Nearly half of the Netherlands’ natural gas consump tion is allocated to heating, with direct -use geothermal heating being one of the available low-carbon energy solutions. A geothermal well doublet, designed with the two primary aims of research and commercial heat supply, is currently being installed on the campus of Delft University of Technology. The project is a key national research infrastructure and is being incorporated into the European sustainable and distributed infrastructure (EPOS: European Plate Observing System, https://www.epos-eu.org/), such that accessibility and data availability will be as wide as possible. All observations will be included in a digital-twin framework, which will allow us to make better decisions in future geothermal projects. The project includes a comprehens ive research program, involving the installation of a wide range of instruments alongside an extensive logging and coring program and monitoring network. The doublet has been cored, with substantial continuous samples from the heterogeneous reservoir, alongside a large suite of well logs in both the reservoir and overlying geological units. Such investigation is rarely undertaken in geothermal projects. A fiber-optic cable will monitor the producer well all the way down to the reservoir section, at approximately 2300m depth, in the Lower Cretaceous Delft Sandstone that is used as a geothermal reservoir in a series of existing and planned doublets in the West Netherlands Basin. A local seismic monitoring network has been installed in the surrounding area with the aim of monitoring very low-magnitude natural or induced seismicity. A vertical observation well with electromagnetic sensors will be drilled in the near future between the injector and producer to monitor cold-front propagation. This paper presents the initial modeling for the project and steps towards the production of a digital twin. Two modeling examples in the paper will emp hasize current operational challenges relevant to the project.@en

A geothermal well doublet, designed with two primary aims; one of research and the second of commercial thermal energy supply, is currently being installed on the campus of Delft University of Technology, with the wells being drilled in the second half of 2023. The project includes a comprehensive research program, involving the installation of a wide range of instruments alongside an extensive logging and coring program and monitoring network. The doublet has been cored, with continuous samples from the heterogenous reservoir being complimented with more distributed side-wall cores, alongside a large suite of open-hole well logs in the reservoir section of both wells. Such investigation is rarely undertaken in geothermal projects. A fiber optic cable will monitor the production well, and will be installed all-the-way down to the reservoir section when the well completion is installed, at approximately 2300m depth. The reservoir is the fluvial Lower Cretaceous Delft Sandstone that is used as a geothermal reservoir in a series of existing and planned doublets in the West Netherlands Basin. A local seismic monitoring network has been installed in the surrounding area with the aim of monitoring very low-magnitude natural or induced seismicity. A vertical observation well with electromagnetic sensors will be drilled in a few y ears’ time between the injector and producer to monitor cold-front propagation. The total project is targeted to supply around 25 MW of thermal energy at peak conditions, next to this project a thermal energy storage system is planned to provide a seasonal buffer. The project is a key national research infrastructure and is being incorporated into the European infrastructure EPOS (European Plate Observing System, https://www.epos-eu.org/), such that accessibility and data availability will be as wide as possible. All observations will be included in a digital-twin framework that will allow better decisions to be made in future geothermal projects. This paper presents the implementation and initial data collection from the project, including an initial evaluation of the logging and coring campaigns.@en

A geothermal doublet has been installed in a sedimentary reservoir for direct-use heating on the TU Delft campus, targeted to supply around 25 MW of thermal energy at peak conditions. This contribution presents the implementation and initial data collection from the doublet, including an initial evaluation of the logging and coring campaign. Nearly half of Netherlands natural gas consumption is allocated to heating, and the on-campus CO2 emissions from heating exceed 50%. The doublet has been designed with two primary aims of research and commercial heat supply, with the wells being completed in December 2023. The project will be operated by a commercial entity, and built into a larger thermal energy system including a high temperature underground storage system, with the first energy production planned in 2025. The research questions relate to field-scale geothermal operations, e.g. how reliable is the long-term energy production?, how do materials perform in the long-term? and how can geothermal projects be best monitored? The research programme involves the installation of a wide range of instruments alongside an extensive logging and coring program and monitoring network. The doublet has been cored, with substantial continuous samples from the heterogenous reservoir, alongside a large suite of open hole well logs in the reservoir and through casing logs in overlying geological units. A fiber-optic cable will monitor distributed pressure throughout the producer reservoir section, at approximately 2300m depth, which will be installed during commissioning. A local seismic monitoring network has been installed in the surrounding area with the aim of monitoring very low-magnitude natural or induced seismicity. The project is a key national research infrastructure and is being incorporated into the European EPOS (European Plate Observing System, https://www.epos-eu.org/), such that accessibility and data availability will be as wide as possible. All observations will be included in a digital-twin framework that will allow to make better decisions in future geothermal projects.@en

In 3D seismic data acquisition, sufficiently dense spatial sampling is most often not possible, because of physical, financial, and temporal constraints. The resulting aliased data is a major obstacle for accurate subsurface images. Therefore, methods are needed to reconstruct these sparse data to an adequate sampling. We develop a novel kinematic wavefront-based seismic data reconstruction method that uses the existing nonlinear beamforming (NLBF) framework, which allows for building a more detailed sampling from a sparse input. We present the theory and methodology of our NLBF reconstruction algorithm and test it on a synthetic Society of Exploration Geophysicists Advanced Modeling (SEAM) Arid dataset and a field dataset. We attempt to answer the following question: can the NLBF framework be used for seismic data reconstruction, and how do these results compare to some conventional reconstruction methods? Control parameter tests are performed to find the optimal NLBF reconstruction, and results are compared to those from several control methods including the convergent alternating projection onto convex sets (POCS) and bootstrap POCS methods, which were also developed for this study. Our NLBF reconstruction method successfully reconstructs high-quality data on both datasets. We find that the optimal NLBF control parameters are ultimately dataset-dependent as the concrete data acquisition geometry plays a central role. Specifically for our datasets, optimal parameters include a time window of 12∆ts, an operator aperture of 600 m x 600 m, and a parameter trace interval of ∆x = ∆y = 60 m. The synthetic SEAM Arid NLBF reconstruction results show high trace fidelity to the ground truth. The field data NLBF results show better-reconstructed gaps, and wavefield variations closer to those of physical propagating waves in comparison to our control methods. These results show the potential of the NLBF reconstruction method to become a common data reconstruction tool used in the seismic industry.

When humans started started exploiting the abundant underground natural resources the Earth has to offer such as hydrocarbons, minerals and heat, we started to experience earthquakes that are related to this exploitation, so called induced earthquakes. Under certain conditions those can damage local infrastructure. However, most events are weak and only sensed by seismic sensors. Microseismic monitoring plays a vital role to optimize and insure the safety of these underground activities and new technologies such as carbon capture and storage. One key task besides the detection of microseimsic events is to determine the source location of these events using data recorded at the surface. In this thesis we investigate a method to localize weak microseismic events, using a deterministic approach, assuming a dense network of sensors. In simple words this method takes the seismic signals recorded at the Earth’s surface and sends them back into the Earth, where the signals start to focus at the point they originated from. This focusing method uses one-way wavefield extrapolation with an estimate of the background velocity model. The advantage of this method is that the weak signals recorded by the different sensors at the surface are amplified as they approach the location of the event that emitted the signal due to constructive interference. However, this is not enough to reliably recover the source location because typically earthquakes do not radiate seismic waves evenly; complex radiation patterns are typically observed depending on the mechanical properties of the rupture. To obtain a strong focused signal at the optimal source location we therefore perform a grid search over possible source mechanisms and increase the strength of the signal by deconvolution. Without taking the source mechanism into account we are not able to obtain accurate source locations, especially at low signal-to-noise ratios. However, by taking the source mechanism into account we are able to retrieve accurate source locations while also retrieving information about the source mechanism. Good results were obtained for 2D synthetic data for both a simple subsurface model as well as the realistic Annerveen salt model even when realistic noise was added... @en

The multi-purpose research borehole at the Delftse Hout is the third of four seismic monitoring locations of the seismic monitoring network for the geothermal research project on the TU Delft campus (Geothermal Delft GTD, also known as DAPwell, https://geothermiedelft.nl/). For the geothermal research project, two deep wells (“a doublet” consisting of an injector and a producer) for geothermal energy extraction will be installed on the TU Delft campus next to the combined heat and power plant (“warmtekrachtcentrale - WKC”). The system will produce geothermal heat to supply the campus of TU Delft and part of the city of Delft.
The herein presented borehole describes the installation of a multi-purpose research borehole (called DAPGEO-02), which was installed in the period February - May 2022. DAPGEO-02 is part of a seismic monitoring system for the shallow and deeper subsurface in the vicinity of the planned geothermal doublet. The locations of all four stations are given in Figure 1. The monitoring network and the related research gathers knowledge about the current status of the subsurface on the basis of periodic data measurements, and possible seasonal effects.
Within the seismic monitoring network, three seismic monitoring stations have already been installed, respectively DAPGEO-01 on the proposed location of the geothermal project near the Leeghwaterstraat in Delft, DAPGEO-03 on the Kerkpolderweg in Delft, and ZH03 in on the Ackersdijkseweg in Pijnacker-Nootdorp (installed and equipped by KNMI).@en

Failure of subsea wind turbine cables are the main cause for wind farm downtimes. Furthermore, 80% of insurance payouts to wind farms come from cable repairs and maintenance. Cable tracking is part of the wind farm cables maintenance scheme. Surveys are required for localisation and determining the depth of burial of the cables. Conventional surveying methods have shortcomings when it comes to localising offshore buried power cables, which can be resolved by using electromagnetic methods. From the measured magnetic field created by the cable, its position and burial depth can be inverted. Forward modelling the magnetic response of cables improves the understanding of their electromagnetic behaviour in one dimensional complex submarine environments. Maxwell's equations are the cornerstones of understanding the behaviour of electromagnetic fields, forming the basis of the models. Implementing numerical modelling packages like Empymod accommodate for boundary conditions in one-dimensional layered media to more accurately investigate the magnetic response of electric cables. Land measurements show that Empymod's numerical models can model cables in the accuracy range of 2-15% depending on the distance. New numerical model analyses show the influence of water depth, underlying layers, depth of burial, geometrical complexities and adjacent cables on the magnetic field. Surrounding resistivity contrasts together with changes in water depth change the measured magnitude of the magnetic field by up to 10%. Geometrical complexities have large effects on the magnetic field, sometimes completely changing the expected response. Therefore, twisted and irregularly shaped cables can pose problems when inverting for their position during surveys.

In a surface-seismic setting, Distributed Acoustic Sensing (DAS) is still not a widely adopted method for near-surface characterisation, especially for reflection seismic imaging, despite the dense spatial sampling it provides over long distances. This is mainly due to the decreased broadside sensitivity that DAS suffers from when buried horizontally in the ground (that is when the upgoing wavefield (e.g. reflected wavefield) is perpendicular to the optical fibre). This is unlike borehole settings (e.g. zero-offset Vertical Seismic Profiling), where DAS has been widely adopted for many monitoring applications. Advancements in the field, like shaping the fibre to a helix, commonly known as helically wound fibre, allow better sensitivity for the reflections. The promise of spatially dense seismic data over long distances is an attractive prospect for retrieving the local variations of near-surface properties. This is particularly valuable for areas impacted by induced seismicity, as is the case in the Groningen Province in the north of The Netherlands, where near-surface properties, mostly composed of clays and peats, play an essential role on the amount of damage on the very near-surface and the structures built on it. Installing fibre-optic cables for passive and active measurements is valuable in this situation. We installed multiple cables containing different fibre configurations of straight and helically wound fibres, buried in a 2-m deep trench. The combination of the different fibre configurations allows us to obtain multi-component information. We observe differences in the amplitude and phase information, suggesting that these differences can be used for separating the different components of the wave motion. We also see that using enhanced backscatter fibres, reflection images can be obtained for the helically wound fibre as well as the straight fibre, despite the decreased broadside sensitivity for the latter. @en

Seismic imaging characteristics of a prototype electrically driven, linear synchronous motor-based, vertical-force seismic vibrator ("e-vib") were evaluated at a site in the Netherlands. The system weighs 1.65 t and excites seismic signals with a peak force of 6.7 kN. Data were recorded along two collocated geophone-based nodal and landstreamer microelectromechanical system - MEMS-based sensor 2D seismic profiles. To obtain a broad bandwidth data set, the e-vib operated with a 1-200 Hz linear sweep. Shot gathers of the merged nodal-landstreamer data set indicated good-quality seismic data of a broadband nature. The processed merged data set demonstrates high-resolution reflections of the stratigraphic members from approximately 200 m to 2 km, with visible reflections as deep as 2.5-2.9 km. As a reference, we also processed a legacy 3D microspread data set acquired at the same site with a magnitude stronger (14.1 t, 67.5 kN) hydraulic vibrator. Comparison of our nodal-landstreamer seismic section versus 2D slices extracted from the processed microspread seismic volume suggested similar signal penetration depth and the same key marker horizons seen in both. Analysis of the reaction mass and base-plate accelerometer signals recorded with the e-vib source operating on grass and on asphalt surfaces indicates that the e-vib has low total harmonic distortion. The results obtained indicate that, although relatively small, the e-vib is capable of generating high-quality broadband seismic data.

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In this thesis, we discuss two pattern recognition techniques, template matching, and neural networks. We discuss how these techniques have been used for the development of two earthquake detection algorithms. The first algorithm is based on template matching and the second is based on deep learning. The algorithms are designed for the detection of small <0.5M events in the subsurface of Zeerijp, Groningen. These two algorithms have been compared to assess their earthquake detectability and practicality. The systems have been compared using field data from Zeerijp. The algorithm based on deep learning (a neural network) produced too many false positives considering the amount of seismic data we would like to use it for. The algorithm based on template matching did not produce any false positives during testing. The template matching system has been fed six months of continuous seismic data fromZeerijp. This resulted in the detection of at least 22 new events.

The cumulative incision rates of ~50–70 m/Ma integrating over the last ~3 Ma have been derived from published terrace-chronological data of the Danube river in the Western Pannonian Basin. An apparent acceleration of uplift rates was observed for shorter timescales culminating at ~200 m/Ma over the last ~140 ka. An examination of the change of the incision rates through time revealed that the incision rate was fairly constant at ~50 m/Ma from ~3 Ma to ~140 ka, and the faster rates are valid only for the last ~140 ka. These findings suggest that the long-term uplift rate of the northwestern limb of the Transdanubian Range is ~50 m/Ma, and the apparent acceleration of river incision during the Late Pleistocene is considered as the result of faster, most probably climate-driven incision during the last glacial cycle, outpacing the long-term uplift rate. The observed upper crustal neotectonic faults are not sufficient to accommodate the deformation necessary for the reported Pliocene to Quaternary vertical motion. The geodynamic model for the explanation of the magnitude and pattern of surface uplift in the western Pannonian Basin involves a complex interplay between (1) deep lithosphere-asthenosphere dynamics, (2) structural inversion governed by the northward drift of Adria, (3) inherited geological structures and (4) climate driven surface processes (denudation and sediment loading).

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Controlled-source electromagnetic (CSEM) data are sensitive to the subsurface resistivity distribution, but 3D inversion results are ambiguous, and in-depth interpretation is challenging. Resolution and sensitivity analysis as well as the influence of noise on resolution have been used to quantify 3D inversion performance. Based on these numerical studies, a land-based CSEM survey was designed and carried out at the Schoonebeek oil field, the Netherlands. The acquired data were processed and subsequently inverted for the resistivity distribution. The 1D and 3D inversion of horizontal electric-field data show the reservoir at the right depth, matching well-log data without using a priori knowledge about the actual reservoir depth. We used a 1D model with fine layering as a starting model for 3D inversion. Synthetic data inversions and sensitivity tests demonstrate that resistive or conductive bodies inside the reservoir zone may be well-detectable with our limited acquisition geometry. Spatial variations in the reservoir resistivity are visible in the measured data and after inversion by assuming good knowledge of the background resistivity distribution. The reservoir resistivity and size, however, have to be interpreted with care considering the intrinsically low resolution of electromagnetic (EM) which is further reduced by manmade EM noise.

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Geophysical methods are widely used for hydrocarbon exploration and time-lapse measurements. One method that can be applied in place of or in addition to the routinely used seismic method, is the Controlled-Source ElectroMagnetic (CSEM) method. The work described in this thesis explores various aspects to improve the land CSEM method for exploration and monitoring purposes. Therefore, three separate active land CSEM field experiments, a baseline and two repeat surveys, were carried out over a period of nearly two years at the Dutch Schoonebeek oil field, where heavy oil is produced by injecting steam to reduce the viscosity of the oil. Steam injection and oil production have to be closely monitored to prevent breakthrough of steam to production wells and to detect possible unwanted leakage or contamination of groundwater such that further measures can be taken.@en

During a seismic experiment, mechanical waves are usually generated by various manmade sources. These waves propagate in the subsurface and are recorded at receivers. Modern seismic exploration methods analyze them to infer the mechanical properties of the subsurface; this is commonly referred as quantitative imaging. These properties assist in the determination of the subsurface rock type and structure. Exploration methods are not only useful while looking for the deposits such as crude oil, natural gas and minerals but also for near-surface geotechnical investigation. A motive of this thesis is to adopt these methods to image the subsurface ahead of a tunnel-boring machine for hazard assessment during excavation. Full-waveform inversion (FWI) is a gradient-based optimization problem that is employed in seismic exploration for quantitative imaging of the recorded waves. During FWI, seismic waves are simulated in a computer by using certain physical laws that govern the wave propagation. After inversion, output subsurface properties simulate waves that fit the recorded waves in a least-squares sense. In other words, the gradient-based optimization aims to find the minimum of the least-squares misfit between the simulated and the recorded waves. Finding such a minimum is not straight forward due to the existence of multiple local minima when using the least-squares objective. As a result, it might often happen that the optimizer converges to local minima, where the simulated waves only partially explain the recorded waves. The presence of local minima is associated to the strong non-linear dependence of the recorded waves on the subsurface properties. In this thesis, we attempt to overcome this difficulty. We propose a new measure of misfit between the recorded and the simulated waves. This measure compares the waveforms in a simplified form after taking the absolute value and blurring. We show that the new misfit measure suffers less from the local-minima problem. For robust inversion, we use a multi-objective inversion scheme, where the new measure is used as an auxiliary objective to pull the trapped solution out of the least-squares local minimum whenever necessary. In multi-parameter FWI, more than one kind of subsurface properties are simultaneously estimated. When only the first-order derivatives of the misfit are used during minimization, different choices of subsurface parameterization are not equivalent; they can be interpreted as different preconditioners. Therefore, the choice of parametrization will affect the rate of convergence in multi-parameter FWI and the best choice of parameterization is the one with the highest rate. In this thesis, we also analyse various choices of subsurface parameterization in search of the best one. It is well known that the local-minima problem in FWI can easily be resolved by reliably generating and recording low-frequency waves in the subsurface. Recently, a seismic source capable of generating such low frequencies is developed based on linear synchronous motors technology. Finally, we demonstrated a shear-wave seismic ground prediction system using these sources to enable imaging ahead of a tunnel boring machine (TBM). @en

The seismic method is an important indirect method to investigate the subsurface of the earth. By analyzing how the earth affects the propagation of mechanical waves, the structure of the earth and its seismic properties can be inferred. The seismic vibrator is the most commonly used land source in active-source exploration and monitoring to generate these waves and is the subject of this thesis. The goal of a seismic vibrator is to produce seismic waves with a known signal signature. Commonly sinusoidal signals whose frequency varies over time, called sweeps, are used for this purpose. These signals are typically quite lengthy to compensate for the fact that the instantaneous amplitudes of the vibrator are relatively weak compared to the ones from impulsive sources and the target depths faced. Via the processing step of correlation, the lengthy source signature is collapsed and virtual records are generated as if the vibrator would have released all energy at once. The quality of these virtual records depends on the ability of the vibrator engines to generate the force signature wanted and the ability of the vibrator mechanics and the vibrator-ground interaction to successfully transform the driving force to a seismic wave. In this thesis we investigate the feasibility of driving a vibrator with linear synchronous motors, the influence of drive level on the signals a vibrator generates, the effect of the vibrator-ground coupling, and the possibilities to design more robust source signals.@en