TY - JOUR
T1 - Thermal state and concentration of gas hydrate and free gas of Coyhaique, Chilean Margin (44°30′ S)
AU - Vargas-Cordero, I.
AU - Tinivella, U.
AU - Accaino, F.
AU - Loreto, M. F.
AU - Fanucci, F.
N1 - Funding Information:
The authors are very grateful to Joyce Alsop for the seismic data provided at Lamount Doherty Earth Laboratory, USA (LDEO). We thank Michela Giustiniani for useful discussions. We thank also to Ernest Ohene Asare and Frank Calixto Mory for useful English corrections. This work was partially supported by International Centre for Theoretical Physics (Trieste). The authors wish to thank the reviewers for their opportune comments.
PY - 2010/5
Y1 - 2010/5
N2 - In the last decades gas hydrate occurrence along the Chilean continental margin has been well documented. In order to better define the seismic character of the hydrate-bearing sediments, we performed a detailed velocity analysis by using the pre-stack depth migration on part of multichannel reflection seismic line RC2901-734 located offshore Coyhaique.The velocity model shows a hydrate bearing layer above the BSR, with high velocity (1700-2200ms-1) and maximum thickness of 250m and a free gas bearing layer below the BSR, characterized by low velocity (1250-1400ms-1). A weak reflector at about 70m below the BSR marks the base of the second layer.By knowing the BSR depth, the seafloor depth, and the sea bottom temperature, the geothermal gradient was estimated. The resulting gradient varies from 35 to 95°C km-1, with highest values at the structural high, and the lowest values located in the accretionary prism and in the fore arc basin.In order to quantify the amount of gas phase, the velocity model was converted into a gas-phase concentration model by using a theoretical approach. The results indicate that highest concentrations of gas hydrates, up to 23% of the total volume, are located in the fore-arc basin, and that highest concentration of free gas, up to 3% of the total volume, are located at the structural high, which may be considered as a natural trap for migrating fluids. Average concentrations are equal to 12% and 1% of total volume for gas hydrate and free gas, respectively.
AB - In the last decades gas hydrate occurrence along the Chilean continental margin has been well documented. In order to better define the seismic character of the hydrate-bearing sediments, we performed a detailed velocity analysis by using the pre-stack depth migration on part of multichannel reflection seismic line RC2901-734 located offshore Coyhaique.The velocity model shows a hydrate bearing layer above the BSR, with high velocity (1700-2200ms-1) and maximum thickness of 250m and a free gas bearing layer below the BSR, characterized by low velocity (1250-1400ms-1). A weak reflector at about 70m below the BSR marks the base of the second layer.By knowing the BSR depth, the seafloor depth, and the sea bottom temperature, the geothermal gradient was estimated. The resulting gradient varies from 35 to 95°C km-1, with highest values at the structural high, and the lowest values located in the accretionary prism and in the fore arc basin.In order to quantify the amount of gas phase, the velocity model was converted into a gas-phase concentration model by using a theoretical approach. The results indicate that highest concentrations of gas hydrates, up to 23% of the total volume, are located in the fore-arc basin, and that highest concentration of free gas, up to 3% of the total volume, are located at the structural high, which may be considered as a natural trap for migrating fluids. Average concentrations are equal to 12% and 1% of total volume for gas hydrate and free gas, respectively.
KW - BSR
KW - CIG analysis
KW - Chilean margin
KW - Gas hydrate
KW - Gas-phase concentration
KW - Pre-stack depth migration
KW - Seismic velocity
UR - http://www.scopus.com/inward/record.url?scp=77950925057&partnerID=8YFLogxK
U2 - 10.1016/j.marpetgeo.2010.02.011
DO - 10.1016/j.marpetgeo.2010.02.011
M3 - Article
AN - SCOPUS:77950925057
VL - 27
SP - 1148
EP - 1156
JO - Marine and Petroleum Geology
JF - Marine and Petroleum Geology
SN - 0264-8172
IS - 5
ER -