3:30 PM - 5:00 PM
[SCG56-P07] Relationship between permeability and resistivity change to shear displacement and vertical stress in fractured rock
Keywords:fracture, permeability, hydrothermal systems, fault
1. Introduction
Fluid is closely related to volcanic hydrothermal systems associated with the geothermal resources and phreatomagmatic eruptions, and to seismic phenomena. Because fractures are ubiquitous in geothermal and volcanic regions and earthquake fault zones and major flow paths for fluid, understanding the properties of fluid flow within fractures is necessary to understand subsurface heat and mass transport. However, fluid flow in fractures is complex, and requires the detailed understanding of the distribution, the volume and the connectivity of the pore space. Moreover, it is hard to establish the way to understand the geometry from the surface.
Changes in electrical resistivity due to stress changes have been observed during geothermal and volcanic activities and earthquakes. Since the change in normal stress changes the fracture opening, the characteristics of subsurface fluid flow may also change at the same time. Therefore, if the relationship between changes in fluid flow characteristics and stress changes can be clarified, it may be possible to predict changes in subsurface fluid flow characteristics from observed changes in electrical resistivity. In this study, shear displacement and vertical stress were applied to digital fractures that constructed based on characteristics measured on rock samples, and the relationship between the permeability and resistivity was investigated using a random resistor network, a model that takes advantage of the similarity between fluid flow and electrical current.
2. Method
Degital fractures were created using nonpositive Brownian motion (Matsuki et al., 2006) based on the fractal nature of the natural fracture material. Where, a number of numerical crack data sets with different properties were prepared by varying the surface roughness s in three steps (0.1, 0.2, 0.3 mm), fractal dimension D in three steps (2.0, 2.2, 2.4), and crack size L in three steps (24 mm, 48 mm, 96 mm square), respectively.
The changes in fluid flow properties and electrcal resistivity of these digital fractures when subjected to shear displacement and vertical stress were determined by a random register network (Kirkby, 2016).
Fluid is closely related to volcanic hydrothermal systems associated with the geothermal resources and phreatomagmatic eruptions, and to seismic phenomena. Because fractures are ubiquitous in geothermal and volcanic regions and earthquake fault zones and major flow paths for fluid, understanding the properties of fluid flow within fractures is necessary to understand subsurface heat and mass transport. However, fluid flow in fractures is complex, and requires the detailed understanding of the distribution, the volume and the connectivity of the pore space. Moreover, it is hard to establish the way to understand the geometry from the surface.
Changes in electrical resistivity due to stress changes have been observed during geothermal and volcanic activities and earthquakes. Since the change in normal stress changes the fracture opening, the characteristics of subsurface fluid flow may also change at the same time. Therefore, if the relationship between changes in fluid flow characteristics and stress changes can be clarified, it may be possible to predict changes in subsurface fluid flow characteristics from observed changes in electrical resistivity. In this study, shear displacement and vertical stress were applied to digital fractures that constructed based on characteristics measured on rock samples, and the relationship between the permeability and resistivity was investigated using a random resistor network, a model that takes advantage of the similarity between fluid flow and electrical current.
2. Method
Degital fractures were created using nonpositive Brownian motion (Matsuki et al., 2006) based on the fractal nature of the natural fracture material. Where, a number of numerical crack data sets with different properties were prepared by varying the surface roughness s in three steps (0.1, 0.2, 0.3 mm), fractal dimension D in three steps (2.0, 2.2, 2.4), and crack size L in three steps (24 mm, 48 mm, 96 mm square), respectively.
The changes in fluid flow properties and electrcal resistivity of these digital fractures when subjected to shear displacement and vertical stress were determined by a random register network (Kirkby, 2016).