Analysis of wellhead growth mechanism and influencing factors of offshore gas wells based on gas-liquid two-phase

Abstract

Due to the short time for production fluid in high temperature and high pressure (HPHT) well to reach the wellhead, severe temperature and pressure disturbance happen to the whole wellbore and the resulting wellhead growth will threaten wellbore safety. Considering the difference in wellbore heat transfer characteristics between seawater section and formation section and the influence of reservoir fluid on the wellbore heat transfer capacity, a new wellhead growth mathematical model for offshore gas well is established combined with the calculation method of multiple annulus temperature and pressure conduction. Compared with the measured data, the errors of wellhead growth, annulus pressure and wellhead temperature data calculated by this new model are all less than 6 %. Based on this model, the wellhead growth mechanism and its influencing factors of offshore gas wells are studied. The results show that the liquid phase in mixed fluid exists as annular flow and changes the radial heat transfer characteristics of the wellbore, resulting in a variation trend of wellhead growth decreases first and then increases with the increase of liquid content. Strong convective heat transfer effect between the wellbore and seawater raises the outer annulus temperature, exacerbating wellhead growth. Higher gas production increases the heat carried by production fluid per unit time and exacerbates wellhead growth. But there is a critical production affecting the wellhead growth rate (case well is 50 ×104m3/d.). Optimizing the production plan, regulating the liquid phase production, and optimizing the annulus filler with rational thermal conductivity can effectively mitigate the growth rate and total height of the wellhead, and improve wellbore safety in the production life cycle.