The Netherlands has set the ambitious goal to be CO2 neutral by 2050 and signed the Paris Treaty in 2015. The contribution of geothermal energy to reaching this goal are outlined in the Masterplan in 2018 which attempts to reduce CO2 emissions. It is imperative to enhance geothermal participation in renewable energy resources, so this thesis proposes a consideration of large scale geothermal field development in order to meet these requirements. For these large scale projects, large scale geological heterogeneities must be taken into account in order to propose a development strategy that honours subsurface variability in properties like porosity or permeability of an aquifer. Furthermore, the nature of the large scale operations, inherently requires the consideration and application of well patterns typically used in oil and gas developments. Operating in these extensive domains, carries a lot of uncertainty in the final economical output of the project, so modelling the process could indicate the optimal conditions that would deliver the best possible operational outcome. Conceptual 2D model approaches were adopted to demonstrate the main ideas behind large-scale geothermal well pattern optimisation. The main objective of this project is to model, evaluate and optimise the performance of large scale geothermal field development. The proposed strategy is based on the use of well patterns as are frequently used in the oil industry. The heterogeneity in geological properties that may be expected to be encountered at larger spatial scales is addressed by the concept of a flexible well density function. This density function allows the well patterns to be resized (or ultimately, reshaped) and adapt to spatial variations in geological characteristics. The flexible well pattern is fed to an objective function created with embedded simulator. The output of the function is the net present value (NPV) of the project. Four test cases are created, starting with a homogeneous static model and building up more heterogeneous aquifer models, aiming to test the performance of the flexible well density function. The aquifer property models are representative of the West Netherlands Basin and specifically the Delft Sandstone Member. Per each aquifer model, line drive and 5-spot development strategies are assessed. Each development scenario is modeled in an objective function and optimised. The optimisation algorithm chosen is the Simplicial Homology Global Optimisation, suitable for black-box functions that show multiple local optimum solution and among them, a global optimum pattern size is found. The NPV of each project realisation is calculated based on the energy recovered and an economic model under Dutch fiscal conditions. The results suggest that, the flexible well placement is successfully aligning with the different aquifer geological properties. Pattern size is inversely correlated to porosity which corresponds to higher volume of pore fluid from which heat can be recovered. The optimisation algorithm managed to identify the global optimum solution of pattern size that delivers the highest possible positive NPV. The most efficient in terms of profitable strategy, is suggested to be the 5-spot pattern. The optimal pattern size ranges between 500 - 2160m depending on the aquifer model. The sweep efficiency, in terms of energy recovery, is also assessed per aquifer model and development strategy. The most efficient is the 5-spot pattern. The performance of the adopted optimisation algorithm, on the fully homogeneous aquifer, is tested with an exhaustive response curve of NPV. It is confirmed that the algorithm manages to identify the global optimum. The character of the NPV as a function of well pattern size/density proved the complexity of the system with respect to the amount and well types introduced. Different sensitivity analyses in the context of the uncertainty of the aquifer thickness, thermal conductivity, thermal heat capacity and full economic model are conducted in order to show the impact on the optimal patter size. The performance of the optimisation algorithm is assessed as well, indicating that further investigation on the tuning meta-parameters could potentially lead to better global optimum solutions in more heterogeneous aquifer models.

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 >70^oC 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.

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.

The importance of gas as a driver of security of energy supply and the influence of the role it currently has and will continue having in the energy transition has stimulated the development of further research studies in unconventional sources of natural gas. Mature gas fields of coarse-grained fluvial reservoirs have already reached their production plateau and are in a production decline with high-water cuts.
The northwest gas province of the Netherlands contains low-permeable fine-grained fluvial deposits of which the reservoir architecture and connectivity have not yet been widely studied using the standard industry techniques. For this reason, the geomorphological and sedimentological characteristics of the Río Colorado fluvial system were used as a modern analogue to determine how the river avulsion process has generated the current fluvial topography and why its repetition has developed a vertical stacking pattern of thin but laterally extensive layers.
Differential Global Positioning System data, Google Earth Pro Imagery, and previous studies focused on the evolution analysis of river positions in this region, allowed the observation of multiple repetitions of avulsion river in an area of approximately 400 km2, describing the fluvial sediments on top of the lacustrine deposits and representing alluvial ridges with an average width of 1500 m. Moreover, a thickness variation between the fluvial and lacustrine deposits up to 2 meters was recognised over 25 km, and a very gentle gradient slope, from 0.02° at the apex of the fluvial fan to 0.0022° in the flattened section towards the Salar de Uyuni.
Borehole data from the West Netherlands Basin and surface data from the Río Colorado were integrated to construct a three-dimensional model that represents the characteristics of the fluvial deposits regarding geobody size, geometry, and potential connectivity. With this, and the distribution of porosity and permeability as a function of channel belt and alluvial ridge width resulted in reservoir volumes up to 2×〖10〗^9 sm^3.
Six wells were simulated to understand the production behaviour in channel belts, alluvial ridges, and floodplain sediments. Water saturation, pressure and streamline maps differ from well to well, and the model contributed to quantify the most efficient production rates per well location in the fluvial fan system. The results allowed to predict the communication between facies and how that connectivity reflected the resultant flow rates and recovery factors, showing the tough gas as potential secondary targets and prolonging the production stages of mature oil fields.

Natural occurring arsenic contamination of shallow aquifer groundwater is a problem affecting millions of people worldwide. Long term exposure to high concentrations results in severe medical conditions. On-going research into the origin and spread of the problem, risk mitigation and problem solving is of great importance. Sediment eroded and transported from mountains adsorbs arsenic (As) from river water onto its iron oxyhydroxides coatings. The geomorphology of the river is related to the concentration of As in shallow aquifers. Helicoidal flow in a meandering river leads to erosion of the cut bank in the outer bend and accumulation of sediment at the point bar in the inner bend. The result is an asymmetrical depth profile. The process of meandering and avulsion sometimes leads to the complete abandonment of a part of the river’s channel. This still-standing water body is known as an oxbow lake. Fine sediment settles from suspension and the oxbow lake gradually fills up with silt and clay. A clay plug forms, surrounding the sands of the adjacent point bar. Clay filled oxbow lakes formed by meandering rivers are high in organic content and the anoxic conditions in the hypolimnion are considered the source for the release of the adsorbed arsenic. Under reducing conditions the As is released from its solid state by microbial respiration. In the geomorphological setting of meandering rivers, abandoned channels and point bar, this process of reductive dissolution is the generally accepted release mechanism for arsenic. This research aims to provide insight in the potential arsenic volume in Holocene clay plugs in Ganges River floodplains and to present ideas on the migration processes of arsenic from clay plug to adjacent point bar. Migration of dissolved As occurs by advection and by diffusion. Satellite data from Google Earth Pro was used to simulate clay plugs with a Matlab model. The simulated data was used for the calculations of the surface area of the clay plug, the volume of the clay plug, the potential volume of As and the contact area between the clay plug and adjacent point bar. These geometric properties and concentrations of As were used to apply Fick’s first law to estimate the initial diffusion flux and the initial discharge. The surface area of the twenty selected clay plugs vary from 10! to 10! m2. The corresponding volumes are in the order of magnitude of 10! to 10! m3. The calculated As volumes range within the orders of 10! to 10! kg. The initial diffusion flux was calculated and ranges approximately between 15-300 g/m2year. For the volume calculations the exact shape of the depth profile turned out to be of little influence. For calculations of the contact area and thus the diffusion flux estimations, the true profile is crucial. In-situ sampling would provide data to minimize uncertainties and improve results.

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

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.

Geothermal energy is strongly dependent on the geothermal gradient; this means that with increasing depth an increase in temperature is found. The targeted formation of our research is the Hardegsen which reaches depths of around three kilometers in the West Netherlands Basin. At three kilometers depth the temperature is around 90 C˚ which is interesting for geothermal exploitation. However, rock at increasing depth generally shows a decrease in reservoir properties.
This study investigates whether the reservoir properties of the Hardegsen formation at a depth of three kilometers are still interesting for geothermal exploitation. This is done by determining to what extent the Hardegsen has been influenced by depositional history, diagenetic processes and inversion.
Determining the reservoir properties is done by studying a data set that consists of core descriptions, core plug measurements, gamma ray logs, microscopy analysis, literature studies and a field study. From the core plug measurements a simple model was created describing how porosity and permeability of the Hardegsen behave with increasing depth.
The Hardegsen succession in the West Netherlands Basin consists mainly out of (cross-bedded) arkosic fine to medium grained sandstones intercalated by 0.2-1 meter thick laterally consistent shales and shaly/silty very fine sands. High minus-porosities (up to 45 %) are reported which could have played an important role in the preservation of the reservoir properties. Core plug measurements show that the Hardegsen has good prospects for a potential reservoir with porosities ranging from 10-20% and permeability’s ranging from 50-1000 mD.
The presence of the laterally consistent shale and sandy/silty very fine sand layers is heavily dependent on the location in the reservoir. This research shows absence of these layers in wells that are located closer to the basin margin. Since these layers decrease vertical flow drastically, further investigation of the extent of these layers is needed to give a better prediction of the quality of the reservoir as a whole.

The sedimentary systems terminating in the Salar de Uyuni, hold modern days analogues for the Permian and Triassic thin-bedded crevasse-splay deposits. In the future, these crevasse-splay deposits could be of importance for hydrocarbon production in Northwest Europe. In this study, the possibility of using satellite data to construct geomorphological maps is investigated. In order to do this, QGIS is used to determine the watershed and river paths based on ASTER GDEM satellite data, and to classify the land cover based on Landsat 7 ETM+ satellite data. The results generated by QGIS are compared to open source available datasets and high resolution Google Earth Pro images. The watershed and river paths determined in QGIS are accurate for high relief areas. In low relief areas, the results are not trustable. Here, the watershed and river path results seems to be controlled by the errors in the ASTER GDEM data. The resolution of the used Landsat 7 ETM+ is not large enough to distinguish various rock types accurately. A map that indicates the amount of clay within the basin could be created using the Landsat 7 ETM+ images though. Lithological classification using satellite images is a promising technique, with a lot of applications. However, to perform accurate lithological classification higher resolution satellite images and more detailed lithological information is necessary.

A good understanding of the reservoir architecture of tough gas reservoirs is necessary to define their potential for the hydrocarbon industry. These tough gas reservoirs have been overlooked until now due to the high economic risks of development. These risks are mainly related to the large uncertainties that exist in the reservoir architecture. Understanding the depositional processes of crevasse-splays will help in minimizing the uncertainties in interpreting the internal depositional setting and deposition processes.
This research focuses on the mapping of thin bedded crevasse splays in a low-net-over-gross floodplain environment in the distal areas of the Huesca fluvial fan (Miocene) of the Ebro basin in Spain. This outcrop is a good analogue to the Permian Rötliegend and Triassic Bundsandstein intervals in the West Netherlands Basin. A field study of the Huesca fluvial fan is used to analyse the reservoir architecture (size, shape, spatial distribution and connectivity) of the reservoirs of fossil crevasse-splay deposits. At two outcrop locations an interval of crevasse-splay deposits is mapped, using detailed lithostratigraphical logs, a type section log, photo-panels and lateral characterizations of sand beds. With these data a correlation panel is constructed to determine the connectivity of the mapped layers, and cross-sections are made to determine the lateral continuity, vertical stacking and grain-size variations.
On a single layer level, results show both a decrease in bed thickness and in grain size from proximal to distal, related to the energy of deposition. Grain size is also related to distributary-channel proximity, decreasing away from the distributary crevasse channels. In multi-storey stacked sheets, incision of distributary channels into underlying crevasse deposits near the crevasse apex creates sand-on-sand contact. The approximation of a crevasse splay as a simple accumulation of homogeneous sheet like layers should be refined in order to lower the uncertainties in the tough gas reservoir model. A quantitative dataset for the size, shape and stacking patterns of crevasse splay sandstone is composed, which can be used as an input in static reservoir models.

Burning oil shales contribute to CO2 emissions. The spatial distribution pattern shows that these _res occur in areas with moderate or dry climates. This paper investigates the mechanism behind the burning oil shales. The first part includes an overview of the geological setting, Fieldwork results and petrophysical analyses. Based on these settings, we defined a horizontal fractured structure above and below the shale beds and vertical fractures with spacing varying from 10{30 cm. The matrix in between is oil shale with a kerogen content of 35% up to 70 %. The oil shale contains lenses of pyrite. Several dynamic models, based on this fractured oil shale structure, have been developed to illustrate aspects leading to enhancements or extinction of oil shale fires. Natural convection supplies air (oxygen) to sustain combustion. Air can penetrate into the matrix, mainly to the highly fractured structure, to react with fuel. The presence of oxidising pyrite may trigger the fire. Favourable conditions for oil shale fires are dryness, mostly during the summer, and a heat source.