GW-14 Geothermal Production Well — Wellhead Valve Change Isolation
Master valve change on a two-phase geothermal production wellhead. Covers a reservoir that cannot be switched off, quench and kill lines, silica-scaled valves that may not seat, flashing brine and hydrogen sulphide.
How Setyr addresses Geothermal andOil & Gas →
It refers to equipment that does not exist and illustrates the elements 29 CFR 1910.147(c)(4)(ii) requires a procedure to contain. It is not a document to adopt. Under (c)(4)(i) the employer must develop and document energy control procedures specific to their own machines, and under (c)(6) must inspect them at least annually.
12 points, in sequence
The geothermal reservoir itself, feeding the well at 240 degrees C and 15 bar.
Method: The reservoir CANNOT be isolated. The well is killed with brine and held dead by hydrostatic column, which is a maintained condition requiring continuous monitoring, not a locked device.
Caution: There is no valve between the crew and the reservoir. Everything else on this procedure controls a well that is still trying to flow.
Lower master valve on the wellhead, the primary barrier.
Method: Close the lower master and lock. Confirm closed by monitoring pressure above the valve.
Caution: Silica scale on a geothermal master valve prevents full seating. A closed handwheel is not a seated valve; the pressure above it is the evidence.
Production wing valve to the two-phase gathering line.
Method: Close and lock the wing valve.
Caution: The gathering line is shared with other wells and remains live and hot on the far side of this valve.
Wellhead bleed to the atmospheric silencer, between master and wing.
Method: Open the bleed to the silencer and lock open. Hold for the full bleed and confirm zero at the annulus gauge before breaking any flange.
Caution: Trapped two-phase fluid between two closed valves flashes violently when a flange is cracked.
Casing annulus vent.
Method: Open the annulus vent and confirm zero pressure. Monitor throughout the job.
Caution: Rising annulus pressure during the work means the well is communicating past the barrier. It is the early warning.
Scale inhibitor and biocide injection line at the wellhead.
Method: Close and lock the injection valve and bleed the injection quill.
Caution: The injection line runs at higher pressure than the wellhead and holds concentrated chemical.
Kill line connection for pumping brine to hold the well dead.
Method: Do NOT isolate. Confirm the kill line is rigged, the kill pump is primed, and brine volume is on site before the master valve is broken.
Caution: The kill line is the response if the well starts to flow during the change. Isolating it removes the recovery.
Quench water injection upstream of the wellhead.
Method: Do NOT isolate. Confirm quench supply is available to cool any release.
Caution: Two-phase brine flashes to steam on release. Quench is what makes a release survivable at the wellhead.
Wellhead emergency shutdown valve and its actuator.
Method: Do NOT isolate. Confirm the ESD remains armed and will close on demand.
Caution: With the master valve removed the ESD is the only automatic barrier remaining.
Wellhead SCADA, pressure and temperature transmitters, and the remote shutdown link.
Method: Do NOT isolate. Confirm transmitters read true and the control room can see the well throughout the job.
Caution: The control room watching the well is part of the barrier. A crew at the wellhead cannot see a reservoir response coming.
Fixed H2S detection at the cellar and personal monitors on the crew.
Method: Do NOT isolate. Confirm fixed detection is in service and every crew member carries a bump-tested monitor.
Caution: H2S collects in the wellhead cellar, which is the low point the crew works in. It deadens the sense of smell before it reaches lethal levels.
Wellhead crane or gin pole used to lift the master valve.
Method: Do NOT isolate. Confirm the lift is rigged and the valve is supported before the studs come out.
Caution: A master valve is heavy and directly over the cellar the crew stands in.
What your site must supply
This example is structurally complete and factually generic. The things below are the things only you can know — and they are exactly what makes a procedure yours.
- Your own asset and isolation-point tag numbers. The tags shown are illustrative and refer to equipment that does not exist.
- The actual location of every disconnect, valve and vent on your equipment.
- Measured stored-energy magnitudes and the dwell time required to dissipate them.
- Your verification method for each point, and who is authorised to perform it.
- Any additional energy sources present on your equipment and absent here.
Author this properly, once
Setyr holds procedures like this as living documents — bound to real isolation points, with lock registries, group lockout, person-in-charge custody and periodic review built in.