Reservoir Geology and Geothermal Potential of the Delft Sandstone Member in the West Netherlands Basin

Abstract

The Delft Sandstone Member (DSSM) of the Lower Cretaceous Nieuwerkerk Formation in the West Netherlands Basin (WNB) is the target of a technology demonstration project for deep geothermal energy production. A prerequisite for the optimal placement of the geothermal well doublet is the assessment of the depositional setting of the target sandstone interval, and of the spatial distribution, connectivity and internal permeability heterogeneity of the reservoir units therein. To achieve this, a study was done on core, cuttings and well-log data from vintage oil exploration wells in and around the geothermal license area. Integration of the analysis results with earlier studies on the regional geological setting and reprocessed PSDM 3D seismic data show that the DSSM was deposited by a northwest-flowing meandering river system in a SE-NW oriented rift basin. The river deposits are subdivided in three depositional units with varying reservoir properties. Unit 1 is sand-prone and comprises loosely-stacked single-storey meandering river sandstone bodies embedded in a floodplain claystone and siltstone matrix. Unit 2 is a low net-to-gross succession of interbedded claystone, siltstone and coal layers, formed in a wet floodplain and swamp environment. Unit 3 is sand-prone and characterized by multi-storey and laterally-amalgamated meandering river sandstone bodies with minor mudstone floodplain intervals. Based on the good porosity and permeability values and the high lateral and vertical sandstone-to-sandstone connectivity this Unit 3 is considered the most promising target for the placement of geothermal doublets. The results will help broaden the understanding of the reservoir heterogeneity and, hence, reduce uncertainty in geothermal energy projects which target the DSSM.