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:

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

Calibration Strategy

When some laboratory data is available:

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

PVT Property Relationships

The Black Oil Model

                    ┌─────────────────────────────────────┐
                    │         Reservoir Oil               │
                    │    (Gas in Solution + Liquid)       │
                    └─────────────────────────────────────┘
                                    │
                    ┌───────────────┼───────────────┐
                    │               │               │
                    ▼               ▼               ▼
            ┌───────────┐   ┌───────────┐   ┌───────────┐
            │    Rs     │   │    Bo     │   │    μo     │
            │ Solution  │   │ Formation │   │ Viscosity │
            │   GOR     │   │  Volume   │   │           │
            └───────────┘   └───────────┘   └───────────┘
                    │               │               │
                    ▼               ▼               ▼
            ┌───────────┐   ┌───────────┐   ┌───────────┐
            │    Pb     │   │    Co     │   │   Stage   │
            │  Bubble   │   │Compress-  │   │  Dead →   │
            │  Point    │   │  ibility  │   │Sat → USat │
            └───────────┘   └───────────┘   └───────────┘

Property Interdependencies

Correlation Selection Guide

By Property

Bubble Point Pressure ($P_b$)

📖 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 ($B_o$)

📖 Full Documentation: Oil Formation Volume Factor

Oil Viscosity ($\mu_o$)

Three-stage calculation:

📖 Full Documentation: Oil Viscosity Correlations

Oil Compressibility ($c_o$)

📖 Full Documentation: Oil Compressibility Correlations

Calculation Workflow

Complete Oil PVT at Any Pressure

┌─────────────────────────────────────────────────────────────┐
│ INPUTS: P, T, γg, γAPI, (Rsob or lab Pb)                    │
└─────────────────────────────────────────────────────────────┘
                            │
                            ▼
┌─────────────────────────────────────────────────────────────┐
│ Step 1: Calculate Bubble Point                              │
│         Pb = f(Rsob, γg, γAPI, T)                           │
│         OR use measured Pb                                   │
└─────────────────────────────────────────────────────────────┘
                            │
                            ▼
┌─────────────────────────────────────────────────────────────┐
│ Step 2: Determine Pressure Regime                           │
│         P > Pb → Undersaturated                             │
│         P ≤ Pb → Saturated                                  │
└─────────────────────────────────────────────────────────────┘
                     │               │
            Undersaturated      Saturated
                     │               │
                     ▼               ▼
┌──────────────────────────┐ ┌──────────────────────────┐
│ Step 3a: USat Properties │ │ Step 3b: Sat Properties  │
│ Rs = Rsob (constant)     │ │ Rs = f(P, T, γg, γAPI)   │
│ Bo = Bob·exp[-co(P-Pb)]  │ │ Bo = f(Rs, T, γg, γo)    │
│ μo = f(μob, P, Pb)       │ │ μo = f(μod, Rs)          │
│ co = f(Rsob, γg, γAPI,   │ │ co = f(P, Pb, T, Rsob,   │
│       T, P)              │ │       γAPI)              │
└──────────────────────────┘ └──────────────────────────┘

Statistical Performance Guidelines

Expected Accuracy

When Correlations Fail

Available Property Documentation

Oil Properties

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

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

Input Validation

Related Documentation

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

1. McCain, W.D. Jr. (1990). The Properties of Petroleum Fluids, 2nd Edition. PennWell Books.

2. Ahmed, T. (2019). Reservoir Engineering Handbook, 5th Edition. Gulf Professional Publishing.

3. Whitson, C.H. and Brulé, M.R. (2000). Phase Behavior. SPE Monograph Vol. 20.

4. Standing, M.B. (1981). Volumetric and Phase Behavior of Oil Field Hydrocarbon Systems, 9th Edition. Society of Petroleum Engineers.

5. Danesh, A. (1998). PVT and Phase Behaviour of Petroleum Reservoir Fluids. Elsevier.