Kyushu University · Earth and Planetary Sciences
Professor Kazuki Sawayama's research lab specializes in subsurface fluid-rock interactions, with a focus on understanding the hydraulic and geophysical properties of fractured rocks under variable stress and fluid conditions. The lab integrates experimental rock mechanics, numerical simulations (including lattice Boltzmann and digital fracture modeling), and geophysical monitoring techniques to investigate permeability, electrical resistivity, and elastic wave velocity changes in response to fluid saturation and stress. Their work bridges fundamental rock physics with practical applications in geoengineering, geothermal energy development, and earthquake hazard assessment.
Figures are computed from collected data and may differ slightly.
Abstract Monitoring the hydraulic properties within subsurface fractures is vitally important in the contexts of geoengineering developments and seismicity. Geophysical observations are promising tools for remote determination of subsurface hydraulic properties; however, quantitative interpretations are hampered by the paucity of relevant geophysical data for fractured rock masses. This study explores simultaneous changes in hydraulic and geophysical properties of natural rock fractures with inc
Abstract The fluid‐flow properties of fractures have received increasing attention regarding the role of geofluids in the genesis of slow and fast earthquakes and recent advances in geoengineering developments. Geophysical observations are promising tools to remotely estimate crustal permeability changes; however, quantitative interpretations are limited by the rock‐physical models' paucity for fractures. This study investigated changes in permeability, resistivity, and their respective relation
Abstract In an effort to reveal the subsurface hydraulic changes in fractures by seismic monitoring, aperture‐related velocity changes need to be investigated. We developed a numerical approach for calculating changes in elastic wave velocity with fracture aperture opening by determining the internal energy of a digitized fracture model based on natural rough surfaces. The simulated local elastic energy revealed that the interaction energy converged within 1.5 mm of the mean fracture position, a
ABSTRACT To reveal the internal structure of the earth, rock physical models are insightful for interpreting geophysical observation data and are often used for estimating subsurface structures. However, as the estimated value of each model significantly depends on the assumed microstructure, the obtained subsurface structure may be biased. Despite the innovations of high-resolution imaging technologies and their application to digital rock physics (DRP) and machine learning (ML), the characteri
庵治花崗岩の三軸圧縮試験を封圧10-40MPa，間隙水圧10-30MPa，ひずみ速度5.0×10－6 s－1の条件下で行い，ひずみゲージで測定した変形中のひずみを解析した．最大軸差応力およびダイラタンシー開始応力は有効圧の上昇に伴い増加し，水の存在下ではやや減少する傾向が確認された．ヤング率は有効圧の上昇とともに若干増加し，水の存在下ではやや低い値を示すが，ポアソン比には有効圧や水による変化はみられなかった．試料中のマイクロクラックに起因するダイラタンシーは，乾燥状態の試験では封圧が低いほど促進されるが，間隙水圧下の試験では有効圧が低いほど抑制される傾向が確認された．この傾向は，間隙水が試料内部の応力集中を緩和させる働きがある可能性を示している．また，いずれの間隙水圧下の試験でも，最大軸差応力の約96%の応力を越えると試料への注入水体積が急増する傾向が確認され，このしきい値を境に試料内の空隙の連結が促進されることが示唆された．
地震探査，電磁探査をはじめとした物理探査による地下流体の分布評価は，地熱資源をはじめとした流体資源の開発に不可欠であり，その探査精度を向上するためには岩石の物理的性質を実験的に詳細に調べる必要がある。本研究では，地熱貯留層を構成する岩石の水飽和度と複素比抵抗ならびに弾性波の関係を実験的手法によって明らかにすることを目的とし，岩石コアの室内透水試験を行った。実験供試体は，既存のマクロクラックに加え人工的に熱性亀裂を造成した安山岩（空隙率10.5%）のコア試料を用い，封圧20 MPa，温度25 ℃の条件下で透水試験中の水飽和度，浸透率，複素比抵抗（測定周波数10－2−105 Hz）および弾性波（P波，測定周波数250 kHz）を測定した。透水試験では，地熱貯留層内の水飽和度変化を再現するため，はじめに過熱蒸気を模擬した窒素ガスで空隙を充填させたのち，塩水（1 wt-% KCl溶液）を一定圧力で注入する窒素−塩水置換試験を行った。この試験の結果，塩水注入前の複素比抵抗は104 Ωmのオーダーであったのに対し，注入後の複素比抵抗は2桁低い102 Ωmのオーダーとなった。また水飽和度の上昇に伴う
Earth and Space Science Open Archive This work has been accepted for publication in Journal of Geophysical Research - Solid Earth. Version of RecordESSOAr is a venue for early communication or feedback before peer review. Data may be preliminary. Learn more about preprints. preprintOpen AccessYou are viewing the latest version by default [v1]Elastic wave velocity changes due to the fracture aperture and density, and direct correlation with permeability: an energetic approach to mated rock fractu
Earth and Space Science Open Archive This work was has been accepted for publication in Geophysical Research Letters. Version of RecordESSOAr is a venue for early communication or feedback before peer review. Data may be preliminary. Learn more about preprints. preprintOpen AccessYou are viewing an older version [v1]Go to new versionRelating Hydraulic-Electrical-Elastic Properties of Natural Rock Fractures at Elevated Stress and Associated Transient Changes of Fracture FlowAuthors Kazuki Sawayam
This study presents the first simultaneous measurements of the hydraulic, electrical, and elastic properties of fractured crystalline rocks under uniaxial loading. To elucidate the fluid-related transport in hydrothermal systems based on geophysical measurements, the correlation between permeability and measurable geophysical properties should be compre-hensively understood. However, no study has investigated detailed simultaneous changes in the permeability and electrical resistivity of rough-w
Earth and Space Science Open Archive This work has been accepted for publication in Other. Version of RecordESSOAr is a venue for early communication or feedback before peer review. Data may be preliminary. Learn more about preprints. preprintOpen AccessYou are viewing the latest version by default [v3]Relating Hydraulic-Electrical-Elastic Properties of Natural Rock Fractures at Elevated Stress and Associated Transient Changes of Fracture FlowAuthorsKazukiSawayamaiDTakuyaIshibashiiDFeiJiangiDTak
Earth and Space Science Open Archive This work has been accepted for publication in Other. Version of RecordESSOAr is a venue for early communication or feedback before peer review. Data may be preliminary. Learn more about preprints. preprintOpen AccessYou are viewing the latest version by default [v1]Scale-independent relationship between permeability and resistivity in mated fractures with natural rough surfacesAuthorsKazukiSawayamaiDTakuyaIshibashiiDFeiJiangTakeshiTsujiiDOsamuNishizawaYasuhi
Fluid flow in fractures controls subsurface heat and mass transport, which is essential for developing enhanced geothermal systems and radioactive waste disposal. Fracture permeability is controlled by fracture microstructure (e.g. aperture, roughness, and tortuosity), but in situ values and their anisotropy have not yet been estimated. Recent advances in geophysical techniques allow the detection of changes in electrical conductivity due to changes in crustal stress and these techniques can be
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