Published on 04 Jul 2015 by Emma Leoni
The purpose of this document is to define the field expansion philosophy for Future Subsea Development of a particular field. This document covers the requirements for subsea infrastructure future expansion.
If wells drilling prove successful, further production wells may be added to the flowline looping, loops extended, or separate flowline loops added to fully develop the subsea field. These can be integrated on the seafloor as additional riser capacity may not be required to fill the FPSO processing limits. The planned and current facilities should facilitate the development and future potential development including:
- Future well tie-ins (for producers and injectors)
- Future developments including expansion of subsea architecture
- Regional tie-backs
- Gas supply and export to shore
Subsea infrastructure expansion should be facilitated by pre-invested connections shown below.
Pre-installed facilities to support future development should be minimized as far as practicable. Pre-investment in the early phase facilities should focus on ensuring that the early phase facilities can be safely and practically modified or expanded as required.
Expansion and Tie-backs
The early phase system must be designed to enable additional production via well tie-ins to the early phase production loops, via expansion of early phase production loops or via new loops to fully develop the field in development.
The early phase production flowline loops may be expanded until the flow assurance constraints are reached. New production flowline loops may be required to reach future wells. The new production loops may be integrated on the seafloor or via the riser slots (production, water injection, gas injection and gas lift) and umbilicals must be designed for expansion by reconfiguration and tie-in at well tie-ins, in-line tees/connection structures, flowline/umbilical ends and riser bases.
Extension from the production flowlines should not be precluded, but phasing and interaction with the late-life performance of the wells will need to be considered at that time (i.e. future flowlines may be connected to the early phase flowlines at their ends, at intermediate points [e.g. well tie-in points, in-line tees/connections], at riser bases, or at new risers, depending on the flow assurance and system design requirements at that time).
Regional prospects may be at such a distance that the early phase flow assurance strategies are not appropriate. Accordingly, the flowlines to/from the regional prospects may involve different flow assurance strategies. Future provisions in the foundation development to enable expansion to the regional prospects include provisions on the FPSO and associated turret/swivel system for subsea multiphase pumps and electrical trace heated flowlines.
The Water Injection, Gas Injection and Gas Lift Systems for regional tie-backs should be designed for expansion by tie-in to the early phase subsea systems at their ends, at intermediate points (e.g. well tie-in points, in-line tees/connections) or at riser bases.
To facilitate field expansions and future phases, the design of the subsea system architecture/components should:
- Provide double block and bleed isolation unless single isolation is demonstrated to be acceptable by a quantitative risk assessment in compliance with Subsea Recommended Practice API RP 17P
- Avoid hydrocarbon release to environment during future tie-in or reconfiguration. If avoidance is not practicable, then releases should be minimized and demonstrated to be ALARP
- Diverless connector system for all future subsea infrastructure connection, provided with suitable isolation in accordance with Subsea Recommended Practice API RP 17P
- Avoid hydrates at the future tie-in connections
- The subsea controls distribution system should provide sufficient capacity and suitable connection points for tie-in of future umbilicals to provide hydraulic/electric power and controls to all future tie-in points. The control system design should be compatible with the total number of wells for early phase of the development
- Preserve the capability for circulation through of the dual production system for any infield expansion and/or future tiebacks
- Production dead-legs should be avoided or designed to be displaced with dead oil and isolated from producing legs with hydraulically/electric actuated valves to prevent forward flow or backflow of live fluids into cold stagnant sections of the subsea production flowline system
- Consider tie in of additional gas injection or gas supply wells to the early phase infrastructure
- Consider tie in of additional water injection wells to the early phase infrastructure and/or expansion of the water injection flowline system to accommodate future development
Seabed Approach Corridors and Space Allowance
The following FPSO approach corridors and associated areas should be identified and protected:
- A future gas export pipeline corridor from the FPSO, including a non-return valve assembly near the riser base
- A flowline loop corridor from the FPSO, connecting to alternate destinations at the FPSO: the production loop riser-base FLETs via a future manifold, and spare production flowline riser slots
- A power and control umbilical corridor for turret sector, connecting to alternate destinations: a future subsea multiphase pump station on the FPSO, and a future electrical trace heated flowline from the FPSO
Gas Export to Shore
The design of the early phase subsea system architecture should allow the future installation of a gas export riser and pipeline to facilitate gas export to shore and to allow gas production wells to be tied into the gas injection flowline (when operating in gas import mode).