A natural hydrate dissolution experiment on complex multi-component hydrates on the sea floor

Hester, Keith C.; Peltzer, Edward T.; Walz, P. M.; Dunk, Rachel M.; Sloan, E. Dendy; Brewer, Peter G.

doi:10.1016/j.gca.2009.08.007

Cited by 30 publications

(29 citation statements)

References 17 publications

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“…This is in line with previous findings at this and nearby sites (Hester et al, 2009;Pohlman et al, 2005). Despite technical challenges encountered during the deployment, the hydrocarbon concentrations measured between 09 October 2009 and 29 December 2009 are the highest ever reported in contact with hydrate and are consistent with expectations from diffusioncontrolled dissolution.…”

Section: Discussionsupporting

confidence: 91%

“…A handful of studies have explored hydrate dissolution in the field and through laboratory experiments (e.g. Egorov et al, 1999;Brewer et al, 2002;Rehder et al, 2004;Bigalke et al, 2009;Hester et al, 2009;Lapham et al, 2010Lapham et al, , 2012Lapham et al, , 2014, however, field results have been highly variable, occasionally contradictory, and remain difficult to reconcile with controlled laboratory findings. Rehder et al (2004) produced artificial hydrate in the lab and then transferred that hydrate to a field site where P/T conditions were within the stability zone for hydrate.…”

Section: Introductionmentioning

confidence: 99%

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Observing methane hydrate dissolution rates under sediment cover

et al. 2015

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Dissolution rates of naturally occurring gas hydrates vary by orders of magnitude across studies suggesting that environmental factors may influence hydrate dissolution. To determine the role that sediment cover plays in hydrate dissolution, we used a mini-pore fluid array sampler (mPFA) to continuously collect sediment porewater adjacent to a hydrate outcrop and maintain it at in situ pressure for later analysis. This allowed us to measure in situ dissolved hydrocarbon concentrations in the porewater over time without sample loss due to degassing. We deployed the mPFA at a hydrate outcrop at Barkley Canyon on the Cascadia Margin for nine months. This novel approach yielded concentration data that were used to determine the steady-state dissolution rate of the hydrate outcrop and test predictions of the diffusion-control model for dissolution in the field. In the lab, we conducted a series of experiments with artificial hydrate to directly compare dissolution rates between exposed and sediment-covered hydrate. The dissolution rate of the natural hydrate outcrop covered with sediment was 0.06 cm y −1 . The laboratory experiments of sediment-covered hydrate yielded dissolution rates of 0.6 ± 0.5 cm y −1 (n = 5). In both laboratory and field observations, the dissolution rate of hydrates exposed directly to bulk water (3.9 ± 1.7 cm y −1 and 3.5 cm y −1 respectively) was at least an order of magnitude faster than the dissolution rate of sediment covered hydrate. These results are consistent with expectations of diffusioncontrol and support this model of hydrate dissolution. In nature, sediment may account for the persistence of hydrate in otherwise methane-depleted environments by increasing the diffusive boundary layer and slowing the rate of molecular diffusion via porosity/tortuosity effects. We provide a number of "Lessons Learned" for improving the instrument design and for consideration during future studies.

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Section: Discussionsupporting

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Observing methane hydrate dissolution rates under sediment cover

et al. 2015

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“…We did not use an inverted barrel or benthic chamber inserted into the sediment [e.g., Sayles and Dickinson , 1991; Linke et al , 1994] to estimate methane seepage or even entrainment of bottom water into the sediments [ Tryon et al , 2002]. Like other authors we assumed that gas hydrate outcrops will dissolve over time in a diffusion‐controlled process and that proper hydrodynamical analyses are needed to determine mass transfer (dissolution) rates [ Egorov et al , 1999; Rehder et al , 2004; Bigalke et al , 2009; Hester et al , 2009; Rehder et al , 2009; Lapham et al , 2010]. Our aim was to use their results from experiments with extracted gas hydrates in‐situ or from pressure laboratory studies to estimate the seepage from gas hydrate outcrops “non‐invasively” with our IOV (without extracting a gas hydrate from sediments or using a benthic chamber).…”

Section: Discussionmentioning

confidence: 99%

Ocean circulation promotes methane release from gas hydrate outcrops at the NEPTUNE Canada Barkley Canyon node

Thomsen¹,

Barnes²,

Best³

et al. 2012

Geophysical Research Letters

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[1] The NEPTUNE Canada cabled observatory network enables non-destructive, controlled experiments and timeseries observations with mobile robots on gas hydrates and benthic community structure on a small plateau of about 1 km 2 at a water depth of 870 m in Barkley Canyon, about 100 km offshore Vancouver Island, British Columbia. A mobile Internet operated vehicle was used as an instrument platform to monitor and study up to 2000 m 2 of sediment surface in real-time. In 2010 the first mission of the robot was to investigate the importance of oscillatory deep ocean currents on methane release at continental margins. Previously, other experimental studies have indicated that methane release from gas hydrate outcrops is diffusion-controlled and should be much higher than seepage from buried hydrate in semipermeable sediments. Our results show that periods of enhanced bottom currents associated with diurnal shelf waves, internal semidiurnal tides, and also wind-generated near-inertial motions can modulate methane seepage. Flow dependent destruction of gas hydrates within the hydrate stability field is possible from enhanced bottom currents when hydrates are not covered by either seafloor biota or sediments. The calculated seepage varied between 40-400 mmol CH 4 m À2 s À1 . This is 1-3 orders of magnitude higher than dissolution rates of buried hydrates through permeable sediments and well within the experimentally derived range for exposed gas hydrates under different hydrodynamic boundary conditions. We conclude that submarine canyons which display high hydrodynamic activity can become key areas of enhanced seepage as a result of emerging weather patterns due to climate change. Citation: Thomsen, L., C. Barnes, M. Best, R. Chapman, B. Pirenne, R. Thomson, and J. Vogt (2012), Ocean circulation promotes methane release from gas hydrate outcrops at the NEPTUNE Canada Barkley

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“…Для разработки подводных газогидратных скоплений такого типа определенный интерес представляет метод растворения газовых гидратов в ненасыщенной метаном воде на месте их залегания и подъема получаемого раствора газа (при понижении давления превраща-ется в газоводяную смесь) на поверхность водоема. Лабораторные опыты в этом направлении показали способность газовых гидратов к растворению [Egorov, Tsypki, 1999;Rehder et al, 2004;Nihous et al, 2006;Hester et al, 2009;Bigalke et al, 2009]. Эксперименты в морских условиях по-казали, что растворение искусственно выращенных чистых гидратов метана можно описать с помощью модели диффузного приграничного слоя, при этом относительная скорость растворения искусственных гидратов чистого метана в морской воде согласуется с простой кинетикой растворения, контролируе-мой диффузией, и близка к 0.4 ммоля CH 4 /м 2 с [Rehder et al, 2004].…”

Section: The Experience Of Mapping Of Baikal Subsurface Gas Hydrates unclassified

“…Растворение гидратов в условиях водоемов рассмотрено в работах [Egorov, Tsypidn, 1999;Rehder et al, 2004;Nihous et al, 2006;Hester et al, 2009;Bigalke et al, 2009]. Дан-Рис.…”

Section: результаты и обсуждениеunclassified

The Experience of Mapping of Baikal Subsurface Gas Hydrates and Gas Recovery

2014

GiG

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Озеро Байкал является единственным пресноводным водоемом, в осадках которого обнаружены природные скопления газовых гидратов. За последнее десятилетие Байкал стал природной лабораторией по изучению их свойств, поисковых признаков и извлечения газа из приповерхностных (поддонных) газовых гидратов. Приведены основные результаты картирования кровли приповерхностных газовых гидратов и натурного эксперимента по извлечению газа из них в районе авандельты р. Голоустная.Газовый гидрат, добыча газа, оз. Байкал. Lake Baikal is the only fresh-water lake where natural gas hydrate accumulations were found in sediments. For the recent decade, Baikal has become a natural laboratory for investigation of the properties of gas hydrates, their indicators, and recovery of gas from subsurface (subbottom) gas hydrates. We present the main results of subsurface gas hydrate mapping and gas recovery test near the delta of the Goloustnaya River. THE EXPERIENCE OF MAPPING OF BAIKAL SUBSURFACE GAS HYDRATES AND GASGas hydrate, gas recovery, Lake Baikal ВВЕДЕНИЕ В настоящее время газовые гидраты рассматриваются как один из перспективных нетрадицион-ных источников природного газа [Макогон, 2003]. Согласно современным данным, для извлечения газа из подводных скоплений гидратов могут использоваться методы, основанные на понижении давления контактирующего с гидратным скоплением свободного газогидратообразователя, на нагреве гидратного скопления, закачке в него ингибитора (например, метанола) и на комбинации этих методов [Sunjay et al., 2011]. Первая опытная добыча такого газа была проведена на севере Канады в дельте р. Макензи (меж-дународный проект «Малик» [Collett, 2005]) и у берегов Японии [Cyranoski, 2013]. Большинство скоп-лений подводных газовых гидратов лежит на значительной глубине под дном, и для добычи из них газа требуется подводное бурение. С другой стороны, во многих районах Мирового океана обнаружены приповерхностные (поддонные) скопления гидратов, находящиеся на глубине до нескольких метров под дном или даже практически на дне (менее 0.5 м). Эти скопления гидратов связаны с очагами раз-грузки газа или газонасыщенных флюидов на дне (грязевые вулканы, газовые сипы и т.д.) [Гинзбург, Соловьев, 1994]. Разработка подходов к извлечению газа из скоплений приповерхностных газовых гид-ратов представляет несомненный интерес.Анализ известных газогидратопроявлений показал, что максимальная плотность запасов газовых гидратов связана как раз с указанными выше приповерхностными скоплениями газовых гидратов. Они расположены непосредственно вблизи дна, часто при относительно небольшой (от 400 м) глубине воды, и характеризуются большим объемным гидратосодержанием в донных отложениях (максимально до 35 %) [Гинзбург, Соловьев, 1994]. Для разработки подводных газогидратных скоплений такого типа

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A natural hydrate dissolution experiment on complex multi-component hydrates on the sea floor

Cited by 30 publications

References 17 publications

Observing methane hydrate dissolution rates under sediment cover

Observing methane hydrate dissolution rates under sediment cover

Ocean circulation promotes methane release from gas hydrate outcrops at the NEPTUNE Canada Barkley Canyon node

The Experience of Mapping of Baikal Subsurface Gas Hydrates and Gas Recovery

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