Fluid Flow of Shirahama Sandstone on laboratory permeability test and numerical approach by LBM under
various stress condition
ABSTRACT
The permeability and specific storage for rocks and sedimentary layers deep underground are
very important parameters for problems related to the buried evaluation of natural gas and oil,
CO2 aquifer storage, various kind of waste storage and so on.
The Shirahama sandstone came from the Wakayama prefecture, Kii peninsular in central
Japan. This sandstone consists mainly of quartz grains with no cracks or rock fragments that are
aggregations of various kind of minerals. The quartz grains have an average size of about 150
micron. Fig.1 shows pore size distributions in intact specimens measured by mercury intrusion
porosimetry. The pre-existing pore sizes distributed dominantly at approximately 1 micron, and
the total porosity was about 13%.
During the confined triaxial compression test, we measured permeability of Shirahama
sandstone by Transient Pulse test for three mutually perpendicular directions under effective
confining pressure and increasing axial differential stress. Permeability of Shirahama sandstone
was almost constant under increasing the effective confining pressure and axial differential stress.
Permeability anisotropy was observed slightly in the normal and two parallel directions to the
bedding planes.
We have introduced micro focus X-ray CT with high resolution of 10 micron to visualize and
measure the voids space information in Shirahama sandstone. We can get three-dimensional data
simultaneously in the intact and stressed sandstone, pore structures and grain boundaries are
distinguished well, pore closure and grain movement also are recognized well with increasing
confining pressure. Micro focus X-ray CT is rather effective tools to visualize and measure the
microstructure in rocks. Fig.2 shows original CT voxel data under zero (atmosphere) and grain,
pore and 3DMA distributions.
In addition, we introduced the three-dimensional medial axis (3DMA) method to quantify the
flow-relevant geometric properties of the voids structure in Shirahama sandstone using μfocus XRay CT data. The number of connecting path between two faces, tortuosity and the shortest path
distribution within an arbitrary region of Shirahama sandstone specimen were analyzed.
Geometrical information on the number of connecting path in an arbitrary volume CT data shows
reasonable correlation between permeability anisotropy and mutually perpendicular directions
normal and parallel to bedding planes. In addition, we introduced numerical simulation of fluid
flow of pressurized Shirahama sandstone by LBM, to discuss the permeability change caused by
pressurization on effective confining pressure. We obtained the detail distributions of fluid
pressure and fluid velocity in rather narrow voids space more than 10 μm. It is confirmed that
pressurization effect on permeability caused by the decrease of the connecting path and the
shortest path between arbitrary faces, and then caused a complex condition on fluid pressure and
fluid velocity.
[Hg]SS-T-1
Porosity = 13.4124 %
Volumetric Ratio (%)
16
12
8
4
0
-3
-2
-1
0
1
Log Radius (μm)
2
3
Figure 1 – Pore size distribution of Shirahama sandstone with Mercury Intrusion Porosimetry.
Figure 2 Original CT voxel data of Shirahama sandstone, and grain , pore and 3DMA
distributions under zero pressure.
KEYWORDS
permeability anisotropy, μ-focus X-Ray CT, medial axis distribution, tortuosity, number of connecting
path, numerical simulation, LBM