US3049920A - Method of determining amount of fluid in underground storage - Google Patents

Description

INVENTOR.

J.H. ALLEN A 7'7'ORNEKS CROSS REFEENC J. H. ALLEN Filed May 29, 1958 METHOD OF DETERMINING AMOUNT OF' FLUID IN UNDERGROUND STORAGE Aug. 21, 1962 United States Patent O 3,049,920 METHOD OF DETERMINING AMOUNT OF FLUID IN UNDERGROUND STORAGE James H. Allen, New York, N.Y., assignor to Phillips Petroleum Company, a corporation of Delaware Filed May 29, 1958, Ser. No. 738,663 8 Claims. (Cl. 73-291) This invention relates to the underground storage of fluids such as gaseous ethylene, liquefied petroleum gases such las propane and butane, and the like. 'In one aspect, it relates to a method of obtaining measurements and data useful in determining the amount of such fluids stored as products in an underground storage cavern, such as those caverns formed below the ground in salt formations and the like.

Constantly expanding production of fluids for the industries of this country and elsewhere has created a denite problem in providing suitable storage facilities for these fluids. In lpetroleum industries, in particular, the problem of storage of fluids such as gaseous ethylene, liquefied petroleum gases such as propane and butane, ammonia, and the like, is presently an urgent one due to the high cost of storage in surface equipment, such as steel tanks, and due to the massive construction required to withstand the vapor pressure of such fluids. Also adding to the problem of adequate storage facilities is the fact that many industries, especially the liquefied petroleum gases industry, experience seasonal peak loads in `the requirements for their .products and corresponding seasonal slack periods. These fluctuations in requirements require large storage facilities and the advantages of storing fluids in underground caverns have lately become very attractive and important.

Underground storage caverns are generally formed in impermeable earth formations, either by conventional mining methods, or, in some cases, by dissolving out a soluble material with solvents to create a storage space in soluble formations, 4for example, in salt domes. The resulting caverns are less expensive to provide than would be an equal volume of orthodox sur-face space and have particularly proven their -value in the storage of liquefied petroleum gases.

The instant invention is particularly concerned with those underground storage caverns formed in underground salt formations. This type of cavern is generally formed by drilling an access bore from the surface of the ground down into a salt formation, such as a salt dome, and then washing out the salt by circulating fresh water down one conduit in the access bore to dissolve the salt, while continuously removing the resulting brine through another conduit in the access bore. After formation of the cavern, product to be stored therein, such as gaseous ethylene or liquefied petroleum gases, is pumped into the cavern under sufficient pressure to displace the brine in the cavern. This is generally done by pumping the product into the annulus between the casing and a central pipe, commonly called an eductor pipe. The brine is generally forced to the surface through the eductor pipe. The product, being lighter than and immiscible with the brine in .the cavern, occupies a space in the cavern above the pool of brine, an interface being formed between the two fluids. When it is desired to remove the product Ifrom storage, brine is generally forced into the cavern via the eductor pipe, thereby displacing the stored product through the annulus between the eductor pipe and casing.

One of the problems involved in this type of storage is that of determining the amount of product stored in the cavern. These caverns are generally located hundreds or even thousands .of feet below the -surface of the ground in regions which are inaccessible to an observer. The

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access bore is, of course, relatively small and this limits the manner in which the amount of product stored in the cavern can be determined. Then, again, the cavern often has generally a somewhat irregular shape which itself presents problems. During storage, there will generally always be a pool of brine in the bottom of the cavern and this lfurther complicates the determination of the amount of product in the cavern. Also, variations in such factors as temperature, pressure, and density of the stored product must be taken into account if a true and accurate determination is to be made of the amount of stored product; the deeper the cavern, the more effect will these factors have on the physical properties of the stored product.

Determining the amount of stored product by metering into and out of the cavern the product and displacing fluid has heretofore proven to be generally an unsatisfactory method of determining the amount of stored product. Metering methods are often unreliable because of errors in metering, especially where the product is stored over a relatively long period during which losses to the formation and errors in metering calibration can occur. These metering methods have especially been found wanting in those cases where it is desirable to periodically determine the exact amount of stored product because these errors are cumulative; after a period of months in which the product has been withdrawn and added, one no longer has confidence in his knowledge of the amount of product stored in the cavern.

Accordingly, it is an object of this invention to provide an improved method of determining the amount of product stored in an underground storage cavern. Another object is to provide an improved mehod for obtaining measurements and data useful in determining the amount of a fluid, such as gaseous ethylene, liquefied petroleum gases such as propane and butane, and the like, in an underground storage cavern, particularly in a cavern formed in a soluble salt formation. Another object is to minimize errors in measuring -factors necessary in determining the true amount of product stored in an underground storage cavern. Other objects and advantages of this invention will become apparent from the following discussion, appended claims, and accompanying drawing i-n which a schematic elevational View in partial section is shown of an underground storage cavern provided 'with appurtenances necessary in determining the amount of product stored in the cavern in accordance with this invention.

Referring now to the drawing, an underground storage cavern generally designated 10 is illustrated. This cavern 10 can be formed by methods well known in the art. For example, a vertical access bore 11 is -drilled from the ground through various overlying formations 12, such as surface soil, shale, limestone, sandstone, and the like, into a soluble formation, such as a salt formation 4or salt dome 13, the latter .generally having thereabove a layer of cap rock such as anhydrite or gypsum, and preferably drilling the access bore to the ultimate depth of the subsequently formed cavern. After drilling the access bore 11 into the salt formation 13, a casing 14 is set in the borehole and cemented at 16 to the surrounding Ifo-rmation so as to form a Ifluid-tight seal against the leakage of fluids past the casing and to securely anchor said casing. A pipe 17, such as an eductor or wash pipe, is inserted through casing 14 in Vspaced relation thereto, thereby forming an annulus 18, the lower end of pipe 17 depending beneath the lower end of casing 14 and extend ing further into the Vaccess bore. Alternatively, another pipe (not shown) can be inserted in .the borehole concentrically surrounding pipe 17, this other protective pipe depending below the bottom of casing 14 and above the Elower end of pipe *17, this other pipe serving to protect the inner pipe 17 during the washing operation. The upper end of casing 14 can be provided with surface pipe 19 having a flow control valve 21 and pressure gauge 22 afixed thereto. The upper end of the inner pipe 17 can also be provided with a branched conduit 23 having n valve 24 and pressure gauge 26 affixed thereto.

In forming the cavern, a solvent such as fresh water is pumped down inner pipe 17 so as to contact the soluble salt formation 13. The resulting pool of brine 27 is thereby formed and it is forced up through the annulus 18 to the surface of the ground where it is removed via conduit 19. During the formation of the cavern, the inner pipe 17 can be vertically moved up and down in order to facilitate the washing operation. Occasionally, the circulation of the fluids in the borehole and the cavern can be reversed, that is, fresh water can be pumped down through annulus 18 and brine removed from the cavern via inner pipe 17. It is also advisable in many cases to protect the roof of the progressively formed cavern and the foot of the casing pipe during the washing operation by injecting a protective blanket of hydrocarbon, such as diesel fuel, L.P.G., or even the subsequently stored product, into the cavern in such a manner that it floats on top of the wash solution or pool of brine in the cavern, the product being lighter than and immiscible with the brine. The cavern resulting from the washing operation will very often have an irregular shape such as that shown in the drawing, this shape being due to the manner of circulation, presence of shale stringers, or insoluble material, such as gypsum, embedded in the salt formation 13.

After the underground storage cavern 10 has been formed, it is general practice to survey its shape and size. This can be accomplished by several methods, such as that disclosed in U.S. Patent 2,792,708, issued May 21, 1957, to R. W. Johnston, Ir., et al., or any other known method. A particularly useful method which may be used to measure the shape and size of the cavern is that provided by the services of Dowell Incorporated, wherein a sonic caliper (an electric-line tool) is employed. This caliper works on pulse-echo system, timing the rate of sound through a fluid medium. It is an adaptation of the devices used in sonic navigation and ranging. In operation, sound waves are emitted from a sonic device or impulse emitter and travel out through the uid medium in the cavern and are reflected back as echoes from the wall defining the cavern to a sound sensitive receiving device. The time interval between transmission and reception of the sound pulse is a `direct measure `of the distance to the wall of the cavern. The transmitting and receiving devices are contained in a slender tool which is lowered by means of an electric line. By incremental lowering of the tool and making these measurements the diameters of the horizontal cross sections of the cavern are found and correlated with depth to give a profile of the cavern and an indication of its size. When making this type of survey, the inner pipe 17 is of course removed from the access bore.

From the above survey, it is possible to determine the incremental volume of the cavern from top to bottom; this will be done in increments of 5 or 10 feet. After determining the shape and size of the cavern 10, product 28 can then be stored in the cavern. Generally, this product will be injected down the annular space 18 and brine will be thereby displaced from the cavern via the inner pipe 17. From a knowledge of the shape and size of the cavern 10, the amount of product stored in the cavern can be readily determined by making the measurements according to the practice of this invention.

According to this invention, the interface 31 formed by the pool of brine 27 and the stored product 28 thereabove is determined in the following manner. An interface detecting device 32 is lowered in inner pipe 17 through a valve 33 afxed to the top of the inner pipe 17 by means of a wire line or insulated electrical conducting cable 34. The cable or line 34 extends through a stuffing box 35 and passes over a depth measuring sheave 36 and is then wound on a storage or hoist drum 37 which may be actuated by any suitable means. The interface detecting device employed can be any of the devices known to be useful for measuring the interface between two immiscible iiuids, such as that disclosed in U.S. Patent 2,648,778, issued August 11, 1953, to D. Silverman et al., the device disclosed therein being capable of detecting the interface between two dissimilar fluids by reason of variations in gamma-ray absorption. A particularly useful interface detect-ing device is a gamma-gamma log device provided by the service offered by the Lane-Wells Company. Once the winterface 31 is detected and its depth recorded, the amount or volume of space in the cavern 10 occupied by the stored product can be readily determined by correlating the interface depth with the previously run cavern survey.

After locating interface 31, a temperature survey is then made of the stored product. According to one method, a temperature recording device is lowered in inner pipe 17 in the same manner as that hereinbefore described in regard to the interface detecting device 32. A particularly useful temperature recording device is that developed by the Schlumberger Well Survey Corporation, described in Petroleum Production Engineering by Lester Charles Uren, 3rd ed., published by McGraw-Hill Book company, Inc., New York (1946), pages 656-658. This device is a surface-recording thermometer of the electrical resistance type which is lowered on an insulated conductor cable. The temperature recording device is incrementally lowered within the inner pipe 17 and the temperature recorded from the top of the inner pipe 17 to the interface depth.

Following the temperature survey, a pressure survey is made according to this invention in the following manner. A pressure recording device is lowered within the inner pipe 17 in much the same manner as that described hereinbefore in regard to the lowering of the interface detector and temperature recording device. The pressure recording device employed can be any one of those known to be useful in the art for recording a temperature in a borehole. A particularly useful pressure recording device is that known as an Amerada Continuous Recording Pressure Gauge described in Petroleum Production by Wilbur F. Cloud, published by the University of Oklahoma Press (1939), at page 207. This pressure gauge operates on the Bourdon tube principle in conjunction with a clock mechanism. With the inner tube 17 filled with brine, the pressure recording device is lowered to the interface depth 31 and the pressure at that point is recorded. The pressure of the gas at gauge 22 is also recorded. The pressures are taken at these two points 22 and 31 and the pressure gradient therebetween can be readily calculated So as to obtain pressures at predetermined depths by gas law calculations of the type explained in the Journal of Petroleum Technology, volume 207, pages 281-287, December 1956. Alternatively, the inner pipe 17 can be filled with product down to the interface level and the pressure detecting device lowered within the inner tube 17 and pressures incrementally determined from the top of pipe 17 to the interface depth.

From a knowledge of the shape and size of the cavern, and the interface, temperature, and pressure surveys obtained in the above-described manner, the amount of product stored in the underground storage cavern can be readily and accurately determined from the measurements taken.

The advantages of this invention are further illustrated in the following example.

An access bore was drilled from the ground surface into an underground salt dome to a depth of 2840 feet, which depth was about 1400 feet below the top of the salt dome. Casing was then run into the access bore to a depth of 2820 feet `and cemented in place. The access bore was then drilled at a reduced diameter to about the projected total depth of the proposed cavern, for example, 3115 feet. Solution of the salt formation was then accomplished in a conventional manner using either one or two strings of tubing to control the Washing action. The tubing was then withdrawn from the access bore and cavern. The shape and size of the resulting cavern was then determined by lowering a sonic caliper in the cavern via the casing. The sound generator or sonic device of the caliper emitted a sound wave which was beamed in a narrow arc toward the cavern wall. The reflected sound wave was picked up by the receiver of the caliper and a direct measurement is made of the distance from the caliper to the wall of the cavern. By rotating the sonic caliper with respect to the cardinal points of the compass, the distance to the cavern wall in all direction was determined. By repeating this determination at different depths, a complete determination was made of the cavern shape and the incremental volume of the cavern from top to bottom was readily calculated.

In the upper portion of the cavern, the incremental volumes of the cavern from 2829 feet to 2918 feet were as follows:

Incremental volume between:

2829' to 2839=l537 cu. ft. 2839' to 2849=1537 cu. ft. 2849 to 2859*:1537 cu. ft. 2859 to 2869'=6154 cu. ft. 2869 to 2879=26,007 cu. ft. 2879 to 2889=l67,534 cu. ft. 2889' to 2899=163,394 cu. ft. 2899 to 2909=160,595 cu. ft. 2909 to 2918=104,820 cu. ft.

The incremental volumes of the lower portion of the cavern below 2918 feet were also determined but are not reported above for purposes of brevity.

After determining the incremental volumes of the entire cavern, the eductor pipe 17 was then reinserted and installed in the cavern and the same was filled or partially filled with product, namely gaseous ethylene. This latter was introduced into the annulus 18 via surface pipe 19 and as it entered the cavern it displaced the brine 27 to the surface via eductor pipe 17 and surface pipe 23, -an interface 31 was formed between the stored product 28 and brine 27. Various withdrawals and additions of stored product were made during the course of normal operations until it was necessary or desirable to make an inventory determination of the exact amount of product stored in the cavern.

With the eductor pipe 17 remaining in the cavern, as shown in the drawing, the depth or location of interface 31 was determined by lowering an interface detector device 32, such as the gamma-gamma log device previously described. The depth of the interface was found to be 2918 feet.

After detecting and locating the interface, the temperature at each of the incremental volumes above the interface was determined by running a temperature survey in the manner described herein-before. For example, the average temperature between 2909 feet 4and 2918 feet was found to be 106 F. The pressure survey was run and the average pressure of the product between 2909 feet and 2918 feet was found to be 1451.75 p.s.i. The density of ethylene at 1451.75 p.s.i. Iand 106 F. could have been found by deriving the same from the gas law PV=ZRT. In practice, the densities of ethylene at various pressures and temperatures were found from graphs prepared beforehand. From these graphs it was found that the density of ethylene at 1451.75 p.s.i. and 106 F. is 16.357 pounds per cu. ft.

'Ihe exact amount or quantity of ethylene in the cavern between 2909 feet and 2918 feet was readily determined by multiplying the aforementioned density by the incremental volume at this depth, e.g. (16.357 pounds per cu. ft.) X (104,820 cu. ft.)=1,7l4,541 pounds. The aforementioned procedure was repeated to determine the amount of product in each incremental volume above 2909 6 feet and the summation of the amounts in the incremental volumes to the surface of the ground gave the total amount of stored product. This did, of course, include the amount of product stored in annulus 18. l

During subsequent operations involving further withdrawals and additions of stored product, the amount of stored product can be periodically determined according to the aforementioned procedure of this invention.

Various modications and alterations of this invention will become apparent to those skilled in the art without departing from the scope and spirit of the invention, and it should be understood that the latter is not necessarily limited to the aforementioned discussion and accompanying drawing.

I claim:

1. In Ia method of determining the amount of fluid stored above a pool of liquid in an underground storage cavern, said stored liuid being lighter than and immiscible with said liquid, said cavern comprising a chamber having known incremental volumes of relatively large diameter and 'an access bore of relatively small diameter extending up from said chamber to the ground, the physical steps comprising suspending an interface detecting device within said cavern and locating the interface between said stored fiuid and said liquid, withdrawing said interface detecting device from said cavern after locating said interface, suspending a temperature recording device in said cavern and recording the temperature of said fluid in each of said incremental volumes above said interface, withdrawing said temperature recording device from said cavern, suspending a pressure recording device within said cavern and determining the pressure of said fluid in each of said increment-al volumes, and withdrawing said pressure recording device from said cavern, whereby the amount of said fluid stored in said cavern can be computed by correlating all of the measurements taken.

2. In a method according to claim 2 wherein said incremental volumes are determined while said storage cavern is initially completely filled with said liquid by the steps comprising incrementally suspending an impulse emitter and a sound sensitive receiver in said cavern, emitting sonic impulses from said emitter, receiving echoes of said impulses reflected from the wall defining said cavity, and measuring the time elapsing between respective sonic impulses and their echoes as a measurement indicative of the distance traveled by said impulses, whereby the incremental volumes of said cavity can be determined.

3. In a method of determining the amount of fluid stored above a pool of liquid in a sealed underground storage cavern formed in a soluble, impermeable earth formation, said stored fiuid being lighter than and immiscible with said liquid, said cavern comprising an irregularly shaped chamber having varying horizontal cross sections of relatively large diameter and an access bore of relatively small diameter extending up from said chamber to the ground, the physical steps comprising incrementally and centrally suspending an impulse emitter and a sound sensitive receiver in said cavern while said storage cavern is initially completely filled with said liquid, radially emitting sonic impulses from said emitter through said liquid, receiving echoes of said impulses reflected from the wall of said formation defining said cavity, measuring the time elapsing between respective sonic impulses and their echoes as a measurement indicative of the diameter of each incremental volume of said cavity, withdrawing said emitter and receiver from said cavern, filling said cavern with said uid so as to form an interface between said fluid and said liquid, lowering a gamma-ray emitter and gamma-ray sensitive receiver in said cavern, radially emitting gamma-rays from said emitter and recording the differential absorption of the gamma-rays in said fiuid and liquid so as to locate said interface, withdrawing said gamma-ray emitter and receiver from said cavern, suspending a temperature recording device in said cavern and recording the temperature of said uid in each of said incremental volumes above said interface, withdrawing said temperature recording device from said cavern, suspending a pressure recording device within said cavern and determining the pressure of said iiuid in each of said incremental volumes, and wi-thdrawing said pressure recording device from said cavern, whereby the amount of said fluid stored in said cavern can be computed by correlating all of the measurements taken.

4. In a method of determining the amount of fluid stored above a pool of liquid in a sealed underground storage cavern formed in a soluble, impermeable earth formation, said stored fluid being lighter than and immiscible with said liquid, said cavern comprising an irregularly shaped chamber having varying horizontal cross sections of relatively large diameter and an access bore of relatively small diameter extending up from said chamber to the ground, the physical steps comprising incrementally and centrally suspending an impulse emitter and a sound sensitive receiver in said cavern while said storage cavern is initially completely filled with said liquid, radially emitting sonic impulses from said emitter through said liquid, receiving echoes of said impulses reflected from the wall of said formation defining said cavity, measuring the time elapsing between respective sonic impulses and their echoes as a measurement indicative of the diameter of each incremental volume of said cavity, withdrawing said emitter and receiver from said cavern, providing said cavern with a conduit extending from the ground to a point adjacent the bottom of said cavern, the upper portion of said conduit and said access bore defining an annulus, introducing said fluid into said cavern via said annulus and displacing a portion of said liquid from said cavern to the ground via said conduit thereby forming an interface in said cavern between said fluid and that portion of said liquid remaining in said cavern, lowering a gammaray emi-tter and gamma-ray sensitive receiver in said cavern, radially emitting gamma-rays from said emitter and recording the differential absorption of the gammarays in said fluid and liquid so as to locate said interface, withdrawing said gamma-ray emitter and receiver from said cavern, lowering a temperature recording device in said conduit and incrementally recording the temperature of said fluid therein above said interface, withdrawing said temperature recording device from said cavern, lowering a pressure recording device in said conduit and incrementally determining the pressure of said fluid therein above said interface, and withdrawing said pressure recording device from said cavern, whereby the amount of said fluid stored in said cavern can be computed by correlating all of the measurements taken.

5. In a method according to claim 3 wherein said fluid is gaseous ethylene, said liquid is brine, and said formation is a soluble salt formation.

6. In a method according to claim 3 wherein said fluid is butane, said liquid is brine, and said formation is a soluble salt formation.

7. In a method according to claim 3 wherein said fluid is propane, said liquid is brine, and said formation is a soluble salt formation.

8, In a method according to claim 3 wherein said fluid is liquefied petroleum gas, said liquid is brine, and said formation is a soluble salt formation.

References Cited in the le of this patent UNITED STATES PATENTS 2,792,708 Johnston et al May 21, 1957 2,817,235 Hunter et al Dec. 24, 1957 UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No. 3,049,920 August 21E 1962 James H. Allen It is hereby certified that error appears n the above numbered pat ent requiring correction and that the said Letters Patent should read as corrected below Column line 37, for the claim reference numeral "2" read l Signed and sealed this 1st day of January 1963.

(SEAL) Attest:

DAVID L. LADD ERNEST W. SWIDER Commissioner of Patem Attestng Officer

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