Dr. Alfons Maier
Blowout – An extremely dangerous and complex hazard
The flame shot 60 m into the air when gas escaped from a production well at a natural gas reservoir and ignited: a blowout.
The underground porous reservoir in a limestone formation in Poland had a capacity of some 600 million m3. Eight wells had been planned with the intention of extending the storage capacity to 3.5 billion m3 – which would make it one of the largest natural gas reservoirs in Europe.
Two days before the loss event, work was in progress on the fourth well – a deep horizontal well with a projected final depth of 1,500 m. Suddenly, workers noticed a distinct loss of drilling fluid (bentonite mud). As usual in well-driving operations, drilling fluid was being pumped through the bore string to equalise the pressure when drilling into a deposit. This means that some of the fluid must have flowed into adjacent rock. As the fluid losses were continually increasing, an attempt was made to remedy the situation immediately but without success.
The resultant lack of drilling liquid led to the gas escaping from the well bore and igniting. The flame shot 60 m into the air and could be seen kilometres away.
An uncontrolled escape of oil or gas from an exploration or production well is extremely dangerous. There are only a few specialists throughout the world who can stop blowouts – regardless of whether the well is burning or not. In the initial response, water must be used to cool the surroundings and rescue services. Then the blowout preventer (an array of special valves on the well bore) must be closed or replaced. This is a perilous, technically elaborate, but also lucrative business – one of the most advanced disciplines of fire-fighting.
Difficult fire-fighting operation
After about 30 minutes, the rig collapsed and had to be removed to permit further fire-fighting efforts. It was extremely difficult for the fire-fighters to attach steel cables to the rig fragments, because in order to do so they had to get very close to the flames. Heat-resistant clothing was needed. About 5 tonnes of scrap steel – roughly a third of the original rig structure – had to be removed using special vehicles.
About 200 fire-fighters were involved in the operation, as well as several drilling and mining specialists. A second rig (around 45 m away) and an extraction facility (some 15 m away) were also in danger and had to be cooled continuously along with other units in the vicinity. This required 22 fire-fighters and 16 water tenders. The water soon began to run short but was supplemented with supplies from a natural well about 2 km away. For safety reasons, the police and fire services cordoned off the area and blocked all the access roads.
Stopping the escape of gas
At this point in time, the emergency plan went into action. The operators, the responsible mining authority, and highly specialised mining experts agreed on the measures to be taken to prevent the gas from escaping. Two completely separate approaches were developed: the one involved closing the blowout preventer by injecting water, the other drilling a relief well.
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