US2922281A - Underground storage of hydrocarbons - Google Patents

Description

Jan. 26, 1960 c. H. BROCKS 2 UNDERGROUND STORAGE 0F HYDROCARBONS Filed July 15, 1954 IN VEN TOR. CHARLES H. BROOKS ivodwn. 3 5

ATTOR EY and the like.

United States Patent This invention relates to :the underground storage of hydrocarbons, and is particularly directed to an integrated process of storing hydrocarbons in a plurality of subsurface salt cavities.

Sub-surface salt cavities have heretofore been used for storing petroleum products, such as propane,'butane, and the like.

maintaining the stored hydrocarbons o'ver brine; thethydrocarbon to be stored is introduced into the cavity under a pressure'sufiicient to displace a quantity Qf-brine therefrom; To recover stored hydrocarbons, brine is intro- Generally such storage has been performed by duced into the cavity to displace the desired quantity of if hydrocarbons therefrom. As generally heretofore operated, each well requires a separate: brine system, in-

cluding for example separate" brine supply. conduits,

pumps, valves, and the like.- Also, the introduction or removal of hydrocarbons requires activation oftheseparate pumps involved, together with the appropriate valves For the foregoing and other reasons, operatiomof a plurality ofsalt cavitieshas: heretofore required expensiveand; complicated equipment and techniques.

-An object of the-present invention is1to,provide an eflicient, integrated pr'ocessof operating .a plurality-of salt. cavities foflhydrocarbonstorage wherein the above and other difliculties areobviated. A further object'is to provide an apparatus for performing the process of J the invention. Another object is to provide aprocess-for operating a plurality of sub-surface salt cavities as an integral part of a refinery. Other objects will appear hereinafter. j

It'has now been'found that storage of hydrocarbons in aplurality of ,sub-sunface salt cavities can be accomplished economically as anefficient, integrated process by maintainingamanifold as aibrine supply conduit communicatingKbetween-a brine storagereservoir and a plurality of sub-surface salt cavities, the manifold having means for continuously supplying; brine to. the cavities, such-as-by continuously pumping brine from, storage into I the brine conduit. Brine is introduced intoand removed from each cavity-through a conduitter'minating near the bottom of thecayity, and hydrocarbons are introduced into and removedfrorn each cavity, as separate streams,

through a conduit terminating near the top of the. cavity, as=-hereinafter described. If the brine introduced into the manifoldis not needed to displace hydrocarbons, from a cavity,,so that the continuous brinesupply causes an increase of pressurejn the manifold, it is returned to brine storage. This may be done automatically by means of apressure relief valve that isactuated tov permit brine to flow from the supply conduit to storage when the pressure in the supply, conduit reaches a predetermined value,

1 or by equivalent means.

Separate means for introducing hydrocarbons, as individual streams, into the cavities are provided. When hydrocarbons are; introduced into a, cavity for storage, the

tionjrnust also be taken into account.

suificientto overcomethe relatively low pressure in the brine conduit and the pressure resulting from the head of: brine as compared to the head of the lower density hydrocarbons. In practice, the pressure drop due to fric- Brine displaced from the cavity-into the brine manifold during hydrocarbon introduction, and the brine constantly supplied to the brine manifold from brine storage through the brine conduit, if not. used to displace hydrocarbons from another'cavity, are both sent back to brine storage.

1 To-recover hydrocarbons from a sub-surface salt cavity,-

due to the difference in specific gravities of brine and bydrocarbons, it is only necessary to open the hydrocarbon outlet. The pressure on the hydrocarbons caused by the static brine head is sutficient to force their displacement from the cavity, and the constant brine supply through themanifold is suficient to maintain the static brine head. In this manner the storage of hydrocarbons in a plurality of salt cavities is achieved as an integrated process, the

brine being available continuously forhydrocarbon displacement, and the brine being relieved to brine storage 'when not required to displace hydrocarbons.

Salt cavities used in the invention should be at a dis tance below ground-surface sothat the pressure caused by the static head of brine creates a pressure above the vapor pressure of the stored hydrocarbons at the hydrocarbonoutlet from the cavity. In general, the cavity will quired forintroducing hydrocarbons will be from about 600'to.900 p.s.i.g.

Attention is now directed to the accompanying schematic flow diagram, which illustrates the process of the pressureiused must. be" suflicientpto displace;- brine from duit represented by line 21. supply conduit and. is in fluid communication, through pump 22, with brine storage means 24, the inlet of coninvention.

Numbers 1, 2 and 4 indicate sub-surface salt cavities prepared in sub-surface salt formation 5. Conduits 6, 8 and 9, positioned within casings 10, 11 and: 12, respectively, provide fluid communication for brine from the ground surface to the bottom of cavities 1, 2. and 4, respectively. Annuli 14, 15 and, 16, formed between the said conduits and casings of cavities. 1,- 2 and 4, respectively, provide fluid communication for hydrocarbons between'the ground surface and the topof said cavities 1, 2 and 4,1'espectively. Conduits represented by lines 18, 19 and 20- provide fluid communication between conduits 6, 8 and 9, respectively, and a single brine supply con- Manifold 21 is the brine duit 21 being below the brine level in storage means 24. Conduit 21 also communicates with brine-storage through pressure relief valve 25 and conduit 26, which conduit preferably terminates above the brine level in brine storage 24.

Cavity 1 communicates with hydrocarbon line 28 through annulus .14, line '29, valve 30 and pump 31, and with hydrocarbon line 32'through. annulus 14, line 29 and valve 34. Cavity 2, in similar manner communicates with hydrocarbon line 35 through annulus its, line 36,v valve 38 and pump 39, and with hydrocarbon-line 40 through annulus 15, line 36 and valve 41. Also, cavity 4 communicates with hydrocarbon line 44 through annulus 16, line.45, valve 46andpump-48, and with hydrocarbon line 49 through annulus 16, line 45 and valve 50. 4 v

p rating th a s r;. yQIOQarb na r ge in accordance with the invention, brine from storage 24 is continuously supplied, by means of pump 22, to conduits 6, 8 and 9 via manifold 21 including conduits 18, 19 and 20, respectively. When brine is not needed to displace hydrocarbons from a cavity, the brine is relieved back to storage 24 from manifold 21 through valve 25 and conduit 26. Valve 25 operates as a pressure relief valve, i.e., when the pressure in conduit 21 reaches a predetermined value, value 25 opens to permit brine to flow to storage 24 and thus relieve the pressure in the brine supply conduit.

In filling a cavity with hydrocarbons for storage, such as introducing butane into cavity 1, for example, butane is introduced through line 28, pump 31 and valve 30, valve 34 being closed. Pump 31 provides sufiicient pressure to force brine from cavity 1 through conduits 6 and 18 and into manifold 21. If the pressure in manifold 21 is thereby caused to exceed a predetermined value, valve 25 is actuated and brine flows from manifold 21 to storage 24. When the desired quantity of butane has been introduced into the cavity, valve 30 is closed and the use of pump 3-1 discontinued. To remove butane from cavity 1, it is only necessary to open valve 34. Butane is then displaced from cavity :1 through annulus I14 and conduits 29 and 32, the pressure for displacement being provided principally by the difference in densities in the brine in conduit 6, and the butane in annulus 14, the brine flowing from conduit 6 into cavity 1 being continuously replaced by the constant brine quired in cavity 2, the excess entering manifold 21 will flow through valve 25 and pass through conduit 26'to storage 24. In the event brine is displaced from cavity 1 at a rate insuificient to supply the brine required by cavity 2, the additional brine is supplied to cavity 2 by means of pump 22 and manifold 21.

In operating the process, valve 25 is actuated at a predetermined pressure. It is preferred to have valve 25 actuated at a pressure of about 10 p.s.i.g. Thus, the pressure in manifold 21 will vary within the limits of about 10 p.s.i.. If desired, manifold 21 can be operated under smaller or larger pressure variations by adjusting valve 25 to be actuated at pressures of from about 5 to 15 p.s.i.g. and variations within this range are considered to meet the term substantially constant pressure and terms of similar import when used with reference to the brine pressure in conduit 21. Still higher operating pressures can be used if desired, but at high pressures care should be taken that the total pressure within the cavity does not cause a fraction of the cavity.

It is preferable to install check valve in manifold 21 immediately at the discharge side of the pump 22 to prevent brine from passing, in reverse, through pump 22 before valve 25 opens due, to increased pressure in the conduit. Other valves, meters, pressure indicators, regulators and the like can be employed where necessary or desirable, the use thereof, in light of the teachings of the present specification, being within the scope of those skilled in the art.

The preparation of underground salt cavities for use in the present invention can be accomplished by methods heretofore known. The usual method is to drill to a point within a salt stratum or salt dome, and to dissolve salt therefrom by circulating water into and out of the borehole. The circulation of water is continued until the cavity has the desired size.

Hydrocarbons that can be stored in accordance with the invention are those which are normally gaseous or liquid, and which are preferably liquid when stored under the conditions of the process of the invention. Such hydrocarbons include, for example, propane, butane, pentane, olefins corresponding thereto, and mixtures of said hydrocarbons; hexanes, heptanes, octanes, olefins corresponding thereto and mixtures thereof; and gasoline and other distillate fuels such as gas oil. Crude oil can also be stored in accordance with the invention with good results. Hydrocarbons that are gases under the conditions of storage, such as methane and ethane, can be stored in accordance with the invention, and brine displacement thereof from the cavity assists in maintaining the pressurethereof at a desired'elevated level. I

Brine used in the invention is preferably substantially saturated. Aqueous sodium chloride solutions having a specific gravity of above about 1.1 give good results. The. use of a substantially saturated brine which has a specific gravity about 1.2 prevents dissolution of additional quantities of salt from the sub-surface cavities when the brine is in contact therewith. However, brine solutions having a lower salt concentration, and even water,

'can be employed if desired, it being understood that such use will cause dissolution of brine from the sub-surface salt cavity surfaces. The use of substantially saturated brine is preferred, as above described, and also for the further reason that the relatively high density thereof assists in maintaining a sharply defined interface between the brine and the stored hydrocarbons. This prevents mixing of hydrocarbons and brine within the cavity, and

integrated storage of hydrocarbons in salt cavities, and

such use of salt cavities as integrated with refinery operations, in accordance with the invention:

Three sub-surface salt cavities were prepared in salt strata as follows: Cavity A at a depth of 2300 feet below ground surface with a capacity of 30,000 barrels; cavity B at a depth of 2300 feet below ground surface with a capacity of 45,000 barrels; cavity C at a depth of 2600 feet below ground surface with a capacity of 50,000 barrels. The three wells were influid communication through a manifold serving as the single brine supply conduit, the brine from the supply conduit being introduced into the cavities through conduits with outlets near the cavity bottoms. Brine storage of a capacity approximately equal to the total capacity of the three cavities was connected with the brine supply conduit. Brine storage was provided by a concrete lined pit. A pump adapted to force brine from the brine storage into the brine manifold was provided. A pressure relief valve provided communication between the brine manifold and brine storage. The pump was designed to supply brine to the manifold at a pressure of up to about 25 p.s.i.g. A check valve at the outlet side of the pump was set to close at a pressure of about 25 p.s.i.g. to prevent reverse fiow'of brine through the pump when the pressure in the manifold exceeded this value. The pressure relief valve was set to open at about 35 p.s.i.g. to'permit brine to flow from the manifold to brine storage. Individual means for introducing hydrocarbons into the several cavities was provided, together with the necessary valves for introducing and withdrawing hydrocarbons, substantially as shown by the accompanying diagram.

To illustrate a typical integrated operation, a mixture of butane and butene from a hydrocarbon pipeline, which was contaminated with other hydrocarbons from a preducing this hydrocarbon mixture into the cavity was to provide storage therefor, until subsequent processing involving the removal of contaminating hydrocarbons and separation of the saturated from the unsaturated hydrocarbons could be undertaken. While introducing hydrocarbons into cavity A, butane, which had previously been introduced into and stored in cavity B, was removed therefrom at a rate of 7,000 bbL/day. The butane was. passed to a refinery operation where it was blended with gasoline to obtain an optimum vapor pressure for the final product. While adding hydrocarbons to cavity A and removing hydrocarbons from cavity B, a mixture of light hydrocarbons, from methane through pentane, was introduced into cavity C at the rate of 3,000 bbl./day, cavity C being used for utility storage of light hydrocarbons. 1

For the introduction of hydrocarbons into cavity A and cavity C, pumps supplying the hydrocarbons to the respective cavities at relatively high pressures were employed, the actual pressurebeing about 860 p.s.i.g. for introducing the hydrocarbons into cavity C and about 765 p.s.i.g. for introducing the hydrocarbons into cavity A. These pressures were suflicient to overcome the static heads of brine, the relatively low pressure supplied by the pump in the, brineconduit, and the pressure-drops in the conduits due to friction.

For the removal of butane from cavity B, it was only necessary to open the butane outlet from the cavity; brine from the brine supply conduit flowed into the cavity to displace the butane, the pressure developed by the static head of brine, as compared to the static head of butane, being sufficient for the removal at the rate stated.

When the input of hydrocarbons to the cavities was greater than the output thereof from the cavities, the pressure within the brine manifold exceeded the value of 35 p.s.i. required to actuate the pressure relief valve, and

hence the brine not employed for displacing butane from cavity C was returned to storage. However, the pump employed for supplying brine remained in continuous operation to insure an adequate brine supply at all times.

To further illustrate the invention, a refinery operaso that brine was always available for displacing hydrocarbons as needed.

The invention claimed is:

1. In the storage of hydrocarbons over brine in a plurality of underground salt cavities wtherein the hydrocarbons are pumped therein at relatively high pressure to displace brine and subsequently are removed therefrom by returning brine to the cavities, the process which comprises continuously supplying, from a brine storage source, brine at relatively low pressure into a manifold communicating with each of said cavities through a conduit extending to a lower part thereof, and cycling brine from 7 said manifold to said brine storage source when the pressure in said manifold exceeds the brine supply pressure, whereby hydrocarbons may be pumped independently to the cavities as individual streams resulting in a corresponding displacement of brine from the cavities into said manifold and whereby hydrocarbons may be independent- 'cavity by brine introduced therein to displace from the cavity the stored hydrocarbons, the improvement that comprises: (A) continuously supplying brine to a supply conduit communicating between brine storage and a plurality of sub-surface salt cavities, (B) returning brine from the supply conduit to brine storage when the pressure of brine in said supply conduit exceeds the brine supply pressure, (C) introducing hydrocarbons to be stored into a salt cavity under a pressure suflicient to displace brine tion required the removal of butane-butene from cavity A at the rate of about 1200 bbl./ day while simultaneously introducing butane into cavity B at the, rate of about 1000 bbl./day. Storage of light hydrocarbons in cavity C remained unchanged, i.e. hydrocarbons were neither introduced nor removed from cavity C during this operation. Operation was as before, with the brine displaced from cavity A flowing into the manifold and thence, at least in part, into cavity B for displacement of butane. The remaining brine required for butane displacement was-supplied from storage through the pump in the manifold.

In all of the foregoing operations, the pressure within the common brine conduit remained within the range of from about 25 to 35 p.s.i., and the pump supplying brine from storage to the brine manifold operated continuously from the cavity into the brine supply conduit, and (D) removing stored hydrocarbons from the cavity by displacement thereof with brine from the brine supply conduit.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Oil and Gas Journal of April 27, 1953, pages 194.

Oil and Gas Journal of August 17, 1953, page 84.

Claims (1)

1. IN THE STORAGE OF HYDROCARBONS OVER BRINE IN A PLURALITY OF UNDERGROUND SALT CAVITIES WTHEREIN THE HYDROCARBONS ARE PUMPED THEREIN AT RELATIVELY HIGH PRESSURE TO DISPLACE BRINE AND SUBSQUENTLY ARE REMOVED THEREFROM BY RETURNING BRINE TO THE CAVITIES, THE PROCESS WHICH COMPRISES CONTINUOUSLY SUPPLYING, FROM A BRINE STORAGE SOURCE, BRINE RELATIVELY LOW PRESSURE INTO A MANIFOLD COMMUNICATING WITH EACH OF SAID CAVITIES TROUGH A CONDUIT EXTENDING TO A LOWER PART THEREOF, AND CYCLING BRINE FROM SAID MANIFOLD TO SAID BRINE STORAGE SOURCE WHEN THE PRESSURE IN SAID MANIFOLD EXCEEDS THE BRINE SUPPLY PRESSURE, WHEREBY HYDROCARONS MAY BE PUMPED INDEPENDENTLY TO THE CAVITIES AS INDIVIDUAL STREAMS RESULTING IN A CORRESPONDING DISPLACEMENT OF BRINE FROM THE CAVITIES INTO SAID MANIFOLD AND WHEREBY HYDROCARBONS MAY BE INDEPENDENTLY DISPLACED FROM SAID CAVITIES BY BRINE FED FROM SAID MANIFOLD WHILE UTILIZING AS THE MOTIVATING FORCES FOR SUCH DISPLACEMENT THE WEIGHT OF THE COLUMN OF BRINE IN EACH OF SAID CONDUITS.

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