Transient prediction method for flow temperature at wellbore bottom

Abstract

For the issue of an increase in the flow temperature at the bottom of the wellbore during the production in ultra-deep gas wells, the current completion design, the strength checks of tubing strings, the selection and combination of downhole tools, and theoretical prediction research do not take into account the micro-scale thermal effects of the formation. Thus, by coupling the temperature and pressure fields of the formation and the wellbore through source sink terms, a transient prediction model of the flow temperature at the bottom of the wellbore is established based on the Darcy seepage mechanism and the micro-scale thermal effects. Then, the influences of formation parameters on the flow temperature and the mechanical behavior of tubing strings are assessed. The results indicate that the gas production rate has the largest influence on the flow temperature, followed by the reservoir height, the initial formation pressure, and the initial formation temperature. Due to the influence of the micro-scale thermal effects, the flow temperature can be increased to 34 ℃ at a gas production rate of 400 × 104 m3/day, which is significantly higher than the rated working temperature of downhole tools. The safety factor of tubing strings is lower than the traditional design of tubing strings when the micro-scale thermal effects are taken into account. Finally, the research presented in this paper provides a theoretical prediction tool for a change in the flow temperature due to the influence of the micro-scale thermal effects.