Explosives Safety • Common Explosive or Highly Reactive Operations – Perforating – Pipe Cut-off (chemical, explosive, Split Shot, Thermite, Collider Tools) – String Shots – Gas Generator charges – Any tool or equipment with an explosive component or highly reactive chemical such as bromine trifluoride. Warning and Disclaimer: Perforating charges, string shots, explosive initiators, gas charges for setting downhole tools, gas propellent tools, chemical cutters, thermite cutters, linear cutters, pipe cutters, and many other tools used in wells contain high and low explosives or ultra fast reacting chemicals and should only be handled by licensed experts. This module reports some of the more common information on explosive safety but it is not a training program for handling these tools!
Transcript
Explosives Safety
• Common Explosive or Highly
Reactive Operations
– Perforating
– Pipe Cut-off (chemical, explosive,
Split Shot, Thermite, Collider
Tools)
– String Shots
– Gas Generator charges
– Any tool or equipment with
an explosive component or highly
reactive chemical such as bromine
trifluoride.
Warning and Disclaimer: Perforating charges, string shots, explosive initiators, gas charges for setting downhole tools, gas
propellent tools, chemical cutters, thermite cutters, linear cutters, pipe cutters, and many other tools used in wells contain
high and low explosives or ultra fast reacting chemicals and should only be handled by licensed experts. This module reports
some of the more common information on explosive safety but it is not a training program for handling these tools!
Accidents with Explosives
• In entire US industry (mfg, mining, demolition,
construction and oilfield) – there are about 50
deaths per year.
• In US oilfield – there are about 12 serious
accidents per year. 8 deaths in worst year.
– In 20 year study of 3 major service providers, there
were 94 incidents, 49 injuries, and 28 deaths.
• All preventable.
Explosive Injury Data from Jim Brooks
Perf Gun and Cutter Danger Radius
• Some Dangers: – High speed very directional shaped charge pulse (jet traveling at 21,000 ft/sec)
– Projectiles and debris – supersonic speed, path unpredictable.
– Highly reactive and/or hot fluids and debris from cutters
– Noxious/Poisonous gasses
– Concussive effects of blast
• Radius of “kill” effect – similar to hand grenade – military spec is roughly 36 m or 118 ft.
• Safe Area – 150 ft and behind a barricade. Off location if at all possible.
• Highest Risk times: – Loading
– During and after arming a gun (electrical and ballistic),
– During pressure testing of a lubricator containing a gun,
– Until the gun is well below ground level (about 1000 ft)
– Recovery of any misfired (still live) gun,
– Hang-fire or delayed fire – unpredictable behavior
– Fired guns until inspected by service co. that all shots fired normally and no trapped pressure remains in the gun.
When did the accidents occur?
• 1980 to 89: 14 injuries 8 fatalities
• 1990 to 94: 18 injuries 10 fatalities
• 1995 to 00 16 injuries 9 fatalities
• These are just from three major US based
service providers, they do not cover the
independents and do have information from
non US operations.
Incidents Injuries Fatilities
Power on Panel 15 19 15
Stray Power 6 0 1
Pinched Explosives 13 7 6
Pressure 5 0 0
Unknown Problems 9 7 2
Causes of Oilfield Accidents with Explosives
Source – James Brooks, Schlumberger, Jan 2002
48 33 24
Oilfield Accidents with Explosives
• Most accidents are the results of missed runs (ref: Cyril Sumner)
– Retrieved guns firing causes (ref: Jim Brooks data) • Power left on panel – 56%
• Pinched explosives – 29%
• Unknown – 12%
• Cause of detonation by cell phone, radio, radar, etc., is a very remote possibility. If proper resistor caps are used, accidental detonation by low power stray current is sharply reduced.
• However: anything that raises the incidence of missed runs (failure to fire the device when on target in the well) significantly raises the possibility of accidents.
• In my opinion - one thing that has increased the number missed runs (from 2% to 10% or more) is the use of “radio safe” firing heads.
Stray Power
• Radio frequency emissions, ground-to-rig electrical differential, static, impressed current, cathode protection, lightning and any other electrical source that uses the well as a ground.
• Procedure – measure stray voltage with equipment isolated from well – do not proceed unless differential is below regulations that set acceptable limits.
Some Other Identified
(Problem?) Electrical Signals • Marine radios on passing ships
• Radar
• Electrical storms (within 5 miles, hearing or sight – whichever is further)
• Mobile phones and radios
• Electric welders
• Thaw machines
• Electrical circuitry that may be in contact with the well (data gathering, cathodic protection, etc.)
• Static and differential voltage potential of the well site. Static is the more important problem.
Some points to consider when retrieving a
perforating gun that failed to fire (missed run)
• A general information E-line sequence:
1. Double check panel off and firing key removed.
2. Pull gun up hole, if possible, to a shallow, cooler, safe location (tight zone) and wait minimum of 1 hour.
3. Pull gun into lubricator, wait minimum of 15 minutes to 1+ hour depending on downhole temperature. Gun must cool down.
4. Lay lubricator down, disconnect head and remove detonator (Examine for signs of low order detonation. Care must be taken for prevention of sudden release of trapped pressure.) Non-experts, DO NOT GO NEAR THE GUN. Inspection of the gun can occur only after it is torn down.
5. Some guns may not be re-run. Some explosives develop a “memory” for temperature and pressure. Some seals may need to be replaced.
These few notes are not a procedure.
Explosive Components
• Detonator or cap (primary explosive in
some cases - most dangerous)
• Detonating Cord
• Charges
– High explosive – TNT, Nitroglycerine , RDX,
etc.
– Low Explosive – gas generators – black powder
Radio Silence
• Why is it needed?
• When is it needed?
• When can it end?
• What other devices are involved?
• Having radio silence is preferable, but offshore
platforms may never be completely free of RF
(radar, near-by fishing boats and ship traffic).
Radio Silence
• Why? – there is a very remote chance that radio transmissions will set off a detonator (actually, it is almost unknown in the Petroleum Industry).
• When to use a radio silence policy – When using any detonator that has not been certified as radio safe.
• When is it over – when the gun is 1000 ft below the ground level. Re-institute radio silence when gun is pulled until it has been confirmed to have all fired.
• However, be cautious. Radio safe detonators are less reliable than other detonators on firing and most industry perforating accidents are from work around missed runs (guns did not fire). “Radio Safe” detonators actually increase the incidence of missed runs.
Special Cases – a Live Gun Stuck in
the Wellhead • Explosives can be fired by shearing a live perforating gun, a
chemical or explosive pipe cutter, or any device with a detonating cord or cap. Shearing or crushing by BOP rams, etc.
• Shearing creates high risk of firing gun high-order by pinching.
• Perforating gun misfire (fail to fire on bottom) rate is about 2% for electric line with standard resistor caps (>10% for so-called "radio safe" firing systems) and 8% for TCP guns (including partial gun firing) (field study information from Amoco in 1994).
• TCP guns don't always fire the whole gun (2% to 5% chance on longer guns), so check even a spent gun before you shear it.
• Experts estimate about 90% to 95% of all perforating gun accidents involving surface firing occur after a missed (fail-to-fire) run.
• A live gun recovery plan should be part of the perforating planning. Most explosive handling companies already have good ones so check with them.
Live Gun Stuck in the Wellhead-
Causes of Sticking • Perforating guns in smaller sizes (<2.5") have a tendency to swell
at least 10% and/or bow by 5o.
• Gun sticking has occurred in the EOT entry guide and well head, usually on fired gun recovery.
– Strip guns can come apart - remove several capsule charges from a well head after a missed run in the Rocky Mountains.
– Stuck a large unfired TCP gun in the wellhead during a recovery of a TCP gun in Trinidad.
• Hammering with a weight bar and a blind box on a on a gun that is stuck at the bottom of the tail pipe may work in tailpipe, but contingency plan needed for live gun recovery at well head.
• Problem frequency increased when:
– if clearance is less than 10% over initial gun OD for guns over 2.5”
– if clearance is less than 20% over initial gun OD for guns less than 2.5".
The Safety Documents
• See the BU or Asset policy on the arming and running of explosive devices. If they don’t have a policy or defer to the service provider – MAKE SURE THEY HAVE AND FOLLOW A SAFETY POLICY.
• Any doubts? – Call me (from off well location). I’ve available 24 hours a day for this type of problem. George E. King 1 281 366 4083 (office), 1 281 851 8095 (Cell), 1 281 693 0371 (home)
Support Documents
• Every service provider that deals with explosives
must have a safety document – ask to see it and
ask help to understand what needs to be done, who
must do it, and who makes the decisions.
• An estimated 70% of the explosive accidents
occur with 30% of the companies involved in
perforating service work (Jim Brooks 2002 data).
Experience and adherence to policy are critical.
• A consistent safety program and strict adherence
to that program makes the safety difference.
Arming Sequence
• An electrically fired explosive device must always be electrically armed before being ballistically armed.
• If this sequence is followed, accidental initiation of the detonator or blasting cap when the electrical connection is made, will not cause the rest of the explosive train (primer cord, shaped charges, cutters and setting tools) to detonate.
Arming
• Electrical arming : electrically connecting the detonator to the E-line.
• Ballistic arming : connecting the armed detonator to the rest of the explosive system, (primer cord and shaped charges)
Arming
• Arm the gun (connect the detonator) just prior to RIH at the jobsite.
Arming – (This is for information
only – it is not a procedure) 1. Place cap in safety tube before removing shunt.
2. Remove shunt after securely closing safety tube cover.
3. Check cap electrically for insulation and continuity.
4. Cut one wire lead to desired length at a time. Do not simultaneously cut both lead wires.
5. Prepare conductor wire lead and check for sparking.
6. Splice and insulate conductor wire to one blasting cap lead.
7. Prepare ground wire lead and splice to remaining cap lead and insulate.
8. Make a fresh square cut on detonating cord using a sharp blade and a block of wood for back-up.
9. Remove cap from tube and insert open end on detonating cord.
10. Push cap until it seats on cord.
11. Hold cap and cord firmly together with one hand and double crimp cap using a standard crimping tool only.
12. Secure detonator and cap end of gun or arming porthole as required.
13. Pick up armed gun, carefully, and stab into the lubricator or BOP’s. Make up lubricator to BOP's.
Disarming Unfired Guns
• All these and other perforating operations to be carried out ONLY by the service company.
• During recovery, the E-line unit and other well operations must be in same safe condition as it was when the gun was armed.
• Always assume the gun has not detonated properly, misfired, when recovering it at surface no matter what the indications were.
• Check for shots fired while gun is exiting lubricator. If no shots have fired, the most dangerous situation, then the blasting cap must be disarmed as soon as possible. The odds of the gun having trapped pressure inside are also much higher when it has not fired.
Recovery and Disarming an
Unfired Perf Gun or Cutter • 95% of perforating accidents occur with misfired
(retrieved) guns.
• The main problem that causes missed runs is electrical connection problems.
• Can the device be dropped and cemented over without creating problems later? The gun will eventually fire low order or the charges will decompose (e.g., burn) in place.
• Absolute fewest people on location – recommend service company experts only.
Recovery and Disarming
• Can the detonator be removed before the
gun is pulled? (some TCP and CT devices
provide this opportunity).
• During recovery, the pad, E-line and well
must be safed-out (same as running).
• Always assume that the gun being pulled is
live, regardless of indications.
Recovery and Disarming
• From a safe distance, check for shots fired as gun is pulled from lubricator.
• If no shots fired: – Most dangerous problem – suspend operations, let the
gun sit, below ground preferably or out of the way, until it cools. Check heat with a remote sensor – don’t approach gun.
– Incidence of trapped gas pressure is also higher (low order firing or burning of charges)
