Journal of MMIJ
Online ISSN : 1884-0450
Print ISSN : 1881-6118
ISSN-L : 1881-6118
134 巻, 1 号
  • − メタンハイドレート貯留層の地層変形挙動予測に関する研究 (第2報)
    覺本 真代, 坂本 靖英, 米田 純, 片桐 淳, 青木 一男, 瀧口 晃, 安井 彩, 森 二郎
    2018 年 134 巻 1 号 p. 1-12
    発行日: 2018/01/25
    公開日: 2018/01/24
    ジャーナル オープンアクセス

    Depressurization process is regarded as the most effective process for gas recovery method from the viewpoints of gas productivity and economic efficiency among in-situ dissociation processes of Methane Hydrate (MH) existing in marine sediments. However, it is supposed that consolidation and deformation of the stratum occurs due to MH dissociation and increase of effective stress in the stratum during operation of depressurization. Consolidation and deformation wreak negative friction on the production well. As a result, the production well may suffer large compressive or tensile stress. In the worst case, it may cause shear failure, tension failure and crushing. Therefore, for optimization of gas production process by depressurization, it is necessary to perform numerical simulation in consideration of a series of phenomenon during MH dissociation in porous media and evaluate the effect of consolidation deformation of the stratum on MH production well. In this study, using the geo-mechanical simulator named as COTHMA developed under MH21 research consortium, we carried out the field-scale numerical simulation for prediction of deformation and stress distribution around production well during depressurization. On the basis of field data for the Eastern Nankai Trough area and the structure of production well for the methane hydrate first offshore production test in 2013, the detailed model for reservoir and production well was constructed. In addition, we conducted push-out test to evaluate the frictional behavior at the interface between screen-gravel pack as the different materials constituting production well and introduced into numerical model for COTHMA. From calculation results, it was found that Mises stress occurring on base pipe installed into the interval of depressurization reached 420 MPa as yield point of steel due to the effect of friction. However, the original shape was maintained because the occurred equivalent plastic strain was about 2.95 % and this strain value was much smaller than 21 % as failure criterion. Furthermore, the effect of interface between casing and cementing was not large. This result suggested that the well structure above the interval of depressurization acted as unit and the interfacial frictional behavior between well and layer was the dominant factor on deformation behavior and stress distribution of casing and cementing.