AAPG Annual Convention and Exhibition

Datapages, Inc.Print this page

Probabilistic Hydrocarbon Migration Modeling in the Utsira High Area, Norwegian North Sea


The Utsira High area in the Norwegian North Sea is a mature prolific hydrocarbon province with numerous proven oil and gas discoveries and fields at different stratigraphic levels. The Johan Sverdrup discovery made in 2010 is the largest new oil field found in Norway for the last 30 years and is believed to contain recoverable oil volumes of more than 300 MSm3 in thin Upper Jurassic sandstones. In order to improve our understanding of the hydrocarbon charge systems in the Utsira High area, a 3D migration modeling study has been undertaken. A probabilistic modeling approach was chosen in order to account for the geological uncertainties and to allow for an objective risking and evaluation of remaining undrilled exploration targets in the area. The stochastic simulations were performed using a Monte Carlo approach, where a large number of independent simulations are run and afterwards post-processed to compile probability distributions for the modeling results. The modeling results are compared to observation data from exploration wells to obtain an objective measure of the goodness of fit for each simulation. An iterative modeling procedure, where the input parameter probability distributions are updated between each Monte Carlo series, is used to improve the model calibration. A calibration database of 141 wells was used in the Utsira High study and the average misfit for the hydrocarbon column heights in the final Monte Carlo series is less than 25 meter. One of the key results from the migration modeling runs is maps of hydrocarbon migration through time. These maps show the modelled migration pathways, phases and oil and gas accumulations at each modelled timestep within a stratigraphic unit. By combining these results for all of the Monte Carlo realisations, estimates of the probability of migration and expected phases may be compiled for any location within the model volume. The results from the Utsira High migration modeling study are presented using different types of probabilistic migration and risk maps. The migration risk maps are shown to give a good match to the known major fields and discoveries in the Utsira High area. Some structures that have not yet been tested also show a high probability of charge in the migration model. These are generally either subtle traps or they are found in less explored sections of the stratigraphy. We find that stochastic migration modeling can be a powerful tool to highlight such overlooked exploration targets