Methods, systems and apparatus for detecting subsurface hydrogen

Abstract

A method of detecting subterranean hydrogen, comprising disposing a network of measurement systems in a geographical region of interest, each measurement system comprising at least a passive seismic sensor. Seismic data is collected and recorded at each of a plurality of locations, each location corresponding to a respective measurement system. Using at least one gravimeter, gravity is also measured at multiple positions over said geographical region of interest. Using at least one magnetometer, magnetic field is also measured at multiple sites in the region of interest. The recorded seismic data, the gravity measurements and / or the magnetic field measurements are then processed to produce two-, three- or four-dimensional tomographic models indicative of the presence of subterranean hydrogen. The present disclosure also covers related measurement systems, and apparatus comprising a plurality of measurement systems forming a network of measurement systems configured to carry out the method described herein.

Description

[0001] Methods, systems and apparatus for detecting subsurface H2

[0002] Technical Field

[0003] The present application relates to methods of detecting subsurface hydrogen, that is naturally occurring H2 gas which may be used as a clean energy source. The present application also discloses related measurement systems and apparatus for detecting subsurface H2.

[0004]

[0005] Hydrogen is a crucial source of energy that offers a clean alternative to fossil fuels in an economy that is increasingly moving towards sustainable energy. When utilised in fuel cells, hydrogen only produces water as a byproduct, rendering it a potential solution in the global fight to reduce carbon emissions and mitigate climate change. Demands for the exploration and mapping of “natural” hydrogen, i.e., hydrogen that is produced by geological processes in the subsurface of the Earth, is growing. In the past, to explore natural hydrogen under the Earth’s surface, geological surveys, drilling of exploration wells, soil and gas sampling, simulation techniques and seismic studies have been conducted.

[0006] Studies relying on passive seismic tomography have been used primarily by academics to monitor seismicity in oil and gas development fields and to image deep crustal structures and mantle bodies in a given area. However, on their own, these seismic studies lack the resolution and reliability required for the identification of subsurface hydrogen systems.

[0007] The present invention, which is defined in accordance with the appended claims, sets out to resolve, or to at least mitigate, at least one of the problems associated with the prior art.

[0008] Statement of Invention

[0009] Seismic tomography in combination with other in-field measurements and, optionally, further in combination with publicly available geophysical and geological data have not so far been applied, or have not been applied systematically, to the exploration of underground natural hydrogen resources. The inventors have appreciated that, instead, these combinations provide a workable approach to identifying and quantifying subterranean hydrogen resources for commercial purposes.According to an aspect of the present disclosure, there is provided a method of detecting subterranean hydrogen, the method comprising:

[0010] selecting a geographical region of interest;

[0011] disposing a network of measurement systems on said geographical region of interest, each measurement system comprising at least a seismic sensor;

[0012] using said network of measurement systems, recording seismic data at each of a plurality of locations on said geographical region of interest, each location corresponding to a respective measurement system;

[0013] using at least one gravimeter, recording gravity data at multiple positions over said geographical region of interest;

[0014] using at least one magnetometer, recording magnetic data also at multiple sites over said geographical region of interest;

[0015] processing the recorded seismic data to produce one or more tomographic models representative of subterranean seismic-wave propagation velocity under the geographical region of interest; and,

[0016] interpreting said one or more tomographic models in light of the recorded gravity data and / or the recorded magnetic data in order to evaluate the presence of subterranean hydrogen in the geographical region of interest.

[0017] Each measurement system may in addition comprise at least one respective gravimeter.

[0018] Each measurement system may in addition comprise at least one respective magnetometer.

[0019] Any gravimeters and / or magnetometers provided as part of respective measurement systems may be used to perform said recording gravity data and / or said recording magnetic data.

[0020] Said selecting a geographical region of interest may comprise evaluating existing and / or publicly available geological and / or geophysical records related to said geographical region of interest.

[0021] Said existing and / or publicly available geological and / or geophysical records may comprise existing seismic records and / or existing gravimetric records and / or existing magnetic records.

[0022] The method may comprise processing the recorded seismic data and said existing seismic records to produce said one or more tomographic models.The method may comprise interpreting said one or more tomographic models in light of said existing gravimetric and / or existing magnetic records to evaluate the presence of subterranean hydrogen in the geographical region of interest.

[0023] Said network may comprise measurement systems disposed to form at least one grid on said geographical region of interest.

[0024] Said network may comprise measurement systems disposed to form two or more grids on said geographical region of interest, at least two of said grids having different spacing between adjacent measurement systems.

[0025] Said adjacent measurement systems may be spaced less than 1 km apart from each other.

[0026] Optionally, adjacent measurement systems may be spaced 500 metres or less apart from each other.

[0027] When a measurement system comprises, in addition, a gravimeter, it will be understood that that that recording of gravitational data will be associated with the location of that measurement system.

[0028] When a measurement system comprises, in addition, a magnetometer, it will be understood that that recording of magnetic data will be associated with the location of that measurement system.

[0029] The method may further comprise:

[0030] using at least one gas analyser, sampling the presence of H2 at multiple points on the geographical region of interest;

[0031] wherein said interpreting said one or more tomographic models may be carried out additionally in light of said H2 samples collected by said at least one gas analyser.

[0032] The method may further comprise:

[0033] disposing the gas analyser underground at said multiple points on the geographical region of interest

[0034] Optionally, the gas analyser may be at least 0.8 metre underground.Each measurement system may comprise, in addition, a gas analyser associated with the location of that measurement system.

[0035] Any gas analysers provided as part of respective measurement systems may be used to perform said sampling the presence of H2.

[0036] When a measurement system comprises, in addition, a gas analyser, it will be understood that that sampling of H2 will be associated with the location of that measurement system.

[0037] Said interpreting said one or more tomographic models in light of the recorded gravity data and the recorded magnetic data, and optionally in light of said H2 samples, in order to evaluate the presence of subterranean hydrogen in the geographical region of interest may comprise identifying gravimetric and / or magnetic anomalies, and optionally anomalies in the H2 samples, which may be associated with a subterranean hydrogen kitchen.

[0038] Said processing the recorded seismic data to produce one or more tomographic models representative of subterranean seismic-wave propagation velocity under the geographical region of interest may comprise producing one or more two-, three- or four-dimensional tomographic models of pressure velocity (Vp) associated with the seismic waves propagating underground.

[0039] Said processing the recorded seismic data to produce one or more tomographic models representative of subterranean seismic-wave propagation velocity under the geographical region of interest may comprise producing one mor more two-, three- or four-dimensional tomographic models of shear velocity (Vs) associated with the seismic waves propagating underground.

[0040] The method may further comprise using at least one of said pressure velocity tomographic models (Vp) and a corresponding one of said shear velocity tomographic models (Vs) to calculate one or more of:

[0041] a degree of serpentinization (S) of an active hydrogen kitchen;

[0042] a volume of mantle rocks already serpentinized (Ms);

[0043] a volume of mantle rocks available for serpentinization (Mr);

[0044] a total amount of hydrogen to be produced by a source mantle rock (H2r); and, a total potential hydrogen production of a source mantle rock (H2i).Interpreting said one or more tomographic models in light of the recorded gravity data and the recorded magnetic data, and optionally in light of said H2 samples, in order to evaluate the presence of subterranean hydrogen in the geographical region of interest may comprise evaluating the presence of one or more of:

[0045] - mantle rocks undergoing serpentinization reactions forming H2;

[0046] - mantle rocks having the potential to undergo serpentinization reactions forming H2; - H2 reservoirs in the form of pockets of gaseous H2; and / or

[0047] - movement of H2 bearing fluids through the plumbing systems made of permeable layers of rocks and / or underground fault lines and / or reservoirs.

[0048] Said recording seismic data, recording gravity data and / or recording magnetic data may be carried out:

[0049] - at specified times over an extended period of time; or

[0050] - continuously over a given time period; or

[0051] - in response to specific events, such as microearthquakes, for example such as microearthquakes caused by events related to subterranean hydrogen formation and migration.

[0052] According to another aspect of the present disclosure, there is provided a computerised apparatus for detecting subterranean hydrogen in a geographical region of interest, the apparatus comprising:

[0053] i.) a plurality of seismic sensors disposed to form a network of measurement systems on said geographical region of interest;

[0054] ii.) at least one gravimeter; and

[0055] iii.) at least one magnetometer;

[0056] wherein the computerised apparatus is configured to carry out at least one of the methods disclosed herein.

[0057] Said at least one gravimeter and / or at least one magnetometer may be part of respective measurement systems forming said network of measurement systems, as disclosed herein.

[0058] The computerised apparatus may further comprise at least one gas analyser.

[0059] The computerised apparatus may further comprise at least one airborne device on which said at least one magnetometer is provided.Drawings

[0060] Fig.1 schematically sets out a method of detecting subsurface hydrogen as disclosed in the present patent specification.

[0061] Fig.2 provides additional details related to the method of Fig.1.

[0062] Fig.3 outlines processing steps related to the method of Fig.1 and Fig.2.

[0063] Fig.4 illustrates an in-field measurement system for detecting subsurface hydrogen.

[0064] Fig.5 a) is an example of measurement of a magnetic signal (along one space direction, i.e. , in one dimension or in “1D”) as part of the method disclosed in this patent specification.

[0065] Fig. 5 b) is an example of the measurement of a gravimetric signal (also in 1D) as part of the method disclosed in this patent specification.

[0066] Fig. 5 c) is a two-dimensional, i.e., “2D”, representation of shear wave velocity (Vs) of seismic waves, forming a tomographic Vs velocity model, based on measurements taken by seismic sensors placed on the Earth’s surface.

[0067] Fig. 5 d) is a 2D representation of pressure wave velocity (Vp) of seismic waves, forming a tomographic Vp velocity model, also based on measurements taken by seismic sensors placed on the Earth’s surface.

[0068] Fig. 5 e) is a 2D second order geological model showing subterranean features including a hydrogen system along the X and Z axes of Figs. 5 c) and 5 d).

[0069] Fig. 6 is a three-dimensional, i.e., “3D” schematic representation of a first network of measurement systems for detecting subsurface hydrogen disclosed in this patent specification, according to a method as also disclosed in the present patent specification, deployed over a target geographical region; Fig. 6. also shows a resulting tomographic Vp velocity model over one X-Z plane.

[0070] Fig. 7 is a schematic representation of a second network of measurement systems for detecting subsurface hydrogen disclosed in this patent specification, according to a method as also disclosed in the present patent specification, deployed over the target geographical regionof Fig.6; Fig. 7 also shows seismic profiles and gravimetric anomalies associated with said target geographical region.

[0071] Definitions

[0072] In the context of the present specification:

[0073] “X” refers to a first linear space coordinate (distance in km along the surface of the Earth, along a given direction).

[0074] “Y” refers to second linear space coordinate (distance in km along a direction perpendicular to the X direction).

[0075] “Z” refers to a third linear space coordinate (distance in km along a direction perpendicular to the X and Y directions, height or depth in km, e.g. measured in the subsurface of the Earth).

[0076] In the context of the present patent application, the wording “tomographic model” is interchangeable with “velocity model”. These models are physics-based reconstructions of subsurface properties, representative of subterranean seismic wave propagation. A tomographic model may comprise one or more two- (X and Y directions) three-(X, Y and Z directions) or four-dimensional models (X, Y and Z directions, over time T) of the pressure velocity (Vp) or shear velocity (Vs) associated with the seismic waves propagating underground.

[0077] The term “geological model” refers to a model which integrates multiple geological and geophysical datasets (field geological data, seismic data, gravity data, magnetic data) and interprets them to reconstruct subsurface structures, such as subsurface hydrogen systems.

[0078] The term “network” refers to the spatial arrangement of multiple measurement systems (each comprising at least one seismic sensor) as described herein or multiple measurement systems comprising the sensors described herein (gravimeter and / or magnetometer), in addition to the at least one seismic sensor, such as a passive seismic sensor, disposed at different locations in space.

[0079] The wording “measurement system” refers herein to a measurement system for detecting subsurface hydrogen, comprising at least a seismic sensor, which may in addition compriseone or more of a gravimeter (i.e. a gravity sensor), a magnetometer (i.e. a magnetic field sensor) and a gas analyser (i.e. a gas sensor).

[0080] The wording “mantle rock” refers to rocks that make up the Earth’s mantle layer between the crust and the core. These rocks primarily comprise silicates rich in magnesium and iron and are capable of “serpentinization” reactions which generate hydrogen.

[0081] The wording “natural hydrogen” refers to hydrogen gas (H2) that is naturally produced under the subsurface through geological and chemical processes; natural hydrogen can be found in subsurface hydrogen reservoirs.

[0082] The terms “H2” and “hydrogen” are used interchangeably in the context of the present patent specification and relate to hydrogen in the gaseous form.

[0083] The wording “hydrogen reservoir” refers to a large-scale underground storage system where hydrogen gas is stored in natural underground formations.

[0084] The wording “hydrogen kitchen” refers to subsurface areas where hydrogen is generated as a result of serpentinization and / or other chemical reactions, and from where the hydrogen migrates to reach hydrogen reservoirs.

[0085] The term “hydrogen plumbing system” refers to subsurface bodies made of permeable rocks or fractures that transport H2 bearing fluids for example, from hydrogen kitchens where they are generated to underground gas pockets.

[0086] The term “hydrogen system” refers to a subsurface entity comprising H2, and which is made of at least: a hydrogen kitchen, a hydrogen plumbing system and a hydrogen reservoir.

[0087] The term “serpentinization” in the context of the present patent specification, refers to chemical reactions in the subsurface Earth, where certain types of rock (and particularly mantle rocks or mafic rocks) react with water to produce hydrogen.Detailed Description

[0088] Disclosed herein are methods and related systems for detecting subsurface H2, and more specifically for detecting characteristics of subsurface H2 systems based on the production of tomographic models of the subsurface. This is crucial information for explorationists tasked with identifying areas of great potential for H2 exploitation, which means potential extraction at a commercial level. The methods described herein rely on passive seismic tomography; passive seismic tomography has not been applied in the past to hydrogen exploration. Further, passive seismic tomography has not been utilised in combination with other field data (such as magnetic field and gravity field data) or publicly available seismic records to ultimately estimate the location, quality and quantities of subsurface hydrogen kitchens, reservoirs, and related hydrogen plumbing systems of fluids in a subsurface environment.

[0089]

[0090] A step in the methods of detecting subsurface H2 described herein comprises an initial analysis of available geological and geophysical data to evaluate the potential for hydrogen exploration in a chosen target geographical region on the Earth’s surface. During this initial step, geological data, for example comprising:

[0091] surface-wave seismic records;

[0092] body-wave seismic records;

[0093] other seismic data;

[0094] local gravitational field data;

[0095] local magnetic data;

[0096] soil gas sampling data;

[0097] is analysed and interpreted. This data is represented in Fig.2 a).

[0098] Further available geological data that may be used comprise:

[0099] - 2D reflection seismic data;

[0100] oil & gas, mining or water well data;

[0101] as represented in Fig.3 a). This first step is combined with preliminary data acquisitions on the target region to collect soil gas measurements and field geological data as further seen in the second half of Fig.3 a). Following this all this data is integrated and modelled in a modelling software 9 to produce a first order 3D geological model as seen in Fig.3 b).As used herein “first order” means a first approximation of a model obtained after integrating a publicly available dataset, field geological data and soil gas measurements collected during an initial measurement campaign, on a selected number of points in space over a geographical region of interest. When the data shows that the first order geological model is promising, then the measurement campaign may be repeated using an increased, or even multiplied, number of points in space on the same geographical region of interest, to obtain a model with an increased spatial resolution. With the addition of measurements and interpretations of those measurements as we described in this patent application, a “second order” model is created, which is therefore a more refined approximation of the real subsurface configuration.

[0102] The target geographical regions for hydrogen exploration should preferably cover the entire suspected hydrogen system including the mantle source of hydrogen, the plumbing system, the reservoir and the surface leaking points of hydrogen.

[0103] Gravimetric anomalies (that is, local changes in the gravity field) identified at low spatial resolutions may provide a first indication of the presence of mantle rocks underground, which are suitable for hydrogen generation through serpentinization reactions. A representation of a publicly available gravimetric dataset may be seen in Fig. 7. This corresponds to a gravimetric anomaly 28 detected by gravimeters. Such gravimetric anomaly 28 is leveraged in the initial step of identifying the initial target geographical region, considered as a geographically favourable area. On a geographically favourable area, seismic sensors 12 may be deployed (each representing a measurement system 15, as defined herein), as also shown in Fig. 7, for continuing in the process of detecting subsurface hydrogen.

[0104] Typical geographical regions of interest may measure 100 to 1000 km-squared. These dimensions are however to be considered as being variable and will need to be selected as a function of the geological model defined above, for example so that an entire hydrogen system may be captured. It would be advantageous for the survey region to cover the mantle kitchen highlighted by the gravity anomaly along with the connected sedimentary basin, extending to any hydrogen leakage points. While the leakage points themselves are not the exploration targets, they could suggest the presence of underlying hydrogen reservoirs. These potential reservoirs could then be further imaged and, if promising, eventually drilled for exploitation.System design

[0105] The design of the network of measurement points is a function of the geographical region covering the entire suspected hydrogen system and the spacing of the sensors required to increase or even maximise the resolution of the tomographic model. The spacing of the sensors is defined by the depth of the target objects and the location of the seismic sources. For example, in an area where ideal hydrogen kitchens are in a 5 to 15 km depth range, the required spacing is about 1km. Going toward the reservoir, where the ideal reservoir targets are in the 0 to 5 km range, the required spacing to maximise the resolution of the images is 500 m or less. The resulting number of sensors and their spatial distribution as a network of sensors can then be calculated based on the required spacing around the targeted features of interest in the geographical region.

[0106] Once a certain area has been identified as a target geographical region for hydrogen exploration, a step is carried out which comprises designing of the overall survey 1, which means identifying a spatial layout of sensors for in-field measurements in the target geographical region. Survey design is informed by the first order geological model seen in Fig.

[0107] 3 b).

[0108] An example of a measurement system 15 deployed in the field can be seen in Fig. 4 c). In each of the described measurement systems 15, there are provided a seismic sensor 12, a gravimeter 13 and an airborne magnetometer 14. Optionally, the measurement systems 15 may also comprise a gas analyser 16 as seen in Fig. 4 d). However, it will be appreciated that the minimum requirement for each measurement system 15 is the presence of a seismic sensor, since the gravity and / or magnetic data measurements may otherwise independently be acquired.

[0109] As mentioned above, the design of the survey 1, and the network of measurement systems 15 may be adapted on the area identified with high potential for hydrogen exploration (e.g. if the target region is a mountainous area); therefore, the measurement systems 15 and their seismic sensors 12 may be arranged according to an irregular pattern, for example with different spacings between the seismic sensors 12 when deployed, as shown in Fig. 7.

[0110] Fig. 6 shows a first network of measurement systems 15 for detecting subsurface hydrogen over a target geographical region in 3D. The measurement systems 15, as it can be appreciated, are generally regularly spaced from each other and are arranged essentiallyacross a “grid” over axes X and Y, also shown in Fig. 6. Other geometries would be possible, but are not shown or described herein. The measurement systems 15 are represented by small cubes. Each measurement system 15 comprises a passive seismic sensor 12 deployed on the Earth’s surface. The measurement systems 15 are designed to detect potential subsurface target areas 27 where hydrogen may be produced. Stars in Fig. 6 represent seismic events 17, such as micro or mini earthquakes that may occur due to serpentinization reactions (or fluid migration) generating hydrogen within a subsurface hydrogen kitchen. Whilst we refer to passive seismic sensors, in principle active seismic sensor could be used too, in conjunction with active production of suitable vibrations.

[0111] Fig. 7 shows a second network of measurement systems 15 deployed on the same geographically favourable area shown in Fig. 6, where gravimetric anomalies 28 have been detected in the area, which may point to potential subsurface hydrogen targets 28. The seismic sensors 12 (or the measurement systems 15, when each measurement system 15 has the magnetometer and / or gravimeter as additional sensors), may be deployed in grids, having different meshes, but alternative patterns such as rings would also be possible. Fig. 7 depicts an irregular network of measurement systems 15 (in order to achieve maximum resolution of the tomographic models, around subterranean features of interest, such as a potential hydrogen reservoir) each comprising a seismic sensor 12, wherein an area to the north has seismic sensors 12 more densely arranged next to each other (at a distance of about around 500m from each other), an area to the south in which the seismic sensors 12 are less densely arranged (the spacing here is around 1km from each other), and an outer area around the latter area wherein the seismic sensors are even more sparsely arranged (at a distance of about 5 km from each other).

[0112] The design of the survey 1 in the field, may comprise, as an example, a relatively large number of seismic sensors 12 as part of corresponding H2-detection measurement systems 15 deployed at a distance of around 500 metres from each other on different locations over an area with a potential for hydrogen exploration. However, as explained above, the systems 15 may be irregularly disposed in space. The network may for example include a relatively dense area with sensors 12 deployed at a relatively lower number of sites spaced 500 meters apart and a relatively less dense, sparse area comprising an even lower number of measurement sites spaced around 1 km apart. This survey may further comprise a further, and even less densely populated area comprising, for example, around 10, 20 or 30 sites that may be spaced 5 km apart.Seismic sensors

[0113] The seismic sensors 12 used in the measurement systems 15 herein are passive seismic sensors. More specifically, 3-component seismic sensors are utilised, that are capable of measuring seismic vibrations along three axes. More specifically, these 3-component seismic sensors are based upon acceleration transducers (i.e., accelerometers) with a 0-200Hz bandwidth, which record seismicity in 3 directions (x, y, z). These sensors may be manufactured by STRYDE (www.strydefurther.com), by SERCEL (www.sercel.com) or by SmartSolo (www.smartsolo.com), just as examples, as part of the nodal seismic technology offer. These seismic sensors 12 have been previously used in geological studies; however, they are now being used in the context of detecting subsurface hydrogen1 2.

[0114] Preferably, the spacing between the seismic sensors 12 could be about 500 m above the basin area where gas accumulation 24 (see Fig. 5 e)) is targeted. This spacing provides optimal tomographic images from the data extracted from the seismic sensors 12. Previous studies to image the crustal structure of a region in the Pyrenees showed that a larger spacing, such as 1km, may decrease the resolutions of the resulting tomographic images in such a way that important data about possible subterranean features may be missed1 2.

[0115] Seismic sensors 12 that are part of a measurement system 15 record passive seismic data at a given location on the Earth’s surface, identified as a potential target region for hydrogen exploration. Passive seismic data therefore represent seismic waves 26 (see Fig. 6). Seismic waves 26 are generated as a result of natural seismic events 17 (e.g. movements along regional faults, micro-earthquakes generated by natural rock cracking due to serpentinization reactions in a hydrogen kitchen, fluid migrations of hydrogen along fracture lines), ambient noise (e.g. waterfalls, winds, precipitation, storms)) or anthropic sources (e.g. vibrations that originate from traffic, constructions, mining blasts). These would all be recorded by the seismic sensors 12 deployed as part of the measurement systems 15 deployed in the field.

[0116] Seismic waves 26 may comprise body waves and surface waves. Surface waves are waves that travel along the Earth’s surface. Body waves, comprise of waves that travel through the Earth’s body. Both are controlled by the materials through which they pass and diminish as they get further away from the source. Both of these types of waves may be utilised in the methods described herein for detecting subsurface hydrogen. Body waves may be pressure (P) waves, or shear (S) waves. The velocities of P- and S-waves depend on the density of thematerials through which they propagate, and therefore will differ depending on what subsurface material (type of rock formation) they travel through.

[0117] By measuring seismic waves 26 as described herein at different locations on a target region for hydrogen exploration using the seismic sensors described herein, differences in the velocities of propagation of the seismic waves 26 recorded can be compared and utilised in the creation of geological models of subsurface structures, such as that seen in Fig. 5 e). This model is a geological model created from the measurement of seismic velocities comprising the velocities of the P and S-waves (measured in km / s, as seen in Figs. 5 c) and d), respectively. These measurements are interpreted to give indications not only of the types of rock present in the exploration area, but also of the presence of potential subsurface hydrogen kitchens and their hydrogen generation potential through serpentinization reactions.

[0118] The Vs model seen in Fig. 5 c) represents a tomographic model of Vs velocities in the subsurface, consistent with the measurements of seismic events 17 measured by the seismic sensors 12 deployed as shown on the Earth’s surface. The Vp model seen in Fig. 5 d) represents a tomographic model of Vp velocities in the subsurface, consistent with the measurements of the same seismic events 17 measured by the same seismic sensors 12 deployed as shown. Differing velocities in Fig. 5 c) and Fig. 5 d) (increasing shading means higher Vp or Vs values, as seen on the scales to the right of the Figures) are associated to the type of rock or the type of material filling the porosity (such as, gas or water) that may be present in the subsurface.

[0119] Gravimeter

[0120] In addition to the seismic sensors 12, a gravimeter 13 is also utilised in each of the measurement systems 15 for detecting subsurface hydrogen described herein. The gravimeter 13 used is preferably a land-based gravimeter, that is a light-weight and portable gravimeter. The gravimeter 13 used may be spring-based and / or a Micro Electrical Mechanical System (MEMS) based gravimeter. Such gravimeters 13 have been previously used in literature3’45. The gravimeter 13 may, for example, be a WEE-G gravimeter (www.wee-g.com) or a CG-6 AUTOGRAV gravimeter (www.scintrexltd.com). Gravity fields are measured (as anticipated above) in mGal over a given target region for hydrogen exploration. An example of gravimetric values plotted in 1D, measured by the gravimeters 13 associated with the seismic sensors 12 of Fig. 4 c) and d) can be seen in Fig. 5 b). Gravimeters are sensitive to the density of underground materials and structures. The velocity of the P-Waves and S-waves also dependson the density of the material through which they propagate. Gravity measurements may therefore be a useful complement to seismic measurements. More precise (and also multidimensional) gravimetric maps than that shown in Fig. 5 b) may also be created using the networks of measurement systems 15 disclosed herein (wherein each measurement system 15 also comprises a gravimeter 13) but are not shown in this application.

[0121] Magnetometer

[0122] The magnetometer 14 utilised in the measurement systems 15 described herein for detecting subsurface hydrogen may be, just as examples, a fluxgate magnetometer or a cesium magnetometer. The magnetometer 14 used is an airborne magnetometer 14 as seen in Fig. 4 c); it may preferably be carried onboard of an ultralight aircraft or a drone. Such magnetometers 14 have been used in literature previously67. The local magnetic field is measured using these airborne magnetometers 14 above the target geographical region. Magnetic fields are usually measured in nano-Tesla (nT). An example showing magnetic values measured by an airborne magnetometer 14 at several locations, in 1 D, corresponding to those of seismic sensors 12 seen in Figs. 5 c) and d) can be seen in Fig.5 a). Similar to the gravimeters 13 discussed above, more precise (and also multi-dimensional) magnetic field maps than that shown in Fig.

[0123] 5 a) may also be created using the networks of measurement systems 15 disclosed herein (wherein each measurement system 15 also comprises a magnetometer 14) but are not shown in this application.

[0124] Gas analyser

[0125] Among gas analysers 16 that may be utilised in the measurement systems 15 for detecting subsurface hydrogen described herein are multi-gas analyser such as THERMOFISHER’s ATEX GEOTECH GA-5000 (www.thermofisher.com), SEWERIN / VARIOTEC 460 Tarcergas (www.sewerin.com) or DRAGER X-am8000 (www.draeger.com). The gas analyser 16 is utilised to measure the percentage of gaseous hydrogen in the soil above an area of potential for hydrogen exploration. Detecting a high concentration at a given area could indicate surface leaking points of hydrogen, which may point to a hydrogen kitchen generating and thereby expelling hydrogen beneath the surface. Soil gas measurements are also utilised initially to determine the potential of a given area for hydrogen exploration. Preferably, the gas analyser 16 is installed approximately around 0.8 metre below the ground at the area.Processing and interpreting the collected data

[0126] Following the collection of data using a plurality of the systems 15 as described above over a geographical area of interest, joint inversion processing 6 is carried out on the data as seen in Fig. 2 b). The joint inversion method2involves: 1) Designing an initial model from the collected dataset, 2) Simulating data based on this model, 3) Comparing simulations with observations, and 4) Iteratively adjusting the model to minimize differences. After several iterations, this process yields a 3D physical model integrating the initial data, as seen in Fig. 3 d) which can be interpreted 11 to form the second order 3D geological model of the subterranean space, below the geographical region of interest. The resulting newly acguired data of the subterranean space are then interpreted to suggest the following characteristics of a hydrogen kitchen:

[0127] - The degree of serpentinization (S) in a hydrogen kitchen;

[0128] - The volume of mantle rock already serpentinized (Ms);

[0129] - The volume of mantle rock to be available for serpentinization (Mr);

[0130] - The total amount of hydrogen to be produced by the source rock (H2r); and,

[0131] - The total potential hydrogen production of the source rock (H2i).

[0132] A second order geological 2D model of a subterranean hydrogen system can be seen in Fig.5 e), as already discussed above. Fig. 5 e) represents the interpretation of the data of Figs. 5 a) to d) to arrive at a model of the subsurface hydrogen system. To exemplify, based on this model, it can be argued that a hydrogen kitchen is located between 10 and 31 km in distance on the X axis, and between 8 and 18 km of depth on the Z axis. Serpentinized mantle rocks 22 and fresh mantle rocks 23 are also identified in the model. A reservoir 20 is supplying water to the hydrogen kitchen, which results in serpentinization reactions in the hydrogen kitchen, generating hydrogen upon reaction with the fresh mantle rocks 23 which escapes back into the reservoir 20, which then carries gaseous hydrogen to form subsurface pockets 24, leading to hydrogen gas accumulation 24.

[0133] The degree of serpentinization (S) in a hydrogen kitchen

[0134] The degree of serpentinization, S, of a hydrogen kitchen lies between a numerical value of 0 and 1. S of a source rock (a rock in the subsurface space associated with the production of hydrogen, such as a mantle rock) can be calculated through the following relationships:

[0135] S =-0.317 * Vp + 2.54 (1)8And,

[0136] S = -45.87 Vs+200.05 (2)9

[0137] In the above equations, Vp represents the velocity of pressure waves (P-waves), and Vs represents the velocity of shear waves (S-waves) in the rocks undergoing serpentinization. Vp and Vs are given in km / s and are measured using the network of passive seismic sensors 12, as seen in Figs. 5 c) and d). It is known from the literature that Vp and Vs decrease linearly with increasing serpentinization rate10. For example, the Vp values (measuring around 7 km / s) and Vs values (measuring around 4 km / s) can be seen to be lower on the outer area of a potential hydrogen kitchen in the velocity models of Fig. 5 c) and of Fig. 5 d), in the area between 10 to 31 km along the X axis, and around 8 to 18 km in depth along the Z axis. They are however higher on the inner part of the potential hydrogen kitchen, with Vp values measuring around 8.5 km / s and Vs values measuring around 5 km / s. In other words, the geological model in Fig. 5 e) suggests that the inside part of the potential hydrogen kitchen likely comprises fresh mantle rocks 23 that are unreacted, and the outer area of the potential hydrogen kitchen comprises instead serpentinized mantle rocks 22, with undergoing oralready undergone serpentinization reactions over time.

[0138] It is worth noting that the Vp and Vs values of the models of Figs. 5 c) and d) already give indications of the presence of a hydrogen kitchen, with serpentinization reactions that are taking place in the subsurface. However, S values (as extracted from the formulas above) closer to 1 will point more accurately to volumes of rocks already serpentinized by hydrogengenerating serpentinization reactions taking place in the subsurface of the associated target region.

[0139] The volume of mantle rocks

[0140]

[0141] s) and the volume of mantle rocks to be

[0142]

[0143] By combining S with the total volume of the mantle body Mi estimated from the first order geological model and Vp and Vs velocity models of Fig. 5 c) and d), the volume of the mantle rocks already serpentinized, Ms, and the volume of the mantle rocks to be serpentinized, Mr, can be derived from the following relationships:

[0144] Sr = 1- S (with 0<Sr<1) (3)

[0145] where Sr define the “yet to react” value,Mr=Mi*Sr (4) Ms=Mi*S (5)

[0146] The total amount of hydrogen to be produced by the source rock (H2r) and the total potential of hydrogen production by the source rock (H2i)

[0147] The serpentinization process can be related to the oxidation of Fe2+to Fe3+by the hydration of iron-bearing olivine minerals (fayalites: Fe2SiC>4) found in mantle leading to the formation of magnetite (Fe3O4), silica (SiO2) and hydrogen through the reaction below.

[0148] 3 Fe2SiO4+ 2H2O = 2 Fe3O4+ 3 SiO2+ 2H2(6)

[0149] The formed magnetite (Fe3O4) is directly proportional to the net guantity of hydrogen produced, as seen in the reaction scheme above. Magnetic anomalies are often caused by the magnetite’s presence in the subsurface mantle rock and can be detected by the magnetometer 14. An example plot of magnetic values versus distance along the X axis can be seen in Fig.

[0150] 5 a), as previously discussed. The increase in magnetic field measured in (nT), from around 0 to 80 nT, between 15 and 31 km in Fig. 5 a), corresponds to one such magnetic anomaly detected by the systems 15 deployed on the Earth’s surface, as shown, over the target exploration region. The amplitude of the magnetic anomaly is believed to be related to the amount of expelled H2(H2s) and the serpentinization rate (S)11. Through the analysis of these magnetic anomalies, the guantities of magnetite can also be estimated (Qtm)11. Qtm, in the below formulas, represents the guantity of magnetite calculated from the measured magnetic anomaly caused by the magnetite. Considering the volume of the mantle rocks calculated in the previous step (Mi) and the total volume of mantle rocks to be serpentinized (Mr), H2r (the total amount of H2yet to be produced by the source rock) and H2i (the total potential of H2production by the source rock) can be estimated through the following eguations:

[0151] H2r = Mr *Qtm / Ms (7)

[0152] H2i = Mi *Qtm / Ms (8)

[0153] The resulting H2r and H2i values will provide the hydrogen explorationist with good indications of the hydrogen generating potential of a given subsurface hydrogen kitchen and the amount of hydrogen that may be trapped in subsurface hydrogen reservoirs. To compare and rank the potential values of the hydrogen kitchens, the initial generative potential of the fresh mantle rock per volume (PH2) will be calculated as follow:PH2 = H2i / Mi =Qtm / Ms (9)

[0154] Further i

[0155]

[0156] based on the

[0157]

[0158] model

[0159] The above method of detecting subsurface hydrogen, can also be used to verify if a hydrogen kitchen is actively generating hydrogen through ongoing serpentinization. It is known that serpentinization causes rock expansion, and that active serpentinization triggers microearthquakes as depicted by the seismic events 17 shown in Figs. 5 c) to e). These microearthquakes are typically located around the rim of the imaged mantle rock body (as can be seen in Fig. 5 e), around the hydrogen kitchen, between 10 to 31 km in distance X and around 8 to 18 km in depth Z and can confirm the presence of an active hydrogen kitchen.

[0160] Since serpentinization is associated with a general fall in the values of Vp and Vs observed in a velocity model, as previously discussed, the detection of microearthquakes in combination with increasing velocity gradients toward the fresh mantle rocks 23 (Vp=8km / sec) observed in models over time can further support serpentinization-induced seismicity. Further, the volumetric expansion of mantle rocks during serpentinization may cause them to split, triggering microearthquakes with an opening-mode focal mechanism. Therefore, identifying seismic events 17 with this focal mechanism would provide additional evidence of serpentinization-induced seismicity.

[0161] Further, the combined analysis of the seismic velocities measured around a given region and of the gravity data, can highlight abnormal Vp / Vs ratios seen in velocity models such as those of Fig. 5 c) and Fig. 5 d) and Vp / densities ratios which could serve as indicators of anomalous mineralisation. Anomalous mineralisation can produce metal alloy catalysts such as Nickel (Ni) and others in hydrogen kitchens, which in turn reduce the optimal temperature of serpentinization and thereby increase the volume of mantle in serpentinization window and the potential of a given kitchen for the production of hydrogen12 13.

[0162] Abnormal Vp / Vs ratios (besides gravity anomalies) can also be leveraged to identify potential Direct Hydrogen Indicators (DH2ls) in reservoirs at depth. This is leveraging the fact that seismic waves 26 propagate differently in gas and water-saturated reservoirs. The geometries of the gas accumulation 24 can be leveraged to ultimately evaluate the quantity and nature of gas trapped.Microearthquakes can also be generated as a result of the migration of fluids within a hydrogen system. These microearthquakes can be followed through space and time to identify the “plumbing network” of underground reservoirs 20 that are recharging and discharging with water14. Identified migration pathways can then be compared to observed seeps (i.e. , areas where water reaches the Earth’s surface from an underground source) and surface hydrogen measurements15.

[0163] The variation of seismic anisotropy over time signifies that the seismic wave velocity changes, which can be as a result of fluid migration. Fluid migration in a reservoir directly influences seismic anisotropy by modifying the stress state, open / close fractures, networks and fluid saturation over time which affect seismic wave propagation. The passive seismic sensors 12 that are deployed in the field would allow the monitoring of these seismic anisotropy changes over time16.

[0164] Further, due to differing seismic velocities detected in cap rocks 19 and underground reservoirs 20, the 3D geometries of hydrogen reservoirs and traps can be directly inferred from the tomographic models produced.

[0165] Data display

[0166] In one example, a plurality of hydrogen detection measurement systems 15 are deployed across a geographical region of interest. Each measurement system 15 includes at least one seismic sensor 12, gravimeter 13, magnetometer 14, and may further include at least one gas analyser 16. During a survey interval, the seismic sensors 12 record seismic data suitable for tomographic processing, including data from natural seismicity and or controlled sources where used. In parallel, gravity data and magnetic data are acquired at multiple locations by the gravimeters 13 and magnetometers 14. Where present, the gas analyser 16 acquires gas measurements indicative of hydrogen at one or more measurement locations.

[0167] A computing system receives the acquired datasets and processes the seismic data to generate a tomographic model of the subsurface. In an example implementation, the tomographic model includes at least one pressure velocity tomographic model Vp and at least one shear velocity tomographic model Vs that are spatially registered to a common coordinate system. The computing system performs joint inversion processing 6 that integrates the tomographic model with the gravity data and the magnetic data, and optionally with the hydrogen measurements from the gas analyser 16, to produce a 3D physical model and to support interpretation 11 into a second order geological model. The computing system furthercomputes deliverable parameters from the produced models, including a degree of serpentinization S and hydrogen potential indicators that include Ms, Mr, H2r, and H2i, each derived for at least a portion of the modelled subterranean volume.

[0168] The system produces a visualization or data display that enables an operator to understand how the acquired data supports the inferred hydrogen system. The visualization includes a surface referenced map view that displays the deployed measurement systems 15 at their respective locations and overlays geological maps and representations of gravimetric anomaly 28 and magnetic anomaly patterns derived from the gravity and magnetic datasets. Where hydrogen measurements are available, the visualization displays hydrogen values at or near the corresponding gas analyser 16 locations, enabling areas of elevated hydrogen concentrations to be directly compared with geological structures and interpreted in the context of the associated gravity and magnetic anomalies.

[0169] The visualization further includes a subsurface view that displays one or more sections or volume renderings of the tomographic model. In an example, the subsurface view shows Vp and Vs in registered form so that the operator can evaluate velocity contrasts that correlate with geological boundaries. The subsurface view also displays seismic events 17 located from the seismic data recorded by the seismic sensors 12. The seismic events 17 are plotted within the same coordinate frame as the tomographic model so that spatial clustering, alignment along structures, or depth dependent changes in event density can be visually compared to the velocity structures.

[0170] The visualization also includes a three-dimensional (3D) representation of the mantle body and its degree of serpentinization derived from the tomographic model. The mantle body is represented as a volumetric domain whose boundary is extracted from a geological interpretation constrained by a seismic velocity model. The degree of serpentinization S is calculated or computed for volumetric cells within the modelled subsurface and is rendered as a spatial field registered to the Vp and Vs model geometry. Regions exhibiting elevated values of S are displayed as volumetric regions or isosurfaces, delineating a serpentinized mantle rock portion (Ms) 22 and a fresh mantle portion (Mr) 23. A . Preferably there is a user-adjustable threshold for S, such that modification of the threshold dynamically alters the visualization between a broader candidate fresh mantle region and a more focused, higher-confidence fresh mantle region. In this way, a user can set a minimum threshold value for the degree of serpentinization to be included in the visual display of the visualisation. Within the same visualization, the system presents quantified outputs corresponding to Ms (serpentinizedmantle rock portion) and Mr (fresh mantle portion) for at least one candidate source region associated with the serpentinized mantle rock portion (22). The system further presents H2r and H2i as quantified outputs that reflect estimated hydrogen production and potential hydrogen production for the source mantle rock volume represented in the geological model.

[0171] In this example, the visualization supports identification of a hydrogen system that includes a hydrogen kitchen, a hydrogen plumbing system, and a hydrogen reservoir. The hydrogen kitchen is visualized as a subsurface region where the serpentinization field indicates active or extensive serpentinization and where the integrated gravity and magnetic responses are consistent with mantle rocks and serpentinization related mineralization. The hydrogen plumbing system is visualized as one or more subsurface pathways inferred from the alignment of seismic events 17 and from tomographic structures that suggest preferential migration along faults, fracture zones, or other conduits. The hydrogen reservoir is visualized as a subsurface volume inferred from the geological model, including a reservoir portion and an overlying cap rocks 19 portion that acts as a trap, with the reservoir geometry shown in spatial registration with the tomographic model and the anomaly overlays. By presenting the surface referenced anomalies together with the subsurface tomographic structures, the plotted seismic events 17, and the derived serpentinization and hydrogen potential parameters, the visualization provides a method for easily communicating how the system produced its evaluation of subterranean hydrogen and where within the region of interest the most prospective locations are indicated.List of reference numerals used in the description and drawings

[0172] 1 Designing a survey (starting from gravimetric anomaly identified on a publicly available gravimetric dataset)

[0173] 2 Obtaining required permits

[0174] 3 Field deployment and acquisitions

[0175] 4 Data harvesting

[0176] 5 Data analysis and interpretation

[0177] 6 Joint inversion processing of the harvested data

[0178] 7 Generation of 4D tomographic images

[0179] 8 Interpretation of the results (after obtaining first and second order geological 3D models) to obtain deliverable parameters

[0180] 9 Integration of data in modelling software

[0181] 10 Design of the survey and data acquisition (starting from available geological and geophysical data)

[0182] 11 Interpretation of the geological model

[0183] 12 Seismic sensor

[0184] 13 Gravimeter

[0185] 14 Magnetometer

[0186] 15 H2-detection measurement system (at least a seismic sensor, and optionally a gravimeter and / or magnetometer)

[0187] 16 Multi-gas analyser

[0188] 17 Seismic event

[0189] 18 Syn-orogenic sediments

[0190] 19 Cap rock

[0191] 20 Reservoir

[0192] 21 Basement

[0193] 22 Serpentinized mantle rocks portion

[0194] 23 Fresh mantle rocks (not serpentinized)

[0195] 24 Gas accumulation pockets (where H2 may be expected to accumulate, after serpentinization)

[0196] 25 Main faults in Earth’s crust

[0197] 26 Seismic waves

[0198] 27 Potential subsurface target areas for H2 extraction

[0199] 28 Gravimetric anomaly

[0200] 29 Seismic profileLiterature references

[0201] 1 Lehujeur, Maximilien, et al. "Three-dimensional shear velocity structure of the Mauleon and Arzacq Basins (Western Pyrenees)." Bulletin de la Societe Geologique de France 192.1 (2021).

[0202] 2 Chevrot, Sebastien, et al. "Passive imaging of collisional orogens: a review of a decade of geophysical studies in the Pyrenees." Bulletin de la Societe Geologique de France 193.1 (2022).

[0203] 3 Prasad, Abhinav, et al. "MEMS Gravimeters for Geophysics." IEEE Instrumentation & Measurement Magazine 27.6 (2024): 46-52.

[0204] 4 Belwanshi, Vinod, et al. "Investigation of temperature sensitivity of a MEMS gravimeter based on geometric anti-spring." Review of Scientific Instruments 9

[0205] 5 Saibi, Hakim, Amir Gabr, and Falah Sheikh Mohamed. "Subsurface structural mapping using gravity data of Al-Ain region, Abu Dhabi emirate, United Arab Emirates." Geophysical Journal International 216.2 (2019): 1201-1213.

[0206] 6 Diaz Michelena, Marina, et al. "Magnetometric surveys for the non-invasive surface and subsurface interpretation of volcanic structures in planetary exploration, a case study of several volcanoes in the Iberian peninsula." Remote Sensing 14.9

[0207] 7 Mostafaei, Kamran, and Mohammadnabi Kianpour. "Application of Magnetometry in Mantotype Copper Deposit Exploration, Case study: Meyami, Iran." Rudarsko-geolosko-naftni zbornik 37.5 (2022): 1-14.

[0208] 8 Pinto, Victor Hugo G., et al. "Seawater storage and element transfer associated with mantle serpentinization in magma-poor rifted margins: a quantitative approach." Earth and Planetary Science Letters 459 (2017): 227-237.

[0209] 9 Horen, H., M. Zamora, and G. Dubuisson. "Seismic waves velocities and anisotropy in serpentinized peridotites from Xigaze ophiolite: Abundance of serpentine in slow spreading ridge." Geophysical Research Letters 23.1 (1996): 9-12.10 Miller, D. Jay, and Nikolas I. Christensen. "Seismic velocities of lower crustal and upper mantle rocks from the slow-spreading Mid-Atlantic Ridge, south of the Kane Transform Zone (MARK)." Proceedings-ocean drilling program scientific results. National Science Foundation, 1997.

[0210] 11 Malvoisin, Benjamin, et al. "Serpentinization of oceanic peridotites: 2. Kinetics and processes of San Carlos olivine hydrothermal alteration." Journal of Geophysical Research: Solid Earth 117.B4 (2012).

[0211] 12 Mayhew, Lisa E., et al. "Hydrogen generation from low-temperature water-rock reactions." Nature Geoscience 6.6 (2013): 478-484.

[0212] 13 Michiels, Koen, et al. "Applicability of fine industrial metallic iron-rich waste powders for hydrothermal production of hydrogen gas: The influence of non-ferrous contaminants." Journal of Cleaner Production 195 (2018): 674-686.

[0213] 14 Chevrot, Sebastien, et al. "Crustal imaging and characterization of active faults with a large-N nodal deployment-Application to the Chainons Bearnais region (western Pyrenees foothills, France)." Tectonophysics 892 (2024): 230531.

[0214] 15 Sylvander, Matthieu, et al. "Spatiotemporal Behavior of an Extremely Small Seismic Swarm in Pyrenean Foreland, France." Bulletin of the Seismological Society of America 113.5 (2023): 2041-2055.

[0215] 16 Pimienta, Lucas, et al. "Anomalous Vp / Vs ratios at seismic frequencies might evidence highly damaged rocks in subduction zones." Geophysical Research Letters 45.22 (2018): 12-210.

Claims

CLAIMS:

1. A method of detecting subterranean hydrogen, the method comprising:selecting a geographical region of interest;disposing a network of measurement systems on said geographical region of interest, each measurement system comprising at least a seismic sensor;using said network of measurement systems, recording seismic data at each of a plurality of locations on said geographical region of interest, each location corresponding to a respective measurement system;using at least one gravimeter, recording gravity data at multiple positions over said geographical region of interest;using at least one magnetometer, recording magnetic data also at multiple sites over said geographical region of interest;processing the recorded seismic data to produce one or more tomographic models representative of subterranean seismic-wave propagation velocity under the geographical region of interest; and,interpreting said one or more tomographic models in light of the recorded gravity data and / or the recorded magnetic data in order to evaluate the presence of subterranean hydrogen in the geographical region of interest.

2. The method of claim 1, wherein selecting a geographical region of interest comprises evaluating existing and / or publicly available geological and / or geophysical records related to said geographical region of interest.

3. The method of claim 2, wherein said existing and / or publicly available geological and / or geophysical records comprise seismic records and / or existing gravimetric records and / or existing magnetic records.

4. The method of claim 3, wherein the method comprises processing the recorded seismic data and said seismic records to produce said one or more tomographic models; and / or,wherein the method comprises interpreting said one or more tomographic models in light of said existing gravimetric and / or existing magnetic records to evaluate the presence of subterranean hydrogen in the geographical region of interest.

5. The method of any preceding claim, wherein said network comprises measurement systems disposed to form at least one grid on said geographical region of interest.

6. The method of claim 5, wherein said network comprises measurement systems disposed to form two or more grids on said geographical region of interest, at least two of said grids having different spacing between adjacent measurement systems.

7. The method of claim 5 or 6, wherein adjacent measurement systems are spaced less than 1 km apart from each other;optionally, wherein adjacent measurement systems are spaced 500 metres or less apart from each other.

8. The method of any preceding claim, wherein each measurement system comprises, in addition, a gravimeter associated with the location of that measurement system.

9. The method of any preceding claim, wherein each measurement system comprises, in addition, a magnetometer associated with the location of that measurement system.

10. The method of any preceding claim, further comprising:using at least one gas analyser, sampling the presence of H2 at multiple points on the geographical region of interest;wherein said interpreting said one or more tomographic models is carried out additionally in light of said H2 samples collected by said at least one gas analyser.

11. The method of claim 10, further comprising:disposing the gas analyser underground at said multiple points on the geographical region of interest; optionally, at least 0.8 metre underground.

12. The method of claim 10 or 11, wherein each measurement system comprises, in addition, a gas analyser associated with the location of that measurement system.

13. The method of any preceding claim, wherein said interpreting said one or more tomographic models in light of the recorded gravity data and the recorded magnetic data, and optionally in light of said H2 samples, in order to evaluate the presence of subterranean hydrogen in the geographical region of interest comprises identifying gravimetric and / or magnetic anomalies which may be associated with a subterranean hydrogen kitchen.

14. The method of any preceding claim, wherein said processing the recorded seismic data to produce one or more tomographic models representative of subterranean seismic-wave propagation velocity under the geographical region of interest comprises producing one or more two-, three-or four-dimensional tomographic models of pressure velocity (Vp) associated with the seismic waves propagating underground.

15. The method of any preceding claim, wherein said processing the recorded seismic data to produce one or more tomographic models representative of subterranean seismic-wave propagation velocity under the geographical region of interest comprises producing one mor more two-, three-or four-dimensional tomographic models of shear velocity (Vs) associated with the seismic waves propagating underground.

16. The method of claim 14 and 15, further comprising using at least one of said pressure velocity models (Vp) and a corresponding one of the shear velocity (Vs) one or more models to calculate one or more of:a degree of serpentinization (S) of an active hydrogen kitchen;a volume of mantle rocks already serpentinized (Ms);a volume of mantle rocks available for serpentinization (Mr);a total amount of hydrogen to be produced by a source mantle rock (H2r); and, a total potential hydrogen production of a source mantle rock (H2i).

17. The method of any preceding claim, wherein said interpreting said one or more tomographic models in light of the recorded gravity data and / or the recorded magnetic data, and optionally in light of said H2 samples, in order to evaluate the presence of subterranean hydrogen in the geographical region of interest comprises evaluating the presence of one or more of:- mantle rocks undergoing serpentinization reactions forming H2;- mantle rocks having the potential to undergo serpentinization reactions forming H2; - H2 reservoirs in the form of pockets of gaseous H2; and / or- movement of H2 bearing fluids through a subsurface plumbing system consisting of one or more of permeable layers of rocks, underground fault lines and / or reservoirs.

18. The method of any preceding claim, wherein said recording seismic data, measuring gravity data and / or measuring magnetic data are carried out:- at specified times over an extended period of time; or- continuously over a given time period; or- in response to specific events, such as microearthquakes, for example such as microearthquakes caused by events related to subterranean hydrogen formation and migration.

19. The method of any preceding claim, further comprising a step of creating a visualisation of the processed data, where the visualisation includes:data from tomographic models,a surface referenced map view that displays the locations of the network of measurement systems,overlays of representations of gravimetric anomaly patterns obtained by the at least one gravimeter, andoverlays of representations of magnetic anomaly patterns obtained by the at least one magnetometer.

20. The method of any claim 19, where the visualisation includes a subsurface view displaying one or more volume renderings of the tomographic model.

21. The method of claim 19 or claim 20, when dependent upon any one of claims 10 to 12, where the visualisation includes a display of hydrogen values at or near the corresponding gas analyser locations.

22. The method of any one of claims 19 to 21, where the visualisation includes a three-dimensional representation of a mantle body and a computed degree of serpentinization (S) of the mantle rock, where the visualisation delineates serpentinized and fresh mantle regions according to an adjustable threshold. .

23. Computerised apparatus for detecting subterranean hydrogen in a geographical region of interest, the apparatus comprising:i.) a plurality of seismic sensors disposed to form a network of measurement systems on said geographical region of interest;ii.) at least one gravimeter; andiii.) at least one magnetometer;wherein the computerised apparatus is configured to carry out the method of any one of claims 1 to 9 or any one of claims 13 to 22.

24. The computerized apparatus of claim 19, further comprising at least one gas analyser, wherein the computerised apparatus is configured to carry out the method of any one of claims 10 to 12, or any one of claims 13 to 22 when dependent from any one of claims 10 to 12.

25. The computerised apparatus of claim 23 or 24, wherein the apparatus further comprises at least one airborne device on which said at least one magnetometer is provided.

26. The computerised apparatus of any one of claims 23 to 25, wherein the apparatus further comprises a visualisation which includes:a surface referenced map view that displays the locations of the network of measurement systems, andoverlays of representations of gravimetric anomaly patterns obtained by the at least one gravimeter, andoverlays of representations of magnetic anomaly patterns obtained by the at least one magnetometer.

27. The computerised apparatus of claim 26, where the visualisation further includes a subsurface view displaying one or more volume renderings of the tomographic model.

28. The computerised apparatus of claim 26 or 27, when dependent upon claim 24 or 25, where the visualisation includes a display of hydrogen values at or near the corresponding gas analyser locations.

29. The computerised apparatus of any one of claims 26 to 28, where the visualisation includes a three-dimensional representation of a mantle body and a computed degree of serpentinization (S), where the visualisation delineates serpentinized and fresh mantle regions according to an adjustable threshold.

Images