A Probabilistic Approach to Clay-Smear Fault Seal in Hydrocarbon Migration Modeling for the Tune Field

Sylta, Øyvind¹, Susanne Sperrevik² (1) SINTEF Petroleum Research, Trondheim, Norway (2) Norsk Hydro, Bergen, Norway

A simulation of hydrocarbon generation and migration into the Jurassic gas-condensate Tune Field south-west of Oseberg has been conducted using a Monte Carlo simulation approach. Tune contains a “proven” fault seal. A model for the entry pressure versus shale-gouge-ratio was implemented in a hydrocarbon migration simulator to account for clay­smear fault sealing. This model accounts for depth of faulting and changes in burial depths through time. The clay-smear model is based upon laboratory measurements of entry pres­sures and permeabilities from cored faults in well bores.

A reasonable match to the hydrocarbon migration pattern in the area was achieved through a manual calibration of the hydrocarbon migration model. It was not possible to completely match the drilled oil and gas columns in Tune. Two new parameters were there­fore introduced into the model: a “maximum diagenesis depth” and an up-scaling factor from the laboratory data to field scale fault seals.

A Monte Carlo simulation approach was adapted by specifying important input parame­ters (not only fault seal parameters) as probability distributions.. A very good match to the Tune wells was provided by the best of the 3000 runs that were completed. The best data fit resulted in an order of magnitude greater entry pressures than modelled by the published formula. There are also quite good simulation runs for scaling factors close to 1, but not for lower values. The study shows that the Monte Carlo approach can be used to bracket fault seal parameter ranges, and thereby reduce uncertainties in fault seal models.