Tech Talk - of grouting, ground freezing and answers at Fukushima (and a gentle cough to PBS)

One of the reasons that I started to write blogs was to help folks to understand some of the technical background that fed into corporate decisions. I was watching the PBS Newshour this past week, and they were discussing the change in philosophy at the Fukushima nuclear plant. After trying to seal the flow of groundwater using a grout wall, the new plan is, instead, to spend some $470 million and build an ice wall.

The problem that I had with the broadcast was that the person appearing to explain the change in philosophy seemed to me to be more concerned with spreading fear and confusion, than in explaining the fairly logical engineering decision to change from one technique to another. And so, with some repetition from earlier posts I thought to explain why the change, and why it is logical, and not a highly dramatic concern.

The ground upon which the Fukushima plant sits is permeable, so that groundwater is continually flowing through it from rainfall in the surrounding countryside, which migrates down into the ground, and then flows down to the sea. At the time of the tsunami the basements in the reactor buildings were damaged, to the point that this groundwater can now enter the buildings. Unfortunately the reactors themselves were also damaged, so that water being used to cool the reactors can escape, and flow down into the basements. Here it can mix with the groundwater, contaminating it, and all the downstream regions to the sea.It has been suggested that there is about 100 tons of cooling water, and 300 tons of contaminated ground water currently flowing into the sea every day. It is not clear if this flow is into the immediately adjacent sea, or whether the contamination is getting into layers of bedrock, which don’t come to the seabed until some distance offshore.

The initial plan was just to rely on a chemical grout that would be injected into the ground to seal the passages in the rock/soil around the plant. I described, in an earlier post, how grouting can be used to seal off the water channels within rock, making it impermeable. At the same time, depending on the grout injected, it is also possible to add strength to the rock/soil so that it is better able to withstand loads. (Thus the rock over and around a tunnel might be grouted). To explain a little of that let me quote from the earlier post:

Figure 1. Drilling pattern used to inject grout around a tunnel line.

In a grouting operation, that is the goal. Normally a ring of holes are drilled into the wall of the tunnel so that they fan out around the planned tunnel path, and they are about 40 ft long. At this point the cement is brought to the site, ready to be injected. However, it is not just a case of bringing in say 8 bags of cement from the local hardware store. When dealing with the choice of cement, its physical and chemical contents and the pressure at which it will be pushed into the rock there are a number of factors that have to be established first.

The temperature and water chemistry of the surrounding rock are some of the initial critical factors. Changing either will change how fast the cement sets, or if it will. The object in this case is to get the cement to flow into the cracks around the drilled holes, so that the cement will flow to fill those spaces completely, before it sets. But it has to set in a reasonable time for work to continue on schedule. And since water chemistry in a tunnel, and temperature, change – so the mix has to be altered to accommodate those changes.


Figure 2. Types of grout used to meet different needs.

The next thing that has to be checked depends on the size of the cracks that the cement is being injected into. If the cracks are very thin, and the cement contains particles that are bigger than the crack, then the wall of the opening will act as a filter paper, stopping the cement particles from getting back into the crack and filling it. On the other hand if the particles are too small, then they will not bridge together to block the crack, and stop the fluid flow long enough for the cement to set up. If there are too many large particles then, when they lock together, they leave too large a gap between them, and fluid can still flow, and the rock will remain weak.

Over the years a rough correlation has been developed between how much fluid is flowing though the rock, and the type of rock, and the size of initial particles needed to provide an initial seal of it. But, as with cementing in an oil well, when the first cement injection has been finished, and allowed to set, then the rock is tested to see if the flows have stopped. Very often they have not, though hopefully they have diminished. This is because the first shot into the rock is more aimed at narrowing the flow passages and slowing the flow of fluid through the rock so that when finer particles are used, in secondary grouting, they won’t be carried away into the rock, before they can set up and block the remaining passages.

And so, typically, after the first grouting operation, there will be a second, to further fill the narrower passages in the rock, and those bits not properly sealed by the first injection. The cement grouts also act to give some strength to the rock, since they are filling the spaces within the rock structure with the set-up cement, that has some strength to it.


Figure 3. Rock after grouting (white lines)

However to fill the finer cracks, and to stop the flow cement may be too coarse a material in some of the rocks found. In such a case, then a chemical gel might be injected into the ground to fill those finer cracks. These tend to set up rather more like Jello, and while strong enough to resist water flow, do not usually give any additional strength to the rock.

There is one caution in injecting grouts into the rock that has to be borne in mind (and I know of cases where it wasn’t). Grouting operations force liquid into existing cracks within the rock surface. The liquid hopefully fills those cracks, before it sets, but if it is injected at too high a pressure, then the force on the walls of the crack can cause it/them to grow. At that point the rock will become weaker, instead of stronger, and the section in the tunnel roof/walls that is already open can fall in. Which is not good!

In the main it is not economic to keep injecting more and finer grouts into a rock until the flow is totally stopped. As the flows diminish the costs to stop them rise, and so it is usually the case that the operator accepts a certain small flow rate as the most economic alternative, and makes arrangements to deal with that water as it enters the tunnel. (If not I have seen tunnel floors lifted by the pressure that develops in the water trapped behind them).

Of course, if all else fails, then you can cut a slot into the wall and fill it with cement to completely seal off the excavation – though this is often done with a series of drilled holes, it can also be done with a variety of saw, known as a soil saw.

Figure 4. Grout wall exposed to show the 12-inch thickness and integrity.

In case the company of Fukushima the company chose to use a form of waterglass which forms a gel when exposed to an acid environment. This has the advantage that the fluid is quite mobile pre-gelling and can thus penetrate even the finer crack networks, and then, when it sets, it forms the seal.

Unfortunately there are a couple of problems with the grouting approach, there is no assurance that all the cracks will be intersected, and it is often necessary to re-inject successively finer grout materials into the ground in order to seal off systems of cracks missed in the earlier injections. The other is that the grout does not have a lot of strength, and if it is being injected into ground with a relatively high lateral flow rate, then the grout can be washed away before it can set.

In circumstances such as these, ground freezing has been an alternative that has been used for decades. It was, for example, used in the Dig Dig in Boston, being at the time the largest frozen earth retaining project in history. To describe that process let me quote from another post I wrote on the topic, back in 2010.

So how does it work? There are a number of different ways of going about the process, but I am only going to briefly describe a couple of them. The first is the more conventional approach, using a brine coolant, and the second is more commonly used when, for example, you’re refurbishing a road tunnel, and the roof suddenly collapses all the way to the surface. (The injection of liquid nitrogen).


Figure 5. Collapse of the Blackwall tunnel(Photos courtesy of Mott McDonald)

By completely freezing the gravel and other constituents of the roof and tunnel line, it was possible to restabilize and excavate through the area, putting in new supports at the same time.


Figure 6. RE-excavating the tunnel, showing the columns of frozen ground that stop water flow and form a wall to hold the ground in place.

Ground freezing can effectively form a temporary roof over an excavation, even if very close to the surface. It was used, for example, during the Big Dig, to create a bridge under the railway lines in Boston, while the new tunnel lining was pushed into place beneath it, using hydraulic jacks. It was also used in Vienna, where a subway had to pass relatively closely under existing buildings.

Figure 7. Ice wall as temporary support (image Joe Summers)

The conventional method of freezing involves inserting two sets of concentric pipes into the ground, inside pre-drilled holes. The outer pipe is sealed at the bottom end, so that as the freezing fluid (typically a chilled brine) is pumped down the inner pipe, and then flows back up the outside, it draws heat from the surrounding rock and soil, lowering the temperature until the water freezes. After circulation the brine returns to the refrigeration plant where it is re-cooled and re-circulated.

It is important to know the chemistry of the water in the ground, since with the wrong combination the water may not freeze at the expected temperature. It is also important that the outer pipe be sealed since if there is any leakage, then the brine may spill into the surrounding rock. At that point it can’t be frozen with the system, any longer, and an alternative method has to be used.

It is generally smart also, particularly when digging near the surface, to make sure that there aren’t any pipes (such as water and sewer) that can act as heat sources during the process. There can be embarrassing results if one of these (particularly the latter) is undetected, and the surrounding ground collapses as the shaft is then dug.


Figure 8. Hole in an ice wall (arrow) note that it depends on how the ground is being dug out, how fast this is detected.

Brine operations generally take a considerable time, and there is a project schedule so that you can get an idea (depending on the depth and size of the hole) of what might be involved in such an operation. Remember that the ice wall has to be kept cold during the excavation, but that keeping the central material unfrozen makes it easier to dig out. Cement poured against a frozen wall, if properly designed, will set as planned, since the heat of hydration overcomes the surrounding heat loss.


Figure 9. A ground freezing schedule.

This requires, obviously, a lot of preplanning. Where there is an emergency this is not possible, and thus the use of faster freezing methods, such as the injection of liquid carbon dioxide, or nitrogen, into the ground, in order to freeze and stabilize it more rapidly.

There are two ways of making the injection. There is the dual-pipe approach where the nitrogen is in a closed circuit, and then there is the simpler process where a lance is, simplistically, pushed into the ground and the resulting gas percolates upward from the end. That is a little less precise, given that the gas moves through the ground following the path of least resistance, but it does have the advantage of being quick, and generally effective in stopping an imminent disaster. Relative to the months of a brine installation the work takes a week or so (depending on size).

Copper freeze pipes with a standard diameter of 2” (54 mm) are installed, at an average distance of 2” (54 mm) On the inside, downpipes with diameters of ½” (10–12) mm are installed.

LIN is fed into the pipes through insulated supply lines. The LIN vaporizes, with 1 kg of LIN extracting about 200 kJ of energy from the surrounding soil, cooling and freezing it. The vaporized cold nitrogen (i.e., exhaust gas) extracts another 100 kJ from the ground. After about one week, this process forms a frozen wall with a diameter of about 1 m. This so-called “establishing phase” lasts four to seven days, and about 300 - 500 gal (1,500–2,500 l) of LIN is used to freeze 1 cubic yard (0.75 m³) of soil.

Notice from the photographs how the equipment can be fielded very quickly to provide emergence stability to the structure, and then other treatments can be used once the flow has stopped, and the structure is stable. One could, for example stop the flow using ground freezing, and then – using the Brown and Root Soil Saw (and a head design that vestigial traces of modesty suggests I don’t discuss) – a channel can be cut down through the permeable ground and filled (as cut) with bentonite, as shown in the figure above.

Prophets of Doom??

Well, knowing one of the participants, and having bought lunch for and accepted drinks from another, I watched “Prophets of Doom”, on the History Channel on Wednesday night. The publicity for the show described it thus:

Today's world has troubles unique to its time in history, from the global financial crisis to technological meltdowns to full scale, computerized global war. Observing the convergence of such events, contemporary prophets have begun to emerge from obscurity to suggest that these conditions might be signs of the demise of the modern world.

Given the critical problems that are facing the world over the next decades I must confess to considerable disappointment with the resulting program. There were a number of interesting gimmicks, each prophet (there were six) discussed his topic on a different method of transport, including a taxi, a ferry, an airplane and a subway car. But sadly, apart from an allocation of a graph of two per participant the very real issues that some of us are concerned about (in my case population, water and fuel) got relatively little detailed explanation. And one of the likely answers, the development of appropriate and more advanced technologies was, instead turned into one of the threats.

The first half of the two-hour show dealt with such problems as over-population, the instability of the current financial system, and the shortage of water. It went on to the shortage of oil, (which was covered by James Howard Kunstler who did not care for the change in title from the original “The Futurists.” That was followed by the risk from robots becoming more intelligent than mankind, to the point that they treat mankind as a pest (where is Asimov when we need him?) and exterminate him/her. And finally it covered the risk from terrorists getting hold of nuclear devices.

Once the basic premise for the different ways we can follow the Roman Empire into extinction had been outlined, and foregoing that, at least according to Gibbons, that took a considerable number of decades, whereas we are now looking at the future over the next four at best, the prophets sat in a circle in an apparently abandoned warehouse to discuss their different viewpoints. (This was one of a number of formatting ideas that didn’t really work very well).

First they appeared to superficially debate which was the most pressing problem and how to deal with it. (And having been both before and behind a camera at different points in my career, to the point that I have spent several hours of shooting to produce about a minute of video, I fully recognize that this apparent superficiality is not the fault of the participants, but likely of the editor) Their conclusion was that the first severe problem that will face the United States (since it is the collapse of the American Empire/Life Style that they were addressing) was water shortage and contamination – for which it was felt that there was no practical solution, because of the local nature of the problem. But there was a minority rebuttal which held that it would be more likely that it would be the collapse of the financial system that is the most imminent.

However, Michael Ruppert, who had led off the program and seemed to have some sort of role as a discussion leader, suggested that the economic collapse is likely to be exacerbated by the coming shortages of water and fuel. He then led the group toward an apparent consensus that we must move toward local food production and a distributed society, rather than the highly integrated network that sustains us today. (Which is, interestingly the diametrically opposed view to the book “Power Hungry” by Robert Bryce that I happened to be reading during the commercials. He points out that the network is too large and well established to be changed significantly in a short amount of real time).

And so the question came as to what the prophets felt that can we do to change the situation? Suggestions ranged from getting some law and regulation into the financial community, to the need to rebuild local economies, to rebuilding the national railroad system. People must accept that they will have to do increasingly with less every year, instead of more, and the country must learn to “Buy American.” We should look into disjointing society to the point that we create local currencies as society moves toward collapse, for we have very little time remaining.

And then they turned to the final question, which was to decide if anyone would listen to them, or were they Cassandras likely to be ignored? The answers were really more like sound bites – “the problems are there and the time to address them is short” – “We need a time out from technology” – “we are going to have to live the way that we should have been living until now” – “If we could learn to work together, but as long as it is thus against them . . . .” - “we are the one species in the planet that would run into a fire to rescue a stranger” - "We will end up taking care of each other". (One thinks of what actually happened during the Depression as a rebuttal to some of these).

And they closed with the conclusion that water shortage and pollution and financial collapse are the greatest threat to the country in the short term. (And, for the record, I don't agree with that either).

I have bought a fair number of DVDs of shows that appeared on the History Channel, and have a number of other DVDs dealing with various potential futures and the problems that we are facing. I don’t think that I will be getting a DVD of this show to put among them, and actually, I think the change in title was justified.

Oh, and as a post script Eyafyjallajokull is a little more active today - Katla erupting is potentially a much greater threat within the next couple of years than any of the topics above, yet notice how little attention or care it is getting in the media anywhere.

The technology of grouting

For the last two technical talks I have been explaining how, by bolting rock layers around an opening, spraying concrete on the walls of the opening or a combination of both, one can stabilize openings underground. Sometimes, however, the rock itself is relatively weak. (This is a common problem when driving subway systems under major cities, as an example). In these cases the rock won’t have enough strength to hold the walls, until a stronger tunnel lining system is installed. Often that is pre-cast concrete liner segments, but the walls have to be kept open until they can be installed.

Another problem, which is common in almost every underground excavation, is that there is water moving through some of the rocks and, if not dealt with it can fill your excavation very quickly, even if the flow rates don’t initially sound that high. There are two fundamental ways of both increasing rock strength and stopping fluid flow through the rock. The first is to inject some form of grout into the rock, under enough pressure that it will fill all the cracks and then set. The alternative, and becoming more popular method, is to lower the temperature of the rock, so that the water freezes. This increases the rock strength, stops the water flow, and is temporary, rather than a permanent change that can be reversed, after the tunnel is finished. I’ll talk about Ground Freezing in a later post, and in this one I will run through some of the simpler descriptions of Grouting.


When the drillers at the Deepwater Horizon well in the Gulf wanted to stop the flow of oil out of the reservoir into the well, or drilled hole, they pushed a cement down into the well, to fill the gap between the internal casing they were leaving in the well, and the surrounding rock. That initial injection of cement into the well did not work well, and the oil was able to penetrate through cracks, weakness layers or perhaps zones where the cement had not properly set. When the well was finally plugged towards the end of the operation, cement was pumped down the well at higher pressure so that it not only filled any gaps that the oil and gas had been flowing though in the original cement plug, but also moved back into the rock, filling the flow channels that had developed to carry oil and gas from further back in the rock, into the well.

Drilling pattern to inject grout around a tunnel line.

In a grouting operation, that is the goal. Normally a ring of holes are drilled into the wall of the tunnel so that they fan out around the planned tunnel path, and they are about 40 ft long. At this point the cement is brought to the site, ready to be injected. However, it is not just a case of bringing in say 8 bags of cement from the local hardware store. When dealing with the choice of cement, its physical and chemical contents and the pressure at which it will be pushed into the rock there are a number of factors that have to be established first.

The temperature and water chemistry of the surrounding rock are some of the initial critical factors. Changing either will change how fast the cement sets, or if it will. The object in this case is to get the cement to flow into the cracks around the drilled holes, so that the cement will flow to fill those spaces completely, before it sets. But it has to set in a reasonable time for work to continue on schedule. And since water chemistry in a tunnel, and temperature, change – so the mix has to be altered to accommodate those changes.



The next thing that has to be checked depends on the size of the cracks that the cement is being injected into. If the cracks are very thin, and the cement contains particles that are bigger than the crack, then the wall of the opening will act as a filter paper, stopping the cement particles from getting back into the crack and filling it. On the other hand if the particles are too small, then they will not bridge together to block the crack, and stop the fluid flow long enough for the cement to set up. If there are too many large particles then, when they lock together, they leave too large a gap between them, and fluid can still flow, and the rock will remain weak.

Over the years a rough correlation has been developed between how much fluid is flowing though the rock, and the type of rock, and the size of initial particles needed to provide an initial seal of it. But, as with cementing in an oil well, when the first cement injection has been finished, and allowed to set, then the rock is tested to see if the flows have stopped. Very often they have not, though hopefully they have diminished. This is because the first shot into the rock is more aimed at narrowing the flow passages and slowing the flow of fluid through the rock so that when finer particles are used, in secondary grouting, they won’t be carried away into the rock, before they can set up and block the remaining passages.

And so, typically, after the first grouting operation, there will be a second, to further fill the narrower passages in the rock, and those bits not properly sealed by the first injection. The cement grouts also act to give some strength to the rock, since they are filling the spaces within the rock structure with the set-up cement, that has some strength to it.

Rock after grouting (white lines)

However to fill the finer cracks, and to stop the flow cement may be too coarse a material in some of the rocks found. In such a case, then a chemical gel might be injected into the ground to fill those finer cracks. These tend to set up rather more like Jello, and while strong enough to resist water flow, do not usually give any additional strength to the rock.

There is one caution in injecting grouts into the rock that has to be borne in mind (and I know of cases where it wasn’t). Grouting operations force liquid into existing cracks within the rock surface. The liquid hopefully fills those cracks, before it sets, but if it is injected at too high a pressure, then the force on the walls of the crack can cause it/them to grow. At that point the rock will become weaker, instead of stronger, and the section in the tunnel roof/walls that is already open can fall in. Which is not good!

In the main it is not economic to keep injecting more and finer grouts into a rock until the flow is totally stopped. As the flows diminish the costs to stop them rise, and so it is usually the case that the operator accepts a certain small flow rate as the most economic alternative, and makes arrangements to deal with that water as it enters the tunnel. (If not I have seen tunnel floors lifted by the pressure that develops in the water trapped behind them).

Of course, if all else fails, then you can cut a slot into the wall and fill it with cement to completely seal off the excavation – though this is often done with a series of drilled holes, it can also be done with a variety of rock saw.

Grout wall exposed to show the 12-inch thickness and integrity.

Deepwater Oil Spill - the relief well restarts, and miners watch TV

Admiral Allen issued a statement today, in regard to the situation at the Deepwater Horizon well:

After extensive consultation between BP engineers and the federal science team, as well as reviewing data collected from measurements I authorized Friday, the Development Driller III today began the final steps towards the completion of the relief well that will intercept the Macondo 252 well and perform the bottom kill procedure.

This accelerated progress was possible after several discussions between BP and the federal scientists and engineers, leading to the installation of a lock-down device over the weekend, which resulted in the necessary conditions to commence the finalization of the relief well. I will continue to provide updates on the progress of the relief well, the final step that will ensure the well is fully and finally killed, as necessary.

Following this BP announced that relief well operations re-started.

BP re-started relief well drilling operations from the Development Driller III (DD3) today at 1:40 p.m. CDT following the successful installation of a lock down sleeve, a mechanical device that secures the MC252 well's casing hangar.

The lock-down sleeve was installed on Saturday, and successfully tested – though I am not quite sure what that would entail, since it is a bit like putting a locking nut above the retaining nut on a bolt, it stops the retaining nut from moving – but how to test?

The DDII is continuing to run diagnostic tests on the original well, as the relief well slowly drills forward, over the last 50 ft to make the intersection. Remember that with the very small target (the unlined section of the borehole annulus) the intent is to drill a short distance, re-survey the location and that of the well (determined from an electro-magnetic field generated in the production casing) to make sure that the well is moving on target, and then drill a little bit more. It will still take some time, perhaps four days, to get to the well, and then the circulation of fluid to determine what is really in the annulus will be one of the last stages, before the well is plugged with cement at the bottom, to fill the annulus above the current levels and provide no potential flow path from the reservoir.

Once that is completed, then the relief well can be also plugged both at the bottom and then at the top, and both wells can start the process of inserting plugs close to the seabed and then removing the wellheads and going through the process of abandoning the wells.

In regard to the miners trapped in Chile, it has now been reported that it may take as long as 3 hours for each miner to be lifted to the surface, which may make the process last some four days.

The miners have been sent a small tv set, through one of the three 6-inch diameter supply holes already in place, and are now being sent electricity as well as cooler fresh air, to help with the environmental conditions, which are otherwise very hot (88 degF) and humid (85%). And by using U/V lights they are apparently also setting up a day/night cycle for them.

Sadly the mine is reported to be broke.

sanctions may be hard to enforce. The mining company has filed papers to declare bankruptcy. The company also says it can't pay anything for the rescue effort, not even the wages owed to its miners.

I do remain concerned about water flows underground over that length of time, unless they have some alternate way of getting the water out of the mine, since I presume that the rock falls stopped any pumping operations that were ongoing. For example:

Morning showers require the men to climb aboard a bulldozer-type mining vehicle that rumbles 300 metres up the tunnel to a natural waterfall where they shower, shampoo and clean off the ubiquitous rust-coloured mud.

There is also another two sets of problems, evident from what is generally considered good practice. The first comes from the rescue effort itself:

Another group of men reinforce the mine walls and divert streams of water seeping into their refuge. Several of the drilling and communications tubes connecting the men to the surface use water as lubricant, meaning a constant stream of muddy gunk trickles into their world.

And then there are the other water needs, that are also provided.

After the (Chilean:Ukraine football) match was over, the men prepared to sleep. They walked down the ramp to the bathroom, an area kept constantly clean by a stream of fresh water that washes away the urine and faeces.

All that water has to be going somewhere.

They do monitor the gas content of the air around the refuge, and are preparing for when the big drill first breaks through to the mine with the pilot drill. That is now expected to happen in about 3 weeks, and then the miners will have to start removing the debris from the larger reaming bit as it moves down, enlarging the hole to the required size for the rescue cage. It could be as much as a thousand pounds of rock an hour, though the rates will hopefully and likely be kept slow enough that there is no risk of the pilot hole being jammed with too large pieces of rock.

Supporting underground tunnels

With thoughts of the miners in Chile, and suggestions that a rescue tunnel will also be started to try and drive down through the broken rock, I thought I would write a little today about holding rock together. For those of a slightly cynical nature, I recently used the example of the Forth Road Bridge, in comparison with one of the bridges that the Romans built in France. The latter is over 2,000 years old and still standing, the former was built in 1964 and is now being scheduled for replacement, since the cables in the old one are corroding and snapping. The point of the comparison being that if you know what you are doing with rock, you can build a structure that can carry load for a long time. (And if you think about it, the rock that the Romans built with is bits of broken rock, rather than the solid structure that a tunnel starts out drilling through).

The Roman Bridge at Chaves (James Martin )

When man first started digging into rock, whether to get flints, create shelter or extract some coal that would burn, it was a relatively slow process. The miner relatively slowly dug out the rock, giving the loads around the hole some time to redistribute, and small holes could be made that would be stable for a long time. That is only a generalized statement and not always true, there are several factors that limit its validity. The first is water. Of the underground hazards water is one of the worst. In its most visible form it can fill the hole, and drown all those in it. There have been many disasters where water has invaded a mine, either from the surface, or from nearby underground workings. (For example Quecreek).

But water has a more insidious role underground, travelling into the mine with the air that the miners must breathe. Underground the ground temperature stays quite constant, and for many mines nearer the surface, the temperature can be quite cool (one I was in recently was at 58 F). So in the days of high humidity of the summer, the moist air moves into the mine, meets the cooler rock, and the moisture condenses onto the rock. It soaks into the rock, and usually weakens it – some shales (the more common rock in coal mine roof) will lose 60% of their strength when they get wet. And it is often why there are more accidents from roof falls in the summer – while in the winter it is more the time for gas explosions – another story).

The second problem that affects the rock relates to the number of cracks in it. If you drive along a road and pass through a road cut where you can see the cracks that develop around individual lumps of rock. Some, the bedding planes, are formed when the rock was first laid down as a sediment, some were formed as the rock was twisted and distorted over geologic time, or during the time that it changed from the sediment into the rock structure encountered today. And some cracks are made as the opening in the tunnel is made. We want to break the rock in the tunnel face into small pieces that we can pick up and carry away, and so we place explosive in known patterns of drilled holes in the face that will break the rock into bits, when the explosive is set off. Generally the charged holes are set off in a sequence, so that after breaking out the middle of the face, successive rounds (they are set off with timed detonators) will blast successive layers of rock into the opening until the desired shape has been removed. In the process some cracks from the outer ring of blast holes will extend out beyond the intended wall of the tunnel and into the final wall. (Seems to happen more on Mondays and Fridays for different reasons).

So there are several concerns that face an engineer that is going to try and drill a tunnel through rock, whether it is solid or already broken into boulders and smaller pieces. The first is to get some idea of the general strength of the rock – designs that work in something like a granite won’t work in a very weak shale, for example. Once the rock strength is known, then the amount of cracking, either natural or man induced needs to be found. There is a very simple way of doing this that a group at Urbana/Champaign developed called the Rock Quality Designation (RQD), under Don Deere to simplify how it is measured, you drill a core through the rock layers that you want to drive the tunnel under. You recover the core and measure the core lengths that are more than 4-inches long. That total value, divided as a percentage over the length of core recovered gives you the RQD. Over time (it is now 40-years old) it has been shown to give a very good first estimate as to how badly broken the rock is, and it is used in many design programs to decide how best to hold the roof up.

When working out how to hold the roof of the tunnel up, the engineer knows that he is not trying to hold the weight of all the rock between the tunnel and the surface. The work that most of us used to refer to as the basis for the support of the tunnel was written by Karl Terzaghi . Again, to simplify a relatively complex subject, he came up with a simple method of classifying rocks so that, the designer of the support would know how much rock load from above the tunnel, the supports would have to carry. And very often it was only a small additional amount above the height equaling the width of the tunnel. (The presence and actions of water being the main factor that would make it a lot worse).


Karl was starting the knowledge base that now allows engineers to classify rock and thus design the tunnel supports before the tunnel gets started. It was only a start, however, because back in those days (beginning in 1925) most of the tunnels were supported with large steel arch girders. Because those had to be ordered and delivered before the tunnel was started, getting that size wrong could be very expensive, and there have been many lawsuits as to whose fault that was. (Very awkward, for example, if the tunnel is half-way under a harbor when you discover the steel beams aren’t big enough).

Possible heights of overbreak that have to be supported over the tunnel

Since then a new method of support, which works more on helping the rock to support itself, along the lines of the Roman arch bridges, has been shown to often be more effective. Although it has been generally more effective, and more flexible, it has become more popular, but I will write about it, and the change from steel arches to sprayed on concrete (shotcrete) and rock bolts, next time.

API, EPA and Hydrofracking gas shale

There has been some ongoing discussions around the country about the possibility of drinking water contamination as a result of hydrofracking natural gas wells, most particularly those that would be placed in the Marcellus shale, which, in part, underlies sections of New York state which provides the watershed for New York City. And to put this in context, it should be born in mind that hydraulic fractures are generally relatively short, and occur in the shale at depths of thousands of feet, while ground water is usually obtained from wells that are less than 500 ft deep.

I first mentioned this at the time of the House hearing on the topic and have returned to the topic intermittently over the past few months as the issue had been dragged more and more before the public. I have also covered the basic technology behind hydrofracking natural gas wells, including direction to a video which illustrates how hydrofracking improves production and makes the well productive. And there is a Primer on the subject (that includes the composition of a typical fracking fluid).

Well a couple of weeks ago the EPA announced that they were going to conduct a study of the process. More precisely:

The U.S. Environmental Protection Agency (EPA) announced that it will conduct a comprehensive research study to investigate the potential adverse impact that hydraulic fracturing may have on water quality and public health. Natural gas plays a key role in our nation’s clean energy future and the process known as hydraulic fracturing is one way of accessing that vital resource. There are concerns that hydraulic fracturing may impact ground water and surface water quality in ways that threaten human health and the environment. To address these concerns and strengthen our clean energy future and in response to language inserted into the fiscal year 2010 Appropriations Act, EPA is re-allocating $1.9 million for this comprehensive, peer-reviewed study for FY10 and requesting funding for FY11 in the president’s budget proposal.

One wonders, given the input from the state agencies at the Congressional Hearing, who said, since they have been doing most of the monitoring for the past several decades, that there wasn’t a problem, who will provide the research study, and who will be doing the peer-review? But perhaps I am being a little cynical so early in the process.

With all that as background, last Thursday the American Petroleum Institute (API) held a phone conference for a number of those of us who blog on energy, so that we could ask questions on hydrofracking from a group of industrial experts.

API had previously noted that EPA had already carried out such a study in 2004, although that one dealt more specifically with hydrofracking coal seams to extract coal bed methane. That study had concluded:

Based on the information collected and reviewed, EPA has concluded that the injection of hydraulic fracturing fluids into CBM wells poses little or no threat to USDWs and does not justify additional study at this time.

It should be noted that that coal seams are typically quite significantly shallower than a typical gas shale, generally by several thousand feet.

And since I haven’t defined an underground source of drinking water (USDW), let me do that by quoting that earlier EPA document:

A USDW is defined as an aquifer or a portion of an aquifer that:
A.1 Supplies any public water system; or
2. Contains sufficient quantity of groundwater to supply a public water system; and
i. currently supplies drinking water for human consumption; or
ii. contains fewer than 10,000 milligrams per liter (mg/L) total dissolved solids (TDS); and
A. 1. B. Is not an exempted aquifer

NOTE: Although aquifers with greater than 500 mg/L TDS are rarely used for drinking water supplies without treatment, the Agency believes that protecting waters with less than 10,000 mg/L TDS will ensure an adequate supply for present and future generations

API noted, both then and at the conference call, that hydrofracking is an integral part of much of the oil and gas industry, and has been for over sixty years, during which time there have been over a million wells that have used the technology.

The transcript of our conversation is now available on the web and I am only going to summarize portions of it, since the full transcript runs to 21 pages. I’ll also add the odd comment of my own.

The experts fielded by API to talk with us were:
Sara Banaszak, Senior Economist
John Felmy, Chief Economist
Stephanie Meadows, Senior Policy Advisor
Erik Milito, the Group Driector for Upstream/Industry Operations
Richard Ranger, Senior Policy Advisor
Andy Radford, Senior Policy Advisor

Jane Van Ryan of API acted as Moderator, and had invited me to join the others in the conference.

Gail Tverberg (representing TOD) opened the discussion by asking about the fate of all the fluids that were used in generating the hydrofrack, which can run from hundreds of thousands, to millions of gallons. Stephanie Meadows answered that most of the water comes back out of the ground, though it may take weeks or months to recover most of the fluid, (Richard Ranger noted that the fractures that are generated don’t typically extend that far – the distance is usually measured in feet,) and recovery rates can range from 30 – 70% of the fluid injected. The rest can slowly trickle out during production, but can remain, within the producing formation until then.

(This was something that I had wanted clarifying and in the three questions I had submitted before the conference, I asked about the risk of various shales being water sensitive. The concern being that if the water in the fracking fluid is in contact with the shale, for a significant time, it can wet and weaken certain shale to the point that it can soften and deform – which would prematurely close the fractures and lower the volume produced, both as a rate and total amount. You can 
inhibit the wetting by adding different polymers (as they do when 
dealing with, for example, the Gumbo shale in Texas when they drill
 through it using a water-based mud), and if I remember the ones that they often use are also used to
 keep the froth in beer from collapsing.)

Jazz Shaw (The Moderate Voice) mentioned that there continue to be repeated claims (he cited one from Maurice Hinchey a Congressman from New York, who claimed on a recent CNN program that there were multiple cases of groundwater from hydraulic fracturing, and refused to acknowledge that the host pointed out that the claim could not be substantiated – which followed a similar comment that I had noted that arose from the state agencies that currently monitor hydrofracking operations when they testified before Congress). It was also pointed out that the Ground Water Protection Council had also been unable to find any instances of this occurring.

Erik Molito pointed out that over the million wells that had been hydrofracked, while there had been some surface spills (which were not defended) there was not one instance where a hydrofrac in the formation had led to groundwater contamination, over the 60-years that the practice has been in existence. At present 90% of current natural gas wells that are drilled are hydrofracked. It is not only practiced in shale, one of my questions related to use in Colorado, where I was told that

Virtually every well 
drilled into the tight Cobell sandstone of the Wattenberg field in the
 Weld County area, or into the Williams Fork sands of the Mesa Verde group 
in the Piceance Basin on the Western Slope involves hydraulic fracturing 
for well completion. HF is also used in a substantial amount of the coal
bed methane production in the San Juan Basin in the southwest part of 
the state.

In later discussion it was also pointed out that Colorado requires that the ingredients in the fracking fluid formation be listed, but not the specific amounts or recipes. (In much the same way that Coke lists the ingredients but not the formula, so that no-one can gain the commercial benefit of copying their recipe). Other states also follow that requirement.

Richard Ranger pointed out that as a protective measure increasingly drillers are working with state agencies to take water samples both before and after drilling and fracking the wells to substantiate the claims of no impact. He also noted that the state agencies work closely together through groups such as the Interstate Oil and Gas Compact Commission to ensure that the wells that are drilled are properly monitored, and that nothing is done without following a detailed permitting process. And knowledge gained, for example in Texas, is quickly transferred to Pennsylvania.

When it came to the impact of any proposed regulation, asked by Rich Trzupek of Big Journalism, the Economists on the panel noted that up to 60% of current natural gas production comes from hydrofracked wells, and that slowing or stopping that amount of natural gas would obviously have significant impact. And it was noted that natural gas increasingly provides a fall-back reserve of power should the wind not blow, or the sun not shine, to support renewable energy supplies. (And in a subsequent follow-up API has pointed to the jobs that could be gained by growing the natural gas industry to get natural gas from the Marcellus shale in Pennsylvania .

Tim Hurst of Ecopolitology raised the question of the EPA project, and he was assured that, at the appropriate time API would have a response.

Gail asked about the source of the water, and in response Richard Ranger noted that while a typical 7 – 10,000 ft well might use 3 million gallons of water, this is the amount used by a typical golf course in a week, a 5-acre cornfield in a season, or a municipality of 8 million people(e.g. New York City) in 4 minutes. The amount of water required to generate a million Btu’s from natural gas is about 10% of that required to produce the same amount from coal, and about 0.1% of that required to get the same amount of energy from corn-based ethanol.

Geoff Styles of Energy Outlook asked about the use of diesel, but it was pointed out that while this is sometimes used as the basis for drilling fluids and muds, where water based muds might create problems in reacting with the rock, diesel is not used in the hydrofracking process.

One of the possible risks of hydrofracking was posited as being that the fractures would intersect other wells drilled in the same location, but Andy Radford pointed out that the degree of control ensures that fractures are grown under tight enough control, and limited ranges, to ensure that this does not happen, and that when wells are spent, that the sealing of the well is done sufficiently well to ensure that there is no risk of subsequent leakage,

The conference went on for over an hour, so I would recommend that those interested in more detail review the entire transcript. It was, as I have tried to illustrate, quite informative.

Coal, water and an Afghan problem of reality

It has been the first full day of the conference on innovations in coal production, and by the evening we delegates were ready for our evening meal. The papers today included the one from Vietnam that concluded that by 2020 the country would produce around 75 million tons of coal a year, but would still need to import another 120 million tons to meet the needs that are already predictable to meet future power needs.

It was another delegate that pointed out that by far the majority of folk were over 40, and so it was no surprise that in the evening, in a field above the village, we sat in an open wooden pavilion, and after bigos, beer, sausage, and other Polish food, sat around the fire and sang.

Around the fire

The photo does not do the group justice, since with a 3-man folk band playing trumpet, accordion and bass, the density of folk was soon about 3-times that shown, and even those of us with no Polish were singing along, as someone else said, “in French” (la, la la!)

But for a little while I, and the sole Afghan delegate, sat in a relatively quiet corner and chatted over (at least for me) a beer. And I came to an appreciation of one of the problems that I had not thought about for that country, and that I will, as a result share.

We went through the usual talk of Afghanistan being an unconquerable country (vide Alexander the Great, the British and the Russians to name but three). But then we talked about what could, realistically, be done to help the country.

I have just ( in Tuesday’s post) quoted figures on electricity availability in the country – at around 10 – 12% percent. “No”, he said sadly,”it’s about eight.”

One of the reasons that I write the Tech Talks on Sundays is that unless you understand some of the “behind the scenes” ways in which things work, you can’t understand why certain “logical” answers actually won’t.

So it is in Afghanistan. With so little available electric power (and this is not the place to explain why that is a critical rung in the ladder of progress) the thing that would cement the local affection for any “invader” would be the provision of power to the populace.

But there is a rather large snag – the operation of a significant sized power station requires a lot of water. (And the TT on that will explain why). But the one thing that Afghanistan does not have is copious amounts of water. It is not part of the world that sees the seasonal rains of the monsoon. Rather it relies on the melting of the snows that fell in the winter and the storage of water in underground tanks and cisterns. (See, among others, Kipling).

Such provision works well for individual homes, it can – under the right circumstances – store enough water for a 40-acre farm that will keep the family alive (different world - different agriculture) – but it can’t meet the needs of a 100 MW coal-fired power generating plant without a whole lot of changes.

(Oh, and a brief aside to Jerome – wind turbines are, in their place, a great alternative source of needed electricity, but in Afghanistan the winds bring the sands from the surrounding desert and in the abrasion of surfaces under wind, sand and rain attack is where I can raise a knowledgeable question of reality).

The coal in the country is found in the North and swings around the edge of the country on the East.

Coal deposits in Afghanistan (USGS)

Because of the growth of the Himalayan mountains the seams are now left in a steep (about 45 degree) incline that makes it more difficult to extract the coal. The immediately logical method of mining in such conditions is to use hydraulic monitors, as they do in New Zealand, but one gets back to the water availability problem.

Water is much more a right that is owned in Afghanistan than it is, in many other parts of the rest of the world. It is a topic that already is capable of stirring riots and anger – even in the United States, where water provision in California is now becoming a major problem.

But in the drier places of the world, such as Afghanistan (but also neighboring Pakistan) the lack of water comes at the same time as the maturing of a great increase in population ( from 24 milion in 2003 to 35.5 million in Afghanistan in 2015) and some attempt to bring industry to the country – both greatly increase water demand, while supply remains relatively flat.

It is a very difficult problem, there is coal for power, not really enough firewood for the future population demand for fuel, and there is not a lot of alternative choice. But other than burning the coal for domestic heating and cooking, how can they use it? How do they find the way to generate the electrical needs that the country has, and without which the future of the country is going to be as restricted as it might have been in the times of Alexander. The need for water is almost ubiquitous to the provision of so many forms of power, and so how do we circumvent it? Or can we?

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.

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