A method for correcting the nuclear magnetic resonance porosity of coal and rock considering the organic carbon content

Abstract

The present invention discloses a method for correcting the nuclear magnetic resonance porosity of coal and rock considering the organic carbon content, which includes performing saturated water treatment on coal and rock samples and obtaining the saturated water nuclear magnetic resonance porosity of the coal and rock samples; selecting the same coal and rock samples to carry out the determination of total organic carbon and obtaining the total organic carbon content of the coal and rock samples; carrying out the determination of the vitrinite reflectance of coal and rock and obtaining the vitrinite reflectance of the coal and rock samples; performing correction on the saturated water nuclear magnetic resonance porosity of coal and rock according to the saturated water nuclear magnetic resonance porosity, the total organic carbon content, and the vitrinite reflectance to obtain the corrected porosity. The present invention introduces the total organic carbon content obtained from the test of basic coal and rock data and the vitrinite reflectance data representing the coal and rock evolution stage for correction to eliminate the nuclear magnetic resonance signals in the coal and rock matrix. The corrected data is more real and reliable, and the method is convenient and affordable, and can be carried out on a large scale, which has important guiding significance for the large-scale exploration and development of coal and rock gas.

Description

Technical Field

[0001] The present invention relates to a method for correcting the nuclear magnetic resonance porosity of coal rock considering the organic carbon content, and belongs to the technical field of geological exploration. Background Art

[0002] As an emerging and important field in the natural gas industry, the analysis of coal rock porosity is crucial for evaluating the storage capacity of coalbed methane and the exploration and development of coalbed methane. Porosity refers to the ratio of the volume of voids not filled with solid matter in a rock to the overall volume of the rock. It is an important geological parameter because it directly affects the permeability and storage capacity of the rock (SY / T 5336-2006 Core Analysis Method). However, due to the particularity of the coal rock characteristics, the porosity of coal is measured using coalbed cores dried in a vacuum dryer. Studies on the weathering of coal have shown that this drying method changes the structure of coal and leads to incorrect results. In the miscible displacement method for measuring bedding porosity using undried cores, incorrect results will occur if the tracer is adsorbed.

[0003] Based on the diffusion and adsorption behavior of gas in rock pores, the porosity is calculated by measuring the equilibrium pressure of gas in the rock. The measurement process may take a long time and is mainly used for the porosity measurement of conventional reservoirs. Especially in rocks with simple pore structures, the connected porosity is mainly measured, and it is difficult to directly measure the unconnected porosity. The data interpretation is relatively intuitive, but the influence of gas saturation and rock type may need to be considered.

[0004] Therefore, to avoid experimental errors of traditional testing methods, nuclear magnetic resonance (NMR) technology is now introduced for pore testing. Based on the magnetic response of atomic nuclei spin in an external magnetic field, NMR technology calculates porosity by measuring the relaxation time of nuclear magnetic resonance signals. It is a fast, repeatable, and non-destructive detection method that can distinguish different types of porosity, such as total porosity, capillary porosity, effective porosity, etc., and can also distinguish free fluid and bound fluid. It is widely used in porosity testing of core samples and reservoirs (especially unconventional oil and gas reservoirs, such as coalbed methane). By measuring the relaxation time of water molecules in core samples, information on pore structure can be obtained indirectly, and then porosity can be calculated. When testing porosity, the principle of NMR is to detect the fluid hydrogen nuclei 1H in the pore structure of rock masses. Since carbon elements in the rock mass skeleton do not generate nuclear magnetic signals during measurement, they will not affect the measurement results. However, in the application process for coal rock, there are some defects in NMR technology. Coal rock is formed by the massive accumulation of ancient plants under specific physicochemical and geological conditions, mainly composed of organic substances and rich in organic matter. In the NMR porosity testing of coal rock, especially for coal rock with a high total organic carbon content (generally higher than 70%), a large number of hydrogen nuclei in organic matter molecules will also be detected by NMR testing, which will lead to a higher measured nuclear magnetic porosity and affect the reliability of NMR results. For example, Figure 2 Yang Wenguang proposed the coal molecular formula C 102 H 96 O 26 It can be seen that coal rock contains H elements equivalent to the C content, and its total organic carbon content can be used to represent its H nucleus content. The total organic carbon content of coal rock is mainly controlled by the organic matter content during coal rock formation and the burial evolution after coal rock formation, and the total organic carbon content and the vitrinite reflectance representing the coal rock evolution degree can be measured quickly and inexpensively. Summary of the Invention

[0005] In order to overcome the defects existing in the prior art, the present invention aims to provide a method for correcting the NMR porosity of coal rock considering the organic carbon content.

[0006] The technical solution provided by the present invention to solve the above technical problems is: a method for correcting the NMR porosity of coal rock considering the organic carbon content, including the following steps:

[0007] S1. Obtain coal rock samples;

[0008] S2. Saturate the coal rock samples with water and obtain the saturated water nuclear magnetic porosity φ w ;

[0009] S3. Dry the coal rock samples and obtain the rock skeleton hydrogen nucleus data R of the coal rock samples in the dry state m ;

[0010] S4. Select the same coal and rock samples to conduct total organic carbon determination, and obtain the total organic carbon content TOC of the coal and rock samples;

[0011] S5. Conduct coal and rock vitrinite reflectance determination, and obtain the vitrinite reflectance R of the coal and rock samples o ;

[0012] S6. Respectively establish unary regression equations of total organic carbon with vitrinite reflectance and rock skeleton nuclear magnetic data;

[0013] S7. Establish a binary regression equation of total organic carbon with vitrinite reflectance and coal and rock skeleton nuclear magnetic data;

[0014] S8. Establish a calculation formula for saturated water nuclear magnetic porosity φ w with total organic carbon content TOC, vitrinite reflectance R o and corrected nuclear magnetic resonance porosity;

[0015] φ R = φ w -2.9768ln(TOC)+0.0543ln(R o )+10.2738

[0016] In the formula: φ R is the corrected porosity; φ w is the saturated water nuclear magnetic porosity; TOC is the total organic carbon content; R o is the vitrinite reflectance;

[0017] S9. According to the saturated water nuclear magnetic porosity φ w , total organic carbon content TOC, and vitrinite reflectance R o conduct correction of coal and rock nuclear magnetic resonance saturated water porosity to obtain the corrected porosity φ R .

[0018] A further technical solution is that the coal and rock samples in step S1 are coal and rock cores or profile outcrop samples in the target area.

[0019] A further technical solution is that in step S2, water saturation treatment is carried out by pressurizing 15 MPa and saturating water for 48 h under vacuum conditions.

[0020] A further technical solution is that after water saturation in step S2, nuclear magnetic resonance analysis and testing of the water-saturated sample are carried out to obtain the nuclear magnetic resonance signal and relaxation time of the water-saturated sample, and the saturated water nuclear magnetic porosity φ w of the coal and rock sample is calculated based on the nuclear magnetic resonance signal of the water-saturated sample.

[0021] A further technical solution is that in step S3, the coal-rock sample is dried at 120 °C for 24 h for drying treatment.

[0022] A further technical solution is that in step S3, nuclear magnetic resonance analysis is performed on the unsaturated fluid to obtain the nuclear magnetic resonance signal and relaxation time of the dried sample, and the rock matrix hydrogen nucleus data of the coal-rock sample in the dried state is calculated.

[0023] A further technical solution is that the unary regression equation in step S6 includes:

[0024] R m = 3.0164ln(TOC) - 10.475

[0025] R m = -4.006ln(R o ) + 4.7922

[0026] In the formula: R m is the rock matrix hydrogen nucleus data; TOC is the total organic carbon content; R o is the vitrinite reflectance.

[0027] A further technical solution is that the binary regression equation in step S7 is:

[0028] R m = 2.9768ln(TOC) - 0.0543ln(R o ) - 10.2738

[0029] In the formula: R m is the rock matrix hydrogen nucleus data; TOC is the total organic carbon content; R o is the vitrinite reflectance.

[0030] The present invention has the following beneficial effects: Aiming at the errors and drawbacks existing in the current nuclear magnetic resonance porosity test of coal-rock, the total organic carbon content obtained from the test of basic coal-rock data and the vitrinite reflectance data representing the coal-rock evolution stage are introduced for correction to eliminate the nuclear magnetic resonance signal in the coal-rock matrix. The corrected data is more real and reliable, and the method is convenient and affordable, and can be carried out on a large scale, which has important guiding significance for the large-scale exploration and development of coal-bed methane. Description of the Drawings

[0031] Figure 1 is a flowchart;

[0032] Figure 2 is a conceptual diagram of nuclear magnetic resonance porosity test;

[0033] Figure 3 is the saturated water nuclear magnetic resonance T2 spectrum of samples from different regions;

[0034] Figure 4 Nuclear magnetic resonance T2 spectra of samples from different regions after drying

[0035] Figure 5 For TOC and R m (a), R o And R m (b) Linear regression graph

[0036] Figure 6 Is the binary regression linear fitting graph Specific implementation mode

[0037] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention

[0038] A testing method for the mechanical strength of natural fractures in deep shale after hydration of the present invention specifically includes the following steps

[0039] S1. Collect samples to obtain coal rock cores and profile outcrop samples with different physical properties in different depth segments of different regions of the basin

[0040] Collect 15 coal rock samples from the Permian of the Balougou section, Carboniferous underground cores in the Shenmu area, Carboniferous underground cores in the Jiaxian area, and Permian and Carboniferous underground cores in the Hengshan area of the Ordos Basin, and conduct total organic carbon and vitrinite reflectance measurements on them

[0041] Table 1 Analysis and test results of coal rock samples

[0042]

[0043]

[0044] S2. Conduct saturation treatment on all coal rock samples by pressurizing with 15 MPa of saturated water for 48 h under vacuum conditions. After saturation, conduct nuclear magnetic resonance analysis and testing on the saturated water samples to obtain the nuclear magnetic resonance signals and relaxation times of the saturated water samples; and calculate the saturated water nuclear magnetic porosity φ of all samples based on the nuclear magnetic resonance signals of the saturated water samples w ;

[0045] S3. Conduct drying treatment on the coal rock samples by drying at 120 °C for 24 h, and then conduct nuclear magnetic resonance analysis on the unsaturated fluid to obtain the nuclear magnetic resonance signals and relaxation times of the dried samples, and calculate the rock skeleton hydrogen nucleus data R of the coal rock samples in the dried state m ;

[0046] S4. Select the same coal-rock sample to conduct total organic carbon measurement and obtain the total organic carbon content TOC of the coal-rock sample;

[0047] S5. Conduct measurement of vitrinite reflectance of coal-rock and obtain the vitrinite reflectance R of the coal-rock sample o ;

[0048] S6. Establish a unary regression equation for total organic carbon and vitrinite reflectance R o and the nuclear magnetic data R of rock skeleton m respectively;

[0049] Among them, the unary regression equation for the total organic carbon content TOC and the nuclear magnetic data R of the rock skeleton of the coal-rock sample is: m The unary regression equation is:

[0050] R m = 3.0164ln(TOC) - 10.475, (R 2 = 0.91)

[0051] In the formula: R m is the hydrogen nucleus data of the rock skeleton; TOC is the total organic carbon content;

[0052] The unary regression equation for vitrinite reflectance R o and the nuclear magnetic data R of the coal-rock skeleton is: m The unary regression equation is:

[0053] R m = -4.006ln(R o ) + 4.7922, (R 2 = 0.92)

[0054] In the formula: R m is the hydrogen nucleus data of the rock skeleton; R o is the vitrinite reflectance;

[0055] S7. Establish a binary regression equation for total organic carbon, vitrinite reflectance and nuclear magnetic data of coal-rock skeleton;

[0056] y = -39.1202x1 + 174.5889x2 - 84.0028

[0057] That is,

[0058] R m = 2.9768ln(TOC) - 0.0543ln(R o ) - 10.2738, (R 2 = 0.94)

[0059] In the formula: R m is the hydrogen nucleus data of the rock skeleton; TOC is the total organic carbon content; Ro is the vitrinite reflectance;

[0060] S8. Establish the saturated water nuclear magnetic resonance porosity φ w and the calculation formulas for the total organic carbon content TOC, the vitrinite reflectance R o and the corrected nuclear magnetic resonance porosity;

[0061] φ R = φ w -2.9768ln(TOC)+0.0543ln(R o )+10.2738

[0062] In the formula: φ R is the corrected porosity; φ w is the saturated water nuclear magnetic resonance porosity; TOC is the total organic carbon content; R o is the vitrinite reflectance;

[0063] S9. According to the saturated water nuclear magnetic resonance porosity φ w , the total organic carbon content TOC, and the vitrinite reflectance R o perform the correction of the nuclear magnetic resonance water saturation porosity of coal rock to obtain the corrected porosity φ R .

[0064] Example

[0065] Collect three coal rock samples, conduct water saturation nuclear magnetic resonance tests, and use the correction formula of the present invention for correction, and calculate the corrected coal rock porosity data. The results are as follows.

[0066]

[0067] For sample 1, the measured porosity is 3.12%, the conventional water saturation nuclear magnetic resonance test porosity is 5.54%, the corrected porosity is 3.10%, the error before correction is 43.68%, and the error after correction is 0.854%;

[0068] For sample 2, the measured porosity is 2.47%, the conventional water saturation nuclear magnetic resonance test porosity is 4.43%, the corrected porosity is 2.49%, the error before correction is 44.24%, and the error after correction is 0.977%;

[0069] For sample 3, the measured porosity is 2.46%, the conventional water saturation nuclear magnetic resonance test porosity is 4.59%, the corrected porosity is 2.44%, the error before correction is 46.41%, and the error after correction is 0.677%.

[0070] The error between the nuclear magnetic resonance porosity correction result and the measured data by the present invention is less than 1%. The technology of the present invention is accurate and reliable, and the calculation effect is good.

[0071] As mentioned above, this is not to impose any formal restrictions on the present invention. Although the present invention has been disclosed through the above embodiments, it is not intended to limit the present invention. Any person skilled in the relevant art can make some changes or modifications to equivalent embodiments with equivalent changes within the scope of the technical solution of the present invention by using the technical content disclosed above. However, as long as it does not depart from the content of the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention shall fall within the scope of the technical solution of the present invention.

Claims

1. A method for correcting the nuclear magnetic resonance porosity of coal and rock considering the organic carbon content, characterized in that, It includes the following steps: S1. Obtain coal-rock samples; S2. Saturate the coal-rock sample with water and obtain the saturated water nuclear magnetic porosity φ of the coal-rock sample w ; S3. Dry the coal and rock sample, and obtain the rock skeleton hydrogen nucleus data R of the coal and rock sample in the dry state m ; S4. Select the same coal-rock samples to conduct total organic carbon determination, and obtain the total organic carbon content TOC of the coal-rock samples; S5. Conduct the determination of vitrinite reflectance of coal and rock, and obtain the vitrinite reflectance R of the coal and rock sample o ; S6. Respectively establish univariate regression equations of total organic carbon with vitrinite reflectance and nuclear magnetic data of rock skeleton; S7. Establish a binary regression equation of total organic carbon with vitrinite reflectance and nuclear magnetic data of coal-rock skeleton; S8. Establish the saturated water nuclear magnetic porosity φ w with the total organic carbon content TOC and the vitrinite reflectance R o and the calculation formula for the corrected nuclear magnetic porosity; φ R = φ w -2.9768ln(TOC×100)+0.0543ln(R o ×100)+10.2738 where: φ R is the corrected porosity; φ w is the nuclear magnetic porosity of water-saturated rock; TOC is the total organic carbon content; R o is the vitrinite reflectance; S9. According to the saturated water nuclear magnetic porosity φ w , total organic carbon content TOC, and vitrinite reflectance R o , perform coal-rock nuclear magnetic resonance saturated water porosity correction to obtain the corrected porosity φ R .

2. A method for correcting the nuclear magnetic resonance porosity of coal and rock considering the organic carbon content according to claim 1, characterized in that, In the step S1, the coal-rock samples are coal-rock cores or profile outcrop samples in the target area.

3. A method for correcting the nuclear magnetic resonance porosity of coal and rock considering the organic carbon content according to claim 1, characterized in that, In the step S2, saturation water treatment is carried out by pressurizing 15 MPa of saturated water for 48 h under vacuum conditions.

4. A method for correcting the nuclear magnetic resonance porosity of coal and rock considering the organic carbon content according to claim 3, characterized in that, In step S2, after saturation with water, nuclear magnetic resonance analysis and testing of the saturated water sample are carried out to obtain the nuclear magnetic resonance signal and relaxation time of the saturated water sample, and the saturated water nuclear magnetic porosity φ of the coal rock sample is calculated based on the nuclear magnetic resonance signal of the saturated water sample w .

5. A method for correcting the nuclear magnetic resonance porosity of coal and rock considering the organic carbon content according to claim 1, characterized in that, In the step S3, the coal-rock samples are dried at 120 °C for 24 h for drying treatment.

6. The method for correcting nuclear magnetic resonance porosity of coal and rock considering organic carbon content according to claim 5, characterized in that, In the step S3, nuclear magnetic resonance analysis is carried out on the unsaturated fluid to obtain the nuclear magnetic resonance signal and relaxation time of the dried sample, and calculate the nuclear data of the hydrogen nuclei of the coal-rock sample in the dried state.

7. A method for correcting the nuclear magnetic resonance porosity of coal and rock considering the organic carbon content according to claim 1, characterized in that, The univariate regression equation in the step S6 includes: R m = 3.0164 ln(TOC × 100) - 10.475 R m = -4.006 ln(R o × 100) + 4.7922 Where: R m is the hydrogen nucleus data of the rock skeleton; TOC is the total organic carbon content; R o is the vitrinite reflectance.

8. A method for correcting the nuclear magnetic resonance porosity of coal and rock considering the organic carbon content according to claim 1, characterized in that The binary regression equation in the step S7 is: R m = 2.9768 ln(TOC × 100) - 0.0543 ln(R o × 100) - 10.2738 Where: R m is the hydrogen nucleus data of the rock skeleton; TOC is the total organic carbon content; R o is the vitrinite reflectance.

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