Shale oil pyrolysis adsorption oil and free oil correction method based on nuclear magnetic experiment

Abstract

The invention provides a shale oil pyrolysis adsorption oil and free oil correction method based on a nuclear magnetic experiment, and belongs to the field of exploration and development of unconventional oil and gas fields. According to the method, on the basis of a shale rock physical experiment and a shale nuclear magnetic resonance experiment, the occurrence space and content of adsorbed oil are determined by using multi-state nuclear magnetic resonance experiments such as original sample, saturated oil, washing oil and different temperatures, so that a nuclear magnetic adsorbed oil model is constructed, and the content of the adsorbed oil is determined by further combining a different-temperature-order parallel crushed sample lithologic pyrolysis experiment-nuclear magnetic combined measurement experiment. The content of the free oil and the content of the adsorbed oil are calculated through the two-dimensional nuclear magnetism T1-T2 spectrum semaphore, the content of the free oil and the content of the adsorbed oil are compared and analyzed, the difference between the nuclear magnetism adsorbed oil and the pyrolysis adsorbed oil is matched with a free hydrocarbon curve to achieve adsorbed oil correction, and the free oil and the adsorbed oil are obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of unconventional oil and gas exploration, and in particular to a method for correcting shale oil thermal desorption oil and free oil based on nuclear magnetic resonance experiments. Background Art

[0002] In recent years, shale oil and gas resources, with their enormous potential, have become a hot topic of research. As an unconventional oil and gas resource, shale exhibits significant compositional diversity, which can be divided into fluid and non-fluid components based on their distribution properties. According to research by Jiang Qigui et al., in shale pyrolysis experiments, hydrocarbons in shale can be divided into free hydrocarbons, adsorbed hydrocarbons, and cracking hydrocarbons based on their release temperatures. Free and adsorbed oil are among the primary hydrocarbon components that influence reserves and are the primary targets in shale oil production. Therefore, accurately identifying and quantitatively calculating adsorbed oil is crucial for shale oil exploration and development research.

[0003] In recent years, domestic and international experts and scholars have proposed numerous methods for calculating shale adsorbed oil. Experimental methods are one of the main approaches for shale oil adsorption. Previous researchers have explored various methods using rock pyrolysis, solvent extraction, adsorption tests, and two-dimensional nuclear magnetic resonance (NMR) to calculate both free and adsorbed oil content in shale. Among them, Lu Shuangfang et al., using swelling and temperature-step pyrolysis experiments, investigated the control of maturity evolution on kerogen adsorption and swelling. Considering the influence of clay pore surface area with adsorbed oil in shale samples and formation temperature, they conducted swelling oil experiments on naturally evolved kerogen samples and adsorbed oil experiments on clay samples separated from mudstone shale. They proposed a model for evaluating shale adsorbed oil that integrates kerogen adsorption and swelling with clay pore adsorption. However, this method also has obvious defects. First, there are insufficient temperature steps for rock pyrolysis. This method uses 90℃, 300℃, 450℃, and 600℃ as temperature steps, which are used as the basis for judging gaseous hydrocarbons, free oil, adsorbed oil, and cracking non-hydrocarbon gases, respectively. It is generally believed that adsorbed oil is precipitated at 300~450℃, but since some products precipitate before 300℃ during the heating process, and are limited by the solvent extraction effect, parameters such as the free oil content and cracking hydrocarbon content obtained by pyrolysis may have errors, resulting in an increase in the free oil content; secondly, the pyrolysis experiment based on the Rock-Eval6 instrument has obvious limitations. It can only be used for experiments on a small amount of broken samples, resulting in inaccurate adsorbed oil content and free oil content, which leads to errors in the evaluation of different hydrocarbon contents. In this regard, further research on adsorbed oil calculation and correction methods is needed.

[0004] Therefore, it is urgent to develop a method for calculating and correcting adsorbed oil and free oil in laboratory shale. Summary of the Invention

[0005] To solve the above technical problems, the present invention discloses a method for correcting shale oil thermal desorption adsorption oil and free oil based on nuclear magnetic resonance experiments. This method solves the problem of inaccurate measurement of adsorbed oil content in shale reservoirs during rock pyrolysis through multi-state nuclear magnetic resonance experiments.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for correcting shale oil thermal desorption adsorption oil and free oil based on nuclear magnetic resonance experiments comprises the following steps:

[0008] s1. Cut the full-diameter core to obtain standard plunger samples and parallel broken core samples for pre-processing;

[0009] s2. Perform nuclear magnetic resonance experiments on standard plug cores at original, oil-saturated, oil-washed, and 200°C temperatures to obtain 2D nuclear magnetic T1-T2 spectra;

[0010] s3. Construct an adsorbed oil evaluation model based on the adsorbed oil position and content in 2D NMR T1-T2 spectra;

[0011] s4. Carry out pyrolysis experiments at different temperature steps on parallel crushed core samples of the same mass to obtain the free oil and adsorbed oil contents;

[0012] s5. Based on the pyrolysis test results, the free oil content S1, adsorbed oil content S 2-1 Make corrections.

[0013] Optionally, in step s1, cores from the study area are collected, and standard plug samples are processed by wire cutting. The length, diameter, and mass of the cores are measured. The remaining cores after the plug samples are processed are crushed to 60 meshes using a core crusher. Subsequently, the crushed samples of the same mass as the plug samples are taken out and heated at a heating rate of 20°C / min in a vacuum environment. The products are collected at 300°C and 450°C as the boundaries to obtain the free oil content S1 and the adsorbed oil content S2. 2-1 .

[0014] Optionally, in step s2, a nuclear magnetic resonance instrument is used to measure the nuclear magnetic resonance signal of the dry core sample, and the parameters include: TE=0.06ms, TW=2000ms; NECH=32, and the nuclear magnetic resonance instrument can measure the nuclear magnetic signals of kerogen, structural water, asphalt and hydrogen-containing substances with higher fluidity than asphalt; and the 2D nuclear magnetic T1-T2 spectrum is obtained by inverting the measured signal.

[0015] Optionally, in step s2, the sample is vacuumed for 4 hours, then saturated with aviation kerosene for 72 hours, pressurized to 35 MPa, and the plunger sample saturated with oil is taken out and tested for 2D nuclear magnetic resonance T1-T2 spectrum; the sample is oil-washed with a mixture of dichloromethane and acetone at 80°C and 0.2 MPa for 7 days; then, the sample is vacuumed and dried at 110°C to fully remove residual oil in the shale pore system; the shale in the oil-washed and dried state is tested for 2D nuclear magnetic resonance T1-T2 spectrum, and the core after oil washing is heated at 200°C for 10 hours, and the 2D nuclear magnetic resonance T1-T2 spectrum is measured after cooling.

[0016] Optionally, in step s3, the NMR spectra of oil standards of different masses are measured, and a linear conversion relationship between the signal intensity of the standard sample and the unit mass of oil is established. The location of the adsorbed oil is determined by comparing the NMR spectra of different states. Based on the linear conversion relationship, the adsorbed oil content per unit sample mass of the laboratory NMR is determined. The correlation between the NMR adsorbed oil content and the organic carbon content and the clay mineral content is analyzed, and the correlation between the adsorbed oil content and the two is formed as follows:

[0017] ;

[0018] Where A is the adsorbed oil content per unit sample mass in laboratory NMR, TOC is the organic carbon content, CLAY is the clay mineral content, and a, b, and c are fitting parameters.

[0019] Optionally, in step s4, the crushed sample is heated at a heating rate of 20°C / min under a vacuum environment, and the products are collected at 300°C and 450°C as the boundaries to obtain the free oil content S1 and the adsorbed oil content S2. 2-1 .

[0020] Optionally, in step s5, the free oil and adsorbed oil contents obtained by rock pyrolysis are calibrated based on the laboratory adsorbed oil content as follows:

[0021] ;

[0022] ;

[0023] Where, is the corrected free oil content, is the free oil content, is the adsorbed oil content, is the corrected adsorbed oil content.

[0024] The beneficial effect of the present invention is that the existing pyrolysis calculation S1, S 2-1 Limited by the incomplete solvent extraction effect, the S1 and S 2-1To address the problem of inaccurate calculation results, the present invention conducts 2D nuclear magnetic resonance measurement experiments on parallel plunger samples of the same mass. Using nuclear magnetic resonance, it can obtain all magnetic resonance signals reflecting oil and water and the characteristics of fluid classification. Using standard samples, it establishes a conversion relationship between the nuclear magnetic signal intensity of the unpyrolyzed plunger sample core and the amount of adsorbed oil. This compensates for the shortcomings of the pyrolysis method, accurately calculates the adsorbed oil content, and constructs an NMR-based adsorbed oil evaluation model based on organic carbon and clay mineral parameters related to adsorbed oil. This model can calibrate the adsorbed oil content and free oil content obtained by pyrolysis. Furthermore, the samples used in the pyrolysis experiments of the traditional Rock-Eval6 instrument are small amounts of crushed samples. The core mass used in the pyrolysis experiments of the present invention is larger, which avoids the problems of inaccurate calculations of adsorbed oil content and free oil content due to small sample mass, as well as errors in the evaluation of different hydrocarbon contents. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a flow chart of a method for correcting shale oil thermal desorption oil and free oil based on nuclear magnetic resonance experiments in the present invention;

[0026] Figure 2 This is a T1-T2 NMR spectrum of the original sample shown in one embodiment of the present invention;

[0027] Figure 3 This is a saturated oil NMR T1-T2 spectrum shown in one embodiment of the present invention;

[0028] Figure 4 This is a T1-T2 NMR spectrum of the wash oil shown in one embodiment of the present invention;

[0029] Figure 5 This is a nuclear magnetic resonance T1-T2 spectrum of heating at 200°C after oil washing according to one embodiment of the present invention;

[0030] Figure 6 A component diagram showing the storage location of adsorbed oil components according to an embodiment of the present invention;

[0031] Figure 7 This is a correlation diagram between the experimental adsorbed oil content and the calculated adsorbed oil content according to one embodiment of the present invention. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are 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 making creative work are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention for which protection is sought, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0033] A method for correcting shale oil thermal desorption oil and free oil based on nuclear magnetic resonance experiments, such as Figure 1 As shown, the following steps are included:

[0034] S1. Obtain shale samples by coring. Use wire cutting to process the core into standard plug samples. The core size used in this example is as follows: length 5 cm, diameter 2.5 cm, mass 57 g. Use a high-speed crusher to crush the same mass of crushed samples into 60 mesh. The crushed samples are heated at a heating rate of 20°C / min under vacuum. The products are collected at 300°C and 450°C as the boundaries to obtain the free oil content S1 and the adsorbed oil content S 2-1。

[0035] s2. Use a MesoMR23-060H-I nuclear magnetic resonance instrument to measure the nuclear magnetic resonance signal of the core plug sample in its original state. The 2D nuclear magnetic resonance T1-T2 spectrum of the original sample is measured. The purpose is to measure the nuclear magnetic signals of all hydrogen-containing components with higher fluidity than asphalt remaining in the sample, including kerogen, structural water, asphalt, and then invert the measured signal to obtain the nuclear magnetic resonance T2 spectrum, such as Figure 2 As shown in the figure, the green, red and blue lines are the scale lines of T1 / T2 of 1, 10 and 100 respectively. The main parameters are: TE=0.06ms, TW=2000ms; NECH=32.

[0036] The sample was then vacuumed for 4 h, saturated with aviation kerosene for 72 h, pressurized to 35 MPa, and the plunger sample saturated with oil was taken out and tested with two-dimensional nuclear magnetic resonance T1-T2 spectrum, such as Figure 3 As shown in the figure, the sample was washed with oil using a mixture of dichloromethane and acetone at a temperature of 80°C and a pressure of 0.2 MPa for 7 days. Subsequently, the sample was vacuumed and dried at a temperature of 110°C to fully remove the residual oil in the shale pore system. The T1-T2 spectrum of the shale in the oil-washed and dried state was tested, as shown in the figure. Figure 4As shown in Figure 2, the core after oil washing was further heated at 200°C for 10 h, and then subjected to two-dimensional nuclear magnetic resonance (NMR) T1-T2 spectrum measurement after cooling. Figure 5 shown.

[0037] s3. By measuring the NMR spectra of oil standards of different masses, a linear conversion relationship between the signal intensity of the standard sample and the unit mass of oil is established, as follows:

[0038] ;

[0039] Where M S is the unit mass of oil, S NMR is the nuclear magnetic signal of the core per unit porosity, and ρ is the density of oil.

[0040] The adsorbed oil position is further clarified by comparing the NMR spectra of the original sample, saturated oil, washed oil, and heated oil after washing, thereby obtaining a fluid partitioning chart of the adsorbed oil components, such as Figure 6 As shown, the above conversion relationship is further used to sum the signals of the adsorbed oil area to obtain the corresponding laboratory NMR adsorbed oil mass.

[0041] By analyzing the correlation between the NMR adsorption oil content and the organic carbon content and clay mineral content, the correlation between the adsorbed oil content and the two is formed as follows:

[0042] ;

[0043] Where A is the adsorbed oil content per unit sample mass in laboratory NMR, TOC is the organic carbon content, and CLAY is the clay mineral content.

[0044] s4. Carry out traditional pyrolysis experiment, heat the crushed sample at a heating rate of 20℃ / min in a vacuum environment, collect the products at 300℃ and 450℃ as the boundaries to obtain the free oil content S1 and adsorbed oil content S 2-1 , the measurement results are as follows:

[0045] Table 1 Measurement results of free oil and adsorbed oil content

[0046]

[0047] s5. Based on the laboratory adsorbed oil content, the following formula is used to calibrate the free oil and adsorbed oil obtained by rock pyrolysis. The calculated adsorbed oil content is compared with the experimentally measured adsorbed oil content. Figure 7 As shown, the relative error between the two is 12%:

[0048] ;

[0049] ;

[0050] Where, is the corrected free oil content, is the free oil content, is the adsorbed oil content, is the corrected adsorbed oil content.

[0051] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the scope of protection of the present invention.

Claims

1. A method for correcting shale oil thermal desorption oil and free oil based on nuclear magnetic resonance experiments, characterized in that: The steps include: s1. Cut the full-diameter core to obtain standard plunger samples and parallel broken core samples for pre-processing; s2. Perform nuclear magnetic resonance experiments on standard plug cores at original, oil-saturated, oil-washed, and 200°C temperatures to obtain 2D nuclear magnetic T1-T2 spectra; s3. Construct an adsorbed oil evaluation model based on the adsorbed oil position and content in 2D NMR T1-T2 spectra; s4. Carry out pyrolysis experiments at different temperature steps on parallel crushed core samples of the same mass to obtain the free oil and adsorbed oil contents; s5. Based on the pyrolysis test results, the free oil content S1, adsorbed oil content S 2-1 Make corrections.

2. The method for correcting shale oil thermal desorption oil and free oil based on nuclear magnetic resonance experiments according to claim 1, characterized in that: In step s1, the cores in the study area were collected and processed into standard plug samples by wire cutting. The length, diameter and mass of the plug samples were measured. The remaining cores after the plug samples were processed were crushed to 60 meshes using a core crusher. Then, the crushed samples of the same mass as the plug samples were taken out and heated at a heating rate of 20°C / min in a vacuum environment. The products were collected at 300°C and 450°C as the boundaries to obtain the free oil content S1 and the adsorbed oil content S2. 2-1 .

3. The method for correcting shale oil thermal desorption oil and free oil based on nuclear magnetic resonance experiments according to claim 2, characterized in that: In step s2, a nuclear magnetic resonance (NMR) instrument is used to measure the NMR signal of the dry core sample. The parameters include: TE = 0.06 ms, TW = 2000 ms; NECH = 32. The NMR instrument can measure the NMR signals of kerogen, structural water, asphalt, and hydrogen-containing substances with higher fluidity than asphalt. The 2D NMR T1-T2 spectrum is obtained by inverting the measured signal.

4. The method for correcting shale oil thermal desorption oil and free oil based on nuclear magnetic resonance experiments according to claim 2, characterized in that: In step s2, the sample was vacuumed for 4 hours, then saturated with aviation kerosene for 72 hours and pressurized to 35 MPa. After removal, the saturated oil 2D NMR T1-T2 spectrum of the plunger sample was measured; the sample was oil-washed using a mixture of dichloromethane and acetone at 80°C and 0.2 MPa for 7 days; Subsequently, the sample was vacuumed and dried at 110°C to fully remove the residual oil in the shale pore system; the 2D NMR T1-T2 spectrum of the shale in the oil-washed and dried state was tested, and the oil-washed core was heated at 200°C for 10 hours and then cooled for 2D NMR T1-T2 spectrum measurement.

5. The method for correcting shale oil thermal desorption oil and free oil based on nuclear magnetic resonance experiments according to claim 3, characterized in that: In step s3, the NMR spectra of oil standards of different masses are measured, and a linear conversion relationship between the signal intensity of the standard sample and the unit mass of oil is established. The location of the adsorbed oil is determined by comparing the NMR spectra of different states. Based on the linear conversion relationship, the adsorbed oil content per unit sample mass of the laboratory NMR is determined. The correlation between the NMR adsorbed oil content and the organic carbon content and the clay mineral content is analyzed, and the correlation between the adsorbed oil content and the two is formed as follows: ； Where A is the adsorbed oil content per unit sample mass in laboratory NMR, TOC is the organic carbon content, CLAY is the clay mineral content, and a, b, and c are fitting parameters.

6. The method for correcting shale oil thermal desorption oil and free oil based on nuclear magnetic resonance experiments according to claim 4, characterized in that: In step s4, the crushed sample is heated at a heating rate of 20°C / min under a vacuum environment, and the products are collected at 300°C and 450°C as the boundaries to obtain the free oil content S1 and the adsorbed oil content S2. 2-1 .

7. The method for correcting shale oil thermal desorption oil and free oil based on nuclear magnetic resonance experiments according to claim 5, characterized in that: In step s5, the free oil and adsorbed oil contents obtained by rock pyrolysis are calibrated based on the laboratory adsorbed oil content as follows: ； ； Where, is the corrected free oil content, is the free oil content, is the adsorbed oil content, is the corrected adsorbed oil content.

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