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Assessing Hydrocarbon Migration in the Hekkingen Formation Source-Rock — A New 3-D Look at the Hammerfest Basin, Barents Sea


The Late Jurassic Hekkingen Formation, an approximate time equivalent to the North Sea Kimmeridge Clay, is as a prolific, oil-prone source-rock in the Norwegian Barents Sea. Despite its limited regional oil window maturity, it is regarded as the main source of many hydrocarbon finds in deeper-seated Early to Middle Jurassic reservoir rocks, particularly within the Hammerfest Basin. This source-rock is a dark gray shale, deposited under restricted marine / deep marine conditions and considered homogenous. Still, thin sand bodies are reported in several wells but their origin and lateral extend are poorly examined. We presume that HC migration pattern within the Hekkingen Formation may play a crucial yet underestimated role in explaining HC observations in associated older reservoirs. We aim to investigate if lithological variations in this source-rock direct HC flow and thus pre-define zones that are particularly prone for HC liberation. Furthermore, we investigate how such intra-source-rock flow relates to the unit's source-rock potential variation and their impact on the secondary migration pattern in the older carrier units in the basin. In order to test our assumptions, we built a detailed Hammerfest Basin model at a lateral resolution of 400m × 400m, with a particular focus on the Hekkingen Formation. This unit was discretized into 100 isochronous sub layers, representing less than a few meters thickness each. Results of a 3-D source-rock modelling study (de Jager et al., 2015, this conference) performed to model the distributions of the inorganic (sand, shale) and the organic (TOC, HI) components of the source, are used to populate the Hekkingen unit in our basin model. Detailed representations of HC migration within fine-grained siliciclastic source-rocks are often very limited in basin models. We employ a novel model approach that accounts for a high-resolution vertical description of the entry pressure field at basin scale. This enables the simulator to model migration into thin porous stringers (e.g. thief zones that transfer oil and gas laterally into faults) embedded in shales and thus exploits 3-D source-model results at high resolution. Important modelling results include the visualization of the detailed HC migration pattern histories within the 3-D Hekkingen Formation source-rock basin model. In-depth analysis can reveal how these results relate to the HC migration pattern and well site observations in the Early/Middle Jurassic Stø Formation.