The Huesca fluvial fan contains a low gradient fluvial system with well-exposed, 3D outcrops. An outcrop study of low-sinuous deposits aims to provide a deterministic reservoir model that predicts correlation lengths, nesting and reservoir potential of thin-bedded fluvial reservoir sandstone in an overall low net-to-gross setting. To correlate the study area, centimetre accurate dGPS measurements of paleosols have been collected to calculate the tectonic dip. This was used to correlate lithostratigraphic logs of the area. Correlation lengths between wells are dependent on how spatial and continuous a paleosol has developed. Photo panels of the outcrop were analysed for net-to-gross ratio and distribution of channel and floodplain deposits. A clear distinction between high and low net-to-gross regions can be observed in the panels, which causes a lateral heterogeneity. This can be explained by the nesting of a river channel. Nesting can be caused by local avulsions triggered by crevasse splays of the river channel in combination with avulsion by annexation. The lateral heterogeneous character can have major implications on reservoir potential. The reservoir volume is dependent on the connectivity between the higher and lower net-to-gross regions. The heterogeneity also has an impact on reservoir modelling as there only is a limited subsurface expression from wells. Therefore, it cannot be known whether the higher or lower net-to-gross zones are being looked at for that particular fluvial system which makes estimates about reservoir volume difficult and inaccurate.

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.

Huge amounts of heat are stored in sedimentary aquifers in the Dutch subsurface. The amount of heat would be sufficient to provide our national heat demand for decades without any greenhouse gas emissions. Exploitation of this type of resource started some 10 years ago in the Netherlands. In 2016, 16 geothermal doublet systems had been installed that produce geothermal heat, and each year 2 to 3 new systems are realised. A doublet system consists of a production well that extracts hot formation water from kilometer deep aquifers. After the heat is extracted from the water in heat exchangers, the cooled water is reinjected into the same aquifer at approximately 1 to 1.5 km distance from the production well. Most of the current Dutch doublet systems provide heat for the horticulture sector. These systems have an average net energy production of approximately 10 MWth and therefore hundreds of additional systems are required to significant amounts of our heat consumption with geothermal energy. This PhD thesis investigated doublet system design and deployment strategies to optimise exploitation and increase the possible number of doublet systems exploiting the same aquifer. Based on detailed geological models, subsurface flow simulations are used to evaluate parameters such as required injector-producer distance, the preferred orientation of a well pair with respect to geological trends and required doublet distance to avoid negative interference. Based on the results, regional doublet deployment strategies can be developed to make optimal use of geothermal heat from sedimentary resources.@en

A generic life cycle applies to crevasse splays in non-degradational fluvial systems, typically ending in healing and abandonment. Crevasse-splay channels adjust to a graded equilibrium profile through proximal erosion and distal deposition, with their distal termini acting as a (prograding) local base level. When proximal incision advances to below the maximum flooding level, a reflux of floodwater occurs during the waning stage of flooding. The resultant decrease in gradient ultimately leads to the backfilling and abandonment of a crevasse splay, provided that the elevation at its distal fringe remains higher than that of the trunk channel floor. Consecutive crevasse splays form an alluvial ridge through lateral amalgamation and subsequent vertical stacking, perching the active river above the surrounding floodplain. Superelevation of the channel thalweg above the distal termini of a prograding crevasse splay leads to avulsion. A high-resolution morphological reconstruction of both the active (and recently abandoned) river(s) and the surrounding floodplain has been established to test the proposed life cycle of crevasse splays and evaluate its role in autogenic avulsion and organisation of the fluvial system. An avulsion can only occur when an overbank path of steepest descent reaches the system base level in a shorter distance (which may partially reuse the existing channel or remnant channel depressions) than the along-channel distance to its terminus. Crevasse splays prograde along this overbank flow path and capture an increasing portion of the total discharge, accelerating their development. When the crevasse apex incises down to or below its trunk channel thalweg, the avulsion is complete. The overbank path of steepest descent (i.e., avulsion path) is governed by floodplain topography, which is largely formed of abandoned alluvial ridges. This leads to compensational stacking of successive prograding channel belts, resulting in fan of amalgamated ridges.@en