ELECTRO-HYDRAULIC
WELLHEAD CONTROL SYSTEM

 

Electronic control in the wellhead area is now possible with 's intrinsically safe programmable logic controller (ISPLC).

Conventional hydraulic and pneumatic control panels are replaced by electronic controllers local to each wellhead.

The ISPLC also monitors wellhead data for transmission to the platform's distributed control system.

Benefits are:

 Cable and piping installation is dramatically reduced

 Significant overall platform weight reduction

 Installation and hook up time is reduced

 System expansion to meet additional wells

Each ISPLC will control two single or one dual completion well. The PLC drives intrinsically safe solenoid valves within a hydraulic interface unit to operate the sub sea, master and wing valves.

Cost Benefit

Typical cost benefit for a 20 well platform compared with conventional hydraulic control panels.

Weight 50%
Capital Cost 60%
Installation hook up time 50%

Significant benefits also exist in lifetime maintenance and support

Connection in the wellhead areas is minimised to common high and low pressure hydraulic headers, and return line, two wire electrical data bus and electrical power linking all wellhead controllers.

The wellhead ISPLC undertakes:

 Logical sequencing including process and platform shutdowns.

 Safety interlocks

 Timing

 Choke valve control

 Pressure flow and status monitoring

Local manual valve control, including emergency shutdown is provided.

Control Logic

The logic system ensures safety valves operate in the correct sequence. Adjustable time delays and interlocks are incorporated. High and low level alarms for any measurement are available. The ISPLC will communicate with the platform DCS via a standard PLC gateway, or can operate stand alone.

Safety

The ISPLC is designed to fail freeze/safe. Power failure will cause solenoids to release so that valves close, with hydraulic sequencing for the down hole safety valve. All solenoid valves have manual control to enable continued production during maintenance.

Emergency Shutdown

The system can be interlocked with central fire and gas or ESD systems to initiate shutdown. High-low flowline pressure sensors enable pipework to be protected from high pressures and line breaks.

Overrides are available for workover and wirelining purposes.

Choke Valve

If required each ISPLC will control upto two choke valves with:

 Auto bean up

 Variable ramping and crackpoint transition optimisation

 Alternate direction of opening

 Flow calculations (AGA)

Specification

The system has 8 control outputs nominally for 3 valves, expandable to operate 6 for dual completion, with capacity for 3 choke valves and with valve position and flowline pressure monitoring.

PLC Power24V CD Supply Bus connected via an Ex'D' shuttered connector
Hydraulic Power345 bar (subsurface safety valve)
207 bar (wing valve and master valve)
(other pressures accommodate if required)
MaterialsPLC is sealed to IP67 in 316 stainless steel enclosure
Local control unit is sealed to IP55 in 316 stainless steel enclosure
Hydraulic tubing is 316 stainless steel annealed to ASTM A/269
PLC ClassificationBASEEFA Standard - Intrinsic Safety Ex 89C2137 (RTU), Ex 90Y206X (PSU)
Group IIB T4
Status Inputs24 Opto isolated
Analogue16 4-20mA or 1-5 Volts (8 bit)
16 (12 bit) additional if required
Control Outputs8 Opto/FET On = 1 A/V Off - 1mA/V
Pulse Control2 Pulse Counter Type Inputs
Serial Digitalup to 3 ports

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