(Table T1) Gas hydrate fabric and dipping angles of ODP Leg 204 sediments

The sediments of Hydrate Ridge/Cascadia margin contain extensive amounts of gas hydrate. A total of 57 sediment samples including gas hydrate were preserved in liquid nitrogen and have been imaged using computerized tomography to visualize hydrate distribution and shape. The analysis gives evidence that gas hydrate in vein and veinlet structures is the predominant shape in the deeper gas hydrate stability zone with dipping angles from 30° to 90°(vertical).

Degradation of [14C]GlcDGD in the marine sediment by monitoring radioactivity in the aqueous and gas phase using liquid scintillation counting (LSC) techniques

An experiment was conceived in which we monitored degradation of GlcDGD. Independent of the fate of the [14C]glucosyl headgroup after hydrolysis from the glycerol backbone, the 14C enters the aqueous or gas phase whereas the intact lipid is insoluble and remains in the sediment phase. Total degradation of GlcDGD then is obtained by combining the increase of radioactivity in the aqueous and gaseous phases. We chose two different sediment to perform this experiment. One is from microbially actie surface sediment sampled in February 2010 from the upper tidal flat of the German Wadden Sea near Wremen (53° 38' 0N, 8° 29' 30E). The other one is deep subsurface sediments recovered from northern Cascadia Margin during Integrated Ocean Drilling Program Expedition 311 [site U1326, 138.2 meters below seafloor (mbsf), in situ temperature 20 °C, water depth 1,828 m. We performed both alive and killed control experiments for comparison. Surface and subsurface sediment slurry were incubated in the dark at in situ temperature, 4 °C and 20 °C for 300 d, respectively. The sterilized slurry was stored at 20 °C. All incubations were carried out under N2 headspace to ensure anaerobic conditions. The sampling frequency was high during the first half-month, i.e., after 1, 2, 7, and 14 d; thereafter, the sediment slurry was sampled every 2 months. At each time point, samples were taken in triplicate for radioactivity measurements. After 300 d of incubation, no significant changes of radioactivity in the aqueous phase were detected. This may be the result of either the rapid turnover of released [14C] glucose or the relatively high limit of detection caused by the slight solubility (equivalent to 2% of initial radioactivity) of GlcDGD in water. Therefore, total degradation of GlcDGD in the dataset was calculated by combining radioactivity of DIC, CH4, and CO2, leading to a minimum estimate.

(Table 1) Mean grain sizes and standard deviations of gas hydrate samples

Methane hydrates are present in marine seep systems and occur within the gas hydrate stability zone. Very little is known about their crystallite sizes and size distributions because they are notoriously difficult to measure. Crystal size distributions are usually considered as one of the key petrophysical parameters because they influence mechanical properties and possible compositional changes, which may occur with changing environmental conditions. Variations in grain size are relevant for gas substitution in natural hydrates by replacing CH4 with CO2 for the purpose of carbon dioxide sequestration. Here we show that crystallite sizes of gas hydrates from some locations in the Indian Ocean, Gulf of Mexico and Black Sea are in the range of 200-400 µm; larger values were obtained for deeper-buried samples from ODP Leg 204. The crystallite sizes show generally a log-normal distribution and appear to vary sometimes rapidly with location.

Gas analysis of sediment cores from the Batumi seep area

Detailed knowledge of the extent of post-genetic modifications affecting shallow submarine hydrocarbons fueled from the deep subsurface is fundamental for evaluating source and reservoir properties. We investigated gases from a submarine high-flux seepage site in the anoxic Eastern Black Sea in order to elucidate molecular and isotopic alterations of low-molecular-weight hydrocarbons (LMWHC) associated with upward migration through the sediment and precipitation of shallow gas hydrates. For this, near-surface sediment pressure cores and free gas venting from the seafloor were collected using autoclave technology at the Batumi seep area at 845 m water depth within the gas hydrate stability zone. Vent gas, gas from pressure core degassing, and from hydrate dissociation were strongly dominated by methane (>99.85 mol.% of Sum[C1-C4, CO2]). Molecular ratios of LMWHC (C1/[C2 + C3] > 1000) and stable isotopic compositions of methane (d13C = -53.5 per mill V-PDB; D/H around -175 per mill SMOW) indicated predominant microbial methane formation. C1/C2+ ratios and stable isotopic compositions of LMWHC distinguished three gas types prevailing in the seepage area. Vent gas discharged into bottom waters was depleted in methane by >0.03 mol.% (Sum[C1-C4, CO2]) relative to the other gas types and the virtual lack of 14C-CH4 indicated a negligible input of methane from degradation of fresh organic matter. Of all gas types analyzed, vent gas was least affected by molecular fractionation, thus, its origin from the deep subsurface rather than from decomposing hydrates in near-surface sediments is likely. As a result of the anaerobic oxidation of methane, LMWHC in pressure cores in top sediments included smaller methane fractions [0.03 mol.% Sum(C1-C4, CO2)] than gas released from pressure cores of more deeply buried sediments, where the fraction of methane was maximal due to its preferential incorporation in hydrate lattices. No indications for stable carbon isotopic fractionations of methane during hydrate crystallization from vent gas were found. Enrichments of 14C-CH4 (1.4 pMC) in short cores relative to lower abundances (max. 0.6 pMC) in gas from long cores and gas hydrates substantiates recent methanogenesis utilizing modern organic matter deposited in top sediments of this high-flux hydrocarbon seep area.

Pore-water concentration of chloride in sediment cores and equilibrium temperatures and gas bubble analysis at ROV stations from the Vodyanitskii mud volcano

Vodyanitskii mud volcano is located at a depth of about 2070 m in the Sorokin Trough, Black sea. It is a 500-m wide and 20-m high cone surrounded by a depression, which is typical of many mud volcanoes in the Black Sea. 75 kHz sidescan sonar show different generations of mud flows that include mud breccia, authigenic carbonates, and gas hydrates that were sampled by gravity coring. The fluids that flow through or erupt with the mud are enriched in chloride (up to 650 mmol L**-1 at 150-cm sediment depth) suggesting a deep source, which is similar to the fluids of the close-by Dvurechenskii mud volcano. Direct observation with the remotely operated vehicle Quest revealed gas bubbles emanating at two distinct sites at the crest of the mud volcano, which confirms earlier observations of bubble-induced hydroacoustic anomalies in echosounder records. The sediments at the main bubble emission site show a thermal anomaly with temperatures at 60 cm sediment depth that were 0.9 °C warmer than the bottom water. Chemical and isotopic analyses of the emanated gas revealed that it consisted primarily of methane (99.8%) and was of microbial origin (dD-CH4 = -170.8 per mil (SMOW), d13C-CH4 = -61.0 per mil (V-PDB), d13C-C2H6 = -44.0 per mil (V-PDB)). The gas flux was estimated using the video observations of the ROV. Assuming that the flux is constant with time, about 0.9 ± 0.5 x 10**6 mol of methane is released every year. This value is of the same order-of-magnitude as reported fluxes of dissolved methane released with pore water at other mud volcanoes. This suggests that bubble emanation is a significant pathway transporting methane from the sediments into the water column.

Gas hydrate investigation at the Amsterdam mud volcano

We investigated gas hydrate in situ inventories as well as the composition and principal transport mechanisms of fluids expelled at the Amsterdam mud volcano (AMV; 2,025 m water depth) in the Eastern Mediterranean Sea. Pressure coring (the only technique preventing hydrates from decomposition during recovery) was used for the quantification of light hydrocarbons in near-surface deposits. The cores (up to 2.5 m in length) were retrieved with an autoclave piston corer, and served for analyses of gas quantities and compositions, and pore-water chemistry. For comparison, gravity cores from sites at the summit and beyond the AMV were analyzed. A prevalence of thermogenic light hydrocarbons was inferred from average C1/C2+ ratios <35 and d13C-CH4 values of -50.6 per mil. Gas venting from the seafloor indicated methane oversaturation, and volumetric gas-sediment ratios of up to 17.0 in pressure cores taken from the center demonstrated hydrate presence at the time of sampling. Relative enrichments in ethane, propane, and iso-butane in gas released from pressure cores, and from an intact hydrate piece compared to venting gas suggest incipient crystallization of hydrate structure II (sII). Nonetheless, the co-existence of sI hydrate can not be excluded from our dataset. Hydrates fill up to 16.7% of pore volume within the sediment interval between the base of the sulfate zone and the maximum sampling depth at the summit. The concave-down shapes of pore-water concentration profiles recorded in the center indicate the influence of upward-directed advection of low-salinity fluids/fluidized mud. Furthermore, the SO42- and Ba2+ pore-water profiles in the central part of the AMV demonstrate that sulfate reduction driven by the anaerobic oxidation of methane is complete at depths between 30 cm and 70 cm below seafloor. Our results indicate that methane oversaturation, high hydrostatic pressure, and elevated pore-water activity caused by low salinity promote fixing of considerable proportions of light hydrocarbons in shallow hydrates even at the summit of the AMV, and possibly also of other MVs in the region. Depending on their crystallographic structure, however, hydrates will already decompose and release hydrocarbon masses if sediment temperatures exceed ca. 19.3°C and 21.0°C, respectively. Based on observations from other mud volcanoes, the common occurrence of such temperatures induced by heat flux from below into the immediate subsurface appears likely for the AMV.

Application of gas hydrate equilibria prediction in process engineering

Desde hace cerca de dos siglos, los hidratos de gas han ganado un rol importante en la ingeniería de procesos, debido a su impacto económico y ambiental en la industria -- Cada día, más compañías e ingenieros ganan interés en este tema, a medida que nuevos desafíos muestran a los hidratos de gas como un factor crucial, haciendo su estudio una solución para un futuro próximo -- Los gases de hidrato son estructuras similares al hielo, compuestos de moléculas huéspedes de agua conteniendo compuestos gaseosos -- Existen naturalmente en condiciones de presiones altas y bajas temperaturas, condiciones típicas de algunos procesos químicos y petroquímicos [1] -- Basado en el trabajo doctoral de Windmeier [2] y el trabajo doctoral the Rock [3], la descripción termodinámica de las fases de los hidratos de gas es implementada siguiendo el estado del arte de la ciencia y la tecnología -- Con ayuda del Dortmund Data Bank (DDB) y el paquete de software correspondiente (DDBSP) [26], el desempeño del método fue mejorado y comparado con una gran cantidad de datos publicados alrededor del mundo -- También, la aplicabilidad de la predicción de los hidratos de gas fue estudiada enfocada en la ingeniería de procesos, con un caso de estudio relacionado con la extracción, producción y transporte del gas natural -- Fue determinado que la predicción de los hidratos de gas es crucial en el diseño del proceso del gas natural -- Donde, en las etapas de tratamiento del gas y procesamiento de líquido no se presenta ninguna formación, en la etapa de deshidratación una temperatura mínima de 290.15 K es crítica y para la extracción y transporte el uso de inhibidores es esencial -- Una composición másica de 40% de etilenglicol fue encontrada apropiada para prevenir la formación de hidrato de gas en la extracción y una composición másica de 20% de metanol en el transporte

Submarine landslides : selected studies in the U.S. Exclusive Economic Zone

Submarine Landslides: An Introduction 1 By RIo Lee, W.C. Schwab, and J.S. Booth U.S. Atlantic Continental Slope Landslides: Their Distribution, General Anributes, and Implications 14 By J.S. Booth, D.W. O'Leary, Peter Popenoe, and W.W. Danforth Submarine Mass Movement, a Formative Process of Passive Continental Margins: The Munson-Nygren Landslide Complex and the Southeast New England Landslide Complex 23 By D.W. O'Leary The Cape Fear Landslide: Slope Failure Associated with Salt Diapirism and Gas Hydrate Decomposition 40 By Peter Popenoe, E.A. Schmuck, and W.P. Dillon Ancient Crustal Fractures Control the Location and Size of Collapsed Blocks at the Blake Escarpment, East of Florida 54 By W.P. Dillon, J.S. Risch, K.M. Scanlon, P.C. Valentine, and Q.J. Huggett Tectonic and Stratigraphic Control on a Giant Submarine Slope Failure: Puerto Rico Insular Slope 60 By W.C. Schwab, W.W. Danforth, and K.M. Scanlon Slope Failure of Carbonate Sediment on the West Florida Slope 69 By D.C. Twichell, P.C. Valentine, and L.M. Parson Slope Failures in an Area of High Sedimentation Rate: Offshore Mississippi River Delta 79 By J.M. Coleman, D.B. Prior, L.E. Garrison, and H.J. Lee Salt Tectonics and Slope Failure in an Area of Salt Domes in the Northwestern Gulf of Mexico 92 By B.A. McGregor, R.G. Rothwell, N.H. Kenyon, and D.C. Twichell Slope Stability in Regions 01 Sea-Floor Gas Hydrate: Beaufort Sea Continental Slope 97 By R.E. Kayen and H.J. Lee Mass Movement Related to Large Submarine Canyons Along the Beringian Margin, Alaska 104 By P.R. Carlson, H.A. Karl, B.D. Edwards, J.V. Gardner, and R. Hall Comparison of Tectonic and Stratigraphic Control of Submarine Landslides on the Kodiak Upper Continental Slope, Alaska 117 By M.A. Hampton Submarine Landslides That Had a Significant Impact on Man and His Activities: Seward and Valdez, Alaska 123 By M.A. Hampton, R.W. Lemke, and H.W. Coulter Processes Controlling the Style of Mass Movement in Glaciomarine Sediment: Northeastern Gulf of Alaska 135 By W.C. Schwab and H.J. Lee Contents V VI Contents Liquefaction of Continental Shelf Sediment: The Northern California Earthquake of 1980 143 By M.E. Field A Submarine Landslide Associated with Shallow Sea-Floor Gas and Gas Hydrates off Northern California 151 By M.E. Field and J.H. Barber, Jr. Sur Submarine Landslide, a Deep-Water Sediment Slope Failure 158 By C.E. Gutmacher and W.R. Normark Seismically Induced Mudflow in Santa Barbara Basin, California 167 By B.D. Edwards, H.J. Lee, and M.E. Field Submarine Landslides in a Basin and Ridge Setting, Southern California 176 By M.E. Field and B.D. Edwards Giant Volcano-Related Landslides and the Development of the Hawaiian Islands 184 By W.R. Normark, J.G. Moore, and M.E. Torresan Submarine Slope Failures Initiated by Hurricane Iwa, Kahe Point, Oahu, Hawaii 197 By W.R. Normark, Pat Wilde, J.F. Campbell, T.E. Chase, and Bruce Tsutsui (PDF contains 210 pages)

Avaliação do possível impacto das técnicas de MEOR (Microbial Enhanced Oil Recovery) no fator de recuperação das reservas de petróleo e gás do Brasil

Os métodos tradicionais de estimular a produção de petróleo, envolvendo a injeção de água, vapor, gás ou outros produtos, estabeleceram a base conceitual para novos métodos de extração de óleo, utilizando micro-organismos e processos biológicos. As tecnologias que empregam os processos de bioestimulação e bioaumentação já são amplamente utilizadas em inúmeras aplicações industriais, farmacêuticas e agroindustriais, e mais recentemente, na indústria do petróleo. Dada a enorme dimensão econômica da indústria do petróleo, qualquer tecnologia que possa aumentar a produção ou o fator de recuperação de um campo petrolífero gera a expectativa de grandes benefícios técnicos, econômicos e estratégicos. Buscando avaliar o possível impacto de MEOR (microbial enhanced oil recovery) no fator de recuperação das reservas de óleo e gás no Brasil, e quais técnicas poderiam ser mais indicadas, foi feito um amplo estudo dessas técnicas e de diversos aspectos da geologia no Brasil. Também foram realizados estudos preliminares de uma técnica de MEOR (bioacidificação) com possível aplicabilidade em reservatórios brasileiros. Os resultados demonstram que as técnicas de MEOR podem ser eficazes na produção, solubilização, emulsificação ou transformação de diversos compostos, e que podem promover outros efeitos físicos no óleo ou na matriz da rocha reservatório. Também foram identificadas bacias petrolíferas brasileiras e recursos não convencionais com maior potencial para utilização de determinadas técnicas de MEOR. Finalmente, foram identificadas algumas técnicas de MEOR que merecem maiores estudos, entre as técnicas mais consolidadas (como a produção de biossurfatantes e biopolímeros, e o controle da biocorrosão), e as que ainda não foram completamente viabilizadas (como a gaseificação de carvão, óleo e matéria orgânica; a dissociação microbiana de hidratos de gás; a bioconversão de CO2 em metano; e a bioacidificação). Apesar de seu potencial ainda não ser amplamente reconhecido, as técnicas de MEOR representam o limiar de uma nova era na estimulação da produção de recursos petrolíferos existentes, e até mesmo para os planos de desenvolvimento de novas áreas petrolíferas e recursos energéticos. Este trabalho fornece o embasamento técnico para sugerir novas iniciativas, reconhecer o potencial estratégico de MEOR, e para ajudar a realizar seu pleno potencial e seus benefícios.

Methane-derived authigenic carbonates from the Ulleung basin sediments, East Sea of Korea

Authigenic carbonates were sampled in methane-enriched piston core sediments collected from gas venting sites on the western continental slope of the Ulleung Basin, East Sea of Korea. Multidisciplinary investigations on these carbonates, including the scanning electronic microscope (SEM) observations and mineralogical-geochemical compositions, were carried out to identify the carbon and oxygen sources and the forming mechanism of these carbonates. The authigenic carbonates from the study area correspond to semi-consolidated, compact concretions or nodules ranging from 2 to 9 cm in size. X-ray diffraction and electron microprobe analyses showed that most of the sampled carbonate concretions were composed of almost purely authigenic high-Mg calcite (10.7-14.3 mol% MgCO3). Characteristically, microbial structures such as filaments and rods, which were probably associated with the authigenic minerals, were abundantly observed within the carbonate matrix. The carbonates were strongly depleted in delta C-13 (-33.85 parts per thousand to -39.53 parts per thousand Peedee Belemnite (PDB)) and were enriched in delta O-18 (5.16-5.60 parts per thousand PDB), indicating that the primary source of carbon is mainly derived from the anaerobic oxidation of methane. Such methane probably originated from the destabilization of the underlying gas hydrates as strongly supporting from the enriched O-18 levels. Furthermore, the strongly depleted delta C-13 values (-60.7 parts per thousand to -61.6 parts per thousand PDB) of the sediment void gases demonstrate that the majority of the gas venting at the Ulleung Basin is microbial methane by CO2 reduction. This study provides another example for the formation mechanism of methane-derived authigenic carbonates associated with gas-hydrate decomposition in gas-seeping pockmark environments. (c) 2009 Elsevier Ltd. All rights reserved.