API gravity

[KMur]

Dear All,
I need to calculate the API gravity for crude oil to calculate corrosion rate for each stream. We have the data water specific gravity, gas specific gravity and oil specific gravity separately, How to calculate the API gravity for crude oil based on these 3 values???
Number of lines are coming from different wells and having different specific gravitites. How to find the common API gravity among these?

Thanks to all

 

[zdas04]

The definition of °API is:

°API=(141.5/SG[sub]at 60F[/sub])-131.5

(pure water has a °API of 10, lower numbers than 10 will not float on water)

If you want a blended mix SG, you have to know the relative mass flow rates of the three components. Multiply each mass flow rate times its SG (relative to water, the 0.7 SG you have for gas is relative to air, convert it to water and get a really tiny number). Add the three products together and divide by the sum of the mass flow rates. Use this SG in the equation above.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

 

[LittleInch]

Whilst I suppose you could calculate a three phase API gravity, I've only ever heard of it applying to the dead crude density. Make sure whatever calculation you're using this in actually needs a combined number. I suspect that information would be quite difficult to obtain as the density of live crude varies depending on the pressure and amount of gas dissolved in it. A blended crude density is simply a multiplication of the density by the fraction that makes up of the total then convert back to API.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[KMur]

Thank you very much for your valuable suggestion.
I need to ask one thing, Can I use oil specific gravity to calculate API gravity instead of blended mix SG?

 

[zdas04]

For almost every use of API Gravity, LittleInch is absolutely correct. For the empirical corrosion calculations that you referenced you have to simulate a "live crude" API by combining the streams on a mass average basis. That equation is pretty weak, but getting to a live crude basis helps some.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist