The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
Tian-jian Hsu - One of the best experts on this subject based on the ideXlab platform.
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Observations of wave-induced Pore Pressure Gradients and bed level response on a surf zone sandbar
Journal of Geophysical Research: Oceans, 2017Co-Authors: Dylan Anderson, Daniel T. Cox, Ryan S. Mieras, Jack A. Puleo, Tian-jian HsuAbstract:Horizontal and vertical Pressure Gradients may be important physical mechanisms contributing to onshore sediment transport beneath steep, near-breaking waves in the surf zone. A barred beach was constructed in a large-scale laboratory wave flume with a fixed profile containing a mobile sediment layer on the crest of the sandbar. Horizontal and vertical Pore Pressure Gradients were obtained by finite-differences of measurements from an array of Pressure transducers buried within the upper several centimeters of the bed. Co-located observations of erosion depth were made during asymmetric wave trials with wave heights between 0.10 m and 0.98 m, consistently resulting in onshore sheet flow sediment transport. The Pore Pressure Gradient vector within the bed exhibited temporal rotations during each wave cycle, directed predominantly upwards under the trough and then rapidly rotating onshore and downwards as the wave front passed. The magnitude of the Pore Pressure Gradient during each phase of rotation was correlated with local wave steepness and relative depth. Momentary bed failures as deep as 20 grain diameters were coincident with sharp increases in the onshore directed Pore Pressure Gradients, but occurred at horizontal Pressure Gradients less than theoretical critical values for initiation of the motion for compact beds. An expression combining the effects of both horizontal and vertical Pore Pressure Gradients with bed shear stress and soil stability is used to determine that failure of the bed is initiated at non-negligible values of both forces.
Toshihiko Shimamoto - One of the best experts on this subject based on the ideXlab platform.
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comparison of klinkenberg corrected gas permeability and water permeability in sedimentary rocks
International Journal of Rock Mechanics and Mining Sciences, 2009Co-Authors: Wataru Tanikawa, Toshihiko ShimamotoAbstract:Abstract We measured intrinsic permeability of sedimentary rocks from the western foothills of Taiwan by using nitrogen gas and distilled water as Pore fluids in effective-Pressure cycling tests at room temperature. The observed difference in gas and water permeabilities was analyzed in view of the Klinkenberg effect. This effect is due to the slip flow of gases at Pore walls, which enhances gas flow when Pore sizes are very small. Our experimental results showed that (1) gas permeability was larger than water permeability by several times to one order of magnitude, (2) gas permeability increased with increasing Pore Pressure, and (3) water permeability increased slightly as the Pore-Pressure Gradient across the specimen increased. Results (1) and (2) can be explained quantitatively by an empirical power law in relation to the Klinkenberg constant b that is applicable in low permeable range. This correlation enables us to estimate water permeability from gas permeability. The Klinkenberg effect is important when permeability is lower than 10−18 m2 and at low Pore-Pressure differentials, and correction for the effect is essential to estimate water permeability from gas permeability measurement data. A simplified Bingham flow model for water can partially explain the trend of result (3), although non-Darcy flow behavior or inertial forces of water–rock interaction are needed to account for the observed deviation from Darcy's law.
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Klinkenberg effect for gas permeability and its comparison to water permeability for porous sedimentary rocks
Hydrology and Earth System Sciences Discussions, 2006Co-Authors: Wataru Tanikawa, Toshihiko ShimamotoAbstract:The difference between gas and water permeabilities is significant not only for solving gas-water two-phase flow problems, but also for quick measurements of permeability using gas as Pore fluid. We have measured intrinsic permeability of sedimentary rocks from the Western Foothills of Taiwan, using nitrogen gas and distilled water as Pore fluids, during several effective-Pressure cycling tests at room temperature. The observed difference in gas and water permeabilities has been analyzed in view of the Klinkenberg effect. This effect is due to slip flow of gas at Pore walls which enhances gas flow when Pore sizes are very small. Experimental results show (1) that gas permeability is larger than water permeability by several times to one order of magnitude, (2) that gas permeability increases with increasing Pore Pressure, and (3) that water permeability slightly increases with increasing Pore-Pressure Gradient across the specimen. The results (1) and (2) can be explained by Klinkenberg effect quantitatively with an empirical power law for Klinkenberg constant. Thus water permeability can be estimated from gas permeability. The Klinkenberg effect is important when permeability is lower than 10?18 m2 and at low differential Pore Pressures, and its correction is essential for estimating water permeability from the measurement of gas permeability. A simple Bingham-flow model of Pore water can explain the overall trend of the result (3) above. More sophisticated models with a Pore-size distribution and with realistic rheology of water film is needed to account for the observed deviation from Darcy's law.
Quan Gan - One of the best experts on this subject based on the ideXlab platform.
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In situ stress distribution and its impact on CBM reservoir properties in the Zhengzhuang area, southern Qinshui Basin, North China
Journal of Natural Gas Science and Engineering, 2019Co-Authors: Saipeng Huang, Dameng Liu, Yidong Cai, Quan GanAbstract:Abstract In situ stress is crucial for hydraulic fracturing during enhanced coalbed methane (CBM) recovery. The study is an attempt to get a better idea of fine evaluation of the stress distribution, and to clarify the stress distribution near the fault zone. The in situ stresses and formation Pore Pressure of coal seams at depths of 300–1300 m in the Zhengzhuang area of the southern Qinshui Basin were systematically analysed using well test data. The research area was divided into three partitions based on formation Pore Pressure Gradient and regional geological structure. The three partitions present various petrophysical properties. Moreover, a 3D simulation was conducted to evaluate the effects of faulting on the stress state. Excellent relations exist among the Pore Pressure, minimum horizontal stress (Po and σh) and depth of the target coal seam, which can be used to predict the distribution of in situ stresses in the research area where few well test data exist. A lower lateral stress coefficient (κ) suggests a higher permeability in the extensional southern Qinshui Basin. Lower horizontal tectonic stress coefficients and relative stress factors suggest a higher permeability area. The simulation and microseismic fracture monitoring results show that the horizontal principal stress direction obviously changes near the fault zone, suggesting the existence of a complex in situ stress state. Faulting has a great influence on σH orientation. The stress simulation could be a means to detect faults and predict the direction and magnitude of σH for areas without adequate well test data. Therefore, these results may have significant implications for the permeability evaluation of coal seams during safety mining and CBM production.
Daniel L. Orange - One of the best experts on this subject based on the ideXlab platform.
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Geomorphology of Headless Submarine Canyons: Prediction of Slope Failure, Sediment Strength and Pore Pressure Gradient, and the Regular Spacing of Submarine Canyons.
1995Co-Authors: Daniel L. OrangeAbstract:Abstract : The long term goal of this project is to understand the interaction between tectonic and hydrologic forcing and the resultant creation and modification of seafloor geomorphology. The initial objective of this project was to ground truth the hypothesis that there is a causative relationship between geomorphology and fluid expulsion at the seafloor. Once that relationship was established, we sought to determine the hydrologic and geotechnical state of the venting and non-venting regions. The hydrologic and geotechnical data can be used together with the seafloor observations to model slope failure.
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the effects of fluid escape on accretionary wedges 2 seepage force slope failure headless submarine canyons and vents
Journal of Geophysical Research, 1992Co-Authors: Daniel L. Orange, Nancy A BreenAbstract:The high Pore Pressure Gradients inherent to accretionary complexes affect the force balance of the wedge via seepage force, which acts in the direction of flow and is proportional to the Pressure (head) Gradient. If sufficiently large, this seepage force can offset gravity and friction and lead to failure. At the toe of the wedge sediments are weak, slopes are over-steepened by folding and faulting, and fluid Pressure Gradients can be high; these conditions are conducive to seepage-induced failure. For the 14–16° slope at the toe of the southern Cascadia wedge, the Pore Pressure Gradient necessary to initiate failure is λ=0.74–0.86. The Gradient necessary to cause failure is sensitive to surface slope and sediment strength, but is insensitive to porosity. Reasonable estimates of sediment strength for most accretionary wedges require Pore Pressure Gradients ranging from 10 to 60% of lithostatic to cause failure. These values are within the range of modeled and measured Pore Pressures in accretionary complexes, suggesting that seepage-induced slope failure should be an expected feature in this environment. If these failure features are observed, then their presence can be used to constrain the Pore Pressure Gradient within the wedge, independent of any assumptions regarding fluid discharge or permeability. If seepage failure repeats and is localized in the same region, then it can lead to channel, gully, and canyon formation. Two convergent margins, southern Cascadia and northern Hispaniola, show many regularly spaced headless canyons that cannot be attributed to downslope erosive flow. We suggest that these canyons are forming from internally driven seepage-induced failure. Both the Oregon and Hispaniola accretionary wedges also contain evidence for non-uniform fluid flow based on the observed and inferred presence of vents. Using Darcy's Law, the Pore Pressure constraint from the slope failure analysis and an estimate of the total fluid discharge, we examine the relationship between wedge and vent permeabilities, the areal extent of focused fluid venting, and the percent of the total fluid discharge that flows out of vents. Given reasonable estimates of the total fluid discharge out of the southern Cascadia wedge, we find that the wedge must be less permeable than 2 × 10−17 m2 in order for focused fluid venting to occur at all. If the permeability of the vents is much higher than the wedge permeability, then the vents will occur over a very small percentage of the wedge; these vents, however, could accommodate much of the fluid flowing out of the wedge. Using permeability measurements from samples collected at the toe of the Oregon margin [Horath, 1989], we estimate that vents at the toe of the southern Cascadia accretionary complex comprise less than 0.2% of the wedge area, but that these vents can accommodate up to 60% of the total fluid discharge.
Nancy A Breen - One of the best experts on this subject based on the ideXlab platform.
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the effects of fluid escape on accretionary wedges 2 seepage force slope failure headless submarine canyons and vents
Journal of Geophysical Research, 1992Co-Authors: Daniel L. Orange, Nancy A BreenAbstract:The high Pore Pressure Gradients inherent to accretionary complexes affect the force balance of the wedge via seepage force, which acts in the direction of flow and is proportional to the Pressure (head) Gradient. If sufficiently large, this seepage force can offset gravity and friction and lead to failure. At the toe of the wedge sediments are weak, slopes are over-steepened by folding and faulting, and fluid Pressure Gradients can be high; these conditions are conducive to seepage-induced failure. For the 14–16° slope at the toe of the southern Cascadia wedge, the Pore Pressure Gradient necessary to initiate failure is λ=0.74–0.86. The Gradient necessary to cause failure is sensitive to surface slope and sediment strength, but is insensitive to porosity. Reasonable estimates of sediment strength for most accretionary wedges require Pore Pressure Gradients ranging from 10 to 60% of lithostatic to cause failure. These values are within the range of modeled and measured Pore Pressures in accretionary complexes, suggesting that seepage-induced slope failure should be an expected feature in this environment. If these failure features are observed, then their presence can be used to constrain the Pore Pressure Gradient within the wedge, independent of any assumptions regarding fluid discharge or permeability. If seepage failure repeats and is localized in the same region, then it can lead to channel, gully, and canyon formation. Two convergent margins, southern Cascadia and northern Hispaniola, show many regularly spaced headless canyons that cannot be attributed to downslope erosive flow. We suggest that these canyons are forming from internally driven seepage-induced failure. Both the Oregon and Hispaniola accretionary wedges also contain evidence for non-uniform fluid flow based on the observed and inferred presence of vents. Using Darcy's Law, the Pore Pressure constraint from the slope failure analysis and an estimate of the total fluid discharge, we examine the relationship between wedge and vent permeabilities, the areal extent of focused fluid venting, and the percent of the total fluid discharge that flows out of vents. Given reasonable estimates of the total fluid discharge out of the southern Cascadia wedge, we find that the wedge must be less permeable than 2 × 10−17 m2 in order for focused fluid venting to occur at all. If the permeability of the vents is much higher than the wedge permeability, then the vents will occur over a very small percentage of the wedge; these vents, however, could accommodate much of the fluid flowing out of the wedge. Using permeability measurements from samples collected at the toe of the Oregon margin [Horath, 1989], we estimate that vents at the toe of the southern Cascadia accretionary complex comprise less than 0.2% of the wedge area, but that these vents can accommodate up to 60% of the total fluid discharge.