Patent Description:
Hydrogen has a high stored energy level in relation to its mass and is free of carbon. Due to these and other attractive properties, hydrogen is foreseen to be used much more in the future. To use hydrogen on a large scale, an infrastructure of production, transportation and storage is needed. One way of storing gas underground is known from <CIT>.

It is an objective of the present invention to provide an improved method of providing a fluid storage, e.g. for pressurized hydrogen gas, but any other compounds or mixtures of compounds in liquid and/or gas form may be stored using a suitable embodiment of the fluid-tight subterranean fluid storage of the present invention.

According to an aspect of the present invention, there is provided a method of preparing/constructing a fluid-tight subterranean fluid storage. The method comprises boring a borehole in a rock mass, e.g. vertically or at an acute angle to a vertical axis with an upper end at a surface/bedrock of the rock mass. The method also comprises inserting a fluid-tight pipe longitudinally, e.g. concentrically, into the borehole, the pipe comprising a lateral wall in the form of a right circular cylindrical shell having an outer diameter which is smaller than a diameter of the borehole, a bottom end cap fastened to a bottom end of the lateral wall (e.g. arranged to rest against a bottom of the borehole either directly or via a rigid frame), and a top end cap fastened to a top end of the lateral wall. The method also comprises, via piping (typically comprising a valve opening/allowing flow or closing off/preventing flow in the piping) through the top end cap, pressurizing the fluid-tight pipe to a pressure above a predetermined threshold, whereby the lateral wall is deformed until it is pressed against an inner surface of the borehole along a longitudinal extent of the lateral wall, forming a fluid-tight lining of the borehole. The lining together with the bottom end cap and the top end cap forms the fluid-tight subterranean fluid storage in the borehole.

According to another aspect of the present invention, there is provided a fluid-tight subterranean fluid storage prepared by an embodiment of the method of the present disclosure.

According to another aspect of the present invention, there is provided a fluid-tight subterranean fluid storage comprising a fluid-tight lining of a bore hole in a rock mass, a bottom end cap fastened to a bottom end of the lining, a top end cap fastened to a top end of the lining, and piping through the top end cap. The lining is formed by a deformed right circular cylindrical shell, inserted longitudinally into the borehole and deformed by means of an overpressure applied via the piping.

By deforming the material of the lateral wall to rest against the rock at the inner surface of the borehole, the thickness of the lateral wall may be reduced since it does not have to by itself withstand the pressure of the stored fluid. Also, there is no need to encapsulate the storage (e.g. in cement). Instead, the pipe (having a slightly smaller diameter than the borehole) can be assembled and inserted into the borehole and then expanded to directly contact the rock mass.

It is to be noted that any feature of any of the aspects may be applied to any other aspect, wherever appropriate. Likewise, any advantage of any of the aspects may apply to any of the other aspects.

The fluid-tight subterranean fluid storage described herein is a vessel in a rock mass borehole, which can be used to store pressurized fluid in gas and/or liquid form, e.g. hydrogen (H<NUM>), methane (CH<NUM>), propane (C<NUM>H<NUM>), natural gas, carbon dioxide (CO<NUM>), nitrogen (N<NUM>), ammonia (NH<NUM>), air, water, and/or ammonium (NH<NUM>), preferably hydrogen.

The storage method can be used for single fluid-tight subterranean fluid storage for fluids with high pressure, underground or for larger storage needs. Fluid-tight subterranean fluid storages can be placed in a suitable pattern with adequate distance between them. There is no upper limit for the number of storages which can be safely deployed provided the rock mass has geologically appropriate characteristics and geomechanical properties. An advantage of the storage method is that it can be made very safe compared to other known storage methods. Any leaks, faults, other breakdowns or terrorist attacks would have a limited impact since the stored fluid could be spread over a large and possibly fenced-in area. Any gas which leaks may rise rapidly into the atmosphere. Proximity to production and/or distribution of hydrogen and electricity may be advantageous, as it opens up the possibility to utilize residual heat during conversion from electricity to hydrogen or back. The possibility of recovering the oxygen from the process during production of hydrogen gas may also be considered.

To understand the applied use of this storage method, here follow some examples of using hydrogen in combination with the fluid-tight subterranean fluid storage of the present disclosure.

<FIG> illustrates that a storage may be built close to an electric grid and on a property and rock mass which is geologically appropriate for the storage method. At the location, electricity and water can be converted to hydrogen and stored. Later, the stored hydrogen can be extracted from the storage, converted to electricity and water, and used in the electric grid.

<FIG> illustrates that a storage may be built close to an electric producer and on a property which is geologically suitable for the storage method. At the location, electricity and water can be converted to hydrogen and stored. Later, the stored hydrogen can be extracted from the storage, converted to electricity and water, and used in the electric grid.

<FIG> illustrates that a storage may be built close to an electric grid, close to a hydrogen consumer and on a property which is geologically suitable for the storage method. At the location, electricity and water can be converted to hydrogen and stored. Later, the stored hydrogen can be extracted from the storage and used by the consumer.

<FIG> illustrates that a storage may be built close to a hydrogen consumer, where hydrogen transport is possible and on a property which is geologically suitable for the storage method. At the location, hydrogen can be unloaded from the transport and stored. Later, the stored hydrogen can be extracted from the storage and used by the consumer.

<FIG> illustrates the pressurizing of the pipe to deform the lateral wall <NUM> to be pressed directly against the inner surface <NUM> of the bore hole <NUM> in the rock mass <NUM>. The pressure P is applied within the fluid-tight pipe, exerting a radial force on the lateral wall <NUM> towards the inner surface <NUM> of the borehole <NUM> as illustrated by the outward pointing arrows. The rock mass will apply a corresponding force in the opposite direction, as illustrated by the inward pointing arrows, when the wall <NUM> has been deformed to directly contact the rock surface <NUM>.

The deformation is plastic deformation, especially when the lateral wall <NUM> is of a rigid material, e.g. a polymeric (plastic) material or a metallic material, e.g. steel as discussed further below. Examples of polymeric materials include thermosetting materials, which may advantageously be cured after deformation, and thermoplastic materials. Thermoplastic materials may have the advantage of enabling joining of segments of the right circular cylindrical shell of the lateral wall <NUM> by heating and then joining segment ends to each other to form the lateral wall. In some embodiments, the polymeric material, e.g. a thermosetting polymeric material (resin) such as epoxy, may be fibre-reinforced, e.g. with glass and/or carbon fibres, to form a composite material.

In some other embodiments, not being a part of the claimed invention, the deformation is elastic deformation, especially when the lateral wall <NUM> is of an elastic material (e.g. an elastomer), e.g. a natural or synthetic rubber. In case of elastic deformation, the lining <NUM> is held in place against the inner surface <NUM> of the borehole <NUM> by an overpressure within the fluid storage <NUM>.

For facilitating the pressurizing with the pressure P to achieve the deformation, e.g. plastic or elastic deformation, of the lateral wall <NUM>, the pipe may preferably be filled with water whereby the pressure P is the pressure of the water in the pipe.

Preferably, the rock mass <NUM> has a strength exceeding the pressure P, to prevent failure of the rock. Table <NUM> shows typical examples of rock strength of rock mass found in Scandinavia.

<FIG> illustrates the over pressure, in mega Pascal (MPa), needed to plastically deform different materials having different yield points, in MPa, at different wall thicknesses, in millimetres (mm). The graph can be used for selecting a suitable thickness of a rigid material of the lateral wall <NUM>, depending on the rigid material used and the pressure P which can be applied.

The rigid material is typically metallic, e.g. steel, but polymeric or composite materials, e.g. being or comprising polyethylene (PE) are also contemplated. Table <NUM> shows the lower yield point for some currently preferred steels, which are relatively cheap, readily available and easy to weld. Note that Table <NUM> shows the lower yield point (ReL) rather than the slightly higher upper yield point (ReH).

Table <NUM> shows some examples of pressure P needed form plastic deformation of the lateral wall <NUM> for different diameters and thicknesses of the wall <NUM>, for two of the steels of Table <NUM>.

In some embodiments of the present invention, the upper yield point (ReH) of the rigid material is within the range of <NUM>-<NUM> MPa, preferably <NUM>-<NUM> MPa. The yield point may be determined using tensile testing in accordance with ISO <NUM> for metallics or ISO <NUM> for plastics/polymerics and composites. Additionally or alternatively, in some embodiments of the present invention, the pressure P to which the fluid-tight pipe is pressurized is within the range <NUM>-<NUM> MPa, preferably <NUM>-<NUM> MPa. Additionally or alternatively, in some embodiments of the present invention, the material, e.g. a rigid material, of the lateral wall <NUM> is metallic or polymeric, preferably steel e.g. S235JR, S275JR, S355N or S420N. Additionally or alternatively, the lateral wall <NUM>, before pressurizing, has a thickness within the range of <NUM>-<NUM>, e.g. <NUM>-<NUM>, preferably <NUM>-<NUM>.

Conveniently, the outer diameter of the lateral wall <NUM> is only slightly less than the diameter of the borehole, allowing the fluid-tight pipe to be readily inserted into the hole but without the need for more plastic or elastic deformation, i.e. in this case elongation of the rigid or elastic material of the wall <NUM>, than necessary, reducing the risk of cracks in the material during the deformation. Thus, in some embodiments of the present invention, the outer diameter of the right circular cylindrical shell forming the lateral wall <NUM> is within the range of <NUM>-<NUM>% of the diameter of the borehole <NUM>.

<FIG> illustrates an embodiment of the fluid-tight subterranean fluid storage <NUM>, formed by the fluid-tight pipe <NUM> inserted into the borehole <NUM>. The storage <NUM>, and thus the pipe <NUM>, comprises the lateral wall <NUM>, e.g. of a rigid or elastic material, in the form of a right circular cylindrical shell, which after plastic or elastic deformation forms a lining of the borehole <NUM> when in contact with the rock of the rock mass <NUM> at the inner surface <NUM> of the borehole. The storage <NUM>, and thus the pipe <NUM>, further comprises a bottom end cap <NUM> fastened to a bottom end of the lateral wall <NUM> and a top end cap <NUM> fastened to a top end of the lateral wall <NUM>. The top end of is the end which is proximal to the earth/bedrock surface (i.e. the end closest to the above ground), while the bottom end is the end distal to the earth/bedrock surface (i.e. the end facing away from the above ground).

The bottom end cap <NUM> may be connected to a bottom of the borehole <NUM>, e.g. by being in direct contact there with or being arranged against a rigid frame <NUM> standing on the bottom of the borehole and acting as a distance between the bottom end cap and the bottom of the bore hole. The space between the bottom end cap and the bottom of the borehole which may be formed by the frame <NUM> may be used to allow debris from the boring or the inner surface <NUM> of the borehole <NUM> to collect without interfering with the bottom end cap <NUM>.

The top end cap <NUM> is typically below ground, i.e. below an upper end of the borehole <NUM>. Conveniently, a cover <NUM> is provided above the top end cap, the weight of which may form a pressure on the top end cap which is close to or above the pressure P or the pressure of the fluid stored therein to help prevent the top end cap from being lifted by the pressure in the storage <NUM>. The cover <NUM> may consist of or comprise any one or more of cement, concrete, crushed stone and macadam. A blocking <NUM>, e.g. a metal ring, may be provided between the top end cap <NUM> and the cover <NUM> to prevent stones or other parts of the cover <NUM> to fall into any gap between the inner surface <NUM> of the borehole <NUM> and the outside of the lateral wall <NUM>, especially before the plastic or elastic deformation thereof. In some embodiments of the present invention, the inserting of the pipe <NUM> into the borehole <NUM> comprises inserting the whole pipe into the borehole such that the top end cap <NUM> is below an upper end of the borehole, e.g. a distance within the range of <NUM>-<NUM> below the upper end of the borehole, preferably within the range of <NUM>-<NUM>. Alternatively, e.g. for smaller diameters of the pipe <NUM>, the top end cap <NUM> may be placed above the ground surface and anchored with rock bolts to the rock mass <NUM>. In that case, the upper part of the pipe, the part above ground, may be dimensioned for full pressure without deformation, e.g. plasticization.

For fluid communication with the inside of the storage <NUM>, at least two pipings <NUM> and <NUM>, typically each comprising at least one valve for turning on or off a fluid flow through the piping, may be arranged from above ground and through the top end cap <NUM>, and thus also through any cover <NUM> there above. A liquid piping <NUM> may extend to close to the bottom of the storage <NUM>, for evacuating liquid from the storage. Similarly, a gas piping <NUM> may be arranged with an opening at the top of the storage <NUM>, for evacuating gas from the storage. When pressurizing the pipe <NUM> for deformation, e.g. plastic or elastic deformation, thereof using water pressurized to the pressure P, water may be pressed into the storage <NUM> via either of the liquid and gas pipings <NUM> or <NUM>. However, after the deformation, the water may be evacuated via the liquid piping <NUM> by pumping gas into the storage <NUM> via the gas piping <NUM>.

The borehole <NUM> may have any suitable size, depending on how much fluid it is desired to store, though there may be some technical or practical constraints depending on the boring technique used. In some embodiments of the present invention, the borehole has a depth within the range of <NUM>-<NUM>, preferably <NUM>-<NUM>. Typically, the borehole is vertical from the earth surface and down, but it is contemplated that also inclined boreholes, e.g. at an acute angle to a vertical axis, may be convenient for some applications. In some embodiments of the present invention, the diameter of the borehole <NUM> is within the range of <NUM>-<NUM>, which are diameters obtained by conventional boring. The boring technique is selected in view of the diameter desired. For a diameter within the range of <NUM>-<NUM>, hammer boring is suitably used. For a diameter within the range of <NUM>-<NUM>, raise boring with a reamer which is folded out after drilling a pilot hole before the drill head is raised. For a diameter within the range of <NUM>-<NUM>, an adjacent shaft or tunnel may be needed, whereby the pilot hole breaks into the adjacent shaft or tunnel and a wider reamer may be attached to the drill string before raising the drill head.

The fluid-tight pipe <NUM>, and thus the resulting fluid storage <NUM>, may have a length which is about <NUM>-<NUM> less than the depth of the bore hole <NUM>, corresponding to the distance of the top end cap <NUM> from the earth surface, e.g. a length within the range of <NUM>-<NUM>, preferably <NUM>-<NUM>. To achieve such a long pipe <NUM>, a plurality of pipe segments may be welded, or otherwise joined, together to form a fluid tight lateral wall <NUM>. Similarly, the top and bottom end caps <NUM> and <NUM> are conveniently welded, or otherwise joined, fluid-tightly, to the respective ends of the lateral wall <NUM>.

<FIG> illustrates some embodiments of the method for preparing or constructing the fluid-tight subterranean fluid storage <NUM>. A bore hole <NUM> is bored (drilled) S1 in a rock mass <NUM>. Then, a fluid-tight pipe <NUM> is inserted S2 longitudinally into the borehole <NUM>. The pipe comprises a lateral wall <NUM>, e.g. of a rigid or elastic, preferably rigid, material in the form of a right circular cylindrical shell having an outer diameter which is smaller than a diameter of the borehole <NUM>, a bottom end cap <NUM> fastened to a bottom end of the lateral wall <NUM>, and a top end cap <NUM> fastened to a top end of the lateral wall <NUM>. Then, via piping <NUM> through the top end cap <NUM>, the fluid-tight pipe <NUM> is pressurized S3 to a pressure P above a predetermined threshold, e.g. dependent on an upper yield point of the rigid material, whereby the lateral wall <NUM> is deformed, e.g. plastically deformed in case of a rigid material or elastically deformed in case of an elastic material, until it is pressed against an inner surface <NUM> of the borehole <NUM> along a longitudinal extent of the lateral wall, forming a fluid-tight lining <NUM> of the borehole. The lateral wall <NUM>, forming the lining <NUM>, together with the bottom end cap <NUM> and the top end cap <NUM> thus form the fluid-tight subterranean fluid storage <NUM> in the borehole.

In case the lateral wall <NUM> is of a thermosetting material, the method may optionally comprise curing (S4) the lining <NUM> of the bore hole formed by the deformed lateral wall <NUM>. The curing typically include raising the temperature of the thermosetting material to above a temperature at which the thermosetting material is cured. However, additionally or alternatively, other curing techniques may be included, such as UV radiation or the use of a curing agent.

In some embodiments of the present invention, the method optionally further comprises filling S5 the fluid storage <NUM>, via piping <NUM> through the top end cap <NUM>, with a pressurized fluid in gas and/or liquid form, e.g. hydrogen, methane, propane, natural gas, carbon dioxide, nitrogen, ammonia, air, water and/or ammonium, preferably hydrogen. In some embodiments, the pressurized fluid is at a pressure within the range of <NUM>-<NUM> bar or <NUM>-<NUM> bar, preferably <NUM>-<NUM> bar.

Table <NUM> shows the amount of hydrogen which can be stored in the fluid storage <NUM> at some example diameters of the fluid storage at a depth/length of the fluid storage of <NUM> and an absolute pressure in the fluid storage of <NUM> bar(a).

In some embodiments of the present invention, the method may further comprise inspecting the inner surface <NUM> of the borehole <NUM> before inserting S2 the pipe <NUM>, optionally mending holes or other irregularities in the surface <NUM> which could damage the lateral wall <NUM> when it is pressurized S3.

In some embodiments, a geological survey is performed at a suitable location to determine suitability for preparing a storage <NUM> at the site. The survey could include locating a suitable rock mass <NUM> where crush or fault zones are not expected to occur. If necessary, core hole drilling, or equivalent, can be carried out in the area to find local crush or fault zones and to investigate other rock parameters.

Then the borehole <NUM> may be drilled. Optionally, a rim of suitable material may be mounted around where the borehole is to be drilled. This may be for personal safety and could prevent the deposition of unwanted material from the ground. A shaft may be drilled to a suitable depth (e.g. <NUM>-<NUM>) and a suitable dimension (e.g. <NUM>-<NUM>). Hammer drilling and/or raise drilling is suitably used, as discussed above. Raise drilling is suitably used if there is access to the lowest level via a rock tunnel. Raise drilling can also be used without access to the lowest level by drilling a pilot hole and in this pushing down a reamer which can then be folded out.

The inner surface <NUM> of the borehole <NUM> may be inspected for holes or other irregularities. The borehole <NUM> may conveniently be filled with water to counteract greater leakage and thus prevent gravel and stone from falling from the inner surface <NUM> wall of the borehole, to create cavities in the wall. The borehole may be measured, and the inner surface <NUM> filmed to find any cavities or other defects.

Optionally, or if needed, a part of the inner surface <NUM> wall may be repaired to be smoother, e.g. at a region where the rock mass has crumbled at the inner surface <NUM> wall. For instance, any cavities may be filled in with a suitable material. The bottom of the borehole <NUM> may be cleaned.

The fluid-tight pipe <NUM> may then be assembled and inserted into the borehole <NUM>. Metal pipes may be axially joined (e.g. welded) to form the lateral wall <NUM>. These pipes typically have a diameter that is slightly smaller than the diameter of the borehole <NUM>. <NUM>-meter pipes may be suitable to use, which in stages are joined together with suitable automatic welding with subsequent checks and, if necessary, normalization of the weld joint. The pipes may be filled with water in stages while being lowered into the water-filled borehole so that the top of the joined pipes is at a suitable working height for welding the next pipe. The pipes may be fixed dumb in a suitable way so that a straight joint is obtained. Note that the upper pipes may have to withstand the external water pressure created by the weight of all submerged lower pipes.

Before the bottom end cap <NUM> is mounted at the bottom of the borehole, a steel frame <NUM> or bearing with an edge may be mounted. The frame may be formed after the bottom of the borehole and if this is done as a distance with openings, any falling stone and gravel can be collected in the frame. This implies that the position of the bottom end cap <NUM> may be fixed exactly laterally and vertically. With this procedure, the bottom end cap may be made completely flat. Alternatively, the bottom of the borehole may be ground as the shape of the bottom end cap, or the bottom may be cast with the same shape as the end cap. Via a service pipe, a hydraulic hammer may be be lowered to the bottom end cap <NUM> and with this hammer, via the end cap <NUM>, smash any loose stones that have fallen down during assembly of the pipe <NUM>. This may give the end cap a desired direct contact with the bottom of the borehole.

At the top of the lateral wall <NUM>, the top end cap <NUM> may be mounted. Both end caps <NUM> and <NUM> may be made to withstand maximum pressure without plasticizing. Evacuation piping <NUM> from the bottom end cap <NUM> to the ground surface, with a lyre or other suitable method for possible expansion, may also be mounted in stages with suitably the same length as the lateral wall <NUM>. The evacuation pipe <NUM> may be sealed from the outside at the upper end cap <NUM> and extended to above the ground. Inlet piping <NUM> may be mounted from above the ground surface through the top end cap <NUM> and may be welded tightly to also withstand the maximum pressure in the storage <NUM>. Optionally, the upper end of the storage <NUM> is provided with a service pipe, e.g. a manhole, in a suitable dimension to the ground surface and designed to withstand the maximum pressure in the storage.

An alternative mounting method of the storage <NUM> may be to build it in its entirety, or in larger parts, above ground and then with cranes lower it into the borehole <NUM>.

The top end cap <NUM> may be cast over with a suitable thickness of concrete and/or may be anchored by means of drilling bolts in the inner surface <NUM> rock wall. Before casting, the space between the inner surface <NUM> and the top end cap <NUM> may be sealed. This may be done with a blocking <NUM>, suitably a wedge-shaped metal ring, which then may also provide a smooth transition when plasticizing the lateral wall <NUM> against the inner surface <NUM>. Thereafter, the remaining borehole above the top end cap <NUM> may be filled and packed with suitable material as part of the cover <NUM>, such as crushed rock or other heavy material that can partially transfer the upward force (from the overpressure in the storage <NUM>) from the top end cap to the surrounding rock. The distance between the top end cap <NUM> and the ground surface may be selected such that the weight of the overlying rock mass is greater than the lifting force from the overpressure in the storage <NUM>. This distance above the top end cap may be dependent on the dimension/diameter of the storage, maximum pressure in the storage, distance between adjacent boreholes <NUM> (if there are several in the same area) and on whether rock bolts are mounted to take all or part of the force from the overpressure on the top end cap.

Then, the pipe <NUM> is plastically expanded against the inner surface <NUM> by pressing it the inside of the pipe <NUM> with water to the pressure necessary.

If needed, the inside of the storage <NUM> may be cleaned from debris before the storage is filled with the fluid to be stored therein.

Filling the fluid storage <NUM> with hydrogen may be achieved by the hydrogen gas pushing away the water as the pressure increases, the hydrogen entering the storage via the gas piping <NUM> while the water exits the storage via the liquid piping <NUM>. Other methods of evacuating the water and filling with fluid such as hydrogen may also be suitable. When the storage <NUM> is filled with a light gas such as hydrogen, pressure control may be installed so that the pressure in the storage is always higher than the groundwater pressure outside the bottom of the storage. Having hydrogen gas in the storage below the external groundwater pressure, or during service, the storage could be filled with oxygen-poor water to balance the external groundwater pressure. The water system outside of the storage may then need to handle the water dissolved hydrogen in a safe way when the pressure is reduced.

Claim 1:
A method of preparing a fluid-tight subterranean fluid storage (<NUM>), the method comprising:
boring (S1) a borehole (<NUM>) in a rock mass (<NUM>);
inserting (S2) a fluid-tight pipe (<NUM>) longitudinally into the borehole (<NUM>), the pipe comprising a lateral wall (<NUM>) of a rigid material in the form of a right circular cylindrical shell having an outer diameter which is smaller than a diameter of the borehole (<NUM>), a bottom end cap (<NUM>) fastened to a bottom end of the lateral wall (<NUM>), and a top end cap (<NUM>) fastened to a top end of the lateral wall (<NUM>); and
via piping (<NUM>) through the top end cap (<NUM>), pressurizing (S3) the fluid-tight pipe (<NUM>) to a pressure (P) above a predetermined threshold dependent on an upper yield point, ReH, of the rigid material, whereby the lateral wall (<NUM>) is plastically deformed until it is pressed against an inner surface (<NUM>) of the borehole (<NUM>) along a longitudinal extent of the lateral wall, forming a fluid-tight lining (<NUM>) of the borehole;
wherein the lining (<NUM>) together with the bottom end cap (<NUM>) and the top end cap (<NUM>) form the fluid-tight subterranean fluid storage (<NUM>) in the borehole.