著者

田中 敦子 坂本 靖英 眞弓 大介 東野 晴行 坂田 将 中尾 信典

雑誌

日本地球惑星科学連合2015年大会

巻号頁・発行日

2015-05-01

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化石燃料をエネルギー源とする発電所で燃焼によって発生するCO2や、天然ガス・石油等の精製所から精製の工程で発生するCO2を処理する手段として、CO2地中貯留技術が期待されている。CO2地中貯留技術は、臨界状態の密度の高いCO2を地中に隔離するため、大量のCO2の固定が可能である。CO2地中貯留の対象とされる地層は主にかん水層や枯渇したガス油田である。 CO2地中貯留(CCS)の重要な候補サイトの一つとなっている枯渇油ガス田には、未回収の原油が半分以上残されている。近年眞弓らは、油ガス貯留層内に自然に存在する嫌気性の特定の微生物のメタン生成能力が、CO2分圧の上昇によって活性化されることを見出した 。これは枯渇油ガス田を対象としたCCSサイトにおける、原位置での天然ガス資源創成の可能性を示唆するものと言える。 このような地下環境における微生物活動を考慮した新たな資源創成型のCCS技術を確立するためには、まず、微生物によるメタン生産量とCO2固定量をはじめとする諸元の定量的に評価して便益を把握する必要がある。 我々は、微生物活動を考慮した新たな資源創成型のCCS技術の基本的な便益を明らかにすることを目標に、地層モデルに地下微生物の働きを組み込み、CCSプロセスにおける地層モデルの挙動とメタン産出量の評価を行うとともに、CO2地中貯留にかかわるサイト周辺の環境インパクト評価および産業安全面のリスクアセスメントを進めている。CO2地中貯留サイトの地下の貯留層・地表・注入井坑口周辺の大気環境をとりあげて、CO2漏洩のリスクの評価を進めるとともに、CO2地中貯留リスク評価プログラムを開発中である。本報告ではこれらの取り組みの中から、とりわけサイト周辺のリスク評価について報告する。

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.