深水气井井下节流工况井筒水合物生成风险分析与预防

Risk Analysis and Prevention of Hydrate Formation in Deepwater Gas Wells Under Downhole Throttling Conditions

水合物流动障碍的形成已经成为深水气井测试和生产过程最为严峻的流动保障问题之一,在分析了深水气井井筒外部环境温度分布的基础上,针对井下节流工况,探究了井下节流对井筒中水合物生成区域分布的影响。结果表明:深水井筒外部环境温度由地面至储层呈现先减小后增大的趋势,泥线处水温为沿程温度的最低点;海水上部200 m以内的混合层和温跃层海水水温受表层温度和季节的影响很大,恒温层海水温度低、变化小;由泥线至储层近似呈线性增大,达储层后温度到达最高值;测试气量增加,井筒流温曲线右移,由于高产气量下携热量升高,受外界低温环境影响更小,温度曲线更加平缓;节流后的水合物生成区域和过冷度分布由受Joule-Thomson效应影响的流体流温和水合物相平衡温度的下降幅度决定;低深度节流往往导致流体温降大于水合物相平衡温降,促使水合物生成区域扩大和过冷度升高,加剧水合物堵塞风险;合理的高深度节流能有效避开水合物生成条件,起到水合物预防的作用。

The formation of hydrate flow barriers has become one of the most severe flow assurance issues in deepwater gas well testing and production processes.On the basis of analyzing the temperature distribution of the external environment of deep-water gas wells,this study explores the influence of downhole throttling on the distribution of hydrate generation areas in the wellbore under downhole throttling conditions.According to the research results:The external environmental temperature of the deep-water wellbore shows a trend of first decreasing and then increasing from the surface to the reservoir,and the water temperature at the mud line is the lowest point along the way;The water temperature in the mixed layer and thermocline layer within 200 m of the upper part of seawater is greatly influenced by surface temperature and season,while the temperature in the constant temperature layer is low and has little variation;The temperature increases approximately linearly from the mud line to the reservoir,reaching the highest value after reaching the reservoir;As the testing gas volume increases,the wellbore flow temperature curve shifts to the right.Due to the increase in heat carrying capacity under high gas production,it is less affected by the external low-temperature environment and the temperature curve becomes smoother;The region of hydrate formation and subcooling distribution after throttling are determined by the decrease in fluid flow temperature and hydrate phase equilibrium temperature affected by the Joule Thomson effect;Low depth throttling often leads to a temperature drop of the fluid greater than the equilibrium temperature drop of the hydrate phase,promoting the expansion of the hydrate generation area and an increase in undercooling,exacerbating the risk of hydrate blockage;Reasonable high depth throttling can effectively avoid the conditions for hydrate formation and play a role in hydrate prevention.