Evaluation method for representing organic matter carbonization degree by considering second-order laser Raman parameters

Abstract

The invention relates to an evaluation method for representing the carbonization degree of sedimentary organic matter by considering second-order laser Raman parameters, a new parameter aiming at a second-order peak is defined, a set of new formula is provided, the formula considers evolution laws of S2 and S3 in the second-order peak on the basis of considering parameters of a first-order D peak and a first-order G peak, and the method is suitable for the evaluation of the carbonization degree of the sedimentary organic matter. The carbonization degree of the organic matter can be represented more comprehensively and reasonably, and the method is more suitable for the carbonization degree S-RmcRo / % of the organic matter with higher thermal evolution degree.

Description

Technical Field

[0001] The invention relates to an evaluation method for characterizing the carbonization degree of sedimentary organic matter by taking into account second-order laser Raman parameters, and belongs to the technical field of oil and gas exploration and development. Background Art

[0002] Organic carbonization (graphitization) refers to the geological phenomenon that organic matter in highly mature shale undergoes degradation and cracking, and is partially or completely converted into graphite or graphite-like substances, suggesting that the hydrocarbon generation capacity of the source rock (shale) is close to exhaustion. These phenomena are fatal to the reservoir performance of unconventional shales, mainly manifested in a large reduction or even disappearance of organic pores and intercrystalline pores of clay minerals, and a reduction in the adsorption capacity of natural gas, which further increases the difficulty of resource evaluation.

[0003] In the study of organic carbonization, the most important experiment is to conduct laser Raman spectroscopy on asphalt slices. A 532nm wavelength Nd-YAG laser is used to obtain the laser Raman spectrum, in which the horizontal axis is the Raman shift and the vertical axis is the intensity. The laser Raman spectrum includes two regions. The first-order region is the Raman shift between 1000 and 1800 cm -1 (including D peak and G peak), the second-order region is the Raman shift between 2500 and 3100 cm -1 (including S2 peak, S3 peak and S4 peak).

[0004] At present, the most widely used and recognized method for identifying and evaluating the carbonization degree of organic matter is the laser Raman parameter method proposed by Liu Dehan et al. (2013), which uses the Raman spectrum parameters of solid organic matter (peak height ratio of D peak and G peak) to characterize thermal maturity. The formula is: Rmc R o / % = 1.1659*h(D h / G h )+2.7588, this formula is for the highly mature organic matter in the asphalt transformation stage, in which the D peak and the G peak are both first-order peaks. On the other hand, although previous studies are different, they are often limited to the analysis of the first-order peaks and ignore the evolution of the second-order peaks. In fact, after reaching the graphitization stage, the secondary region (2500~3100cm -1 The peaks in the ordering process also show a change in the degree of ordering, showing an obvious S2 peak (Raman shift 2700cm -1 Around) and small S3 (Raman shift 2900cm -1 around) and S4 (Raman shift 3200cm -1 With the increase of carbonization degree, the S2 peak strengthens, while the S3 and S4 peaks weaken. Summary of the invention

[0005] In view of the shortcomings of the existing evaluation and analysis methods, in order to more comprehensively and reasonably characterize the carbonization degree of organic matter, the present invention proposes a new parameter for the second-order peak, namely, the second-order peak S RPWR (S RPWR =S3 FWHM / S2 FWHM ), on the basis of considering the first-order D peak and G peak parameters, the evolution law of the S2 and S3 peak parameters in the second-order peak was taken into account (by the new parameter S RPWR The carbonization degree of organic matter with a higher degree of thermal evolution was obtained. S-Rmc R o / % calculation formula:

[0006]

[0007] In formula (1), a is h(D h / G h ) is the ratio of the D peak height to the G peak height, D h is the peak height of the D peak, G h Represents the peak height of the G peak.

[0008] In formula (2), b is S RPWR (The half-peak width ratio of S3 and S2, S RPWR =S3 FWHM / S2 FWHM ),S3 FWHM is the half-peak width of S3, S2 FWHM It is the half-peak width of S2. S2 and S3 peaks will only appear in highly mature organic matter with a high degree of maturity.

[0009] In formula (3), y is S-Rmc R o / % is the maturity calculated by the formula of the present invention.

[0010] In formula (4), a is h(D h / G h ) is the ratio of the D peak height to the G peak height, b is the S RPWR (The half-peak width ratio of S3 and S2, S RPWR =S3 FWHM / S2 FWHM ).

[0011] In formula (5), y is S-Rmc R o / % is the maturity calculated by the formula of the present invention, a is h(D h / G h )(ratio of peak height D to peak height G), b is S RPWR (The half-peak width ratio of S3 and S2, S RPWR =S3FWHM / S2 FWHM ).

[0012] In order to characterize the carbonization degree of organic matter more comprehensively and reasonably.

[0013] Terminology explanation:

[0014] 1. Organic carbonization stage: The mudstone that has entered the high-maturity stage undergoes organic matter degradation, cracking and other processes, and its solid organic matter is partially or completely converted into graphite or graphite-like substances.

[0015] 2. Savitzky-Golay smoothing algorithm: It is a method that combines convolution and polynomial regression to achieve smoothing filtering. It can improve the accuracy of data without changing the trend and width of the signal.

[0016] 3. Laser Raman spectrum: the spectrum of the scattered light intensity with a certain polarization state in a certain direction distributed with the frequency of the scattering medium.

[0017] 4. Raman shift: The difference between the scattered light frequency and the incident light frequency is the horizontal coordinate of the laser Raman spectrum.

[0018] 5. Origin 2021 software: Origin is a scientific drawing and data analysis software developed by OriginLab, which supports a variety of 2D / 3D graphics. The data analysis functions in Origin include statistics, signal processing, curve fitting and peak analysis.

[0019] The technical solution of the present invention is as follows:

[0020] An evaluation method for characterizing the carbonization degree of sedimentary organic matter by taking into account second-order laser Raman parameters, comprising:

[0021] Step 1: Select the laser Raman spectrum of the coal sample at the organic matter carbonization stage;

[0022] Step 2: Obtain the first-order Raman parameters;

[0023] Step 3: Obtain the second-order Raman parameters;

[0024] Step 4: Screen and calculate the obtained second-order Raman parameters, and obtain the half-peak width S3 of S3 by fitting FWHM , half-peak width S2 FWHM and the half-peak width of S3 and S2 is S RPWR , S RPWR =S3 FWHM / S2 FWHM ;

[0025] Step 5: h(D h / Gh ), and h(D h / G h )+S RPWR The linear relationship between the two values ​​is obtained by linear fitting. h / G h ) refers to the ratio of the D peak height to the G peak height, S RPWR refers to the half-peak width ratio of S3 and S2, S RPWR =S3 FWHM / S2 FWHM ), R 2 is through h(D h / G h ) and h(D h / G h )+S RPWR The resulting correlation coefficient is as follows:

[0026] a=0.141(a+b)+0.4228(I)

[0027] In formula (I), a is h(D h / G h ), FWHM refers to the half-peak width of the peak, b is S RPWR ;

[0028] Step 6: Based on the parameter a on the left side of formula (I) and formula (II), obtain formula (III):

[0029] Rmc R o / %=1.1659*a+2.7588(II)

[0030] Rmc R o / %=0.1643919*a+0.1643919*b++0.4228*1.1659+2.7588(III)

[0031] In formula (II) and (III), Rmc R o / % is maturity, a is h(D h / G h ), FWHM refers to the half-peak width of the peak, b is S RPWR ;

[0032] Step 7: Arrange formula (III) to obtain the second-order laser Raman parameters to characterize the carbonization degree of sedimentary organic matter S- Rmc R o / % calculation formula (IV):

[0033] S-Rmc Ro / % = 0.1643919*S RPWR +0.1643919*h(D h +G h )+3.25174252(IV)

[0034] In formula (IV), S-Rmc R o / % is maturity, a is h(D h / G h ), FWHM refers to the half-peak width of the peak, b is S RPWR .

[0035] Preferably, according to the present invention, in step 3, obtaining the second-order Raman parameters comprises:

[0036] Step 3.1: Select the Raman shift between 2500 and 3100 cm in the laser Raman spectrum -1 Perform peak fitting on the data within

[0037] Step 3.2: Perform peak analysis and select peak fitting as the target.

[0038] Preferably, according to the present invention, in step 3.2, peak analysis and target selection peak fitting include:

[0039] Step 3.2.1: Perform baseline calibration;

[0040] Step 3.2.2: Raman spectra include the first-order region and the second-order region. The first-order region is the Raman shift between 1000 and 1800 cm -1 The second-order region is the Raman shift between 2500 and 3100 cm -1 The region includes the S2 peak and the S3 peak;

[0041] Step 3.2.3: Peak search for the laser Raman spectrum, adding the Raman shift between 2680-2720 cm -1 The region and Raman shift are 2900-2930cm -1 The peak of the region;

[0042] Step 3.2.4: Obtain the peak fitting spectrum and second-order Raman parameters;

[0043] Step 3.2.5: The quality of peak fitting is judged by the adjusted R-squared. The R-squared represents the correlation between the Raman spectrum peak fitting result and the Raman spectrum before fitting. If the adjusted R-squared is not less than 0.90, it means that the peak fitting effect is good. Otherwise, it means that the peak fitting effect is poor, and the current sample data point is not considered.

[0044] Further preferably, the first-order Raman parameters include D peak height D h and the peak height of the G peak G h .

[0045] Further preferably, the laser Raman spectrum is peak fitted using Origin 2021 software to obtain second-order Raman parameters.

[0046] Further preferably, the second-order Raman parameters include S2 FWHM 、S3 FWHM ; S3 FWHM is the half-peak width of S3, S2 FWHM is the half-maximum width of S2, and FWHM refers to the half-maximum width of the peak.

[0047] Further preferably, the laser Raman spectrum is smoothed before peak fitting.

[0048] The beneficial effects of the present invention are:

[0049] The present invention defines a new parameter for the second-order peak and proposes a new formula. This formula takes into account the evolution law of S2 and S3 in the second-order peak on the basis of considering the first-order D peak and G peak parameters. It can characterize the carbonization degree of organic matter more comprehensively and reasonably, and is more suitable for the carbonization degree of organic matter with a higher degree of thermal evolution. S-Rmc R o / %. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 This is the Raman spectrum of the coal sample after baseline calibration at the organic matter carbonization stage;

[0051] Figure 2 It is the peak fitting spectrum of coal sample in the organic matter carbonization stage and the schematic diagram of the second-order laser Raman parameters;

[0052] Figure 3 The coal sample h(D h / G h ) and h(D h / G h )+S RPWR Schematic diagram of correlation;

[0053] Figure 4 A schematic diagram of a flow chart of an evaluation method for characterizing the carbonization degree of deposited organic matter by taking into account second-order laser Raman parameters of the present invention;

[0054] Figure 5 For the present invention S-Rmc R o / % Bar graph. DETAILED DESCRIPTION

[0055] The present invention will be further described below with reference to the accompanying drawings and embodiments, but is not limited thereto.

[0056] Example 1

[0057] An evaluation method that takes into account the second-order laser Raman parameters to characterize the carbonization degree of sedimentary organic matter, such as Figure 4 As shown, including:

[0058] Step 1: Select the laser Raman spectrum of the coal sample at the organic matter carbonization stage;

[0059] Step 2: Obtain the first-order Raman parameters;

[0060] Step 3: Obtain the second-order Raman parameters; including:

[0061] Step 3.1: Select the Raman shift between 2500 and 3100 cm in the laser Raman spectrum -1 For the data in (second-order region), peak fitting was performed;

[0062] Step 3.2: Start peak analysis on the smoothed laser Raman spectrum. For the specific implementation process of peak analysis, refer to steps 6 to 10. The target is to select peak fitting; including:

[0063] Step 3.2.1: Perform baseline calibration; select user-defined as baseline mode, cancel automatic search, add 20 points (follow the curve trend), and select B-spline curve as interpolation method.

[0064] Step 3.2.2: Figure 1 ) In the peak fitting, the S2 peak (Raman shift at 2700cm -1 Nearby) and S3 peak at (Raman shift 2900cm -1 ) is more prominent, while the S4 peak (Raman shift at 3200cm -1 The typical Raman spectrum of carbonaceous materials includes the first-order region and the second-order region. The first-order region is the Raman shift between 1000 and 1800 cm -1 The second-order region is the Raman shift between 2500 and 3100 cm -1 The second-order region mainly corresponds to the S2 peak (2700 cm -1 ) and S3 peak (2900cm -1 );

[0065] Step 3.2.3: Peak search for the laser Raman spectrum, adding the Raman shift between 2680-2720 cm -1 The region and Raman shift are 2900-2930cm-1 The peak of the region;

[0066] Step 3.2.4: Obtain peak fitting spectrum and second-order Raman parameters (S3 FWHM , S2 FWHM wait)( Figure 2 );

[0067] Step 3.2.5: The quality of peak fitting is judged by the adjusted R-squared. The R-squared represents the correlation between the Raman spectrum peak fitting result and the Raman spectrum before fitting. If the adjusted R-squared is not less than 0.90, it means that the peak fitting effect is good. Otherwise, it means that the peak fitting effect is poor, and the current sample data point is not considered.

[0068] Figure 2 The meaning and results of each parameter are shown in Table 1:

[0069] Table 1

[0070]

[0071] Figure 2 In the figure, the adjusted R-square = 0.941375 ≥ 0.90, indicating a good fitting effect. Figure 2 The peak number is 1, and the weighted average center of the peak (i.e., Raman shift) is 2699.17 cm -1 represents the S2 peak, and the corresponding row data is the second-order Raman data of S2. Figure 2 The peak number is 2, and the weighted average center of the peak (i.e., Raman shift) is 2926.32 cm -1 represents the S3 peak, and the corresponding row data is the second-order Raman data of S3.

[0072] Step 4: Screen and calculate the obtained second-order Raman parameters, and obtain the half-peak width S3 of S3 by fitting FWHM , half-peak width S2 FWHM and the half-peak width of S3 and S2 is S RPWR , S RPWR =S3 FWHM / S2 FWHM ;

[0073] The comparison of the laser Raman parameter calculation results of coal samples in the carbonization stage is shown in Table 2

[0074] Table 2

[0075]

[0076]

[0077] Note: h(D h / G h )=DMax Height / G Max Height ; Rmc R o / % = 1.1659*h(D h / G h )+2.7588(Liu Dehan et al., 2013);

[0078] S RPWR =S3 FWHM / S2 FWHM ; S-Rmc R o / % = 0.1643919*h(D h / G h )+0.1643919*S RPWR +3.25174252

[0079] As shown in Table 2, for samples 1-14, the Raman shift of S2 is between 2680 and 2720 cm -1 , the Raman shift of S3 is at 2900-2930cm -1 .

[0080] New parameter S RPWR (The half-peak width ratio of S3 and S2, S RPWR =S3 FWHM / S2 FWHM ) has a changing pattern that it increases with the increase of the thermal evolution degree of the coal sample; S RPWR =S3 FWHM / S2 FWHM ;

[0081] Step 5: h(D h / G h ), and h(D h / G h )+S RPWR The linear relationship between the two is obtained by linear fitting. Figure 3 ), the correlation coefficient is very good, R 2 =0.9565:h(D h / G h ) refers to the ratio of the D peak height to the G peak height, S RPWR refers to the half-peak width ratio of S3 and S2, S RPWR =S3 FWHM / S2 FWHM ), R 2 is through h(D h / G h ) and h(D h / G h )+S RPWRThe correlation coefficient, R 2 The larger the value, the better the correlation between the two data, as shown below:

[0082] a=0.141(a+b)+0.4228 (I)

[0083] In formula (I), a is h(D h / G h ) (ratio of the peak height of D to the peak height of G), FWHM refers to the half-peak width of the peak, b is S RPWR (The half-peak width ratio of S3 and S2, S RPWR =S3 FWHM / S2 FWHM );

[0084] Step 6: Based on the parameter a on the left side of formula (I) and formula (II) proposed by Liu Dehan et al. (2013), we obtain formula (III):

[0085] Rmc R o / %=1.1659*a+2.7588 (II)

[0086] Rmc R o / %=0.1643919*a+0.1643919*b++0.4228*1.1659+2.7588 (III)

[0087] In formula (II) and (III), Rmc R o / % is the maturity calculated by the formula proposed by Liu Dehan et al. (2013), a is h(D h / G h ) (ratio of the peak height of D to the peak height of G), FWHM refers to the half-peak width of the peak, b is S RPWR (The half-peak width ratio of S3 and S2, S RPWR =S3 FWHM / S2 FWHM );

[0088] Step 7: Arrange formula (III) to obtain the second-order laser Raman parameters to characterize the carbonization degree of sedimentary organic matter S- Rmc R o / % calculation formula (IV):

[0089] S-Rmc R o / % = 0.1643919*S RPWR +0.1643919*h(D h +G h )+3.25174252 (IV)

[0090] In formula (IV), S-Rmc R o / % is the maturity calculated by the formula of the present invention (obtained by combining the definition of the second-order Raman parameters with the first-order Raman parameters), a is h(D h / G h ) (ratio of the peak height of D to the peak height of G), FWHM refers to the half-peak width of the peak, b is S RPWR (The half-peak width ratio of S3 and S2, S RPWR =S3 FWHM / S2 FWHM ).

[0091] Figure 5 For the present invention S-Rmc R o / % Bar graph.

[0092] Example 2

[0093] The difference between the evaluation method of the carbonization degree of deposited organic matter characterized by the second-order laser Raman parameters described in Example 1 is that:

[0094] The first-order Raman parameters include the peak height D h and the peak height of the G peak G h For the specific acquisition method, see Liu Dehan et al. (2013).

[0095] The laser Raman spectrum was peak fitted using Origin 2021 software to obtain the second-order Raman parameters.

[0096] The second-order Raman parameters include S2 FWHM 、S3 FWHM ; S3 FWHM is the half-peak width of S3, S2 FWHM is the half-maximum width of S2, and FWHM refers to the half-maximum width of the peak.

[0097] Before peak fitting, smooth the laser Raman spectrum. Select the Savitzky-Golay smoothing algorithm in the smoothing interface, set the window points to 50-70, select None for the boundary condition, and set the polynomial order to 2.

[0098] This example selects the laser Raman spectra of organic samples 1-10 at the carbonization stage:

[0099] Peak fitting was performed on coal samples 1-10 and the divalent Raman parameters (S3 FWHM , S2 FWHM wait);

[0100] The second-order laser Raman parameters are sorted and calculated to obtain SRPWR , S3 FWHM , S2 FWHM ;

[0101] S RPWR and h(D h / G h ) into the formula: S-Rmc R o / % = 0.1643919*S RPWR +0.1643919*h(D h +G h )+3.25174252, we get S-Rmc R o / %.

[0102] The statistical results of the data of organic matter samples 1-10 in the carbonization stage are shown in Table 3:

[0103] Table 3

[0104]

[0105] According to the formula S-Rmc R o / % = 0.1643919*S RPWR +0.1643919*h(D h +G h )+3.25174252, to obtain the organic matter samples 1-10 S-Rmc R o The values ​​range from 3.95% to 5.45%, the standard deviation is 0.53, and the variance is 0.27.

[0106] Depend on Figure 3 It can be seen that the formula S-Rmc R o / % = 0.1643919*S RPWR +0.1643919*h(D h +G h )+3.25174252, taking into account the evolution law of S2 and S3 in the second-order peak, it can characterize the carbonization degree of organic matter more comprehensively and reasonably.

Claims

1. An evaluation method for characterizing the carbonization degree of deposited organic matter by taking into account the second-order laser Raman parameters, characterized in that: include: Step 1: Select the laser Raman spectrum of the coal sample at the organic matter carbonization stage; Step 2: Obtain the first-order Raman parameters; Step 3: Obtain the second-order Raman parameters; Step 4: Screen and calculate the obtained second-order Raman parameters, and obtain the half-peak width S3 of S3 by fitting FWHM , half-peak width S2 FWHM and the half-peak width of S3 and S2 is S RPWR , S RPWR =S3 FWHM / S2 FWHM ; Step 5: h(D h / G h ), and h(D h / G h )+S RPWR The linear relationship between the two values ​​is obtained by linear fitting. h / G h ) refers to the ratio of the D peak height to the G peak height, S RPWR It refers to the half-peak width ratio of S3 and S2, S RPWR =S3 FWHM / S2 FWHM ), R 2 is through h(D h / G h ) and h(D h / G h )+S RPWR The resulting correlation coefficient is as follows: a=0.141(a+b)+0.4228(I) In formula (I), a is h(D h / G h ), FWHM refers to the half-peak width of the peak, b is S RPWR ; Step 6: Based on the parameter a on the left side of formula (I) and formula (II), obtain formula (III): Rmc R o / %=1.1659*a+2.7588(II) Rmc R o / %=0.1643919*a+0.1643919*b++0.4228*1.1659+2.7588(III) In formula (II) and (III), Rmc R o / % is maturity, a is h(D h / G h ), FWHM refers to the half-peak width of the peak, b is S RPWR ; Step 7: Arrange formula (III) to obtain the second-order laser Raman parameters to characterize the carbonization degree of sedimentary organic matter S- Rmc R o / % calculation formula (IV): S-Rmc R o / %=0.1643919*S RPWR +0.1643919*h(D h +G h )+3.25174252(IV) In formula (IV), S-Rmc R o / % is maturity, a is h(D h / G h ), FWHM refers to the half-peak width of the peak, b is S RPWR .

2. According to claim 1, a method for evaluating the carbonization degree of deposited organic matter by taking into account the second-order laser Raman parameters, characterized in that: In step 3, the second-order Raman parameters are obtained; include: Step 3.1: Select the Raman shift between 2500 and 3100 cm in the laser Raman spectrum -1 Perform peak fitting on the data within Step 3.2: Perform peak analysis and select peak fitting as the target.

3. The evaluation method of the carbonization degree of deposited organic matter characterized by using second-order laser Raman parameters according to claim 2 is characterized in that: In step 3.2, peak analysis, target selection peak fitting; include: Step 3.2.1: Perform baseline calibration; Step 3.2.2: Raman spectra include the first-order region and the second-order region. The first-order region is the Raman shift between 1000 and 1800 cm -1 The second-order region is the Raman shift between 2500 and 3100 cm -1 The region includes the S2 peak and the S3 peak; Step 3.2.3: Peak search for the laser Raman spectrum, adding the Raman shift between 2680-2720 cm -1 The region and Raman shift are 2900-2930cm -1 The peak of the region; Step 3.2.4: Obtain the peak fitting spectrum and second-order Raman parameters; Step 3.2.5: The quality of peak fitting is judged by the adjusted R-squared. The R-squared represents the correlation between the Raman spectrum peak fitting result and the Raman spectrum before fitting. If the adjusted R-squared is not less than 0.90, it means that the peak fitting effect is good. Otherwise, it means that the peak fitting effect is poor, and the current sample data point is not considered.

4. The evaluation method of claim 1 that takes into account the second-order laser Raman parameters to characterize the carbonization degree of deposited organic matter, characterized in that: The first-order Raman parameters include the peak height D h and the peak height of the G peak G h .

5. The evaluation method of claim 1 that takes into account the second-order laser Raman parameters to characterize the carbonization degree of deposited organic matter, characterized in that: The laser Raman spectrum was peak fitted using Origin 2021 software to obtain the second-order Raman parameters.

6. The evaluation method of claim 1 that takes into account the second-order laser Raman parameters to characterize the carbonization degree of deposited organic matter, characterized in that: The second-order Raman parameters include S2 FWHM 、S3 FWHM ; S3 FWHM is the half-peak width of S3, S2 FWHM is the half-maximum width of S2, and FWHM refers to the half-maximum width of the peak.

7. A method for evaluating the carbonization degree of deposited organic matter by taking into account the second-order laser Raman parameters according to any one of claims 1 to 6, characterized in that: Before peak fitting, the laser Raman spectrum was smoothed.

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