<p>Here is a thermal profile of the borehole:</p>

<p>(Source: Fig 5 in Yuri A. Popov, Sergei L. Pevzner, Vyacheslav P. Pimenov, Raisa A. Romushkevich,
New geothermal data from the Kola superdeep well SG-3,
Tectonophysics,
Volume 306, Issues 3–4,
1999,
Pages 345-366,
ISSN 0040-1951,
<a href="https://doi.org/10.1016/S0040-1951(99)00065-7" rel="noreferrer">https://doi.org/10.1016/S0040-1951(99)00065-7</a>.)</p>

<p><a href="https://i.sstatic.net/Jeu7r.gif" rel="noreferrer"><img src="https://i.sstatic.net/Jeu7r.gif" alt="Figure 5: Thermal Profile of Kola Super Deep"></a></p>

<p>This borehole is (almost) vertical and not an angle, so its depth is true (11662 m) and it is quite warm down there, around 180 degrees Celsius as shown in the above figure. I assume temperatures were similar in other shafts drilled at maximum depth at 12262 m. </p>

<p>The equipment they used initially for the 1982 borehole down to 11662 m was made to be able to work in thermal stability up to 200 degrees Celsius (Source: Kozlovsky, Yevgeny A., and N. I. Adrianov, eds. The superdeep well of the Kola Peninsula. Springer Berlin Heidelberg, 1987.) Consequently I assume the equipment used for the later shaft that reached 12262 m was of similar or better make than the original.</p>

<p>The problem is not the temperature against the barrel only: there is heat due to the shear (rotation) and let's not forget the weight of the shaft down the base. This is why the thermal stability of the system is to be considered in addition to the resistance of single parts of the drill system. So while hotter than they expected, it was within the operating range conform to the specifications of the make - but yet very near the thresholds and thus problematic.</p>

<p>The problem lied also with the rock being more and more plastic deep down in the borehole, due to pressure, porosity and water, making it a very difficult challenge to keep the borehole open each time the shaft need to be replaced or removed, adding difficulties to this already never-been-done-before project.</p>

<p>So this sum of challenges are probable reason why the project was interrupted before reaching the initial goal of 15 km.</p>

CC BY-SA 4.0
2019-05-25T14:11:20.883Z
2019-05-25T14:11:20.883Z
marsisalie
<p>I recently read on another SE site that there's a limitation on how deep we can dig into the earth.</p>
<p>A Google search reveals that temperature is the problem.</p>
<p>I quote from a Popular Mechanics article, <a href="https://www.popularmechanics.com/technology/infrastructure/a27225/deepest-possible-hole/" rel="nofollow noreferrer"><em>How Deep Can You Dig a Hole?</em></a>, which speaks on the <a href="https://en.wikipedia.org/wiki/Kola_Superdeep_Borehole" rel="nofollow noreferrer">Kola Superdeep Borehole</a></p>
<blockquote>
<p>The limiting factor is almost always the temperature. The Kola was abandoned in 1992 when workers hit <strong>356 degrees Fahrenheit</strong>, far hotter than they had anticipated. The tunnel was eventually closed off in the early 2000's.</p>
</blockquote>
<p>356<span class="math-container">$^\circ$</span>F is 180<span class="math-container">$^\circ$</span>C, for those of you who don't get Fahrenheit, like me.</p>
<p>Iron's melting point is well above 1000<span class="math-container">$^\circ$</span>C, and I think it is okay to assume most of our machines have iron as a major constituent. Alloys with iron will only have higher melting points.</p>
<p><strong>Why is 180<span class="math-container">$^\circ$</span>C a problem? Why can't we dig deeper?</strong></p>

CC BY-SA 4.0
2019-05-22T18:23:49.407Z
I think it's not so much a matter of "can't", as it is "it would cost more than we want to spend".  Iron may melt above 1000∘C, but it softens at much lower temperatures.  The drilling bits (at least for conventional oil well drilling) aren't simply solid blocks.  They have moving parts that might be adversely affected by thermal expansion, the cutting parts are often things like tungsten carbide or diamond, &c https://en.wikipedia.org/wiki/Drill_bit_(well)
jamesqf
CC BY-SA 4.0
2019-05-22T19:14:33.403Z
A quibble about terminology. The deepest humans have *dug* is 3900 m at the [Tau Tona Mine](https://en.wikipedia.org/wiki/TauTona_Mine) in  South Africa. The longest hole *drilled* is supposedly the Kola Super Deep Hole. I can vaguely recall reading about a hole drilled later that was longer, but I have forgotten the details. Given that such long holes are never vertical for their entire length - they all bend eventually. I question whether the stated 12 262 m **depth** of the hole is actually its ** length**. If so, being a bent/curved hole would reduce it depth.
Fred
CC BY-SA 4.0
2019-05-22T19:22:17.270Z
@Fred I meant by all means "drill".  As for the hole bending, it certainly might be possible.
William R. Ebenezer
CC BY-SA 4.0
2019-05-22T19:23:08.960Z
@Friddy I think you have a good point.
William R. Ebenezer
CC BY-SA 4.0
2019-05-23T01:05:35.307Z
Temperature of 400 F is no problem for a drill bit. Anyway, it has much cooler mud moving through the bit while drilling . They do all possible to keep the bit moving ( circulating mud) to avoid getting it stuck - big problem.
blacksmith37
CC BY-SA 4.0
2019-05-30T11:06:50.213Z
https://www.nature.com/articles/d41586-019-01551-6 - a very relevant recent article
Gimelist
CC BY-SA 4.0
2020-11-05T04:05:55.473Z
Try reading the wiki article you actually linked to. "The unexpected decrease in density, the greater porosity, and the unexpectedly high temperatures, caused the rock to behave somewhat like a plastic, making drilling nearly impossible"  a drill for cutting thorough hard rock is going to do nothing to taffy. It was not about the properties of the drill but the properties of the rock.
John
<geology><mining>
Why can't we dig deeper?
William R. Ebenezer
# Why can't we dig deeper?

(Asked by: username_0 on 2019-05-22)

I recently read on another SE site that there's a limitation on how deep we can dig into the earth.

A Google search reveals that temperature is the problem.

I quote from a Popular Mechanics article, [*How Deep Can You Dig a Hole?*](https://www.popularmechanics.com/technology/infrastructure/a27225/deepest-possible-hole/), which speaks on the [Kola Superdeep Borehole](https://en.wikipedia.org/wiki/Kola_Superdeep_Borehole)

> The limiting factor is almost always the temperature. The Kola was abandoned in 1992 when workers hit **356 degrees Fahrenheit**, far hotter than they had anticipated. The tunnel was eventually closed off in the early 2000's.

356$^\circ$F is 180$^\circ$C, for those of you who don't get Fahrenheit, like me.

Iron's melting point is well above 1000$^\circ$C, and I think it is okay to assume most of our machines have iron as a major constituent. Alloys with iron will only have higher melting points.

**Why is 180$^\circ$C a problem? Why can't we dig deeper?**

**Tags:** geology, mining

> **Comments:**
> **username_1**: I think it's not so much a matter of "can't", as it is "it would cost more than we want to spend".  Iron may melt above 1000∘C, but it softens at much lower temperatures.  The drilling bits (at least for conventional oil well drilling) aren't simply solid blocks.  They have moving parts that might be adversely affected by thermal expansion, the cutting parts are often things like tungsten carbide or diamond, &c https://en.wikipedia.org/wiki/Drill_bit_(well)  
> **username_2**: A quibble about terminology. The deepest humans have *dug* is 3900 m at the [Tau Tona Mine](https://en.wikipedia.org/wiki/TauTona_Mine) in  South Africa. The longest hole *drilled* is supposedly the Kola Super Deep Hole. I can vaguely recall reading about a hole drilled later that was longer, but I have forgotten the details. Given that such long holes are never vertical for their entire length - they all bend eventually. I question whether the stated 12 262 m **depth** of the hole is actually its ** length**. If so, being a bent/curved hole would reduce it depth.  
> **username_0**: @username_2 I meant by all means "drill".  As for the hole bending, it certainly might be possible.  
> **username_0**: @Friddy I think you have a good point.  
> **username_3**: Temperature of 400 F is no problem for a drill bit. Anyway, it has much cooler mud moving through the bit while drilling . They do all possible to keep the bit moving ( circulating mud) to avoid getting it stuck - big problem.  
> **username_4**: https://www.nature.com/articles/d41586-019-01551-6 - a very relevant recent article  
> **username_5**: Try reading the wiki article you actually linked to. "The unexpected decrease in density, the greater porosity, and the unexpectedly high temperatures, caused the rock to behave somewhat like a plastic, making drilling nearly impossible"  a drill for cutting thorough hard rock is going to do nothing to taffy. It was not about the properties of the drill but the properties of the rock.  

---

## 1 answers

### Answer by username_6 on 2019-05-25. Score: 8 | Accepted answer

Here is a thermal profile of the borehole:

(Source: Fig 5 in Yuri A. Popov, Sergei L. Pevzner, Vyacheslav P. Pimenov, Raisa A. Romushkevich,
New geothermal data from the Kola superdeep well SG-3,
Tectonophysics,
Volume 306, Issues 3–4,
1999,
Pages 345-366,
ISSN 0040-1951,
<https://doi.org/10.1016/S0040-1951(99)00065-7>.)

[![Figure 5: Thermal Profile of Kola Super Deep](https://i.sstatic.net/Jeu7r.gif)](https://i.sstatic.net/Jeu7r.gif)

This borehole is (almost) vertical and not an angle, so its depth is true (11662 m) and it is quite warm down there, around 180 degrees Celsius as shown in the above figure. I assume temperatures were similar in other shafts drilled at maximum depth at 12262 m.

The equipment they used initially for the 1982 borehole down to 11662 m was made to be able to work in thermal stability up to 200 degrees Celsius (Source: Kozlovsky, Yevgeny A., and N. I. Adrianov, eds. The superdeep well of the Kola Peninsula. Springer Berlin Heidelberg, 1987.) Consequently I assume the equipment used for the later shaft that reached 12262 m was of similar or better make than the original.

The problem is not the temperature against the barrel only: there is heat due to the shear (rotation) and let's not forget the weight of the shaft down the base. This is why the thermal stability of the system is to be considered in addition to the resistance of single parts of the drill system. So while hotter than they expected, it was within the operating range conform to the specifications of the make - but yet very near the thresholds and thus problematic.

The problem lied also with the rock being more and more plastic deep down in the borehole, due to pressure, porosity and water, making it a very difficult challenge to keep the borehole open each time the shaft need to be replaced or removed, adding difficulties to this already never-been-done-before project.

So this sum of challenges are probable reason why the project was interrupted before reaching the initial goal of 15 km.


---

