The Beal correlation (1946) is one of the earliest and most well-known methods for estimating undersaturated oil viscosity. It is based on empirical data from North American crude oils and uses a power-law relationship linking viscosity at bubble-point pressure to viscosity at higher pressures. The formula accounts for the effects of pressure, temperature, and oil density, but does not explicitly include gas-oil ratio. Due to its simplicity and age, the correlation is not suitable for oils with unusual properties.
Recommended applicability range:
- Oil density (API Gravity): 15 – 45 °API
- Temperature: 100 – 220 °F
- Viscosity: 0.5 – 50 cP
- Pressure: P_b – 5000 psi
Beggs & Robinson
The Beggs & Robinson correlation (1975) was developed based on a large dataset of laboratory measurements for North American crude oils. It estimates the increase in oil viscosity at pressures above the bubble point. The method accounts for the effects of pressure, saturated oil properties, and temperature. Due to its simplicity and satisfactory accuracy for most oil types, this correlation has become widely used in petroleum engineering.
Recommended applicability range:
- Oil density (API Gravity): 16 – 58 °API
- Temperature: 70 – 295 °F
- Gas-oil ratio: 20 – 2100 SCF/STB
- Pressure: P_b – 8000 psi
Bergman
The Bergman correlation (2004) is designed to calculate the viscosity of undersaturated oil at pressures above the bubble point, particularly for heavy and bituminous fluids (5–25 °API). It employs an exponential relationship with pressure difference and includes a correction factor that accounts for gas-oil ratio and saturated oil viscosity. The model demonstrates good accuracy for high-viscosity oils and is recommended for use in "cold" reservoirs with typical formation conditions.
Recommended applicability range:
- Oil density (API Gravity): 10 – 40 °API
- Temperature: 100 – 300 °F
- Gas-oil ratio: 20 – 1500 SCF/STB
- Pressure: P_b – 5000 psi
De Ghetto
The De Ghetto correlation was developed to predict the viscosity of undersaturated oil, with a particular focus on heavy and bituminous crudes. The method provides separate calculation approaches for light and heavy fluids, ensuring high accuracy across a broad range of conditions.
Recommended applicability range:
- Oil density (API Gravity): 10 – 45 °API
- Temperature: 100 – 250 °F
- Gas-oil ratio: 50 – 2500 SCF/STB
- Pressure: P_b – 8000 psi
De Ghetto Agip
The De Ghetto correlation, developed by Agip, is designed to predict oil viscosity at pressures above the bubble point. It accounts for overpressure, saturated oil viscosity, and gas-oil ratio, delivering high accuracy for medium to heavy crudes (10–35 °API).
Recommended applicability range:
- Oil density (API Gravity): 10 – 35 °API
- Gas-oil ratio: 50 – 1500 SCF/STB
- Pressure: P_b – 8000 psi
Petrosky
The Petrosky correlation was specifically developed for Gulf of Mexico crude oils. It demonstrates good accuracy in predicting undersaturated oil viscosity under high-pressure conditions. The method is based on a modification of the classical Beal approach, incorporating regional fluid characteristics. The formula employs a power-law relationship linking viscosity at bubble point pressure to viscosity at higher pressures.
Recommended applicability range:
- Oil density (API Gravity): 16 – 45 °API
- Gas-oil ratio: 100 – 3500 SCF/STB
- Viscosity: 0.5 – 50 cP
- Pressure: P_b – 10,000 psi
Shilov
The Shilov correlation was developed to address modern field development conditions, particularly considering the characteristics of Russian crude oils. It is based on machine learning and the analysis of an extensive PVT database. The method delivers high accuracy for oils with anomalous properties and under high-pressure conditions. It accounts for thermobaric conditions, oil composition, and gas-oil ratio.
Recommended applicability range:
- Oil density (API Gravity): 12 – 45 °API
- Gas-oil ratio: 50 – 2500 SCF/STB
- Temperature: 100 – 350 °F
- Pressure: P_b – 10,000 psi
Gimatutdinov
The Gimatutdinov correlation was developed based on studies of oil fields in the former USSR. It is widely used in field development practices across CIS countries. The method incorporates the effect of pressure above the bubble point on oil viscosity through a logarithmic relationship. A distinctive feature of this correlation is its adaptation to the conditions of Western Siberia and other traditional oil-producing regions of the USSR/Russia.
Recommended applicability range:
- Oil density (API Gravity): 18 – 40 °API
- Gas-oil ratio: 200 – 4500 SCF/STB
- Temperature: 65 – 250 °F
- Pressure: P_b – 6,000 psi
Mishchenko
The Mishchenko correlation was developed to estimate oil viscosity under high-pressure conditions typical of deep reservoirs. The method is based on a modified exponential approach that incorporates thermodynamic parameters. A key feature of this correlation is its high accuracy for oils with elevated dissolved gas content and under abnormal reservoir conditions.
Recommended applicability range:
- Oil density (API Gravity): 15 – 48 °API
- Gas-oil ratio: 100 – 3000 SCF/STB
- Temperature: 140 – 400 °F
- Pressure: < 12,000 psi
Chu & Connally
The Chu & Connally correlation (1959) is one of the earliest and most widely used models for estimating oil viscosity at pressures above the bubble point. It is based on experimental data from U.S. oilfields and uses a power-law relationship to account for the effect of pressure on viscosity. The method is especially popular due to its simplicity and reliability under standard reservoir conditions.
Recommended applicability range:
- Oil density (API Gravity): 20 – 45 °API
- Gas-oil ratio: 50 – 1500 SCF/STB
- Temperature: 100 – 250 °F
- Pressure: < 5000 psi
Standing
Standing (1947) proposed one of the earliest practical correlations for estimating changes in oil viscosity at pressures above the bubble point. The method is based on data from California oilfields and uses a linear relationship between the logarithm of viscosity and pressure. Although considered outdated, this correlation is still used for preliminary calculations due to its simplicity.
Recommended applicability range:
- Oil density (API Gravity): 15 – 45 °API
- Gas-oil ratio: 90 – 1500 SCF/STB
- Temperature: 100 – 250 °F
- Pressure: < 5000 psi
Kartoatmodjo & Schmidt
The Kartoatmodjo & Schmidt (1991) correlation was developed to predict the viscosity of undersaturated oil with high accuracy, especially for heavy and bituminous crudes. It is based on an extensive database of more than 1,500 analyzed samples. The correlation accounts for the effects of pressure, temperature, gas-oil ratio, and oil density.
Recommended applicability range:
- Oil density (API Gravity): 15 – 40 °API
- Temperature: 100 – 250 °F
- Gas-oil ratio: 20 – 2500 SCF/STB
- Pressure: P_b – 5000 psi
Khan
The Khan correlation was developed to predict the viscosity of undersaturated oil, with particular emphasis on accounting for the effects of pressure, temperature, and fluid composition. Unlike many other methods, this correlation explicitly incorporates temperature dependence, making it especially useful in wide temperature range conditions. The formula is based on data from Pakistani oil fields but has shown good accuracy for other regions as well.
Recommended applicability range:
- Oil density (API Gravity): 15 – 45 °API
- Temperature: 100 – 300 °F
- Gas-oil ratio: 100 – 2500 SCF/STB
- Viscosity: 0.5 – 50 cP
- Pressure: P_b – 10,000 psi
Glaso
The Glaso correlation (1980) is an advanced method for calculating oil viscosity at pressures above the bubble point. It was developed based on an extensive database from North Sea oil fields. A key feature of this method is the use of a logarithmic relationship that captures the nonlinear behavior of viscosity as pressure increases.
Recommended applicability range:
- Oil density (API Gravity): 18 – 52 °API
- Temperature: 100 – 300 °F
- Gas-oil ratio: 100 – 3000 SCF/STB
- Pressure: Pb – 8000 psi
Vazquez & Beggs
The Vazquez & Beggs correlation is designed to estimate oil viscosity in the undersaturated region. It accounts for the effects of pressure, temperature, and oil properties using a power-law relationship based on extensive laboratory data. The formula relates oil viscosity at the bubble point pressure to its value at higher pressures. It is most suitable for light and medium oils (API > 20°), where the correlation provides the highest accuracy.
Recommended applicability range:
- Oil density (API Gravity): 15 – 50 °API
- Temperature: 100 – 300 °F
- Viscosity: 0.5 – 50 cP
- Pressure: Pb – 10000 psi