Analytical theory relating the depth of the sulfate-methane transition to gas hydrate distribution and saturation

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doi: 10.1029/2010GC003397
Author(s): Bhatnagar, Gaurav; Chatterjee, Sayantan; Chapman, Walter G.; Dugan, Brandon; Dickens, Gerald R.; Hirasaki, George J.
Author Affiliation(s): Primary:
Rice University, Department of Chemical and Biomolecular Engineering, Houston, TX, United States
Stockholms Universitet, Sweden
Volume Title: Geochemistry, Geophysics, Geosystems - G<sup>3</sup>
Source: Geochemistry, Geophysics, Geosystems - G>3`, 12(3). Publisher: American Geophysical Union and The Geochemical Society, United States. ISSN: 1525-2027
Note: In English. Includes appendices. 58 refs.; illus., incl. 2 tables
Summary: We develop a theory that relates gas hydrate saturation in marine sediments to the depth of the sulfate-methane transition (SMT) zone below the seafloor using steady state, analytical expressions. These expressions are valid for systems in which all methane transported into the gas hydrate stability zone (GHSZ) comes from deeper external sources (i.e., advective systems). This advective constraint causes anaerobic oxidation of methane to be the only sulfate sink, allowing us to link SMT depth to net methane flux. We also develop analytical expressions that define the gas hydrate saturation profile based on SMT depth and site-specific parameters such as sedimentation rate, methane solubility, and porosity. We evaluate our analytical model at four drill sites along the Cascadia Margin where methane sources from depth dominate. With our model, we calculate average gas hydrate saturations across GHSZ and the top occurrence of gas hydrate at these sites as 0.4% and 120 mbsf (Site 889), 1.9% and 70 mbsf (Site U1325), 4.7% and 40 mbsf (Site U1326), and 0% (Site U1329), mbsf being meters below seafloor. These values compare favorably with average saturations and top occurrences computed from resistivity log and chloride data. The analytical expressions thus provide a fast and convenient method to calculate gas hydrate saturation and first-order occurrence at a given geologic setting where vertically upward advection dominates the methane flux.
Year of Publication: 2011
Research Program: IODP Integrated Ocean Drilling Program
ODP Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; Aliphatic hydrocarbons; Alkanes; Anaerobic environment; Cascadia Basin; Continental margin; Distribution; East Pacific; Expedition 311; Gas hydrates; Hydrocarbons; IODP Site U1325; IODP Site U1326; IODP Site U1329; Integrated Ocean Drilling Program; Leg 146; Marine sediments; Marine transport; Methane; North Pacific; Northeast Pacific; Numerical models; ODP Site 889; Ocean Drilling Program; Ocean floors; Organic compounds; Oxidation; Pacific Ocean; Porosity; Saturation; Sediments; Solubility; Stability; Sulfates; Theoretical models; Transport
Coordinates: N483800 N483800 W1270300 W1270300
N484151 N484159 W1265206 W1265223
N483900 N483900 W1265900 W1265900
Record ID: 2012021699
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