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TitreShallow geohazard assessment, RepsolYPF block30, Demerara Rise, offshore Suriname, South America
AuteurMosher, D C; Goss, S
SourceCommission géologique du Canada, Dossier public 6479, 2010, 24 pages, (Accès ouvert)
ÉditeurRessources naturelles Canada
Documentdossier public
Mediaen ligne; numérique
Lat/Long OENS-56.0000 -54.0000 9.0000 7.0000
Sujetspuits sous-marins; forage, large des côtes; plate-forme continentale; talus continental; sismicité; risque sismique; caractéristiques structurales; failles; bathymétrie; topographie du fond océanique; transport sous-marin; combustibles fossiles; géophysique
Illustrationslocation maps; profiles; seismic profiles; digital elevation models
ProgrammeLa géoscience pour les développements extracôtiers de la côte est, Géoscience en mer
Diffusé2010 06 10
Résumé(Sommaire disponible en anglais seulement)
The 3D seismic volume from Repsol YPF Block 30 of the Suriname continental margin transits from the shelf to slope environments. The region is a passive continental margin and seismicity is rare. A number of features are identified from the shallow, near surface section that represent potential geohazards or constraints to offshore hydrocarbon development. 1) Shallow faults break the seafloor producing clear offsets that correlate across the width of the survey area. Faults provide conduits for overpressured gas and fluids and provide planes of weakness for initiation of mass failures. Faults parallel the shelf break and extend laterally for significant distances, suggesting they are related to sediment loading and subsidence, further increasing their potential role in sediment mass failure. A major fault that offsets the seafloor breaks within 2 km of the West Tapir drill site. 2) Hard substrate: Variable and high amplitude reflections occur on the shelf. Combined with outcropping reflectors, these features suggest an erosional environment with a hard substrate. Strong currents, therefore, may be present. 3) Bright spots (high amplitude anomalies) are common beneath the uppermost slope. These anomalies possibly represent shallow gas or sand bodies (channels). The may be indicative of shallow overpressure, which in turn may pre-condition the sediments to mass failure. In this region also, seafloor slope angles are steepest (~3°) and there is evidence of buried headscarps suggesting mass-failures have occurred. 4) A possible BSR (bottom simulating reflector), indicative of the base of gas hydrate, was noted in the upperslope region. Gas hydrate dissociation can lead to formation overpressures and lead to slope failure. 5) Mass transport deposits are indicated by bodies of incoherent reflections with irregular contacts and surface renders showing 0.1 s high head scarps, lateral escarpments, and rugose surface patterns fanning out downslope. Although the low angles of the slope in this region suggest static stability, these deposits indicate mass failures have occurred in the past. Trigger mechanisms are unknown, but possibly relate to ground motions due to rare earthquakes. Shallow gas, gas hydrate dissociation and periods of high sediment input may be contributing factors. Recurrence intervals are unknown but presumably are rare because of the combination of events required to initiate failure. The shallowest mass transport deposit is buried by ~0.2 s of parallel, coherent reflections forming the present seafloor. Shallow mass transport deposits can consist of a variety of lithologies of varying strength properties and states of consolidation. They can; therefore, pose drilling difficulties.