Geothermal Drilling Research Articles

Overview and design principles of drilling fluids systems for geothermal Wells in Turkey

Joined the 1 GW installed capacity club in 2017, Turkey has undeniable production and potential for geothermal energy, ranking top 5 worldwide. Harnessing geothermal energy has many challenges, from planning to commercial phases. This study features the challenges, experiences and latest advances in drilling fluids utilized in geothermal well construction process in Turkey; focusing to provide a comprehensive information about drilling fluids systems and their design principles in geothermal wells in Turkey.GEOS act as a major player in Turkish geothermal drilling industry; providing drilling and completion fluids, solids control equipment and waste management services; having drilled more than 250 deep geothermal wells in utmost challenging downhole environments of Turkish geothermal fields with major operators.Drilling geothermal wells comes along with several challenges. Most important of which could be high temperatures, relatively high pressures and some of the wells having tough lithologies to drill through. Providing wellbore stability across dispersive shales or pressurized ophiolitic formation requires special attention in planning and execution phases. Another special attention has been given to minimize formation damage in reservoir intervals of geothermal wells. Therefore, different options of reservoir drilling fluids are presented and discussed in detail.Drilling fluids systems used in geothermal wells have evolved over the last decade and tailored to suit the challenges to be faced, not only in top hole and intermediate intervals, but also in reservoir intervals. Main objective of this paper is to share the knowledge and experience gained during the learning curve over the years; extensive laboratory studies and field case studies for geothermal well drilling fluids in Turkey are presented.

Matrix selection and comparison for selecting drilling methods and technologies for a wide range of applications

Oil and gas well construction requires application of an appropriate pair of drilling method and drilling technology that will ensure that the process is conducted safely and cost effectively. Selection of an appropriate drilling method and technology is a lengthy and tedious process which if not properly handled can cause erroneous decisions to be made. This can result to serious drilling problems that can cause additional cost for the company in providing solutions to these problems which are undesirable and should be avoided. In this study, a review of a wide range of drilling methods and technologies was conducted as well as a description of formations which are suitable candidates for their individual application are presented. Ratings for each drilling method and technology against each formation criteria developed on the basis of their candidate selection are also presented. Incorporating the ratings into the decision matrix model and using Visual Basic Programming language, a selection system was developed for selecting drilling methods and technologies using formation description, drilling cost and drilling time as selection criteria. This selection system will assist engineers in making fast and effective decisions regarding the drilling method and technology pair required for drilling a given formation or borehole section. The concept is proving to be useful in those areas where new discoveries are made or as for geothermal drilling in which insufficient nearby well data is available.

The Effect of Invisible Lost Time on Drilling Performance of Geothermal Wells

Drilling activity has been focused in time on each activity to reach target depth (TD) immediately and efficient in cost. The priority also aimed to Geothermal drilling by doing specific measurement on Invisible Lost Time (ILT) as new focus to perform. Time becomes main aspect which it would affect the cost, therefore it is important to complete the well in time manner. The research was done to analyze the offset well of well A, B, C and D in order to identify Productive Time and Non Productive Time. Key Performance Indicator (KPI) has been identified from each activity also targeted from two wells of well B dan Well D due to time efficiency used during operation. The method used by comparing offset wells then continue to identify each KPI by measuring each activity based on ASCII time and Daily Drilling Report (DDR). The result from offset wells showed inefficiency in time with Flat time 49%, Drilling 42% and non-flat time (NPT) 9% from 28 days without completion. KPI based on the crew performance has confirmed that day shift crew performed better than night shift crew. KPI on rate of penetration (ROP) on day shift crew at 6 m/hr and night crew at 3 m/hr. KPI on Weight to Weight on day shift crew at 28.43 minute/stand faster than night shif crew at 34.65 minute/stand. KPI on Tripping in cased hole on day shift crew at 4.5 minute/stand faster than night crew shift at 4.6 minute/stand. KPI on Tripping in open hole on day shift crew at 2.7 minute/stand faster than night shift crew at 3.7 minute/stand. KPI on Tripping out open hole on day shift crew at 3.0 minute/stand slower than night shift crew at 2.8 minute/stand. KPI on Tripping out cased hole on day shift crew at 3.36 minute/stand faster than night crew shift at 3.74 minute/stand. ILT from both wells to 20 % or 5 days inefficiency on each well. It detects of potential savings to 10 billion rupiah from both wells.

Ultradeep Microbial Communities at 4.4 km within Crystalline Bedrock: Implications for Habitability in a Planetary Context.

The deep bedrock surroundings are an analog for extraterrestrial habitats for life. In this study, we investigated microbial life within anoxic ultradeep boreholes in Precambrian bedrock, including the adaptation to environmental conditions and lifestyle of these organisms. Samples were collected from Pyhäsalmi mine environment in central Finland and from geothermal drilling wells in Otaniemi, Espoo, in southern Finland. Microbial communities inhabiting the up to 4.4 km deep bedrock were characterized with phylogenetic marker gene (16S rRNA genes and fungal ITS region) amplicon and DNA and cDNA metagenomic sequencing. Functional marker genes (dsrB, mcrA, narG) were quantified with qPCR. Results showed that although crystalline bedrock provides very limited substrates for life, the microbial communities are diverse. Gammaproteobacterial phylotypes were most dominant in both studied sites. Alkanindiges -affiliating OTU was dominating in Pyhäsalmi fluids, while different depths of Otaniemi samples were dominated by Pseudomonas. One of the most common OTUs detected from Otaniemi could only be classified to phylum level, highlighting the uncharacterized nature of the deep biosphere in bedrock. Chemoheterotrophy, fermentation and nitrogen cycling are potentially significant metabolisms in these ultradeep environments. To conclude, this study provides information on microbial ecology of low biomass, carbon-depleted and energy-deprived deep subsurface environment. This information is useful in the prospect of finding life in other planetary bodies.

Design of Geothermal Drilling Training Curriculum as the Implementation of the National Competence Standard on Onshore Drilling

Indonesia is currently the second largest geothermal installed capacity in the world, with around 1948,5 MW installed capacity. However, this achievement is still far from the Indonesian Government’s target of 7000 MW installed capacity in 2025. Thus, it requires a lot of efforts, supporting policies, and a great deal of competent human resources to achieve this ambitious target. Fulfilling the need for qualified geothermal human resources will take a significant amount of time if it only relies on higher education graduates. Hence, vocational education institutions especially training centers are expected to contribute more to meet these needs. The government has issued a regulation on the Indonesian National Work Competency Standards (SKKNI) which covers aspects of knowledge, skills and work attitudes relevant to the implementation of assigned duties and terms including SKKNI of onshore drilling which is used as a reference for oil and gas and geothermal drilling. However, previous studies have identified the differences between geothermal drilling and oil and gas drilling. This might be due to the government still considers that those two are similar, so they only issued one competency standard for both fields. This paper discusses the implementation of SKKNI on onshore drilling competency standard to produce geothermal drilling curricula. The first part of this paper will map the current conditions of Indonesia’s geothermal drilling human resources development including the estimated number of human resources needed. Furthermore, this study highlights the fundamental differences between the hydrocarbon and geothermal drilling to provide a better understanding of the competency needs of labor in the geothermal industry. Several research or publications and overseas competency standards are discussed and compared to decide which material needs to be included in the curriculum. Several alternative approaches related to human resource capacity development are also proposed in this paper to support the Indonesian Government’s target in 2025.

Specific cutting energy reduction of granite using plasma treatment: A feasibility study for future geothermal drilling

Geothermal Energy is one of the most consistent and viable sources of renewable energy. However, harnessing this energy has proved to be a challenge mainly due to the difficulty in drilling hard igneous rock formations that occur in and around geothermal wells. Therefore, an energy efficient method that can drill hard rocks needs to be developed. In this paper, the effect of micro-scale energy delivery, in the form of plasma, to weaken rock by inducing micro-cracks is studied. Two different types of granite (igneous rock) were sampled and used in this study, out of which the one control group was treated with five, 40kV, 80J pulses of plasma while the other was left uncracked. The effect of the cracks is quantified by conducting facing tests on the plasma cracked and uncracked samples and measuring a reduction in the specific cutting energy. Two different methods were used to estimate the specific cutting energy, where the first method considered the entire cutting process and the second method considered only the stable cutting region. The plasma treatment showed a maximum of 65% and a minimum of 15% reduction in specific cutting energy and was regarded as being dependent on mainly the hardness and size of the samples. All results in this study are validated using statistical analysis.

Selection of IPM Geothermal Drilling Contractor Through a Merit Point System Using the Analytical Hierarchy Process

One method of evaluating the procurement is a merit point system (value system). In a merit point system price is one of the evaluation criteria, with the understanding that the more complex technical requirements and the more difficult to compare bid proposals, the lower the price weights. In general, the total value for technical bids is higher than price bids. At the auction using the merit point system, there are two main things that greatly affect the results of procurement, namely the determination of technical weighting and the price that will be used when evaluating bids and the method of weighing technical bids. When this is done correctly and appropriately, the company will get the right contractor in accordance with needs and can avoid the opportunity to commit fraud or corruption in the process of procurement. For this reason, the authors conduct research on the determination of technical weight and price as well as the method of weighting technical offerings with a case study of the selection of contracting IPM Geothermal Drilling through the Analytical Hierarchy Process (AHP) approach where the results of the study indicate that the AHP can assist the Procurement Planner to determine the technical weight and price as a reference for evaluating bids through the Merit Point System. AHP also helps the Procurement Implementer to rank technical bids during the technical evaluation. Keywords: merit point system, analytical hierarchy process, IPM Geothermal Drilling

Improved drifting oscillator model for dynamical bit-rock interaction in percussive drilling under high-temperature condition

High cost is the main factor restricting the development and utilization of geothermal resources, and the proportion of drilling costs is even higher than 50%. Therefore, it is crucial to find an efficient drilling method and optimize drilling parameters. Percussive drilling is a widely-recognized efficient geothermal drilling method. In this study, an improved drifting oscillator model is developed to determine the optimal drilling parameters by representing the dynamical interaction between drill bit and high-temperature granite (HT-G). The Abel damper is introduced to represent the nonlinear relationship between the damping force and strain rate. Solutions of HT-G Young's modulus and viscosity coefficient as a function of temperature are obtained by experimental data fitting. Then the rock response without and with bit penetration are studied theoretically and numerically, respectively. Finally, experiments are conducted to validate the effects of wave shapes and frequency of the impact load on rate of penetration (ROP). The results show that the ROP increases with the increase of temperature, which proves that percussive drilling is more suitable for HT-G formation than the conventional oil-gas reservoir. There is an optimal frequency ranging from 60 to 120 Hz where the system gives the best drilling performance when sin-shape impacts are applied. Rectangular-shape load gives the fastest ROP among the three evaluated wave shapes of excitation load, especially when the frequency is low. The research of this paper provides a basis for the application of percussive drilling in HT-G formation and is of great significance to the design of downhole impactor and formation adaptability evaluation.

Design of experimental setup for liquid nitrogen assisted polycrystalline diamond compact bit drilling.

A liquid nitrogen assisted polycrystalline diamond compact (PDC) bit drilling method is expected to be suitable for hot dry rock (HDR) drilling because the huge thermal stress induced in the drilling process can help to break the rock and the low temperature liquid nitrogen can efficiently cool the drilling tools. However, there is no experimental research on liquid nitrogen assisted PDC bits breaking high temperature granite, and the rock breaking efficiency of this new drilling method is still unclear. To investigate the feasibility and efficiency of liquid nitrogen assisted PDC bit breaking HDR, a novel experimental setup was designed. This setup is composed of four units: the drilling fluid circulation system, drilling system, formation simulation system, and data acquisition and control system. It can also be used to research the effects of drilling parameters such as weight on bit, rotary speed, drilling fluid jet pressure, and feed speed on drilling efficiency. A series of drilling experiments using liquid nitrogen and water have been successfully carried out with this setup. The results indicate that liquid nitrogen assisted PDC bit drilling has excellent performance in breaking HDR, which can accelerate the application of this new technique in geothermal drilling.

Preliminary study potential of heavy metals in geothermal sludge

One of the New Potential Renewable Energy in Indonesia is geothermal potential which its activity in Indonesia is developed into Geothermal Power Plant XY in West Java and as the utilization of geothermal to reduce the dependency of fossil energy progresses, its utilization will create negative impacts on the environment such as landscapes, noises, subsidence, seismic induction, and heavy metal potential. With this background, it is necessary to conduct the identification of those potentials and the possibility of metals’ utilization. The researcher conducted this research by doing identification on dissolved metals types and its potential to harm the environment. The process was conducted by using Atomic Absorption Spectrophotometry (AAS) method. The sampling process performed on solid waste which was the result of geothermal drilling process or Geothermal Sludge and water sample which came off from the PLTP that headed to public waters around citizens residences. The test result of geothermal sludge showed that it contained heavy metals. The water sample collected around citizens residences also showed there were heavy metals.

Las Pailas geothermal field - Central America case study: Deciphering a volcanic geothermal play type through the combination of optimized geophysical exploration methods and classic geological conceptual models of volcano-tectonic systems

Sustainable exploitation strategies of high-enthalpy geothermal reservoirs in a volcanic geothermal play type require an accurate understanding of key geological structures such as faults, cap rock and caldera boundaries. Of same importance is the recognition of possible magmatic body intrusions and their morphology, whether they are tabular like dikes, layered like sills or domes. The relative value of those magmatic bodies, their age, shape and location rely on the role they play as possible local heat sources, hydraulic barriers between reservoir compartments, and their far-reaching effect on the geochemistry and dynamics of fluids. Obtaining detailed knowledge and a more complete understanding at the early stages of exploration through integrated geological, geophysical and geochemical methods is essential to determine promising geothermal drilling targets for optimized production/re-injection schemes and for the development of adequate exploitation programs. Valuable, extensive geophysical data gathered at Las Pailas high-enthalpy geothermal field at northwestern Costa Rica combined with detailed understanding of the geological structures in the underground may represent a sound basis for an in-depth geoscientific discussion on this topic. Currently, the German cooperation for the identification of geothermal resources in Central America, implemented by the Federal Institute for Geosciences and Natural Resources (BGR), supports an international and interdisciplinary effort, driven by the Instituto Costarricense de Electricidad (ICE) with different international and national research institutions, including the Leibniz Institute for Applied Geophysics (LIAG). The discussions and joint studies refer to the optimized utilization of geophysical and geological methods for geothermal exploration in the Central American region, using the example of Las Pailas Geothermal Field. The results should contribute to a better understanding of the most appropriate geothermal exploration concepts for complex volcanic field settings in Central America.

Process Modelling of Geothermal Drilling System Using Digital Twin for Real-Time Monitoring and Control

Currently, Kenya supplies its energy demand predominantly through hydroelectric power, which fluctuates due to poor and unpredictable rainfall in particular years. Geothermal energy is proposed as a clean and reliable energy source in meeting Kenya’s increasing energy demand. During geothermal drilling operations, disruptions due to tool wear and breakages increases the cost of operation significantly. Some of these causes can be mitigated by real-time monitoring of the tool head during operations. This paper presents the design and implementation of a digital twin model of a drilling tool head, represented as a section of a mechatronic assembly system. The system was modelled in Siemens NX and programmed via the TIA portal using S7 1200 PLC. The digital model was programmed to exactly match the operations of the physical system using OPC (open platform communications) standards. These operations were verified through the motion study by simultaneous running of the assembly system and digital twin model. The study results substantiate that a digital twin model of a geothermal drilling operation can closely mimic the physical operation.

Statistic evaluation of failure criteria in wellbore stability with temperature effects

Geothermal energy is increasingly recognized as a potential of replenishing fossil fuels and meeting decarbonization obligations. HP/HT drilling is also increasingly recognized as a tool to provide an adequate supply of oil/gas. In these two types of activity, the high temperature is the common challenge for drilling. Under high temperature, rocks usually behave differently compared to the ambient condition. Whether the popular failure criteria can be used to evaluate wellbore stability under geothermal conditions is a question which has not been answered yet. In this paper, the triaxial compression tests under different temperature for six types of rock (Strathbogie granite, Tak granite, Tournemire shale, Slate, Carthage marble, and Crab Orchard sandstone) have been used to evaluate six different failure criteria. Two methods have been implemented to obtain rock cohesion and internal friction angle, which are grid search algorithm and Mohr failure line method. Both methods show that Modified Lade is the failure criterion that provides the best performance in predicting rock failure under geothermal drilling. The grid search algorithm guarantees the best performance of the failure criteria, providing with the best-fit rock parameters. The more practical method of Mohr failure line can still generate engineering reasonable predictions if a safety factor of 1.1 is considered, but only the Modified Lade should be used. The thermal influence on rock parameters is also analyzed and the cohesion is found to be decreased with the improvement of temperature, whereas the internal friction angle does not have a consistent relationship with temperature. Overall, considering the considerable variance of depth (several kilometers) and temperature (several hundred degree Celsius) of geothermal and deep oil/gas resources, the Modified Lade has proven to be the best choice to perform wellbore stability analysis.

The Rheology and Performance of Geothermal Spring Water-Based Drilling Fluids

In this study, the rheological properties and performances of mud prepared with geothermal spring water to be used by geothermal drilling operators were examined at ambient and elevated temperatures. In this context, mud samples were prepared in the compositions detailed in the API specification by using five different geothermal spring water types and a distilled water type. Afterwards, density, apparent viscosity, plastic viscosity, yield point, gel strength, fluid loss, pH, and filter cake thickness of these samples were measured. The drilling muds were analyzed by means of rheological tests in accordance with the standards of the American Petroleum Institute (API). The experimental results have revealed that the mud prepared with geothermal water have lower viscosity and yield point compared to those prepared with freshwater at elevated temperatures. The stability of the muds decreases, especially at temperatures higher than 250°F, and they start to become flocculated. It was concluded that geothermal water-based muds have higher API fluid loss and cake thickness than the freshwater-based one. Therefore, it could be interpreted that the muds prepared with geothermal spring water will exhibit lower flow performance and lower ability of hole cleaning and rate of penetration compared to the freshwater muds. Hence, it is recommended that this kind of water should not be used to prepare drilling mud.

Energy technology dependence - A value chain analysis of geothermal power in the EU

The majority of energy used by the European Union has been imported from non-EU countries. The EU desires to increase its own renewable energy use to secure its future energy supply. In this paper, an assessment framework of technology dependence has been proposed that can be used to locate bottlenecks in the value chain of geothermal power generation. The framework consists of an ‘above ground’ and ‘underground’ domain. It was applied to binary Organic Rankine Cycle (ORC) power plants as this type has the highest proliferation potential in the EU. The above ground domain aims to locate potential bottlenecks at a key-component level via a technology hierarchy analysis, company and trade analysis as well as a survey. The underground domain focuses on the potential bottlenecks embedded in the geothermal drilling industry by means of a drilling industry screening, rig screening and a survey. The results suggest that some Binary-ORC key-components may require attention. Furthermore, the geothermal drilling industry's dependence on the oil and gas industry can be seen as a major dependence bottleneck that might jeopardize the future proliferation of binary-ORC technologies in the EU.

3D Printing of Plain and Gradient Cermets with Efficient Use of Raw Materials

3D printing of plastic materials is very popular nowadays, while printing of wear resistant hard materials is still an issue. Gradient or functionally graded structures are providing improved performance in impact-abrasive application (tunnelling, geothermal drilling, mining, etc.) through the optimal positioning of areas providing high wear resistance and high resistance against impacts. However, printing of such structures by widely used powder bed selective laser sintering leads to the high consumption of raw materials (powders) that cannot be used again for next printing. A method to overcome this problem is explored in current work. The cermets were produced from following powders: (1) commercial, (2) obtained by disintegration of cutting tool inserts (recycled) and (3) reused recycled ones. Tungsten and cobalt used for the production of the majority of cermets are critical raw materials and their consumption should be reduced while the rate of recycling needs to be increased. The surfaces were studied with the help of optical microscopy, scanning electron microscopy, and energy-dispersive spectroscopy. The hardness and wear rate of samples in abrasive conditions were measured.

Design and numerical analysis of a large‐diameter air reverse circulation drill bit for reverse circulation down‐the‐hole air hammer drilling

AbstractReverse circulation down‐the‐hole (RC‐DTH) air hammer drilling is a fast and cost‐effective method for hard rock drilling. As the air RC drill bit is the heart for RC‐DTH air hammer drilling system to form the reverse circulation, a large‐diameter RC drill bit was innovatively designed and numerically optimized with respect to the suction ability. Results show that increasing the suction‐nozzle elevation angle and deflection angle can improve the drill bit suction ability. The drill bit performance reaches its optimal state when the air flow rate was about 1.205 kg/s, thereafter it exhibits a reverse variation trend with the increase in air mass flow rate. The optimum diameter of the suction nozzles is 20 mm for the drill bit studied in this work. The RC drill bit with outer diameter of 665 mm and RC‐DTH air hammer with outer diameter of 400 mm were manufactured and a field trial was conducted. Field test results show that the penetration rate using the RC‐DTH air hammer drilling method is more than twice the conventional rotary drilling method. This drilling approach poses a great potential for the large‐diameter hard rock drilling applied in the upper portions of a well bore above the potential producing reservoir formation for land oil and gas drilling, geothermal drilling and relevant field drilling operations.

Geothermal drilling in an Alpine karst aquifer and its impact on downstream springs – A case study from Finkenberg, Tyrol, Austria

A borehole heat exchanger array was installed in an Alpine karst aquifer for the first time in Europe. It is composed of nine 400 m deep boreholes in the dolomitic marble of the Hochstegen Formation. New approaches were developed for this unprecedented application and potential risks were checked throughout the sinking of the initial exploratory wellbore. As Finkenberg is located in a tourist area, drilling operations had to be executed within only a few weeks. Several springs downstream from the drilling site are sources of drinking water and tap water supply. Given that the degree and distribution of the Hochstegen Formation karstification was unknown, a spring monitoring program was mandatory in order to obtain drilling permission from public authorities. A practicable and affordable spring monitoring program including several physical and chemical parameters was developed and implemented to document the potential impact of the drilling activities on the spring water. A temporary and locally limited impact of the drilling works on groundwater quality was detected by turbidity measurements. This paper reports the implementation of geothermal drilling in a karst aquifer with a focus on karstification as well as planning, implementation and the results of the spring monitoring program. Such a program can be recommended for comparable projects or questions, adapting the characteristic parameters to be collected and the measurement intervals in consultation with the relevant authorities. It might also increase the chances of gaining approval for geothermal projects in karst and could enhance public acceptance. Key words: Pneumatic down hole hammer drilling, Borehole heat exchanger, Groundwater monitoring, Turbidity, Hochstegen Formation. Geotermalno vrtanje v alpskem kraskem vodonosniku in njegov vpliv na dolvodne izvire - studija primera Finkenberg, Tirolska, Avstrija V alpskem kraskem vodonosniku je bilo prvic v Evropi vzpostavljeno polje geosond. Vkljucuje devet 400 m globokih vrtin, izvrtanih v dolomitnem marmorju Hochstegenove formacije. Razvili smo nove pristope za to aplikacijo brez primere in potrdili morebitna tveganja v casu potopitve prvotne raziskovalne vrtine. Ker je studijsko obmocje Finkenberg na turisticnem obmocju, je bilo treba opraviti vrtanje v samo nekaj tednih. Vec izvirov od mesta vrtanja so viri oskrbe s pitno vodo. Glede na to, da stopnja in porazdelitev zakraselosti Hochstegenove formacije nista bili znani, je bilo treba za pridobitev dovoljenja za vrtanje nujno opazovati izvire. Da bi dokumentirali vpliv vrtanja na izvirsko vodo, je bilo pri spremljanju izvirov treba upostevati vec fizikalnih in kemijskih parametrov. Zaznali smo obcasen in lokalno omejen vpliv vrtanja na kakovost podzemne vode. V prispevku smo predstavili izvajanje geotermalnega vrtanja v kraskem vodonosniku s poudarkom na identifikaciji zakraselosti ter nacrtovanju ter na izvedbi in spremljanju kakovosti voda na izviru. Tak program se lahko uporabi pri primerljivih projektih ali iskanju odgovorov na podobna vprasanja s prilagojenim programom opazovanih parametrov in intervalov merjenja. Prav tako bi lahko povecal možnosti za pridobitev soglasja za geotermalne projekte na krasu in povecal ozavescenost javnosti. Kljucne besede: vrtanje s pnevmatskim kladivom, geosonda, spremljanje podzemne vode, motnost, Hochstegenova formacija. A borehole heat exchanger array was installed in an Alpinekarst aquifer for the first time in Europe. It is composed of nine400 m deep boreholes in the dolomitic marble of the HochstegenFormation. New approaches were developed for thisunprecedented application and potential risks were checkedthroughout the sinking of the initial exploratory wellbore. AsFinkenberg is located in a tourist area, drilling operations hadto be executed within only a few weeks. Several springs downstreamfrom the drilling site are sources of drinking water andtap water supply. Given that the degree and distribution of theHochstegen Formation karstification was unknown, a springmonitoring program was mandatory in order to obtain drillingpermission from public authorities. A practicable and affordablespring monitoring program including several physical andchemical parameters was developed and implemented to documentthe potential impact of the drilling activities on the springwater. A temporary and locally limited impact of the drillingworks on groundwater quality was detected by turbidity measurements.This paper reports the implementation of geothermaldrilling in a karst aquifer with a focus on karstification aswell as planning, implementation and the results of the springmonitoring program. Such a program can be recommended forcomparable projects or questions, adapting the characteristic

Downhole Transient Flow Field and Heat Transfer Characteristics During Drilling With Liquid Nitrogen Jet

As a novel jet technology, liquid nitrogen jet (LNJ) is expected to effectively break rocks and further provide a high-efficiency method for drilling, especially geothermal drilling. Using this technology, rocks can be broken down by the coupled effects of cryogenic cooling and jet impingement. In this study, transient downhole jet flow field and heat transfer during drilling with LNJ were simulated. Then, the distributions of temperature (including LNJ and ambient rock), velocity, and pressure at different times were analyzed. Finally, the effects of the parameters on jet impingement and rock cooling performance were discussed. Results indicated that cryogenic LNJ could be efficiently generated in the downhole region. The temperature of the rock surface remarkably decreased as the LNJ reached the bottomhole. The high-speed LNJ caused axial impingement and radial shear effects on the bottomhole rock. The rock cooling performance caused by the LNJ was influenced by the initial rock temperature. With the increase of the initial rock temperature, the drop amplitude of the rock temperature also increased. The impingement capability of the LNJ was improved by increasing the nozzle diameter and the nozzle pressure drop. With the increase of standoff distance, the wall pressure and the radial velocity of the bottomhole decreased while increasing the impingement scope. The confining pressure hardly influenced the rock cooling performance and jet impingement capability, thereby indicating that LNJ could work even at high confining pressure conditions.

Monitoring Magma Under Volcanoes: The Future Of Eruption Forecasting And Geothermal Energy

Abstract Magma represents the most extreme environment in Earth's crust. Typical conditions at the top of a magma body are > 50 MPa and > 800°C. The location and conditions of magma storage were entirely speculative until recently when geothermal drilling encountered magma in Iceland, Kenya, and Hawaii. The door is now open, if appropriate sensors can be developed, to monitor conditions at the source of eruptions. This will move eruption forecasting, a concern for 10% of the world's population, from recognizing patterns in proxy surface measurements towards the reliability of weather forecasting. It can also aid in achieving a huge increase in productivity of geothermal energy, a clean, small-footprint, bed-load source. Aqueous fluids associated with magma are superheated to supercritical, providing 10× more effective transport of thermal energy and 3.5× more efficient conversion to electricity than conventional geothermal. As an added benefit, extraction from magma of 1 GWt for 30 years would render > 1 km3 of magma uneruptable.