The SenTREE 3 test tree system includes the following components:
■ valve assembly (EZTV)
■ latch assembly (EZTH)
■ retainer valve (RETV)
■ spanner joint.
Valve assembly
The SenTREE 3 valve assembly (EZTV) (Fig. 5 and Table 2) consists of two hydraulically operated fail-safe valves. The main valve is a ball type; the second is a flapper valve. This combination has proved to be the most reliable fullbore subsea system.
Sequential valve closure ensures that the flapper valve closes only after the ball valve is closed.
The delay allows wireline or coiled tubing (CT) to clear the flapper after being cut by the lower ball assembly.
The pump-through facility of the valve assembly permits well control if hydraulic control is lost. Positive differential pressure applied from above opens a flow area for well kill operations that is equivalent to a 11⁄4-in. line.
Table 2. SenTREE 3 Valve Assembly Specifications
Unit EZTV-DA
Service H2S per NACE MR-01-75
Working pressure psi [bar] 15,000 [1035]
Design temperature °F [°C] –4 to 350 [–20 to 177]
OD in. [mm] 13.0†[330]
With centralizer 16.1 [409]
ID in. [mm] 3.0 [76]
Test pressure (body psi [bar] 22,500 [1550]
only, valves open)
Max tensile load at 90% lbf at 0 psi [kN at 0 bar] 520,000 [2310]
yield and 350°F [177°C] lbf at 15,000 psi [kN at 1035 bar] 255,000 [1130]
Injection line working pressure psi [bar] 15,000 [1035]
Bottom connection 5-in. 4 S.A. box
Wireline cutting capability Up to 5⁄16in. (no assistance required)
[Up to 7.9 mm (no assistance required)]
CT cutting capability Up to 11⁄2in. ×0.156 in. (hydraulic assistance 5000 psi) [Up to 38 mm ×3.9 mm (hydraulic assistance 345 bar)]
Max torque ft-lbf [N⋅m] 7500 [10,200]
Length in. [mm] 32.2 [818]
Weight with centralizer lbm [kg] 1124 [510]
†13-in. OD for the bottom nut only (height 4.1 in.); SenTREE 3 body OD is 12.5 in.
Figure 5. SenTREE 3 valve assembly.
Ball valve Flapper
Ball piston
Latch assembly
The latch assembly (EZTH) (Fig. 6 and Table 3) is the upper part of the subsea tree and connects the landing string to the valve assembly. If hydraulic control is lost, the latch can be disconnected mechanically. Two shear keys, which break at a known torque value, connect the latch body to the shear sub. Figure 7 shows the combined latch and valve assemblies of the SenTREE 3 test tree system.
Table 3. SenTREE 3 Latch Assembly Specifications
Unit EZTH-DA
Service H2S per NACE MR-01-75
Working pressure psi [bar] 15,000 [1035]
Design temperature °F [°C] –4 to 350 [–20 to 177]
OD in. [mm] 12.5 [318]
With centralizer 16.1 [409]
ID in. [mm] 3.0 [76]
Test pressure psi [bar] 22,500 [1550]
Max tensile load lbf at 0 psi [kN at 0 bar] 520,000 [2310]
at 90% yield and 350°F lbf at 15,000 psi [kN at 1035 bar] 255,000 [1130]
Top connection 5-in. 4 S.A. pin
Max torque ft-lbf [N⋅m] 7500 [10,200]
Length in. [mm] 16.0 [406]
Weight with centralizer lbm [kg] 860 [390]
Figure 6. SenTREE 3 latch assembly.
Latch dog
Skirt Piston
Latch dog
Latch profile Latch
assembly
Valve assembly
Retainer valve
The retainer valve (RETV) (Fig. 8 and Table 4) can be run above the SenTREE 3 latch assembly to retain the fluids trapped in the landing string after disconnecting from the SenTREE 3 valve assembly. When disconnecting, the retainer valve prevents the uncontrolled release of hydro-carbons from the landing string into the riser and the sea. When testing wells in deep water or when testing high-pressure gas wells, use of the retainer valve is a safety and environmental requirement.
The RETV is controlled hydraulically in sequence with the subsea test tree. An integral bleed-off valve (BOV) vents the trapped pressure between the retainer valve and the test tree to the riser before unlatching. The RETV uses the same ball valve mechanism as the SenTREE 3 system and is capable of cutting 1.5-in. CT. Hydrocarbons in the landing string can be reversed out as the RETV ball valve is pumped away from its seat with greater pressure below the valve. The RETV is a fail-safe valve when closed, but in case of control line failure, the RETV ball valve can be opened by closing the annular BOP on the spanner joint and pressuring up below.
Features
■ Fail-safe closure
■ Ability to cut 1.5-in. ×0.15-in. CT with pressure assist
■ Integrated bleed-off valve
■ Pump-through facility with the spanner joint
■ Pressure tests from above
■ Reverse circulation (U-tube)
■ Ports for high-rate injection
Table 4. SenTREE 3 Retainer Valve Specifications
Unit RETV-DA
Service H2S per NACE MR-01-75
Working pressure psi [bar] 15,000 [1035]
Design temperature °F [°C] –4 to 350 [–20 to 177]
OD in. [mm] 13.0 [330]
ID in. [mm] 3.0 [76]
Test pressure (valves open) psi [bar] 22,500 [1550]
Max tensile load lbf at 0 psi [kN at 0 bar] 520,000 [2310]
at 90% yield and 350°F lbf at 15,000 psi [kN at 1035 bar] 255,000 [1130]
Connection 5-in. 4 S.A. box with lock key
Max torque ft-lbf [N⋅m] 15,000 [20,300]
Overall length including ft [m] with 5-ft spanner 10.6 [3.2]
spanner joint ft [m] with10-ft spanner 15.6 [4.7]
Overall weight including lbm [kg] with 5-ft spanner 2000 [910]
spanner joint lbm [kg] with 10-ft spanner 2400 [1090]
Figure 8. SenTREE 3 retainer valve.
Ball valve Pins Seal retainer
BOV Open BOV Closed
Ball cage
Piston Ball spring
Sequencing valve
Spanner joint
The spanner joint (Fig. 9 and Table 5) sits on top of the retainer valve and allows closing the annular BOP. This safety feature was introduced in 1997. The spanner joint was developed to fulfill the following functions:
■ enable closure of the annular BOP on the landing string to pressurize the annulus to open the ball valve if hydraulic controls are lost
■ enable, through the hydraulic block manifold, the operating sequence of the SenTREE 3 system and the RETV valves
■ protect the control hoses when closing the BOP.
Table 5. Spanner Joint Specifications
Unit Spanner Joint
Service H2S per NACE MR-01-75
Working pressure psi [bar] 15,000 [1035]
Design temperature °F [°C] –4 to 350°F [–20 to 177]
OD in. [mm] 10.75 [273]
ID in. [mm] 3.0 [76]
Test pressure psi [bar] 22,500 [1550]
Max tensile load lbf at 0 psi [kN at 0 bar] 520,000 [2310]
at 90% yield and 350°F lbf at 15,000 psi [kN at 1035 bar] 255,000 [1130]
Connection 5-in. 4 S.A. box with lock key
Max torque ft-lbf [N⋅m] 15,000 [20,300]
Sealing length ft [m] 5 or 10 [1.5 or 3.0]
Figure 9. Spanner joint.
Skirt
Hydraulic sequencing manifold
Centralizer Hydraulic hose
Retainer valve
Accessories
Figure 10 shows the SenTREE 3 components in both a short configuration and a standard con-figuration. The spanner joints, retainer valve and shear sub extensions are required in both configurations.
Super short configuration Standard configuration
Standard
The type of subsea control system used to operate the subsea test tree depends on the water depth. Schlumberger has developed three systems (Fig. 11) to accommodate different depths and optimize the disconnect time of the latch assembly:
■ standard system for depths to 1500 ft [457 m]
■ deep-sea hydraulic system for depths from 1500 to 4500 ft [457 to 1372 m]
■ electrohydraulic system for depths from 4,500 to 10,000 ft [1372 to 3048 m].
Subsea Control Systems
can be used to decreasedisconnect time
Disconnect times
The disconnect time for any hydraulic system depends on the landing string configuration, on whether a retainer valve is used and on the umbilical hose length.
The downhole hydraulic pod system with surface accumulator was tested and qualified both onshore and offshore. Using the SenTREE 3 system and RETV, the complete cycle (close, bleed-off and disconnect) times are 41 s at 4400 ft [1341 m] and 52 s at 7400 ft [2255 m].
The electrohydraulic pod with 8500 ft [2591 m] of umbilical hose was also tested and qualified both onshore and offshore. Using the SenTREE 3 system and RETV, the complete cycle (close, bleed-off and disconnect) time is 10 s at water depths to 8500 ft.
Standard system features
The standard system (Fig. 12 and Table 6) intended for SenTREE 3 operation in shallow water depths to 1500 ft comprises
■ console
■ reeler
■ hose bundle, 4500-ft long.
A hydraulic logic diagram for the standard control system used with the SenTREE 3 system is shown in Fig. 13. A diagram for use with the SenTREE 3 system and retainer valve is shown in Fig. 14.
Table 6. Standard Control System Reeler and Console Specifications
Unit Reeler Console
Reeler motion Air driven
Reeler capacity three-hose bundle ft [m] 4500 [1370]
Footprint ft [m] 10.5 ×6.9 [3.2 ×2.1] 2.9 ×2.0 [0.9 ×0.6]
Height ft [m] 6.6 [2.0] 3.8 [1.2]
Weight lbm [kg] 5500 [2500] 660 [300]
Figure 12. SenTREE 3 system with standard control system.
1500 ft
SenTREE 3 system
Console Reel
Retainer Spanner joint
Figure 13. Hydraulic logic diagram for standard control system used with SenTREE 3 system.
B
A C
CI
Latch Unlatch Unlatch
Latch
Close Open
Ball valve Chemical injection Flapper valve
Close Open
Close Open
Close Open
Latch connector
Figure 14. Hydraulic logic diagram for standard control system used with SenTREE 3 system with retainer valve.
Deep-sea hydraulic system
The deep-sea hydraulic system (Fig. 15 and Table 7) is for operation of the SenTREE 3 system in medium water depths, between 1500 and 4500 ft. The system comprises
■ deep-sea console
■ accumulator surface unit
■ reeler
■ hose bundle, 4500 ft long
■ hydraulic control pod.
Table 7. Deep-Sea Hydraulic System Component Specifications
Unit Pod
Service H2S
OD in. [mm] 13.0 [330]
ID in. [mm] 3.0 [76]
Mandrel working pressure psi [bar] 15,000 [1035]
Mandrel test pressure psi [bar] 22,500 [1550]
Max tensile loadlbf at 0 psi [kN at 0 bar] 520,000 [2310]
lbf at 15,000 psi [kN at 1035 bar] 255,000 [1130]
Max torque ft-lbf [N⋅m] 7500 [10,200]
Connection 5 in. 4 S.A. box up ×pin down
Accumulator Surface Unit
Working pressure psi [bar] 5000 [345]
Capacity gal [L] 2 ×13 [2 ×50]
Nitrogen pressure psi [bar] 2600 [180]
Footprint ft [m] 8.2 ×2.0 [2.5 ×0.6]
Height ft [m] 2.2 [0.7]
Weight lbm [kg] 1430 [650]
Reeler
Reeler motion Air driven
Reeler capacity three-hose bundle ft [m] 6000 [1830]
Figure 15. SenTREE 3 system with deep-sea hydraulic control system.
4500 ft
SenTREE 3 system Retainer
Spanner joint Hydraulic pod
Accumulator surface unit Console
Reel
Deep-sea electrohydraulic system
The deep-sea electrohydraulic control system (Fig. 16 and Table 8) is for remote control of the SenTREE 3 system in water depths to 10,000 ft.
The system is designed for a closure and unlatching time of 10 s at any water depth. A single umbilical hose is used for all functions, including two surface readout lines for the pressure and temperature monitoring sub. The system comprises
■ surface control unit
■ umbilical hose and air-driven reeler
■ deep-sea pod (hydraulic accumulators and solenoid valves).
Table 8. Deep-Sea Electrohydraulic System Component Specifications
Unit Pod
Service H2S
OD in. [mm] 14.5 [368]
ID in. [mm] 3.0 [76]
Mandrel working pressure psi [bar] 15,000 [1035]
Mandrel test pressure psi [bar] 22,500 [1550]
Max tensile loadlbf at 0 psi [kN at 0 bar] 520,000 [2310]
lbf at 15,000 psi [kN at 1035 bar] 255,000 [1130]
Max torque ft-lbf [N⋅m] 7500 [10,200]
Length ft [m] 22.4 [6.8]
Weight lbm [kg] 4635 [2100]
Connection 5-in. 4 S.A. box up ×pin down
Reeler and Surface Control Unit
Reeler motion Air driven
Reeler capacity three-hose bundle ft [m] 10,000 [3050]
Footprint ft [m] 13.5 ×8.5 [4.1 ×2.6]
Height ft [m] 8.9 [2.7]
Weight lbm [kg] 25,000 [11,340]
SenTREE 3 system Electrohydraulic pod and accumulator Reel
Retainer Surface
control unit
T and P surface readout
10,000 ft
Spanner joint
Drift-off analysis
Drift-off analysis defines the disconnect philosophy and establishes the times required for dis-connection of stack components in the subsea test tree.
As an example, consider a drift-off analysis for North Sea conditions, where a complete dis-connect is required in 37 s or less, including pull-off from the BOP stack. This leaves 20 s for the complete sequence. Of the three control systems, only the electrohydraulic system is capable of making these disconnect times. In the analysis in Fig. 17, the subsea test tree must close, disconnect and clear the riser connector before the emergency disconnect sequence (ESD) procedure can begin.
Figure 17. Deep-sea drift-off analysis example.
9
Storm environment: 1-knot current, 55-knot wind
Vessel offset (% water depth)
Subsea pressure and temperature carrier
The subsea pressure and temperature carrier (EZGC) (Fig. 18 and Table 9) is used to monitor pressure and temperature at the subsea tree level. The well effluent pressure and temperature are recorded in surface readout or recorder mode.
This sub is recommended for use in HPHT tests, particularly to measure temperature at the BOP level and to ensure that the maximum temperature rating of the BOP elastomers is not exceeded. The other application is for hydrates control, especially during deep-sea operations.
Two UNIGAGE* H-Sapphire* pressure gauges are included with the tool. One gauge should have a high-resolution thermometer for direct effluent temperature measurement.
Table 9. Subsea Pressure and Temperature Carrier Specifications
Unit EZGC-A
Service H2S
OD in. [mm] 7.9 [200]
ID in. [mm] 3.0 [76]
Working pressure psi [bar] 15,000 [1035]
Working temperature °F [°C] 375 [190]
Make-up length ft [m] 10.6 [3.2]
Weight lbm [kg] 1320 [600]
Max tensile loadlbf at 0 psi [kN at 0 bar] 520,000 [2310]
lbf at 15,000 psi [kN at 1035 bar] 255,000 [1130]
Max torque ft-lbf [N⋅m] 7500 [10,200]
Connection 5-in. 4 S.A. box ×pin with lock key
Figure 18. Subsea pressure and temperature carrier.
UNIGAGE H-Sapphire SRO module
Direct temperature reading Jumper cable
During offshore testing where slickline, wireline or CT operations are performed, it may be advantageous to use a valve that limits lubricator height above the flowhead. The lubricator valve (LUBV), usually located about 90 ft below the flowhead, enables the upper part of the string to be used as a lubricator. The LUBV is a balanced system and remains in the position in which it was last placed (open or closed) (Fig. 19). If the valve is closed, however, application of 1800-psi differential pressure from above allows pump-through to kill the well. The LUBV can be pressure tested from above (with hydraulic pressure maintained in the closed line); the valve contains an equalizing device to remove any differential prior to opening.
The LUBV can be used alone or as a backup for a conventional lubricator system. It is a surface-operated hydraulic valve that is run on tubing or drillpipe during testing operations (Table 10).
It is normally run in conjunction with the SenTREE 3 system and its retainer valve or with an E-Z Valve* device. The LUBV can be actuated as many times as required for wireline operations.
Conversely, the SenTREE 3 or E-Z Valve products are safety devices and should be actuated only in emergencies.
Lubricator Valve
Table 10. Lubricator Valve Specifications
Unit LUBV-CC LUBV-CCB
Service H2S H2S
Working pressure psi [bar] 15,000 [1035] 10,000 [690]
Working temperature °F [°C] –4 to 350 [–20 to 175] –4 to 350 [–20 to 175]
Fail-safe ClosedClosed
Pump-through differential psi [bar] 1800 [125] 1800 [125]
Max tensile loadlbf at 0 psi [kN at 0 bar] 520,000 [2310] 520,000 [2310]
lbf at 15,000 psi [kN at 1035 bar] 255,000 [1130] 255,000 [1130]
Shearing wireline capability Up to 15⁄32-in. [11.9 mm]
Shearing CT capability 11⁄4-in. ×15⁄32in. wall [32-mm ×11.9-mm wall]
Connection (box/box) 5-in. 4 S.A. 5-in. 4 S.A.
Length ft [m] 5.0 [1.5] 5.0 [1.5]
OD in. [mm] 8.25 [210] 8.25 [210]
ID in. [mm] 3.0 [76] 3.0 [76]
Weight lbm [kg] 700 [320] 700 [320]
Figure 19. Lubricator valve.
Double check valve
Hydraulic fluid
Ball valve
Valve Open Valve Closed Injection Line
Bottom plug Injection point
The E-Z Valve (EZV) retrievable well control safety device is designed for installation in the BOP stack of a jackup or land rig during well testing when there is no unlatch facility (Table 11). The pipe rams close around a slick joint above the valve, protecting the annulus, while the E-Z Valve ball closes to secure the well at BOP level.
The E-Z Valve device is normally closed by a spring and nitrogen pressure and is opened by hydraulic pressure applied from a console on the rig floor (Fig. 20). The valve is designed pri-marily to hold pressure from below, but it can be pressure tested from above to 5000 psi with normal hose and console or to 7500 psi with a high-pressure set. A hydrate inhibitor such as glycol or methanol can be injected below the valve.
E-Z Valve closure can also be assisted by hydraulic pressure, enabling the ball to cut wireline or 11⁄4-in. CT in an emergency. Standard and two optional installations are shown in Fig. 21.
E-Z Valve Retrievable Well Control Valve
Table 11. E-Z Valve Specifications
Unit EZV-CC
Service H2S
Working pressure psi [bar] 15,000 [1035]
Working temperature °F [°C] –4 to 350 [–20 to 175]
Fail-safe Closed
Shearing wireline capability Up to 15⁄32in. [11.9 mm]
Shearing CT capability Up to 11⁄4in. [32 mm]
Pump-through differential psi [bar] 1800 [125]
N2precharge psi [bar] 1200 [83]
Connection (box/box) 5-in. 4 S.A.
Body length ft [m] 3.8 [1.1]
Valve only length ft [m] 5.0 [1.5]
Slick joint length ft [m] 5.7 [1.7]
E-Z Valve system length ft [m] 16. [5.1]
OD in. [mm] 8.25 [210]
ID in. [mm] 3.0 [76]
Slick joint and valve weight lbm [kg] 1230 [560]
Adjustable hanger kit weight lbm [kg] 1500 [680]
Figure 20. E-Z Valve operation.
Hydraulic fluid
Nitrogen and spring
Ball valve
Valve Open Valve Closed Valve Closed with Assistance
Injection Line
Double check valve
Injection point
Bottom plug Slick joint
Figure 21. E-Z Valve installation options.
B C A
Option 2 (only from 95/8-in. casing) Option 1
Standard Installation
Slick joint
E-Z Valve E-Z Valve
E-Z Valve