NaCl溶液浓度及其腐蚀作用对Ⅱ型水合物颗粒黏附力影响

The effect of NaCl concentration and corrosion on cohesion/adhesion forces of structure-Ⅱ hydrate particles

在天然气水合物资源开采和深水油气输运过程中,管道内的低温高压环境会导致气体水合物颗粒的生成和聚集并最终造成管道堵塞,严重影响生产效率.导致这一问题的根本原因是气体水合物颗粒间以及颗粒-表面间存在黏附力.因此,为了探明气体水合物在管道中的沉积和聚集机理,本文利用高压微机械力测量装置,对CH_4/C2H_6混合气生成的Ⅱ型水合物颗粒在不同盐度和碳钢表面腐蚀程度影响下的黏附力进行了原位测量.实验结果表明NaCl(1 wt.%–5 wt.%溶液)的存在能够降低水合物颗粒间的黏附力,根据毛细液桥理论模型估算结果,出现这一现象的可能原因是NaCl的存在降低了液桥与水合物颗粒表面的接触角.此外,经NaCl溶液腐蚀处理后,碳钢表面与水合物颗粒间的黏附力显著上升,最多可升高至无腐蚀条件下颗粒-碳钢表面间黏附力的5倍左右.

Gas hydrates are ice-like solid compounds formed from water and suitably sized gas molecules under high pressure and low temperature conditions. In typical oil and gas transportation flowlines, when water is present gas hydrates particles can form, agglomerate, and accumulate in the flowlines. These particles can also deposit on flowline walls during fluid flow or during shut-in/restart conditions. The formation of hydrate plugs can cause a blockage in the flowline, as well as other safety concerns. Although researchers have studied how temperature and annealing time would affect the cohesion/adhesion forces between hydrate particles and particle-surface systems, the effects of surface corrosion, salinity and water amount on the adhesion force have not been reported. Deep-water flowlines typically contain brine, and water condensation and corrosion can occur on flowline walls. A water layer and corrosion on flowline walls can affect hydrate film growth and deposition, and salt dissolved in the liquid phase may also influence the agglomeration of hydrate particles. Thus, the effects of free water, corrosion and salt on CH4/C2H6 hydrate particle-particle and particle-surface micromechanical forces are essential for advancing the understanding on hydrate agglomeration and deposition mechanisms in gas dominated deep-water pipelines. In order to investigate the mechanism of gas hydrate deposition and agglomeration in gas dominated flowlines, a high-pressure micromechanical force(MMF) apparatus was applied to directly measure CH4/C2 H6 hydrate adhesion/cohesion forces. The influence of NaCl concentration on the cohesion force between CH4/C2 H6 hydrate particles was studied, and the effect of surface corrosion on adhesion forces between hydrate particles and carbon steel(CS) were analysed. It was found that the presence of NaCl decreased the cohesion force between hydrate particles, and a possible explanation of this phenomenon was given based on the capillary liquid bridge model. For the adhesion force measurements, the results indicated that with increasing visual corrosion, the adhesion force between gas hydrate particle and CS surface increased by up to 500%.