METHOD FOR CONTROLLING THE PRESSURE IN AN UNDERGROUND STORAGE VOLUME

Abstract

A method for controlling the pressure in an underground storage volume, wherein the underground storage volume is at least in part filled with an incompressible fluid, the pressure is monitored, a compressible fluid can be introduced into and extracted from the underground storage volume, if the pressure reaches a predetermined upper pressure limit incompressible fluid is extracted from the underground storage volume for reducing the pressure in the underground storage volume; if the pressure volume reaches a predetermined lower pressure limit incompressible fluid is introduced into the underground storage volume for increasing the pressure in the underground storage volume. The method according to the present invention allows the increase the amount of compressible fluid like helium stored in an underground storage volume, e.g. a salt cavern, by adjusting the pressure by the introduction or extraction of an incompressible fluid like brine.

Claims

1. A method for controlling the pressure in an underground storage volume, wherein the underground storage volume is at least in part filled with an incompressible fluid, wherein the pressure within the underground storage volume is monitored, wherein a compressible fluid can be introduced into and extracted from the underground storage volume, wherein if the pressure within the underground storage volume reaches a predetermined upper pressure limit (p.sub.max) incompressible fluid (7) is extracted from the underground storage volume for reducing the pressure (p) in the underground storage volume; wherein if the pressure within the underground storage volume reaches a predetermined lower pressure (p.sub.min) limit incompressible fluid is introduced into the underground storage volume for increasing the pressure in the underground storage volume.

2. The method of claim 1, wherein the introduction or extraction of the compressible fluid is terminated if while introducing compressible fluid the upper pressure limit (p.sub.max) is reached or if while extracting compressible fluid the lower pressure limit (p.sub.min) is reached.

3. The method of claim 2, wherein the introduction or extraction of the compressible fluid is terminated as long as at least one of the following conditions is fulfilled: a) a predetermined delay since the beginning of the termination is elapsed; and b) a predetermined pressure level has been reached.

4. The method of claim 1, wherein the incompressible fluid is delivered to a reservoir after extraction from the underground storage volume and is delivered from the reservoir to the underground storage volume for introduction into the underground storage volume.

5. The method of claim 1, wherein the compressible fluid is at least one of nitrogen, air, carbon dioxide, hydrogen, helium, and argon.

6. The method of claim 5, wherein the compressible fluid is introduced to and extracted from the underground storage volume in the gaseous state.

7. The method of claim 1, wherein the incompressible fluid is at least one of brine, water and water slurry.

8. The method claim 1, wherein the compressible fluid is dehumidified after extraction from the underground storage volume.

9. The method of claim 8, wherein the dehumidification is performed by guiding the compressible fluid through a molecular sieve.

10. The method of claim 1, wherein hydrocarbons are removed from the compressible fluid.

11. The method of claim 10, wherein the compressible fluid is guided through a bed of activated carbon for the removal of hydrocarbons.

12. The method of claim 1, wherein atmospheric contaminants such as oxygen, nitrogen, carbon hydroxide are removed from the compressible fluid by pressure swing adsorption.

13. The method of claim 1, wherein the underground storage volume is an underground salt cavern.

14. The method of claim 1, wherein if compressible fluid has to be introduced into the underground storage volume the following steps are performed at least once: a) reducing the pressure in the underground storage volume by extracting incompressible fluid, and b) introducing the compressible fluid.

15. The method of claim 1, wherein if compressible fluid has to be extracted from the underground storage volume the following steps are performed at least once: ) extracting compressible fluid from the underground storage volume; and ) introducing the incompressible fluid to increase the pressure in the underground storage volume.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] It should be noted that the individual features specified in the claims may be combined with one another in any desired technological reasonable manner and form further embodiments of the invention. The specification, in particular in connection with the figures, explains the invention further and specifies particularly preferred embodiments of the invention. Particularly preferred embodiments of the invention and also the technical field will now be explained in more detail on the basis of the enclosed figures. It should be noted that the exemplary embodiments shown in the figures are not intended to restrict the invention. The figures are schematic and may not be to scale. The figures display:

[0043] FIG. 1 a sample diagram of a pressure in an underground storage volume; and

[0044] FIG. 2 an example of an equipment to perform the method for controlling the pressure in an underground storage volume.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0045] FIG. 1 displays the evolution of the pressure p in an underground storage volume against the time t. The underground storage volume is an underground salt cavern which has due to the geological properties a maximum pressure and a minimum pressure. It is filled both with an incompressible fluid, in this example brine, and a compressible fluid, in this example helium. It is used to store helium. Therefore, helium needs to be introduced and extracted from the underground storage volume frequently.

[0046] If the pressure p in the underground storage volume is above the maximum pressure or below the minimum pressure the structural integrity of the underground storage volume is endangered. Therefore, the pressure p in the underground storage volume is controlled to be within a predetermined pressure interval having a predetermined lower pressure limit p.sub.min and a predetermined upper pressure limit p.sub.max which is well in between the maximum pressure and the minimum pressure. This ensures that the underground storage volume can be used without structural damage of the same.

[0047] Starting from a starting pressure 1 which is close to the upper pressure limit p.sub.max the need for storing more helium arises. If now in this situation helium would be introduced into the underground storage there would be the risk of structural damage to the underground storage volume. Therefore, first of all the pressure in the underground storage volume is reduced by extracting brine 2 from the underground storage volume until a pressure slightly above the lower pressure limit p.sub.min. Then, helium is introduced in step 3 into the underground storage volume until a pressure close to the upper pressure limit p.sub.max has been reached. Then, in another step of extracting brine 2 the pressure is again reduced until a pressure close to the lower pressure limit p.sub.min has been reached. In another step of introducing helium 3 into the underground storage volume another amount of helium is introduced into the underground storage volume. Now, for some time the pressure is kept constant in the underground storage volume until it is necessary to extract helium in a helium extraction step 4. Thereafter, to bring the pressure back to a pressure close to the upper pressure limit p.sub.max a step of introducing brine 5 to the underground storage volume is performed.

[0048] FIG. 2 displays schematically an equipment used to control the pressure in an underground storage volume 6 being a salt cavern. The underground storage volume 6 is filled partly with an incompressible fluid 7 namely brine and a compressible fluid 8 namely helium. The underground storage volume 6 is used to store the compressible fluid 8 which is to be extracted from the underground storage volume 6 in case of need and which has to be introduced into the underground storage volume 6 if it is needed to store the compressible fluid 8. If it is necessary to introduce incompressible fluid 7 into the underground storage volume 6 to increase the pressure within the underground storage volume 6 this is done in the base section of the underground storage volume 6 via a brine pipe 9 which is connected via valves 10 to a brine introduction pump 11. The brine introduction pump 11 convey brine as an incompressible fluid from a not shown reservoir through the brine pipe 9 into the bottom region of the underground storage volume 6. If incompressible fluid has to be extracted from the underground storage volume 6 this is done via the brine pipe 9 as well which is connected via a valve 10 to a brine extraction pump 12 to the reservoir. It is well noted that it is possible to combine the functions of the brine introduction pump 11 and the brine extraction pump 12 in one single pump.

[0049] Compressible fluid is introduced and extracted from the underground storage volume 6 via the helium pipe 13 which ends in the upper head section of the underground storage volume 6. Helium is lighter than brine, therefore, helium is collected in the head area of the underground storage volume 6 whereas brine is collected in the bottom area of the underground storage volume 6. The underground storage volume 6 is sealed via the seal 14 to avoid loss of helium.

[0050] In a first helium transporter 15 an amount of helium in the liquid state to be stored in the underground storage volume 6 is provided. This liquid helium is vaporized in a vaporizer 16 and is subsequently compressed in a compressor 17 to be provided via a valve 10 and the helium pipe to the head section of the underground storage volume 6. Instead of a first helium transporter 15 it is of course possible to convey the helium directly from a helium source to the underground storage volume 6.

[0051] In case of an extraction of helium from the underground storage volume 6 the helium is guided via the helium pipe 13 and a valve 10 to a unit 18 for dehumidifying the helium gas comprising a molecular sieve and, subsequently, to a unit 19 for the removal of hydrocarbons including a bed of activated carbon. Subsequently, the helium gas is provided to a liquefier 20 in which the helium gas is liquefied. The liquefied helium gas is provided to an intermediate helium storage 21 from which it can be filled to a second helium transporter 22. Instead of the second helium transporter 22 the helium can be directly provided to a point of use.

[0052] To control the pressure p within the underground storage volume 6 incompressible fluidin this example brineis introduced into the underground storage volume 6 to increase the pressure and is extracted from the underground storage volume 6 to decrease the pressure in the underground storage volume 6. By this the level of incompressible fluid is changing as is displayed by the arrow 23.

[0053] The method according to the present invention allows to increase the amount of compressible fluid like helium stored in an underground storage volume 6, e.g. a salt cavern, by adjusting the pressure by the introduction or extraction of an incompressible fluid like brine.

REFERENCE NUMERALS

[0054] 1 starting pressure [0055] 2 extracting brine [0056] 3 introducing helium [0057] 4 extracting helium [0058] 5 introducing brine [0059] 6 underground storage volume [0060] 7 incompressible fluid [0061] 8 compressible fluid [0062] 9 brine pipe [0063] 10 valve [0064] 11 brine introduction pump [0065] 12 brine extraction pump [0066] 13 helium pipe [0067] 14 seal [0068] 15 first helium transporter [0069] 16 evaporator [0070] 17 compressor [0071] 18 unit for dehumidifying [0072] 19 unit for the removal of hydrocarbons [0073] 20 liquefier [0074] 21 intermediate helium storage [0075] 22 second helium transporter [0076] 23 change of level of incompressible fluid [0077] p pressure [0078] p.sub.max upper pressure limit [0079] p.sub.min lower pressure limit [0080] t time