Initiation of gas-hydrate pockmark in deep-water Nigeria: Geo-mechanical analysis and modelling

Type Article
Date 2016-01
Language English
Author(s) Riboulot VincentORCID1, Sultan NabilORCID1, Imbert P.2, Ker StephanORCID1
Affiliation(s) 1 : IFREMER, Inst CARNOT EDROME, Ctr Brest, Brest, France.
2 : TOTAL, Pau, France.
Source Earth And Planetary Science Letters (0012-821X) (Elsevier Science Bv), 2016-01 , Vol. 434 , P. 252-263
DOI 10.1016/j.epsl.2015.11.047
WOS© Times Cited 25
Keyword(s) pockmarks, gas hydrates, VHR seismic data, piezocone, numerical modelling, Niger Delta
Abstract A review of recent literature shows that two geomorphologically different types of pockmarks, contribute to gas seepage at the seafloor. Type-1 pockmarks are defined as seafloor craters associated to fluid seepage and are the most classical type referred to as “pockmarks” in the literature. In contrast, Type-2 pockmarks reveal a complex seafloor morphology that may result from the formation/decomposition of gas hydrates in underlying sedimentary layers.

Interpretation of very-high-resolution seismic data, sedimentological analyses and geotechnical measurements acquired from the Eastern Niger Submarine Delta reveal that Type-2 pockmarks are associated to the presence at depth of a conical body of massive gas hydrates. Based on acquired data, theoretical analysis and numerical modelling, it was possible to propose a novel geo-mechanical mechanism controlling the irregular seafloor deformations associated to Type-2 pockmark and to show that pockmark shapes and sizes are directly linked to the initial growth and distribution of sub-seafloor gas hydrates. The study illustrates the role of gas hydrates formation in the fracturation, deformation of the subsurface sediment and the formation of Type-2 pockmarks.
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