Physical and mechanical inversion method for reconstructing kerogen molecular group

Abstract

The invention provides a physical and mechanical inversion method for reconstructing a kerogen molecular group. The method mainly comprises the following steps: 1) obtaining chemical information of the kerogen molecular group through various experiments; 2) constructing a kerogen molecule residual structure, and determining a connection relationship between the pyrolysis product micromolecules and the kerogen residual structure; (3) repeating the step (2) to obtain a kerogen macromonomer structure; (4) repeating the steps (2) and (3) to obtain a kerogen molecular group structure; and verifying the rationality of the kerogen molecular group structure by combining the experiment and the simulation result of the kerogen molecular group. The method is reasonable in conception, and the kerogen molecular group with the molecular weight meeting Gaussian distribution can be constructed.

Description

Technical Field

[0001] The invention relates to the fields of organic matter molecular reconstruction, kerogen mechanical-chemical properties, and shale oil and gas development, and in particular to a physical and mechanical inversion method for reconstructing kerogen molecular groups. Background Art

[0002] Kerogen occupies a very important and fundamental position in the process of oil and gas generation, storage and accumulation of shale oil and gas resources. However, since the chemical characteristics of kerogen depend on its biological precursors and sedimentary environment, it is an amorphous, insoluble complex macromolecular mixture containing various recombinant biodegradable structures. At present, the understanding of the molecular structure and properties of kerogen is still not clear enough, and the study of kerogen molecular structure is an internationally recognized difficult and hot issue. During the burial process, the structure of kerogen is constantly cracked and condensed to form new insoluble organic matter, which also brings great difficulties to the structural study of kerogen. Therefore, a reasonable kerogen model should combine a large number of experimental results and contain sufficient structural information, so as to truly reflect the physical and chemical evolution process of kerogen.

[0003] At present, the methods commonly used to reconstruct the average molecular structure of kerogen include random splicing, trial and error, molecular dynamics-hybrid reverse Monte Carlo (MD-HRMC), machine learning models, etc. The random splicing method is to "randomly" splice the kerogen pyrolysis products and residues to obtain the kerogen molecular structure. The reliability of its structure depends greatly on the researchers' own knowledge reserves. Ning Zhengfu et al. improved this method in "A method for constructing an average molecular structure model of kerogen": using spectral information and other information to analyze the chemical structure parameters of kerogen molecules, obtain functional group information, and then splice the kerogen carbon skeleton and functional groups. However, it does not essentially change the "random" splicing process, and it is still difficult to make the mechanical-chemical properties of the constructed kerogen molecular structure consistent with the mechanical-chemical behavior of real kerogen. The trial and error method adds verification means to the reconstruction process to improve the accuracy of the splicing step, but it also brings huge manpower and material resources to the reconstruction work, limiting the size of its reconstructed molecular model. MD-HRMC uses MD simulation to merge atoms into a series of macromolecular structures, and then quickly selects the appropriate kerogen molecular model through experimental density and other means. However, this method will have isolated atoms and cannot accurately reflect the properties of kerogen functional groups. The machine learning model uses the nuclear magnetic resonance spectrum of the molecule as input to reconstruct the two-dimensional model of kerogen, ensuring the reliability of the connection between the functional group and the matrix on the basis of rapid model construction. Due to the high complexity between molecular structures, the molecular weight of the molecular structure reconstructed by the machine learning model is very small and difficult to be representative.

[0004] Although there are many existing methods for reconstructing kerogen molecular structures, and their advantages and disadvantages can complement each other, these reconstruction methods are mainly aimed at the monomer structure of kerogen molecules. The kerogen molecular models they reconstruct are only statistically significant average molecular formulas of kerogen. The kerogen aggregates they establish are often constructed by copying and combining the same reconstructed kerogen molecular monomer structures, which ignores the fact that the molecular weight of the real kerogen molecular group is non-uniform (CN201810283845.4). Ning Zhengfu et al. considered the distribution of shale organic matter components and directly incorporated small molecular structures such as methane and water into the construction of shale composite models. However, the kerogen macromolecular model constructed by this method still belongs to the monomer structure, and the uneven distribution of kerogen molecular weight in kerogen aggregates is not considered (CN201810283851.X).

[0005] Therefore, a new method is urgently needed to construct a kerogen molecular population whose molecular weight satisfies the Gaussian distribution. Summary of the invention

[0006] In view of the technical problems existing in the above-mentioned background technology, the present invention proposes a physical and mechanical inversion method for reconstructing the structure of kerogen molecular groups, which can realize the construction of kerogen molecular groups whose molecular weight satisfies Gaussian distribution.

[0007] In order to solve the above technical problems, the present invention provides a physical and mechanical inversion method for reconstructing kerogen molecular groups, which mainly includes the following steps: (1) Elemental analysis and XPS spectral information were used to determine the average molecular formula of the entire molecular group of kerogen samples, and the quantitative relationship of the heteroatom functional groups of the entire molecular system was determined by XPS spectroscopy; the functional group type of kerogen was determined by FI-IR instrument and the content was qualitatively characterized; 13 The carbon skeleton of kerogen molecules is obtained from the results of C NMR. The characteristic molecular fragments and pyrolysis residual structures of kerogen pyrolysis are obtained through Py-GC / MS experiments. The bond dissociation energies of different functional groups are then obtained based on the existing chemical bond energy data. (2) constructing a residual structure containing a large amount of aromatic carbon and being not easy to react according to the quantitative relationship determined in the above step (1); using the characteristic molecular fragments of kerogen pyrolysis, the quantitative relationship of heteroatom functional groups and the bond dissociation energy of different functional groups obtained in the step (1), establishing a chemical bond connection between the pyrolysis small molecules and the residual structure to obtain an initial two-dimensional molecular structure; converting the constructed initial two-dimensional molecular structure from two dimensions to three dimensions, and optimizing the molecular structure to obtain a kerogen molecular monomer structure that can be used for simulation; (3) Repeat the above step (2) and adjust the kerogen molecular structure, compare the pyrolysis small molecules produced by the reaction force field molecular dynamics pyrolysis simulation with the small molecule results obtained by the Py-GC / MC experiment, and adjust the connection sites between the small molecules and the residual structure until the products obtained by the pyrolysis simulation of the kerogen molecules are consistent with the Py-GC / MS experimental results, thereby determining the monomer structure of the kerogen molecules; (4) Repeat the above steps (2)-(3) to obtain the kerogen molecule group, and verify the correctness of the kerogen molecule group by experimentally comparing the chemical properties of the kerogen molecule group.

[0008] The physical and mechanical inversion method for reconstructing kerogen molecular groups, wherein: the process of determining the quantitative relationship of the heteroatom functional groups of the entire molecular system through the XPS spectrum in step (1) is: first, the element region of the kerogen is scanned at high resolution by the XPS instrument to obtain a high-resolution narrow spectrum of the corresponding element; then, the obtained XPS high-resolution narrow spectrum is directly subjected to peak separation processing using the XPS peak separation software to obtain fitting peaks and characteristic curves of different functional groups; and then, based on the relative proportion of the area of ​​each fitting peak given by the XPS peak separation software and combined with the results of elemental analysis, the relative abundance of different elemental functional groups is quantitatively obtained.

[0009] The physical and mechanical inversion method for reconstructing kerogen molecular groups, wherein: in the step (1), a Py-GC / MS experiment is used to identify and analyze pyrolysis small molecule fragments and residual structures, and the reaction mechanism given by the pyrolysis simulation and the strength law of the dissociation energy of each functional group bond are combined to determine the connection relationship between the small molecule and the carbon skeleton.

[0010] The physical and mechanical inversion method for reconstructing kerogen molecular groups, wherein: the element analysis in step (1) refers to quantitatively measuring the element content in the kerogen sample by an element analyzer.

[0011] The physical and mechanical inversion method for reconstructing the kerogen molecule group, wherein the correctness of the kerogen molecule group is verified by experimentally comparing the chemical properties of the kerogen molecule group in step (4) by: verifying the relative content of the chemical state of the element according to the XPS experimental results; 13 The rationality of the carbon skeleton of the molecular group was verified by the C NMR spectrum and the positions and relative areas of the experimental peaks. The rationality of the chemical bonds between the pyrolysis small molecules and the residual structure of the kerogen molecular group was verified by the MD / fbMC algorithm.

[0012] The physical and mechanical inversion method for reconstructing kerogen molecular groups, wherein: in the step (4), the ensemble for thermal decomposition simulation of the kerogen molecular groups by the MD / fbMC algorithm is a constant particle number-volume-temperature ensemble, or a constant particle number-pressure-temperature ensemble.

[0013] By adopting the above technical solution, the present invention has the following beneficial effects: The physical and mechanical inversion method for reconstructing kerogen molecular groups of the present invention is rationally conceived. Based on the current advanced structural characterization methods and geochemical test experiments, accurate kerogen components and chemical structure parameters can be obtained. According to the experimental results of the components and chemical structure parameters, the kerogen molecular group model with molecular weight conforming to Gaussian distribution is reconstructed in combination with the bond dissociation energy database and molecular dynamics simulation methods. The reconstructed kerogen molecular group model is a multi-component composite heterogeneous structure, which includes the actual structure of kerogen in the mining area; the reconstructed kerogen molecular group model can not only meet the carbon skeleton information, but also make the small molecules obtained by pyrolysis consistent with the experimental results, which increases the accuracy and reliability of the molecular model and provides a reliable model basis for studying gas adsorption and displacement in kerogen and the mechanical-chemical properties of kerogen by molecular simulation and other methods.

[0014] The method of the present invention has strong portability and can be applied to the reconstruction of organic matter such as kerogen, coal and asphaltene in mining areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0016] Figure 1 A flow chart of the inversion method for reconstructing the physical mechanics of kerogen molecular groups for the present invention; Figure 2 The kerogen molecule group constructed by the present invention; Figure 3 Schematic diagram of the molecular number distribution relationship and molecular distribution amount of the kerogen molecular group constructed by the present invention ( Figure 3 (a) is the molecular quantity distribution relationship diagram of the constructed kerogen molecular group. Figure 3 (b) in the figure is the molecular distribution diagram of the constructed kerogen molecular population). DETAILED DESCRIPTION

[0017] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] The present invention is further explained below in conjunction with specific implementation modes.

[0019] like Figure 1 As shown, the physical and mechanical inversion method for reconstructing kerogen molecular groups provided in this embodiment mainly includes the following steps: S100, elemental analysis and XPS spectral information were used to determine the average molecular formula of the entire molecular group of kerogen samples, and the quantitative relationship of the heteroatom functional groups of the entire molecular system was determined by XPS (X-Ray Photoelectron Spectroscopy) spectroscopy; the functional group type of kerogen was determined by FI-IR (Fourier-Transform Infrared Spectrometry) and the content was qualitatively characterized; 13 The carbon skeleton of kerogen molecules is obtained by C NMR (Nuclear Magnetic Resonance) results. The characteristic molecular fragments and pyrolysis residual structure of kerogen pyrolysis are obtained by Py-GC / MS (Pyrolysis / Gas Chromatography / Mass Spectrometry). The bond dissociation energies of different functional groups are then obtained based on the existing chemical bond energy data (specifically, the bond dissociation energies of different functional groups are obtained by querying the existing chemical bond energy data in the "Chemical Bond Energy Data Handbook").

[0020] The heteroatoms in the above step S100 are atoms other than carbon and hydrogen.

[0021] The element analysis in the above step S100 refers to quantitatively measuring the contents of elements such as C, H, O, N and S in the sample by an element analyzer.

[0022] The FT-IR in the above step S100 is an instrument that converts the interference pattern of the research material (solid, liquid, gas) into an infrared spectrum through Fourier transform, and is used in the present invention to characterize the functional group information in kerogen; by obtaining the transmission spectrum of the kerogen sample through FT-IR, and comparing the absorption band of the functional group with the wave number of the peak position in the FT-IR transmission spectrum, the type of functional group in the kerogen can be qualitatively obtained.

[0023] The XPS in the above step S100 refers to X-ray photoelectron spectroscopy analysis, which is a quantitative spectroscopy technology based on the photoelectric effect and is used to characterize the element content and heteroatom functional group types in kerogen.

[0024] The process of determining the quantitative relationship of the heteroatom functional groups of the entire molecular system by XPS spectrum in the above step S100 is as follows: performing high-resolution scanning on the C1s, O1s, N1s, S2p and other element regions of the kerogen by the XPS instrument to obtain a high-resolution narrow spectrum of the corresponding element; using the XPS peak separation software (XPSPEAK41) to directly perform peak separation on the obtained XPS high-resolution narrow spectrum to obtain the fitting peaks and characteristic curves of different functional groups; and then according to the relative proportion of the area of ​​each fitting peak given by the XPS peak separation software, combined with the results of elemental analysis, the relative abundance of different elemental functional groups can be quantitatively obtained.

[0025] In the above step S100 13 C NMR spectrum refers to the solid carbon nuclear magnetic resonance spectrum, which can characterize the types and relative contents of functional groups of carbon elements in the structure of kerogen. 13 C NMR spectra are used to construct the carbon skeleton structure parameters of kerogen molecular groups and verify the rationality of the reconstructed molecular group structure.

[0026] The Py-GC / MS experiment in the above step S100 refers to pyrolysis-gas chromatography / mass spectrometry analysis. By analyzing the structure of the pyrolysis product, the kerogen structure information can be obtained. The main process of this experiment is: first, the kerogen sample is heated at different temperatures (650°C, 800°C, 950°C) for 60s in a vacuum / inert gas to pyrolyze the sample; then the pyrolysis product is captured, the molecular fragments of the pyrolysis product are loaded into the GC / MS analyzer, and the pyrolysis product is characterized by the NIST MS database. In the present invention, it is mainly used to identify and analyze the pyrolysis small molecule fragments and residual structures, and the connection relationship between the small molecule and the carbon skeleton is judged in combination with the reaction mechanism given by the pyrolysis simulation and the strength law of the dissociation energy of each functional group bond.

[0027] S200, constructing a residual structure containing a large amount of aromatic carbon and not easily reactive according to the quantitative relationship determined in the above step S100; establishing a chemical bond connection between the pyrolysis small molecules and the residual structure using the characteristic molecular fragments of the kerogen pyrolysis obtained in the step S100, the quantitative relationship of the heteroatom functional groups and the bond dissociation energy of different functional groups, and obtaining an initial two-dimensional molecular structure; converting the constructed initial two-dimensional molecular structure from two dimensions to three dimensions using software such as Chemdraw, and optimizing the molecular structure using methods such as density functional theory to obtain a kerogen molecular monomer structure that can be used for simulation.

[0028] In the above step 200, the XPS high-resolution narrow spectrum is separated by using XPS peak separation software (XPSPEAK41) to infer the type of functional group of the element; combined with elemental analysis, the relative content of each functional group can be obtained; by comparing FT-IR and13 C NMR spectra can determine the structural parameters of functional groups in kerogen. At the same time, the spectra can verify and calibrate each other, check the consistency between spectra, and confirm the structural parameters of each element qualitatively and quantitatively. The elements include but are not limited to C, O, N and S.

[0029] The optimization method in the above step S200 is not limited; in the present invention, the structure optimization is mainly performed using Gaussian09 software, and the optimization basis set uses B3LYP / 6-31G (d) to perform optimization calculations. When the calculation results converge, the optimization is completed. The method of structural optimization includes at least one method of geometry optimization, annealing optimization, energy minimization and relaxation.

[0030] S300, repeat the above step S200 and adjust the kerogen molecular structure, compare the pyrolysis small molecules produced during the reaction force field molecular dynamics (ReaxFF-MD) pyrolysis simulation with the small molecule results obtained by the Py-GC / MC experiment, adjust the connection sites between the small molecules and the residual structure, until the product obtained by the pyrolysis simulation of the kerogen molecules is consistent with the Py-GC / MS experimental results, thereby determining the monomer structure of the kerogen molecules.

[0031] The reaction force field molecular dynamics in the above step S300 refers to converting the empirical potential function between atoms into a bond order function to represent the energy of the molecule and the interaction between atoms, and can describe the formation and breaking of chemical bonds. In the present invention, the ReaxFF module of the Amsterdam Modeling Suite software is used, the force field is set to HCONSB.ff, the temperature is increased from 0°C to 3000°C, and the ensemble is NVT.

[0032] The reaction force field molecular dynamics simulation method in the above step S300 adopts a constant population-pressure-temperature ensemble (ie, isothermal-isobaric ensemble, NPT) or a constant population-volume-temperature ensemble (ie, canonical ensemble, NVT).

[0033] S400, repeating steps S200-S300 to obtain kerogen molecular groups; according to the following experimental and MD simulation results (i.e., the subsequent XPS experiment, 13 C spectra, MD / fbMC and other experimental results), compare the chemical properties of the kerogen molecule group to verify the correctness of the kerogen molecule group: verify the relative content of the chemical state of each element in the kerogen molecule group based on the XPS experimental results; 13The rationality of the carbon skeleton of the molecular group (including aromaticity, aliphaticity and oxygen-carbon distribution) was verified by using the C NMR spectrum and the position and relative area of ​​the experimental peaks. The rationality of the chemical bonds between the pyrolysis small molecules and the residual structure of the kerogen molecular group was verified by using the MD / fbMC (Molecular Dynamics / Force-biased Monte Carlo) algorithm. 13 C NMR spectrum of kerogen samples 13 Comparison of C NMR spectra results, adjustment of the kerogen molecular intermediate connection sites, until the kerogen molecular group is reconstructed 13 CNMR spectrum and sample spectrum Figure 1 to).

[0034] The MD / fbMC in the above step S400 is an accelerated molecular dynamics algorithm that can simulate the system under conditions close to the experimental temperature (about 800° C.) and the simulation time scale is much larger than the computer time scale, making the results of molecular dynamics simulation more realistic and reliable, and also proving the rationality of the reconstructed molecular structure.

[0035] The MD / fbMC hybrid simulation method in the above step S400 adopts a constant population-pressure-temperature ensemble (ie, isothermal-isobaric ensemble, NPT) or a constant population-volume-temperature ensemble (ie, canonical ensemble, NVT).

[0036] In this embodiment, the temperature of the MD / fbMC hybrid simulation method is set to 800°C, the ensemble is NVT, the atomic displacement is 0.3Å, the number of steps of Reaxff-MD in each cycle is 500, the number of steps of fbMC is 200, and the total simulation time is set to 100ps.

[0037] The above carbon skeleton structural parameters include but are not limited to at least one of the aromatic carbon ratio, aliphatic carbon ratio, alkane chain branching degree, aromatic substitution degree, and average aliphatic chain length.

[0038] The above carbon skeleton structural parameters are obtained by 13 The areas corresponding to the characteristic peaks of different bands in the C NMR spectrum (Table 1) were calculated as follows: Table 1

[0039] The chemical structure parameters of the kerogen samples were determined by analyzing the FT-IR spectra and the physical definitions in Table 2: Table 2

[0040] Table 3 summarizes the information that can be obtained from analyzing kerogen samples using the above methods. There is some overlap between these information, and the overlapping information is used to verify the consistency between the spectra: Table 3

[0041] The heteroatoms include at least one of O, N and S; the functional group types of the heteroatoms are determined by fitting the characteristic peaks of each spectrum; the functional group types of N atoms include at least one of nitrile, pyrrole and amino; the functional group types of S atoms include at least one of thiol, sulfide, thiophene, sulfoxide and sulfone. The oxygen-containing groups in the functional groups in kerogen include at least one of carbonyl, alcohol, carboxyl, ketone / aldehyde and ether.

[0042] The bond dissociation energy of the above functional groups can be queried through the Chemical Bond Energy Data Handbook. Table 4 lists the bond dissociation energy of some functional groups in kerogen. The larger the bond dissociation energy, the stronger the bond energy and the less likely the chemical bond is to dissociate. Conversely, the weaker the chemical bond, the more likely it is to dissociate. Chemical bonds with weak bond dissociation energy are more likely to become the connection points between molecular fragments and residual structures.

[0043] Table 4

[0044] The present invention also provides a set of three-dimensional bulk kerogen molecular group models, which are constructed by the physical and mechanical inversion method of the present invention for reconstructing kerogen molecular groups.

[0045] Example 1 The average molecular formula of the entire molecular group was determined by elemental analysis and XPS spectrum information, and the quantitative relationship of the heteroatom functional groups of the entire molecular system was determined by the results of XPS spectrum; the type of functional groups of kerogen molecular groups was determined by FT-IR and the content was qualitatively characterized; 13 The results of C NMR obtained the aromaticity, fat content, average chain length and branching degree of kerogen, and established the carbon skeleton of kerogen molecules. The average molecular formula of Ordos kerogen is about C 100 H 88 O 15 NS, the main functional groups of carbon are aromatic carbon, aliphatic carbon, CO, OC=O and C=O; the functional groups of oxygen are ether, alcohol, aldehyde, ester and fatty acid. The functional groups of nitrogen are pyridine, pyrrole and amino, and the functional groups of sulfur are thiol, thioether, thiophene and sulfone. The main photon bands are saturated hydrocarbons (2930, 2850 and 720 cm −1 ), aromatics (1620, 810 cm −1 ) and oxygen-containing structures (1280~1050 cm−1 ). Aromatic carbon and aliphatic carbon are approximately 56% and 42%, respectively.

[0046] Combining FT-IR, elemental analysis, XPS and 13 C NMR results, the residual structure is first constructed. The pyrolysis small molecule structure with a relative peak area greater than 1% of Py-GC / MS is selected as the access molecule, and the access molecule mass is qualitatively determined based on the peak area. Using the pyrolysis product structure information and its semi-quantitative information, combined with the molecular bond dissociation energy database, the site with the lowest bond dissociation energy is selected to establish the chemical bond connection between the small molecule and the residual structure. The pyrolysis mechanism of kerogen shows that the cleavage site of kerogen often appears in places with weak bond dissociation energy. Taking the position with the lowest bond dissociation energy as the connection site can ensure the rationality of the pyrolysis of the kerogen molecular structure.

[0047] The kerogen molecular group reconstructed by the physical mechanics inversion method consists of 15 kerogen molecular monomers: C 100 ~C 200 , C 200 ~C 300 , C 300 ~C 400 , C 400 ~C 600 The kerogen molecules of the kerogens are 5, 4, 4 and 2 respectively. In order to verify the molecular information more realistically, the existing C 800+ The molecular distribution represents the sum of the relative molecular weights of each group of molecules in the above five groups, and the average molecular weight is the average molecular weight of each group. Figure 3 As shown in the figure, the relationship between the relative molecular mass distribution and the number of molecules of kerogen molecule monomers can be analyzed and fitted, which shows that the molecular weight of the molecular group can be represented by a normal distribution curve, which has diversity and meets the characteristics of macromolecules. 300 ~C 400 The mass content of the constructed molecules is the highest. The structural information of the constructed molecules is: the average molecular mass of the molecular group is 4903.60 g / mol (it is believed that the average molecular weight of kerogen is 4000~5000g / mol), and the total molecular formula is C 5061 H 4535 N 73 O 691 S 32, the H / C atomic ratio is 0.90, the O / C atomic ratio is 0.14, the N / C atomic ratio is 0.014, and the S / C atomic ratio is 0.0063. This result is similar to the elemental analysis result. Combined with the experimental information, the structure of the molecular group is continuously adjusted, and finally the kerogen molecular group is obtained by the physical inversion method, as shown in Figure 2. Then, the structure of the entire kerogen molecular group is verified.

[0048] First, the rationality of the molecular groups is verified by the relative content of the chemical state of kerogen elements. For example, the main functional groups of sulfur in kerogen are -S-, sulfoxide (-S(=O)-) and sulfone (-S(=O)2-S). The experimental results show that the proportions of the three structures are 60%, 4% and 36% respectively, while the results of the molecular model are 65%, 4% and 31%. This shows that the molecular groups of the kerogen molecular group constructed by the physical mechanics inversion method are very reasonable. Then, the total molecular group is obtained by MestReNova software. 13 The predicted C NMR spectrum is compared with the experimental spectrum. The predicted NMR spectrum is consistent with the experimental peak position and the relative area is close, which verifies the rationality of the carbon skeleton of the molecular group (including aromaticity, aliphatic degree and oxygen-carbon distribution). Finally, the rationality of the chemical bond between the experimentally obtained pyrolysis molecular structure and the residual structure of kerogen is verified by the MD / fbMC mixed simulation method. The pyrolysis temperature is set to 800°C and the atomic displacement is 0.3Å. The number of steps in each cycle of Reaxff-MD is 500, the number of steps in fbMC is 200, and the total simulation time is 100ps. The rationality of the molecular structure is verified by analyzing the composition of small molecule fragments obtained from the pyrolysis simulation of kerogen molecules. The product of the pyrolysis simulation is consistent with the small molecule structure connected to the kerogen molecule obtained experimentally, indicating that the chemical bond setting is reasonable.

[0049] The physical and mechanical inversion method is based on a large amount of experimental information, combined with pyrolysis experiments and simulations, to construct the molecular structure of kerogen. The constructed molecules not only meet the heteroatom functional group information and carbon skeleton information, but the small molecular fragments obtained by pyrolysis are also consistent with the experimental results. Compared with traditional methods, the molecular bonds constructed by the physical and mechanical inversion method are more reasonable, and the structure contains the actual characteristic structure of kerogen in the mining area. Therefore, the accuracy and reliability of the molecules are improved.

[0050] The present invention has a reasonable concept and can realize the construction of a kerogen molecule group whose molecular weight satisfies Gaussian distribution.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A physical and mechanical inversion method for reconstructing kerogen molecular groups, characterized in that , mainly including the following steps: Step 1: Use elemental analysis and XPS spectral information to determine the average molecular formula of the entire molecular group, and use XPS spectroscopy to determine the quantitative relationship of the heteroatom functional groups of the entire molecular system; use FI-IR instrument to determine the functional group type of kerogen and qualitatively characterize the content; 13 The carbon skeleton of kerogen molecules is obtained from the results of C NMR. The characteristic molecular fragments and pyrolysis residual structures of kerogen pyrolysis are obtained through Py-GC / MS experiments. The bond dissociation energies of different functional groups are then obtained based on the existing chemical bond energy data. Step 2: construct a residual structure containing a large amount of aromatic carbon and not easy to react according to the quantitative relationship determined in the above step 1; use the characteristic molecular fragments of kerogen pyrolysis obtained in the step 1, the quantitative relationship of heteroatom functional groups and the bond dissociation energy of different functional groups to establish the chemical bond connection between the pyrolysis small molecules and the residual structure to obtain an initial two-dimensional molecular structure; convert the constructed initial two-dimensional molecular structure from two dimensions to three dimensions, and optimize the molecular structure to obtain a kerogen molecular monomer structure that can be used for simulation; Step 3: Repeat step 2 above and adjust the kerogen molecular structure. Compare the pyrolysis small molecules generated during the reaction force field molecular dynamics pyrolysis simulation with the small molecule results obtained from the Py-GC / MC experiment. Adjust the connection sites between the small molecules and the residual structure until the products obtained from the pyrolysis simulation of the kerogen molecules are consistent with the Py-GC / MS experimental results, thereby determining the monomer structure of the kerogen molecules. Step 4: Repeat steps 2-3 above to obtain the kerogen molecule group, and verify the correctness of the kerogen molecule group by experimentally comparing the chemical properties of the kerogen molecule group.

2. The physical and mechanical inversion method for reconstructing kerogen molecular groups according to claim 1, characterized in that: The process of determining the quantitative relationship of the heteroatom functional groups of the entire molecular system by XPS spectrum in step 1 is as follows: first, the element region of the kerogen is scanned at high resolution by the XPS instrument to obtain a high-resolution narrow spectrum of the corresponding element; then, the obtained XPS high-resolution narrow spectrum is directly subjected to peak separation processing by using the XPS peak separation software to obtain the fitting peaks and characteristic curves of different functional groups; and then, the relative abundance of different element functional groups is quantitatively obtained according to the relative proportion of the area of ​​each fitting peak given by the XPS peak separation software, combined with the results of elemental analysis.

3. The physical and mechanical inversion method for reconstructing kerogen molecular groups according to claim 1, characterized in that: In step 1, a Py-GC / MS experiment is used to identify and analyze the pyrolysis small molecule fragments and residual structures, and the connection relationship between the small molecule and the carbon skeleton is determined by combining the reaction mechanism given by the pyrolysis simulation and the strength law of the dissociation energy of each functional group bond.

4. The physical and mechanical inversion method for reconstructing kerogen molecular groups according to claim 1, characterized in that: The elemental analysis in step 1 refers to quantitatively measuring the element content in the kerogen sample by an elemental analyzer.

5. The physical and mechanical inversion method for reconstructing kerogen molecular groups according to claim 1, characterized in that: The specific method of verifying the correctness of the kerogen molecule group by comparing the chemical properties of the kerogen molecule group in step 4 is: verifying the relative content of the chemical state of the element according to the XPS experimental results; 13 The rationality of the carbon skeleton of the molecular group was verified by the C NMR spectrum and the positions and relative areas of the experimental peaks. The rationality of the chemical bonds between the pyrolysis small molecules and the residual structure of the kerogen molecular group was verified by the MD / fbMC algorithm.

6. The physical and mechanical inversion method for reconstructing kerogen molecular groups according to claim 5, characterized in that: In step 4, the ensemble for pyrolysis simulation of kerogen molecular groups by the MD / fbMC algorithm is a constant particle number-volume-temperature ensemble, or a constant particle number-pressure-temperature ensemble.

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