Constraining basalt thickness and sub-basalt velocities by combined analysis of ocean-bottom seismic and streamer data

Lau, K. W. H. and White, R. S. and Christie, P. A. F. (2009) Constraining basalt thickness and sub-basalt velocities by combined analysis of ocean-bottom seismic and streamer data. In: 3rd Faroe Islands Exploration Conference, 15th - 16th September 2009, Tórshavn, Faroe Islands. (Unpublished)

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Combined analysis of ocean-bottom seismometer (OBS) and streamer data is critical in reducing uncertainty in sub-basalt exploration. A major concern is that errors in basalt thickness and sub- basalt velocities could result in a missed target in drilling; a mis-identification of base basalt can change the geological model. Standard streamer data analysis offers poor velocity estimation below top basalt while standard OBS data analysis gives weak depth control on base basalt. We provide extra constraint by interpreting the full offset extent of base basalt reflections and basalt diving waves. Our multi-step methods are: 1) identifying base basalt wide-angle reflections in OBS data and then their equivalent in the streamer data; 2) tracing the near-offset continuation of both wide- angle reflections into the respective water wave cones by means of multiple removal through predictive deconvolution, block shift and fk-filtering; 3) inverse ray modelling the basalt velocity using refracted basalt arrivals and base basalt depths from the full offset range of the base basalt reflection; 4) inputting model results to pre-stack depth migration velocity for modelling deeper layers. Here, we present results using data from the integrated Seismic Imaging and Modelling of Margins (iSIMM) Project, acquired across the Faroe-Shetland basin. Our results show well- constrained basalt velocities increasing from 4.5km/s at the top to 5.5km/s at the base, and thicknesses of up to 3km where basalts overlie a low velocity zone. A geologically-satisfying model of this low velocity zone is presented, with its base matching an observed basement reflection.

Item Type: Conference or Workshop Item (Other)
Additional Information: Schlumberger; cml
Uncontrolled Keywords: 09AREP; IA59;
Subjects: 02 - Geodynamics, Geophysics and Tectonics
Divisions: 02 - Geodynamics, Geophysics and Tectonics
Depositing User: Sarah Humbert
Date Deposited: 06 Feb 2010 00:18
Last Modified: 23 Jul 2013 09:56

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