This study represents the first documented field application of micro turbine drilling in a clay formation, conducted from a 5.5 in. (13.97 cm) cased borehole in Marl, Germany. The operation was performed for an operator, whose tasks include the monitoring of the aquifers of the overburden in the greater Ruhr area. The operation was intended to provide the basis for a hydraulic test to determine the vertical permeability of the Emscher Formation, for which more precise information is not yet available. Micro turbine drilling technology is a novel drilling method that allows micro- sidetracks to be drilled into the surrounding rock formation from an existing borehole. The micro- sidetracks, which are several meters in length, can be used to establish a connection between the rock and the borehole. In this project, a 1,161 ft (354 m) deep borehole was penetrated at two specified depths 951 ft (290 m) and 1,083 ft (330 m) by six microsidetracks each with a uniform angular phasing of 60 degrees. One of the key novelties of this new approach is that steel casing and formation can be drilled in a single operation.

An innovative thermal pilot plant at the Fraunhofer IEG location in Bochum is a proof of concept for the technical use of high-temperature heat pumps (HTHPs) with seasonal mine thermal energy storages (MTESs), as a heat source, to supply conventional district heating grids (DHGs), significantly lowering CO2 emissions from fossil fuel employment. In this study, we present the steps involved in plant development, from preparation and planning to construction, testing and heat injection, which were essential for achieving successful operation and advancing the plant from TRL 4 to TRL 8. The implementation phases enabled the injection of heat into the DH grid, currently allowing to save annually up to 4800 tons of CO2 emissions, and represent a solid base for the construction of analogous experimental systems, which will be increasingly required due to greenhouse gas emissions reduction and renewable energy implementation. An important technological accomplishment of the project is the first-time achievement of the HTHP, which features a cascaded system of two units with ammonia and butane as refrigerants, of a supply temperature of 120 degrees C. The plant technology can be transferred and scaled to various applications, including industrial processes and low-temperature DHGs, and locations. Given the abundance of unused mining facilities and high thermal energy needs in these regions, the system can be implemented in former mining areas and paired with other geothermal sources. Depending on the available MTES, various HTHP sizes can be considered, ranging from tens of MW to smaller than the installed one.

The research aims to prove that renewable energy sources in the heating sector can enable the energy transition towards European and German CO2 reduction targets. To do so, at the premises of the Fraunhofer IEG Institute in Bochum a demonstrator for high-temperature heat pumps (HTHPs), coupled with seasonal high-temperature mine thermal energy storage (MTES), was developed. The goal is achieved by demonstrating the feasibility of the technology by connecting mine water present in a small flooded coal colliery (MTES) to solar parabolic trough collectors (SPTCs) and also to a HTHP system that serves the local district heating (DH) grid of Bochum south. The MTES, with an estimated water volume of approximately 20000 m3 is employed as seasonal storage for a 500 kW HTHP system that can reach a supply temperature of 120 degrees C, as needed by the existing DH grid when the ambient temperature is lower or equal to -10 degrees C. During the summer operation, the heat is injected into the MTES from the SPTCs to obtain a mine water temperature of 60 degrees C; and in the winter operation, the heat is extracted through the HTHP until the mine water reaches the unheated temperature of 12 degrees C at the end of the heating season. A literature review of the main components of the plant, the description of the installed system parts and performed tests are reported, along with the results of the successfully executed tests.

Space and water heating for residential and commercial buildings amount to a third of the European Union’s total final energy consumption. Approximately 75% of the primary energy is still produced by burning fossil fuels, leading to high greenhouse gas emissions in the heating sector. Therefore, policymakers increasingly strive to trigger investments in sustainable and low-emission heating systems. This study forms part of the “Roll-out of Deep Geothermal Energy in North-West-Europe”-project and aims at quantifying the spatial heat demand distribution in the Interreg North-West-Europe region. An open-source geographic information system and selected Python packages for advanced geospatial processing, analysis, and visualization are utilized to constrain the maps. These were combined, streamlined, and optimized within the open-source Python package PyHeatDemand. Based on national and regional heat demand input data, three maps are developed to better constrain heat demand at a high spatial resolution of 100 m × 100 m (=1 ha) for the residential and commercial sectors, and for both together (in total). The developed methodology can not only be applied to transnational heat demand mapping but also on various scales ranging from city district level to states and countries. In addition, the workflow is highly flexible working with raster data, vector data, and tabular data. The results reveal a total heat demand of the Interreg North-West-Europe region of around 1700 TWh. The spatial distribution of the heat demand follows specific patterns, where heat demand peaks are usually in metropolitan regions like for the city of Paris (1400 MWh/ha), the city of Brussels (1300 MWh/ha), the London metropolitan area (520 MWh/ha), and the Rhine-Ruhr region (500 MWh/ha). The developed maps are compared with two international projects, Hotmaps and Heat Roadmap Europe’s Pan European Thermal Atlas. The average total heat demand difference from values obtained in this study to Hotmaps and Heat Roadmap Europe is 24 MWh/ha and 84 MWh/ha, respectively. Assuming the implementation of real consumption data, an enhancement in spatial predictability is expected. The heat demand maps are therefore predestined to provide a conceptual first overview for decision-makers and market investors. The developed methods will further allow for anticipated mandatory municipal heat demand analyses.

Summary Exploration risks of geothermal projects are high, as required economic production rates are often not achieved. Stimulation methods from the oil and gas industry, such as radial jet drilling (RJD), which can be used to cost-effectively create flow paths around a main borehole, are usually not applicable in geothermal applications due to especially hard reservoir formations. Because of that, a novel technology called micro-turbine drilling (MTD®) has been developed, which allows for the drilling of micro-sidetracks from cased boreholes even into very hard reservoir rock. The approach is based on the principles of the RJD operation. However, instead of a jetting nozzle, a microdrilling turbine is used to drive a bit that mechanically drills rock. This study presents the results of the proof of concept for MTD, which was conducted in the BedrettoLab in Switzerland at a depth of up to 1,053 ft (321 m) in granite rock.

The research aims to prove that renewable energy sources in the heating sector can enable the energy transition towards European and German CO2 reduction targets. To do so, at the premises of the Fraunhofer IEG Institute in Bochum a demonstrator for high-temperature heat pumps (HTHPs), coupled with seasonal high-temperature mine thermal energy storage (MTES), was developed. The goal is achieved by demonstrating the feasibility of the technology by connecting mine water present in a small flooded coal colliery (MTES) to solar parabolic trough collectors (SPTCs) and also to a HTHP system that serves the local district heating grid of Bochum south. The MTES, with an estimated water volume of approximately 20000 m3 is employed as seasonal storage for a 500 kW HTHP system that can reach a supply temperature of 120°C, as needed by the existing district heating (DH) grid when the ambient temperature is lower or equal to -10°C. During the summer operation, the heat is injected into the MTES from the SPTCs to obtain a mine water temperature of 60°C; and in the winter operation, the heat is extracted through the HTHP until the mine water reaches the unheated temperature of 12°C at the end of the heating season. A literature review of the main components of the plant, the description of the installed system parts and performed tests are reported, along with the results of the successfully executed tests.

The research aims to prove that renewable energy sources in the heating sector can enable the energy transition towards European and German CO2 reduction targets.To do so, at the premises of the Fraunhofer IEG Institute in Bochum a demonstrator for high-temperature heat pumps (HTHPs), coupled with seasonal high-temperature mine thermal energy storage (MTES), was developed.The goal is achieved by demonstrating the feasibility of the technology by connecting mine water present in a small flooded coal colliery (MTES) to solar parabolic trough collectors (SPTCs) and also to a HTHP system that serves the local district heating grid of Bochum south.The MTES, with an estimated water volume of approximately 20000 m3 is employed as seasonal storage for a 500 kW HTHP system that can reach a supply temperature of 120°C, as needed by the existing district heating (DH) grid when the ambient temperature is lower or equal to -10°C.During the summer operation, the heat is injected into the MTES from the SPTCs to obtain a mine water temperature of 60°C; and in the winter operation, the heat is extracted through the HTHP until the mine water reaches the unheated temperature of 12°C at the end of the heating season.A literature review of the main components of the plant, the description of the installed system parts and performed tests are reported, along with the results of the successfully executed tests.

This study introduces and demonstrates a new type of drilling tool that can be used to drill small-diameter deflection holes in hard rock and steel. It principally is a fluid-operated micro drilling turbine which actively generates thrust by using built-in thrust nozzles and attached to a flexible hose, automatically pulls itself into the drilled material. To validate the new technology and its performance under different conditions, a parametric study was performed. Using the micro drilling turbine straight and deflected test boreholes were drilled into granite, quartzite, sandstone and steel. Three newly developed impregnated diamond bits with different ge-ometries were used at different operating pressures and flowrates. It was found that two of the three bits were not suitable for the drilling process. With the other, however, holes could be drilled reliably into all of the samples. With increasing operating pressure, the rate of penetration could be increased to 1.5 m/h in granite at 20 MPa pump pressure. Although the experiments were performed at ambient surface conditions, the results can give recommendations for even downhole applications in deep wells.

AbstractHigh‐pressure water jet drilling technologies are widely used in the drilling industry. Especially in geothermal and hard rock applications, jet drilling is, however, confronted with several limitations like lateral length, hole size, steerability and jetability of the reservoir rock. The application of jet drilling technologies in the field can only be estimated based on the experience of the operator and surface experiments imitating downhole conditions. To predict a successful jetting operation in the field, a modelling framework has been developed, which considers operational and technical parameters as well as reservoir rock specifications. The framework consists of calibrated models describing downhole hydraulics and mechanics during the jetting operation and estimates the required technical equipment to successfully penetrate the reservoir rock and the maximum achievable lateral length for various hole configurations. The modelling framework is applied on a theoretical case study.

The flow structure of a brittle crustal volume is defined by the multi-scale geometric and hydraulic properties of its fracture meshes. The length density distribution n(L,l) and the transmissivity distribution K(L,l) control the hydrologic scaling, where l is fracture length and L is the system size. The flow structure might display at most three key hydrologic scales: the connection scale, above which flow is focused in few critical paths; the channeling scale, above which flow is distributed in several paths; and the homogenization scale, above which permeability approaches a constant value. According to these scales, the hydrological structure could be distributed or clustered, thus having a clear impact in geothermal exploration campaigns and reservoir modeling. In this work, we determine the multi-scale flow structure for the Liquine-Ofqui Fault System (LOFS) and the Andean Transverse Faults (ATF) in the Southern Andes, by establishing the hydrologic scaling they follow. Using fractal statistics, we integrated geological data at the regional, meso-and micro-scale, including image analysis from X-ray microtomography. Our results suggest a self-similar, dense network with n(L,l)similar to l(-a) and a = 2.6-2.9, from the regional scale where the LOFS and ATF interact to the meso-and micro-scale within highly fractured areas of the LOFS. Scaling models are constrained by the length distribution, and other power-law functions reflecting the geometric arrangement of fractures, as well as the spatial distribution of superficial geothermal occurrences. Thus, we expect the hydrologic scaling to depend on the transmissivity distribution. Lognormal transmissivity distribution yields a permeability increase with scale, from the connection to the homogenization scales; whereas power-law transmissivity distribution yields a permeability increase from the connection scale without a limiting value. Approximations of the connection scale are around 10(-3)-10(0) m; the channeling scale, around 100-104 m; and if the homogenization scale exists, it should be equal or greater than 10(3)-10(4) m. Finally, the results presented here could to define the internal architecture of fracture meshes in fault-controlled fluid flow, and be used to select an appropriate hydrologic model according to the analyzed scale. Therefore, these findings must be taken into consideration in future geothermal prospecting, modeling and exploitation.

Across Germany, coal-fired power plants will be shut down not later than 2038. In the Rhine-Ruhr area of western Germany, their waste heat is the main supply for one of Europe's largest district heating networks. Because of the projected shutdown of coal-fired power plants, sustainable alternatives must be implemented. This paper evaluates the hydrothermal potential of Devonian carbonates. A depofacies and mineralogy model is proposed and discussed. Tentative conclusions are drawn based on petrophysical laboratory tests. Extrapolating the thermal and hydraulic rock properties into geothermal reservoir depths offers constraints for associated reservoir simulations. This task applies existing and derived extrapolation equations taking local pressure and temperature gradients into consideration. The change from a non-linear to a linear development at the critical crack-closure pressure provides evidence regarding the petrophysical in-situ reservoir conditions. Results show a positive effect of increased dolomite volumes on reservoir properties. The spatial distribution of fracture networks significantly affects the geothermal reservoir potential, whereas the impact of regionally distributed depofacies variations is moderate. The critical crack-closure pressure equals 40 MPa for limestones and 60 MPa for dolomitic limestones, as well as dolostones, representing depths of approx. 3.6 and 5.4 km, respectively. At depths of 6 km, non-linear and linear extrapolation principles must be applied accordingly. At that depth, the thermal conductivity decreases by 14 to 20% compared to the outcrop values, depending on the sample category. The equivalent decrease in porosity amounts to one to two orders of magnitude. The permeability decrease equals three to four orders of magnitude. The petrophysical values of outcrop samples discussed here plot, within the error range, in the same domain as those of the Malm carbonates in the Munich area. Results are considered encouraging for those concerned with the sustainable transition of the district heating network in the Rhine-Ruhr area. Side-strands of regionally important fault systems, often characterised by hydrothermal dolomitisation, combine tectonic and petrophysical aspects that are advantageous and highly relevant for hydrothermal operations.

High‐pressure water jet drilling technologies are widely used in the drilling industry. Especially in geothermal and hard rock applications, jet drilling is, however, confronted with several limitations like lateral length, hole size, steerability and jetability of the reservoir rock. The application of jet drilling technologies in the field can only be estimated based on the experience of the operator and surface experiments imitating downhole conditions. To predict a successful jetting operation in the field, a modelling framework has been developed, which considers operational and technical parameters as well as reservoir rock specifications. The framework consists of calibrated models describing downhole hydraulics and mechanics during the jetting operation and estimates the required technical equipment to successfully penetrate the reservoir rock and the maximum achievable lateral length for various hole configurations. The modelling framework is applied on a theoretical case study.

Fracturing and damage around faults related to seismogenesis can enhance hydrothermal fluid percolation, causing mineral precipitation. This study uses hydrothermally sealed microfractures across an ancient exhumed fault to unravel the 3D-spatial distribution of fault damage and related anisotropy in permeability. We studied the fault damage zone of the Jorgillo Fault, a left-lateral strike-slip fault, exposed by ca. 20 km in the Atacama Fault System, northern Chile. The study was conducted by addressing the 3D-spatial distribution of the microfracture network through X-ray micro-computed tomography and palaeopermeability modeling using a computational fluid dynamic approach, thus assessing mm-scale fault-related permeability tensors. 3D modeled fault-directed permeability ellipsoids on both sides of the fault core are transverse anisotropic, where palaeopermeability (matrix permeability) in the fault-parallel plane is higher than across-strike of the Jorgillo Fault (2.4 and 1.9 times in the eastern and western block of the fault, respectively). Modeled 3D permeability values (ca. 10(-11) to 10(-15) m(2)) show a mean overestimation factor of 8.4 of the estimated 2D permeability (ca. 10(-9) to 10(-12) m(2)). Permeability anisotropy distribution in the damage zone is related to off-fault damage generation, and could be explained by tip propagation fault growth and dynamic rupture due to earthquakes under the faultvalve mechanism. Whereas the fault would act as an impermeable seal except for post-failure, when it became highly permeable for fluids.

The development of geothermal exploration has benefited from the inclusion of exploration protocols based on geological Plays classically used in hydrocarbon exploration projects. Despite being a research topic in which many efforts have been devoted, it presents weaknesses when evaluating the role of the communities (the social dimension) during the exploration process. To address the lack of studies, a qualitative research has been carried out in Central America (Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua and Panamá) to determine the necessary factors to be considered in the social dimension within the geothermal exploration based in Plays. We have identified the social factors within each social dimension (demand, infrastructure, land access) and from this, a catalogue of the necessary activities required in the social dimension during the geothermal exploration process based on plays is proposed. The results of our survey will greatly contribute to the implementation of the Play-based exploration in geothermal projects because it reduces the risks associated in the initial phase of the exploration process and offers a step-by-step methodology that, when adapted to the needs of each country, can improve the efficiency of the current geothermal exploration protocols.

Chemie Ingenieur TechnikVolume 93, Issue 9 p. 1466-1466 VorschauFree Access Vorschau: Chem. Ing. Tech. 10/2021 First published: 26 August 2021 https://doi.org/10.1002/cite.202170906AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume93, Issue9Special Issue: Membranen zum Schutz von Klima und RessourcenSeptember 2021Pages 1466-1466 RelatedInformation

An in-depth process analysis of water jetting, a promising cost-effective drilling method for the exploration of geothermal reservoirs, is presented. The jetting process is analyzed under submerged and pressurized conditions by complementary high-speed shadow imaging, particle image velocimetry, and rock erosion analysis. The shadowgraphy and velocimetry experiments show that nozzle cavitation dominates the process, and it can be described by a modified cavitation number. Rock erosion experiments show that cloud cavitation governs material erosion. Thus, control of cavitation is essential for the jetting process.

Summary Acoustic Emission (AE) based systems have been under development and used at Fraunhofer IEG to monitor, evaluate, and control conventional and novel drilling processes and their pertinent equipment used in geothermal and drilling applications. Moreover, novel jetting and drilling operations in deep geothermal reservoirs do heavily rely on such new technologies in order to be able to control them properly and thus, to result in a viable technical and economical option. AE monitoring is based on the detection and conversion of elastic waves into electrical signals, which are associated with a rapid release of localized stress-energy propagating within a material. It is passive testing, logging, and analysis method to evaluate changes in the properties and behavior of machines and mineral type materials such as rocks. Such changes may be induced by drilling, jetting, or other drilling methods and being recorded, characterized, and evaluated via an AE system and will be used ultimately used for process performance prediction using machine learning methods. This is the core of the novel monitoring system development, the AE based, so-called Multi-Sensor acoustic parameter analysis as the primary control and monitoring mechanism during rock breaking, drilling, jetting, and stimulation.

Fractures and faults in granitic rocks play an important role in geothermal systems because they permit the circulation of hot fluids. However, the thermo-hydro-mechanical behavior of granitic rocks has predominantly been studied at temperatures exceeding 300 degrees C but many geothermal systems experience temperatures much lower than this. The aim of this study was to evaluate how the depth, temperature, and amount and rate of mechanical loading associated conditions, that are realistic in low temperature geothermal system, influence the physical properties of geothermal reservoir hosting rock. We carried out both room temperature and low temperature thermo-mechanical tests on a granodiorite sample from the Liquine area, Chile, and performed post-experimental X-ray microtomography analysis to numerically estimate the permeability of the generated fractures. The results showed that both rock strength and rock stiffness decreased with increments of temperature treatment related to the development of thermal crack damage at temperatures > 150 degrees C and through the development of sub-critical cracking at constant temperatures between 50-75 degrees C. Slowest deformed samples also exhibited lower strengths, attributed to the development of sub-critical cracking. The cyclic triaxial loading test indicated that significant mechanical fracture damage was only initiated above 80% of the peak stress regardless of the number of repeated loading cycles at lower stresses. Low-temperature treatment appears to be a conditioning factor, but not the dominant factor in controlling the physical properties of reservoir hosting rocks. Our findings indicate that thermal crack damage is likely important for developing microfracture related permeability at depths between around 2-6 km where the temperature is sufficiently high to induce thermal cracking. At shallower depths, such was previously estimated the reservoir of Liquine, thermal crack damage is only generated adjacent to fractures that remain open and circulate the hot fluids but sub-critical cracking over time reduces the strength of rocks in lower temperature regimes. These processes combined to produce a geothermal reservoir in Liquine which likely first required the presence of a highly fractured fault zone.