Setyr worked example — GW-14 Geothermal Production Well — Wellhead Valve Change Isolation Not approved for use. Version 1 · 2026-09-08
Worked example only — your site must author, review and approve its own
procedure under 29 CFR 1910.147(c)(4). setyr.com/procedures
GW-14 Geothermal Production Well — Wellhead Valve Change Isolation
Geothermal
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.
This is a worked example, not a procedure you can adopt. It describes equipment that does not exist, with illustrative tag numbers.
29 CFR 1910.147(c)(4) requires the employer to develop, document and
utilise energy control procedures specific to their own machines, and (c)(6)
requires the employer to inspect those procedures periodically. Neither duty
can be delegated to a vendor or discharged by this document.
Isolation points
| # | Tag (illustrative) | Type | Disposition | What it does and why | Dwell |
|---|---|---|---|---|---|
| 10 | GW-14-RESERVOIR | Bleed | CANNOT BE ISOLATED | The geothermal reservoir itself, feeding the well at 240 degrees C and 15 bar. 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. 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. | — |
| 20 | GW-14-MASTER | Valve | Isolate & lock | Lower master valve on the wellhead, the primary barrier. 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. Close the lower master and lock. Confirm closed by monitoring pressure above the valve. | — |
| 30 | GW-14-WING | Valve | Isolate & lock | Production wing valve to the two-phase gathering line. Caution: The gathering line is shared with other wells and remains live and hot on the far side of this valve. Close and lock the wing valve. | — |
| 40 | GW-14-BLEED | Bleed | Isolate & lock | Wellhead bleed to the atmospheric silencer, between master and wing. Caution: Trapped two-phase fluid between two closed valves flashes violently when a flange is cracked. 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. | 900s |
| 50 | GW-14-ANNULUS | Vent | Isolate & lock | Casing annulus vent. Caution: Rising annulus pressure during the work means the well is communicating past the barrier. It is the early warning. Open the annulus vent and confirm zero pressure. Monitor throughout the job. | 600s |
| 60 | GW-14-CHEM | Valve | Isolate & lock | Scale inhibitor and biocide injection line at the wellhead. Caution: The injection line runs at higher pressure than the wellhead and holds concentrated chemical. Close and lock the injection valve and bleed the injection quill. | 60s |
| 70 | GW-14-KILL | Valve | KEEP ENERGISED | Kill line connection for pumping brine to hold the well dead. Caution: The kill line is the response if the well starts to flow during the change. Isolating it removes the recovery. 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. | — |
| 80 | GW-14-QUENCH | Valve | KEEP ENERGISED | Quench water injection upstream of the wellhead. Caution: Two-phase brine flashes to steam on release. Quench is what makes a release survivable at the wellhead. Do NOT isolate. Confirm quench supply is available to cool any release. | — |
| 90 | GW-14-ESD | Switch | KEEP ENERGISED | Wellhead emergency shutdown valve and its actuator. Caution: With the master valve removed the ESD is the only automatic barrier remaining. Do NOT isolate. Confirm the ESD remains armed and will close on demand. | — |
| 100 | GW-14-SCADA | Breaker | KEEP ENERGISED | Wellhead SCADA, pressure and temperature transmitters, and the remote shutdown link. Caution: The control room watching the well is part of the barrier. A crew at the wellhead cannot see a reservoir response coming. Do NOT isolate. Confirm transmitters read true and the control room can see the well throughout the job. | — |
| 110 | GW-14-H2S | Breaker | KEEP ENERGISED | Fixed H2S detection at the cellar and personal monitors on the crew. 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. Do NOT isolate. Confirm fixed detection is in service and every crew member carries a bump-tested monitor. | — |
| 120 | GW-14-CRANE | Block | KEEP ENERGISED | Wellhead crane or gin pole used to lift the master valve. Caution: A master valve is heavy and directly over the cellar the crew stands in. Do NOT isolate. Confirm the lift is rigged and the valve is supported before the studs come out. | — |
What your site must supply
- 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.
Authorship and validation
This example was authored by Setyr for domain validation. It is not derived from any customer's controlled documents. It illustrates the elements 29 CFR 1910.147(c)(4)(ii) requires a procedure to contain — it does not certify compliance, which is a property of an employer's programme rather than of any document.