Boeut, Sophea (Hokkaido University) | Oshima, Teppei (Hokkaido University) | Fujii, Yoshiaki (Hokkaido University) | Kodama, Jun-ichi (Hokkaido University) | Fukuda, Daisuke (Hokkaido University) | Matsumoto, Hiroyuki (Kushiro Coal Mine) | Uchida, Kazumi (Kushiro Coal Mine)
There are several case studies in which vibration produced by earthquakes or underground explosion affected the level and temperature of ground water, petroleum production, etc. These might be due to the change in permeability by transient stress disturbances creating new pathways, clearing particles clogging the pore spaces of the existing pathways. This paper investigated on the permeability change of intact and triaxially fractured Kushiro Cretaceous sandstone by transient axial and pore pressure disturbances. In the room temperature, the specimens dimensioned 30 mm in diameter and 60 mm in length were triaxailly compressed under 1 MPa of pore water pressure, and 3-15 MPa of confining pressures. The permeability was measured before (kI: intact rock) and after (kDI: disturbed intact rock) transient stress disturbances for pre-failure rock and before (kP: post-failure rock) and after (kDP: disturbed post-failure rock) transient stress disturbances for post-failure rock.
Under 0-11 MPa of the axial stress disturbance amplitudes, the permeability of the specimens decreased from kI to kDI and from kP to kDP due to the disturbance, yet it increased from kDI to kP resulted in rock failure. The permeability of pre-failure rock decreased larger with confining pressure and time; however, the decrease amount was almost constant by the disturbance amplitudes. For post-failure, the decrease amount of permeability became higher with the axial stress disturbances. This clarifies that the permeability of fractured Kushiro Cretaceous sandstone decreased by axial stress disturbance.
Under pore pressure disturbance amplitudes of 0.2 to 1.8 MPa, in the pre-failure regime, the permeability decreased at the lower disturbance amplitudes, but increased at higher disturbance amplitude. The permeability continued to increase by rock failure, though, in the post-failures, the permeability decreased by the pore pressure disturbances. The increase might be utilized for the enhanced methane gas recovery.
Transient stress disturbances from either earthquakes or the underground explosion may induce change in the underground properties. The seismic waves, for instance, resulted in the change in level, (Beresnev &; Johnson, 1994; Elkhoury et al., 2006; Wang &; Manga, 2009; Manga et al., 2012) and the temperature (Mogi et al., 1989) of the ground water or the petroleum production (Beresnev &; Johnson, 1994; Pride et al., 2008; Roegiers, 2016). The Union of Soviet Socialist Republic, the US, etc., did the underground nuclear explosion tests between the 1950s and 1960s; and these underground explosion tests may have reduced the number of earthquakes more than M8.0 (Fujii et al., 2017). These occurrences might be due to the change in permeability of rock mass by the transient stress disturbances creating microcracks, clearing the barrier particles clogged the pore spaces of the pathways, etc. (Manga et al., 2012). This paper focused on the change of permeability of intact and triaxially fractured Kushiro Cretaceous sandstone. Increase in permeability, if it is confirmed, may encourage its utilization to enhance gas recovery, to prevent future large earthquakes by inducing small earthquakes, and to de-route underground water flow for various purposes.