天然气水合物开采立管力学特性研究

Mechanical Characteristics of Natural Gas Hydrate Production Riser

黄鑫 寇鉴 毛良杰 李隽

HUANGXin KOUJian MAOLiangjie LIJuan

中国海洋石油集团有限公司, 北京 东城 100010 油气藏地质及开发工程全国重点实验室 · 西南石油大学, 四川 成都 610500 中国石油勘探开发研究院, 北京 海淀 100083

China National Offshore Oil Corporation, Dongcheng, Beijing 100010, China National Key Laboratory of Oil and Gas Reservoir Geology and Exploration, Southwest Petroleum University, Chengdu, Sichuan 610500, China PetroChina Research Institute of Petroleum Exploration & Development, Haidian, Beijing 100083, China

深水天然气水合物开采立管是开采水合物的关键通道，管内由于水合物分解形成多相内流会导致其受力变形更为复杂，在内外流综合作用下水合物开采立管易发生失效事故。为分析水合物开采立管的力学特性，考虑管内水合物的分解与流动，并将其引入立管动力学方程，建立了海洋环境与管内多相流共同作用下的水合物开采立管动力学模型，采用有限单元法对模型进行离散求解，以固态流化试采工艺为例，分析了浆体密度、排量与出口回压对水合物开采立管力学响应特性影响规律。结果表明，立管内水合物分解形成多相流使得立管系统质量减小，导致立管沿程截面张力增大，水合物开采立管的形变位移、弯矩与偏转角度均比纯液立管小；无浮力块配置的水合物开采立管最大位移出现立管中下段，最大弯矩与偏转角度出现在立管底端；水合物开采立管的弯曲位移、弯矩与偏转角度随着浆体密度、浆体排量和立管出口回压的增大而增大；适当增加水合物开采立管顶部张力或配置浮力块，减小浆体密度与排量，降低立管出口压力均有利于减小立管的弯曲变形。研究结果可以为水合物开采立管的安全控制提供理论指导。

The riser pipe is the key channel of gas hydrate exploitation in deep water, the force and deformation of the riser are more complicated due to the formation of multiphase internal flow due to the decomposition of gas hydrate in the pipeline, and the riser of gas hydrate exploitation is prone to failure accidents under the comprehensive action of internal and external flow. In order to analyze the mechanical characteristics of hydrate production riser, the decomposition and flow of hydrate in the pipe are considered in the model and introduced into the riser vibration equation. The dynamic model of hydrate riser in marine environment coupled with internal multiphase flow is established. Finite element method is applied to discretize and solve the model. The effects of slurry density, flow rate and outlet back pressure on the mechanical response characteristics of riser in hydrate mining are analyzed by taking solid fluidization test mining technology as an example. The results show that the mass of hydrate production riser decreases and the section tension of the riser increases due to the formation of multiphase flow from hydrate decomposition. The deformation displacement, bending moment and deflection angle of hydrate production riser are all smaller than those of pure liquid riser. The maximum displacement of hydrate production riser without buoyancy block appears below the midpoint of the riser, and the bending moment and deflection angle at the bottom of the riser are the largest. The displacement, bending moment and deflection angle of hydrate production riser increase with the increase of drilling fluid density, slurry discharge and outlet return pressure of riser. Appropriate increase of the tension at the top of the riser for hydrate exploitation or configure action of the buoyancy block, reduction of the drilling fluid density and displacement, and reduction of the outlet pressure of the riser are conducive to reducing the hydrate production riser bending deformation. The research results can provide theoretical guidance for protecting the safety of hydrate production riser.

10.11885/j.issn.1674-5086.2021.03.25.02