Skip to comments.Blown out well seals off gas leak by itself; operators ‘lucky’, experts say
Posted on 07/25/2013 6:32:14 PM PDT by thackney
Natural gas stopped flowing from a runaway well in the Gulf of Mexico after sediment in the well blocked the uncontrolled flow, federal authorities reported Thursday.
The Bureau of Safety and Environmental Enforcement said the well bridged over, meaning small pieces of sediment and sand flowed into the well path, restricting the flow and countering the pressure. A fire that had engulfed a portion of the Hercules 265 jack-up rig was put out early Thursday morning, according to a Coast Guard report to Congress.
They are lucky, said Bud Danenberger, a consultant and former chief of offshore regulatory programs at the Minerals Management Service, which has now been reorganized into the Bureau of Safety and Environmental Enforcement.
What really happened is that natural sediment flowed into the well bore and essentially blocked the flow, Danenberger said.
A leak in the natural gas well, owned by Walter Oil & Gas, had ignited a fire on a jack-up rig operated by Hercules Offshore late Tuesday night, hours after its 44 workers had been evacuated, according to the Bureau of Safety and Environmental Enforcement.
The fire possibly was caused by friction from sand in the blowout preventer, which also burst into flames, according to a Coast Guard report to Congress.
A drillers best friend
Danenberger noted that about one third of all blowouts in the Gulf of Mexico since the 1950s have stopped themselves without human intervention, either by bridging or a combination of bridging and the natural slowdown of the flow.
It is fairly common, Danenberger said. Some people call it a drillers best friend.
Justin Vandenbrink of the Houston Geological Society agreed that bridging of oil and natural gas wells is common. Drillers typically hold a well open using steel or cement casing that keeps the hole intact. But a freshly drilled portion remains exposed, leaving loose mud and softer rocks along the walls of the well vulnerable to falling back into the hole, Vandenbrink said. Bridging also can occur above a bit that has just drilled an area, he said.
In the current incident in the Gulf, the leaking natural gas that fueled the fire likely was not strong enough to hold some of the exposed mud and sediment in place, said Don Van Nieuwenhuise, director of petroleum geoscience programs at the University of Houston.
My gut feeling is this reservoir was not a high-energy reservoir and the gas flow rates probably were relatively small compared with what could happen, Van Nieuwenhuise said, adding that the natural gas is not going to be lifting a lot of the sand. Its just going to come straight up and so there was nothing to support the wall of the well and it just collapsed.
Regardless of how it happened, the bridging of the well was a break for everyone involved with responding to the incident, Van Nieuwenhuise said.
The fact that its bridged over is a lucky thing and probably a good thing and will help them do whatever they have to do because its going to cut down the flow of the gas, he said. Itll be easier for them to control the gas flow whether they do it at the surface or subsurface.
Relief well planned
The responding team plans to use the next 24 hours to assess how to take the next steps, which currently includes plans for both a top kill and relief well. The Bureau of Safety and Environmental Enforcement had directed Walter Oil & Gas on Wednesday to begin preparations to move another jack-up rig to the location to drill a relief well to stem the uncontrolled natural gas flow. The company has applied for a permit to drill the relief well and is awaiting approval.
This time will be used to assess the platform from the air and surface to build confidence in the stability of the bridge to enable personnel to safely board the rig tomorrow, said William Colclough, a spokesman for the Coast Guard. Wild Well Control will diagram damage and Source Control will establish source control mitigation, safety plans and timeline to include top kill and relief well operations.
The Coast Guard has confirmed that the jack-up rig is still intact, though the fire caused the cantilever drilling platform to collapse. The cantilever is an appendage of the jack-up rig that moves the drilling equipment over the well platform.
A smaller flame, about 10 feet in height, was still present on the lower derrick Thursday afternoon, but the flame from the wellhead has been extinguished, according to the Coast Guard.
There is no pressure and no natural gas flow coming from the riser of the well.
The natural gas leak appears to have occurred on the drilling rig above the water line, with no gas leaking into the water.
The natural gas which predominately consists of the potent greenhouse gas methane was ignited, reducing its environmental consequences. When methane burns, it produces carbon dioxide, which is less potent than methane in equal quantities and not as significant of a contributor to climate change.
If the leak had occurred in the water, the environmental implications likely would be lower. Some of the methane would have been dissolved and consumed by bacteria that feed on the resource, said John Kessler, an associate professor of earth and environmental sciences at the University of Rochester, who worked on six studies related to the impact of the Deepwater Horizon incident.
Any methane not consumed by bacteria would have floated to the surface and vented into the atmosphere, but likely not at a quantity that would have any measurable impact on the climate, Kessler said.
Even if we look at the amount of methane that was emitted from the Deepwater Horizon disaster, which was by far more than what we have here, that was not able to contribute to the current level to the methane increase in the atmosphere that we are observing, Kessler said. It was just too small to have a global signature.
Debate over regulations
While the source of the accident is not yet known, it has reinvigorated debate over whether increased regulation is necessary to prevent these types of accidents.
It will be interesting to see when the investigation is done what the root cause was and what really happened here, and if it involved a regulation or not, said Charlie Williams, executive director of the Center for Offshore Safety, an industry organization. The Center has advocated for a safety system that encourages participation rather than penalizes non-participation.
Others say that the danger of shallow water drilling has been overshadowed by the specter of another deepwater Macondo-style spill.
There is an awful lot of attention on deep water, but there has been a higher blowout rate on the shelf, Danenberger said, referring to the region of shallower water in the Gulf of Mexico. You cant forget about the shelf, where the wells are so prolific.
The lesson is that Macondo was not a deep-water problem per se. It was a management problem, Danenberg added. The blowout rate is historically higher on the shelf, and we need to address all blowout issues, regardless of where they occur.
Not really lucky at all. Pretty much predictable. Our studies in rock mechanics for blowout wells pretty consistently show that in most rock the well will bridge within about three days or not at all. Simply a matter of rock failure due to local depletion and loss of confining force.
Obama must be pissed
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