US 3906973 A
A method for underground storage of heavy liquid substances, such as No. 2 heavy fuel oil, which solidify at normal storage temperatures, in a storage facility including a series of parallel underground galleries separated by protective piers, the galleries being closed at one of their ends adjacent to a working gallery and opening at their other ends into a common central channel communicating with the well being worked, and the beds of the galleries being in the same substantially horizontal plane. The fuel oil is conveyed into the galleries and solidifies. In order to take the stored substance out of the storage facility, a fluid which may be water with fuel oil trapped in a basin or a portion of the solidified mass of fuel oil itself is heated and then circulated over the surface of the mass of solidified fuel oil. The fuel oil is thus progressively liquefied and entrained in the flow of the fluid so that it may be pumped and taken out of the storage facility.
Claims available in
Description (OCR text may contain errors)
United States Patent 1 1 de Jerphanion et a1.
[451 Sept. 23, 1975 Etienne Schlumberger, both of Paris, France  Assignee: Societe a Responsabilite Limitee:
Societe Francaise de Stockage Geologique GEOSTOCK", Paris, France  Filed: July 8, 1974  Appl. No.: 486,697
 Foreign Application Priority Data July 10, 1973 France 73.25301  References Cited UNITED STATES PATENTS 3,874,399 4/1975 Ishihara 137/13 FOREIGN PATENTS OR APPLICATIONS Sweden 61/.5
Primary ExaminerAlan Cohan Attorney, Agent, or FirmBaldwin, Wight & Brown  ABSTRACT A method for underground storage of heavy liquid substances, such as No. 2 heavy fuel oil, which solidify at normal storage temperatures, in a storage facility including a series of parallel underground galleries separated by protective piers, the galleries being closed at one of their ends adjacent to a working gallery and opening at their other ends into a common central channel communicating with the well being worked, and the beds of the galleries being in the same substantially horizontal plane. The fuel oil is conveyed into the galleries and solidifies. In order to take the stored substance out of the storage facility, a fluid which may be water with fuel oil trapped in a basin or a portion of the solidified mass of fuel oil itself is heated and then circulated over the surface of the mass of solidified fuel oil. The fuel oil is thus progressively liquefied and entrained in the flow of the fluid so that it may be pumped and taken out of the storage facility.
11 Claims, 4 Drawing Figures US Patent Sept. 23,1975 Sheet 1 01 4 3,906,973
F IG] US Patent Sept. 23,1975 Sheet 2 of4 3,906,973
S W Q 222222 h 2 3 N G 8 8 v, 1 R E US Patent Sept. 23,1975 Sheet 3 of4 US Patent Sept. 23,1975
Sheet 4 of 4 METHOD FOR UNDERGROUND STORAGE OF HEAVY FLOWABLE SUBSTANCES The present invention relates to the field of underground or subterranean storage of heavy flowable or liquid substances such as heavy fuel oil, the viscosity characteristics of which are such that the substances congeal or solidify at normal storage temperatures.
At ordinary temperatures C to C) the viscosity of heavy fuel oil is known to increase considerably, and it is necessary to heat up so that it may be pumped. In conventional airborne storage, the heating up of heavy fuel oil is effected by providing in metal tanks steam, water or oil heat exchangers which may be in service continuously or only during effective use.
On the other hand, with subterranean storage the method of heating by means of heating coils alone is not applicable by reason of the geometrical configuration of the storage facility which generally comprises very long galleries which become inaccessible after they are put into service and which would moreover require heating coils of very great length. Further, maintaining the heating coils at the required temperatures demands prohibitive expenditures in energy.
German Pat. No. 1,033,139 is an example of prior art disclosures concerning the use of heating coils for such purposes. In this known arrangement, the heating device is adapted to heat water which is under a layer of petroleum in a storage cavity.
In another prior art document, US. Pat No. 2.17.2,683, ores are extracted by a stream of liquid sulfur. It therefore concerns extraction of ores and nota method of storing and taking out of storage heavy liquid substances such'as fuel oil.
An aim of the present'invention is to overcome the problems of storing heavy fuel oil or any other substances having physicalcharacteristics which lead, t similar contraintsl Generally speaking, the method according to the invention comprises circulating at least one hot fluid in contact with the exposed surface of the storedsubstance in congealed or solidified state and thereby entraining and progressively thawing or liquefying the stored substance so that it may be pumped and taken out of storage. I Y
A more specific object of the invention consists in a method for the subterranean storage of heavy liquid substances solidified at normal storage temperatures, and in particular No. 2 fuel oil comprising, with a view to storage, introducing the substance to be stored, previously heated if necessary, into a series of parallel subterranean galleries separated from their adjacent galleries by protective piers and being then closed at one end, the free ends of all the galleries opening into a common central channel which is connected to a well being worked, the beds or bottoms of all the galleries being located in substantially the same horizontal plane, the substance thus stored being solidified in said galleries; and, with a view for taking the substance out of storage, introducing a heated fluid through the ends of the galleries opposite the central channel, said heated fluid coming into contact with the surface of the stored substance and transferringheat thereto, thereby liquifying at least partially the stored substance and enabling it to be entrained by the stream of heated fluid towards the central channel, separating the-stored substance from the heated fluid entrainingit, and recovering by pumping the substance thus taken out of storage.
In a variation of the present method, the heated fluid used for taking the substance out of storage is taken from thestored substance, in which case the fluid is the substance itself, means are provided in the midst of the stored substance for heating part of the stored substance and circulating it.
It is, however, preferable to employ hot water as the heated fluid used for taking the substance out of storage that is, water previously heated which is permanently found in the subterranean storage facility in the lower portion of the layer of the substance being stored. In this case the hot water is immiscible with the stored substance and therefore during the process of taking the substance out of storage it must be separated for example, by'settling from the thawed or liquefied substance which it has entrained.
The invention will be illustrated by, but without being limited to, the following detailed description, made with reference to the accompanying drawings, in which:
FIG. 1 schematically illustrates in horizontal cross: section the arrangement of the storage galleries;
FIG. 2 is a vertical sectional view illustrating the operation of the method according to the invention;
FIG. 3 schematically illustrates a mock-up installation used for experimental work on the method according to the invention; and
FIG. 4 is a graph showing the results obtained with the mock-up installation of FIG, 3.
In the example given by way of illustration in FIGS. 1 and 2, we are concerned with the underground storage of No. 2 fuel oil. The storage facility is located unnical, geotechnical and economic requirements. As shown in FIG. 1, the rock mass 1 comprises a series of parallel galleries, three such galleries being shown in the drawing. The galleries comprise gallery halves 2a, 2b, 3a, 3b, 4a and 4b and adapted to be closed at one end (schematized by an *X") and opening at the other end into a common central channel 5. The central channel-is in communication with the well being worked to the side indicated by the arrow f (see FIG. 2). The series of gallery halves communicate with a gallery 6, called theworking gallery, which communicates at its end on the side of the arrow f-with the well being worked (see FIG. 2). The galleries are separated respectively by protective piers 7a, 7b, 8a, 8b, etc. The beds or bottoms of all the galleries are in the same substantially horizontal plane.
During the filling operation, the hot fuel oil from the well being worked is introduced into the working gallery by pumping in the direction of the arrow f. The fuel oil then flows into the gallery halves 2a, 2b, 3a, 3b, 4a, 4b, etc. from their ends opposite the central channel 5.
Under normal storage conditions, the temperature in the galleries is in the range of 10C to 20C. The hot fuel oil flows in at a high flow rate so that it cools off sufficiently slowly to retain rather'low viscosity, for example in the order of 300 cst at 50C, in order to be able to spread horizontally over the entire length of the galleries.
When the storage facility is full, the fuel oil may be allowed to cool off completely even if the fuel oil is of the type having a very-high point of solidification. This possibility is particularly desirable in the case of reserve storage facilities which therefore do not necessitate any application of heat for as long as the fuel oil is stored, i.e., for several years.
This is interesting in the case of seasonal storage where the heating is only carried out for the quantity of fuel oil desired and only for the time requiredfor pumping.
The heating power to be employed to obtain the reheating at a given flow rate may be greater than that in the case of constant temperature maintenance, but the device only operates during a small part of the: year.
Another advantage of heating the stored substance cool off resides in the fact that as a result of the lower heat loss in the ground owing to the fact there is an insulating envelope of the solidified substance about a thawed or liquified mass of the substance and that the mean temperature of the substance is low, the mean temperature of the ground remains low which reduces the supplementary geomechanical stresses of thermal origin in the rock mass. This advantage may be important depending on the rock in which the storage facility is dug, for it is then possible to:
1. position the storage facility deeper in order to make it feasible which would not be possible with a storage facility employing permanent heating; or
2. reduce the safety piers between galleries and thereby increase the possible storage volume within a given perimeter.
The process of taking the substance out of storage will now be described in greater detail with reference to FIG. 2. HO. 2 is a schematic vertical cross-section showing the installation provided about a well being worked for carrying out the method according to the invention.
Reference numeral 9 at the right of FIG. 2 corresponds to the well being worked. The line 9 represents the pipe for pumping hot fuel for storage. The well 9 also contains a pipe 11 which conveys the fuel oil for taking it out of the storage facility, and two pipes 12a and 12b for pumping subterranean water out of the facility: the pipe 120 for use when the storage facility is dormant and the pipe 121: for use when subterranean water is previously used to heat the substance in storage, and a pipe 13 for carrying fuel oil for heating. A pipe 35 is also provided for carrying streams as will be described hereinafter. The well 9 contains moreover all the usual operating pipes (for compressed air, aeration, etc.).
At the lower part of FIG. 2 a storage gallery 14 of the type illustrated in FIG. 1 is shown. The fuel oil is stored in the gallery 14, the level of stored fuel-therein being represented by the line au. A small amount of water flows from the surrounding ground into the galleries. In fact, the pressure of the water in the surrounding ground is greater than that of the fuel oil in the: storage facility which is at approximately atmospheric pressure. The rock mass is chosen to be as impermeable as possible, but it is not completely impermeable and a certain quantity of water continually penetrates into the storage facility. This water flows towards the bottom of the galleries towards a basin 15 where it is subjected to a first settling operation and then to the basin 19 where it is subjected to a second settling operation. From there it is carried away and processed on the surface by pipes 22 and 12a. The subterranean water coming from the surrounding underground streams around under the solidified substance along the gallery till it reaches the basin 15 into which .it eventually penetrates. By way of example, the basin 15 has a length in the order of 10 m whereas the galleries may be 500 m long. The sections of the gallery 14 may be between 50 m'- and 400 m depending on the nature of the rock in which the storage facility is formed. 7
The bottom of the basin 15 is below the bottom of the gallery so that water can be collected and can settle in the basin below the substance water interface represented by the line bb. A pump 16 is immersed in-the basin 15, and the pipe 17 connected to its delivery end divides into two lines 17a and 17b along which valves 18a and 1812 are respectively provided. The line 17a terminates at a settling tank 19. The water settled in the tank 19 is drawn via pipe 20 by the pump 21 which delivers the same to a pipe 22 communicating with the pipe 12a (or 12b) through valve 22a (or 2217). Further, the pipe 17b terminates'in a heat'exchanger'23. The water heated in the exchanger 23 leaves through line 24 and arrives at a main pipe 25 for conveying the reheating fluid to the end of the gallery opposite basin 15 where it is introduced at 25a.
The fuel oil circuit comprises a pump 26 immersed in the stored substance in the storage facility, the delivery pipe 27 for the pump 26 arrives at a separator 28 after passing through a valve 29. Two lines branch off from the separator 28, a secondary line 49 which collects water which may have settled in the separator and carries it to the settling tank 19 and a main pipe 11 for taking fuel oilout of the storage facility. The fuel oil separated fromthe water in the settling tank 19 is returned to the gallery via pipe 30.
Alternatively, the hot fuel oil at C taken from the basin 15 may be used to heat up the fuel oil solidified in the galleries, to a temperature of 45C for example.
For this purpose, the fuel oil circuit comprises a special device operatingin conjunction'with the separator 28 enabling at the outlet end of the pipe 27 the adjustment of the overall flow rate of fuel oil, as desired, in
The first direction is the above-described direction in which a portion of the fuel oil is brought to the surface over pipe' 11.
The second direction, after valves 32 and 34, follows the pipes 33 and 25 terminating at the closed ends of the galleries. The flow recirculating in this manner (at 80C for example) is adjusted so as to obtain the liquefaction (at 45C for example) of the fuel oil being taken out of storage. It will be noted that the valve 32a on the pipe 10 must be closed during the circulation of hot fuel oil.
The reheating circuit comprises a steam circuit 35 with the aforementioned heat exchanger 23 and another exchanger 36 for the petroleum for reheating. The petroleum for reheating is introduced via pipe 13 terminating at the tank 37. The petroleum for reheating is carried via pipe 38 through a series of heat exchangers 39 in the midst of the mass of stored fuel oil 14 before passing over line 40 drawn by a pump 41 which de- -livers the petroleum through the exchanger 36 before carrying it back to the tank 37 over line 42.
The operation of the installation shown schematically operate on the mineral oil (petroleum) for reheating introduced along pipe 13 and circulating in closed circuit through the pumps 42, heat exchanger 36 and tank 37. The heat exchangers 39 enable the temperature of the fuel oil in the basin 15 to be raised to about 70C The removal of the No. 2 heavy fuel oil is effected after the reheating with a circulation of hot water in accordanee with the present invention.
When the storage facility is operative i.c., when the stored fuel oil is being taken out of storage, the'water collected in the basin 15 is reheated in the heat exchangers 23 and directed towards the closed ends of the galleries via pipe 25.
From there the water circulates along the surface of the solidified fuel oil towards the central channel and the basin 15. This hot water liquefies a film of fuel oil along the outer surface of the mass of solidified fuel oil which is set in motion with the hot water in the direc tion towards the central channel 5 and the basin 15.
The reheating of themass of fuel oil in storage with the hot water raises the temperature of the surface portion thereof to a value just high enough for it to flow to the basin 15, for example.
As a result of the preliminary operation of the exchangers 39, the fuel oil in the basin is completely liquified when the circulation of the hot water is begun. The liquid water-fuel oil mixture which is formed therefore separates properly. The length of the basin is designed so that the fuel oil has sufficient retention time before being drawn away by the pumps 26 and carried to the surface. 7
The volume of water retained in the basin 15 is calculated so that there is a suffieient quantity of water to ensure the entire circulation.
In order to avoid very high water and heating power requirements when the process of taking the stored substance out of storage is begun, the hot water may be circulated along only several galleries or along only the portions of the galleries in proximity to the basin 15.
After the water originating from the basin 15 has been used to reheat the fuel oil, it is carried to the surface via pipe 121; to a special processing circuit.
Alternatively, the method according to the invention could operate with a heating fluid other than water which would be of particular interest in case it would not be possible to use water to reheat the stored substance. In the present example, it is advantageous to use some of the substance, i.c., the fuel oil per se, as the reheating fluid as shown in FIG. 2.
Generally speaking, however. hot water is preferred as the reheating fluid, for, all things being equal, the efficieney of heat transfer between hot water and the solidified stored subtance is ten times greater than that of hot fuel oil with the solidified stored substance. As water is heavier than the fuel oil, water is permenantly deposited on the surface of the mass of solidified fuel oil which further increases the heat transfer therebetween. It is nevertheless desirable to provide a hot fuel oil circuit for reheating the solidified substance in case of necessity, e.g., if and when the hot water circuit is out of order.
It will be noted that the installation described with respect to FIG. 2 does not include any piping or equipment in the galleries. The basin l5 and the pumping and reheating equipment are all grouped around the base of the well. Nearly all the pipes and valves are disposed in the working galleries of narrow cross-section, accessible to workmen.
FIG. 3 schematically illustrates the mock-up of the installation in which pilot tests of the method according to the invention were carried out; This series of tests was essentially intented to measure in a mock-up speed of liquefaction of various qualities of fuel oil, including heavy fuel oil No. 2, as a function flow rate and temperature of the hot water used.
The working gallery (reference 14 in FIG. 2) is represented by a part of a tank having an anterior plate 51 whereas the basin (reference 15 in FIG. 2) is represented by the residual .part 52 of the tank.
The solidified fuel oil 53 is stored in part 50 of the tank. For filing with fuel oil there is a movable vertical partition 54 on top of the plate 51. When the fuel oil is solidified the partition 54 is removed, the fuel oil then forming a practically solid block or mass 53 of fuel oil. The height h of the block 53 is shown in the drawing. The top surface of the block 53 physically represents the line aa. The combination of the two parts 50 and 52 of the tank is about l0 meters long. Another plate 55 erected in the part 52 is used to separate the part 56 for volume of water from part 57 for the fuel oil taken out of storage as will be seen hereinbelow.
At the extreme left of FIG. 3 and above the block 53 is provided a spray device 58 for supplying hot water in the form of a shower. The water circuit comprises a pump 59 communicating with a reservoir or tank (not shown) through a combination of valves 60 and pipes 61. The pipe 62 conveys flow rate Q of hot water to the spray device 58. A sensor 63 is provided on the pipe 62 for temperature regulation. Water collected at 56 (approximate flow rate Q) is recycled via pipe 64 through valve 65, reheater 66 and flow rate measuring device 67 (schematically represented by a venturi tube).
The fuel oil removed from storage (flow rate q) is collected in part 57 of the tank and recovered via line 68. A device 69 measures the flow rate q. The fuel oil is collected in recovery tank 70. At the bottom of the recovery tank 70 a drain valve 71 is provided for discharging waste water collected therein. Likewise a tube 72 connects the lower end of the recovery tank to the main water recycling pipe 64.
The mock-up installation illustrated in FIG. 3 serves as a model for the method according to the invention.
Hot water at a flow rate Q and a temperature Te is carried by the pipe 62 to the spray device 58 which sprays it onto the block 53 of solidified fuel oil, the upper surface of the block 53 representing the line aa.
The hot water flows towards part 52 of the tank transferring some of its calories to the fuel oil, the upper part of the block of fuel oil is thus liquified. The liquified fuel oil thus formed rises to the surface of the water, owing to the difference in densities, and flows into parts 56-57 of the tank where hot water at a flow rate Q and a temperature Ts lower than Te and liquid fuel oil at a flow rate q and a temperature Ts are collected. The dimensions of parts 56 and 57 of the tank are calculated so that the retention time of the waterfuel oil mixture is sufficient for the water and the fuel oil to be completely separated vertically of the partition 55.
The speed of liquefaction may be measured by the magnitude dh/dt which represents the variation of the height /z of the block of solidified fuel oil as a function of time t.
FIG. 4 shows a graph in which values of the temperature Te of the water at the spray device 58 are given along the X-axis and values of the magnitude dh/dt in cm/hr are given along the Y-axis for showing the change of this speed as a function of temperature for substantially constant rate of flow Q of water equal to 0.27 liter/seczWe see that the speed of liquefaction increases steadily with the temperature of the water. The tests carried out on the mock-up installation demonstrate the practicability of the method according to the invention.
Several advantages of the method according to the invention will now be mentioned in addition to those already mentioned above.
The storage facility according to the invention may be provided for very large quantities of heavy fuel oil, for example in the order of a million cubic meters. The invention brings about savings of -40 over conventional surface storage facilities. In comparison to present-day underground storage facilities, the novel process according to the invention has much lower operating costs since it eliminates the necessity of constantly supplying heat to the stored substance.
From the ecological point of view, underground storage is greatly preferred over surface storage which requires large capacity tanks. The method according to the invention also offers absolute safety against fire. Even if the stored substance comes in contact with a source of combustion, the fire will be stopped immedi-' ately owing to the absence of air in the galleries.
What we claim is:
l. A method for underground storage of heavy flowable substances solidified at normal storage temperatures in a storage facility including a series of parallel underground galleries, closed at one of their ends, the open ends of the galleries opening into a common central channel, the bottoms of the galleries being substantially in the same horizontal plane; comprising the following steps for putting the substance in storage, including introducing the heavy substance into the galleries and letting said heavy substance thus stored in the galleries solidify therein; and comprising the following steps for taking the stored solidified substance out of storage, including introducing a hot fluid through the ends of the galleries closed during the introduction of the heavy liquid substance, circulating said hot fluid in contact with the solidified stored substance in the galleries towards the common central channel and transferring heat to the solidified stored substance thereby progressively liquefying at least part of the solidified substance and entraining it with the circulating hot fluid, whereby the then liquefied substance may be pumped and taken out of the storage facility. A
2. A method according to claim 1, wherein the heavy flowable substance is No. 2 heavyfuel oil (having a kinetic viscosity between 1 10 and 380 centistokes at 50C). y
3. A method according to claim I, wherein the heavy flowable substance is heated before being introduced into the galleries.
4. A method according to claim 1, further comprising separating the liquefied stored substance from the hot fluid with which it is entrained.
5. A method according to claim 4, further comprising, 1 after separating the liquefied stored substance from the hot fluid, pumping away the separated liquefied substance.
6. A method according to claim 1, wherein the hot fluid is hot water, andfurther comprising collecting water in the storage facility under the stored substance and heating the collected water before circulating it.
7. A method according to claim 3, wherein the hot fluid is hot water andwhereinthe separation is effected by settling. I
8. A method according to claim 1, further comprising reheating a portion of the stored substance, the hot fluid being constituted by the reheated portion of the stored substance.
9. A method according to claim 6, further comprising immediately before the steps for taking the stored substance out of storage, circulating a separate reheating fluid in a closed circuit including a heat exchanger through a solidified mass of the substance with subterranean water thereby liquefying .the solidified mass then finding its way into a basin in communication with one of the galleries.
10. A method according to claim 9, wherein the reheating fluid is circulated over only a few galleries of the storagefacility.
ll. Amethod according to claim 9, wherein the reheating fluid is circulated over only the part of the galleries in the proximity of the basin.