Numerical modeling was utilized to simulate natural state condition in Lahendong geothermal field. It is necessary to find out the reservoir characteristics, hydrogeology, location and total energy of the heat source. Lahendong geothermal field is a hydrothermal system which has sufficient fluids, high average thermal gradients, high rock permeability, and high porosity. Thermo-hydro-mechanical coupling model has been applied to enhanced geothermal systems (EGS), however it has seldom been utilized in the hydrothermal system. Several conceptual and numerical models have been created to do such investigation. In this study, we tried to improve the numerical model that was created. COMSOL Multiphysics (COMSOL 5.4, 2018) was utilized for modeling the 3D numerical model to predict the evolution of rock temperature and pore pressure in the natural state condition. The reservoir is treated as a fractured porous medium by adopting discrete fractured model (DFM) which uses grid nodes to represent flow relationship between fracture to fracture, fracture to matrix, and matrix to matrix. Based on the results, the natural state conditions have been reached when the numerical results corresponding to the wells pressure and temperature data. Although some uncertain mismatches between the field data and the model predictions, this model can be utilized to evaluate the sustainability of the reservoir, improve production performance, and develop a new geothermal resource. 1. Introduction Geothermal energy is one of the alternative energies to reduce dependence on fossil fuels. In order to develop new geothermal sites and improve production performance, further theoretical research and numerical simulation in the geothermal field is still needed. A case study from the Lahendong geothermal field, Indonesia is simulated with three dimensional (3D) numerical model to study the characteristics of fluid flow, heat transfer and solid deformation in the geothermal field. The Lahendong geothermal field is located in Tomohon, North Sulawesi, Indonesia (Fig. 1).

Coupled THMC simulator that can describe the long-term evolution in rock permeability and stiffness due to mineral reactions within rock fractures generated by cavity excavation. The developed simulator was applied to perform the long-term prediction by assuming the subsurface environments near the radioactive waste repository. Analysis results show that although generated fractures during excavation of disposal cavity result in the permeability increase and the elastic modulus decrease, after the excavation, the permeability and the elastic modulus of the damaged zone decreased to that of the intact zone and increased to 30 % of the initial state, respectively. These changes of rock permeability and stiffness after excavation were driven by pressure dissolution within rock fractures. Overall, analysis results indicate that pressure dissolution within the fractures has significant influence on the evolution of hydro-mechanical damage of rock generated by cavity excavation. 1. Introduction It is important to predict the evolution of the hydraulic and mechanical properties of rocks surrounding the disposal facility for evaluating the performance of geological disposal system of high level radioactive wastes (HLW). The change of material properties of surrounding rocks should be caused by influence of multi-physics phenomena including the heat transfer from waste package, the transport of groundwater, fracture generation during cavity excavation, and chemical reactions between rock minerals and pore water. Thus, coupled Thermal-Hydraulic-Mechanical-Chemical (THMC) numerical simulation considering above-mentioned multi-physics phenomena should be required. Among the processes of HLW geological disposal, fracture generation during cavity excavation exerts significant influence on the change of hydraulic and mechanical properties of surrounding rocks (Aoyagi et al., 2019). In addition, after cavity excavation, mineral reactions such as pressure dissolution within generated fractures may control the long-term evolution of rock permeability and stiffness (Yasuhara et al., 2011). However, existing coupled THMC simulators cannot evaluate the above long-term evolution of rock permeability and stiffness due to mineral reactions.

In Japan, frequently sediment-related disasters have occurred such as typhoons, torrential rain, landslide, earthquakes, flood, debris flow, etc. To prevent the damage caused by the sediment-related disaster, it is necessary to establish a monitoring system of slope deformation. The system which has been conventionally used, have been using a wired cable to the power supply and data transmission to the equipment. However, the issues of this system are difficult to perform maintenance and monitoring. In this research, the purpose is to develop a slope deformation monitoring system using LPWA (Low Power Wide Area) that can reduce the cost and construction period. It is essential to construct a system that combines wireless technology and inclinometers that can measures movement of slopes and send the information through wireless communication. The data from Inclinometers are collected through the LPWA system. The radio wave propagation has been evaluated around the site. During collecting data from the system, site investigation and experiment has also been conducted to analyze the slope stability. It has been confirmed that the slope monitoring system could detect the slope failure during torrential rain. In the future, developing a monitoring system using LPWA is not only for slope deformation but also in any specific areas such as rock movement, the water level at dam areas, etc. 1. Introduction In Japan, many landslide disasters occur due to natural disasters such as earthquakes, torrential rains, and typhoons. To prevent damage caused by sediment-related disasters, it is necessary to establish a monitoring system for ground deformation and detect changes in observation events and problems at an early stage (Young, 2013). A simple monitoring method for the precaution of rainfall-induced landslides is proposed, which uses tilt sensors on the slope surface to detect abnormal deformation (Uchimura, 2015). However, the conventional monitoring itself is expensive, because it is necessary to initiate a power cable and a communication cable and construct a sensor with some equipment, and also the monitoring period becomes a problem with regular maintenance which makes the cost increase. In this study, we use LPWA (Low Power Wide Area) as the communication system to send the information. In this study, we aim to develop a slope deformation monitoring system using LPWA that has a data collection function and a sensor function by wireless communication that can reduce the cost and construction period. In this paper, we explain the radio wave propagation experiment to the monitoring site and the results of slope deformation monitoring.

Because the topography of the fracture surface evolved in a long-term under different conditions, it exerts a significant influence on the flow behavior. The flow would bypass the contact area between the fracture surfaces under the coupled conditions. In order to study the different characteristic factors which control the flow behavior, this work has studied the hydraulic properties of a single rock fracture by utilizing a granite specimen. The granite specimen was fixed within the triaxial vessel under the confining pressure. Several permeability tests were performed at three different temperatures (20, 60 and 90 °C). The permeability value was evaluated at different times in both short-term and long-term tests. Results show that the permeability values changed regularly in the short-term tests under different confining pressure conditions. In contrast, irregular phenomena of the permeability changing was found in the long-term tests under the constant confining pressure of 3.0 MPa. Especially at 60 °C, the permeability decreased in the early experimental period, but it increased after 60 days and varied with slight oscillation. Moreover, the permeability decrease under a higher temperature can be confirmed in both short- and long-term tests. The reason for the permeability reduction may be considered as the chemical effects under coupled processes. In this study, the effluent from the fractured specimen was also sampled in the long-term tests to evaluate the mineral dissolution. The phenomena that the topography of the fracture surface evolved with time might be controlled by the evolution of the mineral dissolution, which resulted in the permeability variation and changed the contact area between the fracture surfaces. The geometrical alteration in fractures that should have affected the permeability evolution is needed to be further examined. 1. Introduction It is well known that the mechanical and hydromechanical properties of fractures within rock mass would change under various conditions. The coupled THMC (thermal-hydraulic-mechanical-chemical) processes exert significant influence on the subsurface fluid flow in geological systems (Polak et al., 2004; Min et al., 2009). Several previous experimental works have been investigated on the hydraulic properties of rock fracture under coupled hydro-thermal conditions (Polak et al., 2003; Yasuhara et al., 2006). In these researches, the phenomena that chemical and mechanical compaction can reduce the permeability of the fracture was especially focused. The reduction of the permeability may be explained by the mechanism of pressure solution (Polak et al., 2003; Yasuhara et al., 2006). Yasuhara et al. (2004) performed the permeability tests which proved that the chemical interaction on the fracture asperities and the structure of a fracture might be changed by the pressure solution (Yasuhara et al., 2004; 2006). However, the permeability may not reduce monotonously under higher temperature conditions in the long term even though some researchers claimed that the permeability may decrease at a relative high temperature (Yasuhara et al., 2006; Kohl et al., 1995; Morrow et al., 2001; Barnabe, 1986). The complexed processes may alter the fracture surface roughness and further change the permeability of the fractured rock mass. Nevertheless the fracture surface roughness and the fracture aperture change can hardly be obtained directly. Moreover, there is lack of experimental data about the morphology of fractures at various confining stress (Bing et al., 2004). The relationship between the aperture change and the contact area is also difficult to be measured. Therefore, this work studied the short- and long-term permeability variation at different temperatures. The changing of hydraulic aperture under constant stress and temperature conditions was also investigated.

In developing underground rock, it is necessary to understand the hydraulic characteristics of the rock around the facility in order to evaluate safety and performance. The transient pulse method is one of the permeability tests of rock. It is suitable for measuring the permeability of the low-permeability rocks and has the advantage of being able to measure briefly and accurately. In this study, we have developed the apparatus of the transient pulse method based on the previous studies and measured the permeability. The tests were conducted by using two large reservoirs compared with the void volume of the rocks. Then, we also conducted the flow-through permeability tests and the results were compared with those using the transient pulse method so as to examine the validity of the transient pulse method. Both tests were conducted in Toki granite and Berea sandstone. From the data of the transient pulse tests, the permeability of both samples fell in one order. Also, comparing the permeability between the transient pulse method the flow-through procedure, the difference of the permeability by both tests fell in one order. However, the permeability of the transient pulse test was slightly less than that of the flow-through permeability test in Berea sandstone, and further investigation should be necessary. 1. Introduction Underground rock has various characteristics such as rigidity, durability and shielding properties, and the development of underground space utilizing these features is underway. Especially in the energy field, geological disposal of high-level radioactive waste and underground fuel stockpiling are examples. In developing the underground rock, it is necessary to grasp the hydraulic characteristics of the rock around the facility in order to evaluate the safety and performance. Transient pulse tests are often used for the permeability tests of rocks, and they have the advantage of measuring low-permeable rocks in a short time with high accuracy. Therefore, in this study, transient pulse test device was developed and permeability tests were conducted using the developed apparatus. The effectiveness of the transient pulse test was evaluated by comparing the permeability obtained by the flow-through permeability test.

In recent years, the use of underground rock has been more complicated and diversified than ever before in the preparation of social capital. For example, there are geological disposal of radioactive waste, carbon dioxide capture and storage, resource development of methane hydrate, etc. It is essential to transport resources efficiently and to operate facilities stably. For that purpose, it is necessary to grasp the fluid permeability in the cracked rock in detail. In the underground rock, gas-liquid two-phase flow exists by gas and liquid, but it has not been fully elucidated. Therefore, in this research, we developed gas-liquid two-phase flow experimental apparatus, and conducted a permeability test, an air permeability test, a water saturation test, and a relative permeability test. Then, we evaluated the validity of the experimental values and the utility of gas-liquid two-phase flow experimental apparatus by regression analysis of the relative permeability test results using the Van Genuchten model. The developed device can simultaneously flush water and air, and can simultaneously measure the discharged water and air. Water is controlled by pressure using a regulator, and air is controlled by flow rate using a mass flow controller. The flow rate is measured by an electronic scale, and the exhaust air flow rate is measured by a mass flow meter. The relative permeability is measured using the developed device using Berea sandstone. The results obtained in this study are compared with the previous studies, and it is thought that the utility of the apparatus and the reproducibility of the experiment could be confirmed by showing similar behavior. It is expected that this will make it possible to study gas-liquid two-phase flow simply. 1. Introduction Multiphase flow in porous media has become important issues in the rock mechanics and rock engineering problems such as geologic sequestration of CO 2 , methane hydrate, geothermal reservoir, oil and gas reservoir, etc. In order to better understand the transport mechanisms of multiphase flow in porous media, further theoretical and experimental research is still needed. In the multiphase flow, the capillary pressure and relative permeability are the important properties to be measured (Manceau et al., 2015). In this study, the developed experimental apparatus for simulated two-phase flow of the Berea Sandstone is reported. This experimental apparatus was designed to allow water and airflow into the specimen. Finally, the developed experimental apparatus is used to measure the water saturation test and relative permeability test.

Hydraulic fracturing technique has been applied in enhanced geothermal systems to enhance reservoir rock permeability. It is necessary to increase heat production from a geothermal reservoir. In order to implement economical and reasonable hydraulic fracturing simulations, an experimental study was conducted to investigate the crack propagation stage. In this experiment, we used mortar cylindrical specimen with a hole in the center as a preliminary experiment of hydraulic fracturing. The compressive strength and tensile strength of mortar cylinder specimen have been obtained by using uniaxial compression and Brazilian tests, respectively. Then, the minimum and maximum principal stress was used to apply differential pressure in the experiments. Based on the results, the crack propagation stage was not obvious. Therefore, the improvement of the experimental equipment should be done to make water injection concentrated at the center of the specimen. Furthermore, the effects of high pressure and temperature are not considered in this work and should be considered in the future work to obtain more reliable results. 1. Introduction About 8% of the world's active volcanoes exist in Japan. If this heat is used for power generation, it becomes a semi-permanent domestic energy resource. In recent years, the extracting geothermal energy by using enhanced geothermal system (EGS) has attracted attention. This technique uses hydraulic fracturing to extract the heat stored in the hot dry rock (HDR) reservoir. Hydraulic fracturing technology is used to create artificial fractures by injecting cold water into the injection well (Hori, 2001). Kosugi et al. (1980) conducted a hydraulic fracturing simulation experiment with a thick-walled cylindrical specimen and a crushing test with a cylindrical specimen in order to investigate the cracking conditions under sealing pressure. As a result, in hydraulic fracturing, it is clearly shown that the influence of confining pressure is larger than other factors (porosity, Poisson's ratio, etc.). In addition, Ishijima et al. (1981) observed hydraulic fracturing behavior and microfracture sound activity under confining pressure. It shows that the fracture pressure and the sealing pressure are in a linear relationship within the range of the sealing pressure of about 34 MPa or less. In addition, there are roughly two types of micro-breaking sound (AE) behavior that appears due to the increase in pore pressure.

When evaluating the stability of the geological disposal system for the high-level radioactive wastes (HLW), it is necessary to estimate the long-term permeability change of rock fractures that control the groundwater flow within natural barrier by numerical simulation. In the previous study, it is indicated that mineral reactions within rock fractures such as pressure dissolution alter fracture permeability over a long duration. In the actual environment where HLW are disposed, mineral reactions may result in the change of chemical property in groundwater such as a change in pH due to the inflow of the highly alkaline cement solution from an artificial barrier. However, numerical models that can simulate the influence of change in pH of groundwater on rock permeability change driven by mineral reactions observed in the experiment have not been developed well. In this study, a THMC coupled model considering multi-mineral reactions depending on pH condition is presented. Then, the proposed model was applied to replicate the results obtained from flow-through experiments using granite samples with a single fracture under the various pH conditions of permeable water. The model predictions could reproduce the permeability change observed in the experiment under neutral conditions, but couldn't simulate well it under alkaline conditions. The predicted effluent element concentrations showed a relatively good agreement with experimental measurements in several elements under both neutral and alkaline conditions. 1. Introduction When discussing the performance of the natural barrier within the geological disposal facilitiy of high-level radioactive waste (HLW), it is essential to predict the permeability evolution of rock fractures due to coupled thermal-hydraulic-mechanical-chemical phenomena. Espercially, mineral reactions such as pressure dissolution have significant influence on change of fracture permeability with time. During disposal period, mineral reactions may induce the change of chemical conditions such as pH of ground water driven by inflow of alkaline cement solution from an artificial barrier (Acker J. G. and Bricker O. P., 1992; Amrhein C. and Suarez D. L., 1992; Gautier J.-M. et al., 1994; Hellman R., 1994a; Knauss K. G. and Wolery T. J., 1988). However, to date, actual permeability evolution due to mineral reactions depending on pH condition has not been well simulated by existing coupled numerical models.

Abstract Permeability is one of the important rock properties for CO 2 storage capacity and injectivity to investigating potential CO 2 geological storage sites. The core drilling of multiple onshore and offshore boreholes was successfully completed for geological reservoir characterization of CO 2 storage sites in Southeast Korea. The directional core analysis was designed specially to measure vertical and horizontal permeabilities with directionally plugged rock core samples. The directional hydraulic properties were determined using portable probe permeameter and one-dimensional pressure cell with different confining pressures. The experimental method for measuring permeability was selected both steady state and pressure decay method according to the range of expected permeability measurements. A small diameter portable probe permeameter was applied for rapidly determining gas permeability to select the lab experimental method for estimating permeability. The promising geological formations (739 ~ 779m) were found for prospective CO 2 storage reservoirs with high porosity and permeability. Furthermore, flow modelling for CO 2 plum migration pathway was conducted to analyses subsequent flow overlying formations with estimated directional hydraulic properties. Assessed correlation and distribution of directional permeabilities for a potential CO 2 geological storage site would be utilized for CO 2 storage capacity, injectivity, and leakage risk assessment. 1. Introduction The most important properties of a CO 2 storage reservoir are porosity and permeability. The overall purpose of this research was to investigate storability of formation in the sea near Pohang. To investigate storability, hydraulic properties are measured though drilled rock samples in Pohang basin. To analyze hydraulic properties of vertical and horizontal direction, plug rock samples are made through vertical and horizontal directional coring using drilled rock sample. The porosity of plug rock samples is measured using helium porosimeter and mercury porosimeter. The permeability of these samples is measured using portable probe permeameter and the broadband rock permeability measurement system.