With an increase in the demand for heat energy, and the growing conscience of the world to reduce CO2 emissions, the transition to cleaner energy alternatives has gained momentum. In the Netherlands, the potential for cost-effective geothermal heat extraction from sedimentary aquifers has led to the exploration of siliciclastic Triassic reservoirs in the West Netherlands Basin and Roer Valley Graben for their suitability. This thesis primarily focuses on two geothermal target wells namely NDW-01 and NLW-GT-01. These wells lie in the Nederweert and Westland areas respectively.NDW-01 comprises of 292m thick sandstone package which is scarcely studied. While the NLW-GT-01 well was drilled tapping depths of over 4000 meters and encountering temperatures of about 100°C. In contradiction to the pre-drill expectations of having appreciable porosity and permeability values between 10-500mD, the Upper Volpriehausen sandstones in NLW-GT-01 exhibited porosity and permeabilities ranging between 1.4% to 3.9% and ≤0.02mD respectively. The sandstones were highly compacted and severely cemented by dolomite and quartz. These cements blocked all the macropores leaving no visible porosity in the thin sections. Although, the cored interval was extensively fractured the measured permeability values were negligible. This thesis presents the results of an assessment of the factors leading to the deterioration of intrinsic porosity and permeability of Triassic aquifers lying in the Westland and Nederweert regions. In this project, grain-size analysis using core plugs, thin-section study, petrophysical data analysis, and FMI log interpretation were conducted to understand the depositional environment of the Lower Germanic Trias Group precisely the cored sections of the Nederweert Sandstone Member in NDW-01 well and the Volpriehausen sandstones in NLW-GT-01 borehole. Due to the complex tectonic history coupled with locally different paleoenvironments, the current depths of the Triassic deposits in the investigated area did not correlate with the reservoir quality of the adjacent shallower wells. In addition to the local depositional conditions in the basin, the variable precipitation in the source area, and the distance of sediment transport have defined the rock characteristics. The primary grain-textures, such as roundness, sorting, packing, as well as the detrital framework and authigenic minerals, were found to influence the sandstone porosity. The tightness of the reservoir was due to significant mechanical compaction and cementation described by a diagenetic reconstruction explaining the evolution of porosity with depth with a negligible generation of secondary porosity. The deterioration of the reservoir quality is correlatable to the burial history and its resulting consequences, namely mechanical and chemical compaction endured by the rock during periods of basin subsidence and uplift. These analyses have put the deviation of pre-drill results from those that were obtained through post-drill evaluations into perspective.

The decrease in the production of hydrocarbons in combination with a growing urgency to reduce carbon emissions drives a rapid study and application of geothermal energy in the Netherlands. The produced heat from the low enthalpy geothermal energy can be used for heating up the buildings and greenhouses. A doublet system is used in the geothermal scheme, which consists of one production well and one injection well. The reinjection is done to maintain the reservoir pressure and reduce pressure decline due to production, earthquake and subsidence prevention, and environmental safety. Thus, it is crucial to model the aquifer distributions appropriately as the injection and production well should be placed at the communicated sand bodies. In this study, the architecture of the Alblasserdam Member in the Drechtsteden, West Netherlands Basin is modelled. An investigation of the paleo flow and the distribution of sand prone succession within the Alblasserdam Member is done by integrating seismic interpretation, reservoir sedimentology, and petrophysical evaluation. The data used consist of seismic data, well log dataset and core data from the acquired hydrocarbon exploration data. The Alblasserdam Member was deposited during the Late Jurassic to Early Cretaceous when the high tectonic activities occurred in the West Netherlands Basin and followed by series of inversion impulses made this member bounded by various members at the bottom and the top. The seismic response of the Alblasserdam Member shows a high thickness and depth variations. The sediments of the Alblasserdam Member are highly accumulated in the central part of the study area, bounded by two major faults striking SE-NW. Several sections of well correlation are made based on cycles of changing accommodation to sediment supply ratio (A/S cycles). The correlation is supported with seismic interpretation, allow to map the distribution of sand-rich interval of the Alblasserdam Member in the Drechtsteden. Two potential aquifer intervals are found. A southwestward shifting of the main fluvial system is observed from the thickness trend of the shallower aquifer intervals. A petrophysical evaluation is made to analyze the properties of the potential aquifer that encompass net to gross thickness (N/G), average porosity, and average permeability. The deeper potential aquifer has a higher clean sand N/G, but lower average permeability, that might be caused by the compaction, and mineral precipitation after the inversion period, especially in the highly inverted area. In the end, a recommendation to place a pair of production and injection wells are proposed based on the high accumulation of sand-rich intervals, sufficient depth to produce heat >70oC and absences of the fault. The wells are placed toward SE-NW trend which is parallel to the distribution of the main fluvial distribution and the orientation of the faults, with production well placed at the deeper level.