--> ABSTRACT: Seismic Visualization and Reservoir Characterization of Large-Scale Oolitic Carbonate Shoal Systems, Brazil, by Colpaert, Arnout; Dillon, Lucia ; Schwedersky Neto, Guenther; Coleou, Thierry; van Wijngaarden, Aart-Jan ; #90142 (2012)

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Seismic Visualization and Reservoir Characterization of Large-Scale Oolitic Carbonate Shoal Systems, Brazil

Colpaert, Arnout *1; Dillon, Lucia 1; Schwedersky Neto, Guenther 2; Coleou, Thierry 3; van Wijngaarden, Aart-Jan 1
(1) Statoil, Stavanger, Norway.
(2) Petrobras, Rio de Janeiro, Brazil.
(3) CGGVeritas, Paris, France.

Oolitic shoals are a common Albian carbonate play offshore Brazil. A unique dataset with good seismic quality in the Southern Santos Basin allows visualizing the shoals as individual geobodies and calibrating them with four wells. Lateral variability in reservoir quality and connectivity, as well as hydrocarbon saturations are identified and linked in with the shoal system morphology using an innovative workflow combining seismic visualization and extraction techniques (volume based interpretation techniques) together with a rock properties constrained seismic inversion.

Seismic geomorphology techniques with automated multi-attribute analyses, RGB blends from various frequency cubes and seismic facies classifications are linked in with well data. These techniques allow imaging of impressive oolitic shoal systems stacked in time and space revealing subsurface geometries that can be compared directly to present day carbonate shoal complexes. The distribution and shape of the individual shoals is controlled by subtle syn-sedimentary faulting and shows changing shoal shapes and sizes through geological time. Largest shoals are seen near the base of the complex becoming progressively smaller upwards going below seismic resolution in the youngest units. Understanding the geomorphic chance of the shoals is of primary importance for reservoir connectivity.

Our quantitative interpretation workflow is built around a petro-elastic inversion method that provides a direct estimation of reservoir geometry and petrophysical parameters from pre-stack seismic data, in our case: thicknesses, porosities and saturations. As the inversion is constrained by a rock physics model it respects variations in elastic properties due to e.g. multiple pore types and rock facies variability and gives us good estimates of porosity and saturation variability within and between the shoals. The thick individual shoals clearly show the best reservoir properties with dominant inter-particle pore network. Where no individual shoals are observed, the reservoir quality is significantly reduced with lower porosity and a higher percentage of micro-pores. However, we also observed that estimated oil saturation (up to max. 60%) is highest in the inter-shoal areas where the thick shoals only contain brine indicating that hydrocarbons are possibly irreducible in the inter-shoal areas which are characterized by much lower N/G, a lower layer connectivity and a much higher degree of micro-pores.

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California