Gas hydrate and free gas estimation from seismic analysis offshore Chiloé island (Chile).

Vargas Cordero, Iván De la Cruz, Tinivella, Umberta, Villar Muñoz, Lucía Alejandra and Giustiniani, Michela (2016) Gas hydrate and free gas estimation from seismic analysis offshore Chiloé island (Chile). Open Access Andean Geology, 43 (3). pp. 263-274. DOI 10.5027/andgeoV43n3-a02.

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In this study one seismic section offshore Chiloé Island was analyzed to better define the seismic character of the hydrate-bearing sediments. The velocity analysis was used to estimate the gas-phase concentration and relate it to the geological features. The velocity model allowed us to recognize two important layers that characterize hydrate- and free gas-bearing sediments above and below the BSR respectively: one located above the BSR, characterized by high velocity (1,800-2,200 m/s) and a second one, below the BSR, characterized by low velocity (1,600-1,700 m/s). A weak reflector at about 100 m below the BSR marks the base of the second layer. AVO analysis and offset stack sections confirming that the reflector interpreted as BGR is related to free gas presence in the pore space. The velocity field is affected by lateral variation, showing maximum (above the BSR) and minimum (below the BSR) values in the sector. Here, the highest gas hydrate and free gas concentrations were calculated, obtaining 9.5% and 0.5% of total volume respectively. A variable BSR depth (from 300 to 600 mbsf) can be justified supposing a variable geothermal gradient (from 25 to 45 °C/km).

Document Type: Article
Keywords: AVO; BSR; BGR; Seismic analysis; Pre-stack depth migration; Free gas; Gas hydrates
Research affiliation: OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-GDY Marine Geodynamics
Refereed: Yes
Open Access Journal?: Yes
DOI etc.: 10.5027/andgeoV43n3-a02
ISSN: 0718-7092
Date Deposited: 06 Dec 2016 13:30
Last Modified: 01 Feb 2019 15:17

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