Deepwater Oil Spill - sealing the cap and jet pumps

There has not been much change down on the sea bed where last evening BP were able to put a cap onto the short riser section coming out of the Lower Riser Assembly (LRA) that sits on the Blowout Preventer (BOP) at the top of the well. I have looked in a variety of places for information on steps forward, and did discover that there is a second assembly above the cap, that I had seen, but had not been able to recognize until watching the video on capping available at the Deepwater Response site. It is here that the methanol is sent down to the cap to make sure that no crystals form within the cap. So for those who wish to keep the right names for the right parts, take note.

The cap, drill pipe, LMRP and riser assembly used to cap the well.

And given that I was calling the cap the 7th generation LMRP when it was (as the big 4 on the side of the yellow structure showed) neither, means I need to take my own message to heart. In this post I am going to talk about the seal under the cap.

There are four ports on the top of the cap, that continue to allow the oil that is flowing into the cap to flow back out while the cap was initially positioned, and to reduce the flow up the BP, until the system has been checked out to ensure there are no unforeseen problems. BP only slowly raised the flow rate up the pipe when they first started using the Riser Insertion Tool (RIT) starting out with a flow of around 1,000 barrels/day and then ramping it up, at the time reporting that flow ramped up first to 2,000 bd and then up to 4,000 bd. However they later rescinded the latter number and dropped the maximum flow level to around 2,200 barrels a day. Oil and gas have started flowing up to the drillship at the top of the riser where the oil is separated and stored, and the gas is being flared. (This was taken during the flare from the RIT operation).


However the flow out of the RIT was monitored, and higher rates have now been reported.

On May 25, 2010, at approximately 17:30 CDT, the RITT logged oil collection at a rate of 8,000 barrels of oil per day, as measured by a meter whose calibration was verified by a third-party. Based on observations of the riser, the team estimated that at least 10% of the flow was not being captured by the riser at the time oil collection was logged, increasing the estimate of total flow to 8,800 barrels of oil per day. Factoring in the flow from the kink in the riser, the RITTI Team calculated that the lower bound estimate of the total oil flow is at least 11,000 barrels of oil per day, depending on whether the flow through the kink is primarily gas or oil.

With the full flow now being emitted through the single confluence of the riser and BP flows at the top of the remaining riser section on the BOP, a full estimate of the leak will, no doubt, not be long in being announced.

The high volume of flow means that there need to be cautious progress in capturing all the oil and gas and sending it up the DP. However there is still a little communications conflict, since there were some reports that the taps bypassing the oil/gas would be closed later today, however at 10:43 pm the Enterprise ROV 2 was still showing an open port.


Oil was also leaking out of the bottom of the cap, which is, even when almost all the oil is being recovered, likely to be a good thing in small quantities, somewhat less than this.

From Skandi ROV 2 10:55 pm 4th June (The Skandi Rov 1 has the picture from the other side, also of the bottom of the cap).

Why is this? Well the way in which the Shear was used to cut the end of the riser and BP means that it is likely to be impossible at the present time to get a good strong seal around the chamber between the flow into the cap from the BOP and that out into the BP up to the LMRP.

When a stream enters a chamber through one port, and exits through another, both of relatively small size, then the jet will create a vacuum in the chamber, which pulls fluid from the surroundings into the chamber and carries it, with the jet fluid into the second port. I am going to embed a short video of a commercial down-hole video and am not endorsing anything but the animation shows you how the jet pump works. (And the flow in the Gulf is easier than that shown here ).

Animation of an oil well jet pump. There is a competing design here (shorter video too)

The reason that it is critical in this operation is that the fluid outside the cap is seawater. If the jet pumping action were to become too efficient as all the oil flowed from one passage to the other, then the “jet pump effect” would draw cold seawater into the chamber and the problem of hydrate generation and blocking of the flow path would be back to block the cap, as it did top hat. By not getting all the flow into the second pipe it should be possible to drop the suction in the chamber to the point that a little oil still leaks out (treated with dispersants) but the majority goes up the well. Getting this right should prove an interesting exercise. (But isn’t calculating this what the “best and the brightest” – Dr. Chu’s team - are there to do?)

Flow control is achieved, simplistically, with a valve at the top of the riser on the Enterprise. By adjusting the flow the valve effectively controls the pressure at the top of the riser and thus also at the bottom.

Incidentally in other circumstances jet pumps are neat tools. One of my students developed a high pressure one for use in lifting high-level radioactive waste out of nuclear waste storage tanks (you want to minimize water use, and do this by upping the driving jet pressure). Worked like a charm, when used in the real tanks. They are also used as remote inexpensive pumps in mines, lying in depressions where water can collect. The water collects, a float valve lifts and the jet flows, sucking the water away. As the water disappears, the float drops and the jet switches off.

Oh, and for those who have ideas on how to deal with any part of this problem, the Government is stepping up the ways in which you can get funding. The process goes through the Federal Business Opportunities Webpage where there is a Broad Agency Announcement on the subject. It would be more fruitful to contact them.

Deepwater Oil Spill - capping the riser - Part 1

The vertical section of the riser was cut, using a Shear at 9 am this morning.

Lower Riser Assembly (LRA) atop the Blowout Preventer (BOP) at the Deepwater Horizon well, with the bent riser removed, waiting for the arrival of the Lower Marine Riser package (LMRP) The oil and gas are rising vertically, from the top of the riser, the drill pipe (DP) and the saw cut in the side of the riser (just down from the top of the shear).

At 8:30 pm the ROVs maneuvered the latest version of the “top hat”, variation 7, of the LMRP over the top of the LRA. As the new cap was lowered into place it was surrounded by clouds of oil and gas, making the actual progress of the event somewhat difficult to follow. The new variation had been finished yesterday, to accommodate the changing upper surface of the remnants of the well.

Building LMRP 7 on June 2nd at Port Fourchon (BP )

The Lower Marine Riser Package (LMRP) was first connected to the riser, an to a methanol feed that would help, between them, to inhibit the formation of methane hydrides when the gas came into contact with the surrounding cold seawater. It was then slowly lowered to the site. (You can see the seal, referred to later, along the bottom edge - h/t KLR).

Interior of the LMRP as it was lowered. (KLR)

Once it reached the right depth it was moved across into the fountain of oil and gas, and down over the top of the riser.

Lowering the LMRP into the cloud of oil from the riser.

The initial attempt halted after a while, and by 9 pm the situation was, for while static. The cap was sitting apparently on the rubber seal that had been designed to fit between the LMRP and the flange, but the amount of oil that was leaking out of the bottom of the LMRP, was still a considerable amount, even though some of the flow was also being bypassed through ports on the LMRP that could later be closed.

Flow through a relief port on side off the LMRP to relieve the pressure within it.

Leakage around the seal between LMRP 7 (yellow), the seal (greenish black) and the LRA. (white)

The question now arises as to whether the LMRP could be lowered sufficiently that it could seal to the flange surface, since it was no longer possible to get the seal needed on the upper surface of the riser, given that it had been distorted by the Shear which had cut the bent riser away.

There was a pause, while the engineers had a bit think for over an hour. Looking at the cloud of oil coming out, it does contain small white specs that could be either methane hydrates or drops of the dispersant. And now, at 10:30 pm, there is a little more action.

Oil and gas coming out from under the LMRP

Leaks under the LMRP at 10:30 pm

For those who may not remember, this was the initial plan as it was proposed.

The Lower Marine Riser Package (LMRP) option

So far it is not quite as simple as the sketch would suggest. But I will put this up, and then update, as changes appear. But we may be in for a bit of a wait as they may only slowly close the valves and direct the flow to the surface, as they did with the first oil capture at the RIT. They will be checking slowly through the process to see that as little as possible goes wrong, as they ramp up the flow, and slowly turn off the bypass valves.

Deepwater Oil Spill - working on the riser

There has been a lot of activity at the bottom of the Gulf today, not all of it immediately successful, but all working toward to current aim of being able to field the Lower Marine Riser package. That installation requires that the broken existing riser that connects to the Blowout Preventer (BOP) has to be removed. The bent riser has been exerting some lateral pressure on the BOP, and this might be relieved when it is cut off. To minimize the damage the first cut is therefore going to be further down the riser. UPDATE: At 10:45 pm the wire saw is cutting the riser. But at 12:30 am the wire appeared motionless in the slot and could be jammed. While they worked on it on Wednesday they have now given up and are switching to the Shear. I have put an explanation (short) of what happened and how they could have fixed it at the end of this post. END

The Lower Riser Assembly attached to the top of the BOP, the riser has folded over to the left.

I described the plan of attack in an earlier post, and what has happened, over the course of today has tried to follow that script. I say tried, because there have been a couple of glitches develop over the course of the day. The large shearing machine (apparently owned by BTI) appeared on the scene, and in preparation for its use some of the pipes surrounding the main riser (the choke and kill lines) were first cut away using a diamond saw.

10:04 am just before the pipe was severed.

At the same time that this was going on, the wire saw that would make the final cut on the riser had been brought down to the site. The riser assembly has been cleaned of extraneous pipes already, and the wire saw would fit about the flange and below the bend.


The wire saw was then located ready to make the cut.

10:30 am Wire saw on riser

It was now time for the shearing machine (which I’m going to call a Shear from now on) to fit around the riser and to make the first cut through the pipe.

First shear location

Unfortunately the first cut did not appear successful, although there was a cloud of oil and gas released, indicating that the riser was at least breached. There was a pause, and the Shear moved to a new location closer to the riser. Again it tried to shear through the nest of pipes, that now included choke and kill lines. It was not successful, and returned to the surface where it will be either repaired or replaced. (There may be some problem with the hydraulics since it should have been able to handle the job that it was given). It (or a substitute) will likely make an appearance again before long.

While waiting for the Shear the ROVs worked, either alone or in combination, to cut away more of the pipes that surround the riser in the section to be sheared,

Cutting choke/kill line that still contains mud

Well I went away for a couple of hours and thus missed the shear coming back and cutting through the riser. This was the moment (recorded on Youtube) when the two parts of the riser separated.


Just after that the wire saw was activated. It appears, at 10:45 pm, to be half way through the riser. I'll try and note when it it done.

Wire saw at 10:45 pm

In the meanwhile, a little calculation, based on reports that the White House has announced that the removal of the riser and drill pipe that are protruding from the Blowout Preventer (BOP) of the Deepwater Horizon well in the Gulf may increase flow by 20% when the riser section is removed. There are two immediately obvious reasons why this might be the case.

The first of these is that there is a small amount of oil that was leaking up through the drill pipe that extended beyond the broken riser. That flow was one of the first things capped in the remedial effort. It did not have much impact on the overall flow volume, since the flow merely backed up and increased the flow through the main crack in the riser, but there may be a small increment of flow when this channel is re-opened with the cut below the fold in the riser.

The greater change in the flow, however, will likely come because the riser and DP, while not providing much increased resistance, did raise the pressure on the downstream side of the BOP by about 500 psi. We know that though the pressure down at the formation was at around 12,000 psi up on the upstream side of the BOP it fluctuates in the 8,000 to 9,000 psi range. The higher resistance on the downstream side, reduces the pressure drop across the BOP by that 500 psi, and the flow rate will be reduced accordingly (the gap size through the BOP is assumed not to change).

However, if the pressure drop across the nozzle was at 6,000 psi in the current condition, (which with an orifice size of 0.6 inches, would give a flow rate of 512 gpm) then raising the pressure drop by 500 psi would only increase the flow rate to 532 gpm, or a difference of 4%. Which might suggest that there is something about the drill-pipe flow that was initially capped which we don’t know yet. Alternately it may be that they think that removing the bend in the riser might ease the forces on the BOP, relaxing the metal a little and increasing the orifice size. After all it has only to open up by another 0.05 inches to give the increase in flow that the EPA are predicting.

Oh, and I mentioned earlier that an ASJ system had cut through casing and pipes at the bottom of the North Sea. I had the orientation of that cut wrong (at least for the picture below) since in this case it was from the outside in, but I am aware of it being successful the other way. And so here is the picture of casing and cement cut by an ASJ. Sadly it was so long ago - around 23 years, that I can no longer remember exactly the pressure it was cut at, but I believe it was 5,000 psi.

ASJ cuts of casing from the bottom of the North Sea

UPDATE: The wire motionless in the slot at 12:30 am


UPDATE: The wire was apparently stuck for a number of hours and they may have changed the wire, and then restarted with a second cut. BP is still predicting that the cut will be completed today and the LMRP installed.

UPDATE 2 (5 pm Wednesday): Part of the problem was apparently according to a BP spokesman that the cut through the first half had dulled the blade, so that when they got it restarted it would not cut. (What we do in those circumstances, which are not uncommon with diamond blades, is to run the blade through firebrick, and this erodes the material into which the diamonds have been pushed, and sharpen it. Then we drop the cutting pressure a little.) However, BP's current answer is going to be:

The technician said that rather than trying again with the saw, the plan now was to use a large shear to cut the riser. The shear, which is about 20 feet long and nearly 10 feet high, was used to make an earlier cut in the riser about 50 feet from the wellhead. Because the shear will not make as clean a cut as the wire saw, modifications would have to be made to the containment cap that is to be lowered over the cut pipe. But the technician said that even with the switch to the shear and the modifications, he expected the containment cap could be in place by Thursday.

Deepwater Oil Spill - cutting the Riser

At present they have started cutting through the pipes around the riser. At 8:45 am they had the shearing machine set on the riser and then just after 9:am they brought in a circular diamond saw that is now cutting through the choke and kill lines that are running beside the riser. Part of the problem they face is that they don't want to cut into the riser pipe directly behind the current pipe, because that would flood the viewing area with spurting oil and gas. And at 10:05 am they got through it.



10:04 am just before the pipe was severed.

10:10 am Overview

10:30 am Wire saw on riser

11:05 am Given the shift in the source of the oil, I suspect they are shearing the riser, but have backed the ROVs away to ensure they don't get damaged, so the view is somewhat unclear.

1:00 pm They had moved the shearer upstream along the riser to try and make a second cut. This time including the choke and kill lines. Not sure why, perhaps there was a joint in the drill pipe at the first site and they could not get all the way through. However they started to shear at this second location, backed off, and then at about 12:45 pm starting in again.

1:15 pm I had stepped away from the computer for a few minutes, and came back to a screen full of oil, so initially I thought that the shearer had cut through the riser, but apparently just about 12:50 pm the shearer released the pipe, and was hoisted off, perhaps to the surface for evaluation, or replacement or repair. We'll have to wait to find out.

Before the wire saw was put in place on the Lower Riser Assembly (LRA) I took a couple of screen shots to show a) how much stress the BOP may still be under, since the whole frame is tilted in the direction of the riser:


And then this is where the wire saw will be cutting, and it shows how much the riser was deformed.



I'll add more to this post over the course of day as the cutting continues.

Deepwater Oil Spill - cutting metal underwater

The decision to cut the riser and drill pipe (DP) from the top of the Blow-Out Preventer (BOP) as a first step in putting the Lower Marine Riser Package (LMRP) over the leaking oil well in the Gulf of Mexico is not quite as easy as it might sound to a layman. This post is going to talk a little about a couple of the problems, as well as an alternate way of doing it, and should end with a possibly slightly amusing anecdote.

The current plan is to carry out the operation in two parts, first the main body of the riser and contained BP will be cut using a large shearing machine, and then a precision cut will be made with a diamond wire cutter to prepare the surface to act as a support and seal for the LMRP. (Illustrations are below the fold). There are a couple of reasons why this is going to be done this way, and one or two concerns that will need to be watched as the operation continues.

Part of the problem lies in the considerable stress that the metal is under, which may make it more difficult to get the precise cut that is needed for the sealing surface. The weight of the collapsed riser on the kinked section of the riser means that the metal is under a considerable stress, and as the cut is being made that stress is going to be released. This is a particular problem if the saw blade is in the cut as that stress releases. As an illustration large diamond wheels are used in granite quarrying as a way of making the first cut in a new layer of rock. As the quarry works down into the deposit, however, the stress in the rock increases. So that when the diamond saw cuts into the layer, the walls will move in slightly. Now if the diamond saw is rotating until it is removed, it will grind away that small movement and there is no problem. But if the saw is removed, and the cut restarted the next day, then it might be necessary to recut the same depth again, because the walls have moved in that far. The much worse thing to do is to leave the diamond saw in the cut overnight – the walls will move in and pinch the blade and you can’t get it back out without destroying it. Did I mention these blades can cost up to $100,000.

So given that it would be a bad idea to break the diamond wire in the cut, or trap it for that matter, the first step in the process is to take some of the load from the riser by cutting off the majority of the fallen pipe. To make this simpler and since the quality of the cut is not important, this will be done with a large shearing machine.

Large shearing machine used to cut through the main section of the riser (Unified Command )

For the second stage in the process the riser and pipe will be cut, at the top of the BOP using a wire saw to cut through both pipes. The diamond wire, which is held under tension in the design, should give a relatively smooth surface that can be used for the sealing surface to the LMRP.

One of the problems in using this tool, which is rather sensitive (in other circumstances we have broken several wires in a smaller model) is dealing with the central DP as the cut is being made, and with the flow of oil and gas past the wire, which can send it into vibration, over the relatively long cut.

Wire sawing the riser and drill pipe (Unified Command )

The two pulleys at the top of the saw are used, as well as guides, as tools to keep the wire under the correct level of tension.

A version of an underwater wire saw (Wachs)

It is relatively slow to cut, (perhaps 10 to 30 sq ft/ hour, depending on power and blade size) and requires patience to keep the applied loads at the right level (the joy of automatic equipment over manual operation). There are still possible risks, due to the remaining load on the metal being cut as it is being made, since the amount of metal left gets less over time. As a result it is likely that, in the same way as a forester will use wedges to stop the cut closing as he chops down a tree, so small metal wedges will be put into the cut in this case. The only difficulty that this imposes is that it will be difficult to access the central BP and difficult to deal with that, once cut through, since it is within the riser and not accessible. Hopefully it will be held in place by the bend of the pipe and riser, until the wire has passed through it.

Over the past twenty years diamond wire sawing has become more common as a way of cutting through a variety of materials. It has the advantage of making a relatively narrow cut , and the ability to cut through objects made of different materials, such as reinforced concrete. The cutting wire used to have small diamond particles embedded in the steel of the wire, but in more modern varieties the diamonds are embedded in a plastic such as Teflon, and set as beads along the wire, allowing better cooling during the cutting process.

Segmented diamond wire – new so that the paint is still over the diamonds (Wachs)

Now my students will tell you that I have a bad habit of slipping commercials for another technology into lectures, and so I am going to indulge, and mention that there is an alternate technique that could be used instead. And that is the use of a high pressure abrasive laden, waterjet cutting stream. These are becoming increasingly used in industrial manufacturing, although in that use the technique usually involves a different way of adding the abrasive to that which would be used in the current problem. In the conventional way of adding abrasive it is mixed into the jet after the water is accelerated, and, in the right circumstances, we have been able to cut through half-inch titanium with an accuracy of 0.001 inches. Those jet systems operate at pressures from 40,000 psi to about 90,000 psi. In the current case the abrasive is added to the water from a pressure vessel, and the technique is known as abrasive slurry jetting (ASJ). It allows equivalent cutting at about a tenth of the jet pressure (i.e. 5 - 10,000 psi). The tool has been developed for cutting off different oilwell parts from the wells under the North Sea. Because the jet cuts away from the nozzle, it can cut, for example, out from the center of a set of drill pipes, one nested inside the other, and separate them, as one of the last stages in decommissioning a well. It has a problem with range, the jet cutting to a shorter distance as the back pressure in the water increases, and for cutting down to 500 ft (the deepest we have tried) it can be improved to cut large risers by adding an air sheath around the outside of the jet.

One alternate way that is used for cutting tanks and other containers with possibly explosive content is to use a chain crawler around the pipe. This way the jet does not have to cut quite as far through the water.

Cutting a pipe using a crawler (NLB )

(And for those who question whether jets would work under this depth, Gulf Oil – as was – used an abrasive waterjet to drill a well down to 15,000 ft back in the early 1970’s but a fire destroyed the equipment and the research was stopped).

To end with the anecdote – which relates to the cleaning of oil rigs for inspection. The problem that arises is that barnacles and a variety of sea creatures and plants grow on these structures, and need to be removed. The historic method of doing this was to give a diver a chipping hammer, and send him down to chip off the offending coating. Now when a diver is in the sea there is not a lot of resistance, and so one has to clamp onto something to develop enough thrust to effectively use the hammer. The only object available is the rig itself, and wrapping one’s legs around a strut works to give the platform. The only problem is that the strut is covered in barnacles – ouch!

So the waterjet industry developed a zero-thrust gun (in other words the cutting jet on one end is matched by a jet of similar power on the other, so the forces are balanced) and the diver does not need to hold onto anything. It was taken out to one of the rigs in the North Sea and given to one of the divers.

He took it, without a word, and disappeared over the side of the rig. He was down underwater using it for about fifteen minutes and came back to the surface. He didn’t say anything, but walked over to the chipping hammer. He put down the lance, picked up the chipping hammer, and walked to the side of the platform. “So long , you son of a . . . .”, he said, and threw it overboard.

It was one of the fastest adaptations of a change in technology around the world that I have seen. Anyway I will talk about using jets for efficient cleaning in another post. Enjoy the day!