Method for evaluating submarine natural hydrogen distribution and reserves

Abstract

The invention provides a method for evaluating submarine natural hydrogen distribution and reserves, and relates to the field of submarine hydrogen energy exploration. A solution for evaluation through a numerical simulation means is provided in combination with a seabed natural hydrogen favorable zone, and before seabed observation, a potential distribution area is researched based on abnormal characteristics in combination with numerical simulation to determine a favorable target, so that the research purposes of effectively reducing exploration cost and improving detection accuracy are achieved. For the determined serpentine region, simulating material migration, deformation and heat transfer processes by constructing a continental and ocean region lithosphere model so as to obtain a mantle peridotite serpentine process and a corresponding relation between mantle peridotite serpentine and hydrogen production; through carrying out typical profile analysis on a plurality of construction units, the relationship between the crustal thickness and the serpentine quality in different environments is constructed, and finally, the distribution and the resource quantity of seabed hydrogen in a determined area are predicted.

Description

Technical Field

[0001] The present application relates to the field of seabed hydrogen energy exploration, and specifically proposes a method for evaluating the distribution and reserves of natural hydrogen on the seabed based on numerical simulation means. Background Art

[0002] Because the hydrogen content is as high as 80%, it is called hydrogen energy because of its resource value. In recent years, a large amount of hydrogen energy has been discovered in hydrogen surveys conducted in many basins and ophiolite belts on the earth's land, and large-scale hydrogen energy commercial development has been successfully carried out.

[0003] Compared to existing terrestrial exploration and development research, the investigation and potential assessment of natural hydrogen resources in the seafloor, which occupies a larger area of ​​the Earth's surface, remains largely unexplored. Theoretically, the presence of natural hydrogen in the seafloor is a common potential energy source, primarily because the Earth's mantle is composed of olivine-rich rocks, which can produce hydrogen through serpentinization reactions under high temperatures and water. However, under normal seafloor spreading, the average 6km thick oceanic crust typically isolates mantle peridotite from seawater, limiting direct contact and reaction between the two. Earth's unique plate tectonics, with its subduction deep enough to reach the mantle and bring in seawater, allows olivine to come into contact with seawater, leading to hydrogen production and overcoming the isolation of the oceanic crust. Furthermore, subduction can lead to tectonic activity such as faults, fissures, and volcanism. These tectonic activities also facilitate deep infiltration of seawater and provide key pathways for serpentinization between seawater and mantle peridotite, creating favorable tectonic environments for natural hydrogen production, such as microplate boundaries, seafloor fracture systems, ocean floor plateaus, and non-volcanic passive continental margins. For a long time, serpentinization of seafloor peridotite has been primarily studied as a product of fluid-rock interaction, with little consideration of the economic value and exploration potential of seafloor natural hydrogen from an energy perspective. Although the seafloor theoretically possesses extensive favorable zones for hydrogen formation and vast potential resources, the extent of these resources remains unclear due to a lack of research on the distribution characteristics of seafloor natural gas hydrogen and the methods and techniques for resource assessment.

[0004] Based on existing technical research, there is currently a lack of effective methods for assessing the distribution and abundance of natural seafloor hydrogen resources. The seafloor natural hydrogen system consists of three key elements: peridotite, vast ocean water volumes, and plate tectonic movement. Serpentinization of peridotite is the primary geological process responsible for hydrogen production, potentially producing 80% of Earth's hydrogen. Identifying the distribution of serpentinization deep within the Earth is crucial for assessing seafloor hydrogen resources. Preliminary research suggests that, regardless of the seafloor environment, the primary mechanism for natural hydrogen formation is water-rock reactions involving basic minerals such as olivine or pyroxene. Although serpentinization is widespread on the seafloor, the hydrogen production process is governed by multiple factors, including temperature, water-rock ratio, rock type, and fluid environment. To qualify as seafloor hydrogen, hydrogen must accumulate within a tectonic environment at depths accessible to current exploration technology, form reservoirs, and possess significant resource abundance and economic value. Existing basic research suggests that natural hydrogen may be more abundant and more readily available in deep and deep oceans. This is primarily due to the thinness of the oceanic crust, which allows for the ingress of seawater into the mantle during late tectonic activity, leading to the formation of large amounts of hydrogen at the interface between olivine and water. This research suggests that the depleted deep oceans may harbor important new unconventional energy sources, making them a key area for future exploration.

[0005] In view of this, this patent application is filed. Summary of the Invention

[0006] The method for evaluating the distribution and reserves of natural hydrogen on the seabed described in this application aims to solve the problems existing in the above-mentioned existing technologies and proposes a solution for evaluating favorable zones of natural hydrogen on the seabed through numerical simulation. Before conducting seabed observations, the potential distribution areas are studied based on abnormal characteristics combined with numerical simulation to determine favorable targets, thereby achieving the research purpose of effectively reducing exploration costs and improving detection accuracy.

[0007] To achieve the above objectives, the method for assessing the distribution and reserves of natural hydrogen on the seabed is based on the construction of continental and oceanic lithospheric models to simulate the material migration, deformation and heat transfer processes in the identified serpentinized areas, so as to obtain the serpentinization process of mantle peridotite and the corresponding relationship between serpentinization of mantle peridotite and hydrogen production; by conducting typical profile analysis of several tectonic units, the relationship between crust thickness and serpentinization quality under different environments is constructed, and finally the distribution and resource amount of seabed hydrogen in the identified area are predicted.

[0008] Further, the following implementation steps are included:

[0009] Step (1), identifying the seafloor serpentinization zone;

[0010] Using geophysical data, we preliminarily delineate areas where serpentinization may occur;

[0011] Collect lithospheric geological information and data of the study area and pre-process the data;

[0012] Based on the anomalies of P-wave velocity and density, temperature field constraints, and crustal structure, a potential favorable zone for serpentinization was preliminarily identified within the study area.

[0013] Step (2), constructing a numerical model;

[0014] Construct a two-dimensional or three-dimensional geological model reflecting the lithospheric structure of the study area;

[0015] Step (3), constructing a dynamic model;

[0016] The finite difference method was used to construct the dynamic model;

[0017] Step (4), quantitative calculation of the serpentinization process of mantle peridotite and hydrogen production;

[0018] According to the chemical conditions of serpentinization reaction of basic minerals, if the Fe in basic minerals is finally present in the form of magnetite, the reaction equation is:

[0019]

[0020] in, Indicates that the degree of chemical reaction is a function of temperature T;

[0021] From the above reaction equation, we can see that if Fe eventually enters magnetite, 1 mol of hydrogen can be generated for every 15 mol of olivine consumed, that is, the amount of hydrogen produced per kilogram of olivine is about 454 mmol; the amount of hydrogen produced by the water-rock reaction per kilogram of mantle rock is about 227 mmol;

[0022] Step (5), numerical simulation of ocean basin expansion and accompanying serpentinization;

[0023] This includes simulating the dynamic evolution of serpentinization during ocean basin spreading and comparing it with actual observational data;

[0024] By solving the mass conservation equation, momentum conservation equation, and energy conservation equation in step (3), data is continuously transmitted between particles and grids, the positions of particle points are continuously moved, and their physical parameters are changed. Finally, the entire ocean basin evolution process from the continental margin rift stage to the initial ridge expansion stage is obtained;

[0025] Compare the serpentinization distribution, crust thickness, deep velocity and density structure results obtained from the above simulation with the serpentinization zones and actual stratigraphic structures identified by inversion of geophysical data such as reflection seismic and seafloor seismographs in step (1);

[0026] Step (6), numerical simulation analysis of the relationship between crust thickness and serpentinization quality;

[0027] Through numerical simulation results, the relationship between crust thickness and serpentinization quality is quantitatively analyzed and segmented fitting is performed;

[0028] Step (7), estimation of the total mass of natural hydrogen and prediction of its spatial distribution;

[0029] The results of all the previous steps are combined to estimate the total mass of natural hydrogen in a specific area and predict its spatial distribution pattern.

[0030] Furthermore, in step (1), data preprocessing includes but is not limited to data correction, denoising and format unification;

[0031] First, using seafloor reflection seismic data and seafloor seismograph data, the longitudinal wave velocity and density structure deep in the study area are obtained; then, combined with seafloor heat flow data, the underground temperature distribution in the study area is inferred; finally, a crustal structure analysis is performed.

[0032] Furthermore, in step (2), based on the favorable serpentinization zones identified in step (1), one or more two-dimensional models spanning the continent-ocean region are selected, or a regional three-dimensional model is established;

[0033] Layer the above model;

[0034] Subduction is initiated at an inclination between 20° and 40° by prescribing an initial weak zone with wet olivine rheology and low brittle / plastic strength;

[0035] A constant plate velocity of 3-8 cm yr-1 was applied to the left and right sides of the model;

[0036] The initial thermal structure of the lithosphere is defined by a half-space cooling model;

[0037] The model adopts a variable grid subdivision scheme, with a small grid of 100-500m resolution used in the serpentinization target area and a large grid of 1-2km resolution used in the background area.

[0038] Furthermore, in step (3), the following formulas are applied to solve the mass conservation equation, momentum conservation equation, and energy conservation equation:

[0039] div(v)=0, (1)

[0040] div(σ′)=grad(P)-ρg, (2)

[0041]

[0042] Where v is the velocity vector, σ′ is the deviatoric stress tensor, P is the pressure, ρ is the density, g is the acceleration due to gravity, and C P is the constant pressure heat capacity, T is the temperature, k is the thermal conductivity; H r 、H a 、H s 、H L are radiative heat, adiabatic heat, shear heat, and latent heat respectively; DT / Dt is the real derivative of temperature with respect to time at the Lagrange point;

[0043] The following thermodynamic equilibrium equation is used to simulate the serpentinization reaction process:

[0044] k1=751.490422+6.00773668×10 {-3} ×(y-sy1)-0.034690759×10 {-6} ×(y-sy1) 2 (4)

[0045] Among them, k1 represents the phase transition boundary of serpentine at the depth of the location, and the unit is Kelvin (K); the k1 value is used to construct the phase transition process of the material field. When the temperature of a certain grid point is lower than the k1 value corresponding to the depth and meets other serpentinization conditions, the peridotite in the unit can undergo serpentinization; (y-sy1) represents the crustal depth of the location compared to sea level, and the unit is meter, y represents the depth of the location in the model, and sy1 represents the sea level elevation of the corresponding location in the model.

[0046] Furthermore, the step (5) is simulated using I2VIS geodynamic simulation software. Based on the Marker-in-cell technology, the numerical model constructed in step (2) and the control equation set in step (3) are imported into the software as simulation conditions; the downward infiltration and upward escape process of water are realized in the model;

[0047] The coupled mass conservation equation, momentum conservation equation, and energy conservation equation defined in step (3) are solved at each time step.

[0048] Furthermore, the solution process includes the following steps:

[0049] (5.1) Calculate the physical parameters of each particle, mark them on the Euler grid nodes using interpolation, and use boundary conditions to restrict the grid parameters;

[0050] (5.2) Through the matrix method, all grid nodes are connected and their implicit linear equations are solved. Taking advantage of the staggered grid, more accurate pressure values ​​and velocity components are solved;

[0051] (5.3) Based on the velocity field calculated in step (2), determine the optimal time step for the movement of the particle;

[0052] (5.4) Calculate the shear heat and adiabatic heat at the Euler nodes;

[0053] (5.5) Determine the optimal time step for the temperature equation. Select the smallest time step among the three given constraints: absolute time step limit, optimal particle displacement step limit, and node temperature change limit.

[0054] (5.6) Solve the temperature equation;

[0055] (5.7) Insert the calculated node temperature change from the Euler node into the particle point, taking into account the influence of particle movement; determine whether the thermodynamic equilibrium equation of the serpentinization reaction in step (3) is satisfied based on the temperature and pressure of the current grid point, and determine whether the peridotite in the grid will undergo serpentinization reaction;

[0056] (5.8) During the calculation process, use the fourth-order explicit Runge-Kutta method to translate all particles in the grid according to the calculated velocity field v and the time step; return to step (5.1) and execute the next time step until the maximum iteration time or the maximum number of iterations is reached.

[0057] Furthermore, the step (6) includes the following steps:

[0058] First, based on the verified numerical simulation results in step (5), the crust thickness data and serpentinization degree data are extracted from the entire simulation area and different evolution stages;

[0059] Then, the extracted crust thickness and serpentinization degree data were analyzed. Using statistical methods and correlation analysis, the trend of serpentinization quality changing with crust thickness was identified. At the same time, the data from different tectonic units were piecewise fitted using a variety of mathematical models, including linear regression, polynomial regression, and exponential functions, to select the best fitting model.

[0060] Finally, multiple sets of sensitivity analysis numerical simulations are carried out; based on step (5), key geological and geophysical parameters are systematically changed; simulation results under different geological backgrounds and evolutionary histories are extracted, and the crust thickness and serpentinization degree are compared respectively; through comparative analysis, a more robust serpentinization prediction model is established to evaluate the uncertainty in the relationship between the final crust thickness and serpentinization quality.

[0061] Furthermore, in step (7), the spatial distribution data of crust thickness in the study area obtained by geophysical inversion in step (1) is used to interpolate, smooth and unify the data;

[0062] Combined with the functional model between different crust thicknesses and serpentinization degrees established by numerical simulation analysis and geophysical data verification in step (6), for each grid point or data point in the regional crust thickness spatial distribution data, the serpentinization degree of the location is estimated using the relationship established in step (6) according to its corresponding crust thickness value;

[0063] Calculate the total mass of serpentine in the grid cell using the result of the conversion of the serpentinization process to the natural hydrogen production mass determined in step (4);

[0064] Calculate the mass of natural hydrogen that may be produced by serpentinization within this grid cell;

[0065] By performing the above calculation process on all grid cells, a three-dimensional spatial distribution data set of natural hydrogen production is obtained;

[0066] The natural hydrogen mass of each grid point in the entire study area or a specific favorable zone is accumulated to estimate the total natural hydrogen mass in the area.

[0067] In summary, the method proposed in this application for assessing the distribution and reserves of natural hydrogen on the seabed has the following advantages:

[0068] 1. This application simulates the hydrogen production process of serpentinization and combines it with spatial variations in regional crustal thickness to innovatively perform quantitative calculations of the serpentinization process of mantle peridotite and the amount of hydrogen produced. This analysis provides an estimate of the abundance of natural hydrogen resources on the seafloor. This approach enables remote estimation of natural hydrogen resources and rapid prediction of favorable targets for seafloor hydrogen exploration without extensive exploration and drilling, significantly reducing related exploration costs and offering significant economic potential.

[0069] 2. This application constructs a continent-ocean regional structural model, adopts variable grid subdivision to construct a numerical model, and based on dynamic simulation software, sets the extension velocity boundary conditions to carry out dynamic numerical simulation of driving continuous stretching, thinning and rupture of the lithosphere, simulating the process of ocean basin evolution from the continental margin rift stage to the initial ridge expansion stage, and couples and calculates the accompanying key physical and chemical processes such as serpentinization. It has a high-precision prediction result of hydrogen energy distribution and reserves, and the overall detection accuracy meets the requirements of existing actual exploration standards.

[0070] 3. This application's overall solution is simple and cost-effective to implement. It establishes technology for identifying favorable submarine hydrogen zones and provides a rapid prediction method and system. The resulting hydrogen resource assessment scheme is crucial for accurately understanding the distribution and abundance of submarine hydrogen resources and determining clear and complete exploration and drilling targets. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Figure 1 is a flow chart of the method for assessing the distribution and reserves of natural hydrogen on the seabed described in this application;

[0072] Figure 2 This is the calculation flow chart of the finite difference method;

[0073] Figure 3 This is a schematic diagram of the dynamic evolution of the lithosphere in the continental and oceanic regions; Figure 3 (a) is the initial structural model diagram; Figure 3 (b) is a schematic diagram of the evolution;

[0074] Figure 4 is a simulation diagram of different structural units; among them, Figure 4 (a) is a schematic diagram of the change of serpentinization quality; Figure 4 (b) is a schematic diagram of the change in crust thickness;

[0075] Figure 5 This is a comparison chart of the relationship between the segmented fitting crust thickness and the serpentinization quality; Figure 5 (a) is a schematic diagram of the changes in oceanic crust thickness; Figure 5 (b) is a schematic diagram of the changes in continental crust thickness. DETAILED DESCRIPTION

[0076] The technical solutions in the embodiments will be clearly and completely described below in conjunction with the drawings proposed in this application. It is obvious that the described solutions are part of the embodiments of this application rather than all the embodiments. Based on the embodiments proposed in this application, ordinary technicians in this field may make improvements or changes without making any creative work, and all these improvements and changes should fall within the scope of protection of the claims attached to this application.

[0077] Example 1, as Figures 1 to 5 As shown, this application proposes a method for evaluating the distribution and reserves of natural hydrogen on the seabed.

[0078] For the identified serpentinization areas, the material migration, deformation and heat transfer processes are simulated by constructing continental and oceanic lithospheric models to obtain the serpentinization process of mantle peridotite and the correspondence between serpentinization of mantle peridotite and hydrogen production; by conducting typical profile analysis of several tectonic units, the relationship between crust thickness and serpentinization quality under different environments is constructed, and finally the distribution and resource amount of seabed hydrogen in the determined area are predicted.

[0079] The implementation steps include:

[0080] Step (1), identifying the seafloor serpentinization zone;

[0081] Using geophysical data, we preliminarily delineated areas where serpentinization might occur;

[0082] Collect lithospheric geological information and data of the study area, including but not limited to thickness data, gravity data, reflection seismic data, seafloor seismometer data, and seafloor heat flow data;

[0083] The above data were preprocessed, including but not limited to data correction, denoising and format unification, to ensure data quality and availability. Specifically, first, the seafloor reflection seismic data and seafloor seismometer data were used to obtain the P-wave velocity and density structure deep in the study area. There are large differences in the P-wave velocity and density between the olivine mantle and the serpentinized mantle. The P-wave velocity of normal mantle olivine is usually 8.0-8.2 km / s, and the density is about 3.2-3.3 g / cm3. In the serpentinized mantle, due to hydration and mineral phase transition, the P-wave velocity of mantle rocks is reduced to less than 8.0 km / s, and the density is reduced to less than 3.2 g / cm3. cm3; then, combined with seafloor heat flow data, the underground temperature distribution in the study area was inferred; serpentinization typically occurs within a specific temperature window, ranging from 200-400°C; using the temperature field as a constraint, areas where temperatures are too high or too low to be conducive to serpentinization were excluded; finally, based on crustal structure analysis, for continental regions, if the thickness of the continental crust decreases to below 10km, the crust may become brittle and prone to forming deep faults that penetrate the crust, providing channels for surface water to penetrate into the mantle; for oceanic regions, if the thickness of the oceanic crust is less than 5km, it is believed that seawater may directly enter the mantle through infiltration, causing serpentinization;

[0084] Based on the above analysis results, potential favorable zones for serpentinization are preliminarily identified within the study area based on P-wave velocity and density anomalies, temperature field constraints, and crustal structure;

[0085] Step (2), constructing a numerical model;

[0086] This step aims to construct a two-dimensional or three-dimensional geological model reflecting the lithospheric structure of the study area based on geophysical data;

[0087] Specifically, based on the favorable serpentinization zones identified in step (1), one or more two-dimensional models spanning the continent-ocean region are selected, or a regional three-dimensional model is established;

[0088] The above model is layered; Figure 3 As shown, the top is air, with a thickness of 10 km and a density of 1 kg·m -3 The lower part is seawater, with a thickness of 4 km and a density of 1,000 kg·m -3 The oceanic crust is 10 km thick, consisting of a 4 km thick basalt layer and a 6 km thick gabbro layer. The continental crust is 38 km thick, with the upper and lower layers being felsic and mafic respectively. The mantle is composed of peridotite.

[0089] Subduction was initiated at a dip angle of 30° by prescribing an initial weak zone with wet olivine rheology and low brittle / plastic strength;

[0090] Apply 5cm yr on the left and right sides of the model -1 constant plate velocity;

[0091] The initial thermal structure of the lithosphere is defined by a half-space cooling model, with an age of 40 Ma and a lithosphere thickness of 95 km. The lowermost part is the asthenosphere mantle. The upper and left and right boundaries of the model are free slip boundaries, and the lower boundary is a permeable boundary.

[0092] The model uses a variable grid subdivision scheme, with small grids (e.g., 100-500m resolution) in the serpentinization target area and large grids (e.g., 1-2km resolution) in the background area, to optimize computational efficiency while ensuring accuracy.

[0093] Step (3), constructing a dynamic model;

[0094] The finite difference method is used to construct a dynamic model to simulate the material migration, deformation, and heat transfer processes in the lithosphere. The following formulas are used to solve the mass conservation equation, momentum conservation equation, and energy conservation equation:

[0095] div(v)=0, (1)

[0096] div(σ′)=grad(P)-ρg, (2)

[0097]

[0098] Where v is the velocity vector, σ′ is the deviatoric stress tensor, P is the pressure, ρ is the density, g is the acceleration due to gravity, and C P is the constant pressure heat capacity, T is the temperature, k is the thermal conductivity; H r 、H a 、H s 、H L are radiative heat, adiabatic heat, shear heat, and latent heat respectively; DT / Dt is the real derivative of temperature with respect to time at the Lagrange point;

[0099] The following thermodynamic equilibrium equation is used to simulate the serpentinization reaction process:

[0100] k1=751.490422+6.00773668×10 {-3} ×(y-sy1)-0.034690759×10 {-6} ×(y-sy1) 2 (4)

[0101] Where k1 represents the phase transition boundary of serpentine at the depth of the location, that is, the highest temperature at which serpentine can exist stably, and the unit is Kelvin (K); the k1 value is used to construct the phase transition process of the material field. When the temperature of a grid point is lower than the k1 value corresponding to the depth and other serpentinization conditions are met, the peridotite in the unit can undergo serpentinization; (y-sy1) represents the crustal depth of the location relative to sea level, and the unit is meter, y represents the depth of the location in the model, and sy1 represents the sea level elevation of the corresponding location in the model;

[0102] Step (4), quantitative calculation of the serpentinization process of mantle peridotite and hydrogen production;

[0103] According to the chemical conditions of serpentinization reaction of basic minerals such as olivine or pyroxene, if the Fe in basic minerals is finally present in the form of magnetite, the reaction equation is:

[0104]

[0105] in, Indicates that the degree of chemical reaction is a function of temperature (T); during the serpentinization reaction, water molecules react with minerals in the original rock, among which the divalent iron (Fe 2+ ) is oxidized to ferric iron (Fe 3+ ), so that water (H2O) is reduced to hydrogen (H2);

[0106] From the above reaction equation, we can see that if Fe eventually enters magnetite, 1 mol of hydrogen can be generated for every 15 mol of olivine consumed, that is, the amount of hydrogen produced per kilogram of olivine (about 6.81 mol) is about 454 mmol;

[0107] Therefore, it can be seen that the amount of hydrogen produced by water-rock reaction per kilogram of mantle rock is about 227mmol.

[0108] Step (5), numerical simulation of ocean basin expansion and accompanying serpentinization;

[0109] This includes simulating the dynamic evolution of serpentinization during ocean basin spreading and comparing it with actual observational data;

[0110] For example, the simulation can be performed using I2VIS geodynamic simulation software. Based on the Marker-in-cell technology, the numerical model constructed in step (2) and the control equation set in step (3) are imported into the software as simulation conditions; the downward infiltration (controlled by faults or porosity) and upward escape (through convection or diffusion) of water (fluid) are realized in the model to ensure that the required water is provided for the serpentinization reaction;

[0111] The coupled mass conservation equation, momentum conservation equation, and energy conservation equation defined in step (3) are solved in each time step, as Figure 2 As shown, the solution process includes:

[0112] (5.1) First, calculate the physical parameters of each particle (such as viscosity, density, temperature, etc.), mark them on the Euler grid nodes using interpolation, and use boundary conditions to constrain the grid parameters;

[0113] (5.2) Through the matrix method, all grid nodes are connected and their implicit linear equations are solved. Taking advantage of the staggered grid, more accurate pressure values ​​and velocity components are solved;

[0114] (5.3) Based on the velocity field calculated in step (2), determine the optimal time step for the particle movement; usually limit the maximum displacement to 0.01-1.0 of the minimum grid step;

[0115] (5.4) Calculate the shear heat and adiabatic heat at the Euler nodes;

[0116] (5.5) Determine the optimal time step for the temperature equation, typically limiting the variation to 1–20 K. Then, choose the smallest time step given the three constraints: the absolute time step limit, the optimal particle displacement step limit, and the node temperature variation limit.

[0117] (5.6) Solve the temperature equation;

[0118] (5.7) Insert the calculated node temperature change from the Euler node into the particle point, taking into account the influence of particle movement; determine whether the thermodynamic equilibrium equation of the serpentinization reaction in step (3) is satisfied based on the temperature and pressure of the current grid point, and determine whether the peridotite in the grid will undergo serpentinization reaction;

[0119] (5.8) During the calculation process, use the fourth-order explicit Runge-Kutta method to translate all particles in the grid according to the calculated velocity field v and the time step; return to step (5.1) and execute the next time step until the maximum iteration time or the maximum number of iterations is reached.

[0120] By solving the mass conservation equations, momentum conservation equations, and energy conservation equations in step (3), data is continuously transmitted between particles and the grid, the positions of the particles are continuously moved, and their physical parameters are changed. Ultimately, the entire ocean basin evolution process from the continental margin rifting stage to the initial ridge expansion stage is obtained. Specifically, this includes processes such as crustal stretching, thinning, and rupture, mantle uplift and melting, and seawater intrusion.

[0121] The serpentinization distribution, crust thickness, deep velocity and density structure results obtained by the above simulation are compared with the serpentinization zones and actual stratigraphic structures identified by inversion of geophysical data such as reflection seismic and seafloor seismographs in step (1); if the simulation results are consistent with the structure analyzed by traditional geophysical observation data, it is considered that the simulation results can better reflect the actual process and distribution characteristics of serpentinization during the expansion of the ocean basin; if they are inconsistent, the model parameters or serpentinization reaction parameters need to be adjusted and the simulation is repeated until the simulation results reach a reasonable consistency with the actual observation data.

[0122] Step (6), numerical simulation analysis of the relationship between crust thickness and serpentinization quality;

[0123] Through numerical simulation results, the relationship between crust thickness and serpentinization quality is quantitatively analyzed and segmented fitting is performed; including:

[0124] First, based on the verified numerical simulation results in step (5), the crust thickness data and serpentinization degree data are extracted from the entire simulation area and different evolution stages;

[0125] Then, the extracted crust thickness and serpentinization degree (mass or volume fraction) data were analyzed; through statistical methods, correlation analysis was used to identify the changing trend of serpentinization quality with crust thickness, including whether there is a critical thickness, thickening or thinning trend; at the same time, the data of different tectonic units were piecewise fitted, using various mathematical models such as linear regression, polynomial regression, and exponential function to select the best fitting model; specifically, the R2 value, residual distribution, etc. should be evaluated during the fitting process to ensure the reliability of the fitting results; the corresponding relationship between the crust thickness and serpentinization quality of typical tectonic units was obtained, satisfying the following mathematical relationship: S = f(D, T, P); where S is the serpentinization quality or volume fraction, D is the crust thickness, T is the temperature, and P is the pressure.

[0126] Finally, in order to enhance the universality and reliability of the research results, it is necessary to carry out multiple sets of sensitivity analysis numerical simulations; that is, on the basis of step (5), systematically change key geological and geophysical parameters, such as different extension rates, different initial lithospheric structures, and different material parameters; extract the simulation results under these different geological backgrounds and evolutionary histories, and compare the crust thickness and serpentinization degree respectively; through comparative analysis, establish a more robust serpentinization prediction model and evaluate the uncertainty in the relationship between the final crust thickness and serpentinization quality;

[0127] Step (7), estimation of the total mass of natural hydrogen and prediction of its spatial distribution;

[0128] The ultimate goal is to combine the results of all the previous steps to estimate the total mass of natural hydrogen in a specific area and predict its spatial distribution pattern;

[0129] Using the spatial distribution data of crust thickness in the study area obtained by geophysical inversion in step (1), the data are interpolated, smoothed and formatted;

[0130] Combined with the functional model between different crust thicknesses and serpentinization degrees established by numerical simulation analysis and geophysical data verification in step (6), for each grid point or data point in the regional crust thickness spatial distribution data, the serpentinization degree of the location is estimated using the relationship established in step (6) according to its corresponding crust thickness value;

[0131] Using the result of the conversion of the serpentinization process to the natural hydrogen production mass determined in step (4) (i.e., 227 mmol of hydrogen can be produced per kilogram of serpentinite), the total mass of serpentine in the grid cell is calculated, specifically by multiplying the serpentine volume fraction of the cell by the total volume of the rock and then by the serpentine density; the calculated serpentine mass is multiplied by the hydrogen production coefficient determined in step (4);

[0132] Calculate the mass of natural hydrogen that may be produced by serpentinization within this grid cell;

[0133] By performing the above calculation process on all grid cells, a three-dimensional spatial distribution data set of natural hydrogen production is obtained;

[0134] The natural hydrogen mass of each grid point in the entire study area or a specific favorable zone is accumulated to estimate the total natural hydrogen mass in the area.

[0135] Although the above embodiments have shown and described the present invention, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for assessing the distribution and reserves of natural hydrogen on the seabed, characterized by: For the identified serpentinization areas, the material migration, deformation and heat transfer processes are simulated by constructing continental and oceanic lithospheric models to obtain the serpentinization process of mantle peridotite and the correspondence between serpentinization of mantle peridotite and hydrogen production; by conducting typical profile analysis of several tectonic units, the relationship between crust thickness and serpentinization quality under different environments is constructed, and finally the distribution and resource amount of seabed hydrogen in the determined area are predicted.

2. The method for assessing the distribution and reserves of natural hydrogen on the seabed according to claim 1, characterized in that: The implementation steps include the following: Step (1), identifying the seafloor serpentinization zone; Using geophysical data, we preliminarily delineate areas where serpentinization may occur; Collect lithospheric geological information and data of the study area and pre-process the data; Based on the anomalies of P-wave velocity and density, temperature field constraints, and crustal structure, a potential favorable zone for serpentinization was preliminarily identified within the study area. Step (2), constructing a numerical model; Construct a two-dimensional or three-dimensional geological model reflecting the lithospheric structure of the study area; Step (3), constructing a dynamic model; The finite difference method was used to construct the dynamic model; Step (4), quantitative calculation of the serpentinization process of mantle peridotite and hydrogen production; According to the chemical conditions of serpentinization reaction of basic minerals, if the Fe in basic minerals is finally present in the form of magnetite, the reaction equation is: in, Indicates that the degree of chemical reaction is a function of temperature T; From the above reaction equation, we can see that if Fe eventually enters magnetite, 1 mol of hydrogen can be generated for every 15 mol of olivine consumed, that is, the amount of hydrogen produced per kilogram of olivine is about 454 mmol; the amount of hydrogen produced by the water-rock reaction per kilogram of mantle rock is about 227 mmol; Step (5), numerical simulation of ocean basin expansion and accompanying serpentinization; This includes simulating the dynamic evolution of serpentinization during ocean basin spreading and comparing it with actual observational data; By solving the mass conservation equation, momentum conservation equation, and energy conservation equation in step (3), data is continuously transmitted between particles and grids, the positions of particle points are continuously moved, and their physical parameters are changed. Finally, the entire ocean basin evolution process from the continental margin rift stage to the initial ridge expansion stage is obtained; Compare the serpentinization distribution, crust thickness, deep velocity and density structure results obtained from the above simulation with the serpentinization zones and actual stratigraphic structures identified by inversion of geophysical data such as reflection seismic and seafloor seismographs in step (1); Step (6), numerical simulation analysis of the relationship between crust thickness and serpentinization quality; Through numerical simulation results, the relationship between crust thickness and serpentinization quality is quantitatively analyzed and segmented fitting is performed; Step (7), estimation of the total mass of natural hydrogen and prediction of its spatial distribution; The results of all the previous steps are combined to estimate the total mass of natural hydrogen in a specific area and predict its spatial distribution pattern.

3. The method for assessing the distribution and reserves of natural hydrogen on the seabed according to claim 2, characterized in that: In the step (1), the data is pre-processed including but not limited to data correction, denoising and format unification; First, using seafloor reflection seismic data and seafloor seismograph data, the longitudinal wave velocity and density structure deep in the study area are obtained; then, combined with seafloor heat flow data, the underground temperature distribution in the study area is inferred; finally, a crustal structure analysis is performed.

4. The method for assessing the distribution and reserves of natural hydrogen on the seabed according to claim 2, characterized in that: Said step (2) is to select one or more two-dimensional models spanning the continent-ocean region, or to establish a regional three-dimensional model, based on the favorable serpentinization zones identified in step (1); Layer the above model; Subduction is initiated at an inclination between 20° and 40° by prescribing an initial weak zone with wet olivine rheology and low brittle / plastic strength; Apply 3-8cm yr on the left and right sides of the model -1 constant plate velocity; The initial thermal structure of the lithosphere is defined by a half-space cooling model; The model adopts a variable grid subdivision scheme, with a small grid of 100-500m resolution used in the serpentinization target area and a large grid of 1-2km resolution used in the background area.

5. The method for assessing the distribution and reserves of natural hydrogen on the seabed according to claim 2, characterized in that: In step (3), the following formulas are used to solve the mass conservation equation, momentum conservation equation, and energy conservation equation: div(v)=0, (1) div(σ′)=grad(P)-ρg, (2) Where v is the velocity vector, σ′ is the deviatoric stress tensor, P is the pressure, ρ is the density, g is the acceleration due to gravity, and C P is the constant pressure heat capacity, T is the temperature, k is the thermal conductivity; H r 、H a 、H s 、H L are radiative heat, adiabatic heat, shear heat, and latent heat respectively; DT / Dt is the real derivative of temperature with respect to time at the Lagrange point; The following thermodynamic equilibrium equation is used to simulate the serpentinization reaction process: k1=751.490422+6.00773668×10 {-3} ×(y-sy1)-0.034690759×10 {-6} ×(y-sy1) 2 (4) Among them, k1 represents the phase transition boundary of serpentine at the depth of the location, and the unit is Kelvin (K); the k1 value is used to construct the phase transition process of the material field. When the temperature of a certain grid point is lower than the k1 value corresponding to the depth and meets other serpentinization conditions, the peridotite in the unit can undergo serpentinization; (y-sy1) represents the crustal depth of the location compared to sea level, and the unit is meter, y represents the depth of the location in the model, and sy1 represents the sea level elevation of the corresponding location in the model.

6. The method for assessing the distribution and reserves of natural hydrogen on the seabed according to claim 2, characterized in that: The step (5) is simulated using I2VIS geodynamic simulation software. Based on the Marker-in-cell technology, the numerical model constructed in step (2) and the control equation set in step (3) are imported into the software as simulation conditions; the downward infiltration and upward escape process of water are realized in the model; The coupled mass conservation equation, momentum conservation equation, and energy conservation equation defined in step (3) are solved at each time step.

7. The method for assessing the distribution and reserves of natural hydrogen on the seabed according to claim 6, characterized in that: The solution process includes the following steps: (5.1) Calculate the physical parameters of each particle, mark them on the Euler grid nodes using interpolation, and use boundary conditions to restrict the grid parameters; (5.2) By using the matrix method, all grid nodes are connected and their implicit linear equations are solved. Taking advantage of the staggered grid, more accurate pressure values ​​and velocity components are obtained. (5.3) Based on the velocity field calculated in step (2), determine the optimal time step for the movement of the particle; (5.4) Calculate the shear heat and adiabatic heat at the Euler nodes; (5.5) Determine the optimal time step for the temperature equation. Select the smallest time step among the three given constraints: absolute time step limit, optimal particle displacement step limit, and node temperature change limit. (5.6) Solve the temperature equation; (5.7) Insert the calculated node temperature change from the Euler node into the particle point, taking into account the influence of particle movement; determine whether the thermodynamic equilibrium equation of the serpentinization reaction in step (3) is satisfied based on the temperature and pressure of the current grid point, and determine whether the peridotite in the grid will undergo serpentinization reaction; (5.8) During the calculation, the fourth-order explicit Runge-Kutta method is used to translate all particles in the grid according to the calculated velocity field v and the time step; Return to step (5.1) and execute the next time step until the maximum iteration time or the maximum number of iterations is reached.

8. The method for assessing the distribution and reserves of natural hydrogen on the seabed according to claim 2, characterized in that: Said step (6) comprises the following steps, First, based on the verified numerical simulation results in step (5), the crust thickness data and serpentinization degree data are extracted from the entire simulation area and different evolution stages; Then, the extracted crust thickness and serpentinization degree data were analyzed. Using statistical methods and correlation analysis, the trend of serpentinization quality changing with crust thickness was identified. At the same time, the data from different tectonic units were piecewise fitted using a variety of mathematical models, including linear regression, polynomial regression, and exponential functions, to select the best fitting model. Finally, multiple sets of sensitivity analysis numerical simulations are carried out; based on step (5), key geological and geophysical parameters are systematically changed; simulation results under different geological backgrounds and evolutionary histories are extracted, and the crust thickness and serpentinization degree are compared respectively; through comparative analysis, a more robust serpentinization prediction model is established to evaluate the uncertainty in the relationship between the final crust thickness and serpentinization quality.

9. The method for assessing the distribution and reserves of natural hydrogen on the seabed according to claim 2, characterized in that: The step (7) uses the spatial distribution data of crust thickness in the study area obtained by geophysical inversion in step (1) to interpolate, smooth and unify the data; Combined with the functional model between different crust thicknesses and serpentinization degrees established by numerical simulation analysis and geophysical data verification in step (6), for each grid point or data point in the regional crust thickness spatial distribution data, the serpentinization degree of the location is estimated using the relationship established in step (6) according to its corresponding crust thickness value; Calculate the total mass of serpentine in the grid cell using the result of the conversion of the serpentinization process to the natural hydrogen production mass determined in step (4); Calculate the mass of natural hydrogen that may be produced by serpentinization within this grid cell; By performing the above calculation process on all grid cells, a three-dimensional spatial distribution data set of natural hydrogen production is obtained; The natural hydrogen mass of each grid point in the entire study area or a specific favorable zone is accumulated to estimate the total natural hydrogen mass in the area.

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