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Abstract The excavation performance of Water Jet (WJ) technology is affected by many parameters. Therefore, many experiments are required for the development and application of WJ technology. If a realistic numerical simulation of WJ excavation could be produced, we might be able to identify the optimum conditions for excavation, which could reduce the cost of developing new WJ technology. In this study, we focused on the Smoothed Particle Hydrodynamics (SPH) method, which is a type of particle method, for the numerical simulation of WJ excavation of soft rock saturated with water. The main results can be summarized as follows: We developed a three-dimensional SPH simulation code for WJ excavation of soft rock saturated with water. We clarified the usefulness of this numerical simulation code by comparing the calculated results with those from excavation experiments in soft rock saturated with water. 1 Introduction Water jet (WJ) technology is an effective approach to rock excavation. WJ can be used inmany fields, such as in the precision machining of solid materials, medical fields and the food industry. In WJ technology, many parameters influence excavation performance. These parameters include the driving pressure, ambient pressure, nozzle geometry, standoff distance, presence or absence of an abrasive, the properties of the excavated material, etc. Therefore, many experiments are necessary for the development and application of WJ technology. However, both the cost and time needed to develop new WJ technology increase with an increase in the number of experiments required. If a realistic numerical simulation of WJ excavation could be produced, we might be able to identify the optimum conditions for excavation rapidly and at low cost, and thus reduce the overall cost of developing WJ technology. The WJ excavation of rock is a moving boundary problem in which water penetrates the rock, since the interfaces between the solid and liquid are greatly deformed. Therefore, in this study, we used the SPH (Smoothed Particle Hydrodynamics) method (Monaghan 1988), which is a particle method, to numerically simulate the WJ excavation of rock. The SPH method was originally developed to model astrophysical phenomena, and was later widely extended to problems involving continuum solid and fluid mechanics (Liu & Liu 2003). The SPH method is now being applied in various fields, such as in the analysis of the impact of a solid (Komurasaki et al. 1998, Shintate & Sekine 2002) and in the analysis of the large deformation of a solid (Cleary et al. 2006).
- Geology > Rock Type (1.00)
- Geology > Geological Subdiscipline > Geomechanics (0.71)
Effects of Vertical Stress on Fracture Propagation using Super Critical Carbon Dioxide
Kizaki, A. (Graduate School of Environmental Studies, Tohoku University) | Ohashi, K. (City Government of Ageo City) | Tanaka, H. (Tohoku Electric Power Co., Inc.) | Sakaguchi, K. (Graduate School of Environmental Studies, Tohoku University)
Abstract To clarify the effects of the vertical stress along the borehole on the hydraulic fracture formation, we conducted hydraulic fracturing experiments using the fracturing fluids of the water and the super critical carbon dioxide. A borehole was bored perpendicular to the weak plane of the rock, and horizontal stresses of 5 and 3MPa and a vertical stress of 12MPa were applied. The obtained results were compared with the results obtained at a lower applied vertical stress of 1MPa. The total length of the fractures measured at the specimen surfaces for the vertical stress of 12MPa tended to be smaller than that for a vertical stress of 1MPa. This suggests that the horizontally oriented pores and microcracks were compressed by the high vertical stress and that the infiltration of the fracturing fluids significantly affected fracture propagation. 1 Introduction Japan is one of the most volcanically active countries in the world and has rich geothermal resources. Geothermal power generation does not result in discharges of greenhouse gases, such as carbon dioxide, to the same extent as other energy generation methods that combust fossil fuels. This form of energy generation is also stable, not being dependent on weather or season. Geothermal energy therefore constitutes an eco-power generation method that mitigates global warming. To promote geothermal research and development, Muraoka et al. proposed the Japan Beyond-Brittle Project (JBBP) (Asanuma et al. 2012). This international project is designed to demonstrate the feasibility of a new type of power generation method, using an artificial brittle fracture reservoir system in high temperature ductile zones. Figure 1 shows the relation between shear strength and depth obtained by Byerlee's law and the plastic flow law for various strain rates (έ) at a high geothermal gradient of 130°C/km. This high geothermal gradient was observed at the Kakkonda geothermal field, Japan (Muraoka et al. 1998). The creep parameters obtained by Jaoul et al. (1984) were used to produce this figure. In brittle failure, shear strength increases with depth, since confining pressure (σn) increases with depth. Contrastively, in ductile failure, shear strength decreases with depth, since temperature increases with depth.
- Energy > Oil & Gas > Upstream (1.00)
- Energy > Renewable > Geothermal > Geothermal Resource (0.87)