Gas Wells · API 14B Method · Liquid Holdup · BHP Calculation
Understand Gray's dimensionless numbers, R-factor correlation, flow pattern maps, and comparison with Hagedorn-Brown
The Gray correlation is an industry-standard method per API 14B for calculating pressure drop in vertical gas wells producing condensate. It uses dimensionless velocity numbers and an R-factor holdup correlation for mist and annular flow.
Gray correlation uses four dimensionless groups: liquid velocity number (Nvl), gas velocity number (Nvg), pipe diameter number (Nd), and liquid viscosity number (Nl). These are used to determine liquid holdup via the R-factor correlation.
Gray correlation is optimized for vertical wells (0–15° deviation) with high gas-liquid ratios above 5,000 scf/bbl, where mist and annular flow regimes dominate. For highly deviated wells, Beggs-Brill may be more suitable.
Gray was specifically developed for gas wells with condensate at high GLR, while Hagedorn-Brown covers a broader range of liquid loading. Both use dimensionless groups, but Gray's R-factor correlation is tuned for mist/annular flow patterns.