Bhatnagar, Gaurav et al. (2011): Analytical theory relating the depth of the sulfate-methane transition to gas hydrate distribution and saturation

IODP 311
ODP 146
IODP 311 U1325
IODP 311 U1326
IODP 311 U1329
ODP 146 889


Bhatnagar, Gaurav
Rice University, Department of Chemical and Biomolecular Engineering, Houston, TX, United States

Chatterjee, Sayantan
Stockholms Universitet, Sweden

Chapman, Walter G.

Dugan, Brandon

Dickens, Gerald R.

Hirasaki, George J.

Analytical theory relating the depth of the sulfate-methane transition to gas hydrate distribution and saturation
Geochemistry, Geophysics, Geosystems - G (super 3)
American Geophysical Union and The Geochemical Society, United States
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.
Coverage:Geographic coordinates:
West:-127.0300East: -126.5206

Oceanography; aliphatic hydrocarbons; alkanes; anaerobic environment; Cascadia Basin; continental margin; distribution; East Pacific; Expedition 311; gas hydrates; hydrocarbons; Integrated Ocean Drilling Program; IODP Site U1325; IODP Site U1326; IODP Site U1329; Leg 146; marine sediments; marine transport; methane; North Pacific; Northeast Pacific; numerical models; Ocean Drilling Program; ocean floors; ODP Site 889; organic compounds; oxidation; Pacific Ocean; porosity; saturation; sediments; solubility; stability; sulfates; theoretical models; transport;