Coal rock nuclear magnetic resonance porosity correction method considering organic carbon content

Abstract

The invention discloses a coal rock nuclear magnetic resonance porosity correction method considering organic carbon content, which comprises the following steps: performing saturated water treatment on a coal rock sample, and obtaining the saturated water nuclear magnetic porosity of the coal rock sample; selecting the same coal rock sample to carry out total organic carbon determination to obtain the total organic carbon content of the coal rock sample; determining the vitrinite reflectivity of the coal rock to obtain the vitrinite reflectivity of the coal rock sample; and according to the saturated water nuclear magnetic porosity, the total organic carbon content and the vitrinite reflectivity, correcting the nuclear magnetic resonance saturated porosity of the coal rock to obtain the corrected porosity. According to the method, the total organic carbon content obtained through coal rock basic data testing and vitrinite reflectance data representing the coal rock evolution stage are introduced for correction so as to eliminate nuclear magnetic signals in a coal rock matrix, the corrected data are more real and reliable, the method is convenient and practical, large-area expansion can be achieved, and the method is suitable for popularization and application. The method has important guiding significance for large-scale exploration and development of coal rock gas.

Description

Technical Field

[0001] The invention relates to a coal rock nuclear magnetic resonance porosity correction method taking organic carbon content into consideration, belonging to the technical field of geological exploration. Background Art

[0002] Coal rock gas is an important emerging field in the natural gas industry. Coal rock porosity analysis is crucial for evaluating the storage capacity of coal rock gas and the exploration and development of coal rock gas. Porosity refers to the ratio of the volume of cavities in the rock that are not filled with solid matter 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 coal rock rock characteristics, coal porosity is measured using coal seam cores dried in a vacuum dryer. Coal weathering studies have shown that this drying method changes the structure of coal and produces erroneous results. In the miscible displacement method of measuring bedding porosity using undried cores, erroneous results will be produced if the tracer is adsorbed.

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

[0004] Therefore, in order to avoid the experimental errors of traditional testing methods, nuclear magnetic resonance (NMR) technology is now introduced for porosity testing. Nuclear magnetic resonance (NMR) technology is based on the magnetic response of atomic nuclear spins in an external magnetic field. The porosity is calculated by measuring the relaxation time of the nuclear magnetic resonance signal. It is a fast, repeatable, and non-destructive detection method that can distinguish different types of porosity, such as total porosity, capillary porosity, and effective porosity, and can distinguish between free fluid and bound fluid. It is widely used in porosity testing of cores and reservoirs (especially unconventional oil and gas reservoirs, such as coal-rock gas). By measuring the relaxation time of water molecules in core samples, the information of pore structure can be indirectly obtained, and the porosity can be calculated. When testing porosity, the principle of nuclear magnetic resonance is to detect the fluid hydrogen nucleus 1H in the pore structure of the rock mass. Since the carbon element in the rock mass skeleton does not produce nuclear magnetic signals during the measurement, it will not affect the measurement results. However, in the application process for coal and rock, nuclear magnetic resonance technology has some defects. Coal rock is formed by the accumulation of ancient plants under specific physical, chemical and geological conditions. It is mainly composed of organic matter and contains rich organic matter. In the NMR porosity test of coal rock, especially coal rock with high total organic carbon content (generally higher than 70%), a large number of hydrogen nuclei in organic molecules will also be detected by NMR test, which will lead to a high NMR porosity measurement, affecting the reliability of NMR results. Figure 2 The coal molecular formula C proposed by Yang Wenkuan in 1987 102 H 96 O 26 It can be seen that coal contains H elements equivalent to C content, and its total organic carbon content can be used to represent its H core content. The total organic carbon content of coal is mainly controlled by the organic matter content when the coal is formed and the burial evolution after the formation of the coal, and the total organic carbon content and the vitrinite reflectance representing the degree of coal evolution can be measured quickly and cost-effectively. Summary of the invention

[0005] In order to overcome the defects in the prior art, the present invention aims to provide a coal rock nuclear magnetic resonance porosity correction method taking into account the organic carbon content.

[0006] The technical solution provided by the present invention to solve the above technical problems is: a coal rock nuclear magnetic resonance porosity correction method considering organic carbon content, comprising the following steps:

[0007] S1. Obtain coal and rock samples;

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

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

[0010] S4. Select the same coal rock sample to carry out total organic carbon determination to obtain the total organic carbon content TOC of the coal rock sample;

[0011] S5. Carry out coal rock vitrinite reflectance measurement to obtain the vitrinite reflectance R of coal rock samples. o ;

[0012] S6. Establish the one-variable regression equations of total organic carbon, vitrinite reflectance and rock skeleton NMR data respectively;

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

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

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

[0016] Where: φ R To correct the 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, vitrinite reflectance R o Carry out coal rock nuclear magnetic resonance saturated porosity correction to obtain the corrected porosity φ R .

[0018] A further technical solution is that the coal rock sample in step S1 is a coal rock core or profile outcrop sample in the target area.

[0019] A further technical solution is that in step S2, saturated water is pressurized to 15 MPa for 48 hours under vacuum conditions to perform saturated water treatment.

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

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

[0022] A further technical solution is to perform nuclear magnetic resonance analysis on the unsaturated fluid in step S3 to obtain the nuclear magnetic resonance signal and relaxation time of the dry sample, and calculate the rock skeleton hydrogen nucleus data of the coal rock sample in the dry state.

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

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

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

[0026] Where: R m is the rock skeleton 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] Where: R m is the rock skeleton 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: in view of the errors and drawbacks existing in the current nuclear magnetic resonance porosity test of coal rocks, the present invention introduces the total organic carbon content obtained from the basic data test of coal rocks and the vitrinite reflectance data representing the evolution stage of coal rocks, and performs correction to eliminate the nuclear magnetic signal in the rock matrix of coal rocks. The corrected data is more authentic and reliable, and the method is convenient and affordable, which can be carried out on a large area and has important guiding significance for the large-scale exploration and development of coal gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a flow chart;

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

[0033] Figure 3 The saturated water NMR T2 spectra of samples from different regions;

[0034] Figure 4 The NMR T2 spectra of samples from different regions after drying;

[0035] Figure 5 TOC and R m (a) R o With R m (b) Linear regression plot;

[0036] Figure 6 This is a binary regression linear fitting graph. DETAILED DESCRIPTION

[0037] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

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

[0039] S1. Collect samples to obtain coal rock core and profile outcrop samples with different physical properties at different depths in different areas of the basin;

[0040] A total of 15 coal samples were collected from the Permian in the Balougou section of the Ordos Basin, the Carboniferous underground cores in Shenmu area, the Carboniferous underground cores in Jiaxian area, and the Permian and Carboniferous underground cores in Hengshan area, and the total organic carbon and vitrinite reflectance measurements were carried out.

[0041] Table 1 Coal and rock sample analysis and test results

[0042]

[0043]

[0044] S2. All coal and rock samples were saturated with water at 15 MPa for 48 hours under vacuum conditions. After saturation, the saturated water nuclear magnetic resonance analysis test was carried out to obtain the saturated water sample nuclear magnetic resonance signal and relaxation time; and the saturated water nuclear magnetic porosity φ of all samples was calculated based on the sample saturated water nuclear magnetic resonance signal. w ;

[0045] S3. Dry the coal rock sample at 120℃ for 24h, then perform nuclear magnetic resonance analysis on the unsaturated fluid to obtain the nuclear magnetic resonance signal and relaxation time of the dry sample, and calculate the rock skeleton hydrogen nucleus data R of the coal rock sample in the dry state. m ;

[0046] S4. Select the same coal rock sample to carry out total organic carbon determination to obtain the total organic carbon content TOC of the coal rock sample;

[0047] S5. Carry out coal rock vitrinite reflectance measurement to obtain the vitrinite reflectance R of coal rock samples. o ;

[0048] S6. Establish the total organic carbon and vitrinite reflectance R o and rock skeleton NMR data R m The univariate regression equation of

[0049] The total organic carbon content TOC and the rock skeleton nuclear magnetic data R m The univariate regression equation is:

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

[0051] Where: R m is the rock skeleton hydrogen core data; TOC is the total organic carbon content;

[0052] Vitrinite reflectance R o Coal rock skeleton nuclear magnetic data R m The univariate regression equation is:

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

[0054] Where: R m is the rock skeleton hydrogen core data; R o is the vitrinite reflectance;

[0055] S7. Establish a binary regression equation between total organic carbon and vitrinite reflectance and coal rock skeleton nuclear magnetic resonance data;

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

[0057] Right now,

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

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

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

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

[0062] Where: φ R To correct the porosity; φ w is the saturated water nuclear magnetic porosity; TOC is the total organic carbon content; R o is the vitrinite reflectance;

[0063] S9, according to the saturated water nuclear magnetic porosity φ w , total organic carbon content TOC, vitrinite reflectance R o Carry out coal rock nuclear magnetic resonance saturated porosity correction to obtain the corrected porosity φ R .

[0064] Example

[0065] Three coal rock samples were collected, and water-saturated nuclear magnetic resonance tests were carried out. The correction formula of the present invention was used to calibrate the coal rock porosity data after correction, and the results are as follows.

[0066]

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

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

[0069] The measured porosity of sample 3 is 2.46%, the porosity of conventional saturated water nuclear magnetic resonance test is 4.59%, the porosity after correction 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 is less than 1%. The technology of the invention is accurate and reliable, and the calculation effect is good.

[0071] The above description is not intended to limit the present invention in any form. Although the present invention has been disclosed through the above embodiments, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are within the scope of the technical solution of the present invention.

Claims

1. A method for correcting coal rock nuclear magnetic resonance porosity considering organic carbon content, characterized in that: The following steps are involved: S1. Obtain coal and rock samples; S2. Saturate the coal and rock samples with water and obtain the saturated water nuclear magnetic porosity φ of the coal and rock samples. w ; S3. Dry the coal rock sample and obtain the rock skeleton hydrogen nucleus data R of the coal rock sample in the dry state. m ; S4. Select the same coal rock sample to carry out total organic carbon determination to obtain the total organic carbon content TOC of the coal rock sample; S5. Carry out coal rock vitrinite reflectance measurement to obtain the vitrinite reflectance R of coal rock samples. o ; S6. Establish the one-variable regression equations of total organic carbon, vitrinite reflectance and rock skeleton NMR data respectively; S7. Establish a binary regression equation between total organic carbon and vitrinite reflectance and coal rock skeleton nuclear magnetic resonance data; S8. Establish the saturated water nuclear magnetic porosity φ w Total organic carbon content TOC, vitrinite reflectance R o and the calculation formula for corrected NMR porosity; f R =φ w -2.9768ln(TOC)+0.0543ln(R o )+10.2738 Where: φ R To correct the porosity; φ w is the saturated water nuclear magnetic porosity; 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, vitrinite reflectance R o Carry out coal rock nuclear magnetic resonance saturated porosity correction to obtain the corrected porosity φ R .

2. A coal rock nuclear magnetic resonance porosity correction method considering organic carbon content according to claim 1, characterized in that: The coal rock sample in step S1 is a coal rock core or profile outcrop sample in the target area.

3. The method for correcting coal rock nuclear magnetic resonance porosity considering organic carbon content according to claim 1, characterized in that: In the step S2, saturated water treatment is performed by pressurizing saturated water at 15 MPa for 48 hours under vacuum conditions.

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

5. The method for correcting coal rock nuclear magnetic resonance porosity considering organic carbon content according to claim 1, characterized in that: In the step S3, the coal rock sample is dried at 120° C. for 24 hours.

6. A method for correcting coal rock nuclear magnetic resonance porosity considering organic carbon content according to claim 5, characterized in that: In step S3, the unsaturated fluid is subjected to nuclear magnetic resonance analysis to obtain the nuclear magnetic resonance signal and relaxation time of the dry sample, and the rock skeleton hydrogen nucleus data of the coal rock sample in the dry state is calculated.

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

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

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