Geological modelling for site evaluation at the Vedsted structure, NW Denmark

This paper describes a site investigation study that has been performed on the Vedsted structure in NW Denmark, where upper Triassic and Lower Jurassic sandy formations are considered potential reservoirs for large-scale CO₂ injection. The study presents the updated version 1.0 model using new 2D seismic data from the site and compares to results from the screening stage where only existing vintage data were used for the geological modelling. In this early stage of site investigation, the regional geological model and sequence stratigraphic interpretation are important contributors to the construction of a realistic geo-model. The facies interpretation is critical for understanding the geometry and connectivity of the reservoir layers. The main reservoir is at depths of 1700 to 2000 m, and therefore the CO₂ is injected at supercritical conditions. The reservoir rocks are mainly constituted of fluvial to nearshore deposits including shoreface sandstones, interfingering with marine offshore mudstones. The maximum thickness of the sandstone layers of ca. 30 m will restrict the potential for convection of the brine caused by density contrast instability. Therefore the dissolution enhancement normally assumed to be associated with convection must be modified for this geological setting. This is in contrast to the performance predicted for the Sleipner injection site, where convection is interpreted to happen over time, and it therefore illustrates that site specific evaluation is necessary in order to qualify the contribution from enhanced dissolution as storage mechanism. The interpretation of the new 2D seismic data and the resulting revision of the structural model influence the further plans for data collection, drilling planning and injection strategy.