Geothermal energy is expected to play a major role in decarbonizing heat supply in the Netherlands. Knowing the geomechanical behavior of a reservoir and seal can be crucial when engineering in the subsurface[5]. That is why this thesis focuses on characterizing the geomechanical behavior of the upper Delft Sandstone. Due to limited prior research and known lithological heterogeneity, this study seeks to quantify the constitutive behavior of the upper Delft Sandstone Member. Another goal is to measure the static moduli of the upper Delft Sandstone Member and to try to predict these moduli in parts of the reservoir where no cores are available.
From 87 m of core from well DEL-GT-01, 39 suitable samples were tested. Petro-physical measurements and classification into sandstones and shales were followed by UCS (15 samples), triaxial (13 samples), and Brazilian Disc Tests (11 samples). These provided strength, yield stress, Young’s modulus, Poisson’s ratio, and tensile strength.
Results show weak correlations between porosity and strength, but stronger samples had higher Young’s modulus and yielded later. Coarse, organic-rich sands were weaker, while P- and S-wave velocities correlated with strength parameters. Triaxial tests confirmed increasing yield point with confining pressure and lower friction angles in shales.
A linear model predicted static Young’s modulus in parts of the reservoir where no cores have been taken from dynamic moduli with an average absolute error of 2.6 GPa. Uncertainty remains due to limited sample data and high reservoir heterogeneity (REV larger than sample scale). The results in this study were compared to a geomechanical research of the IJsselmonde formation, which is a very similar formation. The data was not found to be very comparable, due to slightly different formations and different test techniques. Nevertheless, this data was the most comparable data out there.
Answering the main research question is and will remain difficult, because one can never know the geomechanical behavior of the complete reservoir. This study however did make a good start. It is now known that the upper Delft Sandstone member is moderately weak to strong. A correlation within the sands was also found with the grain size, or the amount of organic grains. It is not certain which of the two had the greatest effect. The ranges of dynamic moduli are known and we know what we need to test if we want to reduce the uncertainty within certain correlations.
This study shows the importance of extensive geomechanical data collection since the geomechanical behavior is not that easily explained.

This thesis attempts to evaluate the extent to which UAV imagery can complement traditional geological fieldwork and to assess the behaviour of natural fracture networks across multiple scales. By conducting detailed field surveys and capturing high-resolution UAV images, the study provides a comprehensive comparison of the data, particularly in terms of fracture orientations, lengths, density, intensity and topology. The Parmelan plateau in France has been studied as a potential geothermal reservoir analogue. This study utilises an integrated approach combining fieldwork, high-resolution Unmanned Aerial Vehicle (UAV) imagery, and satellite imagery.

Field data collected using field scanlines were compared with data obtained from UAV imagery to evaluate the efficacy of each approach. The results indicate that UAV imagery, while advantageous for covering large and inaccessible areas, faces significant limitations in accurately identifying fracture types and orientations without supplementary field data. This discrepancy is primarily attributed to factors such as image resolution - limited visibility of small-scale fracture-type indicators.

The multi-scale analysis performed in this study shows that natural fracture networks exhibit similar behaviour across different scales, though some scale-dependent variations are evident. The findings highlight the importance of integrating UAV data with traditional field methods to achieve a better understanding of fracture networks. This integration is particularly important for optimizing outcrop analogue data used in modelling subsurface geothermal reservoirs, which can significantly enhance the efficiency of geothermal energy extraction.

The Uppermost Ablasserdam Member and Delft Sandstone Member are of high interest for geothermal energy extraction. The stratigraphy, sedimentology, and depositional environment of these members have been studied by different researchers over time. However, due to the lack of physical and extensive logging data within the West Netherlands Basin, there is still uncertainty about their depositional environment and how these sandstone bodies are vertically and laterally connected. Without this data, determining the depositional environment is challenging, and so is developing an optimized reservoir model.

This study performs a sedimentological analysis on the core, sidewall cores, and plugs, together with an investigation of the wireline logs of the DEL-GT wells. The main goal behind this is to determine the different lithofacies types and facies associations and interpret this while considering the limitations of the available data.

The Uppermost Ablasserdam Member and Delft Sandstone Member show characteristics of a fluvio-deltaic system and is located in an upper to lower delta plain environment. With observed facies associations of multi-stacked fluvial to distributary channels, single fluvial channels, crevasse splays, levees, overbank fines, and paleosols. The wireline logs help determine the vertical distribution of the facies, which showed a trend and lateral heterogeneous distribution between the wells. Thus, I could not correlate the wells to each other due to the lack of clear markers and indications that certain sandbodies are connected. Hence, more research on this is needed.

The wireline logs did show a trend from more sand-prone deposits to more silt-prone deposits, which can be related to the the different allogenic and autogenic controls. The controls likely influencing the depositional patterns are the tectonic activity and eustatic sea level change. In combination with climate change affecting the sediment supply and discharge rate, which influences the autocyclic controls of the channels.

This study is based on physical data from the first 80m interval of the one dimension DEL-GT-01 and side wall cores from DEL-GT-02-S2 wells. This brings an uncertainty in determining the lithofacies types and facies associations. Broader research must be done not only on the lithofacies types and facies associations but also on the lateral and vertical distribution. This will help determine the determine the limits of the reservoir.

Moreover, this study brings attention to the importance of extensive core and wireline log data collection.This data will reduce uncertainty for the reservoir model and increase the efficiency of the project and other future projects. It is also highly advised that all the findings and data should be open and free to use for future projects to reduce the uncertainties within the reservoir model.

CO2 and H2S are reinjected at Hellisheiði, Iceland, to reduce the emissions of greenhouse gases. An active-source seismic campaign was done in July, 2021, to image the reinjection reservoir with various seismic methods for consecutive monitoring. At the same time, passive-source seismic data was recorded for imaging.
We process this passive data with seismic interferometry. For this, an illumination analysis is performed to filter noise panels that are dominated by surface-wave noise and to keep panels dominated by body-wave noise. Afterwards, panels with near-vertical events are autocorrelated to retrieve a zero-offset section. The full set of selected panels is crosscorrelated to retrieve virtual shot records. These are processed with a simple reflection seismological processing workflow to obtain a stacked section.
The results show that the autocorrelated zero-offset sections appear more noisy, but are characterised by higher frequencies, while the crosscorrelated stacked sections are characterised by a lower-frequency content and contain more dipping reflectors. The major, horizontal reflectors correspond between the two types of sections.
A rudimentary interpretation of reflectors is done, based on the two types of sections and compared with a local geological model. This shows that the major lithological differences and the base of the Hengill volcano can be distinguished in the interpreted section.

Permian deposits are found in outcrops and in the subsurface of Southern Tunisia, in the Jeffara Basin. Their stratigraphic and tectonic evolution is not yet fully understood and represents the main focus of this work. Aspects of the Permian system such as, lateral extend of formations, dating and paleo environments are not well constrained. Answering these questions will impact future hydrocarbon exploration and also improve the geological understanding of Tunisia. To achieve this, seismic lines and well data of the Jeffara Basin have been re-interpreted and re-correlated.

The results of the study indicate a lagoon depositional environment for the Early Permian, a carbonate self environment for the Middle-Upper Permian successions, with dimensions of 80 square kilometers and a general east-west orientation. The thickness of the carbonate deposits reaches a maximum of 2500 kilometers to the north of the reconstituted paleoshore. A Sabkha environment has been interpreted for the Upper Permian with significant deposits of anhydrite. Structurally, it was observed that the Permian is not affected by major normal faults.

Conversely, significant folds have been identified at the seismic data, with a general east-west strike and a northwards dip. Based on the displacement of seismic reflectors, two tectonic episodes have been identified. The first is dated to the Upper Carboniferous - Early Permian and the second to the Early-Middle Triassic. Decompaction calculations indicate low subsidence rates and general stability during the Early Permian. This was followed by significantly increased subsidence rates during the Middle and Upper Permian.

This research describes how thermal fractures impact the near-wellbore (NWB) region of a depleted gasfield in a carbon sequestration project. As CO2 is usually injected in its supercritical phase, the injection fluid is injected on high pressures and low temperatures. This is in high contrast with the depleted gasfields, which have a low reservoir pressure. The increase in pressure and decrease in temperature causes a thermoporoelastic response, resulting in a reduction of stress inside the reservoir. Once the fracture initiation stress, the so-called fracture stress, is reached, thermal fractures form.

Thermal fractures form only due to extensive cooling of the reservoir. The fractures impact the NWB region; due to opening of fractures there is a drop in pressure in the bottomhole pressure (BHP). This increases the reservoir's injectivity. This research uses CMG GEM to model this. The simulation uses a homogeneous box dual permeability model with the model being initialized as a generalized depleted gas reservoir in the North Sea. To model the fractures, the Barton Bandis model is used. This model changes the permeability in a fracture cell once fracture conditions are met.

From this model, the moment of fracturing (fracture time), the fracture halflength and the injectivity of the reservoir is researched by performing a sensitivity analysis on key parameters. It is found that the thermal fractures propagate conform to the propagation of the coldest part of the thermal front. The thermal front propagates further once the fracture conditions are met sooner due to fluid highways or when the pressure build up in the reservoir is slower.

The sensitivity on the geomechanical parameters showed that only the stress conditions in the reservoir changed, causing the injection constant to change and thus a different fracture time. The way the reservoir reacted to the initiation of fractures was the same; the injectivity was improved similarly for each parameter.

The effective permeability (thickness and permeability) determines, together with the injection rate, the way the pressure builds up in the reservoir changes the increase of injectivity due to fracturing slightly. Increasing the reservoir volume causes a slower pressure build-up inside of the reservoir, allowing the thermal front to propagate further and thus longer fracture lengths.

Lastly, the sensitivity on the thermal effects showed that a higher difference between the reservoir and injection temperature causes the fracture to be less dependent on the increase of pressure to fracture, resulting in earlier fracturing and longer fracture halflength. The pressure build-up is not changed, so the injectivity remains similar to the basecase scenario.

All in all, this thesis gives an insight on how key parameters impact thermal fracture behavior. It also shows what range of parameters can be expected. Combining these two gives an insight on what parameters the focus should be on to better describe the behavior of thermal fractures, to economize the operation by leaving out or including extensive data collection on key parameters. This helps to improve the injection strategy with CO2 injection projects in depleted gasfields.

Argillaceous (clay-rich) host formations for radioactive waste geological repositories are extensively researched for their capability to decrease the hydraulic conductivity of fractures over time (i.e. self-sealing). This self-sealing behavior is beneficial in the context of radioactive repositories as the excavation of these spaces unavoidably induce fractures in a region called the excavation damaged zone (EDZ), allowing for radioactive particles to leak into the surrounding environment and groundwater. Despite knowing the mechanisms for self-sealing (e.g. swelling of clay minerals), more research is needed into the complexities of self-sealing to fully understand and effectively utilize it widely. To facilitate research of swelling in induced fractures, a quantified method of fracture characterization using morphological descriptors is developed to provide insight into the morphological state of the fracture surface and its influence on the self-sealing capacities of argillaceous rocks. This was carried out by identifying morphological descriptors of a rough surface and their relation to roughness, as it pertains to macroscopic and microscopic roughness. A dynamic script was developed capable of: analyzing and quantifying morphological descriptors of roughness in 2 and 3-dimensions, calculating the surface area of a rough surface, and calculating hydraulic conductivities (kx and ky) of a discrete fracture. This method was tested using two samples of Opalinus Clay (OPA) from the Mont Terri underground research laboratory (URL) in Switzerland. Furthermore, derived data of heterogeneous morphology, along with surface area and hydraulic conductivity, is used to discuss the limitations and constraints of the developed method and compare 2-dimensional versus 3-dimensional morphological analysis to determine what combination of analysis fully captures the breadth of morphological information. It was determined that the morphological descriptors of amplitude, amplitude density, and the bearing area curve (BAC) are suitable descriptors to define the microscopic and macroscopic roughness of a rough surface, where both forms of roughness are defined in the context of influence from local maximums (asperities) and local minimums (valleys) of the surface. Comparison of the 2 and 3-dimensional analyses of these morphological descriptors shows that a combination of the 2D BAC, 3D amplitude, and 2D amplitude densities both fully capture the breadth of morphological information and provide an easier means of interpretation. Using Delaunay triangulation on the surfaces of both OPA samples, the calculated upper and lower bounds of surface area for sample 1 is: 2267.37mm2 and 942.09mm2 and is: 2377.64mm2 and 959.73mm2 for sample 2. Compared to the planar surface area of each OPA sample analyzed, this corresponds to an 847 - 2039% increase for OPA sample 1 and a 998 - 2399% increase in surface area for OPA sample 2. The calculated hydraulic conductivities kx and ky for sample 1 is: 1.78×10−7 m/s and 7.75×10−7 m/s and is: 8.01×10−9 m/s and 2.1×10−7 m/s for sample 2. This is compared to the hydraulic conductivity of the Opalinus clay material, which is 2×10−13 m/s. Future research into discrete fracture characterization using morphological descriptors should focus on increasing the computational efficiency of the existing code, improving the surface area calculations, and transforming the matrices of data into one points of data for easier comparison of discrete fractures across multiple samples. In doing so, it is hoped that this small contribution will aid in understanding morphology influence on swelling development in induced fractures in argillaceous geomaterial.

The use of wireline facies associations can alleviate core data shortage during facies prediction by providing a more extensive input dataset. Wintershall has assigned wireline facies associations directly on cored and un-cored wells in the Carboniferous of the Sothern North Sea. Conducting facies prediction using these wireline facies associations as an input can help with tapping into the remaining exploration and development potential of the area. However, the accuracy of this input must be evaluated using core data before machine learning algorithms are applied. This was quantified as 71% for 9 cored wells, where the background floodplain and braided channel facies had the highest accuracies of 88% and 81% respectively, and the mouth bars and marine shales facies could not be adequately validated due to their insufficient core sampling. Consequently, when using wireline facies associations for training facies prediction algorithms, this input’s intrinsic uncertainty should be accounted for while examining the outputs, especially for facies that are not sufficiently validated by cores. Applying facies prediction with Support Vector Machine (SVM), Multilayer Perceptron Neural Network (MLP) and Recurrent Neural Network (RNN), showed that RNN can achieve the highest overall accuracy of 80.9%, due to the highest F1 scores for braided channel (0.88), point bars (0.60) and coal (0.53). The class imbalance problem is apparent for this dataset where the majority classes of background floodplain, braided channel, point bar and coal, are more predicted than the minority classes of crevasse splay sands, mouth bars, and marine shale. Applying RNN on the Westphalian A, B and C separately served as a form of imbalance correcting technique that increased the F1 scores of underrepresented facies. Future work can further refine the results by exploring imbalance correcting techniques through under-sampling the background floodplain and over-sampling the crevasse splay, mouth bar and marine shale facies.

To optimise mining in a safe, geotechnically controlled and economical most beneficial way in Mine 2 of the Stjernøy mine, a choice has been made to review the current mining method, sublevel open stoping, and a different mining method, vertical crater retreat. The Stjernøy mine is an open pit and underground mine for Nepheline Syenite and this thesis focuses on Mine 2, the underground mine which is partially completed. The stopes of Mine 2 are closely located to old stopes, which can cause stability issues. Between the new and old stopes is a barrier pillar which is a key element in the stability of the underground mine and the infrastructure for the open pit operation as well. This project consists of field work and laboratory testing to create a basis for the numerical stability analysis of the mine and the creation of a cost model for the two different mining methods. The results of the cost modeling show that the use of sublevel open stoping will result in a cost per tonne of 9.86 NOK and the use of vertical crater retreat will result in a cost per tonne of 10.39 NOK. The use of sublevel open stoping as mining method is the most economically beneficial option for the mining operation. It is less expensive as a mining method and it is a proven method at this mine site. The vertical crater retreat method uses a more expensive blasting method, with the same burden and spacing parameters as the sublevel open stoping. The results of the field work and the laboratory testing provided important parameters for the numerical modelling, such as the strength of the material. Based on these results the numerical modelling also showed that it is beneficial for the stability of the pillar if some stopes near the barrier pillar are not extracted. The extraction of these stopes will decrease the factor of safety of certain areas of the barrier pillar to one or for some areas below one. The stope size has also been reviewed. To make sure that the stopes are well connected to drawpoints, it is important to keep them the same size, which is a stable stope size for the roof. Smaller stope sizes are found to be a bit more stable, however the effect of the increasing amount of pillars is not known on the overall stability.

Many laboratory tests of samples where the rock fractures are based on
meso-scale (cm) characterization of effective ‘intact’ strength parameters neglecting the microstructure effects. Understanding fracturing processes at
micro-scale (mm) will require models with microstructure data. However,
data is lacking on micro-scale.
Stylolites are natural rock-rock interlocked interfaces which form by a localized
dissolution process and their interface contains minerals and material
different from that in the surrounding host rock. Microstructures such as
stylolites influence the tensile stress behaviour in a rock formation. We are
interested in stylolites because they can act as drains or as barriers to flow.
Therefore, we introduce a study where we investigate on micro-scale failure
mechanisms of limestone samples with stylolites in diverse orientations.
In preceding study (Pluymakers et al., pers. comm.) a series of Brazilian
Disc Tests was performed on eleven samples all including stylolites of microscale
carbonate samples from the ”Treuchtlinger Marmor” formation from
the Molasse Basin (Munich, Germany). All experiments were filmed using a
DSLR camera.
In this study we aim to develop the use of the Particle Image Velocimetry
method to analyze such type of movies. We use the developed Particle Image
Velocimetry method to analyze three of the movies of the preceding study,
which contained samples where the stylolite is at different angles to the
horizontal axis of the sample, so to s3. Two samples has an angle of 90°
between the stylolite and s3 and one with an angle of 40°.
In this open-source software the pixel displacement is analyzed in frames
(i.e. consecutive images, ’before’ and ’after’ image) and it calculates the velocity
distribution within the framepairs, but it is also used to derive, display
and export multiple parameters of the flow pattern. In this study we derived
and displayed the strain rate on the image pairs.
The results show that the strain field of the two limestone samples of a 90°
stylolite behaves identical in the two major stress drops (i.e. DStress) from
the stress-displacement curve. However, the sample with a stylolite of 40° behaves differently. For the two 90° oriented stylolites random extension and
compression takes place at the first highest negative stress drop and symmetric
extension takes place at the second highest negative stress drop from
the stress-displacement curve. However, for the 40° oriented stylolites asymmetric extension takes place at the first highest negative stress drop from
the stress-displacement curve. And random extension at the second drop.
Another result of this study is that the strain rate obtained from PIVlab, the
strain rate per stress drop (MPa) (i.e. in the stress displacement-curve) in
both the two 90 ° stylolite samples and the 40 ° sample were different.
To put this work in the broader context of the energy transition, we consider
the rapid development of the geothermal sector. Nowadays geothermal
energy is considered as one of many alternative sources of energy using
the hot water in the Earth’s surface to generate electricity and power heating/
cooling systems. The Dinantian carbonates in the Netherlands and the
”Treuchtlinger Marmor” carbonates from Germany are of interest for Ultra
Deep Geothermal wells, because of their high geothermal potential. To enhance
the porosity/permeability in a formation where hot water needs to be
extracted hydraulic fracturing can be an option and this study gives insight
about how the rock formations on micro-scale behave when tensile failure
occurs. Tensile is one of the most important properties to be evaluated for
any textile material (i.e. rocks). Tensile failure is important because it occurs
when the stress on a component exceeds the strength of the material thus it
determines the strength of a rock and consequently is influenced by single
plane of weakness such as stylolites.

In 1990, the 44/21a-6 well was drilled in the Southern North Sea. Core material was taken from the Westphalian A/B part of the core. Some of this core material was recently obtained by the TU Delft via the North Sea Core Initiative. Since the Westphalian A/B in the Pennine Basin is fluvio-deltaic in origin, it is highly variable both vertically and laterally. In this thesis we set out to develop a method to extrapolate facies found in the core material to recognize if these are
present in other locations in the well. This means that core material is correlated to the well log. This correlation is then extended over the rest of the well. Two investigation targets were chosen, the first facies is channel base facies, consisting of very coarse sandstone, the second a swamp facies. This firstly requires a detailed core log, and a short study of the well log data. The core log is interpreted in order to try to establish some form of elektrofacies. The well data is then formatted and different principal component analyses (PCA’s) are performed in order to differentiate the facies from their surroundings. For both analyses more than 90% of the variance was explained by the first two component axes, making them reliable. Both target facies require different data sets in order to distinguish them from their surroundings. The swamp facies
becomes easily visible from the third principal component axis, while the channel base sand is harder to differentiate, being recognizable from a point cloud in a principal component plot. In total 40 coals were found to be present over the researched well interval, starting underneath the Zechstein formation, from 12800 to 13800 ft. No other similar channel base coarse sands
were found over the interval apart from the one in the cored material. Overall, it seems that the basics for this method of detection and extrapolation is quite reliable and better than using the original log data, although it does need some further development and improvement.

The interest in carbonate lithologies has risen in the last few decades, due to discoveries of giant and supergiant carbonate reservoirs. While studying the properties of this lithology, the existence of cave systems at great depths was highlighted, since their presence can lead to drilling related problems, as well as change the flow direction of fluids in the subsurface. The possibility of predicting their orien- tations, dimensions and mechanical stability in the subsurface would therefore be of great help in the hydrocarbon business, which is why in this study, thanks to data provided by a Lidar laser scanner, a dimensional analysis of caves’ conduits related to their position within the karst system is performed. The origin of caves can be hypogenic or epigenic and they can present different patterns of distribution of conduits. When deformation events cause the generation of orthogonal sets of joints in the rock layers and fractures intersect with each other and with bedding planes, the fluid flow in the subsurface becomes channelized into these features. The combination of this and speleogenetic processes leads to the development of maze caves, whose conduits’ dimensions vary within a system as a consequence of differences of continuity and connectivity along a fracture network. Variations in the shapes of caves’ conduits can be observed as well, depending on the supply of sediment and the position relative to the water table during dissolution. Mechanical deformation of karst systems can be simulated by using the linear elastic deformation mathematical model. In this way it is possible to study the influence that mechanical properties such as Young’s modulus and Poisson’s ratio have on the mechanical stability of caves in the subsurface.

The primary reservoirs present in the Southern Chotts Basin, Central Tunisia, are located within Triassic, Permian and Ordovician units. They are mainly sourced by the Silurian -- Lower Devonian Fegaguira formation and its Hot Shale member. Late Paleozoic exhumation has eroded part of the Palaeozoic package, removing the Early Devonian -- Carboniferous and most of the Permian deposits in the Southern Chotts Basin. This resulted in a diachronous unconformity in the present-day stratigraphy and represents significant uncertainties. This study presents a reconstruction of the tectonic and thermal history of the Southern Chotts Basin and the subsequent impact on source rock thermal maturation, with an emphasis on the Hercynian exhumation. Implications on the petroleum systems in the basin are evaluated by means of a migration study. Investigation of adjacent analogue basins allows estimation of the amount of initially deposited sediment in the Early Devonian -- Permian. Calibration with vitrinite reflectance data minimizes exhumation uncertainties in the basin history and indicates ca. $2300$ m sediment eroded during the Hercynian phase. Subsidence analysis shows similar subsidence patterns throughout the area of interest since the Mesozoic. This argued to use a single set of high and low case initial deposition estimates, calibrated with vitrinite reflectance, in source rock maturation modelling. Source rock maturation modelling in the kitchen area indicates hydrocarbon generation occurs in two phases separated by a phase of stable maturity during Hercynian exhumation. Maturation in the kitchen area is found to currently be in the condensate -- wet gas zone. Migration modelling shows that Paleozoic generation in the northern and northeastern portion of the basin primarily sourced the present-day hydrocarbon discoveries. High capillary entry pressures in overlying Fegaguira shales forced hydrocarbons generated in the Hot Shale member to migrate downward into porous Ordovician units. Subsequently, hydrocarbons laterally migrate up-dip into local traps, where they remain trapped wherever the overlying source rock is preserved during Hercynian exhumation. The Ordovician units acts as a reservoir, and as a carrier bed to source present-day accumulation in the Triassic TAGI unit. A newly identified petroleum system primarily hosts accumulations in lower shoreface Ordovician El Atchane deposits, overlain by the Fegaguira and Hot Shales. Simulated hydrocarbon accumulations and projection of shoreface deposits throughout the area of interest mark a sweet spot area with significant reservoir potential in structural traps. Recommendations are given to further investigate the potential of this system.

Accurate and efficient predictions on the behavior of fluid flow and heat transport are required in the development of low-enthalpy geothermal reservoirs in fractured formations. Key challenges include the demand for high-resolution computational grids, the non-linear behavior of the system due to strong mass-heat coupling and the presence of fractures with large heterogeneity contrasts. In this work, a comparison is made between natural and molar variable formulation used to describe the coupled fluid-heat transport under non-isothermal conditions in low-enthalpy fractured porous media. The solutions and performance of the newly implemented molar formulation are compared to those of the existing natural variable formulation in the DARSim2 reservoir simulation framework. A fully implicit scheme (FIM) is applied to solve the coupled discrete system including mass and energy balance equations. Application of the Algebraic Dynamic Multilevel (ADM) method with projection-based Embedded Discrete Fracture Model (pEDFM) provides a scalable and efficient simulation framework for field-scale fractured reservoirs. The ADM method maps the fine-scale system onto a dynamically defined multilevel grid resolution system (Cusini et al., 2016, HosseiniMehr et al., 2020) based on the solution gradient and a series of restriction and prolongation operators, which ensure accurate capturing of fine-scale heterogeneities. Fractures are defined explicitly as either (highly) conductive passageways or flow barriers using the pEDFM formulation (Tene et al., 2017). Simulation results using the molar formulation are compared with an analytical solution as verification of the implementation. Results of various (un-)fractured test cases with homogeneous and heterogeneous permeability fields show that there is no clear difference between the solutions and performance of the different primary variable formulations, and the performance itself is largely dependent on the level of complexity embedded in the numerical model independent of the simulation strategy applied.

Geothermal energy reservoirs can be used as sources of renewable and sustainable energy. The concept of geothermal technology relies on the harvesting of heat from the deep rock by injecting fluid that circulates through the porous, fractured reservoir rock between the injection and production boreholes, and thereby transports the heat to the ground surface. The presence of fractures can strongly increase the permeability of the rock and thus enhance the flow circulation in the system. Properly being able to model the fluid flow through the porous, fractured rock is therefore of importance in the optimisation of reservoir design. For that reason, this study proposes a new material model, which relates fracture initiation and propagation to a change in the permeability of the rock, assuming a smeared approach. The fracture-dependent permeability model is developed using the Diana FEA software, and can be used in combination with other fracture models and the mixture analysis for the simulation of hydro-mechanical behaviour of rock. The study investigates two different methods for the formulation of a fracture-dependent permeability, whereby both methods adhere to the cubic law, which defines the permeability as a quadratic function of its aperture. Evaluation of the model shows that it is capable of simulating extensional (mode I) fractures in the vicinity of geothermal boreholes. However, the analyses also indicate a mesh-dependency as well as a sensitivity to its input parameters. Furthermore, the fracture-dependent permeability model can only simulate hydro-mechanical behaviour in situations other than (enhanced) geothermal energy systems to a limited extent. Further model development is therefore recommended.

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 main objective of this study is to quantify interference effects between production and injection wells for geothermal projects that operate within the same reservoir. The secondary objective is to study the time it takes for the reservoir unit to thermally recharge after production has stopped. Two reservoir simulators are benchmarked to decide which one to use for reaching these objectives. The Ammerlaan, Duijvestijn and DAP doublets, all targeting the the Delft Sandstone Member in the West Netherlands Basin, serve as a case study. A literature review is presented to gain a better understanding of the geological history and the structural setting. A box-model of the study area is created and used to benchmark the two reservoir simulators. A static reservoir model is developed in Petrel through seismic interpretation, structural modelling, facies modelling and petrophysical modelling. Populating this static model with dynamic properties allows us to perform reservoir simulations in Eclipse100 and study the propagation of pressure and temperature. A discrete parameter analysis aims to capture the uncertainties that are associated with reservoir modelling and simulation. In this study, data is used from seismic surveys, wireline logs, core studies, a cuttings study and the monthly production volumes of the Ammerlaan and Duijvestijn doublets. It is shown that interference on temperature has a long term (20-30 years) effect on the Duijvestijn (positively) and the Ammerlaan and DAP doublets (negatively). The combined total energy production of the three doublets over 100 years is small with a decrease of 3% due to temperature interference, compared to when running the doublets in stand-alone configuration. Interference on pressure has a short term (days) effect on the achieved flow rate when the injection well cannot reach its target injection rate and is constraint on the maximum allowable pressure at which it is allowed to inject. This occurs under the low permeability scenarios and can be observed when the pressure wave arrives at the neighbouring injector. The Duijvestijn, Ammerlaan and DAP doublets all benefit from this through a combined increase in energy production of 8% over 100 years of production, averaged over all scenarios. During thermal recharge after production, the average reservoir temperature increases asymptotically. Temperature recharges to 96.1% to 97.4% of the initial reservoir temperature after 1000 years of recharging under different thickness and conductivity scenarios. The absence of a thermal influx at the bottom of the reservoir model is limiting the capacity of the reservoir to recharge to its initial average temperature. Interviews are conducted to investigate the implications that the findings of this research have on the policy measures for geothermal projects. Suggestions for changes in policy are made to optimize the recovery of heat in the subsurface.

The Late Cenozoic Eridanos River brought vast amount of sediments to the North Sea Basin accumulating more than 1000m of deltaic deposits in less than 3.5 Ma. Since the gas discoveries in the shallow sediments were made, more attention is being paid to these deltaic deposits and that resulted in more data availability.
This study concentrates on the Eridanos Delta and identifies the properties of the delta in terms of its progadation distance and sedimentation rate and compare different time models to the ones provided by Overeem (2001) and Kuhlmann (2008). Furthermore, studies the reservoir rocks in terms of their petrophysical properties and facies distribution. Moreover investigates the reasoning behind the shallow sediments gas accumulations and factors behind the concentration of all the discoveries around the A and B blocks. Lastly, constructs a 3D model of the reservoirs distribution in the study area and their properties by integrating the study results of geological, geophysical, petrophysical and reservoir engineering data.
Such results were achieved by interpreting a high resolution 3D seismic survey and 2D lines in combination with wells’ wireline logs and core data. Seismically, a total of 12 units were mapped to categories the successions (3.6 – 1.8Ma) that deposited post the Mid Miocene Unconformity. In addition, more than 20 wells were used to understand the reservoir properties in which seven wells have cores. Sedimentological aspects were assessed by studying the descriptions of cores and thin sections and the measurements of the core plugs. Gas accumulations were studied by evaluating the production data for gas and linking the gas to its source.

Horizontal drilling and hydraulic fracturing have increased unconventional oil and gas extraction from shale reserves in the U.S. in the last decade, making up more than half of total U.S. oil and gas production at present. This activity results in NOx emissions in the extraction regions that are measurable from space using the Ozone Monitoring Instrument (OMI) on the NASA Aura satellite. The NOx emissions are a result of two different activities: (1) the drilling and hydraulic fracturing of new wells, and (2) the extraction of oil and gas after the well is completed. To separate the NOx emissions from drilling and extraction, a multiple linear regression to the NO2 columns as a function of time is calculated for 9 extraction regions using the number of drilling rigs and the oil and gas extraction data from 2007 until 2018. In 3 regions (Permian, Bakken, Eagle Ford) a significant correlation between measured and modeled NO2 columns is found, of which the Permian region shows the highest correlation. The analysis shows that half of the total NOx emissions in the Permian region can be attributed to emissions from oil and gas activities, and that both the drilling and extraction activities have an equal share in the emissions. A fuel-based oil and gas emission inventory shows a different split for NOx emissions from drilling and extraction in the Permian region, indicating drilling as the larger source. In other extraction regions, NO2 columns show poor correlation with the oil and gas activities due to the proximity of urban areas (Barnett, Denver-Julesburg, Haynesville regions), power plants (San Juan) or variations in the drilling and extraction activity over time that are too small (Uintah, Upper Green River).

The upper reservoir intervals of the Lower Jurassic Åre Formation in the Heidrun Field (Offshore mid-Norway) are very heterolithic and have the lowest oil recovery factor of the field despite significant amounts of remaining reserves. One of these reservoir zones is the formation Åre 6.2, which is mainly composed of tide-dominated heterolithic channel belt deposits. It contains particular layers that have excellent properties with permeabilities up to 10 Darcy. These layers are predicted to affect the production results as they can act as ‘thief zones’ within the low permeable heterolithic facies causing large quantities of water to flow through, leading to poor sweep efficiency and early water breakthrough. This study focuses on constructing conceptual depositional models of the Åre 6.2 and building detailed geological models to investigate the effect of the thief zones on overall fluid flow predictions.

Conceptual depositional models were constructed by determining the characteristics of the reservoir and its depositional environment. Seven cored wells were used as the primary data to interpret lithofacies and facies associations. The study showed that Åre 6.2 mainly consisted of structured sandstones and heterolithic lithofacies with features that indicate that tidal process play an important role in the deposition. The influence of tidal process on deposition is further exemplified by the identification of two different types of channel facies associations, which are tidal and distributary channels. The thief zones were found in both facies associations, suggesting that the thief zones were formed during high freshwater discharge into the channels supplying coarse sandy material influx during a phase of high-energy deposition. To make detailed models of the tidal and distributary channels, multiscale modeling techniques were utilized to better represent the reservoir heterogeneities at the lithofacies and facies association scales.

At the lithofacies scale, models were built in SBEDTM and the upscaled values of each lithofacies were obtained by applying the Representative Element Volume (REV) concept. The upscaled values were then used as input in the facies association scale models in order to represent the heterogeneities at the lithofacies scale to the next heterogeneity level. This step is essential since heterogeneities at a smaller scale may affect reservoir flow properties. Two different channel models were built in ReservoirStudioTM based on the conceptual depositional model and using outcrop analogue data from the Gule Horn Formation (Neill Klinter Group) in the Albuen area (Greenland). Flow-based upscaling was used to analyze the model uncertainties and determine a proper upscaling grid size. Finally, streamline simulations were performed to identify the effect of the thief zones. The simulation confirms that the thief zones influence fluid flow in the reservoir zone significantly as most flow was concentrated in the thief zones.