Analysis of the impact of sedimentological heterogeneity and fractures on fluid flow properties in a deltaic reservoir setting using numerical models

Abstract

Process-based numerical simulations in river delta modelling have demonstrated the importance of hydraulic and sedimentary forcing mechanisms on delta morphodynamics. Insights of these simulations on deltaic systems have a high potential to improve reservoir predictions in the industry. However, detailed morphological studies are typically conducted in a qualitative manner which provides unsatisfactory results for reservoir characterisations. This work presents a systematic workflow to perform semi-quantitative classification of process-based deltaic models created in Delft3D-FLOW with the use of dynamic reservoir flow models. The flow response of synthetic reservoir models is investigated using two Delft3D models which were modelled with varying sediment input conditions. Subdomains of the models were extracted and stacked onto each other to model sequence stratigraphic stacking pattern such as progradation, aggradation and retrogradation. Moreover, the effect of different orientations of production-injection well doublet and mechanical unit-confined fractures is investigated. As a proof of concept, a case study is conducted using 48 flow simulations. The results are investigated in terms of flow rates of the oil and water phase at the production well over time which is subsequently compared to average permeability maps of each individual parasequences. The findings are compared to sweep efficiencies per layer at the end of the flow simulation. Compared to finer sediment input compositions, the results suggest that coarser grained sediment input requires a lower pressure differential between injection and production well due to higher permeabilites but also a higher chance of quick water-breakthrough through a single parasequence. Furthermore, it was demonstrated that progradational stacking pattern result in a succession of parasequences with a higher area of incision compared to retrogradational stacking pattern which lead to improved vertical connectivity. The results show that the effect on the flow performance of the synthetic reservoir model is influenced stronger by the local occurrence of channels at the well location than the general stacking pattern. The results also indicate that fractures lead to higher differences in sweep efficiencies of individual parasequences, in particular when the fractures are orientated perpendicular to the main stream direction of the geological deposits. The work does not aim to present conclusive reservoir classification but should motivate other researchers to use the developed workflow for further quantitative reservoir analysis of Delft3D models.