What is a Well Blowout?
A well blowout occurs when control over the pressure in the borehole is lost and oil and gas “blows out” with tremendous pressure and flows to the surface.
While drilling for oil or gas, a drilling rig drills directly deep into the ground. This depth can sometimes be in miles into formations of rocks that have trapped gas or oil.
These pockets of trapped oil and gas are normally under an incredibly high pressure. This high pressure is usually kept under control by various techniques by pumping a drilling fluid in the ground with the drill as it bores deep underground.
This is very dangerous since the spewed stream is highly volatile and with the smallest of spark can catch fire. When this happens it is observed as a spectacular tower of flame shooting high into the air.
The oil or gas which is being extracted has been created and trapped in rock formations deep under the earth’s surface over the period of millions of years.
The combination of the rock squeezing or compressing the fluids and the earth’s gravitational pressures means the majority of the fluid or gases being sought are contained within rock formations under pressure.
The oil or gas that is contained within these pockets of rock did not start out as hydrocarbons but started out as a carbon-based substance at the earth’s surface.
The process of carbon-based plant or animal material becoming hydrocarbons takes millions of years and is caused by the material being covered by sand or rock, sedimentary material that squeezes the water from the carbon-based material and eventually results in formation of either oil, gas or coal.
The formation of these three carbon based hydrocarbon products usually requires enormous pressure. So, when extracting oil or gas through drilling, the first obstacle that has to be overcome is the pressure the hydrocarbons are under while being extracted.
There are three main types of blowouts:
Surface blowout: May blowout oil, sand, mud, rocks, drilling fluid, natural gas, water, etc. over land.
Subsea blowout: A blowout underwater. An example of a subsea blowout is the Deepwater Horizon Well blowout.
Underground blowout: A blowout occurring totally underground. Many surface blowouts begin as underground blowouts.
Safety Measures to prevent Blowout
The drilling process has been developed to enable the safe extraction of hydrocarbons from pressurized formations. The first procedure that is used is cementing.
Surface casing is cemented into the hole and serves as a type of lid, like that on a pressure cooker that holds back the down-hole pressure. This casing is cemented even before drilling begins.
Once the surface casing is cemented into place and the surface cement has been tested, drilling begins. As the well is drilled, an “oil-based drilling mud” is used to lubricate the drilling bit and circulate the cuttings out of the hole as drilling occurs.
The oil-based mud also contains a product called “barite” which increases the mud weight so that this is sufficient to counter the pressure from the hydrocarbons that want to escape to the surface.
In addition to the drilling mud, the rig will have a BOP (Blow Out Preventer) stack in place to help prevent unwanted escape of pressurized hydrocarbons. The BOP stack usually consists of two sets of Rams and one “annular” preventer.
The BOP stack consists of “pipe rams” which are the main means of preventing hydrocarbons from escaping, the ‘blind” rams which are used when no drill pipe is in the hole and completely shuts in the well and “shear” rams which cut away the heavy drill pipe and completely shut in the well.
BOP’s are supposed to be tested on a regular basis to ensure they hold pressure.
Many blow-outs, explosions and serious injuries have occurred when the BOP’s were closed and the well was supposed to be shut-in. BOP’s are not fail-proof, and even if they seal, the pressures they face may exceed their rated capacity. Most BOP’s are rated at either 5,000 or 10,000 pounds.
Sometimes down-hole pressures can exceed the rated pressure of the BOPs. While most rigs are supposed to have enough “safe” or remote BOP stations where the BOPs can or should be capable of safe operation, these do not account for every situation, and it may be that the crew is unable to safely operate the BOPs.
By far, the most common cause of blowouts is drilling “underbalanced” – taking the risks of controlling the hydrocarbons that enter the hole by circulating them out while drilling. Safe drilling practices require the mud to be “weighted” up to hold back the pressure, but operators get in a hurry to produce the well, and time is money, so they drill underbalanced and lose control of the well.
If the well is drilled underbalanced, a choke manifold and sufficient gas buster should be used to flare off gas that migrates to the surface during the procedure.
Adequate safety measures need to be constantly in mind while drilling because a pressurized zone can be encountered at any time and this can result in sudden increases in pressure and a blowout.
Gushers were an icon of oil exploration during the late 19th and early 20th centuries. During that era, the simple drilling techniques such as cable-tool drilling and the lack of blowout preventers meant that drillers could not control high-pressure reservoirs.
When these high-pressure zones were breached, the oil or natural gas would travel up the well at a high rate, forcing out the drill string and creating a gusher.
A well which began as a gusher was said to have “blown in”: These uncapped wells could produce large amounts of oil, often shooting 200 feet (60 m) or higher into the air. A blowout primarily composed of natural gas was known as a gas gusher.
Despite being symbols of new-found wealth, gushers were dangerous and wasteful. They killed workmen involved in drilling, destroyed equipment, and coated the landscape with thousands of barrels of oil; additionally, the explosive concussion released by the well when it pierces an oil/gas reservoir has been responsible for a number of oilmen losing their hearing entirely; standing too near to the drilling rig.
To complicate matters further, the free-flowing oil was susceptible to igniting, causing a huge uncontrolled fire.
The earliest known oil gusher, in 1815, actually resulted from an attempt to drill for salt, not for oil. Joseph Eichar and his team were digging west of the town of Wooster, Ohio, along Killbuck Creek, when they struck oil.
Oil drillers struck a number of gushers near Oil City, Pennsylvania in 1861. The most famous was the Little & Merrick well, which began gushing oil on 17 April 1861.
The spectacle of the fountain of oil flowing out at about 3,000 barrels (480 m3) per day had drawn about 150 spectators by the time an hour later when the oil gusher burst into flame, raining fire down on the oil-soaked onlookers. Thirty people died in that incident.
Recovering from a Blowout
Most commonly, when a well is lost to a blowout, the drilling rig would have collapsed around the well, making a proper assessment of the situation difficult.
Firefighters arrive as quickly as possible and use machinery to remove the damaged rig and associated debris so they can assess the situation and choose the best method to fight the blowout.
In the early days of fighting oil well fires, the most common technique to smother a blowout was to snuff it with a dynamite blast. Pioneered by Myron Kinley, the intention was to blast fuel and oxygen away from the flame, effectively eliminating the fuel source, similar to snuffing out a candle.
Although the first instance of this method dates back to 1913, dynamite blasting continues to be one of the most frequently employed methods.
Another common method employed by oil well firefighters involves drilling a “relief” well or wells into and intersecting the blowing well. This intersection gives the kill fluid a conduit to the surface, enabling what is called a “subsurface kill.”
A more complicated method for bringing a blown-out well under control involves carefully capping the well with a new blowout preventer, or “BOP.”
BOPs are essentially large valves on the surface of the well that quickly shut off the well as a last ditch precaution to prevent a blowout from occurring.
In this procedure, the debris of the collapsed rig is carefully removed and a high-pressure abrasive cutter is used to sever the damaged BOP and wellhead for removal.
A long boom assembly – at the end of which is a replacement BOP – is maneuvered into position. Large amounts of water are sprayed on the replacement BOP to combat the flames and to keep the replacement BOP from getting too hot.
The BOP is quickly lowered onto the well and bolted into place, thus capping the blowout.
Since there is a large activity of oil extraction from digging wells under the sea, there is always a probability of an under-sea blowout. A major undersea blowout is very difficult to control and can result in an environmental disaster as it occurred on April 20, 2010 in the Gulf of Mexico.
This was the largest underwater blowout in U.S. history. The blowout caused the explosion of the Deepwater Horizon, a mobile offshore drilling platform owned by Transocean and under lease to BP at the time of the blowout.
It caused 11 fatalities and loss of billions of dollars, both due to loss of drilling platform, capping efforts and loss of oil at sea. The damage to the environment and to marine life is colossal.
In 1991 during the Kuwait-Iraq war, the retreating Iraqi forces set fire to over 600 oil wells and other oil-bearing entities.
The fires were started in January 1991, and the first well fires were extinguished in early April 1991, with the last well capped on November 6, 1991.
Although this was not strictly a blowout, as it was initiated by deliberate action, the fire-fighting efforts capping of the oil wells were similar in nature. 90% of all the fires in were put out by sea water, sprayed from powerful hoses at the base of the fire pumped from the sea.
Present safety status
After the Deepwater Horizon accident, many lessons were learned; safety procedures were improved, operating techniques were refined, better safety equipment was introduced and above all regulatory safety oversight was strictly implemented. As a result of all these measures, a significant reduction of blowouts has been achieved.