Conduits to transfer materials from the seafloor to
production and drilling facilities atop the water's surface, as well as from
the facility to the seafloor, subsea risers are a type of pipeline developed
for this type of vertical transportation. Whether serving as production or
import/export vehicles, risers are the connection between the subsea field
developments and production and drilling facilities.
Similar to pipelines or flowlines, risers transport produced
hydrocarbons, as well as production materials, such as injection fluids,
control fluids and gas lift. Usually insulated to withstand seafloor
temperatures, risers can be either rigid or flexible.
Types Of Risers
There are a number of types
of risers, including attached risers, pull tube risers, steel catenary risers,
top-tensioned risers, riser towers and flexible riser configurations, as well
as drilling risers.
The first type of riser to be
developed, attached risers are deployed on
fixed platforms, compliant towers and concrete gravity structures. Attached
risers are clamped to the side of the fixed facilities, connecting the seabed
to the production facility above. Usually fabricated in sections, the riser
section closest to the seafloor is joined with a flowline or export pipeline,
and clamped to the side of the facility. The next sections rise up the side of
the facility, until the top riser section is joined with the processing equipment
atop the facility.
Also used on fixed
structures, pull tube risers are pipelines or
flowlines that are threaded up the center of the facility. For pull tube
risers, a pull tube with a diameter wider than the riser is preinstalled on the
facility. Then, a wire rope is attached to a pipeline or flowline on the
seafloor. The line is then pulled through the pull tube to the topsides,
bringing the pipe along with it.
Building on the catenary
equation that has helped to create bridges across the world, steel catenary risers use this curve theory, as well. Used to connect the
seafloor to production facilities above, as well as connect two floating
production platforms, steel catenary risers are common on TLPs, FPSOs and
spars, as well as fixed structures, compliant towers and gravity structures.
While this curved riser can withstand some motion, excessive movement can cause
problems.
Multiple Riser Configurations
Source : http://www.atlantia.com/seastar/
Used on TLPs and spars, top-tensioned risers are a completely vertical riser system that terminates
directly below the facility. Although moored, these floating facilities are
able to move laterally with the wind and waves. Because the rigid risers are
also fixed to the seafloor, vertical displacement occurs between the top of the
riser and its connection point on the facility. There are two solutions for
this issue. A motion compensator can be included in the top-tensioning riser
system that keeps constant tension on the riser by expanding and contracting
with the movements of the facility. Also, buoyancy cans, can be deployed around
the outside of the riser to keep it afloat. Then the top of the rigid vertical
top-tensioned riser is connected to the facility by flexible pipe, which is
better able to accommodate the movements of the facility.
Top-Tensioned Risers
Source : http://www.atlantia.com/seastar/images/scenarios_wettree2.jpg
First used offshore Angola at
Total's Girassol project, riser
towers were built to lift the risers the considerable height
to reach the FPSO on the water's surface. Ideal for ultra-deepwater
environments, this riser design incorporates a steel column tower that reaches
almost to the surface of the water, and this tower is topped with a massive
buoyancy tank. The risers are located inside the tower, spanning the distance
from the seafloor to the top of the tower and the buoyancy tanks. The buoyancy
of the tanks keeps the risers tensioned in place. Flexible risers are then
connected to the vertical risers and ultimately to the facility above.
Hybrid Riser System
Source : http://www.2hoffshore.com/riser_engineering/freestanding.php
A hybrid that can accommodate
a number of different situations, flexible
risers can withstand both vertical and horizontal movement,
making them ideal for use with floating facilities. This flexible pipe was
originally used to connect production equipment aboard a floating facility to
production and export risers, but now it is found as a primary riser solution
as well. There are a number of configurations for flexible risers, including
the steep S and lazy S that utilize anchored buoyancy modules, as well as the
steep wave and lazy wave that incorporates buoyancy modules.
While production and
import/export risers transfer hydrocarbons and production materials during the
production phase of development; drilling
risers transfer mud to the surface during drilling
activities. Connected to the subsea BOP stack at the bottom and the rig at the
top, drilling risers temporarily connect the wellbore to the surface to ensure
drilling fluids to not leak into the water.
Reference :
http://www.rigzone.com/training/insight.asp?insight_id=308&c_id=17
Dega Damara Aditramulyadi
Student ID : 15512046
Course : KL4220 Subsea Pipeline
Lecturer : Prof. Ir. Ricky Lukman Tawekal, MSE, Ph. D.
Eko Charnius Ilman, ST, MT
Ocean Engineering Program, Institut Teknologi Bandung
No comments:
Post a Comment