Oil and gas production handbook An introduction to oil and gas production

Vertical tree. Christmas trees can also be horizontal where the master, 
wing and choke are on a horizontal axis. This reduces the height and may 
allow easier intervention. Horizontal trees are especially used on subsea 
wells. 
3.5.1 Subsea wells 
Subsea wells are essentially the 
same as dry completion wells. 
Mechanically, however, they are 
placed in a subsea structure 
(template) that allows the wells to 
be drilled and serviced remotely 
from the surface, and protected 
from damage, e.g., from trawlers. 
The wellhead is placed in a slot 
in the template where it mates to 
the outgoing pipeline as well as 
hydraulic and electric control 
signals. 
Ill: Statoil
 
 
Control is from the 
surface, where a hydraulic 
power unit (HPU) 
provides power to the 
subsea installation via an