JpGU-AGU Joint Meeting 2017

Presentation information

[EE] Oral

S (Solid Earth Sciences) » S-CG Complex & General

[S-CG62] [EE] Dynamics in mobile belts

Tue. May 23, 2017 10:45 AM - 12:15 PM Convention Hall B (International Conference Hall 2F)

convener:Yukitoshi Fukahata(Disaster Prevention Research Institute, Kyoto University), Robert Holdsworth(Durham University), Jeanne Hardebeck(USGS), Hikaru Iwamori(Geochemical Evolution Research Program, Japan Agency for Marine-Earth Science and Technology), Chairperson:Toru Takeshita(Department of Natural History Sciences, Graduate School of Science, Hokkaido University), Chairperson:Takamoto Okudaira(Department of Geosciences, Graduate School of Science, Osaka City University)

11:45 AM - 12:00 PM

[SCG62-10] Percolation of open grain boundaries and electrical conductivity in fluid-bearing rocks

*Tohru Watanabe1, miho makimura1, Yohei Kaiwa1 (1.Gradudate School of Science and Engineering, University of Toyama)

Keywords:percolation, grain boundary, electrical conductivity

Numerical experiments were conducted on the percolation of open grain boundaries to study the percolation threshold and evolution of connectivity. Open grain boundaries are a major component of pores in crustal materials. Electrical conductivity and permeability are highly sensitive to the connectivity of open brain boundaries. The length and size of the largest cluster was surveyed in a 3D array of cubic grains for various fractions of open grain boundary. For sufficiently large size of array, the percolation threshold was found to be 0.20. If more than 20% of grain boundaries are open, an interconnected network of open grain boundaries is formed. If the aggregate is saturated with brine, the electrical conduction can occur through open grain boundaries. The connectivity of open grain boundaries steeply increases to 1.0 around the threshold. The electrical conductivity is also expected to increase steeply. The crack density parameter for the percolation threshold is estimated to be 0.1. The large change in electrical conductivity for a small change in crack density parameter is thus expected around crack density parameter of 0.1. Simultaneous measurements on elastic wave velocity and electrical conductivity in a brine saturated granitic rock (Watanabe and Higuchi, 2015) showed a steep change in electrical conductivity around the crack density parameter of 0.1. XCT images show that open grain boundaries are the dominant pores in the sample. The steep change in conductivity must thus be related to the percolation of open grain boundaries.