Laboratory Investigation on the Permeability Variation of Fractured Inada Granite by Multiple Transient Axial Stress Dis
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Pure and Applied Geophysics
Laboratory Investigation on the Permeability Variation of Fractured Inada Granite by Multiple Transient Axial Stress Disturbances SOPHEA BOEUT,1
YOSHIAKI FUJII,2 JUN-ICHI KODAMA,2 DAISUKE FUKUDA,2 ANJULA DASSANAYAKE,3 and BADRUL A. K. M. ALAM4
Abstract—A persistent increase in the permeability of rock mass caused by transient stress disturbances could explain the variation in groundwater level caused by earthquakes in the farfields, increase in petroleum production due to artificial vibrations, induction of small earthquakes by seismic waves in intermediate and far-fields, etc. However, the effect of transient stress disturbances on rock permeability has not yet been fully clarified. In this study, the permeability of triaxially fractured Inada granite under multiple transient disturbances in axial stress was measured to clarify the effects of the transient stress disturbances on the fractured rock permeability. In the experiments, the permeability of fractured Inada granite decreased with time. However, the permeability increased with each series of axial stress disturbances whose amplitude was 3 MPa or larger. The degree of increase in permeability increased with the axial stress disturbance amplitudes. The increased permeability decreased with time and the duration in which the permeability decreased to its value before the disturbances was longer for larger axial stress disturbance amplitudes. The increase in permeability could be employed to enhance oil and gas productions, prevent large earthquakes, reroute underground water flow, etc. Keywords: Transient stress disturbance, rock permeability, triaxially fractured Inada granite, enhanced oil recovery.
1. Introduction Large earthquakes can lead to persistent variations in the groundwater level in the near field (within
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Research Unit of Materials Science and Structure, Institute of Technology of Cambodia, Building H, Russian Federation Blvd., P.O. Box 86, Phnom Penh 12156, Cambodia. E-mail: [email protected] 2 Graduate School of Engineering, Hokkaido University, N13W8, Sapporo 060-8628, Japan. 3 Department of Earth Resources Engineering, University of Moratuwa, Moratuwa 10400, Sri Lanka. 4 Faculty of Civil Engineering, Military Institute of Science and Technology, Dhaka 1216, Bangladesh.
the fault length, Bower and Heaton 1978; Gudmundsson 2000; Wang and Chia 2008; Orihara et al. 2014; Lai et al. 2016). This would be a result of persistent variations in the permeability of the rock mass due to a permanent change in the strain through fault movement. Such variations may also occur in an intermediate field (from one to several fault lengthsRoeloffs 1998; Kitagawa et al. 2006; Fujii et al. 2018a). However, previous studies reported that these persistent variations in the groundwater level may even occur in the far-field (many fault lengths), up to thousands of kilometers from the epicenter (Brodsky et al. 2003; Elkhoury et al. 2006; Manga et al. 2012; Manga and Wang 2015). Persistent variations of the groundwater level in t
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