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.

The TU Delft campus geothermal project has joint objectives of research and commercial thermal energy production. It has been developed and will be operated by the Geothermie Delft (GTD) consortium, a commercial cooperation between TU Delft, Aardyn, EBN and Shell Geothermal. This report gives an overview of the research activities that have been carried out during the implementation of the doublet drilling the wells DEL-GT-01 and DEL-GT-02, and the sidetracks DEL-GT-02-S1 and DEL-GT-02-S2 in the period June - December 2023. The research programme and related operations during the installation of the campus geothermal wells have been led by the scientific team of TU Delft department of Geoscience and Engineering. The project is part of the national research infrastructure for solid Earth science (https://epos-nl.nl/), and offers the possibility to do state of the art research on an operating geothermal system.
The main research activities that were carried out during the implementation of the geothermal wells included rock sampling in the form of a detailed drill cutting sampling set, full cores and sidewall cores of the caprock and the geothermal reservoir, open-hole logging of the reservoir formations and the installation of a fibre optic cable in the producer (still to be carried out).
Overall, the following samples and data were collected as part of the scientific programme:
- 15m of 4”core from the direct caprock of the producer reservoir section
- 71m of 4”core from the reservoir section of the producer
- 78 sidewall cores from the injector reservoir section
- 2400 cutting samples
- 3000m of open-hole and closed-hole logging data
Details of these activities can be found in the report and the related appendices. All data presented in this report have been published via TU Delft institutional data repository and can be found online as part of the data collection associated with the research programme of the project: Geothermal Project on TU Delft Campus Collection at https://doi.org/10.4121/85b3725b-80fa-4b0b-9db2-475bfd8f0265.

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.

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.

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).

This study presents a novel geotechnical engineering approach that utilizes naturally occurring processes to reduce soil permeability in-situ. This approach is inspired by a soil stratification process (Podzolization), where a low permeability layer is formed by metal-organic matter precipitates. In a field experiment, a direct aluminum-organic matter (Al-OM) floc injection was applied to create a continuous vertical flow barrier in a dike. Direct injection uses the shear-dependent size of Al-OM flocs. High-shear conditions (i.e., during injection) lead to the breakage of Al-OM flocs and thus allow their transportation in soils. When the injection stops and low-shear conditions prevail, the Al-OM flocs re-grow in size and block the pores, which ultimately reduces soil permeability. Two different Al-OM floc concentrations were applied in the field. Results show that a continuous flow barrier is only formed at lower concentrations; at higher concentrations a scattered permeability reduction was achieved. This demonstrates the viability of this approach in reducing soil permeability in-situ and shows that the spatial distribution of the flocs depends on input concentration.

The European Plate Observing System - Netherlands (EPOS-NL) is the Dutch research infrastructure for solid Earth sciences. EPOS-NL is a cluster of large-scale geophysical facilities for research on georesources and geohazards. It is a partnership between Delft University of Technology (TU Delft), the Royal Netherlands Meteorological Institute (KNMI) and Utrecht University (UU) and is funded by NWO, as part of the national roadmap for large-scale research infrastructure. EPOS-NL facilities include 1) The Earth Simulation Lab at UU, 2) The Groningen gas field seismological network and the ORFEUS Data Centre at KNMI, 3) The deep geothermal (DAP-)well to be installed on the TU Delft campus, and 4) A distributed facility for multi-scale imaging and tomography (MINT) at UU and TU Delft. EPOS-NL aims to further develop the infrastructure for solid Earth scientific research. It also makes cutting-edge research facilities and data available to (inter)national researchers, aiming to address key geo-societal challenges, notably: • Exploration for (renewable) geo-energy resources • Storage of fuels, CO2 and wastewater in the sub-surface, and • Hazards such as induced or natural earthquakes Addressing these challenges requires a multi-physics, multi-scale approach, and open access to state-of-the-art research facilities and data. EPOS-NL contributes to addressing these needs.

Using naturally occurring processes to modify the engineering properties of the subsurface has received increasing attention from industry and research communities as they aid in the development of cost-effective, robust and sustainable engineering technologies. In line with this trend, we propose to use precipitates of aluminum (Al) and organic matter (OM) to reduce soil permeability in-situ. This process is inspired by podzolization: a soil stratification process where a layer with low permeability is developed at depth via the precipitation of metal-OM complexes. In this study, the concept of applying Al-OM precipitates for in-situ soil permeability reduction was for the first time applied in the field. The aim of the field experiment was to create a cylindrical flow barrier in a sand layer at depth. In order to design and engineer the field application, we performed a series of scenario analyses with a site-specific 3D reactive transport model. This led to an in-situ engineering approach where a flow barrier was created by separate injection of Al and OM using a combined injection/extraction strategy. During the field application, the local variation of soil conditions required significant modifications to the design. Further scenario analyses with the model were conducted to adapt the original design and to understand the consequences of these modifications. The results show that a cylindrical flow barrier was created after an injection period of 8 days. The precipitation of Al-OM is a highly localized process, where large amount of precipitates is formed in the close vicinity of the injection filter screens. Evaluation of pumping tests that were performed after the injection activities revealed that the permeability of the treated sand was reduced to 2% of its original value. This first full-scale field test demonstrates that applying Al-OM precipitates is a suitable bio-based engineering tool to reduce soil permeability in-situ.

Using naturally occurring processes to modify the engineering properties of the subsurface has gained increasing attention from industrial and research communities as they aid in the development of cost-effective, robust and sustainable engineering technologies. In line with this trend, we propose to use the interaction between aluminum (Al) and organic matter (OM) to reduce soil permeability in situ. This is inspired by podzolization: a soil stratification process where the mobilization of Al, iron and OM in the topsoil is followed by their precipitation at greater depth. In this study this newly developed engineering technique has been applied for the first time in the field. The aim of the field test was to create a cylindrical flow barrier (5 m i.d.) in a sand layer, located at a depth between 7 to 13 m below ground surface (bgs). A 3D reactive transport model was developed via the coupling between Darcy’s law and solutes transport, meanwhile Al-OM precipitation and its impact on permeability are included. The model was used to design and analyze the results from the field test. At the site Al and OM solutions were injected separately through 20 injection wells distributed in two circles with a radius of 2.5 m for Al injection and 3 m for OM injection. An extraction well was placed in the center of these two circles to control in situ mixing and precipitation of Al and OM and precipitation of these two components in a specific zone. Results demonstrated that after a period of 8 days, we successfully created a cylindrical flow barrier where precipitates formed in close vicinity of the injection filter screens. The permeability of the treated sand was reduced to 2.3 % of its original value. Pumping tests conducted 6 months after the treatment showed no change in the achieved permeability reduction, indicating the stability of the Al-OM precipitates during this period. Further investigation is however necessary to evaluate the long-term stability of the flow barrier. This field study demonstrates the viability of using Al and OM complexation and precipitation as an in situ engineering tool to reduce soil permeability. By separate injection of the two components and a combined injection/extraction strategy, we were able to induce in situ mixing of Al and OM and control the geometry of the formed flow barrier.

The utilization of natural processes for in situ permeability reduction has seen a growing interest in recent years since controlling infiltration or seepage of water is one of the most challenging tasks in water management and civil-engineering. We hereby propose a novel geoengineering tool for in situ permeability reduction, namely Soil Sealing by Enhanced Aluminum and organic matter Leaching (SoSEAL). SoSEAL makes use of the interaction between organic matter (OM) and aluminum (Al). Complexation and subsequent precipitation of OM by Al results in the formation of soil layers with reduced permeability; a process which is well known from podzols. This study demonstrates the suitability of the SoSEAL technique for permeability reduction in laboratory experiments. All experiments have been performed using humic acid (HUMIN P775, Humintech, Germany) as an OM source and aluminum chloride as the metal component. Batch experiments were conducted to study the interaction between OM and Al at various metal to organic carbon (M/C) ratios and pH levels. Results show that the precipitation of Al-OM flocs depends on the Al concentration and therefore the M/C ratio, which is well-known from OM removal in drinking water treatment. Precipitation of the hereby used humic acid starts to occur at a molar M/C ratio of 0.01 and almost all OM is removed at M/C ratios larger than 0.04. The size of the Al-OM flocs ranges between 20 and 1000 m, which enables them to cover micro- and mesopores in porous media and therefore reduce the permeability. In order to quantify the permeability reduction that can be achieved by Al-OM flocs, saturated column experiments were performed using sand with three different grain size distributions and applying various injection strategies to induce in situ mixing of the two separately injected components (i.e. Al and OM). We were able to reduce the hydraulic conductivity in the sand column to a range between 10 and 40% of its initial value. Results show that the reduction in permeability depends on several factors including the sand type, the injection technique, mixing and reaction of the two components in situ, and the orientation of the precipitation band. We conclude that the precipitation of Al-OM flocs induced by in situ mixing of Al and DOM can significantly reduce the permeability of different sand types. These results are the proof of principle of the SoSEAL concept.

This project focuses on the urban renewal of (delta) metropolises and concentrates on the question how to design resilient, durable (subsurface) infrastructure in urban renewal projects using parameters of the natural system – linking in an efficient way (a) water cycle, (b) soil and subsurface conditions, (c) soil improvement technology, and (d) opportunities in urban renewal (e.g. urban growth or shrinkage). The subsurface is the technical space, the engine room of a city, housing the vital functions of water, electricity, sewers and drainage, but also housing the natural system that is crucial for a stable, green, healthy and livable city. Especially the effects of climate change, the boosts for an energy transition and the fact that there are less financial mean makes the intelligent use of the subsurface more important. This prublication reprots on the explorative method to get insight and design methods for the urban renewal of (delta) metropolises where resilient, durable (subsurface) infrastructure is carefully balanced out with parameters of the natural system. The question “how can the different technological artefacts in the subsurface be synchronized offering more space and adding to a better urban quality?” is answered by taking procedural steps from the technology (the knowledge of) to the design of public space and urban main structures. In each step the translation from the engineering language to the language of the urban designer (and vice-versa) is done producing an informative and useful overview in how to relate technological artefacts to urban quality.
In order to reach interdisciplinary design, explorative research is used for creating a shared language. Explorative research has been useful because the problems at hand are wicked problems that has not been clearly defined. The exploration was framed by co-creation in workshops and later a more precise elaboration of these results in the working group.

The utilization of natural processes for engineering purposes has been widely discussed in recent years since they might enable the development of cost-effective, robust and environmentally compatible engineering technologies. Biomineralization is one of the many possible biogeochemical processes that is currently investigated in detail. We propose the use of another natural process, namely podzolisation, as a novel geoengineering tool for in situ permeability reduction. Podzolisation is a soil formation process where the mobilization and subsequent leaching of aluminium, iron and organic matter (OM) in the topsoil is followed by their precipitation at greater depth. The accumulation of Al/Fe-OM precipitates results in the formation of an almost impermeable soil layer [1]. In situ permeability reduction is interesting for several engineering questions, e.g., prevention of piping, leaking water bodies, and contaminant spreading. Preliminary experiments and modelling results revealed that Al-OM precipitates can reduce the hydraulic conductivity in sand by up to 4 orders of magnitude. In order to apply the podzolisation process for engineering purposes, it is, however, necessary to control the reaction kinetics and ensure Al-OM precipitation over the entire desired treatment zone within a porous media. Therefore, a 2D experimental setup (80x160x5 cm) equipped with numerous pressure and electrical resistance tomography (ERT) sensors is used to tests different kind of injection strategies and their effect on the permeability reduction within a porous media. A reactive transport model coupling a MATLABbased toolbox and ORCHESTRA (equilibrium reaction processor) is used (1) to design the injection strategies and (2) to simulate the solute transport, the geochemical reactions and their effect on the permeability within the experimental setup. The experimental results will be used to validate the model and to implement the most promising injection strategy in the field.