Deepwater Oil Spill - why Top Kill may have failed

The Top Kill attempts have failed, and the Government has a response.

He (President Obama) said US Energy Secretary Steven Chu was leading a team of "the world's top scientists, engineers and experts" in devising a contingency plan should the "top kill" attempt fail.

But while waiting for that, and for the Lower Marine Riser Package (LMRP) I thought I would spend a few paragraphs discussing why Top Kill may have failed.

In a couple of earlier posts I wrote about how it was necessary to fill the gaps that ran through the Blow-Out Preventer (BOP) either with spheres and triangles or with wire(string would act similarly). To refresh your memory, in the initial simpler analysis I had put up a simple sketch of the BOP and well, to show how the blocking particles were injected.

Simple approximation of the situation

Now unfortunately that diagram missed a significant part out, and that is that there are three sets of pipes leading down into the well. These are the well outer casing, which, surrounded by a layer of cement, holds the BOP in place. Then there is the production casing, which had just been set to the full depth of the well. And there is the drill pipe that, at the time of the incident, extended down 8,367 ft from the platform, or roughly 3,367 ft below the BOP. That drill pipe (DP) had previously been used to locate the production casing at the bottom of the well, and itself now rode inside that production casing. In most normal operations it is closed at the bottom by a drill bit, but (and I’ll come back to this later) it had just finished the cementing of the production casing into position, and once it detached from that and was being pulled from the well, it was an open pipe all the way up to the rig floor. And in that condition it could be used for other things. By pulling mud out of the DP and transferring it to the mud pits (or standoff vessel), the level in the riser would fall and be replaced by seawater flowing in at the top. Unfortunately this also lowered the weight of mud in the well, and that is what caused the oil and gas to flow into the well.


Outside of the DP is the casing and cement segments that make up the outer lining of the well. The diagram presented in Congressional testimony, shows these various pipes, except for the central drill pipe.

Casing and cement down the Deepwater well

BP do not know, but believe that the oil is getting into the well through the cement wall at the bottom of the well, and probably rising up the well through the empty space (annulus) between the production casing and the outer lining of the well. However the oil and gas may have broken through the bottom of the cement plug and be rising up within the production casing, in which it is also rising through the BP once the oil reaches its lower end.

Most normal blowouts occur when the well is being drilled, and mud is flowing down, through the drill bit, and then back up the space (the annulus) between the DP and the rock wall. Thus, when there is a blowout, the oil and gas that flow into the well normally flow up this outer passage to the rig, and give the spectacular fountain of oil. The BOP was invented (by Harry Cameron and Jim Abercrombie) to stop that flow and to protect the crew at the surface. Because the flow is normally up the outside of the drill pipe, the initial BOP designs were rams that pushed seals across the flow path through the BOP, and sealed against the side of the DP.

BOP open allowing flow through the annulus (ASME )

BOP closed against the pipe, sealing the annulus (ASME )

A BOP could have two of these mounted so that one sealed to the production casing in the well, and one to the drill pipe, but if underwater then the production casing is tied back to the Wellhead Collet Connector, and then the only tube running through the BOP will be the DP, to which they will seal.

BOP connection to casing at the seabed (PCCI report for MMS)

The problem that this leaves, in the current situation is that the pipe that runs through these two seals is open at the bottom to the oil flow. So how can the flow through this be stopped?

The answer is to mount a top ram set that has a set of shear cutting blades on it, that will cut through the pipe and seal the full face of the well.

Shear blades to cut through the DP and seal the well (Varco )

The BP should shear, but would be held in place by the grip of the annular sealing rams below.

In this case it seems to be recognized that for some reason this shear event did not totally succeed. Thus the pipe was not totally severed and the two shear plates did not fully move over one another to complete the seal.

Now this is where the problem arises, because, in part, that pipe is still open at its lower end. If the leak is around the outside of the pipe, through a gap that has generated between the pipe and the annular seals, then the use of the junk shot to fill the cracks and gaps could conventionally have worked. But the configuration of the rams on the Deepwater Horizon had changed from the initial simpler configuration to add seals for occasions where the drill pipe was not in place.

Ram layout on the BOP (Times Picayune)

And the "junk" is being injected at the bottom of this stack.

Section through the BOP, showing the anticipated mud flow path (initially from BP)

If the leak is coming up through the remnants of the drill pipe then life is complicated. It can’t all be coming up through an undamaged pipe alone, since it was the far open end of that which was successfully closed at the beginning of the remedial steps, but if it is coming through the pipe and leaking out at the shear rams into the annulus that feeds into the riser, and out to the sea, then putting sealing particles into the bottom of the BOP to seal the cracks, could have sealed some of the leakage around the DP trapped in the shears, but not that flowing through the shears in the remaining pipe section.

The reason that it can’t is that the access to that flow is occurring 3,367 ft below the riser, and there is no easy way to get the sealing particles down that far. If they are mixed with mud and pushed down the well to that level and then released they have a different problem. The hope when they were released into the well was that the flow of the current would be enough to carry them up to the cracks that they could seal. But if they have to be carried down to the zone where the oil remains, then their density may be sufficient, if they get into the flow without enough speed to lift them up into the BOP to cause them to sink to the bottom of the well.

The materials that BP tried included materials that might float on the surface, and might not

Those materials, including fibrous pieces of rope and chunks of rubber, were supposed to force more of the mud down the wellbore, but ultimately it did not work.

Rubber has a specific gravity of 0.91 and rope varies from 0.9 to 1.4. But remember that at that depth any buoyancy from air entrainment would be lost.

In other circumstances it might have worked, If they could have dropped the DP out of the shears perhaps, but they couldn’t and it didn’t. So on to the LMRP.

UPDATE: Thinking about this a little more, I had two more thoughts. The first is that once the LMRP preparation cuts off the riser and the bent drill pipe that the full weight of the pipe below the shears may come onto the section in the shear jaws at the moment, pulling them further out of alignment and increasing the flows. It could also cause the pipe to drop out of the jaws, pulled out by the underlying weight, and hopefully not distorting them too much so that in the best of worlds they could then be cranked shut.

One could also, once the bent riser and pipe had been cut, go in down the pipe bit that extends up, go down past the annular seals with an abrasive jet lance (most of the flow is around the DP as we have established above) and cut it off, right above the shears. Then partially open the shears, drop the pipe out, and close them again. If they move all the way closed, without the obstruction, then the well may be sealed.

(Note because a) this is really a sort of Tech Talk, and b) its a nice day, there won't be the regular Sunday tech talk which would have been on coal mining today - it is postponed, as was the Saturday discussion of state climate changes - hopefully I'll be able to get back to both of those before long).

Deepwater Oil Spill - varying the junk mix and cutting the flow

The video from the ROVs monitoring the Deepwater oil leak from the well in the Gulf of Mexico show that the at around 10:45 am they may have started another junk shot injection, given that the flow from the riser has just increased, and various large particles have been coming past the camera. When they are injecting mud the contrast on the picture gets somewhat worse, and so it is probably better if you check this out for yourself. The riser is continuing to flow mud.

between about 10:45 am and noon 29/5/2010

In the earlier post I wrote about one way of tackling the leaks in the BOP, using spheres and triangles of rubber. But as you can see from the flows from the leak at the top of the riser, when the cracks get quite small the injected particles get swept past, and end up coming out of the end of the riser. So I am going to look at what the flow path size is, and another answer.


So let us run some numbers to see if we can estimate what the largest width that the particle has to bridge will be. That would be if the hole in the BOP is circular, since in any other geometry one of the dimensions will be smaller and catch the particle.

Assuming that, if for the sake of the discussion we accept that the well is leaking at 17,000 barrels a day, this translates into around 500 gallons of fluid a minute. (Divide by 24 to get flow per hour, divide by 60 to get flow per minute, and multiply by 42 to convert to gallons).

The next step uses an Excel table that I have generated over the years to calculate circuit flows. It has the orifice diameter on the left and across the top the pressure driving the flow. I have modified the table to show the diameter that would be required to allow 500 gpm to pass (roughly) and have highlighted where that flow is reached (roughly) for different combinations of flow and pressure. (i.e. the red numbers in the table, for a given driving pressure across the top read to the left to get the hole diameter that will give this flow).

For those interested in generating their own the equation I used for the value in space N13, for example, was

=$L$1*(3.1412*60*($A$13/2)^2*12*12.5*SQRT(N3))/231.

The values are very dependant on the discharge coefficient (L1) and this value can vary for flows through orifices from about 0.6 to 0.9. To get the largest diameter I made the value 0.6 (as the discharge coefficient increases the diameter of the hole needed to pass that flow reduces).



You can see that the largest dimension of the flow channel is just over 0.7 inches. (Which means that the BOP rams functioned over at least the majority of their stroke). The minimum is about half an inch, and if I change the discharge coefficient from 0.6 to 0.85 then the diameter range goes from 0.4 to 0.6 inches.

So from this we know that the maximum gap in the BOP is 0.7 inches in diameter. Now this is good news because it means that it is less than a third of the diameter of the feed line (which has an effective inner diameter of possibly 2.7 inches or so).

So we can continue, as they are, to send particles down through the riser to the BOP. But we also know that the flow path through the riser could be a long thin crack, rather than the round hole we used in the example above. So to address that problem a different particle shape and type is needed. Consider now what happens if we send some wire down the line with a thin rubber coating (so we don’t damage the fittings on the way down) and give it say a diameter of 0.4 inches. This is small enough to get through the pipes, but if the crack is narrower than this the wire, because of its shape, will be pulled across the crack, thus:

Wire fills a longer part of the crack if it is flexible enough to follow it.

Of course the cracks won’t run straight, and thicker wire is stiff, so after a while they will probably introduce wires of differing diameters. But this may be the next step in the process. There is, however a precaution that has to be taken. Wires tend to clump together and can build a blockage in the feed line if they are too long, so the pieces should be kept short, and fed in a little at a time, over a size range, to ensure that they help rather than hinder the bridging of the flow.

At the moment (noon) it looks as though they are still pumping mud, so they may be trying to use a slightly heavier mud in order to get balance, though again they are constrained on how heavy they can make this before they start losing it into the formations.

Deepwater Oil Spill - restarting the mud, and an apology

It appears that a significant part of what I have written for the past day has been wrong, and the information that I, in good faith, commented on to several radio stations and newspapers about the status of the Gulf leak was similarly not totally correct.

I have reaped, I guess, the rewards for believing statements about transparency. From the LA Times

The company announced late in the day that it had suspended shooting heavy drilling mud into the blown-out well 5,000 feet underwater around midnight Wednesday so it could bring in more materials. Thursday evening, BP PLC said it had resumed the pumping procedure known as a top kill. Officials said it could be late Friday or the weekend before the company knows if it has cut off the oil that has been flowing for five weeks.

The conclusions that I drew about the pressure drop up through UPDATE 8 on Wednesday, when we were losing visual contact with the leak, because of what I thought was mud falling around the well could have been correct.

However, later comments on the relative flow velocity were based in part on the assumption the BP was still pumping mud. They were not. So that while the velocity observation was correct (since BP has stopped pumping) that is the only consolation I have from believing the Admiral’s statement this morning that there was only a slight problem with pressure balance before the company could start pumping cement into the well. (The LA story that I took this from has been updated so I cannot go back to the original quote). As I say this is more than mildly irritating, and I will try and be more cautious in drawing conclusions in the future. It does, however, through the pictures I posted, allow us now to be able to identify the difference between the mud flow (top picture) and the oil/gas flows that are in the remainder, with very little, if any, mud. (and at 8:40 pm on Thursday it is still oil and gas).

There was, however, some additional material available in the article:

Although incident commander Adm. Thad Allen of the U.S. Coast Guard said Thursday morning that BP had temporarily stopped the flow of oil, the company's chief operating officer later said petroleum was still flowing. "Once the well has stopped flowing then we would pump cement down into the hole to fully seal it," Doug Suttles said. "We might finish this in the next 24 hours, or it might take longer." Engineers next plan to inject heavier "bridging material" above the mud to prepare to put a cement seal on the well.

Well I see that the monitoring ROV is back in position to watch the leaks as BP, perhaps, is about to restart pumping mud – if they really are.

I would stop commenting on this, but sadly it is too important a subject not to continue. My apologies if I have, inadvertently misled you.

UPDATE: 9:52 pm the camera is focusing on the cracks in the riser, and it seems that they may be injecting rubber pieces one of which is now stuck in one of the cracks in the riser. (Not very securely it seems)

Piece of "junk" (?) in the riser crack, as BP apparently work to reduce the size of the path through the BOP.

Note that this piece has had to pass through the BOP, and it is sealing the BOP path which is more critical to success. It could also be a piece of the rubber from the annulus seal that broke loose and got caught in the riser. Without knowledge of what BP is trying it is hard to decide, but the flow looks to be still gas and oil without mud, and I would expect that BP would have to use mud as the carrier if they were injecting material into the flow, so this could just be a piece of seal that got caught. If you can't tell where it is, it is in the crack to the immediate right of the center line (without the paint) on the riser. (The view has changed)

UPDATE 2: Mud is clearly visible in the change in the look of the flows out of the riser. But at the moment it does not appear to be under the pressure of the flows on Wednesday. (This could be because it is being pumped in at a lower pressure, or it could be that they have sealed some of the leaks in the BOP and that is cutting back the driving pressure at the riser).

Leak shot at 10:25 pm Central

The problem we saw on Wednesday night with mud being heavier than oil and thus settling more readily and obscuring the view, is also evident.

UPDATE 3: 12:18 AM So it appears that BP have injected "rubber strips" into the flow, and that some of these have lodged in the BOP, reducing the flow channel, while one made it through and is trapped in one of the leaks in the bent portion of the riser.

Now what may happen is that they will slowly increase the mud flow/pressure to a) find out how much the leak rate has been reduced and b) to make sure that the restrictions in the flow channel are stable, and won't blow out. (If they do then they will have to repeat the process). Once they have a sure reduction in leakage then they will re-generate the higher pressures that overcome the pressure in the reservoir and start forcing the oil and gas back down the well, as the mud begins to fill the pipe.

The mud seems to have a slightly different texture from last time, so they could have increased the mud weight so that when the column of mud is re-established that this time it weighs a little more and overcomes the slight pressure imbalance that they were left with the first time they tried this.

Now is a good time for caution and, though the fill time may be reduced because of the smaller leak rate into the Gulf, they may still pump at a relatively only slightly higher pressure that that in the reservoir, to slowly sweep down the well, getting into the necessary channels, and giving time for the oil and gas to be pressed back into the rock that it came from.

UPDATE 4: 9:30 AM The latest report from the Gulf

Hayward told CNN BP engineers had injected a "junk shot" of heavier blocking materials into the failed blowout preventer of the ruptured wellhead, and would also pump in more drilling "mud"- all part of the top kill procedure being attempted.

"We have some indications of partial bridging which is good news," he said.

"I think it's probably 48 hours before we have a conclusive view," he added.

Admiral Allen also noted at that time that the leak had been stopped, but that they were not sure that they could sustain the halt in flow. However at 8:10 am, Sterling925 who wa watching and commenting on The Oil Drum saw some sort of event occur around the BOP.

Chaotic images - looks like an explosion!

09:14 et 5/28/2010

and from SteinarN

It looks like A LOT of gas is coming up from the seabed around the BOP. Considering the large water pressure and the possibly large area this gas is emanating from it ought to be a large flow. This indicate the integrity of the well is not good?

Unfortunately I did not see any of this and haven't been able to see the BOP apart from one short short since, though in that shot it did not appear to have any problem. The PBS viewed ROV at the moment is working with a chain, while the ROV that was monitoring the plume is now staring out into the ocean.

The CNN shot however shows that we are back with oil and gas apparently coming out of the leaks at the top of the riser, and no different to the conditions before they started pumping mud into the well last evening. So the second filling of the well has apparently all been washed out, and they will try again later. The comment from BP was that this might take another couple of days.

UPDATE 5: 10:24 AM Well I am not sure that the CNN feed was actually live and there are other stories catching their attention at the moment, but there is a Youtube recording of what took place (h/t Jessica in Pensacola).

UPDATE 6: 11:09 AM The feed has gone back to the riser, and we are back to the oil and gas flows that we were saw at the beginning. Not quite the same shapes as earlier, so perhaps the block in the BOP was partially effective, but BP have now apparently filled the well twice and failed to get enough weight into the mud to hold the driving pressure from the rock. They could try again with a higher density mud, I am presuming that the second shot had a higher weight than the first, and that while the first left a small pressure imbalance, that the second was closer, but as yet no banana. (Though the Admiral did say that they had stabilized the flow). My presumption is that they will mix up another batch and try again - though whether they will try another junk shot is not clear.

Flow at 11:09 am

The way in which you try and stop leaks is that you put the big stuff in first. If you can get enough of that to stick, it still leaves large flow channels, and so the second shot uses smaller pieces that fit into the gaps. Then you try smaller shots etc until you get as good a seal as you can. Doing this to plug water flows into tunnels can take several shots to get a total seal, working with sequentially smaller sizes of particles.

The Gulf oil spill, recovery and cleanup - Monday's Press Conference

Today’s press conference in Louisiana began with an update on the use of the riser insertion tool. However Coast Guard Admiral Landry cautioned that this only treated part of the spill, and that they were looking forward to the “top kill” program that would follow. The weather is now good enough that four controlled burns are planned, as well as a strong skimming program. To date there has been a minimal impact on the shore from the spill, but teams are in the field ready to react as this becomes more severe. Further the high flow rates from the Mississippi River are helping keep the larger volumes of the spill out in the Gulf. Both NOAA and the EPA are monitoring the use of dispersants recognizing the tradeoff between its use and the damage that it is mitigating.

The Admiral drew attention to the statement by Jane Lubchenco, the head of NOAA, who had said, in regard to the many reports of large underwater oil plumes and their causes and likely effects

"Media reports related to the research work conducted aboard the R/V Pelican included information that was misleading, premature and, in some cases, inaccurate," Lubchenco said in a statement. She was referring to research, including water sampling, done by the National Institute for Undersea Science and Technology.



Lubchenco said those scientists have clarified that (in regard to the plumes) they have not reached "definitive conclusions ... about the composition of the undersea layers they discovered. Characterization of these layers will require analysis of samples and calibration of key instruments. The hypothesis that the layers consist of oil remains to be verified."

This has been later qualified by Vernon Asper, one of the scientists involved who said, among other things:

1) We are not 100% sure that the plumes are oil. We have NOT analyzed the samples yet and won’t know what’s in them until we do. That will take at least a few days or even a week or more and we don’t want to rush these results. The sensor we used is not definitive for oil and other compounds do respond in a manner that is similar to oil and could be confusing us.

2) I NEVER said that these “plumes” could cause a dead zone! It’s really important that you correct that! Consider:

a. We don’t even know if there is any oil in the plumes so the oxygen signal we’re seeing could be due to something else that is going on near the well and, if so, it could disappear overnight (we just don’t know

b. The oxygen levels we saw are lower than “normal” but are no where near the danger zone! For the most part, they are not even as low as the layer above them that we call the “oxygen minimum zone.”)

The NOAA Administrator was also on PBS where she again said that it was too early to speculate on what was in the plumes, and that there was a light oil sheen on the surface that might reach Florida in 9 – 12 days, but that it would be very dilute, and may just show up as tar balls, with little prospect of significant damage to distant beaches. She noted that the threat sounds scarier than it is.

MMS confirmed that the permit for the second well has been approved, and is in process. They pointed out that any procedure being carried out has first to be reviewed and permitted by MMS after ensuring that it will have minimal environmental impact and be safe. They also emphasized that the monitoring and regulatory side of MMS will be strengthened.

For their part Doug Suttles of BP noted that at the time of the briefing on the afternoon of the 17th, they were getting a little over 1,000 bd up through the Riser Insertion Tube (RIT). And they are now slowly opening the choke to ensure no hydrate formation.

Later this week they will run the top kill procedure, that will start to close out the well sealing process. The use of the RIT and of dispersant has reduced the size of the oil slick appearing on the surface.

In response to questions from the floor Mr Suttles said that if the RIT could recover more than half the flow out of the riser (which he characterized as a 2,000 bd target) that they would all be very pleased. He stressed that they did not want to draw too much fluid into the system, since that would lead to hydrate formation and another blockage of the line. And later he noted that they hadn’t decided yet what to do with the oil that they are capturing. (Though he also ducked a more definite confirmation of the actual volume that is leaking).

Admiral Landry said that the oil had not entered the Loop Current at this time. The larger volumes of oil are several miles from it, while there is a surface sheen that is getting closer.

Doug Suttles further explained the top kill by pointing out that the mud will be introduced at high velocity through the two 3-inch diameter choke and kill lines into the BOP. However he also clarified the position of the RIT, which I had thought was close to the BOP. It is, however, almost 5,000 ft up the riser, at the open end. The top kill is anticipated to stop the flow, after which cement will be injected. That will stop the flow, but BP will go ahead with a relief well to reach, and then pump cement into the bottom of the well which will finally secure it. He stressed that there was no intent ever to produce oil from this well. (Because the oil-bearing formation around the well is now degraded into a condition that is no longer controllable). The final decision as to whether to use “top kill” or “junk shot” first has not been made, but the inclination is to use top kill since it has less risk of precluding the alternate technique if it should not work.

Before they committed to the top kill they had to know the pressure on both sides of the BOP. They now have that data, and found that the pressures were quite low, less than expected, and were falling. They then had to remove the “yellow pod” on the BOP sine this carries the controls for the valves to the choke and kill lines, and these controls had to be modified to allow the top kill to take place. The pod has been prepared, but has not yet been taken underwater and replaced. That will happen soon.

The Admiral also emphasized that even though the oil may stop flowing out of the well at the end of the week, the studies and investigations of what is going on will continue for a long time. Further all the steps that are being made are being reviewed at several levels in different government agencies to ensure that they do what is needed, with minimal impact, while working out where all the oil and dispersant has gone.

Charlie Henry of NOAA clarified the comments about the “oil plumes” noting that the samples were so clear that you could not, by eye, see anything in the water. To find out what really is in the water will require an analysis, that has not yet been done, of what is actually there. There is also a lot of research and monitoring to see where the oil is going, and in what condition. This is the adaptive management of the process which must change as results come in on what is going on.