While I don't remember exactly I think that the hopper that you see in the middle of the picture was 3 or 4 ft in width.

Sorry I didn't reply sooner, but I spent the day traveling to Houston.

I'm having a problem viewing the video tonight so I'll answer that part of the question tomorrow.

I'm glad you didn't go ahead with your resonance drilling method or RDM, b/c if successful we would all be part of your planetary dissolvement - :-)

That said - thanks again HO for propagating your know-how..

The idea works, it was used by a company called Hydronautics, under a Dr Andrew Conn, to generate a form of cavitation that proved effective in drilling through rock and other materials.

If I remember correctly Michael Crichton used the same sort of idea in a plan to induce earthquakes or some such in one of his novels.

Actually I think it is going to be in the next one. Because holes are of differing sizes we generally use a measure per unit volume of rock removed - with the number from a good tricone being around 120 joules/cubic centimeter (the energy unit, not your good self).

I will have to dig out the specific energy (that's what we call it) of drilling other rocks, but the post does cover different energy levels for different types of rock drilling.

However, as you know, the energy to break the rock is only part of the process. And in drilling the weight across the bit must be carefully controlled to ensure the bit works well. Since the weight comes from the steel in the pipe above the bit most of that weight is actually carried by pulleys at the top of the drilling rig, and only a small amount allowed to fall on the bit to keep it drilling into the rock. However the whole drill string must be turned by the kelly at the top.

So you can see there are a number of posts still to be added to explain all this.

That's something I wonder about as well. In "drill and blast" excavation methods for mining, a small hole is drilled, using an admittedly large amount of energy for the small volume of material removed from the drill hole. But the hole then enables a large volume from the rock face to be blasted out efficiently. So the overall energy efficiency can be pretty high.

If hydrothermal spalling is able to bore small holes at a rapid rate, it could be part of a cost-effective excavation system. But I wonder about its use for deep drilling; would it even work in a mud-filled hole under very high surrounding pressure?

I don't think it's a clear cut situation. I know TBMs are operated by large electric motors; I suspect that the same is true for most all drilling equipment. However, the electricity is invariably produced by diesel electric generators near the job site. Not practical to run a transmission line tens or hundreds of miles to the nearest power plant or substation. Portable wind turbines? Not for the levels of power needed at these jobs!

Heat mining. The only economical forms of geothermal energy withdraw heat at a far higher rate than the natural heat flow could replace. When the rock the geothermal well is drawing from gets too cool, it's time to drill another well.

The heat resource in deep rocks is vast enough that one can (arguably) ignore the fact that heat mining is not sustainable. A bigger problem is that the only practical way to do it involves creating linked fracture networks between an injection well and an extraction well. The frac'ing operations have an annoying tendency to lubricate any natural faults in the area and trigger earthquakes.

While I liked MacKay's book, and think it is a valuable contribution, sustainable geothermal isn't really a concept we need to embrace. Sustainable geothermal, means we extract the heat slow enough that the small heat flux leaking up from deeper down replenishes any heat we remove. Geothermal isn't used in that way, it is better to consider it as heat mining. Of course heat mining has obvious limits on the resource size, but those limits are actually quite large.

Hmm, looks as though I'm going to have to do another post on current Geothermal operations (see for example the Geysers in California). At the moment the holes don't have to be nearly that deep, since you are tapping into places where igneous rock has penetrated near the surface and so you just have to drill down to it.

Once there the well can tap into natural fractures (which is what they do at the Geysers) or you can hydrofrac the rock. That gets a bit tricky since you then have to intersect that second frac with another well to get a loop for circulation. You need to be some distance from the first well at the point of intersection to get a large enough area of contact with the rock for sufficient heat transfer to the circulating fluid. Then the problem comes in finding the right fracture in the rock at that depth and steering the bit to intersect it at the right place.

Actually granite is anisotropic (means the properties are different in different directions). If you go and talk to an old quarryman he will tell you that there is a rift, an easy way and a hard way to split granite blocks all at right angles to one another. Without that experience you can find the different directions by looking at changes in the speed with which sound travels through the granite.

Water can actually drill granite quite well, more easily if it is weathered than if it is not, but the large grain sizes make it easy to remove individual crystals and we have drilled it at about 90 ft an hour, as I recall. Our slotting rate in quarries and in carving sculptures is around 20 - 25 sq ft an hour depending on the pressure of the jet, and the contour that you are cutting, and the granite which changes properties and composition as you cut through it.

We haven't yet done much work with really hot granite, but have done studies on pressurized granite, down to the equivalent of 6,000 ft and you need to increase the jet diameter to a minimum of about 0.06 inches as you go down in depth and higher in hole back pressure.

Cutting coal with a waterjet at a pressure of about 10,000 psi is like a hot knife through butter. Most coal mines use higher flows (around 1,000 gpm) and low pressure - maybe 1,500 psi - since the high volume of coal produced can then be carried away by the water in a flume, and the jets can mine back up to 100 ft from the operator of the jet.

Grin - caught - but lest you think I get rich with the current price of the book, my actual royalty check each year is about $150 - the agreement was signed long ago when the book was a lot cheaper.

Hard data would certainly be nice.

I wouldn't think that plastic creep would be a problem at just 200 C and 4000 meters. But I'm no expert. I'd expect, however, that pumping sand into the fractures, same as in oil and gas work, would keep the cracks open for at least as long as the rocks could continue to supply heat.

Just speculating, but one way to reduce drilling costs might be if the same bore holes could be used to support multiple horizontal drilling runs in different levels and in different directions. I don't know if technology for that exists yet.

I think that the need to renew wells is a function of how much heat you extract - relative to the make-up rate of the rock in situ. There are, bear in mind, locations around the world where Geothermal energy has been extracted for decades, so there is a body of practical knowledge to fall back on.

Drilling costs have, in some cases, been the issue of concern, since the cutting teeth of the drilling bits also soften as they get hotter (and that includes diamond).

I believe the rock there is a granodiorite containing pitchblende. Alluvial outwash from the hills is mined nearby using in situ leaching at a place called Beverley. In other places the Proterozoic granite is overlain by Cretaceous sandstone which has trapped the heat.

Funny how nuke opponents think this is OK but controlled fission reactors are not.

This may have been the Potter drill, which uses high temperatures. But there have been a number of different thermal methods proposed and a review of some of these is going to be part of my next post in this series.

What are they drilling through?

You are right that you can offset higher drilling costs with an increase rate of penetration. The Flowdril system that I referenced in an earlier post, for example, needed to achieve a gain of around 2.8 times conventional, as I recall, but though it reached 4 times on occasion, sustainably it seemed only able to achieve around 2.4 and is no longer with us.

In regard to what I put into the next Geothermal post, part of my problem is that I have several feet of reports on earlier work and trying to condense some of that down to 1-2,000 words and keep it interesting yet simple enough to follow means I can't put too much into any one post. (But then there will be others).

If you want to see a really different way of combining fire and water in mining, you should look up how the Romans mined gold at Las Medulas in Spain. (Pliny wrote about it).

The simple answer is that the basic technology, either roller cone or diamond drill bits is the same. However these are likely to be straight vertical holes to detect whether there is enough oil/gas in a deposit to be economical. In geothermal you will be generally drilling more deviated wells in the deeper deposits to get the areal surface for high heat transfer if you are fracing hot dry rock. If you are tapping geothermal fluids you would probably be much shallower.