FI108288B - Method for initiating operation of an underground storage cavity for low-boiling hydrocarbons and an installation for the storage of low-boiling hydrocarbons - Google Patents

Description

λ 108288

Method for initiating operation of an underground storage cavity for low-boiling hydrocarbons and a facility for the storage of low-boiling hydrocarbons 5

The present invention relates to a method for introducing an underground cavity for the storage of hydrocarbons in liquid form at a low temperature well below 0 ° C. In particular, the invention can be used to store liquid natural gas (GNL) at a temperature of -162 ° C at atmospheric pressure. However, any other very low temperature liquefied hydrocarbon, such as ethylene, could also be stored by the method 15 of the present invention.

The so-called "cooling technology" for storage enables the product to be stored at atmospheric pressure. Under these conditions, the temperature of this storage comprises the gas and liquid equilibrium temperature at normal pressure of -162 ° C for GNL. The storage can be maintained at a constant temperature by extraction, condensation and re-injection of the gas in liquid form.

Various methods have previously been proposed for the storage of liquefied gases at low temperatures. Although the used storage cavity * ··· can be formed in clay soils with good leakage resistance, the cavity used in most methods: is excavated in a water-saturated rock. For example, in the case of propane, which can be liquefied under normal pressure only at relatively low temperatures, storage does not require any special pre-treatment. The cavity / interior walls comprise a rock impregnated with water. The setting of a / liquefied gas at a low temperature well below 0 ° C in the cavity freezes its interior, thereby forming an impermeable layer of ice. In another method of 2 108288, nitrogen may first be injected into the cavity to freeze its inner walls. Propane can then be placed in a cavity that has already been made leak-proof. Due to the relatively low liquefaction temperature 5, only slight stresses are applied to the inner walls of the cavity which do not damage the leak-tightness of the storage cavity. These stresses are too small to cause any cracks in the rock.

In order to store hydrocarbons having a much lower liquefaction temperature under normal pressure, for example when storing GNL or ethylene, it is not possible to allow the hydrocarbon to come into contact with a rock impregnated with frozen water. The stresses exerted on the rock in this case are considerable, leading either to widening of the cracks already present in the rock prior to excavation of the cavity or to the creation of new cracks at the start-up or during operation of the storage facility. In any event, such cracks will cause a flow of water that is difficult to stop, especially if it does not occur until the temperature begins to drop, or else the gas will begin to leak towards the surface, which is usually not detected before or during operation.

An increase in storage temperature through an increase in pressure would allow for the restoration of storage conditions similar to those for propane storage. However, for practical reasons related to the operation of the plant: · this option is not. not possible.

30 Solving the Rock Cracking Problem ... ·! sex is previously known to equip a cavity with a • ·, ···. with an inner lining fixed to the rock. However, in this case it is necessary to take into account the 'water layer around the cavity, as the probability of finding such a water layer at the intended storage depth (50-100 m) is high. In fact, such a layer of water can be utilized because, when frozen, it forms another leak-tight barrier liner.

When a lined cavity is provided in this manner, it is detrimental to allow ice to come into direct contact with the liner. The liner is usually secured to the rock by bolts, and the pressure caused by the formation of ice pockets can pull the bolts off and change the liner. In addition, in the initial stages prior to the introduction of the hydrocarbon at very low pressure 10, the pressure exerted by the water contained in the water layer which has not yet been frozen is also detrimental to the lining. For this reason, it is necessary to maintain a submerged zone between the inner liner and the ice layer.

15,225,023 proposes a solution according to which the inner lining of the storage cavity mainly comprises an impermeable layer placed on the inner side of the cavity and a permeable concrete layer in contact with the rock. The porous concrete layer includes a tubular mesh that is installed throughout the cavity. By injecting air into the pipeline network at a pressure higher than the pressure of the water below the surface, the water contained in the soil can be pushed back to the cracks in the rock by air. The ··· 'low zone containing water in the soil is thus formed around the cavity. The hydrocarbon can then be inserted into the cavity. After a certain time • *: The water / air equilibrium zone is reached at low I · ·. due to frost 30 caused by storage at temperature. This results in the formation of an ice layer remotely - .. ··! reason behind the liner. This English translator ···. according to the application, a drying tunnel is also dug under the cavity to reduce the pressure of the water in the soil. The introduction of such a cavity 35 containing air injection network is quite complicated and its manufacturing cost is undoubtedly similarly high.

4, 108288

It is an object of the present invention to provide a simplified and relatively inexpensive method for the use of a cavity for the storage of hydrocarbons at very low temperatures.

The invention also relates to a storage plant which is capable of receiving hydrocarbons at very low temperatures, i. a plant that can withstand the stresses of hydrocarbon regulation.

To this end, the invention provides 10 methods for providing an underground storage cavity, the cavity being designed to receive hydrocarbons kept in liquid form at a very low temperature, the cavity being formed inside a water layer and having an inert impermeable liner, characterized in that comprising the following steps: - removing water from the surrounding rock during the initial phase, wherein the cavity is free of hydrocarbon, until the level of the water layer falls below the cavity; - placing the liquid hydrocarbon at low temperature into the cavity while continuing to dewater so that the water depleted in the rock bed surrounding the cavity reaches a temperature low enough to freeze the water; and * ♦ ·· * - to stop dewatering to allow the formation of a predominantly water-free zone around the cavity * · ·., bounded by an ice layer.

· / ·: The emptying step can also be advantageously used when excavating a construction trench, as the effects of leakage and over-pressure will then disappear. ”* J. Water can also cause a harmful factor when setting the * ♦ · shade liner. Since the drainage system is intended for commissioning the cavity, it is desirable to use it earlier to facilitate working conditions when forming the cavity. Unlike the cavity proposed in GB-A-2 215 023, the formation of a substantially water-free zone does not depend on the structure of the inner lining of the cavity. It is thus possible to use the method of the present invention in combination with any type of cavity for use with very low temperature hydrocarbons.

In one embodiment, the drying operation involves pumping water in the soil in the vicinity of the cavity from the excavated well.

It should be noted that the purpose of the drying operation is to cause the aqueous layer to move below the level of the cavity and not merely to reduce the pressure exerted by it at the level of the cavity. In addition, the borehole drilling technology is much cheaper than the technology required to form a drying tunnel down the cavity.

Preferably, the drying stop step comprises an operation that allows the water layer to be lifted to gradually reduce the drying.

Thus, drying is not stopped suddenly, but gradually, thus allowing complete control of the return of water around the cavity. The drying can be controlled in this way by adjusting the pumps at the bottom of the well or the speed at which air is sprayed from the surface.

In another technique, the drying step of drying comprises the operation of allowing the drain well to freeze.

·; * ·· The present method is particularly suitable for use. **. when the hydrocarbon is stored in the cavity at temperatures below * # · -50 ° C, preferably below -100 ° C.

At higher temperatures for hydrocarbons, there is normally no rock cracking problem; : present.

, 108288 6

The invention also provides an underground storage facility comprising a cavity for receiving a hydrocarbon in liquid form and at very low temperature, below 0 ° C, this cavity being contained within a water layer and having a leak-tight inner liner, characterized by , that the leak-tight liner includes at least one solid load-bearing structure fixed to the rock and made of individual block slabs that can move relative to one another, and a structural leak-tight membrane supported by this structure that limits the lining's interior the strain and deformation caused by the low temperature hydrocarbon setting, even when the water layer has been lifted.

The leakproof membrane is exposed to both thermal and mechanical stresses. This is due, on the one hand, to a change in temperature, which causes high thermal stresses, and, on the other, to a possible displacement of the stone blocks. 20 Block slabs may be loaded with individually moving boulders and may change the membrane locally without compromising the leak tightness of the liner.

The drainage wells extending below the depth of the cavity are preferably formed in the vicinity of the cavity to lower the level of the water layer below the cavity.

***. By lowering the level of the water layer, it is possible to form an essentially anhydrous zone around the cavity.

• · · ·· - · Such wells can only be used during initial cavity *. * * Stages. Once the anhydrous zone is stabilized by the presence of a very low temperature hydrocarbon ice surface, the wells can be discarded or destroyed. Wells excavated vertically in the vicinity of the cavity include means for forming ice pockets in the immediate vicinity of the cavity, providing this means; 35 however, the maximum technical and economic benefits were realized.

7 108288

According to one feature of the invention, the block slabs are arranged side by side in a regular order, the leakproof membrane having a network of perpendicular corrugations, at least some of the waves being in line with the edges of the block slabs.

These perpendicular corrugations give the film a voh-like appearance that includes cross-folds. These folds form the most important points of deformation that a film can withstand, so it is essential to align them along the boundary lines of the block slabs. As the slab moves, the stress on the membrane is dampened directly by the corrugations surrounding this slab. This feature allows for further enhancement of the shape-deformability of the liner.

According to another feature, the liner further comprises a layer between the membrane and the load-bearing structure, made of parallel insulating panels delimiting the series laid over the block of slabs.

The insulation boards provide thermal insulation between the cavity and the surrounding soil, as well as between the cavity and the block slabs. The deformation property is thus ensured by superimposing the block slab and insulating board series. Each secretory plate is thus connected to only one of the 25 block plates. The edges of the block slabs and insulation boards are * '··' aligned with some corrugations of the film.

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The present invention will be described in detail with reference to the following drawings, which

Mt 1ί i illustrates, by way of non-limiting example, one of the 30 embodiments of the invention, in which: ... J Fig. 1 is a sectional view of the stock * *. · ♦ ·. a slurry to be prepared by the process of the present invention; v 'Figure 2 shows a larger scale of private ·. 35 at the interior lining structure covering the cavity of Figure 1; s 108288 Fig. 3 is a sectional view of a liner according to the present invention showing the setting of block slabs; Fig. 4 is a plan view of a block slab; Figure 5 is a general view showing the setting of the block panels on the inner wall of the cavity; Figure 6 is a sectional view of a liner according to the invention; Figure 7 is a larger scale view showing 10 a detail of Figure 6; Fig. 8 is a plan view showing a block board coated with a wafer-like leakproof film according to the invention; Figure 9 is a sectional view taken along line B-B of Figure 8; Figure 10 is a sectional view taken along line A-A of Figure 8; and Fig. 11 shows a theoretical diagram showing the primary steps of a method applied to a cavity such as that shown in Fig. 1 20.

As mentioned above, the present invention is particularly applicable to its GNL, but other types of hydrocarbon that are at very low liquefaction temperatures at atmospheric pressure are not excluded. 25 The following description refers to GNL because it is # '·. the most suitable substance.

The cavity 1 shown in Fig. 1 is formed in an underground bedrock containing a layer of water, with a cavity peak at a depth of approximately 50 meters. 30 The cavity is connected to the surface of the well 12. through.

The cavity 1 is closed at its junction with the well 12 by a plug 13 which is anchored in the rock. The stopper 13 contains a series of tubes required for the use of a storage device passing through it.

, * · 9 108288

The inner walls of the cavity 1 are covered with a leaky insulating lining 2. The lining 2 covers the entire cavity up to the stopper 13. Figure 2 is a cross-sectional view of liner 2 in a manner similar to the outline shown in Figure 1. In Figure 2, bare rock 6 is shown as a false smooth surface. In fact, the excavated rock surface is often irregular in shape, as shown in Figure 3. The block slab 22 made of concrete elements is initially anchored into the rock via tie rods 3.

10 These tiles are mechanically independent of each other and freely follow rock movements without causing stress to the block slab structure. This structure comprises a fixed load-bearing structure to which the other lining elements are attached. The concrete used for the block slabs is preferably provided with reinforcement. From Figure 3, it can be seen that the block slabs 22 are not directly placed against the exposed rock 6. If the rock surface is very coarse, low-density concrete foam 21 is injected in stages as block slabs are installed as shown in Figures 2 and 3. However, when the local irregularities in the rock do not exceed about 20 cm, the space between the block slabs 22 and the rock 6 is left empty. The block slabs are then about 30 cm thick and are held in place by means of a triple 25-bar tie bar, while the rock surface is

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. . ·. very coarse, the block slabs are 15 cm thick and are held in place by only two tie rods. The concrete · · · foam 21 transfers the pressure caused by the stored fluid to the rock. The load-bearing structure 30 of the block slabs 22 is made leak-proof by means of seals 220 which are inserted between adjacent block slabs. The circumference of each * · · '... · block tile 22 is staggered. From Fig. 4, voidaan '; discern that each block slab is made as a single concrete block in the form of two be-35 tones of the same size, superimposed and diaphragmally spaced apart to form a stepping around the entire circumference of the block slabs. The block slab of Figure 4 is intended to be attached to a rough rock surface because only five two tie rods 3 are used in connection therewith. The gasket 20 forms a central portion of the step, the shape of which complements the step of the adjacent block board. The block tiles 22 allows the tiles to move independently of each other, utilizing the flexibility of the seal 220. By way of example, the block slabs may be about 1 m wide and about 2 m long. The block slabs are preferably arranged in a regular series as shown in Figure 5. This allows each block plate 22 to move more freely as it depends only on the other four block plates.

The inner side of the block slabs 22 is then covered with a vapor barrier layer 221 made of a two-component epoxy resin intended to prevent moisture transfer from the rock wall to the next layer 23. Such a vapor barrier is similar to that used for open air tanks. However, having regard to the use of block tiles, it is desirable to place this guard in place before the tiles are installed.

The pins or "needles" are also placed in block slabs 25 22 of the insulating plates 23 forming the next layer. for installation.

• * ·

The structure of the insulating sheet 23 comprises a rigid honeycomb-like material such as PVC, both of which have t <· '· * glued on their faces. The insulation thickness is about 30 cm. According to an advantageous feature of the invention, the dimensions of the insulation boards * 1 23 coincide with the dimensions of the blocking boards 22, the insulation boards being additionally arranged such that each blocking board 22 corresponds to a single insulating board, whereby they are superimposed Figures 6 and 7 show 35. This facilitates the transfer of the block slab, since only one u108288 insulating board 23 needs to be moved with it. The boards are glued to the concrete 22 by means of a putty coated on the inner surface of the board. The setting and maintenance of pressure is achieved by means of pins placed on the plates 22. Finally, the glass film 5 is inserted into the space between adjacent plates 23 to provide continuous thermal continuity. It is not essential to use the insulating layer 23 under all conditions. In many cases, the liner is capable of operating without the use of insulation boards 23.

10 Stainless steel metal bodies, or "pins", are placed on the insulating plate top counter plate to serve as anchor points for the deformable leak-proof membrane 24 which forms the inner side of the cavity. This film 24 is made of stainless steel 15 of about 1.2 mm in thickness and has the appearance of an embossed wafer. It was originally intended for use in surface storage and gas tankers. One such film is described in FR-A-1 459 749. It incorporates a system of perpendicular perpendicular waves, which gives it considerable deformation capability. This deformation capability allows for compensation of the heat shrinkage caused by GNL at -162 ° C at low stress levels, and in the present case is also preferably used to withstand any deformation of the rock. . ·. without losing their ability.

* · ·: * ·, In order to obtain a good deformation ability for the entire liner 2, the joints between the block plates 22 and the insulating plates 23 ′ join the leak-proof corrugations of the film 24 as shown in Figs. 9 and 10. cross-sections of liner 2. The corrugated mesh of membrane 24 '... · may include multiple corrugations per block slab, as shown in Figure 8. An essential feature is that the block slabs 22 and / or the insulating panel 35 (if used) may include corrugations around their edges. These corrugations are formed at positions where the membrane 24 is particularly capable of withstanding deformation. Thus, it is very important that the joints 5 between the block plates 22 and the insulating plates 23 join at least some of the corrugations in the membrane 24.

In assembly, the membrane 24 is in the form of embossed sheets about 3 x 1 m in size, welded together and secured to the insulating panels 23 by welding 10 clubs to a stud in the center of each eye of the panel set.

The block slabs 22 also serve as a support structure for the film since the film can be mounted on an uneven support surface such as a bare rock surface. By opting for a block slab structure instead of a cast concrete layer, it is also possible to absorb the stresses due to the thermal creep effect of GNL at -162 ° C through the membrane 24 and possibly the insulating plate 23.

The use of a deformable leak-proof membrane in combination with a "floating" support structure permits the achievement of an inner liner that is leak-tight but deformable and capable of adapting to rock shifts due to temperature changes caused by GNL setting.

A cavity for use according to the present invention. . ·. the method of extraction is described below in connection with the cavity mentioned above. Cavities contained in fields other than those described above may also be treated using the present method, however, the cavity described above is best suited for use with this method. Referring to Figure 11, drain wells 4 • · ♦ * ... · are drilled adjacent to cavity 1, preferably at a distance of 2 to 20 meters from the cavity. Wells 4 are deeper than the bottom of the cavity. Each well is equipped with a bottom pump 35 or a supercharger connected to the compressor to perform an "air lift" operation. According to the invention, the first step comprises emptying the water layer from the water layer until the water layer falls below the bottom of the cavity. The cavity 1, initially surrounded by water, then enters 5 on a substantially anhydrous rock bed. In practice, some water will always remain on the rock surface where it will remain due to capillary action. The intended purpose is not to impregnate the soil surrounding the cavity, but to extract enough water to prevent the formation of too large frost pockets which could cause cracks in the rock. This step of lowering the aqueous layer could also be performed when the cavity is formed. This would make it much easier to install the liner 2 on the walls of the cavity.

The drying step must be continued to fill the water layer 5 pi-15 at a constant level below the cavity 1. As pumping continues, this second step involves placing the GNL in the cavity at a temperature of 1 to 162 ° C and atmospheric pressure.

However, despite the heat-insulating layer 23 of the lining 2, the soil surrounding the cavity reaches a temperature 20 low enough to freeze any remaining water in the rock. Thus, a substantially anhydrous zone is formed around the cavity. At this stage, the small amount of water frozen is insufficient to cause sufficient cracks in the rock to cause damage to the lining 2 of the cavity. By way of example, said water,. The frozen zone may be about 2 m thick when the GNL has been in the cavity for a few months.

♦ · - *! *. * Small amounts of water in liquid form can be left around the frozen zone of the dried rock.

30 Once the frozen zone has reached a sufficient thickness (about 2 meters), drying can be stopped. Sufficient thickness includes the thickness required to ensure, on the one hand, that water flowing toward the cavity freezes. and, on the other hand, that the thick ice ring is capable of absorbing hydraulic pressure from the outside. By gradually reducing the drying rate, it is possible to completely control the way the aqueous layer rises up around the cavity. When the drying is completely stopped, an anhydrous zone remains around the cavity 1 and is limited by the ice front.

5 The water layer 5 outside this ice face is in a liquid state.

Another technique, although less preferred, involves allowing the drain well 4 to freeze. The water layer 5 is then pumped continuously as the frozen zone formed by the GNL expands to the drain well 4. This solution has the disadvantage that it cannot control the controlled rise of water after the well 4 has frozen. As long as the cavity remains in operation and contains GNL, it is certain that the water-free 15 zone will remain.

The inventive embodiment described above is, of course, given by way of example only, and the method of the invention can be applied to any cavity for the storage of hydrocarbons at very low temperatures.

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Claims (9)

A method for commissioning an underground storage facility comprising an underground storage cavity (1) for receiving hydrocarbon in liquid form at a very low temperature below 0 ° C, the cavity being formed within and in the water layer (5). including a leak-tight inner liner (2), characterized in that it comprises the following steps: - in the initial stage, wherein the cavity (1) contains no hydrocarbon, dewatering from the surrounding rock until the level of the water layer (5) falls below the cavity (1); 15. placing the low-temperature liquid hydrocarbon in the cavity (1) while continuing to dewater so that the dewatered calcium carbonate surrounding the cavity (1) reaches a temperature low enough to freeze the water; and 20. stopping the dewatering to allow the formation of a substantially water-free zone around the cavity (1) bounded by an ice layer. 1 08288 lb Pa examining orders 2. A method according to claim 1, characterized in that the drying operation includes a pumping operation for the water in the soil in the vicinity of the cavity (1). . ·. from wells (4) extending to a depth greater than the depth of the cavity. The method according to claim 1 or 2, characterized in that the drying stop step 30 comprises the step of allowing the water layer (5) to rise by gradually reducing the drying. \ mti A method according to claim 1 or 2, characterized in that the drying stop step comprises the operation of allowing the drain wells 35 (4) to freeze. • »16 108288 Method according to any one of the preceding claims, characterized in that the hydrocarbon is stored in the cavity (1) at a temperature below -50 ° C. An underground storage facility made available by the method according to any one of the preceding claims, characterized in that the leak-proof inner liner (2) comprises at least one solid load-bearing structure fixed to the rock and made of individual block slabs (22) 10. moving relative to one another and deforming a leak-tight membrane (24) supported by this structure and limiting the inside of the cavity (1) so that the liner (2) is able to withstand the stresses and deformations caused by the application of extremely low temperature carbon , even when the water layer is raised. Storage plant according to claim 6, characterized in that the drainage wells (4) extending deeper than the depth of the cavity are formed in the vicinity of the cavity to lower the water layer to a level below the cavity. Storage plant according to Claim 6 or 7, characterized in that the block plates (22) are arranged side by side to form a regular series, 25 leak-proof membrane (24) having a network of perpendicular corrugations, at least some corrugated edges. with i «« to give sufficient flexibility to the coating required to adapt it to the rock displacement * · * movement caused by the temperature changes caused by the hydrocarbon regulation. Storage unit according to Claim 6, 7 or 8, characterized in that the liner further comprises a layer made of parallel insulating plates which form a series of arms between the membrane (24) and the load-bearing structure. <«Over a series of block tiles (22). 108288 17