First hand account of Gulf oil rig disaster

by Think About It 3 Replies latest jw friends

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  Think About It

  Here is an interesting first hand account of the Gulf oil rig disaster. I bold faced the operating pressure of the well. In the article BOP= blow out preventer.

  Deepwater Horizon: A Firsthand Account by Mark Levin Show | Tuesday, May 04, 2010

  On Friday, April 30th 2010, an anonymous caller contacted the Mark Levin Show to clarify the events that preceded the Deepwater Horizon tragedy. Rigzone has transcribed this broadcast for your convenience. To hear the actual radio broadcast please visit www.MarkLevinShow.com. Mark: Dallas Texas WBAP. Go right ahead, sir. James: Just want to clear up a few things with the Petroleum Engineer, everything he said was correct. I was actually on the rig when it exploded and was at work. Mark: Alright, let's slow down. Wait, hold on, slow down, so you were working on this rig when it exploded? James: Yes sir. Mark: OK, go ahead. James: We had set the bottom cement plug for the inner casing string, which was the production liner for the well, and had set what's called a seal assembly on the top of the well. At that point, the BOP stack that he was talking about, the blow out preventer was tested. I don't know the results of that test; however, it must have passed because at that point they elected to displace the risers -- the marine riser from the vessel to the sea floor. They displaced the mud out of the riser preparing to unlatch from the well two days later and they displaced it with sea water. When they concluded the BOP stack test and the inner liner, they concluded everything was good. Mark: Let me slow you down, let me slow you down. So they do all these tests to make sure the infrastructure can handle what's about to happen, right? James: Correct, we're testing the negative pressure and positive pressure of the well, the casing and the actual marine riser. Mark: OK, I'm with you. Go ahead. James: Alright, after the conclusion of the test, they simply opened the BOP stack back up. Mark: And the test, as best as you know, was sufficient? James: It should have been, yes sir. They would have never opened it back up. Mark: OK next step, go ahead. James: Next step, they opened the annular, the upper part of the BOP stack Mark: Which has what purpose? Why do you do that? James: So that you can gain access back to the wellbore. Mark: OK James: When you close the stack, it's basically a humongous hydraulic valve that closes off everything from below and above. It's like a gate valve on the sea floor. Mark: OK James: That's a very simplistic way of explaining a BOP. It's a very complicated piece of equipment. Mark: Basically, it's like a plug. But go ahead. James: Correct. Once they open that plug to go ahead and start cementing the top of the well (the well bore), we cement the top, and then basically we would pull off. Another rig would slide over and do the rest of the completions work. When they opened the well is when the gas well kicked, and we took a humongous gas bubble kick up through the well bore. It literally pushed the sea water all the way to the crown of the rig, which is about 240 feet in the air. Mark: OK, so gas got into it and blew the top off of it. James: Right. Mark: Now don't hang up. I want to continue with you because I want to ask you some questions related to this, OK? Including, has this sort of thing ever happened before, and why you think it may have happened, OK? Mark: Alright, back to James, that's not his real name, Dallas WBAP. I'm not going to give the working title of what you did there either, James, but I wanted to finish. So, the gentleman was right about the point that obviously some gas got into the, I'll call it the funnel, OK? James: Correct, and that's not uncommon, Mark. Anytime you're drilling an oil well, there is a constant battle between the mud weight, the drilling fluid that we use to maintain pressure, and the wellbore itself. There's a balance. The well is pushing gas one way and you are pushing mud the other way. So there is a delicate balance that has to be maintained at all times to keep the gas from coming back in, what we call the kicks. You know, we always get gas back in the mud, but the goal of the whole situation is to try to control the kick. Not allow the pressure to differentiate between the vessel and the wellbore. Mark: Well, in this case, obviously, too much gas got in. James: Correct, and this well had a bad history of producing lots of gas. It was touch and go a few times and was not terribly uncommon. You’re almost always going to get gas back from a well. We have systems to deal with the gas, however. Mark: So, what may have happened here? James: Well, the sheer volume and pressure of gas that hit all at once which was more than the safeties and controls we had in place could handle. Mark: And that’s like a mistake on somebody's part or maybe its just Mother Nature every now and then kicks up, or what? James: Mother Nature every now and then kicks up. The pressures that we're dealing with out there, drilling deeper, deeper water, deeper overall volume of the whole vessel itself, you’re dealing with 30 to 40 thousand pounds per square inch range -- serious pressures. Mark: Not to offend you, but we just verified that you are who you are, which I'm sure you already knew that. I would like to hold you over to the next hour because I would like to ask a few more questions about this, as well as what happened exactly after the explosion, during the explosion and after. Can you wait with us? James: Sure, I don't know how much of that I can share, but I'll do my best. Mark: Alright, well I don't want to get you in trouble. So if you can stay, fine, but if you can't, we understand. Part 2 of Mark's Interview: Mark: We are talking to a caller under an assumed name who was on the rig when it blew up, and we've been talking about how it happened. And now James, I want to take you to the point of when it happened. What exactly happened? Where were you standing? James: Well obviously, the gas blew the sea water out of the riser, once it displaced all of the sea water, the gas began to spill out on the deck and up through the center of the rig floor. The rig, you have to imagine a rectangle, about 400 feet by 300 feet, with the derrick and the rig floor sitting directly in the center. As this gas is now heavier than air, it starts to settle in different places. From that point, something ignited the gas, which would have caused the first major explosion. Mark: Now, what might ignite the gas, do you know? James: Any number of things, Mark. All rig floor equipment is what they consider intrinsically safe, meaning it cannot generate a spark, so that these types of accidents cannot occur. However, as much gas that came out as fast as it did, it would have spilled over the entire rig fairly rapidly, you know, within a minute. I would think that the entire rig would be enveloped in gas. Now a lot of this stuff, you can't smell, you can't taste it, it's just there, and it's heavier than oxygen. As it settled in, it could have made it to a space that wasn't intrinsically safe. Something as simple as static electricity could have ignited the first explosion, which set off a series of explosions. Mark: Alright, so what happened? You're standing where? You're sitting somewhere? What happened? James: Well, I was in a location that was a pretty good ways from the initial blast. I wasn't affected by the blast. I was able to make it out and get up forward where the life boats were. The PA system was still working. There was an announcement overhead that this was NOT a drill. Obviously, we have fire drills every single week to prepare for emergencies like this (fire and abandonment drills). Over the intercom came the order to report to life boats one and two, that this was not a drill, that there is a fire, and we proceeded that way. Mark: So, the eleven men who died, were they friends of yours? James: Yes sir, they were. Mark: Did they die instantly? James: I would have to assume so. Yes, sir. I would think that they were directly inside the bomb when it went off, the gas being the bomb. Mark: So, the bomb being the gas explosion? James: Correct. They would have been in the belly of the beast. Mark: Now, let me ask you, and we have to be careful what we say because there are people that will run wild with ideas, so I just want to make sure James: Sure. Mark: So, let me ask you this, why would the government send in a SWAT team to a rig? What’s that all about? James: Well, believe it or not, its funny you would mention that. Transocean, the drilling company, maintains a SWAT team and that's their sole purpose. They're experts in their field. The BOP, the blowout preventer, they call that subsea equipment. They have their own SWAT teams that they send out to the rigs to service and maintain that equipment. Mark: Yeah but I'm talking about what are interior SWAT teams? What is that? James: The interior, from the government now, I don't have an idea about that, that's beyond me. The other gentleman also mentioned the USGS that comes out and does the surveys. I've been on that particular rig for three years, offshore for five years, and I've seen a USGS one time. What we do have on a very regular basis is the MMS, which is the Minerals Management Service. Mark: They're all under the interior department. James: OK. Yes. As a matter of fact, we were commended for our inspection record from the MMS. We are actually receiving an award from them for the highest level of safety and environmental awareness. Mark: Well, I thought you were going to receive that award. Didn't they put it on hold? James: No, we have actually received that award. We received it last year. We may have been ready to receive it again this year. Mark: Let me ask you this, so the life boats, how did you get into these life boats? Where are these life boats? James: There are actually four life boats - two forward and two on the left, depending on where the emergency or the tragedy has taken place. Mark: Did you wind up jumping in the water to get in to the life boat? Sometimes you have to do that. James: I'll just say that there were five to seven individuals that jumped and the rest went down in the life boats. Mark: Alright, I won't ask because you don't want to identify yourself that clearly. Good point. How fast were the rescue efforts? How fast did they reach you? James: It is common to have a very large work boat standing by, to bring tools out, groceries, and supplies; it's a constant turn around. So we actually have a very large vessel real close by. It was actually along the side with the hose attached, taking mud off of our vessel on its own. It had to emergency disconnect and then pull out about a mile to stand by for rescue efforts. So, it was fairly quick. Mark: How quick till the Coast Guard got there? James: Mark, it's hard to say, between 45 minutes to an hour is when I recall seeing the first helicopter. Mark: Which is actually pretty fast because you are 130 miles offshore right? James: Correct. If you look at the nearest spill of land which would be Grand Isle, Louisiana, somewhere in that area, we were only about maybe 50 miles where the crew flies up. From civilization, such as New Orleans, it would be 200 miles. The helicopter was more than likely 80 to 100 miles away. Mark: You are going to be beset by lawyers, with the government, and others looking for an opportunity to make money. It's going to get very, very ugly and the officials going there have really no backgrounds or experience... I mean, to what extent is that going to help anything? It's silly. James: To me it seems knee jerk. The number one focus right now is containment. I like the idea about the boom. They are going to try to lower it down into the water to capture the leak. Mark: How long might that take? I've been reading about this boom and it says that it could take 30 days to do that. James: It very well could. You have to remember that this is a challenging environment. You know its 5,000 feet deep, there's a tangled wreck of a rig with the marine riser still connected and twisted into a big wad down there. So it's going to take some time to get all that stuff in place. The engineering has to be there; obviously they don't want to rush into it. You want to move it expediently but you are risking the lives of those men that are going to go out there and try to attempt it - that’s just not right. Mark: I was just going say that. That's very dangerous, I mean extremely dangerous. James: Absolutely, absolutely. There will be oil. There will be natural gases. All the same things that caused us to explode are still present, and they're there. The pressure had been cut off dramatically, from the simple fact of the folding of the riser. Basically take this big garden hose and kink it several times. Mark: How old is this rig? How long has it been there? James: It was put in service in 2001. It's a fairly new rig. Mark: And, what is the sense in shutting down every rig in the Gulf of Mexico in response to this? James: Absolutely senseless, whatsoever. This literally could very well be a once in a lifetime freak accident, or it could be negligence. That's for other people to figure out. From my position, it just seems like every now and then, you can't win against Mother Nature. She throws a curve ball that you are not prepared for. Mark: But to shut down every rig in response to this? I mean... I'm not sure why. James: The BOP tests are literally mandated from the Mineral Management Service and they are conducted like clockwork. I mean, if any of those tests ever failed, they would have immediately stopped operations, sealed the well up, pulled the BOP stack back up on the deck, which is 48 hours minimum, and made the necessary repairs or replacement parts, and then would get it back down, re-connect, re-test, and keep testing it, until it passed or kept on repairing it until it passed. Mark: So this was a… I mean this must have been harrowing to you. I mean to experience something like this. James: That’s putting it mildly. Mark: Anything else you want to tell me? James: No, I just got into the truck to make a short trip and I heard a gentleman say something about possible terrorism and I want to put that to bed now. I understand you have a large audience. I appreciate your point of view. I try to listen to you as much as I can, the terrorism call just needs to leave everyone's minds and let's focus on the 11 men that are dead and the survivors. That's where the focus of this country needs to be right now. Mark: Alright my friend, we wish you all the best and I tell you that it's really God's blessing that you survived, it really is. James: Yes sir, I completely agree. Mark: Alright James, thank you very much for calling and we appreciate it. James: Thank you, Mark. Mark: Alright, God bless. Think About It
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  awildflower

  Wow, very interesting, thanks for sharing Think.
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  maninthemiddle

  Very intersting. I have to admit I was thinking terrorism also.
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  BurnTheShips

  Thank you for sharing this. It was truly useful. It has the ring of truth. I'd like to link an article from the Oil Drum, which gives a bit more background info about the challenges of deep water drilling, for those interested.

  It gives a good explanation about the "kicks", and what they do with the mud.

  When we fill up our cars with fuel, we really don't think too much of what actually goes into getting it, and making it.

  http://www.theoildrum.com/node/6421

  Tech Talk: Revisiting Oil Well Pressures and Blowout Preventers after BP's Gulf of Mexico Oil Spill

  Posted by Heading Out on May 2, 2010 - 11:01am
  Topic: Supply/Production
  Tags: blowout, blowout preventer, deepwater horizon, gulf of mexico, leak, oil, oil well, tech talk, well pressures [list all tags]

  I thought that it might be useful to explain where and how at least part of the problem with the Transocean Deepwater Horizon fire and sinking spreading oil across the Gulf of Mexico might have started. I am going to start by repeating one of my previous technical posts, where I explain what a blow-out preventer is, then I will add some comments in an update relating to the current leak.

  This post is going to deal with some of the problems that a driller encounters as he reaches the layer of rock (the reservoir) in which the oil or gas is being held. And what I want to talk about is something called Differential Pressure, but to explain that, I need to drag you back to High School for just a minute.

  Let's, in fact, go back to Newton's Three Laws. And, for those who slept through that part of the Physics class in school, don't be too ashamed - I have seen the desk where Newton whittled his name, being similarly bored. Let's start with the first law, which is probably the most relevant.

  Every object in a state of (rest or) uniform motion tends to remain in that state of (rest or) motion unless an external force is applied to it.

  Except that I want to change external force into pressure (which is force divided by area) since it is the way we normally think of it. (Note: I added rest which is a special case of uniform motion since that is specific to the oil we want to talk about). In other words, nothing is going to move unless something pushes it. It is what does the pushing and what does the moving that this is all about.

  And now our drill, is down through the casing, drilling the well open hole and using the circulating mud to carry away the cuttings as it continues to go deeper. I had stopped progress last week just before we went down to total depth (TD) of the well, or into the pay. And the reason I did has to do with this differential pressure. But first, the bit about how you calculate pressure.

  As you go deeper into the earth, the rock at any layer is carrying the weight of all the rock vertically above it. For rough calculations we generally consider that this rock weighs 144 lb a cubic foot. So that 10 ft down the weight of the overlying column on a square foot would be 144 x 10 = 1,440 lb/sq ft. But through convention we reduce the area that we talk about to a square inch (144 sq in= 1 sq ft) so with this division the weight on a square inch would be 10 lb. A remarkable resemblance to the depth number (grin). This means that we can assume, as we go deeper into the earth, that the pressure on the rock increases by 1 lb/sq. inch (psi) for every foot we go deeper. This means that at 6,000 ft, the rock is under a pressure, from the rock above it, of 6,000 psi.

  Now water does not weigh as much as rock, but can be approximated to roughly half the weight. So that, by the same argument, under water, for every foot of depth the pressure goes up roughly half-a-psi. So that at 6,000 ft under water the pressure is 3,000 psi (roughly twice the water pressure in the wand you use at a car wash). Now because we have increased the density of the fluid in the well (the mud) to help lift the cuttings out of the hole it weighs a bit more than water, but for the sake of working the example I'm going to use the half-psi measure for now. We are now at the point where the actual amount that it weighs becomes important.

  Simplified sketch of an oil bearing layer in the ground.

  I have made a very simple sketch of the layer of rock that we are going to drill into. In order to trap the oil it is shaped into a dome, and the sketch shows a vertical slice through that dome, viewed from the side. It has a layer of oil in it (the reddish layer), but above that is a layer of gas that has diffused from the oil (brownish), and below it is water (bluish) which may have been there when the algae died and which has stayed with the remains as they turned into oil under the temperatures and pressures deep in the rock. Oil floats on water, and gas is lighter than oil, so we have the three layers. At the moment the well has not arrived and all three fluids are sensibly in equilibrium at the same pressure.

  Now why do we need to know this before we reach our layer of oil-bearing rock? Well first let's go and interpret that first law a little more.

  If a person on either side of you pushed you with equal force at the same time, you don't move, because the two forces balance out. It is only if there is one force, or if one of the two pushes harder, that you move. In other words, where there are a number of forces acting on a body, it is the size of the difference in pressures, and the direction of that difference, that controls the movement.

  Consider, here we are drilling merrily away (and have cased the well near the surface, and hit no more fluids on the way down) and at 6,000 ft. we penetrate the rock that is capping the well, and enter the rock with the oil in it. The oil (in the rock) is at some fraction of the overburden pressure, since it is trapped in the rock, and for the sake of this example I am going to say that it is at 5,000 psi , the fluid in the well is at 3,000 psi, the height of the mud column.

  There is a difference of 2,000 psi. We are drilling a hole some 6-5/8th inches in diameter. That has an area of about 34.5 square inches. The total force we have suddenly applied to the bottom of the well (bit and fluid) is thus (area x pressure difference) 34.5 x 2,000 = 69,000 lb (or 35 tons). Oops!

  Sadly most catch fire and the rig is destroyed (there are more pictures of such damage at the EIP site). It's called a blow-out, and they still happen.

  This is why we approach the oil/gas producing zone of the rock with caution. And bear in mind that the driller that is controlling the progress of this well is at the surface, trying to guide the bit at the bottom of the hole, with, historically, little immediate information to help.

  Based on the surveys that brought the crew to the site in the first place he knows roughly how thick the layers of rock are, and probably what rock they are, but the only real information on where the bit is in that sequence, is from the returns (cuttings) that come out of the well, and there is the lag, we mentioned before, while those chips make their way up the 6,000 ft pipe. (This is why Measurement While Drilling [MWD] has been such a relatively recent boon to the industry (though not all rigs have it)).

  By monitoring a number of pressure gages the driller can gain a sense of what is happening at the bottom of the well. If he senses that there is going to be a problem, then he can do one of several things, based on the way the well is set up.

  The first thing is to increase the density of the mud. By making the fluid in the well weigh more, the difference in the pressure across that face is reduced, and the change in conditions is easier to handle. However weighting up the hole has the disadvantage that it becomes much slower to drill with a heavier mud (it is a poor bottom-hole cleaner among other things). And, if done during drilling, bear in mind that once the heavier mud is added to the well it won't be fully effective until it has had time to get down to the bit and then fill back up the annulus between the drill string and the casing all the way to the surface.

  So that is an expensive and slow option. Let us take the game a little more interesting and say that there is a gas pocket above the oil, and that the hole is going to go into the layer at A. Gas will enter the well at the down-hole pressure, but as the bubble rises, that pressure is reduced, and the gas expands, pushing the mud above it out ahead of itself. Another potential source for big-time trouble. And this one (which is known as a kick in the well) happens much faster, so there is less time to react.

  How do we handle this? The answer is to invert the problem. Gas or oil flows into the well because the well is at a lower pressure than the fluid in the rock. The fluid in the well is, initially at the pressure created by the depth, and by the weight (density) of the mud in the hole. However, if we put a restriction on the flow of fluid out of the well (such as when you put your finger over the end of a garden hose so that the stream becomes smaller and shoots out further) we can increase the pressure in the well.

  For those who want to know why, if the same volume has to go through a smaller hole in the same amount of time it has to go faster. This means it has to be pushed harder. Bernoulli explained it, and there is an animation available that helps explain it.

  What it means is that by adjusting the flow out of the hole, the driller can adjust the internal pressure, and thus "kill the kick," or if gets to be too much of a problem, “kill the well”. But it is not completely that simple. Bear in mind that there is all the drilling and rotating equipment on the rig floor connected to the drill pipe at the top of the well. None of this can stand much pressure. So we need to place another piece of equipment between the drilling rig, and the top of the well.

  This is the Blow-out Preventer (BOP), which is essentially a ram that very rapidly shuts off fluid flow at the top of the well. These have to be well designed, since they are generally the line of last defense against a blowout, and when they fail as the pictures show, serious problems arise. They also form the basis for the well-known structures, often referred to as Christmas Trees that sit at the top of producing wells. By themselves, however, these aren't enough, since their main function is just to slam the door shut, before all the oil gets out and we have a gusher.

  The more critical tools are the chokes on the well. (Below the rams in the picture above). There are generally several, both hydraulically operated and manual (in case the power dies) which are simply large valves that can be turned to increase or reduce the size of the flow path out of the well over to the mud pits. By adjusting these, in real time, the driller can control the well pressure, and thus the dynamics of the behavior at the bottom of the well. And after the rig leaves, an operator can adjust well pressure, and thereby the production from the well and its long-term performance.

  If the operator is well trained (and you find drilling simulator equipment in Petroleum Engineering Departments so that students can understand how to do this (I last tried some decades ago) the well pressure will be controlled, so that any kicks can be handled, and the drill can now penetrate safely into the rock containing the oil/gas, which we call the reservoir, or the pay.

  Update

  The oil spill is continuing to get worse, and there are growing questions that have been raised on what could have gone wrong, and how it can be fixed. I am in the same position as most, in regard to getting information – it comes from news reports, in the main. But there are some points that can be picked out as the focus of those reports switch to the impact that the oil is going to have on the coast and businesses that are going to be severely damaged.

  An early story noted that the BOP had recently been tested.

  Mr. Hayward said the blowout preventer was tested 10 days ago and worked. He said a valve must be partly closed, otherwise the spillage would be worse.

  There are a number of things that can go wrong with a blowout preventer, said Greg McCormack, director of the Petroleum Extension Service at the University of Texas, which provides training for the industry.

  The pressure of the oil coming from below might be so great that the valves cannot make an adequate seal. Or in the case of a shear ram, which is designed to cut through the drill pipe itself and seal it off, it might have encountered a tool joint, the thicker, threaded area where two lengths of drilling pipe are joined.

  Still, Mr. McCormack said, “something is working there because you wouldn’t have such a relatively small flow of oil.” If the blowout preventer were completely inoperable, he said, the flow would be “orders of magnitude” greater.

  However oil is now flowing through the BOP and out into the water immediately above the well site on the sea bed. When the site was visited by a small remotely operated vehicle with cameras they showed that the riser, the pipe that normally carries the oil from the sea bed to the surface, had kinked over when the rig sank, and oil was coming from three places:

  The Coast Guard said it had not detected oil coming from the well Friday and assumed post-accident efforts to activate the blowout preventer “a huge stack of valves sitting atop the wellhead on the sea floor” had been successful.

  But later trips by the remotely operated vehicles (ROV’s), discovered oil shooting from the end of the pipe-like riser that had connected the rig to the blowout preventer.

  A second, smaller leak was found in a section of drill pipe near the wellhead. That 21-inch-diameter riser had become detached from the rig when it sank. In the process, it was folded over at a 90-degree angle just above the wellhead, which had the effect of kinking it like a garden hose and constraining the flow of oil from the well. It now sits in a long, meandering mess on the ocean bottom. This helps explains why oil was not initially thought to be seeping. , . .

  The preferred option, he said, is still to find a way to engage the blowout preventer. That fix, if it works, could be handled in a matter of days, he said.

  But if that doesn't work, the other option is to drill a deep “relief” well into the damaged well and stem the flow of oil, though that option could take several months, Suttles acknowledged. He said his team would spend the next several days trying to determine the best method.

  The problem lies, in part, with the capabilities of the ROVs and their ability to get access to the well site on the sea-bed.

  There is a report from a survivor (h/t Fractional Flow ) that says that the well was shut in and they were going through the process of separating the rig from the well, and moving it off. They began by cleaning out the drilling mud from the riser, replacing it with sea water. However, when they re-opened the valves at the top of the well, the pipe in the well had become filled with gas from the well, under considerable pressure, and this “Kicked” the well as the valve opened. Gas, as the pressure gets less as it moves up the pipe, expands much more than oil. And unfortunately in the process of disconnection, the pressure to hold the gas, which comes from the density of the drilling mud in the riser initially, had been removed as part of the disconnection process.

  So the high pressure gas was able to blow all the sea water in the riser out onto the deck of the rig. (This happens extremely quickly, well below a minute) The gas then followed, and as it flowed out of the pipe at the top of the well there was some hot source that caused it to ignite. (This could even be from a static electricity spark). Because of the depth of the well, the pressure in the bottom of the well was in the 30-40,000 psi range.

  Part of the problem that arises with flows at that pressure is that any abrasive particles (such as small pieces of rock) will cut through metal at the speeds at which it is carried. (Such jets were used to remove the damaged tops of the wells in Kuwait after the Gulf War, for example). So that it is possible that as the BOP started to function the high-velocity flow may have eroded part of the system to allow some fluid to bypass the plug that the BOP inserted. If that happened then the continued flow would just enlarge the passage again fairly quickly, so that the BOP will become ineffective.

  However there are pictures of the leaks available.

  Pictures of the oil flows ( Drillingahead )

  At this stage there does not appear to be that great a driving pressure for the oil coming out of the well. (If there were, the flow would be more directed horizontally) This suggests that the BOP did at least partially function, and that the passage may have been eroded by the particles in the gas and oil now escaping.

  There is a recent report that the accident may have been caused by a poor cementing job by Haliburton:

  After an exploration well is drilled, cement slurry is pumped through a steel pipe or casing and out through a check valve at the bottom of the casing. It then travels up the outside of the pipe, sheathing the part of the pipe surrounded by the oil and gas zone. When the cement hardens, it is supposed to prevent oil or gas from leaking into adjacent zones along the pipe.

  As the cement sets, the check valve at the end of the casing prevents any material from flowing back up the pipe. The zone is thus isolated until the company is ready to start production.

  The process is tricky. A 2007 study by the U.S. Minerals Management Service found that cementing was the single most-important factor in 18 of 39 well blowouts in the Gulf of Mexico over a 14-year period. But at the time of the accident, "well operations had not yet reached the point requiring the placement of the final cement plug, which would enable the planned temporary abandonment of the well," the Halliburton statement said.

  However it is hard to see from what is known, that this was a cause in this case.

  Some other earlier Tech Talk posts that might be of interest in following the ongoing discussion about the problems encountered include:

  Casing a Well
  The Drilling Part of Creating an Oil Well
  Completing and Perforating a Well

  BTS