A method for storing hydrogen

Abstract

This disclosure relates to a method for storing hydrogen in a subsurface location. The method being particularly suitable for use in 'virgin' or 'native' subsurface locations, where a target formation within the subsurface location is evaluated for its suitability, and a storage volume for hydrogen is calculated based on this evaluation. Within this target formation, one or more wells are formed, from each well, creating one or more storage lenses in the target formation, and subsequently injecting hydrogen into each well at a pressure sufficient to drive the hydrogen into each of the storage lenses, such that a hydrogen storage pressure is greater than the target formation's original in-situ (i.e. vertical) stress.

Description

A METHOD FOR STORING HYDROGENPRIORITY DOCUMENTS

[0001] The present application claims priority from Australian Provisional Patent Application No. 2024903041 titled “A METHOD FOR STORING HYDROGEN” and filed on 23 September 2024, the content of which is hereby incorporated by reference in its entirety.TECHNICAL FIELD

[0002] The present disclosure relates to the field of energy storage. In a particular embodiment, the disclosure relates to a method for storing hydrogen in a subsurface location.BACKGROUND

[0003] Increasing energy demand, population growth, and growing environmental concern has led to widespread recognition that there is a need to increase the share of global energy from renewable sources.

[0004] Many researchers and innovators have been focused on hydrogen as an energy carrier, as it will play a large role in our transition from fossil fuels to renewable sources. Hydrogen is useful as a clean fuel due to its abundance, that it only produces water as a byproduct when used in a fuel cell, and that it can be used for reducing the carbon footprint of various industrial processes.

[0005] One of the key problems faced in unlocking the potential of hydrogen as an energy carrier is the advancement of its storage, particularly storage at a large-scale. Presently available large-scale hydrogen storage solutions include the use of surface storage tanks, underground salt caverns, underground aquifers, or depleted oil and gas reservoirs. However, these storage solutions require a large geographical footprint, involve high safety risk, comprise suboptimal subsurface conditions for storing hydrogen, and can be difficult to economically scale. For example, surface storage tanks impose a large visual / environmental impact, and depleted oil and gas reservoirs often comprise conditions that result in loss of stored hydrogen, both of which are detrimental to the overall environmental benefits of utilising hydrogen as an energy carrier.

[0006] It is against this background and the problems and difficulties associated therewith, that the present invention has been developed.SUMMARY

[0007] Embodiments of the present disclosure relate to a method for storing hydrogen in a subsurface location. In particular, the method comprises steps that include: evaluating the suitability of a subsurface location; identifying a target formation; calculating a storage volume of the target formation; forming at least one well into the target formation; creating one or more storage lenses in the target formation from each well; and injecting hydrogen into each well at a pressure sufficient to drive the hydrogen into each of the storage lenses, such that a hydrogen storage pressure is greater than the target formation’s original in- situ (i.e. vertical) stress.

[0008] According to a first aspect of the present disclosure, there is provided a method for storing hydrogen in a subsurface location, the method comprising: evaluating a target formation within the subsurface location, wherein the target formation comprises low permeability and is preferably water-wet; calculating: a storage volume, a number of storage lenses required to achieve the storage volume, and a storage pressure, each based on the evaluation of the target formation; drilling at least one well into the target formation, preparing each well for hydrogen storage by forming the storage lenses in the target formation from each well to achieve the storage volume, and pressure testing each well to the storage pressure; and injecting hydrogen into each well at an injection pressure sufficient to drive the hydrogen into each of the storage lenses, such that the hydrogen is stored within the lenses at the storage pressure, and subsequently shutting in each well stores hydrogen within the subsurface location.

[0009] In one embodiment, the target formation is under overpressure conditions resultant of an overburden layer.

[0010] In one embodiment, the target formation comprises an in-situ stress that results in the vertical stress being the minor principal stress.

[0011] In one embodiment, the storage pressure is greater than the in-situ (i.e. vertical) stress of the target formation. In this embodiment, the storage pressure is greater than the in-situ (i.e. vertical) stress of the target formation in order to maintain hydrogen within the lenses, and maintain the lens inflated following injection of hydrogen.

[0012] In one embodiment, each of the storage lenses are formed by injecting a first fluid into the target formation at a first location to open and inflate bedding planes within the target formation to create a first storage lens. In this embodiment, the first fluid may be water.

[0013] In one embodiment, the storage pressure maintains the bedding planes, or the lenses, in an inflated state.

[0014] In one embodiment, a second fluid comprising a fine-grained mixture is subsequently injected into the first storage lens to restrict lateral growth of the first storage lens.

[0015] In one embodiment, the second fluid reduces leak-off and provides structural integrity to the first storage lens.

[0016] In one embodiment, in use, the first and second fluids are injected to form each of the storage lenses required to achieve the storage volume.

[0017] In one embodiment, each subsequent storage lens within each well is formed above or below the previous storage lens.

[0018] In one embodiment, subsequent to injecting the first and second fluids to form each of the storage lenses, a final fluid is circulated through the formed storage lenses.

[0019] In one embodiment, for each well, the storage lenses are injected with hydrogen in a bottom-to- top sequence, where the lowermost storage lens is injected with hydrogen for storage, and isolated prior to subsequently higher storage lenses being injected.

[0020] In one embodiment, after a period of time, one or more wells are opened, and hydrogen is recovered from the storage lenses in a top-to-bottom sequence.

[0021] In one embodiment, the number of wells are opened based on a required volume of stored hydrogen.

[0022] In one embodiment, the hydrogen is extracted from the storage lenses at an extraction pressure which is a result of the storage pressure within the wells reducing to the in-situ (i.e. vertical) stress of the target formation.

[0023] In one embodiment, the period of time is a few weeks to a month. In another embodiment, the period of time may vary up to several months, and is dependent on the permeability of the target formation, where the lower the target formation’s permeability, the longer the period of time may be.

[0024] In one embodiment, the target formation is located at a depth that the in-situ stress (i.e. vertical stress) is the minimum stress (depth less than -700 metres).

[0025] In one embodiment, permeability of the target formation is less than 0.01 milli Darcy.

[0026] In one embodiment, the water-wet target formation is initially saturated with water.

[0027] In one embodiment, the target formation is a layered formation such as shale formation.

[0028] In one embodiment, the target formation further comprises a previously undrilled, or undeveloped, region that is considered a virgin formation, a virgin reservoir, or a greenfield reservoir. In this embodiment, the target formation comprises no prior boreholes, or wellbores, that have been drilled for the purposes of extracting hydrocarbons.

[0029] According to a second aspect of the present disclosure, there is provided a method for storing hydrogen in a subsurface location, the method comprising: evaluating a target formation within the subsurface location, wherein the target formation comprises low permeability, is subject to in-situ conditions resultant of an overburden layer, and is preferably water-wet; calculating: a hydrogen storage volume, a number of storage lenses required to achieve the hydrogen storage volume, and a hydrogen storage pressure, each based on the evaluation of the target formation; drilling at least one well into the target formation, and forming storage lenses in the target formation from each well by inflating bedding planes within the target formation by injecting a pressurised fluid followed by a fine-grained mixture to restrict lateral growth and provide structural integrity to the storage lenses, wherein the total number of storage lenses within the wells achieve the hydrogen storage volume; injecting hydrogen into each well at an injection pressure sufficient to drive hydrogen into each of the storage lenses, such that the hydrogen is stored within the lenses at the hydrogen storage pressure, and subsequently shutting in each well stores hydrogen within the subsurface location; and opening one or more wells to recover hydrogen from the storage lenses, wherein the hydrogen is recovered at an extraction pressure which is a result of the hydrogen storage pressure within the wells reducing to the in-situ stress of the target formation.

[0030] For ease of description, a method embodying the present features is described below where references to the term ‘lens’ or ‘lenses’ are made, such as in ‘forming of storage lenses’, in one instance refers to the forming, or creation, of an inflated region, or an opened region, between two bedding planes within a geological formation (i.e. a target formation) to store hydrogen therein. In a second instance, references to the term ‘lens’ or ‘lenses’ made within a method embodying the present features, alternatively refers to the forming, or creation, of fractures (e.g. hydraulic fractures) within a geological formation (i.e. a target formation) to store hydrogen therein. In a further instance, the references to the term ‘lens’ or ‘lenses’ made within a method embodying the present features, may alternatively refer to the opening, or inflating, of existing fractures within a geological formation (i.e. a target formation). Accordingly, it will be appreciated by those skilled in the art that, references to the term ‘lens’ or ‘lenses’ broadly indicate an ‘inflated’ , ‘opened’ , or ‘fractured’ region within a target formation that is formed, or created, for the purposes of storing hydrogen. Additionally, as the disclosed lenses are formed, or created, they may also be considered engineered lenses. Other geological terms within embodiments of the method described below will be understood by those skilled in the art to have their usual meaning.

[0031] Additionally, it will become apparent that a method embodying the present features below is for the purposes of hydrogen storage. In a particular form, the method is for the purposes of hydrogen storage within a subsurface location, where the time period of storage of the hydrogen can range between a few weeks to months, and is dependent on several characteristics, or geological parameters, such as the permeability of the target formation, prior to being extracted from the subsurface location for use as a recovered product.

[0032] Furthermore, it will become apparent that a method embodying the present features below is employed within wells that are drilled, or formed, into a geological formation (i.e. a target formation) are considered ‘virgin’, or ‘native’. That is, the target formation is one that has not previously been utilised for other purposes such as oil and gas production. It will be appreciated that the discussed wells that are drilled into the target formation, may be wells originally drilled for other purposes, or into other formations, however, they are either extended, that is further developed or drilled, either to a deeper or shallower depth, into the target formation, which itself has not been previously utilised for other purposes.

[0033] Further still, for ease of description, a method embodying the present features is described below where terms such as above, below, top, bottom, depth, etc. may be used with reference to a surface, which may be a ground location, a seabed location, or any other location on the Earth’s surface.BRIEF DESCRIPTION OF DRAWINGS

[0034] Embodiments of the present disclosure will be discussed with reference to the accompanying drawings wherein:

[0035] Figure 1 is a schematic process diagram illustrating a method for storing hydrogen in a subsurface location, according to an embodiment;

[0036] Figure 2 is a schematic illustrating a subsurface location comprising a target formation;

[0037] Figure 3 is a subsequent schematic illustrating the subsurface location with a well drilled into the target formation;

[0038] Figure 4 is a subsequent schematic illustrating one or more storage lenses in the target formation extending from the well;

[0039] Figure 5 is a schematic illustrating a subsurface location comprising a target formation, wherein several wells have been drilled into the target formation, and from each well, one or more storage lenses extend into the target formation from their respective originating wells;

[0040] Figure 6 is a graphical representation of an exemplary storage volume of hydrogen for several stiffnesses (E = Young’s modulus) of the target formation;

[0041] Figure 7 is a schematic representation of an exemplary storage lens, illustrating an injection of hydrogen into the storage lens, direction of storage pressure (Pnet), relative direction where leak-off from the lens could occur, and estimated positioning of a TSO product within the storage lens;

[0042] Figure 8 is a graphical representation of an exemplary storage lens with a modelled radius of 250 meters, illustrating the total volume and mass calculated for a plurality of storage lenses located at depths between 100 and 500 meters;

[0043] Figure 9 is a graphical representation of an exemplary set of storage lenses, where the effect of a TSO is modelled to estimate the effects of pressure at a tip of the storage lens, and how long (time in days) this pressure may, with stability, be maintained;

[0044] Figure 10 is another graphical representation of an exemplary set of storage lenses, where the effect of a TSO is modelled to estimate the effects of pressure at a tip of the storage lens, and how long (time in days) this pressure may, with stability, be maintained;

[0045] Figure 11 is a graphical representation illustrating, in the instance TSO is utilised, the portion of a storage lens that may comprise hydrogen, and the portion of the storage lens that may comprise TSO product;

[0046] Figure 12 includes two graphical representations that illustrate modelling of hydrogen saturation after a period of time of 7 days given a target formation (i.e. called caprock in the figure) permeability and a TSO permeability;

[0047] Figure 13 is a graphical representation illustrating the use of TSO and its impact on hydrogen leak off into a target formation (named as caprock); and

[0048] Figure 14 is another graphical illustration of the use of TSO and its impact on hydrogen leak off into a target formation (named caprock).

[0049] In the following description, like reference characters designate like or corresponding parts throughout the figures.DESCRIPTION OF EMBODIMENTS

[0050] Referring to any one of the Figures, there is disclosed a method for storing hydrogen in a subsurface location 100. The method comprising:(a) evaluating a target formation 110 within the subsurface location 100, wherein the target formation 110 comprises low permeability and is preferably water- wet;(b) calculating: a storage volume, a number of storage lenses 20 required to achieve the storage volume, and a storage pressure, each based on the evaluation of the target formation 110;(c) drilling at least one well 10 into the target formation 110, preparing each well 10 for hydrogen storage by forming the storage lenses 20 in the target formation 110 from each well 10 to achieve the storage volume, and pressure testing each well 10 to the storage pressure; and(d) injecting hydrogen into each well 10 at an injection pressure sufficient to drive the hydrogen into each of the storage lenses 20, such that the hydrogen is stored within the lenses 20 at the storage pressure, and subsequently shutting in each well 10 stores hydrogen within the subsurface location 100.

[0051] The target formation 110 evaluated within the method may comprise several properties, wherein some properties are more preferential than others, however, it will be appreciated that only one or more of the properties discussed herein may be required to achieve the desired objective and advantages of the method.

[0052] The target formation 110 is preferably water-wet, that is, the rock / mineral surface within target formation 110 is coated with water. The inventors note that, water-wet formations are desirable for storage of hydrogen due to this formation property allowing for higher pressure limits before a leak off may occur resulting in the loss of stored hydrogen within the formation from a formed, or created, lens 20 to the target formation 110. Advantageously, for the purposes of calculating storage pressure at step (b) of the method disclosed herein, due to the target formation 110 being water-wet, and that may be initially saturated with water, the storage pressure may safely be a higher pressure by virtue of the water-wet formation 110 providing a higher pressure limit before a leak off may occur. As a further advantage, the target formation 110 being water- wet results in the leak off limit (i.e. the limit at which stored hydrogen would be lost from the storage lens 20 to the target formation) being higher. Higher pressure limits before a leak off are present in water-wet formations due to their capillary forces. The capillary forces of a water-wet formation also aid in returning / recovering stored hydrogen that seeps into the target formation 110 during depressurisation / recovery of stored hydrogen from storage lenses 20.

[0053] The target formation 110 may also be under overpressure conditions that are resultant of an overburden layer 120. The overburden layer 120 provides the target formation 110 with ‘weight’ thereon so as to maintain the storage pressure within the formed storage lenses 20 once the hydrogen is injected therein. The inventors note that for this method, to inject and store hydrogen, the injection pressure of hydrogen overcomes the overpressure conditions resultant of the overburden layer 120, and it is the resultant ‘weight’ of the overburden layer 120 that aids in maintaining the storage pressure of the hydrogen, and also aids in the subsequent recovery of the hydrogen when the wells are opened. By virtue of the overburden layer 120 above the target formation 110, the present method does not require the use of a cushion gas, or the like, to assist in maintaining the storage pressure within the formed storage lenses 20 once hydrogen is injected therein. The inventors also note that the overpressure conditions are dependent on the depth of the target formation 110 and the overburden layer 120, and approximate that the ‘weight’ pressure applied by the overburden layer 120 onto the target formation 110 is roughly 20 times the depth. For example, the inventors approximate that for a target formation depth of 500 meters, the ‘weight’ pressure (i.e. overpressure conditions) applied by the overburden layer 120 may be approximately 10 MPa.

[0054] In addition to the overburden layer 120, the subsurface location 100 may also comprise an underburden layer 130 located below the target formation 110.

[0055] The target formation 110 comprises an in-situ stress condition that results in the vertical stress of the formation 110 being the minor (or minimum) principal stress. The inventors note that a vertical stress nominally is expected to be less than 14 MPa.

[0056] When calculating the storage pressure at step (b) of the method, which may also be considered the hydrogen storage pressure, this pressure is calculated as being greater than the in-situ stress of the target formation 110. In this way, the storage pressure is a designed hydrogen storage pressure that overcomes the in-situ pressure (or formation pressure) of the target formation 110, in order to maintain the stored hydrogen within the storage lenses.

[0057] The target formation 110 comprises low permeability, preferably, the permeability of the target formation 110 is less than 0.01 milli Darcy.

[0058] The target formation 110 may be located at a depth between 50 and 700 meters or less, below the Earth’s surface. The inventors note that at this depth range, the target formation 110 comprises one or more of the above properties that are advantageous for hydrogen storage. The inventors also note that at this depth range, operational costs associated with evaluating and drilling wells 10 are reduced by virtue of the target formation 110 being shallow. The inventors further note that the greater the depth of the target formation 110, the less desirable the properties of the formation 110 for hydrogen storage, as itbecomes increasingly more difficult to form, or create, the storage lenses in a sub-horizontal plane within the formation 110. The inventors further note that the target formation 110 being located between 50 and 700 meters provides favourable stress conditions, where the minimum (minor) principal stress component is the vertical stress, and horizontal stresses are larger than the vertical stresses. This implies that the formed storage lens 20 tend to propagate in the horizontal plane rather than the vertical plane. Additionally, the greater the depth of the target formation 110, the greater the required hydrogen density for storage, which the inventors note inherently increase storage pressure requirements, injection pressure requirements (for injecting hydrogen to the storage pressure), and increased costs associated with operationally requiring equipment that is capable of achieving (and being designed to achieve) the higher pressure requirements to store hydrogen at greater density. Furthermore, the inventors note that when the target formation 110 is located at a depth of less than 700 metres, the in-situ, or vertical, stress of the target formation 110 is the minimum stress, which is desirable for the application of the disclosed method.

[0059] The storage lenses 20 may be considered engineered fractures, or engineered lenses, that are created for the purposes of storing hydrogen within the subsurface location 100. The storage lenses 20 are designed and developed based on the evaluation of the target formation 110. The inventors note that some of the major engineering / design aspects of the lenses 20 include their size, volume, storage capacity, storage time, and hydrogen losses, all of which may be considered for their creation.

[0060] A desirable target formation 110 may be a shale formation, which comprise several of the properties of the target formation 110 described in the previous paragraphs. Shale formations comprise bedding planes that act as ‘geological layers’, where it is possible to inflate between these layers, whereby the acting of inflating between these layers may be considered the forming, or creating, of the storage lenses 20 for the purposes of storing hydrogen. These bedding planes / geological layers of a shale formation are ‘inflated’ within the described method at the step of forming the storage lenses 20 within each well, wherein it will be appreciated that the forming of the storage lenses 20 may be considered as the ‘inflation’, ‘injection’, ‘pressurising’, or ‘propping’ between these planes / layers for the purposes of storing hydrogen. As an example, the forming of the storage lenses 20 may be by pressurising the target formation 110 from a well using a fluid mixture (based on liquids or gas, accompanied with gels, proppants, etc.) with the aim of opening, or inflating, the bedding planes within the target formation 110. The inventors note that shale formations, and other formations comprising one or more of the properties of the target formation 110 described in the previous paragraphs, advantageously comprise low diffusivity of hydrogen, due to lower permeability of the target rocks as well as very low diffusivity of hydrogen in water for water-wet formations, which aids in preventing the loss of stored hydrogen to the target formation 110 from the storage lenses 20. The inventors further note that shale formations are ‘layeredformations’ that occur at shallow depths below the Earth's surface, such as at depths of less than 700 metres, which aids in their desirability for the disclosed method.

[0061] Referring now to step c) within the method, subsequent to the drilling of at least one well 10, when each well 10 is prepared for hydrogen storage by forming the storage lenses 20, each of these lenses 20 may comprise sub-steps below: c-1) first, each of the storage lenses 20 are formed by injecting a first pressurised fluid into the target formation 110 at a first location to open, fracture, or inflate bedding planes within the target formation 110 to create a first storage lens. It will be appreciated, as illustrated in Figure 5, each well 10 may comprise a series of (or a number of) storage lenses that propagate, or originate, from the drilled well 10. The first fluid may be water, or a ‘pad water’. c-2) next, for each of the storage lenses 20, a second fluid comprising a fine-grained mixture is subsequently injected into the first storage lens to restrict lateral growth of the lens. It will be appreciated that this sub-step may be a Tip-Screen-Out (TSO) technique, which aids in optimising the geometry of the storage lens 20, by influencing the flow rate, extraction pressure, and hydrogen storage capacity of the lens 20. The fine-grained mixture used at this sub-step may be a proppant that may be injected within a gel, into the storage lens 20, where the gel aids in delivering, or transporting, the proppant into the lenses 20 and away from the well 10. The second fluid also notably reduces leak-off within the formed storage lens 20, and provides structural integrity to the storage lens 20. Further still, the second fluid aids in isolating a fracture tip of each of the storage lenses 20, in this way, the second fluid aids in preventing lens instability, reduces the leak-off of each individual lens 20, and thereby aids in preventing loss of stored hydrogen to the target formation 110 from the lenses 20. c-3) next, the another injection of the first fluid, which may be water, may follow the second fluid.Sub-steps c-1) to c-3) may be repeated, as many times as required, to form the number of storage lenses 20 calculated at step b) of the method to achieve the required storage volume. It will be appreciated that these steps may be repeated and carried out in each of the wells 10 drilled into the target formation 10 to achieve the required storage volume for hydrogen storage within the subsurface location 100.

[0062] Following the above sub-steps, once sufficient storage lenses 20 have been formed within the drilled wells 10 to achieve the storage volume, the pressure test occurs, which tests each well to the hydrogen storage pressure.

[0063] It will be appreciated that the storage pressure, or hydrogen storage pressure, at step b) of the method, may be greater than the in-situ (i.e. vertical) stress of the target formation to maintain hydrogen within the lenses, and maintain the lens ‘inflated’ following injection of hydrogen.

[0064] Within the above sub-steps, where each storage lens 20 is being created for each drilled well 10, every subsequent storage lens 20 for each well 10 may be formed above or below the previously formed storage lens 20. At step d) of the method, for each well 10, the storage lenses 20 are injected with hydrogen in a bottom-to-top sequence, that is, where the lowermost storage lens 20 is injected and inflated with hydrogen for storage prior to subsequently higher storage lenses 20 being injected and inflated with hydrogen, and isolated noting that the lower lens has higher pressure due to higher weight of overburden.

[0065] Figure 5 illustrates a subsurface location 100, comprising three wells 10 drilled through a target formation 110, where each well comprises several (a number of) storage lenses 20 to achieve the required storage volume for hydrogen storage at this location 100.

[0066] An exemplary embodiment of the method for storing hydrogen in a subsurface location 100 may comprise the following steps: a) evaluating a target formation 110 within the subsurface location 100, wherein the target formation 110 is subject to in-situ conditions resultant of an overburden layer 120 and is water wet; b) calculating: a hydrogen storage volume, considering a number of storage lenses 20 required to achieve the hydrogen storage volume, and a hydrogen storage pressure, each based on the evaluation of the target formation; c) drilling at least one well 10 into the target formation 110, and forming storage lenses 20 in the target formation from each well 10 by inflating bedding planes within the target formation 110 by injecting a pressurised fluid followed by a fine-grained mixture to restrict lateral growth and provide structural integrity to the storage lenses 20, wherein the total number of storage lenses 20 within the wells 10 achieve the hydrogen storage volume; d) injecting hydrogen into each well 10 at an injection pressure sufficient to drive hydrogen into each of the storage lenses 20, such that the hydrogen is stored within the lenses 20 at the hydrogen storage pressure, and subsequently shutting in each well 10 stores hydrogen within the subsurface location 100; and e) opening one or more wells 10 to recover hydrogen from the storage lenses 20, wherein the hydrogen is recovered at an extraction pressure which is a result of the hydrogen storage pressure within the wells 10 reducing to the in-situ stress (i.e. vertical stress) of the target formation 110.

[0067] In the exemplary embodiment of the method above, it will be appreciated that at step b), the number of storage lenses 20 required to achieve the hydrogen storage volume may, as an alternative, be considered the number of storage lenses 20 feasible in the target formation to achieve the hydrogen storage volume. The inventors note that the number of storage lenses 20 may be dependent on a vertical thickness of the target formation.

[0068] In the exemplary embodiment of the method above, it will be appreciated that for the number of wells 10 drilled at step c), the number of wells that are opened at step e), are opened based on a required volume of stored hydrogen for use.

[0069] In the exemplary embodiment of the method above, at step c), the pressurised fluid may be water.

[0070] In the exemplary embodiment of the method above, at step e), it will be appreciated that the stored hydrogen is recovered at the extraction pressure by simply opening the shut in well(s). That is, the stored hydrogen is recovered and extracted under its own pressure, advantageously not requiring depressurising to improve the extraction pressure is necessary, as the stored hydrogen is recovered for use as a product, and not recovered for the purposes of producing energy.

[0071] Additionally, still referring to step e), the recovery of the stored hydrogen at the extraction pressure is at a continuous, or controlled, rate based on the hydrogen storage pressure reducing to the target formation 110 original in-situ (i.e. vertical) stress, which in turn, is aided, or maintained, by virtue of the overburden layer 120 above the target formation 110.

[0072] In any one of the above embodiments, it will be appreciated that, after a period of time, one or more wells are opened, and hydrogen is recovered from the storage lenses in a top-to-bottom sequence.

[0073] In any one of the above embodiments, it will be appreciated that the present disclosure is a novel method for storing hydrogen in a subsurface location, where a target formation within the subsurface location is evaluated for its suitability, calculating hydrogen storage parameters based on the evaluation of the target formation, drilling one or more wells into the target formation, forming one or more storage lenses in the target formation extending from the corresponding well, injecting hydrogen into the storage lenses for a period of time until the hydrogen is required and recovered / extracted from the storage lenses for use. It will be appreciated that the method comprises the evaluation and calculation steps to advantageously identify a suitable target formation that allows the method to store hydrogen in a subsurface location, such that the recovered / extracted hydrogen for use is of high purity, that is, the recovered / extracted hydrogen is the same as, or very close, to the same purity as the hydrogen that was originally injected, without being degraded due to storage within the target formation. The inventors note that, if the target formation comprises one or more properties disclosed herein, the recovered / extractedhydrogen may be as close as 95% to the original hydrogen that was injected, without any, or much, additional by-product from the target formation.

[0074] In any one of the above embodiments, it will be appreciated that the present disclosure is only concerned with hydrogen storage within a subsurface location, where the time period (i.e. period of time) of storage of the hydrogen is up to a few weeks, and / or up to one or more months, prior to being extracted from the subsurface location for use as a recovered product. The inventors note that the hydrogen may be stored within the disclosed subsurface location, and thus the target formation with one or more properties disclosed, for longer than this time period, however, the loss of hydrogen into target formation may increase. The inventors also note that the period of time hydrogen may be stored within the subsurface location, is dependent on the permeability of the target formation, where the lower the target formation’s permeability, the longer the period of time may be. An example for hydrogen storage for the period of time being a few weeks, may be for the storage of hydrogen from an ammonium plant that may be shut down for the period of time, and the hydrogen required for the plant process requires storage, and the method disclosed herein is employed to store the hydrogen in a subsurface location proximal to the aluminium plant. It will be understood that an advantage of the present disclosure is that, due to the storage of hydrogen being in a subsurface location, it is possible to employ the method and store hydrogen proximal to use cases, such as the ammonia plant, without requiring expensive surface storage tanks. Another example could be near a hydrogen production hub, or near a hydrogen export terminal.

[0075] In any one of the above embodiments, it will be appreciated that the target formation for the purposes of hydrogen storage is a geological formation that is ‘virgin’, or ‘native’, such that it has not been previously utilised for other purposes such as oil and gas production. The target formation is evaluated, and selected, based on being in its ‘virgin’, or ‘native’ state, as the inventors note that this is more likely to provide the target formation with properties disclosed herein that aid in the storage and recovery of hydrogen, while minimising the loss of stored hydrogen within storage lenses to the target formation during a period of time that the hydrogen is stored. It will be appreciated that the target formation may be considered a previously undrilled, or undeveloped, reservoir, or region, that is a virgin formation, a virgin reservoir, a native formation, a native reservoir, or a greenfield reservoir. The inventors note that the entire target formation itself, or a region of the target formation, may be in a ‘virgin’, or ‘native’, state where no prior boreholes, or wellbores, have been drilled for the purposes of oil and gas production.

[0076] In any one of the above embodiments, the step of drilling at least one well in the disclosed method may be via known conventional drilling techniques used in the oil and gas industry. However, the inventors note that it may be possible to drill, or even form, the required at least one well for the disclosed method by other means, provided that the storage lenses may subsequently be formed extending from the wells into the target formation. It will be appreciated that the drilling, or forming, of the at least one wellinto the target formation, are wells that are purposefully drilled, or formed, to connect, or access, the target formation for use in the method for storing hydrogen in the subsurface location.

[0077] In any one of the above embodiments, where reference is made to injecting hydrogen, pressurised fluids, a fine-grained mixture, or the like, it will be appreciated that these injection processes may be carried out by any known means such as via one or more pumps located at the surface. It will be appreciated that the means utilised for injecting these, such as the types of surface pumps, to achieve desired pressures, are not the subject of the disclosed method.

[0078] In the presently disclosed method, it will be appreciated that the evaluation, and identification, of a suitable target formation at step a) is important to the subsequent steps within the method to achieve the desirable and advantageous effects for storing hydrogen within the subsurface location.

[0079] In any one of the above embodiments, a particular advantage of the disclosed method is realised when comparing to existing techniques of storing hydrogen within depleted oil and gas reservoirs. Within these existing techniques, wells and formations are utilised to store hydrogen, where these wells are those that have been previously been utilised to produce hydrocarbons therefrom (or previously developed), these wells no longer comprise their original properties, which is noted by the inventors as being to the detriment of hydrogen storage, as with the use of these wells that have been previously produced from, when used to store hydrogen, the recovered / extracted stored hydrogen is less likely to be pure (i.e. will likely comprise several impurities from the formation within which it is stored). Additionally, depleted oil and gas reservoirs are likely to require a cushion gas, which, when required, may utilise between 30% to 50% of the usable storage medium (i.e. hydrogen storage within a reservoir). That is, notably in these existing techniques, usable storage for hydrogen within a reservoir is reduced by approximately 30% to 50% due to the requirement of a cushion gas, if hydrogen is used for cushion gas. If in the instance another gas is used as the cushion gas, this generally results in the loss of purity of the stored hydrogen. In contrast, the inventors note that the method of the present disclosure results in loss of less than 5 to 10% of stored hydrogen within storage lenses to the target formation 110. The inventors note that although there is a smaller loss of less than 5 to 10% stored hydrogen when using the method of the present disclosure, this loss may be recovered with repeated use of the method to store hydrogen in the target formation via the effect of the formation being water-wet.

[0080] The inventors also note that in existing techniques for storing hydrogen within previously produced from (or previously developed, or depleted oil and gas reservoirs) wells, or developed / depleted oil and gas reservoirs, hydrogen is often stored within a series of induced fractures that may extend vertically, or in the vertical plane (e.g. in the instance of multilateral or horizontal wells). In contradistinction, in the present disclosure, storage lenses 20 are formed within target formation 110 that comprises favourable stress conditions where the minimum (minor) principal stress component is thevertical stress, and the horizontal stresses are larger than the vertical stresses, and accordingly, the storage lenses 20 propagate in the horizontal plane rather than the vertical plane. Thus, in the present application, hydrogen is stored within storage lenses 20 that propagate in the horizontal plane.

[0081] In any one of the above embodiments, a flow regime of the stored hydrogen within the storage lenses 20 is expected to be in a single -phase (i.e. flow is expected to be only stored hydrogen). The inventors note that the advantage of single-phase flow within the storage lenses 20 eliminates problems with relative permeability hysteresis that may be associated with two-phase flow regimes. Notably, two- phase flow regimes are more likely common within hydrogen storage techniques that utilise oil and gas reservoirs that have been previously drilled, and subsequently utilised for hydrogen storage, as these earlier techniques may comprise other gases that are present within the reservoir (e.g. originally in-situ hydrocarbons, or another gas that is utilised as the cushion gas).

[0082] With reference to Figure 6, there is graphically illustrated an exemplary storage volume of hydrogen for several hydrogen injection pressures. The inventors note exemplary values for a target storage size of 100 tonnes of hydrogen gas, stored in a subsurface location by the disclosed method, may be achieved given target formation 110 that is located at a depth between 300 to 700 meters, the anticipated (or modelled) in-situ stress (i.e. vertical stress) is likely to be in the range of 7 to 12 MPa, the net calculated pressure may be 1 MPa, where the anticipated (or modelled) hydrogen storage pressure is then between 8 to 13 MPa. Following this, the inventors note for these exemplary values, the anticipated hydrogen density is likely to be between 5 to 10 kg / m3, and thus the achievable (calculated) storage volume may be between 10,000 and 20,000 m3. Figure 6 illustrates that the expected storage lens 20 geometry (opening and lateral extent) with a storage capacity of 10,000 m3for different stiffnesses (where E = young’s modulus) of the target formation 110. The inventors note that the higher stiffnesses (E) of the target formation 110, the larger the lateral extent of the lens to create the target volume of 10,000 m3. Shallow layered formations such as shales are expected to have low values of Young’s modulus (i.e. E < 5 to 10 GPa), which indicates that a storage lens 20 will need a radius of 200 to 250 meters to store the target volume of 10,000 m3.

[0083] The inventors also note that for the preferred depth of the target formation 110 being between 50 and 700m, the anticipated (or modelled) in-situ stress (i.e. vertical stress), and thus the hydrogen storage pressure, is expected to be less than 15 MPa, and have a storage temperature within the range of 50 to 100°C. Within these conditions, the inventors note that the stored hydrogen remains in the gaseous phase, with a low viscosity and a relatively low density that is pressure dependent. The inventors also note that, advantageously, the stored hydrogen will typically comprise a uniform pressure across the storage lens 20.

[0084] With reference now to Figure 7 there is provided a schematic representation of an exemplary storage lens. The inventors illustrate with this schematic the effects within a storage lens, that may occur, resultant of the method described herein. Such as, the injection of hydrogen into the lens, direction of storage pressure (Pnet), relative direction where leak-off from the lens could occur, and estimated positioning of a TSO product within the lens. The inventors note that TSO product may be utilised at a ‘near tip region’ of a storage lens 20, so that the storage lens 20 may be further inflated without causing it to extend further in a lateral / horizontal direction. TSO techniques are known and are often fine-grained proppants that are used to stabilise engineered lens geometries by blocking a pressure build up at a ‘near tip region’ of a lens (see ‘Ptip’ within Figure 7).

[0085] With reference now to Figures 8 to 14, the inventors provide graphical representations that illustrate calculations and modelling performed to demonstrate effects of a TSO in: pressure at a tip of a storage lens 20 for a given set of exemplary values (such as those in the above paragraphs, and where a storage lens 20 comprises a radius of 250 meters), the portion of the storage lens 20 utilised by the hydrogen and the TSO, hydrogen saturation within a storage lens after a period of time, potential impact on hydrogen leak off into a geological layer outside of the target formation. The inventors include these graphical representations for illustrative purposes only, to demonstrate the role of TSO material in blocking / slowing down a pressure build up at a tip of a storage lens 20. These Figures illustrate that in instances where a TSO material is not utilised, this results in a pressure at the tip of the storage lens 20 that results in the target storage pressure (which may be, for example 11 MPa) being reached almost instantly due to the low viscosity of hydrogen to be stored. Additionally, the Figures illustrate in instances where a TSO material is utilised, the pressure at the tip of the storage lens 20 is limited by the effects on permeability of the storage lens 20 due to presence of the TSO. Accordingly, the inventors note that the use of TSO material impacts the disclosed method via the leak-off, or pressure build up, and ultimately the target storage pressure achievable within a target formation 110 before stored hydrogen may be leaked, or lost, from the storage lenses 20.

[0086] It will be appreciated that in any one of the described embodiments, the stored hydrogen is preferably in a gaseous state.

[0087] The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that such prior art forms part of the common general knowledge.

[0088] It will be understood that the terms “comprise” and “include” and any of their derivatives (e.g. comprises, comprising, includes, including) as used in this specification, and the claims that follow, is to be taken to be inclusive of features to which the term refers, and is not meant to exclude the presence of any additional features unless otherwise stated or implied.

[0089] In some cases, a single embodiment may, for succinctness and / or to assist in understanding the scope of the disclosure, combine multiple features. It is to be understood that in such a case, these multiple features may be provided separately (in separate embodiments), or in any other suitable combination. Alternatively, where separate features are described in separate embodiments, these separate features may be combined into a single embodiment unless otherwise stated or implied. This also applies to the claims which can be recombined in any combination. That is a claim may be amended to include a feature defined in any other claim. Further a phrase referring to “at least one of’ a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c.

[0090] It will be appreciated by those skilled in the art that the disclosure is not restricted in its use to the particular application or applications described. Neither is the present disclosure restricted in its preferred embodiment with regard to the particular elements and / or features described or depicted herein. It will be appreciated that the disclosure is not limited to the embodiment or embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope as set forth and defined by the following claims.

Claims

CLAIMS1. A method for storing hydrogen in a subsurface location, the method comprising:(a) evaluating a target formation within the subsurface location, wherein the target formation comprises low permeability and is preferably water-wet;(b) calculating: a storage volume, a number of storage lenses required, to achieve the storage volume, and a storage pressure, each based on the evaluation of the target formation;(c) drilling at least one well into the target formation, preparing each well for hydrogen storage by forming the storage lenses in the target formation from each well to achieve the storage volume, and pressure testing each well to the storage pressure; and(d) injecting hydrogen into each well at an injection pressure sufficient to drive the hydrogen into each of the storage lenses, such that the hydrogen is stored within the lenses at the storage pressure, and subsequently shutting in each well stores hydrogen within the subsurface location.

2. The method of claim 1, wherein the target formation is under overpressure conditions resultant of an overburden layer.

3. The method of either claims 1 or 2, wherein the target formation comprises an in-situ stress that results in a vertical stress being the minor principal stress.

4. The method of claim 3, wherein the storage pressure is greater than the in-situ stress, that is the vertical stress, of the target formation.

5. The method of claim 4, wherein the storage pressure maintains the hydrogen within the lenses.

6. The method of any one of the preceding claims, wherein, at step (c), each of the storage lenses are formed by injecting a first fluid into the target formation at a first location to open and inflate bedding planes within the target formation to create a first storage lens.

7. The method of claim 6, wherein the storage pressure maintains the bedding planes, or the lenses, in an inflated state.

8. The method of claims 6 or 7, wherein the first fluid is water.

9. The method of any one of claims 6 to 8, wherein a second fluid comprising a fine-grained mixture is subsequently injected into the first storage lens to restrict lateral growth of the first storage lens.

10. The method of claim 9, wherein the second fluid reduces leak-off and provides structural integrity to the first storage lens.

11. The method of any one of claims 6 to 10, wherein in use, the first and second fluids are injected to form each of the storage lenses required to achieve the storage volume.

12. The method of claim 11, wherein each subsequent storage lens within each well is formed above or below the previous storage lens.

13. The method of claim 12, wherein, at step (d), for each well the storage lenses are injected with hydrogen in a bottom-to-top sequence, where the lowermost storage lens is injected with hydrogen for storage, and isolated prior to subsequently higher storage lenses being injected.

14. The method of any one of the preceding claims, wherein following step (d), after a period of time, one or more wells are opened, and hydrogen is recovered from the storage lenses in a top-to-bottom sequence.

15. The method of claim 14, wherein the number of wells are opened based on a required volume of stored hydrogen.

16. The method of either one of claims 14 or 15, wherein the hydrogen is recovered at an extraction pressure which is a result of the storage pressure within the wells reducing to the in-situ, or vertical, stress of the target formation.

17. The method of any one of claims 14 to 16, wherein the period of time is a few weeks and up to one month.

18. The method of any one of the proceeding claims, wherein the target formation is located at a depth that the in-situ, a vertical stress, is the minimum stress.

19. The method of claim 18, wherein the target formation is located at a depth of less than 700-1000 metres.

20. The method of any one of the preceding claims, wherein permeability of the target formation is less than 0.01 milli Darcy.

21. The method of any one of the preceding claims, wherein the water- wet target formation is initially saturated with water.

22. The method of any one of the preceding claims, wherein the target formation is a layered formation, such as a shale formation.

23. The method of any one of the preceding claims, wherein the target formation further comprises a previously undrilled, or undeveloped, region that is considered a virgin formation, a virgin reservoir, or a greenfield reservoir.

24. A method for storing hydrogen in a subsurface location, the method comprising:(a) evaluating a target formation within the subsurface location, wherein the target formation comprises low permeability, is subject to in-situ conditions resultant of an overburden layer, and is preferably water- wet;(b) calculating: a hydrogen storage volume, a number of storage lenses required to achieve the hydrogen storage volume, and a hydrogen storage pressure, each based on the evaluation of the target formation;(c) drilling at least one well into the target formation, and forming storage lenses in the target formation from each well by inflating bedding planes within the target formation by injecting a pressurised fluid followed by a fine-grained mixture to restrict lateral growth and provide structural integrity to the storage lenses, wherein the total number of storage lenses within the wells achieve the hydrogen storage volume;(d) injecting hydrogen into each well at an injection pressure sufficient to drive hydrogen into each of the storage lenses, such that the hydrogen is stored within the lenses at the hydrogen storage pressure, and subsequently shutting in each well stores hydrogen within the subsurface location; and(e) opening one or more wells to recover hydrogen from the storage lenses, wherein the hydrogen is recovered at an extraction pressure which is a result of the hydrogen storage pressure within the wells reducing to the in-situ stress of the target formation.

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