US2947146A - Sealing method for underground cavities - Google Patents

Description

Aug. 2, 1960 v 4 R. LOOFBOUROW 2,947,146

SEALING METHOD FOR UNDERGROUND CAVITIES Filed March 28, 1955 I A Z- IN V EN TOR. Foss TL ZOOFBOUROW fMWW ArroR/vsKs 2,947,146 Patented Aug. 2, i960 SEALING METHOD FOR UNDERGROUND 'CAVITIES Robert L. Lo'ofbouro'w, 4032 Queen Ave. S., Minneapolis, Minn.

Filed Mar. 28, 19'55, Ser. No. 497,070

5 Claims. (Cl. 61-.S)

' This invention relates to'a method for sealing underground cavities against leakage. More particularly the invention relates to a method for sealing underground storage spaces against leakage both of ground fluids into the storage caverns and of the stored product into surrounding earthstnlcture utilizing fluid pressure to facilitate the sealing operation.

Constantly expanding demandand production of liquid or liquifiable petroleum products such as liquid propane,

gasoline, fueloils and the like, has created a definite problem inprovi'ding extensive and suitable storage facilities for such materials. Due to the high vapor pressure of liquified petroleum gas, particularly propane, butane,

high volatile gasoline, and the like, the cost 'of storage in surface equipment, such as steel tanks, hecomes ex cessive due to the-pressure resistantconstruction required to with-stand the pressure of the stored 'material'ina safe manner. The problem becomes acute where it is neces- --sary-to store large quantities of such materials during the off season. In addition to the expense involved in the construction of massive surface tanlcage, there is an additional disadvantage arising out of necessity of-m-aintenance to prevent rusting or corrosion and fire hazards. Likewise, evaporation losses-may behigh when-petroleum products having fractions volatile at ordinary temperatures are stored in openor vented tanks.

In order to overcome these difiiculties, it has beenproposed to store liquid petroleum products inporous water.

bearing formations, in Water leached caverns and salt formations, or in abandoned mines in impermeable shale or limestone formations.

' It is desirable that underground storage of liquified petroleum ornatural gas be located at or reasonably ad-v jacent the place of consumption rather than the-place of origin so as "to relieve the peak loads: on transportation and production equipment. However,.due to the differing earth formations in different parts of the country, desirable locations for construction of underground storage, chambers are not always present at terminals adjacent points of consumption of the products. The available sites for construction of underground vaults or chambers for the storage of gas liquid and liquifiable. petroleum products may therefore be less than ideal in many-locations. v 1

Because the earth formations available for construction of underground storage systems may present less than ideal conditions a frequent'problem encountered is one of leakage. 'The stored fluid may permeate the surrounding earth formation contaminating wells and streams and resulting in waste of the valuable fluid. Where .the storage vault is in water bearing strata the seepage of Water into the vault "may gradually'fill u'p thevault reducing its capacity and in many cases absorbingor reacting with the stored fluid. For example, the underground storage of anhydrous ammonia is impossible unless water may be excluded from. the 'storage cell.

It is the principal object'of this invention to provide a meflredfor sealing underground'cavities against leakage.

Other objects of the invention will becomeapparent as the descriptionproceeds.

To the accomplishment of theforegoing and related ends, this invention then comprises the features hereinafter fully described and particularly pointed-out in the claims, the following description setting forth "-in detail certain illustrative embodiments of the invention, these being indicative, however, of but a fewof the various ways in which the principles of the invention may be employed.

The invention is illustrated by the drawings wherein corresponding numerals refer to the same parts and in which:

Figure 1 is a simplified and diagrammatic sectional view of an underground cavity having communication with the surface through a shaft fitted for practiceof this invention and r Figure 2 is a similar simplified and diagrammatic view of an underground cavity having communication with the surface through a tunnel or drift.

Broadly stated the method of. this invention comprises closing all of the entrances to an underground cavity providing one of the closures with .an air lock of a size oapab-le'of admittingme'n along with tools and supplies, subjecting the cavity to pressure with air or water suiiiciently to wash dust, clay and the like from leaking fractures and similar structures, reducing the pressure to a comfortable wor kingpressure, sealing the leakages by the application of any suitalble sealing substance depending upon the nature of the leak-ing'formation and again subjecting the cavity to pressure.

A number of adhesive mater-ia'ls are known which are unaffected by water and most hydrocarbons andare therefore useful as sealing agents for. underground excavations adapted to be used to contain such products as propane, butane, anhydrous ammonia, naturalgasand the like. It has -been proposed previouslyjto seal permeable surfaces of underground excavations.by'applying such an adhesive material directly onthe affectedsurface. application isbased upon simple painting of the surface and absorption of the sealing. material into dry pores or fractures of the rock or injection of'the sealing agent'by methods commonly used in grouting, that is, pumping the agent through packer into holes drilledinto therrock which inters'ect the fractures to b'e'sealed.

The first of these met-hods fails .to produce {a satisfactory seal because very scant penetrationis achieved,

even if therock is entirely'freeof moisture. Painting is clearlyimpossible if water'is flowing fromflthe' fracture to besealed. Under'this method'there often exists n indication of the points of leakage.

By the grouting method great doubt may exist as to "the final locus of the sealing agent. Since no "control can be exercised over the sealer after it is pumped into the hole itslocus can only be indicated by drilling a'multitude oftestholes. Where any extent of leakage occurs testing becomes aprohibitively tedious and expensive process. V

According to the sealing process of this invention, after the wall has been cleaned of loose particles, ,dustand the like, the pressure within the excavation is maintained,

during sealing, at a-value sufiicientlyhigh to impede" the how of ground water into the cavity. That'is, the direction of flow of water is reversed away from the storage chamber during "the application of the sealing material. If the fractures to be sealedcarry water underpressures greater than comfortable working air pressure it willifirst be necessary to collect'the water by weeping as-wi1lbe explained in detail hereinafter.

Referring now to the drawings, Figure 1 illustrates diagrammatically one form of storage cavity 10- communicating'by means of a shaftll with the earths surface'l2.

The shaft is suitably cased with metal or concrete and enclosed by a dome 14 having an access manhole 15. The casing is provided with an intermediate wall 16 spaced apart from dome 14 sufficiently to form an airlock 17 capable of receiving several workmen. Wall 16 likewise has a manhole '18 providing access to the remainder of the shaft and the chamber 10. A compressor 19 at the surface driven by motor 20 is connected by means of valved lines 21 and 22 to the air lock 17 and chamber 10 respectively for pressurizing these spaces.

For illustrative purposes there is shown a fracture 24 which carries water under pressures greater than comfortable working air pressures such that the direction of flow cannot be changed at pressures which can safely be used. To overcome this difliculty the water is weeped through holes drilled to intersect the water channels several feet within the rock. Pipes 25 are then inserted into these weeps and by means of pump 26 and pipe line 27 the water is conveyed to the surface and discharged at 28 at atmospheric pressure outside of the storage. By this means the pressure of the water in the fracture at-the face of the storage cavity is relieved to such an extent that the working air pressure within the cavity is sufiicient to hold the water back. As is well understood in the engineering arts, a weep or weep hole is' a hole or a pipe or other vent in a retaining wall,

canal, paving or other structure to drain ofi accumulated water which might otherwise induce inordinate pressure back of or under the structure. 7

Another typical form of storage chamber is shown in Figure 2. The chamber 10A is so situated that communication with the earths surface 12 is by means of a tunnel or drift 30. The tunnel is closed by an outer wall 31 containing a manhole 32 and an inner wall cont aining a manhole 35 is spaced apart from the outer wall to form an air lock 36. The chamber 10A may be pressurizedby compressor 19 through pipe line 22A passing through walls 31 and 34 to the chamber. Air lock 36 is similarly pressurized through line 21A.

An illustrative high pressure leaking fracture is shown on 24A. This leak is weeped and the weep is con nected by means of pipe 25A'and 27A to the atmosphere 'at 28A. Because in this exemplary illustration the mouth of the tunnel is lower than the leaking fracture and weeped water is simply permitted to discharge to atmospheric pressure by gravity flow.

Insealing by the method of this invention, after the entrances have been closed the storage is initially pressurized with air or water sufficiently to wash dust, clay and-the like from leaking fractures and from the walls of the cavities. If leakage is not extensive pressure maybe raised at this stage to twice the planned operating pressure, that is, between about 40 and 10,000 pounds gauge.

.The closures to the storage'should be capable ow withstanding up to twice the planned maximum operating pressure. g

The pressure within the storage cavity is then reduced to the working pressure (2 to 40 pounds gauge), the

workmen enter the air look at atmospheric pressure, the air lock pressure is' equalized with the storage pressure and the workmen enter the storage. Areas of leaking are sought out and tested by means of ear, microphones and amplifiers, feather dusters, suds, or other substances and means well known for readily betraying leakage.

The detected leakage is sealed by application of a coating or layer of a compatible liquid sealing substance in the form of a solution, emulsion or suspension by brushing spraying or the like. A variety of natural and synthetic materials may be employed for this purpose, for example bituminous and asphaltic paints; solutions and suspensions of synthetic latices such as butadiene-acrylonitrile copolymers, butadiene-styrene copolymers, polymerized vinyl chloride and the like; the paints containing compounded modified halide polymers, condensation resins and diene derivatives available under the trade name Tygon; rubber hydrochloride, grout slurry, sodium silicate and calcium chloride; the same thickened with sand, sawdust, etc.; and the like. The sealing material must be compatible with the material to be stored in the sealed cavity, that is, the stored fluid must not have any solvent action on the sealant. The sealing agent must naturally be waterproof and capable of forming an impervious tightly adherent seal and should have a controllable setting rate. The desired objective is to obtain sealing in the depths of the leakages.

Small cracks may be sealed by one or more applications of the sealing material alone. In some instances, such as in the case of somewhat larger fractures, it may be desirable to apply the sealant in thicker paste form, as by troweling or by high pressure spray. Larger openings may require the use of a mechanical bodying agent such as sawdust, bran hulls, or the like to assist in plugging. Still larger openings may have to be formed and concreted prior to treatment with the sealing agent.

If the fractures to be sealed carry water under pressures greater than comfortable working air pressure the water is weeped in the manner heretofore described through holes drilled in the rock to intersect the water channels several feet from the surface of the cavity connected to a pipe discharging at atmospheric pressure outside the storage. With the water pressure thus relieved the sealing coating can be applied in the usual manner.

After the seal has been tested and found to be satisfactory the weeps are plugged and the pumps and drainage pipes may be withdrawn.

The working pressure within the storage cavity during sealing is selected within a comfortable working range (up to 40 pounds gauge) at a value sufficient to change the direction of flow of the ground water holding it away from the storage surfaces during the application and setting of the sealing agent and to assist in forcing the sealing material into the pores of the cavity walls. After the seal is applied the pressure assists in holding it in place until set.

After thorough examination of the storage walls and treatment of all evident leakage the work crews are withdrawn from the storage and the pressure is again raised to the maximum test pressure, that is, up to 10,000 pounds gauge. The test pressure should be as great as the maximum anticipated storage pressure. The purpose of this test pressurization is to determine whether operating pressures will be such as to rupture the seal and permit escape of the stored fluid ouwardly into the earth formation surrounding the storage cavity. It is desirable that the sealing agent set under the lower working pressures so that the action of the higher test pressures against the unset or partially set seal will not rupture the film formed.

The pressure is then reduced and the storage is inspected. If no leakage is detected after the test' pressurizing the storage system is ready for use. Where weeping has been used to collect water the weeps are plugged by grouting or otherwise in the conventional manner and the pumps and other equipment is removed from the storage before introducing the fluid to be stored.

If the test shows further leakage the sealing operation under pressure isrepeated following the above described procedures until no leakage is present.

The method of this invention is applicable not only to the expeditious sealing of walls of a storage which leak only in a few spots, but it is useful as well for sealing of any type leakage over large areas.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to the specific embodiments herein.

to 40 pounds gauge, applying a settable film forming material impervious to the material to be stored over permeable areas in the cavity while maintaining the cavity under pressure to force the settable material into the depths of the leakages in the cavity walls and permitting the material to set while under said pressure and thereafter increasing said pressure to maximum anticipated storage pressure between about 20 and 5000 pounds gauge.

2. The method of sealing an underground storage cavity formed in water-bearing strata which comprises initially subjecting the cavity to increased pressure to about double the maximum anticipated storage pressure to flush the cavity of debris, reducing the pressure to within safe human working limits of about 2 to 40 pounds gauge, applying a settable film forming material impervious to the material to be stored over permeable areas in the cavity while maintaining the cavity under pressure to force the settable material into the depths of the leakages in the cavity walls and permitting the material to set While under said pressure, and thereafter increasing said pressure to maximum anticipated storage pressure between about 20 and 5000 pounds gauge. 7 3. The method of sealing leakagein an underground storage cavity formed in water-bearing strata which'comprises the. steps of initially subjecting the cavity to increased pressure to about double the maximum anticipated storage pressure to flush the cavity of debris, reducing the pressure to .within safe :human working limits between about 2 to 40 pounds gauge to permit workmen to enter the cavity, testing the cavity wall surfaces to detect leakages, applying a settable film forming material impervious to the material to be stored over the areas of leakage in the cavity while maintaining the cavity under pressure to'cEorce the settable material into the depths of the leakages in the cavity walls and permitting the material to set while under said working pressure 6 and thereafter increasing the pressure to maximum anticipated storage pressure between about 20 and 5000 pounds gauge.

4. The method according to claim 3 further characterized in that leakage containing fluid at pressure greater than about 2 to 40 pounds gauge are vented directly to the atmosphere outside of the storage cavity to relieve the pressure of those leakages and the collected fluid is discharged at atmospheric pressure.

5. The method of sealing an underground storage cavity which comprises subjecting the cavity to increased pressure within safe human working limits of about Z to 40 lbs. gauge, venting leakages containing fluid at pressures greater than about 2 to 40 lbs. gauge directly to the atmosphere outside of the storage cavity to relieve the pressures of those leakages and discharging the collected fluid at atmospheric pressure, applying a settable film-forming material impervious to the material to be stored over permeable areas in the cavity while maintaining the cavity under pressure to force the settable material into the depths of leakages in the cavity walls and permitting the material to set While under said pressure, and thereafter increasing said pressure to maximum anticipated storage pressure between 20 and 5,000 lbs. gauge.

References Cited in the file of this patent UNITED STATES PATENTS

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