New insights brought by broadband seismic data on the Brazil-Angola conjugate margins Gregor Duval*, Jaswinder Mann, Lauren Houston and Steven Bowman Content Introductory remarks: why does the seismic interpreter need broadband data? Seismic surveys location (South Atlantic margin equivalence) and acquisition parameters Pre-salt exploration and broadband seismic imaging Post-salt broadband seismic benefits: facies mapping and reservoir characterisation Why does the seismic interpreter need broadband data? Effects and benefits of increasing the bandwidth 10-20Hz 10-25Hz 10-35Hz 10-30Hz Large side-lobes and broad central peak Sharper central peak Increasing high frequencies Increase low frequencies 10-20Hz 5-20Hz 2-20Hz Reduced side-lobes Effects and benefits of increasing the bandwidth BroadSeis Conventional 1000 m 20 m Conventional BroadSeis Courtesy of Total, Cobalt and the Republic of Gabon Effects and benefits of increasing the bandwidth Courtesy of Total, Cobalt and the Republic of Gabon Broadband 3D seismic surveys location and parameters Brazil Santos Basin – Broadband 3D survey Brazil Santos Basin – Broadband 3D survey Total area covered = 13,760km2 Streamer spread = 8000m x 10, 8100m x 12 BroadSeis streamer profile = 10m to 50m Streamer separation = 100m Shot-point interval = 25m Record length = 10sec PreSDM algorithm = Kirchhoff, AP-CBM and RTM Max depth output 10km Angola Kwanza Basin - Broadband 3D surveys Angola Kwanza Basin – Broadband 3D surveys Parameter Block 21 survey Block 22 survey Total area 4,300km2 2,915km2 Streamer length 8100m 8100m Number of streamers 12 12 BroadSeis streamer profile 8-50m 10-50m Streamer separation 100m 100m Shot-point interval 25m 25m Record length 10sec 9sec PreSDM algorithm CBM (fast-track) Kirchhoff (final) CBM and Kirchhoff Max depth output 12km 10km South Atlantic main geological features Cameia Lula Source: USGS Source: Bryant et al. 2012 BroadSeis 3D surveys South Atlantic equivalent margins cross-section Campos and Santos Basins Source: Cobalt International Energy Kwanza Basin, Angola Pre-salt exploration and broadband seismic imaging Brazil Campos/Santos Basins – Deep water pre-salt exploration history Field Year of discovery Water depth (m) Badejo 1975 100 Linguado 1978 100 Trilha 1982 100 Lula (Tupi) 2006 2100 Carioca 2007 2100 Jupiter 2008 2100 Sapinhoa 2008 2100 Guarani 2009 2100 Franco 2010 2000 Libra 2010 2000 Angola Kwanza Basin - Deep water pre-salt exploration history Field Year of discovery Water depth (m) Mucua 1982 200 Denden 1983 200 Falcao 1992 200 Baleia 1996 800 Bicuar 2011 1500 Azul 2011 900 Cameia 2012 1700 Pre-salt seismic interpretation on conventional data Base of Aptian salt or Break-up unconformity ? ? Lower Cretaceous fault blocks ? ? ? Cross fault correlation with multiple choices ?? Any reflector can be correlated through faults 17 Pre-salt seismic interpretation on broadband data Base of Aptian salt or Break-up unconformity Lower Cretaceous fault blocks Cross fault correlation better understood Uniqueness of the correlation through faults 18 Brazil Santos Basin legacy PSTM data Brazil Santos Basin BroadSeis PSDM stretched to time Brazil Santos Basin – BroadSeis PSDM filtered Bandpass filter applied: 2-8 / 15-50 cycles per 1000m Brazil Santos Basin – BroadSeis PSDM Brazil Santos Basin – BroadSeis PSDM interpreted Top Aptian evaporites Base Aptian evaporites Base sag/Top syn-rift? Angola Kwanza Basin – BroadSeis PSDM filtered Cameia structure Bandpass filter applied: 2-8 / 15-50 cycles per 1000m Angola Kwanza Basin – BroadSeis PSDM Cameia structure Angola Kwanza Basin – BroadSeis PSDM interpreted Top Albian carbonates Top salt Base salt Base sag sequence Basement Angola Kwanza Basin – BroadSeis PSDM filtered Cameia structure Bandpass filter applied: 2-8 / 15-50 cycles per 1000m Angola Kwanza Basin – BroadSeis PSDM Cameia structure Angola Kwanza Basin – BroadSeis PSDM interpreted Top Albian carbonates Top salt Base salt Base sag sequence Post-salt broadband seismic benefits: facies mapping and reservoir characterisation Brazil Santos Basin – Phase 6B location Cabo Frio High (north extension of the Abrolhos Volcanic Complex Source: Parsons et al. 2003 Brazil Santos Basin - Post-salt volcanics Brazil Santos Basin - Post-salt volcanics Extensional faults Relic volcano ? Igneous intrusives Top salt 33 Brazil Santos Basin - Post-salt volcanics 34 Brazil Santos Basin - Post-salt volcanics 3 phases of volcanism 35 Brazil Santos Basin - Atlanta Discovery inline 36 Brazil Santos Basin - Atlanta Discovery inline Atlanta field flat spot 37 Brazil Santos Basin - Atlanta Discovery crossline 38 Brazil Santos Basin - Atlanta Discovery crossline 39 Brazil Santos Basin - Atlanta Discovery crossline (zoom) Brightening of top reservoir within closure OWC 40 Time-slice - Conventional vs. Broadband Better fault definition Conventional Broadband Time slice extracted through Atlanta’s OWC 41 Atlanta Discovery - Top reservoir Oligocene depth structure map 42 Oligocene amplitude map Atlanta Discovery - Acoustic inversion results Initial model Filter 2-5Hz ACOUSTIC IMPEDANCE HIGH Conventional Broadband LOW Atlanta Discovery - Acoustic inversion results Conventional Atlanta Discovery - Acoustic inversion results Broadband Building the initial Vp model with broadband data Well A Well C Well B Initial Model (Seismic velocity) Initial model 21 dB VDS Well 2000 m/s 4500 CDS Remarks Constant Depth Streamer Variable Depth Streamer VS. Seismic velocity Well, interpretation,.. Seismic reflectivity Seismic velocity Seismic reflectivity Broadband data very useful for: • Quick look, uncalibrated inversion techniques • Use of seismic inversion in frontier areas (no well data) Angola Kwanza Basin – Sub-salt imaging Gulf of Mexico analogy – Conventional data Gulf of Mexico analogy – Broadband data Angola Kwanza Basin – Broadband PSTM ~2sec TWT DHI BroadSeis would give more high frequencies, as high as 250Hz, for sharp imaging of faults and small scale features Angola Kwanza Basin - Frequency decomposition Time slice at 2844ms 2.5Hz 5.2Hz 11.5Hz Gas cloud? ~2sec TWT Angola Kwanza Basin – Broadband PSTM BroadSeis would give more high frequencies, as high as 250Hz, for sharp imaging of faults and small scale features Angola Kwanza Basin – Frequency decomposition 2.5Hz Frequency decomposition of broadband data and volume blend 8.3Hz 15Hz The full range of frequencies offered by BroadSeis allows for highly detailed facies and structural mapping Angola Kwanza Basin – Frequency decomposition 2.5Hz 8.3Hz 15Hz Conclusions Broadband seismic data gives the following benefits on the South Atlantic Margins – Overall genuine formation signature: no side-lobes and sharper central peak – Strong basis for reservoir characterisation and pre-stack seismic inversion – Low frequencies penetrate deeper to help imaging trough salt bodies and interpret deep syn-rift fault blocks to better understand sub-salt plays – High frequencies allow for high resolution shallow imaging and subtle facies variations in the post-salt turbidite plays Acknowledgements Jaswinder Mann, Lauren Houston and Steven Bowman for their contributions to this presentation CGG multi-client division for permission to show these data examples
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