CA3159645A1 - Augmented generation of hydrogen in deviated or horizontal wells - Google Patents

Abstract

Hydrogen-rich fluid such as molecular hydrogen is produced by artificially inducing or enhancing a serpentinization reaction in an underground reservoir. In a reservoir containing host rock comprising a ferrous iron silicate material, a stimulation action such as heated water injection, steam injection, and fracking using the at least one injection well to induce or enhance a serpentinization reaction between the ferrous iron source and water. The stimulation action can also supply the water required for the serpentinization reaction. If the reservoir does not contain sufficient ferrous material or requires additional ferrous material, particles comprising ferrous iron are injected into the reservoir. Ferrous iron can be injected in the form of nanoparticles or as a proppant. Production can occur in a pair of horizontal or deviated wells, with an injection well at a greater vertical depth than the production well.

Description

Atty Ref: ET-031CA1 / 4336-6 Augmented generation of hydrogen in deviated or horizontal wells Technical Field [0ow] This disclosure relates to the production of hydrogen and hydrogen-rich fluids through serpentinization of ferrous iron sources in underground reservoirs.
Technical Background

[0002] Hydrogen gas has been recognized as a promising alternative fuel. Since pure hydrogen produces only water when combusted, it is generally referred to as a "clean"
fuel. Hydrogen occurs naturally in the Earth's crust, in mid-ocean ridges and Precambrian crystalline shields, as well as in celestial bodies. Natural hydrogen gas reserves, such as the extensive hydrogen field at Bourakebougou in Mali, are currently being exploited.

[0003] Aside from the harvesting of naturally occurring hydrogen gas, efforts to produce hydrogen have concentrated on several known methods, such as electrolysis (i.e., hydrolysis), natural gas reforming, biomass gasification, and natural gas or fossil fuel combustion. The resultant hydrogen may be considered "gray", "blue" or "green" depending on the level of carbon emissions associated with powering the hydrogen generating reaction and the products of the reaction itself. For example, hydrogen produced from combustion is generally considered gray hydrogen, associated with high carbon emissions. Hydrogen produced in this manner may be considered blue if accompanied by carbon capture, utilization and storage, which lowers the net level of carbon emissions. Hydrogen produced via hydrolysis, when powered by a low-carbon source, is considered green since hydrolysis produces only hydrogen and oxygen.

[0004] Currently, using known methods, blue hydrogen is more cost effective to produce than green hydrogen; but even so, blue hydrogen still requires additional measures to mitigate carbon emissions.
For example, methane reforming can be used to produce hydrogen at an industrial scale, but ultimately produces carbon dioxide that must be sequestered or otherwise disposed of.
Accordingly, it is desirable to develop alternative means of hydrogen production that minimizes the production of carbon emissions.

Date Recue/Date Received 2022-05-19 Atty Ref: ET-031CA1 / 4336-6 Summary

[0005] Hydrogen is produced in underground reservoirs through artificial inducement and/or augmentation of a serpentinization reaction between water and a ferrous iron source.

[0006] In some implementations, a suitable reservoir is seeded via an injection well with particles containing ferrous iron, such as ferrous iron nanoparticles. In other implementations, the reservoir already includes host rock containing a suitable ferrous iron source, such as fayalite, but may lack sufficient water or heat to spontaneously react. The serpentinization reaction is artificially triggered or augmented through the application of well stimulation techniques conventionally associated with hydrocarbon production, such as hydraulic fracturing (fracking) to enhance the permeability of the reservoir, or thermal stimulation through water or steam injection. The resultant serpentinization reaction produces molecular hydrogen, which is recovered via a production well. The pH of injected or existing water can be altered to improve the reaction rate. Carbon-containing material present in the reservoir or injected into the reservoir can result in production of a hydrogen-rich fluid such as methane instead of, or in addition to, molecular hydrogen. Thus, spent hydrocarbon wells may be adapted for hydrogen production without requiring the installation of natural gas reforming equipment necessary for production of grey or blue hydrogen.

[0007] Where the reservoir already contains host rock providing a sufficient ferrous iron source to sustain production of hydrogen, any hydrogen produced by naturally occurring serpentinization reactions can be extracted via production wells. Once the naturally occurring hydrogen has been depleted, or if a naturally occurring serpentinization reaction is not detectable in the reservoir, the serpentinization reaction can then be artificially triggered or augmented.

[0008] Since there is no combustion contemplated in this process, there are no waste combustion products to be sequestered. This may be contrasted to techniques such as in situ combustion of underground hydrocarbon reserves which does generate pollutants such as carbon monoxide and carbon dioxide that must then be sequestered within the reservoir.

[0009] Thus, in some implementations, a method for underground production of hydrogen includes injecting particles comprising ferrous iron into an underground reservoir via an injection well, to thereby cause a serpentinization reaction with water in the reservoir, and extracting hydrogen or a hydrogen-rich fluid produced in the underground reservoir via a production well. In other implementations, the method includes locating at least one injection well at an underground reservoir, the underground reservoir comprising host rock comprising ferrous iron silicate material, locating at least one horizontal or deviated production well at the underground reservoir, performing at least one stimulation action to Date Recue/Date Received 2022-05-19 Atty Ref: ET-031CA1 / 4336-6 stimulate a serpentinization reaction in the underground reservoir, and extracting hydrogen or a hydrogen-rich fluid using the at least one production well.

[0010] In all implementations, the serpentinization reaction can be stimulated by increasing a temperature of the underground reservoir, increasing the temperature by water, increasing the temperature by steam injection, and/or hydraulic fracturing, including a combination of two or more of these techniques. At least some water for the serpentinization reaction may be supplied by connate water. In some implementations, the proppant employed in hydraulic fracturing comprises ferrous iron.
Also, in some implementations, the serpentinization reaction is stimulated or produced by injecting the particles of ferrous iron, where the average particle size is smaller than an average pore throat size of the reservoir, 50% or less than the average pore throat size of the reservoir, or nanoparticles. In some implementations, the particles of ferrous iron are fayalite. In some implementations, the stimulation action raises an average temperature of the underground reservoir to at least 200 degrees Celsius.

[0011] In these implementations, the injection and production wells can be drilled at a site of a reservoir comprising host rock with iron silicate material, or previously-drilled wells can be employed for producing hydrogen. The injection and production wells can be horizontal or deviated.
Brief Description of the Drawings

[0012] FIG. 1 is a flowchart illustrating, at a high level, a method for production of hydrogen using artificial induction or augmentation.

[0013] FIG. 2 is a flow chart illustrating, at a high level, a further method for production of hydrogen using artificial induction or augmentation.

[0014] FIG. 3 is a schematic diagram illustrating an example hydrogen production system with a first arrangement of injection and production wells.

[0015] FIG. 4 is a schematic diagram illustrating a further arrangement of injection and production wells.

[0016] FIG. 5 is a schematic diagram illustrating another arrangement of injection and production wells.

[0017] FIG. 6 is a schematic diagram illustrating a further arrangement of a substantially vertical injection well and a plurality of production wells.
Detailed Description

[0018] The generation of naturally occurring subsurface hydrogen has been well documented.
Subsurface hydrogen is naturally created by radiolysis, the disassociation of water due to irradiation by Date Recue/Date Received 2022-05-19 Atty Ref: ET-031CA1 / 4336-6 radioactive ores, or by serpentinization of iron-containing rocks. Hydrogen production by serpentinization in mid-ocean ridges and basins has been documented or modelled. Serpentinization is used to describe the metamorphic hydration and oxidation of ultramafic rock to serpentinite. Typically, the source rock is low in silica, and can include iron-bearing species such as olivine and pyroxenes.

[0019] Olivine, in particular, is a magnesium iron silicate, where the ratio of magnesium to iron varies.
Olivine thus has endmembers consisting of only magnesium silicate (forsterite, Mg2SiO4) and iron silicate (fayalite, Fe2SiO4). Iron-containing silicate forms contain ferrous iron (iron(II)) and can react with water to produce hydrogen.

[0020] In particular, water reacts with fayalite to oxidize the iron(II) and produce magnetite, silicon dioxide (quartz), and hydrogen:
3Fe2SiO4 + 2H20 4 2Fe304 + 3Si02 + 2H2

[0021] This reaction can involve the intermediate production of ferroan brucite or iron(II) hydroxide, MgxFei,(OH)2 or Fe(OH)2; the iron(II) hydroxide can then be converted to magnetite, hydrogen, and water as described by the Schikorr reaction, which may be expressed as:
3Fe(OH)2 4 Fe304 + H2 + 2H20

[0022] When a carbon source is present, some hydrocarbon gases may also be produced from olivine, for example when reacted with carbon dioxide:
18Mg2SiO4 + 6Fe2SiO4 + 26H20 + CO2 4 12Mg3Si205(OH)4 + 4Fe304 + CH4

[0023] A "serpentinization" reaction, as used herein, refers to a reaction of ferrous iron-containing material with water that produces hydrogen, whether in the form of molecular hydrogen or a hydrogen-rich fluid such as methane. Some impurities may be comprised in the hydrogen product depending on the constituents of the reaction components or trace gases present in the reservoir where the reaction occurs.

[0024] While the serpentinization reaction will naturally occur with the fortuitous concomitance of fresh (unreacted) ultramafic rock, water, and suitable temperature, the development of a naturally-occurring hydrogen field also depends on a suitable geologic structure that traps the produced hydrogen and avoids or reduces migration or leakage. In the case of the Bourakebougou field, for example, layers of dolerite shields and aquifers likely confined the naturally produced hydrogen until its discovery.
However, as discussed below, underground reservoirs that do not currently produce a detectable or viable amount of hydrogen¨or that do not produce any hydrogen at all¨can be used for the Date Recue/Date Received 2022-05-19 Atty Ref: ET-031CA1 / 4336-6 production of hydrogen by artificially induced or augmented serpentinization reactions, using stimulation techniques previously associated with hydrocarbon production such as hydraulic fracturing and thermal stimulation. This adaptation can be applied to pre-existing, abandoned or to-be-abandoned wells, or to newly drilled wells, whether or not the reservoir contains sufficient ferrous iron-containing rock.

[0025] An example production method is generally illustrated by the flowchart of FIG. 1. Briefly, at 100, injection and production wells are located at a suitable site for hydrogen production. In this example, the site is an underground reservoir with host rock having sufficient ferrous iron silicate material, such as unreacted fayalite or iron-containing olivine, to support sufficient serpentinization reactions to generate viable hydrogen, that is to say, hydrogen in sufficient quantities for production purposes. It is also presumed that the geologic makeup of the reservoir, including the availability of ferrous iron silicate material and the permeability of the host rock, has already been determined, either from previous production activity at the site (e.g., in the case where pre-existing injection or production wells used for hydrocarbon production are available) or as part of an exploratory phase. If the injection and production wells are not already present at the site, locating the injection and production wells can include some or all of the typical drilling and completion steps. At 105, optionally any naturally occurring hydrogen is extracted prior to engaging in artificial inducement or augmentation of a serpentinization reaction, but this step may be bypassed; if there is naturally occurring hydrogen it may be collected along with the product of the artificially induced or augmented serpentinization reaction. At 110, the basic conditions for a serpentinization reaction in the reservoir are determined, such as availability of sufficient water and the temperature of the reservoir; however, these may be already known from previous production or exploratory activity. This can include measurement of the pH of available water and the presence of other constituents in the reservoir.

[0026] Based on the geologic makeup and reaction conditions, one or more artificial inducement or augmentation actions are performed at 115. As those skilled in the art will appreciate, typical limiting factors of a reaction rate, such as the serpentinization reaction rate, are temperature, availability of source materials (reactants and reagents), and surface contact between source materials. Connate water may supply the serpentinization reaction, but if insufficient water is present, then water is injected 120 and enters the reservoir through perforations in the injection well (assuming the injection well is lined at the reservoir). A serpentinization reaction can occur at about 200 C, or even lower; thus, depending on the depth of the reservoir and a target rate of reaction, heating of the water will generally be required. Thus water heated at the surface (e.g., to 200 C, in the form of wet or dry steam) is injected Date Recue/Date Received 2022-05-19 Atty Ref: ET-031CA1 / 4336-6 into the reservoir 125, for example using techniques and equipment known in hydrocarbon production, such as conventional heaters or boilers. Once condensed in the reservoir, this also provides a water source for the serpentinization reaction. Use of low-carbon energy sources for heating the water will minimize the environmental impact of this step.

[0027] Other sources of heat energy (not illustrated in the drawings) may be used to raise the water temperature in the reservoir or prior to reaching the reservoir. Geothermal energy can be used to raise the temperature of water in the reservoir. Alternatively, heated water can be sourced from existing deeper aquifers; or, if the reservoir is located under existing thermal oil or in situ oilsands operations, the remaining hot water in those oil formations can be circulated into the reservoir. Injection of heated water thus includes circulating the heated water from an underground source rather than from surface.

[0028] Additives may be used to modify the pH of the water 130 in the reservoir. It has been found that the rate of hydrogen production by serpentinization increases with higher pH;
thus, additives such as sodium hydroxide or potassium hydroxide can be useful to accelerate production.

[0029] The rate of a reaction can also be limited by the surface contact with reactants. In the reservoir, relatively low permeability of the rock containing ferrous iron may retard the serpentinization reaction rate. Thus, hydraulic fracturing techniques, as known in hydrocarbon production, can be applied 135 to induce fractures and improve permeability in the reservoir. A wide variety of fracking fluid formulations is available; in view of the possibility of enhancing the reaction rate by increasing pH, alkaline fracking fluid additives such as NaOH and KOH, as noted above, can be useful. Carbon-containing additives such as cellulose may result in the generation of some hydrocarbons, as noted above. Conventional proppants can be used as well. However, in place of conventional frac sand (quartz sand), other substances can be used as proppants while augmenting the serpentinization reaction. For instance, since fayalite has a similar hardness to quartz, sand comprising or consisting of fayalite can serve as a suitable proppant while providing additional ferrous iron for further serpentinization reactions.

[0030] As a result of these one or more inducement or augmentation techniques, serpentinization reactions in the reservoir generate hydrogen in a gas stream which is extracted via a production well 140. If the resultant gas stream includes contaminants or other gases (e.g., nitrogen or methane), a recovery method 145, such as membrane diffusion, can be employed to capture the hydrogen and remove other gases. This can be carried out at surface, or alternatively subsurface in the production well. The hydrogen is brought to surface for storage, transport and use.

[0031] In the production method discussed above, the reservoir included sufficient ferrous iron source material to support a serpentinization reaction and viable hydrogen production. However, suitable Date Recue/Date Received 2022-05-19 Atty Ref: ET-031CA1 / 4336-6 injection and production wells can be located at other sites that by themselves do not provide viable hydrogen quantities, or indeed any at all. This may be the case where an abandoned or to-be-abandoned well providing adequate reservoir pressure and temperature is converted for hydrogen production, or where a reservoir site is chosen based on proximity to a subsurface aquifer or thermal oil operations providing a heated water source, as suggested above. In that case, a similar production method as that described above can be employed, but with the injection of ferrous iron particulate matter to seed the reservoir with a reactant to induce the serpentinization reaction.

[0032] FIG. 2 provides a flowchart illustrating an example of this production method. Similar to the process of FIG. 1, at 200 injection and production wells are located at the desired site. Again, it is presumed that the geologic makeup of the reservoir was previously determined in the course of previous production or exploratory activity. Locating the wells, again, can include some or all of the conventional drilling and completion steps if the wells are not already available. Optionally, any existing hydrogen is extracted (not shown in FIG. 2) prior to artificially inducing generation, although in this implementation this step is not expected. At 205, the basic conditions for a serpentinization reaction are determined. At 210, particles providing ferrous iron are injected into the reservoir to provide source material for the serpentinization reaction. These particles can be fayalite particles, although other materials providing a ferrous iron source can be used instead, and can be transported as an aqueous dispersion, which can also supply some of the water required for the serpentinization reaction. To mitigate the risk of plugging the reservoir, the particles are smaller than the average pore throat size of the rock forming the reservoir (which would have been determined at an earlier stage), e.g., 50% or less than the average pore throat size. Nanoparticles containing ferrous iron, such as fayalite nanoparticles, would ensure passage through most macroporous and some mesoporous rock; in addition, the small size of the particles favours the serpentinization reaction rate since it increases the available reactant surface area available to water.

[0033] At 215 one or more stimulation actions are performed as described above, based on the conditions in the reservoir. If insufficient water is present and not provided with the injection of the ferrous iron-containing particles, then water is injected 220. If heat is required to trigger or accelerate the reaction, this can be supplied in the form of heated water or steam injection 225, whether from surface or from a subsurface source as described above. Additives can be provided to modify the pH 230 to enhance the serpentinization reaction, for example to increase alkalinity as discussed above. Fracking 235 may again be carried out, as described above, to improve permeability in the reservoir. Since some particles may rest in the injection well 310, the serpentinization reaction can thus occur within the Date Recue/Date Received 2022-05-19 Atty Ref: ET-031CA1 / 4336-6 injection well instead of, or as well as, in the surrounding reservoir. The resultant hydrogen then escapes the injection well through perforations and travels through the reservoir to the production well, where it is extracted 240. Again, if the resultant gas stream includes other gases or contaminants, a recovery method 245 is used to capture the hydrogen, which is then stored, transported, and used.

[0034] The technique of injecting particles can be combined with the production method described with reference to FIG. 1 above to further augment the serpentinization reaction with additional reactant. Moreover, the order of steps depicted in FIGS. 1 and 2 can be altered. For instance, determination of the basic conditions for the serpentinization reaction at 110 or 205 can be determined during an exploratory phase prior to locating the injection and production wells at 100, as noted above, or during the extraction of naturally occurring hydrogen 105. Hydraulic fracturing can occur at an earlier stage, for example prior to introduction of additional water 120 or 220, or prior to introduction of ferrous iron-containing particles if this step is undertaken. Stimulation actions undertaken in the method of FIG. 2 may occur concurrently with the injection of particles at 210. The selection of various stimulation techniques, and variations in the steps of the processes shown in FIGS. land 2, are within the skill of the person of ordinary skill in the art.

[0035] Turning to FIG. 3, a schematic depicting main components of a hydrogen production system 300 for implementing the methods described above is shown. One or more injection wells 310 and one or more production wells 350 are located at an appropriate site. The site can be selected based on the presence of one or more of host rock containing a suitable ferrous iron source to support a serpentinization reaction, host rock providing suitable permeability and porosity to accommodate a serpentinization reaction with injected ferrous iron source material, pre-existing wells and/or host rock that may be adapted for hydrogen production, and/or underground heated water sources, as discussed above. For simplicity, FIGS. 3-5 depict only a single injection well 310 and a single production well 350 and FIG. 6 depicts only a single injection well 310 and multiple production wells 350, but more than one injection and production well can be employed. In particular, when particles are injected to supply a ferrous iron source for the serpentinization reaction, the use of multiple injection wells can be useful to increase the rate of introduction of the ferrous iron.

[0036] The injection 310 and production 350 wells can be horizontal or deviated wells, although as can be seen in the example of FIG. 6 the injection well 110 is vertical or substantially vertical. As shown in FIG. 3, the injection well 310 is equipped with an injection system 312 and string 313. This injection system 312 is used to introduce water as a reagent for the serpentinization reaction, and/or heated water or steam to provide thermal stimulation to augment the reaction, with or without additives to Date Recue/Date Received 2022-05-19 Atty Ref: ET-031CA1 / 4336-6 alter the pH of the water. The injection system 312 can also be employed to inject ferrous iron-containing particles to induce or augment the serpentinization reaction. Thus, the injection system 312 will include a number of components for one or more of these purposes, such as water storage tanks, a heater or boiler, storage and hoppers/feeders for ferrous iron particulates, additives for injected water or steam, pumps and a mixer (e.g., a shear unit). If hydraulic fracturing is employed, the system 300 will also include a hydraulic fracturing system 320 including components such as storage and hoppers/feeders and a slurry blender for mixing the fracturing fluid and proppants, if used. In this example, a water-based fracturing fluid would supply hydration for the serpentinization reaction; thus the hydraulic fracturing system 320 could be combined or share components with the injection system 312.

[0037] The injection well 310 extends into or through the reservoir 370, generally a lower part of the reservoir 370. The injection well 310 can also include well monitoring devices such as a fluid analyzer 340 and a temperature sensor 342 proximate to the reservoir 370. The fluid analyzer 340 can be operable to detect the presence of water and gases (e.g., naturally occurring hydrogen) and the pH of water in the reservoir. Readings from the fluid analyzer 340 and temperature sensor 342 are received by a control system 380 at surface, which can be programmed to automatically control the injection system 312, e.g., when injecting water or steam.

[0038] The production well 350 includes production tubing 352 for extracting the hydrogen, connected to storage tanks and associated equipment (e.g., compressors) 354 for storing the produced hydrogen.
As mentioned above this can include hydrogen recovery equipment, if required (not illustrated).

[0039] The production well 350 is located above the injection well 310, and possibly separated from the reservoir 370 by caprock, although in the illustrated examples, at least one region of the production well 350 extends into the reservoir 370 as well. A flow path to the production well 350 is defined. In the example of FIG. 3, the injection well 310 is horizontal and the production well 350 is deviated, and the toe 355 of the production well is positioned a short vertical distance above the toe 315 of the injection well; thus the flow path can be located where the distance between the production and injection wells is shortest. In this example, the closest vertical distance between the toes 315, 355 may be at least about 2m, but less than about 10m.

[0040] As the reaction occurs in the reservoir 370, the generated gas (molecular hydrogen or possibly hydrogen-rich fluids, depending on the reactants in the reservoir) rises in the reservoir 370 to the production well 350, where it can then be extracted. The production well 350 can be perforated at or near this point of greatest proximity to permit hydrogen flow to the tubing 352. If the flow path extends Date Recue/Date Received 2022-05-19 Atty Ref: ET-031CA1 / 4336-6 through caprock, hydraulic fracturing may be employed to increase permeability to permit gas flow upward. As production progresses, further stimulation can occur through perforations along the injection well, for example in the direction of the arrow indicated in FIG. 3.
Additional flow paths can be established between the reservoir 370 and the production well 350. This can occur naturally as the serpentinization reaction continues.

[0041] FIGS. 4 and 5 illustrate other possible arrangements with a horizontal injection well 310 and deviated production well 350. In these examples, the flow path can again be defined at the region of closest proximity, between a portion of the foot 317 of the injection well and the heel 357 of the production well. Since the drawings depict side views of the reservoir, the lateral spread of the injection and production wells is not illustrated, but the production well 350 need not be positioned directly above the injection well 310 for its full length. That is to say, the injection well is positioned at a greater vertical depth than the production well, but the injection and production wells need not be aligned in the same vertical plane.

[0042] FIG. 6 illustrates a further possible arrangement with a vertical, or substantially vertical, injection well 310 and one or more deviated production wells 350. As the serpentinization reaction progresses, the reservoir 370 can extend upwards towards the surface and additional flow paths can be defined upwards along the length of the wells. This configuration can be useful in pinnacle reef formations, which often have good permeability and porosity characteristics thereby reducing the need for fracking.

[0043] In all cases, the specific well geometry will be determined by the characteristics of the host rock.
In some implementations, both the injection and production wells 310, 350 are horizontal, for example in the case where a steam assisted gravity drainage (SAGD) steam chamber is repurposed for hydrogen production. Alternatively, the injection well 310 may be deviated while the production well 350 is deviated or horizontal. In some implementations, an operating SAGD well pair can be employed.
Conventionally in a SAGD operation, an injection well is positioned above a production well. An additional production well for hydrogen can be positioned above the injection well, arranged relative to the injection well similar to the arrangements described above. If the SAGD
reservoir already includes a ferrous iron source, steam introduced by the injection well can be directed to the ferrous iron source as well to stimulate a serpentinization reaction for collection by the hydrogen production well. Optionally ferrous iron can be injected as described above.

[0044] While example implementations have been shown and described, modifications can be made by those of ordinary skill in the art without departing from the scope or teaching herein. Options or Date Recue/Date Received 2022-05-19 Atty Ref: ET-031CA1 / 4336-6 variations described in connection with one implementation may be combined with other options or variations of other implementations. Use of any particular term should not be construed as limiting the scope or requiring undue experimentation to implement the claimed subject matter or embodiments described herein. While this disclosure may have articulated specific technical problems or advantages that are addressed or provided by the implementations described above, this disclosure is not intended to be limiting in this regard; the person of ordinary skill in the art will readily recognize other technical problems addressed or advantages provided by the embodiments discussed above.
Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims.

Date Recue/Date Received 2022-05-19

Claims (38)

Claims

1. A method for underground production of hydrogen, the method comprising:
injecting particles comprising ferrous iron into an underground reservoir via an injection well, to thereby cause a serpentinization reaction with water in the reservoir; and extracting hydrogen or a hydrogen-rich fluid produced in the underground reservoir via a production well.

2. The method of claim 1, further comprising:
stimulating the serpentinization reaction by increasing a temperature of the underground reservoir.

3. The method of claim 2, further comprising increasing the temperature by water or steam injection.

4. The method of claim 1, further comprising:
stimulating the serpentinization reaction by at least one of water injection, steam injection, and hydraulic fracturing.

5. The method of any one of claims 1 to 3, further comprising, prior to injecting the particles, increasing permeability of the underground reservoir by hydraulic fracturing.

6. The method of claim 5, wherein a proppant employed in the hydraulic fracturing comprises ferrous iron.

7. The method of any one of claims 1 to 6, wherein at least some water for the serpentinization reaction comprises connate water.

8. The method of any one of claims 1 to 7, wherein an average particle size is smaller than an average pore throat size of the reservoir.

9. The method of claim 8, wherein the average particle size is 50% or less than the average pore throat size of the reservoir.

10. The method of any one of claims 1 to 9, wherein the particles are nanoparticles.

11. The method of claim 10, wherein the particles comprise ferrous iron nanoparticles.

Date Recue/Date Received 2022-05-19

12. The method of claim 1, wherein injecting particles comprising ferrous iron comprises injecting the particles as a proppant during hydraulic fracturing.

13. The method of claim 12, wherein the proppant comprises fayalite.

14. The method of any one of claims 1 to 13, wherein extracting the hydrogen or hydrogen-rich fluid comprises extracting molecular hydrogen.

15. The method of any one of claims 1 to 13, wherein extracting the hydrogen or hydrogen-rich fluid comprises extracting methane comprising hydrogen produced by serpentinization.

16. The method of any one of claims 1 to 14, wherein the injection well and production well comprise horizontal or deviated wells.

17. The method of claim 16, wherein the injection well and production well comprise horizontal wells.

18. The method of any one of claims 1 to 17, wherein the underground reservoir comprises host rock comprising ferrous iron silicate material.

19. The method of any one of claims 1 to 18, further comprising drilling the injection well and the production well.

20. A method for underground production of hydrogen, comprising:
locating at least one injection well at an underground reservoir, the underground reservoir comprising host rock comprising ferrous iron silicate material;
locating at least one horizontal or deviated production well at the underground reservoir;
performing at least one stimulation action to stimulate a serpentinization reaction in the underground reservoir; and extracting hydrogen or a hydrogen-rich fluid using the at least one production well.

21. The method of claim 20, wherein locating the at least one injection well comprises drilling the at least one injection well.

22. The method of either claim 20 or 21, locating the at least one production well comprises drilling the at least one production well.

Date Recue/Date Received 2022-05-19

23. The method of any one of claims 20 to 22, wherein the at least one injection well is horizontal or deviated.

24. The method of claim 20, wherein the at least one stimulation action comprises at least one of:
heated water injection, steam injection, and hydraulic fracturing using the at least one injection well.

25. The method of claim 24, wherein the at least one stimulation action comprises heated water injection or steam injection to raise an average temperature of the underground reservoir to at least 200 degrees Celsius.

26. The method of either claim 24 or 25, wherein the at least one stimulation action further comprises injecting particles comprising ferrous iron into the underground reservoir using the at least one injection well.

27. The method of any one of claims 20 to 26, wherein an average particle size is smaller than an average pore throat size of the reservoir.

28. The method of claim 27, wherein the average particle size is 50% or less than the average pore throat size of the reservoir.

29. The method of any one of claims 26 to 28, wherein the particles are nanoparticles.

30. The method of claim 29, wherein the particles comprise ferrous iron nanoparticles.

31. The method of any one of claims 20 to 30, wherein extracting the hydrogen or hydrogen-rich fluid comprises extracting molecular hydrogen.

32. The method of any one of claims 20 to 31, wherein extracting the hydrogen or hydrogen-rich fluid comprises extracting methane.

33. Use of particles comprising ferrous iron in an underground reservoir to generate hydrogen through a serpentinization reaction.

34. Use of ferrous iron particles as claimed in claim 33, wherein the ferrous iron particles are fayalite.

35. Use of ferrous iron particles as claimed in either claim 33 or 34 as a proppant in hydraulic fracturing.

Date Recue/Date Received 2022-05-19

36. Use of ferrous iron particles as claimed in either claim 33 or 34, wherein an average particle size is smaller than an average pore throat size of the reservoir.

37. Use of ferrous iron particles as claimed in claim 36, wherein the average particle size is 50% or less than the average pore throat size of the reservoir.

38. Use of ferrous iron particles as claimed in either claim 36 or 37, wherein the particles are nanoparticles.
Date Recue/Date Received 2022-05-19