深海水合物开采中能源土灾变机理与控制理论

Methane hydrate bearing sediments (MHBS) are widely distributed in the seabed of South China Sea as the significant sources of future green energy of China, and hence to extract natural gas from MHBS is significantly important to secure the economic and social development of our country. However, inappropriate exploitation of MHBS from deep seabed may cause local engineering failure, and even trigger regional-scale geohazards such as submarine landslides. The uncertain risk of geohazards becomes the barrier for implementing the strategy of using MHBS in China. The proposed study aims at the fundamental research on the properties of MHBS and failure mechanism of inappropriate exploitation of MHBS, by taking advantage of cutting-edge theories and methods in several relevant disciplines within the framework of micro-to-macro geomechanics. First, the multi-scale mechanical behavior of MHBS leading to failure will be systematically studied under complex thermal-hydro-mechanical-chemical coupled conditions. Second, coupled analysis tools will be developed to analyze multi-field, multi-phase and multi-physics process during MH exploitation, with which the movement of solid-liquid-gas phases and the mechanism behind geohazards triggered during MH production will be revealed under complex conditions. Third, criteria for feasibility evaluation of production technique and geohazard control will be developed with thorough consideration of the specific maritime conditions in South China Sea. The ultimate goal of this proposed study is to establish a fundamental theoretical framework leading to safe and efficient MHBS production specifically applicable in South China Sea. This study is of significant academic value and potential for engineering application for raising the capability of MHBSexploitation from deep seabed of our country.

含天然气水合物土体（能源土）广泛分布在我国南海海床，是我国非常重要的绿色能源储备，深海能源土的开发已经成为我国经济与社会发展的重大需求。但是，深海能源土开采不当可能引发局部工程事故，甚而诱发大规模海底滑坡等一系列区域性重大灾害，阻碍我国深海能源土开发战略的顺利实施。本申请拟围绕深海能源土灾变特性及开采致灾机理等关键基础性问题，采用宏微观土力学研究思路，融合多个交叉学科的前沿理论和方法，研究温-压-力-化学复杂广义应力路径下深海能源土灾变特性；发展深海能源土工程灾变的多场多相多过程耦合分析方法，揭示多因素耦合作用下能源土开采过程的固液气运移规律和致灾机理；建立考虑我国南海特殊条件的深海能源土开采技术适应性评价和灾害控制方法；形成一套适合我国深海能源土高效安全开采的基础理论体系。本研究对提升我国深海能源土自主开发能力具有非常重要的现实意义和学术理论价值。

（1） 深海能源土多场多相耦合宏微观多尺度力学行为的描述与表征。采用微观探测技术明确水合物生长机制、分布形态、分解性状及影响因素等，给出考虑能源土孔隙特征的相平衡曲线。研制三维颗粒接触力学测试系统进行微观试验，建立深海能源土多场耦合学耦合微观接触力学模型，并植入离散元模拟胶结、裹覆、填充型能源土，结合宏观力学特性试验获得宏观力学特性与微观结构的跨尺度关联；给出不同开采路径下宏微观特性演化。建立基于微观力学机制的能源土多场耦合多尺度本构模型，可以很好预测室内试验结果,为可靠的数值方法的建立提供理论基础。.（2）多场多相耦合作用下深海能源土工程问题分析方法和灾变机理分析。建立具有流固耦合稳定化解技术的水合物开采工程高精度数值仿真有限元模拟平台。建立可模拟弱可压缩流体的CFD-DEM耦合方法，探讨能源土力学特性的微观作用机制并进行水合物赋存区边坡地震作用下的稳定性分析，研究了诱发滑坡灾害的多因素关联机制。开发了水合物开采专用计算软件与离散元的耦合仿真技术。建立了井壁稳定多场耦合理论分析模型，探讨了钻井液温压对井壁稳定影响的力学机理。从水合物开采过程力学参数变化特征、开采过程产气规律、水合物分解引起土层变形破坏等方面给出多相介质运移规律和工程扰动效应。项目成果为我国南海水合物安全开采提供了可靠的方法和模型.（3）建立了南海能源土开采工程的灾害控制理论和诊控分析方法。搭建南海水合物富集区GIS基础数据库。引入水合物分解诱发滑坡机制，定义水合物富集区的边坡易发性指标和等级划分方法，建立水合物富集区的滑坡易发性评价方法。建立与GIS结合的区域海底滑坡运动预测模型和模块化的区域海底滑坡冲击管线网络的定量损伤评估模型。将提出的模型应用于中国南海神狐海域模拟海底滑坡的运动过程，分析海底滑坡的规模、起始位置以及多滑坡体对管线网络的影响。所提出的模型和方法，可为水合物开采选址规避风险提供理论依据。