A new approach to bridge the effect of organofacies variations on kinetic modelling and geological extrapolations

Reliable prediction of petroleum formation is impeded by significant variations in organofacies that result from varying conditions during source rock deposition. Basin simulation programs can model lateral variations but are limited in their ability to account for vertical variations due to the impact on computation time and lack of representative kinetic parameters. Here we present a model that merges the petroleum formation characteristics of different organofacies, vertically distributed in a heterogeneous source rock, prior to kinetic modelling. This approach allows the evaluation of one single overall kinetic model that accounts for the different petroleum generation characteristics of a variety of organofacies preserved in a source rock and balance the different petroleum formation processes according to their importance within the different organofacies. Bulk petroleum generation kinetics were determined on eleven Draupne Formation samples taken from a well in the Tampen Spur area using programmed temperature open system pyrolysis at 0.1, 0.7 and 5.0 K/min. The samples covered the entire Draupne Formation from its bottom to its top in the studied well. Individual measurements taken at the same heating rate were summed to one pyrolysis yield curve and normalized to the average Rock-Eval S2 value. The three summed curves were then used as input to determine a kinetic model that is representative of the Draupne Formation in this well. Enhanced kinetic modelling was applied in order to account for the expected variations of frequency factors. After geological extrapolation, the resulting kinetic model represents the petroleum generation characteristics of the entire Draupne Formation in the study area, accounting for the variability in source potential across organofacies.