3 replies to this topic

[chemtan]

I had a query from site on a well head flow line.. while investigating the process (as it was designed by another engineer who is not with the company any more), I found that the pressure profile given to engineer was:

Inlet flow before choke valve:

2008: 0 psia @
2009: 3244 psia @ 36.28 MMSCFD
2010: 3338 psia @ 30.56 "
2011: 3187 psia @ 30.56 "
2013: 3103 psia @ 20.66 "
2015: 2633 psia @ 27.49 "
2017: 1932 psia @ 30.12 "

Required pressure are plant battery limit (13KM from well head) is 1215psia.

The engineer estimated that the inlet of choke valve is at 1800psia and DP across valve is 292psi, 8" line was selected that provides the flow at 1215psia.

My concern:
1. what could be the reasons for selecting choke valve inlet pressure of 1800psia when there were greater pressures available for design estimates?

Is there anything that I'm missing here? Would appreciate if someone can help me understand.

[mehran_ghasemi]

I had a query from site on a well head flow line.. while investigating the process (as it was designed by another engineer who is not with the company any more), I found that the pressure profile given to engineer was:

Inlet flow before choke valve:

2008: 0 psia @
2009: 3244 psia @ 36.28 MMSCFD
2010: 3338 psia @ 30.56 "
2011: 3187 psia @ 30.56 "
2013: 3103 psia @ 20.66 "
2015: 2633 psia @ 27.49 "
2017: 1932 psia @ 30.12 "

Required pressure are plant battery limit (13KM from well head) is 1215psia.

The engineer estimated that the inlet of choke valve is at 1800psia and DP across valve is 292psi, 8" line was selected that provides the flow at 1215psia.

My concern:
1. what could be the reasons for selecting choke valve inlet pressure of 1800psia when there were greater pressures available for design estimates?

Is there anything that I'm missing here? Would appreciate if someone can help me understand.

[mehran_ghasemi]

I think the required flow rate for the life time of project and well head flowing pressure is the result which should be considered as minimum available pressure to design the minimum DP of chock valave as well as pipe line sizing.

[kkala]

My first interpretation on the issue is as follows.
Min required pressure at plant BL (13 km off) 1215 psia
ΔP by the Engineer along the 8" pipe (flow?) 293 psia
Min required pressure downstream of valve 1508 psia
Conservatively selected pressure upstream of valve P 1800 psia
Consequently ΔP across the choke valve 292 psia
So the Engineer has probably chosen minimum P=1800 psia for the specified flow, assuming that a system inside plant BL can handle any pressure exceeding 1215 psia. Downstream pressure of choke valve does not influence flow, it is the downstream conditions to BL that create the pressure of 1508 psia.
Nevertheless the assumption of chocked flow does not seem correct in this specific case. Chocked flow in gas valves occurs when downstream pressure is about half the upstream P, I think. This is not the case (under the data assumed in my interpretation) even if downstream pressure is considered as 1215 psia (I am not aware about choked flow in pipes, though).
Besides, reported ΔP is pressure drop across valve or along the 8" pipe? (figures practically same).
Hope above helps, even though problem is not solved.