Pipeline end
terminators (PLET)/pipeline end manifold (PLEM), and inline structures (ILS)
are subsea structures designed to attach the pipeline end and then lowered to
the seabed in the desired orientation. The PLET/PLEM is located at the end of a
subsea pipeline, while the inline structure is located in the middle of
pipeline.
The design and
installation ofe PLET/ILS include first-end, middle, and second-end options.
The components of them may include from a single hub with manual isolation
valve, to two or three hubs with ROV actuated valves, chemical injection, pig
launching capabilities and more. The foundation of PLET/ILS may be a mudmat, or
a single suction pile. A rigid or flexible jumper is utilized to tie-in the
PLET/ILS to the other subsea structures, eg. Tree, manifold, or other
PLET/PLEM.
Subsea manifold is a flow-routing subsea hardware (subsea flow
router) that connects between subsea trees and flowlines. It is used to
optimize the subsea layout arrangement and reduce the quantity of risers
connected to the platform. If connected to dual flowlines, the manifold can
typically accommodate pigging and have the capability of routing production
from a particular tree to a particular flowline.
Pipeline End Manifold (PLEM)
It a simpler version of a cluster manifold generally designed to
direct fluids for only one or two subsea Christmas trees. A PLEM generally
connects directly to a subsea flow line without the use of a pipeline end
termination (PLET).
Source : https://oilandgastechnologies.files.wordpress.com/2012/08/sans-tithbre.png?w=640&h=327
A manifold is typically composed of the following major
components:
§
Pipework and valves – contains and controls the production and
injection fluids.
§
Structure framework – protects and supports the pipework and
valves.
§
Subsea connection equipment – allows subsea tie-in of multiple
pieces of equipment. Types include vertical, horizontal and stab-and-hinge-over
connections.
§
Foundation – interface between the manifold structure and seabed.
§
Controls Equipment – allows the remote control of any
hydraulically actuated subsea manifold valves and the monitoring of production
and injection fluids. Control pods may be either internal or external to the
manifold.
Valves
Valves on the manifold are essential for directing and controlling
the flows. They can be either manual or hydraulically actuated. Sometimes
chemical injection valves are placed on the manifold as well.
§
Branch valves are generally slab type gate valves (similar to tree
valves). Their sizes are based on the production/injection tree size.
§
Flowline header valves are also gate type, but ball valves have
been used previously. Their sizes are based on the flowline size.
§
Materials are chosen for compatibility with production and
injection fluids. Most of time, it is CRA-clad.
§
Double barrier philosophy generally used against production fluids.
§
Two valves in series
§
One valve and one pressure cap
§
Primary seal is generally a metal-to-metal seal
Pipework
A wide range of pipework configurations is possible. Each header
connects to an individual flowline. the pipework sizing is based on the tree
piping size and the flowline diameters. The main circuit is designed to
accommodate pigging operations. The material of construction needs to be
compatible with production and injection fluids.
§
Test headers can be incorporated to test individual or groups of
trees
§
Test headers can be a second or even third header isolated in the
manifold
§
Insulation may be required for unscheduled or emergency shutdowns
Control System
Control system for the manifolds is the same as the control system
for the trees. Multiple options for the control system have been used in the
manifold design
§
No controls on the manifold. The manifold is controlled by tree
subsea control modules (SCMs).
§
SCMs on the manifold.
§
Manifold with control system distribution units with flying leads
going to trees.
Framework Structure
The framework is a welded structure to provide support for the
pipework and valves and contain the foundation interface structure. The
pipework is allowed to float inside the framework within limits and it is not
rigidly attached to the frame. The frame can also be used for lifting and
landing of the jumper tie-in tools.
Foundation
§
Mud mats – a simple foundation resting directly on the seabed,
generally with a short skirt around the perimeter to resist lateral loads.
§
Piles – long cylindrical structures embedded into the soil
intended to hold a subsea structure above the seabed. Foundations may utilize
one or more individual piles.
§
Intermediate Structures – an intermediate structure can be used to
interface a subsea manifold with a pile foundation to reduce weight of the
manifold structure or to ease retrieval of the manifold. Intermediate
structures can be either retrievable or permanent structures.
Tie-ins to wells and flowlines
The tie-in hubs placed on the outer edge of the manifold, which
are used to tie-in jumpers that bring in fluid from the production wells and
export fluid into the flowlines (production manifold). The tie-in sizing is
based on the tree piping size and the flowline diameters. and the loads applied
from the flowlines
Insulations
Generally gas manifolds are not insulated and oil manifolds are
insulated. For oil production, insulation is necessary to allow adequate
cool-down time to treat or remove trapped production water. Gas production is
generally treated continuously with chemicals to prevent hydrates.
Deployment method
The following vessels are typically used for manifold deployment:
§
Drill Rig: through moon pool or keel-hauled on drill string
§
Heavy Lift vessels (Derrick Barges): through moon pool or over
side
§
Work-class vessels: over side on crane or winch
The following equipments are typically required:
§
Manifold hydraulic installation tool
§
Sling sets, either wire rope or synthetic fiber
Applicable API Specs
§
API Spec 17P – Templates and Manifolds
§
API Spec 17D – Specifications for subsea wellhead and Christmas
tree equipments
§
API Spec 17A – Recommended practice for design and operation of
subsea production systems
§
API Spec 17H, ISO 13628-8 – ROV Interfaces
Source:
Bai, Yong and
Qiang Bai. Subsea Engineering Handbook.
Tidak ada komentar:
Posting Komentar