3. Different types of platforms

06.04.2016
This section describes the different platforms variants or types of unmanned wellhead platforms used in the North Sea area.

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3.1 Main types

Based on reviews of different types of unmanned wellhead platforms, these have been divided into five groups or types. A very short summarisation of the five types is given in Table 3-1.

 

Table 3-1: Overview of UWHPs

Table 3-1: Overview of UWHPs

 

3.2 Access methods

The different potential access methods to unmanned wellhead platforms in the North Sea area are listed below:

  • Helicopter access
  • Access by Fast Rescue Boat (FRB)
  • Access by walk-to-work (W2W) bridge on a support vessel. Based on a hydraulically controlled bridge
  • Access from boat using a Z-step access system, a compensating step-up platform system
  • Heli-hoisting
  • Access from Offshore Service Rig (OSR), a jack-up service rig.

Traditionally, access by helicopter has been the preferred method of access in the Norwegian part of the North Sea. In other parts of the North Sea, boat access has been widely used.

Partly initiated by the offshore wind industry, alternative access methods allowing safe and comfortable access to the installations have been developed. A typical example is the walk-to-work (W2W) bridge. The W2W bridges can become the future method of access to unmanned wellhead platforms in the Norwegian part of the North Sea, provided that there is a sufficient availability of vessels with W2W bridges installed.

 

3.3 Installation methods

The different installation methods and their applications are shown in Table 3-2.

 

Table 3-2: Installation methods.

Table 3-2: Installation methods

 

3.4 Type 0 platforms

The concepts for type 0 platforms are very much the same as for manned installations - but on a smaller scale. The platform is designed for frequent manning and if necessary the crew may stay overnight for periods of time.

The main characteristics and features of the type 0 platforms are:

  • The platform is equipped with a helideck, and the primary evacuation is by helicopter
  • Secondary means of escape are a Totally Enclosed Motor Propelled Survival Craft (TEMPSC).
  • The tertiary means of escape are by life rafts
  • The platform is designed for both coiled tubing (CT) and wireline operations
  • The platform has a crane sized for coiled tubing equipment (50-60 tonnes)
  • The platform is equipped with fixed fire water deluge systems
  • Gas-based firefighting systems are provided in the electrical rooms
  • Fire water/foam coverage of the helideck is provided from the fixed fire water system
  • The electrical equipment room and the shelter for personnel are under HVAC control
  • There are both fixed fire and fixed gas detectors on the installation
  • There are separate wellhead control systems, Emergency Shutdown systems (ESD systems), Fire & Gas Systems (F&G systems) as well as Supervisory Control and Data Acquisition systems (SCADA systems)
  • Remote shutdown can be initiated from the host. Locally initiated shutdowns may require local reset.

The philosophy for the firefighting system is to protect both the platform and the staff on-board. Only if a fire cannot be brought under control, a controlled evacuation including mustering will be initiated.

 

3.5 Type 1 platforms

The platform is designed for manning by helicopter during daytime, but the platform is also equipped with an emergency shelter to be used in case sudden bad weather makes a return to the host platform impossible.

The main characteristics and features of the type 1 platforms are:

  • The platform is equipped with a helideck, and the primary evacuation is by helicopter
  • Secondary means of escape are a Totally Enclosed Motor Propelled Survival Craft (TEMPSC)
  • Tertiary means of escape are life rafts
  • The platform may be designed for both coiled tubing (CT) and wireline operations or only for wireline operations
  • The platform has a crane sized for well intervention equipment (10-50 tonnes)
  • Fire water/foam coverage of the helideck is provided from water/foam tanks pressurised by nitrogen
  • Firefighting of small fires is based on the use of hand-held extinguishers
  • During drilling operation, fire water can be provided from the drilling rig
  • The emergency shelter for personnel is provided with HVAC, when the facility is manned
  • There are both fixed fire and fixed gas detectors on the installation
  • There are separate wellhead control systems, whereas ESD systems, F&G systems as well as SCADA systems are integrated into one common logic solver or computer
  • Remote shutdown can be initiated from the host. Locally initiated shutdowns may require local reset.

The basic firefighting philosophy for this type of platform is only to neutralise smaller fires using hand-held extinguishers, and otherwise there is focus on fast and efficient evacuation and escape in case of any major fire events.

 

3.6 Type 2 platforms

The platform is designed for manning by a Fast Rescue Boat (FRB) launched from a standby vessel during daytime and in calm weather. The standby vessel will stay at the platform, when manned, and will also act as a crew facility.

The main characteristics and features of the type 2 platforms are:

  • Primary evacuation is performed by the FRB
  • Secondary means of escape are life rafts
  • The platform may be designed for light wireline operations
  • The platform has a small crane (1-2 tonnes)
  • Firefighting of small fires is based on the use of hand-held extinguishers
  • During drilling operation, fire water can be provided from the drilling rig
  • There are no overnight facilities on the platform
  • There are fixed fire detection based on fusible plug loops and hand-held gas detectors, when the facility is manned
  • Wellhead control, ESD systems, F&G systems as well as SCADA systems are integrated into one common logic solver or computer
  • Remote shutdown can be initiated from the host. Locally initiated shutdowns may require local reset.

The basic firefighting philosophy for this type of platform is only to neutralise smaller fires using hand-held extinguishers, and otherwise there is focus on fast and efficient evacuation and escape in case of any major fire events.

 

3.7 Type 3 platforms

The concept for the type 3 platform is based on the use of inherent safety principles, noble materials and equipment with documented reliability. The consequence is therefore that visiting frequency is very low. The primary method of access is by walk to work bridges from a standby vessel. During the entire operation or manning period the vessel will be connected to the installation also acting as the crew facility. Access by FRB will only be in exceptional cases.

There will typically be a Closed Circuit TV (CCTV) to monitor the platform, and not least the CCTV will be used, if a remotely controlled re-setting after a shutdown is required (i.e. resetting without manning the installation).

The main characteristics and features of the type 3 platforms are:

  • The primary evacuation takes place via the W2W bridge
  • Secondary means of evacuation are by the FRB or by the standby vessel (if manned by FRB, this is the primary means of evacuation)
  • Tertiary means of evacuation are a life raft and suitable access to the sea (if manned by FRB, this is the secondary means of evacuation)
  • All well intervention operations require the presence of an offshore support rig (OSR)
  • No platform crane, all lifting is based on a cargo transfer system from the standby vessel or the OSR
  • Firefighting of small fires are based on the use of hand-held extinguishers
  • During drilling operations, fire water can be provided from the drilling rig
  • There is no shelter on the facility
  • There is fixed fire detection based on fusible plug loops and hand-held gas detectors, when the facility is manned
  • Wellhead control, ESD systems, F&G systems as well as SCADA systems are integrated into one common logic solver or computer
  • Remote shutdown can be initiated from the host

The basic firefighting philosophy for this type of platform is only to neutralise smaller fires using hand-held extinguishers, and otherwise there is focus on fast and efficient evacuation and escape in case of any major fire events.

 

3.8 Type 4 platforms

The type 4 platform is a super-minimalistic facility with one to two wells. This type of UWHP is mainly known from the US Gulf of Mexico (GoM), however, a few are installed in the Dutch sector of the North Sea.

The platform is very small, and escape is directly back to the FRB, which brought the visiting crew on board. There are no other lifesaving appliances on board.

The platform is equipped with a fusible plug loop (pressurised by hydraulics or lift gas) as the only means of fire detection. The basic philosophy is that there is focus on a fast escape in case of any fire event.