封圧下における岩石試料の比抵抗測定に関する研究  [in Japanese] Electrical resistivity measurements of rocks under confining pressure condition  [in Japanese]

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Author(s)

    • 林 為人 Lin Weiren
    • 国立研究開発法人海洋研究開発機構 高知コア研究所|京都大学大学院工学研究科 Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC)|Graduate School of Engineering, Kyoto University
    • 廣瀬 丈洋 Hirose Takehiro
    • 国立研究開発法人海洋研究開発機構 高知コア研究所 Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC)
    • 谷川 亘 Tanikawa Wataru
    • 国立研究開発法人海洋研究開発機構 高知コア研究所 Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC)

Abstract

<p>電気・電磁探査や孔内電気検層の比抵抗データを高い精度で解釈するためには,地下あるいは海底下の圧力・温度を再現した状態での掘削コア試料による比抵抗測定が必要不可欠である.本研究では圧力と比抵抗の関係について検討するため,封圧および間隙水圧を制御した状態で比抵抗測定ができるシステムを構築し,35 g/L塩化ナトリウム溶液で飽和した4種類の砂岩試料および2種類の火成岩試料について,最大80 MPaの有効拘束圧(間隙水圧:1 MPa)まで段階的に加圧したときの比抵抗を測定した.また,圧力の変化に伴う試料中の間隙水量の変化から,その孔隙状態の変化についても検討した.その結果,全ての試料で圧力の増加とともに間隙水は試料から排出され,比抵抗は上昇した.また,砂岩試料については間隙水量の変化が比抵抗の変化とほぼ一致する結果が得られ,圧力条件下における比抵抗の変化が試料の変形による孔隙率の縮小と強く関連付けられることを直接的に示すことができた.各試料における比抵抗の圧力依存性の違いについては,火成岩試料では微小クラックの存在により低圧域(~10 MPa)で比抵抗が大きく上昇することが示唆された.砂岩試料では,試料自体の変形特性や孔隙の形状などが比抵抗の変化傾向に影響した可能性がある.</p>

<p>Laboratory experiment of electrical resistivity measurement under in situ pressure and temperature conditions is essential to precisely interpret the DC resistivity and electro-magnetic survey and logging data. We constructed a resistivity measurement system under confining and pore pressure control, and examined the pressure dependence of electrical resistivity of rocks. Electrical resistivity of four sandstone and two igneous rock samples saturated with 35 g/L NaCl solution were measured under different effective pressure conditions (maximum 80 MPa with pore pressure of 1 MPa). We also estimated geometric change of pore space by measuring the drained pore water volume under confining pressure. The result showed that pore water in all the samples were drained with increasing pressure, and at the same time resistivity were increased. Resistivity changes of sandstone samples were highly correlated with changes of pore water volume, which directly indicates the strong relationship between resistivity increase and closure of pore space under pressure condition. Pressure dependence of resistivity was different among the rock types. Rapid increase of resistivity at low confining pressure (~10 MPa) might be caused by closure of microcracks in igneous rocks. Resistivity changes of sandstone samples possibly depended on the shape and size distribution of pores, and their deformation characteristics.</p>

Journal

  • JAMSTEC Report of Research and Development

    JAMSTEC Report of Research and Development 24(0), 1-9, 2017

    Japan Agency for Marine-Earth Science and Technology

Codes

  • NII Article ID (NAID)
    130005519986
  • Text Lang
    JPN
  • Article Type
    journal article
  • ISSN
    1880-1153
  • Data Source
    IR  J-STAGE 
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