深水陆坡区碎屑流对海底管道潜在冲击影响的定量研究-以荔湾3-1气田为例

High-speed submarine debris, as a consequence of submarine landslide, poses a great threat to the safety operation of submarine pipelines in deepwater continental slope area. How to quantitatively obtain the potential impact effect of debris flow on submarine pipelines has become a hot and difficult subject in the international deep water oil and gas field development project. In this study, the South China Sea Liwan 3-1 gas field is taken as the research area. The flow characteristic study of large scale debris is carried out by the numerical simulation method with Euler-Euler two-phase model; Combined with rheological experiment, the equivalent rheological parameters of field debris are studied by back analysis calculation method, based on the submarine identification parameters. By the comparison of geological conditions, equivalent rheological parameters are taken as the bridge，which is an innovation, between the predictive state of debris flow and the debris - pipeline - seabed coupling model,and then the response regularity and failure mechanism of marine pipeline, under running state, impacted by debris flow are quantitatively revealed, which are not involved in current researches. This study can realize the quantitative prediction of potential impact effect of debris flow on submarine pipeline under running state, and the research results can provide theory and technique reserve for the submarine pipeline design in deepwater continental slope area of China, as well as the quantitative evaluation and prevention of submarine debris flow.

深水陆坡区海底滑坡产生的高速碎屑流给海底管道安全运行带来巨大威胁，如何定量解决碎屑流对运行状态下海底管道的潜在冲击影响，成为当前国际上深水油气开发工程中的热点与难点问题。本项目以南海荔湾3-1气田为研究区，在开展基于欧拉-欧拉两相流模型的大尺度碎屑流流动数值模拟研究的基础上，结合流变测试实验，进行基于海底识别参数的碎屑流等效流变参数反分析研究；通过地质条件对比，创新性的以等效流变参数为桥梁，实现碎屑流预测状态与碎屑流-管道-海床冲击耦合模型的连接，定量揭示目前研究尚未涉及的运行状态海底管道受碎屑流冲击的响应规律与破坏机制。本项目可实现碎屑流对运行状态海底管道潜在冲击影响的定量预测，能够为我国深水陆坡区海底管道设计以及碎屑流地质灾害定量评价与防治提供理论与技术储备。

深水陆坡区海底滑坡产生的高速碎屑流可能给海底管道的安全运行带来巨大威胁。本项目基于流体多相流理论与有限元理论分别建立了海底碎屑流的运动状态模拟预测模型和管道受到碎屑流冲击后的非线性分析模型。通过与实验结果或文献中已有模型结果的对比，验证了上述模型的有效性。采用小尺度碎屑流数值模型，研究由海底滑坡产生的碎屑流的一般运动特性，并分析了多种工况参数对滑动状态影响的敏感性。针对实际大尺度海底滑坡，采用基于等效流变参数的反分析方法，模拟研究实际尺度碎屑流的运动特性。数值分析表明土体扰动以及混水后土体强度的降低是滑坡发生后碎屑流长距离运移的根本原因，同时运动过程中滑体端部发生的滑水效应，减小了海床摩擦力的影响，增加了运动距离。最后以荔湾3-1气田海底管道路由峡谷区为例，首先采用有限元强度折减法对海底斜坡进行稳定性评价分析以获得碎屑流的初步规模参数，之后针对典型二维剖面采用多相流模型模拟预测潜在滑坡发生后碎屑流的运动状态和特性。根据研究区实际的海床土特性，采用非线性弹簧模拟管土相互作用，研究分析了海底管道在运行状态下受碎屑流冲击的响应规律。研究成果可以为我国深水陆坡区海底管道设计以及碎屑流地质灾害定量评价与防治提供参考。