High Gas Hydrate and Free Gas Concentrations: An Explanation for Seeps Offshore South Mocha Island

Iván Vargas-Cordero, Umberta Tinivella, Lucía Villar-Muñoz and Joaquim P. Bento
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Iván Vargas-Cordero: Facultad de Ingeniería, Universidad Andres Bello (UNAB), 2531015 Viña del Mar, Chile
Umberta Tinivella: Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS), 34010 Trieste, Italy
Lucía Villar-Muñoz: Helmholtz Centre for Ocean Research (GEOMAR), 24148 Kiel, Germany
Joaquim P. Bento: Escuela de Ciencias del Mar, Pontificia Universidad Católica de Valparaíso, 2360007 Valparaíso, Chile

Energies, 2018, vol. 11, issue 11, 1-13

Abstract: Recent studies have reported cold seeps offshore of Mocha Island. Gas hydrate occurrences along the Chilean margin could explain seeps presence. Gas-phase (gas hydrate and free gas) and geothermal gradients were estimated analysing two seismic sections. Close to Mocha Island (up to 20 km) were detected high (up to 1900 m/s) and low (1260 m/s) velocities associated with high gas hydrate (up to 20% of total volume) and free gas (up to 1.1% of total volume) concentrations, respectively. A variable and high geothermal gradient (65–110 °C/km) was obtained. These results are related to high supply of deep fluids canalised by faults and fractures. Faraway from Mocha Island (>60 km), free gas concentrations decrease to 0.3% of total volume and low geothermal gradient (from 35 to 60 °C/km) are associated with low fluids supply. Finally, we propose gas hydrate dissociation processes as the main supply source for seeps in the vicinity of Mocha Island. These processes can be caused by: (a) active faults and seismic activity; and (b) warm fluid expulsion from deeper zones altering hydrate stability conditions. In both cases, gas hydrate dissociation could generate slope instability and landslides, as occurred in the past in this region and reported in the literature.

Keywords: gas hydrate; bottom simulating reflector (BSR); Mocha Island (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2018
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (2)

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