Fault Seal Analysis Incorporating Shale Smear - Implications for Upscaling

Abstract

A simple 1D model has been built to include shale smear in quantitative fault seal prediction. The model uses well data in much the same way as the familiar triangle diagram. Instead of presenting the results as complex juxtaposition diagrams however, the model uses graphical outputs that focus only on windows in the predicted shale smear envelope. Individual smears are calculated using the shale Smear factor (SSF). The smear envelope is generated by mapping each potential smear onto the fault plane using a probabilistic approach, tied to a range of different shale smear geometries. The results show that the across-fault connectivity is affected by the smear placement model used together with the critical SSF for smear discontinuity. The 1D model also allows the impact of geocellular up-scaling to be assessed. First a high-fidelity layer model is built using the well data. This is then up-scaled to create a blocked model, which is then resampled to derive the equivalent “upscaled” layering. Layer thickness (rather than cell dimension) is an implicit requirement for smear prediction using the Shale Smear Factor (SSF). The 1D model is able to assess the impact of varying geocell dimensions on the fault seal prediction. Whether a fault becomes more or less sealing due to upscaling is a function of the net/gross and stacking pattern of the reservoir and seal layers.