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1.
Pore pressures in marine sediments: An overview of measurement techniques and some geological and engineering applications 总被引：1，自引：0，他引：1
P. J. Schultheiss 《Marine Geophysical Researches》1990,12(1-2):153-168
Pore pressures in the seabed are extremely sensitive to any imposed stress because of the low permeabilities commonly exhibited by marine sediments. Consequently, the measurement of sediment pore pressures can be used to infer either the nature of the imposed stress (if the sediment properties are known) or the physical properties of the sediment (if the imposed stresses are known). Stresses of many different types may be exerted on the seabed either through hydrostatic forces (e.g. tidal and wave effects), or directly by lithospheric forces (e.g. tectonic and thermal forces). Several techniques for measuring in situ pore pressures in the upper few metres of sediments have been developed, and one instrument, the PUPPI, will operate autonomously in water depths up to 6000 m. Basic sediment properties and processes can already be inferred from pore pressure responses using this technique. However, further application and development could greatly enhance its capability, especially for long-term monitoring of sediment conditions. In this Chapter, pore pressure measurement techniques are briefly reviewed and problems are highlighted. An outline is given of some of the many ways in which pore pressure measurements could be used to gain further insight into geological processes and to determine some of the pertinent sediment properties more accurately for engineering applications. 相似文献
2.
Michael Anthony Lovell 《Marine Georesources & Geotechnology》2013,31(2):205-240
Abstract The problem of radioactive waste containment, the modeling of hydrocarbon formation processes, and the proposed laying of fiber‐optic communication cables on the seafloor have recently focused attention on the thermal and fluid flow properties of porous media. Both properties are difficult to determine accurately for large volumes of material, particularly where disturbance is inevitable either on sampling or penetration of the measuring device. Both properties, however, have been tentatively identified as bearing some form of analogy with electrical flow, and evaluation of these relationships with electrical measurements may provide practical means of obtaining rapid coverage of the sediment from a semi‐remote position. Using a variety of laboratory cells, an attempt has been made to evaluate useful relationships between electrical formation factor and thermal conductivity and/or permeability for both sands and clays. Formation factor exhibits a close relationship with permeability, and the capability of predicting permeability to within an order of magnitude is shown providing the grade of sediment is identified (e.g., sand or clay). Formation factor is related to porosity and while any one sample is best represented by Archie's (sands) or Winsauer's (clays) empirical law, the overall trend is a third‐degree polynomial; particle shape appears to dominate both porosity and permeability relationships with electrical formation factor. Thermal conductivity shows a clear dependence on the porosity of a saturated sediment. The successful prediction of thermal conductivity using a geometrical model requiring volume and thermal conductivity values for the components has been demonstrated for a variety of particle shapes and sizes. Thermal conductivity may be related to formation factor through the porosity of the sample for both sands and clays. 相似文献
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Richard H. Bennett William R. Bryant Wayne A. Dunlap George H. Keller 《Marine Georesources & Geotechnology》2013,31(4):327-335
Abstract This report describes the instrumentation, initial results, and progress of an experiment designed to measure and monitor submarine sediment pore water and hydrostatic pressures in a selected area of the Mississippi Delta. The experiment also is intended to monitor significant pressure perturbations during active storm periods. Initial analysis of the data revealed excess pore water pressures in the silty clay sediment at selected depths below the mudline. Continuous monitoring of the pore water and hydrostatic pressures was expected to reveal important information regarding sediment pore water pressure variations as a function of the geological processes active in the Mississippi Delta. 相似文献
5.
The hydrostatic energy of high-pressure seawater is a renewable and green energy source for ocean exploration and have been used to replace underwater electrical energy transmission through the cable and underwater battery pack to power seafloor equipment. The advantage of the energy supply method is the cost-effective and the robustness. In the paper, the energy performance of the existing hydrostatic seafloor sediment samplers powered by seawater hydrostatic energy are modelled and analyzed and compared. In view of the common shortcoming of existing technology, a novel hydrostatic seafloor sediment sampler is proposed. The model of energy conversion of the new sampler is built, and its energy performance is obtained. The analysis results indicate that the energy conversion efficiency of the novel sediment sampler is much higher than the existing ones, which means that the new sampler can collect much longer sample with the limited amount of hydrostatic energy. The seawater hydrostatic energy conversion system of the new sampler can also be used to power other seafloor equipment. 相似文献
6.
A seabed instrument called Lancelot has been developed to measure pore pressure characteristics within potentially unstable marine sediment deposits, in any water depth. An estimate of the coefficient of consolidation can be obtained from the sediment pore pressure dissipation response that occurs following penetration into the seabed. This data can be used to calculate the coefficient of hydraulic conductivity, which is useful in analyzing the seepage velocity of pore fluids moving within the sediment mass. Pore-water pressures in excess of the normal hydrostatic profile are detected and used in static and dynamic liquefaction analyses, with a view toward understanding the origin of unusual seabed features such as pockmarks, as well as short-term instability caused by wave loading. An example of static liquefaction due to seepage stress is given for sites in and adjacent to the well-known 1929 Grand Banks debris flow, along with an example of incomplete liquefaction caused by dynamic wave loading within Miramichi Inner Harbor, New Brunswick. The adoption of in situ measurement techniques is shown to produce data of a quality not normally obtainable from recovered core samples, due to pressure relief and sampling disturbance effects. 相似文献
7.
G. Vasseur I. Djeran-Maigre D. Grunberger G. Rousset D. Tessier B. Velde 《Marine and Petroleum Geology》1995,12(8)
To provide a better understanding of sedimentary basin geological history, it is important to describe correctly the evolution of the various physical, mechanical and hydraulic properties of clayey rocks as a function of burial depth. As a contribution to this field, a programme of experimental studies on reworked clay samples compacted under various load pressures in oedometric conditions has been set up. The evolution of samples under compaction was followed with microscopic and macroscopic measurements. In a specially designed oedometric cell, samples are compacted under different total stresses from 0.1 to 50 MPa. In this cell, cylindrical cores are submitted to progressive loading from both ends under controlled pore pressure conditions. The symmetrical loading allows more even deformation about the midplane of the sample. This device allows the evolution of hydraulic pressure, radial stress, displacement and expelled pore fluid to be followed as a function of time. In a first step, kaolinite was chosen because it retains a high permeability (compared with other clays such as illite or smectite), which allows compaction tests to be performed within a few days. A complete set of measurements was performed after the tests. These measurements are: (1) micro-structures investigated by means of transmission electron microscopy (TEM), mercury porosimetry, water removal under low water vapour pressure, granulometry and specific area measured by ethylene glycol adsorption; and (2) various physical parameters measured including hydraulic conductivity and thermal conductivity. TEM gives an understanding of the arrangement of particles. It was found that each particle is composed of several crystal units, each unit formed by ≈25 individual kaolinite layers. During compaction, these particles remain undeformed, but are rotated. The angular distribution of grain orientation is a function of the applied effective stress. This reorientation is in agreement with the observed decrease in porosity and pore size. It also explains the occurrence of a strong anisotropy in the thermal conductivity and hydraulic permeability. The combination of these experimental results allows a qualitative and quantitative understanding of the behaviour of kaolinite with respect to parameters such as permeability, porosity, mechanical and thermal properties, the knowledge of which are necessary for basin modelling. 相似文献
8.
Reservoir pressures within the Bullwinkle minibasin (Green Canyon 65, Gulf of Mexico continental slope) increase at a hydrostatic gradient whereas pressures predicted from porosity within mudstones bounding these reservoirs increase at a lithostatic gradient: they are equal at a depth 1/3 of the way down from the crest of the structure. Two- and three-dimensional steady-state flow models demonstrate that bowl-shaped structures will have lower pressures than equivalent two-dimensional structures and that if a low permeability salt layer underlies the basin, the pressure is reduced. We conclude that at Bullwinkle, pressure is reduced due to an underlying salt body and the bowl-shape of the basin. A geometric approach to predict sandstone pressure is to assume that the reservoir pressure equals the area-weighted average of the mudstone pressure. When the mudstone pressure gradient is constant, as at Bullwinkle, the reservoir pressure equals the mudstone pressure at the average depth (centroid) of the reservoir. 相似文献
9.
N.T.T. Binh T. Tokunaga T. Nakamura K. Kozumi M. Nakajima M. Kubota H. Kameya M. Taniue 《Marine and Petroleum Geology》2009
Understanding the evolution of abnormally high fluid pressures within sedimentary formations is critical for analysing hydrogeological processes and assessing drilling risks. We have constructed a two-dimensional basin model and have performed numerical simulations to increase the understanding of the history of fluid flow and shallow overpressures in the Pleistocene and Holocene formations in the Ursa basin, deepwater Gulf of Mexico. We measured physical properties of sediments, such as porosity and permeability, in the laboratory and estimated in situ pore pressures from preconsolidation pressures. We obtained porosity–effective stress relationships from measurements of bulk density, grain density and preconsolidation pressures in the laboratory. Porosity–effective stress relationships were also obtained from downhole density logs and measured pore pressures. The porosity–effective stress and porosity–permeability relationships obtained were applied in two-dimensional basin simulations. Results showed that high pore pressures developed shortly after sediment deposition. Peaks in pore pressure ratios were related to high sedimentation rates of mass transport deposits and the incision of the Ursa channel. Lateral flows from the area where the overburden is thick towards the area where it is thin have occurred at least since 30 ka. Present pore pressure and temperature distributions suggest that lateral flows play a role in re-distributing heat in the basin. 相似文献
10.
The design and use of a marine heat probe with capability for measuring thermal conductivity insitu with high accuracy, and providing digital acoustic transmission of data to the ship, is described. The instrument employs the violin bow strength member and parallel sensor string configuration suggested by C. R. B. Lister. Several hundred measurements have been made in the deep ocean on multipenetration or pogostick profiles using a 3 m probe and in deep inlets of western Canada using a 7 m probe. The insitu thermal conductivity technique using a calibrated heat pulse has been studied in detail through laboratory calibration of the probe in materials of known conductivity, through numerical models, and through comparison of insitu measurements with needle probe measurements on sediment cores taken from the same sites. The insitu technique permits a conductivity accuracy of better than ±5% with a recording time of 7 minutes following 7 minutes in the bottom to establish the geothermal gradient. The pulse heating is also more energy efficient than the conventional continuous heating technique.Contribution from the Earth Physics Branch No. 807. 相似文献
11.
The paper presents the design and preliminary test results of a corer used for hard seafloor sediments sampling.Generally the sediment cores are provided by either gravity-type coring or deep-ocean drilling for a range of studies.However,in consideration of the operability and available sample length in collecting hard sediments,these methods exhibit no advantages.In this paper,a new corer which can exploit both hydrostatic energy and gravity energy for hard sediments coring is presented.The hydrostatic energy is provided by pressure differential between ambient seawater pressure and air pressure in an empty cavity.During sampling process,the corer penetrates into the sediment like a gravity corer and then automatically shifts to the percussion mode.The experiments in the laboratory indicate that the corer can complete 40 cycles in the sea with a cycle time of 2.8 seconds in percussion mode and impact the sample tube with the velocity of 0.2 m/s during each cycle.Besides,its adjustable falling velocity can make the corer achieve the maximum efficiency in coring different sediments. 相似文献
12.
Shusaku Goto Tomonobu Mizoguchi Ryo Kimura Masataka Kinoshita Makoto Yamano Hideki Hamamoto 《Marine Geophysical Researches》2012,33(3):269-283
We investigated the relationship between variations in the thermal conductivity of surface sediments and the topography in the Nankai subduction zone off Tokai, central Japan, the easternmost part of the Nankai subduction zone, which has an accretionary prism with varied topography. We analyzed sediment thermal conductivity data obtained from the trough floor and accretionary prism. Variations in the thermal conductivity of sediments were related to the topographic features formed by accretionary prism development. Thermal conductivities of 1.1?W/m?K were measured on the trough floor where thick terrigenous turbidites have been deposited. The thermal conductivity of Nankai Trough floor sediments decreases from northeast to southwest along the trough, probably because of the decreased grain size and/or changes in sediment mineral composition. High thermal conductivities (??1.0?W/m?K) were measured in fault scarps on the accretionary prism. A landward increase in these values on the prism may be explained by decreased porosity of the sediments attributable to tectonic deformation during accretionary prism development. At the base of the fault scarp of the frontal thrust, low thermal conductivities (<0.9?W/m?K) were measured, likely reflecting the high porosity of the talus deposits. Low thermal conductivity (0.9?W/m?K) was also measured in slope basins on the accretionary prism, likely also related to the high porosity of the sediments. Our results demonstrate that, for accurate heat flow measurement in an area of varied topography, the geothermal gradient and the thermal conductivity of the sediments must be measured within regions with similar topographic features. 相似文献
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Fundamental response of pore-water pressure to microfabric and permeability characteristics: Eckernförde Bay 总被引：1，自引：0，他引：1
R. H. Bennett M. H. Hulbert M. M. Meyer D. M. Lavoie K. B. Briggs D. L. Lavoie R. J. Baerwald W. A. Chiou 《Geo-Marine Letters》1996,16(3):182-188
Ambient and dynamic in situ pore pressures were measured, and microfabric was examined in finegrained, shallow-water sediment in Eckernförde Bay, Germany. In situ permeabilities were calculated from piezometer data. Pore-water pressure decay times in sediments 0.5–1.0 m subbottom are indicative of clayey materials. Shallower sediments, although of similar classical grain size as the deeper sediments, have quicker decay times typical of silty marine sediment. Pore pressure response is a function of the microfabric, porometry, and sediment permeability. Aggregates (composed of fine-grained material, biota, and extracellular polymers) produce large pores and complex microstructure, resulting in effective permeabilities characteristic of silts. 相似文献
15.
《Deep Sea Research Part I: Oceanographic Research Papers》2005,52(6):1085-1092
A flow-type apparatus has been developed to study thermotolerance of microorganisms under conditions simulating submarine hydrothermal circulation. The apparatus is designed so that microorganisms can be exposed to high temperature for periods of only a few seconds duration, and can be operated at temperatures up to 400 °C and hydrostatic pressures up to 30 MPa, even under strict anaerobic conditions. The performance of the apparatus was tested by studying the thermotolerance of a mesophilic bacterium, Escherichia coli strain W3110, after heat treatment at temperatures between 59.0 and 64.5 °C for 1.5 s. The results compared favorably with the literature data obtained by a conventional batch method at lower temperatures and longer heating durations. Thermotolerance of a hyperthermophilic archaeon, Pyrococcus horikoshii strain OT3, was successfully determined by the apparatus at temperatures up to 119 °C and pressures up to 25 MPa under anaerobic conditions. 相似文献
16.
Stable backfill materials for the heat sensitive structures of buried power cables, hot water pipes, and gas pipelines are suggested to have low permeability and high heat transfer characteristics. The hydraulic and thermal conductivities of backfill materials or clay liners are important parameters in proper design and construction of geotechnical structures involved with heat transfers. In this study, to investigate the optimal natural backfill or liner materials, thermal and hydraulic conductivities of kaolin–silica mixtures examined based on the results from laboratory tests under different consolidation conditions. From the experiment results, the thermal conductivity increases while hydraulic conductivity decreases with increasing density during consolidation process. As a result, back-fill materials with high kaolin content under low consolidation stress were desirable materials for burial of heat sensitive structures. 相似文献
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The hydrostatic motor: Utilization of hydrostatic pressure differentials in the deep sea 总被引：1，自引：0，他引：1
A hydrostatic motor that converts hydrostatic pressure gradients in the deep sea into harnessable mechanical energy has been
developed and successfully tested. Controlled equalization between higher ambient hydrostatic pressures at oceanic depths
and lower pressures retained from atmospheric or sea-level conditions—sealed within a chamber as part of the motor assembly—produces
reciprocating motion of a piston. This motion is utilized for power or work requirements. Our needs have been directed toward
oceanographic instrumentation requirements but many other applications are likely. 相似文献
19.
Bennett R. Burns J. Nastav F. Lipkin J. Percival C. 《Oceanic Engineering, IEEE Journal of》1985,10(1):17-22
Two single-sensor piezometer probes, 8 mm in diameter, were developed for deep-ocean geotechnical investigations. These probes were tested in a hyperbaric chamber pressurized to 55 MPa (8000 psi). Testing was performed for a period of five weeks under high hydrostatic pressure with the probes inserted in reconstituted illitic marine sediment. Small differential pore-water pressures were generated in response to both mechanically and thermally generated forcing functions. During deep-ocean simulated pressure tests, the sensors exhibited excellent sensitivity and stability. These developments in piezometer-probe technology provide a quantitative means of assessing important geotechnical parameters of fine-grained seabed deposits. 相似文献
20.
Mohammed Chemmam Mostefa Belkhatir Rachid Bouferra 《Marine Georesources & Geotechnology》2016,34(4):384-394
This article presents a laboratory study of static behavior of silty-sand soils. The objective of this laboratory investigation is to study the effect of initial confining pressures and fines content on the undrained shear strength (known as liquefaction resistance) response, pore pressure, and hydraulic conductivity of sand–silt mixtures. The triaxial tests were conducted on reconstituted saturated silty-sand samples at initial relative density Dr = 15% with fines content ranging from 0 to 50%. All the samples were subjected to a range of initial confining pressures (50, 100, and 200 kPa). The obtained results indicate that the presence of low plastic fines in sand–silt mixture leads to a more compressible soil fabric, and consequently to a significant loss in the soil resistance to liquefaction. The evaluation of the data indicates that the undrained shear strength can be correlated to fines content (Fc), inter-granular void ratio (eg), and excess of pore pressure (Δu). The undrained shear strength decreases with the decrease of saturated hydraulic conductivity and the increase of fines content for all confining pressures under consideration. There is a relatively high degree of correlation between the peak shear strength (qpeak) and the logarithm of the saturated hydraulic conductivity (ksat) for all confining pressures. 相似文献