AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Salt Tectonic Controls on Fluid Flow, Gas Hydrate Occurrence and Surface Heat Flow, Kwanza Basin, Offshore Angola
(1) SEAES, University of Manchester, Manchester, United Kingdom.
(2) Maersk Oil, Copenhagen, Denmark.
The occurrence of bottom simulating reflections (BSRs) in a recently acquired, high resolution, three-dimensional seismic survey in the Kwanza Basin indicates the likely and widespread existence of gas hydrate. BSRs are predominantly observed within salt withdrawal mini-basins and occur progressively shallower, up to depths very close to seafloor when directly overlying salt diapirs.
Thickness variations of the gas hydrate stability zone (GHSZ) are likely to be associated with local variation in the regional geothermal gradient, either linked to the presence of highly conductive salt diapirs, focused fluid flow pathways, or a combination of both.
Located in the contractional domain, salt re-mobilization into salt nappes and salt diapirs causes large heterogeneity within the sedimentary basin fill. The presence of large salt structures influences the overall thermal conductivity of the sedimentary column, but also enhances preferential fluid flow pathways, as shown by the presence of seep-related seafloor features including pockmarks, mud volcanoes, and potential gas hydrate mounds.
Thermal regime and heat flow distribution are essential to understand sedimentary basin evolution, and associated generation and migration of hydrocarbon and other fluid. Estimation of surface heat flow based on depths at the base of the GHSZ can help to constrain the upper boundary of the present state thermal regime generally derived from deep crustal structure and basal heat flow, as well as to highlight zone of preferential fluid flow pathways.