Calculating Standard Volume 1

[sysengineer]

I have a metering application (non-fiscal) for a test separator where there is a requirement to calculate standard volume of produced oil, gas and water from totalised gross volume. The current system monitors gas temperature and pressure and oil temperature automatically and is recorded for the entire test duration. A manual sampling and laboratory exercise is performed to determine oil and gas density at base conditions along with BS&W values. These results seem to be used to calculate standard volumes from the observed gross volume and averaged flowing conditions.

I have no information on what calculations are performed and to what standard although it is unlikely to meet any current petroleum metering standard. I need to upgrade this system but I have no idea how standard volumes for petroleum liquids and gas are calculated (I am instrumentation & controls biased).

Could anybody explain or refer me to some information that would help me to understand how standard volumes are calculated?

Also, is it possible at all to calculate standard volumes from just gross volume, BS&W and density and flowing and base conditions? or does the flowing pressure and temperature absolutely have to be known? (Hence why I would like to know how standard volumes are calculated)

Thanks

 

[LittleInch]

Try searching this site and you find things like this

http://www.eng-tips.com/viewthread.cfm?qid=194412

Try asking a meter vendor or do a seach on some of the better vendro websites and you'll figur eit out better than we can expplain it.

AGA8 is a commonly used set of calulations to obtain standard volumes, but yes, as far as I know, you need to input pressure and temeprature to get any sor tof a decent correction to standard volumes. Defining you stnadard conditions also helps as this can vary, surprisingly enough. The only real difference with fiscal systems is the accuracy and calibration of the sensors (flow, presusre, temp) and the power of the processing unit to undertake the calcualtions. Most also need the base conditions and or compositon loaded into them.

My motto: Learn something new every day

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

 

[sysengineer]

Actaully I found a fairly good website [URL unfurl="true"]http://www.squinch.org/[/url]

While it is very good at providing calculations to convert observed flowing densities to densities at base conditions it doesn't really explain how to convert then from gross to standard volume.

 

[zdas04]

LittleInch,
AGA 8 is all about calculating compressibility and "super compressibility". You meant to say AGA-3 or API 14.3.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"

 

[ScotchWhisky]

AGA8 will calculate a base density

 

[sysengineer]

Actually this raises a valid point. AGA8 will determine a base density but it does not calculate a volume correction factor. I'm still not sure how to calculate standard volume for gases.

For liquids an equivalent would be API chapter 11 table 53 which will calculate a volume correction factor given density at flowing conditions.

 

[zdas04]

There is no such concept as "volume correction factor" for gas. You input gas composition, meter configuration, upstream pressure, dP, and flowing temperature into the AGA-3 equation and get a standard volume out. No multipliers or fudge factors other than those in the AGA 3 equation.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"

 

[ScotchWhisky]

Is this a 2 or 3 phase separator? Which meters are installed?

 

[sysengineer]

Ok let me explain...

I have a gas meter (ultrasonic) which I have connected to a flow totaliser which calculates total gas volume over a test period. The gas is sampled during this test and density measured at flowing conditions then is corrected to density at base conditions using look up tables. I want to use the base density and flow conditions to correct the totalised flow volume to standard volume.

 

[dcasto]

Using look up tables, that's a four dimensional table. As stated above, at a minimum you'll need temperature, Pressure and gas gravity (which can be found with on line gravitometers, but normally by a gas chromatograph analysis). Next you'll need to know the composition to get an accurate super compressibility, but there are equations and some tables that will get you close enough for allocation measurement (nonfiscal ) Your ultra sonic measures velocity then arrives at cubic feet based on area of pipe and over time you get actual cubic feet and applying the gas laws you correct to standard conditions. The easiest way to picture this is to find the density at flowing conditions in Kg/m^3 then calculate density at your standard conditions. The density times the volumes = mass and mass is conserved

pv=znRT n and R are constants so v= zT/p

Their are loads of vendors including the one that sold you the ultrasonic meter that have all this automated in a flow meter, I can't believe that there isn't a flow meter with a totalizer somewhere in the whole package.

 

[ScotchWhisky]

Perhaps the meter can be reconfigured to output std volume?

Otherwise, you could convert your volume to mass using the density, then convert it again to std volume units using the std density. Quite messy though and unlikely to any reporting requirements.

 

[LittleInch]

I think you need something like this

http://www.elstermetering.co.uk/en/volume_correctors.html

My motto: Learn something new every day

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