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GOR - What is it?

Introduction

GOR or the Gas Oil Ratio is a common property in the Oil and Gas Industry. It is a representation of one of the key variables in a process – the ratio of vapor to liquid. It is usually used to indicate the amount of associated gas that will evolve when crude oil is brought to atmospheric conditions, but it is used in other contexts as well.

For something that is essentially the volume of gas divided by the volume of liquid, we receive a lot of inquiries about this property. Let’s explore why the GOR is significant and how the Symmetry process software platform calculates the property.

GOR – Where is it in the Symmetry Process Platform?

In the Symmetry process platform, the user interface was improved to ensure that a user shouldn’t have to look very far for a property. We introduced the More Properties tab in the Material Stream Unit Operations, and here the category of appropriate properties can be selected.

For GOR, enable “Phase Flows” in the More Properties Tab:

GOR_1.png

The GOR is presented on the Phase Flows Tab:

GOR_2.png

Note:

  • In this stream, there is a mixture of Gas and Oil with a GOR of 15 SCF/bbl.
  • There is no water in this mixture, so the GLR (Gas to Liquid Ratio) has the same value.
  • For completeness, the CGR (Condensate to Gas Ratio) is 2799.9 gal / MSCF, which is the inverse of the GOR presented in different units.

Keep in mind that any property of interest in the stream can be shown on the PFD by right-clicking and selecting “Add to PFD Datasheet”:

GOR_3.png

“Stream” is all liquid – how can this fluid have a Gas to Oil Ratio of 15 SCF/bbl?

GOR – How is it calculated in the Symmetry Process Platform?

In the Symmetry process platform, we define the GOR to be the amount of gas evolving from the oil at reference conditions, which are by default 60 F and 1 atm. The Volume of Gas is measured at Standard Conditions (Standard Volume units) and the Volume of Liquid is measured at Reference Conditions.

Keep in mind that the tooltip of the variable can provide additional information not presented on the form:

GOR_4.png

Let’s model this calculation on the flowsheet level for the scenario presented above: 

GOR_5.png

  • Reference Conditions are 60 F and 1 atm (default).
  • The separation of the gas and oil is done at reference conditions.
  • The volume of gas is measured at standard conditions, which in this case is also 60 F and 1 atm.
  • The volume of liquid is measured at reference conditions.

In other words, the separation is done at Reference Conditions, the Volume of Gas is equivalent to the Standard Gas Volume Flow, and the Volume of Oil is the Actual Volume Flow at separation (i.e. reference) Conditions.

GOR – Why is it in the Symmetry Process Platform?

A common request is for the ability to specify GOR at the inlet separator. Usually, this inlet separator is not at standard conditions. The Reference Conditions can be changed to adjust the conditions that the flash is performed at, but keep in mind that the Gas Volume will still be calculated at Standard Conditions.

Any volume ratio can be calculated or input into the Symmetry process platform, but both the conditions at which the separation is performed and the conditions at which the volume is measured must be known.

Additionally, the PVT Unit Operation can be used to provide the Solution Gas to Oil Ratio (Rs) and the Separator Gas to Oil Ratio (Sep Rs). These ratios are sometimes referred to interchangeably with the label “GOR” so it is important to know the convention being used.

Finally, the GOR or other Ratios can be useful parameters to define the basis of flow into a specific system. In the Process workspace the Recombination Unit Operation can be used for this purpose, as the Gas, Condensate, and Water Flows can be specified out of the Recombination as they appear out of a separator. In the Pipe workspace the user can define the GOR, GLR or Water Cut of a Source into the system. 

Linnea Russell, P.Eng, VMG Calgary

Please contact your local VMG office for more information.

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