Reduced Reservoir Quality in the Triassic Lower Volpriehausen Sandstone of the Southern Netherlands: Insights from a new Offshore Well

The Lower Volpriehausen Sandstone (LVS) in the southern Netherlands, part of the Main Buntsandstein Subgroup, has been a reservoir targeted for hydrocarbon exploration for decades. However, recently it has also been considered for potential deep geothermal energy and/or underground gas storage. The enigmatic distribution in reservoir quality requires site-specific evaluation. In order to get an understanding of the controlling processes, and ultimately to predict point of reservoir quality, the newly acquired offshore core section (Well-X) with reduced reservoir quality was evaluated in light of published data from nearby LVS wells.

This study reveals a strong control of primary depositional features (grain size and sorting) with a complex interplay of secondary diagenetic processes (e.g. recrystallisation, cementation, and dissolution). Despite early diagenetic carbonate cementation, which helped preserve initial porosity by stabilising the primary rock framework during compaction, cementation significantly occluded porosity and reduced reservoir quality. The reduced reservoir quality of Well-X is caused by a combination of local and regional controls, whereby reduced reservoir properties of finer-grained sediments are related to their (local) relative position within the braided river depositional setting. Diagenetic occlusion of porosity and associated reservoir quality reduction was mainly controlled at a regional scale by the palaeo-evolution of the Triassic coastline associated with the deposition of Middle to Late Triassic sabkha deposits and related reflux dolomitisation. These new insights from Well-X are crucial in predicting reservoir properties in the Buntsandstein reservoirs of relevance for future sustainable subsurface applications, such as geothermal exploration, as well as CO₂/H₂ storage.