Subsea production trees can be segmented into
two main types: horizontal trees and vertical trees. Horizontal trees
are so called because the primary valves are arranged in a horizontal
configuration, and likewise vertical trees have the primary valves
arranged in a vertical configuration.
A
key requirement of a subsea tree is that access is enabled to the “A”
annulus between the production tubing and casing. This is required for a
number of reasons, including pressure monitoring and gas lift. As an
example, any pressure buildup in the A annulus can be bled to the
production flowline via a crossover loop on the tree.
The
original designs of subsea vertical trees and tubing hangers were of a
dual-bore configuration. Prior to removal of the BOP, it is necessary to
set plugs in both the production and annulus bores. Access to both
bores requires the use of a dual-bore riser or landing string. The
handling and operation of dual-bore systems compared to monobore systems
is more complex, and time-consuming and, therefore, more costly.
On
a horizontal tree, access to the A annulus is incorporated into the
tree design and controlled by gate valves rather than plugs. This
enables operations with a mono-bore, less-complex riser or landing
string, which can deliver significant advantages, particularly in deep
water. It is exactly this logic that led to the introduction of
tubing-head spools for use with vertical trees, thereby offering many of
the advantages of a horizontal tree.
Daftar Pustaka :
http://www.epmag.com/drivers-influencing-evolution-horizontal-and-vertical-trees-698041#p=2
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