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W.J. Winters

Publications and source records attributed to W.J. Winters.

At least 19 recordsLinked to original sources
USGS2008

Physical property changes in hydrate-bearing sediment due to depressurization and subsequent repressurization

Physical property measurements of sediment cores containing natural gas hydrate are typically performed on material exposed, at least briefly, to non-in situ conditions during recovery. To examine the effects of a brief excursion from the gas-hydrate stability field, as can occur when pressure cores are transferred to pressurized storage vessels, we measured physical properties on laboratory-formed sand packs containing methane hydrate and methane pore gas. After depressurizing samples to atmospheric pressure, we repressurized them into the methane-hydrate stability field and remeasured their physical properties. Thermal conductivity, shear strength, acoustic compressional and shear wave amplitudes, and speeds of the original and depressurized/repressurized samples are compared. X– ray computed tomography images track how the gas-hydrate distribution changes in the hydrate-cemented sands owing to the depressurizaton/repressurization process. Because depressurization-induced property changes can be substantial and are not easily predicted, particularly in water-saturated, hydrate-bearing sediment, maintaining pressure and temperature conditions throughout the core recovery and measurement process is critical for using laboratory measurements to estimate in situ properties.

Journal of Geophysical Research B: Solid Earth↗
USGS2007

Origin of pockmarks and chimney structures on the flanks of the Storegga Slide, offshore Norway

Seafloor pockmarks and subsurface chimney structures are common on the Norwegian continental margin north of the Storegga Slide scar. Such features are generally inferred to be associated with fluid expulsion, and imply overpressures in the subsurface. Six long gravity and piston cores taken from the interior of three pockmarks were compared with four other cores taken from the same area but outside the pockmarks, in order to elucidate the origins and stratigraphy of these features and their possible association with the Storegga Slide event. Sulfate gradients in cores from within pockmarks are less steep than those in cores from outside the pockmarks, which indicates that the flux of methane to the seafloor is presently smaller within the pockmarks than in the adjacent undisturbed sediments. This suggests that these subsurface chimneys are not fluid flow conduits lined with gas hydrate. Methane-derived authigenic carbonates and Bathymodiolus shells obtained from a pockmark at >6.3 m below the seafloor indicate that methane was previously available to support a chemosynthetic community within the pockmark. AMS 14C measurements of planktonic Foraminifera overlying and interlayered with the shell-bearing sediment indicate that methane was present on the seafloor within the pockmark prior to 14 ka 14C years B.P., i.e., well before the last major Storegga Slide event (7.2 ka 14C years B.P., or 8.2 ka calendar years B.P.). These observations provide evidence that overpressured fluids existed within the continental margin sediments off Norway during the last major advance of Pleistocene glaciation.

Geo-Marine Letters↗
USGS2007

Methane gas hydrate effect on sediment acoustic and strength properties

To improve our understanding of the interaction of methane gas hydrate with host sediment, we studied: (1) the effects of gas hydrate and ice on acoustic velocity in different sediment types, (2) effect of different hydrate formation mechanisms on measured acoustic properties (3) dependence of shear strength on pore space contents, and (4) pore pressure effects during undrained shear. A wide range in acoustic p-wave velocities (V p ) were measured in coarse-grained sediment for different pore space occupants. V p ranged from less than 1 km/s for gas-charged sediment to 1.77–1.94 km/s for water-saturated sediment, 2.91–4.00 km/s for sediment with varying degrees of hydrate saturation, and 3.88–4.33 km/s for frozen sediment. V p measured in fine-grained sediment containing gas hydrate was substantially lower (1.97 km/s). Acoustic models based on measured V p indicate that hydrate which formed in high gas flux environments can cement coarse-grained sediment, whereas hydrate formed from methane dissolved in the pore fluid may not. The presence of gas hydrate and other solid pore-filling material, such as ice, increased the sediment shear strength. The magnitude of that increase is related to the amount of hydrate in the pore space and cementation characteristics between the hydrate and sediment grains. We have found, that for consolidation stresses associated with the upper several hundred meters of sub-bottom depth, pore pressures decreased during shear in coarse-grained sediment containing gas hydrate, whereas pore pressure in fine-grained sediment typically increased during shear. The presence of free gas in pore spaces damped pore pressure response during shear and reduced the strengthening effect of gas hydrate in sands.

Journal of Petroleum Science and Engineering↗
USGS2007

Characterization of methane hydrate host sediments using synchrotron-computed microtomography (CMT)

The hydrate-sediment interaction is an important aspect of gas hydrate studies that needs further examination. We describe here the applicability of the computed microtomography (CMT) technique that utilizes an intense X-ray synchrotron source to characterize sediment samples, two at various depths from the Blake Ridge area (a well-known hydrate-prone region) and one from Georges Bank, that once contained methane trapped as hydrates. Detailed results of the tomographic analysis performed on the deepest sample (667??m) from Blake Ridge are presented as 2-D and 3-D images which show several mineral constituents, the internal grain/pore microstructure, and, following segmentation into pore and grain space, a visualization of the connecting pathways through the pore-space of the sediment. Various parameters obtained from the analysis of the CMT data are presented for all three sediment samples. The micro-scale porosity values showed decreasing trend with increasing depth for all three samples that is consistent with the previously reported bulk porosity data. The 3-D morphology, pore-space pathways, porosity, and permeability values are also reported for all three samples. The application of CMT is now being expanded to the laboratory-formed samples of hydrate in sediments as well as field samples of methane hydrate bearing sediments.

Blake Ridge, Georges Bank↗
USGS2007

Simultaneous determination of thermal conductivity, thermal diffusivity and specific heat in sI methane hydrate

Thermal conductivity, thermal diffusivity and specific heat of sI methane hydrate were measured as functions of temperature and pressure using a needle probe technique. The temperature dependence was measured between −20°C and 17°C at 31.5 MPa. The pressure dependence was measured between 31.5 and 102 MPa at 14.4°C. Only weak temperature and pressure dependencies were observed. Methane hydrate thermal conductivity differs from that of water by less than 10 per cent, too little to provide a sensitive measure of hydrate content in water-saturated systems. Thermal diffusivity of methane hydrate is more than twice that of water, however, and its specific heat is about half that of water. Thus, when drilling into or through hydrate-rich sediment, heat from the borehole can raise the formation temperature more than 20 per cent faster than if the formation's pore space contains only water. Thermal properties of methane hydrate should be considered in safety and economic assessments of hydrate-bearing sediment.

Geophysical Journal International↗
USGS2006

Estimating thermal diffusivity and specific heat from needle probe thermal conductivity data

Thermal diffusivity and specific heat can be estimated from thermal conductivity measurements made using a standard needle probe and a suitably high data acquisition rate. Thermal properties are calculated from the measured temperature change in a sample subjected to heating by a needle probe. Accurate thermal conductivity measurements are obtained from a linear fit to many tens or hundreds of temperature change data points. In contrast, thermal diffusivity calculations require a nonlinear fit to the measured temperature change occurring in the first few tenths of a second of the measurement, resulting in a lower accuracy than that obtained for thermal conductivity. Specific heat is calculated from the ratio of thermal conductivity to diffusivity, and thus can have an uncertainty no better than that of the diffusivity estimate. Our thermal conductivity measurements of ice Ih and of tetrahydrofuran (THF) hydrate, made using a 1.6 mm outer diameter needle probe and a data acquisition rate of 18.2 pointss, agree with published results. Our thermal diffusivity and specific heat results reproduce published results within 25% for ice Ih and 3% for THF hydrate. ?? 2006 American Institute of Physics.

Review of Scientific Instruments↗
USGS2005

Fundamental challenges to methane recovery from gas hydrates

The fundamental challenges, the location, magnitude, and feasibility of recovery, which must be addressed to recover methane from dispersed hydrate sources, are presented. To induce dissociation of gas hydrate prior to methane recovery, two potential methods are typically considered. Because thermal stimulation requires a large energy input, it is less economically feasible than depressurization. The new data will allow the study of the effect of pressure, temperature, diffusion, porosity, tortuosity, composition of gas and water, and porous media on gas-hydrate production. These data also will allow one to improve existing models related to the stability and dissociation of sea floor hydrates. The reproducible kinetic data from the planned runs together with sediment properties will aid in developing a process to economically recover methane from a potential untapped hydrate source. The availability of plentiful methane will allow economical and large-scale production of methane-derived clean fuels to help avert future energy crises.

Topics in Catalysis↗
USGS2005

Physical properties of sediment containing methane gas hydrate

A study conducted by the US Geological Survey (USGS) on the formation, behavior, and properties of mixtures of gas hydrate and sediment is presented. The results show that the properties of host material influence the type and quantity of hydrates formed. The presence of hydrate during mechanical shear tests affects the measured sediment pore pressure. Sediment shear strength may be increased more than 500 percent by intact hydrate, but greatly weakened if the hydrate dissociates.

Conference Paper↗
USGS2005

Morphology of methane hydrate host sediments

The morphological features including porosity and grains of methane hydrate host sediments were investigated using synchrotron computed microtomography (CMT) technique. The sediment sample was obtained during Ocean Drilling Program Leg 164 on the Blake Ridge at water depth of 2278.5 m. The CMT experiment was performed at the Brookhaven National Synchrotron Light Source facility. The analysis gave ample porosity, specific surface area, mean particle size, and tortuosity. The method was found to be highly effective for the study of methane hydrate host sediments.

Conference Paper↗
USGS2004

Methane hydrate formation in partially water-saturated Ottawa sand

Bulk properties of gas hydrate-bearing sediment strongly depend on whether hydrate forms primarily in the pore fluid, becomes a load-bearing member of the sediment matrix, or cements sediment grains. Our compressional wave speed measurements through partially water-saturated, methane hydrate-bearing Ottawa sands suggest hydrate surrounds and cements sediment grains. The three Ottawa sand packs tested in the Gas Hydrate And Sediment Test Laboratory Instrument (GHASTLI) contain 38(1)% porosity, initially with distilled water saturating 58, 31, and 16% of that pore space, respectively. From the volume of methane gas produced during hydrate dissociation, we calculated the hydrate concentration in the pore space to be 70, 37, and 20% respectively. Based on these hydrate concentrations and our measured compressional wave speeds, we used a rock physics model to differentiate between potential pore-space hydrate distributions. Model results suggest methane hydrate cements unconsolidated sediment when forming in systems containing an abundant gas phase.

American Mineralogist↗
USGS2004

Physical properties and rock physics models of sediment containing natural and laboratory-formed methane gas hydrate

This paper presents results of shear strength and acoustic velocity (p-wave) measurements performed on: (1) samples containing natural gas hydrate from the Mallik 2L-38 well, Mackenzie Delta, Northwest Territories; (2) reconstituted Ottawa sand samples containing methane gas hydrate formed in the laboratory; and (3) ice-bearing sands. These measurements show that hydrate increases shear strength and p-wave velocity in natural and reconstituted samples. The proportion of this increase depends on (1) the amount and distribution of hydrate present, (2) differences, in sediment properties, and (3) differences in test conditions. Stress-strain curves from the Mallik samples suggest that natural gas hydrate does not cement sediment grains. However, stress-strain curves from the Ottawa sand (containing laboratory-formed gas hydrate) do imply cementation is present. Acoustically, rock physics modeling shows that gas hydrate does not cement grains of natural Mackenzie Delta sediment. Natural gas hydrates are best modeled as part of the sediment frame. This finding is in contrast with direct observations and results of Ottawa sand containing laboratory-formed hydrate, which was found to cement grains (Waite et al. 2004). It therefore appears that the microscopic distribution of gas hydrates in sediment, and hence the effect of gas hydrate on sediment physical properties, differs between natural deposits and laboratory-formed samples. This difference may possibly be caused by the location of water molecules that are available to form hydrate. Models that use laboratory-derived properties to predict behavior of natural gas hydrate must account for these differences.

American Mineralogist↗
USGS2003

Critical pressure and multiphase flow in Blake Ridge gas hydrates

We use core porosity, consolidation experiments, pressure core sampler data, and capillary pressure measurements to predict water pressures that are 70% of the lithostatic stress, and gas pressures that equal the lithostatic stress beneath the methane hydrate layer at Ocean Drilling Program Site 997, Blake Ridge, offshore North Carolina. A 29-m-thick interconnected free-gas column is trapped beneath the low-permeability hydrate layer. We propose that lithostatic gas pressure is dilating fractures and gas is migrating through the methane hydrate layer. Overpressured gas and water within methane hydrate reservoirs limit the amount of free gas trapped and may rapidly export methane to the seafloor.

Geology↗
USGS2000

Relation between gas hydrate and physical properties at the Mallik 2L-38 research well in the Mackenzie delta

As part of an interdisciplinary field program, a 1150-m deep well was drilled in the Canadian Arctic to determine, among other goals, the location, characteristics, and properties of gas hydrate. Numerous physical properties of the host sediment were measured in the laboratory and are presented in relation to the lithology and quantity of in situ gas hydrate. Profiles of measured and derived properties presented from that investigation include: sediment wet bulk density, water content, porosity, grain density, salinity, gas hydrate content (percent occupancy of non-sediment grain void space), grain size, porosity, and post-recovery core temperature. The greatest concentration of gas hydrate is located within sand and gravel deposits between 897 and 922 m. Silty sediment between 926 and 952 m contained substantially less, or no, gas hydrate perhaps because of smaller pore size.

Conference Paper↗
USGS2000

Formation of natural gas hydrates in marine sediments. Gas hydrate growth and stability conditioned by host sediment properties

The stability conditions of submarine gas hydrates (methane clathrates) are largely dictated by pressure, temperature, gas composition, and pore water salinity. However, the physical properties and surface chemistry of the host sediments also affect the thermodynamic state, growth kinetics, spatial distributions, and growth forms of clathrates. Our model presumes that gas hydrate behaves in a way analogous to ice in the pores of a freezing soil, where capillary forces influence the energy balance. Hydrate growth is inhibited within fine-grained sediments because of the excess internal phase pressure of small crystals with high surface curvature that coexist with liquid water in small pores. Therefore, the base of gas hydrate stability in a sequence of fine sediments is predicted by our model to occur at a lower temperature, and so nearer to the seabed than would be calculated from bulk thermodynamic equilibrium. The growth forms commonly observed in hydrate samples recovered from marine sediments (nodules, sheets, and lenses in muds; cements in sand and ash layers) can be explained by a requirement to minimize the excess of mechanical and surface energy in the system.

Conference Paper↗
USGS2000

Stress history and geotechnical properties of sediment from the Cape Fear Diapir, Blake Ridge Diapir, and Blake Ridge

Geotechnical properties of sediment from Ocean Drilling Program Leg 164 are presented as: (1) normalized shipboard strength ratios from the Cape Fear Diapir, the Blake Ridge Diapir, and the Blake Ridge; and (2) Atterberg limit, vane shear strength, pocket-penetrometer strength, and constant-rate-of-strain consolidation results from Hole 995A, located on the Blake Ridge. This study was conducted to understand the stress history in a region characterized by high sedimentation rates and the presence of gas hydrates. Collectively, the results indicate that sediment from the Blake Ridge exhibits significant underconsolidated behavior, except near the seafloor. At least 10 m of additional overburden was removed by erosion or mass wasting at Hole 993A on the Cape Fear Diapir, compared to nearby sites.

Conference Paper↗
USGS1999

Formation of natural gas hydrates in marine sediments 1. Conceptual model of gas hydrate growth conditioned by host sediment properties

The stability of submarine gas hydrates is largely dictated by pressure and temperature, gas composition, and pore water salinity. However, the physical properties and surface chemistry of deep marine sediments may also affect the thermodynamic state, growth kinetics, spatial distributions, and growth forms of clathrates. Our conceptual model presumes that gas hydrate behaves in a way analogous to ice in a freezing soil. Hydrate growth is inhibited within fine-grained sediments by a combination of reduced pore water activity in the vicinity of hydrophilic mineral surfaces, and the excess internal energy of small crystals confined in pores. The excess energy can be thought of as a "capillary pressure" in the hydrate crystal, related to the pore size distribution and the state of stress in the sediment framework. The base of gas hydrate stability in a sequence of fine sediments is predicted by our model to occur at a lower temperature (nearer to the seabed) than would be calculated from bulk thermodynamic equilibrium. Capillary effects or a build up of salt in the system can expand the phase boundary between hydrate and free gas into a divariant field extending over a finite depth range dictated by total methane content and pore-size distribution. Hysteresis between the temperatures of crystallization and dissociation of the clathrate is also predicted. Growth forms commonly observed in hydrate samples recovered from marine sediments (nodules, and lenses in muds; cements in sands) can largely be explained by capillary effects, but kinetics of nucleation and growth are also important. The formation of concentrated gas hydrates in a partially closed system with respect to material transport, or where gas can flush through the system, may lead to water depletion in the host sediment. This "freeze-drying" may be detectable through physical changes to the sediment (low water content and overconsolidation) and/or chemical anomalies in the pore waters and metastable presence of free gas within the normal zone of hydrate stability.

Journal of Geophysical Research B: Solid Earth↗