Solution Gas-Oil Ratio (Solution GOR ≡ Rs) - Online Calculator

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Introduction

Undersanding Solution Gas-Oil Ratio

The Solution Gas-Oil Ratio which is also known as gas solubility (Rs) is defined as the number of standard cubic feet of gas which will dissolve in one stock-tank barrel of crude oil at certain pressure and temperature. This value is constant at pressures greater than the bubble point pressure as there is no free gas in the reservoir (undersaturated oil reservoir) and below the bubble point pressure, the solution gas-oil ratio decreases as the pressure decreases. The dissolved gas consists mostly of the light hydrocarbons (Methane, Ethane, Propane, and Butane) and some inorganic impurities (Nitrogen, Carbon Dioxide, Hydrogen Sulfide, etc.). The typical Oilfield unit of Rs is standard cubic feet of gas per stock tank barrel of oil (scf/stb).

Main Factors Affecting Rs

  1. Pressure (P): The solubility of gas in liquid is directly proportional to the pressure of the gas in contact with liquid.
  2. Temperature (T): The solubility of gas in liquid decreases as temperature increases. This is because higher temperatures provide more energy for gas molecules to escape from the liquid.
  3. Oil gravity (API): The solubility of gas in liquid is directly proportional to the API gravity of the oil in contact with gas; the higher the API gravity, the higher the solubilty.
  4. Gas specific gravity (γg): The solubility of gas in liquid is directly proportional to the specific gravity of the gas in contact with liquid. Gases with higher specific gravity (heavier gases) tend to be more soluble in oil.

Key Points

PVT laboratories can provide actual solution gas-oil ratios from direct measurement, and empirical correlations can be made based on PVT laboratory data. Although most of the empirical correlations presented to estimate the solubility of gases in oil use affecting parameters listed above, some empirical relationships have been developed based on other additional parameters. It must be noted that at known pressure and temperatures below bubble point pressure, oil-gas solubility can be calculated precisly using material balance. Below are some common correlations developed for estimating oil-gas solubility.

Correlations

The following box contain some popular correlations that are used to estimate Solution gas-oil ratio under knwon condition(s). It must be noted that the selection of correlation(s) control the active input parameter(s) and the calculated result(s) listed in the next sections (only input parameter that is used by selected correlation and the result of selected correlation will become visible).

Input Parameters

The following table contain the required input parameter(s) that are used by selected correlation(s) to estimate Solution gas-oil ratio. In this table the input variable(s) is checked to be physically correct and the result is shown in Validity column by for valid values and for invalid values. It worth to mention that for some input parameter(s) there is extra information that will appear by hovering over the .
Note: you can use the available link(s) in the last column of table to navigate to calculation page of input parameter(s) if needed.

NameInput Value - UnitConverted ValueValidityLink to Calculation Page
Temperature

677.67

°R

Pressure

3045

psi

Stock Tank Oil Specific Gravity (ɣo) More Details

44.2

deg API

Solution Gas Specific Gravity (ɣg) Weighted average of separated gas specific gravities from each separation stage
More Details

0.781

SG

 Solution Gas Specific Gravity (ɣg)
Bubble Point Pressure (Pb) Saturation pressure at reservoir temperature
More Details

3045

psi

 Bubble Point Pressure (Pb)
Separator Pressure Actual separator pressure (first stage separator pressure at two stage separation)
More Details

200

psi

Separator Temperature Actual separator temperature (first stage temperature pressure at two stage separation)
More Details

519.67

°R

Oil Density (ρo) More Details

44

lb/ft³ - pcf

 Saturated Oil Density (ρo,s)
Oil Formation Volume Factor (Bo) Experimentally measured Bo @ desired pressure
More Details

1.57

bbl/STB

Solution Gas/Oil Ratio @ Pb (Rs,b)

943

SCF/STB


CALCULATE

Results

The following table contains the calculated results based on the selected aforementioned correlation(s). In this table the input variable(s) of each correlation(s) is(are) checked to be in the valid range (if available). If the input value(s) are out of range, a popup message will be shown in Warnings column.

CorrelationCalculated ValueWarningsRemarks
1-Standing1005.882scf/STBCalifornia crude oils and natural gases
2-Glaso862.995scf/STBNorth Sea crude oil- Rs range is 90 to 2639 scf/STB
3-Marhoun840.163scf/STBMiddle Eastern crude oil systems- Rs range is 26 to 1602 scf/STB
4-Petrosky Farshad861.396scf/STBGulf of Mexico crude oil system- Rs range is 217 to 1406 scf/STB
5-Velarde et al943scf/STBRs range is 100 to 1800 scf/STB
6-De Ghetto et al0scf/STBRs range is 17 to 640 scf/STB
7-Vasquez and Beggs937.593scf/STBRs range is 0 to 2199 scf/STB
8-Material Balance1772.441scf/STB

Oil Gas Solubility (Rs) - Chart

The parameter considered for creating oil-gas solubility chart can be selected from the combo list filled using "Input Paremeters" names. It must be noted that the user must select the combo list parameter which is also active (visible) in "Input Paremeters" table. The following assumptions also must be considered using this tool:

  1. If the selected parameter is not used in selected correlation(s), that correlation(s) will not be displayed in the graph.
  2. By default, the minimum and maximum values of the selected parameter are considered equal to 0.5 and 1.5 times the corresponding value entered in "Input Paremeters" table. (The user is allowed to change the values resonably)
  3. Other essential parameter values needed are taken from the "Input Paremeters" table.
  4. The values calculated in the "Results" table are displayed as black dots on the graph.
Sensitivity Plot for selected variable on X-axis
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