EAGE/AAPG Workshop on Basin-Margin Wedge Exploration Plays

The Equatorial Brazilian Margin basins have experienced a complex tectonic history as a result of continental rifting and it is suggested that the margin hosts an abundance of structural traps generated by the wrench tectonics experienced during continental break-up. As the fault architecture displayed within each of the Equatorial Brazilian basins varies due to this transform tectonism, future exploration success within this region will depend on improved understanding of the structural and stratigraphic framework of each of the basins as trap identification is vital for prospect evaluation. This abstract compares the structural trapping mechanisms throughout the Equatorial Brazilian Margin basins and how this affects the hydrocarbon prospectivity of the province. CGG’s high quality seismic data will be used to provide an understanding of the structural development throughout the continental rifting phase into the present day structural styles. The structures are illustrated by example seismic sections taken from CGG’s 3D BM-FZA-6, BM-PAMA-8 and BM-CE-1&2 surveys.

Linking extensional basin formation and fill observational data to conceptual models is essential in order to reduce play element uncertainty, particularly as the high demand for new hydrocarbon resources drive exploration farther offshore where the technical challenges and cost increase significantly. The geologic variability on this kind of margin is considerable and margin-scale hydrocarbon system archetypes are only end-member combinations of a continuum of tectonic and depositional variables. In order to optimize the assessment of extensional margin hydrocarbon plays, we suggest a “Building Block” approach that isolates the characteristic tectonic and basin fill elements responsible for the basin architecture and the geometry of the basin infill, and from this, environments of deposition and the distribution of hydrocarbon system elements are predicted. Several key themes have emerged from this approach: 1) commonly used tectono-stratigraphic terminology, such as “syn-rift”, needs to be used with extreme caution when describing play elements as basin events are not a direct predictor of facies, the criteria for interpretation are non-diagnostic, and tectonic events are not always synchronous with stratigrahy; 2) extensional basin motifs can be delineated by contrasting the tectonic timing with the marine incursion timing and/or character, and that these motifs can help focus play prediction analogs; and 3) this methodology can be used for improved regional context specifically for basin margin wedge plays.

Within the last few years, exploration companies have applied principles of plate tectonics to extend and relate upper cretaceous turbidites fan plays westward from West Africa across the Equatorial Atlantic to French Guiana and Brazil and other countries of South America. Before Ghana oil discoveries, gravity tectonic was seen as for the main success key of the deep water exploration activities with the most favorable environment to preserve large accumulations in structural closures, highly prolific when HC charging is recent.

Short Abstract: “Reservoir Characteristics of Four Key Turbidite Depositional Facies”. John R. Dribus, Deposition of turbidite sediments can be divided into four distinct depositional members: the Upper Fan is comprised of a proximal canyon geometry, filled with highly amalgamated channels with little to no levee development. The Middle Fan develops at the toe of slope and is characterized by extensive aggrading channel levee systems which may be amalgamated at the central channel axis, but grade outward from the proximal levee to distal layered overbank facies. The Lower Fan member is comprised of unconfined massive to channelized amalgamated to layered sheets comprising the basin floor fan complex. These sheets are often comprised of numerous Bouma ab sequences forming a massive reservoir unit with excellent lateral continuity and rock volume. The fourth member of the system is the Mass Transport Complex (MTC) which forms along the slope away from the incised canyon systems and present a series of geometries ranging from slides and rafts, to slumps, to debris flows. These four depositional members comprise the laterally emplaced members of the turbidite system, and are often intercalated with very to ultra-fine-grained ductile pelagic mud condensed section.

In contrast to time seismic, reliable depth seismic is a good screening tool for petroleum systems analysis. With a constant temperature gradient across the area, the oil and gas windows are parallel to the water depth in a depth seismic section. Inversion of seismic processing velocities can be used to predict lithologies, porosity, pore pressure and uplift / erosion. Our presentation will show how we are using a consistent set of regional depth seismic sections together with Velocity Inversion as tools from the early play screening phase to the beginning of prospect evaluation. This method is especially well adapted to passive margins with deep water and little well control. We will show examples from passive margins in Australia and Norway.