The upper reservoir intervals of the Lower Jurassic Åre Formation in the Heidrun Field (Offshore mid-Norway) are very heterolithic and have the lowest oil recovery factor of the field despite significant amounts of remaining reserves. One of these reservoir zones is the formation Åre 6.2, which is mainly composed of tide-dominated heterolithic channel belt deposits. It contains particular layers that have excellent properties with permeabilities up to 10 Darcy. These layers are predicted to affect the production results as they can act as ‘thief zones’ within the low permeable heterolithic facies causing large quantities of water to flow through, leading to poor sweep efficiency and early water breakthrough. This study focuses on constructing conceptual depositional models of the Åre 6.2 and building detailed geological models to investigate the effect of the thief zones on overall fluid flow predictions.

Conceptual depositional models were constructed by determining the characteristics of the reservoir and its depositional environment. Seven cored wells were used as the primary data to interpret lithofacies and facies associations. The study showed that Åre 6.2 mainly consisted of structured sandstones and heterolithic lithofacies with features that indicate that tidal process play an important role in the deposition. The influence of tidal process on deposition is further exemplified by the identification of two different types of channel facies associations, which are tidal and distributary channels. The thief zones were found in both facies associations, suggesting that the thief zones were formed during high freshwater discharge into the channels supplying coarse sandy material influx during a phase of high-energy deposition. To make detailed models of the tidal and distributary channels, multiscale modeling techniques were utilized to better represent the reservoir heterogeneities at the lithofacies and facies association scales.

At the lithofacies scale, models were built in SBEDTM and the upscaled values of each lithofacies were obtained by applying the Representative Element Volume (REV) concept. The upscaled values were then used as input in the facies association scale models in order to represent the heterogeneities at the lithofacies scale to the next heterogeneity level. This step is essential since heterogeneities at a smaller scale may affect reservoir flow properties. Two different channel models were built in ReservoirStudioTM based on the conceptual depositional model and using outcrop analogue data from the Gule Horn Formation (Neill Klinter Group) in the Albuen area (Greenland). Flow-based upscaling was used to analyze the model uncertainties and determine a proper upscaling grid size. Finally, streamline simulations were performed to identify the effect of the thief zones. The simulation confirms that the thief zones influence fluid flow in the reservoir zone significantly as most flow was concentrated in the thief zones.