Bubble point pressure and gas solubility

Al-Marhoun

The Al-Marhoun correlation (1988) was developed to calculate the bubble point pressure of crude oil based on data from Middle Eastern oilfields. It takes into account temperature, gas-oil ratio, gas density, and oil density. It was specifically designed for Middle Eastern crude oils. The correlation provides good accuracy for high-sulfur oils and serves as an alternative to the Standing and Vasquez & Beggs correlations for certain regions.
Recommended applicability range:

• Oil density (API Gravity): 20 – 55 °API
• Gas-oil ratio: 25 – 1600 SCF/STB
• Temperature: 75 – 240 °F
• Pressure: 130 – 3500 psi

De Ghetto et al.

The De Ghetto et al. correlation (1995) provides several specialized formulas for calculating bubble point pressure based on oil density. The method is derived from data from Mediterranean and Venezuelan oilfields. The correlation offers high accuracy for heavy and medium crudes, where traditional correlations (Standing, Vasquez & Beggs) often produce significant errors. For extra-heavy oils (<10 °API), it is the only correlation that delivers acceptable accuracy.
Recommended applicability range:

• Oil density (API Gravity): 5 – 40 °API
• Gas-oil ratio: 20 – 1500 SCF/STB
• Temperature: 100 – 280 °F

Glaso

The Glaso correlation was developed based on an extensive database of crude oils from the North Sea and other regions. It accounts for the influence of gas-oil ratio, temperature, oil density, and gas specific gravity, making it applicable to various types of fluids. The method uses logarithmic transformations and polynomial relationships, providing high accuracy, especially for light and medium oils. Unlike earlier correlations (e.g., Standing), the Glaso correlation performs better for oils containing dissolved gas over a wide pressure range.
Recommended applicability range:

• Oil density (API Gravity): 22 – 48 °API
• Gas-oil ratio: 90 – 2500 SCF/STB
• Temperature: 80 – 280 °F
• Pressure: 100 – 5000 psi

Lasater

The Lasater correlation is one of the earliest reliable methods for calculating the bubble point pressure of crude oil. The calculation is based on the mole fraction of dissolved gas. It shows particular accuracy for medium and heavy oils (< 40 °API). The method uses empirical relationships derived from the analysis of oils from Canada and the United States.
Recommended applicability range:

• Oil density (API Gravity): 15 – 45 °API
• Gas-oil ratio: 50 – 3500 SCF/STB
• Temperature: 100 – 300 °F
• Pressure: 100 – 5000 psi

Petrosky

The Petrosky correlation was developed for crude oils from the Gulf of Mexico. It demonstrates improved accuracy for this region compared to traditional methods. The correlation accounts for the thermodynamic properties of offshore shelf crudes and serves as an alternative to the Standing and Vasquez & Beggs correlations for offshore fields. The average error is ±6.5% compared to laboratory data.
Recommended applicability range:

• Oil density (API Gravity): 16 – 45 °API
• Gas-oil ratio: 200 – 1500 SCF/STB
• Temperature: 110 – 300 °F
• Pressure: 1500 – 4000 psi

Standing

The Standing correlation is used to calculate the bubble point pressure of crude oil based on the gas-oil ratio, gas specific gravity, oil gravity, and temperature. Originally developed for California crude oils, it has since been widely applied to other regions. The correlation is known for its simplicity, minimal input requirements, and good accuracy for light oils (25–40 °API). However, it tends to overestimate results for heavy oils (<20 °API).
Recommended applicability range:

• Oil density (API Gravity): 16 – 45 °API
• Gas-oil ratio: 20 – 1500 SCF/STB
• Temperature: 100 – 300 °F

Vasquez & Beggs

The Vasquez & Beggs correlation improves the calculation of bubble point pressure by: normalizing gas specific gravity to a reference pressure of 100 psi; dividing oils into three groups based on API gravity; and accounting for temperature and gas-oil ratio. It was developed using a global database of 600 PVT analyses. The correlation also considers separation conditions. It is less accurate for heavy oils (<20 °API).
Recommended applicability range:

• Oil density (API Gravity): 15 – 45 °API
• Gas-oil ratio: 20 – 2070 SCF/STB
• Temperature: 75 – 295 °F

Kartoatmodjo & Schmidt

The Kartoatmodjo & Schmidt correlation provides two separate formulas: one for oils with API ≤ 30 and another for API > 30, allowing for higher accuracy across different fluid types. The method accounts for the influence of gas-oil ratio, temperature, oil gravity, and separator gas properties. A key feature is the use of a correction factor to account for gas separation conditions. It is particularly effective for Southeast Asian crudes and other regions with similar characteristics.
Recommended applicability range:

• Oil density (API Gravity): 14 – 45 °API
• Gas-oil ratio: 20 – 2500 SCF/STB
• Temperature: 100 – 300 °F