The influence of fault geometric uncertainty on hydrocarbon reservoir and simulation models

The impact of uncertainty in the geometry of normal faults upon hydrocarbon reservoir models has been assessed at the exploration-, field- and individual fault scale. At the exploration-scale synthetic 2D seismic sections generated using mapped geometries from the Gulf of Corinth rift illustrate the uncertainty in along strike fault geometry and displacement continuity when correlating between disparate seismic lines. This uncertainty has implications for pore pressure prediction, spill point identification and calculation of hydrocarbon column heights. At the hydrocarbon field-scale, incorporation of sub-seismic structure has been quantified using reservoir production simulations. Although the inclusion of sub-seismic fault tips often leads to increased reservoir segmentation, this does not necessarily imply a detrimental impact upon hydrocarbon production. Earlier onset of oil production decline for more segmented reservoirs is offset by a lower rate of decline due to an enhanced sweep pattern as well as a lower volume of produced water when compared to less segmented cases. 3D seismic forward modelling highlights the discrepancies between realistic, outcrop-derived fault geometries and those geometries resolvable in seismic data, with seismically resolvable faults significantly simplified in comparison to those observed at outcrop. Complex geometries such as displacement partitioning across multiple slip surfaces are hence not incorporated within reservoir models leading to the area of across-fault reservoir:reservoir juxtaposition being severely underestimated. In turn faults are modelled as overly retardant to flow, with the influence of fault rock properties being overstated. Where realistic (i.e. larger) areas of across-fault juxtaposition are modelled, the fault rock properties have less impact upon acrossfault hydrocarbon flux. Juxtaposition is therefore the first order control on hydrocarbon flow across faults.