Gas occurrence dynamic response modeling method based on coal matrix surface multi-parameter coupling

Abstract

The invention provides a gas occurrence dynamic response modeling method based on coal matrix surface multi-parameter coupling, which mainly comprises the following steps: (1) collecting a coal sample, and then processing and preprocessing the coal sample; (2) carrying out micro-scale surface parameter detection on the processed and pretreated coal sample; (3) performing coupling model construction and parameter calibration on the detected coal sample; and (4) carrying out model verification and comparative analysis on the constructed coupling model. Quantitative correlation of microscopic surface property evolution and macroscopic adsorption behaviors in the gas occurrence process is achieved for the first time, the prediction error is improved by 2-3 times compared with the prediction precision of a traditional single-parameter model, and theoretical support can be provided for efficient development of coal bed gas.

Description

Technical Field

[0001] The present invention belongs to the technical field of unconventional natural gas development, and in particular relates to a gas occurrence dynamic response modeling method based on multi-parameter coupling of a coal matrix surface. Background Art

[0002] Coalbed methane is a clean energy source associated with coal. Its efficient and safe extraction is crucial to promoting the optimization of energy structures and achieving carbon neutrality in various countries. Fluids (coalbed methane, formation water, etc.) in coal reservoirs exist in different forms, with overlapping storage spaces, and the microscopic pore network structural parameters of microscale occurrence are complex and diverse. The occurrence of gas and liquid induces the expansion and contraction of the coal matrix and the dissolution of minerals, resulting in changes in the pore network structure and various sensitivity characteristics, affecting the interface properties of the coal reservoir, such as roughness, wettability, and electrochemical characteristics. At present, the structural characteristics of the pore and fracture system of coal reservoirs, the gas occurrence behavior and the response of interface properties are mainly explored through multi-scale characterization methods and numerical simulations, but there is a lack of systematic research on the multi-parameter coupling mechanism of the coal matrix surface for microscale gas occurrence.

[0003] The traditional coalbed methane storage model is mainly based on the Langmuir monolayer adsorption theory, and its basic equation is:

[0004]

[0005] In formula (10), V L is the Langmuir volume, cm 3 / g,P L is the Langmuir pressure, MPa.

[0006] Although this model can describe the adsorption behavior of a single gas on an ideal surface, it has significant defects: ① The coal matrix surface has a complex pore structure and chemical composition, and the actual adsorption process involves multiple mechanisms such as multilayer adsorption and capillary condensation. The model ignores the surface heterogeneity of the coal matrix; ② Gas adsorption will cause the surface roughness of the coal matrix to increase and the wettability to change. However, this model regards the surface parameters as static constants and cannot reflect the dynamic changes in the surface properties of the coal matrix during the adsorption-desorption process.

[0007] In addition, existing studies on the characterization of coal matrix surface properties are mostly limited to single parameter analysis. For example: ① A quantitative relationship between roughness changes and adsorption amount has not yet been established; ② The existing model does not incorporate the impact of dynamic changes in wettability on capillary forces, resulting in failure in the prediction of low-permeability coal seams; ③ The existing adsorption model does not incorporate the surface charge density σ into the energy balance equation.

[0008] In summary, it is necessary to make further innovations to the existing technologies. Summary of the Invention

[0009] In response to the technical problems existing in the above-mentioned background technology, the present invention proposes a gas occurrence dynamic response modeling method based on multi-parameter coupling of the coal matrix surface. The conception is reasonable. By constructing a surface parameter response matrix through atomic force microscopy morphology analysis, contact angle measurement and surface charge density calculation, the parameter contribution weights obtained by principal component analysis can be effectively determined, and the coupling equation of adsorption energy and surface parameters can be clarified.

[0010] To solve the above technical problems, the present invention provides a gas occurrence dynamic response modeling method based on multi-parameter coupling of coal matrix surface, which is characterized by mainly comprising the following steps:

[0011] (1) Collect coal samples and then process and pretreat them;

[0012] (2) Conduct micro-scale surface parameter testing on processed and pre-treated coal samples;

[0013] (3) Constructing coupling models and calibrating parameters for the tested coal samples;

[0014] (4) Conduct model verification and comparative analysis on the constructed coupling model.

[0015] The gas occurrence dynamic response modeling method based on multi-parameter coupling of coal matrix surface, wherein the specific process of step (2) is:

[0016] (2.1) Obtaining three-dimensional morphological data of coal sample surface

[0017] The irregular morphology of the microscopic geometric shape of the coal sample surface is composed of the peak-to-valley spacing and the degree of height, and is expressed as the arithmetic mean roughness R a RMS roughness R q Quantitative characterization, where:

[0018]

[0019]

[0020] In the above formulas (1)-(3), N x With N y Respectively represent the number of pixels in the X-axis and Y-axis directions of the image;

[0021] Arithmetic mean roughness R a and root mean square roughness R q Detection: AFM tapping mode is used, and the scanning area is divided into 5×5μm 2 The macro roughness and 1×1μm 2The probe has a nano-scale pore, a probe elastic coefficient k = 40 N / m, a resonance frequency f = 70 kHz, a scanning range of 5 μm × 5 μm macroscopic topography → 1 μm × 1 μm microscopic topography, a resolution of 512 × 512 pixels, and a z-axis accuracy of ≤ 0.1 nm.

[0022] (2.2) Obtaining coal sample surface wettability data

[0023] Wettability is the interaction between coal molecules and liquid molecules when the coal surface contacts the liquid. It is specifically manifested as the degree of spreading, adsorption, or wetting of the liquid on the coal surface. It is quantitatively characterized by the deionized water contact angle θ, where:

[0024] cosθ w =rcosθ Y (4);

[0025]

[0026] In the above formulas (4)-(5), θ w is the actual contact angle; θ Y is the Young contact angle; r is the roughness factor;

[0027] Actual contact angle θ w and Young contact angle θ Y Measurement: Use an optical contact angle meter to drip a 2μL droplet on the surface of the coal sample, and use the instrument to measure the contact angle between the droplet and the surface of the coal sample. The measurement time is 0-60s;

[0028] (2.3) Obtaining coal sample surface electrical property data

[0029] The surface electrical properties are the electrical conductivity, dielectricity, and surface charge characteristics of coal under the action of an electric field. Its core indicators include the dielectric constant ε, zeta potential ζ, and charge density σ. The conversion equation between the surface charge density σ and zeta potential ζ of a coal sample is:

[0030]

[0031] In the above formula (6), ε0 is the dielectric constant of vacuum; ε r is the relative dielectric constant of the sample; κ is the inverse of the Debye length; e is the elementary charge; φ0 is the initial surface potential; k B is the Boltzmann constant;

[0032] Detection of Zeta potential ζ: A Zeta potential analyzer was used to detect and analyze the suspension on the surface of the coal sample with a concentration of 0.1 wt%, pH=7, and a temperature of 25°C.

[0033] The gas occurrence dynamic response modeling method based on multi-parameter coupling of coal matrix surface, wherein in the step (2.1), the arithmetic mean roughness R a and root mean square roughness R q During the detection, in order to ensure the R a and R q To be accurate, you need to do the following:

[0034] Scanning area selection: It is necessary to ensure that the scanning area covers the typical morphological features of the coal matrix and avoid selecting areas with surface contamination or mechanical damage. In actual operation, a low-magnification optical microscope pre-scan should be performed first to mark representative areas;

[0035] Probe parameter calibration: The probe elastic modulus and frequency need to be calibrated regularly with standard samples to avoid data deviation due to probe wear;

[0036] Environmental Control: Scanning must be performed on a constant temperature, shockproof platform, and humidity must be below 40% to prevent interference from surface water film. If testing is performed in a non-ideal environment, environmental parameters must be noted in the data and correction factors must be introduced.

[0037] The gas occurrence dynamic response modeling method based on multi-parameter coupling of coal matrix surface, wherein the arithmetic mean roughness R is used in step (2.1) a RMS roughness R q When quantitatively characterizing, R a With R q The calculation requires the following operations:

[0038] Data filtering: The original height data needs to be fitted with a second-order polynomial plane to eliminate the base tilt, and then Gaussian filtering is used to remove high-frequency noise. The deviation between the unfiltered data and the filtered data should be less than 5%, otherwise rescanning is required;

[0039] Multi-region statistics: For each sample, at least three different regions were selected to calculate R a With R q The final value is the arithmetic mean. If the standard deviation between regions exceeds 10%, the number of detection regions needs to be increased to 5.

[0040] In the gas occurrence dynamic response modeling method based on multi-parameter coupling of coal matrix surface, the following operations are required to control the error during the zeta potential ζ detection in step (2.3):

[0041] Preparation of suspension: The particle size of coal powder needs to be controlled within 1-5 μm by a laser particle size analyzer, and the concentration needs to be weighed by an electronic balance. The ultrasonic dispersion time is strictly limited to 10 minutes to avoid particle agglomeration or breakage;

[0042] pH and ionic strength: The test liquid needs to have a concentration of 10 -3 mol / L KCl solution was prepared and the pH was adjusted to 7.0±0.2 with 0.1M HCl / NaOH. Before each batch of testing, the Zeta potential analyzer status should be verified with standard colloids.

[0043] Limitations of the potential conversion formula: The conversion equation (6) between the charge density σ of the coal sample surface and the Zeta potential ζ is only applicable when the Zeta potential ζ is in the range of -100 mV to +100 mV. When the range is outside this range, the Ohshima soft surface model should be used instead.

[0044] The gas occurrence dynamic response modeling method based on multi-parameter coupling of coal matrix surface, wherein the step (3) is to establish a coupling response matrix of roughness, wettability and surface electrical properties to quantify the dynamic effect of gas adsorption on each parameter; the specific process is:

[0045] (3.1) Surface synergistic effect factor

[0046] The arithmetic mean roughness R a , actual contact angle θ w , and the surface charge density σ were analyzed for principal components to determine the contribution weights of each parameter. The calculation equation for the surface synergistic effect factor was obtained as follows:

[0047] SCE=0.35R a * +0.45θ * +0.20σ * (7);

[0048] In the above formula (7), R a * is the normalized roughness; θ * is the normalized contact angle; σ * is the normalized surface charge density; weight coefficients 0.35, 0.45, and 0.20 are obtained through principal component analysis;

[0049] (3.2) Dynamic compensation algorithm

[0050] The following dynamic compensation algorithm equation (8) is constructed to compensate for the hysteresis effect caused by the difference in gas adsorption-desorption paths in coal reservoirs:

[0051]

[0052] In the above formula (8), ΔP comp is the dynamic compensation term; k d is the dynamic compensation coefficient; E a is the activation energy, CH4 is taken as 12.5 kJ / mol, and R is the gas constant;

[0053] (3.3) Quantitative conversion of electrical parameters and adsorption energy

[0054] The relationship between surface charge density σ, contact angle θ and adsorption energy E was established for the first time. ads Direct relationship:

[0055] E ads =2.5σ+1.8(1-cosθ) (9);

[0056] The derivation process of formula (9) is as follows: the interaction energy between the coal surface and CH4 is calculated by density functional theory (DFT), and the charge density term coefficient of 2.5 is obtained by fitting; the wettability term coefficient of 1.8 comes from the linear regression of contact angle and surface energy;

[0057] (3.4) Dynamic response model of gas storage parameters

[0058] The multi-parameter coupling dynamic equation between the change in gas content ΔP and the microscopic surface roughness R, contact angle θ, and Zeta potential ζ is as follows:

[0059] ΔP=αΔR+βΔcosθ+γΔ|ζ|+ΔP comp (10);

[0060] In formula (10), ΔP is the change in gas content calculated by the improved formula, mol / g, ΔR is the change in roughness, nm; Δcosθ is the change in wettability; Δ|ζ| is the change in the absolute value of Zeta potential, mV; α is the roughness coupling weight coefficient, β is the contact angle coupling weight coefficient, γ is the Zeta potential coupling weight coefficient, and ΔP comp is the dynamic compensation term.

[0061] The gas occurrence dynamic response modeling method based on multi-parameter coupling of coal matrix surface, wherein the following requirements must be met when determining the parameter weight of the surface synergistic effect factor in step (3.1):

[0062] Principal component analysis requirements: Input data must contain at least 30 groups of R a , θ, σ complete data set, the data needs to be normalized by Z-score to avoid weight distortion caused by dimension difference;

[0063] Coefficient verification: The weight coefficient needs to be cross-validated by the leave-one-out method. When the relative error exceeds 15%, the data needs to be re-collected. For high-ash coal samples with ash content >20%, a separate weight system needs to be established.

[0064] The gas occurrence dynamic response modeling method based on multi-parameter coupling of coal matrix surface, wherein, when constructing the dynamic compensation algorithm in step (3.2), the following operations need to be performed:

[0065] Time derivative calculation: dSCE / dt needs to be calculated using the five-point numerical differentiation method with a time step of Δt = 1 minute. The experimental data must cover at least three complete adsorption-desorption cycles.

[0066] Activation energy value: E a It needs to be determined by Arrhenius curve fitting, the test temperature range is 20-50℃, if the coal sample vitrinite reflectance R o,max >2.5% requires additional consideration of thermal maturity correction items;

[0067] Hysteresis effect correction: compensation coefficient k d Need to distinguish adsorption k d,ads With desorption k d,des path, typical values ​​are 0.12 for adsorption and 0.08 for desorption.

[0068] The gas occurrence dynamic response modeling method based on multi-parameter coupling of coal matrix surface, wherein the Zeta potential in step (3.3) is related to the adsorption energy E ads The scope of application of the direct relationship limitation must meet the following requirements:

[0069] Coal rank adaptability: E ads =2.5σ+1.8(1-cosθ) only applies to R o,max =1.0-2.5% of medium-high coal rank, R o,max For low coal rank less than 0.5%, the organic matter content correction item needs to be added: E ads '=E ads [1 + 0.05(TOC-60)], where TOC is the total organic carbon content;

[0070] Gas type expansion: For CO2 adsorption, the coefficient of the electrical parameter term needs to be adjusted to 3.1, and the coefficient of the wettability term needs to be adjusted to 2.2, and verified by molecular simulation.

[0071] The gas occurrence dynamic response modeling method based on multi-parameter coupling of coal matrix surface, wherein the experimental calibration requirements in step (3.3) are:

[0072] Density functional theory (DFT) calculation parameters: VASP software was used, with PBE-D3 as the functional, a cutoff energy of 400 eV, and a k-point grid of 3 × 3 × 1. The surface model must contain at least 5 layers of carbon atoms, with the bottom 2 layers fixed.

[0073] Measured data matching: at least 15 groups of E of different coal samples are required ads Fitting with σ and θ data, the coefficient of determination R 2 When <0.85, the charge density measurement error needs to be checked.

[0074] The gas occurrence dynamic response modeling method based on multi-parameter coupling of coal matrix surface, wherein: the step (4) specifically compares the V value calculated using the traditional coalbed methane occurrence model with the measured ΔP to verify the calculation effect of the gas occurrence parameter dynamic response model.

[0075] The gas occurrence dynamic response modeling method based on multi-parameter coupling of coal matrix surface, wherein the specific process of step (1) is: first cutting the collected coal sample into thin slices, and then performing argon ion polishing on the thin slices to a surface roughness R a <5nm to remove impurities on the coal matrix surface, followed by vacuum drying to a moisture content of <0.5wt%, and finally gas adsorption pretreatment by injecting CH4 gas using a high-pressure adsorption instrument.

[0076] By adopting the above technical solution, the present invention has the following beneficial effects:

[0077] The modeling method for the dynamic response of gas occurrence on the coal matrix surface coupled with multiple parameters of the present invention is well conceived. The surface parameter response matrix is ​​constructed by atomic force microscopy morphology analysis, contact angle measurement and surface charge density calculation. The parameter contribution weights obtained by principal component analysis can be effectively determined, and the coupling equation of adsorption energy and surface parameters can be clarified. The dynamic response characteristics of the multiple parameters of the coal matrix surface to gas occurrence can be effectively analyzed and evaluated.

[0078] Compared with the existing technology, the present invention adds roughness, wettability, and surface electrical properties as microscopic surface property parameters of the coal matrix, which more comprehensively reflects the dynamic changes of the coal matrix surface; the average error of the gas content calculated by the present invention is ≤8.3%, which is smaller than the traditional method (average error of 15-25%), and the prediction accuracy is improved by 2-3 times.

[0079] The present invention introduces a dynamic compensation algorithm, namely formula (8), to compensate for the hysteresis effect caused by the difference in the adsorption-desorption path of coal reservoir gas, which is applicable to non-equilibrium conditions; the present invention establishes the surface electrical properties and adsorption energy correlation equation (9), which realizes the quantitative application of electrical parameters in the field of coalbed gas storage research for the first time.

[0080] In addition, the present invention avoids the traditional method of relying on high-cost high-pressure adsorption experiments to determine the adsorption characteristics of coalbed gas. Based on conventional equipment such as AFM and contact angle meter, all parameters can be detected by standardized equipment without the need for special experimental conditions, reducing detection costs by more than 30%. BRIEF DESCRIPTION OF THE DRAWINGS

[0081] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0082] Figure 1 This is a flow chart of the method for dynamic response of gas storage in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0083] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0084] The present invention will be further explained below with reference to specific embodiments.

[0085] like Figure 1 As shown, this embodiment provides a gas occurrence dynamic response modeling method based on multi-parameter coupling of coal matrix surface, which mainly includes the following steps:

[0086] S100, sample preparation and pretreatment

[0087] S101. Coal sample collection and processing

[0088] Sample source: Anthracite from Qinshui Basin, Shanxi Province (vitrinite reflectance R o,max =2.3%±0.2%)

[0089] Processing requirements:

[0090] Cut into 10×10×5mm 3 Block, argon ion polished to surface roughness R a <5nm (Bruker Ilion+ system, accelerating voltage 2kV, polishing time 2h)

[0091] Vacuum drying (60°C, 48h) until the moisture content is <0.5wt%;

[0092] S102, gas adsorption pretreatment

[0093] Inject CH4 gas into the high-pressure adsorption instrument (IS-300 model) and set the conditions:

[0094] Temperature: 30℃±0.5℃, pressure gradient: 0.5 / 2 / 4 / 6 / 8MPa, each pressure point is balanced for 24h.

[0095] S200, multi-scale surface parameter detection

[0096] S201. Obtaining three-dimensional morphological data of the coal sample surface

[0097] The irregular morphology of the microscopic geometric shape of the coal sample surface is composed of the peak-to-valley spacing and the degree of height, and is expressed as the arithmetic mean roughness R a RMS roughness R q Quantitative characterization, where:

[0098]

[0099]

[0100] In the above formulas (1)-(3), N x With N y Respectively represent the number of pixels in the X-axis and Y-axis directions of the image;

[0101] Arithmetic mean roughness R a and root mean square roughness R q Detection: AFM tapping mode is used, and the scanning area is divided into 5×5μm 2 The macro roughness and 1×1μm 2 The probe has a nano-scale pore, a probe elastic coefficient k = 40 N / m, a resonance frequency f = 70 kHz, a scanning range of 5 μm × 5 μm macroscopic topography → 1 μm × 1 μm microscopic topography, a resolution of 512 × 512 pixels, and a z-axis accuracy of ≤ 0.1 nm.

[0102] In this embodiment, the instrument parameters are selected as follows:

[0103] Equipment: Bruker Dimension Icon AFM;

[0104] Mode: PeakForce Tapping, probe model RTESPA-300 (k = 40 N / m);

[0105] Scanning area: 5×5μm 2 (macro), 1×1μm 2 (nanometer level), resolution 512×512 pixels.

[0106] Pressure (MPa) <![CDATA[R a (nm) Macro]]> <![CDATA[R q (nm) Microscopic]]> 0 (before adsorption) 52.1±1.2 6.8±0.3 8 (after adsorption) 68.7±1.5 9.2±0.4

[0107] Among them, the arithmetic mean roughness R a and root mean square roughness R q During the detection, in order to ensure the R a and R qTo be accurate, you need to do the following:

[0108] Scanning area selection: It is necessary to ensure that the scanning area covers the typical morphological features of the coal matrix and avoid selecting areas with surface contamination or mechanical damage. In actual operation, a low-magnification optical microscope pre-scan should be performed first to mark representative areas;

[0109] Probe parameter calibration: The probe elastic modulus and frequency need to be calibrated regularly with standard samples to avoid data deviation due to probe wear;

[0110] Environmental Control: Scanning must be performed on a constant temperature, shockproof platform, and humidity must be below 40% to prevent interference from surface water film. If testing is performed in a non-ideal environment, environmental parameters must be noted in the data and correction factors must be introduced.

[0111] At the same time, the arithmetic mean roughness R a RMS roughness R q When quantitatively characterizing, R a With R q The calculation requires the following operations:

[0112] Data filtering: The original height data needs to be fitted with a second-order polynomial plane to eliminate the base tilt, and then Gaussian filtering is used to remove high-frequency noise. The deviation between the unfiltered data and the filtered data should be less than 5%, otherwise rescanning is required;

[0113] Multi-region statistics: For each sample, at least three different regions were selected to calculate R a With R q The final value is the arithmetic mean. If the standard deviation between regions exceeds 10%, the number of detection regions needs to be increased to 5.

[0114] S202. Obtaining coal sample surface wettability data

[0115] Wettability is the interaction between coal molecules and liquid molecules when the coal surface contacts the liquid. It is specifically manifested as the degree of spreading, adsorption, or wetting of the liquid on the coal surface. It is quantitatively characterized by the deionized water contact angle θ, where:

[0116] cosθ w =rcosθ Y (4);

[0117]

[0118] In the above formulas (4) and (5), θ w is the actual contact angle; θ Y is the Young contact angle; r is the roughness factor;

[0119] Actual contact angle θ wand Young contact angle θ Y Measurement: Use an optical contact angle meter to drip a 2μL droplet on the surface of the coal sample, and use the instrument to measure the contact angle between the droplet and the surface of the coal sample. The measurement time is 0-60s.

[0120] In this embodiment, the device is a Krüss DSA100 optical contact angle meter, the droplet volume is 2 μL (deionized water), and the ambient humidity is 45% RH;

[0121] Dynamic contact angle measurement (0-60s) was corrected using the Wenzel model:

[0122] (Measured θ Y =78.5°);

[0123]

[0124] S203. Obtaining coal sample surface electrical property data

[0125] Surface electrical properties refer to the electrical conductivity, dielectricity, and surface charge characteristics of coal under the action of an electric field. Its core indicators include dielectric constant ε, zeta potential ζ, and charge density σ.

[0126] Equipment selection: zeta potential analyzer (Malvern Zetasizer Nano ZS90);

[0127] Sample preparation: Coal powder (200 mesh) was suspended in 0.001 M KCl solution and ultrasonically dispersed for 10 min. The conversion equation between the surface charge density σ and the zeta potential ζ of the coal sample is:

[0128]

[0129] example

[0130] In formula (6), ε0 is the dielectric constant of vacuum, ε0 = 8.854 × 10 -12 F / m; ε r is the relative dielectric constant of the sample, ε r =78.5 (water); κ is the reciprocal of the Debye length, nm -1 , κ -1 =9.6nm (0.001M KCl solution, 25℃); e is the elementary charge, 1.602×10 -19 C;φ0=ζ=-28.6×10 -3 V; T = 303K.

[0131]

[0132] Zeta potential ζ detection: Zeta potential analyzer was used to measure the concentration of 0.1wt%, pH=7,

[0133] The suspension on the surface of the coal sample at a temperature of 25°C is tested and analyzed;

[0134] The following operations are required to control the error during Zeta potential ζ detection:

[0135] Preparation of suspension: The particle size of coal powder needs to be controlled within 1-5 μm by a laser particle size analyzer, and the concentration needs to be weighed by an electronic balance. The ultrasonic dispersion time is strictly limited to 10 minutes to avoid particle agglomeration or breakage;

[0136] pH and ionic strength: The test liquid needs to have a concentration of 10 -3 mol / L KCl solution was prepared and the pH was adjusted to 7.0±0.2 with 0.1M HCl / NaOH. Before each batch of testing, the Zeta potential analyzer status should be verified with standard colloids.

[0137] Limitations of the potential conversion formula: The conversion equation (6) between the charge density σ of the coal sample surface and the Zeta potential ζ is only applicable when the Zeta potential ζ is in the range of -100 mV to +100 mV. When the range is outside this range, the Ohshima soft surface model should be used instead.

[0138] S300, coupling model construction and parameter calibration

[0139] S301, surface synergistic effect factor SCE

[0140] The arithmetic mean roughness R a , actual contact angle θ w , and the surface charge density σ were analyzed for principal components to determine the contribution weights of each parameter. The calculation equation for the surface synergistic effect factor was obtained as follows:

[0141] SCE=0.35R a * +0.45θ * +0.20σ * (7);

[0142] In the above formula (7), R a * is the normalized roughness; θ * is the normalized contact angle; σ * is the normalized surface charge density; weight coefficients 0.35, 0.45, and 0.20 are obtained through principal component analysis;

[0143] Normalization parameters:

[0144]

[0145] The following requirements must be met when determining the parameter weights of the surface synergy effect factor:

[0146] Principal component analysis requirements: Input data must contain at least 30 groups of R a , θ, σ complete data set, the data needs to be normalized by Z-score to avoid weight distortion caused by dimension difference;

[0147] Coefficient verification: The weight coefficient needs to be cross-validated by the leave-one-out method. When the relative error exceeds 15%, the data needs to be re-collected. For high-ash coal samples with ash content >20%, a separate weight system needs to be established.

[0148] In this embodiment, the SCE value is calculated (under 8 MPa conditions) as follows:

[0149] SCE = 0.35 × 1.0 + 0.45 × 1.0 + 0.20 × 1.0 = 1.0 (maximum value);

[0150] S302, dynamic compensation algorithm

[0151] The following dynamic compensation algorithm equation (8) is constructed to compensate for the hysteresis effect caused by the difference in gas adsorption-desorption paths in coal reservoirs:

[0152]

[0153] In the above formula (8), ΔP comp is the dynamic compensation term; k d is the dynamic compensation coefficient; E a is the activation energy, CH4 is taken as 12.5 kJ / mol, and R is the gas constant;

[0154] When building a dynamic compensation algorithm, the following operations are required:

[0155] Time derivative calculation: dSCE / dt needs to be calculated using the five-point numerical differentiation method with a time step of Δt = 1 minute. The experimental data must cover at least three complete adsorption-desorption cycles.

[0156] Activation energy value: E a It needs to be determined by Arrhenius curve fitting, the test temperature range is 20-50℃, if the coal sample vitrinite reflectance R o,max >2.5% requires additional consideration of thermal maturity correction items;

[0157] Hysteresis effect correction: compensation coefficient k d Need to distinguish adsorption k d,ads With desorption k d,des path, typical values ​​are 0.12 for adsorption and 0.08 for desorption.

[0158] In this embodiment, the adsorption-desorption path difference is corrected to:

[0159]

[0160] In the above formula, ΔP comp is the dynamic compensation term (mol / g); k d is the dynamic compensation coefficient (taken as 0.12±0.03, calibrated by experiment); E a is the activation energy (kJ / mol), which is 12.5 kJ / mol for CH4; R is the gas constant, which is 8.314 J / (mol·k).

[0161] S303. Quantitative conversion of property parameters and adsorption energy

[0162] The relationship between surface charge density σ, contact angle θ and adsorption energy E was established for the first time. ads Direct relationship:

[0163] E ads =2.5σ+1.8(1-cosθ) (9);

[0164] The derivation process of formula (9) is as follows: the interaction energy between the coal surface and CH4 is calculated by density functional theory (DFT), and the charge density term coefficient of 2.5 is obtained by fitting; the wettability term coefficient of 1.8 comes from the linear regression of contact angle and surface energy;

[0165] Zeta potential and adsorption energy E ads The scope of application of the direct relationship limitation must meet the following requirements:

[0166] Coal rank adaptability: E ads =2.5σ+1.8(1-cosθ) only applies to R o,max =1.0-2.5% of medium-high coal rank, R o,max For low coal rank less than 0.5%, the organic matter content correction item needs to be added: E ads '=E ads [1 + 0.05(TOC-60)], where TOC is the total organic carbon content;

[0167] Gas type expansion: For CO2 adsorption, the coefficient of the electrical parameter term needs to be adjusted to 3.1 and the coefficient of the wettability term needs to be adjusted to 2.2, and verified by molecular simulation;

[0168] The experimental calibration requirements (when calculating the interaction energy between the coal surface and CH4 by density functional theory (DFT), it is necessary to set the DFT calculation parameters described below and match them with the following measured data to ensure that the fitted charge density term coefficient of 2.5 and the wettability term coefficient of 1.8 are reliable) are as follows:

[0169] Density functional theory (DFT) calculation parameters: VASP software was used, with PBE-D3 as the functional, a cutoff energy of 400 eV, and a k-point grid of 3 × 3 × 1. The surface model must contain at least 5 layers of carbon atoms, with the bottom 2 layers fixed.

[0170] Measured data matching: at least 15 groups of E of different coal samples are required ads Fitting with σ and θ data, the coefficient of determination R 2 When <0.85, the charge density measurement error needs to be checked.

[0171] In this embodiment, the electrical-wettability equation is:

[0172] E ads =2.5×(−0.028)+1.8×(1−cos41.5°)=−0.07+0.82=0.75 kJ / mol (<5% deviation from DFT calculated value 0.78 kJ / mol);

[0173] S304. Dynamic response model of gas occurrence parameters

[0174] The multi-parameter coupling dynamic equation between the change in gas content ΔP and the microscopic surface roughness R, contact angle θ, and Zeta potential ζ is as follows:

[0175] ΔP=αΔR+βΔcosθ+γΔ|ζ|+ΔP comp (10);

[0176] In formula (10), ΔP is the change in gas content calculated by the improved formula, mol / g, ΔR is the change in roughness, nm; Δcosθ is the change in wettability; Δ|ζ| is the change in the absolute value of Zeta potential, mV; α is the roughness coupling weight coefficient, β is the contact angle coupling weight coefficient, γ is the Zeta potential coupling weight coefficient, and ΔP comp is the dynamic compensation term;

[0177] The multivariate linear equation used in this embodiment is:

[0178] ΔP=0.17ΔR+2.38Δcosθ-0.009Δ|ζ|+ΔP comp ;

[0179] Parameter change:

[0180] ΔR = 68.7-52.1 = 16.6 nm;

[0181] Δcosθ=cos41.5°-cos63.2°=0.749-0.452=0.297;

[0182] Δ|ζ|=|-28.6|-|-15.2|=13.4mV;

[0183] final:

[0184] ΔP=0.17×16.6+2.38×0.297-0.009×13.4+1.04×10 -5 =2.822+0.707-0.121+0.00001

[0185] ≈3.408mol / g.

[0186] S400, Model Verification and Comparative Analysis

[0187] S401, Comparison with the traditional Langmuir model

[0188]

[0189] S402, Summary of Key Parameters and Technical Advantages

[0190] Parameters / Technology The present invention requires Disadvantages of conventional methods Roughness detection accuracy ±0.5nm(AFM) Optical microscope ±50nm Contact angle correction model Wenzel+ dynamic correction Young equation only Adsorption energy calculation correlation parameters Electrical properties + wettability Rely only on isotherms Temperature and pressure application range 20-50℃,0-10MPa Temperature-pressure coupling effects are often ignored

[0191] S403. Example data table (part)

[0192] Coal sample number <![CDATA[R o,max (%)]]> SCE(8MPa) <![CDATA[E ads (kJ / mol)]]> Prediction error (%) MX-1 2.1 0.92 0.71 5.8 MX-2 2.4 0.95 0.77 4.3 MX-3 1.8 0.87 0.68 7.1 MX-3 1.9 0.89 0.70 6.3

[0193] The present invention has a reasonable concept and can effectively analyze and evaluate the dynamic response characteristics of multiple parameters of the coal matrix surface to gas occurrence. It realizes the quantitative correlation between the evolution of microscopic surface properties and macroscopic adsorption behavior during gas occurrence for the first time. The prediction error is 2-3 times higher than the prediction accuracy of the traditional single-parameter model, which can provide theoretical support for the efficient development of coalbed methane.

[0194] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A gas occurrence dynamic response modeling method based on multi-parameter coupling of coal matrix surface, characterized in that: The main steps include: (1) Collect coal samples and then process and pretreat them; (2) Conduct micro-scale surface parameter testing on processed and pre-treated coal samples; (3) Constructing coupling models and calibrating parameters for the tested coal samples; (4) Conduct model verification and comparative analysis on the constructed coupling model.

2. The gas occurrence dynamic response modeling method based on multi-parameter coupling of coal matrix surface according to claim 1, characterized in that: The specific process of step (2) is as follows: (2.1) Obtaining three-dimensional morphological data of coal sample surface The irregular morphology of the microscopic geometric shape of the coal sample surface is composed of the peak-to-valley spacing and the degree of height, and is expressed as the arithmetic mean roughness R a RMS roughness R q Quantitative characterization, where: In the above formulas (1)-(3), N x With N y Respectively represent the number of pixels in the X-axis and Y-axis directions of the image; Arithmetic mean roughness R a and root mean square roughness R q Detection: AFM tapping mode is used, and the scanning area is divided into 5×5μm 2 The macro roughness and 1×1μm 2 The probe has a nano-scale pore, a probe elastic coefficient k = 40 N / m, a resonance frequency f = 70 kHz, a scanning range of 5 μm × 5 μm macroscopic topography → 1 μm × 1 μm microscopic topography, a resolution of 512 × 512 pixels, and a z-axis accuracy of ≤ 0.1 nm. (2.2) Obtaining coal sample surface wettability data Wettability is the interaction between coal molecules and liquid molecules when the coal surface contacts the liquid. It is specifically manifested as the degree of spreading, adsorption, or wetting of the liquid on the coal surface. It is quantitatively characterized by the deionized water contact angle θ, where: cosθ w =rcosθ Y (4); In the above formulas (4) and (5), θ w is the actual contact angle; θ Y is the Young contact angle; r is the roughness factor; Actual contact angle θ w and Young contact angle θ Y Measurement: Use an optical contact angle meter to drip a 2μL droplet on the surface of the coal sample, and use the instrument to measure the contact angle between the droplet and the surface of the coal sample. The measurement time is 0-60s; (2.3) Obtaining coal sample surface electrical property data The surface electrical properties are the electrical conductivity, dielectricity, and surface charge characteristics of coal under the action of an electric field. Its core indicators include the dielectric constant ε, zeta potential ζ, and charge density σ. The conversion equation between the surface charge density σ and zeta potential ζ of a coal sample is: In the above formula (6), ε0 is the dielectric constant of vacuum; ε r is the relative dielectric constant of the sample; κ is the inverse of the Debye length; e is the elementary charge; φ0 is the initial surface potential; k B is the Boltzmann constant; Detection of Zeta potential ζ: A Zeta potential analyzer was used to detect and analyze the suspension on the surface of the coal sample with a concentration of 0.1 wt%, pH=7, and a temperature of 25°C.

3. The gas occurrence dynamic response modeling method based on multi-parameter coupling of coal matrix surface according to claim 2, characterized in that: In the step (2.1), the arithmetic mean roughness R a and root mean square roughness R q During the detection, in order to ensure the R a and R q To be accurate, you need to do the following: Scanning area selection: It is necessary to ensure that the scanning area covers the typical morphological features of the coal matrix and avoid selecting areas with surface contamination or mechanical damage. In actual operation, a low-magnification optical microscope pre-scan should be performed first to mark representative areas; Probe parameter calibration: The probe elastic modulus and frequency need to be calibrated regularly with standard samples to avoid data deviation due to probe wear; Environmental Control: Scanning must be performed on a constant temperature, shockproof platform, and humidity must be below 40% to prevent interference from surface water film. If testing is performed in a non-ideal environment, environmental parameters must be noted in the data and correction factors must be introduced.

4. The gas occurrence dynamic response modeling method based on multi-parameter coupling of coal matrix surface according to claim 2, characterized in that: In the step (2.1), the arithmetic mean roughness R a RMS roughness R q When quantitatively characterizing, R a With R q The calculation requires the following operations: Data filtering: The original height data needs to be fitted with a second-order polynomial plane to eliminate the base tilt, and then Gaussian filtering is used to remove high-frequency noise. The deviation between the unfiltered data and the filtered data should be less than 5%, otherwise rescanning is required; Multi-region statistics: For each sample, at least three different regions were selected to calculate R a With R q The final value is the arithmetic mean. If the standard deviation between regions exceeds 10%, the number of detection regions needs to be increased to 5.

5. The gas occurrence dynamic response modeling method based on multi-parameter coupling of coal matrix surface according to claim 2, characterized in that: The following operations are required to control the error during the zeta potential ζ detection in step (2.3): Preparation of suspension: The particle size of coal powder needs to be controlled within 1-5 μm by a laser particle size analyzer, and the concentration needs to be weighed by an electronic balance. The ultrasonic dispersion time is strictly limited to 10 minutes to avoid particle agglomeration or breakage; pH and ionic strength: The test liquid needs to have a concentration of 10 -3 mol / L KCl solution was prepared and the pH was adjusted to 7.0±0.2 with 0.1M HCl / NaOH. Before each batch of testing, the Zeta potential analyzer status should be verified with standard colloids. Limitations of the potential conversion formula: The conversion equation (6) between the charge density σ of the coal sample surface and the Zeta potential ζ is only applicable when the Zeta potential ζ is in the range of -100 mV to +100 mV. When the range is outside this range, the Ohshima soft surface model should be used instead.

6. The gas occurrence dynamic response modeling method based on multi-parameter coupling of coal matrix surface according to claim 1, characterized in that: The step (3) is to establish a coupled response matrix of roughness, wettability and surface electrical properties to quantify the dynamic effect of gas adsorption on each parameter; the specific process is: (3.1) Surface synergistic effect factor The arithmetic mean roughness R a , actual contact angle θ w , and the surface charge density σ were analyzed for principal components to determine the contribution weights of each parameter. The calculation equation for the surface synergistic effect factor was obtained as follows: SCE=0.35R a * +0.45θ * +0.20σ * (7); In the above formula (7), R a * is the normalized roughness; θ * is the normalized contact angle; σ * is the normalized surface charge density; The weight coefficients 0.35, 0.45, and 0.20 were obtained through principal component analysis; (3.2) Dynamic compensation algorithm The following dynamic compensation algorithm equation (8) is constructed to compensate for the hysteresis effect caused by the difference in gas adsorption-desorption paths in coal reservoirs: In the above formula (8), ΔP comp is the dynamic compensation term; k d is the dynamic compensation coefficient; E a is the activation energy, CH4 is taken as 12.5 kJ / mol, and R is the gas constant; (3.3) Quantitative conversion of electrical parameters and adsorption energy The relationship between surface charge density σ, contact angle θ and adsorption energy E was established for the first time. ads Direct relationship: E ads =2.5σ+1.8(1-cosθ) (9); The derivation process of formula (9) is as follows: the interaction energy between the coal surface and CH4 is calculated by density functional theory (DFT), and the charge density term coefficient of 2.5 is obtained by fitting; the wettability term coefficient of 1.8 comes from the linear regression of contact angle and surface energy; (3.4) Dynamic response model of gas storage parameters The multi-parameter coupling dynamic equation between the change in gas content ΔP and the microscopic surface roughness R, contact angle θ, and Zeta potential ζ is as follows: ΔP=αΔR+βΔcosθ+γΔ|ζ|+ΔP comp (10); In formula (10), ΔP is the change in gas content calculated by the improved formula, mol / g, ΔR is the change in roughness, nm; Δcosθ is the change in wettability; Δ|ζ| is the change in the absolute value of Zeta potential, mV; α is the roughness coupling weight coefficient, β is the contact angle coupling weight coefficient, γ is the Zeta potential coupling weight coefficient, and ΔP comp is the dynamic compensation term.

7. The gas occurrence dynamic response modeling method based on multi-parameter coupling of coal matrix surface according to claim 6, characterized in that: In step (3.1), the following requirements must be met when determining the parameter weight of the surface synergistic effect factor: Principal component analysis requirements: Input data must contain at least 30 groups of R a , θ, σ complete data set, the data needs to be normalized by Z-score to avoid weight distortion caused by dimension difference; Coefficient verification: The weight coefficient needs to be cross-validated by the leave-one-out method. When the relative error exceeds 15%, the data needs to be re-collected. For high-ash coal samples with ash content >20%, a separate weight system needs to be established.

8. The gas occurrence dynamic response modeling method based on multi-parameter coupling of coal matrix surface according to claim 6, characterized in that: When constructing the dynamic compensation algorithm in step (3.2), the following operations are required: Time derivative calculation: dSCE / dt needs to be calculated using the five-point numerical differentiation method with a time step of Δt = 1 minute. The experimental data must cover at least three complete adsorption-desorption cycles. Activation energy value: E a It needs to be determined by Arrhenius curve fitting, the test temperature range is 20-50℃, if the coal sample vitrinite reflectance R o,max >2.5% requires additional consideration of thermal maturity correction items; Hysteresis effect correction: compensation coefficient k d Need to distinguish adsorption k d,ads With desorption k d,des path, typical values ​​are 0.12 for adsorption and 0.08 for desorption.

9. The gas occurrence dynamic response modeling method based on multi-parameter coupling of coal matrix surface according to claim 6, characterized in that: The Zeta potential and adsorption energy E in step (3.3) ads The direct relationship application scope limitation must meet the following requirements: Coal rank adaptability: E ads =2.5σ+1.8(1-cosθ) only applies to R o,max =1.0-2.5% of medium-high coal rank, R o,max For low coal rank less than 0.5%, the organic matter content correction item needs to be added: E ads '=E ads [1 + 0.05(TOC-60)], where TOC is the total organic carbon content; Gas type expansion: For CO2 adsorption, the coefficient of the electrical parameter term needs to be adjusted to 3.1, and the coefficient of the wettability term needs to be adjusted to 2.2, and verified by molecular simulation.

10. The gas occurrence dynamic response modeling method based on multi-parameter coupling of coal matrix surface according to claim 6, characterized in that: The experimental calibration requirements in step (3.3) are: Density functional theory (DFT) calculation parameters: VASP software was used, with PBE-D3 as the functional, a cutoff energy of 400 eV, and a k-point grid of 3 × 3 × 1. The surface model must contain at least 5 layers of carbon atoms, with the bottom 2 layers fixed. Measured data matching: at least 15 groups of E of different coal samples are required ads Fitting with σ and θ data, the coefficient of determination R 2 When <0.85, the charge density measurement error needs to be checked.

11. The gas occurrence dynamic response modeling method based on multi-parameter coupling of coal matrix surface according to claim 1, characterized in that: The step (4) specifically involves comparing the V value calculated using the traditional coalbed methane occurrence model with the measured ΔP to verify the calculation effect of the gas occurrence parameter dynamic response model.

12. The gas occurrence dynamic response modeling method based on multi-parameter coupling of coal matrix surface according to claim 1, characterized in that: The specific process of step (1) is: first, the collected coal sample is cut into thin slices, and then the thin slices are polished by argon ion to a surface roughness of R a <5nm to remove impurities on the coal matrix surface, followed by vacuum drying to a moisture content of <0.5wt%, and finally gas adsorption pretreatment by injecting CH4 gas using a high-pressure adsorption instrument.

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