Two flowlines(NB 6

[NimalJayaratne]

Hi all
Has anyone of you come across a situation where two flowlines(NB 6&quotare connected to another larger line (NB 8&quot? The wellheads are high pressure(340 barg) and high velocity. I am keen to know your experiences in the selection of a suitable tee for connecting the two branches. Material is duplex stainless steel to ASTM A790 Gr 31803. Lighter the weight the better from stress point of view. Note that the wells are growing around 8" under flowing conditions.

I guess erosion is a major worry...Has anyone used Anson flow tees (which are normally used in mud and cement injection into well heads)in this service? Anyone with experience, please comment.
Thanks for your help.

 

[mgp]

Use a standard reducing tee to ASME B16.9.

I've worked on a project where six 8" flowlines were tied into a 20" manifold by weldolets (with similar material). Sometimes it may be more feasible to use an extruded manifold but in your case I guess having only two flowlines and going from 6" to 8" only, I don't see why you should not use standard fittings.

You still have to make considerably long flowlines to make an acceptable design which can cope with the 8" vertical wellhead/Xmas tree expansion. You should also check for:

1.Horizontal and angular deflection of wellheads depending on layout of conductor guides

2. Platform settlement. How much is a platform allowed to sink before flowlines should be re-analysed and maybe modified. This settlement should be included also in the initial analysis.

Extent of erosion depend very much on the nature (sand content) of the production fluid. This should be stated in the design spec.

Tee's may be a solution although I don't have any experience with the Anson Tee's.

Erosion problems will be worst after the choke valve.
You should ensure to have at least 1.5-2 meter of straight pipe downstream the choke valve. (I've seen a tungsten carbide trim of a choke valve which were cut up like butter by sand.)

I know that Shell has a spec for wellhead flowline and manifold design but I don't have a copy. Have you checked with the company you work for if they have any?

regards

Mogens

 

[NimalJayaratne]

Thanks Mogens for that. Yes I have considered the settlement in the analysis and the length of the flowline was determined with appropriate criteria...I appreciate your comments of the conductor movements. The design was completed a year and a half ago and the platform was completed and the drilling phase started... with individual 6" flowlines. The operator has realised that the well is capable of producing a lot more than that could be handled by a 6" line hence he is trying to 'dual' the flowline to get more production out. Hence the rush.
I have a copy of the Shell spec but it does not say much about the tees.
Regards