Bubble Point Pressure Correlations

Overview

The bubble point pressure ( $P_b$ ) is the pressure at which the first bubble of gas evolves from an oil at reservoir temperature. This thermodynamic property is fundamental to reservoir characterization:

Phase behavior prediction — distinguishes undersaturated from saturated flow conditions
Material balance calculations — determines oil compressibility above versus below $P_b$
Production forecasting — gas evolution affects mobility ratios and recovery
Facilities design — separator sizing requires saturation pressure knowledge

When laboratory PVT data are unavailable, engineers rely on empirical correlations derived from regression analysis of measured datasets.

Physical Significance

At the bubble point:

Reservoir oil transitions from a single-phase liquid to a two-phase gas-liquid system
Solution gas begins evolving from the oil phase
Oil compressibility changes discontinuously
Formation volume factor reaches its maximum value ( $B_{ob}$ )

The bubble point pressure depends on:

Property	Effect on $P_b$
Solution gas-oil ratio ( $R_s$ )	Higher $R_s$ → higher $P_b$
Gas specific gravity ( $\gamma_g$ )	Higher $\gamma_g$ → higher $P_b$
Oil API gravity ( $\gamma_{API}$ )	Higher API → lower $P_b$
Temperature ( $T$ )	Higher $T$ → higher $P_b$

Correlation Equations

All correlations covered here solve the inverse problem: given measured $R_s$ , $\gamma_g$ , $\gamma_{API}$ , and $T$ , calculate $P_b$ .

Standing (1947)

The earliest widely-used correlation, developed from 105 California crude oil samples:

P_b = 18.2 \left[ \left( \frac{R_s}{\gamma_g} \right)^{0.83} \frac{10^{0.00091 \, T}}{10^{0.0125 \, \gamma_{API}}} - 1.4 \right]

Where:

$P_b$ = bubble point pressure, psia
$R_s$ = solution gas-oil ratio, scf/STB
$\gamma_g$ = gas specific gravity (air = 1.0)
$\gamma_{API}$ = oil API gravity, °API
$T$ = temperature, °F

Applicability Range:

Parameter	Min	Max
$\gamma_g$	0.59	0.95
$\gamma_{API}$	16.5	63.8
$R_s$	20	1,425 scf/STB
$T$	100	258 °F
$P_b$	130	7,000 psia

Vasquez and Beggs (1980)

Developed from over 5,000 data points with API gravity-dependent coefficients:

P_b = \left[ \frac{R_s}{C_1 \, \gamma_g \, \exp \left( \frac{C_3 \, \gamma_{API}}{T + 459.67} \right)} \right]^{1/C_2}

Coefficients:

API Range	$C_1$	$C_2$	$C_3$
$\gamma_{API} \le 30$	0.0362	1.0937	25.724
$\gamma_{API} > 30$	0.0178	1.187	23.931

Where:

$T$ = temperature, °F (converted to °R with +459.67)

Applicability Range:

Parameter	Min	Max
$\gamma_g$	0.511	1.351
$\gamma_{API}$	15.3	59.5
$R_s$	10	5,000 scf/STB
$T$	60	300 °F
$P_b$	200	6,000 psia

Glasø (1980)

Developed from 45 North Sea crude oil samples using a correlation factor $P_b^*$ :

P_b^* = \left( \frac{R_s}{\gamma_g} \right)^{0.816} T^{0.172} \, \gamma_{API}^{-0.989}

P_b = 10^{\, 1.7669 + 1.7447 \log P_b^* - 0.30218 (\log P_b^*)^2}

Applicability Range:

Parameter	Min	Max
$\gamma_g$	0.65	1.276
$\gamma_{API}$	22.3	48.1
$R_s$	90	2,637 scf/STB
$T$	80	280 °F
$P_b$	165	7,142 psia

Al-Marhoun (1988)

Developed from 160 Middle East crude oil samples:

P_b = 5.38088 \times 10^{-3} \, R_s^{0.715082} \, \gamma_g^{-1.87784} \, \gamma_o^{3.1437} \, (T + 460)^{1.32657}

Where:

$\gamma_o$ = oil specific gravity = $\frac{141.5}{131.5 + \gamma_{API}}$
$T$ = temperature, °F (converted to °R with +460)

Applicability Range:

Parameter	Min	Max
$\gamma_g$	0.752	1.367
$\gamma_{API}$	19.4	44.6
$R_s$	26	1,602 scf/STB
$T$	74	240 °F
$P_b$	130	3,573 psia

Petrosky and Farshad (1993)

Developed from Gulf of Mexico crude oil samples:

X = 7.916 \times 10^{-4} \, \gamma_{API}^{1.5410} - 4.561 \times 10^{-5} \, T^{1.3911}

P_b = \frac{112.727 \, R_s^{0.577421}}{\gamma_g^{0.8439} \, 10^X} - 1391.051

Applicability Range:

Parameter	Min	Max
$\gamma_g$	0.752	1.367
$\gamma_{API}$	19.4	44.6
$R_s$	26	1,602 scf/STB
$T$	74	240 °F
$P_b$	130	3,573 psia

Dokla and Osman (1992)

Developed from UAE crude oil samples:

P_b = 8363.86 \, R_s^{0.724047} \, \gamma_g^{-1.01049} \, \gamma_o^{0.107991} \, (T + 460)^{-0.952584}

Where:

$\gamma_o$ = oil specific gravity = $\frac{141.5}{131.5 + \gamma_{API}}$

Applicability Range:

Parameter	Min	Max
$\gamma_g$	0.752	1.367
$\gamma_{API}$	19.4	44.6
$R_s$	26	1,602 scf/STB
$T$	74	240 °F
$P_b$	130	3,573 psia

Dindoruk and Christman (2004)

Developed from Gulf of Mexico deepwater crude oils using complex regression:

A = \frac{a_1 \, T^{a_2} + a_3 \, \gamma_{API}^{a_4}}{\left( a_5 + \frac{2 \, R_s^{a_6}}{\gamma_g^{a_7}} \right)^2}

P_b = a_8 \left[ \frac{R_s^{a_9}}{\gamma_g^{a_{10}}} \cdot 10^A + a_{11} \right]

Coefficients:

Coefficient	Value
$a_1$	$1.42828 \times 10^{-10}$
$a_2$	2.844591797
$a_3$	$-6.74896 \times 10^{-4}$
$a_4$	1.225226436
$a_5$	0.033383304
$a_6$	−0.272945957
$a_7$	−0.084226069
$a_8$	1.869979257
$a_9$	1.221486524
$a_{10}$	1.370508349
$a_{11}$	0.011688308

Applicability Range:

Parameter	Min	Max
$\gamma_g$	0.6017	1.0270
$\gamma_{API}$	14.7	40.0
$R_s$	133	3,050 scf/STB
$T$	117	276 °F
$P_b$	926	12,230 psia

Functions Covered

The following functions implement these bubble point correlations. See each function page for detailed parameter definitions, Excel syntax, and usage examples.

Function	Correlation	Regional Basis
PboStanding	Standing (1947)	California
PboVasquezBeggs	Vasquez-Beggs (1980)	Multiple regions
PboGlaso	Glasø (1980)	North Sea
PboAlMarhoun	Al-Marhoun (1988)	Middle East
PboPetroskyFarshad	Petrosky-Farshad (1993)	Gulf of Mexico
PboDindorukChristman	Dindoruk-Christman (2004)	Deepwater GOM
PboDoklaOsman	Dokla-Osman (1992)	UAE

Correlation Selection Guidelines

By Region

Oil Source	Recommended Correlation
California	Standing (1947)
North Sea	Glasø (1980)
Middle East	Al-Marhoun (1988)
Gulf of Mexico (shelf)	Vasquez-Beggs (1980) or Petrosky-Farshad (1993)
Deepwater GOM	Dindoruk-Christman (2004)
UAE	Dokla-Osman (1992)

By Fluid Properties

Fluid Characteristic	Recommended Correlation
Low GOR ( $R_s < 200$ )	Standing, Al-Marhoun
High GOR ( $R_s > 1000$ )	Dindoruk-Christman, Vasquez-Beggs
Light oil ( $\gamma_{API} > 40$ )	Standing, Glasø
Heavy/Medium oil ( $\gamma_{API} < 30$ )	Vasquez-Beggs, Al-Marhoun
High-pressure reservoir	Dindoruk-Christman

Statistical Performance

Based on the Brazilian Campos Basin study comparing 20 correlations:

Correlation	AARE (%)	Best For
Vasquez-Beggs	7-12	General-purpose
Al-Marhoun	8-15	Middle East analogs
Standing	10-18	Light California-type oils
Glasø	12-20	North Sea analogs

Note: Statistical performance varies significantly by dataset. Regional correlations typically outperform global correlations when applied to their development region.

Solution Gas-Oil Ratio (Rs) — input parameter for Pb correlations
Oil Formation Volume Factor (Bo) — property at bubble point
Oil Viscosity Correlations — μo above and below bubble point
PVT Properties Overview — correlation selection strategy

References

Standing, M.B. (1947). "A Pressure-Volume-Temperature Correlation for Mixtures of California Oils and Gases." Drilling and Production Practice, API, pp. 275-287.
Vazquez, M. and Beggs, H.D. (1980). "Correlations for Fluid Physical Property Prediction." Journal of Petroleum Technology, 32(6), pp. 968-970.
Glasø, Ø. (1980). "Generalized Pressure-Volume-Temperature Correlations." Journal of Petroleum Technology, 32(5), pp. 785-795.
Al-Marhoun, M.A. (1988). "PVT Correlations for Middle East Crude Oils." Journal of Petroleum Technology, 40(5), pp. 650-666.
Petrosky, G.E. and Farshad, F.F. (1993). "Pressure-Volume-Temperature Correlations for Gulf of Mexico Crude Oils." SPE Reservoir Engineering, 8(4), pp. 416-420.
Dokla, M.E. and Osman, M.E. (1992). "Correlation of PVT Properties for UAE Crudes." SPE Formation Evaluation, 7(1), pp. 41-46.
Dindoruk, B. and Christman, P.G. (2004). "PVT Properties and Viscosity Correlations for Gulf of Mexico Oils." SPE Reservoir Evaluation & Engineering, 7(6), pp. 427-437.
Santos, R.G., Silva, J.A., Mehl, A., and Experiment, P.E. (2019). "Comparison of PVT Correlations with PVT Laboratory Data from the Brazilian Campos Basin." Brazilian Journal of Petroleum and Gas, 13(3), pp. 129-157.

Bubble Point Pressure Correlations

Overview

Physical Significance

Correlation Equations

Standing (1947)

Vasquez and Beggs (1980)

Glasø (1980)

Al-Marhoun (1988)

Petrosky and Farshad (1993)

Dokla and Osman (1992)

Dindoruk and Christman (2004)

Functions Covered

Correlation Selection Guidelines

By Region

By Fluid Properties

Statistical Performance

Related Documentation

References

Related Excel Functions