Saturated oil formation volume factor

Al-Marhoun

The Al-Marhoun correlation (1988) was specifically developed for Middle Eastern crude oils based on an extensive PVT database. The method takes into account the effects of gas-oil ratio, oil and gas specific gravity, and temperature, offering improved accuracy compared to classical correlations such as Standing and Glaso. A key feature is the use of a power-law relationship optimized for Middle Eastern reservoir conditions. The formula is not applicable to oils with abnormal composition (e.g., high content of harmful components). 
Recommended applicability range:

• Oil density (API Gravity): 20 – 45 °API
• Gas-oil ratio: 100 – 2500 SCF/STB
• Gas specific gravity: 0.65 – 1.2
• Temperature: 100 – 300 °F

De Ghetto et al.

The De Ghetto et al. correlation represents an advanced method for calculating the formation volume factor of saturated oil, specifically designed for use with heavy and highly viscous oils (API < 25°). Unlike classical methods (e.g., Standing, Vasquez & Beggs), this correlation applies separate calculation approaches for light and heavy fluids, resulting in improved prediction accuracy. The formula incorporates the combined effects of gas-oil ratio, temperature, oil and gas densities through a system of power-law relationships. 
Recommended applicability range: 

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

Glaso

The Glaso correlation allows calculation of the formation volume factor of saturated oil based on the gas-oil ratio, gas and oil density, and temperature. It was developed for North Sea crude oils but is also applicable to other regions. The method is known for its high accuracy with light and medium oils but tends to be less precise for heavy fluids. 

Recommended applicability range:

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

Lasater

The Lasater correlation (1958) is based on the analysis of North American crude oils with a focus on the effect of gas solubility. The method uses the mole fraction of gas in the system for calculation, which makes it particularly accurate for gas-saturated oils. The approach is physically based but requires knowledge of the oil’s molecular weight. It tends to overestimate values for heavy oils. It does not account for sulfur or paraffin content. 
Recommended applicability range: 

• Oil density (API Gravity): 15 – 40 °API
• Gas-oil ratio: 50 – 3500 SCF/STB
• Temperature: 100 – 220 °F

Petrosky

The Petrosky correlation is used to estimate the formation volume factor of saturated oil based on reservoir oil parameters such as gas-oil ratio, gas and oil density, and temperature. It was developed for crude oils from the Gulf of Mexico, but the correlation also shows good accuracy for similar reservoirs. The formula takes into account the influence of dissolved gas. 
Recommended applicability range: 

• Oil density (API Gravity): 15 – 40 °API
• Gas-oil ratio: 90 – 3000 SCF/STB
• Pressure: up to 7000 psi
• Temperature: 120 – 300 °F

Standing

The Standing correlation is one of the most widely used empirical models for estimating the formation volume factor of saturated oil. It is based on data from California oilfields and takes into account the gas-oil ratio, specific gravity of oil and gas, and reservoir temperature. Simple to apply, this correlation delivers acceptable accuracy for "black oil" models. 
Recommended applicability range:

• Oil density (API Gravity): 22 – 58 °API
• Gas-oil ratio: 20 – 2100 SCF/STB
• Pressure: up to 5000 psi
• Temperature: 100 – 260 °F

Vasquez & Beggs

The Vasquez & Beggs correlation is one of the most versatile and widely used models for calculating the formation volume factor of saturated oil. It was developed based on an extensive database of over 600 oil samples. The formula categorizes oils into several groups based on API gravity. A distinguishing feature of the correlation is the normalization of gas parameters to standard separation conditions, which enhances its accuracy. 
Recommended applicability range:

• Oil density (API Gravity): 15 – 55 °API
• Gas-oil ratio: 0 – 3000 SCF/STB
• Gas specific gravity (air = 1): 0.58 – 1.18
• Temperature: 70 – 295 °F

Ahmed

The Ahmed correlation was developed as a modification of existing models to provide more accurate predictions of the saturated oil formation volume factor. It performs particularly well for heavy oils and considers the relationship between gas-oil ratio, fluid properties, and reservoir conditions. The model demonstrates good accuracy for Middle Eastern fields and yields reliable results for both heavy and medium crude oils. 
Recommended applicability range:

• Oil density (API Gravity): 15 – 50 °API
• Gas-oil ratio: 50 – 3500 SCF/STB
• Gas specific gravity (air = 1): 0.65 – 1.2
• Temperature: 100 – 300 °F

Arps

The Arps correlation is a simplified linear formula used to estimate the formation volume factor of saturated oil. It relates the volume factor directly to the gas-oil ratio. The model is suitable for quick approximation calculations; however, it does not account for the effects of temperature, oil gravity, or gas gravity. This oversimplification limits its accuracy. 
Recommended applicability range (exact boundaries are not defined; model is applicable within the “Black Oil” model):

• Oil density (API Gravity): 20 – 35 °API
• Gas-oil ratio: 100 – 1000 SCF/STB
• Gas specific gravity (air = 1): 0.65 – 1.0
• Temperature: 100 – 200 °F

Kartoatmodjo & Schmidt

The Kartoatmodjo & Schmidt correlation was developed based on an extensive database of over 740 crude oil samples. It is considered one of the most versatile models available. The correlation demonstrates good accuracy across a wide range of crude types—from light to heavy oils. A distinguishing feature of the method is its use of power-law relationships to account for the effects of temperature, gas-oil ratio, and fluid properties. 
Recommended applicability range:

• Oil density (API Gravity): 14 – 59 °API
• Gas-oil ratio: 20 – 2900 SCF/STB
• Gas specific gravity (air = 1): 0.56 – 1.18
• Temperature: 75 – 320 °F