Veranstaltungsprogramm

Kurzfassung Geothermie Kongress 2021, Essen

W. Littmann[i], G. Pusch[ii]

Für die Planung von Tiefengeothermie Projekten ist das geothermische Potenzial, repräsentiert durch Aquifertemperatur und Produktivität der Aquiferschichten, von großer Bedeutung. Wenn die erforderlichen Temperaturen am Standort vorhanden, die Transmissibilitäten aber marginal sind, kann mit Hilfe der Bohrungsarchitektur nachgesteuert werden. Lateral- oder Horizontalbohrungen vermögen die Produktivität auf ein wirtschaftliches Maß zu erhöhen. Mit Hilfe analytischer oder numerischer Simulationsprogramme können Prognosen der erwarteten Produktivität für unterschiedliche Bohrungstypen erstellt und in der Planung genutzt werden. In dieser Studie wurden die bekannten analytischen Modelle mit den Ergebnissen eines numerischen Simulationsprogramms verglichen und der Einfluss der geologischen und technischen Parameter auf die Produktivität anhand eines Modellaquifers untersucht.

Mehrschichtaquifere weisen für Lateralbohrungen in der Regel kleinere Kapazitäten auf als adäquate Einschichtaquifere. Der Neigungswinkel der Bohrung sollte nicht unter 60° liegen, um einen wesentlichen Beitrag zur Produktivitätsverbesserung zu liefern. Horizontalbohrungen unterschreiten die Produktivität von Lateralbohrungen bei mächtigen Aquiferen (>100 m) oder verlieren ihre Produktivitätsverbessrung bei Anisotropiewerten < 0,2. Eine wichtige Rolle spielt die Lage der Bohrung in Bezug auf geologische Störungen oder Schichtbegrenzungen, die den Drainageraum und damit die Produktionsraten einschränken können.

Der Mehrwert der Produktivität muss jedoch an den erhöhten Kosten für aufwendigere Bohrungsarchitekturen gemessen werden. Bei mittleren Bohrteufen und bekannter Geologie kann der Produktivitätszuwachs durch Lateral- und Horizontalbohrungen prozentual stärker wachsen als die Zusatzkosten, so dass komplexere Bohrungsarchitekturen lohnend sein können.

[i] Dr. Wolfgang Littmann, Consulting Reservoir Engineering, Wunstorf,

[ii] Prof. Dr. Günter Pusch, Celle

Downthe-hole (DTH) hammer drilling technology has been used successfully for many years in the mining as well as oil and gas industry to access hydrocarbon reservoirs. Typical DTH hammers use a piston moved by hydraulic power or compressed air, applying alternating loads onto the drill bit to crush the rock at the borehole bottom and thus, eroding the rock. Due to this alternating movement of the piston this technology is called hammer drilling. The internal components of any DTH hammer are called percussion system and include mainly the piston itself and a valve system controlling its movement. Currently, most DTH hammer systems have a maximum operating temperature of 150 °C and are limited to use compressed air or clean water as drilling fluid. As a result, the wellbore control and cuttings transport are more difficult compared to conventional rotary drilling technologies using drill mud with tri-cone or PCD bits. Furthermore, the lifetime of hydraulic type DTH hammers depends much on the quality of the liquid being used, while the achievable rate of penetration (ROP) in hard rock formation is multiple times higher compared to other rotary drilling technologies. The more widespread use of DTH hammer technology towards geothermal reservoirs requires the use of more conventional type of drill mud with additvies, higher lifetime of the device and tool functionality at high-pressure and high-temperature (HPHT) conditions. Therefor, a novel DTH hammer for deep reservoir exploration is being developed using a fluidic switch, instead of a mechanical valve system, and advanced surface coatings to increase tool lifetime. The development of the novel prototype hammer is realized by experimental as well as numerical work (simulations), and iteratively optimizing each component of the percussion mechanism. For this purpose a numerical model of this mechanism is developed based on a mass-spring-damper approach. The model allows to evaluate the efficiency of numerous variations of the mechanism and, therefore, straightens the path of investigation.

The GEODRILL project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 815319.

The deep geothermal drilling industry has been facing numerous challenges, ranging from poor overall drilling performance to the lack of complete bottom hole awareness resulting in tripping times, expensive non-productive times, etc. Consequently, the OptiDrill concept was born out of the fact that there is a need to overcome these challenges and make the exploration and exploitation of geothermal resources feasible, more attractive, and worthwhile. The idea behind the OptiDrill advisory system is to use a combination of real-time monitoring systems and novel AI based approaches to characterize, analyze, predict, and optimize various aspects of the drilling process including drilling efficiency, real time lithology prediction, well completion process optimization, and early drilling problem detection and prevention.

The OptiDrill consortium consists of 11 main partners from 5 different countries and multiple other entities supporting the project substantially, each contributing by bringing expertise in drilling-related domains by laying the foundation and realizing the OptiDrill concept under the coordination of the Fraunhofer Institute for Energy Infrastructures and Geothermal Systems (IEG). In addition to their expertise, the project partners will also provide drilling data from all over the world, which will be used to build an extensive drilling database that has never been realized before and will set the foundation for developing the AI modules. Apart from the intelligent software modules, an advanced monitoring system consisting of a real-time measurement-while-drilling (MWD) system, acoustic emission, temperature, pressure, and vibrations sensors is to be developed to complement the available drilling data from the drill rig reliably and accurately.

The overall objective of the OptiDrill project and the underlying concept is to develop an advisory system to consult and support drilling operators in their day-to-day business. This will be done by providing them with specific suggestions for optimizing the ongoing drilling process based on real-time data and the gathered knowledge extracted from the data collected in advance. It is important to clarify that the OptiDrill project is not aiming at automating the drilling process, but at facilitating the decision making, improving and digitalizing the reporting and documentation, as well as optimizing the whole process by giving well-founded suggestions and reducing the risk of common uncertainties and hazards. Furthermore, the digitalization of the drilling process will greatly benefit future research in this field and significantly simplify the subsequent development of data-driven applications in deep geothermal applications.

To make the heat and energy transition of Europe a reality, deep geothermal resources must be accessed safely and at low risk in all geothermal play types, including hard / igneous type rocks via EGS like implementation. Available resources able to deliver such low risk engineered processes across Europe demonstrated within the ZODREX consortium ( ZoDrEx | Geothermica ) that such deep geothermal systems could be installed confidently. Herein, one key issue is proper connectivity between a production wellbore and its surrounding reservoir. In case of insufficient conditions, e.g. the fracture network could be extended artificially through hydraulic stimulation, but often this measure is of questionable and limited success and, moreover, criticized for the associated risk of induced seismicity and environmental impact.

Ultra-short radius (radial) Jet Drilling, where high pressure water jet based rock erosion drills off laterally from an existing wellbore, remains the key topic of interest for geothermal well enhancement, now even being called the 3rd dimension of drilling. It comprises a rock erosion / milling process (jetting) as well as the integration into a functional downhole system. As part of its work within ZODREX and other projects, Fraunhofer IEG has investigated and further developed the impact of high-pressure jetting in hard rock, e.g. through variation and controlling of rotation, cavitation and pulsation, as well as stand-off distance, flow rate, jet diameter and velocity. Moreover, mechanically assisted high pressure milling has been investigated and successfully introduced as a prospective addition, particularly for application in hard rock and casing milling. Such new systems have been tested by Fraunhofer IEG together with Geo Energie Suisse, RWTH Aachen and others in ETH´s Bedretto Underground Laboratory in the Gotthard Massif, CH. Several field trials proved the concept and yielded many micro-laterals, notches and drainholes in the vicinity of the wellbore, making for better reservoir connection und thus, geothermal production.

Furthermore, a complete system embodying more energy for reservoir stimulation, fit-for-purpose jetting BHA including deviation tools, coils and monitoring modules are being developed at Fraunhofer IEG, pushing the technology further to high TRLs for industrial application.