Well Constrained Reservoir Analogues — The Non-Tidal Skagen Spit System and the Tidal RøMø Barrier Island

Lars H. Nielsen¹, Peter N. Johannessen¹, Morten Pejrup², Lars H. Nielsen^2
1Stratigraphy, Geological Survey of Denmark and Greenland, Copenhagen, Denmark
²Department of Geography and Geology, University of Copenhagen, Copenhagen, Denmark

Definition of high-resolution reservoir models for optimizing hydrocarbon production from deeply buried reservoirs requires a detailed understanding of the facies and their lithology and geometry. The Holocene-Recent Skagen spit system and the Rømø barrier island are two major sedimentary systems located at the Danish North Sea coast and both may serve as excellent reservoir analogues. They have developed in the latest 7000 years and are still growing, and their physiographic setting and development is well understood. Two well-constrained depositional models are defined based on historical records of erosion, transport and sedimentation, excellent outcrops, continuously cored wells, ground penetrating radar profiles, numerous dates of peat and shells (C14) and quartz sand (luminescence dating). The dimension of the spit system is 20km x 5km x 35m corresponding to a reservoir volume of 3.5x109m³, while the barrier island is 10km x 5km x 15m corresponding to a reservoir volume of 0.8x109m³. Both systems are mainly composed of fine-grained sand with minor proportions of mud and peat. The detailed understanding of the depositional dynamics of the spit system, in particular the up to 25m thick subaqueous spit platform, may lead to definition of new exploration targets as thick spit system sand bodies are most likely to occur in accommodation zones down drift from paleo-highs. The model of the barrier system has been used to qualify the volumetric considerations for an Upper Jurassic barrier island reservoir in the North Sea. The oil-bearing reservoir consists of 80m stacked barrier island sand. This extraordinary great thickness was attained because the combination of sea-level rise and a steep topography, possibly caused by faults, allow stacking and amalgamation of several barrier islands.

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