Calculators›Gray Correlation
⬆️

Gray Vertical Two-Phase Flow Correlation

Gas Wells · API 14B Method · Liquid Holdup · BHP Calculation

Gray Vertical Two-Phase Flow Correlation
Industry-standard method for vertical gas wells producing condensate. Calculates bottomhole pressure from wellhead conditions using dimensionless velocity numbers (Nvl, Nvg, Nd, Nl) and R-factor holdup correlation. Best accuracy for high GLR (>5,000 scf/bbl) in mist/annular flow.

Well Geometry

in
ft
deg
in
Applicability: Gray correlation is optimized for vertical wells (0-15° deviation). For highly deviated wells, consider Beggs-Brill.

Production Rates

bbl/day
Mscfd
%
psia
Note: Gas rate at standard conditions (14.7 psia, 60°F). Liquid rate includes condensate + water.

Fluid Properties

lb/ft³
-
cP
dyne/cm
Typical Values:
Condensate: 40-50 lb/ft³, 1-5 cP, 15-25 dyne/cm
Sweet gas SG: 0.60-0.70

📚 Learn the Theory

Understand Gray's dimensionless numbers, R-factor correlation, flow pattern maps, and comparison with Hagedorn-Brown

Read Engineering Guide →

About Gray Correlation

H.E. Gray's (1974) empirical correlation for vertical two-phase flow in gas wells. Developed for API 14B subsurface safety valve sizing.

Key Features:

  • Dimensionless Numbers: Nvl, Nvg, Nd, Nl
  • R-Factor: Slip-based holdup correlation
  • Best For: High GLR gas wells, mist/annular flow
  • Accuracy: ±10-15% for gas wells

Industry Standards:

  • API 14B Safety Valve Sizing
  • GPSA
  • SPE Multiphase Flow Guidelines

Common Tubing Sizes

OD ID Weight
2-3/8"1.995"4.7 lb/ft
2-7/8"2.441"6.5 lb/ft
3-1/2"2.992"9.3 lb/ft
4-1/2"3.958"12.6 lb/ft

Related Calculators

📊

Hagedorn-Brown

Alternative correlation for oil wells with higher liquid loading
↗️

Beggs-Brill

Two-phase flow for inclined and horizontal pipelines
💨

Gas Density

Calculate gas density at operating conditions with Z-factor
💧

Pipeline Hydraulics

Single-phase and two-phase pipeline pressure drop