The Chilean Miners - nearing a rescue

The rate of progress in rescuing the miners from the copper mine in Chile continues to be better than expected. After the completion of the rescue shaft on Saturday, it was inspected, and the top 300 ft was considered to be possibly unstable and so has had to be lined with a metal casing. This is somewhat similar to that used in oilwells, except that it does not have to be water-tight and can be hung from the top, through a lip that extends outwards, again without need for a seal. This liner was inserted in 20 segments, and is only needed for the first 300-ft since a survey of the rest of the 2,300 ft long shaft has shown that the rock around it is solid, and does not need support.

Preparing the casing for the shaft

Schramm T-130

There were three different drills used to try and create the rescue shaft. The first of these, a Strata 950 was brought to the site on August 22nd, and drilled its own access bore, which would then be subsequently reamed to the necessary diameter for the rescue capsules. As a back-up a second drill, a Schramm T-130 was brought to the site at the beginning of September (the fourth) . In contrast with the first drill, which was drilling its own access borehole, this unit was set up to ream one of the existing boreholes (of which there were 3). By doing this, and reaming the hole in two stages, rather than just one, progress could be considerably faster . The initial diameter of the hole was 6 inches, this was first reamed out to 12-inches, and then to the final 26-inches. After set-up the benefit of the two-stage operation became evident early on, with the T-130 being able to ream the initial bore out to 12-inches by the 17th of September. Fifty days after the collapse of the mine tunnel, progress for what was now three different operations, was shown in this graphic.



Plan C, a drilling rig which is drilling a hole at full diameter from the beginning was set-up later, but has been making very good progress, and is being continued to provide a possible back-up in case something goes wrong with the initial shaft.

One of the concerns with the existing shaft is that, as a result of the way that the hole was drilled, it is not straight but has a number of curves in it. These are not severe, but could possibly cause a problem with the cage. By this morning the lining had been completed, and the infrastructure is being assembled over the shaft to be able to wind the cage in and out of the mine.

Moving the liner into place

It is now expected that the cage will be tested today to ensure that it can easily move up and down the shaft, and that the miners will be able to start being lifted out of the mine starting at 3 am Wednesday morning. And in a more recent story the cage has been reported as having been able to move down the shaft without any problems .

Deepwater Oil Spill - locking the hanger and relief well role

A short time ago I wrote about the concerns with the casing hanger in the Deepwater Horizon well, and the risk that it might lift and allow whatever fluid is in the annulus between the production casing and the well lining to be released. In his remarks on Friday Admiral Allen discussed that situation. At some point there has to be a seal on the top of the well to prevent fluid escaping from the annulus. The solution that he, the science team, and BP have reached is that the casing hanger will be locked into place, so that it cannot lift off the seat. This was the illustration that I used back then:

Labelled section showing the parts of the casing hanger (note that there is an animation at the source site)

With the casing hanger itself looking like this:

Casing hanger.

The lack of a locking ring was a bit of a bone of contention when the initial Congressional hearings took place back in June, being one of the five issues that Congressman Waxman brought up in a letter to Tony Hayward. (The other four were the design of the well itself; the “centralizer” issue; the failure to run a bond log; and the failure to circulate possible gas-bearing mud out of the well. ) It may not have been necessary back when the well first started to flow (if the annulus is, in fact, still full of mud rather than oil) and the seal is currently working, but by putting a lock on the casing hanger so that it cannot rise out of the seat they are ensuring that it will not move, even if pressure increases in the annulus, after the relief well makes contact. Locking it can be carried out by running a string of drill pipe down to engage the top threads of the hanger, so that it can’t move. Alternatively it can be connected to the surrounding wellhead structure, perhaps by running a sleeve back up to the overlying BOP. It could have been locked with special locking screws that ran through the wellhead, but they aren't in play at this point.

Admiral Allen noted:

In essence, we're going to put a ring or what they call a sleeve around the top that'll lock that casing hanger in place, will not allow it to move. There is always concern that when we pressurize the annulus, that casing hanger would lift, allow free communication between the annulus up into the blowout preventer.

Cement in the annulus will be one way to preclude that from happening. But after some consultation and looking at various alternatives, the BP engineers and our science team agreed that if we could ascertain that the casing hanger had not been dislodged, in other words, where we need it to be, then we could actually put a sleeve around it and basically lock it down.

And the order that I issued to BP, I ordered them to take what are called lead impressions. You go down, you take an impression of the top of the casing hanger. And then that allows you to take measurements on where its location is. Based on that measurement that they took, it appears that the casing hanger has not been dislodged to the point where we'd have a problem with the seal, so we just need to lock it in place, and that would substitute for the pressure control that cementing the annulus would have provided.

Once BP tells the Admiral how long it is going to take to lock the hanger down, and it is done, then he will give permission to restart the relief well. The impressions of the seat were apparently made by lowering lead blocks onto the hanger and deforming them. This provided the required impression of the position of the top of the hanger, from which it was possible to decide that it hadn’t moved.

With that seal in place it is no longer necessary, at this time, to perforate the top of the casing to insert a cement plug, since the seal will itself provide a plug during the relief well operations. (The plug will still be needed for the abandonment part of the process).

MoonofA has illustrated the process that is now to be followed in complying with the Admiral’s instructions. I am copying the comments that go with two of the illustrations from that comment:

(This) picture shows what will happen in the next days.

1. The casing hanger lockdown sleeve will get installed (not shown).

2. Developer Driller II above the original Macondo well will put its drill pipe into the hole and will perforate the production liner long string just above the top-kill cement. (If the annular is pressurized from the reservoir it may take a kick doing this.)

Pumping cement into the annular in this state would be dangerous and difficult as whatever is in there now, mud or oil, has no place to go. To avoid any damage when pushing cement down in there we need some communication to be able to retrieve the stuff that the cement will replace.Therefore:
3. Developer Driller III doing the relief well will intersect below the outer casing into the annular between the long string and the well bore. This will then form a U-tube between the DDII down through the annular between the long string and the outer casing and up to the DDIII. Mud can then be pumped from one rig down the hole up to the other rig to test the communication through the annular.


4. Fresh cement (green) will then be pumped from the DDII down its drill pipe into the annular. As communication is established, whatever is then in the annular, mud or oil, can be pushed by the cement up to the DDIII.


With this the annular is then truly dead and The Admiral’s point 5 demand will be fulfilled.

However, to get the perforations just above the cement, the perforating tool has to reach that position, which it can only do if there is no old drill pipe in the way. We will see if any is found, and they fish for it.

Deepwater Oil Spill - stopping the fish

The attempts to recover pipe from within the blowout preventer (BOP) on the Deepwater well have now halted, without being able to recover any of the pipe. Instead attention is now being given to the removal of the BOP itself and its replacement with the BOP from the second relief well. In his remarks on Friday Admiral Allen gave, as his explanation:

What we have found is we have gone down there, the pipes have settled against the side of the BOP and we can't successfully put the overshot devices over them. We've come to the conclusion that any more attempts at fishing are probably not going to result in success.

And at a meeting this morning between our science team and the BP engineers it was decided to recommend to the principals, the cabinet secretaries we go ahead with the removal of the blowout preventer and the replacement of the blowout preventer with the one that's on Development Driller 2.

This is due to the one whose apparent fragility of the pipe that keeps breaking and falling off to the side and also the unknown condition of the BOP below that and I can talk about that in a little bit.

So the plans are right now to replace the BOP. The approximate timeline going ahead is as follows, starting today and through Saturday and Sunday we will make preparations to remove the BOP and replace it.

This did not agree with what I saw occurring during the time that I watched both the recovery attempts over the last two nights, and from the videos that others posted on Youtube, and which I referred to in those posts. However, not being a part of the team running this operation there may have been some things happening that I and others are not aware of.

I still remain concerned about the condition of the lower section of the BOP and the presence of either hydrates or cement, both in the area of the BOP rams, and around the drill pipe as it extends down into the well. To explain the concern in perhaps a little more detail, let me first talk a little about the casing hanger that the Admiral referred to as one of the limiting well conditions today.

The casing hanger is the device at the top of the well that holds the production casing in place. In the extended transcript of his press conference on Friday, he referred to the company that made the hanger (Dril-Quip) and gave a link to the drawing of the hanger, this one, which I have labeled, because I am going to try and explain, using this and other diagrams, what the Admiral meant with some of his remarks, as I interpret them, and some of the concerns I continue to have.

Labelled section showing the parts of the casing hanger (note that there is an animation at the source site)

In essence, at the top of the production casing, the long continuous tube that was placed from the sea bed down to the bottom of the well, there is a hanger that holds the top of the casing against the surrounding liner and well head assembly. To show that in more detail I am going to use a different source, to highlight the hanger section.)

Casing hanger.

The casing comes up through the center and connects to the top element. The weight of the casing now pulls the upper section down, seating the conic surface, and also spreading the elastomeric packer (the black layer) which pushes out against the sides of the surrounding wellhead wall, providing the seal. This seal is between the liners around the top of the well, and the production casing, it is, in other words, the seal at the top of the annulus between the production casing and the wall of the well.

I have put this in to explain what the Admiral meant when he was talking about trying to lift the BOP off the well head, which means unlatching it from the top of the well head assembly. The BOP latches around the top of the assembly shown in the top figure.

To remove the assembly, the Admiral has approved the following process:

Commencing on Monday and through Tuesday the Discoverer Enterprise will latch on and remove the capping stack. And the capping stack will be temporarily stored nearby on the ocean floor. Once that has been completed the Q4000 will move in and connect to the BOP and will unlatch it.

And then there'll be a series of two decision points will occur. We will attempt to pull it free and we are prepared to apply up to 80,000 of force in addition to the weight of the blowout preventer to lift it. We call this the gentle tug.

If the blowout preventer comes free we will then use the (Boa Sub-C) and the ROV's to attach a line to it and cut it (the drill pipe) just above the well and at that point we can bring the BOP to the surface on the Q4000.

If for some reason the blowout preventer does not come free with a gentle pull, our intention then is to manually open the ram sequentially down through the blowout preventer and then raise the blowout preventer and cut the pipe at the well head.

He later explains why there is this limit of 80,000 lb in the “gentle pull.”

What they’re concerned about is somehow potentially dislodging the hanger and the casing hanger that is at the top of the well. That is also the – as you know that is a device that contains the seal between the annulus and the well and the blow out preventer. So the threshold for the pull has more to do with the potential to unseat the casing hanger and the seals that seal off in the annulus.

So that if you go back to the second illustration, the seal is maintained by the weight of the production casing, pulling the head of the hanger down so that the elastomeric seal spreads. If the upward lift on the BOP is transferred through the drill pipe to the top of the casing, they are concerned that if the DP is held within the casing hanger, that pulling it too hard may take the weight of the seal, so that it contracts back from the wall, and opens up the annulus.

Now to explain why that might happen, and why there might be all sorts of other concerns, let me move away from the hanger itself, and go to a modified frame from the Dril-Quip video. (For those looking at the video I have changed the picture to show the center as though it were the drill pipe).


To make life easier for me I am just showing the lower end of the BOP, below the rams, the central drill pipe and the upper end of the well head (without the hanger detailed).

Now in a normal situation the drill pipe would be held by the three rams at the bottom end of the BOP, and slightly above the picture. In an ideal world there would be nothing else in the gap around the drill pipe (i.e. the annulus).

But we know that above the rams, that there is either hydrate or cement around the DP.

View from the fishing camera showing the top of the drill pipe above the BOP rams, surrounded by what may be either a hydrate or cement fill.

And the pipes are held and seem unable to be moved

What we know is, the pipes that we can see are in pieces, sitting inside the lower marine riser package and we are having trouble lifting them out with the fishing devices. We have no further information and cannot tell the condition of the pipe below the blowout preventer.

If the material holding the pipes extends down into the rams of the BOP and below it could fill the upper annulus down through the casing hanger. Thus pulling on the BOP would exert a pull, through the DP and this fill, on the hanger and could unseat it.

Should the BOP not move, the plan is to open the rams on the BOP, so that it no longer holds the pipe. But if the rams are cemented in place by the fill, this may be very difficult to do, since trying to flush out that fill on Thursday evening didn’t work. And even if it did work, the fill may occupy the annulus between the BOP and the DP below the rams and above the latch, so that the DP is still held by the cement. (At which point if the chemicals don’t release it they might try the jetting again, since that works both on cement and hydrate). It is only by freeing the BOP from the drill pipe, and hoping that the pipe remains held by the underlying fill within the hanger, that the BOP can be released, removed and replaced.

The problem is that if, when the rams are opened, the cement/hydrate holding it is not strong enough, then the pipe may fall to the bottom of the well, carrying with it the evidence on what actually happened to it within the BOP. (Opening the rams will also drop out the other two pieces of pipe currently above the rams). Tough decisions.

Deepwater Oil Spill - the last cement job?

The first relief well at the Deepwater Horizon site appears to be close to setting the last casing in the new hole, before the final step of drilling down to and through the original well casing. While this is bringing the initial major concern (stopping the oil flow) closer to closure, there is still some time to go. Wind and weather are not cooperating and the depression over the Yucatan is reminiscent of Alex, which held up work until wave sizes dropped at the site. Sadly wave heights are now back up to the point that they are holding up work on completing the connections for the new cap to the well. At present, while the connection to the Helix Producer will carry an additional volume away from the BOP through the kill line, perhaps allowing some of the vents on the original cap to be closed, some leakage must still be maintained.

Since the stage is ripe for the final installation of casing at the lower end of the relief well, I thought I would just repeat a very simplified description of the process that is going on, so that you can understand the delay, before they drill over to intersect the leaking well.

As the well has been drilled down through the ground, it passes through layers where the rock might either be porous enough that the drilling fluids will flow into them, or might itself contain fluid at pressure that can flow into the well, and dilute that mud. In order to stop either event from happening, the drilling process is stopped and a process undertaken that seals off the rock on the sides of the well from the well itself. This is known as casing the well, and running casing and for this relief well the process has been carried out a number of times as the well was driven. The well is now at the point that the final casing is about to be set, following which the connecting passage over to the flowing well will be undertaken.

The drill string is first taken out of the hole, and the drill bit is removed. The drill string can then be used to lower a larger steel pipe into the well to encase the well, from the bottom of the earlier lining run down to the current bottom end of the well. (Hence the name casing). Having this continuous length of casing in the hole will stop, say water, from getting in and diluting the drilling mud or the mud itself from flowing out into the rock. But if this was all that we did, then it would still leave a problem, since the steel pipe does not completely fit up against the rock wall created by the drilling bit. In other words there will be a gap between the casing and the rock wall, and this will allow fluids to travel up or down. This gap has to be filled, and the filler is normally a special form of cement. The casing has, therefore, been fitted with a small ring, called a shoe, that fits on the bottom end of the casing as it is set in place.

Components used in cementing casing into place (after Schlumberger

The way that the cement is placed is simple in principle, but a fair bit more difficult to do properly and effectively. Think of the long thin tube of casing, filled with a cement that acts something like toothpaste. This cement has to be pushed down the tube so that it squeezes out of the bottom and then flows back up between the casing and the rock wall, filling all the gaps as it is pushed back up to the top of the previous run. Particularly when this last casing is run, it is important that the gap is fully filled. This is because this is the casing that seals the well so that no fluid can escape back up around the casing, rather than flowing from the relief well into the well that is flowing oil and gas. Since the cement will move more easily thorough a larger passage, than a very narrow one, this gap has to be above a certain minimum size. Small centralizers are attached at points down the steel casing to keep it in the middle of the hole, rather than pressing up against one of the walls (since this might leave an open channel up through the cement). (And it was the number of these that caused some of the concerns in the final casing of the well that the Deepwater Horizon ran).

Cementing plugs

A small plastic plug (the bottom plug) is put into the casing ahead of the cement. This separates it from the mud that is already in the hole. It is fitted with wipers, that clean mud from the walls of the casing, and it is pushed down to the bottom of the casing by the cement that is pumped into the well behind it. There are some pictures of some of the tools and descriptions of the process here, here and here.

Once the bottom plug gets to the end of the casing, there are ports it passes that allow the cement to flow out of the casing and back up the outside. Once the cement has been pumped into the casing a second, top plug, also fitted with wipers, is put into the casing and this is then pushed down by the conventional drilling mud. As it is pumped down it forces the plug down, and the cement out and back up to the surface. Because of possible variations in hole size and other possible problems, perhaps about 50% more cement might be pumped into the well than the calculations might suggest. When the top plug hits the bottom plug, then there is a pressure spike at the pumping station, telling the operator that it is finished. The rig then waits on cement (WOC) until the cement is hardened. The drill pipe can then be put back in the hole with the mud motor on it ready to make the connection over to the flowing well.

At present the debate over exchanging the cap on top of the old well does not appear to be totally settled, and Admiral Allen has been meeting with BP to move this part of the operation forward.

Incidentally, while Tony Hayward who has left the scene in the US is still busy on BP business, but was spending the day in Azerbaijan

Mr Hayward re-iterated BP’s commitment to Azerbaijan and to continuing successful cooperation with the government and SOCAR. Mr Hayward once again highlighted the importance of the Azeri-Chirag-Gunashli and Shah Deniz oil and gas development, as well as the Baku-Tbilisi-Ceyhan and South Caucasus Pipeline projects to Azerbaijan, the region and global energy markets.

I’ll add information on oil production when available, since the BP server appeared down when I just went to access it.

Deepwater Oil Spill - The Admiral on casing and connections, and an update or two

I am following a number of different events this week, and so today is as much a set of updates, as anything. Firstly the oil in the Gulf.

For the first 12 hours on June 21 (midnight to noon), approximately 8,410 barrels of oil were collected and approximately 5,015 barrels of oil and 25.3 million cubic feet of natural gas were flared.

On June 20, total oil recovered was approx. 23,290 barrels:
• approx. 14,570 barrels of oil were collected,
• approx. 8,720 barrels of oil were flared,
and approx. 48.3 million cubic feet of natural gas were flared.

Total recovery was slightly down on June 20 due to shut-ins from a lightning storm in the area of the Enterprise and Q4000 heading changes to accommodate wind shifts.

One of the concerns in the Gulf relates to the arrival of a hurricane, and the National Hurricane Center is showing the development of an area of low pressure that could cause problems later in the week. It has changed from yellow to orange in the past day.

National Hurricane Center


Admiral Allen held a telephone conference call today. In this he mentioned that the deeper relief well has now reached 10,677 ft. They intend sending electrical pulses down the casing of the existing well (WW), which will induce an electro-magnetic field that will help locate it and allow the relief well (RW) to be steered towards it. This will start about now, and will allow a much more accurate estimate of position than they now have. The RW operation is currently scheduled for the second week of August

Given concerns over the integrity of the borehole, Admiral Allen specifically noted (in response to a question from the AP) that during Top Kill they had evaluated the highest pressure that they could use in injecting mud, without impacting the integrity of the casing. When they reached that pressure, without being able to kill the well, then they stopped the operation. But that did not damage the wellbore, and though there may be a problem with the wellbore near the top there is no way to check it, and thus they will rely on the bottom-up filling with mud. This will exert less pressure on the casing, and if, at that time, there is a casing failure it will be with the well full of mud, and thus of less consequence. It is also why they don’t want to cap the well at the surface now. They are capturing the oil and gas, and the RW will be able to perform a safer kill.

Apparently the vents on the top of the LMRP cap are still open, and the 23,000 plus bd that is being produced does not count the amount that is still being vented. However they are bringing in another vessel so that they can tap into the kill line out of the BOP (they are currently only producing through the vent and the choke lines). That will allow an increase in volume collected to a capacity level of 53,000 bd sometime next week.

Following the tests on unbolting with the ROVs the new plan is to unbolt the current cut riser segment and then bolt the new cap onto the top of the BOP. That will then produce through 4,000 ft-long flexible risers (rather than the current rigid pipe) and should be in place by the middle of July. (With a capacity at that time in the 60,000 to 80,000 bd range). This will give the flexibility of totally sealing the end and directing the flow up the risers. BP has been tasked to put instruments that will measure flow into the new cap. The current intent is to carry this change through in the next 7 – 10 days.

He noted that there is no sign of ongoing erosion, and that the BOP is tilting at an angle of 10 - 12 degrees.

In regard to the fielding of the suction barges he said that the Coast Guard had carried out a safety inspection and found some safety issues with electrical grounding, and the barges were kept in port until those had been fixed. Which they now have been, and the barges are being used.

Two different procedures are also now being described for connecting between the RW and the WW. In one option the RW will intersect the well, and break through the rock wall of the well. Then a path will be milled through the casing to inject mud to fill the well, before pumping in cement, at the bottom of the WW to totally kill production.

If there are problems with the connection, and it is not a good intersection, then perforating charges will be used to penetrate between the two wells and provide the pathways for the mud and then the cement. This process also allows the area around the bottom of the RW to be separated from the main well with a packer, if it is needed, as extra protection.

To complete the updates for the evening: The Solar Car race had a slight change in order as they reached the Topeka checkpoint: (The times taken to get there from Broken Arrow are, in hours and minutes)

1) Michigan 7:25
2) Minnesota 7:50
3) Bochum 8:05
4) Calgary 8:41
5) Missouri S&T 9:21
6) Stanford 9:50
7) Koahsiung 10:31
8) New Paltz 11:44
9) Kentucky 12:30
10) Northwestern 13:22

Iowa and Texas-Austin are still in the race. After getting to Topeka the teams rested, and then tomorrow will leave Topeka and head, via Jefferson City, to Rolla, where they will rest on Wednesday evening.

And for those who wonder about the volcanoes in Iceland, the areas of concern are, at least for the last few days, relatively quiescent.

Deepwater Oil Spill - waiting for the Top Kill

This is the day when the top kill of the leaking BP well in the GOM will likely be attempted. Kent Wells, Senior Executive VP for Exploration and Production, has given a technical brief on what is likely to happen. Having tried a number of other ways of describing the underlying idea, a more mundane example came to mind. If you have roots growing into the drain that runs out of your house, and you turn the tap on in a bathroom, the water will still be able to get down past the roots, and there is no problem. However if you flush a toilet or equivalent higher flow, this can’t easily get past the roots, and thus the water backs up and flows back out into your basement.

Essentially that is what is being tried. The well has a certain ability to get oil through the BOP at a given (though debated) flow rate. If the volume is increased, by pumping mud into the well below the BOP, then the well will “back up” and the oil will flow back down the well. As it does more mud enters the well. This is dense enough that, as the column grows longer it pushes down on the oil, and applies enough pressure, due to this weight, to overcome the pressure in the rock. Without that positive difference , there is nothing to drive the oil out, and thus the well is “killed.”

UPDATE: For those watching the live feed, the whilte fluid coming out of the riser is the dispersant that BP is injecting with the the oil, and this is mixing with the black oil to give the brown color. BP had earlier said that this flow was 10 gpm, and if that is so, then at 9:38 am CDT there is a significantly less flow coming out of the riser). END UPDATE

One thing that should be noted, however, is that most illustrations show a section of the BOP such as the one just below (which I modified from one in the WP) . Life is actually more complex since there are large rams sitting in the side ports that appear as notches on the main flow line. The actual position of the rams and the condition of the pipe that runs through the assembly somewhat in question (through BP used gamma rays to check it out), and this flow channel complexity may play a little part in the response to the Top Kill injection. Hopefully it will tend to act as "roots" and make it more difficult for the flow to reach the riser, and then leak onto the seabed, and more likely for the flow to be directed down the well.

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

In his presentation Kent Wells noted that there is not just flow from the Q4000 available, but that additional vessels, including the HOS Centerline are connected into the Q4000 and available to add additional flows and volumes of mud if needed.

HOS Centerline

This can carry up to 30,000 barrels of mud, and deliver this to the Q4000 at a flow rate of 50 bbl/min. It is supported by a second vessel, the M/V Blue Dolphin, which carries 11,800 bbl of mud, that can deliver it at a rate of 80 bpm, using 9 pumps. If needed this has more than enough capacity and flow for the job required.

It is equipped with eight skid-mounted 3,000 brake horsepower Gorilla
 fracturing units can store 2.75 million lb of proppant. The vessel can provide up to 23,000 hydraulic horsepower and 80 bbl/min blending rates to meet high-rate fracturing and stimulation requirements of ultra-deepwater projects. At more than 300 ft (91 m) in length, the multipurpose vessel includes additional storage for up to 11,800 bbl of fluids or completion brines, 12,600 gal of raw acid and 6,300 gal of solvent. The Blue Dolphin has a maximum on-the-fly acid blending capacity of 50 bbl/min.

“The advanced capabilities of the Blue Dolphin vessel have made it the flagship of BJ Services’ stimulation fleet,” said Ronney Coleman, vice president for North America pressure pumping services, BJ Services. It is the first 20,000-psi pressure-rated stimulation vessel specially designed for Lower Tertiary conditions, which include long, multiple-pay zones and intense pressure and temperature variations.

With such capabilities there is more than enough pressure and volume to overcome what pressures and flow rates are found in the well.

However it should be remembered that the mud has to get to the well through delivery lines from the surface, and the riser and supply lines will themselves exert a resistance to the flow at higher rates. So the amount likely to be used will, at least at the beginning, likely be restricted to the 50 barrels (2,000 gpm) flow which has been reported. (The oil flow at 5,000 barrels a day, is equivalent to 150 gpm. )

At the moment the rig is undergoing final diagnostic tests to ensure that the valves, fittings, hoses pumps etc are all operational and that there are no leaks. (At these pressures – perhaps 10,000 psi or so – the drilling mud can cut into metals, so that a leak can very rapidly grow to unacceptable size).

“What we learn during the diagnostic phase will be absolutely crucial to us,” Wells said. The top kill procedure, which may begin as early as tomorrow, might take as little as 12 hours or as much as a “couple of days” to carry out, Wells said.

The operation may, if seen to be needed, include a variation of the “junk shot” since there are rubber strips on hand, that could be added to the mud flow and which would, if caught in the BOP, restrict further the flow path out of the riser, and make it easier to get the mud down the well. (Like adding additional roots to your drain to make it back up faster).

Over the next few hours, engineers will test the pressure at each opening, aiming to design a pumping procedure that will “outrun” the flow of oil and gas, forcing it back down into the petroleum reservoir.

Should pressure from the well outrun the drilling fluids, engineers may inject heavy fluid mixed with rubber scraps through valves above the mud flow to hold it in the well, Wells said.

Even if the mud starts down the well as planned, there may be complexities in the flow, based on where the oil appears to be coming from.

Doug Suttles commented on Tuesday

Flow from the Macondo well is not travelling up the main well bore, BP operations boss Doug Suttles said Tuesday, a revelation that would support theories that a cement failure played a part in the blowout.

“We actually believe the flow path is between two strings of the casing and not up the main wellbore,” Suttles said.

Suttles said BP could not be certain of the flow path but diagnostic tests on the well seem to indicate the flow is not coming up main bore.

As the complexity of the job becomes evident there are also reports that the Government are stepping back from taking over the problem, should this try fail.

After days of lambasting the company's handling of the spill, the Obama administration appeared to step back from Interior Secretary Ken Salazar's threat on Sunday to "push out" BP if it did not do enough to plug the leak.

The U.S. government needs BP's deepwater technology to try to shut off the oil well, said Carol Browner, President Barack Obama's adviser on energy and climate change.

"Obviously, we need the BP technology, but we are not relying on them ... we have our own minds in there," she told CNN, referring to the team of government scientists working with BP to battle the disaster.

Some longer term punishment is, however, apparently now being considered.

ProPublica is reporting that that the Environmental Protection Agency is considering whether to bar BP from receiving U.S. government contracts, a move it said would cost the company billions of dollars in revenues and could end its drilling in federally controlled oil fields.

But hopefully the leak will be stopped before the President visits on Friday. And then we won’t need to consider those nukes. (after all only 3 out of 4 worked in the Soviet Union, and one site may still be burning, all those years later.)

BP has also released a statement about the incident. As they note:

"I understand people want a simple answer about why this happened and who is to blame. The honest truth is that this is a complex accident, caused by an unprecedented combination of failures," said Chief Executive Tony Hayward. "A number of companies are involved, including BP, and it is simply too early – and not up to us – to say who is at fault."

Among the possible mechanisms, BOP is considering:

1. The cement that seals the reservoir from the well;
2. The casing system, which seals the well bore;
3. The pressure tests to confirm the well is sealed;
4. The execution of procedures to detect and control hydrocarbons in the well, including the use of the BOP;
5. The BOP Emergency Disconnect System, which can be activated by pushing a button at multiple locations on the rig;
6. The automatic closure of the BOP after its connection is lost with the rig; and
7. Features in the BOP to allow Remotely Operated Vehicles (ROV) to close the BOP and thereby seal the well at the seabed after a blow out.

The House Committee has also released a memo about this investigation:

A memo released by Democrats on the House energy committee said that BP has found three “flow indicators” from the well before the explosion, one of which occurred 51 minutes before the blast, a time when more fluid began to flow out of the well than was being pumped in. When the pump was shut down, 41 minutes before the explosion, the well continued to flow instead of stopping, and drill pipe pressure “unexpectedly increased”. Then, just 18 minutes before the explosion, abnormal pressures were observed by the rig crew. Eleven men died as a result of the explosion.

It should be noted, since there were comments on both PBS and ABC News tonight about the change in the oil color coming out of the riser in the last two days, that the clear difference in the photos they showed was the lack of the injected dispersant in the later pictures, and BP have stated that they have cut back on the volume of this, under EPA orders. Since it was mixing with the oil and changing its color, this may be part of the change that folk have been noticing.

And, after some debate today, BP has announced that they will continue the live feed from the seabed during the time that the top kill is initiated.

(And for those interested, yes the downstairs carpet should be dry again by tomorrow night. Now if we could only get rid of the smell.)

Progress on the Gulf oil leak and comments on cementing pipes

BP held a press conference yesterday in which they reported on progress in trying to stop the oil leak in the Gulf of Mexico, following the blow-out and sinking of the Deepwater Horizon. The well was in the final stages of being closed down, after having been completed, so that the initial drilling rig could leave the site. This meant that the pipe that would ultimately carry the oil and gas to the surface, the production casing string, had been put into place. To hold that pipe in place, and to make sure that it is sealed so that no fluid can flow into the gaps between this tube and the rock walls left by the initial drilling of the hole, the casing had been cemented in place. I am going to repeat part of the post where I talked about that, to explain what this involves. I begin as the hole is still being drilled.

As the bit goes deeper we add additional lengths of drilling pipe to form the drill string, and the bit penetrates through rocks that are of different types and some of these will have fluid in them. Water, whether fresh, which might be the supply for a local community, or salt, is quite common. The hole cannot be left open any longer, because the water flowing from the surrounding rock into the well will dilute the mud, so that it no longer works as it was supposed to, plus, we might start losing some of the drilling fluid into the surrounding rock. Plus different layers of non-drinkable water can work back up the well into the drinking water aquifer.


To stop this from happening we have to stop drilling and seal off the rock on the sides of the well from the well itself. This is known as casing the well, and running casing will hopefully (but not always) be only needed once before we get to the bottom of the well.

So we pull all the drill string out of the hole, remove the drill and lower steel pipe into the well to encase the well, from the bottom of the conductor pipe down to where the bit has found (and hopefully drilled through) the rock that is giving us the problem. (Hence the name casing). Having this continuous length of casing in the hole will likely stop, say water, from getting in and diluting the drilling mud, but if this was all that we did, then it would still leave a problem, since the steel pipe does not completely fit up against the rock wall created by the drilling bit. In other words there will be a gap between the casing and the rock wall, that will allow fluids to travel up or down. This gap has to be filled, and the filler is normally a special form of cement.

The way that the cement is placed is simple in principle, but a fair bit more difficult to do properly and effectively. Think of the long thin tube of casing, filled with a cement that acts something like toothpaste. This cement has to be pushed down the tube so that it squeezes out of the bottom and then flows back up between the casing and the rock wall, filling all the gaps as it is pushed back up to the top or surface. (Hence the name surface casing). Particularly when this casing is run, it is important that the gap is fully filled. This is because this is the casing that seals the well from local groundwater, used for domestic and industrial supply. Since the cement will move more easily thorough a larger passage, than a very narrow one, this gap has to be above a certain minimum size. Small centralizers will be attached at points down the steel casing to keep it in the middle of the hole, rather than pressing up against one of the walls (since this might leave an open channel up through the cement). There are also “scratchers” which are put on the casing so that when it is rotated in place it will scratch the walls of the borehole and remove any mud cake that might have formed, so as to give a better bond between the cement and the rock wall.

Cementing plugs

A small plastic plug (the bottom plug) is put into the casing ahead of the cement. This separates it from the mud that is already in the hole. It is fitted with wipers, that clean mud from the walls of the casing, and it is pushed down to the bottom of the casing by the cement that is pumped into the well behind it. There are some pictures of some of the tools and descriptions of the process here, here and here.

Once the bottom plug gets to the end of the casing, there are ports it passes that allow the cement to flow out of the casing and back up the outside. Once the cement has been pumped into the casing a second, top plug, also fitted with wipers, is put into the casing and this is then pushed down by the conventional drilling mud. As it is pumped down it forces the plug down, and the cement out and back up to the surface. Because of possible variations in hole size and other possible problems, perhaps about 50% more cement might be pumped into the well than the calculations might suggest. When the top plug hits the bottom plug, then there is a pressure spike at the pumping station, telling the operator that it is finished. The rig then waits on cement (WOC) until the cement is hardened. The drill pipe can then be put back in the hole and drilling can restart.

Illustration of a cased well

But whoops, the bit won't fit in the hole any longer! For the sake of discussion lets say we ran half-inch thick casing. And that we had an inch of cement behind it all around the casing. Then the hole we have available to get the drill through down to the bottom is now only 6-7/8th inches in diameter. So we now might use a 6-5/8th inch diameter bit to continue drilling (since we don't want it rubbing against the casing wall).

If we run into another layer of problem rock as we drill down to the bottom of the hole, then we are going to have to run another set of casing. This is known as intermediate casing, and the process is the same, and it leaves us with an even smaller hole through which to get a drill bit through.

That describes a little of the process of how a casing is cemented in position. The well that the Deepwater Horizon had drilled had reached the zone where the oil was, and in preparation for leaving the site had, as I mentioned above, run in the production casing. Let me add the post on well completion to explain this a little more.

There are a number of different steps, after the well has reached total depth that have to be gneo through before we can finish what is commonly called, the completion, of the well. At this point in the process the bottom of the well is still an open hole. And one of the first things that we do is to flush out the drilling fluid, and then clean the walls of the well – firstly be washing the remaining mud from the well down in the production zone. That means that the rock wall is exposed, just as it was drilled. There are several issues that can come about as a result of this. The first is that the rock we have drilled into can be fairly weak. This is one of the peculiarities of geology. To a degree the richer in oil the rock is, the weaker the rock will be. (And that also holds true for oil shale - of which more at a later date). Why is that?

Well let's talk a little about the rock structure, particularly in this post the porosity that it has. (I’ll talk about permeability next time). There are, simplistically, two types of rock, that oil is usually found in and for now, to make a simple generalization, I am going to call them sandstone and carbonate (as I said holding shale until a later time). Sandstone rock is made up of relatively large grains that are glued together at the edges with various different types of natural cement. The grains do not fit that well together (think apples filling up a room, and connected where they touch). We call the gaps between the grains, the pore space of the rock, and it is these gaps that the oil fills up to form the reservoir. And so we can calculate the "free volume", as it were, of the rock as the (relative amount of free space in the rock, you can get this by subtracting the weight of the rock from the weight of the same sized piece cut from solid quartz and it will tell you how much empty space there is in the rock, and thus, how much oil there could be in that volume.

Section of sand with oil in the pores –this is actually an oil sand, so the grains aren’t that well cemented together. (Syncrude)

So say we had a core that weighed 144 lb/cu ft and the weight of solid quartz (flint) is 220 lb/cu ft. Then only 65% of the rock (144/220) is solid rock and the remainder is what is known as pore space. Now these holes can be connected or totally separated, with each pore surrounded by a solid piece of rock. Normally the percentage given is reversed, i.e porosity = proportion of void space to total volume, or in this case 35% of the total volume is not rock. (Another picture showing porosity of a sandstone can be found here. Now in the reservoir rock this space is going to be filled with a fluid, either gas, oil or water. For now let us assume that it is filled with oil.

What I have described so far is known as primary porosity,i.e. that which is created by this initial structure of the rock. With carbonates more than sandstone there is a secondary porosity, and this is the porosity induced by rock movement and the dissolving of channels and holes in the rock by the movement of fluid over the rock through the millennia. Again put simply the oil found in a sandstone will occur between the grains of the rock. In the case of the carbonates, which normally have a much smaller individual particle size, the oil is more often usefully found in the cracks and joints formed were the rock bedding planes were created (and which can be seen in exposed rock in a lot of road cuts along the highway).

The voids and spaces in the rock are also formed from the spaces from what might have been old coral reefs, or where water dissolved holes through the rock. But sometimes the two methods of formation mix, and I would like to quote from Kenneth Deffeyes book "Hubbert's Peak" (my favorite text as an explanation of the geological case).

Fine grained calcium carbonate mud usually gets consolidated into massive limestones, usually with little or no porosity. . . . . . . .About 10 percent of ancient limestones do have porosity. . . . . . .Most massive and nonporous limestones contain textures made by invertebrate animals that ingest sediment and turn out fecal pellets. Usually the pellets get squished into the mud. Rarely do the fecal pellets themselves form a porous sedimentary rock. . . .I twisted Aramco's collective arm for samples from the supergiant Ghawar field. . . . .Examining the reservoir rock of the world's biggest oil field . . .a small part of the reservoir was dolomite, but most of it turned out to be fecal pellet limestone. I had to go home that evening and explain to my family that the reservoir rock in the world's biggest oil field was made of shit.

So there you have it. And the reason for the quote is that the rock at the bottom of our well can be very weak, and may be left in poor shape by the oil drilling bit that just passed it by. Now remember it is this wall around the hole that is the barrier through which all the oil in that rock must pass to get into the well. So before we leave it we have to ensure that it is in as good a condition to allow that flow as possible. (Hence the reason for the removal of the mud and the cleaning of the wall). We also have to isolate the production zone from the rest of the well, and we do this with what is known as a completion or production packer.

Production packer (B.J. Services ) - the three rings swell out and fill the gap (pack it) between the tool and the rock wall of the hole acting as a seal to separate the well below, from the well above – note the internal pipe to allow flow from the underlying part of the well.

One of the problems is that the drill bit may have overly crushed the rock, so that fine carbonate particles are pushed into the cracks and pores of the rock, right around the bore. These can block the passages that will allow the oil to enter the well. And so, in order to get rid of these particles, a strong acid can be poured into the bottom of the well. This acidizing dissolves these fine particles and opens up the cracks leading out into the surrounding rock, so that the oil can flow into the well bore more easily.

Process of isolating and acidizing the formation.

Another problem is that the rock may be very weak, since a lot of its strength comes from the oil that fills the holes within it. This oil only provides strength as long as the rock is totally confined on all sides, but when the pressure is removed on one side (think of popping a champagne cork) then the oil can flow away, taking the support for the surrounding rock with it. If the rock bridges that are left are weak then they can crush. This will cause the crushed rock (sand) to mix with the oil, which will require a de-sanding process at the surface, but it will also close some of the passages through which the oil is flowing to the well. A well operator that speeds the flow of oil out from the rock around the well, can reduce the support that the oil gives to the surrounding rock to the point that it crushes, and permanently reduces oil flow into the well. We can put in a screen that will hold the rock in place, but allow the oil to seep through slots in the screen wall.

Completion screen

Or, to stop that rock crushing from happening and to reinforce the rock , we can pump a layer of concrete into the bottom of the well, cementing a steel liner into the rock, just as we cased the well higher up the well. The steel liner, or production casing, has, however, one problem. Once it is cemented into place, there is this hollow tube all the way to the surface, but there is no way that the oil can get through the cement and the steel into that passage.

And this is where Her Majesty's Explosive comes in. Small, specially designed, explosive charges, known as shaped charges are now put together into specifically designed charge packages, and lowered down into the well into the completion zone.

Arrangement of shaped charges (the yellow cylinders) – when the explosive goes off the cones collapse and small liquid metal jets shoot out of the open end, through the casing, concrete and into the rock, creating a channel. (Core Labs)

Here they are detonated, sending small jets of metal against the wall of the casing and perforating the steel and concrete into the surrounding rock. There is an animation that shows the jet being produced (see also information here) .

Representation of shaped charges firing and penetrating the casing, cement and wall (OSHA

At the time that the explosion occurred on the oil rig, it appears that they had cemented the production casing in place, and were cleaning the mud from the well, prior to putting a temporary cement cap at the top of the well. This would allow them to leave the site (abandon the well), with the well ready to be connected to the pipes that would more permanently carry the oil and gas from the well.

Thus this rig would not carry out the perforation of the well that I have just described, and the production casing should have been surrounded by a cement jacket, that would help seal, temporarily, the bottom of the well. It is the condition of this cement that is, I gather, why Haliburton, who were responsible for that part of the operation, are now in the picture.

The latest report from Upstream, suggests that there have been a number of attempts to get the current BOPs on the well to work, and that they may be providing some restriction to the flow, or this may be coming from the kinks in the riser above the BOP. However they have cut off the riser to give a better target, and they will do this again before lowering a new BOP arrangement that will “stab” onto the initial structure, and allow them to possibly seal the well with that (depending on how good a seal they can achieve with the stabbing operation – these are normally fairly tight).

They will still have to drill the relief wells, and are apparently already drilling the first well, while a second rig is completing another well in the Gulf, and then will come over and provide a back-up to the first in drilling a second relief well.

Unfortunately I am carrying a new laptop, and I forgot to bring the passwords that allow me to reactivate Strata, which is the modelling program I use, and so won't be able to put in new illustrations until later in the week, Sorry!

Casing a well

There has been some concern (that among other things has led to the actions in the House to bring hydrofracing fluid under the Safe Drinking Water Act) about the use of different fluids in oil and gas wells and the risk that they can get into and contaminate surface ground waters that may be used as drinking water. So I thought that I would write a little about well casing today.

Not that well casing is the only thing in the local environment that has to be protected or designed for. Because the odds are that where you want to drill does not sit right next to a highway. That means that you are going to have to install some sort of a road to get to where you want to put the drill. That may sound fairly straightforward in somewhere like Texas, (though it got some folks upset in Wyoming), but it becomes a lot more complicated if your oil patch is in the middle of the North Slope of Alaska, or the Empty Quarter in Saudi Arabia.

In the North Slope, for example, they make the roads out to the sites out of ice. Because the ice must carry the weight of the units that haul the rig into place, the road has to be of a certain thickness, and it has to be at a certain level of coldness to give it strength, (which means winter which is also dark). This means that they can only move rigs at certain times of the year and that restricts the rate at which they can develop new fields and wells. As a result the season is only about four months long, I believe (though have not been up there at that time of year to check).

Having got to the site then it has to be prepared, among other things we need to have a way of getting the cuttings that come out of the hole separated from the drilling mud, and then having a place to put both them, and to store the mud until it can be drawn back into the pumps and circulated back into the hole. And we need to create an initial hole, or cellar, where we can start the drilling pipe into the ground. I will cover all the different things that go into the surface layout in another post, let’s for now concentrate on that hole, that is going to head down for up to several miles in order to get to the oil or gas.

This initial part of the well has to be fairly large, for reasons explained below. Let us begin the well with a fairly large sized drill bit, say 9-7/8 inches in diameter. So we thread this into the drill collar, lower it to the rock surface and start to rotate the string. As the bit advances we can monitor the rock that it drilling through by looking at the cuttings that come out of the hole. We have some idea of what rocks are down there from the surveys that convinced us to drill here in the first place, but it helps to have this confirmed. Plus we need to know if there are any unpleasant surprises down at the sharp end. As the hole gets deeper the time for these cuttings to reach the surface, and be cleaned and examined, the lag for return, gets longer, and so it gets a bit trickier to know what is happening at the bottom of the well.

This can lead to short-term problems. Bear in mind that the hole is being drilled as an open hole. In other words, once the drill goes beyond the conductor pipe, it is drilling in rock, with only the rock walls on either side of the well holding it open. This can be a problem in drilling through weak or jointed rock, since bits can fall into the hole behind the bit, and if enough of those fall they can jam the bit in place (since they fall on the bit above the cutting surfaces).

As the bit goes deeper we add additional lengths of drilling pipe to form the drill string, and the bit penetrates through rocks that are of different types and some of these will have fluid in them. Water, whether fresh, which might be the supply for a local community, or salt, is quite common. The hole cannot be left open any longer, because the water flowing from the surrounding rock into the well will dilute the mud, so that it no longer works as it was supposed to, plus, we might start losing some of the drilling fluid into the surrounding rock. Plus different layers of non-drinkable water can work back up the well into the drinking water aquifer.

To stop this from happening we have to stop drilling and seal off the rock on the sides of the well from the well itself. This is known as casing the well, and running casing will hopefully (but not always) be only needed once before we get to the bottom of the well.

So we pull all the drill string out of the hole, remove the drill and lower steel pipe into the well to encase the well, from the bottom of the conductor pipe down to where the bit has found (and hopefully drilled through) the rock that is giving us the problem. (Hence the name casing). Having this continuous length of casing in the hole will likely stop, say water, from getting in and diluting the drilling mud, but if this was all that we did, then it would still leave a problem, since the steel pipe does not completely fit up against the rock wall created by the drilling bit. In other words there will be a gap between the casing and the rock wall, that will allow fluids to travel up or down. This gap has to be filled, and the filler is normally a special form of cement.

The way that the cement is placed is simple in principle, but a fair bit more difficult to do properly and effectively. Think of the long thin tube of casing, filled with a cement that acts something like toothpaste. This cement has to be pushed down the tube so that it squeezes out of the bottom and then flows back up between the casing and the rock wall, filling all the gaps as it is pushed back up to the top or surface. (Hence the name surface casing). Particularly when this casing is run, it is important that the gap is fully filled. This is because this is the casing that seals the well from local groundwater, used for domestic and industrial supply. Since the cement will move more easily thorough a larger passage, than a very narrow one, this gap has to be above a certain minimum size. Small centralizers will be attached at points down the steel casing to keep it in the middle of the hole, rather than pressing up against one of the walls (since this might leave an open channel up through the cement). There are also “scratchers” which are put on the casing so that when it is rotated in place it will scratch the walls of the borehole and remove any mud cake that might have formed, so as to give a better bond between the cement and the rock wall.

Cementing plugs

A small plastic plug (the bottom plug) is put into the casing ahead of the cement. This separates it from the mud that is already in the hole. It is fitted with wipers, that clean mud from the walls of the casing, and it is pushed down to the bottom of the casing by the cement that is pumped into the well behind it. There are some pictures of some of the tools and descriptions of the process here, here and here.

Once the bottom plug gets to the end of the casing, there are ports it passes that allow the cement to flow out of the casing and back up the outside. Once the cement has been pumped into the casing a second, top plug, also fitted with wipers, is put into the casing and this is then pushed down by the conventional drilling mud. As it is pumped down it forces the plug down, and the cement out and back up to the surface. Because of possible variations in hole size and other possible problems, perhaps about 50% more cement might be pumped into the well than the calculations might suggest. When the top plug hits the bottom plug, then there is a pressure spike at the pumping station, telling the operator that it is finished. The rig then waits on cement (WOC) until the cement is hardened. The drill pipe can then be put back in the hole and drilling can restart.

Illustration of a cased well

But whoops, the bit won't fit in the hole any longer! For the sake of discussion lets say we ran half-inch thick casing. And that we had an inch of cement behind it all around the casing. Then the hole we have available to get the drill through down to the bottom is now only 6-7/8th inches in diameter. So we now might use a 6-5/8th inch diameter bit to continue drilling (since we don't want it rubbing against the casing wall).

If we run into another layer of problem rock as we drill down to the bottom of the hole, then we are going to have to run another set of casing. This is known as intermediate casing, and the process is the same, and it leaves us with an even smaller hole through which to get a drill bit through.

So that, when you get toward the bottom of the well you may end up drilling with a bit that is only 3-3/4 inches in diameter. These drill with a smaller thrust than the larger bits, and so, although you may have a very powerful drilling platform, with thousands of horsepower available, you may end up, as you approach the pay zone where the oil is, using only a fraction of that power.

We'll discuss what happens when you hit oil next time, but perhaps by now you might begin to understand why, in drilling a well that might cost $1.25 million, the actual drilling part alone may be no more than a third of the cost.

As usual I welcome comments, questions or criticism. But to catch the obvious one - yes, after running casing, the first thing you have to drill through are the two plugs and the remaining cement in the bottom of the well, before you can reach and start drilling through the rock again.

.