Write a risk assessment for oil producer well with a passing DHSV

For an oil production well with a passing downhole safety valve (DHSV), the risk assessment should treat the condition as a well integrity and barrier management issue with potential for loss of containment, escalation to fire/explosion, toxic gas exposure, and major accident hazards. The assessment should be task-based and scenario-based, covering normal production, intervention, isolation, maintenance, start-up/shutdown, and emergency conditions. Hazards should be identified for each step of the work, with risk evaluated by likelihood and severity, then controls confirmed or upgraded before work starts. The assessment should include routine and non-routine work, interactions with other activities, worker exposure, equipment used, task duration/frequency, location, training/competence, and foreseeable abnormal situations. [1] [2] [2]

• Primary well integrity hazard: the DHSV is passing and therefore cannot be credited as a fully effective barrier until tested, diagnosed, and formally accepted under the well barrier philosophy.
• Barrier failure scenarios: failure of the DHSV to seal, tubing leak, packer failure, tree/wing/master valve leakage, control line malfunction, failed pressure indication, and ineffective isolation during intervention or maintenance.
• Hydrocarbon release scenarios: release to atmosphere from tree, flowline, bleed-off points, vents, drains, sampling points, or opened equipment; liquid spray; gas jet release; accumulation in enclosed or low-lying areas.
• Pressure control hazards: trapped pressure, unexpected pressure communication across barriers, overpressure during bleed-down or testing, failure of temporary pressure control equipment, and incorrect valve line-up.
• Toxic and flammable gas hazards: potential hydrogen sulfide exposure in sour service wells, oxygen-deficient atmospheres in pits/enclosures, and ignition of hydrocarbon gas clouds.
• Occupational HSE hazards: dropped objects, line-of-fire, stored mechanical energy, manual handling, slips/trips/falls, noise, vehicle interaction, electrical hazards, and simultaneous operations.
• Human and organizational hazards: inadequate competence, poor shift handover, weak permit controls, incomplete isolation plans, deficient communication, and failure to learn from near misses.

[2] [2] [18] A practical barrier philosophy is to verify at least two independent barriers between the reservoir and the environment before intrusive work, and to avoid relying on a passing DHSV as one of those barriers. If the well must be entered, bled down, or worked on, positive isolation should be established and verified by pressure testing, monitored bleed-off, and locked valve configurations. Where line or space isolation is required, a single valve should not be treated as sufficient isolation for hazardous energy or hazardous material release; use more robust isolation such as double block and bleed, blinds, or physical disconnection where applicable. Any uncertainty in barrier status should force the job back to planning and management approval. [10] [10] [5]

• Stop or restrict production if continued operation cannot be justified within the well integrity management process.
• Confirm current well schematic, barrier diagram, valve status, pressure history, annulus status, fluid composition, H2S/CO2 content, and previous DHSV test results before work.
• Perform a formal risk assessment/JSA and a field-level risk assessment immediately before the task, with workforce participation.
• Define the task step-by-step: diagnose passing DHSV, establish alternate barriers, bleed down, test isolation, repair/replace valve, return to service, and contingency actions.
• Use the hierarchy of controls: eliminate the task if possible, substitute safer methods, apply engineering controls first, then administrative controls, then PPE.
• Install and verify engineered safeguards such as pressure-rated isolation, check valves where appropriate, remote-operated valves, gas detection, ESD functionality, ignition control, and barricading/exclusion zones.
• Control hazardous energy with lockout/tagout or equivalent isolation of mechanical, hydraulic, pneumatic, and electrical sources associated with actuators, pumps, panels, and moving equipment.
• Use only trained and competent personnel for well operations, pressure control, gas testing, and emergency duties.

[1] [4] [4] For hydrocarbon release and sour gas risk, continuous or frequent atmospheric monitoring should be part of the control strategy wherever gas could be released, accumulate, or migrate. Hydrogen sulfide is especially critical because it is highly toxic, flammable, and can rapidly disable workers; odor is not a reliable warning at hazardous concentrations. Test the atmosphere before entry into enclosed, low-lying, or suspect areas, ventilate where needed, and if gas cannot be controlled, require suitable respiratory protection and rescue arrangements. Areas with potential gas release should have ignition source control, explosion-proof/intrinsically safe equipment as appropriate, and clear evacuation triggers. [12] [12] [12] [16]

• Typical PPE for this work may include eye/face protection, head protection, hand protection, foot protection, hearing protection, flame-resistant clothing, high-visibility clothing, and respiratory protection based on the hazard assessment.
• For sour service or suspected gas release, respiratory protection selection must be based on measured or credible exposure and emergency escape needs.
• Chemical-resistant gloves and coveralls may be needed where produced fluids, treatment chemicals, or contaminated equipment are handled.
• PPE must not be the primary control where engineering or administrative controls are feasible; it is the last layer in the hierarchy.

[9] [17] [15] ALARP should be demonstrated by showing that major hazards from the passing DHSV have been reduced as low as reasonably practicable through a structured process: identify credible major accident scenarios, assess consequence and likelihood, implement inherently safer and engineered controls first, verify barrier effectiveness, and only proceed when residual risk is tolerable and further risk reduction would be grossly disproportionate to the benefit gained. In practice, this means documenting why the selected isolation method, monitoring, staffing, competence, emergency preparedness, and operating envelope are sufficient for the specific well condition. If barrier uncertainty remains, the risk is not ALARP and the job should not proceed until additional controls are implemented. [1] [3] [7]

Permit to work controls should be applied to any non-routine, intrusive, pressure-related, hot work, confined space, electrical, or isolation activity associated with the well. The permit should confirm scope, exact location, authorized personnel, responsible supervisor, isolations, gas testing requirements, validity period, simultaneous operations review, emergency arrangements, and handback conditions. For confined spaces or enclosed process areas, the permit must document the hazard assessment and the controls that require verification, such as atmospheric monitoring, isolation, lockout, ventilation, safeguarding devices, and respiratory protection. [5] [5] [5]

Emergency response planning should assume sudden gas release, fire/explosion, loss of well control, medical emergency, and rescue from a contaminated area. The plan should define alarms, shutdown actions, evacuation routes, muster points, exclusion zones, accountability, communications, rescue capability, first aid, external emergency interface, and criteria for stopping work. Workers should be trained and drilled, and emergency equipment must be available and suitable for the identified hazards. For H2S or hydrocarbon release, immediate actions generally include raising the alarm, stopping work, isolating ignition sources if safe, evacuating upwind or crosswind as appropriate, isolating the area, and preventing unprotected personnel from entering. [5] [5] [16]

From a compliance and standards perspective, the work should align with applicable oil and gas regulations, company well integrity standards, permit-to-work rules, hazardous energy isolation requirements, confined space requirements where relevant, PPE hazard assessment requirements, and recognized industry practices for barrier management and pressure control. The source material distinguishes production operations from drilling and servicing/workover activities, which matters because regulatory requirements can differ by phase of operation. Regardless of phase, the employer should document hazard assessments, inspect for changing conditions, communicate PPE decisions, and review the program whenever circumstances change. [6] [14] [8]

• Recommended risk assessment output: well description and current barrier status; DHSV failure mode; credible release and escalation scenarios; affected personnel and environment; existing safeguards; risk ranking; additional controls; responsible persons; verification steps; stop-work criteria; emergency actions; and approval to proceed.
• Minimum good practice before intrusive work on a passing DHSV well: verified barrier diagram, tested alternate barriers, pressure bleed-off and monitoring plan, gas testing plan, ignition control, exclusion zone, competent crew, permit to work, toolbox talk/field-level risk assessment, emergency equipment, and management authorization.
• Do not restart or return the well to normal service until barrier integrity is restored, function-tested, documented, and formally handed back.

[1] [11] [13]