Fracture flow by LBM

Kazuki Sawayama

Assistant Professor

Institute for Geothermal Science,

Graduate School of Science, Kyoto University

He received his Ph.D. from Kyushu University in 2021 and took a position as an assistant professor at Kyoto University. He has been actively contributing to rock physics and organizing its study group. He is now involved in a NEDO project for geothermal development and also in the Slow-to-Fast Earthquakes Project. He was awarded the Rocha Medal 2024 by the International Society for Rock Mechanics.

My research interest is in the relationship between rock physical properties and fluid flow behavior. Crustal fluids have a significant influence on various phenomena such as geothermal and seismic activities. Subsurface rocks are composed of a variety of minerals, and voids (pores) exist between the minerals. These pores provide pathways for crustal fluids to form hot springs and geothermal resources. Recently, the presence of underground water has been found to influence earthquakes and phreatic eruptions. To address the question of how water exists and moves in the subsurface, I have studied the physical properties of rocks using experiments and numerical calculations. However, fluid flow in the subsurface cannot be observed directly. We cannot look into the earth, so we can only imagine it by digging directly into underground rocks or by geophysical observation from the ground.

To understand these phenomena from a microscopic point of view, I perform experiments and numerical simulations on actual rock samples collected from different fields. In the experiments, I measure seismic velocities and electrical properties that can be observed remotely from the ground. My experimental equipment can mimic stress conditions down to a depth of 10 km. Using this equipment, I am attempting to update the rock physics model to access fluid flow behavior from geophysical observations. To support the experimental results, a theory based on solid state physics and mathematics (such as percolation, fractals, and an effective medium) is incorporated. In addition to the pore scale flow, I am particularly interested in the scale gap from microscale fractures to larger scale fractures, since fluid flow in fractures dominantly controls subsurface heat and mass transport in the deep subsurface. To date, there are no models to describe the physical properties of fractured rocks, which is my priority. In numerical analysis, I am working on Digital Rock Physics, which can simulate microscopic physical behavior using digitized rocks obtained from micro X-ray CT images or fracture surface profiles. This technique allows the evaluation of various physical properties under conditions that are difficult to evaluate experimentally. In addition, we can estimate flow, electrical conduction, and seismic wave propagation in rocks that cannot be visualized by experiments or field observations, and investigate the relationship between microscopic behavior and macroscopic physical properties.For field-scale fluid flow, I am also involved in numerical simulations of geothermal and hot spring resources and hydrothermal systems developing in the shallow parts of volcanic bodies. In addition, I am involved in AI-based estimation of rock properties, geothermal projects in Japan and overseas, and development of reservoir simulators as collaborative research. Through these studies, my goal is to directly visualize how water flows in rock fractures. If the subsurface structure can be fully interpreted using such rock-physical models, we will be able to better understand the Earth, which in turn will contribute to earthquake and volcano disaster prevention and sustainable development of hot springs and geothermal resources.

Research keywords: Rock Physics, Rock Mechanics, Fluid Dynamics, Permeability, Electrical resistivity, Seismic velocity, Seismic attenuation, Fracture flow, Porous flow, Percolation, Two-phase flow, Fractal, Effective medium, Poroelasticity, Dilatancy, Strain analysis, Electrical impedance, Cracks, Faults, Precipitation, micro X-ray CT, Segmentation, Convolutional Neural Network, Lattice Boltzmann Method, Level-Set method, FEM, FDM, FDTD, FVM, BEM, Geothermal, Hot springs, EGS, Slow earthquakes, Phreatic eruption, Regolith