US2976691A - Storage of oil and other waterimmiscible fluids - Google Patents

Description

March 1951 H. EDHOLM 2,976,691

STORAGE OF OIL AND OTHER WATER-IMMISCIBLE FLUIDS Original Filed July 6, 1955 Fig.1

INVENTOR HARALD EDHOLM A ATTORNEYS STORAGE OF OR OTHER WATER- ISCBLE FLUIDS Harald Edholm, Solsidan, Saltsjobaden, Sweden Continuation of application Ser. No. 520,326, July 6, 1955. This application Dec. 14, 1959, Ser. No. 859,456

Claims priority, application Sweden Nov. 2, 1954 Claims. (Cl. 61-.5)

This invention relates to apparatus and method for the storage on a water bed of oil or other water-immiscible fluids, primarily viscid oils having specific gravities less than that of water, the apparatus being in the form of a container arranged in a cavity in subsoil wa ter bearing rock, porous ground, concrete or the like, and in which the water bed is maintained in equilibrium by a water column communicating therewith and being essentially separated from the oil column and from the subsoil water and serving for the control of the oil col- .umn, and in which container the oil is in direct contact ter, the oil was allowed to penetrate to a certain extent into the rock or the like and thus to impregnate the same whereby the oil disposed within the cavity proper was completely protected from water seepage. In this case, the water to be pumped out in order to control the water column emanates from the subsoil water seeping inwardly through the Walls and bottom of the container in the region of the water bed.

The drawback involved in such an arrangement primarily resides in the fact that the pressure head of water columns, and thus of theoil, which corresponds to these conditions will result in that the extrusion of oil will be considerable at the upper surface of the oil and, in addition, will be very sensitive to variations in the general level of the subsoil water.

On the other hand, it has been proposed so to relate the pressure head of the water column to that of the subsoil water that, from the uppermost point of the walls of the cavity at which oil directly contacts cracks and fissures in communication with subsoil water and down to the water pool, the pressure of the subsoil water equals or surmounts that of the oil, whereby the subsoil water present in such cracks or fissures will be forced as far oil.

Such an arrangement offers the advantage of preventing any oil penetration into the water impregnated walls of the cavity, and in addition the arrangement will be "more insensitive to variations in the general level of the as the wall surface of the cavity and possibly into the atent f ice for keeping the water seepage within reasonable limits without, however, permitting excessive penetration of oil into the ground, and for the object stated the invention mainly resides in the fact that the pressure head of the water column is so related to that of the subsoil water that, at those portions of the cavity where the oil is in direct contact with cracks or fissures in communication with subsoil water, the oil pressure at a lower portion (the seepage region) of the container is less than the pressure of the subsoil water, causing subsoil water to seep into the oil, whereas above this seepage region oil is allowed to penetrate into the cracks or fissures in the wall of the cavity.

This and other objects, features and advantages of the invention will be described in, or become apparent from, the following description thereof as read in conjunction with the accompanying drawing in which:

Fig. l is a vertical section through a container according to one specific embodiment of the invention and illuspool is a water column in the pipe 4 having its upper level at a height h above the level 13. These levels are interrelated according to the equation:

where a is the specific gravity of the oil relative to that of the water concerned.

The oil level 12 intersects the wall of the rock at C and the level of the water column is flush with the level point C on the wall of the rock. A water accumula- 'tion 3 has a surface which can be varied between the levels A A and A The accumulation 3 may represent the sea, the varying heights of the water being caused by the tide. On the other hand, the accumulation 3 may represent an artificial or natural body of Water, the depth of which may be varied by any suitable means, or maintained constant. The water accumulation is assumed to communicatepwith cracks and fissures in the rock 5. By pumping or in any other suitable way, any water penetrating through the rock 5 to the water pool 2 is removed so that, according to a first example, the oil level 12 is maintained constant. Due to the level difference between the water column in pipe 4 and the water accumulation 3, the upper surface of the subsoil Water will slope inwardly towards the cavity 1 along the lines A B A -B and A B respectively, and will form a so-called cone of depression. These lines in the accompanying drawing are shown as being straight lines which may be true under certain conditions, but they can also be curved. As far as the points B B and B; at which the oil level 12 intersects the subsoil water surface lines, oil will penetrate into the rock. At the water level A the extension of the line A B intersects the wall of the cavity at C flush with the upper level of the water column within the pipe 4. The oil will be found then to penetrate to the line B -D forming a walls and bottom of the cavity which are contacted by the water pool 2.

On the other hand, if the level of thewater accumulation is raised to A then the subsoil water boundary line will be parallel-displaced to the position A B This will cause the intersection B to coincide with the oil level 12. In such a case oil cannot penetrate into the rock whereas, on the other hand, a flow of water will seep inwardly through the walls of the cavity between the levels 12 and 13. If the rock is highly water pervious the rate of water seepage may be considerable.

If, however, according to the present invention, the surface of the accumulation 3 is placed at an intermediate level, such as, for instance, A then the subsoil water curve will intersect the oil level at B The parting line between oil and water will be parallel-displaced towards the cavity to the position B D Then water will seep inwardly into the container at the portion D D of the wall of the cavity whereas any extrusion of oil into the rock will be prevented in this portion. This portion may be called the seepage zone. Above the seepage zone oil will penetrate into the rock whereas water is prevented from seeping into the cavity. It is possible by variation of the level A to control the height h, of the seepage zone. In addition to the rate of flow of water seeping into the container through the walls and bottom of the water pool 2 already at the position A --B D there will be added, in the case A -B D a rate of flow Q which is dependent on the height h of the seepage zone. This condition is illustrated in Fig. 2 in which rates of flow of seepage water, Q are plotted as abscissae against height of the seepage zone as ordinates. In its beginning the curve thus obtained shows but slight increase in Q for increasing values of k However, the rate of increase gradually grows up to a value of h =h i.e., corresponding to the limit case A B in which the seepage zone covers the entire wall of the cavity. From this it will apparently be possible by limiting h to a value less than h but greater than zero, firstly, to control and, secondly, to reduce to a high degree the inflow of seepage water, and at the same time the penetration of oil into the rock will be reduced relative to the amount of oil extrusion in case there is no water seepage zone. It should be noted, however, that even a water seepage zone of small extension will involve not only a reduction of the oil extrusion but also that the same will be more stable and thus less sensitive to variations in the subsoil water conditions, and this thus without any material increase of the water seepage into the container.

The operating conditions pertaining tothis intermediate case are illustrated in Fig. 3. In the seepage zone 11 water flows into the container and forms drops 6 in the oil. Such drops will also partly be seen below the level 13 in the form of water inclusions surrounded by films of oil. However, these inclusions will soon burst causing separation of the oil from the water.

When the level of the accumulation 3 is subject to change, the elevation of the point D varies accordingly, and if it is desired to maintain k constant, it is necessary to suitably vary the pressure head of the water column h 0n the other hand, when the level of the accumulation 3 is not subject to change, the elevation of the point D remains constant. unless varied by suitably varying the pressure head of the water column h In other Words, the line B D is disposed more or less near the cavity, depending upon the rise and fall of the accumulation 3, if any, and also depending upon the pressure head of the water column.

When the quantity of oil is subject to variations, i.e., when oil is removed firom the stored supply or fresh oil is introduced, the pressure head of the water column relative to that of the subsoil water can be raised when the quantity of oil is increased whereby the line B -D will be displaced away from the cavity as the interfacial line '13 moves downwardly, whereas, upon a reduction of the quantity of oil, said pressure head is decreased and the line B D is displaced further towards the cavity causing the point D to be moved upwardly. Thus this enables the attainment of the result that, where the quantity of oil stored is subject to variations, the rate of flow of seepage water through the oil is maintained approximately constant, or at least is prevented from exceeding a predetermined maximum value. With a somewhat diiierently defined object in view, the control can be exercised in such a manner as to cause the seepage region to be maintained at a size which is substantially unchanged for varying quantities of oil in the container.

When, at an unchanged level of the subsoil water and at a constant upper oil level, oil is withdrawn from the container, then the pressure head of the water column will rise gradually to the upper level of the surface of the oil when all the oil has been withdrawn and the pool of water 2 has reached the level 12. Then, in the case illustrated, the final value of the slope of the surface of the subsoil water in the rock will be represented by the line A C which means that the slope of the subsoil water has been reduced in spite of the fact that both the level of the subsoil water and that of the oil have been maintained constant. This in its turn leads to an increase of the height of the oil impregnated region relative to the total height of the oil column when oil is withdrawn which may be of advantage in cases where the upper region of the wall of the container is highly pervious. The converse will be true when oil is supplied into the container.

On the other hand it is possible by lowering the oil level when oil is withdrawn to maintain constant or to increase the slope of the subsoil water, which will cause all the oil present in the rock to be driven more effectively by the subsoil water back into the cavity before the entire quantity of oil in the container has been withdrawn. This method would be of particular importance where deep containers are concerned.

Under certain conditions it would be of advantage when oil is withdrawn to raise the oil level gradually, if this be done to a moderate degree which precludes the risk of a free escape of oil into the surrounding terrain. This may be of importance, for instance where highly pervious containers of a comparatively small depth are concerned. The advantage of this method resides in that the water seepage into the container will be reduced also below the oil column which will reduce the pumping work and the maintenance when the oil quantity in the container is small.

When storing oils having elevated points of solidification in containers equipped with a heating device it would be possible permanently to seal that region of the wall of the cavity which is situated above the seepage zone by operating the plant for a suflicient period of time at a comparatively high oil temperature enabling oil in a fluid state, in accordance with the present invention, to penetrate into cracks and fissures, after which the operation of the plant may be continued at a fairly moderate over-temperature, whereby the oil will solidify in cracks and fissures in the walls of the cavity and will form a permanently sealing impregnation in the whole or a portion of the zone contacted by the oil whereby the container could possibly be used for storing non-solidifying oils, without any water seepage in the region thus impregnated.

The invention is valuable also for storage in cavities surrounded by a more or less inclined subsoil water surface, such as, for instance, in sloping ground. In this case it will be possible to adjust the oil level or the level of the water column in such a way as to cause the present invention to be exercised on the side where the subsoil water is low whereas on the side where the subsoil water is high the storage is effected utilizing the storage method referred to in the preamble and according to which the pressure of the subsoil water throughout this side would be higher than that of the oil.

The invention is also of importance where the subsoil water available is subject to great variations. In this case it is of great practical advantage if the oil column, or a so-called floating roof supported thereon, can be maintained at a substantially constant height irrespective of the variations in the level of the subsoil water. This result is attainable if the level of the oil is so chosen that, when the level of the subsoil water is low, the inventive principles will be carried into eifect using a relatively low seepage region having the height h and extensive oil penetration, and, when the subsoil water rises to its highest levels, the inventive principles are exercised using a large seepage region, or the method is practiced referred to in the preamble operating by a positive subsoil water pressure, i.e., in which the subsoil water pressure prevents any oil penetration into the ground. This application of the invention will minimize the average seepage.

It is understood that the invention is not restricted to the case hereinbefore described in conjunction with the accompanying drawing in which a crack is assumed to extend vertically throughout the height of the container. The invention isapplicable to underground containers at all subsoil water conditions.

I claim:

'1. A method of controlling the storage of oil in a column above a water bed in an arrangement comprising a container provided by a cavity in a subsoil water-bearing pervious formation, in which container the water bed is maintained in equilibrium by a water column communicating therewith and essentially separated from the oil column and from the subsoil water and serving for the control of the oil column, and in which container the oil is in direct contact with the water pervious walls thereof, and characterized by the fact that the pressure head of the water column is less than that of the subsoil water adjacent said walls so that the oil pressure at the lower end of he oil column is less than the pressure of the subsoil water whereby to allow subsoil water to seep into the oil, and so that the oil pressure above said lower end oil column portion is greater than the pressure of the subsoil water adjacent said walls whereby to allow oil to penetrate the wall of the cavity, comprising increasing the pressure head of the water column relative to that of the subsoil water when the oil quantity stored is increased, and reducing said pressure head when the oil quantity stored is reduced, said changes of said pressure head being to such an extent as to cause the rate of flow of seepage water to be maintained approximately constant for varying quantities of oil and less than a predetermined maximum value.

2. The method of claim 1 characterized in that the pressure head of the water column is so adjusted as to cause said lower end oil column portion to be maintained approximately unchanged in size for varying quantities of oil stored.

3. The method of claim 1 characterized in that the water column is so adjusted that, at a relatively low level of the subsoil water, said lower end oil column portion will be relatively restricted and the oil penetration into the container wall above said lower end oil column portion will be relatively extensive, whereas, at a relatively high level of the subsoil water, the lower portion will be relatively extensive.

4. A method of storing oil in a column above a water bed in an arrangement comprising a container provided by a cavity in a subsoil water-bearing previous formation, in which container the water bed is maintained in equilibrium by a water column communicating therewith and essentially separated from the oil column and from the subsoil water and serving for the control of the oil column, and in which container the oil is in direct contact with an area of the water previous walls thereof, comprising withdrawing water from the water bed to bring the oil column pressure head to be sufficiently less than that of the subsoil water adjacent said walls to induce subsoil water to seep into the oil through the lower end of the pervious wall area against the pressure of the oil while maintaining the oil column pressure head sufficiently high to induce the oil to penetrate out through said walls at the upper portion of said pervious wall area against the pressure of the subsoil water to form an oil curtain restricting said seeping-in of water through said upper portion of said pervious wall area.

5. The method of claim 4 comprising readjusting the pressure head of the oil column when the height of the subsoil water varies.

6. The method of claim 4, comprising readjusting the pressure head of the oil column when the height of the subsoil water varies to cause the rate of flow of water seeping into the cavity to be maintained between predetermined upper and lower limits.

7. A method of storing oil in a column in a cavity having porous walls in a previous subterranean formation containing subsoil water and having a water column separated from the cavity and communicating with the water in said formation, the oil in said cavity being in direct contact with an area of the porous walls thereof, the steps comprising adjusting the pressure head of the water column to render the pressure of the subsoil water at the lower end portion of the oil column greater than the pressure of the oil adjacent thereto and the subsoil water pressure adjacent to an upper portion of said pervious wall area less than the oil pressure in the oil column adjacent thereto whereby the water seeps into the cavity through a lower portion of the porous wall area and forms a water bed at the bottom of the cavity below the oil column and oil seeps through an upper portion of the porous wall area to seal it against seepage of water.

8. A method of controlling the storage of oil in a column above a water bed in an arrangement comprising a container provided by a cavity in a subsoil water bearing pervious formation, the upper boundary of said subsoil water representing an inclined surface and said Water bed in the container being maintained in equilibrium by a water column communicating therewith and being essentially separated from the oil column and from the subsoil water and serving for the control of the oil column, and in which container the oil is in direct contact with an area of the water pervious walls thereof, comprising withdrawing water from the water bed to bring the oil column pressure head to be sufliciently less than that of the subsoil water adjacent said wall area to induce subsoil water to seep against the pressure of the oil into the oil in the lower end of the oil column and in a first section of an upper portion of said area adjacent the higher portion of said inclined subsoil water surface while maintaining the oil column pressure head sufficiently high to induce the oil to penetrate out through said walls against the pressure of the subsoil water in a second section of said upper portion of said area adjacent the higher portion of said inclined subsoil water surface to form at that second section an oil curtain restricting said seeping-in of water into the oil in said lower end and in said first section of the upper end of the oil column.

9. A method of storing oil in a column in a cavity having porous walls in a pervious subterranean formation containing subsoil water with an inclined surface and having a water column separated from the cavity and communicating with the water in said formation, the oil in said cavity being in direct contact with the porous walls thereof, the steps comprising adjusting the pressure head of. the water column to render the pressure of the subsoil water at the lower end portion of the oil column greater than the pressure of the oil adjacent thereto and the subsoil water pressure adjacent to an upper portion of the oil column less than the oil pressure in the oil column adjacent the lower portion of said inclined subsoil water surface but higher than the oil pressure in the column adjacent the higher portion of said inclined subsoil water surface, whereby the water seeps into the cavity at said lower end portion and adjacent said higher portion of said inclined subsoil water surface and forms a water bed at the bottom of the cavity below the oil column and oil seeps into the wall of the cavity adjacent to said upper portion of the oil column at said lower portion of said subsoil water surface, to seal said wall portion at said lower subsoil water surface portion against seepage of water.

References Cited in the file of this patent UNITED STATES PATENTS 2,661,062 Edholm Dec. 1, 1953 FOREIGN PATENTS 11,505 Denmark Aug. 15, 1924 104,349 Sweden Apr. 21, 1942

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