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John T Germaine - One of the best experts on this subject based on the ideXlab platform.
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permeability porosity relationships of shallow mudstones in the ursa basin northern deepwater gulf of mexico
Journal of Geophysical Research, 2012Co-Authors: Julia S Reece, Brandon Dugan, P B Flemings, Hui Long, John T GermaineAbstract:[1] In the Ursa Basin, Gulf of Mexico, in situ mudstone permeability near the seafloor declines from 1.1 × 10−16 to 5.8 × 10−19 m2over a depth of 578 m. We can reproduce this in situ permeability-porosity behavior through consolidation experiments in the laboratory. We use uniaxial constant-rate-of-strain consolidation experiments to measure permeability-porosity relationships and derive in situ permeabilities of 31 mudstone samples collected at Integrated Ocean Drilling Program (IODP) Sites U1324 and U1322. Although these mudstones have similar grain-size distributions, permeability at a given porosity varies significantly between the samples due to small variations in composition or fabric. We calculate an upscaled permeability relationship based on the observed permeability variation in the samples and determine a resultant large-scale permeability anisotropy of around 30. Based on this upscaled relationship and observations of in situ pressure, we calculate upward fluid flow rates of 0.5 mm/yr. We find that given the observed compressibility, permeability, and the geologic forcing at Ursa, Overpressures are predicted as observed in the subsurface. The primary mechanism for Overpressure generation at Ursa is sediment loading due to rapid burial. Low vertical permeabilities, accompanied by high sedimentation rates, can cause severe Overpressure near the seafloor, which controls fluid flow and can reduce slope stability as observed in the Mississippi Canyon region. Such flow systems, especially at intermediate depths on passive margins, are important due to their control over macroscale behavior such as topographic gradient of continental slopes and submarine landslides, but have been largely understudied in the past.
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consolidation and Overpressure near the seafloor in the ursa basin deepwater gulf of mexico
Earth and Planetary Science Letters, 2011Co-Authors: Hui Long, P B Flemings, John T Germaine, Demian M SafferAbstract:Abstract In mudstones of the Ursa Basin, Gulf of Mexico, the volume of voids to solids, or void ratio, ranges from 4 (porosity = 80%) at the seafloor to 0.6 (porosity = 37%) at 600 m below seafloor. This seven-fold change in void ratio can only be described by a compaction model that includes greater sediment stiffening with stress than has commonly been used in geotechnical or geological approaches. Through uniaxial consolidation experiments, we show that specific volume (v = 1 + void ratio) declines as an exponential function of effective stress. We use this relationship to successfully predict in-situ Overpressures at Integrated Ocean Drilling Program (IODP) Sites U1322 and U1324. This technique can be used around the world to describe sediment compaction and predict pore pressure in the first 1000 m below seafloor. Rapid sediment consolidation near the seafloor provides the fluid source that generates Overpressure despite the fact that these sediments have high permeability. Ultimately sediment consolidation is a first order control on when and at what depth Overpressure will be generated in the subsurface. This in turn will impact whether submarine landslides are expected and the regional gradient of continental margins.
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erratum to pore pressure penetrometers document high Overpressure near the seafloor where multiple submarine landslides have occurred on the continental slope offshore louisiana gulf of mexico earth and planetary science letters 269 3 4 2008 309 32
Earth and Planetary Science Letters, 2008Co-Authors: P B Flemings, Brandon Dugan, H Long, John T Germaine, Cedric M John, Jan H Behrmann, Dale S Sawyer, Iodp Expedition ScientistsAbstract:Abstract Overpressures measured with pore pressure penetrometers during Integrated Ocean Drilling Program (IODP) Expedition 308 reach 70% and 60% of the hydrostatic effective stress ( λ * = ( u − u h ) ( σ v h ' ) ) in the first 200 meters below sea floor (mbsf) at Sites U1322 and U1324, respectively, in the deepwater Gulf of Mexico, offshore Louisiana. High Overpressures are present within low permeability mudstones where there have been multiple, very large, submarine landslides during the Pleistocene. Beneath 200 mbsf at Site U1324, pore pressures drop significantly: there are no submarine landslides in this mixture of mudstone, siltstone, and sandstone. The penetrometer measurements did not reach the in situ pressure at the end of the deployment. We used a soil model to determine that an extrapolation approach based on the inverse of square root of time ( 1 / t ) requires much less decay time to achieve a desirable accuracy than an inverse time (1/t) extrapolation. Expedition 308 examined how rapid and asymmetric sedimentation above a permeable aquifer drives lateral fluid flow, extreme pore pressures, and submarine landslides. We interpret that the high Overpressures observed are driven by rapid sedimentation of low permeability material from the ancestral Mississippi River. Reduced Overpressure at depth at Site U1324 suggests lateral flow (drainage) whereas high Overpressure at Site U1322 requires inflow from below: lateral flow in the underlying permeable aquifer provides one mechanism for these observations. High Overpressure near the seafloor reduces slope stability and provides a mechanism for the large submarine landslides and low regional gradient (2 degree) offshore from the Mississippi delta.
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pore pressure penetrometers document high Overpressure near the seafloor where multiple submarine landslides have occurred on the continental slope offshore louisiana gulf of mexico
Earth and Planetary Science Letters, 2008Co-Authors: P B Flemings, Brandon Dugan, H Long, John T Germaine, Cedric M John, Jan H Behrmann, Dale S SawyerAbstract:Overpressures measured with pore pressure penetrometers during Integrated Ocean Drilling Program (IODP) Expedition 308 reach 70% and 60% of the hydrostatic effective stress (View the MathML sourceλ*=(u−uh)(σvh')) in the first 200 meters below sea floor (mbsf) at Sites U1322 and U1324, respectively, in the deepwater Gulf of Mexico, offshore Louisiana. High Overpressures are present within low permeability mudstones where there have been multiple, very large, submarine landslides during the Pleistocene. Beneath 200 mbsf at Site U1324, pore pressures drop significantly: there are no submarine landslides in this mixture of mudstone, siltstone, and sandstone. The penetrometer measurements did not reach the in situ pressure at the end of the deployment. We used a soil model to determine that an extrapolation approach based on the inverse of square route of time (View the MathML source1/t) requires much less decay time to achieve a desirable accuracy than an inverse time (1/t) extrapolation. Expedition 308 examined how rapid and asymmetric sedimentation above a permeable aquifer drives lateral fluid flow, extreme pore pressures, and submarine landslides. We interpret that the high Overpressures observed are driven by rapid sedimentation of low permeability material from the ancestral Mississippi River. Reduced Overpressure at depth at Site U1324 suggests lateral flow (drainage) whereas high Overpressure at Site U1322 requires inflow from below: lateral flow in the underlying permeable aquifer provides one mechanism for these observations. High Overpressure near the seafloor reduces slope stability and provides a mechanism for the large submarine landslides and low regional gradient (2°) offshore from the Mississippi delta.
P B Flemings - One of the best experts on this subject based on the ideXlab platform.
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permeability porosity relationships of shallow mudstones in the ursa basin northern deepwater gulf of mexico
Journal of Geophysical Research, 2012Co-Authors: Julia S Reece, Brandon Dugan, P B Flemings, Hui Long, John T GermaineAbstract:[1] In the Ursa Basin, Gulf of Mexico, in situ mudstone permeability near the seafloor declines from 1.1 × 10−16 to 5.8 × 10−19 m2over a depth of 578 m. We can reproduce this in situ permeability-porosity behavior through consolidation experiments in the laboratory. We use uniaxial constant-rate-of-strain consolidation experiments to measure permeability-porosity relationships and derive in situ permeabilities of 31 mudstone samples collected at Integrated Ocean Drilling Program (IODP) Sites U1324 and U1322. Although these mudstones have similar grain-size distributions, permeability at a given porosity varies significantly between the samples due to small variations in composition or fabric. We calculate an upscaled permeability relationship based on the observed permeability variation in the samples and determine a resultant large-scale permeability anisotropy of around 30. Based on this upscaled relationship and observations of in situ pressure, we calculate upward fluid flow rates of 0.5 mm/yr. We find that given the observed compressibility, permeability, and the geologic forcing at Ursa, Overpressures are predicted as observed in the subsurface. The primary mechanism for Overpressure generation at Ursa is sediment loading due to rapid burial. Low vertical permeabilities, accompanied by high sedimentation rates, can cause severe Overpressure near the seafloor, which controls fluid flow and can reduce slope stability as observed in the Mississippi Canyon region. Such flow systems, especially at intermediate depths on passive margins, are important due to their control over macroscale behavior such as topographic gradient of continental slopes and submarine landslides, but have been largely understudied in the past.
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consolidation and Overpressure near the seafloor in the ursa basin deepwater gulf of mexico
Earth and Planetary Science Letters, 2011Co-Authors: Hui Long, P B Flemings, John T Germaine, Demian M SafferAbstract:Abstract In mudstones of the Ursa Basin, Gulf of Mexico, the volume of voids to solids, or void ratio, ranges from 4 (porosity = 80%) at the seafloor to 0.6 (porosity = 37%) at 600 m below seafloor. This seven-fold change in void ratio can only be described by a compaction model that includes greater sediment stiffening with stress than has commonly been used in geotechnical or geological approaches. Through uniaxial consolidation experiments, we show that specific volume (v = 1 + void ratio) declines as an exponential function of effective stress. We use this relationship to successfully predict in-situ Overpressures at Integrated Ocean Drilling Program (IODP) Sites U1322 and U1324. This technique can be used around the world to describe sediment compaction and predict pore pressure in the first 1000 m below seafloor. Rapid sediment consolidation near the seafloor provides the fluid source that generates Overpressure despite the fact that these sediments have high permeability. Ultimately sediment consolidation is a first order control on when and at what depth Overpressure will be generated in the subsurface. This in turn will impact whether submarine landslides are expected and the regional gradient of continental margins.
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erratum to pore pressure penetrometers document high Overpressure near the seafloor where multiple submarine landslides have occurred on the continental slope offshore louisiana gulf of mexico earth and planetary science letters 269 3 4 2008 309 32
Earth and Planetary Science Letters, 2008Co-Authors: P B Flemings, Brandon Dugan, H Long, John T Germaine, Cedric M John, Jan H Behrmann, Dale S Sawyer, Iodp Expedition ScientistsAbstract:Abstract Overpressures measured with pore pressure penetrometers during Integrated Ocean Drilling Program (IODP) Expedition 308 reach 70% and 60% of the hydrostatic effective stress ( λ * = ( u − u h ) ( σ v h ' ) ) in the first 200 meters below sea floor (mbsf) at Sites U1322 and U1324, respectively, in the deepwater Gulf of Mexico, offshore Louisiana. High Overpressures are present within low permeability mudstones where there have been multiple, very large, submarine landslides during the Pleistocene. Beneath 200 mbsf at Site U1324, pore pressures drop significantly: there are no submarine landslides in this mixture of mudstone, siltstone, and sandstone. The penetrometer measurements did not reach the in situ pressure at the end of the deployment. We used a soil model to determine that an extrapolation approach based on the inverse of square root of time ( 1 / t ) requires much less decay time to achieve a desirable accuracy than an inverse time (1/t) extrapolation. Expedition 308 examined how rapid and asymmetric sedimentation above a permeable aquifer drives lateral fluid flow, extreme pore pressures, and submarine landslides. We interpret that the high Overpressures observed are driven by rapid sedimentation of low permeability material from the ancestral Mississippi River. Reduced Overpressure at depth at Site U1324 suggests lateral flow (drainage) whereas high Overpressure at Site U1322 requires inflow from below: lateral flow in the underlying permeable aquifer provides one mechanism for these observations. High Overpressure near the seafloor reduces slope stability and provides a mechanism for the large submarine landslides and low regional gradient (2 degree) offshore from the Mississippi delta.
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pore pressure penetrometers document high Overpressure near the seafloor where multiple submarine landslides have occurred on the continental slope offshore louisiana gulf of mexico
Earth and Planetary Science Letters, 2008Co-Authors: P B Flemings, Brandon Dugan, H Long, John T Germaine, Cedric M John, Jan H Behrmann, Dale S SawyerAbstract:Overpressures measured with pore pressure penetrometers during Integrated Ocean Drilling Program (IODP) Expedition 308 reach 70% and 60% of the hydrostatic effective stress (View the MathML sourceλ*=(u−uh)(σvh')) in the first 200 meters below sea floor (mbsf) at Sites U1322 and U1324, respectively, in the deepwater Gulf of Mexico, offshore Louisiana. High Overpressures are present within low permeability mudstones where there have been multiple, very large, submarine landslides during the Pleistocene. Beneath 200 mbsf at Site U1324, pore pressures drop significantly: there are no submarine landslides in this mixture of mudstone, siltstone, and sandstone. The penetrometer measurements did not reach the in situ pressure at the end of the deployment. We used a soil model to determine that an extrapolation approach based on the inverse of square route of time (View the MathML source1/t) requires much less decay time to achieve a desirable accuracy than an inverse time (1/t) extrapolation. Expedition 308 examined how rapid and asymmetric sedimentation above a permeable aquifer drives lateral fluid flow, extreme pore pressures, and submarine landslides. We interpret that the high Overpressures observed are driven by rapid sedimentation of low permeability material from the ancestral Mississippi River. Reduced Overpressure at depth at Site U1324 suggests lateral flow (drainage) whereas high Overpressure at Site U1322 requires inflow from below: lateral flow in the underlying permeable aquifer provides one mechanism for these observations. High Overpressure near the seafloor reduces slope stability and provides a mechanism for the large submarine landslides and low regional gradient (2°) offshore from the Mississippi delta.
N R Goulty - One of the best experts on this subject based on the ideXlab platform.
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compaction of diagenetically altered mudstones part 2 implications for pore pressure estimation
Marine and Petroleum Geology, 2016Co-Authors: N R Goulty, C SargentAbstract:Diagenetically altered mudstones compact mechanically and chemically. Consequently, their normal compaction trends depend upon their temperature history as well as on the maximum effective stress they have experienced. A further complication is that mudstones are commonly Overpressured where clay diagenesis occurs, preventing direct observation of the hydrostatic normal compaction trend. A popular way to estimate pore pressure in these circumstances is to calculate the sonic normal compaction trend in a well with a known pressure–depth profile by applying Eaton's method in reverse, and then to estimate pore pressure in offset wells using Eaton's method conventionally. We tested this procedure for Cretaceous mudstones at Haltenbanken. The results were inconsistent because the sonic log responds differently to disequilibrium compaction Overpressure and unloading Overpressure, and their relative contributions vary across the basin. In theory, a two-step method using the density and sonic logs could estimate the contributions to Overpressure from disequilibrium compaction and unloading. The normal compaction trend for density should be the normal compaction trend at the maximum effective stress the mudstones have experienced, not at hydrostatic effective stress. We advocate the Budge-Fudge approach as a starting point for pore pressure estimation in diagenetically altered mudstones, a two-step method that requires geological input to help estimate the Overpressure contribution from disequilibrium compaction. In principle, the Budge-Fudge approach could be used to estimate the normal compaction trend for mudstones at the maximum effective stress they have experienced, and so form the basis of the full two-step method through the use of offset wells. Our initial efforts to implement the full two-step method in this way at Haltenbanken produced inconsistent results with fluctuations in estimated pore pressure reflecting some of the fluctuations in the density logs. We suspect that variations in the mineralogical composition of the mudstones are responsible.
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budge fudge method of pore pressure estimation from wireline logs with application to cretaceous mudstones at haltenbanken
Petroleum Geoscience, 2015Co-Authors: C Sargent, N R Goulty, A M P Cicchino, Agus M RamdhanAbstract:Using wireline logs to estimate pore pressure in mudstones at the chemical compaction stage is not straightforward because clay diagenesis proceeds independently of effective stress, and neither density nor velocity is uniquely related to the maximum effective stress experienced by the mudstones. We propose the Budge–Fudge method, in which we assume there is a unique trend on the sonic–density cross-plot for mudstones at the chemical compaction stage that have not been unloaded. In addition to the sonic–density chemical compaction trend, an initial guestimate of maximum effective stress previously experienced by the mudstones is required. Additional Overpressure from unloading processes is then estimated from the sonic log, referenced to the density response. The initial guestimate of maximum effective stress may be adjusted to fit any available measured pressures or pressures estimated from geological knowledge. We have applied the Budge–Fudge method to Cretaceous mudstones at Haltenbanken, and find that estimated pressures match measured pressures and expected pressure–depth profiles. Furthermore, the analysis suggests that the lateral variations in mudstone porosity, previously reported, result from lateral variations in Overpressure build-up immediately following rapid burial by glaciogenic sediments; subsequently, Overpressures have increased through clay diagenesis and equilibrated laterally across the area.
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Overpressure and mudrock compaction in the lower kutai basin indonesia a radical reappraisal
AAPG Bulletin, 2011Co-Authors: Agus M Ramdhan, N R GoultyAbstract:Lateral drainage and high temperatures in the shelfal area of the Lower Kutai Basin provide an exceptional opportunity to study compaction of Miocene mudrocks and Overpressure generation. Previous workers agreed that the principal mechanism of Overpressure generation is disequilibrium compaction, but sonic and resistivity logs in several fields display reversals at a transition zone into high Overpressure, indicating that Overpressure is generated by unloading processes. The transition zone coincides with the vitrinite reflectance threshold for gas generation. Extreme Overpressures in some wells are associated with reversals on density logs too, interpreted to result from opening cracks. The density-depth trends through the mudrocks are similar in all wells and independent of Overpressure until extreme Overpressures are encountered. This observation strongly suggests that porosity reduction is controlled by chemical compaction and that cementation has caused the mudrocks to become overcompacted, relative to the prevailing effective stress, at burial depths of approximately 3 km (1.9 mi) where the top of Overpressure is encountered. Hence, the Lower Kutai Basin contains a unique reported example, to date, of a Neogene succession in which high Overpressures are generated by unloading processes with no contribution from disequilibrium compaction. Density logs from the Peciko field have been used to derive the empirical porosity-depth trend ϕ = 0.434 e −0.164 z for mudrocks in the depth range 6000 to 15,000 ft (1800 to 4600 m), where z is depth in thousands of feet. The corresponding temperature range is 85 to 170°C, so this compaction curve applies for mudrocks in the chemical compaction regime, where no discrete smectite is present.
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Overpressure generating mechanisms in the peciko field lower kutai basin indonesia
Petroleum Geoscience, 2010Co-Authors: Agus M Ramdhan, N R GoultyAbstract:ABSTRACT The Peciko Field contains gas in multiple stacked reservoirs within a Miocene deltaic sequence. In the deeper reservoirs, gas is trapped hydrodynamically by high lateral Overpressure gradients. We have analysed Overpressure and compaction in this field by using wireline log, pressure, temperature and vitrinite reflectance data. The top of the Overpressure is located below 3 km burial depth, below the depth range for transformation of discrete smectite to mixed-layer illite/smectite. Density-sonic and density-resistivity crossplots for mudrocks show reversals within the transition zone into hard Overpressure below 3.5 km depth. Vitrinite reflectance measurements indicate that the start of unloading coincides with the onset of gas generation. Moreover, mudrock density continues to increase with depth in the Overpressured section to values above 2.6 g cm –3 . We conclude that gas generation and chemical compaction are responsible for Overpressure generation, contradicting previous interpretations that disequilibrium compaction is the principal mechanism for generating Overpressure in the Lower Kutai Basin. The particular circumstances which make our radical interpretation plausible are that it is a warm basin with lateral reservoir drainage, so the Overpressured mudrocks are probably overcompacted as a result of diagenesis.
Brandon Dugan - One of the best experts on this subject based on the ideXlab platform.
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permeability porosity relationships of shallow mudstones in the ursa basin northern deepwater gulf of mexico
Journal of Geophysical Research, 2012Co-Authors: Julia S Reece, Brandon Dugan, P B Flemings, Hui Long, John T GermaineAbstract:[1] In the Ursa Basin, Gulf of Mexico, in situ mudstone permeability near the seafloor declines from 1.1 × 10−16 to 5.8 × 10−19 m2over a depth of 578 m. We can reproduce this in situ permeability-porosity behavior through consolidation experiments in the laboratory. We use uniaxial constant-rate-of-strain consolidation experiments to measure permeability-porosity relationships and derive in situ permeabilities of 31 mudstone samples collected at Integrated Ocean Drilling Program (IODP) Sites U1324 and U1322. Although these mudstones have similar grain-size distributions, permeability at a given porosity varies significantly between the samples due to small variations in composition or fabric. We calculate an upscaled permeability relationship based on the observed permeability variation in the samples and determine a resultant large-scale permeability anisotropy of around 30. Based on this upscaled relationship and observations of in situ pressure, we calculate upward fluid flow rates of 0.5 mm/yr. We find that given the observed compressibility, permeability, and the geologic forcing at Ursa, Overpressures are predicted as observed in the subsurface. The primary mechanism for Overpressure generation at Ursa is sediment loading due to rapid burial. Low vertical permeabilities, accompanied by high sedimentation rates, can cause severe Overpressure near the seafloor, which controls fluid flow and can reduce slope stability as observed in the Mississippi Canyon region. Such flow systems, especially at intermediate depths on passive margins, are important due to their control over macroscale behavior such as topographic gradient of continental slopes and submarine landslides, but have been largely understudied in the past.
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Overpressure and earthquake initiated slope failure in the ursa region northern gulf of mexico
Journal of Geophysical Research, 2010Co-Authors: Justin Stigall, Brandon DuganAbstract:[1] We use fluid flow and slope stability models to study the evolution of Overpressure and slope stability in the Ursa region, northern Gulf of Mexico. Our predictions match measured Overpressures (pressures in excess of hydrostatic) from Integrated Ocean Drilling Program Expedition 308 Site U1324 above 200 m below seafloor (mbsf) but overpredict deeper (200–610 mbsf) Overpressures by 0.4–1.1 MPa. Modeled Overpressure at Site U1322 matches measurements for the entire section (0–240 mbsf) with exception of the measurement at 240 mbsf. Slope stability models that integrate modeled Overpressure, vertical stress, and effective stress during deposition predict slope failure at 61 ka on the eastern end of the region. This failure corresponds to the base of a mass transport deposit that has been interpreted as a retrogressive failure initiated by high Overpressure. Overpressure alone could not drive failure of a second mass transport deposit (MTD2) that has its base along the 27 ka horizon. With an earthquake acceleration model coupled with our slope stability model, we predict that horizontal acceleration from a magnitude 5 earthquake within 140 km of the Ursa region at 27 ka would initiate the failure that created MTD2; the same earthquake at 20 ka would have to be within 40 km for failure. This magnitude and maximum rupture distance are consistent with seismicity near the Ursa region. We therefore propose that in some cases, Overpressure drives failure on low-angle slopes; however, earthquakes, even on passive margins, may play a critical role in initiating slope failure in sediments weakened by Overpressure.
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erratum to pore pressure penetrometers document high Overpressure near the seafloor where multiple submarine landslides have occurred on the continental slope offshore louisiana gulf of mexico earth and planetary science letters 269 3 4 2008 309 32
Earth and Planetary Science Letters, 2008Co-Authors: P B Flemings, Brandon Dugan, H Long, John T Germaine, Cedric M John, Jan H Behrmann, Dale S Sawyer, Iodp Expedition ScientistsAbstract:Abstract Overpressures measured with pore pressure penetrometers during Integrated Ocean Drilling Program (IODP) Expedition 308 reach 70% and 60% of the hydrostatic effective stress ( λ * = ( u − u h ) ( σ v h ' ) ) in the first 200 meters below sea floor (mbsf) at Sites U1322 and U1324, respectively, in the deepwater Gulf of Mexico, offshore Louisiana. High Overpressures are present within low permeability mudstones where there have been multiple, very large, submarine landslides during the Pleistocene. Beneath 200 mbsf at Site U1324, pore pressures drop significantly: there are no submarine landslides in this mixture of mudstone, siltstone, and sandstone. The penetrometer measurements did not reach the in situ pressure at the end of the deployment. We used a soil model to determine that an extrapolation approach based on the inverse of square root of time ( 1 / t ) requires much less decay time to achieve a desirable accuracy than an inverse time (1/t) extrapolation. Expedition 308 examined how rapid and asymmetric sedimentation above a permeable aquifer drives lateral fluid flow, extreme pore pressures, and submarine landslides. We interpret that the high Overpressures observed are driven by rapid sedimentation of low permeability material from the ancestral Mississippi River. Reduced Overpressure at depth at Site U1324 suggests lateral flow (drainage) whereas high Overpressure at Site U1322 requires inflow from below: lateral flow in the underlying permeable aquifer provides one mechanism for these observations. High Overpressure near the seafloor reduces slope stability and provides a mechanism for the large submarine landslides and low regional gradient (2 degree) offshore from the Mississippi delta.
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pore pressure penetrometers document high Overpressure near the seafloor where multiple submarine landslides have occurred on the continental slope offshore louisiana gulf of mexico
Earth and Planetary Science Letters, 2008Co-Authors: P B Flemings, Brandon Dugan, H Long, John T Germaine, Cedric M John, Jan H Behrmann, Dale S SawyerAbstract:Overpressures measured with pore pressure penetrometers during Integrated Ocean Drilling Program (IODP) Expedition 308 reach 70% and 60% of the hydrostatic effective stress (View the MathML sourceλ*=(u−uh)(σvh')) in the first 200 meters below sea floor (mbsf) at Sites U1322 and U1324, respectively, in the deepwater Gulf of Mexico, offshore Louisiana. High Overpressures are present within low permeability mudstones where there have been multiple, very large, submarine landslides during the Pleistocene. Beneath 200 mbsf at Site U1324, pore pressures drop significantly: there are no submarine landslides in this mixture of mudstone, siltstone, and sandstone. The penetrometer measurements did not reach the in situ pressure at the end of the deployment. We used a soil model to determine that an extrapolation approach based on the inverse of square route of time (View the MathML source1/t) requires much less decay time to achieve a desirable accuracy than an inverse time (1/t) extrapolation. Expedition 308 examined how rapid and asymmetric sedimentation above a permeable aquifer drives lateral fluid flow, extreme pore pressures, and submarine landslides. We interpret that the high Overpressures observed are driven by rapid sedimentation of low permeability material from the ancestral Mississippi River. Reduced Overpressure at depth at Site U1324 suggests lateral flow (drainage) whereas high Overpressure at Site U1322 requires inflow from below: lateral flow in the underlying permeable aquifer provides one mechanism for these observations. High Overpressure near the seafloor reduces slope stability and provides a mechanism for the large submarine landslides and low regional gradient (2°) offshore from the Mississippi delta.
Dale S Sawyer - One of the best experts on this subject based on the ideXlab platform.
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erratum to pore pressure penetrometers document high Overpressure near the seafloor where multiple submarine landslides have occurred on the continental slope offshore louisiana gulf of mexico earth and planetary science letters 269 3 4 2008 309 32
Earth and Planetary Science Letters, 2008Co-Authors: P B Flemings, Brandon Dugan, H Long, John T Germaine, Cedric M John, Jan H Behrmann, Dale S Sawyer, Iodp Expedition ScientistsAbstract:Abstract Overpressures measured with pore pressure penetrometers during Integrated Ocean Drilling Program (IODP) Expedition 308 reach 70% and 60% of the hydrostatic effective stress ( λ * = ( u − u h ) ( σ v h ' ) ) in the first 200 meters below sea floor (mbsf) at Sites U1322 and U1324, respectively, in the deepwater Gulf of Mexico, offshore Louisiana. High Overpressures are present within low permeability mudstones where there have been multiple, very large, submarine landslides during the Pleistocene. Beneath 200 mbsf at Site U1324, pore pressures drop significantly: there are no submarine landslides in this mixture of mudstone, siltstone, and sandstone. The penetrometer measurements did not reach the in situ pressure at the end of the deployment. We used a soil model to determine that an extrapolation approach based on the inverse of square root of time ( 1 / t ) requires much less decay time to achieve a desirable accuracy than an inverse time (1/t) extrapolation. Expedition 308 examined how rapid and asymmetric sedimentation above a permeable aquifer drives lateral fluid flow, extreme pore pressures, and submarine landslides. We interpret that the high Overpressures observed are driven by rapid sedimentation of low permeability material from the ancestral Mississippi River. Reduced Overpressure at depth at Site U1324 suggests lateral flow (drainage) whereas high Overpressure at Site U1322 requires inflow from below: lateral flow in the underlying permeable aquifer provides one mechanism for these observations. High Overpressure near the seafloor reduces slope stability and provides a mechanism for the large submarine landslides and low regional gradient (2 degree) offshore from the Mississippi delta.
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pore pressure penetrometers document high Overpressure near the seafloor where multiple submarine landslides have occurred on the continental slope offshore louisiana gulf of mexico
Earth and Planetary Science Letters, 2008Co-Authors: P B Flemings, Brandon Dugan, H Long, John T Germaine, Cedric M John, Jan H Behrmann, Dale S SawyerAbstract:Overpressures measured with pore pressure penetrometers during Integrated Ocean Drilling Program (IODP) Expedition 308 reach 70% and 60% of the hydrostatic effective stress (View the MathML sourceλ*=(u−uh)(σvh')) in the first 200 meters below sea floor (mbsf) at Sites U1322 and U1324, respectively, in the deepwater Gulf of Mexico, offshore Louisiana. High Overpressures are present within low permeability mudstones where there have been multiple, very large, submarine landslides during the Pleistocene. Beneath 200 mbsf at Site U1324, pore pressures drop significantly: there are no submarine landslides in this mixture of mudstone, siltstone, and sandstone. The penetrometer measurements did not reach the in situ pressure at the end of the deployment. We used a soil model to determine that an extrapolation approach based on the inverse of square route of time (View the MathML source1/t) requires much less decay time to achieve a desirable accuracy than an inverse time (1/t) extrapolation. Expedition 308 examined how rapid and asymmetric sedimentation above a permeable aquifer drives lateral fluid flow, extreme pore pressures, and submarine landslides. We interpret that the high Overpressures observed are driven by rapid sedimentation of low permeability material from the ancestral Mississippi River. Reduced Overpressure at depth at Site U1324 suggests lateral flow (drainage) whereas high Overpressure at Site U1322 requires inflow from below: lateral flow in the underlying permeable aquifer provides one mechanism for these observations. High Overpressure near the seafloor reduces slope stability and provides a mechanism for the large submarine landslides and low regional gradient (2°) offshore from the Mississippi delta.
