U.S. patent application number 10/592475 was filed with the patent office on 2007-03-15 for hydrothermal mineral extraction.
This patent application is currently assigned to UNIVERSITY OF MANITOBA, AN INSTITUTION OF HIGHER LEARNING. Invention is credited to Daniel Fraser.
Application Number | 20070056770 10/592475 |
Document ID | / |
Family ID | 32075107 |
Filed Date | 2007-03-15 |
United States Patent
Application |
20070056770 |
Kind Code |
A1 |
Fraser; Daniel |
March 15, 2007 |
Hydrothermal Mineral Extraction
Abstract
Described herein is a system and method for hydrothermal mineral
extraction wherein the conditions surrounding hydrothermal systems
are used advantageously to extract a mineral-rich brine.
Specifically, hydrothermal fluid from ocean based or saline based
hydrothermal systems contain a variety of minerals suspended in
supercritical water and can be drawn up a well. As long as the
water remains a supercritical fluid, the minerals remain largely in
solution; however, as the hydrothermal fluid moves away from the
this state, the water can cool and exit the supercritical state,
causing the depositing or scaling of minerals along the walls of
the well pipe. In the instant invention, non-supercritical
conditions are rapidly induced onto the hydrothermal fluid such
that the brine containing the minerals rapidly precipitates and
forms a slurry which is then isolated from the water. Another
aspect regards altering the chemistry of the fluid to precipitate
the minerals. Another aspect of the invention is related to
mineral-rich slurries isolated by this method and to specific
minerals isolated therefrom.
Inventors: |
Fraser; Daniel; (Manitoba,
CA) |
Correspondence
Address: |
Ade & Company Inc
1795 Henderson Highway
PO Box 28006
Winnipeg Manitoba
R2G 4E9
CA
|
Assignee: |
UNIVERSITY OF MANITOBA, AN
INSTITUTION OF HIGHER LEARNING
Winnipeg Manitoba
CA
R3T 5V4
|
Family ID: |
32075107 |
Appl. No.: |
10/592475 |
Filed: |
October 10, 2003 |
PCT Filed: |
October 10, 2003 |
PCT NO: |
PCT/CA03/01522 |
371 Date: |
September 11, 2006 |
Current U.S.
Class: |
175/14 |
Current CPC
Class: |
Y02P 10/20 20151101;
C22B 3/00 20130101; Y02P 10/234 20151101; C22B 3/02 20130101 |
Class at
Publication: |
175/014 |
International
Class: |
E21B 7/14 20060101
E21B007/14 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 11, 2002 |
CA |
2,407,878 |
Claims
1. A method of hydrothermal mining comprising: withdrawing a
quantity of a supercritical hydrothermal fluid from a magma fluid
source surrounding a hydrothermal vent, said hydrothermal fluid
comprising a brine phase and a supercritical water phase; and
rapidly reducing the solubility of the hydrothermal fluid, thereby
separating the hydrothermal fluid into water and a slurry.
2. The method according to claim 1 including pumping the
hydrothermal fluid to increase flow rates.
3. The method according to claim 1 wherein the brine phase
comprises dissolved mineral salts.
4. The method according to claim 1 including extracting valuable
gases from the hydrothermal fluid.
5. The method according to claim 4 wherein the valuable gases
include hydrogen and methane.
6. The method according to claim 1 wherein the solubility is
rapidly reduced by shocking the supercritical fluid into a
sub-supercritical state.
7. The method according to claim 6 wherein the supercritical fluid
is shocked by lowering the temperature of the supercritical fluid,
adjusting the pH of the supercritical fluid, adjusting the chloride
content of the supercritical fluid, or a combination thereof.
8. The method according to claim 7 wherein the temperature is
lowered using cold water.
9. The method according to claim 7 wherein the temperature is
lowered just below a supercritical temperature of the fluid.
10. The method according to claim 1 including providing a tubing
string to withdraw the hydrothermal fluid and reducing the
solubility of the fluid adjacent a bottom end of the tubing
string.
11. The method according to claim 10 including reducing the
solubility of the hydrothermal fluid by injecting a solubility
reducer into tubing string above an inlet of the tubing string
which receives the hydrothermal fluid.
12. The method according to claim 10 including providing a first
conduit in the tubing string for withdrawing the hydrothermal fluid
and a second conduit in the tubing string for injecting a
solubility reducer adjacent the bottom end of the tubing
string.
13. The method according to claim 12 including injecting air into
the solubility reducer within the second conduit for subsequent
injection into the first conduit with the solubility reducer to
provide lift to the hydrothermal fluid within the first
conduit.
14. The method according to claim 1 including reducing the
solubility by either adjusting the pH of the supercritical phase or
adjusting the chloride content while maintaining temperature of the
fluid near but just below a supercritical temperature of the
fluid.
15. The method according to claim 1 including providing a
production tubing string for withdrawing the hydrothermal fluid and
locating a well head of the tubing string on land adjacent a body
of salt water.
16. The method according to claim 1 including providing a
production tubing string for withdrawing the hydrothermal fluid,
reducing the solubility of the fluid adjacent a bottom end of the
tubing string and isolating the slurry from the water adjacent a
top end of the tubing string.
17. A hydrothermal mining system comprising: a tubing string for
withdrawing a quantity of a supercritical hydrothermal fluid from a
magma fluid source surrounding a hydrothermal vent, said
hydrothermal fluid comprising a brine phase and a supercritical
water phase; and a solubility reducer for injection into the
hydrothermal fluid for rapidly reducing the solubility of the
hydrothermal fluid, thereby separating the hydrothermal fluid into
water and a slurry.
18. Minerals isolated by the method according to claim 1.
19. A slurry containing a plurality of minerals isolated by the
method according to claim 1.
20. Hydrogen gas isolated by the method according to claim 4.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to the field of
mineral and energy extraction. More specifically, the present
invention relates to a method of hydrothermal mineral and energy
extraction.
BACKGROUND OF THE INVENTION
[0002] Hydrothermal (hot water) regions within vast water-permeable
fractured rock areas form continuous re-circulation zones that can
produce supercritical fluids if temperatures and pressures are high
enough. These fluids can contain high concentrations of dissolved
metals/minerals (such as gold, zinc and copper) and gases (such as
hydrogen and methane) [1-5].
[0003] These hydrothermal regions exist along the mid-ocean ridge
(MOR) spreading centres that circle the globe (e.g. the Pacific Rim
of Fire). Other similar geological areas that have near surface
magmatic chambers may also be mineable. Much of the interest and
research in these areas has so far been focussed on the potential
to tap into limitless amounts of geothermal energy [6-7] . However,
the mining potential may surpass the economic benefits of the
energy, making the energy a by-product.
[0004] The whole concept of a so-called hydrogen economy is
predicated on finding or producing large sources of hydrogen
efficiently. A large source of geothermal energy, methane, hydrogen
and metals/minerals exists in hydrothermal fluids that originate
from high temperature reaction zones near magma chambers close to
the earth surface [6-7]. Such zones could initially be harnessed
from land-based systems using existing technology in the many
locations around the world where mid-ocean ridge spreading centres
occur on or close to land. Iceland, where the Mid-Atlantic Ridge
occurs on land, is such a location [6]. However, many other similar
regions exist worldwide (e.g. Azores, African Rift Valley, Red Sea
etc.).
SUMMARY OF THE INVENTION
[0005] According to a first aspect of the invention, there is
provided a method of hydrothermal mining comprising: withdrawing a
quantity of a supercritical hydrothermal fluid from a magma fluid
source surrounding a hydrothermal vent, said hydrothermal fluid
comprising a brine phase and a supercritical water phase; and
rapidly reducing the solubility of the hydrothermal fluid, thereby
separating the hydrothermal fluid into water and a slurry.
[0006] The method may include air-lift pumping using a hydraulic
air compressor or similar device.
[0007] The brine phase may comprise dissolved mineral salts.
[0008] The hydrothermal fluid may include valuable gases.
[0009] The valuable gases may include hydrogen and methane.
[0010] The solubility will be reduced by shocking the supercritical
fluid out of a supercritical state. This mimics the natural
environment that occurs surrounding black smokers at ocean floor
vent sites such as the Juan De Fuca Ridge off the West coast of
Canada.
[0011] The supercritical fluid may be shocked by adding a
solubility reducing to lower the temperature of the supercritical
fluid or also, to adjust the pH or chloride content of the
supercritical fluid.
[0012] The temperature may be lowered using a coolant fluid, for
example fresh water. Other coolants may include saltwater or water
with additives to perform such functions as adjusting the pH. In
other embodiments the material introduced may be water or steam or
other fluid with characteristics to adjust the pH or chloride
content of the hydrothermal fluid while maintaining the temperature
and hence buoyancy of the hydrothermal fluid.
[0013] The pH may be increased by using alkaline additives in the
fluid.
[0014] The chloride content may be lowered by adding fluid.
[0015] Seeding the flow with particles may help nucleate the
sulfides more rapidly.
[0016] The temperature may be lowered just below a supercritical
temperature of the fluid.
[0017] When a tubing string is provided to withdraw the
hydrothermal fluid, solubility of the fluid is preferably reduced
adjacent a bottom end of the tubing string.
[0018] The method preferably includes reducing the solubility of
the hydrothermal fluid by injecting a solubility reducer, as
described above, into tubing string above an inlet of the tubing
string which receives the hydrothermal fluid.
[0019] The tubing string preferably includes a first conduit for
withdrawing the hydrothermal fluid and a second conduit for
injecting a solubility reducer adjacent the bottom end of the
tubing string.
[0020] The method may include injecting air into the solubility
reducer within the second conduit for subsequent injection into the
first conduit with the solubility reducer to provide lift to the
hydrothermal fluid within the first conduit. In further
embodiments, many variations of pump means are conventionally
available in place of air injection to provide lift.
[0021] When reducing the solubility by either adjusting the pH of
the supercritical phase or adjusting the chloride content,
temperature of the fluid can be maintained near or just below a
supercritical temperature of the fluid.
[0022] The method preferably includes locating a well head of the
tubing string on land adjacent a body of salt water. Water is
preferably isolated from the slurry adjacent a top end of the
tubing string.
[0023] According to a second aspect of the invention, there is
provided a quantity of a mineral isolated by the any of the
above-described methods.
[0024] According to a third aspect of the invention, there is
provided a slurry containing a plurality of minerals isolated
according to the any of the above-described methods.
[0025] According to a fourth aspect of the invention, there is
provided hydrogen and/or methane gas isolated according to any of
the above-described methods. Such gases will evolve from the fluid
as the fluid is de-pressurized.
[0026] According to a further aspect of the present invention there
is provided a hydrothermal mining system comprising:
[0027] a tubing string for withdrawing a quantity of a
supercritical hydrothermal fluid from a magma fluid source
surrounding a hydrothermal system, said hydrothermal fluid
comprising a brine phase and a supercritical water phase; and
[0028] a solubility reducer for injection into the hydrothermal
fluid for rapidly reducing the solubility of the hydrothermal
fluid, thereby separating the hydrothermal fluid into water and a
slurry.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] In the accompanying drawings, which illustrate exemplary
embodiments of the present invention:
[0030] FIG. 1 is a graph of the solubility of supercritical
water;
[0031] FIG. 2 is an elevational view of a well extending into a
layer of highly fractured basalt;
[0032] FIG. 3 is a sectional view of a first embodiment of the well
pipe.
[0033] FIG. 4 is a sectional view of a second embodiment of the
well pipe.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0034] Unless defined otherwise, all technical and scientific terms
used herein have the same meaning as commonly understood by one of
ordinary skill in the art to which the invention belongs. Although
any methods and materials similar or equivalent to those described
herein can be used in the practice or testing of the present
invention, the preferred methods and materials are now described.
All publications mentioned hereunder are incorporated herein by
reference.
Definitions
[0035] As used herein, "magma fluid" refers to fluids that
originate from close to or directly from the magma source. This can
include juvenile waters (waters that originate from the magma
itself and not seawater or meteoric water sources).
[0036] As used herein, "supercritical water" refers to pure water
that is above approximately 374.degree. C. and 200 bars
pressure.
[0037] As used herein, "hydrothermal fluid" refers to a
multi-component fluid mixture that originates from the hydrothermal
convection cell. The fluid when in a supercritical state is
composed of a brine phase (salts and dissolved species) and a more
purer vapour-like water phase. The supercritical pressure and
temperature of these fluids will be higher than that for pure water
as defined above.
[0038] Described herein is a method of hydrothermal mineral
extraction wherein the conditions surrounding hydrothermal vents
are used advantageously to extract a mineral-rich brine.
Specifically, hydrothermal fluid surrounding the hydrothermal vent
and containing a variety of minerals suspended in supercritical
water, is drawn up a well pipe. As will be appreciated by one of
skill in the art, as long as the water remains a supercritical
fluid, the minerals remain largely in solution [3-4], however, as
the hydrothermal fluid moves away from the vent, the water cools
and exits the supercritical state, causing the deposition or
scaling of minerals along the walls of the well pipe. In the
instant invention, the solubility of the supercritical fluid is
rapidly reduced, either by rapidly introducing non-supercritical
conditions by lowering the temperature of the hydrothermal fluid,
altering the pH of the supercritical fluid or flooding the
hydrothermal fluid with fresh water, such that the brine containing
the minerals rapidly precipitates and forms a slurry which is then
isolated from the water. Another aspect of the invention is related
to mineral-rich slurries isolated by this method and to specific
minerals isolated therefrom.
[0039] In many areas of the world magma from within the earth rises
close to or exits onto the seafloor. The enormous thermal energy
continuously released creates a unique hydrothermal environment.
Hydrothermal vents on the ocean floor release large amounts of
fluids at temperatures that can reach above the critical point
(approximately 374.degree. C. for water) [3]. Because of this they
contain large amounts of dissolved minerals and gases such as
hydrogen. Below these vents are vast water-permeable fractured rock
areas, a continuous recirculation zone that produces these vents.
Further beneath is magma at approximately 1200.degree. C. Drilling
into to such environments should allow attaining fluid temperatures
as high as currently technically possible (up to 500-600.degree.
C.) [6-7]. Saline hydrothermal system areas may be tapped with
minimal disturbance to marine ecosystems. These regions are usually
highly stable, virtually on a geological time scale and may well be
mused as an environmentally benign source of power, metals/minerals
and gases.
[0040] Seawater (Saline) source hydrothermal systems can be
harnessed from land by drilling through the land at locations where
a mid-ocean ridge spreading centre occurs on the landmass.
Hydrothermal regions close to and on the land exist in Japan,
Iceland, the Azores, Hawaii, Mid East, African Rift Valley, the
Aleutian Islands and New Zealand.
[0041] Mining companies have already gone to considerable lengths
in the attempt to exploit hydrothermal vents on the seafloor.
Success to date has been limited to the recovery of vent chimney
material [8-9]. This disrupts the ancient marine ecosystem of the
vent environment.
[0042] What has been overlooked by those in the art seeking to
understand hydrothermal vent fluid composition is that
supercritical aqueous chloride solutions are highly solvent and
hence readily strip metals from the surrounding rock and absorb
gases and possibly metals emanated from the magma source fluids
themselves. In some locations, valuable metals such as gold are in
very significant quantities as dissolved metal ion complexes. In
virtually all locations significant quantities of zinc, copper and
other valuable metals exist. Many additional metals/minerals exist
as well although in lesser quantities. Such metals may include the
rare but very valuable Platinum Group Elements PGE's.
[0043] Drilling to temperatures of 450.degree. C. or greater and
depths of 3.5 to 5 km presents unique technical challenges.
Specifically, the prior art teaches that when drilling a well at
this depth, water is applied to the drill bit to cool the drill
bit. Once drilling is complete, the water-cooling of the drill bit
is discontinued and the drill bit is removed. Hydrothermal fluid,
comprised of supercritical water, and dissolved metals, minerals
and gasses is then brought to the surface via the well pipe.
However, as the hydrothermal fluid travels up the well pipe, the
fluid cools and the water exits the supercritical state. As a
consequence, the solubility of the metals and minerals in the water
decreases, and minerals precipitate on the inner surface of the
well pipe. This mineral scaling can be a serious problem during
geothermal energy development and exploitation, as flow up the well
pipe becomes restricted and may eventually plug. This happened at
Reykanes Well #9 in Iceland. [10].
[0044] As shown in FIG. 2, the present invention makes use of a
production tubing string including a well pipe 25, to be described
in further detail later herein, which communicates with a land
based well head 24 of the tubing string which is supported above
ground. The well pipe 25 is located to extend down into the ground
from the well head to terminate within a layer of highly fractured
rock usually mostly basalt 22 which is located directly above a
layer of magma 21. The highly fractured rockt 22 is directly
adjacent a body of salt-water such as the ocean 23. In this
configuration, with the well pipe directly adjacent a body of water
while remaining land based, salt water circulated through the
highly fractured basalt from the ocean is drawn up through the well
pipe 25 as a hydrothermal fluid as described herein. The well pipe
25 may be directionally drilled or drilled perpendicular to the
ground.
[0045] Turning now to FIG. 1, the properties of the hydrothermal
fluid are demonstrated in further detail. FIG. 1 is a pressure vs.
enthalpy diagram for pure water with selected isotherms being
illustrated. The saturation curve is illustrated by reference
character 1 and is a boundary of the conditions under which steam
and water co-exist in a two phase fluid. The dotted line
illustrated by reference character 4 is the high solubility line
while the dotted line indicated by reference character 2 is the
supercritical line which together form the boundaries of the high
solubility region 3.
[0046] As long as the fluid state of a hydrothermal fluid remains
within this high solubility region 3, it will transport minerals
and metals dissolved in solution and suspended or dissolved in the
brine phase. Moving outside of the high solubility region will
cause the metals and minerals to precipitate out of solution. The
faster this fluid is brought out of this region, the more rapid the
precipitation. Shock precipitation is the most rapid in which the
thermodynamic properties of the solution are driven along the path
indicated by reference character 5 to cross over the high
solubility line while remaining above the supercritical line. Shock
precipitation occurs very rapidly across this path as solubility
can vary by orders of magnitude across the pseudocritical or high
solubility line [4].
[0047] The temperatures and pressures over which the solubility
varies are intended to only be shown qualitatively in FIG. 1. FIG.
1 is a representative diagram of a two phase system for pure water.
Actual temperature and pressure may vary considerably, for example
the critical temperature increases with increasing salt, metal or
mineral concentration, etc. Solubility variation when crossing the
pseudocritical temperature line 4 happens extremely rapidly such as
that which occurs at the exit of a black smoker vent. Solubility
variation within the superheated region below the super critical
line to and to the right of the saturation curve 1, results in
precipitation occurring very slowly. This is what occurs in a
normal well such as Reykanes well #9 [10], when the fluid cools
slowly over the length of the pipe to produce scaling and plugs in
the pipe.
[0048] In the diagram of FIG. 1 the fluid acts as a two phase
mixture of a more pure water phase and a highly saline brine phase
in the highly soluble region 3. The brine phase is mostly
responsible for the transport of the metals, minerals and the
salts. The brine can precipitate as sticky salts even within the
highly soluble region. These salts may become anhydrous and form a
solid coating. Since the brine will carry the metals, minerals and
the like, some one these will likely precipitate along with it.
Injecting a boundary layer of cold water will prevent this. As the
fluid passes outside of the highly soluble region across the
pseudocritical temperature line 4, the salts become redissolved in
the water and hence may no longer carry the metals as dissolved ion
complexes although this chemistry is poorly understood at present.
Precipitation occurs much faster here. In general solubility is a
function of both pressure and temperature in all regions. As
pressure increases, solubility increase. Also as temperature
increases, solubility increases.
[0049] The instant invention represents an improvement over the
prior art and is based on the understanding from natural systems
such as seafloor vents that hydrothermal fluid exists as a
supercritical fluid before exiting any hydrothermal vent. The
hydrothermal fluid contains valuable gases, for example, hydrogen,
methane and the like, supercritical vapour-like water and a brine
of dissolved minerals and for metals. Shifting the hydrothermal
fluid away from being a supercritical fluid causes the minerals to
precipitate out of solution. Thus, as long as the hydrothermal
fluid is within the very high solubility region (see FIG. 1), it
will transport the minerals and metals dissolved in solution and
suspended or dissolved in the brine phase. Moving outside of this
region or otherwise reducing the solubility of the water, for
example, by altering pH, will cause the minerals and metals to
precipitate out of solution. As discussed above, in the prior art
methods, precipitation occurs gradually as the brine travels up the
pipe. In the instant invention, the supercritical fluid is shocked,
for example, by rapidly or dramatically reducing the temperature of
the fluid, thereby causing the minerals and metals to precipitate
out of solution. This is identical to that which occurs at the exit
of a black smoker vent on the ocean floor causing the metal
sulfides to precipitate as fine (micrometer sized) particles [5].
The resulting slurry is then brought to the surface with minimal
scaling of the pipe. In fact, the metal sulfide particles should
continuously scrub the pipe walls and keep them clean of any other
deposition problems. On land, the individual metals and/or minerals
may then be separated and/or isolated using means known in the art.
Similarly, valuable gases will exit the solution as the fluid
de-pressurizes and hence, will also be brought to the surface by
this method and stored or incorporated into fuel cells, as
described below. As can be seen in FIGS. 3-4, in some embodiments,
cold water is used to dramatically reduce the temperature, and
thereby the solubility of the fluid, although other suitable means
may also be used. A further aspect of the invention is directed to
slurries, gases and minerals recovered by the instant method.
[0050] It is of note that under certain conditions which depend on
the local hydrostatic gradient in the ground, it may be necessary
to add some pumping force (or equivalent lift) at the well location
to ensure large wellhead pressures and hence, large flow rates. In
yet other embodiments, the method includes pump means for drawing
the slurry to the surface. The pump means may comprise for example,
an air-lift pump wherein air is added to the injected cold water to
increase the lift by reducing the density of the mix; or a Venturi
pump or Jet Pump, wherein the pumping power of the injected fluid
is used to add additional motive (pumping power) at the downhole
location where the device is. Another possibility is the use of
down-hole pumps similar to that used in geothermal energy systems
today.
[0051] The point at which the water temperature ceases to be a
supercritical fluid is referred to as the pseudo-critical
temperature line. As will be appreciated by one of skill in the
art, solubility can vary-by orders of magnitude across the
pseudo-critical line [4]. In one embodiment of the instant
invention, shock precipitation occurs while crossing the
pseudo-critical temperature line.
[0052] It is of note that even in the highly soluble region where
water exists as a supercritical fluid, the material exists in two
phases--purer vapour-like water and a brine. As the fluid passes
outside of the highly soluble region across the pseudo-critical
temperature line, salts become re-dissolved in the water and hence
can no longer carry the metals as dissolved in ion complexes. As
will be appreciated by one of skill in the art, other suitable
means which reduce the solubility of the supercritical fluid may
also be used. As discussed above, the minerals precipitating out of
solution form a slurry which is then transported up the well
pipe.
[0053] As will be appreciated by one of skill in the art, the
solubility shock or pseudo-critical temperature line may be
established anywhere along the length of the well pipe, provided
that the water in the hydrothermal fluid is in the supercritical
state. That is, the shock zone does not need to be established near
the well hole but may be established up the well pipe, as discussed
below.
[0054] Turning now to FIGS. 3 and 4, two embodiments of the well
pipe 25 of the tubing string are illustrated in further detail. The
common features of both will first be described herein. In each
instance the well pipe includes a first conduit in the form of an
extraction pipe 11 for collecting the hydrothermal fluid at an
inlet 14 at a bottom end thereof. Pumps may be provided along the
extraction pipe partway along the pipe or above ground at the well
head 24. The well pipe 25 also includes a second conduit in the
form of an injection pipe 12. The injection pipe 12 acts as a
conduit for receiving an injection fluid 16 which acts as a
solubility reducer to cause precipitation within the hydrothermal
fluid when the injection fluid is injected into the hydrothermal
fluid. The pipes 11 and 12 may be concentric with one another or
positioned alongside one another so as to both extend the full
length of the well pipe 25. At the bottom of the injection pipe 12
a suitable end cap 13 is provided adjacent the inlet 14 of the
extraction pipe. Injection hole 15 are provided which communicate
between the extraction pipe and the injection pipe near the bottom
free end of the well pipe spaced above the inlet 14, downstream
therefrom. The injection holes 15 may comprise a series of nozzles
directed from the injection pipe into the extraction pipe which are
suitably oriented to direct the injection fluid into the direction
of flow of the supercritical fluid drawn up through the inlet 14
towards the well head 24. In other variations the injection holes
may comprise the holes in a porous wall separating the extraction
pipe from the injection pipe. In this arrangement the injection
fluid is forced through the porous wall into the extraction pipe to
come into contact with the supercritical fluid to cause
precipitation thereof by rapidly reducing solubility. The
continuous flow through the porous wall prevents scaling on the
porous wall itself or around the injection holes 15.
[0055] Turning now more specifically to FIG. 3, the extraction pipe
11 is located concentrically within the injection pipe 12 so that
the end cap 13 generally comprises an annular plate sealing the
annular opening at the bottom end of the injection pipe. Fluid 16
forced down into the injection pipe is thus forced through the
injection holes inwardly towards the extraction pipe 11. The inlet
14 of the extraction pipe is centrally located at the bottom free
end of the well pipe.
[0056] As illustrated in FIG. 4 the injection pipe 12 is instead
concentrically located within the extraction pipe 11. The inlet 14
thus comprises an annular opening at the bottom free end of the
well pipe which surrounds the end cap 13 sealing the bottom end of
the injection pipe 12 closed.
[0057] In further arrangements, the injection holes 15 may be
oriented to produce a cyclone effect when the injector pipe is
located externally of the extraction pipe and the injection fluid
16 is accordingly directed inwards to an interior of the centrally
located extraction pipe 11. The injection fluid in some instances
may include a suspension of particles to help nucleate salt
particles and/or continuously scrub the lower pipe entrance. When
the injectors are oriented to produce a hydro cyclone, the heavy
particles will tend to stay along the walls for scrubbing action.
Centrifugal force will keep them along the wall. Absorbent type
materials may also be added to the injection fluid to nucleate
sulphides and prevent them from sticking to the walls. Fresh cold
water may be used as the injection fluid 16 as the solubility of
mineral salts in fresh water increase dramatically as you cool
through the pseudocritical temperature line, for example when the
injected water is fresh water with no salt. Hence the salts
attempting to form at the wall would be continuously dissolved.
[0058] In further embodiments selective wall coatings may be
provided to prevent adhesion of sticky salts in particular.
Electrical inductance heating of the inner pipe to raise the
adjacent fluid and scale into the high solubility region may be
desirable. Further prevention of plugging would likely result. Jet
pumps may be provided at the well head 24 to prevent possible flow
reversal due to increasing fluid density in the pipe with respect
to the surroundings as the mix is cooled. The prevention of sub
surface blowouts is also a desirable effect.
[0059] In the first embodiment of the invention shown in FIG. 3,
the well pipe comprises two pipes--a first pipe for withdrawing the
material and a second pipe containing a coolant, in which the first
pipe is within the second pipe. As will be apparent to one of skill
in the art, other suitable arrangements may also be used, provided
that the shocking agent or coolant is able to rapidly reduce the
solubility of the contents of the first pipe, for example by
reducing the temperature of the contents of the first pipe, thereby
shocking the minerals and metals out of solution. In some
embodiments, the coolant is water. Other coolants may include
saltwater or water with additives to perform such functions as
adjusting the pH. In other embodiments the material introduced may
be water or steam or other fluid with characteristics to adjust the
pH or chloride content of the hydrothermal fluid while maintaining
the temperature and hence buoyancy of the hydrothermal fluid.
[0060] In other embodiments, the walls of the pipes may be coated
with compounds known in the art for preventing or reducing adhesion
and/or corrosion.
[0061] In yet other embodiments, the first pipe may be arranged to
include electric inductance heating for raising the temperature of
the material, thereby preventing plugging of the pipe.
[0062] In yet other embodiments, the first pipe may be arranged to
include electric inductance heating for raising or maintaining
temperature of the material and the first pipe may be arranged to
have pressure maintained by methods disclosed elsewhere in this
document. This is in order to maintain the hydrothermal fluid in
the supercritical state to surface and ensure that metals/minerals
and gasses remain in solution to be processed at surface.
[0063] Seawater source systems, such as in Iceland, contain
dissolved NaCl resulting in hydrothermal fluid rich in chloride
(Cl.sup.-). The addition of hydrogen, possibly from gases emanating
from the magma chamber. This renders the fluid highly solvent
(acidic) and capable of voraciously stripping metals from the
surrounding vast water-permeable fractured basaltic regions that
overlie the magma chamber.
[0064] The most important variable on metal solubility is the
dissolved chloride (Cl.sup.-) content. Metal solubility is
dependent on Cl.sup.- concentration due to the effect of Cl.sup.-
on the formation of aqueous metal complexes, ionic strength and
charge balance constraints [3-4]. This is apparent when
hydrothermal fluids derived from seawater (rich in dissolved
Cl.sup.- and metals) is compared to hydrothermal fluids derived
from meteoric water (poor in dissolved C.sup.- and hence, metals).
In addition, dissolved Cl.sup.- has a dramatic effect on dissolved
H.sub.2 and H.sub.2S causing both dissolved gases to decrease with
increased Cl.sup.- (gassing-out effect).
[0065] The temperature and the pH of Cl.sup.- bearing hydrothermal
fluids have a significant effect on metal solubility. Metal
solubility increases with an increase in temperature. For example,
copper solubility increases by a factor of four if the temperature
increases from 350.degree. C. to 400.degree. C. Above 400.degree.
C. this can increase further by orders of magnitude. Metal
solubility increases with a decrease in pH. For example there is a
dramatic increase in dissolved Fe and Cu when pH adjusted from 5.0
to 4.8 [11].
[0066] The pressure and degree of oxidation of Cl.sup.- bearing
hydrothermal fluids have an effect on metal solubility. At
subcritical pressures, metal solubility increases with a decrease
in pressure and increases with an increase in degree of oxidation.
The degree of oxidation has a significant effect on metal ratios in
solution. For example, High Fe/Cu ratio of metal content in
solution in relatively reducing conditions, Low Fe/Cu ratio in
relatively oxidizing conditions [10].
[0067] Water in a supercritical state behaves very differently than
ordinary (subcritical) water. Supercritical conditions for pure
water is defined as water at pressures and temperatures greater
than 200 bars and 374.degree. C. respectively whereas supercritical
conditions for seawater (3.2% NaCl) occur at pressures and
temperatures greater than 300 bars and 405.degree. C.
[0068] Supercritical water is highly solvent, particularly if
dissolved Cl.sup.- is present. If dissolved Cl.sup.- is present
supercritical water will separate into a dissolved Cl.sup.- poor
vapour-like water phase and a dissolved Cl.sup.- rich brine phase.
The solubility of Cl.sup.- and hence the solubility of metals, is
significantly higher in the supercritical brine phase than in
sub-supercritical hydrothermal fluids. Large variations of Cl.sup.-
concentration in hydrothermal fluids indicate at least some of
hydrothermal fluids at mid-ocean ridge spreading centres have
intersected the two-phase boundary and unmixed into vapour-like
water and brine components [10].
[0069] Hence, additives to the injected water circuit may be used
that reduce either or both the pH or Cl.sup.- concentration. Pure
water alone, for example, will reduce the Cl.sup.- concentration
and hence, metal solubility. An alkaline such as lime will increase
the pH and hence decrease the metal solubility as well. These
factors may make it possible to precipitate metal sulfides while
still maintaining the temperature within the supercritical state.
This would allow for higher thermal energy extraction and larger
wellhead pressures (by maintaining the buoyancy of the fluid--lower
density).
[0070] The solubility of minerals and metal ions increases
dramatically above the critical point in a water/chloride solution.
Hence, supercritical aqueous chloride solutions circulating through
the bedrock strip metals from the water-permeable rock. Some metal
may be derived from the magma. Therefore, water emanating from a
vent has very high metal concentrations. The solubility of metals
as aqueous chloride complexes in supercritical water can be orders
of magnitude greater than in seawater derived hydrothermal fluids
at lower than supercritical conditions. Evidence of the latter can
be observed at white smoker vents, which predominantly discharge
precipitated sulphates and silica (hence, the white colour), rather
than black smokers, which are at high temperature (supercritical)
and precipitate metal-sulphides (which results in black rather than
white suspended particulates).
Benefits Over Conventional Land Based Geothermal Systems
[0071] The surrounding rock is highly porous (water permeable)
which is ideal and in fact, far better than conventional land based
geothermal systems.
[0072] No possible shortage of water.
[0073] No possible loss of resource pressure as may occur, over
time, as with conventional land-based geothermal power plants.
[0074] Much higher temperature, hence, much more energy available
per unit mass flow rate than conventional land based systems.
[0075] Higher temperature differences mean higher plant thermal
efficiencies. This means higher power outputs for a given cycle
size (e.g. flow capacity).
[0076] Minerals and gases exist in significant quantities and may
be extracted.
[0077] Since local seawater temperatures are near 0.degree. C.,
precipitation occurs naturally on the seafloor. The result has been
the formation of enormous metal-sulphide deposits at vent sites.
Such sulphide deposits are in a continuous flux with the
surrounding fluids. Deposition and dissolution into the surrounding
seawater occurs continuously. Dissolution occurs since the
sulphides are not in chemical equilibrium with the surrounding
seawater.
[0078] In yet another embodiment of the invention, there is
provided a method, which involves drilling to a location where
temperature and pressure conditions are supercritical and then
bringing the fluids in a quasi-isothermal fashion to the surface,
where pressure and temperature conditions are lower. Hence,
precipitation can be delayed until the fluid reaches the surface.
Such a process will also help dissolve existing overlying
metal-sulfide deposits. Dissolved minerals will be deposited and
sent for further processing or possible extraction technologies may
be developed to selectively precipitate the metals out of solution
at the well location. Unused process water could be returned via
re-injection well after the metals and minerals are removed and
thus this is essentially an environmentally benign process.
[0079] The continuous sustainable energy obtainable from
supercritical hydrothermal fluids is enormous. For example, a
6-inch diameter hydrothermal vent can have the equivalent thermal
capacity of a small commercial power stations electrical capacity
(around 60 MW). The energy flux from such systems far exceeds that
of an equivalent oil or gas stream. Water temperatures can exceed
550.degree. C. and by drilling deeper it is likely that one can
attain temperature as high as metallurgicaly possible.
Supercritical power cycles promise to produce affordable
energy.
[0080] Current drilling technologies can reach depths in excess of
5 km. Basalt is a volcanic rock that results from the cooling of
lava and is highly fractured in such systems. These fractures occur
during the thermal cycle of the basalt.
[0081] The large amount of dissolved metal and gases present will
likely render this enormous amount of energy as a by-product of the
metals and gas recovery. Such a high temperature energy source
could be used in-situ for many extraction technologies such as;
metal extraction methods, thermal catalytic splitting of water into
hydrogen and oxygen, liquefying hydrogen cryogenically etc.
[0082] Storage methods for hydrogen are being investigated
worldwide. One of the most promising to date is carbon fibre
nanotubes (adsorption storage), which could probably be used to
economically store and ship pure H.sub.2. Fuel cells operating on
methanol emit greenhouse gases such as CO.sub.2. Conversely,
H.sub.2 cells are environmentally benign and produce only water
vapour. An ultimate long-term objective is to evaluate, design and
extract hydrothermal resources in a sustainable manner. Fuel cells
operating on hydrogen are environmentally benign with water vapour
as the only by-product. Currently, barriers to a hydrogen economy
are fuel cell costs, vehicle storage, distribution infrastructure
and a sustainable hydrogen source. Transportation fuel cells will
be commercial in the next few years. Highly improved storage
methods on vehicles such as metal hydrides and carbon nanotubes are
at the early research level but offer promise. Larger scale storage
and distribution can be rationalized using extensions of existing
technologies. However, sustainable large-scale hydrogen sources are
problematic as electrolysis and other conversion technologies are
relatively inefficient, which is a problem when using power from
limited renewable sources, even for off-peak hydroelectric and
natural gas reforming. Finding sustainable hydrogen sources would
eliminate greenhouse gases and emission problems in general. It
would also help solve a large number of associated environmental
problems such as resource extraction concerns and land and water
pollution.
[0083] The whole concept of hydrogen as a clean energy source is
predicated on producing hydrogen without damaging the environment.
Using conventional fossil energy sources to produce hydrogen could
be worse than their direct use, when considering the low conversion
efficiency. The need for a clean, large, and relatively benign
source of energy is crucial. One such source is land-based
geothermal energy. Iceland, for example, has been chosen as a model
for a hydrogen based economy in the near future. Iceland is blessed
with significant land-based geothermal sources and hence, their use
to produce hydrogen makes good environmental and economic sense.
Similar saline hydrothermal resources exist worldwide.
[0084] According to the present invention hydrothermal mining is
accomplished by withdrawing a quantity of hydrothermal fluid from a
magma fluid source surrounding a hydrothermal vent adjacent a land
based well head. The hydrothermal fluid comprises a brine phase and
a supercritical water phase. The solubility of the hydrothermal
fluid is rapidly reduced from the high solubility region across the
high solubility line or pseudocritical temperature line to cause
precipitation which separates the fluid into water and a slurry of
precipitated metals, minerals and salts. In the process valuable
gases including hydrogen and methane may be released from the fluid
and captured. The solubility may be rapidly reduced by shocking the
supercritical fluid into a sub-supercritical state. This may be
accomplished by lowering the temperature of the supercritical fluid
by injecting a solubility reducer in the form of a coolant.
Alternatively the pH of the supercritical fluid may be adjusted by
injecting a suitable solubility reducer to affect pH of the fluid
and thereby rapidly reduce the solubility by shocking. In a further
variation, the solubility reducer which is injected may comprise a
chloride content adjuster to thereby affect the solubility in the
fluid. Any combination of the solubility reducers may be used. When
solubility is adjusted using pH or chloride content as the active
means the fluid may be maintained at high temperature as it is
brought up the well pipe by providing an insulated pipe to make the
best use of captured heat from the fluid. Alternatively the fluid
may be cooled just below the supercritical line, for example just
below 350.degree. C. so as to cause precipitation, and then this
high temperature fluid can be maintained isothermally again using
an insulated pipe for capturing as much heat as possible. Ideally
the injection of the solubility reducer occurs near the bottom end
of the well pipe 25 spaced slightly above the inlet just downstream
therefrom. The slurry is then brought up to the well head for
isolation of the water and precipitated particles above ground. The
method may include injecting air into the solubility reducer within
the second conduit for subsequent injection into the first conduit
with the solubility reducer to provide lift to the hydrothermal
fluid within the first conduit.
[0085] While the preferred embodiments of the invention have been
described above, it will be recognized and understood that various
modifications may be made therein, and the appended claims are
intended to cover all such modifications which may fall within the
spirit and scope of the invention.
REFERENCES
[0086] 1. Fraser D. W. H. "Hydrogen From High Temperature Saline
Geothermal Systems", Hydrogen and Fuel Cells Conference, June 8-11,
Available on CD, Vancouver (2003).
[0087] 2. Fraser, D. W. H., "Ocean Hydrothermal Resources", First
International Workshop for The Icelandic Deep Drilling Project,
Reykjavik, Iceland, on CD, March (2002).
[0088] 3. Berndt, M. E., and Seyfried, W. E. "Boron, Bromine and
Other Trace Elements as Clues to the Fate of Chlorine in Mid Ocean
Ridge Vent Fluids", Geochim. Cosmochim. Acta, 54, 2235-2245,
(1990a).
[0089] 4. Berndt, M. E., and Seyfried, W. E. "D/H Fractionation and
Partitioning of Trace and Major Elements During Phase Seperation of
NaCl Dominated Fluids at 400-450 Degrees C., 250-450 bars", Eos
Trans, AGU, 73, 650, (1992).
[0090] 5. Feely, R, Massoth, J et. Al., "Composition and
Sedimentation of Hydrothermal Plume Particles From North Cleft
Segment, Juan De Fuce Ridge", Jrnl. Of Geophysical Research, Vol.
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[0091] 6. Fridleifsson, O., Elders, W. A., Saito, S., "Drilling
into Supercritical Fluid in Iceland", WRI 10, 2001
[0092] 7. Fridleifsson, G. O. & Albertsson A. 2000. Deep
Geothermal Drilling on the Reykjanes Ridge. Opportunity for
International Collaboration. Proceedings World Geothermal Congress
2000: 3701-3706.
[0093] 8. Scott, Steve, "Deep Ocean Mining",
"http://www.cseg.ca/conferences/2000/727.PDF"
[0094] 9. Anonymous,
"http:/lwww.geology.utoronto.ca/marinelab/intro/"
[0095] 10. Vigdis Haroardottir, Orkusofnun Geoscience Division,
Grensasvegur 9, 108 Reykjavik, Iceland, Private Communication and
Internal OS report.
[0096] 11. Seyfried, W, Ding, K. D., "Phase Equilibria in
Subseafloor Hydrothermal Systems: A Review of the Role of Redox,
Temperature, pH and Dissloved Cl on the Chemistry of Hot Spring
Fluids at Mid-Ocean Ridges", Geophysical Monograph 91, (1995).
* * * * *
References