Preprint Article Version 1 This version is not peer-reviewed

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

Version 1 : Received: 9 August 2018 / Approved: 9 August 2018 / Online: 9 August 2018 (09:46:14 CEST)

A peer-reviewed article of this Preprint also exists.

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. 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.

Journal reference: Energies 2018, 11, 3062
DOI: 10.3390/en11113062

Abstract

Recent studies have reported shallow and deep seep areas offshore Mocha island. Gas hydrate occurrences along the Chilean margin could explain seeps presence. Gas phases (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. These values are in agreement with a variable and high geothermal gradient (65 to 110 °C/km) related to high supply deep fluids canalised by faults and fractures. Faraway from Mocha island (more than 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 triggered by ancient sliding reported in literature.

Subject Areas

gas hydrate; BSR; Mocha island; gas-phases

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