PVT Properties Overview

Introduction

PVT (Pressure-Volume-Temperature) properties describe how reservoir fluids behave under changing conditions. Accurate PVT data is essential for:

Reservoir simulation — fluid flow and recovery calculations
Material balance — reserves estimation
Well performance — inflow and outflow analysis
Facilities design — separator and pipeline sizing
Production forecasting — rate predictions

When laboratory PVT measurements are unavailable, engineers rely on empirical correlations developed from measured datasets.

Correlation Philosophy

Regional Basis

Most PVT correlations were developed from specific geographic datasets:

Region	Typical Crude Type	Representative Correlations
California	Light, low-sulfur	Standing (1947)
North Sea	Light to medium, waxy	Glasø (1980)
Middle East	Medium, sulfur	Al-Marhoun (1988)
Gulf of Mexico	Variable	Vasquez-Beggs (1980), Petrosky-Farshad (1993)
Deepwater GOM	Light, high GOR	Dindoruk-Christman (2004)
UAE	Medium	Dokla-Osman (1992)

Best Practice: Use correlations developed from oils similar to your reservoir.

Calibration Strategy

When some laboratory data is available:

Tune correlations to match measured points
Validate consistency across related properties
Use measured values at calibration points, correlations elsewhere

PVT Property Relationships

The Black Oil Model

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Property Interdependencies

Property	Depends On	Used By
$P_b$ (Bubble Point)	$R_s$ , $\gamma_g$ , $\gamma_{API}$ , $T$	$B_o$ , $\mu_o$ , $c_o$ at $P_b$
$R_s$ (Solution GOR)	$P$ , $T$ , $\gamma_g$ , $\gamma_{API}$	$B_o$ , $\mu_o$
$B_o$ (Formation Volume)	$R_s$ , $T$ , $\gamma_g$ , $\gamma_o$	Material balance, flow calculations
$\mu_o$ (Viscosity)	Stage: $\mu_{od} \to \mu_{ob} \to \mu_o$	Flow calculations, mobility
$c_o$ (Compressibility)	$P$ relative to $P_b$	Material balance, PTA

Correlation Selection Guide

By Property

Bubble Point Pressure ( $P_b$ )

Oil Type	First Choice	Alternative
Light California	Standing	Glasø
North Sea	Glasø	Standing
Middle East	Al-Marhoun	Vasquez-Beggs
Gulf of Mexico	Petrosky-Farshad	Vasquez-Beggs
Deepwater/High GOR	Dindoruk-Christman	-
UAE	Dokla-Osman	Al-Marhoun
General purpose	Vasquez-Beggs	Standing

📖 Full Documentation: Bubble Point Correlations

Solution Gas-Oil Ratio ( $R_s$ )

Same regional preferences as bubble point — the correlations are mathematically related (inverses of each other).

📖 Full Documentation: Solution GOR Correlations

Oil Formation Volume Factor ( $B_o$ )

Condition	Correlation	Notes
Saturated ( $P \le P_b$ )	Match $R_s$ correlation	Use same author for consistency
Undersaturated ( $P > P_b$ )	From $B_{ob}$ and $c_o$	$B_o = B_{ob} \exp[-c_o(P - P_b)]$

📖 Full Documentation: Oil Formation Volume Factor

Oil Viscosity ( $\mu_o$ )

Three-stage calculation:

Stage	Function	Correlation
1. Dead oil ( $\mu_{od}$ )	$f(\gamma_{API}, T)$	Egbogah (1983)
2. Saturated ( $\mu_o$ , $P \le P_b$ )	$f(\mu_{od}, R_s)$	Beggs-Robinson (1975)
3. Undersaturated ( $\mu_o$ , $P > P_b$ )	$f(\mu_{ob}, P, P_b)$	Vasquez-Beggs (1980)

📖 Full Documentation: Oil Viscosity Correlations

Oil Compressibility ( $c_o$ )

Condition	Correlation	Typical Values
Undersaturated ( $P > P_b$ )	Vasquez-Beggs (1980)	10-30 × 10⁻⁶ 1/psi
Saturated ( $P \le P_b$ )	Villena-Lanzi (1985)	50-200 × 10⁻⁶ 1/psi

📖 Full Documentation: Oil Compressibility Correlations

Calculation Workflow

Complete Oil PVT at Any Pressure

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Statistical Performance Guidelines

Expected Accuracy

Property	AARE Range	Best Achievable
$P_b$	5-15%	< 5% with tuning
$R_s$	5-12%	< 5% with tuning
$B_o$	1-5%	< 2% with tuning
$\mu_o$	10-25%	5-10% with tuning
$c_o$	15-30%	10-15% with tuning

When Correlations Fail

Symptom	Likely Cause	Solution
$P_b$ off by > 20%	Wrong correlation for oil type	Try regional correlation
$B_o$ too high/low	Inconsistent $R_s$ and $B_o$	Use matched pair
$\mu_o$ unrealistic	Dead oil viscosity wrong	Check API gravity input
Non-physical values	Outside correlation range	Check input ranges

Available Property Documentation

Oil Properties

Property	Functions	Documentation
Bubble Point	7 correlations	Bubble Point
Solution GOR	6 correlations	Solution GOR
Formation Volume Factor	7+ correlations	Formation Volume Factor
Viscosity	3-stage	Oil Viscosity
Compressibility	2 correlations	Oil Compressibility

Gas Properties (Reference materials needed)

Z-factor correlations
Gas viscosity
Gas density

Water Properties (Reference materials needed)

Water formation volume factor
Water compressibility
Water viscosity

Best Practices

Consistency Checks

$B_o$ at $P_b$ should be maximum value
$\mu_o$ at $P_b$ should be minimum value
$R_s = R_{sb}$ for all $P \ge P_b$
$B_o$ decreases for $P > P_b$ (undersaturated)
$B_o$ decreases for $P < P_b$ (saturated, as gas evolves)

Input Validation

Parameter	Typical Range	Check
$\gamma_g$	0.55 - 1.5	Air = 1.0, methane ≈ 0.55
$\gamma_{API}$	10 - 60	Water = 10, very light > 40
$R_s$	0 - 3000 scf/STB	Higher = more volatile
$T$	60 - 350 °F	Reservoir temperature
$P_b$	100 - 10000 psia	Must be < initial pressure

Oil Properties

Bubble Point Correlations — 7 methods with regional guidance
Solution GOR Correlations — Rs calculation methods
Oil Formation Volume Factor — Bo saturated/undersaturated
Oil Viscosity Correlations — Three-stage viscosity calculation
Oil Compressibility Correlations — Co above and below Pb

Gas Properties

Gas Properties — Z-factor, viscosity, density, pseudo-criticals

Water Properties

Water Properties — Bw, Cw, μw, Rsw correlations

Other Properties

Interfacial Tension — Gas-oil IFT for multiphase flow

Supporting Functions

Unit Conversions — API/SG conversions
Interpolation — For PVT table lookup

References

McCain, W.D. Jr. (1990). The Properties of Petroleum Fluids, 2nd Edition. PennWell Books.
Ahmed, T. (2019). Reservoir Engineering Handbook, 5th Edition. Gulf Professional Publishing.
Whitson, C.H. and Brulé, M.R. (2000). Phase Behavior. SPE Monograph Vol. 20.
Standing, M.B. (1981). Volumetric and Phase Behavior of Oil Field Hydrocarbon Systems, 9th Edition. Society of Petroleum Engineers.
Danesh, A. (1998). PVT and Phase Behaviour of Petroleum Reservoir Fluids. Elsevier.

Introduction

Correlation Philosophy

Regional Basis

Calibration Strategy

PVT Property Relationships

The Black Oil Model

Property Interdependencies

Correlation Selection Guide

By Property

Bubble Point Pressure (PbP_bPb​)

Solution Gas-Oil Ratio (RsR_sRs​)

Oil Formation Volume Factor (BoB_oBo​)

Oil Viscosity (μo\mu_oμo​)

Oil Compressibility (coc_oco​)

Calculation Workflow

Complete Oil PVT at Any Pressure

Statistical Performance Guidelines

Expected Accuracy

When Correlations Fail

Available Property Documentation

Oil Properties

Gas Properties (Reference materials needed)

Water Properties (Reference materials needed)

Best Practices

Consistency Checks

Input Validation

Related Documentation

Oil Properties

Gas Properties

Water Properties

Other Properties

Supporting Functions

References

Bubble Point Pressure ( $P_b$ )

Solution Gas-Oil Ratio ( $R_s$ )

Oil Formation Volume Factor ( $B_o$ )

Oil Viscosity ( $\mu_o$ )

Oil Compressibility ( $c_o$ )