OS22B-05
Preferential accumulation of gas hydrate in the Andaman accretionary wedge and relationship to anomalous porosity preservation
Tuesday, 15 December 2015: 11:20
3009 (Moscone West)
Marta E Torres1, Kelly Rose2, Joel E Johnson3, WeiLi Hong4, Liviu Giosan5, Evan A Solomon6, Miriam Kastner7, Thomas Cawthern3, Phillip Long8 and Todd Schaef9, (1)Oregon State Univ, College of Earth, Ocean, and Atmospheric Sciences, Corvallis, OR, United States, (2)National Energy Technology Lab, Albany, OR, United States, (3)University of New Hampshire Main Campus, Earth Sciences, Durham, NH, United States, (4)University of Tromso, CAGE, Tromso, Norway, (5)Woods Hole Oceanographic Inst, Woods Hole, MA, United States, (6)University of Washington, School of Oceanography, Seattle, WA, United States, (7)Scripps Institution of Oceanography, La Jolla, CA, United States, (8)Lawrence Berkeley National Laboratory, Berkeley, CA, United States, (9)Joint Global Change Research Institute, College Park, MD, United States
Abstract:
In the marine environment, sediments in the gas hydrate stability zone often correspond to slope and basin settings. These settings are dominantly composed of fine-grained silt and clay lithofacies with typically low vertical permeability, and pore fluids frequently under-saturated with respect to methane. As a result, the pressure-temperature conditions requisite for a GHSZ to be present occur widely worldwide across marine settings, however, the distribution of gas hydrate in these settings is neither ubiquitous nor uniform. This study uses sediment core and borehole related data recovered by drilling at Site 17 in the Andaman Sea during the Indian National Gas Hydrate Program Expedition 1 in 2006, to investigate reservoir-scale controls on gas hydrate distribution. In particular, this study finds that conditions beyond reservoir pressure, temperature, salinity, and gas concentration, appear to influence the concentration of gas hydrate in host sediments. Using field-generated datasets along with newly acquired sedimentology, physical property, imaging and geochemical data with mineral saturation and ion activity products of key mineral phases such as amorphous silica and calcite, we document the presence and nature of secondary precipitates that contributed to anomalous porosity preservation at Site 17 in the Andaman Sea. This study demonstrates the importance of grain-scale subsurface heterogeneities in controlling the occurrence and distribution of concentrated gas hydrate accumulations in marine sediments, and document the importance that increased permeability and enhanced porosity play in supporting gas concentrations sufficient to support gas hydrate formation. This illustrates the complex balance and lithology-driven controls on hydrate accumulations of higher concentrations and offers insights into what may control the occurrence and distribution of gas hydrate in other sedimentary settings.
