May 07, 2014Yutaek Seo

해양자원개발시스템개론: Introduction to Offshore Petroleum Production System

Subsea manifoldsVincent 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)

• Ichthys gas field

• 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.

• 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.

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.

ISO/FDIS 13628-15Petroleum and natural gas industries –Design and operation of subsea production Systems –

Part 15:Subsea structures and manifolds

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

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

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 fluidsNote – there are no wells on a cluster manifold

3.1.17 template: seabed structure that provides guidance and support for drilling and includes production/injection pipingNote 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 locationNote 2 production from the templates can flow to floating production systemsNote 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

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

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

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

4.4 Cluster manifold requirements: consists of a framework that supports piping, pull-in and connection equipmentand 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

5. Design consideration

5.1 System designThe 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-user5.1.1 Number of wells: greatly influence the size and design5.1.2 Well spacing5.1.3 Maintenance: Clear access space, retrievable components, height above seabed, fault detection5.1.4 Barrier philosophy: Two barriers for pressurized manifold piping: One barrier for non-pressurized manifold piping5.1.5 Safety5.1.6 External corrosion protection design

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

5.2 Loads5.2.1 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 object5.2.2 Thermal effects: End user is responsible for specifying or approving the temp. requirement5.2.3 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

5.3. Piping design

5.3.1 General requirementManifold 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 piggingRecommendations: 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 codesASME B31.8, ASME B31.4, ASME 31.3, ASME VIII, DNV-OS-F101, DNV-RP-F112 or API Spec 1111.

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 accumulationsto prevent hydrate formation: ISO 13628-1:2005 : MEG distribution for gas producing manifolds

• 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

5.4 Structural design

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

5.5 Foundation design• The anchoring systems were designed based on soil conditions and load

considerations and can be categorized into three groups

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

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

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

5.6 Components5.6.1 General: valves, controls, and connectors: Table 1- Industry standards for manifold components5.6.2 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 use5.6.3. 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.

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.

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.

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.

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 checksubsystem checkinterface checkunitized system check

6.2 Design validation: Design validation is performed to ensure that the specific operational requirementshave 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

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.

Summary

1. Manifold and template functional considerationsGeneral / System requirements / System interfacesCluster manifold requirements / Template system requirements

2. Design considerationsSystem design / LoadsPiping design / Structure design / Foundation design / Components

3. Verification and validation of designDesign verificationDesign validation