Is P2 after the oriffice the same even when P1 changes?

[Iradah]

Hello,

If I have an orifice with a certain area, What happens to the flow rate calculation if the pressure of the inlet gas to the orifice increased but the standard volumetric flow rate is the same? will this affect the flow rate calculated from Bernoulli’s equation? this will affect the flow rate if the pressure at the outlet of the orifice stays the same. So, is the pressure drop constant? or Pressure after the orifice is the same when the pressure of the fluid before the orifice is increases?

 

[MortenA]

Even with choked flow you cant change one parameter and keep all other constant.

Std. flow is just another word for molar flow, and if the MW of the gas does not change then its also fixed mass flow. So unless you have a variable choke (also known as a valve ;-) ) then either upstream pressure, temperature or downstream pressure must change.

So if the pressure increases while the downstream pressure is constant then the flow rate (be it mass, molar or std. volume flow) must increase. For the un-choked its the same - but its a different formula. Looking for a good formula for choked flow? Check API 520.

Best regards

Morten

 

[Iradah]

Thank you MortenA for your reply.
I asked this question because for last few months, the flow from one of the gas wells is showing a sudden increase and then drops gradually. when the flow was compared to the well head pressure, it was found that the flow follows the Well head pressure. as the pressure increases the flow increases. the increase in the well head is big and not understandable at least for me as a chemical engineering graduate and not petroluem. I thought about the flow rate, is it real or it is affected by pressure? I mean that what we can see is a calculated flow rate from the pressures up and down stream the orifice meter, so if the pressure up stream increased for the same flow rate and the pressure down stream remained the same, this will give a higher delta P across the orifice and consequently a higher calculated flow rate which we see in the chart. From the chart attached, do you think that this well performance is real or there is some measurment issue?? Do you think that the well head P can increase like that?

Regards, Iradah

 

[chemebabak]

Iradah,

It appears that your question is not regarding P1, P2 or flow rate. What you really want to know is what the conditions are that cause the wellhead pressure to jump up and down as shown in the graph. This is a question best answered by the petroleum engineers in the Petroleum Production engineering forum.

http://eng-tips.com/threadminder.cfm?pid=469

With respect to the flow vs. DP issue:
1. Increased DP across the orifice measures increased flow.
2. Increased P1 pressure at the wellhead forces more flow through the pipes.