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Water saturation estimation faced a great challenge in tight gas sandstone reservoirs because of the effect of pore structure and strong heterogeneity. The classic Archie's equation cannot be always well used. To quantify the effect of pore structure to rock resistivity in tight gas sandstones, taking Triassic Xujiahe Formation of northwestern Sichuan Basin as an example, 35 core samples were recovered and applied for resistivity experiments in laboratory under the simulated formation temperature and pressure environment, and 18 of them were simultaneously applied for nuclear magnetic resonance (NMR) and high-pressure mercury injection experimental measurements. Relationships between pore structure and resistivity parameters were analyzed. The results clearly illustrated that cementation exponent (m) and saturation exponent (n) were heavily affected by pore structure. Rocks with superior pore structure contained relatively higher cementation exponent and lower saturation exponent, and vice versa. Afterward, we raised a parameter of pore size index, which was defined as the ratio of macropore and micro-pore percentage contents, to characterize rock pore structure, and established a model to calculate optimal saturation exponent from NMR data. Meanwhile, cementation exponent prediction model was also raised by combining with porosity and irreducible water saturation (Swirr). Combining with calculated cementation exponent and saturation exponent, we optimized the Archie's equation to predict water saturation in our target tight gas sands. Field examples illustrated that the predicted cementation exponent and saturation exponent matched well with core-derived results. The absolute errors between predicted cementation exponent and saturation exponent with core-derived results were lower than 0.05 and 0.07, separately. By using optimized Archie's equation, water saturations were precisely predicted from well logging data in our target tight gas sandstone reservoirs; whereas, the classic Archie's equation underestimated formation water saturation. [ABSTRACT FROM AUTHOR]

In-depth research on the impact of water saturation on the mechanical properties of rocks is crucial for safe and reliable rock engineering. This study conducted uniaxial compression tests and acoustic emission (AE) monitoring on coarse-grained sandstone, fine-grained sandstone, and their composites under natural and saturated water conditions. The results revealed that under saturated water conditions, the mechanical properties of coarse-grained sandstone deteriorated significantly, with peak stress (σp), crack damage stress (σcd), crack closure stress (σcc), and elastic modulus (E0) decreasing by 35%, 52%, 33%, and 47%, respectively. The deterioration of fine-grained sandstone was less severe, with σp, σcd, σcc, and E0 reducing by 13%–24%. The mechanical properties of the composites were significantly affected by the water state. Under natural water conditions, the σp, E0, and σcd values of the composites were between those of the individual rock samples. However, when the composites contain saturated samples, the σp, σcd, and σcc of the composites were lower than those of the individual rock samples. Under saturated conditions, the total absorbed energy (U) and stored elastic energy (Ue) of the rock samples decreased, AE counts and crack signals reduced. [ABSTRACT FROM AUTHOR]

To investigate the relationship between the radon diffusion coefficient and free-radon production rate with ambient temperature and water saturation of uranium tailings under frozen and non-frozen conditions, a method was proposed to simultaneously determine the free-radon production rate as well as the diffusion coefficient in porous emanation media based on the pure diffusion migration theory of radon. The diffusion coefficient (α), the free-radon production rate (D), and gas permeability (K) of radon at different temperatures (20 °C, 0 °C, − 10 °C and − 20 °C) and water content saturation (m = 0 and m = 0.52) were determined by a self-made experiment device. The results showed that: (1) the free-radon production rate and the diffusion coefficient of uranium tailings increased with the increase of temperature in the range of 0.77–4.80 Bq·m−3·s−1 and 1.56 × 10–6–3.27 × 10–6 m2·s−1, respectively, when the temperature was in the range of − 20 to 20 °C. (2) With the increase of temperature, the free-radon production rate of dry uranium tailings and uranium tailings with a water saturation of 0.52 increased linearly, and the diffusion coefficient increased nonlinearly; (3) the permeability of uranium tailings with a water saturation of 0.52 at the same temperature was less than that of dry uranium tailing, and the former increased with increasing temperature, while the latter was the opposite. The methods and data obtained in this study can provide references for further research in this field, and the relevant results can be used to evaluate the potential environmental effects of radon migration parameters in uranium tailings ponds under different seasonal temperatures and water saturation conditions. [ABSTRACT FROM AUTHOR]

The effect of water saturation in the Himalayan region is a critical factor influencing the physico-mechanical properties of rocks. Typically, the anisotropic and fragile rock formations are vulnerable to it, as it may directly/indirectly cause directional variation of rock properties. One such notable formation is phyllite, within which numerous geotechnical engineering projects are ongoing or completed. This study aimed to assess the impact of water saturation on the physico-mechanical properties of highly foliated Chandpur phyllite at varying foliation angles. The findings revealed a decreasing trend in P-wave velocity with increasing foliation angles, where higher values were observed in saturated specimens. Mechanical properties exhibited a "U-shoulder" type anisotropic curve with the foliation angle, reaching minimum values at β = 30° and maximum values at β = 90°. Although the overall trend of the mechanical properties remained consistent with the foliation angle, the intensity and magnitude were significantly influenced by saturation. At the microscopic level, the failure surface of the specimen having β = 30° displayed a smooth surface with negligible broken fragments indicating reduced cohesion and lower strength with failure along foliation, regardless of saturation. In contrast, specimens at β = 90° exhibited a rough/jagged surface with numerous broken fragments suggesting increased cohesion and higher strength with failure across foliation. The mineralogical analysis further highlighted the role of well-developed micaceous minerals, in the form of foliation planes, with the rock matrix present between them, influencing the directional behavior of phyllite. [ABSTRACT FROM AUTHOR]

Microwave-assisted rock-breaking is highly promising in the process of hard rock tunnel excavation due to its safety and high efficiency. Water plays a pivotal role in the microwave heating process, significantly impacting the effectiveness of microwave-assisted rock fragmentation. Nevertheless, there is a lack of comprehensive research on the influence of water in the process of microwave heating of rocks. This study investigated the influence of water on the response characteristics of granite under microwave irradiation by analyzing the changes in the real-time acoustic emission (AE) signals, porosity, wave velocity, and uniaxial compressive strength of samples with different levels of water saturation. The experimental results revealed the real-time AE characteristics of rock samples were categorized into three periods: a quiet period, a violent period, and an attenuation period. The maximum temperature in the quiet period was about 150 ℃, resulting in the proliferation of mineral crystal defects under the action of water, and the intensity of AE counts was positively correlated with water saturation. Simultaneously, the degree of thermal damage to porosity, wave velocity, and uniaxial compressive strength also increased with increasing water saturation. During the violent and attenuation periods, the activity of AE signals increased, yet remained largely unaffected by the the water saturation level. Moreover, the presence of water facilitated the transition of rock samples from elastic to ductile behavior under microwave irradiation. This investigation holds significant importance for the practical application and advancement of water utilization in microwave-assisted rock fragmentation technology. Highlights: Real-time monitoring of acoustic emission during microwave heating was realized. Acoustic emission characteristics of granite with different saturations were similar. Acoustic emission characteristics before 150 ℃ were closely related to saturation. [ABSTRACT FROM AUTHOR]

Copyright of Advances in New & Renewable Energy is the property of Editorial Office of Advances in New & Renewable Energy and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Iraqi Journal of Chemical & Petroleum Engineering is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Lovozero rare-metal deposit is represented by a series of sheet-like ore bodies of small and medium thickness exposing on the northwestern slopes of the Lovozero massif. The purpose of the work is to assess the impact of water inflows on the strength characteristics of the rocks of the Lovozero rare-metal deposit developed by the Karnasurt mine. The data on water inflow into Karnasurt mine workings, which exploits two ore bodies of the Lovozero rare-metal deposit, are considered. Statistical processing of the data on water volumes collected by the mine over the latest 4 years was performed, with assessment of their changes during a calendar year. The peculiarities associated with calendar climatic changes were identified. The main purpose of the study was to assess the effect of water inflows on the strength characteristics of the rocks composing the support pillars. The analysis and calculations of precipitation accumulation within the mine allotment and water inflows into the mine workings were performed and compared with actual data on mine waters. The samples of the most representative rocks of the deposit were collected and tested for dry and water-saturated compressive and tensile strength. The quantitative indicators of the changes in the strength characteristics of rocks due to water saturation were determined. It was found that the water saturation led to a decrease in the rock strength by up to 10–20%, especially for compressive strength values.

Abstract Underground rocks are generally subjected to water erosion and dynamic disturbances. To exclude the effect of clay minerals on the water–rock interaction mechanism, clay-free artificial porous rock (APR) was used to investigate the coupling effect of water saturation and loading rate on tensile behavior. Dynamic Brazilian disc experiments were performed on APR with six water saturation levels (100, 80, 60, 40, 20, and 0%) using a split Hopkinson pressure bar (SHPB) combined with a high-speed camera. The results indicated that the number of cracks in the APR specimens increased with the water saturation level during the dynamic damage process, with more radial cracks at the water saturation of 80–100%. The dynamic tensile strength (DTS) and dissipated energy density exhibited different change trends with water saturation levels under different loading rates and the rate dependence was most significant in the fully saturated state (100%). At lower loading rates, DTS initially decreased rapidly and then more slowly with increasing water saturation. At higher loading rates, DTS exhibited a ‘decrease then increase’ trend. Moreover, the water-affecting factor exhibited an overall decreasing trend with the loading rate and gradually converged to 1.0. These phenomena can be attributed to the interplay between the weakening and strengthening water-effect mechanisms based on the microstructure and water distribution in the APR specimens.

Abstract The longevity of waste asphalt can be considerably improved through cold recycling techniques combined with various additives. This research investigates the cold regeneration of aged asphalt concrete using Reclaimed Asphalt Pavement (RAP), Portland cement, cationic bitumen emulsion, and additional aggregates. The primary goal is to evaluate the performance enhancements in terms of average density, compressive strength, water resistance, and swelling across different mix compositions. Three distinct mixtures were formulated and assessed. Mix No. 1, composed solely of RAP, showed the lowest average density and highest swelling, indicating poor performance due to the lack of binding agents. Mix No. 2, which incorporated RAP, Portland cement, and water, exhibited the highest density and compressive strength, highlighting the crucial role of Portland cement in improving structural integrity. Mix No. 3, a more complex mixture including RAP, aggregates, Portland cement, water, and bitumen emulsion, displayed balanced properties with enhanced moisture resistance and reduced swelling. The experimental findings emphasize the effectiveness of adding Portland cement and bitumen emulsion to improve the mechanical and durability characteristics of recycled asphalt mixtures. Specifically, Mix No. 2 and Mix No. 3 demonstrated significant performance improvements, making them suitable for road maintenance applications. This study advocates for the widespread use of cold recycling methods with additive integration to achieve sustainable and cost-effective pavement restoration solutions.

Tight sandstone water-bearing gas reservoirs typically exhibit low porosity and low permeability, with reservoir rocks characterized by complex pore structures, often featuring micron-scale or smaller pore throats. This intricate reservoir structure significantly restricts fluid flow within the reservoir, necessitating a certain threshold pressure gradient (TPG) to be overcome before flow can commence. This study focuses on the Ordos Basin and explores the influence of high water content tight sandstone gas reservoirs on TPG under different water saturation and formation pressure conditions through experiments. A mathematical model of TPG is established using multiple linear regression method. The results show that TPG is primarily affected by water saturation, followed by formation pressure. As the water saturation increases, the TPG of the core decreases, and the change becomes more pronounced when the water saturation exceeds 50%. As formation pressure increases, the weakening of the slippage effect in gas molecules leads to TPG stabilization, especially when local pressure exceeds 25.0 MPa. The research also shows that low-permeability cores exhibit greater TPG variation with pressure changes, while high-permeability cores remain more stable. A mathematical model was developed and validated to predict TPG based on permeability, water saturation, and formation pressure. These findings highlight the need to monitor formation water content during tight sandstone gas reservoir development to optimize production strategies, providing valuable insights for improving reservoir management and guiding future research. [ABSTRACT FROM AUTHOR]

The proton exchange membrane fuel cell (PEMFC), with a high energy conversion efficiency, has become an important means of hydrogen energy utilization. However, water condensation is unavoidable in the PEMFC because of low operating temperatures. The impact of liquid water on PEMFC performance and stability is significant. The gas diffusion layer (GDL) provides a critical transport path for liquid water in the PEMFC. Liquid water saturation and distribution in the GDL determine water flooding and mass transfer efficiency in the PEMFC. In this study, focusing on the effects of the water introduction method, osmotic pressure, and contact angle, the liquid water transport in the GDL was numerically investigated based on a pore-scale model using the volume of fluid (VOF) method. The results showed that compared with the conventional water introduction method without cracks, the saturation and spatial distribution of water inside the GDL obtained in the simulation were more consistent with the experimental results when the water was introduced through the microporous layer (MPL) crack. It was found that increasing the osmotic pressure resulted in a faster rate of water penetration, faster approaching the steady-state performance, and higher saturation. The ultra-high osmotic pressure contributed to the secondary breakthrough with a significant increase in saturation. Increasing the contact angle caused higher capillary resistance, especially in the region with small pore sizes. At a constant osmotic pressure, as the contact angle increased, the liquid water gradually failed to penetrate into the small pores around the transport path, causing saturation reduction and an ultimate failure to break through the GDL. Increasing the contact angle contributed to a higher breakthrough pressure and secondary breakthrough pressure. [ABSTRACT FROM AUTHOR]

The performance of fuel cells is greatly influenced by the design of the flow channels, making it one of the most significant factors impacting their overall performance. In this work, numerical simulations on serpentine, parallel, and interdigitated geometries are carried out using an open-source toolbox at 0.5, 0.4, and 0.3 V to observe the liquid water saturation distribution at the cathode side of a three-dimensional multiphase non-isothermal model of a protonic exchange membrane fuel cell. The results indicate that the serpentine flow channel shows the maximum current density and the minimum saturation distribution. Also, it is shown that maximum saturation values are located at the edges of the membrane-electrode assembly. There is an important change in the ionic distribution which directly impacts the current density. [ABSTRACT FROM AUTHOR]

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]

The article describes experimental studies on water saturation of samples of major rock types typical of the Donbas. The alterations of deformation properties of moist rocks are generalized. The procedure of modeling with regard to the effect of flooding on displacement parameters in different rocks is presented. Using laboratory data, a finite-element model of activation of geomechanical processes initiated by rock mass undermining and flooding is constructed. It is found how rock mass lithology influences displacement parameters in flooding of underground roadways in coal mines being closed. The research results can help improve effective regulatory documents on ground surface displacement prediction in coal mining and mine closure through lithological analysis of coal–rock mass. [ABSTRACT FROM AUTHOR]

Understanding the counter-flow of liquid inlet and gas outlet at the interface between the electrolyte and cathode gas diffusion layer (GDL) is crucial for water management in proton exchange membrane fuel cells. Existing studies typically overlook air outlets and assume a fixed liquid inlet direction. This study uses a volume of fluid method to model two-phase interactions in a T-shaped GDL and gas channel (GC) assembly, with GDL geometry derived from nano-computer tomography. Considering potential electrode deformations, such as local cracks and blockages, this research investigates the impact of the size and shape of liquid invasion on the liquid-gas behavior in the cathode GDL and GC using five liquid injection configurations. Simulations also incorporate GDL gas outlets, integrating them with a tailored liquid inlet setup. Results show that the injection site and configuration significantly affect water behavior in the GDL, affecting saturation, stabilization, and breakthrough, followed by drainage in the GCs. Comparisons of simulations with and without air outflow show distinct counter-flow interactions, highlighting variations in water distribution and discrepancies in two-phase transport across the GCs. [ABSTRACT FROM AUTHOR]

Copyright of Special Oil & Gas Reservoirs is the property of Special Oil & Gas Reservoirs Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Water enters engine oil in different ways and moves in the lubrication system causing an increase in wear, oil degradation and additives depletion. It has been proposed that water in the lubricants can transfer from dissolved to free phase leading to additives depletion in the oil. Different additives in the lubricants can easily latch to water molecules forming reverse micelles. The separation of reverse micelles from the oil causes additives depletion. This experimental and analytical study aims to investigate how the separation of free water above the saturation level can diminish the efficiency of additives in engine oils. The effect of varied levels of water on oil performance and its additives was investigated in this study. A new saturation method was used to determine the water saturation level in engine oil at different temperatures. The results reveal a decrease in additive concentration with increased separation of free water from the oil. Free water separation from engine oil is expected to reclaim the tribological performance, however, the results demonstrate that tribological performance after the separation of free water from the oil has been affected. The study showed not only does the removal of free water diminish the efficiency of additives due to additives depletion (≈ 10 wt%), but also the remaining dissolved water which is ≈ 2600 ppm can also affect wear and tribofilm chemistry. The results prove that two main mechanisms influence oil performance expressed as additives depletion by free water and remaining dissolved water. [ABSTRACT FROM AUTHOR]

The longevity of waste asphalt can be considerably improved through cold recycling techniques combined with various additives. This research investigates the cold regeneration of aged asphalt concrete using Reclaimed Asphalt Pavement (RAP), Portland cement, cationic bitumen emulsion, and additional aggregates. The primary goal is to evaluate the performance enhancements in terms of average density, compressive strength, water resistance, and swelling across different mix compositions. Three distinct mixtures were formulated and assessed. Mix No. 1, composed solely of RAP, showed the lowest average density and highest swelling, indicating poor performance due to the lack of binding agents. Mix No. 2, which incorporated RAP, Portland cement, and water, exhibited the highest density and compressive strength, highlighting the crucial role of Portland cement in improving structural integrity. Mix No. 3, a more complex mixture including RAP, aggregates, Portland cement, water, and bitumen emulsion, displayed balanced properties with enhanced moisture resistance and reduced swelling. The experimental findings emphasize the effectiveness of adding Portland cement and bitumen emulsion to improve the mechanical and durability characteristics of recycled asphalt mixtures. Specifically, Mix No. 2 and Mix No. 3 demonstrated significant performance improvements, making them suitable for road maintenance applications. This study advocates for the widespread use of cold recycling methods with additive integration to achieve sustainable and cost-effective pavement restoration solutions. [ABSTRACT FROM AUTHOR]

Abstract Water flooding is one of the most important methods for oil field development, It accounts for more then 70% of China's crude oil production. However, in the progress of water flooding, preferential flow paths often formed between oil and water wells, which seriously restricts production rate. How to effectively identify the preferential flow paths has become the key to improving the effect of water flooding. In this paper, to solve the problem of difficult identification of preferential flow paths in reservoirs, through the change of core seepage law with high pore volume water flooding experiment, parameters such as multiple of water flux, change value of permeability, and water saturation were selected for analysis. The weight coefficient for each parameter was determined by the variation coefficient method of objective weight. Subsequently, a comprehensive reservoir identification index was obtained by weighting each parameter, which was used to describe the development degree of the preferential flow paths. Finally, quantitative criteria of preferential flow paths were given. The spatial characterization of preferential flow paths was realized by post processing of the Eclipse software. The new method for identifying preferential flow paths fully considers the changes in physical properties and fluid mobility of water-flooded reservoirs. The results of the new applied to a typical water-flooded reservoir in the Bohai Bay Basin show that the preferential flow paths calculated by the new method were highly consistent with the judgment results of tracers. It can accurately and quickly identify the preferential flow paths. This study provides a scientific basis for adjusting measures of water-flooded reservoirs to further enhance oil recovery. Moreover, the new method holds broader prospects for application in the field of porous media transport.

Abstract Moisture content of rock/coal can change its mechanical properties and absorption capacities, which can directly affect gas diffusivity, change the stress distribution and hence cause significant impacts on the overall gas or coal extraction process. Observation of the water penetration process and water distribution in the coal matrix will be beneficial for the understanding of the fluid-solid coupling mechanism in hydraulic fracturing, aquifer cracking and coal seam infusion. However, the observation of water penetration process and the determination of water distribution mode were hard to be non-destructively achieved as coal is a non-uniform, inhomogeneous and un-transparent material. µ-CT imaging, which is based on variation of X-ray attenuation related to the density and atomic composition of the scanned objects, enables a four-dimensional (spatial-temporal) visualise of the heterogeneous and anisotropic coal samples. The primary aim of this paper is extending the application of µ-CT imaging to explore the moisture penetration and distribution within coal samples during water infusion process, which has been reported by very little literature. The working principle and procedures of CT imaging was firstly introduced. Then, the determination equation of moisture distribution based on density profile was established. The CT determined moisture content has been compared with weighting method for verification. The paper has demonstrated that µ-CT can be used for non-destructively imaging the moisture distribution within coal samples.

Fracture is an early symptom of ground movement related to the physical properties of soil, including permeability, porosity, density, cohesion and internal friction angle, where these physical properties affect the stability of the soil. This research aims to identify soil fracture in landslide-prone areas using the values of water saturation and soil pressure based on electrical resistivity tomography (ERT) data. Water saturation values are obtained using the Waxman-Smits model based on the relationship between porosity and resistivity. The advantage of this model is its ability to apply correction due to clay-containing soil layers found in the research area. Another parameter used to determine soil fracture is the soil stress value. In this study, the Rankine method is used to calculate soil stress, and this method can be applied to the soil conditions that experienced deformation, caused by weathering of breccia and tuff rocks, allowing water to penetrate the rock medium. Consequently, the weathered layers of breccia and tuff act as slip planes. The presence of water on the slip planes leads to soil movement. Based on the analysis results, soil fractures are correlated with low water saturation values and contrast in soil stress values. A profound contrast in water saturation and soil stress values appears only at fractured slopes. Based on our analysis, soil fractures correlate with low water saturation values (5 - 15 %) accompanied by apparent contrast of soil stress values, i.e. the fractured soil is having lower soil stress (< 15 KN/m²) in comparison to the surrounding. Such a contrast was not found in slopes without fractures. [ABSTRACT FROM AUTHOR]

Moisture content of rock/coal can change its mechanical properties and absorption capacities, which can directly affect gas diffusivity, change the stress distribution and hence cause significant impacts on the overall gas or coal extraction process. Observation of the water penetration process and water distribution in the coal matrix will be beneficial for the understanding of the fluid-solid coupling mechanism in hydraulic fracturing, aquifer cracking and coal seam infusion. However, the observation of water penetration process and the determination of water distribution mode were hard to be non-destructively achieved as coal is a non-uniform, inhomogeneous and un-transparent material. µ-CT imaging, which is based on variation of X-ray attenuation related to the density and atomic composition of the scanned objects, enables a four-dimensional (spatial-temporal) visualise of the heterogeneous and anisotropic coal samples. The primary aim of this paper is extending the application of µ-CT imaging to explore the moisture penetration and distribution within coal samples during water infusion process, which has been reported by very little literature. The working principle and procedures of CT imaging was firstly introduced. Then, the determination equation of moisture distribution based on density profile was established. The CT determined moisture content has been compared with weighting method for verification. The paper has demonstrated that µ-CT can be used for non-destructively imaging the moisture distribution within coal samples. [ABSTRACT FROM AUTHOR]

Water content is an important factor affecting the rock-breaking efficiency of tunnel boring machine (TBM) disc cutters. However, limited efforts have been made to study the fracturing mechanism of sandstone excavation by TBM disc cutters under varying water content conditions. To investigate the breakage behavior of water-soaked sandstone by TBM disc cutters, five sets of penetration tests on sandstone specimens with different water content levels were performed. The tests were conducted using a modified RYL-600 computer-controlled rock shear rheometer. An acoustic emission (AE) monitoring system was utilized throughout the entire process to track the AE activity of the specimens. The force–depth curves of the penetration process at various water content levels were investigated. The effects of water content on AE characteristics, rock fracture properties, and specific energy were analyzed. The results indicate that AE activity can be divided into three stages: quiet period, slow rise period, and active period. With increasing water content, peak penetration force, consumed energy, and specific energy decrease gradually, while chip volume increases. Water promotes mutual penetration of surface and internal cracks of the specimen, resulting in the formation of larger chip volumes. These findings provide theoretical guidance for designing and improving TBM cutter head parameters in water-rich soft rock formations. [ABSTRACT FROM AUTHOR]

The CO2 miscible flooding is an effective technology for development of low permeability reservoirs due to high oil displacement efficiency. However, CO2 miscible flooding for tertiary recovery technology typically occur after water flooding. Water hindered the contact and mass transfer of CO2 and oil, produce water resistance effect. Water can block CO2 and contact and mass transfer of crude oil (ie water blocking effect). The impact of this effect on the miscibility pressure and oil displacement effect is still unclear. In this study, homogeneous artificial cores with the same permeability as the reservoir were designed according to the miscible mechanism. Subsequently, the minimum miscibility pressure(MMP) between CO2 and crude oil at different water saturation was measured by the coreflood test. Based on the MMP, CO2 miscible flooding experiments were conducted by natural cores at different water saturation. The results showed that when the water saturation was 30%, 45%, and 60%, respectively, the corresponding MMP between CO2 and crude oil was 18.56, 19.48, and 21.76 MPa. The higher the water saturation, the longer the gas breakthrough time. But the oil recovery factor did not rise with the increase of water saturation. When the water saturation was 45%, the oil recovery factor in the miscible flooding experiment was the highest. In addition, the higher the water saturation, the weaker the CO2 extraction of various components in the crude oil. And the light components below C5 were most affected by water saturation. The mechanisms underlying these results are discussed. This study contributes to the development of CO2 miscible flooding reservoir plan. [ABSTRACT FROM AUTHOR]

Tight sandstone gas has become an important field of natural gas development in China. The tight sandstone gas resources of Yan'an gas field in Ordos Basin have made great progress. However, due to the complex gas–water relationship, its exploration and development have been seriously restricted. The occurrence state of water molecules in tight reservoirs, the dynamic change characteristics of gas–water two-phase seepage and its main controlling factors are still unclear. In this paper, the water-occurrence state, gas–water two-phase fluid distribution and dynamic change characteristics of different types of tight reservoir rock samples in Yan'an gas field were studied by means of water vapor isothermal adsorption experiment and nuclear magnetic resonance methane flooding experiment, and the main controlling factors were discussed. The results show that water molecules in different types of tight reservoirs mainly occur in clay minerals and their main participation is in the formation of fractured and parallel plate pores. The adsorption characteristics of water molecules conform to the Dent model; that is, the adsorption is divided into single-layer adsorption, multi-layer adsorption and capillary condensation. In mudstone, limestone and fine sandstone, water mainly occurs in small-sized pores with a diameter of 0.001 μm–0.1 μm. The dynamic change characteristics of gas and water are not obvious and no longer change under 7 MPa displacement pressure, and the gas saturation is low. The gas–water dynamic change characteristics of conglomerate and medium-coarse sandstone are obvious and no longer change under 9 MPa displacement pressure. The gas saturation is high, and the water molecules mainly exist in large-sized pores with a diameter of 0.1 μm–10 μm. The development of organic matter in tight reservoir mudstone is not conducive to the occurrence of water molecules. Clay minerals are the main reason for the high water saturation of different types of tight reservoir rocks. Tight rock reservoirs with large pore size and low clay mineral content are more conducive to natural gas migration and occurrence, which is conducive to tight sandstone gas accumulation. [ABSTRACT FROM AUTHOR]

The seismic attributes of water‐rich sandstone contain much information about the rock's physical properties and seismic wave parameters. They are commonly used to predict the rock's physical properties (e.g. porosity). However, the seismic attributes of water‐rich sandstone are affected by porosity, water saturation and thickness. To eliminate the influence of thickness on the porosity prediction of water‐rich sandstone and improve the accuracy of the porosity prediction, the authors propose a Lambert W–R transform method to isolate the contribution of thickness and porosity from seismic attributes. First, a rock physical model is used to calculate the equivalent elastic parameters of water‐rich sandstones with different porosity values and water saturation levels. Second, the seismic attribute dataset of water‐rich sandstone is established by forward modelling the seismic response of the wedge‐shaped water‐rich sandstone model, and the selection of sensitive physical properties is completed. Then, the transformation parameters (ζAhRs and ηAhRs) are obtained by Lambert W–R transformation, which is exponentially related to instantaneous amplitude. ζAhRs and ηAhRs are sensitive to thickness and porosity, respectively. Finally, an interpretative template for porosity prediction of water‐rich sandstone is established by cross‐plot analysis (ζAhRs and ηAhRs) and verified by a practical case. The verification results show that the porosity predicted by the interpretation template is consistent with drilling fluid consumption. However, it is lower than the porosity of logging constrained P‐wave impedance inversion. [ABSTRACT FROM AUTHOR]

In-depth investigations into the effect of water saturation on the damage and failure mechanisms of rock have significance for analyzing the stability of the surrounding rock in water-rich rock masses. Uniaxial compression tests were carried out on two types of sandstone to explore the influence and mechanism of water saturation on their strength and deformation, stress thresholds, energy evolution, and acoustic emission (AE) characteristics. The deduced the following after water saturation: (1) water saturation had an obvious softening effect on both types of sandstone, manifested by a reduction in uniaxial compressive strength and elastic modulus, and an increase in the Poisson's ratio; (2) the normalized crack initiation stress (σci/σf) increased and the normalized crack damage stress (σcd/σf) decreased; (3) the total energy (U), elastic energy (Ue), and dissipated energy (Ud) at the peak strength decreased and the ratio of elastic energy to total energy (Ue/U) decreased; and (4) the peak values of AE count and AE cumulative count decreased in both types of sandstone. Based on our analysis of the AE b-values, the proportion of small-scale ruptures increased. An analysis based on the AE ratio of the rise time to amplitude (RA) value and average frequency (AF) value showed that the proportion of shear fracture increased after water saturation. Our findings provide an indication of the significance of determining the failure mechanism of water-saturated rocks. [ABSTRACT FROM AUTHOR]

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Tight sandstone water-bearing gas reservoirs typically exhibit low porosity and low permeability, with reservoir rocks characterized by complex pore structures, often featuring micron-scale or smaller pore throats. This intricate reservoir structure significantly restricts fluid flow within the reservoir, necessitating a certain threshold pressure gradient (TPG) to be overcome before flow can commence. This study focuses on the Ordos Basin and explores the influence of high water content tight sandstone gas reservoirs on TPG under different water saturation and formation pressure conditions through experiments. A mathematical model of TPG is established using multiple linear regression method. The results show that TPG is primarily affected by water saturation, followed by formation pressure. As the water saturation increases, the TPG of the core decreases, and the change becomes more pronounced when the water saturation exceeds 50%. As formation pressure increases, the weakening of the slippage effect in gas molecules leads to TPG stabilization, especially when local pressure exceeds 25.0 MPa. The research also shows that low-permeability cores exhibit greater TPG variation with pressure changes, while high-permeability cores remain more stable. A mathematical model was developed and validated to predict TPG based on permeability, water saturation, and formation pressure. These findings highlight the need to monitor formation water content during tight sandstone gas reservoir development to optimize production strategies, providing valuable insights for improving reservoir management and guiding future research.

Abstract Understanding water saturation levels in tight gas carbonate reservoirs is vital for optimizing hydrocarbon production and mitigating challenges such as reduced permeability due to water saturation (Sw) and pore throat blockages, given its critical role in managing capillary pressure in water drive mechanisms reservoirs. Traditional sediment characterization methods such as core analysis, are often costly, invasive, and lack comprehensive spatial information. In recent years, several classical machine learning models have been developed to address these shortcomings. Traditional machine learning methods utilized in reservoir characterization encounter various challenges, including the ability to capture intricate relationships, potential overfitting, and handling extensive, multi-dimensional datasets. Moreover, these methods often face difficulties in dealing with temporal dependencies and subtle patterns within geological formations, particularly evident in heterogeneous carbonate reservoirs. Consequently, despite technological advancements, enhancing the reliability, interpretability, and applicability of predictive models remains imperative for effectively characterizing tight gas carbonate reservoirs. This study employs a novel data-driven strategy to prediction of water saturation in tight gas reservoir powered by three recurrent neural network type deep/shallow learning algorithms—Gated Recurrent Unit (GRU), Recurrent Neural Networks (RNN), Long Short-Term Memory (LSTM), Support Vector Machine (SVM), K-nearest neighbor (KNN) and Decision tree (DT)—customized to accurately forecast sequential sedimentary structure data. These models, optimized using Adam's optimizer algorithm, demonstrated impressive performance in predicting water saturation levels using conventional petrophysical data. Particularly, the GRU model stood out, achieving remarkable accuracy (an R-squared value of 0.9973) with minimal errors (RMSE of 0.0198) compared to LSTM, RNN, SVM, KNN and, DT algorithms, thus showcasing its proficiency in processing extensive datasets and effectively identifying patterns. By achieving unprecedented accuracy levels, this study not only enhances the understanding of sediment properties and fluid saturation dynamics but also offers practical implications for reservoir management and hydrocarbon exploration in complex geological settings. These insights pave the way for more reliable and efficient decision-making processes, thereby advancing the forefront of reservoir engineering and petroleum geoscience.

Abstract The dynamic compression test of geopolymer concrete (GC) before and after water saturation was carried out by the split Hopkinson pressure bar (SHPB). And the effects of water saturation and strain rate on impact toughness of GC were studied. Based on Weibull statistical damage distribution theory, the dynamic constitutive model of GC after water saturation was constructed. The results show that the dynamic peak strain and specific energy absorption of GC have strain rate strengthening effect before or after water saturation. The impact toughness of GC decreases after water saturation. The size distribution of GC fragments has fractal characteristics, and the fractal dimension of GC fragments after water saturation is smaller than that before water saturation. The dynamic constitutive model based on Weibull statistical damage distribution theory can accurately describe the impact mechanical behavior of GC after water saturation, and the model fitting curves are in good agreement with the experimental stress–strain curves.

The technology of CO2-enhanced coalbed methane (CO2-ECBM) can reduce greenhouse gas emissions, and has the function of clean energy production and environmental protection. In order to study the drainage and production laws of CH4 production by CO2 injection in water-bearing coal seams under gas-water two-phase flow conditions, as well as the effects of different initial water saturation and CO2 injection conditions on CH4 production, CO2 storage, and reservoir permeability. A coupled fluid-solid-thermal model for competitive adsorption, temperature changes, coal deformation, and water transport was constructed. The high accuracy of the model was demonstrated by comparing with the field data, existing experiments and numerical solutions of existing model, and the advantages of the model were specified. CO2-ECBM numerical simulation were subsequently carried out using COMSOL. The results shown that, CO2 injection can enhance the rate and amount of CH4 production, which indicated the feasibility of CO2 injection to increase production. With the continuous CO2 injection, the CH4 concentration in the reservoir decreased, the CO2 concentration increased, the temperature near the gas injection well increased, the temperature near the production well decreased and the temperature from the gas injection well to the production well slowly decreased. Water phase relative permeability gradually decreased and gas phase relative permeability gradually increased during gas injection and extraction period. Due to the combined effect of effective stress and matrix shrinkage/expansion, the reservoir permeability exhibited a trend of “decrease-increase-decrease”. The higher the initial water saturation of the coal seam, the lower the CH4 production and the lower the permeability decrease. The maximum decrease in cumulative CH4 production was 15.19%. Ignoring the impact of water in coal seams can overestimate CH4 production, and the impact of coal seam water should be considered in numerical simulation. The higher the CO2 injection temperature and pressure, the greater the CH4 production and the greater the permeability decrease. The cumulative CH4 production increased by 13.27% and 39.77%, and permeability decreased by 20.4% and 46.14%, respectively. Increasing the CO2 injection temperature and pressure was conducive to increase CH4 production.

Understanding water saturation levels in tight gas carbonate reservoirs is vital for optimizing hydrocarbon production and mitigating challenges such as reduced permeability due to water saturation (Sw) and pore throat blockages, given its critical role in managing capillary pressure in water drive mechanisms reservoirs. Traditional sediment characterization methods such as core analysis, are often costly, invasive, and lack comprehensive spatial information. In recent years, several classical machine learning models have been developed to address these shortcomings. Traditional machine learning methods utilized in reservoir characterization encounter various challenges, including the ability to capture intricate relationships, potential overfitting, and handling extensive, multi-dimensional datasets. Moreover, these methods often face difficulties in dealing with temporal dependencies and subtle patterns within geological formations, particularly evident in heterogeneous carbonate reservoirs. Consequently, despite technological advancements, enhancing the reliability, interpretability, and applicability of predictive models remains imperative for effectively characterizing tight gas carbonate reservoirs. This study employs a novel data-driven strategy to prediction of water saturation in tight gas reservoir powered by three recurrent neural network type deep/shallow learning algorithms—Gated Recurrent Unit (GRU), Recurrent Neural Networks (RNN), Long Short-Term Memory (LSTM), Support Vector Machine (SVM), K-nearest neighbor (KNN) and Decision tree (DT)—customized to accurately forecast sequential sedimentary structure data. These models, optimized using Adam's optimizer algorithm, demonstrated impressive performance in predicting water saturation levels using conventional petrophysical data. Particularly, the GRU model stood out, achieving remarkable accuracy (an R-squared value of 0.9973) with minimal errors (RMSE of 0.0198) compared to LSTM, RNN, SVM, KNN and, DT algorithms, thus showcasing its proficiency in processing extensive datasets and effectively identifying patterns. By achieving unprecedented accuracy levels, this study not only enhances the understanding of sediment properties and fluid saturation dynamics but also offers practical implications for reservoir management and hydrocarbon exploration in complex geological settings. These insights pave the way for more reliable and efficient decision-making processes, thereby advancing the forefront of reservoir engineering and petroleum geoscience. [ABSTRACT FROM AUTHOR]

The conventional Archie formula struggles with the interpretation of water saturation from resistivity well log data due to the increasing complexity of exploration targets. This challenge has prompted researchers to explore alternative physical parameters, such as acoustic characteristics, for breakthroughs. Clarifying the influencing factors of porous media acoustic characteristics is one of the most important approaches to help understanding the mechanism of acoustic characteristics of carbonate reservoirs. The article uses digital rock technology to characterize the pore structure, quantitatively identify fractures and pore structures in carbonate rocks, and establish digital models. Through conventional acoustic testing, the pressure wave (P-wave) and shear wave (S-wave) velocities of rock samples at different water saturations are obtained, and the dynamic elastic modulus is calculated. A finite element calculation model is established using the digital rock computational model to provide a basis for fluid saturation calculation methods. Based on real digital rock models, different combinations of virtual fractures are constructed, and factors affecting acoustic parameters are analyzed. The study finds that as porosity increases, the velocity difference between porous cores and fractured cores also increases. These findings provide important technical support and a theoretical basis for interpreting acoustic well logging data and evaluating carbonate reservoirs with different pore and fracture types. [ABSTRACT FROM AUTHOR]