Contents
Stop
Mucking With Geothermal
Before
reading on, please note:
The
Theme
But
the Main Topic is More Ambitious
Geothermal
Schemes in General
The
"Power Bubble" Concept
Power
Bubble Bootstrapping, or "Why Bother?"
Power
Bubble Applications
Drilling
Wet or Drilling Dry?
Power
Bubble Politics
Technical
alternatives to Power Bubbles
Objections
and Concerns
Adverse
Effects of Salt Injection or Disposal
Blowouts
and Pressure Excursions
Bubble
wandering
Drilling
in Hot Rock
Impossible
Pressures
Impossible
Temperatures
Bursts
and Seismic Effects
Shaft
Collapse
Quakes
and Geological Flaws
So...
What
to aim for
What
to do
This is not a
document cast in stone, but a non-technical draft proposal. Anyone with doubts, queries, suggestions,
objections, or corrections should please feel welcome to contact me.
If you do so,
please let me know whether your correspondence is in confidence, or you would
like to be credited with any changes or additions that you might inspire.
Of course there
also would be no hard feelings if you preferred to write an independent
document of your own without consulting me.
We know very little, and
yet it is astonishing that we know so much,
and still more astonishing that so
little knowledge
can give us so much power.
Bertrand Russell
This essay remarks briefly on geothermal power
as a range of resources that in most forms are intrinsically so transient, so
feeble, and on so small a scale, as to be mainly of local interest. It then deals at greater length with certain
strategies of exploitation of particular classes of geothermal energy resources
that diverge from that pattern. In their
implications and objectives they differ relevantly from any geothermal schemes
usually contemplated. They are the only
ones that bid fair to solve global energy problems and radically transform
international energy politics and economics.
They offer prospects on a scale exceeding that of the organic fossil
fuel industries.
The implications are of
critical importance in determining the nature and scope of the long term future
of human energy usage on the planet. If
the proposals are successfully implemented, our current usage patterns of
organic fossil fuel consumption will be obsolete. The international political consequences will
be enormous. Successful implementation
obviously must change the face of industry in many ways. For one thing we could belatedly begin to use
our carbonaceous fossil materials predominantly as chemical feedstocks instead
of simply burning them. Burning fossil
carbonaceous material (and oxygen with it) is about as sensible as burning
money. For certain currencies it may be
a good deal less sensible yet.
I realise that some readers will be puzzled to
see that I apparently do not know that fossil petrochemical feedstocks have
been used for other purposes than fuel for over a century. I hasten to reassure them that I am
thoroughly aware of it. What they may
not realise is what a tiny proportion of the material (a few percent at most;
in many countries a fraction of a percent) is used as anything but fuel. We burn a staggering proportion of our
birthright for far less than a mess of pottage, but a great mess all the
same.
Existing or projected geothermal schemes are of
several types. You may read some
accessible articles on the subject in Wikipedia, and of course thousands of
items of assorted levels of reliability and rationality may be found through
various search engines. Books on such
subjects also are no novelty. I do not
discuss such material in much detail here.
From the point of view of this article most of the various conventional
geothermal options differ mainly in their duration, scale, and intensity of
production of energy. Some, such as the
use of heat pumps to extract heat from warm ground, are only of local interest
and many produce energy of marginal quality at a marginal profit. Some even work at a loss, either
thermodynamic or monetary, and those are justified only by special
circumstances or special needs, rather than by primary energy production as
such. Some amount to heat storage or
heat conditioning rather than heat production.
Some geothermal projects have been accused of pollution of ground water with salty ground water, but I regard that as a planning and management problem; in fact I
suspect that it is one of those proverbial cases of opportunity posing as
problems. The chemical value of deep brines may be worth investigation, and in
fact there is currently investigation into brine dilution as a source of
significant energy. That however, still is too speculative to be taken
seriously here.
Other installations running on low-grade energy
certainly are prime power producers, but at marginally useful temperatures,
barely above the boiling point of water. Some actually work at still lower
temperatures. Those are of little
interest here. Another class, such as
"hot dry rock" sources, also are of little interest here. They do produce heat at attractive
temperatures, but their scope of production is local and their duration is
modest. More valuable sources of heat,
such as in Iceland,
variously produce hot water, steam and so on.
I mean no disrespect to local schemes of modest
scope and function. They often meet
needs of great importance, but such is not the theme of this discussion. What I have in mind is energy production of
global significance for centuries or millennia at least. The scale of energy production that I urge is
to be of major national or international importance, for periods of many
millennia at least.
The objective is to establish an energy regime
at least as significant as those based on all fossil organic fuels combined,
and eventually to replace them for the foreseeable future.
For really high efficiency and versatility one
needs high temperatures and indefinite resources. Consumers like Iceland can put up with low
efficiency because they have plentiful supplies and modest consumer
requirements. That is very well in its
place, but it is not the subject at issue.
It will occur to the reader that there is
increasing interest in hot magma geothermal sources. They do meet the need for high temperatures (several hundred
K, sometimes over 1000K), but I will point out that not even these meet the
requirements of this discussion. Some
such schemes have great implications, of which not all are primarily concerned
with energy production, but they still are not particularly relevant to the
subject of this essay. They do not all
lend themselves to indefinite production, or indefinite expansion.
In particular they do not achieve what I shall
call "bootstrapping". By this
I refer to the ability to use part of the energy production directly to
increase the yield of a scheme indefinitely.
There already is an aspect however, that could
achieve bootstrapping of a sort, and that could achieve great material
importance in practice, using current technology, but I am not aware of anyone
working on the principle. Wind and solar power are of increasing importance,
but they produce power only when there is suitable sun or wind, and also are
likely to produce more than is required when sunlight or wind is plentiful. For
comprehensive service they then must rely on either conventional power supply
to handle the base load, while wasting any excess, or they must bank excess
energy in batteries or in other media such as compressed gas, pumped
hydro-power, heat storage in crushed rock, or whatever is available. These vary
in their value, but necessarily, all of them are more or less leaky and
inefficient.
However, there is another aspect to geothermal,
even geothermal sources that are cooling to the point of becoming unprofitable
to use in their own right. If one has a suitable geothermal source near solar
or wind power farms, then one not only can supplement the transient power with
round-the-clock geothermal power, but can use periodic wind and solar power
excess to pump air into the geothermal shaft.
Now, normally compressing air is an inefficient
way of storing energy, because much of the energy used in compression goes into
heating the air, and that heat tends to get lost; however, in this case, with
suitable engineering, the heated air is confined where hot gas is precisely
what one wants to get out, and in addition, the air that the system compresses
can pick up extra energy from the surrounding rock -- possibly not a great
deal, but more than one had put into compressing the air in the first place, in
fact, making a net energetic profit from the storage of the energy in a medium
that contributes more energy than had been stored.
Note in particular that such a power storage
role, using compressed air, could be of exceptional value in supporting
renewable power supply: suitably designed, such a system could act as a rapid
response power buffer, either absorbing surges of excess power, or rapidly
supplementing solar or wind power generation when its output falls below
demand. Simply on the assumption that the geothermal plant itself is a stable
major component of the power supply
system, would imply that the buffer capacity would be on a scale to meet
challenging demands.
The same process could be elaborated in some
cases, by increasing the pressure of the injected air to extend the depth and
volume of subterranean cracks and cavities; this would increase the total
energy output of the hot rock. It could extend the effective life of the
geothermal source indefinitely; a modest, but worthwhile example of
bootstrapping. Such marginal sources often are used to provide warm air for
district heating, but used to store solar or wind energy in this way, they
could provide far more valuable and versatile electric power.
However, such
modest scales of power generation are not the main point of this essay; I wish
to introduce a concept of energy production that could attain all those objectives. It must do so on a basis of technology that
is feasible, if in some ways ambitious.
It could achieve certain other objectives as well, but that too is
beyond the scope of the essay.
As it happens,
the source of energy I propose is in fact geothermal, but that does not imply
that it simply is an elaboration of traditional geothermal energy schemes. To argue that would make about as much sense
as to regard the internal combustion engine as an elaboration of coal burning
on open fires.
Readers might
occasionally wonder whether I have considered concepts such as various
connotations of the term "hubris".
If they do not, then to that extent at least I have failed in my
objectives.
The general approach of most geothermal schemes
is to drill down to some hot material and extract the heat for use. Typically extraction takes the form of
pumping up subterranean liquids or vapours, or, increasingly often, injecting
fluids and extracting the heat from them.
Note that in these contexts I use the term
"fluid" to denote substances that can flow appropriately, whether
liquid or gaseous.
Typically it sooner or later becomes necessary
to drill extra holes so that cold fluids pumped down one hole can be extracted
hot from other holes. Such multiple hole
designs may or may not be appropriate to the proposals under consideration in
this discussion.
So far this description of geothermal schemes is
largely consistent with the proposal below.
Certain principles are pretty well common to any geothermal work, and
some of the common ones follow.
Readers no doubt accept that:
· Ground
temperatures increase more or less progressively as one digs down. At a sufficient depth the rocks become hot,
even plastic or actually molten (magma).
· The
depth at which the temperatures become high enough to melt rock into magma is
variable, though in the absence of actual volcanoes, it is usually at some tens
of km.
· Sometimes
magma rises and forms isolated pockets without any prominent connection to
deeper sources of molten material.
Sometimes there still is a connection to the source, but narrow enough
to be trivial. In such cases the amount
of heat one might extract from such a pocket is practically limited to what
already is inside the pocket. Such
limited deposits may be rewarding, but they are not the subject addressed in
this essay.
· Within
manageable limits the higher the temperature of a heat source, the the greater
the efficiency with which one could exploit energy from that source, and the
greater the versatility with which one might use it. For instance, pressurised air at temperatures
approaching 1000C can be sold either for generating electricity directly, for
metallurgical purposes, or for generation of hydrogen, and so on. Alternatively air that is too hot for other
purposes can be diluted with cooler fluids as part of the heat extraction. In contrast, fluids at 100C can hardly be
used for more than district heating and inefficient generation of
electricity.
· Depending
on their location and nature, magma temperatures typically are in the range of
about 700C to 1200C. Rock might be
plastic within similar temperature ranges, depending on the pressure and their
constitution. Factors that affect the
rate of energy transfer include the temperature of the rock, the area exposed, and the thermal
conductivity of the rock. By flow in
general, and convection in particular, fluid rock can transfer heat over
significant distances (metres or more) dramatically faster than solid rock can
transfer heat by conduction.
· The
behaviour of rock in very hot regions under high pressures is strongly
hydrostatic and in some respects it may have hydrodynamic aspects as well. It exerts powerful effects
of buoyancy and convection etc. Where
the materials are cooler this remains true, but there the hydrostatic effects
are not pronounced enough for us to take it into account in most
connections, and the hydrodynamic effects practically vanish. For example small-scale
convection in cooler materials is negligible.
Even
where rock is effectively solid, it is elastic to a degree that can show
dramatically in the curvature of masonry pillars under stress for example. (See the brilliant book by J. E. Gordon:
"Structures, or Why Things Don't Fall Down".) The combined effects often are of great
importance. For example, where rock is
placed under stress by overlying ice or other overburden, it sinks, eventually
to isostatic levels. When such
overburden is removed the rock then slowly rebounds. Finland for example still is
rebounding from its most recent period of glaciation. Conversely, where underground fluids thrust
up under pressure, they cause the rocks above them to bulge. Usually this is hardly perceptible, but
sometimes they bulge dramatically before they burst out as volcanic
eruptions. Such bulges are among the
most significant intimations of imminent eruptions.
· The
plasticity of hot rock has important implications for deep engineering
techniques that depend on the displacement of rock by pressure. If one digs down to thoroughly plastic or
marginally molten rock, one can apply hydraulic pressure to form a bubble or a
fracture, depending on the nature, pressure, and temperature of the rock. Even rock that one would hardly imagine to be
capable of distortion can deform plastically under such conditions. For example, if surrounded by sufficient
pressure, apparently solid marble can be deformed amazingly without cracking,
almost like putty.
· Conversely,
as a rule the higher the temperature of any rock that does not decompose chemically or physically under
the ambient conditions, the more easily it flows. This is a familiar effect to anyone with
experience in glass blowing, though of course, it is dangerous to extrapolate
too simplistically from experience of a homogeneous material like glass, to
heterogeneous, partly crystalline, materials such as molten rock mixtures that
might fractionate or react chemically.
Suppose that we have drilled down to rock that is hot enough to be thoroughly
plastic. We apply internal pressure
by injecting gas or fluids such as water into the plastic. At those temperatures such fluids of course will quickly become
supercritical. Possibly we even might
use liquids such as molten salts and similar compounds and fill the shaft with
them to counteract back-pressure. If we
pump in fluids at sufficient pressure, a bubble in the plastic rock must result. The shape and behaviour of the bubble depend
on the texture and buoyancy of the rock and the nature of the injected fluid. There should be little obvious distortion on
the surface of the ground above, because the bubble is at least several km below the surface, so any surface bulge would be spread over a wide area.
The inner surface temperature of such a bubble should be roughly 700C to 1700C, depending on the nature of the surrounding
rock, the depth, and so on. Large
surfaces at such high temperatures can be used as a source of enormous amounts
of power for long periods of time. For
example, energy may be extracted thermoelectrically or by pumping working
fluids suitable for driving electric power generators through the bubble. So in this essay I refer to such bubbles as
"power bubbles".
As the bubble
grows, especially if it is partly or even completely filled with dense molten
salt or possibly molten alkali, or with a puddle of iron, the tendency to
expand downwards will compete with the
tendency to expand upwards. However, the
heat flow generally will be from below,
so that especially if the molten salts act as a flux, that would
increase the tendency for the bubble to expand downwards, because hotter rock
deforms more easily than cooler.
The implications will be familiar to anyone with experience of glass blowing.
To increase such downward tendencies in the
expansion of the bubble, the sides of the growing bubble could be cooled to
increase their viscosity. The most
convenient means of doing this might be by spraying them with (relatively) cool
incoming working fluids or powders.
The eventual effect would be to produce a bubble
in the plastic rock. If all worked
perfectly, it would progressively expand to force its way through the yielding
material downwards into deeper, hotter, softer rock. Ideally this should continue until eventually
its lower surface reached completely liquid rock. However, such depths probably would only be
practical in limited circumstances, such as near a mid-ocean ridge or a hot
spot.
The pressures required for bubble expansion at
depths of tens of kilometres would be in the range of mega-pascals. Currently such pressures are non-standard in
industry, but certain approaches could change that.
Supercritical fluids such as steam could be bled
off from the bubble to yield heat and high pressure, much as existing very hot
sources do, only more so than most. They
could be used to drive generators and machinery, supply heat, and extract
industrially valuable dissolved substances.
The best form in which to supply fluids to the
bubble would depend on the requirements and the processes to be serviced. Water, either fresh or in the form of brine, would be an
obvious candidate. Residual salt from
the brine should act as a flux in contact with the softest, hottest rock. Other candidate fluids include CO2,
air, and molten salts from other sources.
Sodium chloride, which is about as cheap and plentiful a salt as any,
has some quite interesting properties in such applications. It becomes especially cheap when it is available
in the form of raw seawater or of the highly salty ground water that renders some soils
unusable until the brine can be removed.
Whether to use hot material direct from the
bubble, or extract energy via heat exchangers, would depend on the practical
factors such as might be associated with any particular installation.
A crucial attribute of the bubble scheme is that
once a bubble is well established and yielding power at a sufficient rate, it
can be expanded continuously simply by using part of its excess power yield to
continue indefinite inflation of the bubble.
On the venerable principle of assuming a spherical cow, we safely and
conservatively may assume a spherical bubble, because, short of various
disastrous outcomes, a sphere is the least productive shape for extracting
heat.
In practice a highly spherical bubble is
vanishingly unlikely of course, because hydrostatic factors would tend to
flatten the bubble drastically, if nothing else did.
Two examples of disastrous shapes include:
- nodes
that pinch off or extrude sideways to such an extent as to be effectively
excluded from the heat extraction flow, and
- parts
of the bubble floating up to well above the nozzle of the drill
hole.
Such effects
would be wasteful at best, and possibly destructive. Continuous control of the hole shape might be
necessary. Selective heat extraction and
directing the injection of working fluid so as to cool areas where high
viscosity is desirable, should be a promising and economical approach. Elsewhere I also describe how to encourage
continuous downward growth with added fuel.
At all events, assume a spherical hole with a
volume of perhaps 1 cubic km, giving a wall surface of about 5 km2. Assume a wall temperature of 1000C. This is a ridiculous oversimplification of
course, because in real life not only would the wall be all sorts of shapes,
but the wall temperature would vary considerably over its surface. However, any deviation from a true spherical
shape would improve the surface to volume ratio. The only concern would be to prevent the
resulting cavity from developing deep bulges that would frustrate good heat
exchange.
Consider in contrast another academic
example. If the 1 cubic km sphere were
flattened to a disk with an average thickness say, of 10 m it would have a surface area of some 200 km2,
about forty times better than the sphere.
Without taking that figure too seriously, it still is plain that less
compact proportions are more attractive than spherical bubbles.
It is certain that many people who read as far
as this will be objecting that the whole scheme, apart from being a
technologically inane pipe dream, is just a dusting-off of the weary, limited,
and ineffectual theme of geothermal power.
Without digressing to point at Iceland or other geothermal success
stories, I point out that just because a given system relies on power from
underground, does not imply that it is identical to other technologies that
draw power from the same direction.
By way of helpful illustration, a monkey might
sneer at a proposal for an Atlas rocket.
"Firstly," he might say, "we already know about going
up. We monkeys have been going up trees
for millions of years. This rocket thing
of yours obviously is just the same as climbing trees, but noisier, more
expensive and plainly impossible anyway.
And besides, even if it worked, what is the point? Who wants to go to the moon in the first
place? It will never pay. Rather gather the low-hanging fruit!"
To such a reasonable monkey it is difficult to
point out that not only would climbing a tree not get anyone into orbit, but
getting into orbit enables us to do many more marvellous and worthwhile things
than going to the moon. The profits from
either weather observation or communications alone, however unromantic, could
pay handsomely for the whole of our space investments so far.
Similarly, power bubbles may resemble existing
geothermal technology in no more than a sense in which rocketry might be seen
as analogous to tree climbing. The most
important difference is that not one of the "conventional" geothermal
technologies takes the bootstrapping concept beyond trivial levels. Consider hot rock heat extraction for
example. If all goes well (which
understandably it sometimes doesn't) we drill down to hot rock, generally
creating at least two shafts. We then
interconnect the shafts by cracking the intervening body of hot rock. As a rule one uses hydraulic pressure to do
so. Then, for as long as circumstances
permit the cracks to stay open, one pumps the working fluid down one hole and
up the other.
This may sound a little unpractical, but it
really does work, sometimes quite profitably.
What is more, it has a very interesting implication. A non-obvious opportunity arises from the
situation once the hole is established.
As the rock gives up its heat, why should one not apply more pressure
from time to time, either to extend the period of viable yield, or to increase
the rate of yield?
An excellent idea; so excellent indeed, that
this does get done in practice. It is a
sort of low-grade bootstrapping. Get
your first hole going at some acceptable level of performance, then use part of
your new asset to increase its own scale.
Now, hot rock, and every other form of
geothermal energy extraction, is limited to obtaining such energy as is
available from the immediately surrounding hot material. Such energy may well be not only profitable,
but plentiful, and more strength to the industry, say I. However, the accessible energy still is
limited. In most sites one may estimate
the expiry date with a reasonable degree of accuracy.
In contrast consider the idealised power
bubble. Yes, it is dug into very, very
hot material with very, very large amounts of energy available in forms that
offer far wider ranges of applications than conventional geothermal. But those are matters of detail rather than
the essential contrasts. Yes, its own
power can be used to bootstrap its size.
But that is the end of the resemblance to other technologies that lend
themselves to bootstrapping. (Most
geothermal technologies do not lend themselves to anything of the type at
all!)
When one can blow bubbles into what amounts to
soft, flowing rock and grow the bubbles to huge size, important qualitative
differences emerge. Firstly, one can aim
for a scale of production that can serve whole countries. As opposed to mere profit, this has
implications for political power. (Ask
the OPEC leaders!)
From the point of view of the investor the
initial investment into a working installation goes on increasing its yield
indefinitely by balancing the power offtake constructively. Simply by controlling the rate and choice of
materials injected, together with the rate of power extraction, one keeps the
bubble growing and exposing more hot material.
All it takes to complete the process is competence in managing the shape
and state of the bubble.
Growing the bubbles sounds good, but what about
the supply of new heat? Not even power
bubbles violate thermodynamics.
True.
However, when the bubble has penetrated far enough into rock that is
fluid enough to exhibit significant convection on time scales relevant to the
process, then simply cooling the bottom of the bubble by extracting power will cause
it to sink into hotter rock beneath, exposing new hot surfaces
indefinitely.
In fact, it suggests horizons of power
extraction at depths and temperatures that currently would seem
nonsensical.
Infinite power?
Certainly not. Eternal
power? Of course not. Free power?
Definitely not — not even nearly free for some time, and who at this
time can guess what the running cost may be?
Do remember old forecasts of "power too
cheap to meter". This turned out to
be a hopelessly over-optimistic idea.
And yet nuclear technology did prove to be clean and economical.
It still is, in spite of widespread hysteria about irresponsible and
incompetent engineering.
All the same, clean as such power has turned out
to be, bubble power promises to be even less polluting. In fact, any "pollution" it
produces might well be worth extracting as ore or raw materials. The calcium, magnesium, aluminium, silicon,
and trace elements extracted from material pumped out, could provide your camera
lenses, window glass, electronics, metals, and building bricks.
Though neither infinite nor eternal,
bootstrapped power production could serve the planet for longer into the future
than our species has been clearly human in the past. If by the time that bubble power begins to tail
off we humans have not found our way off the planet, maybe we do not deserve
to.
It all is quite enough to make bootstrapped
power worth serious thought and serious effort.
There are more applications and implications to
bubble power than appear at first sight.
This follows from the sheer pervasiveness of power in our civilisation
and its infrastructure. The only other
resource that even approaches the ubiquity of power is information, which in
many senses is related. For one thing,
we are by now conditioned to think of power in terms of electricity, or in
terms of fuel for transport if we are a little more sophisticated.
Think
of the effects of altering the costs or availability of either.
Certainly electricity is our most versatile
medium for conveying power. If we were
to replace most of our power generation with power bubbles, it is practically
certain that the primary product would be electricity.
There are other products of course. For one thing we need energy for chemical
processing. The layman cannot for one
moment conceive the sheer variety of chemical products in our lives, let alone
the variety of the nature of chemical processing. Stop chemical processing today and you would
starve, paralyse, and poison nearly the whole human world within months. For one thing you could say goodbye to the
production of our fossil transport fuels or the production of metals ranging
from lithium to actinoids. Some people
seem to think that one simply pumps diesel and petrol out of the ground (those
rare spirits that think at all) but of course that is not quite how things
happen.
Much of the energy we need to drive chemical and
many material manufacturing processes is in the form of heat. Electricity can supply heat with great
efficiency, but if we first have to generate that electricity from heat, the
overall efficiency drops precipitately.
Accordingly, industries that use a lot of heat are only too happy to buy
hot air or other suitable gases at about 1000C, instead of electricity or fuel
with which to heat the gases themselves.
Steel-working plants, cement producers, and nitrogen fixation are just
three examples of power-intensive processing that could drastically reduce
their electricity consumption if they had adequate sources of cheap heat.
Also, processing of fossil organic material such
as tar sand or coal to produce fuels, requires huge amounts of heat. It requires so much heat in fact that
sometimes the resulting yield hardly is worth it in absolute terms. The real profit in such cases is not in the amount
of energy processed into usable transport fuels, so much as in the form
of fuel produced. Not all fuels are
of much use for transport.
Other forms of energy consumption that rely
largely on heat or electricity or both, include the production of fuels such as
hydrogen by the sulfur-iodine or hybrid sulfur cycles.
High-temperature
electrolysis for production of hydrogen also is efficient, and would have the
advantage of producing oxygen as well.
In general, if we can get heat sufficiently
cheaply and plentifully from below the earth, the hydrogen economy might become
as familiar as the petroleum economy is today.
Actually, there are other fuel chemicals, such as metals and alcohols or
other organic materials, that in some ways would be more valuable than
hydrogen, and they also could become economical to use on a large scale. The details hardly matter. The point is that, given sufficient clean
energy in useful forms we can change the nature of our effect on the planet and
in the process we could extend our viability as a species by thousands of years
at least.
Apart from delivering power, power bubbles would
be the finest storage medium for power that one could ask for. They would have
every desirable attribute except portability. Compressed air is another medium
that they could produce for transport or power storage. Compressed air is beginning to look promising
for increasing numbers of applications already. Use off-peak power to pump cold air into the
bubbles, and at peak times the hot air could be tapped off for power. The
volumes available for such storage would be huge.
Another
emergent consideration might result from the contact between magma and solvents
such as super-heated water or molten salts. Even under far milder conditions
than those in power bubbles, such as in existing geothermal power schemes, we
inadvertently extract troublesome minerals that currently we need to dispose of
as wastes. In power bubbles however, we might find that the solvent extraction
of live magma would yield large quantities of precious or at least valuable
elements that are painfully rare on the surface or in the shallower parts of
the crust.
Temptingly
possible candidates might include rare earths, cobalt, iridium, platinum and
other elements desperately in short supply for industrial purposes. If we
strike it rich in some of our power bubbles, their waste streams might play a
rewarding role in the economy of the power generation process. They might for
example more than pay for all the waste processing. Gross concentrations of the
elements would not be necessary; some of them would be attractive to extract
from easily processed wastes even at concentrations of a few parts per million.
The obvious choice for where to drill for power
bubbles is on land. It really seems
stupid to drill shafts under three to five kilometres of seawater. Having to work through layers of up to half a
kilometre of ooze does not look very encouraging either. Having to convey terawatts of energy up to
the surface for use on land, perhaps hundreds of kilometres from the shaft,
seems positively perverse.
After
all, to establish a power bubble would require far more than running a drill
string from a surface ship, down a Mohole, to the mantle.
And yet, one could make a very strong case for
submarine power bubbles. Oceanic
lithosphere is possibly half as thick as typical continental lithosphere. Much of it is more seismically stable than
most continental lithosphere as well.
Drilling large shafts many kilometres deep is horrendously expensive, so
thin lithosphere is attractive. In
certain areas beneath the ocean the magma is moving comparatively briskly,
which implies huge heat flows.
In
short, whoever establishes a workable technology for deep-sea power bubbles
will have the world by the tail.
It is not immediately clear how to balance the
risks of digging into mid-oceanic ridges, where vulcanism and instability are
threats, against the comparatively trivial depths that one would have to drill
to reach enough magma to make bubble blowing worth while. There certainly are areas of level oceanic
floor where the lithosphere is especially thin and yet the geology is
acceptably stable for our purposes.
Without belittling the challenges, it should be
practical either to construct an igloo-type structure on the ocean floor,
through the floor of which the shaft construction could proceed, or to
construct the igloo on land, tow it out, and lower it to the sea floor where
desired. A tall ooze-penetrator might be
dropped to establish itself on the hard basement where it could establish a
foundation through which to sink a shaft.
Nor is it clear that drilling power bubble shafts on land is
unacceptable. Hot areas like Yellowstone may or may not be long-lived in comparison to
some other sites, but even a productive lifetime of no more than a few
centuries should yield a good profit for such a scheme. In fact, given the uncertainty of the future
of Yellowstone, Vesuvius, and various other
active spots, it would seem to be grossly irresponsible not to try
controlling their development. Bleeding
off their gases and magma for a few decades at a time might forestall even very
large explosive accumulations. An
eruption that otherwise might have covered several mid-western states or large
cities, would be reduced to a massive source of power and possibly of mineral
wealth as well.
How far to combine such safety punctures with
power bubbles is a question for the future.
There is no doubt that the only option with more
disastrous political implications than the successful introduction of power
bubbles world wide, would be failure to introduce them. On this planet the only alternative sources
with anything like the same scope would involve importation of fuels or power
from outside our planet, which is not the subject of this discussion.
There are two scenarios to consider:
(a)
Suitable sites for power bubbles might turn out
to be so common that most countries could construct as many power bubbles as
they desired. This would affect a lot of vested interests and reduce the
current local concentrations of fuel sources into few hands. However, even the wide availability of power
sources would lead to vast transitional problems. Those who got in first and quietly developed
the competence and technology would hold a huge advantage for a long time. Countries that did not seize the opportunity
by the forelock might suffer the consequences for generations. Within each community vested interests of
short-sighted parties would resist development, even when it meant destruction
of their own interests within a generation.
(b) More
likely, areas of sufficiently thin and stable continental crust, though
plentiful, would be regional, so that many countries would lack economic
options for constructing power bubbles.
This would have even more drastic consequences than ubiquitous power
bubble schemes. For one thing the
countries that lagged in the race to establish a healthy energy surplus would
be left in a very unhealthy economic and social situation. For another, most of those that currently
have very rich oilfields are not situated very promisingly for power
bubbles. For example, much of the middle
east is unpromising for several reasons.
If ever there were a time when the major OPEC nations should be quietly
preempting a revolution in their own future interests, by buying into power
bubble development in promising regions, that time is now. Conversely, if ever there were a time when
the major industrialised countries should be preparing to throw off the
constraints of fuel politics, now certainly is the time.
In either case, there should at the moment be a
major move towards developing subterranean power sources, not morsel by morsel,
but on a scale to take over the world.
Power bubbles would take time to develop into a routine technology, so
there would be intermediate objectives, but those with a view to the future
should already have been on the way a long time now if far-sightedness or
concern for the future were political strengths.
As a rule they are not.
That is the Achilles’ heel of both democracy and
short-sighted despotism.
- Fossil
organic fuels are widely regarded as either practically inexhaustible or
sustainably exploitable. People
bandy figures about that differ wildly, partly because they differ in what
they prefer to believe, in their choice of definition of what counts as
resources, or what proportions of resources will be recoverable at what
prices.
There
is one main point on which everyone agrees although they think they
differ, namely that the end of organic fossil fuel supplies is urgently at
hand. Some speak of decades, some
of centuries, but no rational person speaks even of millennia, let alone
significantly long periods. Bear in
mind that in speaking of the survival of our "civilisation",
centuries hardly count. They hardly
count even in the history of a country worthy of its name or people.
Some
characteristically technically illiterate economists seem to think that
because the stone age did not end with the supply of stones, that we need
not worry about the energy age ending with the supply of energy. If we do not prepare for the transition,
that is just how it might end. The energy age simply might end with the
supply of accessible energy. The foolish virgins among nations that have
failed to establish a future for their peoples will have doomed themselves
and pauperised their populations by not having prepared alternative power
sources for their future economies. And power bubbles or some rival
bootstrapping source of geothermal heat are the most promising successors
to fossil organic fuels.
One
constant in our history and prehistory that has varied only in its scale,
variety, and inefficiency, has been our dependence on energy. Until economists explain how to
transcend the laws of thermodynamics, their only option is to point out
alternative sources of energy, or more likely, hope that some stupid
technologist somewhere will point out a new source from which they could
make money. Discussion of at least
one source is the theme of this essay.
Even
the limited supply of fossil organic fuels is not the whole story. New sources of energy had better not
rely on fuels that are too oxygen consuming. We are consuming oxygen at a rate that
should scare anyone spitless who takes our planetary budget
seriously. After all, where did the
oxygen came from in the first place, and how fast?
So,
anyone who for example relies on a long-term hydrogen budget that does not
produce as much oxygen as hydrogen, is leading us down the mortuary
path. With due and generous respect
for the cap and trade bandwagon, we could multiply our CO2
budget by a factor of ten with no clear risk of harm, but if we consumed
just a few percent of our free oxygen, the consequences would be
disastrous, in fact murderous. In
comparison global warming would be trivial in consequences and trivial to
control. Recent palaeontological
evidence suggests that since the Cambrian period, the oxygen level has
never dropped nearly as far as some had supposed. Even if it turned out that the recent
evidence were wrong, it does not follow that we would comfortably survive
such a change. We already see
intimations that to increase the rate of photosynthesis is not nearly as
simple as people had imagined.
- Nuclear
energy is particularly attractive in that it consumes oxygen only
incidentally and in trivial amounts.
In effect power bubbles consume stored nuclear and gravitational
energy for the most part, but in many ways they tempt us to use their power
to produce materials such as hydrogen that also consume a fair amount of
oxygen. It would make sense to
watch the implications of emergent technologies with caution.
The
fashionable current concern about nuclear power is the hysteria about the
nearly irrelevant problem of nuclear "waste disposal". I shall not go into that matter, except
to remark that I never have seen any such “waste disposal” that did not
amount to criminal waste of irreplaceable resources. The only rival to such criminality has been
irresponsibly incompetent waste accumulation such as by the US and no
doubt certain other major nuclear powers, where politicians and management
were only interested in their pockets and short term careers.
Nuclear
energy has important roles, for example for heavy-duty transport fuel and
transportable generators. It also
will have valuable functions in space, if only for expeditions far from
the sun, and deflection of threatening asteroids. On Earth it also has important
functions in isotope manipulations and so on. However, fission power almost certainly
will have a shorter fuel supply and less versatile output than power
bubbles.
Fusion
power currently seems likely to be even less versatile than fission and it
is not clear how much harmful waste it will produce. Apart from some recent and sophisticated
proposals, most claims that fusion power will be clean are exaggerated or
ill-informed. There also is the
question of whether it ever will be practical at all, and if so on what
scale, in which form, and using which fuels. Though the technology deserves attention
it is too early to rely on its success as a general purpose source of
power.
- Space-based solar energy is notionally attractive, but current proposals look
very expensive and doubtfully practical.
Its main attraction is that if it works at all, a well engineered
installation should work for a long time.
Some versions look more practical than others, but certain schools
of partisans have quaint ideas concerning geosynchronous orbits instead of
precessing polar orbits. One hopes
that they will grow out of it before their failures harm the prospects for
serious development of a promising technology. Meanwhile, I refuse to take any
large-scale power project seriously before the ISS becomes a success. If we cannot manage a toy project like
ISS, what hope do we have of establishing spaced based solar power
generators on a scale to serve New
York, let alone the planet?
- Space
based sources of nuclear fuel are another option. He3 has been proposed as a fusion fuel
of surpassing value. If so, there
are some tempting sources out there, but not yet any clear assurance of
our being able to use He3 profitably down here. Conversely there is no short term
prospect of importing fission fuels at a profit. I do propose a scheme for environmentally responsible harvesting of huge quantities of He3, but as yet we do not even have solid evidence that we ever could use it for power production.
The He3 article is at:
https://fullduplexjonrichfield.blogspot.com/2011/01/one-theme-that-occurs-frequently-among.html
It should be thousands of
years at least before we are so short of actinoid elements on Earth that
it would pay to prospect for them in space.
- Unpredictable
discoveries of new power technologies are always possible. Someone might find out how to harness
sunlight at trivial cost, negligible inefficiency, full portability,
arbitrary scalability, and with huge storage capacity. That would drastically affect the
attractions of digging for power.
But history does not encourage us to wait for that discovery before
considering how to improve our current buggy whips.
- An
interesting possibility would be to drill for hot rock or localised magma
in thin sea floor or near volcanoes, where there certainly is a great deal
of energy to be extracted on a non-bootstrap basis. However it might prove to be prohibitive
to install power bubbles in a submarine environment. All the same, submarine hot magma power
might turn out to be a valuable resource.
It certainly would outlast oil and should be much cleaner than
coal. It even might be as clean as
nuclear energy.
In comparison
to most of those, bubble power offers us indefinite capacity, indefinite
lifetime, low running costs, a wide compatibility with existing technologies,
and a trivial ecological footprint. It
is not clear how widespread and plentiful sites for exploitation might be. To ignore the prospects for such a field of
technology would be irresponsible.
A very reasonable question concerns the
ecological hazards of soluble inorganic materials such as salts. Most of them should not be very hazardous
under the conditions contemplated. If
the working fluids are gases such as air or argon, which are not solvents at
temperatures around 700C-1700C, there should be very little discharge and we
could ignore pollution problems stemming from their use.
Where more powerfully solvent fluids such as
water and CO2 are extracted from or pumped through deep hot rock, they are
likely to carry substances that one does not normally think of as being
soluble, substances such as silica and various ore chemicals. Some are harmful and are best removed,
preferably for commercial exploitation of their chemical content. Most are perfectly safe to discard at sea in
diluted forms once any toxic components have been removed or immobilised. Insoluble sludges are harmless as long as
they are not allowed to smother large areas.
Soluble chemicals of low toxicity that occur routinely in sea water are
harmless as long as they are diluted soon enough; in fact, most common
substances to be expected in solutions leached from rocks, such as Ca, Mg and K
compounds, would be desirable as nutrients in sea water. They would have the added attraction of precipitating
or neutralising dissolved CO2.
This is a very desirable option in the light of current increases in ocean acidity.
If molten salts were used in or extracted from
the shaft, most of them would be moderately benign and could be discharged into
the sea without any ecological threat whatever.
The most obvious candidates would be salts of sodium, magnesium, calcium
and so on. Any breakdown products in the
event of overheating or chemical reaction, say chlorine from chlorides, could
easily and cleanly be scrubbed and neutralised.
One certainly would not want too much of most
salts to escape into the soil on land, and certainly not noticeable amounts of sodium
and chloride salts. Soil salination is a
widespread problem and to pollute fresh ground water with more than a few parts
per thousand of sodium or even nutrient salts, would be unacceptable. Firstly, this means that effluent must be
disposed of with care, and secondly, if the shaft contains any substances
undesirable in ground water, suitable precautions must be routine and
reliable.
The necessary precautions vary with the site and
conditions. For example, where ground
water is already uselessly salt and has been stagnant in a limited area for a
long time, one need not be too fussy about small spills. In fact one could extract such salty groundwater for injection into the bubble, using the steam to extract energy, leaving the agricultural land with more acceptably low residues of salt, and leaving the salt in the bubble to render the surrounding rock more fluid and easier to expand downward. Such sites with soil poisoned by saline ground water, are common in various regions, some naturally, and some as a result of improvident human activity.
The sheer scale of the energy available from the power bubbles is such that the bubbles could supply most of human power needs for thousands of years at least; and one implication is that bubbles could supply much of our requirement for fresh water as well. If we feed a large power bubble with seawater, leaving the salt behind as a flux, and driving our power generators with the steam, then the sheer volume of the steam would make it worth condensing to produce practically pure fresh water. That supply would be insufficient for our total water requirements, but it could well supply major markets for potable domestic water, and that is a very great need world wide.
Also, as a rule, serious drilling or shaft
sinking of types relevant to this discussion tends to be many times deeper than
any ground water of practical importance.
In fact, saline ground water often is a serious nuisance, so power schemes of
this type probably would shun sites where usable ground water is plentiful. Instead it
could improve local agriculture by extracting saline ground water that has
accumulated to disastrous levels. It then could drain the saline water into the power bubble along with sea water, condensing the steam to yield a profit from saline water that currently is a curse.
Oil drillers must be on the alert for blowouts
when the shaft structure or the surrounding material cannot contain the
pressure of fluids below ground. This is
a matter of concern for any deep drilling, but really, it is less of a risk for
power bubble drilling than for oil wells.
· Oil
wells tend to be drilled where there are likely to be pockets of compressed
gas, such that unexpectedly drilling into one could lead to the drill string
being practically lifted out of the shaft.
Power-bubble drilling would generally be exactly where one is not likely
to find such pockets. One wants a thin
crust in geologically uniform and stable areas, not a salt dome to drill
through.
· One
is not likely to begin a power bubble drilling project at the surface, then
drill down to magma and proceed to blow fluid down the hole to make a
bubble. The structure of a power bubble
project would be far different.
Excavations for the first three km or so would almost certainly be
conventional shaft sinking such as is by now established technique for deep
mines. In fact, it might well be started
at the bottom of suitable existing mine shafts.
Much of the infrastructure probably would be constructed within chambers
branching off the shaft. So far there is
not much scope for concern.
· Deeper
down, where the bubble shaft itself begins, it is not yet clear whether
conventional drilling would be used at all.
We require bores much wider than simple geothermal injection wells. Even if we do drill conventionally for a
while, it would be for limited depths in solid rock. Existing studies (e.g. Google for: magma
energy engineering feasibility, R. K. Traeger, and Research Project John L. Colp, Sandia National Laboratories)
show that current drilling technology can proceed far deeper into hot rock than
we require, but very hot rock is where we might well encounter bubbles of CO2
for example.
· When
the hot rock phase of the drilling begins, we would need to establish a
strongly-anchored well lining. Once we
reach plastic rock we would not only install linings, but anchor them into the
walls and cool those walls to render the rock stronger than surrounding
material. At such depths we very likely should be
using thermal drilling by burning hydrogen or methane at pressures higher than
ambient, so that any gas bubbles we encounter would be at lower pressure
than what we apply. Any really large gas
bubble we find probably would be a bonus that could be bled for power or for
bubble inflation.
There are two types of event that might cause a
power bubble to wander. The first would
be buoyancy of the bubble within soft rock.
There are several approaches to dealing with that, of which I prefer the
idea of designing the injection mechanism to spray the incoming relatively cool
working fluid radially or tangentially so that it flows down the walls. That would cool the upper areas
preferentially and create turbulence calculated to circulate the contents of
the chamber through any minor diverticula.
It still might happen that a portion of the bubble would rise beyond its
most useful level, but within reason that would be a minor problem, something
to be avoided as far as practical, but not disastrous in itself.
The other major type might occur in a
long-standing bubble if relatively rapidly drifting magma carries it off to one
side faster than the bubble can be inflated.
If this should occur, it should be regarded as a bonus. Such drift still would probably be slow,
centimetres per year, and could be slowed even further by increasing the rate
of injection of cool material and extraction of hot. Another shaft could be sunk into either the
leading edge of the bubble, or where the leading edge is anticipated to reach
in the near future, or possibly into an upward bulge if a sufficiently large
one developed.
Extra shafts not only would increase the options
for pinning the bubble by cooling its surroundings, but greatly increase the
rate at which energy could be extracted by passage of the injected fluids down
some shafts and up others. In fact, it
is unclear at the time of writing whether such multiple shafts shouldn't be
standard practice anyway.
As I already have mentioned, studies show that existing drilling technology can
penetrate far deeper into hot rock than we require. All the same I actually am not currently
contemplating conventional forms of drilling, except during specific phases
where engineering experts might see it as advantageous.
There are several problems with drilling through
deep, hot rock with the conventional drill string. One is the sheer difficulty and cost of
dealing with such a long string, and another is removal of the drilled-out
material from the hole.
Instead I propose approaches based on drilling
by application of heat and pressure.
Near the surface this would be costly at least, and might be unpractical
in other ways too, but as we go below the zones where the environment is cool
enough for humans to work the rock, the shaft sinking would be taken over by
automated equipment. At levels where
this too becomes unpractical, we can begin to exploit the very heat that had
been an obstacle at shallower levels.
Whether to use chemical or nuclear energy for drilling is an open question. Possibly first one then the other.
There are two obvious chemical options. One would be to pump down oxygen and a
suitable fuel, possibly hydrogen, carbon, or hydrocarbon fuels. The drill head
would be a torch nozzle of a suitable diameter, design, and material, and the
whole unit would work under pressurised gas (oxygen?).
I rather suspect that an alternative design
would be better, based at least partly on solid fuels such as solid carbon.
Oxidisers such as nitrates, perchlorates or peroxides could be dumped in
blocks, or pumped down, perhaps in
slurry form. Other fuels such as aluminium or sodium might get their oxygen
directly from the ambient molten rock instead.
In general the chemistry of the process would offer an interesting field
for study and prudent experiment.
In any case, the mix would be designed to melt
its way down as a pool of molten rock continuously enriched with fuel.
The molten pool principle could be especially
valuable during the early phases of extending the actual bubble downwards. By continually adding modest amounts of fuel
to the molten pool of salts, extra heat could be applied selectively to make
sure that the hottest rock and flux would be at the lowest point below the
inlet. If working fluid were injected
radially to cool the walls, this should increase the tendency of the bubble to
grow downwards rather than sideways.
By systematically injecting fuels and
maintaining pressure, the whole system could melt its way down. The resulting hole would not be a narrow
puncture such as a drill would produce, but perhaps metres in diameter.
An interesting version of the molten pool
approach would be to form a pool of molten iron, manganese, or other suitable
metal, feeding it with alternating doses, first of oxidisers such as peroxides,
oxygen, and perchlorates, and then of reducing agents such as carbon,
aluminium, sodium and hydrogen or hydrides.
The metal pool not only would be designed to be chemically reactive, but
also dense. Properly controlled it
should eat and melt its way through most kinds of rock, largely catalytically,
because molten slag of various kinds could be reclaimed by feeding in reducing
agents such as sodium. Temperatures
could be raised by feeding in oxidisers.
The high density would concentrate the forces on the bottom of the
cavity. Slag of various kinds would
float to the surface of the pool, where they could be drawn out onto the sides
of the cavity. Some of the fuels, such
those that produce volatile oxides, would react to increase the pressure. Others, such as reactive metals, would reduce
pressures, yielding carbides and carbon instead of CO and CO2. These reactions could be reversed by adding
more oxidisers as required.
Melting rock instead of drilling through it
might sound very inefficient, but it has its compensations. Firstly there is hardly any drill string
problem, which otherwise could be prohibitive in terms of time and mechanical
problems. The heat produced would
generally be very effectively contained, stored, and conserved on the way
down. It largely could be
reclaimed from the coolants when they re-emerge, and the cooling would
contribute to the congealing of the walls.
Alternatively, at a suitable depth we could
begin to melt our way down by installing a high temperature fission reactor
that relies on Doppler broadening to increase neutron absorption for temperature
control by negative feedback. Such a
reactor would be designed to be of considerably greater density than any molten
rock it might encounter. It therefore would sink through any rock that it
melted.
If switching the reactor off turned out to be
difficult, it could simply be permitted to consume its residual fuel in sinking
away from the site of the bubble once we had reached the most desirable
depth. Otherwise it might be possible to
keep it at the bottom of the bubble, supplying energy to assist in the
inflation.
As the heat source melted its way down, the hole
would be kept open with pressure maintained from above. Exactly what would happen behind the drill
would depend on many factors. A fair
amount of experiment would be necessary to establish the best principles, let
alone to design actual equipment. I
doubt that the actual rock itself would be strong enough to withstand the
ambient pressures at the depths desired, even if cooled, but if forming and cooling would do the
trick, that would be an attractive option.
Alternatively, as the shaft progresses, it could
be expanded by pressure to somewhat wider than its desired diameter. Then perhaps a molten refractory lining could
be shaped and cooled in place. The wall
of the lining could formed to contain any channels required for carrying down
coolants or extracting hot fluids.
Another option would be to install voussoirs
forming the tunnel wall together with any incorporated structures or
mechanisms. The rock around the
voussoirs could be allowed to settle in behind them while still soft, holding
them in place as it cooled. Coolant
entering the walls would keep the surrounding rock stronger than the rest of
the rock in the region.
A still simpler, but possibly more attractive
approach would be simply to stop melting the way down once reaching rock of a
suitable temperature, but instead just apply pressure to expand both the walls
and the floor. Pause the process while
installing the next set of voussoirs, then apply cooling to the walls. Once the voussoirs were set in place, apply
pressure till the floor once again began to sink and make room for the next set
of voussoirs. Ultimately this process
would end in blowing the power bubble itself, installing no more voussoirs, but
only cooling the walls enough to prevent expansion of the bubbles from creating
buoyancy problems.
One of the most rational objections concerns the
difficulty of applying the necessary pressures for working at such depths at
all, let alone for forcing bubbles into the soft rock tens of km down.
Well, I never said it would be easy. I am as aware as anyone that forcing such
pressures down a tube in the field is not at all the same thing as playing
tricks in the laboratory.
One might of course dismiss that objection with
hand-waving reassurances: after all, we have overcome problems in the past that
at first had seemed not just equally challenging, but equally absurd. And yet, many such technologies are nowadays
routine, not only taken for granted, but regarded as boring by that minority of
the couch potato population as have so much as heard of them. I am tempted to cite Clarke's law of
technologies: that any sufficiently advanced technology is indistinguishable
from magic, except that a far more powerful influence is that any effective
technology soon seems far more tedious than marvellous to the smuggest and most
petulant sector of humanity: the Great Uneducated and Uneducable.
However, although a direct assault on
multi-megapascal pressures might well be forbidding, multistage hydraulic
devices of modest performance could be stacked at intervals on the way down the
shaft, such that both the mechanisms and the surrounding rocks could handle
individual levels of forces with comfortable safety margins.
Another class of technique could also contribute
to the effort. Filling the hot parts of
the shaft with molten salts or similar substances could partly or completely
counter the surrounding hydrostatic forces.
Challenging in general? Definitely.
And yet, I regard the challenge of achieving of profitable nuclear
fusion as far more challenging yet.
The temperatures in question certainly are challenging,
but they are not beyond practical limits.
I doubt that any exit gas temperature beyond about 1200C would be under
consideration.
Temperatures
for melting the way down might be higher, perhaps more like 2000C, but those
would be contained at the workface.
Perfectly practical alloys could survive such temperatures, and many
ceramics could resist them indefinitely.
During the process of melting the way down, powerful oxidising and
reducing agents would be used, but afterwards the operating environment would
be chemically bland. This greatly
increases the range of candidate materials for the working structures. In reducing or neutral atmospheres many
carbides would work well at very high temperatures. I could list several pure or composite materials
with promising characteristics, but it is a safe bet that whatever we guessed
at present, the engineers on the job would prefer their own alternatives for
reasons of strength, chemical resistance, flexibility, cost, availability, and
so on.
In particular, I suspect that some of the most
useful materials could be partly formed in situ under the influence of the very
temperatures and pressures that they were to withstand. This would hardly surprise anyone who in
kitchen, workshop, or laboratory, has ruined an expensive utensil or tool by
clogging it with a refractory, resistant, adherent char of one sort or
another. Many promising linings,
matrices, cements and fillings might well be applied as polymers or mixes
designed to char in place.
It is well known that among the most worrying
problems in drilling really deep shafts, geological faulting and unexpected
rock movement and fractures are among the worst and hardest to predict. Furthermore, some such conditions are
particularly common in places where magma is temptingly near the surface.
However, such a challenge is not as forbidding
as it seems. We do not need a shaft
every ten km. One or a strategically
distributed few should be adequate for even a large nation. This means that in most regions far more
usable sites than needed would be available.
We could pick and choose. For
once, commercial considerations would coincide with ecological
considerations. No one in his right mind
would want to drill a multi-billion-dollar shaft that needed constant
maintenance or threatened imminent shutdown with every earth tremor.
Geologically unstable regions such as large
parts of the Himalayas or the Rocky
Mountains/Andes certainly would be poor prospects. Certainly it is not always obvious from
surface inspections whether a given site is suitable, or even whether the best
prospects would be on land or submarine abyssal plains. Equally certainly one
would not select sites overlying particularly thick crust, but every digging
project has its own elements of speculation, and this speculation offers vast
rewards.
When problems match rewards, they are called
challenges.
A very interesting question is whether the
rewards are as irregularly scattered as they have turned out to be in the case
of prospecting of oilfields. Either way
the political implications could be immense.
Obviously, without support no shaft could
survive at depths of any use in such
schemes. But then, not even a
shallow underground mine of modest scale could survive long enough to be useful
without pit props and similar precautions. There are several kinds of measures to apply
in plastic rock shafts. Which kinds to
use would be a matter for engineers to develop during the establishment of the
technology and decide on in any given case in the light of experience.
The most obvious option would be to cool the
rock round the shaft to well below the temperature of the surrounding
material. Such cooling should harden it
significantly. At modest depths relatively
cool rock walls might be strong enough, depending on the nature of the rock. The fluids pumped down to cool the walls
would of course carry usable heat to the surface. From the deeper levels this alone could be an
indefinite supply of high grade heat.
The next option, and at greater depths, would be
to line the hole with strong, refractory materials. Different materials might be used at
different depths, depending on their nature and cost. For example, silicon carbide would be strong,
pressure-resistant, and able to withstand adequate temperatures. In its raw
form it should be cheap enough, though I am not at present confident about the
costs of fabrication. As described
elsewhere in this document, automated equipment could apply such materials as
lining voussoirs by first using fluid pressure to expand the hole as it gets dug,
a length at a time, then packing the voussoirs from within and permitting the
external rock to settle back, locking the voussoirs into place. Channels within the voussoirs could carry the
cooling fluids that would congeal the rock to cement and hold the blocks in
place.
If a suitable lining could be cast in place on
the way down, a sort of high-pressure, high temperature concrete or char
moulded in place could result.
Thirdly, the pressure of the working fluid in
the shaft would prevent shaft collapse.
If the shaft was not filled with suitable molten salts or similarly
dense fluids, this pressure would of course be too great for the walls of the
shallower horizons of the shaft. There
would have to be stages at which some pressure got relieved, probably by
driving turbines at set levels in the shaft, or perhaps by bleeding off working
gas to drive turbines nearer the surface.
A major fault could wreck any shaft, no matter
how large, no matter what its lining.
However, a suitably flexible or well-enough articulated shaft should be
able to survive modest movements; there would be no moving parts running the
length of the tube. To put it mildly,
serious damage to anything as valuable and costly as a power bubble shaft would
be unwelcome, but not all is doom and gloom.
By careful selection of sites where the nature
of the geology does not encourage drastic movement, we can reduce the risk of
major failures, but minor failures are likely to present a more constant, and
therefore a more serious problem. No
matter how perfect the shaft, minor shifts are likely to distort and stress the
tube from time to time. If the stressed
regions of the shaft can be heated up enough to anneal the surrounding rock to
conform and relax the stress, that should be effective.
By tapping our (by current standards) deep
crustal or (by any standards) shallow mantle heat, we could extract energy on a
scale to dwarf anything humanity has consumed to date. As a source of energy it would be clean and
versatile, and would outlast our requirements on this planet for many millennia
at least, longer than we have used any fuel in any systematic way.
The nature of the installations, namely bubbles
inflated in hot rock in the deepest levels of the lithosphere, lends itself to
bootstrapping larger, more productive installations, starting from working
installations of modest size. The
bootstrapping facility alone radically distinguishes this type of energy extraction
from all other geothermal enterprises or technologies. So does the scale and viable duration of the
installations.
The nature of the energy is versatile, lending
itself to generation of electric power, chemical processing and various
industrial physical processes. Although
it should end our dependence on fossil organic fuels, it simultaneously will
enable us to redirect the consumption of such materials into production of
chemical feedstocks and intermediates.
It also may develop into a major source of
mineral extraction, though that is more speculative, and not for the
foreseeable future a prime driver for any such project.
A new source of power on such a gigantic scale
would have intense effects on the international political scene. Countries that fail to develop competence in
the necessary skills and infrastructures will find themselves pauperised or at
least at as great a disadvantage as those that currently, for different
reasons, are hostage to OPEC.
What we know about what we want or can get from
the earth beneath us, is precious little.
Accordingly, a good way to start would be to drill a lot of moholes at
various points around the planet. That
it has not yet been done is a stinging rebuke to the foresight and enterprise
of the human community. That inaction
bodes ill for our continued survival, never mind our self-sufficiency.
A mohole project need not begin very
aggressively. In combination with
sufficient numbers of smaller exploratory drillings and a really aggressive
seismic programme, two or three moholes on each continent and a couple of dozen
on the ocean floor might do to start with.
It should be a sound basis for deciding where to drill the next
generation of moholes. We need to
establish a map of the conditions beneath the outer crust, and of the materials
and temperatures at various sites and depths.
Given how little progress we have made with deep
drilling, not even one respectable Mohole to date, this might seem to be an
extravagant pilot investigation, but really it is long overdue. Everyone agrees that we are blind ignorant of
whole ranges of matters concerning the structures and processes we live
above. If ever there was any doubt that
our ignorance is dangerous, there can hardly be doubt now. Every deep hole presents us with unexpected
findings. It is past time to do
something about it, and the nation that acts first might be the one that
becomes richest thereby.
Meanwhile, there are many lines of applied
research that we must get underway in parallel with the drilling projects. We do not yet have even a firm basis for
designing large-scale deep-sea igloos, much less excavating multi-metre-wide
shafts beneath them or exporting electric or hot-air power from them. Who knows whether the ocean-floor ooze would
be a serious challenge or an aid to the project?
What about the principle of sinking shafts by
melting, whether by nuclear reactor, raw chemical heat, or pressure? Or the techniques for lining them with
voussoirs or with heat-cured char? All
these technologies sound marvellous, almost trivial, but all we really know
about them is that if we do not get down to business, we still will not know
how or even whether we ever can master them.
Too expensive to be realistic?
It is a really disgusting reflection that we
could get a good project going for less than the political advertising
expenditures of a single presidential race in the US alone. And as for the money
wasted on the accommodation of politicians in international conferences of the Kyoto type...!
In
sum, I meant it when I said "stop mucking with geothermal"; it is
past time for us to stop mucking about: we need to get down to serious
business.
Jon Richfield
Posted by Jon Richfield at 1/05/2011 06:00:00 AM
