U.S. patent application number 11/648936 was filed with the patent office on 2007-07-19 for system for drilling the ground to obtain circulation of fluid in a plant for the exploitation of geothermal energy.
This patent application is currently assigned to SOILMEC S.p.A.. Invention is credited to Davide Trevisani.
Application Number | 20070163805 11/648936 |
Document ID | / |
Family ID | 37912506 |
Filed Date | 2007-07-19 |
United States Patent
Application |
20070163805 |
Kind Code |
A1 |
Trevisani; Davide |
July 19, 2007 |
System for drilling the ground to obtain circulation of fluid in a
plant for the exploitation of geothermal energy
Abstract
A system for high-depth drilling of the ground aimed at reaching
hot rocks for extraction of geothermal energy by means of
introduction of a heat-conveying fluid and extraction thereof after
adequate heating uses just one borehole containing two coaxial
tubes: an internal tube (3, 11, 13), through which the cold fluid
is introduced, and an external or coating tube (4, 6), through
which said fluid returns to the surface after it has been heated by
the hot rocks either directly or through said coating tube.
Inventors: |
Trevisani; Davide; (Cesena
(FO), IT) |
Correspondence
Address: |
MERCHANT & GOULD PC
P.O. BOX 2903
MINNEAPOLIS
MN
55402-0903
US
|
Assignee: |
SOILMEC S.p.A.
Cesena (FO)
IT
|
Family ID: |
37912506 |
Appl. No.: |
11/648936 |
Filed: |
January 3, 2007 |
Current U.S.
Class: |
175/11 ;
175/17 |
Current CPC
Class: |
Y02E 10/10 20130101;
F24T 10/20 20180501; F24T 10/10 20180501; E21B 17/18 20130101; Y02E
10/14 20130101; Y02E 10/12 20130101 |
Class at
Publication: |
175/011 ;
175/017 |
International
Class: |
E21B 7/14 20060101
E21B007/14 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 13, 2006 |
IT |
TO2006A000021 |
Claims
1. A system for high-depth drilling of the ground aimed at reaching
hot rocks for extraction of geothermal energy by introduction of a
heat-conveying fluid and extraction thereof after adequate heating,
said system comprising one borehole containing two coaxial tubes:
an internal tube, in which introduction of the fluid is carried
out, and an external or coating tube, along which said fluid
returns to the surface after it has been heated by the hot rocks
either directly or through said coating tube.
2. The system according to claim 1, wherein the internal tube is
thermally insulated to minimize passage of heat between the
descending fluid and the ascending fluid.
3. The system according to claim 1, wherein the external tube is
thermally insulated with the exception of a portion in contact with
the hot rock.
4. The system according to claim 1, wherein the external tube is
closed at the end and extends throughout the length of the piping,
wherein the internal tube for introduction of fluid terminates at a
small distance from the end of the external tube.
5. The system according to claim 1, wherein the fluid returns to
the surface inside the external tube, after it has been heated by
the hot rocks through said tube that is in direct contact with the
hot rocks.
6. The system according to claim 1, applied to fractured rocks,
wherein the dispersion of fluid is small, wherein the internal tube
extends beyond the end of the external tube, with a first portion
and a second portion that is not coated for introduction of the
fluid into the fractured rock through said second portion and its
recovery in an area corresponding to the final mouth of the
external tube.
7. The system according to claim 6, wherein the main borehole is
drilled inside the hot rock without any coating for a certain
section, beyond which the internal tube extends.
8. The system according to claim 6, wherein the first portion of
internal tube is cemented to the rock, from where the portion that
is not coated of the main borehole terminates as far as where the
second portion of internal tube starts, to cause return of the
heated fluid only through the cracks of the rock up to the second
portion that is not coated of the main borehole.
9. The system according to claim 6, wherein the internal tube is
thermally insulated.
10. The system according to claim 6, wherein the external tube is
thermally insulated.
11. The system according to claim 6, wherein the internal tube
branches off in a plurality of branches to increase the surface of
infiltration of the fluid in the rock.
12. The system according to the claim 1, wherein a portion of tube
in contact with the hot rock is deviated in a nearly horizontal
direction to increase the length of path useful for heat exchange
in the case where the hot layer is of small depth.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to the sector of exploitation
of geothermal resources for the purpose of production of electrical
and heating energy.
[0002] More in particular, the invention regards a system for
drilling the ground aimed at enabling circulation of fluid in a
plant for the exploitation of geothermal energy.
[0003] Known to the art is the idea of exploiting the heat of hot
dry rocks, which are present over a large part of the Earth's
surface at a depth of over three thousand meters. In these rock
masses the temperature is between 200.degree. C. and 300.degree.
C., and there is no presence of water.
[0004] For the extraction of heat, it is possible to resort to a
conveying fluid such as water, which, however, is to be purposely
introduced into the rock mass, heated by contact, and then
extracted in the state of superheated water or steam.
[0005] Up to now, one approach has been to make boreholes for
introduction of the fluid and boreholes for its extraction, between
which a continuous circulation of the heat-conveying fluid is set
up. This system envisages that the step of heating prevalently
occurs during passage from a borehole of the first type to a
borehole of the second type, a passage that develops through the
natural or artificially induced porosities and cracks in the
rock.
[0006] The patent application No. RM2002A000521, filed in the name
of D'Offizi, describes a first exploitation system by sinking a
vertical shaft of a mining type that leads to a network of
horizontal galleries within the rock mass. Departing from these
galleries are subhorizontal boreholes for introduction and
extraction of the circulation water.
[0007] The patent application No. TO2005A000797, filed in the name
of the present applicant, describes a second exploitation system by
initially sinking vertical shafts with subsequent deviation in a
horizontal direction and multiple branches to widen as much as
possible the extension of the area of influence of each individual
shaft.
[0008] This latter system, which is already much less costly than
the former, as compared to the most obvious solution constituted
just by vertical shafts with a small stretch within the hot rock
achieves two purposes, namely, that of limiting the cost of the
vertical passive part of the shaft with respect to the horizontal
useful part, and that of limiting the number of vertical shafts and
hence the area of the installation on the surface from which the
shafts depart.
SUMMARY OF THE INVENTION
[0009] One purpose of the present invention is to achieve a further
considerable limitation of the costs of installation of this latter
solution.
[0010] A further purpose of the present invention is to enable heat
exchange to be ensured even in unfavourable cases, such as the ones
in which the natural fracturing of the rocks is very extensive, up
to the point where the fluid introduced could dissipate without any
possibility of recovery.
[0011] In order to achieve the above purposes, the subject of the
invention is a system for drilling the ground in order to enable
circulation of fluids in a plant for exploitation of geothermal
energy according to claim 1, in which in order to obtain a
circulation of fluid just one borehole is used.
[0012] A tube must be inserted within the borehole for introduction
of the cold fluid, whilst the annular gap between the internal tube
and the wall of the borehole is used for extracting the heated
fluid, in countercurrent. In order to minimize the heat exchange
between the two fluids, the internal tube will be appropriately
thermally insulated.
BRIEF DESCRIPTION OF DRAWINGS
[0013] The invention will now be described in two preferred
embodiments thereof with reference to the annexed plate of
drawings, in which:
[0014] FIG. 1 is a side-on profile of the typical borehole for
excessively fractured rocks;
[0015] FIG. 2 is a top plan view of the same borehole;
[0016] FIG. 3 is a side-on profile of the typical borehole for
rocks with modest dispersion; and
[0017] FIG. 4 is a top plan view of the latter borehole.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] In FIGS. 1 and 3, the reference number 1 designates the soil
and rock cover that is to be traversed in order to reach the bank
of hot rock 2.
[0019] In excessively fractured ground (see FIGS. 1 and 2), a
borehole of large diameter is drilled, within which a piping made
up of two coaxial tubes is inserted. In FIG. 1, the reference
number 3 designates the internal tube, which is thermally insulated
and is designed for the introduction of cold fluid into the rock.
The reference number 4 designates the external tube for extraction
of the hot fluid, which is cemented and coated.
[0020] The hole for return of the hot fluid to the surface carries
inside it the stretch of thermally insulated tube 9.
[0021] The reference number 7 designates, as a whole, the active
area, and the reference number 8 the passive area.
[0022] According to the invention, the external coating tube 4 must
be closed at the end and must extend throughout the length of the
piping. The internal tube 3 for introduction of water terminates at
a small distance from the end of the external tube, as may be noted
once again in FIG. 1.
[0023] The arrows of FIG. 1 indicate the direction of advance of
the fluid which is initially cold and subsequently hot.
[0024] In this way, the external wall of the external tube 4
functions as heat-exchange surface directly in contact with the hot
rock. Its length in the hot area will have to be as extensive as
possible. With the cost of just one borehole it will thus be
possible to provide a complete closed circuit for introduction,
heating, and extraction of the fluid, preventing any dispersion in
the excessively fractured rock.
[0025] In ground where the fracturing, whether natural or induced,
is not such as to lead to dispersion of fluid, in the active area
the heat exchange with the rock is optimized by adopting the
solutions described in what follows, illustrated in the embodiment
of FIGS. 3 and 4.
[0026] The main borehole of larger diameter is made in the hot rock
and provided with the coating 6 in its initial stretch, whilst it
remains without any coating for a second stretch 5. Introduced
inside said borehole is a battery of rods 11 of smaller diameter,
which provides the hole designed for introduction of the fluid.
[0027] The complete plant envisages a terminal stretch 13, which
extends from the free end of the rods 11, is not coated, and has
the purpose of diffusing the cold fluid in the rock, using a large
area of contact (see arrows in FIGS. 3 and 4).
[0028] The stretch of rods 11, which is coated, is also thermally
insulated and cemented in the borehole. The length of said stretch
increases the path that the fluid introduced from the end must
follow in order to reach the borehole for return to the surface.
Cementing closes the most direct return path, i.e., the one that
immediately surrounds the internal tube, which is the less
efficient one in terms of heat exchange, since it does not extend
into the cracks and porosities.
[0029] The stretch of borehole 5 with larger diameter is not
instead coated and its purpose is to offer a wide area of
collection of the heated fluid.
[0030] The rest of the borehole up to exit from the ground is
preferably coated to prevent any dispersion of fluid and houses
inside it the thermally insulated tube 9 for introduction of the
cold fluid. Said stretch starts from the bank of hot rock 2 and
arrives at the surface, as has been seen in the case of the first
embodiment of FIGS. 1 and 2.
[0031] Indicated with the arrows in FIGS. 3 and 4 is the preferred
direction of circulation of the fluid, but it is understood that
said direction of circulation of the fluid can be opposite to the
one described by way of example, without thereby altering the
characteristics and advantages of the device.
[0032] In FIG. 4 it may be noted that the internal tube 13 can
branch off into a certain number of branches to increase the
surface of infiltration of the fluid in the rock.
[0033] Finally, it is advantageous for the stretch in contact with
the hot rock to be deviated in a nearly horizontal direction to
increase the length of path useful for heat exchange, in the case
where the hot layer is of small depth.
* * * * *