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中文核心期刊

中国海域盆地CO2地质封存选址方案与构造力学分析

STRATEGIC AND GEODYNAMIC ANALYSES OF GEO-SEQUESTRATION OF CO2 IN CHINA OFFSHORE SEDIMENTARY BASINS

  • 摘要: 本文围绕“碳达峰、碳中和”国家战略目标, 从断裂活动、盆地压力、构造沉降特征、地震活动性和地温梯度等角度综合分析中国海域盆地适宜大规模CO2地质封存的条件与目标, 在宏观上认为东海陆架盆地、珠江口盆地、琼东南盆地东部以及南海中央海盆是最佳CO2地质封存区域, 但这并不排除其他盆地内部存在适宜的CO2地质封存点, 因为具体某个地质封存工程目标的范围相对较小. 东海陆架盆地、珠江口盆地和琼东南盆地内适用于CO2地质封存的地层包括盆地晚期快速沉降期沉积层的底部咸水层和热沉降沉积层内的含油气单元, 在适宜的海底之下800~4000 m深度范围内, 孔隙度大于10%, 静水压力约在8~40 MPa之间、静岩压力约在13~83 MPa之间变化. 在此压力范围和合适的地温梯度范围内, CO2以超临界状态存在, 其密度随温压变化相对稳定, 有利于CO2的流动和渗透. 另外, 盆地内的基性岩浆岩建造的规模和数量也为CO2地质封存和永久矿化提供了很好的条件. 虽然工程难度大和代价高, 但南海中央海盆是非常安全的适宜封存CO2的区域, 注入到海底大洋玄武岩的CO2因为玄武岩矿化需要较长时间, 可能存在CO2泄露, 但是除了玄武岩矿化以外, 可能泄露的CO2在后面的逃逸中还可以被多次封存, 包括: 火山碎屑岩矿化、海底沉积物封存、海底沉积物CO2水合物封存、碳酸钙中和反应、海底碳湖和海洋溶解CO2等. 南海中央海盆目前6个钻遇基底大洋玄武岩的国际大洋发现计划(IODP)钻孔可以为先导性南海海盆CO2封存实验提供很好的科学与工程基础.

     

    Abstract: Focusing on the national strategic goal of "Carbon Peaking and Carbon Neutrality", this paper comprehensively analyzes the strategic conditions and targets suitable for large-scale CO2 geo-storage in the China offshore basins, from the perspectives of fault activity, basin pressure, tectonic subsidence, seismicity, and geothermal gradient. It is considered that the East China Sea Shelf Basin, Pearl River Mouth Basin, eastern Qiongdongnan Basin, and the central South China Sea basin are the best geological storage areas for CO2, although this does not exclude suitable targets in other unfavorable sedimentary basins since a specific geo-sequestration target is small in area. The suitable CO2 storage strata in the East China Sea Shelf, Pearl River Mouth, and Qiongdongnan Basins include the bottom salt-water layer of the late rapid subsidence sediments in the open-sea environment and the hydrocarbon-bearing units in the thermal subsidence sedimentary sequences. Between 800 and 4000 m depths beneath the seafloor, the porosity is greater than 10%, and the hydrostatic and lithostatic pressures vary from ~ 8 to ~ 40 MPa and from ~ 13 to ~ 83 MPa, respectively. In this pressure and suitable geothermal gradient ranges, CO2 exists in a supercritical state, and its density is relatively stable with temperature and pressure changes, which is beneficial to the flow and permeation of CO2. The scale and number of mafic magmatic rock formations in the basins also provide good conditions for CO2 geological sequestration and permanent mineralization. Although operationally difficult and expensive, CO2 storage in the central South China Sea basin is very safe. CO2 injected deep into the oceanic basalt can undergo basalt mineralization, but if CO2 is escaped as the mineralization process is relatively slow, escaped CO2 can be further trapped by multiple other storage processes, including pyroclastic rock mineralization, seafloor sediment sequestration, seabed sediment CO2 hydrate storage, carbonate neutralization reaction, seabed carbon lake, ocean dissolution, etc. The existing six International Oceanic Discovery Program (IODP) boreholes that have encountered basement basalt in the central basin of the South China Sea can provide a good scientific and engineering foundation for the pilot CO2 storage experiment in the South China Sea basin.

     

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