The “C2” unit in the Morichal Member of the Miocene Oficina Formation at the Sincor field (East Venezuela Basin) is characterised by a succession of superposed deltaic cycles which control vertical and horizontal reservoir connectivity. In order to model this reservoir in three dimensions, a workflow was developed which addressed a series of specific challenges. First, the deltaic nature of the succession required that both distributary channel and mouth bar sandbodies had to be modelled according to the defined sequence stratigraphic framework. Second, the relationship between distributary channels and mouth bars had to be honoured. A third issue was that individual distributary channel sandbodies were on occasion thicker than the cycle to which they belonged (i.e. they eroded down into the underlying cycle), and the relationship between mouth bar and channel sandbodies in adjacent sequences was therefore broken. Although conceptually simple from a geological viewpoint, this aspect proved particularly difficult during 3D modelling.
This paper discusses the construction of the stratigraphic model, as well as that of the channel and mouth bar models. The workflow is based on existing stochastic approaches, arranged in nested steps dependent on the stratigraphic framework and on defined depositional processes in order to simulate reservoir distribution and partitioning. By integrating sedimentological observations and interpretations with existing modelling procedures, a reliable reservoir model can be built. The model is based on the observed sequence stratigraphic framework, and its infill takes into account the relationship between distributary channels and mouth bar deposits, derived from depositional processes. The model provides realistic distributions of the channel fills and mouth bar deposits at Sincor field using a multi-realisation scheme. Improved local vertical connectivity between individual sequences, caused by erosion of highstand mudstone seals and baffles, can effectively be simulated; this is of particular significance at Sincor where planned second-phase heavy oil recovery will depend on the use of steam-assisted gravity drainage.