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Transocean Deepwater Horizon Explosion-A Discussion of What Actually Happened?

 I will start the discussion with this which came in email a moment ago...

Anybody with any thoughts?


April 26, 2010       Transocean
Rig Disaster: The Well From Hell

Once more unto the breach, dear friends, once more. Here's another update on the disaster that befell Transocean Ltd. and BP last week in the Gulf of Mexico.
(Thanks to OI reader Steve, in Texas, for sending some of the photos in today’s alert.)

As you know by now, the drilling vessel Deepwater Horizon exploded, burned and sank last week, with the loss of 11 workers and injuries to many more. What happened? What's happening now? What's going to happen? I've spent the weekend working to piece things together.

An Ill-fated Discovery
According to news accounts, at about 10 p.m. CDT last Tuesday, Deepwater Horizon was stable, holding an exact position in calm, dark seas about 45 miles south of the Louisiana coastline. Water depth in the area is 5,000 feet. The vessel manifest listed 126 souls on board.

Deepwater Horizon was finishing work on an exploration well named Macondo, in an area called Mississippi Canyon Block 252. After weeks of drilling, the rig had pushed a bit down over 18,000 feet, into an oil-bearing zone. The Transocean and BP personnel were installing casing in the well. BP was going to seal things up, and then go off and figure out how to produce the oil -- another step entirely in the oil biz.

The Macondo Block 252 reservoir may hold as much as 100 million barrels. That's not as large as other recent oil strikes in the Gulf, but BP management was still pleased. Success is success --
certainly in the risky, deep-water oil environment. The front office of BP Exploration was preparing a press release to announce a "commercial" oil discovery.

This kind of exploration success was par for the course for Deepwater Horizon. A year ago, the vessel set a record at another site in the Gulf, drilling a well just over 35,000 feet and discovering the 3 billion barrel Tiber deposit for BP. SoDeepwater Horizon was a great rig, with a great crew and a superb record. You might even say that is was lucky.

But perhaps some things tempt the Gods. Some actions may invite ill fate. Because suddenly, the wild and wasteful ocean struck with a bolt from the deep.

The Lights Went out;
and Then.
.. 

Witnesses state that the lights flickered on the Deepwater Horizon. Then a massive thud shook the vessel, followed by another strong vibration. Transocean employee Jim Ingram, a seasoned
offshore worker, told the U.K. Times that he was preparing for bed after working a 12-hour shift. "On the second [thud]," said Mr. Ingram, "we knew something was wrong." Indeed, something was very wrong.

Within a moment, a gigantic blast of gas, oil and drilling mud roared up through three miles of down-hole pipe and subsea risers. The fluids burst through the rig floor and ripped up into the gigantic draw-works. Something sparked. The hydrocarbons ignited. In a fraction of a second, the drilling deck of the Deepwater Horizon exploded into a fireball. The scene was an utter conflagration.

Transocean Deepwater Horizon Listing

Evacuate and Abandon
Ship 


There was almost no time to react. Emergency beacons blared. Battery-powered lighting switched on throughout the vessel. Crew members ran to evacuation stations. The order came to abandon ship.
Then from the worst of circumstances came the finest, noblest elements of human behavior. Everyone on the vessel has been through extensive safety training. They knew what to do. Most crew members climbed into covered lifeboats. Other crew members quickly winched the boats, with their shipmates, down to the water. Then those who stayed behind rapidly evacuated in other designated emergency craft.

Some of the crew, however, were trapped in odd parts of the massive vessel, which measures 396 feet by 256 feet -- a bit less than the size of two football fields laid side by side.( This is one big
Drill Ship) They couldn't get to the boats. So they did what they had to do, which for some meant jumping -- and those jumpers did not fare so well. Several men broke bones due to the impact of their 80-foot drop to the sea. Still, it beat burning.

With searchlights providing illumination, as well as the eerie light from the flames of the raging fire, boat handlers pulled colleagues out of the water beneath the burning rig. In some instances, the plastic fittings on the lifeboats melted from the heat.

The flames intensified.
Soon it was impossible for the lifeboats to function near the massive vessel. The small boats moved away from the raging fountain of fire fed by ancient oil and gas from far below.

Transocean Horizon Burning At Night

The lifeboat skippers saved as many as they could find -- 115 -- but couldn't account for 11 workers who were, apparently, on or around the drill deck at the time of the first explosion. Nine of the missing are Transocean employees. Two others work for subcontractors.

Damon
Bankston to the Rescue 


Fate was not entirely cruel that night. Indeed, a supply boat was already en route to the Deepwater
Horizon. It was the Tidewater Damon Bankston, a 260-foot long flat-deck supply vessel.

Damon Bankston heard the distress signal. Her captain did what great captains do. He aimed the bow toward the position of Deepwater Horizon. Then he tore through the water, moved along by four mighty Caterpillar engines rated at 10,200 horsepower. Soon, the Damon Bankston arrived on scene,
sailed straight into the flames and joined the rescue.

Meanwhile, Coast Guard helicopters lifted off from pads in southern Louisiana, and Coast Guard
rescue vessels left their moorings. "You have to go out," is the old Coast Guard saying. "You don't have to come back."

The helicopters flew in the black of night toward a vista of utter disaster. Arriving on scene, the pilots watched in awe as columns of flame shot as high as a 50-story building. The helicopters were buffeted by blasts of super-heated wind coming from the flames, while chunks of soot the size of your hand blew by.

The pilots hovered in the glow of the blazing rig, while Coast Guard medics fast-roped down to the deck of Damon Bankston . The medics quickly assessed the casualties, strapped critically injured crewmen to backboards and hoisted them up to the helicopters. Then the pilots turned north and sped ashore to hospitals.

Uninjured survivors returned to land on the Damon Bankston. And others came out to fight
the blistering flames.

But the Deepwater Horizon wasn't going to make it. The situation deteriorated, to the point of complete catastrophe. The ship was lost.

Transocean Horizon On Fire Sinking

At about 10 a.m. CDT on Thursday morning, 36 hours after the first explosion, the Deepwater Horizon capsized and sank in 5,000 feet of water. According to BP, the hulk is located on the
seafloor, upside-down, about 1,500 feet away from the Macondo well it drilled.

Still Spilling Oil 
On Friday, I told you that the oil well drilled by the Deepwater Horizon was sealed in. The "official" word was that the well wasn't gushing oil into the sea. My sources were no less than U.S. Coast Guard Rear Adm. Mary Landry, of the New Orleans district, as quoted in The New York Times. 

But over the weekend, Rear Adm. Landry and The New York Times reported that the well IS leaking oil, at a rate of about 1,000 barrels per day.

The on-scene information comes from remotely operated underwater robots that BP and Transocean are using to monitor the well and survey all the other wreckage of the Deepwater Horizon. There's now a large amount of equipment and pipe and a myriad of marine debris on the seafloor near the well. It's a mess.

Apparently, the blowout preventer is not controlling the flow of oil. According to Transocean, the blowout preventer on Deepwater Horizon was manufactured by Cameron Intl. (CAM: NYSE). 

What happened? We don't know that just yet. Earlier reports that underwater robots sealed the blowout preventer were wrong. It's possible that the blowout preventer is only partially closed. We'll find out, eventually. Meanwhile, BP and Transocean have announced that they will make another effort to activate the blowout preventer. They need to stop that oil.

BP is also preparing to drill one or more relief wells to secure the site permanently. BP has mobilized the drilling rig Development Driller III, which is moving into position to drill a second well to intercept the leaking well. With the new well, the drillers will inject a specialized heavy fluid into the original well. This fluid will secure and block the flow of oil or gas and allow BP to permanently seal the first well.

Riser Problems? 

According to the Coast Guard and BP, oil is leaking from two spots along what is left of the riser system. Here's a schematic view:

Transocean Horizon Sea Floor Diagram

Originally, the risers (represented by the blue line in the graphic above) were affixed to the blowout preventer on the seafloor, and extended 5,000 feet straight up to the "moon pool" of the Deepwater Horizon. When the drilling vessel sank, it took the riser piping and bent it around like a pretzel.

The remnants of the riser system now follow a circuitous underwater route. According to BP, the risers extend from the wellhead up through the water column to about 1,500 feet above the seabed.
Then the riser system buckles back down toward the seafloor. (Frankly, I'm astonished that it all held together as well as it has. It's a credit to the manufacturer, which I'll discuss below.)

According to the Transocean website, the riser devices on the Deepwater Horizonwere manufactured by VetcoGray, a division of General Electric Oil & Gas. The specific designation is a "HMF-Class H, 21-inch outside diameter riser; 90 foot long joints with Choke & Kill, and booster and hydraulic  supply lines."

Here's a photo of something similar. These are Vetco risers sections that I saw on another vessel, the Transocean Discoverer Inspiration, when I visited that ship last month:

Transocean Horizon Riser Sections

The different color stripes on the risers indicate differing amounts of buoyancy. The idea is to put heavy riser pipe down at the bottom, connected to more buoyant risers above. The buoyancy
keeps the entire riser system in more or less neutral buoyancy, so that the drill ship doesn't have to somehow hoist up the huge weight of all that pipe.

As you can see, there's a large-diameter pipe in the middle of each riser. That pipe is then encased in a buoyant foam substance. The risers are bolted together at the flange sections. The bolts are about as big as the arm of a very strong man. The nuts, which tighten things down, are the size of paint cans.

After the risers are assembled and hanging down from the drilling vessel, the drilling personnel lower and raise drilling pipe through the large-diameter center riser pipe. All the drilling mud stays inside the drill pipe on the way down hole, and inside the riser pipe on the return.

On the side of the riser sections, you can see smaller-diameter pipes. These are choke & kill, booster and hydraulic pipe components. The pipes run parallel to the large-diameter inner pipe. These pipe systems run down to the blowout preventer on the seafloor.

The idea is to keep the drilling process an enclosed system. All the "drilling stuff" -- the drill-pipe, drilling-mud and drill-cutting returns -- stays inside the large-diameter pipe. The smaller pipes
hold fluid to transmit hydraulic power and help control drilling. In particular, the pipes on the side aid in communicating with and controlling the blowout preventer.

Technical Specs 

Ideally, when the risers are working as intended, nothing leaks out into the sea. Then again, you're not supposed to twist and bend the riser sections like a pretzel. So how strong is a riser
system? Extremely strong, actually.

According to technical literature from GE Oil & Gas, the riser equipment is "designed for use in
high-pressure, critical service and deep-water drilling and production applications." The pressure-containing components are rated for working pressures of 15,000 psi. That's the same as the Cameron blowout preventer on the Deepwater Horizon. The materials used in risers have
exceptional tensile and bending load characteristics.

According to Vetco paperwork that I've seen, the Class H riser sections have a 3.5 million pound
load-carrying capacity. That's the equivalent weight of about four fully fueled
Boeing 747s. These risers are super strong.

Still, it's not just any one single piece of riser section that does it all. These sections all get bolted
together, for 5,000 feet in this case. The riser sections all have to work together as a system. The whole string is only as strong as the weakest spot. And yes, even the strongest steel will break if you apply enough stress.

It all has to work together. You've got the riser sections, along with things called HMF flanged riser connectors. Then there are HMF riser joints; flex joints; telescopic joints; and, near the top, things called "fluid-bearing, nonintegral tensioner rings." Together, these all comprise the marine riser system.

In general, the riser components compensate for heave, surge, sway, offset and torque of the drilling vessel as the ship bounces around on the sea surface. The bottom line is to maintain a tight seal -- what's called "integrity" -- between the subsea blowout preventer stack and the surface
during drilling operations.

Down at the bottom, at the seafloor, the risers are connected to the blowout preventer by a connector device. The GE-Vetco spec is for a device that accommodates 7 million foot-pounds of bending
load capacity. That's about eight fully fueled Boeing 747s.

What's the idea? You want a secure connection between the high-pressure wellhead system and
the subsea blowout preventer stack. That's where mankind's best steel meets Mother Nature's high pressures.

High pressures? You had better believe it. And in this case, Mother Nature won. So looking forward, there's going to be a lot of forensic engineering on the well design and how things got monitored
during drilling. Transocean drilled the well, but BP designed it. So the key question is how did the down-hole pressures get away like they did?

What Happens
Now? 


It's a good thing that the Deepwater Horizon didn't settle right on top of the well. At least there's room for the remotely operated vehicles to maneuver. Also, there's still a lot of riser still floating in the water column. So there's some element of integrity going down to the blowout preventer.

It's absolutely imperative to shut off that oil flow. We just have to hope and pray that the BP and Transocean people can get the blowout preventer shut off. Or that there's enough integrity to the risers somehow to get in there and control the leaks, perhaps with some sort of plug. One other idea is to lower a large "hood" over the leak and capture the oil so it can be pumped up to a storage tanker ship.

Meanwhile, the relief well has to go down -- carefully and safely. This Macondo well is history. Seal it. Mark it. Give it back to the sea. Move on. Don't tempt fate on this
one. And wow... for a relatively modest-sized deep-water discovery, this
thing sure has turned into the well from hell.

Welcome to the World of Deep-water Risk 

As I've said before, this accident is Mother Nature's wake-up call to everyone. Deep-water drilling is a high-stakes game. It's not exactly a "casino," in that there's a heck of a lot of settled science,
engineering and technology involved.  But we're sure finding out the hard way what all the risks are. And it's becoming more and more clear how the totality of risk is a moving target. There's geologic risk, technical risk, engineering risk, environmental risk, capital risk and market risk.


With each deep well, these risks all come together over one very tiny spot at the bottom of the ocean. So for all the oil that's out there under deep water -- and it's a lot -- the long-term calculus of risk and return is difficult to quantify.

There's more to discuss, but I'll end here today. I'll update you as things evolve. This is big news all through the offshore industry. There are HUGE environmental issues, and certainly big political repercussions. I won't go there just now. For now, I'll just send out collective best wishes to the people at Transocean, BP, the Coast Guard, Minerals Management and so many more. I'm sure they're doing their best.

Thanks for reading...

(Name Withheld)

Tags: Transocean, cause, deepwater, discussion, explosion, happened, horizon, what

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Replies to This Discussion

I think both riser lengths/water depth and BOP weights has come to a limit and that the discussions and developments after this disaster will focus on SBOP´s and more reliable acoustic back-up systems.
Again, as a novice, the RIG site lists THREE BOPS or SBOP. There were two Duals and one single, which I thought made a total of 5. Don't quite understand HOW you could have more redundancy. As to the Accoustic, I have not read anywhere that they had been tested at the 5000 ft depth. In addition, the ROVERS have actually repaired the hydraulic leaks and also worked directly on the BOPS.

What I am trying to understand....how big an opening (in square inches) would it take to leak 200K GPD.

If I understand the physics, the well had a pressures of 10K PSI (+/-). The water at that depth, based on what I have read, has a pressure of 2K PSI (+/-). This leaves a Delta P of about 8K.

I have read various fluid flow velocities (ft/sec) for fluids (oil). The first one is 20 FPS @ 3K. What is the velocity of the oil, estimated, at 8K. It seems to me that there may be as little as 1 square inch of opening from the well...versus (based on 7" pipe) 38 square inches. It would seem that the well is effectively 95+% CHOKED or Shut Down.

Could someone with some REAL engineering background explain how large the actual opening (the leak size) is? And, HOW you calculate that?

Please forgive this retired engineer's curiosity, I am just trying from a engineering and physics perspective to understand WHAT they are dealing with and the size (opening) of the leak.

There is also, based on what I read, a MAJOR concern about the abrasiveness of the oil (picking up rock, cement, whatever) and whether it is actually eroding the BOPS (assuming is has partially closed). Therefore, the leak will increase as the erosion increase.

Any comments would be appreciated.
Surface BOP's DO NOT solve the problem.
Surface BOP's put the BOP where you can work on it if necessary.
Surface BOP's are just as suseptable to failure as a Subsea BOP.

IF a failure is Subsea with a Surface BOP, you have a different problem.

Surface BOP's can ONLY be used in moderate sea condition areas.
Surface BOP's DO NOT have a very efficient compensation system.
Yes, I agree that SBOP is not "all singing and dancing" but combined with suitable equipped SSA (Subsea Shutoff Assembly) with acoustic back-up, this may sound like an attractive solution to oil majors and authorities for deep water drilling. Some changes will be required!
If the riser was 30" in diameter and 5,000 ft long, it held @ 4,370 bbls of heavy oil based mud. It had to come out via the rig, or be released into the gulf and be accounted for as a spill.

Nothing is easy.

Deeper
The ID of the riser is LESS than 20".
The thump was the riser collapsing. What hardly anyone knows is that with all the rubber inserts installed in the diverter it only holds 2,000 lb. of axial loading...not 1,500 psi. So the kick would have not even slowed down at the RT.
IF the diverter element WAS activated (closed) the diverter lines (minumum 12" ID) would have diverted the flow.
For information: The telescopic joint normally has less than 50 psi of air pressure applied to the packer, this will not hold high pressure.
Transocean Deepwater Horizon Image Slideshow


Greetings All. Simple dumb question from a non-E&P type. Ages ago, I recall using a variety of different type of freeze plugs to address piping problems on some unique and highly pressurized DOD systems. Are any of the well informed folk here aware of thoughts of trying to "ice cube" the entire BOP assembly, with either a brine recirc system (or LN2 as an even better agent)? Perhaps utterly unworkable given distances and flow rates, but with enough BTU's sucked out of the BOP and related piping, I wonder if you could freeze the danged thing shut, especially since it seems portions of the horizontal pipe shears are reportedly partially closed.
What about gas censors...Csg pres. indcators. pit gain alarms... flow alarms?? None of these were going off?
This Just In...
Guys, I received this in email earlier. It appears to be legit and is an account of what operations on Deepwater Hmorizon at the time of explosion by an individual who was there. I am going to post the text of the email here 'as is" for you to toss around and give your thoughts on. Please do not ask me for information other than what is posted below. I cannot and will not reveal anymore information about the source.


" ...They had set A 9-5/8 Tapered Production Liner, did their cement job, had positive tested, and also negative tested, they were going to set a balanced plug around 3000' below the well head which would be at about 8000', the senior company man wanted to set the balanced plug in mud, but the engineers wanted to displace with water prior to setting balanced plug, so they displaced from 3000' below mud line, and were getting ready to set plug. The derrickman called the driller and said he needed help, he had mud going everywhere, and about this time the drill floor disapeared, then there was an explosion, then a second explosion.

The flames are now going straight up allowing evacuation of men, then you know the rest.

The hands that are missing are the ones that were on the drill floor and pump room. You know the results of that. This all took place in less than a minute.

Rig was evacuated in about 25 minutes.

It is believed that the seal assembly at the well head gave up. If that is the case and they would have set the balanced plug in mud then displaced the riser, it would only have delayed what happened by a couple of hours.

Gas must have channeled through the cement job and up the back side of the 9-5/8 production casing.

This is all I know at present."


What follows below was also attached to the email and is a 3rd party account/opinion in his own words


"I continue getting calls asking what happened on this problem so here’s a response from a friend in the oil business with possible inside info on the blowout. Please keep in mind this is an “UNOFFICIAL” report so this may or may not be factual. However, the scenario as written makes reasonable sense as far as I am concerned. The focus needs to be on well control now and not speculation as to what may or may not have happened. BP, the MMS and most likely a third party will certainly provide a very in-depth investigation which will be the official report. Having said that I would certainly not look forward to a copy of that report as it will be furnished only to those in need due to the possible liabilities of the findings."



Details as conveyed to me:

This well had been giving some problems all the way down and was a big discovery. Big pressure, 16ppg+ mud weight. They ran a long string of 7" production casing - not a liner, the confusion arising from the fact that all casing strings on a floating rig are run on drill pipe and hung off on the wellhead on the sea floor, like a "liner". They cemented this casing with lightweight cement containing nitrogen because they were having lost circulation in between the well kicking all the way down.



The calculations and the execution of this kind of a cement job are complex, in order that you neither let the well flow from too little hydrostatic pressure nor break it down and lose the fluid and cement from too much hydrostatic. But you gotta believe BP had 8 or 10 of their best double and triple checking everything.



On the outside of the top joint of casing is a seal assembly - "packoff" - that sets inside the subsea wellhead and seals. This was set and tested to 10,000 psi, OK. Remember they are doing all this from the surface 5,000 feet away. The technology is fascinating, like going to the moon or fishing out the Russian sub, or killing all the fires in Kuwait in 14 months instead of 5 years. We never have had an accident like this before so hubris, the folie d'grandeur, sort of takes over. BP were the leaders in all this stretching the envelope all over the world in deep water.



This was the end of the well until testing was to begin at a later time, so a temporary "bridge plug" was run in on drill pipe to set somewhere near the top of the well below 5,000 ft. This is the second barrier, you always have to have 2, and the casing was the first one. It is not know if this was actually set or not. At the same time they took the 16+ ppg mud out of the riser and replaced it with sea water so that they could pull the riser, lay it down, and move off.



When they did this, they of course took away all the hydrostatic on the well. But this was OK, normal, since the well was plugged both on the inside with the casing and on the outside with the tested packoff. But something turned loose all of a sudden, and the conventional wisdom would be the packoff on the outside of the casing.



Gas and oil rushed up the riser; there was little wind, and a gas cloud got all over the rig. When the main inductions of the engines got a whiff, they ran away and exploded. Blew them right off the rig. This set everything on fire. A similar explosion in the mud pit / mud pump room blew the mud pumps overboard. Another in the mud sack storage room, sited most unfortunately right next to the living quarters, took out all the interior walls where everyone was hanging out having - I am not making this up - a party to celebrate 7 years of accident free work on this rig. 7 BP bigwigs were there visiting from town.



In this sense they were lucky that the only ones lost were the 9 rig crew on the rig floor and 2 mud engineers down on the pits. The furniture and walls trapped some and broke some bones but they all managed to get in the lifeboats with assistance from the others.



The safety shut ins on the BOP were tripped but it is not clear why they did not work. This system has 4 way redundancy; 2 separate hydraulic systems and 2 separate electric systems should be able to operate any of the functions on the stack. They are tested every 14 days, all of them. (there is also a stab on the stack so that an ROV can plug in and operate it, but now it is too late because things are damaged).



The well is flowing through the BOP stack, probably around the outside of the 7" casing. As reported elsewhere, none of the "rams", those being the valves that are suppose to close around the drill pipe and / or shear it right in two and seal on the open hole, are sealing. Up the riser and out some holes in it where it is kinked. A little is coming out of the drill pipe too which is sticking out of the top of the riser and laid out on the ocean floor. The volumes as reported by the media are not correct but who knows exactly how much is coming?



2 relief wells will be drilled but it will take at least 60 days to kill it that way. There is a "deep sea intervention vessel" on the way, I don't know if that means a submarine or not, one would think this is too deep for subs, and it will have special cutting tools to try to cut off the very bottom of the riser on top of the BOP. The area is remarkably free from debris. The rig "Enterprise" is standing by with another BOP stack and a special connector to set down on top of the original one and then close. You saw this sort of thing in Red Adair movies and in Kuwait, a new stack dangling from a crane is just dropped down on the well after all the junk is removed. But that is not 5,000 ft underwater.



One unknown is if they get a new stack on it and close it, will it broach around the outside of all the casing??



In order for a disaster of this magnitude to happen, more than one thing has to go wrong, or fail. First, a bad cement job. The wellhead packoff / seal assembly, while designed to hold the pressure, is just a backup. And finally, the ability to close the well in with the BOP somehow went away.



A bad deal for the industry, for sure. Forget about California and Florida. Normal operations in the Gulf will be overregulated like the N. Sea. And so on.

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