Validation of Fault Seal Prediction Tools, a Case Study in the Permian Rotliegend, Dutch North Sea

Summary Two case studies of Permian Rotliegend fields from the Dutch offshore area have been carried out to investigate the validity of property transformation functions estimating threshold entry pressures of fault rock ( Bretan et al. 2003 , Sperrevik et al. 2002 ). These SGR (Shale Gouge Ratio) based functions have been calibrated to Jurassic, Brent type of rock and field data, with clay smearing as the dominant fault sealing mechanism. The theoretical foundation for these algorithms however does not appear to capture the (cataclastic) mechanisms likely to be at play in the fault rocks observed to be present in core at Permian Rotliegend level. One case study is presented here in which the estimated threshold entry pressures are compared against actual pressure data from two wells on either side of a partly-sealing fault, both on a geological and a production timescale. Conclusions from this case study are a.o. that the two functions tested appear to predict required threshold entry pressure levels accurately, within an uncertainty range, which was somehow unexpected in view of the above.