Managing New Development Uncertainty with Scenarios and Multiscale Modelling: An Integrated Study of the Fogelberg Discovery

Recent hydrocarbon developments are generally characterised by high complexity and uncertainty with lower margins for error in an unpredictable financial market. This is further compounded by new oil and gas discoveries being typically smaller today, than in the past; highlighting the need for robust and fit-for-purpose reservoir models that accurately capture key uncertainties to inform management decisions and to help avoid substantial financial losses.

To make an informed decision on either field development or relinquishment of the Fogelberg production license on the Norwegian Continental Shelf (NCS), an alternative full field reservoir model was commissioned by one of the License partners of a complex stacked tidal bar system in the Norwegian Sea. The model includes an accurate representation of the underlying heterogeneities observed in a drill stem test (DST) performed in 2018, incorporating the spatial evolution of the tidal bar system including the placement of low permeability inter-bars to stylolitisation at core-plug scale. Furthermore, the model is robust enough to permit future forecasting and well planning required to enable a management decision.

A scenario-based modelling approach (after Bentley and Smith, 2008) based on three discrete concepts was undertaken, accounting for uncertainty in the spatial geometry of the tidal bar complexes. This approach was combined with a hierarchical modelling strategy to honour the depositional concept model and to provide modelling flexibility. Sub-cell resolution heterogeneity in the form of stylolites that were prevalent in cored intervals were incorporated using a multi-scale approach in the form of a representative elementary volume (REV). A full uncertainty ensemble was generated for each of the three modelling scenarios.

The model produced a robust match to the bottom hole pressure (BHP) reported during the DST and was used to generate production potential and optimize lower completion strategy, including a side-by-side comparison of recovery of horizontal wells with fishbone stimulation, hydraulic fracturing stimulation and unstimulated slotted liner completions. Based on new static and dynamic understanding of the reservoir, the license will be re-applied for with a view to future development.

This paper highlights the importance of managing uncertainty through the use of scenarios, their flexibility with ensembles and the use of a multi-scale approach to accurately represent the respective lengths at which heterogeneities occur to build a better knowledge of the subsurface. The work undertaken for this petroleum system is both highly relevant and transferable for the future transition of safe and permanent storage of carbon, hydrogen and nuclear storage.