Hydrate dissolution as a potential mechanism for pockmark formation in the Niger delta

Type Article
Date 2010-08
Language English
Author(s) Sultan Nabil1, Marsset Bruno1, Ker StephanORCID1, Marsset TaniaORCID1, Voisset Michel1, Vernant Antoine-Mathieu1, 3, Bayon Germain1, Cauquil Eric1, 2, Adamy J.2, Colliat J. L.2, Drapeau D.2
Affiliation(s) 1 : IFREMER, Dept Geosci Marines, F-29280 Plouzane, France.
2 : Total, F-92069 Paris, France.
Source Journal Of Geophysical Research-solid Earth (0148-0227) (Amer Geophysical Union), 2010-08 , Vol. 115 , N. B08101 , P. 1-33
DOI 10.1029/2010JB007453
WOS© Times Cited 62
Keyword(s) methane gas hydrate, sea floor, marine sediments, pore pressure, porous media, continental margin, clathrate hydrate, fluid flow, stability, slope
Abstract Based on acquired geophysical, geological and geotechnical data and modeling, we suggest hydrate dissolution to cause sediment collapse and pockmark formation in the Niger delta. Very high-resolution bathymetry data acquired from the Niger delta reveal the morphology of pockmarks with different shapes and sizes going from a small ring depression surrounding an irregular floor to more typical pockmarks with uniform depression. Geophysical data, in situ piezocone measurements, piezometer measurements and sediment cores demonstrate the presence of a common internal architecture of the studied pockmarks: inner sediments rich in gas hydrates surrounded by overpressured sediments. The temperature, pressure and salinity conditions of the studied area have allowed us to exclude the process of gas-hydrate dissociation (gas hydrate turns into free gas/water mixture) as a trigger of the observed pockmarks. Based on numerical modeling, we demonstrate that gas-hydrate dissolution (gas hydrate becomes mixture of water and dissolved gas) under a local decrease of the gas concentration at the base of the gas-hydrate occurrence zone (GHOZ) can explain the excess pore pressure and fluid flow surrounding the central hydrated area and the sediment collapse at the border of the GHOZ. The different deformation (or development) stages of the detected pockmarks confirm that a local process such as the amount of gas flow through faults rather than a regional one is at the origin of those depressions.
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Sultan Nabil, Marsset Bruno, Ker Stephan, Marsset Tania, Voisset Michel, Vernant Antoine-Mathieu, Bayon Germain, Cauquil Eric, Adamy J., Colliat J. L., Drapeau D. (2010). Hydrate dissolution as a potential mechanism for pockmark formation in the Niger delta. Journal Of Geophysical Research-solid Earth, 115(B08101), 1-33. Publisher's official version : https://doi.org/10.1029/2010JB007453 , Open Access version : https://archimer.ifremer.fr/doc/00012/12300/