Methods for assessing the distribution and reserves of natural hydrogen on the seabed

Abstract

This invention proposes a method for assessing the distribution and reserves of natural hydrogen on the seabed, relating to the field of seabed hydrogen energy exploration. It proposes a solution for assessment using numerical simulation, combining favorable zones for natural hydrogen on the seabed. Before conducting seabed observations, it studies potential distribution areas based on anomaly characteristics and numerical simulations to identify favorable targets, thereby effectively reducing exploration costs and improving detection accuracy. For identified serpentinized areas, it simulates material migration, deformation, and heat transfer processes by constructing continental and oceanic lithosphere models to obtain the serpentinization process of mantle peridotite and the correspondence between mantle peridotite serpentinization and hydrogen production. Through the analysis of typical profiles of several tectonic units, it establishes the relationship between crustal thickness and serpentinization quality under different environments, ultimately predicting the distribution and resource quantity of seabed hydrogen in the identified areas.

Description

Technical Field

[0001] This application relates to the field of seabed hydrogen exploration, specifically proposing a method for evaluating the distribution and reserves of natural hydrogen on the seabed based on numerical simulation. Background Technology

[0002] Because it contains up to 80% hydrogen and has resource value, it is called hydrogen energy. In recent years, large amounts of hydrogen energy have been discovered in hydrogen surveys conducted in multiple basins and ophiolite belts on Earth's landmass, and large-scale commercial development of hydrogen energy has been successfully carried out.

[0003] Compared to existing terrestrial exploration and development studies, the investigation and potential assessment of natural hydrogen resources in the seafloor, which covers a much larger area of ​​the Earth's surface, remains a blank. Theoretically, the presence of natural hydrogen on the seafloor is a common potential energy source, primarily because the mantle is composed of olivine-rich rocks, which can produce hydrogen through serpentinization under high temperatures and in the presence of water. However, in normal seafloor spreading environments, the average 6 km thick oceanic crust typically isolates mantle peridotite from seawater, thus limiting direct contact and reaction between the two. Earth's unique plate tectonics, with subduction depths reaching the mantle and bringing in seawater, allows olivine to come into contact with seawater, thereby producing hydrogen and overcoming the isolation limitations of the oceanic crust. Furthermore, subduction can lead to tectonic activities such as faulting, fractures, and volcanic activity. These tectonic activities also provide key channels for seawater to infiltrate deeper and for serpentinization reactions to occur between seawater and mantle peridotite, creating favorable tectonic environments for natural hydrogen, such as microplate boundaries, seafloor fracture systems, oceanic plateaus, and non-volcanic passive margins. For a long time, the serpentinization of submarine peridotite has been mainly studied as a product of fluid-rock interaction, with very little consideration given to the economic value and exploration potential of submarine natural hydrogen from an energy perspective. Although theoretically the seabed possesses extensive favorable areas for hydrogen formation and enormous potential resources, the scale of these resources remains unclear due to a lack of research on the distribution characteristics, resource assessment methods, and technologies for submarine natural gas hydrogen.

[0004] Current research indicates a lack of effective methods for assessing the distribution and resource volume of natural hydrogen on the seabed. Three key factors contribute to the seabed's natural hydrogen system: peridotite, massive amounts of seawater, and plate tectonics. The serpentinization process of peridotite is the primary geological process for hydrogen production, potentially accounting for 80% of Earth's hydrogen. Identifying the distribution areas of deep-sea serpentinization is crucial for evaluating seabed hydrogen resources. Preliminary studies suggest that, regardless of the seabed environment, the formation mechanism of natural hydrogen primarily involves water-rock reactions involving various basic minerals such as olivine and pyroxene. Although seabed serpentinization is widespread, the hydrogen production process is controlled by multiple factors, including temperature, water-rock ratio, rock type, and fluid environment. For hydrogen to be considered seabed hydrogen energy, it needs to accumulate within the depth range detectable by current exploration techniques under tectonic conditions, forming a reservoir with sufficient resources and economic value. Based on existing fundamental research, it is believed that naturally occurring hydrogen on the deep seabed is likely more abundant and easier to utilize, primarily due to the thinner oceanic crust and the greater ease with which late-stage tectonic activity allows seawater to penetrate the mantle, resulting in the formation of large amounts of hydrogen at the interface between olivine and water. Research into naturally occurring hydrogen on the seabed suggests that the barren deep ocean may hold important new unconventional energy sources, making it a crucial area for future exploration.

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

[0006] The method for assessing the distribution and reserves of natural hydrogen on the seabed described in this application aims to solve the problems existing in the prior art by proposing a solution for assessing favorable zones of natural hydrogen on the seabed through numerical simulation. Before conducting seabed observations, potential distribution areas are studied based on anomaly characteristics combined with numerical simulation to identify favorable targets, thereby achieving the research objective 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, for the identified serpentinized areas, simulates the processes of material migration, deformation, and heat transfer by constructing lithosphere models of continental and oceanic regions, in order to obtain the serpentinization process of mantle peridotite and the correspondence between mantle peridotite serpentinization and hydrogen production; by conducting typical profile analysis of several tectonic units, the relationship between crustal thickness and serpentinization quality under different environments is constructed, and finally the distribution and resource quantity of seabed hydrogen in the identified areas are predicted.

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

[0009] Step (1): Identify the serpentinized zones on the seabed;

[0010] Based on geophysical data, areas where serpentinization may occur have been preliminarily delineated;

[0011] Collect lithospheric geological data and information for the study area, and preprocess the data;

[0012] Based on the longitudinal wave velocity and density anomalies, temperature field constraints, and crustal structure, potential favorable zones for serpentinization were preliminarily delineated within the study area.

[0013] Step (2): Construct a numerical model;

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

[0015] Step (3): Construct a dynamic model;

[0016] A dynamic model is constructed using the finite difference method;

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

[0018] Based on the chemical conditions for the serpentinization reaction of basic minerals, if Fe in the basic minerals ultimately exists in the form of magnetite, then the reaction equation is:

[0019]

[0020] in, This indicates that the extent of a chemical reaction is a function of temperature T;

[0021] From the above reaction equations, it can be seen that if Fe eventually enters magnetite, then every 15 mol of olivine consumed can generate 1 mol of hydrogen gas, that is, the amount of hydrogen gas generated per kilogram of olivine is about 454 mmol; the amount of hydrogen gas generated per kilogram of mantle rock through water-rock reaction is about 227 mmol.

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

[0023] This includes simulating the dynamic evolution of serpentinization during basin expansion and comparing it with actual observation data for verification;

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

[0025] The results of the above simulation of serpentinization distribution, crustal thickness, deep velocity and density structure are compared with the serpentinization zones and actual stratigraphic structures identified by geophysical data such as reflection seismographs and submarine seismographs in step (1).

[0026] Step (6): Numerical simulation analysis of the relationship between crustal thickness and serpentinization quality;

[0027] Based on numerical simulation results, the relationship between crustal thickness and serpentinization quality is quantitatively analyzed and piecewise fitted.

[0028] Step (7): Estimation of total mass of natural hydrogen and prediction of its spatial distribution;

[0029] By combining the results of all the aforementioned steps, the total mass of natural hydrogen in a specific region can be estimated and its spatial distribution pattern can be predicted.

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

[0031] First, using submarine reflection seismic data and submarine seismograph data, the P-wave velocity and density structure at depth in the study area are obtained; then, combined with submarine heat flow data, the underground temperature distribution in the study area is inferred; finally, crustal structure analysis is conducted.

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

[0033] The above model is divided into layers;

[0034] By defining an initial weak zone with wet olivine rheology and low brittle / plastic strength, the dive is initiated at an angle between 20° and 40°.

[0035] A constant plate velocity of 3-8 cm yr-1 is applied to both 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 mesh partitioning scheme, using small meshes with a resolution of 100-500m in the serpentine target area and large meshes with a resolution of 1-2km in the background area.

[0038] Furthermore, in step (3), the following formulas are used 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 gravitational acceleration, and C is the velocity vector. P For constant pressure heat capacity, T is temperature, k is thermal conductivity; H r H a H s H L These represent 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 serpentinization reaction process is simulated using the following thermodynamic equilibrium equation:

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

[0045] Where k1 represents the phase transition boundary of serpentine at the depth of this location, in 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 this depth, and other serpentinization conditions are met, the peridotite in this unit can undergo serpentinization; (y-sy1) represents the crustal depth of this location relative to sea level, in meters, where y represents the depth of this location in the model, and sy1 represents the sea level elevation of the corresponding location in the model.

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

[0047] Solve the coupled mass conservation equation, momentum conservation equation and energy conservation equation defined in step (3) 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 constrain the grid parameters using boundary conditions;

[0050] (5.2) Using a matrix method, solve the implicit linear equations of all grid nodes. Leveraging the advantages of staggered grids, obtain relatively accurate pressure and velocity components.

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

[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. Among the three given constraints—absolute time step constraint, optimal particle displacement step size constraint, and nodal temperature change limit—select the smallest time step.

[0054] (5.6) Solve the temperature equation;

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

[0056] (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) to execute the next time step until the maximum iteration time or the maximum number of iterations is reached.

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

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

[0059] Then, the extracted crustal thickness and serpentinization data were analyzed; through statistical methods, correlation analysis was used to identify the trend of serpentinization quality with crustal thickness; at the same time, the data of different tectonic units were piecewise fitted, and various mathematical models such as linear regression, multinomial regression, and exponential function were used for fitting, and the best fitting model was selected.

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

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

[0062] Combining the function model between different crustal thicknesses and serpentinization degrees established in step (6) through numerical simulation analysis and geophysical data verification, for each grid point or data point in the regional crustal thickness spatial distribution data, the serpentinization degree at that location is estimated using the relationship established in step (6) based on its corresponding crustal thickness value.

[0063] Using the conversion result of the serpentinization process to the mass of natural hydrogen generated determined in step (4), calculate the total mass of serpentine in the grid cell;

[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 dataset of natural hydrogen production is obtained.

[0066] The total mass of natural hydrogen in the study area is estimated by summing up the mass of natural hydrogen at each grid point within the entire study area or a specific favorable zone.

[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 innovatively conducts quantitative calculations of the hydrogen production process in mantle peridotite serpentinization and its generation by simulating the hydrogen production process of serpentinization and combining it with spatial differences in regional crustal thickness. Based on this, it analyzes and estimates the amount of natural hydrogen resources on the seabed. This method enables remote estimation of natural hydrogen resources and rapid prediction of favorable targets on the seabed without extensive exploration or drilling, thus significantly reducing related exploration costs and demonstrating high economic potential.

[0069] 2. This application constructs a continental-oceanic regional structural model, uses variable grid subdivision to build a numerical model, and, based on dynamic simulation software, conducts dynamic numerical simulations of the continuous stretching, thinning, and fracturing of the lithosphere by setting extensional velocity boundary conditions. It simulates the process of ocean basins evolving from the continental margin rift stage to the initial mid-ocean ridge spreading stage, and couples the calculations of key physicochemical processes such as serpentinization. It has high-precision prediction results of hydrogen energy distribution and reserves, and the overall detection accuracy meets the requirements of existing practical exploration standards.

[0070] 3. The overall scheme proposed in this application is simple to implement and has a low cost. It establishes a technology for identifying favorable zones for seabed hydrogen energy and provides a rapid prediction method and system. The resulting hydrogen energy resource assessment scheme is of great significance for accurately understanding the distribution and quantity of seabed hydrogen energy and for identifying clear and complete exploration and drilling targets. Attached Figure Description

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

[0072] Figure 2 This is a flowchart of the finite difference method calculation.

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

[0074] Figure 4 These are simulation diagrams of different structural units; among them, Figure 4 (a) is a schematic diagram showing the changes in serpentinization quality; Figure 4 (b) is a schematic diagram showing the variation in crustal thickness;

[0075] Figure 5 This is a comparative graph showing the relationship between piecewise fitted crustal thickness and serpentinization quality; among them... Figure 5 (a) is a schematic diagram showing the variation in oceanic crust thickness; Figure 5 (b) is a schematic diagram of the changes in continental crust thickness. Detailed Implementation

[0076] The technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described solutions are some embodiments of this application, but not all embodiments. Based on the embodiments proposed in this application, those skilled in the art can make improvements or modifications without creative effort, and all such improvements and modifications should fall within the protection scope of the appended claims.

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

[0078] For the identified serpentinization areas, we simulated the material migration, deformation, and heat transfer processes by constructing lithosphere models of continental and oceanic regions to obtain the serpentinization process of mantle peridotite and the correspondence between mantle peridotite serpentinization and hydrogen production. By conducting typical profile analysis of several tectonic units, we constructed the relationship between crustal thickness and serpentinization quality under different environments, and finally predicted the distribution and resource quantity of seafloor hydrogen in the identified areas.

[0079] The implementation steps include the following:

[0080] Step (1): Identify the serpentinized zones on the seabed;

[0081] Based on geophysical data, areas where serpentinization may occur have been preliminarily delineated;

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

[0083] The above data underwent preprocessing, including but not limited to data correction, noise reduction, and format standardization, to ensure data quality and usability. Specifically, firstly, submarine reflection seismic data and submarine seismograph data were used to obtain the P-wave velocity and density structure of the deep parts of the study area. There are significant differences in P-wave velocity and density between olivine mantle and serpentinized mantle. The P-wave velocity of normal olivine mantle is typically 8.0-8.2 km / s, and the density is approximately 3.2-3.3 g / cm³. However, in serpentinized mantle, due to hydration and mineral phase transformation, the P-wave velocity of mantle rocks decreases to less than 8.0 km / s, and the density decreases to less than 3.2 g / cm³. cm3; then, combined with seafloor heat flow data, the underground temperature distribution in the study area is inferred; serpentinization usually occurs within a specific temperature window, ranging from 200-400℃; using the temperature field as a constraint, areas with excessively high or low temperatures that are unfavorable for serpentinization are excluded; finally, based on crustal structure analysis, for continental regions, if the continental crust thickness decreases to less than 10km, the crust may become brittle and prone to forming deep faults that penetrate the crust, providing channels for surface water to infiltrate into the mantle; for oceanic regions, if the oceanic crust thickness is less than 5km, it is considered that seawater may directly enter the mantle through infiltration, resulting in serpentinization.

[0084] Based on the above analysis results, and considering the longitudinal wave velocity and density anomalies, temperature field constraints, and crustal structure, potential favorable zones for serpentinization have been preliminarily delineated within the study area.

[0085] Step (2): Construct a numerical model;

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

[0087] Specifically, based on the serpentinization favorable zones delineated in step (1), select one or more two-dimensional models spanning the continent-ocean region, or establish a three-dimensional regional model.

[0088] The above model is divided into layers; such as Figure 3 As shown, the uppermost part is air, with a thickness of 10 kilometers and a density of 1 kg·m³. -3 The lower part is seawater, with a thickness of 4 kilometers and a density of 1,000 kg·m³. -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, consisting of felsic and mafic crusts, respectively. The mantle is composed of peridotite.

[0089] By defining an initial weak zone with wet olivine rheology and low brittle / plastic strength, the dive is initiated at an angle of 30°.

[0090] Apply 5cm yr to the left and right sides of the model respectively. -1 Constant plate velocity;

[0091] The initial thermal structure of the lithosphere is defined by a half-space cooling model, such as an age of 40 Ma and a lithosphere thickness of 95 km; the lowest part is the asthenospheric 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 adopts a variable mesh partitioning scheme, using a small mesh (e.g., 100-500m resolution) in the serpentine target area and a large mesh (e.g., 1-2km resolution) in the background area, thereby optimizing computational efficiency while ensuring computational accuracy.

[0093] Step (3): Construct a dynamic model;

[0094] A kinetic model was constructed using the finite difference method to simulate material migration, deformation, and heat transfer processes within the lithosphere. The following equations were then 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 gravitational acceleration, and C is the velocity vector. P For constant pressure heat capacity, T is temperature, k is thermal conductivity; H r H a H s H L These represent 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 serpentinization reaction process is simulated using the following thermodynamic equilibrium equation:

[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 this location, that is, the highest temperature at which serpentine can exist stably, in 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 this depth, and other serpentinization conditions are met, the peridotite in this unit can undergo serpentinization; (y-sy1) represents the crustal depth of this location relative to sea level, in meters, where y represents the depth of this 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] Based on the chemical conditions for the serpentinization reaction of basic minerals such as olivine or pyroxene, if Fe in the basic minerals ultimately exists in the form of magnetite, then the reaction equation is:

[0104]

[0105] in, The degree of chemical reaction is a function of temperature (T); during serpentinization, water molecules react with minerals in the original rock, including ferrous iron (Fe2+) in olivine. 2+ It is oxidized to trivalent iron (Fe). 3+ This process reduces water (H2O) to hydrogen (H2);

[0106] From the above reaction equation, it can be seen that if Fe eventually enters magnetite, then every 15 mol of olivine consumed can generate 1 mol of hydrogen gas, that is, the amount of hydrogen gas generated per kilogram of olivine (about 6.81 mol) is about 454 mmol.

[0107] Therefore, it can be known that approximately 227 mmol of hydrogen is produced per kilogram of mantle rock during the water-rock reaction.

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

[0109] This includes simulating the dynamic evolution of serpentinization during basin expansion and comparing it with actual observation data for verification;

[0110] The I2VIS geodynamic simulation software can be used for simulation. 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] Solve the coupled mass conservation equation, momentum conservation equation, and energy conservation equation defined in step (3) at each time step, such as... Figure 2 As shown, the solution process includes:

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

[0113] (5.2) Using a matrix method, solve the implicit linear equations of all grid nodes. Leveraging the advantages of staggered grids, obtain relatively accurate pressure and velocity components.

[0114] (5.3) Based on the velocity field calculated in step (2), determine the optimal time step for the particle's movement; usually, the maximum displacement is limited 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, usually limiting the variation to 1-20K; then, among the three given constraints - the absolute time step constraint, the optimal particle displacement step constraint, and the nodal temperature variation limit, select the smallest time step.

[0117] (5.6) Solve the temperature equation;

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

[0119] (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) to execute the next time step until the maximum iteration time or the maximum number of iterations is reached.

[0120] By solving the mass conservation equation, momentum conservation equation, and energy conservation equation in step (3), data is continuously transmitted between particles and the grid, the positions of particle points are constantly moved, and their physical parameters are changed, ultimately yielding the entire ocean basin evolution process from the continental margin rift stage to the initial mid-ocean ridge spreading stage. Specifically, this includes processes such as crustal extension, thinning, fracturing, mantle uplift, melting, and seawater intrusion.

[0121] The simulation results of serpentinization distribution, crustal thickness, deep velocity, and density structure are compared with the serpentinization zones and actual stratigraphic structures identified in step (1) using geophysical data such as reflection seismograms and submarine seismometers. 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 basin expansion. If they are inconsistent, the model parameters or serpentinization reaction parameters need to be adjusted and the simulation needs to be repeated until the simulation results reach a reasonable consistency with the actual observation data.

[0122] Step (6): Numerical simulation analysis of the relationship between crustal thickness and serpentinization quality;

[0123] Based on numerical simulation results, the relationship between crustal thickness and serpentinization quality is quantitatively analyzed and piecewise fitted; including,

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

[0125] Then, the extracted crustal thickness and serpentinization degree (mass or volume fraction) data are analyzed. Statistical methods, including correlation analysis, are used to identify the trend of serpentinization mass variation with crustal thickness, including whether there is a critical thickness, or a thickening or thinning trend. Simultaneously, data from different tectonic units are piecewise fitted using various mathematical models such as linear regression, multinomial regression, and exponential functions, and the best-fit model is selected. Specifically, the R² value and residual distribution are evaluated during the fitting process to ensure the reliability of the fitting results. The correspondence between crustal thickness and serpentinization mass for typical tectonic units is obtained, satisfying the following mathematical relationship: S = f(D, T, P); where S is the serpentinization mass or volume fraction, D is the crustal thickness, T is the temperature, and P is the pressure.

[0126] Finally, in order to enhance the universality and reliability of the research results, multiple sets of sensitivity analysis numerical simulations need to be carried out; that is, based on step (5), key geological and geophysical parameters are systematically changed, such as different extension rates, different initial lithosphere structures, and different material parameters; the simulation results under these different geological backgrounds and evolution histories are extracted, and the crustal 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 crustal thickness and the serpentinization quality.

[0127] Step (7): Estimation of total mass of natural hydrogen and prediction of its spatial distribution;

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

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

[0130] Combining the function model between different crustal thicknesses and serpentinization degrees established in step (6) through numerical simulation analysis and geophysical data verification, for each grid point or data point in the regional crustal thickness spatial distribution data, the serpentinization degree at that location is estimated using the relationship established in step (6) based on its corresponding crustal thickness value.

[0131] Using the conversion result of the serpentinization process to the natural hydrogen generation mass determined in step (4) (i.e., 227 mmol of hydrogen can be generated per kilogram of serpentine), the total mass of serpentine in the grid cell is calculated. Specifically, it is calculated by multiplying the serpentine volume fraction of the cell by the total rock volume and then by the serpentine density. The calculated serpentine mass is then multiplied by the hydrogen generation 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 dataset of natural hydrogen production is obtained.

[0134] The total mass of natural hydrogen in the study area is estimated by summing up the mass of natural hydrogen at each grid point within the entire study area or a specific favorable zone.

[0135] Although the present invention has been shown and described in the above embodiments, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which 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 in that: The implementation steps include the following: Step (1): Identify the serpentinized zones on the seabed; Based on geophysical data, areas where serpentinization may occur have been preliminarily delineated; Collect lithospheric geological data and information for the study area, and preprocess the data; Based on the longitudinal wave velocity and density anomalies, temperature field constraints, and crustal structure, potential favorable zones for serpentinization were preliminarily delineated within the study area. Step (2): Construct a numerical model; Construct a two-dimensional or three-dimensional geological model that reflects the lithospheric structure of the study area; Step (3): Construct a dynamic model; A dynamic model is constructed using the finite difference method; Step (4): Quantitative calculation of the serpentinization process of mantle peridotite and hydrogen production; Based on the chemical conditions for the serpentinization reaction of basic minerals, if Fe in the basic minerals ultimately exists in the form of magnetite, then the reaction equation is: 15Mg 1.8 Fe 0.2 SiO4+20.5H2O 7.5Mg3Si2O5(OH)4+4.5Mg (OH)2+Fe3O4+H2 (5) in, This indicates that the extent of a chemical reaction is a function of temperature T; From the above reaction equations, it can be seen that if Fe eventually enters magnetite, then every 15 mol of olivine consumed can generate 1 mol of hydrogen gas, that is, the amount of hydrogen gas generated per kilogram of olivine is about 454 mmol; the amount of hydrogen gas generated per kilogram of mantle rock through water-rock reaction is about 227 mmol. Step (5), numerical simulation of basin expansion and accompanying serpentinization process; This includes simulating the dynamic evolution of serpentinization during basin expansion and comparing it with actual observation data for verification; By solving the mass conservation equation, momentum conservation equation and energy conservation equation in step (3), data is continuously transmitted between the particles and the grid, the position of the particle points is continuously moved and their physical parameters are changed, and finally the entire ocean basin evolution process from the continental margin rift stage to the initial mid-ocean ridge expansion stage is obtained. The results of the above simulation of serpentinization distribution, crustal thickness, deep velocity and density structure are compared with the serpentinization zones and actual stratigraphic structures identified by inversion using geophysical data from reflection earthquakes and submarine seismographs in step (1). Step (6): Numerical simulation analysis of the relationship between crustal thickness and serpentinization quality; Based on numerical simulation results, the relationship between crustal thickness and serpentinization quality is quantitatively analyzed and piecewise fitted. Step (7): Estimation of total mass of natural hydrogen and prediction of its spatial distribution; By combining the results of all the aforementioned steps, the total mass of natural hydrogen in a specific region can be estimated and its spatial distribution pattern can be predicted.

2. The method for assessing the distribution and reserves of natural hydrogen on the seabed according to claim 1, characterized in that: In step (1), the data preprocessing includes, but is not limited to, data correction, noise reduction, and format unification; First, using submarine reflection seismic data and submarine seismograph data, the P-wave velocity and density structure at depth in the study area are obtained; then, combined with submarine heat flow data, the underground temperature distribution in the study area is inferred; finally, crustal structure analysis is conducted.

3. The method for assessing the distribution and reserves of natural hydrogen on the seabed according to claim 1, characterized in that: The steps described (2) Based on the favorable serpentinization zones delineated in step (1), select one or more two-dimensional models that span the continent-ocean region, or establish a three-dimensional model of the region. The above model is divided into layers; By defining an initial weak zone with wet olivine rheology and low brittle / plastic strength, the dive is initiated at an angle between 20° and 40°. Apply 3-8cm yr to the left and right sides of the model respectively. -1 Constant plate velocity; The initial thermal structure of the lithosphere is defined by a half-space cooling model; The model adopts a variable mesh partitioning scheme, using a small mesh with a resolution of 100-500 m in the serpentinized target area and a large mesh with a resolution of 1-2 km in the background area.

4. The method for assessing the distribution and reserves of natural hydrogen on the seabed according to claim 1, characterized in that: In step (3), the following formulas are used to solve the mass conservation equation, momentum conservation equation, and energy conservation equation: in, It is a velocity vector. Let P be the deviatoric stress tensor, and P be the pressure. Let g be the density and g be the acceleration due to gravity. The heat capacity is at constant pressure, and T is the temperature. Thermal conductivity; These are radiative heat, adiabatic heat, shear heat, and latent heat, respectively. Let be the real derivative of the temperature at the Lagrange point with respect to time; The serpentinization reaction process is simulated using the following thermodynamic equilibrium equation: in, This indicates the phase transition boundary of serpentine at that depth, measured in Kelvin (K). The value is used to construct the phase transition process of the material field. When the temperature at a certain grid point is lower than the temperature corresponding to that depth, If the value is met and other serpentinization conditions are satisfied, then the peridotite in this unit can undergo serpentinization; (y-sy1) represents the crustal depth of this location relative to sea level, in meters, where y represents the depth of this location in the model and sy1 represents the sea level elevation of the corresponding location in the model.

5. The method for assessing the distribution and reserves of natural hydrogen on the seabed according to claim 1, characterized in that: In step (5), the I2VIS geodynamics simulation software is used for simulation. Based on the Marker-in-cell technology, the numerical model constructed in step (2) and the control equations set in step (3) are imported into the software as simulation conditions; the process of water seeping downward and escaping upward is realized in the model. Solve the coupled mass conservation equation, momentum conservation equation and energy conservation equation defined in step (3) at each time step.

6. The method for assessing the distribution and reserves of natural hydrogen on the seabed according to claim 5, 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 constrain the grid parameters using boundary conditions; (5.2) By using the matrix method, all grid nodes are combined and their implicit linear equations are solved. Taking advantage of the staggered grid, the pressure value and velocity component are solved more accurately. (5.3) Based on the velocity field calculated in step (2), determine the optimal time step for the particle's movement; (5.4) Calculate the shear heat and adiabatic heat at the Euler nodes; (5.5) Determine the optimal time step for the temperature equation. Among the three given constraints—absolute time step constraint, optimal particle displacement step size constraint, and nodal temperature change limit—select the smallest time step. (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 effect of particle movement; determine whether the thermodynamic equilibrium equation of serpentinization reaction in step (3) is satisfied based on the temperature and pressure of the current grid point, and determine whether the peridotite of 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) to execute the next time step until the maximum iteration time or maximum number of iterations is reached.

7. The method for assessing the distribution and reserves of natural hydrogen on the seabed according to claim 1, characterized in that: Step (6) includes the following steps: First, based on the numerical simulation results that have been verified in step (5), crustal thickness data and serpentinization degree data are extracted from the entire simulation area and different evolution stages; Then, the extracted crustal thickness and serpentinization data were analyzed; through statistical methods, correlation analysis was used to identify the trend of serpentinization quality with crustal thickness; at the same time, the data of different tectonic units were piecewise fitted, and various mathematical models such as linear regression, multinomial regression and exponential function were used for fitting, and the best fitting model was selected. Finally, multiple sets of sensitivity analysis numerical simulations were carried out; based on step (5), key geological and geophysical parameters were systematically changed; simulation results under different geological backgrounds and evolution histories were extracted, and crustal thickness and serpentinization degree were compared respectively; through comparative analysis, a more robust serpentinization prediction model was established, and the uncertainty in the relationship between final crustal thickness and serpentinization quality was evaluated.

8. The method for assessing the distribution and reserves of natural hydrogen on the seabed according to claim 1, characterized in that: In step (7), the spatial distribution data of crustal thickness in the study area obtained by geophysical inversion in step (1) is used to interpolate, smooth and unify the format of the data; Combining the function model between different crustal thicknesses and serpentinization degrees established in step (6) through numerical simulation analysis and geophysical data verification, for each grid point or data point in the regional crustal thickness spatial distribution data, the serpentinization degree at that location is estimated using the relationship established in step (6) based on its corresponding crustal thickness value. Using the conversion result of the serpentinization process to the mass of natural hydrogen generated determined in step (4), calculate the total mass of serpentine in the grid cell; 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 dataset of natural hydrogen production is obtained. The total mass of natural hydrogen in the study area is estimated by summing up the mass of natural hydrogen at each grid point within the entire study area or a specific favorable zone.

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