The Beggs & Robinson correlation estimates the viscosity of dead (degassed) oil based on oil density and temperature. It performs well for light and medium crude oils (above 22°API) but is less accurate for heavy oils (below 16°API) and highly viscous fluids.
Recommended applicability range:
- Oil density (API Gravity): 16 – 58 °API
- Temperature: 70 – 295 °F
- Viscosity: 0.5 – 50 cP
Bergman
The Bergman correlation (2004) was developed specifically for heavy and bituminous crude oils, where classical models (such as Beggs & Robinson) often produce significant errors. This model is based on an extensive database that includes high-viscosity oil samples and provides more accurate predictions under complex conditions.
Recommended applicability range:
- Oil density (API Gravity): 5 – 30 °API
- Temperature: 60 – 300 °F
- Viscosity: 10 – 20,000 cP
De Ghetto
The De Ghetto correlation was developed to estimate the viscosity of dead oil based on data from Mediterranean and Middle Eastern crude oils. It is particularly useful for medium and heavy oils, where many classical correlations (such as Beggs & Robinson) yield significant errors. The correlation is well-suited for high-sulfur crude oils.
Recommended applicability range:
- Oil density (API Gravity): 10 – 45 °API
- Temperature: 80 – 300 °F
- Viscosity: 1 – 500 cP
De Ghetto (Agip)
The De Ghetto et al. correlation (developed for Agip) is designed to estimate the viscosity of dead oil, with a focus on heavy and bituminous crudes. It is based on a comprehensive database including samples from various regions and provides two separate formulas for heavy and light oils.
Recommended applicability range:
- Oil density (API Gravity): 10 – 48 °API
- Temperature: 60 – 300 °F
- Viscosity: 1 – 50,000 cP
Petrosky
The Petrosky (1990) correlation was developed based on the analysis of PVT properties of crude oils from Gulf of Mexico fields. A key feature of the model is its adaptation to high-temperature conditions and oils with elevated gas content, which are typical for the region. The correlation performs well for paraffinic oils.
Recommended applicability range:
- Oil density (API Gravity): 15 – 45 °API
- Temperature: 80 – 320 °F
- Viscosity: 0.5 – 200 cP
Egbogah
The Egbogah correlation was specifically developed for accurate prediction of dead oil viscosity, especially under high-temperature conditions and for heavy fluids. Unlike classical methods (Beal, Beggs & Robinson), this correlation incorporates an enhanced temperature dependence and modified coefficients, providing better accuracy for oils with API < 25°. The formula is based on statistical analysis of data from Canadian oil fields, making it particularly useful for oils with atypical properties.
Recommended applicability range:
- Oil density (API Gravity): 10 – 45 °API
- Temperature: 50 – 300 °F
- Viscosity: 1 – 100,000 cP
Kartohadiprodjo & Schmidt
This correlation was developed based on an extensive database comprising over 4,500 crude oil samples from around the world. It is considered one of the most universal and accurate methods for estimating dead oil viscosity, especially across a wide range of oil densities. Additionally, it accounts for the nonlinear dependence of viscosity on both temperature and oil gravity. It is claimed to outperform Beggs & Robinson and Glaso correlations in terms of accuracy, particularly for heavy oils.
Recommended applicability range:
- Oil density (API Gravity): 6 – 50 °API
- Temperature: 70 – 295 °F
- Viscosity: 1 – 10,000 cP (highest accuracy in the range of 10 – 1,000 cP)
Khan
The Khan correlation is a modified version of the classical Beggs & Robinson method, specifically developed for accurate prediction of dead oil viscosity across a wide range of temperatures and oil gravities. The method introduces additional correction factors that enhance accuracy for heavy oils and high-temperature conditions. The formula is based on statistical analysis of data from Pakistani oil fields but has demonstrated good applicability to other regions.
Recommended applicability range:
- Oil density (API Gravity): 10 – 45 °API
- Temperature: 70 – 300 °F
- Viscosity: 1 – 10,000 cP (highest accuracy in the range of 10 – 1,000 cP)
Glaso
The Glaso correlation was developed based on PVT data analysis for North Sea crude oils. It estimates dead oil viscosity at atmospheric pressure using oil density and temperature. Compared to the Beal and other early correlations, Glaso offers a wider temperature applicability range. It is particularly suitable for North Sea oils but has been validated on fields in other regions as well.
Recommended applicability range:
- Oil density (API Gravity): 15 – 50 °API
- Temperature: 50 – 300 °F
- Viscosity: 0.5 – 50 cP
A2.3.2. Saturated Oil Viscosity
Beggs & Robinson
The Beggs & Robinson correlation estimates the viscosity of saturated oil containing dissolved gas. It is based on data from North American crude oils and involves two steps: calculating the viscosity of dead oil, and then applying a correction for the presence of dissolved gas. The correlation is known for its simplicity and reliable accuracy for light and medium oils (20–45 °API).
Recommended applicability range:
- Oil density (API Gravity): 16 – 58 °API
- Temperature: 70 – 295 °F
- Viscosity: 0.5 – 50 cP
- Solution gas–oil ratio (GOR): 20 – 2000 SCF/STB
Beal
The Beal correlation is one of the earliest fundamental methods for calculating the viscosity of saturated oil. It was developed based on experimental data from North American crude oils. The method defines viscosity as a function of bubble point pressure, temperature, and oil density using a set of empirical coefficients. Its key feature is simplicity and reliability under standard conditions, although additional adjustments may be required for heavy oils or extreme conditions.
Recommended applicability range:
- Oil density (API Gravity): 15 – 45 °API
- Temperature: 100 – 220 °F
- Viscosity: 0.5 – 50 cP
Bergman
The Bergman correlation (2004) is designed to estimate the viscosity of saturated oil based on the viscosity of dead oil and solution gas-oil ratio. It is most suitable for medium-density oils with moderate gas content but may introduce errors for heavy oils, condensates, or extreme gas-oil ratios. The formula is simple to apply but should not replace laboratory measurements when working with non-standard fluids.
Recommended applicability range:
- Oil density (API Gravity): 15 – 45 °API
- Temperature: 70 – 300 °F
- Viscosity: 0.5 – 50 cP
- Gas-oil ratio: 50 – 2000 SCF/STB
De Ghetto
The De Ghetto empirical correlation was developed based on an extensive analysis of experimental data for saturated oil. It was primarily designed for application to Brazilian oilfield conditions but has demonstrated good versatility and applicability beyond this region.
Recommended applicability range:
- Oil density (API Gravity): 16 – 45 °API
- Temperature: 20 – 260 °F
- Viscosity: 0.1 – 1000 cP
- Gas-oil ratio: 10 – 2000 SCF/STB
De Ghetto Agip
The De Ghetto correlation, developed by Agip, is designed to estimate the viscosity of saturated oil based on its density, gas-oil ratio, and temperature. It is derived from a statistical analysis of various oil types, including heavy and highly viscous oils, making it more versatile than many other methods. The formula includes correction factors to account for the influence of oil density and dissolved gas content, allowing for application across a wide range of conditions.
Recommended applicability range:
- Oil density (API Gravity): 6 – 50 °API
- Temperature: 80 – 300 °F
- Viscosity: 0.5 – 1000 cP
- Gas-oil ratio: 50 – 2000 SCF/STB
Petrosky
The Petrosky correlation was specifically developed for Gulf of Mexico crude oils, considering the high temperatures and pressures typical of deepwater reservoirs. It provides high accuracy for light to medium oils (20–40 °API) and includes a correction for gas-oil ratio. Compared to Beggs & Robinson, it demonstrates 10–15% better accuracy for Gulf of Mexico conditions.
Recommended applicability range:
- Oil density (API Gravity): 15 – 45 °API
- Temperature: 80 – 320 °F
- Viscosity: 0.5 – 50 cP
- Gas-oil ratio: 100 – 2500 SCF/STB
Egbogah
The Egbogah correlation was specifically developed for heavy and bituminous oils (5–25 °API). It accounts for the effects of gas-oil ratio, dead oil viscosity, and temperature. This model is especially useful for "cold" reservoirs and crudes with high asphaltene content. It is not applicable to light oils.
Recommended applicability range:
- Oil density (API Gravity): 5 – 25 °API
- Temperature: 60 – 250 °F
- Viscosity: 50 – 50,000 cP
- Gas-oil ratio: 20 – 800 SCF/STB
Chu & Connally
The Chu & Connally correlation estimates the viscosity of saturated oil based on dead oil viscosity and gas-oil ratio. It is especially useful for light and medium oils and is widely used in engineering calculations. The model accounts for the nonlinear effect of dissolved gas on oil viscosity, but it is less accurate for heavy oils (API < 20) and highly viscous fluids (>50 cP).
Recommended applicability range:
- Oil density (API Gravity): 15 – 50 °API
- Temperature: 70 – 295 °F
- Viscosity: 0.5 – 50 cP
- Gas-oil ratio: 50 – 3500 SCF/STB
Standing
Standing proposed an empirical correlation to estimate the viscosity of saturated oil based on data from California oil fields. The method relates viscosity to pressure, temperature, gas-oil ratio, and oil density. The correlation is simple to apply and suitable for "Black oil" models without significant amounts of non-hydrocarbon components. At high gas-oil ratios, it may overestimate viscosity.
Recommended applicability range:
- Oil density (API Gravity): 15 – 45 °API
- Temperature: 100 – 250 °F
- Pressure: < 5000 psi
- Gas-oil ratio: 90 – 1500 SCF/STB
Kartotomojo & Schmidt
The early version of the Kartotomojo & Schmidt (1991) correlation was developed as an improvement over the Standing and Beggs & Robinson models. It provides more accurate viscosity predictions for a wide range of crude oils, especially for fields in Southeast Asia. This version of the correlation uses a power-law dependency on gas-oil ratio and dead oil viscosity, delivering better accuracy for heavy and high-viscosity oils.
Recommended applicability range:
- Oil density (API Gravity): 10 – 45 °API
- Temperature: 100 – 300 °F
- Viscosity: 1 – 5000 cP
- Gas-oil ratio: 50 – 2500 SCF/STB
Khan
The Khan correlation was developed for predicting saturated oil viscosity by accounting for the effects of gas-oil ratio, temperature, and oil density. It is particularly useful across a wide range of oil properties, including heavy fluids. Its main advantage is versatility, as it is applicable to light, medium, and heavy crude oils. Additionally, the model accounts for the significant impact of high gas-oil ratios on viscosity.
Recommended applicability range:
- Oil density (API Gravity): 15 – 45 °API
- Temperature: 100 – 300 °F
- Viscosity: 1 – 1000 cP
- Gas-oil ratio: 200 – 2500 SCF/STB
Glaso
Glaso (1980) proposed a generalized correlation for estimating oil viscosity, taking into account gas-oil ratio, oil and gas density, and temperature. It is better suited for light and medium crude oils than Standing’s method, especially under high gas-oil ratios. The correlation offers improved accuracy compared to older models due to the generalization of a large dataset. However, it is not recommended for heavy oils (API < 15°).
Recommended applicability range:
- Oil density (API Gravity): 15 – 55 °API
- Temperature: 70 – 295 °F
- Gas-oil ratio: 50 – 3500 SCF/STB