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Natural gas hydrates are solid crystalline substances found in the subsurface. Since gas hydrates are stable at low temperatures and moderate pressures, gas hydrates are found either near the surface in arctic regions or in deep water marine environments where the ambient seafloor temperature is less than 10°C. This work addresses the important issue of geomechanical stability in hydrate bearing sediments during different perturbations. I analyzed extensive data collected from the literature on the types of sediments where hydrates have been found during various offshore expeditions. To better understand the hydrate bearing sediments in offshore environments, I divided these data into different sections. The data included water depths, pore water salinity, gas compositions, geothermal gradients, and sedimentary properties such as sediment type, sediment mineralogy, and sediment physical properties. I used the database to determine the types of sediments that should be evaluated in laboratory tests at the Lawrence Berkeley National Laboratory. The TOUGH+Hydrate reservoir simulator was used to simulate the gas production behavior from hydrate bearing sediments. To address some important gas production issues from gas hydrates, I first simulated the production performance from the Messsoyakha Gas Field in Siberia. The field has been described as a free gas reservoir overlain by a gas hydrate layer and underlain by an aquifer of unknown strength. From a parametric study conducted to delineate important parameters that affect gas production at the Messoyakha, I found effective gas permeability in the hydrate layer, the location of perforations and the gas hydrate saturation to be important parameters for gas production at the Messoyakha. Second, I simulated the gas production using a hydraulic fracture in hydrate bearing sediments. The simulation results showed that the hydraulic fracture gets plugged by the formation of secondary hydrates during gas production. I used the coupled fluid flow and geomechanical model "TOUGH+Hydrate- FLAC3D" to model geomechanical performance during gas production from hydrates in an offshore hydrate deposit. I modeled geomechanical failures associated with gas production using a horizontal well and a vertical well for two different types of sediments, sand and clay. The simulation results showed that the sediment and failures can be a serious issue during the gas production from weaker sediments such as clays.

Thesis (M.S.)--West Virginia University, 2000. / Title from document title page. Document formatted into pages; contains xiii, 111 p. : ill. Includes abstract. Includes bibliographical references.

Thesis (M.S.)--West Virginia University, 2008. / Title from document title page. Document formatted into pages; contains xi, 208 p. : ill. (some col.), col. map. Includes abstract. Includes bibliographical references (p. 205-208).

Thesis (M.S.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains x, 72 p. : ill. (some col.), maps. Includes abstract. Includes bibliographical references (p. 69-72).

Methane hydrates have drawn the attention of climate scientists in the past decades due to the potency of methane as a greenhouse gas and the widespread occurrence of hydrates both in terrestrial and marine environments, which, if destabilised, could enhance global warming. This study aims to investigate how much impact sediment type has on modeled methane escape at the feather edge of stability for methane hydrates in the high latitude Northern Hemisphere (45° to 75° N). This area is characterised by cool bottom-water temperatures leading to a shallow gas hydrate stability zone (GHSZ), and has been disproportionally influenced by contemporary seawater warming. Calculations were performed to establish the depths of the upper and lower boundaries of the feather edge of the GHSZ. These limits were used to estimate seafloor areas covered by three select sediment types that have different petrophysical properties - hemipelagic clay, calcareous ooze and siliceous ooze. Modeling of methane flux for 300 years following a 3°C warming during the first 100 years was performed using TOUGH + HYDRATE for each of the three sediment types. The sediments behaved significantly differently, with siliceous ooze releasing the most methane gas, and calcareous ooze releasing the least. Estimates of total methane gas release were also performed on the areas covered by the three sediments between latitudes 45° to 75° N, and showed that, over the course of 300 years, up to 5 times the current methane concentration in the atmosphere could become susceptible to leaving methane hydrate reservoirs.

Methane hydrates are frozen deposits of methane and water found in high pressure or low temperature sediments. When these deposits destabilize, large quantities of methane can be emitted into the atmosphere. This is significant to climate change because methane has 25 times more greenhouse gas potential than Carbon Dioxide. Worldwide, it is estimated there are between 2500 and 10000 gigatons of methane stored in hydrate deposits. This represents more carbon than all fossil fuels on Earth. It is estimated that between 200 and 2000 gigatons of methane are stored in hydrates in Arctic waters acutely vulnerable to greenhouse warming. Over the last decade, researchers have identified instances of hydrate destabilization that have already begun. To gain insight into the potential climatic effects widespread hydrate dissociation would have, researchers have examined hydrate dissociation during the Paleocene Eocene Thermal Maximum 55 million years ago as a geologic precedent. In this period, large-scale hydrate dissociation contributed to 5-8 degree Celsius warming worldwide. If such a climatic shift were to transpire today, impacts on society would be enormous. There is currently a debate in the scientific community as to whether the risk of methane hydrate dissociation is relevant to the present generation. One side argues that not enough methane could be emitted into the atmosphere from today’s hydrate sources to have a meaningful impact on climate warming, where the other side contends that more than enough methane could be emitted from present day hydrate deposits to cause significant impacts to the global greenhouse effect. Given the information currently known about hydrates, it is reasonable to conclude there is a moderate risk of widespread destabilization that could impact global climate change in the coming decades. Significant acceleration of the conversion to alternative energies and implementation of geoengineering strategies should be considered.

Methane hydrates are naturally-occurring ice-like substances found in permafrost and in ocean sediments along continental shelves. These compounds are often the source of cold seeps—plumes which vent methane into aquatic environments, and may subsequently release the potent greenhouse gas into the atmosphere. Methane hydrates and methane gas seeps are of particular interest both for their potential as an energy source and for their possible contribution to climate change. In an effort to improve location of hydrates through the use of seismic surveys and echo-sounding technology, this work aims to describe the low-frequency (10 Hz to 10 kHz) acoustic behavior of methane gas bubbles and methane hydrates in water under simulated ocean-floor conditions of low temperatures and high pressures. Products of the experiments and analysis presented in this thesis include (a) passive acoustic techniques for measurement of gas flux from underwater seeps, (b) a modified form of Wood's model of low-frequency sound propagation through a bubbly liquid containing real gas, and (c) low-frequency measurements of bulk moduli and dissociation pressures of four natural samples of methane hydrates. Experimental procedures and results are presented, along with analytical and numerical models which support the findings. / text

Methane hydrate has a unique structure that the host water framework forms two kinds of cages, which contain one methane molecule each. Therefore, it has been expected that there may exist three kinds of translational modes of a methane molecule and also the distortion of translational mode of host water molecules compared with normal ice. We need information of the host and guest molecular dynamics over the wide momentum and energy transfer region for studying such dynamics. In this study inelastic neutron measurements were carried under 40 K with MARI spectrometer at ISIS in UK, TAS at JRR-3 and CAT at KENS in Japan. For the methane molecular motion we could confirm its freelike rotation by complementary use of MARI and TAS spectra. After the subtraction of the scattering intensity of the rotation evaluated by the free rotation model from the experimental data, three kinds of translation modes were identified at first experimentally. On the experimental spectra there still remains the excess intensity which could not explain the single mode excitation. The libration mode of the water framework shows the different momentum and energy transfer dependence with those of normal ice. The feature of the libration mode is resemble to ice-IX, that could be considered as a proton ordering of the cage structure appeared in ice-II, VIII and IX.

In order to evaluate the productivity of methane hydrate (MH) by the depressurization method, Japan Oil, Gas and Metals National Corporation and Natural Resources Canada carried out a full scale production test in the Mallik field, Mackenzie Delta, Canada in April, 2007. An extensive wire-line logging program was conducted to evaluate reservoir properties, to determine production/water injection intervals, to evaluate cement bonding, and to interpret MH dissociation behavior throughout the production. New open hole wire-line logging tools such as MR Scanner, Rt Scanner and Sonic Scanner, and other advanced logging tools such as ECS (Elemental Capture Spectroscopy) were deployed to obtain precise data on the occurrence of MH, lithology, MH pore saturation, porosity and permeability. Perforation intervals of the production and water injection zones were selected using a multidisciplinary approach. Based on the results of geological interpretation and open hole logging analysis, we picked candidate test intervals considering lithology, MH pore saturation, initial effective permeability and absolute permeability. Reservoir layer models were constructed to allow for quick reservoir numerical simulations for several perforation scenarios. Using the results of well log analysis, reservoir numerical simulation, and consideration of operational constraints, a MH bearing formation from 1093 to 1105 mKB was selected for 2007 testing and three zones (1224-1230, 1238-1256, 1270-1274 mKB) were selected for injection of produced water. Three kinds of cased-hole logging, RST (Reservoir Saturation Tool), APS (Accelerator Porosity Sonde), and Sonic Scanner were carried out to evaluate physical property changes of MH bearing formation before/after the production test. Preliminary evaluation of RST-sigma suggested that MH bearing formation in the above perforation interval was almost selectively dissociated (sand produced) in lateral direction. Preliminary analysis using Sonic Scanner data, which has deeper depth of investigation than RST brought us additional information on MH dissociation front and dissociation behavior.