Blowout and Subsequent Fire On Offshore Platform – Investigation Report

This incident took place almost a decade ago and refers to a rig blowout and the subsequent fire that broke on the platform. Initially the Rig was conducting directional drilling operations. After a stand being pulled the well began flowing at an increasing rate. The annular diverter element was closed and the well was put into the diverter system. The alarm was sounded to evacuate the Rig and Platform. After a while the end of the port diverter pipe blew off and an uncontrolled flow of gas, water, sand, and hydrocarbons caught fire. The fire from the uncontrolled flow out of the diverter was spread on the Rig floor.

Accident timeline

The following chronology is based on testimony and notes by drilling operations personnel.

18 July 2002. Diamond Offshore Drilling Rig No. 128 Ocean King moved on location to begin the drilling of the well. The well plan called for plugging an old well, reclaiming the slot, placing drive pipe, and installing new conductor casing at 1,201 ft. The plan was then to kick off the deviated hole at approximately 2,421’, and drill to target, deviating a total of approximately 5,500 ft. from the vertical.

6-7 August 2002. Completed plugging of the old well, pulled old casing, conductor pipe, and drive pipe. Installed new drive pipe. Drilled and drove new conductor pipe for the well to 1,201’ MD, and cemented to surface.

8 August 2002. Normal drilling operations, drilled to 3,592’. At 3,592’ MD the deviation of the well had reached 27 degrees as planned. Increasing drag indicated the need for a wiper trip. At 0800 hrs,

8 August, 0800 hours. A short trip to pull up into the conductor began. Trip operations were preceded by circulating and conditioning 1.5 times hole volume and getting bottoms up. During drilling, the gas detector had registered only a maximum of about 21 units, no spikes. During drilling, the returns were loading up with cuttings, so the ditch and shaker were each separately being monitored by a crewmember. A camera was employed, focused on the return line into the shaker. The camera had monitor screens in the driller’s shack and company-man’s office. Present in the driller’s shack on the rig floor were the driller, company-man, directional driller, and tool pusher (OIM). Other work during that time included pulling pipe, pulled stand #1, filled the hole with 2 bbls. Pulled stand #2, filled hole, took 1 bbl. Pulled stand #3, the driller observed a slight weight bobble, worked pipe some, filled with about 1 bbl. The string was pulling wet. When the driller pulled stand #4, he observed a 20,000-lb over-pull. He worked the string up and down for gumbo. Working the pipe decreased the overpull; hole fill for stand #4 was 0.25 bbls.

8 August, 0815 hours. According to testimony, when the driller screwed into the 5th stand, he had a plunger type flow in string. The crew filled the hole, pumping below at 33 strokes per minute with 9.3 water-based mud. After fill, the driller shut the pumps down and observed no flow on line. When stand was pulled, still no flow was observed while racking stand #5.

8 August, 0817 hrs. Screwed into stand #6, rotated to try and get assumed gumbo ball off, pumped all the way to get ready to break out. Discussion ensued between the driller and the company-man on the need for a nut plug to help break up a suspected gumbo mud balling. The driller worked 6th stand, pumped on it. Some flow began showing on shaker after racking 6th stand, but not particularly unusual in a string pulling wet. The flow was about 2-3 fingers wide and appeared to be declining. The driller, directional driller, OIM all thought it was hydrostatic.

8 August, 0830 hours. Broke out stand #6 and screwed into the 7th stand. Suddenly, the flow became obvious on the monitoring camera, the stream growing to about two handswide. The OIM and directional driller started out of the driller’s shack to go look at the stream. Immediately they noticed and yelled that the mud was boiling out of the rotary. Almost immediately, before the OIM and directional driller got fully out of the driller’s shack, a full flow began spewing out of the mud return line. The driller immediately chained the brake down, closed the diverter, checked all valves, and saw about 500 lbs on the diverter packer. The diverter began to leak and the OIM raised the pressure to 900 psi, which contained the leakage. The flow began to shake the rig and a stream of mud started to shoot 30’ out of both diverter lines. The diverter system was set up so that initially both lines are automatically open, after which one, but only one, could be closed to direct flow into whichever diverter line was desired. At this time, the flow was apparently directed into the portside diverter partly because the starboard side line braces were beginning to deform from the pressure. Pumps were brought up to an estimated 40 strokes/min. amid increasingly violent shaking of the Rig. The derrickman saw the mud flow and boil, and rapidly abandoned his position, evacuating down the ladder with aid of an assist belt. All hands immediately abandoned the Rig floor to the sound of the alarm. The diverter was observed to be twisting and bending on the portside, which was taking most or all of the flow from the well. At some point, the starboard diverter may have been re-opened to try to relieve the pressure of the flow on the portside.

8 August, 0840 hrs. The crew collected at the abandon stations. The company-man called the Platform and informed them that the Rig was being evacuated. The production crew decided to ESD the Platform and abandon from the Platform’s plus-ten deck onto the field boat. The OIM asked the driller to switch pumps to seawater. The driller, derrickman and motorman went back below deck and swapped the pumps over to pumping seawater, an operation that took about 40 seconds. The driller then checked through the living quarters to confirm complete evacuation. The Company-man tried to phone several superintendent and supervisory personnel without success. The diverted flow from the well was now rocking the rig as the company-man gave up the effort to establish phone contact with supervisory personnel. The OIM contacted and briefed the Rig area manager on the situation until the company-man re-entered the office and suggested they quit trying to contact supervisors, at which time all went to abandon stations. At the abandon stations, the roster was checked but there was some uncertainty because of the confusion generated by crew change earlier in the morning and a discrepancy in the onboard roster, which was being updated to reflect the crew change. Consensus review and radio contact with the two capsules already launched indicated that everyone was believed accounted for.

8 August, 0900 hours. Two capsules had been launched when the sound dynamics of the flow from the diverter changed. This was likely caused by the end of the portside diverter blowing off. The uncontrolled flow now began to blow directly off the portside with increasing violence. Launch of the remaining capsules was completed and the four escape capsules, with the entire 47 man crew from the Rig, steered toward Diamond Drilling rig Ocean Star, which was stacked about 3 miles away. The production field boat completed evacuation of the eight-man production crew and proceeded to another platform.

8 August, 0905 hours. The Rig escape capsules had progressed a short distance when the flow out of the portside of diverter ignited, followed by ignition of combustibles on the rig itself.

8 August, 0915 hours. Flow from diverter declined and finally ceased, causing the fire to abate, apparently limited thereafter to combustibles on the Rig.

8 August, 1030 hours. All capsules were lifted onto deck of the Ocean Star. Supervisors gathered everyone on the heli-deck, double-checked roster until they were satisfied all were safe. The flow from the diverter had bridged after about 10 minutes, though combustibles on the Rig itself continued to burn.

8 August,1650 hours. Fire on the Rig burned out, though electrical arcing caused by burned cables was occurring. Under the supervision of Wild Well Control, seven people boarded the Rig and shut down all power, turned water on arcing cables, and departed after one hour.

9 – 16 August 2002. Crew conducted sundry daily efforts to kill the well, assess damage, clear debris, isolate pipelines, production systems, and repair essential systems.

17 – 27 August 2002. Completed installation of the freeze plug to secure the well, repaired the diverter and other essential equipment, rigged up, ran, and analyzed well with logs, etc. Discovered two thick “formation plugs” thought to be caused by bridging; no evidence of cross flow or flow to surface; therefore completed P&A operations. Rig moved east of platform for repairs.

Photo above: Starboard diverter piping discharge after blowout.

Photo above: Portside diverter piping exit after loss of pipe end.

Photo above: Portside diverter after blowout: and abraded burned cablebundles.

Root causes

The loss of control was caused by gas swabbed into the wellbore, probably from a normally pressured gas productive zone at approximately 2,660 ft., during short trip operations. There is no evidence the zone was over-pressured or had been charged up by producing or drilling during the course of operating the field.
The failure of the well plan to identify the presence of a potentially gas productive zone at about 2,700’ may have precipitated a default from precautionary shallow-gas hazard drilling activities to normal drilling operations, which in turn introduced the swabbing effect. The shallow-gas hazards for this well were reviewed by Operator personnel according to the methodology usually applied in producing fields. No new seismic or sparker surveys were shot to check the possibility of a shallow-gas zone. Though previous electric logs indicated the presence of probable gas in the 2,700’ sand in the general proximity of the planned wellbore path, no mention of the possibility of gas in this zone was included in the well plan.
It is possible that, despite the heavy loading of the mud system, the base weight of the mud used to drill the surface hole was not sufficient to allow a containment margin during tripping operations.

The resulting damage to the Rig was caused by the ignition of the uncontrolled hydrocarbon flow and the subsequent spread of the resulting fire to the combustibles on the Rig floor. Possible cause of the fire are:

The failure of the diverter, specifically the end of the portside line, possibly led to fire on the Rig floor by allowing uncontrolled hydrocarbons to exit the diverter beneath the Rig floor rather than outboard.
The diverter failed in two locations, possibly because of insufficient tie down supports, an unapproved routing plan, and a marginal design that allowed the flow to impact an inclined pipe wall immediately upon exiting the diverter housing.
Ignition of the uncontrolled hydrocarbon flow was possibly caused by electrical arcing in the electrical cable bundles that were subjected to the diverter flow stream. These bundles were routed in close proximity to the diverter and were subjected to direct impact of an abrasive mixture after the failure of the portside diverter. Once the insulation of the cables was abraded, arcing may have been allowed.
After the end of the portside diverter was blown off, the uncontrolled flow directly impacted acetylene bottles stored on the catwalk next to the diverter system. The ignition of the flow led to the explosion of some of these bottles, possibly contributing to the intensity of the fire and damages.

Photo above: Portside floor adjacent to diverter, exploded acetylene bottles.

Photo above: Portside drill floor motor shed, above diverter, after fire.

Photo above: Portside drill floor motor shed aft above diverter. Destroyed cables and damage.

Photo above: Fire damage to beam above port diverter, beneath drilling floor.

Lessons to be learned

Shallow-gas hazard studies prepared for new wells from previously drilled surface locations should include a study of the old logs as well as seismic data. Drilling operations should be explicitly warned of shallow-gas deposits identified in previously drilled wells.
Care should be taken in the design, installation, and bracing of diverter systems to allow enough rigidity to resist flexing failure and to allow uncontrolled flows to exit the system downwind and outboard of the rig. Proper design, construction, and targeting to limit the direct impact of flow upon pipe walls should be observed.
Where possible, electric cable bundles should be routed so as to be clear of the diverter system. Storage of flammable supplies next to the diverter system should be restricted where possible.