Choke - AOF - Max Rate
Choke - AOF - Max Rate
(OP)
I apologize already if this is a dumb question. I am reservoir engineer and I am trying to learn some production engineering basics but don't have a good mentor to ask questions too. I have a well that was just perf and frac and is producing 3 MMcf/d on a 12/64 choke. There is 5000 psi wellhead pressure with 650 psi of line pressure. I understand at the current conditions the flow is critical and any reduction in the backpressure won't increase the rate for the given choke size, but I am wondering if there is a way to know what the rate would be as a function of the orifice size. The production engineer is babying the choke due to worries of bringing in tons of sand, due to this being a very unconsolidated formation, and I want to know what the rate would be if he wasn't babying it. Even if I don't have enough information to solve this I want to know if there are any rules of thumb that the wise old timers would use to get an estimate.
Thanks!
Thanks!





RE: Choke - AOF - Max Rate
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You can find on-line calculators too.
Also, most college fluid flow textbooks have what you need.
Perry's Chemical Engineers' Handbook has what you need.
Good luck,
Latexman
RE: Choke - AOF - Max Rate
RE: Choke - AOF - Max Rate
Good luck,
Latexman
RE: Choke - AOF - Max Rate
To answer your question, I will be changing the orifice and will hold the downstream pressure constant, the wellhead pressure will change and that is where I have been trying to go with this thread but haven't asked very well. Different gas wells have different inflow performances. In the first few weeks of production you don't know how large the "tank is" therefore if it is very large you change the orifice size and the wellhead pressure will only change a little; however, if you have a small "tank" and change the orifice size you will change the wellhead pressure alot. With this being known I didn't know if there were rules of thumb on how to go about this calculation with multiple things changing (orifice size and well head pressure). I think the answer is isochronal well testing. You fix the choke and measure the stabilized rate and wellhead pressure, change the choke multiple times and measure the same thing and solve Q=C(Pr^2-Pwh^2)^n with a semi log plot to get your deliverability equation (Beggs - Gas Production Operations. Is this thinking sound or am I missing anything.
An additional question. How do you do this analysis if you are critical (Pup=5000, Pdown=650 Pup/Pdo=13% well below the 55% needed for critical flow) because you will change the orifice size and you won't get a different wellhead pressure until you are sub critical, correct or incorrect?
I attached the spreadsheet with the data I am speaking about. At the 12/64 I am locked in around 3MM a day.
Thanks again replys are very appreciated!
RE: Choke - AOF - Max Rate
Keep the replies coming, your helping me work myself through actually visualizing this.
RE: Choke - AOF - Max Rate
Good luck,
Latexman
RE: Choke - AOF - Max Rate
q=878 x C x A x Pupstream * (big constant in square root)
combing all the constants
q= C x d^2 x P
d = (q/p)^1/2
all = signs should be proportional signs
So if I change the orifice diameter by 2 times lets say from a 12/64 to 24/64 and I held the wellhead pressure constant the rate would quadruple
On the flipside if I change the orifice diameter by 2 times and held the rate constant the well head pressure would be cut by 4. Is this true?
I know you can't assume either of these extreme cases when you go to a large orifice size or choke size but is there a rule of thumb somewhere in the middle like: "If you increase the orifice size by 2 (double it) the rate doubles and pressure is cut in half. The keeps the equation solved, just don't know if that happens in real life.
If there is no real of thumb, is the only way to solve this is to use the isochronal testing as I mentioned a few posts above at different choke size and see the relationship with pressure and rate with respect to choke size?
Thank you very much again for the replies, I promise I won't ask much more if anything.
RE: Choke - AOF - Max Rate
Good luck,
Latexman
RE: Choke - AOF - Max Rate
I'm new to this forum and I was wondering if you have any references for the spreadsheet you have created in this thread. Great spreadsheet btw! Thanks!