Changing times and mining shovels

I have been discussing the technologies for oil well drilling and coal mining for quite some time, and am thinking that with that review available and just about complete, it might be time to switch the focus of these Sunday information topics. While I could give a more detailed discussion of the different topics that I have covered in the past, I suspect that this would be of decreasing interest to most and so I thought to change the subject matter. What I am planning on doing is to shift focus, and start to write about the different countries that have oil reserves (or had) and what we know about them. The idea, in much the same way as with the technical talks, will be to provide an informative set of background notes, so that, for example, if the topic of the Yamal gas fields comes up, you would know a little about where they are (a peninsula in Russia), and how much gas (maybe 30 trillion cubic meters) is there, as well as how soon they will be developed (not this year).

That is the plan for the future, but before moving there, I would like to revisit coal mining to wrap up the discussion with a small number of posts about surface mining. The first use of coal came from finding outcrops where the coal could easily be picked out of the seam, or where, in the North of England, the sea would do the mining and wash the coal up on the beach, where it could be collected.

Even today there are still areas around the world where there is coal very close to the surface, which can easily be uncovered and removed. Some years ago a farmer came to my office to discuss what he needed to do to mine a layer of coal he had found in his farm (in central Missouri) just below the surface. All that was needed, he thought, was a blade for his tractor to push the soil away, and then a loader to scoop up the coal and take it to market. I had to explain that those simple times had passed, and that there was a considerable body of regulation that he had to comply with before he could do that. And also he had to restore the land to the way it was, after he was done. The profit he had anticipated, faded as he went through some of the costs that he would have to face.

However, and this was part of my first talk at the ASPO-USA meeting in Washington earlier in the month) the technology for mining that coal on the surface remains at about the level of simplicity that he anticipated. Coal supplies, whether in Africa, Asia, Europe (though to a more limited extent) and America are still available that can be extracted with nothing more than a shovel. Now, having said that, the size of the shovel has undergone a significant change since the time that I manually wielded one, to move 15 yards of coal from the face to the conveyor (as I recounted in the video). And as an aside, the shape of mining shovels differs a bit from those usually seen at the surface.

Mining shovels and a pick (with the Engineer at an early age) at the Beamish Museum in the UK

The heart-shape allowed you to get under the coal and pry in a way that the square and molded shovels more common on the surface did not, though most of them came without the cross piece at the top end. Today’s shovels are electrically powered and have bucket sizes that can pick up between 7 and 36 cubic yards of material in a single scoop. They routinely fill 400-ton haul trucks in two to three scoops in operations at the tar sands, and in mines around the world.

Modern shovel loading a haul truck (P&H )

Shovel schematic to give an idea of size – the bucket can hold 170 tons, some 60 cu yds. of material.

With that relatively large-volume, simple approach it is difficult to envisage something that can be simpler or more economic, in the mining of minerals. And as long as this technology can be applied, the need for more advanced mining means does not exist. (And this was part of the talk that I gave at the ASPO meeting).

Mining shovels such as that shown above, which are generally powered by electricity – you can see the cable if you look closely – are used for the more precise removal of material that is needed when mining the valuable material, whether tar sand, coal or a metal ore. To remove the rock and dirt that lie on top of this valuable material, where there is not quite the same need for precision, it is quite common to use a machine known as a dragline. (There is a video of one working here ) Here the bucket is not rigidly connected to the boom as with the shovel shown above, but is instead connected through ropes. This, historically, made the bucket more difficult to control. However the arrival of the computer to both monitor and control rope position, now makes it much easier to "spot" and unload the bucket than in the past.

Working dimensions for a dragline (P&H )

A bucket might move 150 cu. yds at one time with an operating radius of some 350 ft, digging down to a depth of 180 ft and dropping the spoil in a height of up to 160 ft. That doesn't mean that they don't get stuck, or collapse on occasion.

The size of the shovels thus make it possible to mine very large quantities of material at one time, and make the economics of large-scale mining practical. The critical dimension is typically the relative depth of the soil and rock over the coal seam, in relation to the thickness of the coal. It is known as the stripping ratio, so that a coal seam that is 5 ft thick, for example, at a depth of 100 ft, would have a stripping ratio of 20. Depending on the costs of mining, and the quality of the coal, that may or may not be worth going after at this time.

There are other machines that are used in different parts of the world, the largest being the bucketwheel excavator, which usually only get into the news when they are on the move.



These machines work extremely well in a controlled environment, but are extremely expensive, and when they are down, so is production. (One of the main reasons that they are no longer used in mining tar sand in Canada). Mind it is not wise to get one irritated, since they have been know to eat uppity other equipment.



That aside, the nature of the rock and other material overlying the seam will also influence how that material (which is called overburden) is removed, and I’ll discuss that process in more detail next time.

The Avatar movie and the mining of oil sands

The movie Avatar gets the mining bit wrong. And not by just a little – but then us villains are rarely understood, so what should we expect? OK so what is a popular, nay perhaps even genre changing movie got to do with technical talks about fossil fuel production? Well fairly early in the movie it is made clear that the sole purpose for the plot is to mine “unobtainium” which is a mineral with all sorts of value. Now I’m not going to give away much of what goes on in this movie (and I agree with most of that review by the way) but the fallacy over how they mine the deposits on the planet is one of the lessons learned from the mining of the oil sands in Alberta, which is actually what I want to discuss a little today. In the movie they use a variation on a bucket wheel excavator – which in today’s world looks like this


Bucket wheel excavator on the move

They were, at one time used for mining up at Fort McMurray where the large oil sand deposits are found in Northern Alberta. However the reason that they were discontinued (and which formed part of the plot of the book “Athabasca” by Alistair MacLean) is that they are the single machine whose health totally controls production. When they are working the mine is producing, and when they aren’t it isn’t. (The plot of the movie was to disable the machine and thus stop oil production - possible where there was only one machine.) The problem that really developed was that maintenance and repair of such a behemoth is such that it is more reliable and productive to rely on a multitude of smaller machines, with truck haulage, rather than the single large machine with conveyors. As the mines have learned these lessons they have pensioned off or sold most of those they had. Now, if some of the shovels have maintenance problems, with some dozen or more working at one time then the drop in production is not nearly that significant. You can see one of the problems in this picture of the teeth on the buckets (since this is the one on display I suspect that towards the end replacements weren't as frequent, but you can see how many teeth were missing and these take significant time (and money) to replace).

Note the broken and missing teeth on the front of the buckets (the bright spots are hardened buttons to reduce side wear on the buckets as they cut through the abrasive sand)

I first wrote about the oil sands back in June of 2006 and back then the production was just over a million barrels of crude a day. When Gail Tverberg wrote about her visit up there on The Oil Drum last August (Part 1 and Part 2) she noted that in 2008 production had risen to 1.2 mbd and that with current construction projects this would increase to 1.94 mbd. The current Alberta state web site expects that these projects will raise production to 3 mbd by 2018. (Which is down a bit from earlier projections)

There is some controversy that exists with regard to crude production from these mines, and the area in general. There are basically three different processes that are currently being used for oil extraction, and it is only the first of these – the mining and processing of the sand, that I will discuss today. The use of steam to recover oil from underground wells (Steam Assisted Gravity Drainage – SAGD) and the partial combustion of some of the oil to recover some of the remainder (a process called THAI for Toe to Heel Air Injection) will be written about in subsequent posts.

Part of the reason that the topic is controversial is due to the need for natural gas to create the steam used in the SAGD process, but there are other concerns that have arisen because the sand does contain some natural gas that can be drawn off and sold commercially. Last October the Energy Resources Conservation Board ruled that 158 wells that were producing natural gas from the sand should be shut-in (that means closed) since gas production from them might interfere with the SAGD process. In particular the drop in pressure as the gas is removed may negatively impact subsequent SAGD production. A hearing on this will be held early this year. It is also a target for additional taxes and regulations in order to “green” the industry.

So what is there to green? Let me run through the process. The oil sand lies below a relatively thin cover of vegetation, soil and rock, which is first removed and stockpiled so that it can be replaced, after mining is completed. Once that has been done (using the same large shovels and trucks that are used for mining the sand) then the sand is mined using large shovels that can load a truck with 100 tons of material at a time.

loading the truck, it will take 2 to 4 shovel loads to fill the truck bed, depending on its size.

In the summer, when the temperatures are higher, the sand is easier to move, and thus dozers can be used to push down the material into the arc of the shovel, so that it does not have to reposition itself that often, and production from higher benches can be kept up.

Dozer loading shovel

The trucks are used to carry the material to the initial processing plant. The sand as well as being heavy, is also abrasive, so that there is considerable wear on not only the teeth of the shovel, but also on the tires (my head is about the height of the axle) but also on the beds of the trucks so that these have to be periodically replaced.

Relining the bed of a truck.

The trucks are used to carry the mined material to a central processing plant within the pit, and it is first dumped into a primary breaker.

Tipping into the breaker

The oil sand is relatively soft, but contains layers of rock that have little oil in them, and these are generally harder, so that they survive the crushing - which also means that they are bigger, and can be separated out and removed from the system, before the oil sand passes into a mixing tank, where it is mixed with hot water, agitated, which breaks it down into particles, since the individual sand grains are coated with a thin layer of water, under the intervening oil that ties it all together.

Mixing the sand with water

The resulting slurry is then passed to a pump station, that pushes the slurry through a pipeline, which carries it to the initial separator at the refinery.

Pump station and delivery pipeline

The pipe is about a mile long, and in the time that the sand passes along it the oil and sand are separated. At the beginning of the refinery the slurry is then pumped into a large tank. Simplistically the sand settles to the bottom of the tank, the water lies in the middle (where it can be drawn off for re-use) and the oil floats on the top and can be drawn off to feed into the refinery.

Initial sand:oil separator

The heavy crude is treated in this initial refinery so that the resulting liquid can be sent as a sweet crude down to other refineries further south.

Upgrading refinery

This requires among other things, removing the sulfur from the oil. Sometimes that can be marketed but sometimes it must be stock-piled, and there are thus the start of "sulfur pyramids" being constructed around the refinery.

Start of a sulfur pyramid.

Once the oil sand has been removed down to the underlying bed rock, the sand can be replaced and the land reclaimed. Gail did a tour of some of the sites, and has posted pictures - unfortunately I did not have have that opportunity.

As usual this has been an abbreviated explanation of a process, comments and questions might indicate where I need to explain things in more detail.