US3491540A - Method of storing liquids underground - Google Patents

Description

Jam 27, 1970 w. LENNEMA NN METHOD OF STQRING LIQUIDS UNDERGROUND 2 Sheets-sheaf I INVENTOR. William L. Lennemam ATTORNEY.

Jan. 27, 1970 w. L. LENNEMANN METHOD OF STORING LIQUIDS UNDERGROUND 2 SheetsSheet 2 Filed May 21, 1968 I IHU'EH" RwMV INVENTOR. Will/am L.Lennemann 4414 44- ATTORNEY.

United States Patent 3,491,540 METHOD OF STORING LIQUIDS UNDERGROUND William L. Lennemann, Rockville, Md., assignor to the United States of America as represented by the United States Atomic Energy Commission Filed May 21, 1968, Ser. No. 730,853 Int. Cl. B65g 05/00; E2113 17/16 US. Cl. 61-.5 3 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Field of invention This invention pertains to underground storage of liquids and, more particularly, to underground storage of liquids wherein underground water is prevented from leaking into the storage cavern. This invention is useful in storing all types of liquids, especially aqueous liquids (for example aqueous radioactive waste liquids) that would be diluted by the underground water were it to leak into the storage cavern. This invention is also useful in situations wherein only small quantities of liquid to be stored are available at any one time which requires that the storage cavern be maintained in a condition to receive liquid to be stored at all times.

Description of prior art Caverns excavated underground by either conventional mining or dissolution methods are being used to store natural gas and liquid petroleum gas. Caverns sometimes are an economical means of storage because of their relatively low excavation costs, low maintenance costs, and large storage capacities.

Underground storage presents certain difiiculties not found in other methods of storage. The primary difficulty is leakage of underground water into the cavern. Water is prevalent in virtually all earth and rock formations, held in place by subterranean superatmospheric pressures in equilibrium. When a cavern is formed in communication with the surface of the earth the pressure within the cavern becomes atmospheric, resulting in loss of equilibrium. The resulting pressure differential will then cause water to flow into the cavern. The pressure which forces the underground water to leak into the storage cavern is the dilference between the pressure of the hydrostatic head of the water, measured from the top of the water table down to the cavern, and the pressure lost in overcoming the friction exerted by the rock crevices through which the underground water must travel. Underground water leakage into the cavern will reduce storage capacity, dilute miscible liquids, and, unless continually removed or stopped altogether, will eventually fill up the cavern.

This problem of underground Water leakage becomes acute in storing aqueous liquids. Whereas in the storage of hydrocarbons the leaking underground water forms a separate liquid phase which is capable of removal, leaking underground water will mix with the aqueous liquids causing a dilution of the liquids to be stored. In the event the stored aqueous liquid is to be reused at its stored con- 3,491,540 Patented Jan. 27, 1970 ICC centration or lesser concentration, the leakage :would cause the necessity of additional concentration. In storing aqueous radioactive waste liquids the storage could be long term, that is, the liquids are placed in the storage cavern with no foreseeable intent to remove them later. Leaking underground water will mix with the aqueous radioactive waste liquids and reduce the usable storage capacity of the cavern.

Another difficulty encountered in underground storage is in making provisions for gradual addition of liquid to be stored to the storage cavern. In most underground storing, the cavern is completely filled with liquid or gas to be stored. Thereafter, part or all of it is removed from the cavern for subsequent use. In some underground storing, such as storing aqueous radioactive waste liquids, either a relatively small volume of liquid is available for storage at any one time or the rate of addition is small compared to the volume of the cavern. Therefore, the storage cavern must be kept in a condition wherein usable storage capacity is not impaired by underground water leakage into it, and at the same time it is possible to add these small volumes of liquid at spaced intervals or continuously.

The prior art attempts to avoid underground water leakage into caverns concerned chiefly water-proofing (conditioning) the cavern walls, placing in the cavern a tank or cavern lining, or storing in anhydrous rock formations. Conditioning the cavern walls is very expensive and, in some cases, renders underground storage uneconomical compared with other methods. Additionally, earth shifting could cause cracks in the cavern wall conditioning thereby allowing resumption of underground water leakage. Placing a tank or artificial lining in the cavern could be as expensive as surface tank storage. In addition, repair of the tank or lining could be hampered because of limited space between the lining and the cavern walls and by accumulation of the underground water in this space. The requirement for storage in anhydrous rock may be in an area quite removed from such formations and the cost of transporting liquid to be stored to and from the distant anhydrous rock formations would make such storage impractical.

Therefore, one object of this invention is a method of storing liquid underground, overcoming the problem of underground water leakage.

Another object of this invention is to store liquids underground by a method that permits gradual addition of liquid to be stored in the cavern at the same time overcoming the problem of concurrent underground water leakage.

Another object is a method of preventing underground water leakage into existing caverns without the necessity of surfacing the cavern walls or use of containment vessels or where these latter storage methods have failed and concurrently using the cavern for storage of liquid.

A still further object of this invention is to provide an improved method for the storage of aqueous radioactive waste liquids underground.

A still further object of this invention is to provide a method of storing liquid in a cavern underground which is relatively independent of the water bearing nature of the rock forming the cavern.

Other objects of my invention will appear upon reading the description of invention which follows:

SUMMARY OF THE INVENTION The present invention comprises filling an underground cavern with a bulk liquid which is immiscible with and has a diiferent density from the liquid to be stored, pressurizing the bulk liquid to the extent necessary to prevent the leakage of underground water into the cavern transferring a volume of liquid to be stored into the cavern at a pressure slightly greater than the pressure exerted by the bulk liquid, and simultaneously removing an equal volume of displaced bulk liquid. My invention may also be used in existing caverns as well as in caverns formed for use of the method. By this underground storage method underground water leakage is prevented, there is substantially no dilution of the liquid as it is stored there is no loss Of usable cavern space and the cavern is continually ready to receive new liquid to be stored.

By this method the pressure that would normally drive underground water into the cavern is balanced by the combination of hydrostatic head of the bulk liquid in the shaft (which will hereinafter be explained) and possible additional applied pressure to the bulk liquid in the storage cavern. Hence, leakage of underground water into the storage cavern would be prevented, usable cavern space would be maximized and dilution of the stored liquid would be minimized.

Prior to using the method of this invention a determination of the pressure of the underground water at storage cavern depth should be made. Such determination may be made by any one of many conventional methods, such as the use of a piezometer or other pressure measure-, ments. This pressure will be the pressure which must be offset by the combined hydrostatic head of the bulk liquid and possibly additional applied pressure. Using this pressure value, the density of the bulk liquid, and the vertical depth of the cavern and shaft, the position of the level of bulk liquid in the shaft can be calculated to give a back pressure which will equilibrate the leakage pressure of the underground water into the cavern. Also prior to using my method, all open streams or other large flows of underground water in the storage cavern should be sealed up by conventional means such as grouting, etc.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a view partially in vertical cross-section showing a storage cavern and partially in schematic showing transfer times, pumps, etc., of a preferred embodiment.

FIGURE 2 is another embodiment shown partially in vertical cross-section and partially in schematic.

FIGURE 3 is still another embodiment shown partially in vertical cross-section and partially in schematic of an embodiment having a plurality of caverns.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGURE 1 shows, in vertical cross-section, a storage cavern 1 formed underground, enclosed by walls and ceiling 3, and floor 7. Shaft 9 connects storage cavern 1 with the earths surface. Shaft 9 has a lining 11 made of a material relatively impervious to water, such as concrete or steel casing, which prevents transfer of underground water and bulk liquid between shaft 9 and the surrounding earth and prevents the surrounding earth from collapsing into shaft 9 and storage cavern 1. Liquid transfer line 13 extends from pump 15 down shaft 9 into storage cavern 1 and terminates a few feet above floor 7. Liquid transfer line 17 extends from pump 19 down shaft 9 and terminates at the base of shaft 9. Air pressure transfer line 21 extends into shaft 9 and terminates below the top of shaft 9. A conventional liquid level indicator 23 located at the top of shaft -9 extends to the bottom of shaft 9. Shaft pressure seal 25 is positioned at the top of shaft 9 to prevent loss of any imposed air pressure from storage cavern 1 to the atmosphere.

In FIGURE 1 storage cavern 1 is formed by conventional means, such as excavation or dissolution methods. Bulk liquid, immiscible with and of a lesser density than the liquid to be stored, is transferred from bulk liquid source (not shown) by pump 15 and liquid transfer line 13 into storage cavern 1 to level 27 The position of level 27 has been calculated as deser b d h reinbe ore to he the level giving a bulk liquid hydrostatic head which, with either further applied pressure or alone, is sufiicient to balance the pressure of the underground water seeking entrance into storage cavern 1. Such underground water pressure has been determined at walls and ceiling 3 by conventional methods hereinbefore mentioned. If more pressure than the hydrostatic head of the bulk liquid is required, such pressure may be applied by conventional means such as air pressure delivered into shaft 9 by air pressure transfer line 21 from a source (not shown). The position of level 27 is monitored by liquid level indicator 23. Liquid level indicator 23 is connected by conventional regulator means (not shown) to air pressure transfer line 21 so that, during periods when no liquid transfer takes place to or from storage cavern 1, air pressure can be added to shaft 9 to prevent a rise in level 27 or air pressure can be vented from shaft 9 to prevent a fall in level 27. In other words, when level 27 is maintained constant the underground water pressure and storage cavern pressure are in balance and no underground water leakage into storage cavern 1 or bulk liquid or liquid to be stored leakage into the earth occurs. Liquid to be stored is transferred from its source (not shown) by pump 15 through liquid transfer line 13 to the bottom of storage cavern 1. The immiscibility between the liquid to be stored and the bulk liquid causes the two liquids to form separate horizontal layers, the lighter bulk liquid as the top layer and the heavier liquid to be stored as the bottom layer. Simultaneous with the addition of liquid to be stored is the equal volume displacement of bulk liquid. This displaced volume is pumped from storage cavern 1 by pump 19 or could be forced by displacement, through liquid transfer line 17 to a bulk liquid storage container (not shown). The liquid level 27 is reestablished at a newly calculated level, this level could be different from the original level of the change in hydrostatic head caused by the more dense liquid to be stored. Thereafter, liquid level indicator 23 will monitor level 27 as hereinbefore described. Liquid to be stored may be transferred into storage cavern 1 by this method until storage cavern 1 becomes full wherein the interface between the bulk liquid and the liquid to be stored becomes positioned at or near the bottom of shaft 9.

FIGURE 2 shows a storage cavern 1 with the same elements as shown in FIGURE 1 except that the bulk liquid is the heavier bottom layer and the liquid to be stored is the top layer. In this embodiment storage cavern 1 is filled with bulk liquid through pump 15 and liquid transfer line 13 from a source (not shown) to level 27. Liquid to be stored is transferred into storage cavern 1 through pump 19 and liquid transfer line 17 from a source (not shown). Displaced bulk liquid is transferred from storage cavern 1 through liquid transfer line 13 and pump 15 to a bulk liquid container (not shown). Liquid level 27 is monitored in shaft 9' by liquid level indicator 23. Indicator 23 controls air pressure imposed on the liquid level through air pressure transfer line 21 frOm a source (not shown) and consequently the pressure exerted by the liquid in the cavern against the hydrostatic pressure of the ground water surrounding the cavern.

In FIGURE 1 the density of the immiscible bulk liquid is less than that of the liquid to be stored. For example, if the liquid to be stored is an aqueous solution a usable immiscible bulk liquid would be any hydrocarbon of less density that is a liquid at ambient temperature and pressure and at the temperatures normally encountered in underground caverns, and the storage conditions. In FIG- URE 2 the density of the immiscible bulk liquid is greater than the density of the liquid to be stored. Either a less dense or more dense bulk liquid can be used in my method as long as the bulk liquid and the liquid to be stored are immiscible with respect to each other.

FIGURE 3 shows a plurality of underground storage caverns (29', 31 and 33) connected to the earths surface y Shafts nd respectivel Shafts s5, 37

and 39 are interconnected at the earths surface by lines 41 and 43 and pumps (not shown). This arrangement of caverns and lines eliminates the requirement for a bulk liquid storage container. Storage cavern 29 is filled with immiscible bulk liquid as hereinbefore described. Storage caverns 31 and 33 are left empty. As liquid to be stored is transferred into storage cavern 29 the displaced immiscible bulk liquid is transferred by pump (not shown) and line 41 to storage cavern 31. As storage cavern 29 is filled with liquid to be stored, storage cavern 31 is filled with the immiscible bulk liquid and made ready for use once storage cavern 29 is completely full. Similarly, when storage cavern 31 is being filled with liquid to be stored, displaced immiscible bulk liquid is transferred to storage cavern 33 by pump (not shown) and line 43. Of course, storage caverns 31 and 33 would have to be periodically pumped free of underground water prior to the final preparations for use for storage.

What I claim is:

1. A method of storing liquids underground, comprising the steps of:

(a) filling an underground cavern with a bulk liquid that is immiscible With a liquid to be stored; (b) pressurizing the bulk liquid to a pressure suflicient to balance the pressure of underground water near the cavern, thereby preventing leakage of underground water into the cavern;

(c) transferring a volume of liquid to be stored into the cavern, thereby displacing an equal volume of said bulk liquid;

(d) removing the equal volume of bulk liquid; and

(e) adjusting the pressure in the cavern to again balance the pressure of underground water near the cavern.

2. The method of storing liquids underground as in claim 1 wherein the bulk liquid is a hydrocarbon and the liquid to be stored is an aqueous radioactive waste liquid.

3. A method of storing liquids underground as in claim 1 wherein a plurality of caverns are employed and the bulk liquid is sequentially moved from a first to a second of the caverns as the first cavern is filled with the liquid to be stored.

References Cited UNITED STATES PATENTS 2,942,424 6/ 1960 Koble 61.5 3,083,537 4/1963 Dougherty 61.5 3,151,462 10/1964 Raetzsch 61'.5

PETER M. CAUN, Primary Examiner

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