Fractured reservoirs modelling: a review of the challenges and some recent solutions

Although the specific flow behaviour of fractured reservoirs was identified and modelled a relatively long time ago (Barenblatt et al., 1960; Warren and Root, 1963), until recently no consistent methodology and software really enabled the integration of field information about natural fracturing in reservoir engineering studies. The availability of direct information about fractures, in particular borehole images, was an incentive for such integration. The unexpected production behaviour of many fields arising from an insufficient consideration of fracture effects on flow also emphasized the need for better characterizing the distribution of fractures at various scales and transferring the meaningful part of this information to field simulation models. A recent example concerns a giant Middle East Carbonate field where sub-seismic fracture swarms and stratiform super-K intervals were found to establish preferential flow paths between injection and production wells (Cosentino et al., 2001). Therefore, the present trend in fractured field studies is toward the use of methodologies and software platforms to integrate all information about fractures into flow simulation models. The main features of those methodologies are described here, on the basis of fracture modelling examples set up using our own workflow (Bourbiaux et al., 2002). The latter involves the following steps: ■ constrained modelling of the geological fracture network based on the analysis, interpolation, and extrapolation of fracture information acquired in wells and derived from seismic data, sometime completed by outcrop analogue data; ■ characterizing the hydrodynamic properties of this natural network from flow-related data; ■ choosing a flow simulation model suited to the role played by fractures and faults at various scales and assigning to this model upscaled parameters derived from the flow-calibrated geological fracture model; ■ simulating the reservoir flow behaviour on the basis of a physical assessment of multiphase flow mechanisms acting in transfers between matrix and fractures. In the following, those four steps are reviewed and illustrated from a representative synthetic field case. Emerging techniques to further capture the complexity and flow behaviour of fractured reservoirs are also identified.