Manifold design tips.

1. May 07, 2014
Yutaek Seo
해양 자원 개발 시스템 개론
: Introduction to Offshore Petroleum Production System

2. Subsea manifolds
Vincent oil field
: gather production fluids and gas from wells via rigid spools,
: transfer them to FPSO via flowlines and risers
: Manifold A direct treated gas from FPSO to gas reinjection well
: Manifold A and B direct treated gas into the wells for gas lift
: They control the individual flow from each of wells and to gas injection wells
: Size W19m * D12m * H10m (228 m2), weight 250 tonnes
: Foundation include an inbuilt mud mat for a stable base and to prevent sinking or sliding
Actually 10-slot manifold
(6 production, 1 gas injection, 1 distribution)
Actually 7-slot manifold
(4 production, 1 distribution, 2 tie-in points)

3. • Ichthys gas field

4. • Subsea manifolds have been used to simplify the subsea system,
minimize the use of subsea pipelines and risers, and optimize the fluid
flow of production in the system.
• The manifold is an arrangement of piping and/or valves designed to
combine, distribute, control, and often monitor fluid flow.
• Subsea manifolds are installed on the seabed within an array of wells
to gather produced fluids or to inject water or gas into wells.

5. • The subsea manifold system is mainly comprised of a manifold
and a foundation.
• A manifold is a structural frame with piping, valves, control
module, pigging loop, flow meters, etc.
• The foundation provides structural support for the manifold. It
may be either a mudmat with skirt or a pile foundation,
depending on seabed soil conditions and manifold size.
• The structure includes bottom frame/guide base/support
structure providing an interface between the manifold and
foundation. It also includes protection structure.

6. Manifold types
• Production and/or test manifolds, for controlling flow of
individual wells into production and test headers, which is
connected with pipelines;
• Gas injection manifolds, for injecting gas into the riser base to
decrease slugs in the production flow;
• Gas lift manifolds, for injecting gas into the tubing to lighten the
fluid column along the tubing in order to increase oil production;
• Water injection manifolds, for supplying water to the last valve
in the well before the shutdown valve to increase oil production.
• A template is a subsea structure on the seabed that provides
guidance for drilling or other equipment. It is typically used to
group several subsea wells at a single seabed location.

7. ISO/FDIS 13628-15
Petroleum and natural gas industries –
Design and operation of subsea production
Systems –
Part 15:
Subsea structures and manifolds

8. 1. Scope
• Equipment within this scope
: Structural components and piping systems of subsea production system
- Production and injection manifolds
- Satellite and multiwell templates
- FRB, ERB, PLEM, PLET, T- & Y- connection, SSIV
: Subsea controls and distribution structures
: Protection structures

9. • Outside the scope
: Pipeline and manifold valves
: Flowline and tie-in connectors
: Choke valves
: Production control systems

10. 3. Terms, abbreviated terms, and definitions
3.1.6 manifold
: Systems of headers, branched piping and valves used to gather produced fluids
or to distribute injected fluids in subsea oil and gas production systems.
: valves,
: connectors for pipeline and tree interfaces,
: chokes for flow control,
: control system equipment (distribution for hydraulic and electrical functions),
: interface connections to control modules,
: header can include lines for water or chemical injection, gas lift and well control
3.1.6.1 cluster manifold
: structure used to support a manifold for produced or injected fluids
Note – there are no wells on a cluster manifold

11. 3.1.17 template
: seabed structure that provides guidance and support for drilling and includes
production/injection piping
Note 1 typically comprises a structure that provides
- A guide for drilling and/or support for other equipment
- Provisions for establishing a foundation
: typically used to group several subsea ells at a single seabed location
Note 2 production from the templates can flow to floating production systems
Note 3 Templates can be of a unitized or modular design
3.1.17.1 modular template
: installed as one unit or as modules assembled around a base structure
3.1.17.2 drilling template
: multi-well template used as a drilling guide to perdrill wells prior to installing a
surface facility

12. 4. Manifold and template functional considerations
4.1 General
: Manifold system design typically fulfils the functions of gathering and/or
distributing fluids, direct flow through headers, allow isolation of individual well slot
from header, incorporate flowline connections, and allow continuity of pigging
: The end user should define or approve the performance and configuration
requirements
- Performance: P&T ratings, WD, design life, geotechnical & geomechanical
data, metocean data
- Configuration: max. dimension, weight, interfaces, P&ID, materials, dropped-
objects protection, over-trawling requirement
: All equipment should be designed to comply with the end user’s product
requirement (P&T rating, installation, and operation environment)
: Material selection for individual components should meet the requirements of
ISO 13628-1 concerning
- production, injection fluids, and completion fluids for wetted area
- Exposure to chemical injection and service fluids

13. 4.2 System requirements
: Installation
- transportation, lifting, installation, abandonment
: Drilling/Commissioning
- pull-in, connection and testing
- Well drilling, completion, workover, and XT installation
- Precommissing and commissioning
: Production/Injection
- Injection of chemicals, MeOH or MEG
- Thermal performance
- Pressurization and depressuization of piping system, well testing, barrier testing
- Planned and emergency shutdown of wells and manifold
- Pigging
- ROV/ROT inspection and intervention
- Seawater ingress during tie-in operations
- Corrosion and erosion protection
- Monitoring WT, flow rate, pressure drop, composition, flow regime

14. 4.3. System interfaces
: should maintain integrity and functionality in the service conditions
: take into account the following
- Pressure, internal & external
- Temperature, expansion & contraction
- Zero leakage and seawater ingress
- Protection against dropped objects and fishing gear
- Structure settlement
- External: Marine growth, scaling, loads for installation, pull-in & connection,
ROV impact
- Internal: corrosion & erosion, hydrate formation
- Life span, serviceability, control connection, and chemical injection
: Interface data sheet describes design limitation, weight, and dimensions for well
system, installation contractor, and jumpers

15. 4.4 Cluster manifold requirements
: consists of a framework that supports piping, pull-in and connection equipment
and Protective framing
: commingles flow from a number of subsea wells into one ore more headers
: includes control module, subsea distribution unit, and electrical distribution unit.
: provide Alignment capacity for interface with other subsystems
: provide for a guidance system to support operations
4.5 Template system requirements
: Framework supports manifolds, risers, drilling and completion equipment, pull-in
and connection equipment, and protective framing as one integrated structure
: provide a guide for drilling and completion interface, and mechanical positioning
and alignment for the trees
: provide Alignment capacity for interface with other subsystems
: provide for a guidance system to support operations

16. 5. Design consideration
5.1 System design
The manifold should provide a sufficient amount of piping, valves, and flow controls
to, in a safe manner, collect produced fluids or distribute injected fluids such as gas,
water, or chemicals. Following information needs to be considered or provided from
the end-user
5.1.1 Number of wells
: greatly influence the size and design
5.1.2 Well spacing
5.1.3 Maintenance
: Clear access space, retrievable components, height above seabed, fault detection
5.1.4 Barrier philosophy
: Two barriers for pressurized manifold piping
: One barrier for non-pressurized manifold piping
5.1.5 Safety
5.1.6 External corrosion protection design

17. 5.1.7 Templates
: Integrated or modular template
: field development strategy, schedule, infrastructure
: reuse of predrilling wells
: onshore facilities and infrastructure
: installation availability

18. 5.2 Loads
5.2.1 External loads
: Applicable loads – fabrication, storing, testing, transportation, installation,
drilling/completion, operation and removal
: Accidental loads (project specific) – dropped objects, snag loads, abnormal
environmental loads like eqrthquakes
: ISO 13628-1 and NORSOK U-001 for protection against trawl load and dropped
object
5.2.2 Thermal effects
: End user is responsible for specifying or approving the temp. requirement
5.2.3 Templates
: Drilling loads can be transferred into the structure and the structure
accommodates all loads addressed in ISO 13628-1 including
- Drilling loads
- Thermal expansion of casing
- Tie-in loads and flowline expansion
- Impact

19. 5.3. Piping design

20. 5.3.1 General requirement
Manifold systems
: have sufficient piping, valves, and flow controls to gather produced fluids and/or
distribute injected fluids
: provide for the connection of flowlines and the connection to the tree
: designed to account for hydrostatic loads
: have appropriate valve and line-bore dimension to allow pigging
Recommendations
: The minimum length of straight pipe downstream of the choke valve should be
seven times the pipe ID
: The size (ID, WT) should be determined from well flow rates and pressure
: Fluid velocities is considered to reduce pressure drop and erosion
5.3.2 Applicable piping codes
ASME B31.8, ASME B31.4, ASME 31.3, ASME VIII, DNV-OS-F101, DNV-RP-
F112 or API Spec 1111.

21. 5.3.3 Pigging
: The diameter of the testing gauge plate is 95% of nominal ID of manifold header
piping
: All piping include a minimum bend radius of 3D nominal
5.3.4 Erosion
: Critical flow velocity can be calculated as given in ANSI/API RP 14 E to
determine critical production rate and required erosion allowance
5.3.5 Flow assurance
: avoid/minimize low points, dead ends, location of possible water accumulations
to prevent hydrate formation
: ISO 13628-1:2005
: MEG distribution for gas producing manifolds

22. • The manifold piping loop is designed to allow passage of pigs through the main
headers to provide round-trip pigging of the flowlines from the production
platform.
• Pigging loop system design should consider the following:
: Piping size
: Bend radius
: Valve types
: Pig launcher/receiver
: Pig location determination

23. 5.4 Structural design

24. 5.4.1 General
: ISO 19900, ISO 19902, API RP 2A
: The classification of structural components and welds joint shall be used to
determine material selection, joint design, welding requirement, type of inspection
5.4.2 Bottom frame/guide base/support structure
: The structure transfer all design loads from interfacing system and equipment to
the foundation system.
: Loads from soil condition, well system, bottom frame against vertical deflection,
structure/well interface design, casing thermal expansion
: alignment capability for interface between subsystems (wellhead, tree, etc) and
piping systems, PLET, and installation aids.
5.4.3 Protection structure
: Size should take into account all fabrication, installation and operational
tolerance of the structure and production equipment
: Height – minimized but avoid the physical contact of the roof with the production
equipment in case of dropped-object impact
: Roof hatches for simultaneous operation, retrieve, and access of ROV
: Wire guide on protective cover

25. 5.5 Foundation design
• The anchoring systems were designed based on soil conditions and load
considerations and can be categorized into three groups

26. • A suction pile or anchor is a cylindrical unit with an open bottom

27. 5.5.1 General
: The foundation design should be selected based on site-specific soil conditions
: Configurations include mudmats, skirts, driven piles, suction piles, conductors,
or combination of these
: Design consideration
- Seabed slope, suction loads, well-supporting structures, arrangements for air
escape, skirt foundation for self-penetration
- Impact of heat from produced hydrocarbons, if gas hydrates are present (in soil)
5.5.2 Requirements
: The foundation design should be able to withstand loads from tie-in of flowlines,
spool-pieces, pipelines, umbilicals and other flowlines.
: A system for measuring well growth and settlement
: Erosion/washout due to drilling – 2% of the circumference of one foundation
should be considered eroded when drilling through the same conductor
: Contingency methods where the foundation fails to penetrate into the seabed.
(adding weight or filling grouting into the skirt compartment)
: Suction piles, Driven piles, Skirted structures, Non-skirted structures

28. 5.5.3 Levelling
: subsea systems require that the manifolds be reasonably level in their final
position for proper interface and mating of the components and subsystems.
: one- & two-sat slips between piles and pile guides, jacking systems at the
template corner, and the active-suction method
: Template level within 0.5o, Cluster manifold and PLEMs level less than 1.0o.
5.5.4 Grouting system
: A stab/receptacle system for contingency grouting of suction anchors should be
provided

29. 5.6 Components
5.6.1 General
: valves, controls, and connectors
: Table 1- Industry standards for manifold components
5.6.2 Chemical injection
: layout and arrangement of the chemical injection piping and valves should be
evaluated
: Location of injection points in the manifold header should be approved by the end
use
5.6.3. Fluid characteristics should be considered
: Produced hydrocarbons, formation water, completion fluids, injected water and
gases, and injected chemicals
: pour point, P, T, composition, viscosity, gas/oil/water ratio, sand/paraffin/hydrate,
corrosivity.

30. Subsea valves - Ball valve
• Ball valves also are proven items and their use in deeper water depths is
increasing.
• In some deepwater applications, ball valves can provide operational and cost
advantages over gate valves, and improvements in non-metallic seals and
coatings are raising the reliability of ball valves.

31. Subsea valves - Gate valve
• Gate valves have a long history of use in subsea blowout preventer (BOP)
stacks, trees, and manifolds and are considered reliable devices because both
the valve and the valve actuators have been through extensive development
with proven field use and design improvements.

32. Chokes
• The choke is used to control the flow of the well by adjusting the downstream
pressure in a production manifold or upstream pressure in an injection manifold
to allow commingled production/injection.
• For diverless subsea manifolds, hydraulic-actuated variable chokes are used.
These chokes can be residents at the manifold or installed at retrievable
modules.

33. 6. Verification and validation of design
6.1 Design verification
: Design verification should be performed to ensure the design output has been met.
: Design verification can achieved by
- Producing design documentation such as drawing, specifications, and procedures
- Performing design calculations (structural analysis, piping analysis, material
selection analysis)
- Performing design reviews (inputs, outputs, material selection, customer
requirements, internal/external interfaces, ease of maintenance and operation,
installation and retrieval issues)
- Hydrostatic testing (Factory acceptance testing)
individual component check
subsystem check
interface check
unitized system check

34. 6.2 Design validation
: Design validation is performed to ensure that the specific operational requirements
have been met
: Design validation is achieved by
- Performing first article testing
- Performing qualification testing
- Performing system integration testing
: Tests should include simulations of actual field and environmental conditions
: Performance tests can supply data on response time, operating pressures, fluid
volume, and fault-finding and operation of shutdown systems.
: Individual components should be qualified independently (Qualification testing)
: System integration testing
- Simulate all operations that can be done offshore, to the extent practical, and to
verify all equipment/systems related to the seabed installations.
- Simulated installation, intervention, and production mode operations

35. Thermal analysis
• Based on the 3D thermal analysis, the thermal insulation thickness can be
optimized to avoid cold spots to meet the cooldown requirements.
• The insulation on any part of a manifold piping system is usually of sufficient
thickness to meet the cooldown time required for hydrate management.
• This insulation coupled with high fluid temperatures may exceed the
qualification temperature of the electronic components for instruments.

36. Summary
1. Manifold and template functional considerations
General / System requirements / System interfaces
Cluster manifold requirements / Template system requirements
2. Design considerations
System design / Loads
Piping design / Structure design / Foundation design / Components
3. Verification and validation of design
Design verification
Design validation