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The physics of gas chimney and pockmark formation, with implications for assessment of seafloor hazards and gas sequestration
Cathles, L. M.1; Su, Zheng2; Chen, Duofu3
2010
Source PublicationMARINE AND PETROLEUM GEOLOGY
ISSN0264-8172
Volume27Issue:1Pages:82-91
Contribution Rank[Cathles, L. M.] Cornell Univ, Dept Earth & Atmospher Sci, Ithaca, NY 14883 USA; [Su, Zheng] Chinese Acad Sci, Guangzhou Inst Energy Convers, CAS Key Lab Renewable Energy & Gas Hydrate, Guangzhou 510640, Guangdong, Peoples R China; [Chen, Duofu] Chinese Acad Sci, Guangzhou Inst Geochem, CAS Key Lab Marginal Sea Geol, Guangzhou 510640, Guangdong, Peoples R China
Corresponding Authorlmc19@cornell.edu
Cooperation Status国际
AbstractPockmarks form where fluids discharge through seafloor sediments rapidly enough to make them quick, and are common where gas is present in near-seafloor sediments. This paper investigates how gas might lead to pockmark formation. The process is envisioned as follows: a capillary seal traps gas beneath a fine-grained sediment layer or layers. perhaps layers whose pores have been reduced in size by hydrate crystallization. Gas accumulates until its pressure is sufficient for gas to invade the seal. The seal then fails completely (a unique aspect of capillary seals), releasing a large fraction of the accumulated gas into an upward-propagating gas chimney, which displaces water like a piston as it rises. Near the seafloor the water flow causes the sediments to become "quick" (i.e., liquefied) in the sense that grain-to-grain contact is lost and the grains are suspended dynamically by the upward flow. The quickened sediment is removed by ocean-bottom currents, and a pockmark is formed. Equations that approximately describe this gas-piston-water-drive show that deformation of the sediments above the chimney and water flow fast enough to quicken the sediments begins when the gas chimney reaches half way from the base of its source gas pocket to the seafloor. For uniform near-surface sediment permeability, this is a buoyancy control, not a permeability control. The rate the gas chimney grows depends on sediment permeability and the ratio of the depth below seafloor of the top of the gas pocket to the thickness of the gas pocket at the time of seal failure. Plausible estimates of these parameters suggest gas chimneys at Blake Ridge could reach the seafloor in less than a decade or more than a century, depending mainly on the permeability of the deforming near-surface sediments. Since these become quick before gas is expelled, gas venting will not provide a useful warning of the seafloor instabilities that are related to pockmark formation. However, detecting gas chimney growth might be a useful risk predictor. Any area underlain by a gas chimney that extends half way or more to the surface should be avoided. (C) 2009 Elsevier Ltd. All rights reserved.
SubtypeArticle
Other AbstractPockmarks form where fluids discharge through seafloor sediments rapidly enough to make them quick, and are common where gas is present in near-seafloor sediments. This paper investigates how gas might lead to pockmark formation. The process is envisioned as follows: a capillary seal traps gas beneath a fine-grained sediment layer or layers. perhaps layers whose pores have been reduced in size by hydrate crystallization. Gas accumulates until its pressure is sufficient for gas to invade the seal. The seal then fails completely (a unique aspect of capillary seals), releasing a large fraction of the accumulated gas into an upward-propagating gas chimney, which displaces water like a piston as it rises. Near the seafloor the water flow causes the sediments to become "quick" (i.e., liquefied) in the sense that grain-to-grain contact is lost and the grains are suspended dynamically by the upward flow. The quickened sediment is removed by ocean-bottom currents, and a pockmark is formed. Equations that approximately describe this gas-piston-water-drive show that deformation of the sediments above the chimney and water flow fast enough to quicken the sediments begins when the gas chimney reaches half way from the base of its source gas pocket to the seafloor. For uniform near-surface sediment permeability, this is a buoyancy control, not a permeability control. The rate the gas chimney grows depends on sediment permeability and the ratio of the depth below seafloor of the top of the gas pocket to the thickness of the gas pocket at the time of seal failure. Plausible estimates of these parameters suggest gas chimneys at Blake Ridge could reach the seafloor in less than a decade or more than a century, depending mainly on the permeability of the deforming near-surface sediments. Since these become quick before gas is expelled, gas venting will not provide a useful warning of the seafloor instabilities that are related to pockmark formation. However, detecting gas chimney growth might be a useful risk predictor. Any area underlain by a gas chimney that extends half way or more to the surface should be avoided. (C) 2009 Elsevier Ltd. All rights reserved.
KeywordHydrate Seal Capillary Seal Quick Sediments Gas Seepage Gas Chimneys Rate Of Gas Chimney Formation Pockmarks Seafloor Hazards Risk Co(2) Sequestration
Subject AreaGeology
WOS HeadingsScience & Technology ; Physical Sciences
DOI10.1016/j.marpetgeo.2009.09.010
WOS Subject ExtendedGeology
URL查看原文
WOS KeywordLOWER CONGO BASIN ; FLUID-FLOW ; NORWAY ; SLIDE
Indexed BySCI
Language英语
Funding Organization973 Program [2009CB219508]; National Science Foundation of China [40725011, U0733003]; China Scholarship Council
WOS SubjectGeosciences, Multidisciplinary
WOS IDWOS:000272308200007
Citation statistics
Document Type期刊论文
Identifierhttp://ir.giec.ac.cn/handle/344007/8521
Collection中国科学院广州能源研究所
Affiliation1.Cornell Univ, Dept Earth & Atmospher Sci, Ithaca, NY 14883 USA
2.Chinese Acad Sci, Guangzhou Inst Energy Convers, CAS Key Lab Renewable Energy & Gas Hydrate, Guangzhou 510640, Guangdong, Peoples R China
3.Chinese Acad Sci, Guangzhou Inst Geochem, CAS Key Lab Marginal Sea Geol, Guangzhou 510640, Guangdong, Peoples R China
Recommended Citation
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Cathles, L. M.,Su, Zheng,Chen, Duofu. The physics of gas chimney and pockmark formation, with implications for assessment of seafloor hazards and gas sequestration[J]. MARINE AND PETROLEUM GEOLOGY,2010,27(1):82-91.
APA Cathles, L. M.,Su, Zheng,&Chen, Duofu.(2010).The physics of gas chimney and pockmark formation, with implications for assessment of seafloor hazards and gas sequestration.MARINE AND PETROLEUM GEOLOGY,27(1),82-91.
MLA Cathles, L. M.,et al."The physics of gas chimney and pockmark formation, with implications for assessment of seafloor hazards and gas sequestration".MARINE AND PETROLEUM GEOLOGY 27.1(2010):82-91.
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