Influence of Vertical Downward Annulus Eccentricity on Steam-Water Two-Phase Flow Pressure Drop

Concentric dual-tubing steam injection technique is one of the main methods to improve heavy oil recovery efficiency. From field data, it was discovered that hot fluid at high temperature and pressure caused steam injection casing to have elongation strain and “necking†eccentric buckling, and the eccentricity change affected the accurate prediction of steam-water two-phase flow pressure drop in the steam injection casing. This paper established a coupling model for the steam-water two-phase flow pressure drop in vertical downward eccentric annulus and the wellbore heat transfer and developed a mathematical model calculation program, to validate the accuracy of calculating the liquid holdup and pressure gradient of fully eccentric annulus. This revealed the influential law of eccentricity on the annulus steam-water two-phase pressure, dryness, and enthalpy value. The results indicated that when the eccentricity e increased from 0 to 1, the saturation pressure of steam at annulus wellbore bottom increased by 0.265 MPa, and the dryness and enthalpy value decreased by 8.54 × 10−3 and 11.22 kJ kg−1, respectively. Compared to the concentric layout, the eccentrically arranged steam injection inner tube cannot promote the wet steam dryness at annulus wellbore bottom.