Oil density

McCain

The McCain (1990) correlation is one of the most reliable methods for calculating the density of reservoir oil. It was developed using an extensive PVT database from U.S. oilfields. A key feature of this method is its consideration of the effects of dissolved gas, pressure, and temperature on oil density. The correlation is widely used in engineering calculations due to its strong accuracy and physical relevance.
Recommended applicability range:

• Temperature: 100 – 300 °F
• Oil density (API Gravity): 18 – 45 °API
• Gas-oil ratio: 50 – 3000 SCF/STB
• Pressure: 500 – 10,000 psi

Ahmed

This correlation was developed by Tarek Ahmed and published in his classic work Reservoir Engineering Handbook (1989). It is intended for estimating the density of gas-saturated crude oil under standard conditions. The correlation is widely used in PVT analysis when laboratory data is unavailable. It expresses oil density as a function of gas-oil ratio, oil specific gravity, and gas specific gravity.
Recommended applicability range:

• Oil density (API Gravity): 10 – 50 °API
• Gas-oil ratio: 0 – 2000 SCF/STB
• Gas specific gravity (air = 1): 0.6 – 1.3

Katz

The Katz (1942) correlation is one of the earliest and most well-known empirical models for estimating reservoir oil density, accounting for the effect of dissolved gas. It is based on extensive experimental data. This correlation was widely used before the development of more advanced models such as Standing and Vasquez & Beggs.
Recommended applicability range:

1. Temperature: 60 – 220 °F
2. Oil density (API Gravity): 15 – 45 °API
3. Gas-oil ratio: 20 – 1000 SCF/STB
4. Pressure: 100 – 5000 psi

Standing

The Standing (1947) correlation is a classical method for calculating oil density under reservoir conditions. It accounts for the effects of dissolved gas, pressure, temperature, and the properties of both oil and gas. Based on experimental data from California oilfields, the correlation remains widely used today in black oil models.
Recommended applicability range:

• Temperature: 60 – 250 °F
• Oil density (API Gravity): 15 – 45 °API
• Gas-oil ratio: 20 – 1500 SCF/STB
• Pressure: 50 – 5000 psi