An improved thermal model for predicting wellbore temperature distribution in deep-water gas well

Abstract

Accurate prediction of wellbore temperature plays an extremely important role in the production design of deep-water gas wells. This study overcomes the shortcomings of the previous literature in temperature calculations, comprehensively studies the heat transfer mechanism in the annulus and tubing, and an improved thermal model for predicting wellbore temperature in deep-water gas well is established. This model includes two important innovations: the natural convection heat transfer model in the annulus and the gas–liquid two-phase heat transfer model in the tubing. Firstly, the mechanism of heat transfer through natural convection in annulus is revealed by a numerical study, and a new calculation method for the annulus convective-heat-transfer coefficient, which can be applied to non-Newtonian fluids, is proposed. Secondly, considering that the two-phase flow in the tubing often presents an annular-mist flow in water-bearing gas well, a heat transfer model of the annular-mist flow in the tubing is developed considering the gas–liquid distribution characteristics and droplet dynamics. The results obtained using this improved thermal model are in good agreement with the field data of deep-water gas well, and the model prediction error is within 10%. Further, the sensitivity analysis is carried out on the parameters of annulus testing fluid that affect the wellbore temperature, and a novel solution for the annular insulation testing fluid was designed. Compared with ordinary annulus testing fluids, the wellbore temperature are more than doubled after adopting the new solution, thereby providing effective guidance for the development of insulation testing fluid system during deep-water gas well testing.