Shale relaxation time determination method, apparatus, device, and storage medium

Abstract

This invention discloses a method, apparatus, device, and storage medium for determining shale relaxation time, comprising: simulating a pre-defined molecular simulation model in a pre-set experimental simulation environment to obtain the inter-pair distance and inter-pair angle of hydrogen proton pairs in the molecular simulation model; obtaining the residual dipole coupling relaxation time based on the inter-pair distance and inter-pair angle; and obtaining the transverse relaxation time based on the residual dipole coupling relaxation time and the theoretical relaxation time. The shale relaxation time determination method, apparatus, device, and storage medium disclosed in this application solve the problem of uncertainty or significant mismatch between the pore size distribution derived from the transverse relaxation time based on NMR theory and the actual pore size distribution. This allows for a more accurate reflection of the actual pore size distribution through the calculation of the residual dipole coupling relaxation time under nano-constraint effects, thereby ensuring the accuracy of shale oil reservoir evaluation.

Description

Technical Field

[0001] This invention relates to the field of nuclear magnetic resonance technology, and in particular to a method, apparatus, device, and storage medium for determining the relaxation time of shale. Background Technology

[0002] In the field of oil and gas exploration, nuclear magnetic resonance technology is widely used in the analysis of oil and gas reservoir characteristics to characterize reservoir porosity, permeability, fluidity and pore size distribution, and has achieved fruitful results in experimental studies of conventional sandstone, carbonate reservoirs, unconventional tight sandstone reservoirs and coal reservoirs.

[0003] In some techniques, transverse relaxation time is of great significance for reservoir evaluation, as it can effectively characterize the reservoir's pore structure and identify the type of fluid. Shale reservoirs are generally characterized by small rock skeleton grains, large specific surface area, and well-developed micro- and nano-pores. Numerous complex interfacial effects exist between the fluid and the reservoir porous medium, especially under strong nano-confinement, where residual dipole coupling between fluid molecules is significantly enhanced. This coupling effect significantly affects the transverse relaxation process of hydrogen protons.

[0004] However, in the existing nuclear magnetic resonance relaxation (NMR) theory, the pore size distribution derived from the transverse relaxation time based on the NMR theory is uncertain or significantly mismatched with the actual pore size distribution, thus weakening the accuracy of reservoir evaluation. Summary of the Invention

[0005] The purpose of this invention is to provide at least one method, apparatus, device, and storage medium for determining shale relaxation time. This invention addresses the technical problem of uncertainty or significant mismatch between the pore size distribution derived from NMR theory's lateral relaxation time and the actual pore size distribution, which weakens the accuracy of reservoir evaluation. Specifically, by calculating the residual dipole coupling relaxation time under nano-constraint effects, this invention effectively reduces the probability of uncertainty or significant mismatch between the pore size distribution derived from NMR theory's lateral relaxation time and the actual pore size distribution, thus more accurately reflecting the actual pore size distribution and ensuring the accuracy of shale oil reservoir evaluation.

[0006] To address the aforementioned technical problems, at least one embodiment of this application provides a method for determining shale relaxation time, comprising:

[0007] The preset molecular simulation model is simulated in a pre-defined experimental simulation environment to obtain the inter-pair distance and inter-pair angle of hydrogen proton pairs in the molecular simulation model. The molecular simulation model is a simulation model used to characterize the kerogen porous media type and characteristic components of n-alkanes in shale crude oil under the nano-confined effect.

[0008] Based on the inter-pair distance and inter-pair angle of the hydrogen proton pairs, the residual dipole coupling relaxation time is obtained.

[0009] Based on the residual dipole coupling relaxation time and the theoretical relaxation time, the transverse relaxation time is obtained.

[0010] At least one embodiment of this application also provides a shale relaxation time determination device, comprising:

[0011] The simulation module is used to simulate a preset molecular simulation model in a pre-defined experimental simulation environment to obtain the interpair distance and interpair angle of hydrogen proton pairs in the molecular simulation model. The molecular simulation model is a simulation model used to characterize the kerogen porous media type and characteristic components of n-alkanes in shale crude oil under the nano-confined effect.

[0012] The residual dipole coupling module is used to obtain the residual dipole coupling relaxation time based on the inter-pair distance and inter-pair angle of the hydrogen proton pairs.

[0013] The transverse relaxation calculation module is used to obtain the transverse relaxation time based on the residual dipole coupling relaxation time and the theoretical relaxation time.

[0014] At least one embodiment of this application also provides an electronic device, including: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, the instructions being executed by the at least one processor to enable the at least one processor to perform the shale relaxation time determination method described above.

[0015] At least one embodiment of this application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described shale relaxation time determination method.

[0016] The shale relaxation time determination method, apparatus, equipment, and storage medium provided in the embodiments of this application simulate a molecular simulation model in an experimental simulation environment to obtain the inter-pair distance and inter-pair angle of hydrogen proton pairs in the molecular simulation model. Based on the inter-pair distance and inter-pair angle of hydrogen proton pairs, the residual dipole coupling relaxation time is obtained. Then, based on the residual dipole coupling relaxation time and the theoretical relaxation time, the transverse relaxation time is obtained. Thus, by calculating the residual dipole coupling relaxation time under nano-constraint effects, the probability of uncertainty or significant mismatch between the pore size distribution derived from the transverse relaxation time based on NMR theory and the actual pore size distribution is effectively reduced, more accurately reflecting the actual pore size distribution and ensuring the accuracy of shale oil reservoir evaluation.

[0017] In some optional embodiments, the molecular simulation model is obtained through the following steps:

[0018] The characteristic components of n-alkanes and the type of kerogen porous media in the shale crude oil were obtained;

[0019] Based on the characteristic components of n-alkanes in the shale crude oil and the porous media type of kerogen, a molecular structure model was constructed using molecular simulation software.

[0020] The molecular structure model is subjected to energy minimization processing to obtain a molecular simulation model.

[0021] By simulating the molecular model in an experimental environment, the interpair distance and interpair angle of hydrogen proton pairs in the molecular simulation model are obtained. Then, based on the interpair distance and interpair angle of hydrogen proton pairs, the residual dipole coupling relaxation time is obtained. Finally, based on the residual dipole coupling relaxation time and the theoretical relaxation time, the transverse relaxation time is obtained. The calculated transverse relaxation time is more accurate, which ensures the accuracy of shale oil reservoir evaluation.

[0022] In some optional embodiments, the experimental simulation environment is set up through the following steps:

[0023] Obtain environmental parameters of shale reservoirs;

[0024] The environmental parameters of the shale reservoir are used as simulation parameters for the molecular simulation software to set the experimental simulation environment.

[0025] The environmental parameters of the shale reservoir are determined based on the actual reservoir formation conditions. The simulation parameters used to set the experimental simulation environment in the molecular simulation software are then set according to the environmental parameters of the shale reservoir, so that the molecular simulation model simulated in the molecular simulation software is closer to the actual reservoir formation conditions of the shale.

[0026] In some optional embodiments, the step of simulating a preset molecular simulation model in a pre-defined experimental simulation environment to obtain the inter-pair distance and inter-pair angle of hydrogen proton pairs in the molecular simulation model includes:

[0027] The molecular simulation model is simulated in the experimental simulation environment for a preset time;

[0028] During the simulation, the spatial trajectory of hydrogen proton pairs of n-alkanes in the molecular simulation model is obtained;

[0029] Based on the spatial trajectory of the hydrogen proton pairs, the distance between the hydrogen proton pairs and the angle between them are obtained.

[0030] A molecular simulation model with a stable configuration is used to obtain the interpair distance and interpair angle of hydrogen proton pairs. By calculating the interpair distance and interpair angle of hydrogen proton pairs, the residual dipole coupling relaxation time can be obtained. By calculating the residual dipole coupling relaxation time under the nano-confinement effect, the probability of uncertainty or significant mismatch between the pore size distribution derived from the transverse relaxation time based on NMR theory and the actual pore size distribution is effectively reduced.

[0031] In some optional embodiments, the construction of a molecular structure model using molecular simulation software based on the characteristic components of n-alkanes in the shale crude oil and the type of porous kerogen medium includes:

[0032] A kerogen structure model was constructed using the aforementioned molecular simulation software;

[0033] The kerogen structure model was subjected to simulated annealing to obtain a kerogen porous media model;

[0034] Obtain a shale oil molecular structure model, and determine the molecular structure model based on the shale oil molecular structure model and the kerogen porous media model.

[0035] By using a porous kerogen medium model to realistically reflect the pore structure and properties of kerogen, and combining it with a shale oil molecular structure model, a molecular structure model is determined to reflect the existence state and migration law of shale crude oil in the porous kerogen medium, providing strong theoretical support for the exploration and development of shale oil.

[0036] In some optional embodiments, obtaining the residual dipole coupling relaxation time based on the inter-pair distance and inter-pair angle of the hydrogen proton pairs includes:

[0037] Based on the inter-pair distance and inter-pair angle of the hydrogen proton pairs, the residual dipole coupling second moment is obtained;

[0038] The residual dipole coupling relaxation time is obtained based on the residual dipole coupling second-order moment.

[0039] The residual dipole coupling second moment is calculated, and the residual dipole coupling relaxation time is calculated under the nano-constraint effect. After obtaining the residual dipole coupling second moment, the residual dipole coupling relaxation time is obtained.

[0040] In some optional embodiments, obtaining the transverse relaxation time based on the residual dipole coupling relaxation time and the theoretical relaxation time includes:

[0041] The autocorrelation function of the hydrogen proton pair is obtained based on the distance between the hydrogen proton pairs and the angle between them.

[0042] The spectral density function is obtained by performing a Fourier transform on the autocorrelation function of the hydrogen proton pair.

[0043] The theoretical relaxation time is obtained based on the spectral density function, and the transverse relaxation time is obtained based on the residual dipole coupling relaxation time and the theoretical relaxation time.

[0044] The transverse relaxation time is obtained by comparing the residual dipole coupling relaxation time with the theoretical relaxation time. Thus, by calculating the residual dipole coupling relaxation time under nano-constraint effects, the probability of uncertainty or significant mismatch between the pore size distribution derived from the transverse relaxation time based on NMR theory and the actual pore size distribution is effectively reduced. This more accurately reflects the actual pore size distribution, ensuring the accuracy of shale oil reservoir evaluation. Attached Figure Description

[0045] One or more embodiments are illustrated by way of example with reference to the accompanying drawings, and these illustrative descriptions do not constitute a limitation on the embodiments.

[0046] Figure 1 This is a flowchart illustrating a method for determining shale relaxation time according to an embodiment of this application;

[0047] Figure 2 This is a schematic flowchart of a shale relaxation time determination device provided in one embodiment of this application;

[0048] Figure 3 This is a schematic diagram of the structure of an electronic device provided in another embodiment of this application;

[0049] Figure 4 This is a schematic diagram illustrating the construction of a molecular structure model provided in one embodiment of this application;

[0050] Figure 5 This is a schematic diagram illustrating the variation of the inter-pair distance and inter-pair angle of a hydrogen proton pair according to an embodiment of this application;

[0051] Figure 6 This is a schematic diagram of the lateral relaxation time provided in another embodiment of this application. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the various embodiments of this application will be described in detail below with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the various embodiments of this application to help readers better understand this application. However, the technical solutions claimed in this application can be implemented even without these technical details and various changes and modifications based on the following embodiments. The division of the various embodiments below is for the convenience of description and should not constitute any limitation on the specific implementation of this application. The various embodiments can be combined with and referenced by each other without contradiction.

[0053] To facilitate understanding of the embodiments of this application, the relevant content regarding the method for determining shale relaxation time will be introduced first.

[0054] In the field of oil and gas exploration, nuclear magnetic resonance technology is widely used in the analysis of oil and gas reservoir characteristics to characterize reservoir porosity, permeability, fluidity and pore size distribution, and has achieved fruitful results in experimental studies of conventional sandstone, carbonate reservoirs, unconventional tight sandstone reservoirs and coal reservoirs.

[0055] In some techniques, transverse relaxation time is of great significance for reservoir evaluation, as it can effectively characterize the reservoir's pore structure and identify the type of fluid. Shale reservoirs are generally characterized by small rock skeleton grains, large specific surface area, and well-developed micro- and nano-pores. Numerous complex interfacial effects exist between the fluid and the reservoir porous medium, especially under strong nano-confinement, where residual dipole coupling between fluid molecules is significantly enhanced. This coupling effect significantly affects the transverse relaxation process of hydrogen protons.

[0056] Shale crude oil is an unconventional oil and gas resource. At the nanoscale, the structure and properties of shale crude oil undergo significant changes, exhibiting a nano-confinement effect. This nano-confinement effect influences the storage, migration, and extraction processes of shale crude oil during exploration and development. In shale crude oil reservoir evaluation, nuclear magnetic resonance (NMR) technology is used to detect parameters such as relaxation time and diffusion coefficient of fluids (including oil and water) within the reservoir, thereby analyzing the fluid's properties, distribution, and content. In shale crude oil, hydrogen protons are the primary active nuclei in NMR, and their residual dipole coupling may be affected by the nano-confinement effect. However, existing NMR relaxation theories neglect the residual dipole coupling effect, leading to uncertainties or significant mismatches between the pore size distribution derived from the NMR theory's lateral relaxation time and the actual pore size distribution, thus weakening the accuracy of reservoir evaluation.

[0057] To address the technical problem mentioned above, where existing nuclear magnetic resonance relaxation (NMR) theory neglects the residual dipole coupling effect, leading to uncertainties or significant mismatches between the pore size distribution derived from the NMR theory's lateral relaxation time and the actual pore size distribution, thus weakening the accuracy of reservoir evaluation, this invention proposes a method for determining shale relaxation time. The implementation details of this shale relaxation time determination method are described below. These details are provided for ease of understanding and are not essential for implementing this solution.

[0058] Example 1:

[0059] The shale relaxation time determination method of this embodiment can be applied to electronic devices with communication, computing, and data storage capabilities. Its specific process can be as follows: Figure 1 As shown, it includes:

[0060] Step 101: Simulate the preset molecular simulation model in a pre-defined experimental simulation environment to obtain the inter-pair distance and inter-pair angle of hydrogen proton pairs in the molecular simulation model. The molecular simulation model is a simulation model used to characterize the kerogen porous media type and characteristic components of n-alkanes in shale crude oil under the nano-confined effect.

[0061] Specifically, shale crude oil, as an unconventional oil and gas resource, differs from conventional crude oil in composition and properties. Regarding n-alkanes, shale crude oil typically exhibits specific distribution characteristics. Kerogen, a major organic component in shale, is a nanoscale porous medium with a complex pore structure. The porous medium type of kerogen significantly influences its storage performance and fluid flow patterns. Therefore, molecular simulation models are used to characterize the porous medium type of kerogen and the characteristic components of n-alkanes in shale crude oil under nano-confinement effects.

[0062] In this embodiment, the experimental simulation environment is used to mimic the actual reservoir formation conditions of shale, so that the molecular simulation model can simulate these conditions as closely as possible. When the molecular simulation model is placed in the pre-set experimental simulation environment, it simulates the process of nano-constraint effects occurring in shale crude oil under actual reservoir formation conditions. During the simulation, the distance between two hydrogen proton pairs and the angle between them are determined by the movement of hydrogen proton pairs in n-alkanes. It should be noted that the distance between two hydrogen proton pairs refers to the distance between the two hydrogen proton pairs, and the angle between them refers to the angle between the line connecting the two hydrogen proton pairs and the external magnetic field. Specifically, the structural formula of n-alkanes is C_nH_(2n+2), where n represents the number of carbon atoms. N-alkanes are alkane molecules in which carbon atoms are linked by single bonds, arranged in a chain, and are unbranched. Carbon atoms are linked by single bonds to form a straight chain, and hydrogen atoms are connected to carbon atoms. In this structure, each carbon atom forms a stable covalent bond with the surrounding hydrogen atoms. As can be seen, n-alkanes have multiple hydrogen protons. In a n-alkane molecule, a hydrogen proton pair does not refer to two hydrogen protons existing in a special form, but rather to the interaction or relationship between adjacent or non-adjacent hydrogen atoms in the molecule.

[0063] In some cases, organic geochemical and pore structure characterization experiments are conducted before simulation. These experiments include, but are not limited to, high-pressure mercury intrusion porosimetry, nano-CT scanning, scanning electron microscopy (SEM), and whole-hydrocarbon gas chromatography to identify the characteristic components of n-alkanes and the porous media type of kerogen in shale crude oil, providing a basis for model construction and optimization of force field parameters. In other cases, force field parameters can be determined through quantum chemical calculations and experimental data fitting. When determining force field parameters, the influence of molecular structures, functional groups, and pore structures of kerogen and n-alkanes on the interactions needs to be considered.

[0064] Step 102: Based on the interpair distance and interpair angle of the hydrogen proton pairs, the residual dipole coupling relaxation time is obtained.

[0065] Specifically, under the nanoconfinement effect, the residual dipole coupling between fluid molecules in shale reservoirs is significantly enhanced, and this coupling significantly affects the transverse relaxation process of hydrogen protons. That is, in shale crude oil, hydrogen protons, as the main active nuclei in NMR, are affected by the residual dipole coupling due to the nanoconfinement effect. Specifically, residual dipole coupling is a phenomenon in NMR used to describe the electromagnetic interaction between spatially adjacent but chemically bonded dipoles. In this embodiment, after obtaining the inter-pair distance and inter-pair angle of hydrogen proton pairs, the residual dipole coupling relaxation time is obtained through calculation processing of the inter-pair distance and inter-pair angle. Through in-depth analysis of the residual dipole coupling effect, the problem of excessively long transverse relaxation times in traditional NMR theory is effectively corrected, thereby more accurately reflecting the actual pore size distribution.

[0066] Step 103: Based on the residual dipole coupling relaxation time and the theoretical relaxation time, the transverse relaxation time is obtained.

[0067] Specifically, the theoretical relaxation time is the transverse diffusion relaxation time calculated based on the traditional nuclear magnetic resonance relaxation theory of fluids. After obtaining the residual dipole coupling relaxation time, the residual dipole coupling relaxation time and the theoretical relaxation time are calculated and processed to obtain the total transverse relaxation time of shale crude oil.

[0068] In this embodiment, a molecular simulation model is simulated in an experimental environment to obtain the inter-pair distance and inter-pair angle of hydrogen proton pairs in the molecular simulation model. Based on the inter-pair distance and inter-pair angle of hydrogen proton pairs, the residual dipole coupling relaxation time is obtained. Then, based on the residual dipole coupling relaxation time and the theoretical relaxation time, the transverse relaxation time is obtained. Thus, by calculating the residual dipole coupling relaxation time under the nano-constraint effect, the probability of uncertainty or significant mismatch between the pore size distribution derived from the transverse relaxation time based on NMR theory and the actual pore size distribution is effectively reduced. This more accurately reflects the actual pore size distribution, ensuring the accuracy of shale oil reservoir evaluation.

[0069] In some embodiments, the molecular simulation model is obtained through the following steps:

[0070] To obtain the characteristic components of n-alkanes and the type of kerogen porous media in shale crude oil;

[0071] Based on the characteristic components of n-alkanes in shale crude oil and the porous media type of kerogen, a molecular structure model was constructed using molecular simulation software.

[0072] The molecular structure model is subjected to energy minimization to obtain the molecular simulation model.

[0073] Specifically, by obtaining the characteristic components of n-alkanes (C_nH_(2n+2)) and the type of porous kerogen medium (such as organic matter content), a molecular structure model is constructed based on the characteristic components of n-alkanes in shale crude oil and the type of porous kerogen medium using molecular simulation software. The force field parameters of the n-alkanes are then determined, such as bond length parameters, bond angle parameters, and non-bonded interaction parameters. In some embodiments, the molecular simulation software includes, but is not limited to, LAMMPS, GROMACS, and AMBER.

[0074] In this embodiment, after constructing the molecular structure model, the energy of the constructed molecular structure model is very high. If the transverse relaxation time is calculated based on the current molecular structure model, the calculation result will have a large error. Therefore, it is necessary to minimize the energy of the molecular structure model to reduce its energy, thereby obtaining a molecular simulation model with the lowest energy, that is, a model with a stable configuration. It should be noted here that the molecular structure in the molecular structure model and the molecular simulation model are the same, but their energies are different. By simulating the molecular simulation model in an experimental simulation environment, the interpair distance and interpair angle of hydrogen proton pairs in the molecular simulation model are obtained. Then, based on the interpair distance and interpair angle of hydrogen proton pairs, the residual dipole coupling relaxation time is obtained. Finally, based on the residual dipole coupling relaxation time and the theoretical relaxation time, the transverse relaxation time is obtained. The calculated transverse relaxation time is more accurate, ensuring the accuracy of shale oil reservoir evaluation.

[0075] In some embodiments, the experimental simulation environment is set up through the following steps:

[0076] Obtain environmental parameters of shale reservoirs;

[0077] The environmental parameters of the shale reservoir were used as simulation parameters in the molecular simulation software to set the experimental simulation environment.

[0078] Specifically, environmental parameters of the shale reservoir are determined based on actual reservoir formation conditions. These environmental parameters are then used to set simulation parameters in the molecular simulation software to define the experimental simulation environment, ensuring that the molecular simulation model more closely approximates the actual reservoir formation conditions of the shale. In some examples, environmental parameters include, but are not limited to, temperature, pressure, and density.

[0079] In some embodiments, a preset molecular simulation model is simulated in a pre-defined experimental simulation environment to obtain the inter-pair distance and inter-pair angle of hydrogen proton pairs in the molecular simulation model, including:

[0080] The molecular simulation model is simulated in an experimental simulation environment for a preset time;

[0081] During the simulation, the spatial trajectory of hydrogen proton pairs in the n-alkanes in the molecular simulation model is obtained;

[0082] Based on the spatial trajectory of hydrogen proton pairs, the distance between hydrogen proton pairs and the angle between them are obtained.

[0083] Specifically, after setting up the experimental simulation environment of the molecular simulation software, a molecular simulation model with a stable configuration is simulated for a preset time within the experimental simulation environment. During the simulation, the spatial trajectories of hydrogen proton pairs in the x, y, and z directions are recorded. Then, the spatial trajectories of the hydrogen protons in the x, y, and z directions are monitored, and the inter-pair distance and inter-pair angle of the hydrogen proton pairs are calculated. That is, the distance between two hydrogen protons and the angle between the line connecting the two hydrogen protons and the external magnetic field are calculated based on the spatial trajectories. In some examples, the molecular simulation model is simulated in LAMMPS under actual reservoir conditions of 353 K and 20 MPa for 2 ns. At the same time, the spatial trajectories of hydrogen protons in the x, y, and z directions within this 2 ns time range are extracted, and the average inter-pair distance and inter-pair angle of the hydrogen proton pairs are calculated.

[0084] In some embodiments, based on the characteristic components of n-alkanes in shale crude oil and the type of porous kerogen media, a molecular structure model is constructed using molecular simulation software, including:

[0085] A molecular simulation software was used to construct a kerogen structural model.

[0086] Simulated annealing was performed on the kerogen structural model to obtain a porous kerogen medium model.

[0087] Obtain the molecular structure model of shale oil, and determine the molecular structure model based on the molecular structure model of shale oil and the porous media model of kerogen.

[0088] Specifically, experimental data was obtained through organic geochemistry and pore structure characterization experiments. Based on this data, the characteristic components of n-alkanes in shale crude oil and the type of kerogen porous media were identified. A kerogen structural model, also known as a kerogen unit molecular structure model, was constructed using molecular simulation software. The kerogen structural model underwent simulated annealing to obtain a kerogen porous media model. Furthermore, a shale oil molecular structure model was obtained, and n-alkanes from the shale oil molecular structure model were added to the kerogen porous media model. Structural optimization was then performed to form a kerogen porous media-n-alkanes system molecular structure model, i.e., a molecular structure model. The kerogen porous media model realistically reflects the pore structure and properties of kerogen. Combined with the shale oil molecular structure model, a molecular structure model was determined to reflect the existence state and migration patterns of shale crude oil in the kerogen porous media, providing strong theoretical support for shale oil exploration and development.

[0089] In some embodiments, the residual dipole coupling relaxation time is calculated based on the inter-pair distance and inter-pair angle of hydrogen proton pairs, including:

[0090] Based on the interpair distance and interpair angle of hydrogen proton pairs, the residual dipole coupling second moment is obtained;

[0091] The residual dipole coupling relaxation time is obtained based on the residual dipole coupling second moment.

[0092] Specifically, the residual dipole coupling second moment is calculated using the following relationship:

[0093]

[0094] In the formula, Δω RDC For the residual dipole coupling second moment, r ij θ is the interpair distance (the distance between two hydrogen protons). ij The angle between the two hydrogen protons is the angle between the line connecting them and the external magnetic field, where the unit of the residual dipole coupling second moment is s. -1 .

[0095] After calculating the residual dipole coupling second moment, substitute the residual dipole coupling second moment into the following relationship to calculate the residual dipole coupling relaxation time:

[0096]

[0097] In the formula, T 2，RDC The residual dipole coupling relaxation time, Δω RDC It is the residual dipole coupling second moment.

[0098] In nuclear magnetic resonance, the residual dipole coupling second moment can be used to describe the distribution characteristics of the residual dipole coupling strength between hydrogen protons. In this embodiment, the residual dipole coupling second moment is calculated to obtain the residual dipole coupling relaxation time.

[0099] In some embodiments, the transverse relaxation time is calculated based on the residual dipole coupling relaxation time and the theoretical relaxation time, including:

[0100] The autocorrelation function of hydrogen proton pairs is obtained based on the distance between pairs and the angle between pairs.

[0101] The spectral density function is obtained by performing a Fourier transform on the autocorrelation function of the hydrogen proton pair.

[0102] The theoretical relaxation time is obtained based on the spectral density function, and the transverse relaxation time is obtained based on the residual dipole coupling relaxation time and the theoretical relaxation time.

[0103] Specifically, the theoretical relaxation time is calculated using the following formula:

[0104]

[0105] In the formula, T 2，disp J(0), J(ω0), and J(2ω0) are the theoretical relaxation times, and J(0), J(ω0), and J(2ω0) are the magnetic dipole-dipole spectral density functions of the hydrogen proton pair.

[0106] The calculation process for the magnetic dipole-dipole spectral density function of hydrogen proton pairs is as follows: Substituting the interpair distance and the interpair angle of the hydrogen proton pairs into the following relationship, the autocorrelation function of the hydrogen proton pairs (also known as the magnetic dipole-dipole autocorrelation function of hydrogen proton pairs) is calculated:

[0107]

[0108] In the formula, G(t) is the autocorrelation function of the hydrogen proton pair, and τ is the autocorrelation lag time. γ is Planck's constant, γ / 2π = 42.58 MHz / T is the gyromagnetic ratio of a hydrogen nucleus with spin 1 / 2, and N is the ensemble of dipole-dipole interactions of hydrogen proton pairs.

[0109] After obtaining the autocorrelation function of the hydrogen proton pair, the magnetic dipole-dipole spectral density function of the hydrogen proton pair is obtained by performing a Fourier transform on the autocorrelation function:

[0110]

[0111] In the formula, G(t) is the autocorrelation function of the hydrogen proton pair, and J(ω) is the magnetic dipole-dipole spectral density function of the hydrogen proton pair.

[0112] In this embodiment, after calculating the theoretical relaxation time using equations (3)-(5), the transverse relaxation time is obtained based on the theoretical relaxation time and the residual dipole coupling relaxation time. The transverse relaxation time is calculated using the following equations:

[0113]

[0114] In the formula, T 2，Total T is the lateral relaxation time. 2，disp For the theoretical relaxation time, T 2，RDC The residual dipole coupling relaxation time is given.

[0115] In this embodiment, the transverse relaxation time is obtained based on the residual dipole coupling relaxation time and the theoretical relaxation time. Thus, by calculating the residual dipole coupling relaxation time under the nano-constraint effect, the probability of uncertainty or significant mismatch between the pore size distribution derived from the transverse relaxation time based on NMR theory and the actual pore size distribution is effectively reduced. This more accurately reflects the actual pore size distribution, ensuring the accuracy of shale oil reservoir evaluation.

[0116] Example 2:

[0117] This embodiment provides an exemplary content of Embodiment 1, namely, an exemplary process for determining the relaxation time of shale oil. Compared with the prior art, it adopts a method combining molecular dynamics simulation and nuclear magnetic resonance relaxation theory. Based on the magnetic dipole-dipole interaction between hydrogen protons in shale oil molecules under the residual dipole coupling effect, it achieves accurate calculation of the transverse relaxation time of fluids in porous media. Specific content includes:

[0118] S1. Conduct organic geochemistry and pore structure characterization experiments, including but not limited to high-pressure mercury intrusion, nano-CT scanning, scanning electron microscopy (SEM) and whole-hydrocarbon gas chromatography, to identify the characteristic components of n-alkanes and the type of kerogen porous media in shale crude oil, and provide a basis for model construction and force field parameter optimization.

[0119] S2. Molecular structure model of kerogen porous medium-n-alkane system is constructed using molecular simulation software (including but not limited to LAMMPS, GROMACS, AMBER), and the corresponding force field parameters are determined. Energy optimization algorithm is then used to minimize the energy of the system to obtain the stable configuration of the system (i.e., molecular simulation model).

[0120] S3. Set the simulated external environmental parameters (including but not limited to temperature, pressure and density) to the actual reservoir formation conditions, and conduct a simulation process for a certain duration for the simulation system with stable configuration under these environmental conditions, while recording the spatial trajectory of hydrogen protons in n-alkane.

[0121] S4. Based on the spatial trajectory of hydrogen protons obtained in step S3, the residual dipole coupling second-order moment between hydrogen protons in shale oil under strong nano-confinement effect can be obtained:

[0122]

[0123] In the formula, Δω RDC For the residual dipole coupling second moment, r ij θ is the interpair distance (the distance between two hydrogen protons). ij The angle between the two hydrogen protons is the angle between the line connecting them and the external magnetic field, where the unit of the residual dipole coupling second moment is s. -1.

[0124] S5. Based on the second-order moment of the residual dipole coupling interaction between hydrogen protons in step S4, the transverse residual dipole coupling relaxation time can be obtained:

[0125]

[0126] In the formula, T 2，RDC The residual dipole coupling relaxation time, Δω RDC It is the residual dipole coupling second moment.

[0127] S6. The transverse diffusion relaxation time in the traditional nuclear magnetic resonance relaxation theory of fluids is:

[0128]

[0129] In the formula, T 2，disp J(0), J(ω0), and J(2ω0) are the theoretical relaxation times, and J(0), J(ω0), and J(2ω0) are the magnetic dipole-dipole spectral density functions of the hydrogen proton pair.

[0130] S7. Based on the transverse residual dipole coupling relaxation time and the theoretical transverse diffusion relaxation time in steps S5 and S6, the total transverse relaxation time of shale oil within the nanopores of the porous medium can be obtained:

[0131]

[0132] In the formula, T 2，Total T is the lateral relaxation time. 2，disp For the theoretical relaxation time, T 2，RDC The residual dipole coupling relaxation time is given.

[0133] In some examples, the actual application process is as follows:

[0134] (1) Based on experimental data such as core organic geochemistry and pore structure characterization of typical shale reservoir areas such as Songliao Basin and Boxing Depression, the characteristic components of n-alkanes and the types of organic kerogen in shale oil were identified.

[0135] (2) Based on experimental data from shale cores in typical work areas, characteristic n-alkane molecules and kerogen types were identified. The 3D Atomistic module in Materials Studio software was used to construct molecular structure models of n-alkanes, kerogen, and the kerogen porous medium-n-alkane system, respectively. The results of the model construction are as follows: Figure 4 As shown;

[0136] (3) The molecular structure model of the kerogen porous medium-n-alkane system was obtained by using the conjugate gradient algorithm and NVT ensemble in the large-scale atomic and molecular parallel simulator (LAMMPS) to perform a 2ns energy minimization process, thus obtaining the most stable configuration of the system (i.e., the molecular simulation model).

[0137] (4) Based on step (3), the kerogen porous medium-shale oil molecular structure model is simulated in LAMMPS under actual reservoir conditions of 353K and 20MPa for 2ns, and the spatial motion trajectory of hydrogen protons in the x, y and z directions is extracted within this 2ns time range.

[0138] (5) Based on step (4), the distance between hydrogen proton pairs in the averaged shale oil hydrogen proton pairs and the angle between the line connecting the hydrogen proton pairs and the direction of the external magnetic field were calculated respectively. The results are as follows: Figure 5 As shown;

[0139] (6) Based on step (5), the magnetic dipole-dipole autocorrelation function G(t) of the hydrogen proton pair can be obtained:

[0140]

[0141] In the formula, G(t) is the autocorrelation function of the hydrogen proton pair, and τ is the autocorrelation lag time. γ is Planck's constant, γ / 2π = 42.58 MHz / T is the gyromagnetic ratio of a hydrogen nucleus with spin 1 / 2, and N is the ensemble of dipole-dipole interactions of hydrogen proton pairs.

[0142] (7) Based on step (6), firstly, calculate the magnetic dipole-dipole spectral density functions J(0), J(ω0), and J(2ω0) of the hydrogen proton pair, and obtain the spectral density function by performing a Fourier transform on the magnetic dipole-dipole autocorrelation function:

[0143]

[0144] In the formula, G(t) is the autocorrelation function of the hydrogen proton pair, and J(ω) is the magnetic dipole-dipole spectral density function of the hydrogen proton pair.

[0145] Based on the theoretical relaxation time and the residual dipole coupling relaxation time, the transverse relaxation time T2 is obtained, as shown in the following results. Figure 6 As shown;

[0146] In this embodiment, organic geochemistry and pore structure characterization experiments were conducted. These experiments included, but were not limited to, high-pressure mercury intrusion spectroscopy, nano-CT scanning, scanning electron microscopy (SEM), and whole-hydrocarbon gas chromatography, to clarify the characteristic components of n-alkanes and the type of kerogen porous media in shale crude oil, providing a basis for model construction and force field parameter optimization. Based on the experimental data, the n-alkane molecules and kerogen type were determined, and molecular simulation software was used to construct molecular structure models of n-alkanes, kerogen, and the kerogen porous media-n-alkane system, respectively. The molecular structure model of the kerogen porous media-n-alkane system was then applied at the large-scale atomic and molecular level. An energy optimization algorithm is used in a parallel simulator to minimize the energy and obtain the most stable configuration of the system. Based on the stable molecular structure of the kerogen porous medium-n-alkane system, the actual reservoir conditions are simulated in molecular simulation software, and the spatial trajectories of hydrogen protons in the x, y, and z directions are extracted within the simulation time range. The average values ​​of the hydrogen proton pairs in shale oil and their variation with simulation time are calculated. Based on these values, the magnetic dipole-dipole spectral density function, the values ​​of the hydrogen proton pairs, and the second moment of the residual dipole coupling interaction are calculated, yielding the total transverse relaxation time of shale oil molecules in the constructed kerogen porous medium. This invention, by introducing a strong nano-confinement effect in the porous medium, can accurately calculate the influence of residual dipole coupling of fluid molecules on the transverse relaxation time, significantly improving the accuracy and reliability of NMR technology in shale oil reservoir evaluation. Through in-depth analysis of the residual dipole coupling effect, this method can effectively correct the problem of excessively long transverse relaxation time in traditional NMR theory, thereby more accurately reflecting the actual pore size distribution and providing a solid theoretical foundation and data support for the development and evaluation of shale reservoirs.

[0147] Example 3:

[0148] Another embodiment of this application relates to a shale relaxation time determination device. The implementation details of this shale relaxation time determination device are described below. The following details are for ease of understanding and are not essential for implementing this solution. A schematic diagram of the shale relaxation time determination device in this embodiment can be seen as follows: Figure 2 As shown, it includes:

[0149] The simulation module 201 is used to simulate the preset molecular simulation model in a pre-set experimental simulation environment to obtain the inter-pair distance and inter-pair angle of hydrogen proton pairs in the molecular simulation model. The molecular simulation model is a simulation model used to characterize the kerogen porous media type and characteristic components of n-alkanes in shale crude oil under the nano-confined effect.

[0150] The residual dipole coupling module 202 is used to obtain the residual dipole coupling relaxation time based on the inter-pair distance and inter-pair angle of hydrogen proton pairs.

[0151] The transverse relaxation calculation module 203 is used to obtain the transverse relaxation time based on the residual dipole coupling relaxation time and the theoretical relaxation time.

[0152] In some embodiments, the shale relaxation time determination device further includes:

[0153] The first acquisition module is used to acquire the characteristic components of n-alkanes and the type of kerogen porous media in shale crude oil.

[0154] A module is built to construct molecular structure models using molecular simulation software based on the characteristic components of n-alkanes in shale crude oil and the type of porous kerogen media.

[0155] The processing module is used to perform energy minimization on the molecular structure model to obtain the molecular simulation model.

[0156] In some embodiments, the shale relaxation time determination device further includes:

[0157] The second acquisition module is used to acquire environmental parameters of the shale reservoir;

[0158] The configuration module is used to set the experimental simulation environment by using the environmental parameters of the shale reservoir as simulation parameters for the molecular simulation software.

[0159] In some embodiments, the simulation module 201 includes:

[0160] The simulation unit is used to simulate molecular simulation models in an experimental simulation environment for a preset time.

[0161] The trajectory acquisition unit is used to acquire the spatial motion trajectory of hydrogen proton pairs of n-alkanes in the molecular simulation model during the simulation process.

[0162] The trajectory analysis unit is used to obtain the distance and angle between hydrogen proton pairs based on their spatial motion trajectories.

[0163] In some embodiments, the building module includes:

[0164] Building blocks are used to construct kerogen structural models using molecular simulation software.

[0165] The simulated annealing unit is used to simulate annealing the kerogen structure model to obtain the kerogen porous media model.

[0166] The unit is determined to obtain the molecular structure model of shale oil. Based on the molecular structure model of shale oil and the porous media model of kerogen, the molecular structure model is determined.

[0167] In some embodiments, the residual dipole coupling module 202 includes:

[0168] The second-order moment calculation unit is used to obtain the residual dipole coupling second-order moment based on the inter-pair distance and inter-pair angle of hydrogen proton pairs.

[0169] The residual coupling calculation unit is used to obtain the residual dipole coupling relaxation time based on the residual dipole coupling second moment.

[0170] In some embodiments, the lateral relaxation calculation module 203 includes:

[0171] The function calculation unit is used to obtain the autocorrelation function of hydrogen proton pairs based on the inter-pair distance and the inter-pair angle.

[0172] The transformation unit is used to perform a Fourier transform on the autocorrelation function of hydrogen proton pairs to obtain the spectral density function;

[0173] The transverse relaxation calculation unit is used to obtain the theoretical relaxation time based on the spectral density function, and to obtain the transverse relaxation time based on the residual dipole coupling relaxation time and the theoretical relaxation time.

[0174] It is worth mentioning that all modules involved in this embodiment are logical modules. In practical applications, a logical unit can be a physical unit, a part of a physical unit, or a combination of multiple physical units. Furthermore, to highlight the innovative aspects of this application, this embodiment does not introduce units that are not closely related to solving the technical problems proposed in this application; however, this does not mean that other units are absent in this embodiment.

[0175] Example 4:

[0176] Another embodiment of this application relates to an electronic device, such as... Figure 3 As shown, it includes: at least one processor 901; and a memory 902 communicatively connected to the at least one processor 901; wherein the memory 902 stores instructions executable by the at least one processor 901, the instructions being executed by the at least one processor 901 to enable the at least one processor 901 to perform the shale relaxation time determination method in the above embodiments.

[0177] The memory and processor are connected via a bus, which can include any number of interconnecting buses and bridges, connecting various circuits of one or more processors and memories. The bus can also connect various other circuits, such as peripheral devices, voltage regulators, and power management circuits, which are well known in the art and will not be described further herein. The bus interface provides an interface between the bus and the transceiver. The transceiver can be a single element or multiple elements, such as multiple receivers and transmitters, providing a unit for communicating with various other devices over a transmission medium. Data processed by the processor is transmitted over the wireless medium via an antenna, which further receives data and transmits it to the processor.

[0178] The processor manages the bus and general processing, and also provides various functions, including timing, peripheral interfaces, voltage regulation, power management, and other control functions. Memory is used to store data used by the processor during operation.

[0179] Example 5:

[0180] Another embodiment of this application relates to a computer-readable storage medium storing a computer program. When executed by a processor, the computer program implements the method embodiments described above.

[0181] That is, those skilled in the art will understand that all or part of the steps in the methods of the above embodiments can be implemented by a program instructing related hardware. This program is stored in a storage medium and includes several instructions to cause a device (which may be a microcontroller, chip, etc.) or processor to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0182] Those skilled in the art will understand that the above embodiments are specific embodiments for implementing this application, and in practical applications, various changes can be made to them in form and detail without departing from the spirit and scope of this application.

Claims

1. A method for determining the relaxation time of shale, characterized in that, include: The preset molecular simulation model is simulated in a pre-defined experimental simulation environment to obtain the inter-pair distance and inter-pair angle of hydrogen proton pairs in the molecular simulation model. The molecular simulation model is a simulation model used to characterize the kerogen porous media type and characteristic components of n-alkanes in shale crude oil under the nano-confined effect. Based on the inter-pair distance and inter-pair angle of the hydrogen proton pairs, the residual dipole coupling relaxation time is obtained. Based on the residual dipole coupling relaxation time and the theoretical relaxation time, the transverse relaxation time is obtained.

2. The method for determining shale relaxation time according to claim 1, characterized in that, The molecular simulation model is obtained through the following steps: The characteristic components of n-alkanes and the type of kerogen porous media in the shale crude oil were obtained; Based on the characteristic components of n-alkanes in the shale crude oil and the porous media type of kerogen, a molecular structure model was constructed using molecular simulation software. The molecular structure model is subjected to energy minimization processing to obtain a molecular simulation model.

3. The method for determining shale relaxation time according to claim 2, characterized in that, The experimental simulation environment is set up through the following steps: Obtain environmental parameters of shale reservoirs; The environmental parameters of the shale reservoir are used as simulation parameters for the molecular simulation software to set the experimental simulation environment.

4. The method for determining shale relaxation time according to claim 2, characterized in that, The step of simulating a preset molecular simulation model in a pre-defined experimental simulation environment to obtain the inter-pair distance and inter-pair angle of hydrogen proton pairs in the molecular simulation model includes: The molecular simulation model is simulated in the experimental simulation environment for a preset time; During the simulation, the spatial trajectory of hydrogen proton pairs of n-alkanes in the molecular simulation model is obtained; Based on the spatial trajectory of the hydrogen proton pairs, the distance between the hydrogen proton pairs and the angle between them are obtained.

5. The method for determining shale relaxation time according to claim 1, characterized in that, The process of constructing a molecular structure model using molecular simulation software based on the characteristic components of n-alkanes in the shale crude oil and the porous media type of kerogen includes: A kerogen structure model was constructed using the aforementioned molecular simulation software; The kerogen structure model was subjected to simulated annealing to obtain a kerogen porous media model; Obtain a shale oil molecular structure model, and determine the molecular structure model based on the shale oil molecular structure model and the kerogen porous media model.

6. The method for determining shale relaxation time according to claim 1, characterized in that, The method of obtaining the residual dipole coupling relaxation time based on the inter-pair distance and inter-pair angle of the hydrogen proton pairs includes: Based on the inter-pair distance and inter-pair angle of the hydrogen proton pairs, the residual dipole coupling second moment is obtained; The residual dipole coupling relaxation time is obtained based on the residual dipole coupling second-order moment.

7. The method for determining shale relaxation time according to any one of claims 1 to 6, characterized in that, The process of obtaining the transverse relaxation time based on the residual dipole coupling relaxation time and the theoretical relaxation time includes: The autocorrelation function of the hydrogen proton pair is obtained based on the distance between the hydrogen proton pairs and the angle between them. The spectral density function is obtained by performing a Fourier transform on the autocorrelation function of the hydrogen proton pair. The theoretical relaxation time is obtained based on the spectral density function, and the transverse relaxation time is obtained based on the residual dipole coupling relaxation time and the theoretical relaxation time.

8. A device for determining the relaxation time of shale, characterized in that, include: The simulation module is used to simulate a preset molecular simulation model in a pre-defined experimental simulation environment to obtain the interpair distance and interpair angle of hydrogen proton pairs in the molecular simulation model. The molecular simulation model is a simulation model used to characterize the kerogen porous media type and characteristic components of n-alkanes in shale crude oil under the nano-confined effect. The residual dipole coupling module is used to obtain the residual dipole coupling relaxation time based on the inter-pair distance and inter-pair angle of the hydrogen proton pairs. The transverse relaxation calculation module is used to obtain the transverse relaxation time based on the residual dipole coupling relaxation time and the theoretical relaxation time.

9. An electronic device, characterized in that, include: At least one processor; as well as, A memory communicatively connected to the at least one processor; wherein, The memory stores instructions that can be executed by the at least one processor to enable the at least one processor to perform the shale relaxation time determination method as described in any one of claims 1 to 7.

10. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the shale relaxation time determination method according to any one of claims 1 to 7.

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