海洋天然气水合物储层蠕变行为的主控因素与研究展望

Controlling factors and research prospect on creeping behaviors of marine natural gas hydrate-bearing-strata

  • 摘要: 蠕变是指沉积物在特定应力状态下变形与时间的关系,属于沉积物的固有力学属性。厘清海洋天然气水合物开采过程中储层蠕变的主控因素及其控制机理,对量化评价潜在工程地质风险的发生和演变规律具有重要意义。本文将在综述海洋天然气水合物储层破坏特征的基础上,梳理海洋天然气水合物储层蠕变特征及主控因素,厘清关键科学问题;结合最新研究成果,阐述天然气水合物储层蠕变特征多尺度表征与探测技术体系的基本内涵,简要探讨该领域的未来研究方向。初步分析认为,海洋天然气水合物开采过程中储层蠕变行为是水合物本身及其分解产出过程中的应力、温度、渗流等动态因素综合作用的结果,现有蠕变本构模型无法完全反映上述相变-传热-渗流-应力多场多相多组分耦合过程。为建立适合南海北部水合物储层的蠕变本构,进而为后续开采工程安全设计提供理论支撑,建议从天然气水合物储层的力学性能弱化特征及蠕变各阶段的时效参数两方面入手,从分子尺度、纳微尺度、岩心尺度、中试尺度、矿藏尺度5个层面,建立天然气水合物储层蠕变行为的跨尺度研究方法体系;以南海实际储层样品为研究对象,剖析天然气水合物开采过程中储层蠕变行为的主控因素。

     

    Abstract: Creeping of HBS is a common behavior of hydrate-bearing strata in the process of gas production and has great impact on the occurrence and development of engineering geohazards. In this paper, we summarized the main failure modes of HBS based on the investigation of a large number of literatures. Then the research thoughts and strategies on strata creeping behaviors during hydrate exploitation are comprehensively discussed, based on the key scientific issues expounded. Afterwards, a multi-scale creeping detection and characterization approach for HBS is put forward, together with its future research trends. It is supposed that creeping behaviors of HBS during gas extraction are the result of combination of hydrate distribution and its dissociation-induced changes in multi-physical fields such as phase transformation, heat exchange, seepage, and stress evolution. The current constitutive models for conventional soils are not effective enough to reflect such a complex dynamic multifield, multiphase and multicomponent coupling effect, which are doubtlessly inadaptable for evaluating the geotechnical issues during hydrate exploitation in the case of northern South China Sea. For this reason, a multi-scale detection and characterization system needs to be established to analyze the dynamic damage behaviors of HBS during hydrate production, which consists of the molecular scale, nano-to-micro scale, core scale, pilot scale, and field scales techniques. Using the sediments collected from the HBS at the northern South China Sea, the control mechanisms of different geological and engineering parameters on hydrate-bearing strata creeping should be quantitatively modeled.

     

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