UNDERGROUND STORAGE SYSTEM FOR FLUID STORAGE

Abstract

An underground storage system for storing fluid includes a hole having a bottom, a support element including at least one opening able to receive a joining element, at least one reservoir having a longitudinal axis, a bottom end and a top end, a first closure able to close the reservoir at its bottom end, and a second closure able to close the reservoir at its top end. The top end is able to be joined to the support element via the joining element such that the reservoir is hung inside the hole and such that an axial clearance able to absorb axial thermal expansion of the reservoir remains between the first closure and the bottom.

Claims

1-9. (canceled)

10. An underground storage system for storing fluids, said storage system comprising: a hole made in a ground, said hole having a bottom; a support element comprising at least one opening; a joining element inserted in the opening of the support element; at least one reservoir, said reservoir having a longitudinal axis, a bottom end closed by a first closure means, and a top end closed by a second closure means; the joining element being attached to the top end, and said top end being joined to the support element via the joining element such that the reservoir is hung inside the hole and such that an axial clearance able to absorb axial thermal expansion of said reservoir remains between the first closure means of the reservoir and the bottom of the hole.

11. The storage system according to claim 10, wherein the reservoir comprises at least one metal tube, said metal tube having at least one end provided with at least one threaded portion.

12. The storage system according to claim 10, wherein the reservoir comprises at least two metal tubes screwed to each other so as to form a column of tubes.

13. The storage system according to claim 10, wherein the axial clearance satisfies the following inequality: $\begin{array}{cc}G\left(L^2**\right)+\left[20**80*\left(1-e^{-0.11*L}\right)\right]& \left[\mathrm{Math}1\right]\end{array}$ in which: G is a length of the axial clearance expressed in metres, L represents the length of the reservoir expressed in metres, represents a geothermal gradient expressed in degrees Celsius per metre, and a represents a coefficient of thermal expansion of a metal expressed in metres per degree Celsius.

14. The storage system according to claim 10, wherein the first closure means and/or the second closure means is configured to close the reservoir by screw-fastening.

15. The storage system according to claim 10, wherein said system comprises a plurality of reservoirs, each reservoir having a longitudinal axis, a bottom end and a top end, said top end of each reservoir being able to be joined to the support element via a joining element such that each reservoir is hung inside the hole.

16. The storage system according to claim 10, wherein the hole has at least one casing.

17. The storage system according to claim 16, wherein the casing is made of concrete, cement, or steel.

18. An underground storage method for storing fluids, said method comprising: making a hole in a ground, said hole having a bottom; providing a support element comprising at least one opening able to receive a joining element; providing at least one reservoir, said reservoir having a longitudinal axis, a bottom end and a top end; providing a first closure means configured to close said reservoir at the bottom end, and a second closure means configured to close the reservoir at the top end; and joining said top end to the support element via the joining element, and inserting the reservoir and the joining element in the opening such that the reservoir is hung inside the hole and such that an axial clearance able to absorb axial thermal expansion of said reservoir remains between the first closure means of the reservoir and the bottom of the hole.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0064] The invention will be better understood, and further objects, details, features and advantages thereof will become more clearly apparent during the course of the following description of several particular embodiments of the invention, which are given solely by way of nonlimiting example with reference to the attached drawings.

[0065] It should however be understood that the present application is not limited to the arrangements, structures, features, embodiments and precise appearance that are indicated. The drawings are not to scale and are not intended to limit the scope of the claims to the embodiments shown in these drawings.

[0066] Consequently, it should be understood that where features mentioned in the claims are followed by references, said references are provided exclusively to aid comprehension of the claims and under no circumstances limit the scope of said claims.

[0067] FIG. 1 is a diagram of a sectional view through a storage system according to one embodiment of the invention.

[0068] FIG. 2 is a three-dimensional diagram of the support element of the storage system illustrated in FIG. 1, on its own.

[0069] FIG. 3 is a three-dimensional diagram of an alternative support element, on its own, that can be used in one embodiment of the invention.

[0070] FIG. 4 is a three-dimensional diagram of a joining element that can be used in the storage system illustrated in FIG. 1.

DESCRIPTION OF EMBODIMENTS

[0071] FIG. 1 illustrates a sectional view through a storage system 1 according to one embodiment of the invention, in a coordinate system (x; y). The axis x of the coordinate system (x; y) is a horizontal axis, and the axis y of the coordinate system (x; y) is a vertical axis.

[0072] The storage system 1 comprises a hole 2 made in a ground 40, a support element 4 laid on a surface S of the ground 40, and six reservoirs 10 hung in the hole 2 from the support element 4 (only four reservoirs are shown in FIG. 1).

[0073] The hole 2 has a bottom 3 and comprises a casing 30. The hole 2 can be obtained by boring or by excavating, and has a depth of 500 metres, measured between the ground surface S and the bottom 3. The hole 2 is of substantially circular cylindrical shape and has a mean diameter of 4 metres.

[0074] The casing is made of cement and extends vertically from the ground surface S to the bottom 3 of the hole 2.

[0075] As shown in FIGS. 1 and 2, the support element 4 is a circular cylindrical plate having a central body 50 and a flange 52, said flange 52 having a bottom surface 56 which rests on the ground surface S. The central body 50 has a first thickness E that may range between 10 mm and 500 mm. The flange 52 has a second thickness e which may range between 5 mm and 200 mm. In the embodiment illustrated in FIGS. 1 and 2, the support element 4 is a metal plate in which the first thickness E is equal to 250 mm and the second thickness e is equal to 100 mm.

[0076] The support element 4 also comprises a top surface 54, said top surface 54 being situated opposite the bottom surface 56 of the flange 52, said top surface 54 having a surface area equal to 8.6 m.sup.2.

[0077] As illustrated in FIG. 2, the support element 4 also comprises six openings 7. The openings 7 are through-holes made in the first thickness E of the body 50 of the support element 4. According to FIG. 3, which illustrates a support element 4 that can be used in one embodiment according to the invention, the support element 4 comprises fourteen openings 7 made in the first thickness E of the body 50.

[0078] Each reservoir 10 is hung from the support element 4 via a joining element 18. Thus, for each reservoir 10 of the storage system 1, an axial clearance G remains between the first closure means 16, which closes the reservoir 10 at its bottom end 14, and the bottom 3 of the hole 2. The purpose of this axial clearance G is to absorb any axial thermal expansion of the reservoir 10, which occurs notably during filling and emptying operations. Thus, for each reservoir 10, the dimensioning of the axial clearance G, and notably its length, depends directly on the conditions of the surrounding area of the storage system 1, notably conditions regarding temperature, pressure and the ability of the reservoir 10 to expand when it is subjected to temperature and pressure variations, notably during filling and emptying operations. Thus, the axial clearance G of any reservoir 10 of the storage system 1 satisfies the following inequality:

[00002]$\begin{array}{cc}G\left(L^2**\right)+\left[20**80*\left(1-e^{-0.11*L}\right)\right]& \left[\mathrm{Math}1\right]\end{array}$

in which: G is the length of the axial clearance expressed in metres. L represents the length of a reservoir 10 expressed in metres. represents the geothermal gradient expressed in degrees Celsius per metre. The geothermal gradient varies depending on the geological formation in which the storage system 1 is placed. Thus, is such that 0.02/m2/m. represents the coefficient of thermal expansion of the metal expressed in degrees Celsius.sup.1. The coefficient of thermal expansion varies depending on the type of metal from which the tubes used to form a reservoir 10 are made. Thus, is such that 8*10.sup.6oC.sup.1 18*10.sup.6oC.sup.1.

[0079] The reservoirs 10 are tubular, with a circular cross section, and each have a longitudinal axis (1), a bottom end 14 and a top end 12.

[0080] Each reservoir is closed at its top end 14 by a first closure means 16, and each reservoir 10 is closed at its bottom end 12 by a second closure means 17. In the embodiment illustrated in FIG. 1, the bottom end 14 and the top end 12 of each reservoir 10 are threaded ends, and the first closure means 16 and the second closure means 17 also have a thread, said thread complementing the thread of the bottom end 14 and of the top end 12. As a result, the bottom end 14 is fluidtightly closed by screw-fastening with the first closure means 16, and the top end 12 is fluidtightly closed by screw-fastening with the second closure means 17.

[0081] The second closure means 17 is fitted with sensors 19 which are pressure gauges, thermometers and leak detectors. Of course, the first closure means 16 may also contain pressure gauges, thermometers and leak detectors. Other types of sensors can be used depending on the objective set.

[0082] Each reservoir 10 may be composed of a plurality of tubes A. In the embodiment illustrated in FIG. 1, the reservoirs 10 are composed of multiple threaded tubes A. Thus, the tubes A are screwed to one another so as to form a column C of tubes A. In this way, an assembly composed of a column C, closed at its ends 12 and 14 by the closure means 16 and 17, forms a reservoir 10. A reservoir 10 may also be composed of a single tube A, closed at its ends 12 and 14 by closure means 16 and 17.

[0083] Each reservoir 10 is joined to a joining element 18. Each joining element 18 is inserted in an opening 7 and held there by a flange 62 which abuts the top surface 54 of the support element 4. Each joining element 18 is thus hung from the support element 4. In this way, each reservoir 10 is hung from the support element 4 via the joining element 18 to which it is joined.

[0084] As illustrated in FIG. 4, a joining element 18 is a tubular metal part of circular cross section which comprises a tubular body 60 and a flange 62.

[0085] The body 60 of the joining element 18 is attached, preferably screw-fastened, to the top end 12 of a reservoir 10. It is possible to use welding in an alternative embodiment. The body 60 of the joining element 18 has a complementary male or female thread (not shown) to the thread of the top end 12 of the reservoir 10 to which said joining element 18 is joined. The flange 62 comprises a top surface 64 and a bottom surface 66.

[0086] In the embodiment illustrated in FIG. 1, the tubular body 60 of each joining element 18 is inserted in an opening 7 in the support element 4. Each joining element 18 rests on the support element 4 via its bottom surface 66 which abuts the top surface 54 of the support element 4. In addition, each joining element 18 is screw-fastened to a reservoir 10 at the top end 12 of said reservoir 10.

[0087] The flange 62 of the joining element 18 thus allows the latter to rest on the top surface 54 of the support element 4. As a result, the joining element 18 does not need to be attached to the support element 4, for example by welding or by screw-fastening, thereby making it easier to assemble the storage system 1, notably in order to hang the reservoirs 10.