2 choke valves in series

[d.durante4486]

Hi everybody,
I'd like to know if anybody has ever considered in its design the possibility of installing a set of two choke valves in series on a XT, namely a non-regulating choke valve, whose opening should be sized to reduce the well pressure to a desired value, followed downstream by a traditional flow control choke valve.
Which are the advantages of such a configuration? Does it help in some way with hydrate formation control in very high pressure wells?
API 14E quotes that the number and location of chokes depend on the amount of pressure drop, well fluid, flow rate and possible solids presence. Furthermore in Chapter 5 of "Lease Pumper's Handbook" it is reported that "Permitting this pressure reduction to occur in two steps instead of one can reduce the possibility of the line freezing", but since the cooling of the fluid across the choke is due to the Joule-Thomson cooling effect, I think that no matter in how many steps I reduce the pressure from P1 to P2, the final T2 should be the same (give or take, we are moving along the same isoenthalpic curve).

Thank you in advance for your help..

[kochichiro]

Well, when you are installing two chokes of decreasing sizes, you’ll actually receive pretty large temperature drop. I saw old USSR well tests were two chokes were used to lower pressure in flow line on wildcat wells. During testing with two chocks flow line temperature was lowered from +10 deg C (with one choke) to -30 deg C (with two chokes) and severe hydrate formation occurs.
From the other hand, I saw one well where cascade of chokes with increasing sizes were used to fight against hydrate and solids precipitation.

[d.durante4486]

Thank you kochichiro..
the problem is that I'm not confident enough to say that this technical solution (i.e. providing two choke in series on the production string of a very high pressure well) could be an effective method to prevent/reduce the heavy issue of hydrate formation across choke valve.

[kochichiro]

Well, actually I cannot say that increasing chokes cascade was terribly effective, the temperature remained at minus values, and thus they used methanol injection. Personally, I think that is the best option available.
The reason USSR drilling teams used decreasing chokes in line, was pretty simple. Sometimes wellhead pressure was higher than expected and there was no test separator readily available with such pressure ratings, so they had to lower pressure in flow line before the separator with any possible means.

There is also common practice on some of Russian fields to use double choking in condensate stealing, but I think that is too exotic XD