THE REACTIVATION MECHANISM OF ANCIENT OCEAN LANDSLIDES DURING HYDRATE PRODUCTION: A PRELIMINARY STUDY
-
摘要: 我国南海北陆坡水合物富集区广泛发育古滑坡,若水合物开采不当可能导致古滑坡再次滑动。为了探究水合物开采诱发古滑坡再启滑机制,针对含下卧型水合物藏和伴生型水合物藏的两个典型古滑坡体,在边坡极限平衡分析框架内考虑了水合物开采过程中的瞬态孔压与土体抗剪强度变化,分析了水合物开采过程中不同古滑坡体的稳定性演变与失稳模式。研究表明,水合物分解导致所赋存土体的胶结强度弱化,同时逸出气体可能被阻滞于渗透性较低的古滑坡体下方,从而形成横向扩展的高压区。下卧型储层边坡的潜在滑移面贯穿古滑移面,一般表现为滑动型滑坡;开采初期因孔压积聚而导致边坡稳定性降低,开采中后期因二次水合物生成可能导致边坡稳定性有所回升,在本文计算条件下未触发古滑坡复活。伴生型储层边坡的稳定性受土体强度劣化与孔压积聚的共同影响,水合物开采导致古滑坡重新滑动,表现为滑塌型滑坡。Abstract: Ancient landslides are widely developed in hydrate-rich areas in the northern continental slope of the South China Sea. Imprudent hydrate production may result in the reactivation of the ancient submarine landslides. In order to explore the mechanism of the ancient landslide reactivation induced by hydrate production, we analyzed the slope stability and instability modes of two typical ancient landslides: the underburden-type and the associated-type. The analysis accounted for the changes of the transient pore pressure and the soil shear strength during hydrate production within the limit equilibrium analysis framework. The results suggest that hydrate dissociation results in the reduction of the cementing strength and meanwhile, the released gas may be trapped below the ancient landslide body with low permeability, giving rise to a laterally extending high-pressure zone. The potential slip surface of the underburden-type reservoir goes through the ancient slip surface, showing a slide pattern. In the early stage of production, the slope stability decreases due to the pore pressure build-up. Then, during the middle and late stages of production, the slope stability recovers because of the secondary hydrate formation. The production would not trigger the ancient reactivation with the calculation configuration in this study. The slope stability of the associated-type reservoir is affected by both the soil strength reduction and the pore pressure build-up. Hydrate production from an associated-type reservoir may trigger the reactivation of the ancient landslide, showing a slump pattern.
-
表 1 计算模型
Table 1. Models used in this study
参数 计算模型 热导率(Moridis et al., 2005) $ {\lambda _\mathit{\Theta }}{\rm{ = }}\left({\sqrt {{\mathit{S}_{\rm{H}}}} + \sqrt {{\mathit{S}_{\rm{A}}}} } \right)\left({{\mathit{\lambda }_{{\rm{SW}}}} - {\mathit{\lambda }_{{\rm{sd}}}}} \right) + {\mathit{\lambda }_{{\rm{sd}}}}$ λsd/W·(mK)-1
λsw/W(mK)-1
SH
SA干热导率
湿热导率
水合物饱和度
液相饱和度毛细压力(Genuchten,1980) $ {P_{\rm{c}}} = {P_0}{\left[ {{{\left({\frac{{{S_{\rm{A}}} - {S_{{\rm{irA}}}}}}{{1 - {S_{{\rm{irA}}}}}}} \right)}^{ - 1/\xi }} - 1} \right]^\xi }$ ξ
SirA
P0/Pa孔隙尺寸分布指标
残余液相饱和度
进气压强值含水合物沉积物渗透率(Moridis et al., 2014) $ k = {k_0}{\left[ {\frac{{\varphi \left({1 - {S_{\rm{H}}}} \right) - {\varphi _{\rm{c}}}}}{{\varphi - {\varphi _{\rm{c}}}}}} \right]^n}$ k0/mD
φ
φc
n固有渗透率
实际孔隙率
临界孔隙率
衰减指数液相(A)与气相(G)相对渗透率(Moridis,2014) $ {k_{{\rm{r}}\alpha }} = {\left[ {\frac{{\left({{S_{\rm{ \mathsf{ α} }}} - {S_{{\rm{ir}}\mathit{\alpha }}}} \right)}}{{1 - {S_{{\rm{ir}}\mathit{\alpha }}}}}} \right]^{{n_\alpha }}}, \mathit{\alpha }{\rm{ \equiv A, G}}$ nA,nG
SA,SG
SirA
SirG经验指数
液相与气相饱和度
液相残余饱和度
气相残余饱和度表 2 地层的物理力学参数
Table 2. Physical and mechanical parameters of the strata
参数* 泥质粉砂 古滑坡主体 古滑移面 含水合物层 ρ/kg·m-3 2650 2650 2650 2650 c′/kPa 20 20 0 1000 φ′/(°) 25 25 25 25 λd/W·(mK)-1 1.0 1.0 1.0 1.0 λw/W·(mK)-1 3.1 3.1 3.1 3.1 P0/Pa 105 104 104 104 ξ 0.45 0.15 0.45 0.45 nA 3.5 5.0 3.5 3.5 nG 2.5 3.0 2.5 2.5 SirA 0.25 0.55 0.25 0.25 SirG 0.01 0.05 0.01 0.01 φ 0.4 0.1 0.6 0.4 φc 0.02 0.005 0.05 0.02 k0/mD 75 10-5 — 75 *命名:ρ为土粒密度;c′为有效黏聚力;φ′为有效内摩擦角 -
Chen D X, Wang X J, Völker D, et al. 2016. Three dimensional seismic studies of deep-water hazard-related features on the northern slope of South China Sea[J]. Marine and Petroleum Geology, 77 : 1125-1139. doi: 10.1016/j.marpetgeo.2016.08.012 Dugan B. 2012. Petrophysical and consolidation behavior of mass transport deposits from the northern Gulf of Mexico, IODP Expedition 308[J]. Marine Geology, 315-318 : 98-107. doi: 10.1016/j.margeo.2012.05.001 Genuchten V A N. 1980. A closed-form equation for predicting the hydraulic conductivity of unsaturated soils[J]. Soil Science Society of America Journal, 44 (5): 892-898. doi: 10.2136/sssaj1980.03615995004400050002x GEO-SLOPE InternationalLtd., 2017. Stability Modeling With Geostudio[EB/OL]. https://www.geoslope.com/learning/support-Resources#dnn_BooksHeaderPane. Guo X S, Zheng D F, Nian T K, et al. 2020. Large-scale seafloor stability evaluation of the northern continental slope of South China Sea[J]. Marine Georesources and Geotechnology, 37 : 804-817. doi: 10.1080/1064119X.2019.1632996 Hance J J. 2003. Submarine slope stability[D]. Austin: University of Texas at Austin. He J, Liang Q Y, Ma Y, et al. 2018. Geohazards types and their distribution characteristics in the natural gas hydrate area on on the northern slope of the South China Sea[J]. Geology in China, 45 (1): 15-28. http://en.cnki.com.cn/Article_en/CJFDTOTAL-DIZI201801003.htm He Y, Zhong G F, Wang L L, et al. 2014. Characteristics and occurrence of submarine canyon-associated landslides in the middle of the northern continental slope, South China Sea[J]. Marine and Petroleum Geology, 57 : 546-560. doi: 10.1016/j.marpetgeo.2014.07.003 Huo Y D, Nian T K, Jiao H B, et al. 2019. Seismic stability of submarine clay slopes based on upper bound approach[J]. Journal of Engineering Geology, 27 (2): 408-414. http://en.cnki.com.cn/Article_en/CJFDTotal-GCDZ201902022.htm Lall D, Vishal V, Lall M V, et al. 2022. The role of heterogeneity in gas production and the propagation of the dissociation front using thermal stimulation, and huff and puff in gas hydrate reservoirs[J]. Journal of Petroleum Science and Engineering, 208: 109320. doi: 10.1016/j.petrol.2021.109320 Lei Y N, Wang G J, Wu S G. 2018. Preliminary research on characteristics, distribution patterns and origins of submarine slides in deepwater oil and gas exploration area of Baiyun Sag[J]. Marine Geology & Quaternary Geology, 38 (2): 106-114. http://en.cnki.com.cn/Article_en/CJFDTOTAL-HYDZ201802011.htm Li G, Moridis G J, Zhang K N, et al. 2011. The use of huff and puff method in a single horizontal well in gas production from marine gas hydrate deposits in the Shenhu Area of South China Sea[J]. Journal of Petroleum Science and Engineering, 77 (1): 49-68. doi: 10.1016/j.petrol.2011.02.009 Li L, Lei X H, Zhang X, et al. 2013. Gas hydrate and associated free gas in the Dongsha Area of northern South China Sea[J]. Marine and Petroleum Geology, 39 (1): 92-101. doi: 10.1016/j.marpetgeo.2012.09.007 Li W, Wu S G, Wang X J, et al. 2014. Baiyun Slide and its relation to rluid migration in the northern slope of Southern China Sea[C]//Krastel S, et al. Submarine Mass Movements and Their Consequences. Advances in Natural and Technological Harzards Research, 37: 105-115. Li X S, Wang Y, Li G, et al. 2011. Experimental investigation into methane hydrate decomposition during three-dimensional thermal huff and puff[J]. Energy & Fuels, 25 : 1650-1658. http://www.onacademic.com/detail/journal_1000036712656810_591e.html Liu F, Tan L, Crosta G, et al. 2020. Spatiotemporal destabilization modes of upper continental slopes undergoing hydrate dissociation[J]. Engineering Geology, 264: 105286. doi: 10.1016/j.enggeo.2019.105286 Ma Y, Li S Z, Liang J Q, et al. 2012. Characteristics and mechanism of submarine landslides in the Qiongdongnan Basin, northern South China Sea[J]. Journal of Jinlin University(Earth Science Edition), 42 (S3): 196-205. http://www.researchgate.net/publication/287910409_Characteristics_and_mechanism_of_submarine_landslides_in_the_Qiongdongnan_Basin_Northern_South_China_Sea Moridis G J, Pruess K. 2014. User's manual of the TOUGH+CORE code v1.5: A general-purpose simulator of non-isothermal flow and transport through porous and fractured media[R]. Berkeley, America: Lawrence Berkeley National Laboratory. Moridis G J, Queiruga A F, Reagan M T. 2018. Geomechanical stability and overall system behavior of sloping oceanic accumulations of hydrates responding to dissociation stimuli[C]//Kuala Lumpur, Malaysia: Offshore Technology Conference Asia. Moridis G J, Seol Y, Kneafsey T J. 2005. Studies of reaction kinetics of methane hydrate dissocation in porous media[R]. Berkeley, America: Lawrence Berkeley National Laboratory. Moridis G J. 2014. User's manual for the HYDRATE v1.5 option of TOUGH+v1.5: A code for the simulation of system behavior in hydrate-bearing geologic media[R]. Berkeley, America: Lawrence Berkeley National Laboratory. Moscardelli L, Wood L. 2008. New classification system for mass transport complexes in offshore Trinidad[J]. Basin Research, 20 (1): 73-98. doi: 10.1111/j.1365-2117.2007.00340.x Nian T K, Guo X S, Zheng D F, et al. 2019. Susceptibility assessment of regional submarine landslides triggered by seismic actions[J]. Applied Ocean Research, 93: 101964. doi: 10.1016/j.apor.2019.101964 Nian T K, Song X L, Zhao W, et al. 2020. Submarine slope failure due to overpressure fluid associated with gas hydrate dissociation[J/OL]. Environmental Geotechnics, https://doi.org/10.1680/jenge.19.00070 Song B J, Cheng Y F, Yan C L, et al. 2019. Seafloor subsidence response and submarine slope stability evaluation in response to hydrate dissociation[J]. Journal of Natural Gas Science and Engineering, 65 : 197-211. doi: 10.1016/j.jngse.2019.02.009 Su P B, Liang J Q, Zhang W, et al. 2020. Natureal gas hydrate accumulation system in the Shenhu sea area of the northern South China Sea[J]. Natural Gas Industry, 40 (8): 77-89. Sun Q L, Alves T, Xie X N, et al. 2017. Free gas accumulations in basal shear zones of mass-transport deposits(Pearl River Mouth Basin, South China Sea): An important geohazard on continental slope basins[J]. Marine and Petroleum Geology, 81 : 17-32. doi: 10.1016/j.marpetgeo.2016.12.029 Sun Q L, Leslie S. 2020. Tsunamigenic potential of an incipient submarine slope failure in the northern South China Sea[J]. Marine and Petroleum Geology, 112: 104111. doi: 10.1016/j.marpetgeo.2019.104111 Sun Y B, Wu S G, Wang Z J, et al. 2008. The geometry and deformation characteristics of Baiyun submarine landslide[J]. Marine Geology & Quaternary Geology, 28 (6): 69-77. http://www.researchgate.net/publication/281468040_The_geometry_and_deformation_characteristics_of_Baiyun_Submarine_Landslide Tan L, Liu F, Huang Y, et al. 2021. Production-induced instability of a gentle submarine slope: Potential impact of gas hydrate exploitation with the huff-puff method[J]. Engineering Geology, 289: 106174. doi: 10.1016/j.enggeo.2021.106174 Tan L, Liu F. 2020. Submarine slope stability during depressurization and thermal stimulation hydrate production with horizontal wells[J]. Chinese Journal of Theoretical and Applied Mechanics, 52 (2): 567-577. Wan L, Yu X H, Steve T, et al. 2016. Submarine landslides, relationship with BSRs in the Dongsha area of South China Sea[J]. Petroleum Research, 1 : 59-69. doi: 10.1016/S2096-2495(17)30031-5 Wang W W, Wang D W, Wu S G, et al. 2018. Submarine landslides on the north continental slope of the South China Sea[J]. Journal of Ocean University of China, 17 : 83-100. doi: 10.1007/s11802-018-3491-0 Wu X M, Liang Q Y, Ma Y, et al. 2018. Submarine landslides and their distribution in the gas hydrate area on the North slope of the South China Sea[J]. Energies, 11: 3481. doi: 10.3390/en11123481 Yang S X, Lei Y, Liang J Q, et al. 2017. Concentrated gas hydrate in the Shenhu Area, South China Sea: Results from drilling expeditions GMGS3 & GMGS4[C]//Proceedings of 9th International Conference on Gas Hydrates. Yin S R, Wang L L, Guo Y Q, et al. 2015. Morphology, sedimentary characteristics, and origin of the Dongsha submarine canyon in the northeastern continental slope of the South China Sea[J]. Science China Earth Sciences, 58 : 971-985. doi: 10.1007/s11430-014-5044-8 Yoneda J, Oshima M, Kida M, et al. 2019. Permeability variation and anisotropy of gas hydrate-bearing pressure-core sediments recovered from the Krishna-Godavari Basin, offshore India[J]. Marine and Petroleum Geology, 108 : 524-536. doi: 10.1016/j.marpetgeo.2018.07.006 Zhang X H, Lu X B, Chen X D, et al. 2016. Mechanism of soil stratum instability induced by hydrate dissociation[J]. Ocean Engineering, 122 : 74-83. doi: 10.1016/j.oceaneng.2016.06.015 Zhou Q J. 2015. Identification of submarine landslides and characteristics analysis in the Baiyun sag of the South China Sea northern slope[D]. Shandong: The First Institute of Oceanography. Zhu C Q, Jia Y G, Liu X L, et al. 2015. Classification and genetic machanism of submarine landslide: A review[J]. Marine Geology & Quaternary Geology, 35 (6): 153-163. http://www.researchgate.net/publication/287948956_Classification_and_Genetic_Mechanism_of_Submarine_Landslide_A_Review 何健, 梁前勇, 马云, 等. 2018. 南海北部陆坡天然气水合物区地质灾害类型及其分布特征[J]. 中国地质, 45 (1): 15-28. https://www.cnki.com.cn/Article/CJFDTOTAL-DIZI201801003.htm 霍沿东, 年廷凯, 焦厚滨, 等. 2019. 基于极限分析上限方法的海底斜坡地震稳定性[J]. 工程地质学报, 27 (2): 408-414. doi: 10.13544/j.cnki.jeg.2017-621 雷亚妮, 王广建, 吴时国. 2018. 白云凹陷深水油气开发区海底滑坡的特征、分布以及成因初探[J]. 海洋地质与第四纪地质, 38 (2): 106-114. https://www.cnki.com.cn/Article/CJFDTOTAL-HYDZ201802011.htm 马云, 李三忠, 梁金强, 等. 2012. 南海北部琼东南盆地海底滑坡特征及其成因机制[J]. 吉林大学学报(地球科学版), 42 (S3): 196-205. https://www.cnki.com.cn/Article/CJFDTOTAL-CCDZ2012S3021.htm 苏丕波, 梁金强, 张伟, 等. 2020. 南海北部神狐海域天然气水合物成藏系统[J]. 天然气工业, 40 : 77-89. https://www.cnki.com.cn/Article/CJFDTOTAL-TRQG201803022.htm 孙运宝, 吴时国, 王志君, 等. 2008. 南海北部白云大型海底滑坡的几何形态与变形特征[J]. 海洋地质与第四纪地质, 28 : 69-77. https://www.cnki.com.cn/Article/CJFDTOTAL-HYDZ200806012.htm 谭琳, 刘芳. 2020. 水平井降压法和热激法水合物开采对海底边坡稳定性的影响[J]. 力学学报, 52 (2): 567-577. https://www.cnki.com.cn/Article/CJFDTOTAL-LXXB202002025.htm 周庆杰. 2015. 南海北部陆坡白云凹陷区海底滑坡的识别与特征分析[D]. 山东: 国家海洋局第一海洋研究所. 朱超祁, 贾永刚, 刘晓磊, 等. 2015. 海底滑坡分类及成因机制研究进展[J]. 海洋地质与第四纪地质, 35 (6): 153-163. https://www.cnki.com.cn/Article/CJFDTOTAL-HYDZ201506023.htm -