| 講演要旨(和文) | | 実験室内でMHを含有する試料の弾性波速度と比抵抗を計測するシステムを新たに構築した。計測対象の試料は、海底地盤から採取されたMHを胚胎する砂試料と人工的に作成したMHを含有する砂試料である。MH天然コアは、採取後液体窒素で低温保管された試料を用いた。また、MH模擬コアは、今回製作した試験装置の三軸セル内で作製した。塩水飽和状態でのP波速度、S波速度、Vp/Vsについて、MH飽和率との関係を示すとともに、東部南海トラフ海域で実施された坑井検層データと比較したところ、類似の傾向を示すことがわかった。また、MH胚胎層を表す岩石物理モデルとして提案されているMatrix-supportモデルの理論曲線とも調和的である。塩水飽和試料の比抵抗も同様に、東部南海トラフ海域で実施された坑井検層データと同様の傾向を示した。またArchieの式にもとづく理論曲線と調和的であることがわかった。 |
|
|
| | 講演要旨(英文) | | In order to clarify physical properties of methane hydrate-bearing sediments, seismic wave velocities and electric resistivities of natural and artificial samples were measured in relation to methane hydrate saturation. First, a laboratory experiment system was developed so that P- and S-wave velocities and electric resistivities were measured simultaneously under the condition of in situ pressure and temperature. Natural methane hydrate samples were prepared from the stored cores kept in liquid nitrogen at a low temperature. Artificial methane hydrate samples were produced in the tri-axial cell of the experiment device. All core samples were saturated by brine just before the measurements. These measurement results agreed well with those obtained by the previous study on the relationship between MH saturation and seismic wave velocities of the wireline logging around the Eastern Nankai Trough area offshore Japan. In addition, it was found that the relationship was explained by one of the rock physics models for the MH bearing sediments as matrix-support type. Electric resistivities of the same samples as those used to measure the seismic velocities increased with increased MH saturation, though the resistivities run up as the saturation was more than 50%. These also agreed well with those obtained from the wireline logging. |
|
|
|
| |
|