The Tordis Subsea Separation System will be installed between the existing Tordis Subsea Field and the Gullfaks C platform.

By installing a full-scale subsea separation facility, StatoilHydro expects to improve the Tordis field’s recovery factor from 49 to 55 per cent.

Along with other upgrades to the field, our separation system will allow StatoilHydro to extract roughly 35 million extra barrels from the Tordis field, with our new technology accounting for approximately 19 million barrels of the improved oil recovery (IOR).

This is achieved by removing water from the well stream subsea, reinject the water in a separate well subsea, thereby reducing the back pressure towards the Tordis field and allow more hydrocarbons to be processed at the Gullfaks C platform.

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System Description

Pipeline Inline Manifold (PLIM)

The PLIM will be installed summer 2006 to interconnect the flowlines from the Tordis Subsea Manifold to the Gullfaks C platform allowing re-routing of the Tordis Well Stream to Gullfaks C via the Subsea Separation Station.

The PLIM allows full bypass of the Tordis Subsea Separation, and will be installed during a planned maintenance shut-down of the Gullfaks C Platform

Water Injection Tree

The Water Injection Tree is a simple Xmas Tree consisting of a 12” ball valve. A conventional internal tree cap is installed in the vertical entry section of the tree allowing for workover of the well. The reinjected water is pumped through this Xmas Tree through a 13 5/8 casing direct into the Utsira water reservoir. This is a non hydrocarbon reservoir with ambient pressure.

Subsea Separation Boosting and Injection (SSBI) Station

The Subsea Separation Station separates the water from the well stream which is reinjected through the large bore Water Injection Tree. After separation, gas and oil is mixed and pumped via a multiphase pump back to the Gullfaks C platform. The SSBI Station is installed in October 2007.

The Separation Station contains the following main elements:

• Foundation Structure and Manifold 
  The Tordis SSBI Station has an independent conventional, overtrawlable foundation structure supporting the manifold, the separation module and all other components. The structure has four suction anchors, one in each corner for foundation and leveling.
  
  The manifold module provides connection to the flowlines via Rovcon connection system and interconnects the various modules. The estimated installed weight of the Subsea Separation Station with manifolds and separation modules is approx. 900 tons.
  
• Separation Module
  The well fluid from the Tordis field is first routed into the separation tank. The inlet cyclone separator in the tank does a first separation where the majority of the gas is separated out and routed through a separate pipe outside of the tank, thereby minimizing the size of the separation tank. The remaining water, oil and gas are separated through the gravity principle inside the tank. The water is the heaviest part which is pumped via a water injection pump directly back into the Utsira reservoir through the Xmas Tree. Oil and gas are remixed and pumped through a multiphase pump back to the Gullfaks C platform. Any deposit of sand inside the separation tank is handled by the sand removal system.
  
  The Separation Module is retrievable as a separate unit.
  
• Sand Removal System
  Any sand from the well stream will deposit at the bottom of the separation tank. A flushing system with specially designed nozzles has been developed to flush out the sand at certain intervals. The sand is transported into the Desander Module where it can be remixed with the injection water and reinjected into the reservoir downstream of the water injection pump. Alternatively the sand can be remixed with the oil and gas flow and pumped back to the Gullfaks C platform.
  
• Water Injection Pump
  The Water Injection Pump is a standard Framo pump system which is driven by an electrical motor powered through an electrical power cable from the Gullfaks C platform. The pump can be retrieved for maintenance by a separate pump running tool.
  
• Multiphase Pump
  The Multiphase Pump is a standard Framo pump, similar to the Water Injection Pump, and is powered through an electrical power cable from the Gullfaks C platform.
  
  It can also be retrieved by a separate pump running tool.
  
• Other
  The Subsea Separation Station is equipped with two multiphase flow meters (Roxar) which will measure the composition of the well flow to prepare the separation system settings. A level monitoring system is installed in the separation tank to monitor water, oil and gas interfaces which again provide input to the water pump speed and the multiphase pump speed. The Subsea Separation Station includes one subsea control module with 51 functions to control the various functions of the station and communicate back to the Gullfaks C platform.

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