Christian Mueller1, Friedrich Theilen1, Bernd Milkereit1
(1) Kiel University, Kiel, Germany
ABSTRACT: Deep-Water Bright Spot Reflections in the Southern Canary Basin
A combined vertical-incidence and wide-angle seismic study provide strong evidences for the presence of large deep-water hydrocarbon reservoirs in Middle Miocene-age sediments with areal extents of more than 50 km2 in the Southern Canary Basin. Pronounced seismic bright spots at 300-800 m below seafloor are well imaged on multichannel reflection seismic sections (MCS) and Ocean-Bottom-Hydrophone (OBH) records, acquired on R/V POSEIDON in 1997 and 1999. Normal incidence reflection coefficients of R=-0.4, calculated from MCS shot records, indicate strong negative acoustic impedance contrasts, and mud diapirs, observed in the vicinity of the bright spots, outline vertical migration paths.
Recently, most seismic surveys approaching the deep-water area lack sufficient wide-angle reflections. During the second cruise, 15 OBHs have been deployed on the seafloor (3800 m water depth) to specify the seismic origin of the bright spots. The strong direct water wave, generally masking shallow primary reflections, could successfully be suppressed, enabling the application of semblance and amplitude-versus-offset analyses and full waveform inversion. Results confirm the assumption of a low acoustic impedance zone below the bright spots.
However, natural origin of the prominent bright spots remain unresolved. Circumstantial evidences such as occurrence of bright spots within the hydrate-stabilty-zone and existence of large magma volumes in the lower crust and upper mantle, point towards methane or carbon dioxide-rich volatiles trapped in the sedimentary sequence.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado