Showing papers on "Pore water pressure published in 2018"
TL;DR: In this paper, a reduction in pore water pressure is proposed to improve the stability of slopes. Deep draining trenches can be used for this purpose, and they can be found in many places in the world.
Abstract: Reduction in pore water pressure is a useful strategy to improve the stability of slopes. Deep draining trenches can be used for this purpose. For the realization of deep trenches, the usua...
190 citations
TL;DR: In this paper, the authors defined the critical dehydration temperature for accurate pore size distribution interpretation in Permian Carynginia shale, Western Australia to determine T2 cutoff for CBW.
123 citations
TL;DR: In this article, the pore structures inside a coal sample and its permeability during coal seam water infusion were analyzed using nuclear magnetic resonance (NMR) technology; the influence rule of confining pressure and pore water pressure during the test on the coal sample structure and seepage characteristics is analyzed.
Abstract: Coal seam water infusion is a universal comprehensive mine disaster prevention method practiced worldwide. The result of water infusion is determined by the structure and seepage characteristics of the coal sample around the borehole. In this paper, the structure and seepage characteristics of the coal sample under various stress and pore water pressures are measured via nuclear magnetic resonance (NMR) technology; the influence rule of confining pressure and pore water pressure during the test on the coal sample structure and seepage characteristics is analyzed. Based on fractal geometrical theory, the fractal model of permeability is created. The results show that the coal sample with water infusion has an intertwined internal fracture-pore structure and that the pore radius distribution is diverse. Through theoretical analysis and discussion, we found that there are no large changes in the pore area fractal dimension and the measured pore volume fractal dimension, but the trends of changes in these two fractal dimensions are opposite, because the pore area fractal dimension characterizes the homogeneity of the pore area distribution on the surface of a coal sample, and the measured pore volume fractal dimension characterizes the cumulative volumetric changes in the pores inside a coal sample. The changes in these two fractal dimensions validate that the pore structures inside a coal sample have similar in fractal characteristics and demonstrate that the coal seam water infusion technique will not damage the skeleton of the coal sample. The variation rules of theoretical permeability from the fractal model and the value from the liquid measurement versus confining pressure and pore water pressure are consistent, an increase in the water pressure will result in an increase in the permeability, and an increase in the confining pressure will result in a decrease in the permeability. However, because the seepage channels with a large diameter in the tested coal sample were blocked, there is a relatively large difference between the two permeabilities. Therefore, increasing the connectivity between the seepage channels with a large diameter will improve the effects of water infusion, which is implemented to prevent disasters. Through NMR experiment and theoretical analysis, this study establishes a quantitative relationship between the pore structures inside the coal sample and its permeability during coal seam water infusion process, provides an advanced experimental approach and theoretical analysis method, which will be of great importance in the improvement in the water infusion process implemented in deep working coal seams to prevent disasters and in the determination of the range of application of this process and the evaluation metrics for this process.
116 citations
TL;DR: In this article, the authors simulated the diffusion behavior of supercritical methane in shale nanopores composed of different matrix mineral types (organic matter, clay, and calcite) and studied the effects of pore size, pore pressure, and moisture content on the diffusion process.
Abstract: Using molecular dynamics, we simulated the diffusion behavior of supercritical methane in shale nanopores composed of different matrix mineral types (organic matter, clay, and calcite). We studied the effects of pore size, pore pressure, and moisture content on the diffusion process. Our results show that confined methane molecules diffuse more rapidly with increases in pore size and temperature but diffuse slowly with an increase in pressure. Anisotropic diffusion behavior is also observed in directions parallel and perpendicular to the basal surfaces of nanoslits. We also found that mineral types composing the pore walls have a prominent effect on gas diffusion. The perfectly ordered structure and ultrasmooth surface of organic matter facilitate the transport of methane in dry pores, even though its adsorption capability is much stronger than that of inorganic minerals. Moisture inhibits methane diffusion, but this adverse effect is more evident in organic pores because water migrates in the form of clu...
112 citations
TL;DR: The results support the premise that arsenic can reside within pore water of clay strata within aquifers and is released due to overpumping, and provide a quantitative model for using subsidence as an indicator of arsenic concentrations correlated with groundwater pumping.
Abstract: Water resources are being challenged to meet domestic, agricultural, and industrial needs. To complement finite surface water supplies that are being stressed by changes in precipitation and increased demand, groundwater is increasingly being used. Sustaining groundwater use requires considering both water quantity and quality. A unique challenge for groundwater use, as compared with surface water, is the presence of naturally occurring contaminants within aquifer sediments, which can enter the water supply. Here we find that recent groundwater pumping, observed through land subsidence, results in an increase in aquifer arsenic concentrations in the San Joaquin Valley of California. By comparison, historic groundwater pumping shows no link to current groundwater arsenic concentrations. Our results support the premise that arsenic can reside within pore water of clay strata within aquifers and is released due to overpumping. We provide a quantitative model for using subsidence as an indicator of arsenic concentrations correlated with groundwater pumping.
112 citations
TL;DR: In this article, the pore size distribution of coal bed methane reservoirs and the effects of testing pressure were investigated using two sets of NMR measurements and the results showed that the increasing pore pressure significantly changes the coal sample with developed and poor connected macro pores.
108 citations
TL;DR: In this article, a series of methane adsorption isotherms were measured at pore pressures up to 60MPa and at 60°C, 100°C and 140°C for dried and overmature Paleozoic shales and isolated kerogen from the Sichuan Basin.
103 citations
TL;DR: In this paper, the authors investigated the failure of the tunnel face induced by the steady state seepage, and a series of the centrifuge model tests was performed, and they found that the effective support pressure firstly decreases steeply to the limit effective pressure and then increases gradually to a steady value.
82 citations
TL;DR: In this article, the same authors compared the MICP data collected from 46 Montney wells in Alberta and British Columbia with the results obtained using other measurements, such as pressure fall-off and pressure pulse-decay measurements.
Abstract: Permeability is a critical parameter for evaluating unconventional shale or tight gas and oil reservoirs such as the Montney Formation in the Western Canada Sedimentary Basin. Permeability is also one of the most difficult parameters to be accurately and consistently determined in the laboratory and field as it is a second-order tensor and is dependent on many factors (e.g. test methods, sampling or testing scales, heterogeneities in fabrics, pore networks and pore-throat size distribution, transport mechanisms, pore pressure and confining stress). Although laboratory permeability measurement is limited to samples on the scale of centimeters or less, it provides valuable insights on hydrocarbon transmissibility of the reservoir matrix rock. Several methods have been developed for permeability measurements of unconventional reservoirs but each method has limitations and specific applications and often yields different permeability values even for the same sample. In this study, various permeability measurements on samples from 46 Montney wells in Alberta and British Columbia are examined. The permeability data set has primarily been obtained using transient pressure fall-off and pressure pulse-decay methods due to the relatively low permeability seen throughout the Montney Formation. A unique data set of permeability determined from canister desorption tests is also analyzed and compared to other permeability measurements. Direct permeability measurements obtained using different techniques are further compared with permeability values predicted using models based on mercury intrusion capillary pressure (MICP) data. The results show that the pressure fall-off (kpf) or GRI (kgri) permeability to helium correlates strongly with porosity. The kpf of crushed samples (20/35 meshes) ranges from 1e-3 md with porosity increasing from 3% to 13%. The pressure fall-off permeability (kpf) of plug samples is about two orders of magnitude higher than kpf of crushed samples. Pressure pulse-decay permeability (kpdp) under initial in-situ effective confining stress conditions is generally higher than the pressure fall-off permeability of crushed samples but lower than that of core plugs. Pressure pulse-decay permeability (kpdp) of visually intact samples varies over two orders of magnitude for a given porosity, which is likely a result of variable sample characteristics (e.g. with or without micro fractures, net confining stresses applied due to different sample depths and regional locations, mineralogy, amount and type of organic matter, and pore-throat size). The pulse-decay permeability of fractured samples varies widely over three orders of magnitude and is up to three orders of magnitude higher than kpdp of intact samples, indicating favorable enhancement of permeability by unpropped fractures in the Montney Formation. Out of eight MICP-based permeability models tested in this study, the Winland model (Kolodzie, 1980) and the modified Winland model by Di and Jensen (2015) predict the most comparable permeability to the pulse-decay permeability measured on intact samples, and the rest models also predict acceptable values if proper conformance and compaction corrections are done to MICP data. The permeability from these models has stronger correlations with pressure fall-off permeability measured on both intact and fractured core plugs than the other models. For the Montney Formation, the strong dependence of gas permeability on pore pressure and confining stress is also highlighted. The pore pressure and stress dependence of permeability is characterized by a modified Klinkenberg effects correction equation. Liquid permeability to decane or oil is about one order of magnitude lower than gas permeability under similar confining stresses. Variable permeability from different methods, even on the same Montney samples, underlines the limitations and specific applications of each method, and implies the strong heterogeneities in mineralogical fabrics, organic matter distribution and pore size distributions of the Montney samples. The implications of different laboratory methods for formation evaluation are further discussed, and a practical fit-for purpose approach is recommended for the measurement of permeability, which allows for a more rigorous evaluation of in-situ matrix permeability of the Montney Formation and other unconventional shale and tight reservoirs.
81 citations
TL;DR: In this paper, a coupled T-H-M model for freezing rock is proposed, which is proved to be well expressed by exponential weighted mean model, and the governing equations for THM coupling of freezing rock under low temperature are deduced based on energy conservation law, mass conservation law and the principle of static equilibrium considering water/ice phase transition.
63 citations
Michigan State University1, Woods Hole Oceanographic Institution2, University of California, Riverside3, Oklahoma State University–Stillwater4, Yale University5, Florida State University6, Stony Brook University7, Georgia Institute of Technology8, Virginia Tech9, Northwestern University10, Harvard University11
TL;DR: In this article, a literature compilation from modern localities is used to provide a new empirical evaluation of coupled Fe speciation and Mo concentrations as a proxy for pore water sulfide accumulation at non-euxinic localities.
Abstract: Iron speciation and trace metal proxies are commonly applied together in efforts to identify anoxic settings marked by the presence of free sulfide (euxinia) or dissolved iron (ferruginous) in the water column. Here, we use a literature compilation from modern localities to provide a new empirical evaluation of coupled Fe speciation and Mo concentrations as a proxy for pore water sulfide accumulation at non-euxinic localities. We also present new Fe speciation, Mo concentration, and S isotope data from the Friends of Anoxic Mud (FOAM) site in Long Island Sound, which is marked by pore water sulfide accumulation of up to 3 mM beneath oxygen-containing bottom waters. For the operationally defined Fe speciation scheme, ‘highly reactive’ Fe (FeHR) is the sum of pyritized Fe (Fepy) and Fe dominantly present in oxide phases that is available to react with pore water sulfide to form pyrite. Observations from FOAM and elsewhere confirm that Fepy/FeHR from non-euxinic sites is a generally reliable indicator of pore fluid redox, particularly the presence of pore water sulfide. Molybdenum (Mo) concentration data for anoxic continental margin sediments underlying oxic waters but with sulfidic pore fluids typically show authigenic Mo enrichments (2–25 ppm) that are elevated relative to the upper crust (1–2 ppm). However, compilations of Mo concentrations comparing sediments with and without sulfidic pore fluids underlying oxic and low oxygen (non-euxinic) water columns expose non-unique ranges for each, exposing false positives and false negatives. False positives are most frequently found in sediments from low oxygen water columns (for example, Peru Margin), where Mo concentration ranges can also overlap with values commonly found in modern euxinic settings. FOAM represents an example of a false negative, where, despite elevated pore water sulfide concentrations and evidence for active Fe and Mn redox cycling in FOAM sediments, sedimentary Mo concentrations show a homogenous vertical profile across 50 cm depth at 1 to 2 ppm. A diagenetic model for Mo provides evidence that muted authigenic enrichments are derived from elevated sedimentation rates. Consideration of a range of additional parameters, most prominently pore water Mo concentration, can replicate the ranges of most sedimentary Mo concentrations observed in modern non-euxinic settings. Together, the modern Mo and Fe data compilations and diagenetic model provide a framework for identifying paleo-pore water sulfide accumulation in ancient settings and linked processes regulating seawater Mo and sulfate concentrations and delivery to sediments. Among other utilities, identifying ancient accumulation of sulfide in pore waters, particularly beneath oxic bottom waters, constrains the likelihood that those settings could have hosted organisms and ecosystems with thiotrophy at their foundations.
TL;DR: In this paper, the pore pressure distribution in the aquifer, external water pressure on the grouted zone and water inflow were investigated for a subsea grouted tunnel and analytical solutions were obtained by the complex variable method (CVM), mirror image method (MIM) and axisymmetric modeling method (AMM).
TL;DR: Wang et al. as discussed by the authors constructed a centrifuge slope model based on the Liangshuijing landslide and combined the geological conditions of the Three Gorges Reservoir area, in which the fluctuation of the water level is simulated in the centrifuge model test.
TL;DR: In this article, a series of triaxial shear tests was conducted on a reconstituted Wenzhou clay, to investigate the effects of consolidation stress paths on the stress-strain, pore water pressure and effective stress path behaviors of overconsolidated samples.
TL;DR: In this article, the authors discuss the field investigations, geotechnical characterization and time evolution of horizontal displacements in a wide landslide, which is located in Sicily and involves a thick body of stiff and highly fissured clays belonging to a Varicoloured Clay formation.
TL;DR: In this paper, a full-scale landslide-triggering experiment was conducted on a natural sandy slope subjected to an artificial rainfall event, which resulted in mobilisation of 130m3 of soil mass.
Abstract: A full-scale landslide-triggering experiment was conducted on a natural sandy slope subjected to an artificial rainfall event, which resulted in mobilisation of 130 m3 of soil mass. Novel slope deformation sensors (SDSs) were applied to monitor the subsurface pre-failure movements and the precursors of the artificially triggered landslide. These fully automated sensors are more flexible than the conventional inclinometers by several orders of magnitude and therefore are able to detect fine movements (< 1 mm) of the soil mass reliably. Data from high-frequency measurements of the external bending work, indicating the transmitted energy from the surrounding soil to these sensors, pore water pressure at various depths, horizontal soil pressure and advanced surface monitoring techniques, contributed to an integrated analysis of the processes that led to triggering of the landslide. Precursors of movements were detected before the failure using the horizontal earth pressure measurements, as well as surface and subsurface movement records. The measurements showed accelerating increases of the horizontal earth pressure in the compression zone of the unstable area and external bending work applied to the slope deformation sensors. These data are compared to the pore water pressure and volumetric water content changes leading to failure.
TL;DR: In this paper, the authors measured Mg stable isotopes, radiogenic Sr isotope ratios, and element concentrations in the Earth's Critical Zone (bedrock, saprolite, soil, soil pore water, stream water and vegetation) as tracers for element mass fluxes and pathways.
TL;DR: In this article, the wave-induced soil response and liquefaction risk around a hexagonal gravity-based offshore foundation is investigated by applying an integrated multiphysics model developed in the finite volume method (FVM) based OpenFOAM framework.
TL;DR: In this paper, the effects of two site-specific conditions (e.g., soil saturation and thermal insulation at ground surface) on pile-soil heat exchange and ground temperature response are investigated through a series of thermal tests under laboratory-controlled conditions.
TL;DR: Wang et al. as mentioned in this paper investigated the response of a loess landslide to rainfall, a series of artificial rainfall experiments were conducted on a natural loess slope, located in the Bailong River Basin, in southern Gansu Province.
Abstract: Rainfall-induced landslides are a significant hazard in many areas of loess-covered terrain in Northwest China. To investigate the response of a loess landslide to rainfall, a series of artificial rainfall experiments were conducted on a natural loess slope, located in the Bailong River Basin, in southern Gansu Province. The slope was instrumented to measure surface runoff, pore water pressure, soil water content, earth pressure, displacement, and rainfall. The hydrological response was also characterized by time-lapse electrical resistivity tomography. The results show that most of the rainfall infiltrated into the loess landslide, and that the pore water pressure and water content responded rapidly to simulated rainfall events. This indicates that rainfall infiltration on the loess landslide was significantly affected by preferential flow through fissures and macropores. Different patterns of pore water pressure and water content variations were determined by the antecedent soil moisture conditions, and by the balance between water recharge and drainage in the corresponding sections. We observed three stages of changing pore water pressure and displacement within the loess landslide during the artificial rainfall events: Increases in pore water pressure initiated movement on the slope, acceleration in movement resulting in a rapid decrease in pore water pressure, and attainment of a steady state. We infer that a negative pore water pressure feedback process may have occurred in response to shear-induced dilation of material as the slope movement accelerated. The process of shear dilatant strengthening may explain the phenomenon of semi-continuous movement of the loess landslide. Shear dilatant strengthening, caused by intermittent or continuous rainfall over long periods, can occur without triggering rapid slope failure.
TL;DR: In this article, the effects of compressibility on the apparent permeability of nanoporous organic matter and inorganic material were analyzed at different pore sizes, pore pressures and for different gas compositions.
25 Sep 2018
TL;DR: In this article, the authors investigated how four different injection schemes, i.e., constant rate, stepwise increasing rate, iii stepwise decreasing rate, and iv cyclic rate, constrained by the cumulative amount of CO2 injected, affect the likely extent of pressure buildup and CO2 plume, which play a role in the appraisal of environmental risk performance at CO2 storage sites.
Abstract: This study investigates how four different injection schemes, (i. constant rate, ii. stepwise increasing rate, iii. stepwise decreasing rate, and iv. cyclic rate), constrained by the cumulative amount of CO2 injected, affect the likely extent of pressure buildup and CO2 plume, which play a role in the appraisal of environmental risk performance at CO2 storage sites. This objective is achieved using a representative model of a realistic site consisting of multi-layer sandstone that is extremely permeable (between 1 to 2 Darcy) and separated by thin layers of shale extending laterally with sporadic discontinuities in form of perforations. Results show that cyclic injection tends to keep the pore pressure lower than the other three injection schemes, while the highest pressure increase over the entire injection period (50 years) is observed with stepwise decreasing rate. The compressibility of CO2 plays a role in attenuating the impact of fluctuating cyclic injection signals on pressure after 30 years of injection, where this time decreases by 5 years in case of heterogeneous scenario. Except for the cyclic injection scheme, all other three injection schemes lead to almost the same magnitude and areal extent of CO2 saturation, while it shows a cyclic behavior in the case of the cyclic injection. Major observations are similar in both homogeneous and heterogeneous scenarios, although layered heterogeneity in the representative site introduces small differences in results. The results imply that it would be preferable to store CO2 using a cyclic injection scheme in storage reservoirs that may be prone to high pressure buildup during injection because of their geology (e.g. fractured shale reservoirs). These results also carry important implications for enhanced oil recovery (EOR) using CO2 where the primary goal is to drive the oil out by increasing pore pressure; for EOR by CO2 , stepwise decreasing rate would be most preferable as it leads to highest increase in pore pressure. Cited as : Singh, H. Impact of four different CO2 injection schemes on extent of reservoir pressure and saturation. Advances in Geo-Energy Research, 2018, 2(3): 305-318, doi: 10.26804/ager.2018.03.08
TL;DR: In this article, the authors show that the microstructural elements that offer the shortest route through the sample, estimated to have an average radius ~0.1-0.5μm using the Klinkenberg slip factor, are accessible to gas, but restricted or inaccessible to water.
TL;DR: In this paper, simulations are performed on hollow-squared samples at laboratory scale using fully coupled discrete element method to elucidate the effects of these variables, and the model is first validated by comparing the stress around the borehole wall measured numerically with that calculated theoretically.
Abstract: Hydraulic fracturing in permeable rock is a complicated process which might be influenced by various factors including the operational parameters (e.g., fluid viscosity, injection rate and borehole diameter) and the in situ conditions (e.g., in situ stress states and initial pore pressure level). To elucidate the effects of these variables, simulations are performed on hollow-squared samples at laboratory scale using fully coupled discrete element method. The model is first validated by comparing the stress around the borehole wall measured numerically with that calculated theoretically. Systematic parametric studies are then conducted. Modeling results reveal that the breakdown pressure and time to fracture stay constant when the viscosity is lower than 0.002 Pa s or higher than 0.2 Pa s but increases significantly when it is between 0.002 and 0.2 Pa s. Raising the injection rate can shorten the time to fracture but dramatically increase the breakdown pressure. Larger borehole diameter leads to the increase in the time to fracture and the reduction in the breakdown pressure. Higher in situ stress requires a longer injection time and higher breakdown pressure. The initial pore pressure, on the other hand, reduces the breakdown pressure as well as the time to fracture. The increase in breakdown pressure with viscosity or injection rate can be attributed to the size effect of greater tensile strength of samples with smaller infiltrated regions.
TL;DR: In this paper, a nonlinear elasto-viscoplastic damage model based on a modified Mohr-Coulomb criterion was proposed to study the creep and seepage in clayey rock during construction of a high-level radioactive waste repository through laboratory experiments and field tests.
TL;DR: In this article, the pore-water pressures induced by pile driving could have a detrimental effect on a project, especially on the construction sequence and ground settlement, and measures that can effectively accele...
Abstract: Excess pore-water pressures induced by pile driving could have a detrimental effect on a project, especially on the construction sequence and ground settlement. Measures that can effectively accele...
TL;DR: In this paper, a cutting model based on the theory of linear poroelasticity was developed to predict coupled stresses and pore pressure in the rock and give a better understanding of the poro-elastic effect in the cutting process.
TL;DR: In this paper, a single-sided 1H nuclear magnetic resonance (NMR) signal is split into four pore species C-S-H interlayer water, gel pore water, interhydrate water, and capillary water by multi-exponential analysis.
TL;DR: In this paper, the relationship between energy state and occurrence mode of water in lignite as well as dehydration difficulty and structural changes during dewatering were clarified by DSC, NMR, FTIR and BET, respectively.
TL;DR: In this paper, a fully coupled hydromechanical three-dimensional model that accounts for the main aspects of tunnel construction and the hydromachanical interactions due to tunneling process is developed.
Abstract: This paper numerically investigates the slurry shield tunneling in fully saturated soils with different hydraulic conductivities in short- and long-term scales. A fully coupled hydromechanical three-dimensional model that accounts for the main aspects of tunnel construction and the hydromechanical interactions due to tunneling process is developed. An elasto-plastic constitutive model obeying a double hardening rule, namely hardening soil model, is employed in the numerical simulations. The research mainly focuses on assessing the influence of soil hydraulic conductivity and the method to simulate backfill grouting in the tail void on the evolution of ground subsidence, excess pore water pressure and lining forces. Two different consolidation schemes have been taken into account to computationally address the tunnel construction in soil with low and high hydraulic conductivities. In addition, different methods are employed to simulate the tail void grouting as a hydromechanical boundary condition and to study its effects on the model responses. Finally, the influences of infiltration of the fluidized particles of grouting suspension into the surrounding soil and its corresponding time–space hydraulic conductivity evolution on the displacements and lining forces are studied.