Modeling Source Rock Quality and Distribution of the Upper Jurassic in the Northern North Sea: An OF-Mod (Organic Facies Modeling) Application

Mann, Ute, Janine Zweigel, Sintef Petroleum Research, Trondheim, Norway

The OF-Mod (Organic Facies Modelling) program is a process-based modeling tool, which mimics the development and the variation of source rock facies. It allows quantitative prediction of source rock potential away from well control and results in significantly improved input for kinetics, expulsion and migration studies.

In this study the program was applied to model the development of the Upper Jurassic Heather and Draupne fms. in the northern North Sea. As most of the available geochemical data of this area were from mature samples, the time-equivalent strata of the Froan basin (mid-Norway) were used as an ancient analogue to derive suitable input parameters for OF-Mod. In the Froan basin an extensive geochemical data set from immature samples was available, that allowed e.g. quantification of terrestrial versus marine organic material, esti­mation of palaeo-productivities and preservation.

Due to some uncertainty concerning oxygenation and thus preservation during the dep­osition of the Heather Fm, several scenarios were tested. All show the heterogeneous char­acter of the formation. Due to the high terrigenous organic matter component and dilution effects even the models assuming anoxic preservation exhibit only locally very good source rock potential. During the deposition of the Draupne Fm. anoxic conditions prevailed. Lower sedimentation rates and reduced input of terrigenous organic matter lead to the develop­ment of generally good to very good source rock potential. In contrast to previous models that predict the best source rock quality in the basin centers, the OF-Mod model predicts a rim pattern. Source rock richness and quality first increase away from the basin highs, but decrease again more basin wards due to the increasing dilution effect.