Condensate Gas Ratio Calculator

The Condensate Gas Ratio Calculator estimates condensate-to-gas ratio using PVT data, phase behaviour, and standard conditions for petroleum reservoir analysis.

Condensate Gas Ratio Calculator Explained

Condensate Gas Ratio, often shortened to CGR, describes how much liquid hydrocarbon drops out of produced gas when brought to surface conditions. It is the volume of stock tank condensate per volume of gas at standard conditions. Engineers use CGR to design separators, size pipelines, and estimate liquids revenue.

This calculator focuses on physics-based relationships between measured rates and standard conditions. It treats standard temperature and pressure as constants tied to your chosen unit system. You can compute CGR from instantaneous rates or from cumulative production, depending on your workflow and data quality.

With a clear result and the right units, you can compare wells and reservoirs, track trends over time, and validate models against production tests. The tool supports common oilfield units and metric conversions so teams stay aligned.

The Mechanics Behind Condensate Gas Ratio

Understanding how condensate forms helps you enter the right inputs. Gas from a reservoir may carry heavy components in vapor form. When pressure and temperature drop through the wellbore and surface equipment, some heavy components condense into liquid. CGR measures that liquid yield at stabilized tank conditions compared to the gas at standard conditions.

• Reservoir fluid flows to surface and cools as pressure decreases, crossing dewpoint and forming liquid droplets.
• Separators remove free liquid. Stabilization tanks flash remaining light ends until stable stock tank conditions are met.
• Gas volume is reported at a defined standard condition, set by temperature and pressure constants in your unit system.
• Condensate is reported as stock tank barrels or cubic meters after stabilization and shrinkage.
• Ratioing these volumes yields CGR, commonly in stb per MMscf or m3 per 10^3 Sm3.

Because CGR depends on pressure, temperature, and composition, it is not fixed for all times. Changes in choke settings, separator pressure, or fluid composition can shift the observed ratio. Measure carefully and use consistent conditions when comparing results.

Condensate Gas Ratio Formulas & Derivations

The core definition is simple: condensate volume at stock tank conditions divided by gas volume at standard conditions over the same period. You can apply it to rates or totals. The calculator uses these direct and unit-safe formulations.

• Instantaneous CGR: CGR = QC / QG, where QC is condensate rate (e.g., stb/d) and QG is gas rate at standard conditions (e.g., MMscf/d).
• Cumulative CGR: CGR = NC / NG, where NC is total condensate produced and NG is total gas produced at standard conditions.
• Unit-normalized form: CGR(bbl/MMscf) = (QC,bbl/d) / (QG,MMscf/d). For m3/10^3 Sm3, multiply by the correct conversion factor.
• Uncertainty estimate: σCGR ≈ CGR × sqrt((σQC/QC)² + (σQG/QG)²), when QC and QG errors are independent.
• Conversion to condensate yield per Mscf: CGR(bbl/Mscf) = CGR(bbl/MMscf) / 1000.

These expressions require only measured volumes and consistent units. More complex derivations can relate CGR to compositional PVT, liquid dropout curves, and separator stage performance. When those data exist, you can predict how operational changes move CGR and then check the prediction against measured results.

Inputs and Assumptions for Condensate Gas Ratio

Gather clean data before you calculate. The tool expects quantities referenced to stated conditions and uses fixed constants for standard temperature and pressure according to your unit choice.

• Condensate rate or volume at stock tank conditions (stabilized liquid).
• Gas rate or volume at standard conditions (dry gas volume, not at meter pressure).
• Time basis for both measurements (ensure the same period for rates or totals).
• Chosen unit system and standard conditions (e.g., 60°F and 14.696 psia; or 15°C and 1 bar).
• Optional: Separator pressure and temperature if you plan to compare different operating points.
• Optional: Measurement uncertainties to estimate error bars on the result.

Typical CGR values range from near zero up to several hundred stb/MMscf, depending on fluid composition. Extremely low results can occur for very lean gas. Extremely high results may suggest misreported gas rates, unstable tank conditions, or entrained water counted as condensate. Negative values are not physically possible and indicate a data or sign error.

Using the Condensate Gas Ratio Calculator: A Walkthrough

Here’s a concise overview before we dive into the key points:

1. Select whether you will use rates or cumulative totals.
2. Choose your units for gas and condensate, and confirm the standard conditions.
3. Enter condensate volume at stock tank conditions for the selected time period.
4. Enter gas volume at standard conditions for the same period.
5. (Optional) Enter measurement uncertainties for both streams.
6. Click Calculate to compute the CGR and view the result with units.

These points provide quick orientation—use them alongside the full explanations in this page.

Case Studies

A deep retrograde gas well produces 45 MMscf/d of gas and 3,600 stb/d of condensate through a two-stage separator. Using rates, CGR = 3,600 / 45 = 80 stb/MMscf. After lowering first-stage separator pressure by 50 psi, condensate increases to 3,900 stb/d while gas drops to 44 MMscf/d; CGR = 88.6 stb/MMscf. The higher CGR reflects more liquid dropout at lower pressure, consistent with PVT expectations. What this means: Facilities must handle higher liquid loads when separator pressure decreases.

A lean gas field delivers 120 MMscf/d and 960 stb/d of condensate from a cluster. CGR = 960 / 120 = 8 stb/MMscf, which aligns with prior well tests. A later test shows 7.2 stb/MMscf after installing a heated separator; liquid dropout decreased as temperature rose. The change supports the expected thermal effect on retrograde condensation. What this means: Warmer separation can reduce condensate yield and shift revenue from liquids to gas.

Accuracy & Limitations

CGR is straightforward to compute, but several factors can bias the result. Use consistent standards and verify how each meter reports volumes. Ensure liquids are stabilized and that water is excluded from condensate totals.

• Allocation error can distort volumes when multiple wells share meters.
• Changing choke settings or separator conditions between gas and liquid measurements skews the ratio.
• Unstabilized liquids or carry-under/over in separators misstate true condensate yield.
• Standard-condition constants vary by region; mixing standards creates conversion mistakes.
• Short sampling windows can be noisy; use longer periods for representative values.

When precision matters, include measurement uncertainty and compare rate-based CGR to the cumulative value. If they diverge, investigate data quality, PVT consistency, and operating conditions before making design decisions.

Units & Conversions

Units matter because CGR compares two different volumes at specific conditions. Mixing standards leads to wrong conclusions. Use consistent constants for standard temperature and pressure, and convert only after you compute the result.

Choose the row that matches your current units and the target units. Multiply your CGR by the factor to convert. For example, 80 bbl/MMscf equals 80 × 0.0056146 = 0.449 m3/10^3 Sm3. Keep the same standard conditions when comparing values across reports.

Tips If Results Look Off

If your CGR seems unrealistic, check the basics first. Most issues come from inconsistent time bases, wrong units, or mixed standards. Confirm where meters report volumes and whether liquids are stabilized.

• Verify that condensate and gas volumes cover the same period.
• Confirm gas is reported at standard conditions, not at line conditions.
• Exclude water from condensate totals; check tank BS&W measurements.
• Revisit unit conversions and standard-condition constants.

Still unsure? Compare rate-based CGR to the cumulative value. Large differences point to transient operations, allocation changes, or measurement drift.

FAQ about Condensate Gas Ratio Calculator

What is a normal range for CGR?

Lean gas may have CGR near 0–10 stb/MMscf, while rich gas-condensate can exceed 100 stb/MMscf. The exact range depends on fluid composition and operating conditions.

Should I use rates or cumulative volumes?

Use rates for quick checks and operational tuning. Use cumulative volumes for performance benchmarking and reserves analysis because they average out short-term noise.

Do standard conditions affect the result?

Yes. CGR depends on gas volume at standard conditions. Set the correct standard temperature and pressure constants, and keep them consistent across datasets.

Can I estimate CGR from PVT data alone?

You can model expected CGR using compositional PVT and separator conditions. However, always validate with measured rates, because equipment and operations affect the realized yield.

Glossary for Condensate Gas Ratio

Condensate Gas Ratio (CGR)

The volume of stabilized condensate produced per volume of gas at standard conditions over the same time interval.

Standard Conditions

Reference temperature and pressure used to report gas volumes, such as 60°F and 14.696 psia or 15°C and 1 bar.

Stock Tank Conditions

Stabilized surface conditions at which condensate volume is measured after flashing and separation of light ends.

Retrograde Condensation

A phase behavior where liquid forms from gas as pressure drops below dewpoint, common in gas-condensate systems.

Dewpoint Pressure

The pressure at which the first drop of liquid forms from a gas mixture at constant temperature.

Allocation

The method of distributing measured production among wells or streams that share metering equipment.

Separator

A vessel that splits wellstream into gas and liquid phases at controlled pressure and temperature.

Measurement Uncertainty

The estimated error bounds on a measured value due to instrument accuracy, calibration, and sampling variance.

References

Here’s a concise overview before we dive into the key points:

• Schlumberger Oilfield Glossary: Condensate gas ratio
• SPE PetroWiki: Gas condensate reservoirs
• SPE OGF: Understanding gas condensate behavior and liquid dropout
• Springer Encyclopedia of Petroleum Engineers: Gas Condensate Systems
• API Standards: Measurement and sampling references

These points provide quick orientation—use them alongside the full explanations in this page.