Method for testing organic carbon content and oil content of shale based on nuclear magnetic resonance

Abstract

The invention discloses a method for testing organic carbon content and oil content of shale based on nuclear magnetic resonance, which belongs to the technical field of oil exploration, and is characterized by comprising the following steps: a, exciting hydrogen-containing substances in a shale standard sample through an SMC pulse sequence to obtain a feedback nuclear magnetic resonance signal; b, constructing a calculation model of shale kerogen and an oil content standard sample; c, determining nuclear magnetic semaphore and relaxation parameters of content substances in the shale standard sample to be detected; and d, calculating the organic carbon content and the oil content in the to-be-detected shale standard sample according to the nuclear magnetic signal. According to the method, the organic carbon content and the oil content in the shale sample can be conveniently and effectively tested at the same time, the testing process is simple, consumed time is short, real reservoir minerals and crude oil are selected as the established model, and good applicability and authenticity are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of petroleum exploration, and in particular to a method for testing the organic carbon content and oil content of shale based on nuclear magnetic resonance. Background Art

[0002] As a technology that can directly detect the state of hydrogen protons, nuclear magnetic resonance has a wide range of applications in conventional reservoir evaluation in biology, chemistry, agriculture, and petroleum energy. For example, rock porosity is obtained by combining saturation with nuclear magnetic resonance, and the oil content in conventional sandstone samples is obtained by combining manganese leaching with nuclear magnetic resonance testing.

[0003] Shale oil reservoirs have a complex material composition. In addition to liquid oil, gas and water, they are also rich in solid organic carbon components, such as kerogen. These problems affect the accuracy of conventional nuclear magnetic resonance testing and interpretation.

[0004] The current evaluation of hydrogen-containing fluids in shale is mainly to obtain the liquid oil content through extraction, and then to obtain the solid organic carbon content through high-temperature combustion. These two methods not only require the destruction of shale samples, are time-consuming, but also the solvents used for extraction are polluting to the environment.

[0005] A Chinese patent document with publication number CN111912958A and publication date November 10, 2020 discloses a method for detecting the amount of adsorbed oil in shale inorganic mineral oil, which is characterized by comprising: obtaining a shale sample and a shale oil compound component, and loading the shale oil compound component into the pores of kaolinite to obtain a kaolinite pore-shale oil model; performing molecular dynamics simulation on the kaolinite pore-shale oil model to obtain the shale oil density in the pores of kaolinite. The invention relates to a method for preparing a shale oil density curve; determining the oil adsorption capacity per unit area of ​​the kaolinite surface according to the shale oil density curve in the kaolinite pores and the surface area of ​​the kaolinite pore-shale oil model; determining the specific surface area of ​​the inorganic minerals in the shale sample according to the number of inorganic pores in the shale sample and the surface area of ​​the inorganic pores in the shale sample; and determining the product of the oil adsorption capacity per unit area of ​​the kaolinite surface and the specific surface area of ​​the inorganic minerals in the shale sample as the amount of oil adsorbed in the inorganic mineral oil in the shale.

[0006] The patent document discloses a method for detecting adsorbed oil in shale inorganic mineral deposits, which can improve the accuracy of adsorption and free oil detection results. However, the model uses a single type of clay mineral for simulation, which is inconsistent with the characteristics of diverse mineral types and diverse pore structure types in real reservoir rocks, and cannot truly reflect the pore structure characteristics of the reservoir and the adsorbed oil content in the pores. The process is complicated, time-consuming, and has poor applicability. Summary of the invention

[0007] In order to overcome the defects of the above-mentioned prior art, the present invention provides a method for testing the organic carbon content and oil content of shale based on nuclear magnetic resonance. The present invention can conveniently and effectively test the organic carbon content and oil content in shale samples at the same time, the testing process is simple and time-saving, and the constructed model uses real reservoir minerals and crude oil, and has good applicability and authenticity.

[0008] The present invention is achieved through the following technical solutions: A method for testing the organic carbon content and oil content of shale based on nuclear magnetic resonance, characterized in that it comprises the following steps: a. Excite hydrogen-containing substances in shale standard samples through SMC pulse sequence to obtain feedback nuclear magnetic resonance signals; b. Constructing the calculation model of shale kerogen and oil content standard samples; c. NMR signal quantity and relaxation parameters of the substance in the shale standard sample to be tested; d. Calculate the organic carbon content and oil content in the shale standard sample to be tested based on the nuclear magnetic resonance signal.

[0009] In the step a, obtaining the feedback nuclear magnetic resonance signal refers to obtaining the nuclear magnetic resonance spectra of the kerogen sample and the oil sample corresponding to the shale standard sample, which specifically includes screening different types of kerogen samples and constructing an identification model based on nuclear magnetic resonance.

[0010] It also includes obtaining the corresponding sample components based on the shale standard sample calibration process and establishing a quantitative model for kerogen and oil in simulated shale.

[0011] The sample components are separated by processing shale standard samples to obtain components in shale, specifically by crushing shale and identifying microscopic components to obtain different types of kerogen, and by obtaining shale oil samples from nearby wells and obtaining a quantitative model of shale oil through nuclear magnetic resonance.

[0012] The screening of different types of kerogen samples and the construction of an identification model based on nuclear magnetic resonance means that the type of kerogen samples is determined by principal component analysis before quantitative calculation, and the principal component factor is the average time T of the transverse relaxation peak. 2g , longitudinal relaxation peak average time T 1g , relaxation peak ratio T 1g / T 2g , the hydrogen nuclear signal intensity per unit mass of kerogen, different masses of the three types of kerogen were selected, and quantitative models of different types of kerogen were established through nuclear magnetic resonance.

[0013] The step c specifically refers to performing nuclear magnetic resonance spectroscopy on the shale standard sample to be tested, processing the nuclear magnetic resonance signal through two-dimensional inverse Laplace transformation, obtaining a distribution spectrum (T1, T2) of the signal amount of hydrogen-containing substances and the correlation between the transverse relaxation distribution and the longitudinal relaxation distribution, identifying kerogen and shale oil through the spectrum, and bringing them into the calculation model respectively.

[0014] The pretreatment is performed before the hydrogen-containing substances in the shale standard sample are excited by the SMC pulse sequence. The pretreatment refers to low-temperature drying of the shale standard sample.

[0015] The temperature of the low-temperature drying treatment is 55-60°C.

[0016] The low-temperature drying treatment takes 6-8 hours.

[0017] In step a, the shale standard sample is prepared by using kerogen extracted from shale by mixing clay minerals and quartz sand as the skeleton mineral, and then quantitatively injecting shale oil to simulate the framework.

[0018] The beneficial effects of the present invention are mainly manifested in the following aspects: 1. The present invention, a, excites hydrogen-containing substances in shale standard samples through SMC pulse sequence to obtain feedback nuclear magnetic resonance signals; b, constructs calculation models of shale kerogen and oil content standard samples; c, calculates the nuclear magnetic signal quantity and relaxation parameters of the content substances in the shale standard samples to be tested; d, calculates the organic carbon content and oil content in the shale standard samples to be tested according to the nuclear magnetic signal. Compared with the prior art, the present invention can conveniently and effectively test the organic carbon content and oil content in the shale samples at the same time, the test process is simple, the time consumption is short, and the constructed model uses real reservoir minerals and crude oil, and has good applicability and authenticity.

[0019] 2. The present invention, by exciting the hydrogen-containing substances in the shale standard sample through the SMC pulse sequence, can better compensate for the loss of solid-state material signal acquisition caused by the simple echo sequence affected by the echo time, and ensure the reliability of signal acquisition.

[0020] 3. The present invention performs pretreatment before exciting the hydrogen-containing substances in the shale standard sample through the SMC pulse sequence. The pretreatment refers to low-temperature drying of the shale standard sample, which can eliminate the interference of free water in the shale standard sample, reduce the loss of retained shale oil signals, and improve the test accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments: Figure 1 It is a flowchart of the present invention; Figure 2 This is a diagram showing the relationship between the organic carbon content of the simulated shale standard sample and the organic carbon signal measured by NMR; Figure 3 This is a diagram showing the relationship between the oil content of the simulated shale standard sample and the oil signal quantity of the nuclear magnetic resonance test. DETAILED DESCRIPTION

[0022] Example 1 See also Figure 1-Figure 3 , a method for testing the organic carbon content and oil content of shale based on nuclear magnetic resonance, comprising the following steps: a. Excite hydrogen-containing substances in shale standard samples through SMC pulse sequence to obtain feedback nuclear magnetic resonance signals; b. Constructing the calculation model of shale kerogen and oil content standard samples; c. NMR signal quantity and relaxation parameters of the substance in the shale standard sample to be tested; d. Calculate the organic carbon content and oil content in the shale standard sample to be tested based on the nuclear magnetic resonance signal.

[0023] This embodiment is the most basic implementation method, a. Excite hydrogen-containing substances in shale standard samples through SMC pulse sequence to obtain feedback nuclear magnetic resonance signals; b. Construct calculation models of shale kerogen and oil content standards; c. Calculate the nuclear magnetic signal quantity and relaxation parameters of the content substances in the shale standard sample to be tested; d. Calculate the organic carbon content and oil content in the shale standard sample to be tested based on the nuclear magnetic signal. Compared with the existing technology, it can conveniently and effectively test the organic carbon content and oil content in the shale sample at the same time, the testing process is simple, time-saving, and the constructed model uses real reservoir minerals and crude oil, and has good applicability and authenticity.

[0024] Example 2 See also Figure 1-Figure 3 , a method for testing the organic carbon content and oil content of shale based on nuclear magnetic resonance, comprising the following steps: a. Excite hydrogen-containing substances in shale standard samples through SMC pulse sequence to obtain feedback nuclear magnetic resonance signals; b. Constructing the calculation model of shale kerogen and oil content standard samples; c. NMR signal quantity and relaxation parameters of the substance in the shale standard sample to be tested; d. Calculate the organic carbon content and oil content in the shale standard sample to be tested based on the nuclear magnetic resonance signal.

[0025] In the step a, obtaining the feedback nuclear magnetic resonance signal refers to obtaining the nuclear magnetic resonance spectra of the kerogen sample and the oil sample corresponding to the shale standard sample, which specifically includes screening different types of kerogen samples and constructing an identification model based on nuclear magnetic resonance.

[0026] It also includes obtaining the corresponding sample components based on the shale standard sample calibration process and establishing a quantitative model for kerogen and oil in simulated shale.

[0027] The sample components are separated by processing shale standard samples to obtain components in shale, specifically by crushing shale and identifying microscopic components to obtain different types of kerogen, and by obtaining shale oil samples from nearby wells and obtaining a quantitative model of shale oil through nuclear magnetic resonance.

[0028] Furthermore, the screening of different types of kerogen samples and the construction of an identification model based on nuclear magnetic resonance means that the type of kerogen samples is determined by principal component analysis before quantitative calculation, and the principal component factor is the average time T of the transverse relaxation peak. 2g , longitudinal relaxation peak average time T 1g , relaxation peak ratio T 1g / T 2g , the hydrogen nuclear signal intensity per unit mass of kerogen, different masses of the three types of kerogen were selected, and quantitative models of different types of kerogen were established through nuclear magnetic resonance.

[0029] Furthermore, the step c specifically refers to performing nuclear magnetic resonance spectroscopy on the shale standard sample to be tested, processing the nuclear magnetic resonance signal through two-dimensional inverse Laplace transformation, obtaining a distribution spectrum (T1, T2) of the signal amount of hydrogen-containing substances and the correlation between the transverse relaxation distribution and the longitudinal relaxation distribution, identifying kerogen and shale oil through the spectrum, and bringing them into the calculation model respectively.

[0030] The pretreatment is performed before the hydrogen-containing substances in the shale standard sample are excited by the SMC pulse sequence. The pretreatment refers to low-temperature drying of the shale standard sample.

[0031] The temperature of the low-temperature drying treatment is 55°C.

[0032] The low-temperature drying treatment time is 6 hours.

[0033] This embodiment is a preferred implementation method. By exciting the hydrogen-containing substances in the shale standard sample through the SMC pulse sequence, it can better compensate for the loss of solid material signal acquisition caused by the simple echo sequence due to the influence of echo time, and ensure the reliability of signal acquisition.

[0034] Example 3 See also Figure 1-Figure 3 , a method for testing the organic carbon content and oil content of shale based on nuclear magnetic resonance, comprising the following steps: a. Excite hydrogen-containing substances in shale standard samples through SMC pulse sequence to obtain feedback nuclear magnetic resonance signals; b. Constructing the calculation model of shale kerogen and oil content standard samples; c. NMR signal quantity and relaxation parameters of the substance in the shale standard sample to be tested; d. Calculate the organic carbon content and oil content in the shale standard sample to be tested based on the nuclear magnetic resonance signal.

[0035] In the step a, obtaining the feedback nuclear magnetic resonance signal refers to obtaining the nuclear magnetic resonance spectra of the kerogen sample and the oil sample corresponding to the shale standard sample, which specifically includes screening different types of kerogen samples and constructing an identification model based on nuclear magnetic resonance.

[0036] It also includes obtaining the corresponding sample components based on the shale standard sample calibration process and establishing a quantitative model for kerogen and oil in simulated shale.

[0037] The sample components are separated by processing shale standard samples to obtain components in shale, specifically by crushing shale and identifying microscopic components to obtain different types of kerogen, and by obtaining shale oil samples from nearby wells and obtaining a quantitative model of shale oil through nuclear magnetic resonance.

[0038] The screening of different types of kerogen samples and the construction of an identification model based on nuclear magnetic resonance means that the type of kerogen samples is determined by principal component analysis before quantitative calculation, and the principal component factor is the average time T of the transverse relaxation peak. 2g , longitudinal relaxation peak average time T 1g , relaxation peak ratio T 1g / T 2g , the hydrogen nuclear signal intensity per unit mass of kerogen, different masses of the three types of kerogen were selected, and quantitative models of different types of kerogen were established through nuclear magnetic resonance.

[0039] The step c specifically refers to performing nuclear magnetic resonance spectroscopy on the shale standard sample to be tested, processing the nuclear magnetic resonance signal through two-dimensional inverse Laplace transformation, obtaining a distribution spectrum (T1, T2) of the signal amount of hydrogen-containing substances and the correlation between the transverse relaxation distribution and the longitudinal relaxation distribution, identifying kerogen and shale oil through the spectrum, and bringing them into the calculation model respectively.

[0040] The pretreatment is performed before the hydrogen-containing substances in the shale standard sample are excited by the SMC pulse sequence. The pretreatment refers to low-temperature drying of the shale standard sample.

[0041] The temperature of the low-temperature drying treatment is 60°C.

[0042] The low-temperature drying treatment time is 8 hours.

[0043] In step a, the shale standard sample is prepared by using kerogen extracted from shale by mixing clay minerals and quartz sand as the skeleton mineral, and then quantitatively injecting shale oil to simulate the framework.

[0044] This embodiment is the best implementation method. Pretreatment is performed before the hydrogen-containing substances in the shale standard sample are excited by the SMC pulse sequence. Pretreatment refers to low-temperature drying of the shale standard sample, which can eliminate the interference of free water in the shale standard sample, reduce the loss of retained shale oil signals, and improve test accuracy.

[0045] The present invention is described below using specific examples: 10 kg of organic-rich shale with TOC greater than 1.0% in different sedimentary environments in the study area was selected and sampled. The samples were crushed to 1.0-0.5 mm, and kerogen was separated from the shale samples according to the SY / T 5123 standard to obtain kerogen standard samples.

[0046] The extracted kerogen was identified by microscopic components to determine the organic matter type of each sample, and type I, II and III kerogen samples were selected as sample 1, sample 2 and sample 3 respectively; Three samples of sample 1, sample 2 and sample 3 were selected, each weighing 3 g, and NMR experiments were performed to obtain the NMR spectrum characteristics of kerogens of different organic matter types. The identification method of NMR spectrum and kerogen type was established by principal component analysis of SPSS software, and the identification of various types of kerogen was established; The principal component factors of the principal component analysis method described above are T 2g , T 1g , T 2g / T 1g , Amp; T 2g : is the geometric mean of T2; Where: T 2i For the i-th T2 point on the T2 spectrum, A i is the signal amplitude corresponding to the i-th T2 distribution on the T2 spectrum; T 1g : is the geometric mean of T1; Where: T li For the i-th T1 point on the T1 spectrum, A i is the signal amplitude corresponding to the i-th T1 distribution on the T1 spectrum; Amp: the signal amount per unit mass of kerogen; 0.5 g, 1.0 g, 2.0 g, 3.0 g and 5.0 g of sample 1 were uniformly mixed with 49.5 g, 49.0 g, 48.0 g, 47.0 g and 45.0 g of dry clay minerals and dry quartz sand, respectively, and put into a 2.5 cm cylindrical mold for compaction to obtain cylindrical samples sample 1-1, sample 1-2, sample 1-3, sample 1-4 and sample 1-5 with a diameter of 2.5 cm and a height of 5 cm, and the organic carbon contents were 1.0%, 2.0%, 4.0%, 6.0% and 10.0%, respectively; Weigh the masses of sample 1-1, sample 1-2, sample 1-3, sample 1-4 and sample 1-5 to obtain m1-1, m1-2, m1-2, m1-3, m1-4 and m1-5, in g; The density of crude oil produced from adjacent wells was tested to obtain the ρ1 unit of g / cm 3 ; According to the mass of sample 1-1, sample 1-2, sample 1-3, sample 1-4 and sample 1-5 and the density of crude oil, the volume of crude oil required to reach 5 mg / g, 10 mg / g, 15 mg / g, 20 mg / g and 30 mg / g oil content samples is calculated, V1-1, V1-2, V1-3, V1-4 and V1-5, in μL; Use a microsampler to take a corresponding volume of crude oil and inject it into sample 1-1, sample 1-2, sample 1-3, sample 1-4 and sample 1-5 respectively; Sample 1-1, sample 1-2, sample 1-3, sample 1-4 and sample 1-5 were subjected to SMC nuclear magnetic resonance experiments.

[0047] According to the range of kerogen and hydrocarbon signal samples, the 2D NMR signals of sample 1-1, sample 1-2, sample 1-3, sample 1-4 and sample 1-5 are segmented; A correlation formula was established based on the signal strength of the kerogen area and the organic carbon content of sample 1-1, sample 1-2, sample 1-3, sample 1-4 and sample 1-5.

[0048] AK1=AM1 / K1; Among them, AK1 is the content of type I kerogen in unit mass sample, AM1 is the type I kerogen signal per unit mass sample tested by NMR, and K1 is the coefficient of type I kerogen calibration; Create the formula: AK2=AM2 / K2; Among them, AK2 is the content of type II kerogen in unit mass sample, AM2 is the type II kerogen signal per unit mass sample tested by NMR, and K3 is the coefficient of type II kerogen calibration; AK3=AM3 / K3; Among them, AK3 is the content of type III kerogen in unit mass sample, AM3 is the type III kerogen signal per unit mass sample tested by NMR, and K3 is the coefficient of type III kerogen calibration; A correlation formula was established based on the signal strength of the hydrocarbon region and the oil content of the three series of samples; AO=AM4 / K4; Among them, AO is the shale oil content per unit mass of the sample, AM4 is the shale oil signal per unit mass of the sample tested by nuclear magnetic resonance, and K4 is the coefficient of shale oil calibration; The 2D NMR signals of other shale plug samples were tested and compared with the 2D NMR images of different organic matter types to obtain the organic matter type of the samples.

[0049] Select the corresponding formula according to the type of organic matter in the sample, and calculate the organic carbon content based on the signal strength.

[0050] The oil content is then calculated based on the strength of the hydrocarbon signal in the sample.

[0051] The SMC sequence of the present invention refers to: The S-segment saturation band pulse uses a series of 90° RF pulses in the X+ direction to achieve a saturation magnetic vector of the NMR signal in the Z direction of 0; The M segment is a dipole coupling, and the kerogen signal is effectively excited and collected through pulse sorting; The C-segment sequence is a CPMG sequence that mainly collects the measurement of T2 relaxation of shale oil components in shale samples; The purpose of the recovery time is to test the T1 relaxation of each hydrogen-containing component by setting different recovery times.

Claims

1. A method for testing the organic carbon content and oil content of shale based on nuclear magnetic resonance, characterized in that: The following steps are involved: a. Excite hydrogen-containing substances in shale standard samples through SMC pulse sequence to obtain feedback nuclear magnetic resonance signals; b. Constructing the calculation model of shale kerogen and oil content standard samples; c. NMR signal quantity and relaxation parameters of the substance in the shale standard sample to be tested; d. Calculate the organic carbon content and oil content in the shale standard sample to be tested based on the nuclear magnetic resonance signal.

2. The method for testing the organic carbon content and oil content of shale based on nuclear magnetic resonance according to claim 1, characterized in that: In the step a, obtaining the feedback nuclear magnetic resonance signal refers to obtaining the nuclear magnetic resonance spectra of the kerogen sample and the oil sample corresponding to the shale standard sample, which specifically includes screening different types of kerogen samples and constructing an identification model based on nuclear magnetic resonance.

3. The method for testing the organic carbon content and oil content of shale based on nuclear magnetic resonance according to claim 1, characterized in that: It also includes obtaining the corresponding sample components based on the shale standard sample calibration process and establishing a quantitative model for kerogen and oil in simulated shale.

4. The method for testing the organic carbon content and oil content of shale based on nuclear magnetic resonance according to claim 3, characterized in that: The sample components are separated by processing shale standard samples to obtain components in shale, specifically by crushing shale and identifying microscopic components to obtain different types of kerogen, and by obtaining shale oil samples from nearby wells and obtaining a quantitative model of shale oil through nuclear magnetic resonance.

5. The method for testing the organic carbon content and oil content of shale based on nuclear magnetic resonance according to claim 2, characterized in that: The screening of different types of kerogen samples and the construction of an identification model based on nuclear magnetic resonance means that the type of kerogen samples is determined by principal component analysis before quantitative calculation, and the principal component factor is the average time T of the transverse relaxation peak. 2g , longitudinal relaxation peak average time T 1g , relaxation peak ratio T 1g / T 2g , the hydrogen nuclear signal intensity per unit mass of kerogen, different masses of the three types of kerogen were selected, and quantitative models of different types of kerogen were established through nuclear magnetic resonance.

6. The method for testing the organic carbon content and oil content of shale based on nuclear magnetic resonance according to claim 5, characterized in that: The step c specifically refers to performing nuclear magnetic resonance spectroscopy on the shale standard sample to be tested, processing the nuclear magnetic resonance signal through two-dimensional inverse Laplace transformation, obtaining a distribution spectrum (T1, T2) of the signal amount of hydrogen-containing substances and the correlation between the transverse relaxation distribution and the longitudinal relaxation distribution, identifying kerogen and shale oil through the spectrum, and bringing them into the calculation model respectively.

7. The method for testing the organic carbon content and oil content of shale based on nuclear magnetic resonance according to claim 1, characterized in that: The pretreatment is performed before the hydrogen-containing substances in the shale standard sample are excited by the SMC pulse sequence. The pretreatment refers to low-temperature drying of the shale standard sample.

8. The method for testing the organic carbon content and oil content of shale based on nuclear magnetic resonance according to claim 7, characterized in that: The temperature of the low-temperature drying treatment is 55-60°C.

9. The method for testing the organic carbon content and oil content of shale based on nuclear magnetic resonance according to claim 7, characterized in that: The low-temperature drying treatment takes 6-8 hours.

10. The method for testing organic carbon content and oil content in shale based on nuclear magnetic resonance according to claim 1, characterized in that: In step a, the shale standard sample is prepared by using kerogen extracted from shale by mixing clay minerals and quartz sand as the skeleton mineral, and then quantitatively injecting shale oil to simulate the framework.

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