著者

覺本 真代 坂本 靖英 宮崎 晋行 青木 一男 瀧口 晃 安井 彩 森 二郎

出版者

一般社団法人 資源・素材学会

雑誌

Journal of MMIJ (ISSN:18816118)

巻号頁・発行日

vol.134, no.9, pp.117-130, 2018-09-30 (Released:2018-09-12)

参考文献数

37

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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, in order to improve the accuracy for evaluation of stress distribution occurring on production well during depressurization, it is necessary to construct the numerical model enable to reproduce unsteady change of the relationship between shear stress and strain occurring on the contact surface between well and layer and introduce into geo-mechanical simulator. In this study, targeting three contact surface locating above depressurization interval such as 1) casing-cement, 2) casing-layer and 3) cement-layer consisting of different material, we conducted push-out test in laboratory in order to evaluate the frictional behavior at these contact surface based on the relationship between displacement and axial load. From experimental observation, it was found that shear stress occurring on the contact surface linearly increased at the initial stage in the case of steel-cement specimen. On the other hand, for specimens consisting steel-clay and cement-clay, non-linear increase of shear stress was confirmed in the process leading to the shear strength. In addition, shear strength τmax for each contact surface increased depending on effective stress σ ', effective friction angle δ' and effective cohesion c' as failure criteria was estimated based on τmax and σ '. Then, constitutive equation of variable compliance type was applied for reproduction of the relationship between displacement and shear stress observed in a series of push-out test. Through numerical simulation by introduction of this constitutive equation, we confirmed the validity of modeling of the frictional behavior.

著者

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

出版者

一般社団法人 資源・素材学会

雑誌

Journal of MMIJ (ISSN:18816118)

巻号頁・発行日

vol.134, no.1, pp.1-12, 2018-01-25 (Released:2018-01-24)

参考文献数

38

被引用文献数

1

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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.