Gas hydrate and free gas petroleum system in 3D seismic data, offshore Angola

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doi: 10.1190/geo2012-0048.1
Author(s): Nyamapfumba, Martin; McMechan, George A.
Author Affiliation(s): Primary:
University of Texas at Dallas, Center for Lithospheric Studies, Richardson, TX, United States
Volume Title: Geophysics
Source: Geophysics, 77(6), p.O55-O63. Publisher: Society of Exploration Geophysicists, Tulsa, OK, United States. ISSN: 0016-8033 CODEN: GPYSA7
Note: In English. 25 refs.; illus., incl. sketch map
Summary: Evidence of gas hydrate and free gas occurrences in a 3D seismic volume from the West-Central Coastal Province of the Congo Fan, offshore Angola, illustrates all the components of a complete petroleum system. Analysis and interpretation are based on the information in attributes calculated from three 3D time-migrated common-angle seismic volumes; the attributes include seismic amplitude, spectral components, dip magnitude, amplitude variation with angle, and instantaneous frequency. The source is organic-rich muds associated with late Cretaceous to early Tertiary channels, the migration paths are along growth faults, and the traps are partly defined by the gas hydrate stability zone (for the gas hydrate), partly by the bottom-simulating reflector (for the subhydrate free gas), and partly by faults (for both). The spatial distribution of free gas is further supported by the associated seismic bright spots, and also by the attenuation of high frequencies of P-waves that traverse the gas-saturated zone. Locally higher temperatures, associated with upward fluid circulation along fault zones, facilitate gas transmission through the gas hydrate and forms gas chimneys that extend to the sea floor.
Year of Publication: 2012
Research Program: ODP Ocean Drilling Program
Key Words: 20 Geophysics, Applied; 29 Economic Geology, Energy Sources; Africa; Angola; Angola Basin; Atlantic Ocean; Bathymetry; Body waves; Cenozoic; Central Africa; Common-depth-point method; Congo Basin; Congo Delta; Congo Fan; Cretaceous; Elastic waves; Fault zones; Faults; Fluid phase; Gas hydrates; Geophysical methods; Leg 175; Lower Congo Basin; Lower Tertiary; Mesozoic; Natural gas; ODP Site 1075; ODP Site 1076; ODP Site 1077; Ocean Drilling Program; Offshore; P-waves; Petroleum; Petroleum exploration; Reflection methods; Seismic methods; Seismic waves; South Atlantic; Tertiary; Three-dimensional models; West Africa
Coordinates: S051048 S051048 E0102611 E0102611
S050408 S050408 E0110606 E0110606
S044707 S044707 E0100430 E0100430
Record ID: 2013010828
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