[S-CG56] Dynamics in mobile belts

[SCG56-05] Characteristics of fluid migration under anisotropic stress based on geometrical information of fractures

*Takato Takemura¹, Masanobu Oda², Kenichiro Suzuki³ (1.Nihon University, 2.Saitama University, 3.Obayashi Co.Ltd.)

Keywords:Permeability Tensor

It is known that the main path of fluid migration in rocks and bedrock is through fractures. In the double porosity model, the migration paths include both fractures and voids in the host rock, but the time scales required for migration are different between fractures and pores. For example, in the case of mineral veins, it is known that hydrothermal fluids have migrated or remained in fractures even at depths of several kilometers below the surface (Hosono et al., 2022). When considering fluid movement in such fractured rocks (fractured bedrock), hydraulic conductivity is often used to evaluate fluid flow. When the permeability is relatively isotropic, such as in porous media, a single hydraulic conductivity can be used to describe the hydraulic properties. Fractures in rocks under anisotropic stress can either close or open depending on the stress applied to the fracture. In considering such problems, it is important to introduce a permeability tensor (Oda, 1985; Oda et al., 2002) that reflects field-derived information as much as possible in order to consider subsurface fluid movement. Methods for estimating crack density from field-derived information (Oda, 1984; Takemura and Oda, 2004; Takemura and Oda, 2005) have been proposed, and their applicability is discussed in this study. We also attempt to formulate a permeability tensor for fluid movement characteristics in subduction zones and other locations with significant stress anisotropy.

References

Hosono, H., Takemura, T., Asahina, D., and Otsubo, M., 2022, Estimation of paleo-permeability around a seismogenic fault based on permeability tensor from observable geometric information of quartz veins. Earth Planets Space 74, 141.
Oda, M., 1984. Similarity rule of crack geometry in statistically homogeneous rock masses. Mech Mater 3, 119-129.
Oda, M., Takemura, T., Aoki, T., 2002. Damage growth and permeability change in triaxial compression tests of Inada granite. Mech Mater 34, 313-331.
Suzuki, K., Oda, M., Yamazaki, M., Kuwahara, T., 1998. Permeability changes in granite with crack growth during immersion in hot water. Int J Rock Mech Min Sci 35, 907-921.
Takemura, T., Oda, M., 2004. Stereology-based fabric analysis of microcracks in damaged granite. Tectonophysics 387, 131-150.
Takemura, T., Oda, M., 2005. Changes in crack density and wave velocity in association with crack growth in triaxial tests of Inada granite. J Geophys Res 110.