Improving regional geothermal reservoir characterization using forward stratigraphic modelling on the Danish Gassum Formation

Denmark has a large potential to utilize geothermal energy as a baseline heating and cooling solution, due to the occurrence of widespread sandstone reservoirs and a large portion of the households are connected to district heating networks. However, data coverage onshore Denmark is generally poor so that using geostatistical methods alone to estimate reservoir properties æleads to large uncertainties. To overcome this challenge, we demonstrate the use of forward stratigraphic modelling on the most promising geothermal reservoir of Denmark, the Upper Triassic-Lower Jurassic Gassum Formation, which has been studied extensively for geothermal purposes and more recently for CO2 storage. Model parameterization was therefore following previous geological and sequence stratigraphic knowledge of the Gassum Formation, and around 40 boreholes were available for calibration to arrive at a best-fit model. The results are a 4D (3D space and geotime) grid (5x5km) that contains quantified information on sediment proportions, sedimentation rates, water depths, river water flow etc. Sensitivity and risk analysis, which sample the parameter uncertainty ranges using several 100s of models, help to quantify the importance of different parameters on sand thickness, and probabilities of having a sand of certain thickness. The results are useful to update the geothermal webportal.