--> --> Advanced Seismic Characterization and Reservoir Modeling of Deep-Water Turbidity System in Angola Offshore

2018 AAPG International Conference and Exhibition

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Advanced Seismic Characterization and Reservoir Modeling of Deep-Water Turbidity System in Angola Offshore

Abstract

Scope of work is to characterize at field scale a Miocene turbidity channel system, by a multidisciplinary approach integrating well, sedimentology and seismic inversion data with the ultimate goal to condition facies and reservoir property within the modeling workflow. The target field is hosted in the Tertiary clastic continental slope of the Angola passive margin. The reservoir is represented by an aggradational channel system, with amalgamated sinuous channels, deposited within a weakly confined context, slightly erosional at its base and with an overall fining upward pattern. The trap is mixed, with a fault-controlled culmination closed laterally by facies variations and sealed by a thick shale sequence. The seismic characterization was a multi-phase process which progressed in parallel with the appraisal and development phases, integrating, at each step, the new available G&G data, following ad hoc workflows. After the appraisal stage, the field-scale reservoir layering and its characterization were updated based on the seismic-sedimentological interpretation, considering both amplitudes and elastic parameters coming from deterministic inversion. The main depositional elements were identified and defined at various scale. Due to the complexity of reservoir response, their identification within the layering framework was supported by a seismic waveform classification. The computed facies maps provided the unbiased base to define, for each layer, the relevant segments, used to refine the properties-based seismic interpretation. The final elements of deposition and the Net Sand maps, quantitatively estimated from inverted properties, were harmonized in the structural framework and used to support the reservoir model update and, ultimately, derisk the new well locations. The production wells proved the robustness of the post-appraisal model, confirming the predicted net to gross and the overall reservoir quality. The drilling campaign supplied new data to refine the structural framework and calibrate the PSDM velocity (used to stretch the seismic partial stacks and run the inversion in depth domain). The revised depositional framework and the expected facies proportion were integrated as input for the reservoir model update and used, as prior condition, for geostatistical inversion. This approach led to robust litho-facies realizations, integrated in the final geological model and allowed managing the production phase at best.