HR: 1340h
AN: T53C-1445    [Abstracts]
TI: Estimation of Porosity and Permeability Structures of Miyazaki Group, Japan
AU: * Kitajima, H
EM: hkitajima@geo.tamu.edu
AF: Center for Tectonophysics, Department of Geology & Geophysics, Texas A&M University, Center for Tectonophysics, Department of Geology & Geophysics, Texas A&M University, College Station, TX 77843-3115 United States
AU: Shimamoto, T
EM: shima@kueps.kyoto-u.ac.jp
AF: Department of Geology and Mineralogy, Division of Earth and Planetary Sciences, Graduate School of Kyoto University , Kitashirakawaoiwakecho, Sakyo-ku, Kyoto, 606-8502 Japan
AU: Tanikawa, W
EM: watarusama@kueps.kyoto-u.ac.jp
AF: Department of Geology and Mineralogy, Division of Earth and Planetary Sciences, Graduate School of Kyoto University , Kitashirakawaoiwakecho, Sakyo-ku, Kyoto, 606-8502 Japan
AB: Determination of porosity and permeability structures of a whole basin is significant for many problems such as basin analysis (analysis of sedimentation and fluid flow processes), simulation of underground fluid flow, and evaluating potential of waste isolation and deep underground CO₂ sequestration. We show that these structures can be estimated (1) by measuring permeability and porosity at elevated effective pressures, covering conditions for the entire basin, and (2) by evaluating the long-term cementation effect from similar measurements for samples from all stratigraphic horizons, using Miyazaki group as an example. Miyazaki group is Miocene to Quaternary slope sediments on top of Shimanto accretionary complex, with monocline structure and with porosity ranging from 43 % to 8 %. Results for fresh surface samples are very close to those for drilled samples down to about 1km for hot springs and methane gas production. Thus, the basin-scale permeability and porosity structures can be estimated at very low cost using fresh surface samples. We also have evaluated the effects of fault zones and fractures on fluid flow by measuring hydraulic properties of fault rocks and fractured rocks and by conducting deformation and fluid flow experiments. Permeability and porosity have been measured with N₂ gas flow method and with a picnometer, respectively, at confining pressures up to 100 MPa, using an intra-vessel deformation and fluid-flow apparatus in Kyoto University. Permeability and porosity of sandstone ranges from 10^-13 to 10^-18 (m²) and from 35 to 8 %, respectively, and they both decreases with increasing effective pressure. Permeability of siltstone is smaller than that of sandstone of the same formation by one to two orders of magnitudes. Siltstone has porosity ranging from 43 to 14 % and is more porous than corresponding sandstone even at pressures. Porosity and permeability shows decrease as a linear and an exponential function of depth, respectively. Porosity of both sandstone and siltstone decreases nearly linearly with increasing age of the sediments. Clastic grains in sandstone exhibit pressure solution textures indicating that solution/precipitation process is an important mechanism for long-term cementation. Our data set enables one to construct underground porosity and permeability structures at any depth. A basin analysis has revealed that abnormal pore pressure does not develop in Miyazaki group, consistent with drilled data. Thus our estimates of underground permeability and porosity structures are reasonable. It is also essential to evaluate fluid flow along faults and fractures. The permeability of Heiwadai fault gouge in Neogene formation is lower than that of host sandstone and is higher than that of host siltstone. Thus fault zones have potential to prevent lateral fluid flow through sandstone. Fractures begin to act as fluid conduit when porosity reduces down to about 20 %., which is according to a striking field observation showing that joints have not much formed in rocks with porosity greater than 20 %.
DE: 1832 Groundwater transport
DE: 1859 Rocks: physical properties
DE: 8010 Fractures and faults
DE: 8169 Sedimentary basin processes
SC: Tectonophysics [T]
MN: Fall Meeting 2005