A physical and mechanical inversion method for reconstructing kerogen molecular groups

Abstract

The present invention provides a physical and mechanical inversion method for reconstructing kerogen molecular groups, mainly including: 1) obtaining chemical information of kerogen molecular groups through various experiments; 2) constructing the residual structure of kerogen molecules and determining the connection relationship between small molecules of pyrolysis products and the residual structure of kerogen; 3) repeating step (2) to obtain the monomer structure of macromolecular kerogen; 4) repeating steps (2) and (3) to obtain the structure of kerogen molecular groups; combining the experiments and the simulation results of kerogen molecular groups to verify the rationality of the structure of kerogen molecular groups. The present invention has a reasonable concept and can realize the construction of kerogen molecular groups with molecular weights satisfying Gaussian distribution.

Description

Technical Field

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

[0002] Kerogen occupies a very important and fundamental position in the processes of oil and gas generation, reservoir formation 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 and insoluble complex macromolecular mixture containing various recombined biodegradation structures. At present, the understanding of the molecular structure and properties of kerogen is still not clear enough, and the research on the molecular structure of kerogen is a difficult and hot issue recognized internationally. During the burial process, the structure of kerogen continuously cracks and condenses to form new insoluble organic matter, which also brings great difficulties to the study of the structure 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 the random splicing method, the trial-and-error method, the Molecular Dynamics-Hybrid Reverse Monte Carlo method (MD-HRMC), machine learning models, etc. The random splicing method "randomly" splices between the pyrolysis products and residues of kerogen to obtain the molecular structure of kerogen, and the reliability of its structure greatly depends on the knowledge reserve of the researchers themselves. Ning Zhengfu et al. improved this method in "A Method for Constructing an Average Molecular Structure Model of Kerogen": using information such as spectra to analyze the chemical structure parameters of kerogen molecules and obtain functional group information, so as to splice the carbon skeleton and functional groups of kerogen. However, in essence, it does not change the "random" splicing process, and it is still difficult to make the mechanical-chemical properties of the constructed kerogen molecular structure conform to 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 losses of manpower and material resources to the reconstruction work and limits 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 a suitable 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. Machine learning models use the nuclear magnetic resonance spectrum of molecules as input to reconstruct the two-dimensional model of kerogen, ensuring the reliability of the connection between functional groups and the matrix on the basis of quickly constructing the model. Due to the high complexity between molecular structures, the molecular structure reconstructed by machine learning models has a very small molecular weight and is difficult to be representative.

[0004] Although the existing methods for reconstructing the molecular structure of kerogen are diverse and their respective advantages and disadvantages can complement each other, these reconstruction methods mainly focus on the monomer structure of kerogen molecules. The kerogen molecular models they reconstruct are only the average molecular formulas of kerogen with statistical significance. The kerogen aggregates they establish often replicate and combine the same reconstructed kerogen molecular monomer structures, which ignores the fact that the molecular weights of real kerogen molecular groups are non-uniform (CN201810283845.4). Ning Zhengfu et al. considered the distribution problem of shale organic matter components and directly incorporated small molecule structures such as methane and water into the construction of the shale composite model. However, the kerogen macromolecular model constructed by this method still belongs to the monomer structure and does not consider the characteristic of uneven molecular weight distribution of kerogen in the kerogen aggregate (CN201810283851.X).

[0005] Therefore, there is an urgent need for a new method to construct a kerogen molecular group with a molecular weight that satisfies the Gaussian distribution. Summary of the Invention

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

[0007] To solve the above technical problems, a physical and mechanical inversion method for reconstructing a kerogen molecular group provided by the present invention mainly includes the following steps:

[0008] (1) For the kerogen sample, use elemental analysis and XPS spectral information to determine the average molecular formula of the entire molecular group, and determine the quantitative relationship of heteroatom functional groups in the entire molecular system through XPS spectroscopy; use a FI-IR instrument to determine the types of functional groups of kerogen and qualitatively characterize the content; obtain the carbon skeleton of the kerogen molecule through the results of 13 13C NMR; obtain the characteristic molecular fragments and pyrolysis residual structures of kerogen pyrolysis through Py-GC / MS experiments; and then obtain the bond dissociation energies of different functional groups based on the existing chemical bond energy data;

[0009] (2) Construct a structure containing a large amount of aromatic carbon and residual structures that are not easily reactive according to the quantitative relationship determined in the above step (1); use the characteristic molecular fragments of kerogen pyrolysis, the quantitative relationship of heteroatom functional groups, and the bond dissociation energies of different functional groups obtained in the step (1) to establish chemical bond connections between pyrolysis small molecules and residual structures to obtain an initial two-dimensional molecular structure; convert the constructed initial two-dimensional molecular structure from two-dimensional to three-dimensional and optimize the molecular structure to obtain a kerogen molecular monomer structure that can be used for simulation;

[0010] (3) Repeat the above step (2) and adjust the molecular structure of kerogen. Compare the pyrolysis small molecules generated during the reactive 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 pyrolysis products obtained from the kerogen molecular pyrolysis simulation are consistent with the results of the Py-GC / MS experiment, thereby determining the monomer structure of the kerogen molecule;

[0011] (4) Repeat the above steps (2)-(3) to obtain a kerogen molecular group, and verify the correctness of the kerogen molecular group by experimentally comparing the chemical properties of the kerogen molecular group.

[0012] In the physical and mechanical inversion method for reconstructing the kerogen molecular group, wherein: the process of determining the quantitative relationship of heteroatom functional groups in the entire molecular system by XPS spectroscopy in step (1) is as follows: first, perform high-resolution scanning on the elemental region of the kerogen by an XPS instrument to obtain high-resolution narrow spectra of the corresponding elements; then directly perform peak fitting on the obtained XPS high-resolution narrow spectra using XPS peak separation software to obtain fitting peaks and characteristic curves of different functional groups; then, according to the relative proportion of the area of each fitting peak given by the XPS peak fitting software, combined with the results of elemental analysis, quantitatively obtain the relative abundances of different elemental functional groups.

[0013] In the physical and mechanical inversion method for reconstructing the kerogen molecular group, wherein: in step (1), the Py-GC / MS experiment is used to identify and analyze pyrolysis small molecule fragments and residual structures, and combined with the reaction mechanism given by the pyrolysis simulation and the strength law of bond dissociation energy of each functional group to judge the connection relationship between the small molecules and the carbon skeleton.

[0014] In the physical and mechanical inversion method for reconstructing the kerogen molecular group, wherein: the elemental analysis in step (1) refers to quantitatively measuring the elemental content in the kerogen sample by an elemental analyzer.

[0015] In the physical and mechanical inversion method for reconstructing the kerogen molecular group, wherein, in step (4), the specific method of verifying the correctness of the kerogen molecular group by experimentally comparing the chemical properties of the kerogen molecular group is as follows: verify the relative content of the chemical state of elements according to the XPS experiment results; verify the rationality of the carbon skeleton of the molecular group according to the comparison of the 13 C NMR spectra and the positions and relative areas of experimental peaks; perform pyrolysis simulation on the kerogen molecular group by the MD / fbMC algorithm to verify the rationality of the chemical bonds between the pyrolysis small molecules and the residual structure in the Py-GC / MS experiment.

[0016] The physical and mechanical inversion method for the reconstructed kerogen molecular group, wherein: in the step (4), the ensemble for pyrolysis simulation of the kerogen molecular group by the MD / fbMC algorithm is the constant particle number-volume-temperature ensemble or the constant particle number-pressure-temperature ensemble.

[0017] Adopting the above technical solution, the present invention has the following beneficial effects:

[0018] The physical and mechanical inversion method for the reconstructed kerogen molecular group of the present invention is reasonably conceived. Based on the current advanced structure characterization means 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, combined with the bond dissociation energy database and molecular dynamics simulation means, a kerogen molecular group model with a molecular weight conforming to the Gaussian distribution is reconstructed. The reconstructed kerogen molecular group model is a heterogeneous structure composed of multiple components, including the actual structure of the kerogen in the mining area; the reconstructed kerogen molecular group model can not only satisfy the carbon skeleton information, but also make the small molecules obtained by pyrolysis consistent with the experimental results, increasing the accuracy and reliability of the molecular model, and providing a reliable model basis for studying gas adsorption and displacement in kerogen and the mechanical-chemical properties of kerogen by methods such as molecular simulation.

[0019] The method of the present invention has strong portability and can be applied to the reconstruction work of organic matters such as kerogen, coal and asphaltene in the mining area. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0021] Figure 1 It is a flow chart of the physical and mechanical inversion method for reconstructing the kerogen molecular group according to the embodiment of the present invention;

[0022] Figure 2 It is the kerogen molecular group constructed by the present invention;

[0023] Figure 3 It is a schematic diagram of the molecular number distribution relationship and molecular distribution amount of the kerogen molecular group constructed by the present invention ( Figure 3 in which (a) is the molecular number distribution relationship diagram of the constructed kerogen molecular group, Figure 3 and (b) is the molecular distribution amount diagram of the constructed kerogen molecular group). DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0025] The present invention will be further explained below in combination with specific embodiments.

[0026] As Figure 1 shown, a physical and mechanical inversion method for reconstructing kerogen molecular groups provided in this embodiment mainly includes the following steps:

[0027] S100. For the kerogen sample, use elemental analysis and XPS spectral information to determine the average molecular formula of the entire molecular group, and determine the quantitative relationship of heteroatom functional groups in the entire molecular system through XPS (X-Ray Photoelectron Spectroscopy) spectroscopy; determine the functional group type of kerogen through FI-IR (Fourier-Transform Infrared Spectrometry) and qualitatively characterize the content; through 13 the results of 13C NMR (Nuclear Magnetic Resonance) to obtain the carbon skeleton of the kerogen molecule; obtain the characteristic molecular fragments and pyrolysis residual structure of kerogen pyrolysis through Py-GC / MS (Pyrolysis / Gas Chromatography / Mass Spectrometry); then based on the existing chemical bond energy data, obtain the bond dissociation energy of different functional groups (specifically, obtain the bond dissociation energy of different functional groups by querying the existing chemical bond energy data in the "Chemical Bond Energy Data Handbook").

[0028] Among them, the heteroatom in the above step S100 is an atom other than carbon and hydrogen.

[0029] The elemental 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 through an elemental analyzer.

[0030] The FT-IR in the above step S100 is an instrument that converts the interference pattern (solid, liquid, gas) of the substance under study into an infrared spectrum through Fourier transform, and is used in the present invention to characterize the functional group information in kerogen; obtain the transmission spectrum of the kerogen sample through FT-IR, and compare the absorption band of the functional group with the wave number of the peak position in the FT-IR transmission spectrum, and the type of functional group in kerogen can be qualitatively obtained.

[0031] XPS in the above step S100 refers to X-ray photoelectron spectroscopy, which is a quantitative spectroscopic technique based on the photoelectric effect and is used to characterize the elemental content and the types of heteroatom functional groups in kerogen.

[0032] The process of determining the quantitative relationship of heteroatom functional groups in the entire molecular system through the XPS spectrum in the above step S100 is as follows: High-resolution scanning is performed on the elemental regions such as C1s, O1s, N1s, and S2p of kerogen by an XPS instrument to obtain high-resolution narrow spectra of the corresponding elements; The XPS peak separation software (XPSPEAK41) is used to directly perform peak separation on the obtained XPS high-resolution narrow spectra to obtain the fitting peaks and characteristic curves of different functional groups; Then, according to 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 abundances of different elemental functional groups can be quantitatively obtained.

[0033] In the above step S100 13 The 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 kerogen. In the present invention 13 The C NMR spectrum is used to construct the carbon skeleton structure parameters of the kerogen molecular group and verify the rationality of the reconstructed molecular group structure.

[0034] The Py-GC / MS experiment in the above step S100 refers to pyrolysis-gas chromatography / mass spectrometry analysis. By analyzing the pyrolysis product structure, kerogen structure information can be obtained. The main process of this experiment is: First, the kerogen sample is heated in vacuum / inert gas at different temperatures (650 °C, 800 °C, 950 °C) for 60 s to pyrolyze the sample; Then, the pyrolysis products are captured, and the pyrolysis product molecular fragments are loaded into a GC / MS analyzer, and the pyrolysis products are characterized through the NIST MS database. In the present invention, it is mainly used to identify and analyze pyrolysis small molecule fragments and residual structures, and combine the reaction mechanism given by pyrolysis simulation and the strength law of bond dissociation energy of each functional group to judge the connection relationship between small molecules and the carbon skeleton.

[0035] S200. Construct a structure containing a large amount of aromatic carbon and residual structures that are not prone to reaction according to the quantitative relationship determined in the above step S100; Utilize the quantitative relationship of characteristic molecular fragments, heteroatom functional groups, and bond dissociation energy of different functional groups obtained in the above step S100 during the pyrolysis of kerogen to establish the chemical bond connection between pyrolysis small molecules and residual structures, and obtain the initial two-dimensional molecular structure; Convert the constructed initial two-dimensional molecular structure from two-dimensional to three-dimensional through software such as Chemdraw, and use methods such as density functional theory to optimize the molecular structure to obtain the kerogen molecular monomer structure that can be used for simulation.

[0036] In the above step 200, the high-resolution narrow spectrum of XPS is deconvoluted using XPS peak separation software (XPSPEAK41) to infer the types of functional groups of elements; combined with elemental analysis, the relative content of each functional group can be obtained; by comparing the FT-IR and 13 C NMR spectra, the structural parameters of the functional groups in kerogen can be determined, and at the same time, the spectra can prove and correct each other, check the consistency between the spectra, and qualitatively and quantitatively confirm the structural parameters of each element. The elements include but are not limited to C, O, N, and S, etc.

[0037] In the above step S200, the optimization method is not limited; in the present invention, structure optimization is mainly carried out using Gaussian09 software, and the optimization basis set is B3LYP / 6-31G(d) to perform the optimization calculation. When the calculation result converges, the optimization is completed. The methods of structure optimization include at least one of geometric optimization, annealing optimization, energy minimization, and relaxation.

[0038] S300. Repeat the above step S200 and adjust the kerogen molecular structure. Compare the pyrolysis small molecules generated during the reactive force field molecular dynamics (ReaxFF-MD) pyrolysis simulation with the small molecule results obtained from the Py-GC / MC experiment, and adjust the connection sites between the small molecules and the residual structure until the products obtained from the kerogen molecular pyrolysis simulation are consistent with the Py-GC / MS experimental results, so as to determine the monomer structure of the kerogen molecule.

[0039] The reactive force field molecular dynamics in the above step S300 refers to converting the empirical potential function between atoms into a function of bond order to represent the energy of the molecule and the interaction between atoms, and can describe the formation and breakage of chemical bonds. In the present invention, the ReaxFF module of 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.

[0040] The reactive force field molecular dynamics simulation method in the above step S300 adopts the constant particle number-pressure-temperature ensemble (i.e., the isothermal-isobaric ensemble, NPT), or the constant particle number-volume-temperature ensemble (i.e., the canonical ensemble, NVT).

[0041] S400. Repeat steps S200 - S300 to obtain a kerogen molecular group; according to the following experimental and MD simulation results (i.e., the subsequent XPS experiment, 13 C spectrum, MD / fbMC these experimental results), compare the chemical properties of the kerogen molecular group to verify the correctness of the kerogen molecular group: verify the relative content of the chemical states of each element in the kerogen molecular group according to the XPS experimental results; according to comparing the kerogen molecular group 13The 13C NMR spectra, as well as the positions and relative areas of the experimental peaks, are used to verify the rationality of the carbon skeleton of the molecular groups (including aromaticity, aliphaticity, and oxygen-carbon distribution); the pyrolysis simulation of the kerogen molecular group is carried out through the MD / fbMC (Molecular Dynamics / Force-biased Monte Carlo) algorithm to verify the rationality of the chemical bonds between the pyrolytic small molecules and the residual structure in the Py-GC / MS experiment (that is, the 13 13C NMR spectra of the kerogen molecular group are compared with the 13 13C NMR spectra results of the kerogen sample, and the connection sites of the kerogen molecular intermediates are adjusted until the 13 13C NMR spectra of the reconstructed kerogen molecular group are Figure 1 consistent with the sample spectra).

[0042] The MD / fbMC in the above step S400 is an accelerated molecular dynamics algorithm, which can make the simulation system simulate at a time scale much larger than the computer time scale under the condition close to the experimental temperature (about 800 °C), making the results of the molecular dynamics simulation more realistic and credible, and at the same time can also prove the rationality of the reconstructed molecular structure.

[0043] The MD / fbMC hybrid simulation method in the above step S400 adopts the constant particle number-pressure-temperature ensemble (that is, the isothermal-isobaric ensemble, NPT), or the constant particle number-volume-temperature ensemble (that is, the canonical ensemble, NVT).

[0044] In this embodiment, the temperature setting of the MD / fbMC hybrid simulation method is 800 °C, the ensemble is NVT, the atomic displacement is 0.3 Å, the number of steps of Reaxff-MD in each cycle is 500 steps, the number of steps of fbMC is 200 steps, and the total simulation time is set to 100 ps.

[0045] The above carbon skeleton structure parameters include but are not limited to at least one of aromatic carbon ratio, aliphatic carbon ratio, alkane chain branching degree, aromatic substitution degree, and average aliphatic chain length.

[0046] The above carbon skeleton structure parameters are obtained by calculating the areas corresponding to the characteristic peaks of different spectral bands (Table 1) in the 13 13C NMR spectra:

[0047] Table 1

[0048]

[0049] The chemical structure parameters of the kerogen sample are determined by analyzing the FT-IR spectra and the physical definitions in Table 2:

[0050] Table 2

[0051]

[0052] Table 3 summarizes the information that can be obtained by analyzing kerogen samples using the above methods. There is some overlap among this information, and the overlapping information is used to verify the consistency between spectra:

[0053] Table 3

[0054]

[0055] The above-mentioned heteroatoms include at least one of O, N, and S; the types of functional groups of the above-mentioned heteroatoms are determined by fitting the characteristic peaks of each spectrum; the types of functional groups of N atoms include at least one of nitrile, pyrrole, and amino; the types of functional groups of S atoms include at least one of thiol, thioether, thiophene, sulfoxide, and sulfone. The oxygen-containing groups in the functional groups of kerogen include at least one of carbonyl, alcohol group, carboxyl group, ketone / aldehyde group, and ether group.

[0056] The bond dissociation energy of the above-mentioned functional groups can be queried from the "Chemical Bond Energy Data Handbook". Table 4 lists the bond dissociation energies 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. On the contrary, it means that the chemical bond is weaker and more likely to dissociate. The chemical bond with a weak bond dissociation energy has a greater probability of becoming the connection point between the molecular fragment and the residual structure.

[0057] Table 4

[0058]

[0059] The present invention also provides a group of three-dimensional bulk kerogen molecular group models, which are constructed by the physical mechanics inversion method for reconstructing the kerogen molecular group of the present invention.

[0060] Example 1

[0061] The average molecular formula of the entire molecular group was determined by elemental analysis and XPS spectral information, and the quantitative relationship of the heteroatom functional groups in the entire molecular system was determined through the results of the XPS spectrum; the types of functional groups of the kerogen molecular group were determined by FT-IR and the content was qualitatively characterized; 13 The results of 13C NMR gave the aromaticity, aliphaticity, average chain length, and degree of branching of kerogen, and established the carbon skeleton of the kerogen molecule. The average molecular formula of Ordos kerogen is about C 100 H 88 O 15NS, the main types of carbon functional groups are aromatic carbon, aliphatic carbon, C-O, O-C=O and C=O; the types of oxygen functional groups are ether, alcohol, aldehyde, ester and fatty acid. The types of nitrogen functional groups are pyridine, pyrrole and amino group, and the types of sulfur functional groups are mercaptan, thioether, thiophene and sulfone. The main light functional group bands are saturated hydrocarbons (2930, 2850 and 720 cm −1 )), aromatic hydrocarbons (1620, 810 cm −1 ) and oxygen-containing structures (1280 - 1050 cm −1 ). Aromatic carbon and aliphatic carbon are about 56% and 42% respectively.

[0062] Combined with FT-IR, elemental analysis, XPS and 13 C NMR results, the residual structure is first constructed. The pyrolysis small molecule structures with relative peak areas greater than 1% in Py-GC / MS are selected as the access molecules, and the mass of the access molecules is qualitatively determined based on the peak area. Using the structural information and semi-quantitative information of the pyrolysis products, combined with the bond dissociation energy database of molecules, the site with the lowest bond dissociation energy is selected to establish the chemical bond connection between the small molecules and the residual structure. The pyrolysis mechanism of kerogen shows that the cleavage sites of kerogen often appear in the places where the bond dissociation energy is weak. 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.

[0063] 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 There are 5, 4, 4 and 2 kerogen molecules respectively. In order to more realistically verify the molecular information, the existing C 800+ kerogen macromolecular monomer structure is added to the kerogen molecular group and its structure is corrected. The molecular distribution represents the total relative molecular mass of each group of molecules in the above 5 groups of molecules, and the average molecular mass is the average molecular mass of each group. As Figure 3 shown, by analyzing and fitting the relationship between the relative molecular mass distribution and the number of molecules of the kerogen molecular monomers, it can be shown that the molecular weight of the molecular group can be represented by a normal distribution curve, which has diversity and meets the characteristics of high polymers, among which C 300 ~C 400has the highest mass content. Statistical analysis of the structural information of the constructed molecules: The average molecular mass of the molecular group is 4903.60 g / mol (the average molecular weight of kerogen is considered to be in the range of 4000 - 5000 g / 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 approximate to the elemental analysis result. Combining the experimental information, continuously adjusting the structure of the molecular group, finally obtaining the kerogen molecular group by the physical inversion method, as shown in Figure 2. Then, the structure of the entire kerogen molecular group is verified.

[0064] First, verify the rationality of the molecular groups through the relative content of the chemical states of the elements in kerogen. For example, the main functional group types of sulfur elements in kerogen are -S-, sulfoxide (-S(=O)-), and sulfone (-S(=O) 2 -S), and 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 indicates that the molecular groups of the kerogen molecular group constructed by the physical mechanics inversion method are very reasonable. Then, obtain the total 13 C NMR prediction spectrum of the molecular group by MestReNova software. Comparing with the experimental spectrum, the positions of the predicted NMR spectrum and the experimental peaks are consistent, and the relative areas are close, verifying the rationality of the carbon skeleton of the molecular groups (including aromaticity, aliphaticity, and oxygen-carbon distribution). Finally, use the MD / fbMC hybrid simulation method to verify the rationality of the chemical bonds between the pyrolysis molecular structure obtained experimentally and the kerogen residual structure. The pyrolysis temperature is set at 800°C, and the atomic displacement is 0.3 Å. The number of Reaxff-MD steps per cycle is 500 steps, the number of fbMC steps is 200 steps, and the total simulation time is 100 ps. Verify the rationality of the molecular structure by analyzing the composition of the small molecule fragments obtained from the pyrolysis simulation of the kerogen molecules. The products of the pyrolysis simulation are consistent with the small molecule structures connected to the kerogen molecules obtained experimentally, indicating that the chemical bond setting is reasonable.

[0065] The physical mechanics inversion method constructs the kerogen molecular structure based on a large amount of experimental information, combined with pyrolysis experiments and simulations. The constructed molecules not only satisfy the heteroatom functional group information and carbon skeleton information, but also the small molecule fragments obtained from their pyrolysis are consistent with the experimental results. Compared with traditional methods, the molecular bonds constructed by the physical mechanics inversion method are more reasonable, and the structure contains the actual characteristic structures of the mine area kerogen. Therefore, the accuracy and reliability of the molecules are improved.

[0066] The inventive concept is reasonable and can realize the construction of a kerogen molecular group with a molecular weight satisfying a Gaussian distribution.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and 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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