Method for evaluating methane release flux caused by hydrate decomposition based on environmental fluctuation
By fitting global sea level altitude records and simulating ocean bottom water temperature changes, combined with hydrate phase transformation models, the methane flux decomposition due to hydrate instability in global marine sediments was evaluated, solving the problem of the inability of existing technology to accurately evaluate methane leakage at the global scale, and achieving a more comprehensive assessment of the marine carbon leakage process.
Patent Information
- Application Number
- CN202411813975.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-11
- Publication Date
- 2025-03-28
AI Technical Summary
The prior art cannot accurately evaluate the hydrate instability decomposition of methane fluxes induced by temperature and sea level rise on the global scale, and cannot fully understand the impact of marine sediment carbon leakage processes on global greenhouse effects.
By fitting global sea level height records, the changes in static pressure in sediments in different regions around the world were simulated; combined with global ocean bottom water temperature and geothermal gradient distribution data, the methane flux explained by hydrate instability in global ocean sediments under rising sea level and bottom water temperature were simulated.
An accurate assessment of the methane fluctuation of marine hydrate distribution under sea level and bottom water temperature fluctuations is achieved, and a more comprehensive understanding of the impact of marine carbon leakage processes on global carbon cycle and greenhouse effects is achieved.
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Figure CN119724428A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the field of marine sediment carbon cycle and marine geological research, and specifically relates to a method for evaluating the methane release flux of hydrate decomposition caused by environmental fluctuations. Background Art
[0002] The ocean is the world's largest reservoir of hydrates. The overlapping effects of ocean bottom water temperature and sea level rise profoundly affect the stability of hydrates in sediments. Considering the low temperature and high pressure conditions in sediments, methane is mainly stored in sediments in the form of solid hydrates. However, since the end of the last ice age, changes in global sea level and ocean bottom water temperature have destroyed the stability of hydrates in sediments, resulting in the discovery of a large number of methane decomposition phenomena due to hydrate instability around the world.
[0003] At present, underwater exploration technology (such as seabed crawling robots) is mainly used to observe and evaluate the methane release flux at a certain leakage point over a period of time. This method can only evaluate the carbon leakage process of sediments within a limited time and space, and cannot accurately evaluate the scale of carbon leakage in marine sediments over a longer time scale globally. Therefore, constructing a model of methane release from hydrate instability in global sediments under the conditions of rising sea level and bottom water temperature can not only accurately evaluate the impact of various environmental fluctuations on the stability of hydrates in marine sediments, but also has important significance for evaluating the impact of marine carbon leakage processes on the global greenhouse effect. Summary of the invention
[0004] In order to solve the problem that existing exploration methods cannot accurately evaluate the methane flux of hydrate decomposition induced by temperature and sea level rise on a global scale, the present invention proposes a method for evaluating the methane release flux of hydrate decomposition caused by environmental fluctuations. By fitting the global sea level height record, the changes in static pressure in sediments in different regions of the world are simulated; combined with the global ocean bottom water temperature and geothermal gradient distribution data, according to the hydrate phase transformation model, the methane flux released due to hydrate decomposition in global marine sediments under the conditions of rising sea level and bottom water temperature is simulated, so as to provide technical support for comprehensively evaluating the impact of sediment methane leakage process on the marine ecological environment, and the impact of the marine carbon cycle process on the global carbon cycle.
[0005] The present invention is implemented by adopting the following technical solution: a method for evaluating the methane release flux of hydrate decomposition caused by environmental fluctuations, comprising the following steps: Step A, determining the change in static pressure in marine sediments caused by sea level change; Collect global sea level data over the global geological period, select the binomial fitting method to simulate the changes in sea level over the geological period; and simulate the changes in sediment static pressure over time when the sea level changes based on the binomial expression of sea level change over time obtained by fitting; Step B, determining the temperature field changes in the marine sediments caused by the bottom water temperature changes; Collect the ocean bottom water temperature data obtained by oxygen isotopes in the global marine geological period, or the global ocean bottom water temperature data obtained by the International Ocean Organization through sensors in the past half century; and simulate the temporal and spatial distribution of the temperature field in the global ocean sediments based on the obtained global ocean bottom water temperature data and the geothermal gradient data in the global ocean sediments; Step C, combining the static pressure and temperature field changes determined in Step A and Step B, determining the methane flux released by the decomposition of marine hydrates induced by the fluctuation of sea level and bottom water temperature; (1) Based on the temperature field and pressure field distribution in the global ocean sediments obtained in step A and step B, combined with the hydrate phase distribution curve, simulate the amount of solid hydrate resources in the global ocean sediments at a certain time; (2) Calculate the amount of hydrate resources in global marine sediments at different times, compare the differences at different times, and then evaluate the methane flux released by the decomposition of marine hydrates when the sea level and bottom water temperature fluctuate.
[0006] Furthermore, in step A, the simulation of the change in sea level during the geological period is implemented in the following manner: The collected sea level data are plotted in a graph with time as the horizontal axis and sea level as the vertical axis. The change of sea level over time is simulated by binomial fitting method, as follows: (1) Where h(t) represents the height of the sea level at time t, and f i is the binomial fitting coefficient; this scheme uses the least squares method based on the target minimization method to obtain each f i The specific values of the coefficients are as follows: (2) In the formula, S(t i ) indicates t i The actual value of the sea level height at time, h(t i ) indicates t i The fitted value of the sea level height at time is obtained by adjusting f in formula (1) i The size of the coefficient is used to minimize λ, thereby obtaining the optimal binomial expression for simulating the change of sea level height over time.
[0007] Furthermore, in the step A, when simulating the change of the static pressure of the sediment with time when the sea level changes, the water depth of various places in the global ocean at different times and the static pressure in the sediment are determined based on the obtained curve of the change of the sea level height with time, which is specifically expressed as follows: (3) Where P(t,i) represents the static pressure at depth i in ocean station i at time t, and Z i represents the water depth at station i, h0 represents the current sea level, h0-h(t) represents the correction of the water depth at station i due to the change in sea level, φ represents the porosity, ρ s Represents the net density of sediment.
[0008] Furthermore, in step B, the change of ocean bottom water temperature in the geological period can be searched in published academic papers by searching for keywords such as paleo-ocean environment, global surface sediment oxygen isotope change in the geological period, etc. Global ocean geothermal gradient data can be obtained from the global heat flow database.
[0009] Furthermore, in step B, the simulation of the change in the temperature field in the global ocean sediments is specifically expressed as follows: (4) In the formula, T represents the temperature distribution in the sediment, α represents the geothermal gradient, and T BW represents the bottom water temperature. Substituting the bottom water temperature and geothermal gradient data at different ocean stations into Formula 4, the distribution of temperature field in marine sediments can be obtained.
[0010] Furthermore, in step C, the simulation of the amount of solid-phase hydrate resources in global marine sediments at a certain moment is implemented in the following manner: Due to the changes in pressure and temperature fields in marine sediments, hydrates appear in the form of solid and gaseous methane. Therefore, this scheme uses the following hydrate phase curve to represent the distribution of hydrate stability zones in sediments. The specific method is as follows: (5) Where P e Characterizes the equilibrium pressure that maintains hydrate stability, T e It represents the equilibrium temperature for maintaining hydrate stability, where the coefficients e1 and e2 are as follows: (6) Substituting the distribution of pressure field in global ocean sediments obtained in step A and the distribution of temperature in global ocean sediments obtained in step B into formula (5), the length (L) of the hydrate stability zone at different times in each station in the ocean sediment can be calculated. Based on the length (L) of the hydrate stability zone at each station in the global ocean, the temperature at different times (t i ) Hydrate resources at each site (M(t i )), as follows:
[0011] (7) Among them, the function f(OM, w) represents the influence of organic matter content (OM) and sedimentation rate (w) on the hydrate resources within the site.
[0012] Furthermore, in step C, the methane flux released by decomposition of marine hydrates when the sea level and bottom water temperature fluctuate is evaluated by the following method: Combined with the amount of hydrate in the sediments of a single site at time t, the amount of hydrate in the global ocean sediments at time t can be calculated. i Hydrate resources at TM(t i )): (8) In the formula, S represents the global ocean area. Based on the data of sea level rise and bottom water temperature rise at different time points, the temperature rise at different times (for example, t i Time and t j The difference between the two can be used to estimate the methane flux (Flux) released by the decomposition of marine hydrates when the sea level and bottom water temperature rise, as follows: (9) Compared with the prior art, the advantages and positive effects of the present invention are: (1) Fully consider the impact of sea level changes and global temperature changes over geological time on the marine sedimentary environment and their impact on the stability of hydrates in global marine sediments; simulate sea level changes over geological time by using the binomial fitting method, combine global ocean bottom water temperature data and ocean geothermal gradient data, and comprehensively evaluate the methane flux released by the decomposition of marine hydrates when the sea level and bottom water temperature rise based on the hydrate phase change curve; (2) It effectively overcomes the defect that the current seabed observation technology is still unable to fully detect the seabed methane leakage flux on a regional or global scale. It can not only quantify the impact of sea level changes or bottom water temperature fluctuations on the amount of marine hydrate resources, but also help calculate the seabed methane release flux caused by environmental fluctuations on a regional or global scale. It has important scientific significance for improving the understanding of the carbon exchange mechanism between the lithosphere and the ocean hydrosphere and further understanding the co-evolution of marine geology, environment and biology. BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Figure 1 The figure is a flow chart of the evaluation method according to an embodiment of the present invention. DETAILED DESCRIPTION
[0014] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described below in conjunction with the accompanying drawings and embodiments. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can also be implemented in other ways different from those described herein. Therefore, the present invention is not limited to the specific embodiments disclosed below.
[0015] Embodiment, a method for evaluating the methane release flux of hydrate decomposition caused by environmental fluctuations, such as Figure 1 As shown, the following steps are included: Step A: Determine the change in static pressure in marine sediments caused by sea level change: (1) Collect global sea level data over the geological period, and use the binomial fitting method to simulate the changes in sea level over the geological period; plot the collected sea level data in a graph with time as the horizontal axis and sea level as the vertical axis, and use the binomial fitting method to simulate the changes in sea level over time: (1) Where h(t) represents the height of the sea level at time t, and f i is the binomial fitting coefficient. This scheme uses the least squares method based on the target minimization method to obtain each f i The specific values of the coefficients are as follows: (2) In the formula, S(t i ) indicates t i The actual value of the sea level height at time, h(t i ) indicates t i The fitted value of the sea level height at time is obtained by adjusting f in formula (1) i The size of the coefficient is used to minimize λ, thereby obtaining the optimal binomial expression for simulating the change of sea level height over time.
[0016] (2) Based on the fitted expression of sea level height changing with time, a model of the change of sediment static pressure with time when sea level changes is constructed to represent the water depth in various parts of the global ocean at different times and the static pressure in the sediment. The specific expression is as follows: (3) Where P(t,i) represents the static pressure at depth i in ocean station i at time t, and Z i represents the water depth at station i, h0 represents the current sea level, h0-h(t) represents the correction of the water depth at station i due to the change in sea level, φ represents the porosity, ρ s Represents the net density of sediment.
[0017] Step B, determining the temperature field changes in the marine sediments caused by the bottom water temperature changes; Collect the ocean bottom water temperature data obtained by oxygen isotopes during the global marine geological period, or the global ocean bottom water temperature data obtained by the International Ocean Organization through sensors in the past half century; among them, the changes in ocean bottom water temperature during the geological period can be searched in published academic papers, and searched by searching for keywords such as ancient marine environment, changes in oxygen isotopes of global surface sediments during the geological period, and the global ocean geothermal gradient data can be obtained from the global heat flow database.
[0018] Based on the global ocean bottom water temperature data obtained, combined with the data of geothermal gradient in global ocean sediments, the temporal and spatial distribution of the temperature field in global ocean sediments is simulated, as follows: (4) In the formula, T represents the temperature distribution in the sediment, α represents the geothermal gradient, and T BW represents the bottom water temperature. Substituting the bottom water temperature and geothermal gradient data at different ocean stations into Formula 4, the distribution of temperature field in marine sediments can be obtained.
[0019] Step C, combining the static pressure and temperature field changes determined in Step A and Step B, determining the methane flux released by the decomposition of marine hydrates induced by the fluctuation of sea level and bottom water temperature; (1) Based on the distribution of temperature and pressure fields in global marine sediments, combined with the hydrate phase transformation model, the amount of solid hydrate resources in global marine sediments at a certain moment is simulated; due to the changes in pressure and temperature fields in marine sediments, hydrates appear in the form of solid and gaseous methane. Therefore, this embodiment represents the distribution of hydrate stability zones in sediments through the following hydrate phase curve:
[0020] (5) Where P e Characterizes the equilibrium pressure that maintains hydrate stability, T e It represents the equilibrium temperature for maintaining hydrate stability, where the coefficients e1 and e2 are as follows: (6) Substituting the distribution of pressure field in global ocean sediments obtained in step A and the distribution of temperature field in global ocean sediments obtained in step B into formula (5), the length (L) of the hydrate stability zone at different times in each station in the ocean sediment can be calculated. Based on the length (L) of the hydrate stability zone at each station in the global ocean, the temperature at different times (t i ) Hydrate resources at each site (M(t i )):
[0021] (7) The amount of hydrate resources in marine sediments is not only related to the thickness of the hydrate stability zone, but also the content of organic matter (OM) and sedimentation rate (w) in the sediments are important factors affecting the amount of hydrate resources. Therefore, the function f(OM, w) is introduced in Formula 7 to characterize the influence of the content of organic matter (OM) and sedimentation rate (w) on the amount of hydrate resources in the site.
[0022] (2) Combined with the hydrate resources in the sediments of a single site at time t, the hydrate resources in the global marine sediments at different times are calculated, and the hydrate resources in the global marine sediments at time t are recorded as i Hydrate resources at TM(t i )) is as follows: (8) In the formula, S represents the global ocean area. Based on the data of sea level rise and bottom water temperature rise at different time points, we can solve the i Time and t j The amount of hydrate in global marine sediments at different times is then compared with the difference in hydrate resources at different times. The difference between the two can be used to estimate the methane flux (Flux) released by the decomposition of marine hydrates when the sea level and bottom water temperature rise, as follows:
[0023] (9) This enables the assessment of the methane flux released by the decomposition of ocean hydrates when sea level and bottom water temperatures fluctuate.
[0024] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.
Claims
1. A method for evaluating the methane release flux from hydrate decomposition caused by environmental fluctuations, characterized in that: The following steps are involved: Step A, determining the change in static pressure in marine sediments caused by sea level change; Based on the global sea level data in the global geological period, the changes in sea level in the geological period are fitted, and then the changes in the static pressure of sediments with time when the sea level changes are simulated; Step B, determining the temperature field changes in the marine sediments caused by the bottom water temperature changes; Based on the global ocean bottom water temperature data and the geothermal gradient data in the global ocean sediments, simulate the temporal and spatial distribution of the temperature field in the global ocean sediments; Step C, combining the static pressure and temperature field changes determined in step A and step B, determining the methane flux released by the decomposition of marine hydrates caused by the fluctuation of sea level and bottom water temperature; (1) Based on the changes in the temperature field and static pressure in the global marine sediments obtained in step A and step B, combined with the hydrate phase distribution curve, simulate the amount of solid-phase hydrate resources in the global marine sediments at a certain time; (2) Calculate the amount of hydrate resources in global marine sediments at different times, compare the differences at different times, and then evaluate the methane flux released by the decomposition of marine hydrates when the sea level and bottom water temperature fluctuate.
2. The method for evaluating the methane release flux of hydrate decomposition caused by environmental fluctuations according to claim 1, characterized in that: In step A, the simulation of the change of sea level in geological period is implemented in the following way: The curve of sea level data changing with time is plotted with time as the horizontal axis and sea level as the vertical axis. The change of sea level with time is simulated by binomial fitting method: (1) Where h(t) represents the height of the sea level at time t, and f i is the binomial fitting coefficient; The objective minimization method based on the least squares method is used to obtain the i The specific values of the coefficients are: (2) In the formula, S(t i ) indicates t i The actual value of the sea level height at time, h(t i ) indicates t i The fitted value of the sea level height at time is obtained by adjusting f in formula (1) i The size of the coefficient is used to minimize λ, thereby obtaining the optimal expression for simulating the change of sea level height over time.
3. The method for evaluating methane release flux from hydrate decomposition caused by environmental fluctuations according to claim 1, characterized in that: In step A, based on the obtained curve of sea level height changing with time, the change of static pressure of sediments with time when the sea level changes is simulated to determine the water depth of various places in the global ocean and the static pressure in the sediments at different times: (3) Where P(t,i) represents the static pressure at depth i in ocean station i at time t, and Z i represents the water depth at station i, h0 represents the current sea level, h0-h(t) represents the correction of the water depth at station i due to the change in sea level, φ represents the porosity, ρ s Represents the net density of sediment.
4. The method for simulating and evaluating the methane flux released by decomposition of marine natural gas hydrate according to claim 1, characterized in that: In step B, the simulation of the change of the temperature field in the global ocean sediment is specifically expressed as follows: (4) In the formula, T represents the temperature distribution in the sediment, α represents the geothermal gradient, and T BW represents the bottom water temperature. Substituting the bottom water temperature and geothermal gradient data at different ocean stations into Formula 4, the distribution of temperature field in marine sediments can be obtained.
5. The method for simulating and evaluating the methane flux released by decomposition of marine natural gas hydrate according to claim 1, characterized in that: In step C, the simulation of the amount of solid-phase hydrate resources in global marine sediments at a certain moment is implemented in the following manner: The distribution of hydrate stability zones in sediments is shown by the hydrate phase curve: (5) Where P e Characterizes the equilibrium pressure that maintains hydrate stability, T e It represents the equilibrium temperature for maintaining hydrate stability, where the coefficients e1 and e2 are as follows: (6) Substitute the distribution of pressure field in global ocean sediments obtained in step A and the distribution of temperature in global ocean sediments obtained in step B into formula (5) to calculate the length L of the hydrate stability zone at different times in each station in the ocean sediments; based on the length L of the hydrate stability zone at each station in the global ocean, estimate the temperature at different times t i The amount of hydrate resources M(t i ): (7) Among them, the function f(OM, w) represents the influence of the organic matter content OM and the sedimentation rate w on the hydrate resources within the site.
6. The method for simulating and evaluating the methane flux released by decomposition of marine natural gas hydrate according to claim 1, characterized in that: In step C, the methane flux released by decomposition of marine hydrates when the sea level and bottom water temperature fluctuate is evaluated by the following method: Combined with the hydrate resources in the sediments of a single station at time t, the hydrate resources in the global ocean sediments at time t are calculated. i Hydrate resources TM(t i ): (8) In the formula, S represents the global ocean area. Based on the data of sea level rise and bottom water temperature rise at different time points, the i With t j The amount of hydrate resources in global marine sediments at t i Time and t j The difference in time is used to estimate the methane flux released by the decomposition of ocean hydrates when the sea level and bottom water temperatures rise, as follows: (9) Where Flux represents the methane flux released by the decomposition of ocean hydrates when the sea level and bottom water temperature rise, M(t i ) represents the time t i The amount of hydrate resources at each site, M(t j ) represents the time t j The amount of hydrate resources at each site.