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.
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.
Typical cost benefit for a 20 well platform compared with conventional hydraulic control panels.
|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.
Choke valve control
Pressure flow and status monitoring
Local manual valve control, including emergency shutdown is provided.
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.
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.
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.
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)
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 Power||24V CD Supply Bus connected via an Ex'D' shuttered connector|
|Hydraulic Power||345 bar (subsurface safety valve)|
207 bar (wing valve and master valve)
(other pressures accommodate if required)
|Materials||PLC 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 Classification||BASEEFA Standard - Intrinsic Safety Ex 89C2137 (RTU), Ex 90Y206X (PSU)|
Group IIB T4
|Status Inputs||24 Opto isolated|
|Analogue||16 4-20mA or 1-5 Volts (8 bit)|
16 (12 bit) additional if required
|Control Outputs||8 Opto/FET On = 1 A/V Off - 1mA/V|
|Pulse Control||2 Pulse Counter Type Inputs|
|Serial Digital||up to 3 ports|