US2981070A - Seal structure for underground liquid storage facility - Google Patents

Description

April 25, 1961 SEELY, JR 2,981,070

SEAL STRUCTURE FOR UNDERGROUND LIQUID STORAGE FACILITY Filed Aug. 31, 1955 2 Sheets-Sheet 1 INVENTOR. DWIGHT H. SEELY, JR.

BY 2 ATTgRN EY April 25, 1961 D. H. SEELY, JR 2,981,070

SEAL STRUCTURE FOR UNDERGROUND LIQUID STORAGE FACILITY Filed Aug. 51, 1955 2 Sheets-Sheet 2 INVENTOR. DWIGHT H.

Y ffpELY JR.

ATTO NEY United States Patent SEAL STRUCTURE FOR UNDERGROUND LIQUID STORAGE FACILITY Dwight H. Seely, J12, Oklahoma City, Okla, assignor to Sohio Petroleum Company, Cleveland, Ohio, a corporation of Ohio Filed Aug. 31, 1955, Set. o. 531,689

3 Claims. 01. 61.5)

The present invention relates to new and useful improvements in underground storage facilities. Particularly, it relates to improved sealing means for underground facilities used for the storage of liquids or gases under pressure.

Recent developments in the design and construction of storage facilities have led to extensive use of underground facilities for the storage of fluid products produced in the petroleum, chemical and petrochemical industries. It has been determined that underground facilities substantially reduce the amount of capital required heretofore to provide aboveground storage facilities. Underground facilities for storage of liquids or gases under pressure have been constructed in many places in this country. Generally, such facilities are of one or two types, the first type involving storage in underground salt domes and the second involving mined underground caverns. My invention relates particularly to improvements in the construction of underground facilities of the latter type.

In choosing a suitable underground stratum for the construction of a mined cavern, it is customary to drill one or more cores by conventional core drilling methods in the general location where the facility is to be installed. The cores obtained by such drilling make it possible to select a geological formation having the properphysical characteristics and located at the proper depth underground to serve as a storage cavern.

Of first consideration is the depth of the excavation to be used and this is determined by the geological information available concerning theability of the overburden to retain pressure. For example, for a pressure of 100 pounds (gauge) an excavation or storage cavity should be located at least 100 feet belowgro-und according to a rule is impermeable, hard, and substantially free of fractures,

andfone having sufficient beam strength to support the necessary overburden. .An example of a suitable formation for a roof structure would be massive limestone.

Of equal importance are the properties required for the walls of the excavation. The walls of the excavation should preferably be impermeable, reasonably dry and.

devoid of impurities or properties which might have a deleterious effect upon'the liquid stored. A suitable formation for the cavern walls would be tight, sandy, shale to shaly sandstone and silty grey shale. This formation is dry, non-waterbearing, tight, andwill not effect the stored materials. If such a formation is not available, a water-bearing formation may be'employed as the stored material will displace the water.

It is desirable, although not necessary, that the cavern formation be followed immediately below by a hard formation suitable for a cavern'floor, such, for example, as

hard brittle limestone. However, if the walls of the cavitypossess the desired properties, a special'floor formation per se, is not required.

The foregoing information is generally known in the industries where such underground caverns have been employed as storage facilities. Underground caverns are usually constructed by conventional mining methods, e.g., a mine shaft may be first sunk to the desired depth and the cavern is then excavated.

The particular problem I have overcome is concerned with the sealing of the mine shaft with respect to the cavern. The object of my invention is to provide an impermeable seal between the mine shaft and the oavern to effectively preclude the escape of any of the material which is to be stored in the cavern.

Seals of the type contemplated herein may be disposed in any relative position, e.g., either vertical or horizontal. When it is desired to form one or more caverns by means of a common mine shaft, tunnels may be excavated in several directions from the mine shaft and a cavern may then be excavated at the terminus of each tunnel. In such a case, it will usually be more convenient to looate the seal structure in the tunnels extending from the mine shaft. Merely for the purposes of description, such a case is contemplated herein below.

There are several known methods by which such a tunnel could be sealed. For example, the tunnel leading from the cavern to the mine shaft may be .filled and sealed with concrete or cement. Alternatively the tunnel could be sealed by means of an impervious plate embedded in the walls of the tunnel. In the underground storage of liquids at atmospheric or near atmospheric pressures, such methods have generally been found to be suitable. However, when liquids or gases are stored at superatmospheric pressure, such sealing methods are not wholly effective and lose utility. For example, in the case of the underground storage of liquefied petroleum gas, it has been found that cement is relatively porous to such a liquid and that a dangerous amount of the liquid will escape through the concrete no matter how thick it may be, creating a considerable safety hazard. Since underground caverns are generally located in shale formations and it is a characteristic of shale that it has a low shearing strength, the use of an impervious plate in such a tunnel is not considered a satisfactory solution to the problem.

If an impervious plate is employed, such as a metal plate embedded in the tunnel walls, there is considerabledanger of a breaking away of the tunnel wall with consequent collapse of the seal. The tunnels are frequently ten feet or larger in diameter and consequently a metal plate inserted in the Wall to seal the tunnel imposes a substantial shearing stress on the walls of the tunnel at pressures substantially above atmospheric pressure. Another drawback of this type of seal is that the stored ma- I terial has a tendency to escape around the perimeter of the plate.

I have now invented a seal structure for underground storage facilities which efiectively overcomes the defects inherent in the sealing means of the prior art. 7

In brief, the seal structure of my invention comprises an impervious mass embedded in the Walls of the section V to be sealed having a cross-sectional area greater than the area of that section. The structure may also have provision for access therethrough.

As the incompressible material which is used in conby a mixture of water and cement as the incompressible material.

The invention will be better understood by reference to the accompanying drawing wherein similar figures denote similar parts throughout, and in which:

Figure l is a diagrammatic cross-sectional view cut through the center of the underground cavern, mine shaft and the tunnel connecting the cavern to the mine shaft;

Figure 2 is an expanded cross-sectional detail View of the seal structure of this invention;

Figure 3 is a front view of the seal structure looking down the tunnel from the mine shaft prior to installation of the tile.

Referring now to Figure 1, the construction of the underground cavern will first be described. Ordinarily, the first step in the construction is to drill a hole to the desired depth of the proposed cavern floor. This hole may be formed in the preliminary coring operation.

The next step in the construction of the cavern is the excavation of a mine shaft 13. The mine shaft may be.

provided for part or all of its length with a suitable casing 14 such as a concrete wall, if necessary. A tunnel 15 is then excavated perpendicularly to the mine shaft 13. Depending upon the number of caverns desired, one or more tunnels such as 15 may be connected to the same mine shaft. When the approximate area is reached by the tunnel 15 where it is desired to construct the cavern, the main excavation takes place and the cavern 16 is constructed. The diggings from the cavern H are removed through the tunnel 15 and the mine shaft 13. The excavation is accomplished by the usual mining techniques.

The cavern 16 may take various shapes insofar as the profile of its wall structure is concerned, depending upon the nature of the formation of the stratum and giving due consideration to the most economical method of excavation. For example, if the substance of the cavern walls has no tendency to slough or cave in, the walls may be substantially vertical as shown by the profile of Figure 1. On the other hand, in a stratum of dense shale or silty grey shale where there is a likelihood of sloughing, the cavern is excavated with sloping sides to obviate this fault. When the cavern is complete, ap-

propriate connections between the hole 10 and the cavern 16 are made to provide for the ingress and egress of the liquid to be stored. These will include the valve means 17, a string of pipe 11 and a pump 18 which are known in the art and are not a part of my invention. The tunnel 15 connecting the cavern 16 to the mine shaft 13 must be sealed to prevent the escape of the stored liquid or gas from the cavern 1'6.

The seal structure A of this invention is shown on Figure 1 in cross-section but the manner of construction of the seal structure can be better understood by reference to the expanded view shown in Figure 2 and referred to now.

The first step in constructing the seal structure A of this invention is to excavate a recess 19 in the wall of the tunnel 15. This excavation can be conveniently accomplished by means of hand operated pneumatic rock chisels and drills. When the excavation of the recess 19 is completed, the surface of the recess may desirably be coated with a sealing compound to seal any voids or crevices therein. As a sealing compound, it may be desirable to employ a compound which is impervious to the material to be stored in the cavern. In some instances it may also be desirable to support the roof of the recess 19 by means of roof support jacks (not shown). All surfaces of the recess 19 which are to be in contact with metal should be made as smooth as possible.

Before proceeding with the construction of the seal structure, a bolt 24 should be set intothe roof of the tunnellS a short distance from the cavern facelof the recess 19. A ring and chain 25 are welded to the bolt 24 for a purpose which will be described hereinafter.

The next step in the construction of the seal structure is to construct a plate 20 adjacent to the wall 19a of the recess 19. This plate 20 is desirably constructed from a number of pre-formed sections which are assembled in situ by a seal welding or other suitable means. The thickness of the plate 20 need not be great and in the present instance a thickness of A was found to be suitable. For the purpose of providing structural support, stifieners such as angle bars 22 may be welded to the plate 20. Plate 20 is held against the wall 19a by means of the expansion bolts 21. Void spaces between the recess wall 19a and the plate 20 may be filled with cement or other sealing material.

In order to complete the cavern side bulk head, a plate 23 is constructed adjacent recess Wall 19b. This plate is similar to the plate 20 and is constructed in a like manner. Expansion bolts 21 hold the plate adjacent to the wall 1%. When plate 23 is finally assembled, a number of reinforcing spacer rods 26 are welded to the plates 20 and 23. A cement fill pipe 27 and an air vent pipe 28 are then installed communicating with the area between plates 23 and 20. A conduit 29 which will be used as a manway is then welded to the plates 23 and 20 in an area provided in the plates 20 and 23 at the time ofconstruction. The section 29 has a flange 30 on the cavern side.

The area 31 between the plates 20 and 23 is filled with an incompressible material such as cement through the fill pipe 27. If cement is employed to fill the space 31, the high heat of hydration of cement may render it impractical to completely fill the space 31 in a single dump. If such is the case, several dumps can be spaced at suitable intervals. The last dump should be continued until material begins to come out through the vent pipe 28.

The next step in the construction of the seal involves the center section. I beams 32 are placed on the floor of the recess 19 and these beams support a center cylinder form 33. The center cylinder form 33 is assembled by welding or other suitable means from a number of pre-formed sections. The center cylinder form 33 should preferably be as nearly circular as is practicable, but it is not necessary that it 'be perfectly circular.

When the center cylinder form 33 has been assembled and has been welded to the plate 23, the shaft end form plate 34 is constructed in the same manner as plates 20 and 23 but several sections of this plate are left out for later insertion for reasons that will become apparent hereinafter. The plate 34 is held against the recess wall 19d by the expansion bolts 21. Plate 34 has stiffeners 22 welded to its face.

The conduit section 35 is installed and welded to conduit section 29 and plate 34. Conduit section 35 has a flange 36 at its shaft end. Stiffeners 37 may be welded to the top side of the conduit section 35 and to the roof of the center cylinder form 33.

Ring form 38 is assembled adjacent to the wall 190. This form is constructed in a manner similar to that employed in the construction of plate 34 and is held in place by means of the expansion bolts 21. The ring form 38 is Welded to the outer edge of the center cylinder form 33.

The fill pipe 39 and the vent pipes 40 and 41 are now installed. Vent pipe 44 is installed in the squeeze void 43 and a fill pipe 45 is also installed to service the void 43. The remaining sections of plate 34 are now installed. Concrete or like material may now be dumped into the vold space 42 Within the center cylinder form 33 through the fill pipe 39. Once again, because of the heat of hydration of such materials, it will probably be necessary to fill the space 42 by dumping the concrete or like material in small amounts at suitable intervals.

When the center void space 42 is completely filled with concrete, a suitable interval for the complete setting. of

this material should be allowed. When this interval has elapsed, the void space 43 should be filled and maintained under a high pressure with a cement which is impervious to the material to be stored and which is capable of forming a tight bond with the surrounding stratum. The cement should preferably contain an additive, many of which are known to the art, which will prevent its shrinkage upon setting. The filling is accomplished by pumping a mixture of this cement under a high pressure through the fill line 45. The pumping is continued until the special cement begins to discharge through the vent line 44. When the cement begins to flow out of the vent line 44, the valve 46 should be closed and pumping continued until the pressure within the squeeze void 43 is at least 300 lbs. per square inch and preferably somewhat higher. When this pressure is attained, the valve 47 in the fill line isclosed.

As the last step in completing the construction of the seal, the cavern side manway blind flange 48 is secured to the flange 30 by rneansof bolts 49. In order to hold the blind flange 43 in position while securing it to the flange 30, it will be necessary to employ the chain 25 heretofore mentioned by securing it to the flange 48. The seal is completed by installation of the shaft side manway blind flange 50 which is secured to the flange 36 by means of bolts 49. The blind flanges 48 and 50 are sealed by appropriate gaskets (not shown).

When the seal has been completed, a tile or pipe 51 is laid from the shaft side of the sealed structure part way' up the shaft 13. .The area 52 around the tile 51 is filled to a level above the highest point within the cavern with concrete or a mixture of crushed rock and concrete so that the seal structure will. be subjected to a compressive stress. As a final precaution, the area 53 shown on Figure 1 within the tile may be filled with water.

Figure 3 of the patent drawing shows the various parts of the sealed structure looking from the shaft 13 towards the cavern 16. The important feature to be noted in this figure is that all of the main structural elements of the seal structure have a diameter larger than the diameter of the tunnel 15. It is this feature of the seal structure which makes it particularly useful as the stress imposed on the surrounding stratum is largely compressive in nature rather than shearing.

It will be obvious to those skilled in the art that modifications of the particular sealing means disclosed may be made. modifications of the invention as would reasonably fall within the scope of the appended claims.

I claim:

1. In combination with an underground storage cavern, a passage communicating with the cavern having a pair of spaced-part lateral enlargements in the wall thereof forming continuous trenches of appreciable depth and limited axial extent in the material bounding the passage, the side walls of said trenches being substantially normal to the axis of the passage and the extent of the latter between the trenches also beingenlarged with respect to the normal cross-section of the passage but to.a lesser However, it is intended to cover all such extent than the trenches, a pair of metal bulkheads of considerably larger area than the passage disposed in one of said trenches with their peripheral portions respectively against the side walls of said one trench, whereby said bulkheads extend in substantially parallel axially spaced relation transversely of the passage and substantially into the boundary material beyond the wall of the passage, a first mass of substantially incompressible set material completely filling said one trench between the peripheral portions of the bulkheads therein and against the bottom of the trench, said first mass further extending inwardly between the bulkheads well beyond the thus embedded peripheral portions of the same, a second mass of substantially incompressible material extending along the wall of the passage between the two trenches and filling the other of said trenches, the second mass also extending inwardly over the length thereof well beyond the portions thereof embedded in the boundary material between the trenches and in said other trench, said pair of metal bulkheads. and first and second masses of substantially incompressible material together forming an embedded seal structure of general spool shape in the passage, and sealing compound disposed under substantial pressure between the outer periphery of the intermediate portion of said structure, between the relatively enlarged ends thereof defined by the trenches, and the boundary material surrounding said intermediate portion to form a tight bond therewith.

2. The combination set forth in claim 1 wherein the intermediate portion of the seal structure between the enlarged ends thereof is enclosed by a continuous metal liner, and the sealing compound under pressure is between said liner and the surrounding boundary material.

3. The combination set forth in claim 2 wherein one end of said liner is disposed against the inboard bulkhead of the pair of the same in said one trench, the other end of the liner is approximately in the plane of the inboard side wall of said other trench, a metal flange section extends outwardly from about said other end of the liner into said other trench against the inboard side wall thereof, and a further metal bulkhead of considerably larger area than the cross-section of the tunnel is disposed in the other trench against the outboard side wall of the same, that portion of the second incompressible mass filling said other trench being between said metal flange section and further bulkhead therein.

References Cited in the file of this patent UNITED STATES PATENTS D. 18,104 Levering June 16, 1931 2,208,302 Fernandez July 16, 1940 2,433,896 Gay Jan. 6, 1948 2,459,227 Kerr Jan. 18, 1949 2,508,949 Howard May 23, 1950 2,659,209 Phelps Nov. 17, 1953 2,780,289 Garrison Feb. 5, 1957 2,787,125 Benz Apr. 2, 1957 2,855,757 Meade Oct. 14, 1958

Images