ISRM 2023 - PUBLICATIONS

T03: Deep geothermal energyYandong YANG (1,2), Duli YAN (1), Feifei HUANG (1), Hualin LIAO (2)1: Yan‘an University, People's Republic of China; 2: China University of Petroleum (East China）Hot dry rock breaking with PDC bit under various of impact loadsDeep dry hot rock geothermal energy is a new type of renewable energy, which is environmental friendly and abundant. The ROP improvement is one of the bottleneck faced in deep hot dry rock drilling. Regarding to the high temperature, strength of hot dry rock, the combination of downhole impact drilling tools and PDC bits has become an effective method to increase the ROP of hot dry rock, and the waveform of the impact load generated by percussive drilling tool is an important factor influencing the ROP of the hot dry rock. Therefore, a 3D polycrystalline diamond compact (PDC)bit-hot dry rock model is established, in order to evaluate the ROP of dry hot rock under the coupling of impact loads. The research results shows that ROP improvement rate of rectangle impact load is the best，which could provide a theoretical basis for the design of rock breaking percussive drilling tool. | Hot dry rock, percussion drilling, rock breaking, energy transfer efficiency, impact load
T03: Deep geothermal energyMarlene VILLENEUVE (1), Ben KENNEDY (2), Anette MORTENSEN (3), Elodie SAUBIN (2), Aliaa HAMMOUD (1)1: Montanuniversität Leoben, Leoben, Austria; 2: University of Canterbury, Christchurch, New Zealand; 3: Landsvirkjun, Reykjavik, IcelandInforming deep geothermal reservoir rock mass properties from drilling data - experience from Krafla, IcelandDuring geothermal drilling it is important to know the quality of the rock mass for well completion, mud weight selection, interpreting features of interest, to characterise the subsurface in the absence of core. In deep geothermal drilling, tens to hundreds of meters are drilled without cutting retrieval and, therefore, without insight into the rock mass. Wireline logs are commonly used to interpret the subsurface, however, these data are typically collected after drilling an interval. Despite their increasing development, studies using drilling parameters and logging-while-drilling to interpret the rock mass in high-temperature, deep geothermal environments remain rare. In this paper we present a method where the drilling parameters from previous drilling at Krafla are used to assess the quality of the rock mass, with particular focus on its effect on drillability. This demonstrates how methods from geotechnical drilling and tunnelling can inform geothermal drilling. | Supercritical fluid, drilling performance, ROP, WOB, fractures
T03: Deep geothermal energyKohei TAKUMA (1), Yuto WATANABE (1), Kiyotoshi SAKAGUCHI (1), Kazumi OSATO (2), Amane TERAI (3), Noriaki WATANABE (1)1: Tohoku University, Japan; 2: Geothermal Energy Research and Development Co., Ltd. (GERD), Japan; 3: Japan Organization for Metals and Energy Security (JOGMEC), Tokyo, JapanCarbon dioxide (CO2) fracturing of volcanic rocks under geothermal conditionsAn enhanced geothermal system that uses carbon dioxide (CO2) for both reservoir creation and thermal energy extraction has been attracting attention in Japan. For this system, CO2 fracturing is conducted to create highly permeable fractures in low-permeability reservoirs, for instance, consisting of volcanic rocks. However, there is no previous study on CO2 fracturing of volcanic rocks under geothermal conditions, and possibility and characteristics of such fracturing are therefore unknown. Here we present results of CO2 fracturing experiments on andesite and basalt at 250 °C and a confining pressure of 30 MPa. It is demonstrated that CO2 fracturing occurs at a lower pressure than water fracturing and produces a more complex fracture pattern with a substantial permeability improvement. Additionally, it is shown that CO2 fracturing with water, in which CO2 is chased and pressurized by water, can produce larger-aperture fractures (i.e., larger permeability improvement) with keeping the advantage in CO2 fracturing. | carbon dioxide, fracturing, volcanic rock, enhanced geothermal system, breakdown pressure, fracture pattern
T03: Deep geothermal energyWeiren LIN (1), Osamu TADAI (2)1: Kyoto University, Japan; 2: Marin Works Japan LTD, JapanRelationship between thermal conductivity and porosity in sedimentary soft rocks by an experimental approachRelationship between thermal conductivity and porosity in sedimentary rocks are required for understanding the fundamental characteristics of rock thermal property in geoscience and geoengineering areas. To examine the relationship by laboratory experiments, we used core samples collected from a deep ocean drilling program called Nankai Trough Seismogenic Zone Experiment by Integrated Ocean Drilling Program. The thermal conductivity of the core samples was measured at high pressure to simulate subduction by reducing the sample porosity. The experimental results revealed a clear inverse relationship between thermal conductivity and porosity of the sedimentary rocks. | Sedimentary soft rock, Thermal conductivity, Porosity, High pressure, Laboratory experiment
T03: Deep geothermal energyHeng ZHENG (1), Ersi XU (2), Jie LI (3), Jin CHEN (3)1: Yangtze University, People's Republic of China; 2: Engineering technology research institute of Southwest Oilfield company; 3: Engineering technology research institute of Xinjiang Oilfield companyStudy on the fracture propagation in geothermal during the hydraulic fracturing based on a coupled thermal-hydraulic-mechanical modelingIn this paper, a coupled thermal-hydraulic-mechanical modeling was proposed based on the linear elastic fracture mechanics to understand the effect of thermal stress field on fracture propagation. Due to a cooling zone was formed in the matrix when the fracturing fluid injection, the rock had a shrink dramatically when the temperature reached the threshold value. The simulations indicated that when the temperature increased to 180℃ from 155℃, the breakdown pressure and extension pressure decreased by 14.56% and 13.27%, and the total fracture length of multiple fractures propagation increased by 28.51%, which demonstrated that increasing the temperature difference can not only decrease the breakdown pressure and extension pressure, but also can offset the stress shadow caused in multiple fractures extension. This research was helpful for the hydraulic fracturing design when the horizontal well with multiple stage fracturing was adopted in the development of geothermal systems. | thermal stress, hydraulic fracturing, thermal-hydraulic-mechanical, thermo-elastic deformation, volume shrinkage
T03: Deep geothermal energyYujie ZHU (1,3), Chen XU (2,3), Yingguo HU (1), Xiaoli LIU (3), Enzhi WANG (3)1: Key Laboratory of Geotechnical Mechanics and Engineering of Ministry of Water, Changjiang River Scientific Research Institute, Wuhan, China; 2: Changjiang Institute of Survey Planning Design and Research, Wuhan, China; 3: Tsinghua University, Beijing, ChinaInfluence of stress state based on hydraulic-mechanical coupling and water loading path on fault activityIn the exploitation of shale gas and enhanced geothermal energy, reservoir water storage and carbon dioxide storage projects, induced earthquakes are closely related to the activity of primary faults. A fractured cylinder sample with 60° inclination is adopted in the indoor test.The shearing test is used to explore the impact of different stress critical conditions and pore water pressure loading paths on the triggering mechanism and mechanical behavior of fault activity, providing reference for the reservoir impounding plan. The test shows that when the increased pore water pressure is the same, the higher the critical pressure, the greater the displacement of fault sliding and the more energy released. Pore pressure under different path loading has influence on the process of fault dislocation, but has less effect on the displacement of the fault. The stress state and pore water pressure determine the fault displacement. | Stress state, HM coupling, loading path, induced seismicity
T03: Deep geothermal energyJustin MATTHEIS, Catharina DREXL, Martin POTTEN, Georg Maximilian STOCKINGER, Kurosch THUROChair of Engineering Geology, Technical University of Munich, GermanyBorehole stability in geothermal reservoirs – A combined laboratory and numerical approachDespite the well-known geothermal potential in the North Alpine Foreland Basin, large scale exploration is still limited by the economic risk of well instabilities originating from inadequate prediction of the heterogeneous rock mass conditions in the reservoir. One decisive factor is the rocks toughness against fracture propagation. Hence, analogs to the reservoir rocks are subject to Semi-circular Bend tests to determine the required energy for tensile fractures (mode I) and accordingly Double-edge Notched Brazilian Disk tests for shear fractures (mode II). The subsequent finite-discrete numerical simulations, in which the experimental results are implemented, show varying fracture patterns in the rock mass caused by drilling. The fracturing depends on the rock type, the pre-existing discontinuities, and the stresses in up to 5 km depth. Further expansion of this investigation to other scenarios and rock types, paired with a reliable geological prediction, reduces the associated risks for deep geothermal projects. | geothermal reservoir characterization, borehole stability, fracture energy, laboratory tests, numerical FDEM modeling; North Alpine Foreland Basin (SE Germany)
T03: Deep geothermal energyShuai FENG (1), Weiren LIN (1), Susumu SHIBUTANI (2), Terasu SANO (3), Nana KAMIYA (4)1: Graduate School of Engineering, Kyoto University; 2: Chi-ken Sogo Consultants Co., Ltd; 3: Daigas Gas and Power Solution Co., Ltd; 4: Doshisha UniversityCorrelations between thermal properties and elastic wave velocities of volcanic rocksThermal properties such as thermal conductivity are necessary to understand the subsurface thermal structure. It remains difficult to obtain such thermal properties without laboratory measurement on rock core samples, while such core samples are usually difficult to obtain especially at great depths. This research seeks to derive an empirical equation between thermal properties and elastic wave velocities by analysing laboratory measurement data on volcanic rock core samples. Measurements of thermal properties and elastic wave velocity have been conducted on volcanic rock core samples collected from Aso volcanic region, Japan. And correlations between measured physical properties have been discussed. Both thermal conductivity and P-wave velocity were found to decrease with increasing porosity. And thermal conductivity presented a tendency to increase as P-wave velocity increased, while an acceptable empirical equation failed to be obtained which indicated the need for further research. | Thermal properties, elastic wave velocity, volcanic rocks, Aso volcanic area
T03: Deep geothermal energyArno ZANG (1,2), Hannes HOFMANN (1,3), Gergö HUTKA (1,2), Bakul MATHUR (1), Mauro CACACE (1), Serge SHAPIRO (4), Beau WHITNEY (5), Cedric DUVAIL (5), Ramon Secanell GALLART (5), Niels GROBBE (6), Annemarie MUNTENDAM-BOS (6)1: German Research Centre for Geosciences GFZ, Germany; 2: Institute of Geosciences, University of Potsdam, Germany; 3: Institute of Applied Sciences, Technical University of Berlin, Germany; 4: Institute of Geosciences, Free University of Berlin, Germany; 5: Fugro NL Land BV, Groningen, The Netherlands; 6: Dutch State Supervision of Mines, The Hague, The NetherlandsStress and seismicity related to cooling of geothermal wellsDeep geothermal energy (~3-6 km depth) is a candidate for sustainable and carbon-free energy supply. One of the main concerns of deep geothermal systems is induced seismicity that may produce earthquakes of economic concerns, challenging the development of this form of alternative energy. So far, cold water injection has been overlooked but may contribute to induced seismicity due to fault reactivation through thermal stresses also beyond the cooling region. This can be of importance, in particular, in fractured and faulted geothermal reservoirs. In this study, we first compare different approaches to estimate induced seismic risk from slip-tendency analysis, rate-and-state friction theory and modified Gutenberg-Richter statistics based on frictional Coulomb-stress perturbations. Then, we systematically investigate effects of both, intrinsic geological parameters (e.g., fault-, host rock properties and in-situ stress), and operational parameters (e.g., well geometry and placement, injection schemes, induced pressure perturbation) on induced seismicity. | Coulomb failure stress, deep geothermal energy, induced seismicity, rate-and-state friction theory and thermo-hydraulic-mechanical modelling
T03: Deep geothermal energyChuangchuang WANG, Xueyu PANG, Guodong CHENG, Jiankun QIN, Huajie LIUChina University of Petroleum(East China), People's Republic of ChinaDesign of CaO-Al2O3-SiO2-H2O hydrothermal synthesis systems for high temperature and high pressure applicationsHydrothermal synthesis (HS) system is known to have better high temperature resistance than conventional Portland cement-based system. However, there are still many problems with its field application, as thickening time, rheology, and sedimentation stability of HS systems are difficult to tune. In this study, the design of the HS system was optimized in three stages. In the first stage, experiments were conducted to verify the high temperature resistance of the HS system and study the reactivity of different components. In the second stage, experiments were conducted to optimize the engineering performance of the HS system. In the third stage, experiments were conducted to analyze the influence of material ratio, retarder type and alumina on the performance of the HS system. Test results revealed that the AMPS retarder had better performance than tartaric acid at high temperature and all systems had extremely stable physical and mechanical properties. | Hydrothermal synthesis system, Retarders, Field application, Mechanical properties
T03: Deep geothermal energyJuan Miguel REYES-MONTESApplied Seismology Consulting, United KingdomInduced fracture analysis from microseismic catalogues: Salton Sea EGS case studyEnhanced Geothermal Systems (EGS) use hydraulic fracturing to create a fracture network that facilitate the circulation of water between injection and extraction boreholes. Microseismic monitoring provides a unique method for the evaluation of the effectiveness and impact of the stimulation and reducing potential risks such as uncontrolled growth or induction of high magnitude seismic events. This study presents tools to interpret the geometry of the induced fracture network and quantify the changes in fluid conductivity induced in the reservoir during stimulations applied to a catalogue of over 8,000 events recorded at the Salton Sea Geothermal field over a 4-year period. The method integrates the temporal, spatial and size characteristics of the induced events to quantify the degree of interaction and connectivity between the fractures within the network, identify enhanced paths for fluid flow and highlight potential zones of induction of larger seismic events. | Microseismicity, Induced seismicity, Enhanced Geothermal Systems, Clustering, Discrete Fracture Network