From stacking patterns to flow units: The approach to reservoir zonation and characterisation based on sequence stratigraphy

Stratal stacking patterns describe the architecture of the sedimentary record and provide the basis for defining all units and surfaces in sequence stratigraphy, in both upstream and downstream settings. At the high-resolution scale (i.e. below seismic resolution and generally referred to as the reservoir scale), sequence-stratigraphic surfaces determine reservoir zonation. A stratigraphic zone coincides with a systems tract because it is vertically separated from adjacent ones by sequence-stratigraphic surfaces. Within it, facies models rationalise the occurrence and lateral contacts between facies associations, which are vital for reservoir characterisation. A stratigraphic zone contains conformable, laterally adjacent facies associations that exhibit distinct petrophysical properties, which is consistent with the definition of flow units as distinct, mappable rock bodies based on their petrophysical properties. Hence, flow units naturally emerge from reservoir characterisation based on facies models constrained by stacking patterns that define reservoir zonation. This approach provides a common ground for understanding the reservoir's spatial distribution and heterogeneities, which are essential elements for 3D geological and fluid-flow models.