the presence of clay minerals in the rock texture could affect the evaluation process. There are different correlations from which the cementation factor can be estimated. In addition, applying rock classification techniques revealed an excellent prospect for better estimating this parameter. However, in most of the mentioned approaches, the effect of clay minerals is missed. In this study, a newly developed modified form of electrical rock typing technique (i.e. classification of rock samples according to their electrical properties) incorporating the effect of clay minerals for improving the prediction of cementation factor in clay-bearing rocks is proposed. In doing so, a new form of electrical quality index is defined based on which the modified formation resistivity factor versus porosity data for 204 clayey rock samples are classified into nine distinct rock types. Comparative studies demonstrated the priority of the suggested methodology rather than classic hydraulic flow unit-based methods such as flow zone indicator and discrete rock type. The latter showed a high degree of scattering in the classification stage. For each rock type, developed based on the proposed scheme, the equations were proposed in which the modified form of formation resistivity factor and cementation factor versus porosity were correlated. Linear relationships with reasonable values of coefficient of determination were then demonstrated for the developed equations. In addition, the effect of clay minerals on the rock's electrical quality and electrical properties (i.e., rock conductivity and cementation factor) is discussed. The results of this study offer a better framework to incorporate the effect of clay constituents in the prediction of cementation factor, as compared to classical rock typing approaches. • A rock typing-based framework was proposed for prediction of cementation factor (m*) in clay-bearing rock. • The effect of clay minerals on the electrical properties of the rock was investigated. • The role of clay content on the resistivity factor (F*) at low salinities was attributed to clay-bound water. • For each rock class, a unique relationship between the m* and newly defined parameter; F*× φ 2 , was suggested. [ABSTRACT FROM AUTHOR]

Iron phthalocyanine (FePc) was used as iron/nitrogen/carbon source and templated with an ordered mesoporous silica (SBA-15), followed by heat treatment and leaching of SiO 2 with hydrofluoric acid (sacrificial method). The Fe–N–C catalyst was tested for the oxygen reduction reaction using a rotating disk electrode (three electrode configuration) in the presence of methanol at different concentrations. Furthermore, the catalyst was investigated in a single cell configuration of a direct methanol fuel cell (DMFC) under different methanol concentrations and temperatures. The optimal operating condition was found to be 1 M at 110 °C, reaching 11.2 mW cm −2 using a commercial Pt-Ru black at the anode and the Fe–N–C at the cathode side. Interestingly, the cathodic catalyst was not dramatically affected by the presence of crossovered methanol, showing only a 12% drop in maximum power density with the highest methanol concentration of 10 M at the anode. A 3D multiphysics model was implemented to further explain the experimental DMFC performance data using a commercial platform (Comsol ® Multiphysics v4.4a). The model agreed with the experimental data, showing a direct relationship between water saturation, and oxygen consumption, consequently oxygen starvation at the cathodic catalytic layer. The model considered two phases on the cathode side computed by extended Darcy law within the catalytic layer and the gas diffusion layer domains. [ABSTRACT FROM AUTHOR]

Breakthrough pressure plays an important role in shale gas flow, mining, and caprock evaluation. A series of breakthrough experiments were conducted under different water saturation conditions for four shales taken from the Carboniferous Hoit Taria Formation in the eastern Qaidam Basin, China to investigate the influence of water saturation on breakthrough pressure. Relevant geochemical tests (mineral composition, clay content, total organic carbon, thermal maturity and vitrinite reflectance) and micro structural characteristics of micro pores were also conducted. Breakthrough pressures under at least five different water saturations (from 0 to 100%) were obtained and relationship between breakthrough pressure and water saturation was fitted for each sample. We found that breakthrough pressure increases exponentially with water saturation. The decrease in effective pore diameter caused by both the bound water films and the swelling of the clay minerals resulted in the increase in the breakthrough pressure. After water saturation reached about 60%, breakthrough pressure increased rapidly from connectivity reduction, caused by the sealing off of smaller pores and partial water saturation of the macropores. By analyzing the correlation between breakthrough pressure and pore structure characteristics, breakthrough pressure is inversely related to porosity, and is primarily affected by macropores. Because macropores consist of many microfractures with lengths up to dozens of micrometers, they determine the porosity and then affect the connectivity of the rock. Correlation analysis between the mineral compositions and breakthrough pressure showed that TOC content exhibits a positive correlation with breakthrough pressure, but neither quartz content nor the clay mineral content exhibits a correlation. By combining this information with Field Emission Scanning Electron Microscope results, we found that microfractures are easily created where the TOC (total organic carbon) is concentrated, and these microfractures substantially contribute to the number of macropores. However, dissolution pores in the quartz and clay minerals are rare. Therefore, the correlation between TOC content and breakthrough pressure primarily results from the microfractures. This study provides practical information for further studies of shale gas migration as well as shale gas mining and caprock evaluation. [ABSTRACT FROM AUTHOR]

A model for coupling thermal, hydraulic, and mechanical properties of GMZ bentonite is presented. The model considers a binary classification of the pores into macropores and micropores and describes the effect of the changes in the two classes under free swelling conditions on the bentonite water retention behaviour. The macropores are assumed to be water conduits, while the water occupying the micropores is assumed to be immobile. The effects of temperature on the mobile and immobile water are considered separately. Variation of mobile water is determined by the water retention curve considering temperature effects, and immobile water is calculated from the deformation of micropores due to different relative humidities (RHs) and temperatures. The model is used to simulate free swelling tests of GMZ bentonite carried out from low RH to high RH under different temperature conditions. A comparison with available experimental data shows that the model offers a good predictive capability and can be used for further understanding the temperature effects on the hydraulic-mechanical behaviour of bentonite. The work underpins engineering assessments of the GMZ bentonite behaviour required for the construction of the deep geological repository at Beishan under coupled thermo-hydro-mechanical effects. [ABSTRACT FROM AUTHOR]