In the Netherlands, the geothermal application is implemented to produce heat from a sedimentary aquifer in the subsurface for greenhouses and district heating. The most commonly used configuration is a doublet of wells, in which one injection- and one production well is drilled to produce warm water and re-inject cool water in the same target reservoir. One of the most important issues in operating this project is to maintain pressure communication of the doublet, with injector-producer well distance limitation and geological heterogeneity provide the main challenge to be solved. Moreover, as this application depends on flow behavior from injector to producer well, thus the determination of doublet wells location and spacing must be correctly evaluated to reduce the risk of an unsuccessful project.
In this research, the Triassic successions within the Drechtsteden area in the West Netherlands Basin (WNB) are evaluated for its potential for geothermal energy production. A reservoir characterization approach is implemented to answer the above challenges by utilizing subsurface data such as 3D seismic and well data. The process consists of seismic interpretation, reservoir sedimentology, and petrophysical evaluation analysis to determine the reservoir architecture and properties within the study area.
The regional study shows that most of the sandstone intervals within the Triassic successions occur in the Röt-, Hardegsen-, Detfurth- and Volpriehausen Formation. Based on reservoir sedimentology analysis, the sandstone intervals are composed of the stacked low sinuous river and sheet flood deposits with some interbedded lake margin deposits. The regional correlation suggests that the sand bodies within each formation can be correlated over distances of kilometers and were deposited along an SE-NW direction. The petrophysical evaluation result displays some variation in the reservoir properties (N/G, average porosity, and permeability) at a different location within the study area. A notable decrease is observed in reservoir porosity and permeability at greater depths which might indicate a compaction effect due to several tectonic episodes during and after the deposition of the Triassic Successions.
At the end of this research, two doublet locations are determined based on the analysis results which fulfill the required conditions for geothermal application. Both of the proposed doublets are designed to follow the SE-NW overall trend of the deposition and main faults orientation to maintain the pressure communication and avoid the presence of faults in between the wells. The injector is designed to be located at the shallower level than the producer to allow for gravity-driven flow propagation. A rough estimation of temperature distribution in doublet location displays that the proposed locations have sufficient estimated temperature for greenhouses and district heating. The expected reservoir properties at the proposed doublet locations are estimated from the depth range of penetrated doublet, the generated isopach maps, and petrophysical averages on the evaluated wells within the study area by a statistical approach.