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Energies 2018, 11(11), 3062; https://doi.org/10.3390/en11113062

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

1
Facultad de Ingeniería, Universidad Andres Bello (UNAB), 2531015 Viña del Mar, Chile
2
Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS), 34010 Trieste, Italy
3
Helmholtz Centre for Ocean Research (GEOMAR), 24148 Kiel, Germany
4
Escuela de Ciencias del Mar, Pontificia Universidad Católica de Valparaíso, 2360007 Valparaíso, Chile
*
Author to whom correspondence should be addressed.
Received: 8 August 2018 / Revised: 28 August 2018 / Accepted: 31 August 2018 / Published: 7 November 2018
(This article belongs to the Section Energy Sources)
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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. View Full-Text
Keywords: gas hydrate; bottom simulating reflector (BSR); Mocha Island gas hydrate; bottom simulating reflector (BSR); Mocha Island
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Vargas-Cordero, I.; Tinivella, U.; Villar-Muñoz, L.; Bento, J.P. High Gas Hydrate and Free Gas Concentrations: An Explanation for Seeps Offshore South Mocha Island. Energies 2018, 11, 3062.

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