Effect Of Water Saturation Research Articles

Water saturation effects on mechanical performances and failure characteristics of rock-concrete disc with different interface dip angles

The mechanical performance of rock-concrete interface is greatly affected by water and dip angles in many rock or concrete engineering projects. To investigate the coupled effects of water saturation and dip angle on the mechanical performances and failure characteristics of rock-concrete interface, series of Brazilian splitting tests were carried out on rock-concrete bi-material disc specimens containing a rough interface. During the test, the interface dip angle θ is set to 0°, 15°, 45° and 90°, respectively. A high-speed camera was used to capture the whole failure process, and the displacement field on the specimen surface was also analyzed. The test results show that regardless of dip angle, the peak load of sample decreases after water saturation. The loss percentages of peak load are very close around 20% when the interface dip angles are 0°, 45° and 90°. However, the reduction of peak load is the most dramatic at the 15° dip angle. When the specimen becomes saturated, its stiffness unexpectedly increases at the dip angle of 0° which is followed by a significant drop at 15°, and finally tends to no obvious change. The stress state at the interface of rock-concrete disc under radial compressive load is discussed. The strength weakening degree of rock-concrete disc specimen by water has a very strong correlation with the ratio of shear stress to tensile stress at the interface. The weakening of water on the bearing capacity of rock-concrete structure is the most obvious at θ≈18.43°.

Luminescence dating of quartz from ironstones of the Xingu River, Eastern Amazonia

This study reports on the first investigation into the potential of quartz luminescence dating to establish formation ages of ferruginous duricrust deposits (ironstones) of the Xingu River in Eastern Amazonia, Brazil. The studied ironstones comprise sand and gravel cemented by goethite (FeO(OH)), occurring as sandstones and conglomerates in the riverbed of the Xingu River, a major tributary of the Amazon River. The Xingu ironstones have a cavernous morphology and give origin to particular habitat for benthic biota in an area that hosts the largest rapids in Amazonia. So far, the Xingu ironstones have uncertain formation ages and their sedimentary origin is still poorly understood. In this way, seven samples of ironstones distributed along the lower Xingu River were collected for optically stimulated luminescence (OSL) dating of their detrital quartz sand grains. Additionally, the organic content of some samples was dated by radiocarbon ( 14 C) for comparison with quartz OSL ages. The luminescence ages of the sand-sized quartz grains extracted from the ironstones were obtained from medium (100–300 grains) and small (10–20 grains) aliquots using the single aliquot regenerative-dose (SAR) protocol. Equivalent doses (D e ) distributions have varied overdispersion (OD) both for medium size aliquots (OD = 19–58 %) and small size aliquots (OD = 29–76 %). No significant trend was observed between D e and aliquot size. The studied ironstones grow over the riverbed, but stay below or above water throughout the year due to the seasonal water level variation of the Xingu River. However, the effect of water saturation in dose rates is reduced due to relatively low porosity of ironstones. Water saturated dose rates (dry sample dose rates) range from 2.70 ± 0.21 (2.79 ± 0.22) Gy/ka to 12.34 ± 0.97 (13.26 ± 1.12) Gy/ka, which are relatively high when compared to values reported for Brazilian sandy sediments elsewhere (∼1 Gy/ka). Samples with high overdispersion (>40 %) are mainly attributed to mixing of grains trapped in different time periods by goethite cementation. The obtained OSL ages for water saturated (dry) samples range from 3.4 ± 0.3 (3.3 ± 0.4) ka to 59.6 ± 6.0 (58.1 ± 6.4) ka, using D e determined from medium size aliquots and dose response curves fitted by an exponential plus linear function. Radiocarbon ages of the bulk organic matter extracted from selected ironstone varied from ca. 4 cal ka BP to ca. 23 cal ka BP. Significant differences were observed between OSL and radiocarbon ages, suggesting asynchronous trapping of organic matter and detrital quartz within the ironstone matrix. These late Pleistocene to Holocene ages indicate that ironstones of the Xingu River result from an active surface geochemical system able to precipitate goethite and cement detrital sediments under transport. The obtained ages and differences between OSL and radiocarbon ages point out that the ironstones have multiphase and spatially heterogeneous growth across the Xingu riverbed. Our results also expand the application of luminescence dating to different sedimentary deposits.

Effect of Initial Water Saturation on Oil Displacement Efficiency by Nanosuspensions

This article deals with the study of the initial water saturation effect of a porous medium on the oil recovery factor using a water-based nanosuspension. The initial water saturation of the porous medium in the computations varied within the range from 0 to 90%. The nanoparticle SiO2 concentration varied from 0 to 1 wt%. The particle sizes were equal to 5, 18, 22, and 50 nm. Experimentally measured wetting angles and the interfacial tension coefficient depending on the concentration and size of nanoparticles were used in computations. A mathematical model was developed, describing the transfer and diffusion of nanoparticles within the aqueous phase during immiscible displacement of oil by nanosuspension from a porous medium. Using the developed model, a systematic computational study of the effect of the initial water saturation of the core micromodel on the oil recovery factor using nanosuspension was carried out. It was revealed that with an increase in the initial water saturation, the oil recovery factor monotonically decreased in the case of displacement both by water and nanosuspension. It was shown that with an increase in the concentration of nanoparticles and a decrease in their size, the oil recovery factor increased. At that, the relative increase in the recovery factor had a maximum at an initial water saturation equal to 60%.

Investigation on effective stress coefficients and stress sensitivity of different water-saturated coals using the response surface method

The relative magnitude of confining pressure and pore pressure, a key parameter for stress sensitivity of coal permeability, can be characterized by the effective stress coefficient (ESC). In this study, the stress sensitivity experiments of different water-saturated coals were carried out according to the dewatering of coalbed methane (CBM) wells. The ESC was calculated based on the response surface method (RSM), revealing the effect of water saturation on the ESC and stress sensitivity of high-rank coal. The results showed that the stress sensitivity coefficient of these high-rank coals ranged from 0.8136 to 1.5631, indicating a strong stress sensitivity. With growing net pressure and water saturation, the gas permeability of coals changed in a negative power exponential form. Compared with the binary linear regression (BLR), the effective stress calculated by the ESC using the RSM could better reflect the stress sensitivity of permeability. In addition, the ESC increased significantly along with water saturation. Finally, a mathematical model considering ESC and reservoir pressure was established to calculate the “turning point” of dynamic permeability, where the controlling factors of permeability transform from effective stress to matrix shrinkage.

Effects of pore connectivity and water saturation on matrix permeability of deep gas shale

Shale matrix permeability is an important indicator for evaluating gas transport and production. However, the effects of pore connectivity and water saturation on the matrix permeability in deep gas shales have not been adequately studied. In this study, the permeability of deep shales in the Yichang area of the Middle Yangtze was characterized using three methods. These included the determination of apparent permeability in different directions via pulse-decay, also matrix permeability obtained via the Gas Research Institute method, and the connected pore network permeability via the mercury injection capillary pressure technique. The results revealed a significant difference between the horizontal and vertical permeability of deep shales. The smaller the size of the multiple connected pore network, the larger was the effective tortuosity and the lower the permeability. Comparison of the three permeabilities and combined microscopic observations revealed that microfractures and laminae were the dominant gas transport channels. Importantly, the matrix permeability decreased exponentially with increasing water saturation, with water vapor adsorption experiments revealing that water occupation of pores and pore-throat spaces smaller than 10 nm in diameter was the main reason for this decrease in matrix permeability. Collectively, proposed method of evaluating effective permeability with an index for shale gas reservoirs is significant for sweet spot selection and production prediction of shale gas reservoirs around the globe. Cited as: Zhao, J., Sun, M., Pan, Z., Liu, B., Ostadhassan, M., Hu, Q. Effects of pore connectivity and water saturation on matrix permeability of deep gas shale. Advances in Geo-Energy Research, 2022, 6(1): 54-68. https://doi.org/10.46690/ager.2022.01.05

Behaviours of Methane and Water in Heterogeneous Shale Nanopores: Effect of Water Saturation and Pore Size

Behaviours of Methane and Water in Heterogeneous Shale Nanopores: Effect of Water Saturation and Pore Size

Structural-temporal peculiarities of dynamic deformation of rock

Instability of theoretical rate dependencies of the stress intensity factor and fracture energy is considered from the point of view of force and energy limiting criteria formulated on the basis of the concepts of the structural-temporal approach. Applying both approaches separately, the water saturation effect on dynamic stress intensity factor and dynamic fracture energy is predicted. Using the dynamic fracture of sandstone as an example, the incubation times as a characteristic of the rate sensitivity of the material determined by the force and energy fracture are compared.

Effect of Initial Water Saturation on the Performance of Fracturing Fluids with and Without Polyallylamine Under Simulated Egs Conditions

Effect of Initial Water Saturation on the Performance of Fracturing Fluids with and Without Polyallylamine Under Simulated Egs Conditions

Синтез гидрата метана в пористых средах с использованием эффекта «памяти воды»

The «memory (melt) water» effect accelerates the synthesis of methane hydrate in low-clay and clay porous media. The duration of the «memory» effect of water at 22-24°C is at least 3 days. The main factors determining the rate of methane hydrate synthesis in a porous medium when using the «water memory» effect are the degree of excess methane pressure and/or a decrease in temperature relative to the equilibrium values for methane hydrate. Inporous media made of quartz (river) sand, when the methane pressure exceeds the equilibrium value by 1.4 times or more and/or at a temperature below the equilibrium value by 3°C or more, the induction period of methane hydrate synthesis is minimal and does not depend on the degree of deviation from the equilibrium parameters. There was no effect of permeability, water saturation and wettability of the rock on the synthesis of methane hydrate in a permeable porous medium from river sand using the «water memory» effect. The conversion of ~10% of residual water into gas hydrate in the clay model of the Turonian horizon formation led to a decrease in gas permeability. Clay particles in the rock significantly reduce the methane/water ratio in the hydrate, i.e. in clay cores, the main amount of water is not part of the hydrate. Filtration of methane through a porous medium contributes to the formation of gas hydrate. If the synthesis of methane hydrate is stopped under static conditions, the process resumes in the gas stream.

ФІЛЬТРАЦІЙНО-ЄМНІСНІ ПАРАМЕТРИ УЩІЛЬНЕНИХ ТЕРИГЕННИХ ПОРІД КЕМБРІЮ СХІДНОГО СХИЛУ ЛЬВІВСЬКОГО ПАЛЕОЗОЙСЬКОГО ПРОГИНУ

The paper concerned the researches of porosity and permeability properties of consolidated terrigenous reservoir rocks of Cambrian period of the Eastern slope of the Lviv depression. The purpose of the research was to study the petrophysical parameters of the consolidated reservoir rocks, as the basis of the integrated analysis of their physical properties. Such reservoir parameters as the open porosity factor and void factor, permeability coefficient and residual water saturation factor have been studied. The article presents the limits of changes and the average values of porosity and permeability properties of rocks, and the classification of their reservoir properties. On the basis of capillarimetric research, an evaluation of the structure of the void space of rocks was made. The correlation analysis has allowed to establish a series of empirical relationships between the reservoir parameters (density, porosity coefficient, effective porosity factor and residual water saturation factor) and, also, to determine correlation dependences between porosity coefficients measured in atmospheric and reservoir conditions. These relationships can be used in the data interpretation of geophysical studies of wells and in the modeling of porosity and permeability properties of consolidated rocks of the Eastern slope of the Lviv depression.

КОЛЕКТОРСЬКІ ВЛАСТИВОСТІ ГЛИБОКОЗАНУРЕНИХ УЩІЛЬНЕНИХ ПОРІД КАРБОНУ ЦЕНТРАЛЬНОГО ГРАБЕНА ДДЗ

Paper concerns the researches of porosity and permeability properties of deep-seated consolidated rocks (siltstones, poor-porous sandstones) of Carboniferous period of the central graben of the Dnieper-Donetsk depression. The purpose of the research was to study the petrophysical parameters of the consolidated reservoir rocks, as the basis of the integrated analysis of their physical properties. Such reservoir parameters as the open porosity factor and void factor, permeability coefficient and residual water saturation factor have been studied. The article presents the limits of changes and the average values of porosity and permeability properties of rocks, and the classification of their reservoir properties. On the basis of capillarimetric research, an evaluation of the structure of the void space of rocks was made. The correlation analysis has allowed establishing a series of empirical relationships between the reservoir parameters (density, porosity coefficient, effective porosity factor and residual water saturation factor) and, also, determining correlation dependences between porosity coefficients measured in atmospheric and reservoir conditions. These relationships can be used in the data interpretation of geophysical studies of wells and in the modeling of porosity and permeability properties of consolidated rocks of the central graben of the Dnieper-Donetsk depression.

Application of maximum likelihood and model-based seismic inversion techniques: a case study from K-G basin, India

AbstractSeismic inversion is a geophysical technique used to estimate subsurface rock properties from seismic reflection data. Seismic data has band-limited nature and contains generally 10–80 Hz frequency hence seismic inversion combines well log information along with seismic data to extract high-resolution subsurface acoustic impedance which contains low as well as high frequencies. This rock property is used to extract qualitative as well as quantitative information of subsurface that can be analyzed to enhance geological as well as geophysical interpretation. The interpretations of extracted properties are more meaningful and provide more detailed information of the subsurface as compared to the traditional seismic data interpretation. The present study focused on the analysis of well log data as well as seismic data of the KG basin to find the prospective zone. Petrophysical parameters such as effective porosity, water saturation, hydrocarbon saturation, and several other parameters were calculated using the available well log data. Low Gamma-ray value, high resistivity, and cross-over between neutron and density logs indicated the presence of gas-bearing zones in the KG basin. Three main hydrocarbon-bearing zones are identified with an average Gamma-ray value of 50 API units at the depth range of (1918–1960 m), 58 API units (2116–2136 m), and 66 API units (2221–2245 m). The average resistivity is found to be 17 Ohm-m, 10 Ohm-m, and 12 Ohm-m and average porosity is 15%, 15%, and 14% of zone 1, zone 2, and zone 3 respectively. The analysis of petrophysical parameters and different cross-plots showed that the reservoir rock is of sandstone with shale as a seal rock. On the other hand, two types of seismic inversion namely Maximum Likelihood and Model-based seismic inversion are used to estimate subsurface acoustic impedance. The inverted section is interpreted as two anomalous zones with very low impedance ranging from 1800 m/s*g/cc to 6000 m/s*g/cc which is quite low and indicates the presence of loose formation.

Permeability analysis of hydrate-bearing sediments considering the effect of phase transition during the hydrate dissociation process

Permeability is the most important factor affecting water and gas production in hydrate-bearing sediments (HBS). In this study, we combined in-situ microfocus X-ray computed tomography (CT) and pore network model simulation to obtain insights into the dynamic permeability of the hydrate dissociation process. Microfocus X-ray CT is used to visualize the three-dimensional pore structures of the specimen. Then an equivalent pore network can be extracted, which is used as input to pore network flow simulator to simulate the water and gas flow process. Results show that secondary hydrate formation causes effective permeability keff decreases and effective connate water saturation increases as hydrate saturation Sh increases from 0.40 to 0.48. The water relative permeability krw decreases and gas relative permeability krg increases due to larger patchy hydrates (Sh = 0.33). The krw and krg are largely affected by the pore and throat sizes and pore space connectivity. Hydrate dissociation in HBS also influences its permeability anisotropy. Secondary hydrate formation causes keff decreases in the x, y, and z directions when Sh increase from 0.40 to 0.48. Large patchy hydrates influence preferential flow direction for water flow. Predicting the dynamic permeability of the hydrate dissociation process would improve pore-scale water and gas flow analyses in HBS.

Landslide Investigation Using Seismic Refraction Tomography Method: A Review

Since the early 1960s, near-surface seismic refraction tomography (SRT) has been extensively used as a non-invasive and cost-effective geophysical method to characterize complex geological structures for landslide investigation. This geophysical technique is able to characterize the slope material, the sliding surface's geometry, the landslide mass movement, the physical properties of media, and the water saturation effects on the slope. Therefore, this method has become an appropriate method due to the increasing progress of novel algorithms and the improvements of field-data collection systems. In this paper, we attempt to review the essential research that investigated various types of landslides influenced by water saturation and landslide materials and identified in various areas, since the year 2000. Significant conclusions obtained by applying different survey strategies and data processing algorithms in seismic refraction surveys are widely discussed concentrating on the advantages and disadvantages of this method. The main results obtained by the few available studies applying time-lapse SRT (TLSRT) are particularly analyzed.

Effect of water saturation on mechanical characteristics and damage behavior of cemented paste backfill

In this study, a series of experiments was conducted to examine the mechanical and damage properties of cemented paste backfill (CPB) with different water saturations (ws = 0%, 22.1%, 47.0%, 65.3%, 82.8%, and 100%). The results reveal that the UCS, peak strain, and elastic modulus first increased and then decreased, and the porosity and fractal dimension of cracks first decrease and then increase with the increase of ws. In addition, the UCS, peak strain, and elastic modulus is maximum, and the porosity and fractal dimension are minimum when the ws is 65.3%. The UCS increases with the increase of peak strain and elastic modulus, and decreases with the increase of porosity and fractal dimension, and the UCS present good quadratic polynomial functions relationship with the porosity and fractal dimension. The SEM images show that with the increase of ws from 0% to 65.3%, the hydration products increases and the pore structure decreases. When the ws exceeds 65.3%, and the pore structure begins to increase. The failure mode of the CPB is mainly tensile failure. A new damage constitutive model of CPB with different ws was constructed. The total damage D of the CPB is composed of initial damage Dp and load damage DL. The total damage evolution curve shows an S-shaped distribution, and the total damage rate evolution curve shows a normal distribution. With the increase of ws, the damage rate and the peak value of damage rate of CPB first increases and then decreases.

Effects of gas saturation and reservoir heterogeneity on thermochemical sulfate reduction reaction in a dolomite reservoir, Puguang gas field, China

Varying concentrations of H2S have been found in the carbonate reservoir, Puguang gas field, China. Thermochemical sulfate reduction (TSR) is considered the most important process to generate a high level of hydrogen sulfide (H2S) in the reservoir. Although TSR has been intensively studied in this field, it is still not clear on (1) the controls of H2S concentration variations in the reservoir, (2) effects of variable gas and water saturations and reservoir heterogeneity on the TSR reactions, (3) reservoir quality changes during the TSR reactions, (4) potential sources and sinks of sulfur and carbon and their quantification. In this study, we conducted reactive transport modeling to quantitatively simulate the TSR and H2S generation processes in the Upper Permian Changxing Formation and Lower Triassic Feixianguan Formation in Puguang gas field, using log-based depth and thickness, paleo mineralogy assemblages and paleo temperature in late Jurassic, and hydrostatic pressure. The modeling results are relatively reliable as the predicted H2S and CO2 concentrations are comparable with the observed ones in the wells after calibration. The results indicated that both mineralogical composition and gas saturation in the reservoir affect the local efficiency and extent of TSR reactions, of which the abundance of effective anhydrite is an important control on the extent of the TSR reactions. The modeling durations of TSR reactions were ∼6 m.y. and TSR had a small impact on the reservoir porosity (porosity changes generally less than 0.1 porosity unit). The sources and sinks of carbon and sulfur were locally balanced with each other, respectively, and the minor imbalances were likely due to the molecular diffusion. The calibrated models have predictive potential on the H2S and CO2 concentrations changes and porosity modifications during the TSR processes in the subintervals with limited samples. The validated TSR models will facilitate the investigation of organic-inorganic interactions and their impacts on both non-hydrocarbon (H2S and CO2) generation and reservoir qualities.

A wing-crack extension model for tensile response of saturated rocks under coupled static-dynamic loading

Saturated rocks, widely existing in various deep underground engineering, are likely to be encountered coupled static-dynamic loading. It is thus vital to acquire the combined effect of water saturation and static pre-tension on the dynamic tensile strength, and establish a reasonable crack extension model for describing the fracturing mechanism of saturated rocks under coupled static-dynamic tension. In this study, from the perspective of meso-mechanics, the relationship between pore water pressure and static pre-tension loading are first deduced, and then the analytic solution of stress field of elliptical crack orifice under coupled pore water pressure and far-field stress is solved using complex function. The effect of pore water pressure is considered into Griffith theory, and the most dangerous fracture azimuth angle of elliptical crack in rocks under combined far-field stress and pore water pressure are determined. Second, the length of fracture process zone of initial crack in saturated rocks under static pre-loading is estimated based on Schmidt's maximum tensile stress criterion. Finally, a wing-crack extension model is proposed to analyze the dynamic fracturing behavior of saturated rocks under pre-tension, and the theoretical calculation formula for tensile strength of saturated rocks under combined static-dynamic loading is obtained. To validate this new model, nine coupled static-dynamic tension tests with different pre-static loading ratio are performed on saturated flattened Brazilian disc (FBD) specimens, in virtue of the split Hopkinson pressure bar (SHPB) specialized with an axial confining apparatus. A rational consistency is observed between the experimental and theoretical results in terms of the dynamic tensile strength of saturated rocks.

Compressibility of Abnormal Pressure Gas Reservoirs and Its Effect on Reserves.

The compressibility of abnormal pressure gas reservoirs is hard to test, and the interpretation is confusing, leading to many misunderstandings in the current understanding of abnormal pressure gas reservoirs. In this research, a high-pressure experimental system was designed, and a series of high-pressure compressibility tests of pure water, nitrogen, and rocks under different water saturations were carried out. Then, the effective compressibility of gas reservoirs was calculated; the effect of water saturation on abnormal pressure gas reservoirs and the dynamic prediction was studied. The results show that the compressibilities of water and rock are effectively constant values over the range examined, while the compressibility of gas decreases exponentially with the increase in pressure. The effective compressibility of the stratum increases with the rise of water saturation. The theory of stress and strain of rock mechanics also shows that the rock compressibility is determined by Young’s modulus, Poisson’s ratio, and porosity and has no connection with the formation pressure. With the increase in water saturation, the swelling degree of the production indicator curve of the simulation experiment becomes larger and larger. After introducing the effective compressibility of the stratum into the gas–water material balance equation, the gas reserves predicted by the revised production indicator curve are the same as the original reserves. The research results have important guiding significance for the efficient development of gas reservoirs.

Study on Calculation Model for Compressive Strength of Water Saturated Recycled Aggregate Concrete

It has been proved that the compressive strength of water saturated concrete is lower than that of air dry concrete. Due to the water absorption of recycled aggregate (RA) is noticeably higher than that of natural aggregate (NA), the mechanical properties of water saturated recycled aggregate concrete (RAC) are quite different from those of water saturated natural aggregate concrete (NAC). At the same time, the calculation of concrete compressive strength is the first step of concrete mix proportion design. Therefore, it is essential to investigate the compressive strength of RAC in water saturated state. In this study, firstly, the water content and effective water absorption of NA, recycled brick aggregate (RBA) and recycled concrete aggregate (RCA), as well as the water content and effective water absorption of concrete specimen were tested; secondly, the effects of water/cement ratio, water saturation and coarse aggregate types on the compressive strength of water saturated concrete were studied; finally, the calculation model for compressive strength of water saturated concrete was proposed. The test results show that: Within 120 hours, the maximum effective water absorption of NA, RCA and RBA is 0.32%, 0.61% and 8.18%, respectively. Within 240 hour, the maximum effective water absorption of NAC, recycled concrete aggregate concrete (RCAC) and recycled brick aggregate concrete (RBAC) is 0.73%, 0.81% and 1.89%, respectively. In air dry and water saturated state, the descending order of compressive strength of concrete is: NAC > RCAC > RBAC. The average relative error of the calculation model for compressive strength of water saturated concrete is 7.1%. In the calculation model, water/cement ratio, effective water absorption, water saturation and coarse aggregate types are considered. The results of this study have great significance for the mix proportion design of water saturated concrete.

Soil Classification: A New Approach for Grouping Soils Using Unsaturated Hydraulic Conductivity Data

AbstractGrouping soils based on similarities in their textural, taxonomic, and/or structural properties has broad applications to pedology, hydrology, and soil science. In this study, we present a new approach for classifying soils using hydraulic conductivity data. We apply concepts from critical path analysis and calculate critical pore sizes at various water saturations from the unsaturated hydraulic conductivity curves. Soils with similar critical pore size at the same effective water saturation are then grouped into the same class. To demonstrate the practical application of the proposed soil classification method, we use 102 samples including nine soil textures from the UNSODA database. Applying a curve clustering method, we find eight different soil classes within the studied data set.