| Citation: |
Peng-fei Xie, Lin Yang, Qian-yong Liang, Xu-hui Zhang, Liang-hua Zhang, Bin Zhang, Xiao-bing Lu, Hui-ce He, Xue-min Wu, Yi-fei Dong, 2022. Stability analysis of seabed strata and casing structure during the natural gas hydrates exploitation by depressurization in horizontal wells in South China Sea, China Geology, 5, 300-309. doi: 10.31035/cg2022018
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Stability analysis of seabed strata and casing structure during the natural gas hydrates exploitation by depressurization in horizontal wells in South China Sea
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Abstract
Natural gas hydrates (NGHs) are a new type of clean energy with great development potential. However, it is urgent to achieve safe and economical NGHs development and utilization. This study established a physical model of the study area using the FLAC3D software based on the key parameters of the NGHs production test area in the South China Sea, including the depressurization method, and mechanical parameters of strata, NGHs occurrence characteristics, and the technological characteristics of horizontal wells. Moreover, this study explored the law of influences of the NGHs dissociation range on the stability of the overburden strata and the casing structure of a horizontal well. The results are as follows. With the dissociation of NGHs, the overburden strata of the NGHs dissociation zone subsided and formed funnel-shaped zones and then gradually stabilized. However, the upper interface of the NGHs dissociation zone showed significant redistribution and discontinuity of stress. Specifically, distinct stress concentration and corresponding large deformation occurred in the build-up section of the horizontal well, which was thus prone to suffering shear failure. Moreover, apparent end effects occurred at the end of the horizontal well section and might cause the deformation and failure of the casing structure. Therefore, it is necessary to take measures in the build-up section and at the end of the horizontal section of the horizontal well to prevent damage and ensure the wellbore safety in the long-term NGHs exploitation.
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References
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Peng-fei Xie, Lin Yang, Qian-yong Liang, Xu-hui Zhang, Liang-hua Zhang, Bin Zhang, Xiao-bing Lu, Hui-ce He, Xue-min Wu, Yi-fei Dong, 2022. Stability analysis of seabed strata and casing structure during the natural gas hydrates exploitation by depressurization in horizontal wells in South China Sea, China Geology, 5, 300-309. doi: 10.31035/cg2022018
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Figure 1.
Map showing the geographical location of the study area. PRMB‒Pearl River Mouth Basin; QDNB‒Qiongdongnan Basin.
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Figure 2.
Time-varying curves of NGHs saturation and pore pressure at different positions (after Sun FF, 2019). a‒pore pressure at different positions under different dissociation times; b‒NGHs saturation at different positions under different dissociation times.
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Figure 3.
Schematic diagram of the FLAC3D calculation model.
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Figure 4.
Experimental devices for the synthesis, dissociation, and static and dynamic mechanical property measurement of NGHs-bearing sediments.
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Figure 5.
Contour chart showing the distribution of vertical stress.
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Figure 6.
Contour chart showing the minimum principal stress of local structures.
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Figure 7.
Contour chart showing the maximum principal stress in local structures.
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Figure 8.
Contour chart showing the vertical displacement.
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Figure 10.
Subsidence curves of seabed surface under different radii of the NGHs dissociation zone.
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Figure 9.
Schematic diagram showing the development trend of the maximum vertical displacement.
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Figure 11.
Subsidence curves of the upper interface of the NGHs dissociation zone under different radii of the NGHs dissociation zone.
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Figure 12.
Contour chart showing the vertical displacement distribution in local structures under the dissociation radius of R = 10 m.
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Figure 13.
Contour chart showing the vertical displacement distribution in local structures under the dissociation radius of R = 25 m.