Stack Up Facility

The stack up facility was used in 2003 by ENI to carry out the largest subsea tree stack up that year, the total package was around 76 tons and stacked up to a height of 42ft.

This included the Subsea Tree/Lower Riser package/Emergency Disconnect package plus Workover Control System.

This project involved an enormous amount of planning, hard work from project teams within – ENI, FMC, APA, Subsea 7, Ross Deep Tech and eProduction Solutions.

Subsea Tree

The subsea tree consists of the following major components:

• DX tree connector
• Valve block assembly and valve components
• Flowline and flowline connection system
• Controls and accessories
• Tree cap and associated running tools
• Tree frame

Valve Block Assembly and Valve Components



The production bore of the valve block is configured with a lower master, upper master and swab valves. The annulus wing and crossover valves are installed in separate side porting that intersects the annulus bore and terminates at the valve block face with studded outlets.

The upper end of the valve block assembly includes an integral tree mandrel with an OD locking profile and production and annulus bore seal pockets in the ID. The seal pockets interface with the primary metal seals on the tree cap stab subs. The mandrel mates with the following as required:

• Tree cap
• Tree running tool
• Lower riser package

A hydraulic stab plate containing male hydraulic couplers connected to all tree functions set below the tree mandrel.

Control and Accessories

An upper stab plate actuating mechanism on the tree interfaces with the control jumper termination assembly (CJTA) on the completion guide base. The upper stab plate contains seven female hydraulic couplers for all platform controlled tree functions and three female electrical couplers.

The hydraulic couplers connect to the following:

• Upper production mater valve (UPMV)
• Production wing valve (PWV)
• Annulus master valve (AMV)
• Annulus wing valve (AWV)
• Cross over valve (XOV)
• Downhole safety valve (DHSV)
• Methanol injection valve (MIV)

The couplers are capable of being made up and broken out under pressure. All couplers except the tree cap hydraulic couplers are able to seal to prevent ingress of seawater on disconnection. The tree cap couplers vent pressure on disconnection.

The electrical couplers connect to:

• Downhole pressure transducer (DHPT)
• Production pressure transducer (PPT)
• Annulus pressure transducer (APT)

Lower Riser Package

Lower riser package (LRP) plays a major role in emergency shutdown (ESD) operations as dictated by the control logic system. Additionally, the LRP provides unrestricted access for wireline tools and coiled tubing when the LRP, tree, and tubing hanger are connected together. All pressure containing components have a 10,000 psi pressure rating.

The LRP runs at the bottom end of the workover/completion riser string with the EDP latched to its upper mandrel profile. The assembled unit is then run on the 5” x 2” dual bore system. The LRP lands and locks to the tree upper mandrel profile. The workover umbilical, which mates with a stab plate on the EDP/LRP assembly, provides communication from the workover control panel to selected tree functions.

Emergency Disconnect Package

A stab plate, which mates with a corresponding plate mounted to the frame of the EDP terminates the workover umbilical. A swing bolt mechanism makes up the stab plate.

Quick-connect couplings that engage during the stab plate make up provide hydraulic communication. Grade 316 stainless steel tubing and fittings hard plumb all hydraulic functions from the EDP stab plate couplings.

Hydraulic communication to the EDP, LRP and tree functions is routed through a stab plate mounted on the EDP frame. A hydraulic stab plate containing female hydraulic couplers is fit to the lower connector body. This plate engages with a corresponding plate on the LRP to establish communication. The couplers can be separated out under pressure. Where required, selected couplers are capable of venting fluid pressure upon disconnection.