Permafrost-associated Gas Hydrate Research Articles

Characterization of the Structural–Stratigraphic and Reservoir Controls on the Occurrence of Gas Hydrates in the Eileen Gas Hydrate Trend, Alaska North Slope

One of the most studied permafrost-associated gas hydrate accumulations in Arctic Alaska is the Eileen Gas Hydrate Trend. This study provides a detailed re-examination of the Eileen Gas Hydrate Trend with a focus on the gas hydrate accumulation in the western part of the Prudhoe Bay Unit. This integrated analysis of downhole well log data and published geophysical data has provided new insight on structural, stratigraphic, and reservoir controls on the occurrence of gas hydrates in the Eileen Gas Hydrate Trend. This study revealed the relatively complex nature of the gas hydrate occurrences in the Eileen Gas Hydrate Trend, with gas hydrates present in a series of coarsening upward, laterally pervasive, mostly fine-grained sand beds exhibiting high gas hydrate saturations. Most of the gas hydrate-bearing reservoirs in the Eileen Gas Hydrate Trend are laterally segmented into distinct northwest- to southeast-trending fault blocks, occur in a combination of structural–stratigraphic traps, and are only partially hydrate filled with distinct down-dip water contacts. These findings suggest that the traditional parts of a petroleum system (i.e., reservoir, gas source, gas migration, and geologic timing of the system formation) also control the occurrence of gas hydrates in the Eileen Gas Hydrate Trend.

Experimental study of frozen gas hydrate decomposition towards gas recovery from permafrost hydrate deposits below freezing point

Enormous natural gas hydrate reserves have been identified in the global permafrost and oceanic regions. How the existence of ice influences the hydrate dissociation is a fundamental issue related to the development of the permafrost-associated gas hydrate resources. The dissociation behaviors of frozen methane hydrate in hydrate-ice-gas saturated porous media below freezing point are studied in a high pressure reactor. The hydrate-bearing permafrost layer is simulated through decreasing the temperature of the methane hydrate samples to −0.60 °C, and then they are safely dissociated by depressurization and thermal stimulation. Results show that the disturbance on gas and water in the pores can induce secondary hydrate formation during the cooling of the system. The gas recovery rate by depressurization below freezing point is extremely slow, which is caused by the obstructive effect of ice on the diffusion of methane molecules. The self-preservation of frozen gas hydrate could be effectively broken under wellbore heating. Heat is primarily transferred by conduction mode across the hydrate and ice particles. The solid ice tends to absorb heat first and then melts into liquid water. The dissociated fluids play a role in promoting the heat transfer through thermal convection. Moreover, the net energy gain is found to be much higher than the energy consumption, and desirable energy efficiency has been obtained. Sensitivity analyses indicate that higher heat injection rate and lower ice saturation will be more favorable for the exploitation, while the production pressure seems to have negligible influence on the overall production efficiency.

An experimental study on gas production from fracture-filled hydrate by CO2 and CO2/N2 replacement

The fracture-filled gas hydrate commonly occurs in marine fine-grained sediments and the fracture of rock in permafrost regions. Gas production from fracture-filled methane hydrate by the CO2 replacement method has been investigated. The reservoir condition of permafrost-associated gas hydrate in Muri Basin, Qilian Mountains was taken as an example to set up the experimental parameters. CO2, CO2/N2 (3:1) and CO2/N2 (1:3) were selected for gas replacement. Based on the results from six sets of laboratory experiments, we can learn that the factors affecting gas replacement included gas composition for replacement, pressure and the morphology of the hydrate. When the pressure was lower than the equilibrium pressure of CO2/N2 binary hydrate and the equilibrium pressure of methane hydrate, there was a rapid decomposition process of methane hydrate and might be a transient water freezing process at the first few minutes. The ice around methane hydrate might inhibit the further decomposition of methane hydrate. A higher replacement rate and accumulative methane recovery ratio can be obtained when the morphology of methane hydrate was well distributed thin layer, which could be obtained with the ice layer by gradually increasing its temperature. The thin layer of hydrate is the main morphology of the fracture-filled gas hydrate found in the Qilian Mountain permafrost. Therefore, the gas production from hydrate by CO2/N2 (3:1) replacement might be a good choice for gas production from hydrate in Muri Basin, Qilian Mountain.

The mechanism and verification analysis of permafrost-associated gas hydrate formation in the Qilian Mountain, Northwest China

Muri Basin in the Qilian Mountain is the only permafrost area in China where gas hydrate samples have been obtained through scientific drilling. Fracture-filling hydrate is the main type of gas hydrate found in the Qilian Mountain permafrost. Most of gas hydrate samples had been found in a thin-layer-like, flake and block group in a fracture of Jurassic mudstone and oil shale, although some pore-filling hydrate was found in porous sandstone. The mechanism for gas hydrate formation in the Qilian Mountain permafrost is as follows: gas generation from source rock was controlled by tectonic subsidence and uplift--gas migration and accumulation was controlled by fault and tight formation--gas hydrate formation and accumulation was controlled by permafrost. Some control factors for gas hydrate formation in the Qilian Mountain permafrost were analyzed and validated through numerical analysis and laboratory experiments. CSMGem was used to estimate the gas hydrate stability zone in the Qilian permafrost at a depth of 100–400 m. This method was used to analyze the gas composition of gas hydrate to determine the gas composition before gas hydrate formation. When the overlying formation of gas accumulation zone had a permeability of 0.05 × 10−15 m2 and water saturation of more than 0.8, gas from deep source rocks was sealed up to form the gas accumulation zone. Fracture-filling hydrate was formed in the overlap area of gas hydrate stability zone and gas accumulation zone. The experimental results showed that the lithology of reservoir played a key role in controlling the occurrence and distribution of gas hydrate in the Qilian Mountain permafrost.

Permafrost-Associated Gas Hydrate: Is It Really Approximately 1 % of the Global System?

Permafrost-associated gas hydrates are often assumed to contain ∼1 % of the global gas-in-place in gas hydrates based on a study26 published over three decades ago. As knowledge of permafrost-associated gas hydrates has grown, it has become clear that many permafrost-associated gas hydrates are inextricably linked to an associated conventional petroleum system, and that their formation history (trapping of migrated gas in situ during Pleistocene cooling) is consistent with having been sourced at least partially in nearby thermogenic gas deposits. Using modern data sets that constrain the distribution of continuous permafrost onshore5 and subsea permafrost on circum-Arctic Ocean continental shelves offshore and that estimate undiscovered conventional gas within arctic assessment units,16 the analysis done here reveals where permafrost-associated gas hydrates are most likely to occur, concluding that Arctic Alaska and the West Siberian Basin are the best prospects. A conservative estimate is that 20 Gt C (2...

Numerical studies of gas production from several CH 4 hydrate zones at the Mallik site, Mackenzie Delta, Canada

The Mallik site represents an onshore permafrost-associated gas hydrate accumulation in the Mackenzie Delta, Northwest Territories, Canada. A gas hydrate research well was drilled at the site in 1998. The objective of this study is the analysis of various gas production scenarios from five methane hydrate-bearing zones at the Mallik site. In Zone #1, numerical simulations using the EOSHYDR2 model indicated that gas production from hydrates at the Mallik site was possible by depressurizing a thin free gas zone at the base of the hydrate stability field. Horizontal wells appeared to have a slight advantage over vertical wells, while multiwell systems involving a combination of depressurization and thermal stimulation offered superior performance, especially when a hot noncondensible gas was injected. Zone #2, which involved a gas hydrate layer with an underlying aquifer, could yield significant amounts of gas originating entirely from gas hydrates, the volumes of which increased with the production rate. However, large amounts of water were also produced. Zones #3, #4 and #5 were lithologically isolated gas hydrate-bearing deposits with no underlying zones of mobile gas or water. In these zones, thermal stimulation by circulating hot water in the well was used to induce dissociation. Sensitivity studies indicated that the methane release from the hydrate accumulations increased with the gas hydrate saturation, the initial formation temperature, the temperature of the circulating water in the well, and the formation thermal conductivity. Methane production appears to be less sensitive to the specific heat of the rock and of the hydrate, and to the permeability of the formation.

Reservoir Characterization of Marine and Permafrost Associated Gas Hydrate Accumulations with Downhole Well Logs

Abstract: Gas volumes that may be attributed to a gas hydrate accumulation depend on a number of reservoir parameters, one of which, gas‐hydrate saturation, can be assessed with data obtained from downhole well‐logging devices. This study demonstrates that electrical resistivity and acoustic transit‐time downhole log data can be used to quantify the amount of gas hydrate in a sedimentary section. Two unique forms of the Archie relation (standard and quick look relations) have been used in this study to calculate water saturations (Sw) [gas‐hydrate saturation (Sh) is equal to (1.0 −Sw)] from the electrical resistivity log data in four gas hydrate accumulations. These accumulations are located on (1) the Blake Ridge along the Southeastern continental margin of the United States, (2) the Cascadia continental margin off the Pacific coast of Canada, (3) the North Slope of Alaska, and (4) the Mackenzie River Delta of Canada. Compressional wave acoustic log data have also been used in conjunction with the Timur, modified Wood, and the Lee weighted average acoustic equations to calculate gas‐hydrate saturations in all four areas assessed.

Permafrost‐Associated Gas Hydrate Accumulationsa

Annals of the New York Academy of SciencesVolume 715, Issue 1 p. 247-269 Permafrost-Associated Gas Hydrate Accumulationsa TIMOTHY S. COLLETT, TIMOTHY S. COLLETT Branch of Petroleum Geology United States Geological Survey Denver Federal Center Box 25046, MS-940 Denver, Colorado 80225Search for more papers by this author TIMOTHY S. COLLETT, TIMOTHY S. COLLETT Branch of Petroleum Geology United States Geological Survey Denver Federal Center Box 25046, MS-940 Denver, Colorado 80225Search for more papers by this author First published: April 1994 https://doi.org/10.1111/j.1749-6632.1994.tb38839.xCitations: 12 a This study was partially funded by the U.S. Geological Survey Global Change and Climate History Program and the U.S. Department of Energy (interagency agreement no. DE-AI21-83MC20422). AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume715, Issue1Natural Gas HydratesApril 1994Pages 247-269 RelatedInformation