Artykuły w czasopismach na temat „Pore Pressure”
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1
Christensen, N. I., i H. F. Wang. "The Influence of pore pressure and confining pressure on dynamic elastic properties of Berea sandstone". GEOPHYSICS 50, nr 2 (luty 1985): 207–13. http://dx.doi.org/10.1190/1.1441910.
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Compressional‐ and shear‐wave velocities of watersaturated Berea sandstone have been measured as functions of confining and pore pressures to 2 kbar. The velocities, measured by the pulse transmission technique, were obtained at selected pressures for the purpose of evaluating the relative importance of confining pressure and pore pressure on elastic wave velocities and derived dynamic elastic constants. Changes in Berea sandstone velocities resulting from changes in confining pressure are not exactly canceled by equivalent changes in pore pressure. For properties that involve significant bulk compression (compressional‐wave velocities and bulk modulus) an incremental change in pore pressure does not entirely cancel a similar change in confining pressure. On the other hand, it is shown that a pore pressure increment more than cancels an equivalent change in confining pressure for properties that depend significantly on rigidity (shear‐wave velocity and Poisson’s ratio). This behavior (as well as observed wave amplitudes) is related to the presence of high‐compressibility clay that lines grains and pores within the quartz framework of the Berea sandstone.
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Bruce, Bob, i Glenn Bowers. "Pore pressure terminology". Leading Edge 21, nr 2 (luty 2002): 170–73. http://dx.doi.org/10.1190/1.1452607.
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Li, Yanzhi, Yue Wu, Weiguo Qiao, Shuai Zhang i Xungang Li. "The Permeability Evolution of Sandstones with Different Pore Structures under High Confining Pressures, High Pore Water Pressures and High Temperatures". Applied Sciences 13, nr 3 (30.01.2023): 1771. http://dx.doi.org/10.3390/app13031771.
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Seepage from the pores of sandstone exposed in deep mines is difficult to block by grouting. In this paper, the permeability evolution of four subcategories of sandstone with different pore structures under different confining pressures, pore water pressures and temperatures is analyzed by experiments. (1) With increasing confining pressure, the permeabilities of the four tested subcategories of sandstone all decrease, but at different rates and to different extents. (2) With increasing pore water pressure, the permeability of subcategory I1, I2 and II1 sandstones increases linearly, while that of subcategory II2 sandstone decreases following a power function under low confining pressures and tends to be stable under high confining pressures. (3) With increasing temperature, the permeabilities of the four sandstone subcategories decrease at different rates. (4) The orthogonal experimental results show that the confining pressure has the greatest influence on the permeability, followed by the water pressure and temperature. (5) The confining pressure, pore water pressure and temperature produce stress-strain in sandstone and thus change the sandstone pore structure and permeability. The permeability evolution of sandstones varies with pore structure. The findings of this study can inform the classified grouting of deep sandstone and optimize grouting parameters.
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Cao, Hanxue, Ziwei Luo, Chengcheng Wang, Jing Wang, Tao Hu, Lang Xiao i Junqi Che. "The Stress Concentration Mechanism of Pores Affecting the Tensile Properties in Vacuum Die Casting Metals". Materials 13, nr 13 (6.07.2020): 3019. http://dx.doi.org/10.3390/ma13133019.
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The absolute pressure strongly affects the porosity and mechanical properties of castings produced by vacuum high-pressure die casting (V-HPDC) technology. The pore size, quantity and distribution of AlSi9Cu3 samples under three absolute pressures were evaluated by X-ray tomography and optical and electron microscopy. The paper presents an elaboration the stress concentration mechanism of pores affecting the tensile properties. According to a mathematical analysis of a sample under uniaxial stress, the greater the radius of the pore, the higher the stress value is at the pore perimeter. When the absolute pressure drops from 1013 mbar to 100 mbar, the porosity decreases from 6.8% to 2.8%, and the pore number and mean size decreases. In tensile tests, the pore sizes of the fracture surface decrease with decreasing absolute pressure, and the pore distribution becomes uniform. The tensile properties and extensibility of the sample are improved, and the microscopic fracture surface of the sample changes from cleavage fracture to quasi-cleavage fracture. The number, size and distribution of pores in die casting collectively affect the properties of the sample. Large-size or complex pores or pores with concentrated distributions produce large stress concentrations, decreasing the strength of the metal.
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Du, Hao, Jian Zhong Qi, J. X. Wu, S. Q. Du i Tian Ying Xiong. "Structure of Porous Copper Fabricated by Unidirectional Solidification under Pressurized Hydrogen". Materials Science Forum 654-656 (czerwiec 2010): 1030–33. http://dx.doi.org/10.4028/www.scientific.net/msf.654-656.1030.
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Porous copper with elongated cylindrical pores were fabricated by a unidirectional solidification method in a mixture of hydrogen and argon with high pressures. The porous copper with longitudinal pores and radial pores were compared on structure. The effect of both hydrogen pressure and argon pressure on structure of the porous copper including pore size, pore density, and porosity was investigated. The reason for the effect is explained.
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Drake, R. E., S. Dhother, R. A. Teague i J. C. Gabel. "Protein osmotic pressure gradients and microvascular reflection coefficients". American Journal of Physiology-Heart and Circulatory Physiology 273, nr 2 (1.08.1997): H997—H1002. http://dx.doi.org/10.1152/ajpheart.1997.273.2.h997.
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Microvascular membranes are heteroporous, so the mean osmotic reflection coefficient for a microvascular membrane (sigma d) is a function of the reflection coefficient for each pore. Investigators have derived equations for sigma d based on the assumption that the protein osmotic pressure gradient across the membrane (delta II) does not vary from pore to pore. However, for most microvascular membranes, delta II probably does vary from pore to pore. In this study, we derived a new equation for sigma d. According to our equation, pore-to-pore differences in delta II increase the effect of small pores and decrease the effect of large pores on the overall membrane osmotic reflection coefficient. Thus sigma d for a heteroporous membrane may be much higher than previously derived equations indicate. Furthermore, pore-to-pore delta II differences increase the effect of plasma protein osmotic pressure to oppose microvascular fluid filtration.
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Letham, Eric Aidan, i Robert Marc Bustin. "Investigating Multiphase Flow Phenomena in Fine-Grained Reservoir Rocks: Insights from Using Ethane Permeability Measurements over a Range of Pore Pressures". Geofluids 2018 (2018): 1–13. http://dx.doi.org/10.1155/2018/5098283.
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The ability to quantify effective permeability at the various fluid saturations and stress states experienced during production from shale oil and shale gas reservoirs is required for efficient exploitation of the resources, but to date experimental challenges prevent measurement of the effective permeability of these materials over a range of fluid saturations. To work towards overcoming these challenges, we measured effective permeability of a suite of gas shales to gaseous ethane over a range of pore pressures up to the saturated vapour pressure. Liquid/semiliquid ethane saturation increases due to adsorption and capillary condensation with increasing pore pressure resulting in decreasing effective permeability to ethane gas. By how much effective permeability to ethane gas decreases with adsorption and capillary condensation depends on the pore size distribution of each sample and the stress state that effective permeability is measured at. Effective permeability decreases more at higher stress states because the pores are smaller at higher stress states. The largest effective permeability drops occur in samples with dominant pore sizes in the mesopore range. These pores are completely blocked due to capillary condensation at pore pressures near the saturated vapour pressure of ethane. Blockage of these pores cuts off the main fluid flow pathways in the rock, thereby drastically decreasing effective permeability to ethane gas.
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Chen, Ke Lin, Jin Bo Lei i Zhi Liu. "Numerical Analysis on the Excess Pore Water Pressure of Pipe-Pile with Hole during the Static-Sinking Pile". Applied Mechanics and Materials 744-746 (marzec 2015): 540–46. http://dx.doi.org/10.4028/www.scientific.net/amm.744-746.540.
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The time-space change rules of the environmental effects of the analysis of excess pore water pressure dissipation have also been studied during the static sinking-pile of the pipe-pile with hole. The results show: The excess pore water pressure will be dissipated with the time extending during the static sinking-pile of the 3 kinds of pipe-pole with hole. On the condition of the same effective radius, the depth of the observation dot is bigger, the excess pore water pressure will be bigger. On the contrast to the pipe-pole without hole, to some extent, the pipe-pole with hole can reduce the maximum of excess pore water pressure, and expedite the excess pore water pressure dissipation. This results can be provided the credible base for the theory research on the pipe-pole with hole and its application.
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Ruth, P. J. van, R. R. Hillis i R. E. Swarbrick. "DETECTING OVERPRESSURE USING POROSITY-BASED TECHNIQUES IN THE CARNARVON BASIN, AUSTRALIA". APPEA Journal 42, nr 1 (2002): 559. http://dx.doi.org/10.1071/aj01032.
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Overpressure has been encountered in many wells drilled in the Carnarvon Basin. Sonic logs are used to estimate pore pressure in shales in the Carnarvon Basin using the Eaton and equivalent depth methods of estimating pore pressure from velocity data with reference to a normal compaction trend. The crux of pore pressure estimation from the sonic log lies in the determination of the normal compaction trend, i.e. the acoustic travel time (Δt)/depth (z) trend for normally pressured sediments. The normal compaction trend for shales in the Carnarvon Basin was established by fitting an Athy-type exponential relationship to edited sonic log data, and is: Δt = 225 + 391exp(-0.00103z) Vertical stress estimates are also needed for the Eaton and equivalent depth methods used herein. A vertical stress (σv) relationship was obtained by fitting a regression line to vertical stress estimates from the density log, and is: σv = 0.0131 z1.0642 The Eaton and equivalent depth methods yield similar pressure estimates. However, the equivalent depth method can only be applied over a limited range of acoustic travel times, a limitation that does not apply to the Eaton method. The pressure estimates from the Eaton method were compared to pressures measured by direct pressure tests in adjacent permeable units. There is a good correlation between Eaton and test pressures in normally pressured intervals in three wells and overpressured intervals in two wells. Eaton pressure estimates underestimate overpressured direct pressure measurements in four wells by up to 13 MPa. This is consistent with overpressure being generated (at least in part) by a fluid expansion mechanism or lateral transfer of overpressure. The Eaton pressures in one well are, on average, 11 MPa lower than hydrostatic pore pressure recorded in direct pressure measurements below the Muderong Shale. The sediments in this well appear to be overcompacted due to exhumation. Mud weights can be used as a proxy for pore pressure in shales where direct pressure measurements are not available in the adjacent sandstones. The Eaton pressure estimates are consistent with mud weight in the Gearle Siltstone and Muderong Shale in 4 of the 8 wells studied. The Eaton pressures are on average 10 Mpa in excess of mud weight in the Muderong Shale and Gearle Siltstone in three wells. It is unclear whether the predicted Eaton pressures in these three wells accurately reflect pore pressure (i.e. the mud weights do not accurately reflect pore pressure), or whether they are influenced by changes in shale mineralogy (because the gamma ray filter does not differentiate between shale mineralogy).
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Burstein, Leonid. "Friction Force of the Sliding Surface with Pores Having a Semicircular Cross Section Form". International Journal of Surface Engineering and Interdisciplinary Materials Science 4, nr 2 (lipiec 2016): 1–22. http://dx.doi.org/10.4018/ijseims.2016070101.
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A theoretical solution of the mathematical model is represented for obtaining the hydrodynamic pressure and friction force of the non-contacting sliding surfaces with pores having a semicircular cross section form. The expressions for the hydrodynamic pressure, shear stress, and friction force were obtained for a control cell that includes the inside and outside of the pore areas. The pore radii have been studied in the range from 0.5µm to about 18 µm. The parametric study of the pore performance is obtained with the specially written MATLAB program used the theoretically defined expressions. It is found that better performance in terms of positive hydrodynamic pressure and optimal friction forces can be achieved with proper selection of pore and outside of pore sizes. Better hydrodynamic pressures were observed at the gap-pore radii and cell-pore radii ratios range between 0.5 … 1 and 2.5 … 5, respectively. The maximal friction forces are achieved at pore radii values about 0.64 of the cell dimensions, which correspond to a r1 range of about 5 … 13 µm.
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Kim, Changkyu, Woong Kwon, Moon Hee Lee, Jong Seok Woo i Euigyung Jeong. "Correlation between Pitch Impregnation Pressure and Pore Sizes of Graphite Block". Materials 15, nr 2 (12.01.2022): 561. http://dx.doi.org/10.3390/ma15020561.
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This study aimed to investigate the effect of impregnation pressure on the decrease in porosity of impregnated bulk graphite. The correlation between pitch impregnation behavior and the pore sizes of the bulk graphite block was studied to determine the optimal impregnation pressure. The densities and porosities of the bulk graphite before and after pitch impregnation under various pressures between 10 and 50 bar were evaluated based on the Archimedes method and a mercury porosimeter. The density increased rates increased by 1.93–2.44%, whereas the impregnation rate calculated from the rate of open porosity decreased by 15.15–24.48%. The density increase rate and impregnation rate were significantly high when the impregnation pressures were 40 and 50 bar. Compared with impregnation pressures of 10, 20, and 30 bar, the minimum impregnatable pore sizes with impregnation pressures of 40 and 50 bar were 30–39 and 24–31 nm, respectively. The mercury intrusion porosimeter analysis results demonstrated that the pressure-sensitive pore sizes of the graphite blocks were in the range of 100–4500 nm. Furthermore, the ink-bottle-type pores in this range contributed predominantly to the effect of impregnation under pressure, given that the pitch-impregnated-into-ink-bottle-type pores were difficult to elute during carbonization.
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Kan, Jiaguang, Guichen Li, Nong Zhang, Peng Wang, Changliang Han i Shun Wang. "Changing Characteristics of Sandstone Pore Size under Cyclic Loading". Geofluids 2021 (3.03.2021): 1–9. http://dx.doi.org/10.1155/2021/6664925.
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The size and distribution of pores in rocks are closely related to their physical and mechanical properties. It is important to study the structure and distribution of pore size inside the rock to assess the risk of damage to a given rock volume. These characteristics were studied under different pressures, pore diameters, and pore throat size distribution laws using a UTM5540 electronic universal testing machine, magnetic resonance imaging scanning, and low field nuclear magnetic resonance spectroscopy with cyclic loading on yellow sandstone. We found the following. (1) Under 0–10 MPa load, the peaks of the sandstone T 2 spectrum move left as load increases, and the porosity of the sandstone decreases. The peak area of the middle relaxation spectrum increases as pressure increases from 10 to 20 MPa, and a peak for the long relaxation time spectrum appears. (2) Under 0–10 MPa load, the spectral peak associated with a large pore moves left and decreases in area as pressure increases. Under 10–20 MPa load, the large-pore spectral peak moves right and increases in area as pressure increases. (3) Under the applied 0–10 MPa load, the porosity of water-saturated sandstone gradually decreases, and the sandstone NMR images darken with increasing load. The porosity of saturated sandstone gradually increases under 10–20 MPa pressure, and its NMR image brightens. (4) The number of small pore throats increases with increasing load, but the number of large- and medium-sized pore throats decreases. From 0 to 15 MPa, crack (>1 micron) abundance decreases, and fractures are generated by compaction under a 20 MPa load. The pore interconnectivity is enhanced, as are the number and size of pores in the sandstone. With continuing increasing pressure, the numbers of pores and penetration of cracks increase, which damages the sandstone.
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Eigenbrod, K. D., i W. H. Wurmnest. "Pore-water pressure response during undrained isotropic load changes in layered soils". Canadian Geotechnical Journal 36, nr 3 (25.10.1999): 544–55. http://dx.doi.org/10.1139/t99-015.
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Low pore-water pressure responses observed during undrained isotropic loading of thinly interbedded varved clay specimens were related to internal pore-water pressure equalization and internal shearing between soft clay seams and stiff silt layers of the varved clay. Both processes were analyzed in two separate models: a finite element analysis of the layered soil specimen with different elastic properties for each layer showed that shear stresses can develop along the layer interfaces during undrained isotropic loading. However, because the shear stresses are small and restricted to a narrow zone close to the surface of the cylindrical specimen, it appeared that the effect of shearing on the overall pore-water responses is negligible. The analysis of the pore-water pressures during undrained, isotropic loading demonstrated that hydraulic gradients between the two layers will develop. As a result, pore water will drain from the clay into the silt, leading to consolidation of the clay and swelling of the silt seams. The stabilized pore-water pressures should be the same as the pore-water pressures measured for the overall specimen, if the effect of internal shearing is negligible. Comparison of the computed with the measured overall pore-water pressure responses during testing for Skempton's pore-pressure coefficient B indicated reasonable agreement.Key words: Skempton's pore-pressure coefficient B, pore-water pressure response, varved clays, internal shearing, internal pore-water pressure equalization.
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Brower, K. R., i N. R. Morrow. "Fluid Flow in Cracks as Related to Low-Permeability Gas Sands". Society of Petroleum Engineers Journal 25, nr 02 (1.04.1985): 191–201. http://dx.doi.org/10.2118/11623-pa.
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Abstract A problem in formation evaluation of tight gas sands is that their permeabilities are sometimes surprisingly sensitive to variations in overburden pressure. Photomicrographs of pore casts show an interconnected system of Photomicrographs of pore casts show an interconnected system of sheet pores, which are somewhat like the surfaces of a randomized honeycomb. A mathematical relation for predicting the pressure dependence of flow rate in sheet predicting the pressure dependence of flow rate in sheet pores has been derived from the dimensions of the pores pores has been derived from the dimensions of the pores and the elastic constants of the matrix. The equation has been validated by measurements on artificial media containing cracks of known dimensions in glass and concrete. The observed pressure sensitivity of the gas sands used in this study requires the aspect ratio of the pores (in this case, the ratio of average large dimensions to sheet thickness) to be greater than 100. Aspect ratios have been determined by taking the large dimension from photomicrographs of pore casts or grain size and the thickness photomicrographs of pore casts or grain size and the thickness from mercury injection pressure or the slope of a plot of apparent permeability vs. the reciprocal of mean gas pressure. The latter gives the diffusive contribution to gas pressure. The latter gives the diffusive contribution to gas flow from which the pore size can be calculated. The two methods for measuring pore size give satisfactory agreement. The aspect ratio's for the sheet pores in tight gas sands are large enough to explain the dependence of permeability on overburden pressure. permeability on overburden pressure. Introduction Sensitivity of permeability to overburden pressure is often a key factor in formation evaluation of tight gas sands. Gas permeability reductions of more than an order of magnitude have been observed in dry cores when overburden pressure is increased to typical formation values. Although this sensitivity to pressure has been related to the presence of clays and shales, the current consensus is that the pressure behavior of crack-shaped pores-i.e., pores characterized by two large dimensions and one small pores characterized by two large dimensions and one small one-is largely responsible. A similar conclusion was reached earlier by Fatt with respect to the less severe, but still significant, sensitivity exhibited by conventional sandstones. In this paper, the effect of pressure on pore structure and consequent changes in gas permeability pore structure and consequent changes in gas permeability are examined for a variety of natural and synthetic porous media. Pore Structure Pore Structure Pore Casts The pore structure of tight sands is revealed Pore Casts. The pore structure of tight sands is revealed in three dimensions by resin pore casts such as those shown in Fig. 1. The cast is prepared by injection of epoxy resin into the sample, followed by etching after the epoxy is set. Pore casts for over 20 samples, 12 of which were selected for the variety they provided in geologic character, typically showed sheet pores that are linked to give random polyhedra. Within this structure are distributed relatively large pore spaces commonly formed by solution of individual grains and cements. These spaces are often filled partially with matrix material. Inspection of pore casts before and after etching, and dun sections of samples containing injected resin, indicates that individual grains are largely bounded by sheet pores; individual polyhedra, seen in the pore cast, appear to be associated with individual grains or local regions bounded by grain surfaces. Thin sections generally show that, as a sediment is compacted over geologic time by pressure-solution and recrystallization processes, the grains fit pressure-solution and recrystallization processes, the grains fit together more and more snugly and may even fracture, but they maintain their individual identities with respect to neighboring grains. The polyhedral structure, therefore, is related strongly to grain size distribution. Contact Between Grains The ability of etchant, used in preparation of pore casts, to penetrate the sheet pores through many layers of particles may imply the existence of areas of cementation or direct contact between grains. However, from examination of sheet pores studied to date, the areas of actual contact between grains generally are difficult to identify from the pore casts and probably are small. For some sediments with permeability less than about 0.005 md, it was difficult to prepare satisfactory pore casts, possibly because the casts had very poor pore casts, possibly because the casts had very poor structural integrity or because the resin did not penetrate the space, if any, between grains. From our observations to date, it seems likely that most tight sands of potential commercial interest contain a network of polyhedral sheet pores that largely control permeability. pores that largely control permeability. Pore Thickness. Electron micrographs of the sheet pore Pore Thickness. Electron micrographs of the sheet pore edges, such as shown in Fig. Id, for sands of less than 1 md permeability, show their thicknesses to range typically from about 0.2 to 4 mu m. The lower limit may be related to difficulties of preparing casts of even finer cracks, since the presence of much smaller pores is indicated by mercury porosimetry and NMR measurements. Surface Area The two-dimensional network at the surface of the pore cast permits estimates of crack length per unit area to be made. These can be translated to approximations of crack surface area, Ac, per unit volume. SPEJ P. 191
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Prasad, Mahesh R. G., Siwen Gao, Napat Vajragupta i Alexander Hartmaier. "Influence of Trapped Gas on Pore Healing under Hot Isostatic Pressing in Nickel-Base Superalloys". Crystals 10, nr 12 (17.12.2020): 1147. http://dx.doi.org/10.3390/cryst10121147.
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Under the typical hot isostatic pressing (HIP) processing conditions, plastic deformation by dislocation slip is considered the primary mechanism for pore shrinkage, according to experimental observations and deformation mechanism maps. In the present work, a crystal plasticity model has been used to investigate the influence of applied pressure and holding time on porosity reduction in a nickel-base single crystal superalloy. The influence of trapped gas on pore shrinkage is modeled by coupling mechanical deformation with pore–gas interaction. In qualitative agreement with experimental investigations, we observe that increasing the applied pressure or the holding time can effectively reduce porosity. Furthermore, the effect of pore shape on the shrinkage is observed to depend on a combination of elastic anisotropy and the complex distribution of stresses around the pore. Simulation results also reveal that, for pores of the same shape, smaller pores (radius < 0.1 μm) have a higher shrinkage rate in comparison to larger pores (radius ≥ 0.1 μm), which is attributed to the increasing pore surface energies with decreasing pore sizes. It is also found that, for smaller initial gas-filled pores (radius < 0.1 μm), HIP can result in very high gas pressures (on the order of GPa). Such high pressures either act as a driving force for argon to diffuse into the surrounding metal during HIP itself, or it can result in pore re-opening during subsequent annealing or mechanical loading. These results demonstrate that the micromechanical model can quantitatively evaluate the individual influences of HIP processing conditions and pore characteristics on pore annihilation, which can help optimize the HIP process parameters in the future.
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He, Jun, Mingke Wang, Jienan Pan, Xianglong Wang i Yiju Tang. "Effect of Temperature and Pressure on Nanoscale Pores in Closed Coal". Journal of Nanoscience and Nanotechnology 21, nr 1 (1.01.2021): 567–77. http://dx.doi.org/10.1166/jnn.2021.18467.
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To understand the nanoscale pore development characteristics of closed coal under the combined influence of temperature and confined pressure, a series of experiments at different temperatures and pressures were carried out using a custom closed coal temperature and pressure experimental system. The lean coal samples were taken from a mining area in Qinshui Basin, North China. In these experiments, the temperature was 200 °C or 300 °C, the pressure was 14 MPa or 23 MPa, respectively, and the experiment duration was 12 h. The CH4/N2/CO2 isothermal adsorption tests were carried out on all samples. The results show that the custom experimental system can be used to effectively study the effect of mechanical-thermal interaction on the nanoscale pores in closed coal. Before and after the experiment, the Langmuir volume increases, and the methane adsorption capacity increases. The specific surface area and pore volume of the micropores (<1 nm) decrease, but the specific surface area and pore volume of the pores (6–100 nm) increase. The specific surface area and pore volume of the micropores (<1 nm) are negatively correlated with the temperature and decrease with increasing temperature. Fractal analysis results show that under the influence of temperature and pressure, the heterogeneity of the nanoscale pore structure and the roughness of the pore surface increase. This research is of important theoretical significance for the safe mining of deep coal seams and for the development of coalbed methane resources.
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Samarasekera, L., i Z. Eisenstein. "Pore pressures around tunnels in clay". Canadian Geotechnical Journal 29, nr 5 (1.10.1992): 819–31. http://dx.doi.org/10.1139/t92-089.
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The pore-pressure generation and dissipation around shallow tunnels excavated in both normally and overconsolidated clays are investigated. The influence of the diameter D, depth of cover to diameter ratio H/D, coefficient of earth pressure at rest K0, and strength and modulus variations with depth on pore-pressure generation are examined. The effects of immediate support on pore pressure are also studied by defining a quantity termed effective stiffness ratio (ESR). A two-dimensional, nonlinear finite element analysis is performed to obtain the pore-pressure generation behav-iour. Strength, modulus, initial stress field, and unloading due to excavation are reflected in this analysis. The pore-pressure dissipation behaviour is investigated by employing an uncoupled consolidation theory using finite elements. A dimensionless time factor is used to present the results of pore-pressure dissipation. These results are presented using nondimensional quantities and in normalized forms. The results are directly applicable to estimation of pore pressures for determining long-term stability of tunnels. Key words : clay, pore pressure, tunnels, uncoupled consolidation, finite elements, stress-strain.
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Mahmud, Walid Mohamed. "Rate-Controlled Mercury Injection Experiments to Characterize Pore Space Geometry of Berea Sandstone". E3S Web of Conferences 366 (2023): 01016. http://dx.doi.org/10.1051/e3sconf/202336601016.
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Interpretation of the relationship between heterogeneity and the flow in porous media is very important in increasing the recovery factor for an oil or gas reservoir. Capillarity for instance, controls fluids static distribution in a reservoir prior to production and remaining hydrocarbons after production commences. Therefore, capillary pressure data are used by petroleum engineers, geologists, and petrophysicists to evaluate production characteristics of petroleum accumulations. Conventional pressure-controlled mercury porosimetry produces an overall capillary pressure curve and pore throat size distribution data that provide little information about the porous medium structure and pore geometry. The present study provides information on three capillary pressure curves obtained from rate-controlled mercury injection porosimetry; one describes the larger pore spaces or pore bodies of a rock, another describes the smaller pores or pore throats that connect the larger pores, and a final curve which corresponds to the overall capillary pressure curve obtained from the conventional pressure-controlled mercury injection. An experimental constant-rate mercury injection apparatus was constructed that consists of a piston displacement pump, a computer controlled stepper motor drive and a core sample cell designed to minimize dead volume. The apparatus was placed in a glass chamber and subjected to an air bath to maintain a constant temperature of 27o C throughout the experiments. Then constant rate mercury injection experiments were performed on three Berea Sandstone core plugs. Results show that volume-controlled or rate-controlled porosimetry provides considerably more detailed data and information on heterogeneity and the statistical nature of pore space structure than the conventional pressure-controlled porosimetry as pressure fluctuations with time reveal menisci locations in pore bodies and pore throats. Moreover, pore size distributions based on volume-accessed pores and pore radii were obtained from the pressure versus saturation relationship.
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Marcolli, Claudia. "Technical note: Fundamental aspects of ice nucleation via pore condensation and freezing including Laplace pressure and growth into macroscopic ice". Atmospheric Chemistry and Physics 20, nr 5 (17.03.2020): 3209–30. http://dx.doi.org/10.5194/acp-20-3209-2020.
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Abstract. Pore condensation and freezing (PCF) is an ice nucleation mechanism that explains ice formation at low ice supersaturation. It assumes that liquid water condenses in pores of solid aerosol particles below water saturation, as described by the Kelvin equation, followed by homogeneous ice nucleation when temperatures are below about 235 K or immersion freezing at higher temperatures, in case the pores contain active sites that induce ice nucleation. Porewater is under tension (negative pressure) below water saturation as described by the Young–Laplace equation. This negative pressure affects the ice nucleation rates and the stability of the pore ice. Here, pressure-dependent parameterizations of classical nucleation theory are developed to quantify the increase in homogeneous ice nucleation rates as a function of tension and to assess the critical diameter of pores that is required to accommodate ice at negative pressures. Growth of ice out of the pore into a macroscopic ice crystal requires ice supersaturation. This supersaturation as a function of the pore opening width is derived, assuming that the ice phase first grows as a spherical cap on top of the pore opening before it starts to expand laterally on the particle surface into a macroscopic ice crystal.
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Zhang, Jincai, i Shangxian Yin. "Real-Time Pore Pressure Detection: Indicators and Improved Methods". Geofluids 2017 (2017): 1–12. http://dx.doi.org/10.1155/2017/3179617.
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High uncertainties may exist in the predrill pore pressure prediction in new prospects and deepwater subsalt wells; therefore, real-time pore pressure detection is highly needed to reduce drilling risks. The methods for pore pressure detection (the resistivity, sonic, and corrected d-exponent methods) are improved using the depth-dependent normal compaction equations to adapt to the requirements of the real-time monitoring. A new method is proposed to calculate pore pressure from the connection gas or elevated background gas, which can be used for real-time pore pressure detection. The pore pressure detection using the logging-while-drilling, measurement-while-drilling, and mud logging data is also implemented and evaluated. Abnormal pore pressure indicators from the well logs, mud logs, and wellbore instability events are identified and analyzed to interpret abnormal pore pressures for guiding real-time drilling decisions. The principles for identifying abnormal pressure indicators are proposed to improve real-time pore pressure monitoring.
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Frempong, P., A. Donald i S. D. Butt. "The effect of pore pressure depletion and injection cycles on ultrasonic velocity and quality factor in a quartz sandstone". GEOPHYSICS 72, nr 2 (marzec 2007): E43—E51. http://dx.doi.org/10.1190/1.2424887.
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Passing seismic waves generate transient pore-pressure changes that influence the velocity and attenuation characteristics of porous rocks. Compressional ultrasonic wave velocities [Formula: see text] and quality factors [Formula: see text] in a quartz sandstone were measured under cycled pore pressure and uniaxial strain conditions during a laboratory simulated injection and depletion process. The objectives were to study the influence of cyclical loading on the acoustic characteristics of a reservoir sandstone and to evaluate the potential to estimate pore-fluid pressure from acoustic measurements. The values of [Formula: see text] and [Formula: see text] were confirmed to increase with effective stress increase, but it was also observed that [Formula: see text] and [Formula: see text] increased with increasing pore pressure at constant effective stress. The effective stress coefficient [Formula: see text] was found to be less thanone and dependent on the pore pressure, confining stress, and load. At low pore pressures, [Formula: see text] approached one and reduced nonlinearly at high pore pressures. The change in [Formula: see text] and [Formula: see text] with respect to pore pressure was more pronounced at low versus high pore pressures. However, the [Formula: see text] variation with pore pressure followed a three-parameter exponential rise to a maximum limit whereas [Formula: see text] had no clear limit and followed a two-parameter exponential growth. Axial strain measurements during the pore-pressure depletion and injection cycles indicated progressive viscoelastic deformation in the rock. This resulted in an increased influence on [Formula: see text] and [Formula: see text] with increasing pore-pressure cycling. The value [Formula: see text] was more sensitive in responding to the loading cycle and changes in pore pressures than [Formula: see text]; thus, [Formula: see text] may be a better indicator for time-lapse reservoir monitoring than [Formula: see text]. However, under the experimental conditions, [Formula: see text] was unstable and difficult to measure at low effective stress.
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Mavko, Gary, i Richard Nolen‐Hoeksema. "Estimating seismic velocities at ultrasonic frequencies in partially saturated rocks". GEOPHYSICS 59, nr 2 (luty 1994): 252–58. http://dx.doi.org/10.1190/1.1443587.
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Seismic velocities in rocks at ultrasonic frequencies depend not only on the degree of saturation but also on the distribution of the fluid phase at various scales within the pore space. Two scales of saturation heterogeneity are important: (1) saturation differences between thin compliant pores and larger stiffer pores, and (2) differences between saturated patches and undersaturated patches at a scale much larger than any pore. We propose a formalism for predicting the range of velocities in partially saturated rocks that avoids assuming idealized pore shapes by using measured dry rock velocity versus pressure and dry rock porosity versus pressure. The pressure dependence contains all of the necessary information about the distribution of pore compliances for estimating effects of saturation at the finest scales where small amounts of fluid in the thinnest, most compliant parts of the pore space stiffen the rock in both compression and shear (increasing both P‐ and S‐wave velocities) in approximately the same way that confining pressure stiffens the rock by closing the compliant pores. Large‐scale saturation patches tend to increase only the high‐frequency bulk modulus by amounts roughly proportional to the saturation. The pore‐scale effects will be most important at laboratory and logging frequencies when pore‐scale pore pressure gradients are unrelaxed. The patchy‐saturation effects can persist even at seismic field frequencies if the patch sizes are sufficiently large and the diffusivities are sufficiently low for the larger‐scale pressure gradients to be unrelaxed.
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Hu, Zhiming, Ying Mu, Qiulei Guo, Wente Niu, Xianggang Duan, Jin Chang i Zhenkai Wu. "Occurrence and Migration Mechanisms of Methane in Marine Shale Reservoirs". Energies 15, nr 23 (29.11.2022): 9043. http://dx.doi.org/10.3390/en15239043.
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The occurrence mechanism of methane is very important as evaluating the gas-bearing properties of marine shale reservoirs, and the evaluation of the development effect of shale gas wells need to focus on the migration mechanism of methane. In this study, LTNA technology and NMR technology were used to analyze the pores and methane of shale. The results show that inorganic pores have better connectivity, larger pore size, and micro–nano cracks between pores compared to organic pores. Most of the pores in shale are micropores and mesopores, which provide most of the specific surface area, but the contribution of macropores to pore volume cannot be ignored. Adsorbed gas volume depends on the pore surface area and gas pressure, while free gas volume depends on pore volume and gas pressure. The pore structure of micropores and mesopores is complex, and the specific surface area is large. The dispersion force between pore surface molecules and methane molecules is firm, which makes the pore wall an ideal enrichment space for adsorbed gas. Macropores have larger pore volumes and can store more free gas. In the process of gas well development, free gas is first discharged from pores under the action of the pressure gradient. As the pore pressure is lower than the critical desorption pressure, adsorbed gas begins to desorb in large quantities. It should be noted that the desorption process of adsorbed gas is slow and persistent, which makes it impossible for gas wells to achieve higher recovery in a shorter production cycle. Therefore, improving the recovery rate of adsorbed gas is the key to future research on shale gas development effects. This study is helpful in clarifying the occurrence and migration mechanism of methane in marine shale reservoirs and guiding the development of gas wells.
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Yu, Hua, Kam Ng, Dario Grana, John Kaszuba, Vladimir Alvarado i Erin Campbell. "Experimental investigation of the effect of compliant pores on reservoir rocks under hydrostatic and triaxial compression stress states". Canadian Geotechnical Journal 56, nr 7 (lipiec 2019): 983–91. http://dx.doi.org/10.1139/cgj-2018-0133.
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The presence of compliant pores in rocks is important for understanding the stress–strain behaviors under different stress conditions. This paper describes findings on the effect of compliant pores on the mechanical behavior of a reservoir sandstone under hydrostatic and triaxial compression. Laboratory experiments were conducted at reservoir temperature on Weber Sandstone samples from the Rock Springs Uplift, Wyoming. Each experiment was conducted at three sequential stages: (stage 1) increase in the confining pressure while maintaining the pore pressure, (stage 2) increase in the pore pressure while maintaining the confining pressure, and (stage 3) application of the deviatoric load to failure. The nonlinear pore pressure – volumetric strain relationship governed by compliant pores under low confining pressure changes to a linear behavior governed by stiff pores under higher confining pressure. The estimated compressibilities of the matrix material in sandstone samples are close to the typical compressibility of quartz. Because of the change in pore structures during stage 1 and stage 2 loadings, the estimated bulk compressibilities of the sandstone sample under the lowest confining pressure decrease with increasing differential pressure. The increase in crack initiation stress is limited with increasing differential pressure because of similar total crack length governed by initial compliant porosity in sandstone samples.
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Rollins, Kyle M., J. Dusty Lane, Emily Dibb, Scott A. Ashford i A. Gray Mullins. "Pore Pressure Measurement in Blast-Induced Liquefaction Experiments". Transportation Research Record: Journal of the Transportation Research Board 1936, nr 1 (styczeń 2005): 210–20. http://dx.doi.org/10.1177/0361198105193600124.
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Blast-induced liquefaction experiments have been conducted at a number of test sites to evaluate lateral foundation resistance and soil improvement techniques. Tests can be constructed at full scale without waiting for an earthquake. In this extreme environment, pore pressure transducers must survive transient blast pressures of 41.4 MPa (6,000 psi) yet have enough resolution to measure residual pore pressures of ±0.69 kPa (0.1 psi). Three transducer types were evaluated under these demanding conditions, and the piezoresistive transducer was found to be the most robust. These sensors were repeatedly subjected to extreme blast pressures and vibration, but they still provided accurate time histories of residual pore pressure. Although these piezometers are more expensive than other types, installation techniques allowed them to be recovered and reused in subsequent tests and thus reduced overall costs. These pore pressure sensors make it possible to define the extent of the liquefied zone during blast liquefaction experiments and to understand the soil behavior during cyclic loading of deep foundations.
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Wang, H., L. Zhang, Q. Zhao, Z. Qiu, D. Liu, Q. Zhang, Y. Wang i D. Dong. "Reservoir Characteristics of the Lower Permian Marine-Continental Transitional Shales: Example from the Shanxi Formation and Taiyuan Formation in the Ordos Basin". Geofluids 2021 (7.12.2021): 1–17. http://dx.doi.org/10.1155/2021/9373948.
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The pore types and pore structure parameters of the heterogenetic shale will affect the percolation and reservoir properties of shale; therefore, the research on these parameters is very important for shale reservoir evaluation. We used X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), low-pressure CO2 adsorption analysis, mercury injection capillary pressure (MICP), and high-pressure methane adsorption analysis to analyze the characteristics of different pore types and their parameters of the Lower Permian Shanxi Formation and Taiyuan Formation in the Ordos Basin. The influence of different mineral contents on the porosity and pore size is also investigated. The Shanxi Formation (SF) is composed of quartz (average of 38.4%), plagioclase, siderite, Fe-dolomite, calcite, pyrite, and clay minerals (average of 50.1%), while the Taiyuan Formation (TF) is composed of calcite (average of 37%), siderite, Fe-dolomite, quartz, pyrite, and clay minerals (average of 32.3%). The most common types of pores observed in this formation are interparticle pores (InterP pores), intraparticle pores (IntraP pores), interclay pores, intercrystalline pores (InterC pores), organic matter pores (OM pores), and microfractures. CO2 adsorption analysis demonstrates the type I physisorption isotherms, showing microporous solids having comparatively small external surfaces. The similar types of isothermal shapes of the Shanxi Formation (SF) and Taiyuan Formation (TF) suggest that both types have similar pore size distribution (PSD) within the measured pore range by the low-pressure CO2 adsorption experiment. The micropore pore size of the TF is larger than that of the SF. MICP shows the larger pores (>50 nm), and most of the volume was adsorbed by macropores. Methane gas sorption capacity increases with increasing pressure. Clay minerals and quartz played an important role in providing adsorption sites for methane gas. The overall analysis of both formations shows that TF has good reservoir properties than SF.
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Zheng, Binshuang, Xiaoming Huang, Jingwen Ma, Zhengqiang Hong, Jiaying Chen, Runmin Zhao i Shengze Zhu. "Evaluation on Distribution Characteristics of Pore Water Pressure within Saturated Pavement Structure Based on the Proposed Tire-Fluid-Pavement Coupling Model". Advances in Materials Science and Engineering 2022 (28.01.2022): 1–12. http://dx.doi.org/10.1155/2022/5849418.
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To investigate the flow characteristics of pore water in asphalt pavement and the variation law of the pore water pressure under vehicle loading, a novel method based on BA network and quartet structure generation set method was proposed to reconstruct the three-dimensional (3D) pavement model with pores. The permeability coefficient and the gradation curve were adopted to evaluate the reliability and stability of the random growth pavement model. Then, the tire-fluid-pavement coupling model was established with FLUENT 3D based on the fluid Mie–Gruneisen state equation. According to the built fluid-solid coupling model, the pressure-velocity coupled finite volume algorithm was applied to study the distribution of the pore water pressure in asphalt pavement. Results show that the pore water pressure in asphalt pavement decays periodically with time under vehicle loading. For different types of asphalt pavement, the pore water pressure in open-graded friction course (OGFC) pavement is the smallest during the whole process. Moreover, the peak values of the pore water pressure decrease in the order of asphalt concrete (AC) pavement, stone mastic asphalt (SMA) pavement, and OGFC pavement. The maximum negative value of the pore water pressure is generally less than 0.3 times the maximum positive values. As for saturated pavement pores, the pore water pressure is hardly affected by the water film thickness. The positive peak value of the pore water pressure increases on an approximate parabolic curve as the vehicle speed improves gradually, while the negative one remains largely unchanged. The results are expected to help reduce tire hydroplaning risk and provide guidance for the selection of asphalt mixtures of drainage asphalt pavement.
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St-Arnaud, Guy. "The high pore pressures within embankment dams: an unsaturated soil approach". Canadian Geotechnical Journal 32, nr 5 (1.10.1995): 892–98. http://dx.doi.org/10.1139/t95-085.
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Pore pressures substantially higher than expected are frequently measured within the cores of large dams. Typical observations are presented, and various hypotheses proposed to explain this phenomenon are summarized and briefly discussed. The hypothesis suggested herein is that the pore pressures are influenced by the free gases trapped during the submergence. These gases are compressed at the ambient pore pressure, which is decreasing in the flow direction. The degree of saturation and, therefore, the permeability decrease in the same direction. The pore pressures are thus higher than predicted in a uniform permeability condition. Free gases are dissolved in the water due to the increase of the pore pressures. They are carried in the seepage flow and come out of solution in the core or finally in the downstream filter after some decrease of the pore-water pressures. The increase of pore pressure with respect to the steady-state conditions is a function of many factors and is necessarily transient. Key words : pore pressure, embankment dam, unsaturated soil, permeability, seepage.
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John, Ajesh. "Pore-pressure prediction challenges in chemical compaction regimes: An alternative VP/VS-based approach". Interpretation 4, nr 4 (1.11.2016): T443—T454. http://dx.doi.org/10.1190/int-2015-0106.1.
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Understanding pressure mechanisms and their role in porosity-effective stress relationship is crucial in pore-pressure prediction estimation, particularly in complex geologic and high-temperature regimes. Overpressures are commonly associated with undercompaction and/or unloading mechanisms; those associated with undercompaction generally possess a direct relationship between effective stress and porosity, whereas those associated with unloading do not provide such direct indications from porosity trends. The type of associated unloading mechanism can be correlated when the effective stress and velocity become distorted with the onset of unloading. In the Ravva field, the pore-pressure distribution and overpressure mechanism in the Miocene and below it is a classic example of the unloading mechanism related to chemical compaction, thereby making it difficult to resolve the magnitude and trend of pore pressures. Here, the ratio of P- and S-wave velocities ([Formula: see text]) is analyzed from the drilled locations to understand the effects of lithology, pressure, and fluids on formation velocities and indicates a distinct decreasing trend across the overpressure formations, which I have corresponded to excess pressure resulting from chemical compaction. Across the high-pressured zones, [Formula: see text] ratios show low values compared with normally pressured zones possibly due to the presence of hydrocarbon and/or overpressures. A velocity correction coefficient ranging 0.83–0.71 is resolved for overpressure zones by normalizing the [Formula: see text] values across the normally pressured formations, and thereby assuring that a pore-pressure estimation using corrected velocity from [Formula: see text] analysis shows a high degree of accuracy on prediction trends. Pore-pressure predictions based on [Formula: see text] are a more effective and valid approach in high-temperature settings, in which numerous factors can contribute to pressure generation and a direct effective stress-porosity relationship deviates from the trend.
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Wu, Di, Yuke Wang, Fei Zhang i Yue Qiu. "Influences of Pore-Water Pressure on Slope Stability considering Strength Nonlinearity". Advances in Civil Engineering 2021 (25.05.2021): 1–16. http://dx.doi.org/10.1155/2021/8823899.
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The pore-water pressure is a vital factor in determining the slope stability. To deal with the stability of slopes undergoing pore-water pressures, this paper used the pore-water pressure coefficient to develop the three-dimensional limit analysis method for slope stability evaluation with a nonlinear strength envelope. For numerical slope examples, the critical heights and corresponding critical slip surfaces associated with linear and nonlinear envelopes were derived by using a numerical optimization procedure. The influences of pore-water pressures on the slope stability were addressed by comparing the upper-bound solutions derived by linear and nonlinear strength envelopes (the linear and nonlinear results for short). The obtained two critical inclinations between the linear and nonlinear results both decrease and gradually approach with increasing pore-water pressure coefficient. For most slopes subjected to pore-water pressures, using the linear Mohr–Coulomb envelope will obviously overestimate the slope critical height. The overestimation resulted from the linear criterion will become more distinct for slopes with smaller widths. Besides, the presented results showed that the equivalent internal friction angle tends to have a weaker increasing trend for steeper slopes as pore-water pressure coefficient increases. Hence, when pore-water pressure coefficient increases, the critical slip surfaces of gentle slopes with nonlinear strength criteria become shallower, but the critical slip surfaces of steep slopes seem to have no consistent change law. These results and analyses can illustrate the significance of the application of nonlinear strength envelopes in slope stability evaluation considering pore-water pressures and provide certain reference advice in slope engineering design and landslide prevention.
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Erdős, Máté, Olav Galteland, Dick Bedeaux, Signe Kjelstrup, Othonas A. Moultos i Thijs J. H. Vlugt. "Gibbs Ensemble Monte Carlo Simulation of Fluids in Confinement: Relation between the Differential and Integral Pressures". Nanomaterials 10, nr 2 (9.02.2020): 293. http://dx.doi.org/10.3390/nano10020293.
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The accurate description of the behavior of fluids in nanoporous materials is of great importance for numerous industrial applications. Recently, a new approach was reported to calculate the pressure of nanoconfined fluids. In this approach, two different pressures are defined to take into account the smallness of the system: the so-called differential and the integral pressures. Here, the effect of several factors contributing to the confinement of fluids in nanopores are investigated using the definitions of the differential and integral pressures. Monte Carlo (MC) simulations are performed in a variation of the Gibbs ensemble to study the effect of the pore geometry, fluid-wall interactions, and differential pressure of the bulk fluid phase. It is shown that the differential and integral pressure are different for small pores and become equal as the pore size increases. The ratio of the driving forces for mass transport in the bulk and in the confined fluid is also studied. It is found that, for small pore sizes (i.e., < 5 σ fluid ), the ratio of the two driving forces considerably deviates from 1.
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Wu, Yong Fu, Hui Xue Jiang, Chun Zou, Kang Cai Yu i Hiromi Nagaumi. "Numerical Simulation of Pore Evolution of 7050 Aluminum Alloy during Hot Compression Process". Materials Science Forum 879 (listopad 2016): 2119–24. http://dx.doi.org/10.4028/www.scientific.net/msf.879.2119.
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Evolution behavior of pores in 7050 aluminum alloy during hot compression process has been investigated by finite element (FE) numerical simulation. The representative volume element (RVE) model containing one isolated pore is built, in which the gas in pore is treated as ideal gas. Effects of initial pore inner pressure and deformation temperature on pore evolution have been investigated. The simulation results indicate that stress concentration exists around the pore in the compressing process. At the simple compression condition, the inner pressure of the pore increases but the volume decreases as the bulk metals deforms. However, the volume reaches a plateau after the yield point of bulk metal. The plateau volume depends on the initial inner pressure of the pore and the flow stress of the bulk metal. Since the inner pressure of the pore balances with the flow stress of bulk metal at the interface, the temperature affects the evolution behavior of the pore through its influence on the flow stress of the bulk metal primarily.
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Burstein, Leonid. "Hydrodynamic Behavior of the Sliding Surface with Semicircular Pores". International Journal of Surface Engineering and Interdisciplinary Materials Science 4, nr 1 (styczeń 2016): 45–68. http://dx.doi.org/10.4018/ijseims.2016010103.
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A mathematical model, theoretical and numerical solutions are represented for non-contacting sliding surfaces with pores having a half-round form. The theoretically based expressions for the hydrodynamic pressure, the maximum positive pressure and the load capacity were obtained for a cell which includes the inside and outside of the pore areas. The cell and pore dimensions were studied in the range 7.5…100 and 5... 20 micron respectively. The obtained expressions were validated with the MATLAB ODE-solver. It is shown that behavior of the sliding surfaces with semicircular pores can be achieved for the pores with pore radii-gap ratio about 0.5 … 2 and the control cell dimensions to pore radii ratios about 3 … 5. The rate of performance improvement becomes small above these values. In general, the optimum pore size decreases at higher pore cell-pore ratios and lower pore-gap ratio values.
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Alymov, М. I., S. I. Averin, E. M. Morozov, I. V. Saikov i F. F. Galiev. "Determination of the pressure inside pores". Industrial laboratory. Diagnostics of materials 87, nr 10 (18.10.2021): 40–43. http://dx.doi.org/10.26896/1028-6861-2021-87-10-40-43.
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Determination of the porosity, structural characteristics of pores, and gas pressure in closed pores is the most important part of assessing physical and mechanical properties of materials. The internal pressure inside the pore can be used in estimating the level of strength reliability of the porous volume of the product to optimize the technological processes of product manufacturing, control their structure and properties, and avoid the formation of cracks at the boundaries of the particles consisting the material. We present a method for calculating the internal pressure in a spherical pore that has arisen in the material of a product obtained using powder metallurgy or additive technologies. The proposed procedure for measuring internal pressure in a pore consists in application of an external pressure to the product, measurements of the displacements of the points on the pore surface, and calculation of the internal pressure from the difference between the displacements. In this case, the known solutions of the problem of the theory of elasticity regarding the deformation of a spherical cavity located in the center of a spherical hollow ball are used. The results obtained can be used to assess the properties and structure of the products obtained by additive technology and methods of powder metallurgy, as well as to improve the technology of their manufacture.
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Sultan, Nabil, i Sara Lafuerza. "In situ equilibrium pore-water pressures derived from partial piezoprobe dissipation tests in marine sediments". Canadian Geotechnical Journal 50, nr 12 (grudzień 2013): 1294–305. http://dx.doi.org/10.1139/cgj-2013-0062.
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Excess pore-water pressure has a significant effect on submarine slope stability and sediment deformation, and therefore its in situ equilibrium measurement is crucial in carrying out accurate slope stability assessments and accurately deriving geotechnical design parameters. In situ equilibrium pore-water pressure is usually obtained from pore pressure decay during piezocone tests. However, submarine shelves and slopes are often characterized by the existence of low-permeability (fine-grained) sediments involving long dissipation tests that are an important issue for offshore operational costs. Consequently, short-term and (or) partial dissipation tests are usually performed and in situ equilibrium pore-water pressures are predicted from partial measurements. Using a modified cavity expansion approach, this paper aims to predict for four different sites the in situ equilibrium pore-water pressures. Comparisons between predicted and observed in situ equilibrium pore-water pressures allowed the development of a guide to evaluate the minimum time required to perform short-term dissipation tests for a given marine sediment. The main finding of this Note is that the second derivative of the pore pressure, u, versus the logarithm of time, t, ∂2u/∂ln(t)2 must be positive to calculate accurately the in situ equilibrium pore-water pressures from partial measurements.
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A, Tanko. "A Machine Learning Approach to Modeling Pore Pressure". Petroleum & Petrochemical Engineering Journal 4, nr 1 (2020): 1–6. http://dx.doi.org/10.23880/ppej-16000213.
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Machine Learning techniques and applications have lately gained a lot of interest in many areas, including spheres of arithmetic, finances, engineering, dialectology, and a lot more. This is owing to the upwelling of ground-breaking and sophisticated machine learning procedures to exceedingly multifaceted complications along with the prevailing advances in high speed computing. Numerous usages of Machine learning in daily life include pattern recognition, automation, data processing and analysis, and so on. The Petroleum industry is not lagging behind also. On the contrary, machine learning approaches have lately been applied to enhance production, forecast recoverable hydrocarbons, augment well placement by means of pattern recognition, optimize hydraulic fracture design, and to help in reservoir characterization. In this paper, three different machine learning models were trained and utilized to explore the feasibility of forecasting pore pressure of a well. The machine learning algorithms include, Simple Linear Regression, Decision Stump and Multilayer Perceptron (ANN). The predictive accuracies of the algorithm was analyzed using statistical measures. Five (5) parameters were utilized as input variables in the models: hydrostatic pressure, overburden pressure, observed and normal sonic velocities and pore pressure. 80% of the data was used in training while the remaining 20% was used for testing of the models. A sensitivity analysis of the five variable was conducted so as to identify correlations of the variables. Results of the sensitivity analysis revealed that both hydrostatic and overburden pressures appear to have the strongest correlation with pore pressure (0.766) and closely followed by normal compacted sonic velocity (0.753). Meanwhile, observed sonic velocity has the least correlation (0.046). The models were appraised by determining their Relative Absolute Errors. Results indicate that Multilayer Perceptron has the best prediction and least Relative Absolute Error of 5.77%. While the Decision Stump model had a Relative absolute error of 54.41%. The Simple Linear Regression had a relative absolute error of 67.93%. By and large, all three models appear to be suitable for modeling pore pressure but the Multilayer Perceptron is the most accurate.
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Li, Qing Feng, Yong Zhou Cheng, Yun Pan i Wen Cheng Wang. "Study on Relationship between Sediment Transport and Excess Pore Water Pressure under Regular Breaking Wave Action". Applied Mechanics and Materials 212-213 (październik 2012): 169–76. http://dx.doi.org/10.4028/www.scientific.net/amm.212-213.169.
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Based on the wave flume experiments, the response of excess pore water pressure was studied under the regular breaking wave action on a 1:30 slope sandy seabed. The topographic change was observed in the wave broken zone and its causes were analyzed. The results show that the variation gradient of excess pore water pressure are larger in the surface layer and the changing amplitude of variation gradient of excess pore water pressure is bigger in the wave broken zone. The water depth is the most influential factor of excess pore water pressure and the wave height and period has little influence on excess pore water pressure in the same wave steepness range in the wave broken zone. The topographic change is greatly in the wave breaking zone. Excess pore water pressures changing amplitude at the top are significantly higher than it at the bottom. When the seabed scours, the amplitude of the excess pore water pressure increases; and when the sand seabed accumulates, the amplitude of the excess pore water pressure decreases.
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Alwan, Dr Kareem A. Alwan, Ahmed K. H. Alhusseini Alhusseini i Dr Faleh H. M. Almahdawi Almahdawi. "Distribution of Pore Pressure Gradient for Some Deep Formations in Iraqi Oil Fields". Journal of Petroleum Research and Studies 7, nr 5 (5.05.2021): 7–19. http://dx.doi.org/10.52716/jprs.v7i5.207.
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Pore pressures are the fluid pressures in the pore spaces in the porous formations.Interactive Petrophysic (IP) software is used to determine the pore pressure gradient from logdata. These data are (GR log, Bulk Density and Sonic log).Surfer software is used to create the formation pressure distribution maps. These mapsshow the pore pressure gradient (PPG) for sex formations in contour forms. The formations arechosen depending upon the availability of formation in 11wells/11 fields. These maps areprovided the pore pressure distribution in middle and south of Iraq and eventually, give a clearimagination for high and low pressure regions for each formation separately.Six formation are considered in this research, these formations which existed in earlyCretaceous and late Jurassic (deep formations) are Shuaiba, Zubair, Ratawi, Yammama, Sulaiyand Gotnia.Finally, the outputs of these software helps to explain the abnormal pressure location andtheir distribution for the formation under study, this assists to expected the drilling mud programfor these formation.
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Mustafa, M. R., R. B. Rezaur, H. Rahardjo, M. H. Isa i A. Arif. "Artificial Neural Network Modeling for Spatial and Temporal Variations of Pore-Water Pressure Responses to Rainfall". Advances in Meteorology 2015 (2015): 1–12. http://dx.doi.org/10.1155/2015/273730.
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Knowledge of spatial and temporal variations of soil pore-water pressure in a slope is vital in hydrogeological and hillslope related processes (i.e., slope failure, slope stability analysis, etc.). Measurements of soil pore-water pressure data are challenging, expensive, time consuming, and difficult task. This paper evaluates the applicability of artificial neural network (ANN) technique for modeling soil pore-water pressure variations at multiple soil depths from the knowledge of rainfall patterns. A multilayer perceptron neural network model was constructed using Levenberg-Marquardt training algorithm for prediction of soil pore-water pressure variations. Time series records of rainfall and pore-water pressures at soil depth of 0.5 m were used to develop the ANN model. To investigate applicability of the model for prediction of spatial and temporal variations of pore-water pressure, the model was tested for the time series data of pore-water pressure at multiple soil depths (i.e., 0.5 m, 1.1 m, 1.7 m, 2.3 m, and 2.9 m). The performance of the ANN model was evaluated by root mean square error, mean absolute error, coefficient of correlation, and coefficient of efficiency. The results revealed that the ANN performed satisfactorily implying that the model can be used to examine the spatial and temporal behavior of time series of pore-water pressures with respect to multiple soil depths from knowledge of rainfall patterns and pore-water pressure with some antecedent conditions.
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Lee, Jack, Richard Swarbrick i Stephen O'Connor. "Kicks and their significance in pore pressure prediction". Petroleum Geoscience 28, nr 2 (7.02.2022): petgeo2021–061. http://dx.doi.org/10.1144/petgeo2021-061.
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Knowledge of subsurface formation pressures is critical for the calibration of predictions and models needed for safe drilling of deep wells, historically for oil and gas wells. The same details apply to the sequestration of CO2, ephemeral storage of gases such as hydrogen and for geothermal power. An estimated 10–14% of wells globally experience an unexpected influx of formation fluid, indicative of the controlling mud in the borehole at that time having a lower pressure than the surrounding formation. The drilling events, known as kicks and wellbore breathing, lead to, at best, downtime on the drilling rig which might affect the economic viability of the well, or in the extreme its safety with possible loss of life such as in the case of an uncontrolled blowout. Not all kicks are of equivalent value: dynamic and static kicks can be classified with a high degree of confidence and may become values for true formation pressure. Other types of fluid influx during drilling, including swab kicks and wellbore breathing, need to be identified and will not be accepted in a kick database. These types of influx may be eliminated as potential formation pressure values but, along with mud weights, can be valuable data to constrain the range of possible formation pressures, of significant where no other data exist. A new, rigorous evaluation procedure for determining formation pressure is presented, and compared with direct pore pressure measurements (e.g. RFT, MDT, RCI values). The comparison shows that the proposed methodology illustrates typical uncertainty of about 10 bar (145 psi) pressure over the full range of pressures for which data are available in this study.Thematic collection: This article is part of the Geopressure collection available at: https://www.lyellcollection.org/cc/geopressure
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Rahardjo, Harianto, i Delwyn G. Fredlund. "Experimental verification of the theory of consolidation for unsaturated soils". Canadian Geotechnical Journal 32, nr 5 (1.10.1995): 749–66. http://dx.doi.org/10.1139/t95-074.
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An experimental program was designed to study the behavior of unsaturated soils during undrained loading and consolidation. A Ko cylinder was designed and built for the testing program. Simultaneous measurements of pore-air and pore-water pressures could be made throughout a soil specimen using this Ko cylinder. Four types of tests were performed on a silty sand. These are (1) undrained loading tests where both the air and water are not allowed to drain, (2) constant water content tests where only the water phase is not allowed to drain, (3) consolidation tests where both the air and water phases are allowed to drain, and (4) increasing matric suction tests. Undrained loading tests or constant water content loading tests were conducted for measuring the pore pressure parameters for the unsaturated soil. Drained tests consisting of either consolidation tests or increasing matric suction tests were conducted to study the pore pressure distribution and volume change behavior throughout an unsaturated soil during a transient process. The experimental pore pressure parameters obtained from the undrained loadings and constant water content leadings agreed reasonably well with theory. The pore-air pressure was found to dissipate instantaneously when the air phase is continuous. The pore-water pressure dissipation during the consolidation test was found to be faster than the pore-water pressure decrease during the increasing matric suction test. The differing rates of dissipation were attributed to the different coefficients of water volume change for each of the tests. The water volume changes during the consolidation test were considerably smaller than the water volume changes during the increasing matric suction tests for the same increment of pressure change. Key words : consolidation, Ko loading, matric suction, pore-air pressures, pore-water pressures, unsaturated soils
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Nojabaei, B., R. T. T. Johns i L. Chu. "Effect of Capillary Pressure on Phase Behavior in Tight Rocks and Shales". SPE Reservoir Evaluation & Engineering 16, nr 03 (4.07.2013): 281–89. http://dx.doi.org/10.2118/159258-pa.
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Summary Phase behavior is important in the calculation of hydrocarbons in place and in the flow of phases through the rocks. Pore sizes can be on the order of nanometers for shale and tight-rock formations. Such small pores can affect the phase behavior of in-situ oil and gas because of increased capillary pressure. Not accounting for increased capillary pressure in small pores can lead to inaccurate estimates of ultimate recovery, and of saturation pressures. In this paper, capillary pressure is coupled with phase equilibrium equations, and the resulting system of nonlinear fugacity equations is solved to present a comprehensive examination of the effect of small pores on saturation pressures and fluid densities. Binary mixtures of methane with heavier hydrocarbons and a real reservoir fluid from the Bakken shale are considered. The results show that accounting for the impact of small pore throats on pressure/volume/temperature (PVT) properties explains the inconsistent gas/oil-ratio (GOR) behavior, high flowing bottomhole pressures, and low gas-flow rate observed in the tight Bakken formation. The small pores decrease bubble-point pressures and either decrease or increase dew-point pressures, depending on which part of the two-phase envelope is examined. Large capillary pressure also decreases the oil density in situ, which affects the oil formation volume factor and ultimate reserves calculations. A good history match for wells in the middle Bakken formation is obtained only after considering a suppressed bubblepoint pressure. The results show that the change in saturation pressures, fluid densities, and viscosities is highly dependent on the values of interfacial tension (IFT) (capillary pressure) used in the calculations.
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Jena, Akshaya, i Krishna Gupta. "Pore Volume of Nanofiber Nonwovens". International Nonwovens Journal os-14, nr 2 (czerwiec 2005): 1558925005os—14. http://dx.doi.org/10.1177/1558925005os-1400204.
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Pore volume, pore diameter, pore volume distribution and pore throat diameters of nanofiber mats were measured using mercury intrusion porosimetry, liquid extrusion porosimetry and capillary flow porometry. Analysis of results showed that mercury intrusion distorts the structure due to application of high pressure. Liquid extrusion does not require high pressures, gives good resolution and measures pore structure relevant for application. Capillary flow porometry uses low pressures, measures pore throat diameter, but does not measure pore volume.
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Du, Changbo, Xinqi Jiang, Laigui Wang, Fu Yi i Ben Niu. "Development law and growth model of dynamic pore water pressure of tailings under different consolidation conditions". PLOS ONE 17, nr 10 (31.10.2022): e0276887. http://dx.doi.org/10.1371/journal.pone.0276887.
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Tailings dams are in danger of liquefaction during earthquakes. The liquefaction process can be indirectly reflected by the evolution rule of the dynamic pore water pressure. To study the development law of dynamic pore water pressure of tailing sand under different consolidation conditions, the evolution equation of critical dynamic pore water pressure of tailings under isotropic and anisotropic consolidation conditions was derived based on the limit equilibrium theory. Moreover, the development law of dynamic pore water pressure was expounded theoretically. The dynamic triaxial tests of tailing silty sand and tailing silt under different dry densities, consolidation ratios, and confining pressures were performed. The dynamic pore water pressure ratio and vibration ratio curves of tailings under isotropic and anisotropic consolidation were analyzed, and a dynamic pore water pressure growth index model suitable for both isotropic and anisotropic consolidation was derived. The results showed that the critical dynamic pore water pressure was positively correlated with the confining pressure and average particle size of tailings under isotropic consolidation conditions. The tailings have a limit dynamic effective internal friction angle φdc under the anisotropic consolidation condition. The evolution law of critical dynamic pore water pressure can be judged according to the dynamic effective internal friction angle of tailing sand φd and φdc values. The consolidation ratio significantly affects the dynamic pore pressure growth curve while confining pressure and dry density do not. For different tailing materials, the dynamic pore water pressure ratio is positively correlated with tailing particles. The dynamic pore water pressure growth process of tailing silty sand and tailing silt can be divided into two stages: rapid and stable growths. The development law of two types of tailings can be described by the dynamic pore water pressure growth index model. The research results can provide a theoretical basis for the seismic design of tailings dams in practical engineering.
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Anochikwa, Collins Ifeanyichukwu, Garth van der Kamp i S. Lee Barbour. "Interpreting pore-water pressure changes induced by water table fluctuations and mechanical loading due to soil moisture changes". Canadian Geotechnical Journal 49, nr 3 (marzec 2012): 357–66. http://dx.doi.org/10.1139/t11-106.
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Pore pressures within saturated subsurface formations respond to stress changes due to loading as well as to changes in pore pressure at the boundaries of the formation. The pore-pressure dynamics within a thick aquitard in response to water table fluctuations and mechanical loading due to soil moisture changes have been simulated using a coupled stress–strain and groundwater flow finite element formulation. This modelling approach isolates the component of pore-pressure response of soil moisture loading from that caused by water table fluctuations, by using a method of superposition. In this manner, the contributions to pore-pressure fluctuations that occur as a result of surface moisture loading (e.g., precipitation, evapotranspiration) can be isolated from the pore-pressure record. The required elastic stress–strain properties of the aquitard were obtained from the measured pore-pressure response to barometric pressure changes. Subsequently, the numerical simulations could be calibrated to the measured response by adjusting only the hydraulic conductivity. This paper highlights the significance of moisture loading effects in pore-pressure observations and describes an efficient technique for obtaining in situ stress–strain and hydraulic properties of near-surface aquitards.
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Lan, Yuzheng, Rouzbeh Ghanbarnezhad Moghanloo i Davud Davudov. "Pore Compressibility of Shale Formations". SPE Journal 22, nr 06 (17.08.2017): 1778–89. http://dx.doi.org/10.2118/185059-pa.
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Summary This study introduces a novel outlook on a shale-pore system and on the potential effect of pore compressibility on the production performance. We divide porosity of the system into accessible and inaccessible pores, and incorporate inaccessible pores with grains into the part of the rock that is not accessible. In general, accessible pores contribute to flow directly, whereas inaccessible pores do not. We present a mathematical model that uses mercury-injection capillary pressure (MICP) data to determine the accessible-pore and inaccessible part of the rock (IRP) compressibility as a function of pressure. During MICP testing in a typical shale sample, the rock sample experiences conformance, compression, and intrusion as effective pressure increases. We characterize the compressibility value dependent on MICP data as a function of pressure. The calculated compressibility values for accessible pores generally appear to be much greater (two to three orders of magnitude) than those of IRP. Next, we evaluate how calculated accessible-pore-compressibility values affect gas recovery in several shale-gas plays. Our results suggest that substitution of total pore compressibility with accessible-pore compressibility can significantly change the reservoir-behavior prediction. The fundamental rock property used in many reservoir-engineering calculations including reserves estimates, reservoir performance, and production forecasting is the total pore-volume (PV) compressibility, which has an approximate value typically within the range of 1 × 10−6 to 1 × 10−4 psi−1 (Mahomad 2014). By recognizing the part of the pore system that actually contributes to production and identifying its compressibility, we can substitute total pore compressibility with accessible-pore compressibility. The result changes the value by nearly two orders of magnitude. The outcome of the paper changes the industry's take on prediction of reservoir performance, especially the rock-compaction mechanism. This study finds that production caused by rock compaction is in fact much greater than what has often been regarded, which will change the performance evaluation on a great number of reservoirs in terms of economic feasibility.
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Zhang, Chunming, Zaixing Jiang, Yuanfu Zhang, Qi Chen, Wei Zhao i Jie Xu. "Reservoir Characteristics and its Main Controlling Factors of the Siegenian Formation of Devonian in X Block, Algeria". Energy Exploration & Exploitation 30, nr 5 (październik 2012): 727–51. http://dx.doi.org/10.1260/0144-5987.30.5.727.
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The Siegenian Formation reservoir is a tight sandstone reservoir with relatively poor porosity and low permeability. In this paper, the reservoir characteristics and its main controlling factors of the Siegenian Formation in X block have been studied based on cores, well-logs, and formation test data including the thin sections and cast thin sections, observation of scanning electron microscope, pressured-mercury testing and X-ray diffraction analysis of clay minerals. During deposition of the Siegenian Formation, the depositional environment was predominated by lower shoreface, middle shoreface and offshore. The fine sandstone and siltstone formed in the middle shoreface environment is the main reservoir of the Siegenian Formation in X block. Six pore types including primary intergranular pores, intragranular dissolved pores, intergranular dissolved pores, moldic pores, cement dissolved pores and microfractures are identified in the Siegenian Formation reservoir. The quartz intergranular dissolved pores and the quartz overgrowth cement dissolved pores are found for the first time in this area. The secondary dissolution pore is the main pore type in X block. The pore throat has a small radius, poor connectivity and the pore structure parameters are poor. Combined with the petrophysical property and capillary pressure curves, the reservoir of the research area is divided into three types: mesopore-ultra low permeability reservoir (type I), low-middle porosityultra low permeability reservoir (type II) and low porosity-ultra low permeability reservoir (type III). Type II is the main reservoir in this area. The sedimentary environment, tectonism and diagenesis are the main controlling factors. Diagenesis is the most important controlling factor in this area. Diagenesis may play a catalytic role or may play a negative role on damage in the reservoir pore evolution. The compaction, pressure solution, cementation, replacement and cementation are the main diagenesis types which reduce the pore volume during the reservoir pore evolution. The dissolution including acidic dissolution and alkaline dissolution are the main diagenesis types which produce extra pore volume during the reservoir pore evolution. This study of the reservoir will guide the future exploration of this area.
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Zeng, Zhixiong, Yu-Jun Cui, Feng Zhang, Nathalie Conil i Jean Talandier. "Effect of technological voids on swelling behaviour of compacted bentonite–claystone mixture". Canadian Geotechnical Journal 57, nr 12 (grudzień 2020): 1881–92. http://dx.doi.org/10.1139/cgj-2019-0339.
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The effect of technological voids on the swelling pressure of compacted MX80 bentonite–Callovo-Oxfordian (COx) claystone mixture was investigated by simulating the technological voids with a pre-defined space between the compacted disks of the mixture. Both axial and radial swelling pressures were monitored. After the tests, the microstructure of samples at different positions was investigated using mercury intrusion porosimetry (MIP), together with the determination of dry density and water content. Results showed that two main processes, filling and homogenization, occurred during soil hydration. In the filling process, the initial technological voids were gradually filled and the axial swelling pressure tended to increase. In the homogenization process, the samples had a sealing zone and a swelling zone. The sealing zone was characterized by a lower dry density than the expected final dry density while the swelling zone was characterized by a larger one. From the MIP results, the sealing zone showed larger inaccessible-pore, medium-pore, and large-pore void ratios and a lower small-pore void ratio than the swelling zone. Over time, the medium and large pores in the sealing zone were compressed, while the small pores in the swelling zone decreased. The stabilized axial swelling pressure followed a unique relationship with the expected final dry density. Moreover, the swelling pressure anisotropy was found to decrease as the technological voids increased.
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Deng, Jia, Qi Zhang, Lan Zhang, Zijian Lyu, Yan Rong i Hongqing Song. "Investigation on the adsorption properties and adsorption layer thickness during CH4 flow driven by pressure gradient in nano-slits". Physics of Fluids 35, nr 1 (styczeń 2023): 016104. http://dx.doi.org/10.1063/5.0134419.
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In shale gas exploration, gas adsorbed on the surface of porous medium results in a change in pore size, which is closely relevant to permeability, flow rate, and production capacity of shale gas reservoirs, especially for the reservoir containing large numbers of pores and slits. Thus, the present work investigates the adsorption mechanism and adsorption layer thickness during CH4 flow driven by the pressure gradient in nano-slits by using molecular dynamics simulation. Herein, a slit-pore model in terms of gas storage and grapheme pore is developed, implemented, and verified. The effects of the pressure, temperature, pressure gradient, and pore size on adsorption properties and adsorption layer thickness of CH4 are also examined. Results show that the relative adsorption capacity is positively correlated with the pressure gradient and pore size and negatively correlated with the system pressure, whereas unaffected by temperature. Moreover, the adsorption layer thickness decreases with the pressure and is almost unaffected by the pore size under the small pore size, whereas increasing with the pressure gradient and temperature. The descending order of sensibility to the adsorption layer thickness is temperature, pressure gradient, pore size, and system pressure. Hence, based on those findings, a new formula for calculating the adsorption layer thickness is proposed for the quantitative determination of the effective pore size of porous medium when gas flows in slits, thereby contributing to shale gas high-efficient exploration.
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Yuan, Liao i Zhou. "Experimental Study on the Distribution of Wave-Induced Excess Pore Pressure in a Sandy Seabed around a Mat Foundation". Journal of Marine Science and Engineering 7, nr 9 (3.09.2019): 304. http://dx.doi.org/10.3390/jmse7090304.
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Mat foundations are widely used in jack-up offshore platforms to support and transfer loads. Regarding mat foundations working on the seabed, the excess wave-induced pore pressure is critical to seabed stability, which may finally cause structural failure. Therefore, it is important to investigate the distribution of the excess pore pressure in the seabed around the mat foundation. In this study, experiments were performed to study the excess pore pressure distribution around a mat foundation in scale considering the true load state by recording wave profiles and pore pressures inside a sandy seabed. To guarantee the reliability of experiments, a numerical study was conducted and compared with the experimental results. Experimental results indicate that with the existence of the mat foundation, the excess pore pressure is higher at the region, the range of which is the width of the model mat (Wm) before the structure. The maximum pore pressure appears at 0.55 Wm in front of the center of the mat foundation. In addition, the current significantly increases the range of high pore pressure area and the amplitude of the excess pore pressure. As the mat orientation changes, the position of the maximum pore pressure changes from the front to the edge of the mat.