Physical properties of sediments containing gas hydrates
TL;DR: In this article, the authors conducted a program of experimental research to study thermal conductivity and acoustic wave velocity in hydrates and sediments containing hydrate and found that the formation of hydrate tends to cause a decrease in the thermal conductivities of a sediment.
Abstract: In order to better understand the occurrence and distribution of gas hydrates and their effects on acoustic and thermal measurements in ocean sediments, the authors have conducted a program of experimental research to study thermal conductivity and acoustic wave velocity in hydrates and sediments containing hydrate. The most significant result of these studies is that the formation of hydrate tends to cause a decrease in the thermal conductivity of a sediment. This is contrary to what might be expected on the basis of an analogy with the behavior of frozen sediment and implies that some thermal gradients assumed in earlier studies of in situ deposits of hydrate may be too small. Other results of the research based on measurements of acoustic wave velocity confirm that both pure water and water-bearing sediment are converted to a stiff elastic mass by the formation of a sufficient quantity of hydrate. This clearly establishes the potential for a sharp acoustic impedance contrast at the boundary of a region of sediment containing a significant quantity of hydrate.
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TL;DR: The authors summarizes the main thrusts in mud volcano research as well as the various regions in which mud volcanism has been described, including the collision zones between Africa and Eurasia, where fluid flux through mud extrusion exceeds the compaction-driven pore fluid expulsion of the accretionary wedge.
Abstract: [1] Mud volcanism and diapirism have puzzled geoscientists for ∼2 centuries. They have been described onshore and offshore in many places on Earth, and although they occur in various tectonic settings, the majority of the features known to date are located in compressional tectonic scenarios. This paper summarizes the main thrusts in mud volcano research as well as the various regions in which mud volcanism has been described. Mud volcanoes show variable geometry (up to tens of kilometers in diameter and several hundred meters in height) and a great diversity regarding the origin of the fluid and solid phases. Gas (predominantly methane), water, and mud may be mobilized at subbottom depth of only a few meters but, in places, can originate from several kilometers depth (with minor crustal or mantle input). The possible contribution of mud extrusion to global budgets, both from quiescent fluid emission and from the extrusive processes themselves, is important. In regions where mud volcanoes are abundant, such as the collision zones between Africa and Eurasia, fluid flux through mud extrusion exceeds the compaction-driven pore fluid expulsion of the accretionary wedge. Also, quiescent degassing of mud volcanoes may contribute significantly to volatile budgets and, hence, to greenhouse climate.
747 citations
Cites background from "Physical properties of sediments co..."
...Although plausible in an environment of hydrate stability entrained by a (warmer) fluid from depth (thus destroying the hydrate cap), the physical properties of gas hydrates are only incompletely understood [e.g., Stoll and Bryan, 1979; Zhang et al., 1999]....
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TL;DR: In this paper, the authors found that anomalous reflections in marine seismic reflection data from continental slopes are often correlated with the base of gas hydrated sedimentary rocks, and that gas hydrates are present in water depths of 700 to 4,400 m and extend from 100 to 1,100 m subbottom.
Abstract: Anomalous reflections in marine seismic reflection data from continental slopes are often correlated with the base of gas hydrated sedimentary rocks. Examination of University of Texas Marine Science Institute reflection data reveals the possible presence of such gas hydrates along the east coast of the United States, the western Gulf of Mexico, the coasts of northern Colombia and northern Panama, and along the Pacific side of Central America in areas extending from Panama to near Acapulco, Mexico. Suspected hydrates are present in water depths of 700 to 4,400 m and extend from 100 to 1,100 m subbottom. Geometric relations, reflection coefficients, reflection polarity, and pressure-temperature relations all support the identification of the anomalous reflections as the base of gas hydrated sediments. In most places, gas hydrate association is related to structural anomalies (anticlines, dipping strata), which may allow gas to concentrate and migrate updip into pressure and temperature conditions suitable for hydrate formation. The gas hydrate boundary can be used to estimate thermal gradients. In general, thermal gradients estimated from the gas hydrate phase boundary are higher than reported thermal gradients measured by conventional means.
541 citations
TL;DR: In this paper, a new analytical formulation was proposed to solve the coupled momentum, mass, and energy equations that govern the evolution and accumulation of methane gas hydrate in marine sediments and derive expressions for the locations of the top and bottom of the hydrate stability zone, the position of actual hydrate occurrence, the timescale for hydrate accumulation in sediments, and the rate of accumulation as a function of depth in diffusive and advective end member systems.
Abstract: Using a new analytical formulation, we solve the coupled momentum, mass, and energy equations that govern the evolution and accumulation of methane gas hydrate in marine sediments and derive expressions for the locations of the top and bottom of the hydrate stability zone, the top and bottom of the zone of actual hydrate occurrence, the timescale for hydrate accumulation in sediments, and the rate of accumulation as a function of depth in diffusive and advective end-member systems. The major results emerging from the analysis are as follows: (1) The base of the zone in which gas hydrate actually occurs in marine sediments will not usually coincide with the base of methane hydrate stability but rather will lie at a more shallow depth than the base of the stability zone. Similarly, there are clear physical explanations for the disparity between the top of the gas hydrate stability zone (usually at the seafloor) and the top of the actual zone of gas hydrate occurrence. (2) If the bottom simulating reflector (BSR) marks the top of the free gas zone, then the BSR should occur substantially deeper than the base of the stability zone in some settings. (3) The presence of methane within the pressure-temperature stability field for methane gas hydrate is not sufficient to ensure the occurrence of gas hydrate, which can only form if the mass fraction of methane dissolved in liquid exceeds methane solubility in seawater and if the methane flux exceeds a critical value corresponding to the rate of diffusive methane transport. These critical flux rates can be combined with geophysical or geochemical observations to constrain the minimum rate of methane production by biogenic or thermogenic processes. (4) For most values of the diffusion-dispersion coefficient the diffusive end-member gas hydrate system is characterized by a thin layer of gas hydrate located near the base of the stability zone. Advective end-member systems have thicker layers of gas hydrate and, for high fluid flux rates, greater concentrations near the base of the layer than shallower in the sediment column. On the basis of these results and the very high methane flux rates required to create even minimal gas hydrate zones in some diffusive end-member systems, we infer that all natural gas hydrate systems, even those in relatively low flux environments like passive margins, are probably advection dominated.
476 citations
TL;DR: This review summarizes the different properties of gas hydrates as well as their formation and dissociation kinetics and then reviews the fast-growing literature reporting their role and applications in the aforementioned fields, mainly concentrating on advances during the last decade.
Abstract: Gas hydrates have received considerable attention due to their important role in flow assurance for the oil and gas industry, their extensive natural occurrence on Earth and extraterrestrial planets, and their significant applications in sustainable technologies including but not limited to gas and energy storage, gas separation, and water desalination Given not only their inherent structural flexibility depending on the type of guest gas molecules and formation conditions, but also the synthetic effects of a wide range of chemical additives on their properties, these variabilities could be exploited to optimise the role of gas hydrates This includes increasing their industrial applications, understanding and utilising their role in Nature, identifying potential methods for safely extracting natural gases stored in naturally occurring hydrates within the Earth, and for developing green technologies This review summarizes the different properties of gas hydrates as well as their formation and dissociation kinetics and then reviews the fast-growing literature reporting their role and applications in the aforementioned fields, mainly concentrating on advances during the last decade Challenges, limitations, and future perspectives of each field are briefly discussed The overall objective of this review is to provide readers with an extensive overview of gas hydrates that we hope will stimulate further work on this riveting field
349 citations
TL;DR: In this paper, the amplitude variation with offset (AVO) data from a bottom simulating reflector (BSR) offshore Florida was used to infer the internal structure of the hydrated sediment.
Abstract: We interpret amplitude variation with offset (AVO) data from a bottom simulating reflector (BSR) offshore Florida by using rock-physics-based synthetic seismic models. A previously conducted velocity and AVO analysis of the in-situ seismic data showed that the BSR separates hydrate-bearing sediments from sediments containing free methane. The amplitudes at the BSR are increasingly negative with increasing offset. This behavior was explained by P-wave velocity above the BSR being larger than that below the BSR, and S-wave velocity above the BSR being smaller than that below the BSR. We use these AVO and velocity results to infer the internal structure of the hydrated sediment. To do so, we examine two micromechanical models that correspond to the two extreme cases of hydrate deposition in the pore space: (1) the hydrate cements grain contacts and strongly reinforces the sediment, and (2) the hydrate is located away from grain contacts and does not affect the stiffness of the sediment frame. Only the second model can qualitatively reproduce the observed AVO response. Thus inferred internal structure of the hydrate-bearing sediment means that (1) the sediment above the BSR is uncemented and, thereby, mechanically weak, and (2) its permeability is very low because the hydrate clogs large pore-space conduits. The latter explains why free gas is trapped underneath the BSR. The seismic data also indicate the absence of strong reflections at the top of the hydrate layer. This fact suggests that the high concentration of hydrates in the sediment just above the BSR gradually decreases with decreasing depth. This effect is consistent with the fact that the low-permeability hydrated sediments above the BSR prevent free methane from migrating upwards.
299 citations
References
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01 Jul 1977
TL;DR: In this paper, a mathematical model for calculating thermal conductivity of soils with ordinary soil parameters as input data is presented. But the model is not suitable for the measurement of heat transfer mechanisms in moist materials, and it is difficult to obtain bounds for the different domains where the various mechanisms have an appreciable influence on the total heat transfer.
Abstract: : The aim of this investigation has been to create a mathematical model for calculating thermal conductivity of soils with ordinary soil parameters as input data. One part of this work has been devoted to literature studies on heat-transfer mechanisms in moist materials. These studies have made it possible to give bounds for the different domains where the various mechanisms have an appreciable influence on the total heat transfer.
946 citations
TL;DR: In this article, the transient heating of a needle probe is used to measure the thermal conductivity of deep-sea sediments in 10 minutes or less, with an accuracy of 3 to 4 percent.
Abstract: The transient heating of a needle probe is used to measure the thermal conductivity of deep-sea sediments in 10 minutes or less. An accuracy of 3 to 4 per cent compares favorably with steady-state methods, and measurements by both methods on the same sediments show good agreement. Thermal diffusivity of deep-sea sediments is shown to be proportional to thermal conductivity, in agreement with theoretical expectations.
520 citations
Book•
01 Aug 1974
TL;DR: In this paper, a review of Gas Hydrates with Implication for Ocean Sediments is presented, where the authors discuss pathways and environmental requirements for biogenic gas production in the Ocean.
Abstract: Pathways and Environmental Requirements for Biogenic Gas Production in the Ocean.- Depth Distributions of Gases in Shallow Water Sediments.- Methane and Carbon Dioxide in Coastal Marsh Sediments.- Hydrocarbon Gas (Methane) in Canned Deep Sea Drilling Project Core Samples.- Dissolved Gases in Cariaco Trench Sediments: Anaerobic Diagenesis.- Isotopic Analysis of Gas from the Cariaco Trench Sediments.- The Origin and Distribution of Methane in Marine Sediments.- Geothermal Gases.- The Nature and Occurrence of Clathrate Hydrates.- Review of Gas Hydrates with Implication for Ocean Sediments.- Occurrence of Natural Gas Hydrates in Sedimentary Basins.- Experiments on Hydrocarbon Gas Hydrates in Unconsolidated Sand.- Effects of Gas Hydrates in Sediments.- Acoustics and Gas in Sediments: Applied Research Laboratories (ARL) Experience.- Gas Bubbles and the Acoustically Impenetrable, or Turbid, Character of Some Estuarine Sediments.- In Situ Indications of Gas Hydrate.- Pagoda Structures in Marine Sediments.- List of Contributors.
310 citations
TL;DR: In this article, the effect of high pressure on gas hydrate equilibrium curve determined experimentally for methane, argon and nitrogen hydrates was investigated for different types of gases.
Abstract: Effect of high pressure on gas hydrate equilibrium curve determined experimentally for methane, argon and nitrogen hydrates
232 citations
TL;DR: In this article, the thermal conductivities of sediment from the Pacific, Atlantic, and Mediterranean areas have been determined in the laboratory by a steady-state method, and average values over a wide range of water content are found to depend more on water content than on solid phase constituents, and conductivities can be read from a diagram if the amount of contained sea water or the wet density of the sediment is known.
Abstract: As a part of the measurement of heat flow through the ocean floor, the thermal conductivities of samples of sediment from the Pacific, Atlantic, and Mediterranean areas have been determined in the laboratory by a steady-state method. Average values over a wide range of water content are found to depend more on water content than on solid phase constituents, and conductivities can be read from a diagram if the amount of contained sea water or the wet density of the sediment is known. A graph is included, showing the conductivities of wet, granular materials other than ocean sediment.
202 citations