(PLEASE HELP) What is the temperature of oil when it emerges onto the sea in the North sea. Is the oil directed to dry land from the well or does it have to go via the oil platform.

It depends on the well, tubing size and wellhead (eg. choke). The great majority go through a manifold/separator/platform.

North Sea oil wells may be on the production unit above sea level, or they may be on the seabed and conencted to a production unit via a short (a few km) pipeline.  On the production unit (which may be a platform fixed to the seabed or a converted oil tanker or a converted semi submersible rig), the oil goes through a very basic processing offshore: the produced fluids are a mixture of oil, water and gas, and the three things are separated in a separator.  

The oil, stable at roughly atmospheric pressure & temperature, is then either pipelined to shore, or stored on the production unit in big tanks and transferred to shore by oil tankers. The gas may be pipelined to shore or  used as fuel or injected back into the oil field.  The water, cleaned up of the oil, is dumped into the sea.

The wellehad temperture really depends upon the field: the deeper the field, the hotter the flowing wellhead temp.  'Normal' fields might be 80- 120°C, high temperature fields can have a Flowing Wellhead Temperature of as much as 200°C

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DrillerNic - Thanks for that interesting post. I was in oil sands and refining for 50 years and often wondered about wellhead temperatures.

HAZOP at www.curryhydrocarbons.ca

The wellheads that have been mentioned; are they surface wellheads or subsea wellheads?

Many Thanks

Surface wellheads are preferred- they're cheaper and much easier to get to.  But to have a surface wellhead offshore, you need a platform.  And platforms are expensive and reach a limit of about 1000ft of water (Shell's Congac platform was the deepest at about 1000ft).  The guyed tower concept was an attempt to push the fixed platform deeper; Lena is still the only such installation  I think.

So for deeper water, or for smaller fields that can't support the economics of a platform, you go for subsea wells and a floating host: FPSOs, FPFs.  Floating hosts are often cheap as you can use off the shelf tanker or semi sub designs (and Keppel FELS will build you a tanker in about 3 days).  You can even buy a semi or a tanker second hand and convert it.

The other application for subsea trees are for small satellite oilfields near an exisitng platform: in the North Sea now, many of the platforms no longer produce oil from the fields they were installed on, but from many, many other fields producing through subsea wells tied back to the platform by short, subsea infield flowlines.

The operational advantage of a surface, wellhead ("dry tree" is the jargon), is what has driven the efforts to come up with floating hosts that can use dry trees: TLPs, MiniTLPs, Spars, Deep draught semis and so on.