WO2025195842A1

WO2025195842A1 - Method for generating hydrogen

Info

Publication number: WO2025195842A1
Application number: PCT/EP2025/056548
Authority: WO
Inventors: Dhruv Arora; David Booth Burns; Michael Anthony Reynolds; Nishank SAXENA; Thomas Sandison; Theodericus Johannes Henricus Smit; Alexei TCHERNIAK
Original assignee: Shell Internationale Research Maatschappij BV; Shell USA Inc
Current assignee: Shell Internationale Research Maatschappij BV; Shell USA Inc
Priority date: 2024-03-18
Filing date: 2025-03-11
Publication date: 2025-09-25
Anticipated expiration: 2026-09-18

Abstract

This invention provides a method for generating hydrogen. The comprises using a heater cable (511), provided inside a wellbore (510) in a mafic or ultramafic rock formation (400), to heat the rock formation (400) to a temperature of about 200 to 600 degrees Celsius.

Description

METHOD FOR GENERATING HYDROGEN

Field of the Invention

This invention relates to a method for generating hydrogen in mafic or ultramafic rock formations. Background of the invention

The environmental impact of greenhouse gases, primarily carbon dioxide (CO2) and methane (CH4) , has been the subject of much public debate over the past several decades. Large amounts of greenhouse gases are emitted when producing and burning fossil fuels for, for example electricity production, transport, and heating. To reduce the production of greenhouse gases, many innovative individuals, companies, and organizations are constantly looking for alternatives to the use of fossil fuel.

One promising alternative to carbon-containing fossil fuels is the use of hydrogen (H2) gas. Hydrogen can, for example, be used as an energy carrier for storing energy produced by renewable energy sources such as solar panels and wind turbines. Hydrogen can be used in fuel cells to produce electricity, or via combustion to generate heat. Advantageously, the combustion of hydrogen gas yields just water as a reaction product.

Traditionally, hydrogen has primarily been produced using fossil fuels, for example using natural gas conversion in a steam reformer, which doesn't do much to reduce the emission of greenhouse gas into the atmosphere. Alternatively, hydrogen gas may be generated by the electrolysis of water into hydrogen gas and oxygen. Electrolysis requires a substantial amount of electricity. At least some of the required electricity may be obtained from renewable sources (e.g. , wind, solar, and hydroelectric) . However, all renewable energy used for hydrogen production is renewable energy that can't be used for other purposes and may need to be compensated for by the use of more fossil fuels. A more carbon neutral application of hydrogen is its use for temporarily storing renewable electrical energy in times of high supply and low demand. Using hydrogen for storing renewable energy may further allow transporting electrical energy from off- grid power plants such as, e.g. , off-shore wind turbines or solar power plants in remote locations, such as in the middle of a desert. However, both the conversion from electrical energy from the renewable energy source to chemical energy in the produced hydrogen, and the later use of that hydrogen to generate electricity cause energy losses that reduce the overall efficiency of the electricity production.

One way to minimize such energy losses is to mine natural resources of hydrogen gas. As, for example, described in European patent EP0236480 Bl, hydrogen may be formed in some mafic and ultramafic rock formations through naturally occurring serpentinization reactions. In US patent application US20230272698 Al, a method is described for producing hydrogen gas from a geological formation comprising mafic or ultramafic igneous rock. This known method includes steps of providing a wellbore that at least partially traverses the geological formation and injecting a water-based stimulant through the pathway provided by the wellbore. Hydrogen is formed through serpentinization when the stimulant gets in contact with reactive surfaces of the geological formation, and the now hydrogen-containing fluid is then recovered from the same wellbore. In order to produce a commercially relevant amount of hydrogen, it is important that the wellbore is drilled to a location at a suitable depth where the right types of minerals are abundantly available, and temperatures are optimal for allowing the serpentinization reaction to occur.

It is an aim of the current invention to overcome at least some of the disadvantages of the known method for producing hydrogen gas. Summary of the Invention

According to an aspect of the invention, this aim is achieved by providing a new method for generating hydrogen. The new method comprises a step of using a heater cable, provided inside a wellbore in a mafic or ultramafic rock formation, to heat the rock formation to a temperature of about 200 to 600 degrees Celsius.

Mafic rock is a type of igneous, i.e. magmatic, rock that is rich in magnesium and iron. Mafic rock commonly includes significant amounts of f erromagnesian minerals, such as olivine and pyroxene that are susceptible to serpentinization. Serpentinization is a form of redox reaction, wherein water acts as an oxidizing agent and is itself reduced to hydrogen. Typically, the term mafic rock is used for rocks having a silicon dioxide content of between 45% and 52%, and the term ultramafic rock is used for rocks having a silicon dioxide content of less than 45% .

In naturally occurring mafic and ultramafic rock, serpentinization primarily occurs at depths where the temperature is around 200 degrees Celsius and water is present .

By using a heater cable to heat the rock formation, various technical advantages are obtained. First of all, the heater cable allows for much larger volumes of naturally occurring mafic and ultramafic rock to be used for hydrogen production. At shallower depths where the temperature is normally insufficient for enabling serpentinization, heating the rock formation can start and accelerate the mildly exothermic serpentinization process. Igneous rock has a high thermal conductivity, which allows for efficient heating of large volumes of mafic and ultramafic rock to temperatures leading to the desired production of hydrogen. As a further advantage, the heater cable allows for heating the mafic and ultramafic rock formations to be heated to temperatures that exceed the typical temperatures in geological formations used for hydrogen production through serpentinization. At these higher temperatures, up to about at least 600 degrees Celsius, the serpentinization reaction is accelerated and larger amounts of hydrogen are generated. Furthermore, higher temperatures at locations closer to the wellbore with the heater cable, result in larger volumes of the rock formation getting to a temperature suitable for serpentinization, thereby further increasing the hydrogen production rate.

In preferred embodiments, the heater cable is a mineral insulated heater cable comprising a temperature limited heater. Mineral insulated heater cables are generally well-equipped to heat the mafic or ultramafic rock to temperatures up to and possibly exceeding 600 degrees Celsius and to withstand the high voltages and electric currents that are used for this purpose. "Temperature limited heater" generally refers to a heater that regulates heat output (for example, reduces heat output) above a specified temperature without the use of external controls such as temperature controllers, power regulators, rectifiers, or other devices. The temperature limited heater in the mineral insulated cables has a negative temperature coefficient of resistant, which causes the resistance to decrease as the overall temperature increases. As the electrical current (I) in the core of the heater remains constant throughout the entire length of the heater cable , the decrea se in local resistance ( R) would result in a reduction of power ( P=I 2 *R) in that local section of the heater cable , thereby mitigating hotspots and an pos sible thermal runaway event that could severely damage the wellbore or the heater cable . An example of such a mineral insulated heater cable with a temperature limited heater as the heating member is dis closed in US 10119366 .

In some embodiments the temperature limited heater comprises a semiconductor material . When selecting an appropriate semiconductor material with a particular bandgap , the re sistivity of the semiconductor material can be made to change rapidly when the temperature exceeds a selected value . When the heater cable is designed such that this change of resistivity leads to a significant decrease in power in the respective section of the heater cable , overheating may be prevented .

Although , at the elevated temperatures provided by the heater cable , the serpentinization proces s may generate a suff icient amount of hydrogen using the water that is naturally available in the respective rock formation , the method of generating hydrogen may further comprise a step of inserting a fluid into the wellbore to further stimulate the hydrogen production .

The hydrogen produced underground may be recovered in various ways . In an embodiment of the invention , for example , the inserted fluid absorbs the hydrogen produced in the heated rock formation , thereby resulting in a hydrogen-rich f luid . This hydrogen-rich f luid i s then recovered from the wellbore . After extracting the hydrogen from the recovered hydrogen-rich fluid, the f luid may then be sent back down the wellbore for stimulating the rock formation to generate more hydrogen . Repeatedly using the same fluid to stimulate the serpentinization proces s in the rock formation , for example by pumping it around in a closed circuit , results in a more efficient use of water or other f luids used for thi s purpose .

Depending on the local geological situation , the hydrogen produced in the heated rock formation may migrate through the heated rock formation into a nearby underground hydrogen reservoir . In that case , the method for generating hydrogen may further comprise extracting hydrogen f rom the hydrogen reservoir , through a producer well . The hydrogen re servoir may, for example , be a hollow reservoir or a volume of porous rock , covered by a hydrogen-impermeable shale layer . The producer well is , at least partly, separate from the wellbore and taps into the hydrogen reservoir .

The method according to the invention may further include the step of inserting the heater cable into the wellbore , or even the step of drilling the wellbore in the mafic or ultramafic rock formation . Similarly, the method according to the invention may further include the step of drilling the producer well .

The drilling of the wellbore may be in the vertical direction only, but preferably includes at least some directional drilling too . Mafic and ultramafic rock formations typically extend primarily horizontally within a certain depth range . By drilling in a horizontal , or partly horizontal , direction , larger volumes of mafic or ultramafic rock may be activated and used for hydrogen production . The drilling of the producer well may include at least some directional drilling too . Brief Description of the Drawings

Figure 1 schematically illustrates a cross section of an underground hydrogen production site according to a first embodiment . Figure 2 schematically illustrates a cross section of an underground hydrogen production site according to a second embodiment .

These drawings depict one or more implementations in accordance with the present teachings , by way of example only, not by way of limitation . Detailed Description of the Drawings

Figures 1 and 2 schematically illustrate cros s sections of underground hydrogen production s ites . The method according to the invention makes use of some of the geological properties of the earth below the ground surface 300 at or near the location of the hydrogen production site . In these illustrative examples , a large mafic or ultramafic rock formation 400 starts at a f irst depth di and vertically extends to a second depth d2 .

A wellbore 510 i s drilled into the ultramafic rock formation 400 to enable the insertion of a heater cable 511 and , optionally, a fluid that stimulates the natural production of hydrogen in the mafic or ultramaf ic rock formation 400 . As shown , the wellbore 510 may compri se a horizontal , or otherwise non-vertical , section to ensure that it extends through a large portion of the mafic or ultramafic rock formation 400 , thereby allowing more hydrogen to be produced . While the embodiment shown herein uses a single wellbore 510 for both the heater cable 511 and the stimulating f luid, the cable 511 and the fluid may use separate ( or partly separate ) compartment s within the wellbore 510 . In an equivalent way, two separate wellbores 510 may be provided leading to substantially the same location in the ultramafic rock formation 400 .

The heater cable 511 preferably is an electric heater cable 511 and may have a proximal inactive cold section 511A and a di stal active hot section 511B . Alternative forms of heating may, for example rely on nuclear energy, gas heaters , or superheated steam . The heater cable 511 may include one or more temperature sensors for allowing more precise control of the local temperature in the immediate vicinity of the hot section 511B of the heater cable 511 . The active hot section 511B may compri ses multiple subsections for which the temperature can be controlled independently . By controlling the temperature of the hot section 511B of the heater cable 511 , the rock formation 400 in the direct vicinity of the hot section 511B is heated to a temperature of about 200 to 600 degrees Celsius to stimulate the natural production of hydrogen .

The temperature control may be implemented in conventional ways , for example by active regulation of the power supply of an electric heater cable 511 . Preferably, the temperature of the hot section 511B of the heater cable 511 is controlled pas s ively, for example by us ing a mineral insulated heater cable comprising a temperature limited heater 511B .

Mineral insulated heater cables are generally well- equipped to heat the mafic or ultramafic rock 400 to temperatures up to and pos sibly exceeding 600 degree s Celsius and to withstand the high voltage s and electric current s that are used for this purpose . "Temperature limited heater" generally refers to a heater that regulates heat output ( for example , reduces heat output ) above a specified temperature without the use of external control s such a s temperature controllers , power regulators , rectifiers , or other devices . The temperature limited heater in the mineral insulated cable s has a negative temperature coefficient of resistant , which cause s the resi stance to decrease a s the overall temperature increases . As the electrical current ( I ) in the core of the heater 511B remains constant throughout its entire length , the decrease in local resi stance ( R) results in a reduction of power ( P=I 2 *R) in that local section of the heater cable 511 , thereby mitigating hotspot s and a pos sible thermal runaway event that could severely damage the wellbore 510 or the heater cable 511 . An example of such a mineral insulated heater cable with a temperature limited heater 511B as its heating member i s disclosed in US patent 10 , 119 , 366 .

In some embodiments the temperature limited heater 511B comprises a semiconductor material . When selecting an appropriate semiconductor material with a particular bandgap , the re sistivity of the semiconductor material can be made to change rapidly when the temperature exceeds a selected value . When the heater cable 511 is de signed such that this change of resistivity leads to a significant decrease in power in the respective section of the heater cable 511 , overheating may be prevented .

Although , at the elevated temperatures provided by the heater cable 511 , the serpentinization proces s may generate a suff icient amount of hydrogen using the water that is naturally available in the respective rock formation 400 , the method of generating hydrogen may further comprise a step of inserting a fluid into the wellbore 510 to further stimulate the hydrogen production .

Because of the high thermal conductivity of igneous rock , large portions of the rock formation 400 further away from the wellbore 510 and the heater cable 511 are heated to sufficiently high temperatures too . At the elevated temperatures provided by use of the heater cable 511 , serpentini zation of the mafic or ultramafic rock 400 may occur in the presence of naturally occurring water supplie s . However , in order to maximize the hydrogen production in the heated rock formation 400 , a fluid may be actively inserted into the wellbore 510 . The fluid comprises water to stimulate the serpentinization process where the water gets into contact with the mafic or ultramafic rock 400 around the wellbore 510. Due to a continuous, preferably pressurized, supply of fluid, and the porosity of the mafic or ultramafic rock 400, part of the supplied fluid migrates deeper into the rock formation 400. The water pushed into the rock formation through the thermally induced or conventional fractures 403 produced by this fracking process accelerates the serpentinization process in a larger volume around the wellbore 510.

The hydrogen produced underground may be recovered in various ways. In embodiments of the invention, for example as illustrated in Fig. 1, the inserted fluid may absorb the hydrogen produced in the heated rock formation 400, thereby resulting in a hydrogen-rich fluid. This hydrogen-rich fluid is then recovered from the wellbore 510. After extracting the hydrogen from the recovered hydrogen-rich fluid, the fluid may then be sent back down the wellbore 510 for stimulating the rock formation 400 to generate more hydrogen. Repeatedly using the same fluid to stimulate the serpentinization process in the rock formation, for example by pumping it around in a closed circuit, results in a more efficient use of water or other fluids used for this purpose. Because part of the water migrates into the rock formation 400, is consumed in the serpentinization process, or may evaporate and disappear due to the high temperatures, also a closed circuit will require a continuous or periodic supply of new fluid.

Additionally, or alternatively, the generated hydrogen may migrate upwards 402 through the rock formation 400 into a separate producer well 520 from which the hydrogen is then retrieved. Also here, a conventional fracking process may be used for allowing the generated hydrogen to flow through the resulting fractures 403 into the producer well 520 . Like the wellbore 510 with the heater cable 511 , the producer well 520 may comprise vertical , horizontal , and diagonal sections .

Depending on the local geological situation , the hydrogen produced in the heated rock formation 400 may migrate through the heated rock formation 400 into a nearby underground hydrogen reservoir 200 as shown in Figure 2 . In this case , the method for generating hydrogen may further comprise extracting hydrogen from the hydrogen reservoir 200 , through a producer well 520 . The hydrogen reservoir 200 may, for example , be a hollow reservoir or a volume of porous rock , covered by a hydrogen-impermeable shale layer 100 . The producer well 520 is , at least partly, separate from the wellbore 510 and taps into the hydrogen reservoir 200 .

While many pos sible variations of methods for generating hydrogen have been described above , it will be clear to the s killed person that additional variations and modif ications can be made without departing f rom the scope of the invention as claimed in the appended claims .

Claims

C L A I M S

1. A method for generating hydrogen, the method comprising :

- using a heater cable (511) , provided inside a wellbore (510) in a mafic or ultramafic rock formation (400) , to heat the rock formation (400) to a temperature of about 200 to 600 degrees Celsius.

2. A method for generating hydrogen as claimed in Claim 1, wherein the heater cable (511) is a mineral insulated heater cable comprising a temperature limited heater (511B) .

3. A method for generating hydrogen as claimed in Claim 2, wherein the temperature limited heater (511B) comprises a semiconductor material.

4. A method for generating hydrogen as claimed in any preceding Claim, further comprising inserting a fluid into the wellbore (510) to stimulate hydrogen production through serpentinization in the heated rock formation (400) .

5. A method for generating hydrogen as claimed in Claim 4, further comprising:

- the fluid absorbing hydrogen produced in the heated rock formation (400) , thereby resulting in a hydrogen-rich fluid, and

- recovering the hydrogen-rich fluid from the wellbore (510) .

6. A method for generating hydrogen as claimed in Claim 5, further comprising extracting hydrogen gas from the recovered hydrogen-rich fluid.

7. A method for generating hydrogen as claimed in any preceding Claim, further comprising: - hydrogen produced in the heated rock formation (400) migrating through the heated rock formation (400) into an underground hydrogen reservoir (200) , and

- extracting hydrogen from the hydrogen reservoir (200) , through a producer well (520) .

8. A method for generating hydrogen as claimed in any preceding Claim, further comprising inserting the heater cable (512) into the wellbore (510) .

9. A method for generating hydrogen as claimed in Claim 5, further comprising drilling the wellbore (510) in the mafic or ultramafic rock formation (400) .

10. A method for generating hydrogen as claimed in Claim

9, wherein the drilling of the wellbore (510) comprises directional drilling.

11. A method for generating hydrogen as claimed in any of Claims 8 to 10, when depending on Claim 7, further comprising drilling a hole for the producer well (520) .

12. A method for generating hydrogen as claimed in Claim 11, wherein the drilling of the producer well (520) comprises directional drilling.