Hydrocarbon-bearing turbidite reservoirs are complex features, and their description needs to take into account heterogeneities at seismic and sub-seismic scales. The morphology and internal distribution of elementary channels are dependent on depositional setting, which controls the distribution of the main heterogeneities. The internal architecture of a channel complex is composed of multiple individual (elementary) channel stacks formed during repeated erosion/deposition cycles. A turbidite channel is not a simple funnel transporting sand to deep-sea areas but also may preserve slumps, collapse breccias and internal levees on its borders, resulting in the formation of internal heterogeneities (below seismic resolution). The sideways and down-dip movements of elementary channels in turbidite complexes show two typical patterns: lateral migration and vertical stacking. The spatial distribution of heterogeneities at the elementary channel margin is therefore constrained by the different channel patterns. Seismic data only display the outside geometry of channel lateral stack, i.e. a turbidite fairway.

Complexes of Laterally Offset Stacked Turbidite Channels (LOSCs) require a description based on the scale of individual channel bodies. The most common representation of channels in a fairway is by stochastic object modeling; i.e. populating the observed fairway with realistic forms representing individual channels, but with no established consistency between the individual channels. Furthermore, one essential characteristic of LOSCs is that they evolve by progressive migration laterally and/or down-dip. Stochastic object modeling provides an inadequate representation of this progressive evolution, and consequently a poor rendering of the heterogeneity distribution in the reservoir.

The methodology we propose consists of defining a realistic succession of individual channels that can accurately build the fairway observed on seismic. ‘Realism’ is defined using criteria from the shape of individual channels, and based on the amount of displacement necessary between successive episodes based on seismic interpretation.

This workflow, based on geometrical modeling, is illustrated using distinct Oligo-Miocene reservoirs from offshore Congo. The final result is a deterministic succession of channels laterally stacked to reproduce the envelope and lateral migration observed on seismic. Associated heterogeneities are integrated into the reservoir models using transmissibility multipliers, calibrated to match DST results and then applied to the entire models. The resulting architecture respects the natural architecture of the complex and provides a better simulation of flow pathways than that achieved by random object modeling. In the context of a pre-development initial reservoir model, the main interest of this method is to provide much more realistic long-term recovery factors for such complex reservoirs.

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