Method and device for discriminating source of hydrocarbon source rock by using carbon isotope in propane molecule

Abstract

The invention provides a method for discriminating a source of hydrocarbon source rock by using carbon isotopes in propane molecules. The method comprises the following steps: S1, taking a sample to be detected for thermal desorption; s2, separating the propane in the desorbed gas and measuring the delta 13C value of the propane; s3, the desorbed gas is separated, separated propane is subjected to high-temperature decomposition, separation is conducted again, and the delta 13 Cross value in the separated pyrolysis fragments is measured; s4, a known hydrocarbon source rock sample is taken, and the delta 13C value of propane in desorbed gas and the delta 13Cterial value of propane in desorbed gas are measured according to the same steps of S1 to S3; and S5, marking numerical values of the sample to be detected and the known hydrocarbon source rock sample in the rectangular coordinate system by taking the delta 13C value of propane as a horizontal coordinate and the delta 13Cterial value in propane as a vertical coordinate, observing the overlapping degree of the numerical values, and determining the source of the hydrocarbon source rock of the sample to be detected when the overlapping degree is high.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil and gas geochemistry, and particularly relates to a method and device for discriminating the source of hydrocarbon source rocks by using the carbon isotope within propane molecules. Background Art

[0002] In the research of oil and gas geochemistry, the accurate identification of gas source rocks is an important part of the research on oil and gas accumulation. Traditional gas source identification methods mainly rely on indirect indicators such as biomarker compound combinations and stable carbon isotope compositions. These methods face significant challenges of multiple solutions in practical applications. Especially when potential source rock series have similar sedimentary environments, organic matter types, and thermal maturities, conventional indicators often fail to effectively distinguish them.

[0003] Therefore, there is an urgent need to provide a simple and high-precision method for identifying gas sources in complex superimposed basins to provide a theoretical basis for further exploitation. Summary of the Invention

[0004] In view of this, the present invention provides a method and device for discriminating the source of hydrocarbon source rocks by using the carbon isotope within propane molecules.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for discriminating the source of hydrocarbon source rocks by using the carbon isotope within propane molecules, comprising the following steps:

[0007] S1. Take a sample to be tested, crush it, sieve it, place it in a pyrolysis furnace, heat and desorb it to generate desorbed gas;

[0008] S2. Use a gas chromatograph to separate propane in the desorbed gas and measure the δ 13 C value;

[0009] S3. Separate the desorbed gas through gas chromatographic column I, decompose the separated propane at high temperature, separate the heating decomposition products through gas chromatographic column II, and measure the δ 13 C terminal value in the separated pyrolysis fragments;

[0010] S4. Take a known hydrocarbon source rock sample and measure the δ 13 C value of propane in the desorbed gas and the δ 13 C terminal value in propane according to the same steps as in steps S1 to S3;

[0011] S5. Using the δ 13 C value of propane as the abscissa and the δ 13 C terminalPlot the values of the sample to be tested and the known source rock sample on the vertical axis in a rectangular coordinate system, observe the degree of overlap of the values, and when there is a high degree of overlap, the source rock origin of the sample to be tested can be determined.

[0012] Further, the sample to be tested is placed in a quartz tube with solid quartz rods filled on both sides, and the air in the quartz tube is removed by argon purge before pyrolysis desorption.

[0013] In some specific embodiments, preferably, the mesh number for sieving in step S1 is 20 - 60 meshes; the purity of argon is ≥99.999%, and the purge time is 8 - 12 min.

[0014] In some specific embodiments, preferably, the heating conditions of the pyrolysis furnace in step S1 are: heating at a heating rate of 20°C / min to 180°C and holding for 60 min.

[0015] In some specific embodiments, preferably, the parameters of the gas chromatograph in step S2 are as follows: the initial temperature is 30°C, hold for 10 min, then increase at a rate of 20°C / min to 180°C, and hold for 2 min.

[0016] In some specific embodiments, preferably, the separation conditions of gas chromatographic column I in step S3 are: the initial temperature is 50°C, hold for 3 min, then increase at a rate of 10°C / min to 200°C, and hold for 8 min.

[0017] In some specific embodiments, preferably, the pyrolysis conditions in step S3 are: the high-temperature decomposition temperature is 790°C.

[0018] In some specific embodiments, preferably, the separation conditions of gas chromatographic column II in step S3 are: the initial temperature is 50°C, hold for 25 min, then increase at a rate of 20°C / min to 200°C, and hold for 5 min.

[0019] A pyrolysis desorption device for implementing the above method, wherein the pyrolysis desorption device is sequentially connected by a control system, a pyrolysis desorption system, and a detection system through pipelines;

[0020] Among them, the control system consists of an argon gas tank and a flow controller connected to the outlet, and is used to provide argon to remove the residual air in the quartz tube;

[0021] The pyrolysis desorption system consists of a pyrolysis furnace and a quartz tube, and is used to place the sample in the quartz tube and then perform pyrolysis desorption in the pyrolysis furnace;

[0022] The detection system consists of a helium gas tank, a gas chromatograph, and an isotope ratio mass spectrometer, and is used to separate and detect the desorbed gas.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] The present invention utilizes the δ 13 C value at the terminal carbon position of propane, which can well record the isotopic composition of propane initially generated from source rocks. Since the terminal carbon of propane is hardly affected by epigenetic processes, it can record the isotopic composition of the initially generated propane. Based on the thermal desorption analysis of source rocks and the intramolecular carbon isotope analysis of propane, the isotopic fractionation between in-situ hydrocarbons and accumulated hydrocarbon fluids in the source area can be carried out, and the hydrocarbon sources with multiple similar source rocks can be directly distinguished. Applying this new method to trace gas sources can not only maintain accuracy but also be simple to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Graph of the δ 13 C terminal and δ 13 C3 ratio results for propane in tight sandstone gas and pyrolysis gas of source rocks.

[0026] Figure 2 Graph of the δ 13 C terminal and δ 13 C3 ratio results for propane in tight sandstone gas and pyrolysis gas of source rocks.

[0027] Figure 3 Graph of the δ 13 C value results for alkanes in tight sandstone gas.

[0028] Figure 4 Graph of the δ 13 C value results for alkanes in pyrolysis gas of source rocks.

[0029] Figure 5 Graph of the δ 13 C ratio results for different alkanes in tight sandstone gas and pyrolysis gas of source rocks; among them, Figure a is δ 13 C2 vs δ 13 C1, Figure b is δ 13 C2 vs. δ 13 C1, Figure c is δ 13 iC4 vs. δ 13 nC4, Figure d is δ 13 iC5 vs. δ 13 nC5. DETAILED DESCRIPTION OF THE INVENTION

[0030] The present invention will be further described in detail below with reference to specific embodiments, so that those skilled in the art can understand the present invention more clearly. Unless otherwise specified, the technical means used in the following embodiments are all conventional means well known to those skilled in the art, and all reagent consumables are commercially available products.

[0031] Example 1

[0032] In this embodiment, the method for discriminating the source rock source by using the carbon isotope in propane molecules is used to identify the gas source of the collected samples, and the details are as follows:

[0033] Sample source:

[0034] Samples with known source rock types were collected from different wells in the Turpan-Hami Basin, specifically as follows:

[0035] 5 mudstone samples and 2 coal samples from the Xishanyao Formation (J2x) of the Middle Jurassic;

[0036] 7 source rock samples from the Sangonghe Formation (J1s) of the Lower Jurassic;

[0037] 2 mudstone samples and 1 coal sample from the Badaowan Formation (J1b) of the Lower Jurassic.

[0038] In addition, 5 deep tight sandstone gas samples (samples to be tested) were collected in the Qiudong Depression of the Turpan-Hami Basin.

[0039] The specific operation steps are as follows:

[0040] S1. Take the sample to be tested (tight sandstone gas sample), crush it, pass it through a 40-mesh sieve, place it in a quartz tube in a pyrolysis furnace, fill the two sides of the quartz tube with solid quartz rods, and introduce argon with a purity of 99.999% for 10 min to remove the residual air in the quartz tube.

[0041] S2. Heat the pyrolysis furnace (heating condition: heat it to 180 °C at a heating rate of 20 °C / min and keep it for 60 min.) to desorb the hydrocarbon gases in the sample; use a gas chromatograph (initial temperature is 30 °C, keep it for 10 min, then increase the temperature to 180 °C at a rate of 20 °C / min and keep it for 2 min) to separate propane in the desorbed gas and measure the δ 13 C value for determination.

[0042] S3. Further, separate the desorbed gas in step S2 through gas chromatographic column I (separation parameters: initial temperature is 50 °C, keep it for 3 min, then increase the temperature to 200 °C at a rate of 10 °C / min and keep it for 8 min.), and send the separated propane into a pyrolysis furnace-ceramic reactor for pyrolysis (pyrolysis temperature 790 °C) with helium; separate the pyrolysis products through gas chromatographic column II (separation parameters: initial temperature is 50 °C, keep it for 25 min, then increase the temperature to 200 °C at a rate of 20 °C / min and keep it for 5 min.), and introduce the separated pyrolysis fragments into an isotope ratio mass spectrometer to measure the δ 13 C terminal value (the results are shown in Table 1).

[0043] S4. Sequentially take samples of known source rock types (J2x, J1s, J1b), and measure the δ 13 C value in the desorbed gas and the δ 13 C terminal value in propane according to the same steps as in S1 - S3 (the results are shown in Table 2).

[0044] S5. Use the δ 13 C value of propane as the abscissa and the δ 13 C terminal value of propane as the ordinate to mark the values of the samples to be tested and the known source rock samples in a rectangular coordinate system (the results are shown in Figure 1 ). When the overlap degree of the values of the samples to be tested and the known source rock samples is high, it indicates that the samples to be tested and the known source rock have a high genetic relationship, and further the source of the source rock of the samples to be tested can be determined.

[0045] Table 1 δ 13 C and δ 13 C terminal values in the desorbed gas of different tight sandstone gas samples

[0046]

[0047] As can be seen from Table 1: The average value of δ 13 C in the desorbed gas of the tight sandstone gas samples is -27.0‰, and the range of the δ 13 C end value ranges from -26.5‰ to -25.2‰, with an average of -25.9‰.

[0048] Table 2 δ 13 C and δ 13 C terminal values in the desorbed gas of samples of different known source rock types

[0049]

[0050]

[0051] As can be seen from Table 2: For samples of different known source rock types (in J2x, J1s, and J1b source rocks), the average values of δ 13 C of propane are -25.7, -27.5, and -24.7‰, and the average values of the δ 13 C end values are -24.3, -26.1, and -24.3‰ respectively.

[0052] Combined with Figure 1 it can be known that: By observing the overlap degree of the δ 13 C end value, for propane in the tight sandstone gas samples and J1s source rocks, the δ 13The C-terminal values have a high degree of overlap, so it is possible to determine that the tight sandstone gas samples are sourced from the hydrocarbon source rocks of the Lower Jurassic Sangonghe Formation (J1s).

[0053] Comparative Example 1

[0054] This comparative example provides a method for determining the source of hydrocarbon source rocks. The specific steps are basically the same as those in Example 1, except that: propane δ 13 C terminal is replaced with propane δ 13 C central , and the rest remains unchanged.

[0055] Among them, the propane δ 13 C and δ 13 C central values in the desorbed gas of different tight sandstone gas samples are shown in Table 3; the propane δ 13 C and δ 13 C central values in the desorbed gas of samples of different known hydrocarbon source rock types are shown in Table 4. Taking the propane δ 13 C value as the abscissa and the δ 13 C central value in propane as the ordinate to establish a rectangular coordinate system (the result is shown in Figure 2 ).

[0056] Table 3 Propane δ 13 C and δ 13 C central values in the desorbed gas of different tight sandstone gas samples

[0057]

[0058]

[0059] As can be seen from Table 3: The average value of propane δ 13 C in the desorbed gas of tight sandstone gas samples is -27.0‰, and the C-terminal value range of δ 13 C is from -30.4‰ to -28.1‰, with an average of -29.1‰.

[0060] Table 4 Propane δ 13 C and δ 13 C central values in the desorbed gas of samples of different known hydrocarbon source rock types

[0061]

[0062] As can be seen from Table 4: The average values of propane δ 13 C in the desorbed gas of samples of different known hydrocarbon source rock types (in J2x, J1s, and J1b hydrocarbon source rocks) are -25.7, -27.5, and -24.7‰, and δ13 The average values of the C central values are -29.5‰, -29.0‰, and -25.6‰ respectively.

[0063] Combined with Figure 2 it can be known that by observing δ 13 the C central value overlap degree, and the δ of propane in the tight sandstone gas samples and the J1s and J2x source rocks 13 all have an overlap degree for the C central values. Therefore, the specific source rock origin of the tight sandstone gas samples cannot be determined.

[0064] Comparative Example 2

[0065] This comparative example provides a method for determining the source rock origin, and the specific steps are as follows:

[0066] S1. Take each sample to be tested (tight sandstone gas samples), crush them, pass through a 40-mesh sieve, place them in a quartz tube in a pyrolysis furnace, fill solid quartz rods on both sides of the quartz tube, and introduce argon with a purity of 99.999% for 10 minutes to remove the residual air in the quartz tube.

[0067] S2. Heat the pyrolysis furnace (heating condition: heat at a heating rate of 20°C / min to 180°C and hold for 60 minutes) to desorb the hydrocarbon gases in the samples; use an Agilent 7890B gas chromatograph (initial temperature is 60°C, then increase to 290°C at a rate of 4°C / min and hold for 15 minutes) to detect the chemical composition in the desorbed gas (monomers: hydrocarbon gases (C1-C5), and inorganic gases), and the results are shown in Table 5.

[0068] S3. Use the same steps as in Steps S1 to S2 to detect the chemical composition in the desorbed gas of samples of different known source rock types ((J2x, J1s, J1b)), and the results are shown in Table 6.

[0069] Table 5 Chemical composition in the desorbed gas of different tight sandstone gas samples

[0070]

[0071] As can be seen from Table 5: The chemical components in the desorbed gas of the tight sandstone gas samples are mainly hydrocarbon gases, with an average proportion of 94.50%. Methane C1 is the main gas, and the concentrations of propane to pentane (C2-C5) decrease with the increase in carbon number. The proportions of inorganic gases N2 and CO2 are very low in most samples.

[0072] Table 6 Chemical composition in the desorbed gas of samples of different known source rock types

[0073]

[0074]

[0075] As can be seen from Table 6, the concentrations of propane to pentane hydrocarbons in the pyrolysis desorbed gas of the source rocks are relatively low, ranging from 0.45% to 14.68%, with an average of 3.79%. In the pyrolysis desorbed gas of the J2x and J1b source rocks, propane C3 gas is the main component, while in most of the J1s source rocks, methane C1 gas is the main component, but there is no trend of decreasing concentration of propane to pentane (C2-C5) with the increase of carbon number.

[0076] Except for these components, there are no obvious differences in other source rock components in the pyrolysis desorbed gas. Therefore, discrimination cannot be carried out through gas components.

[0077] Comparative Example 3

[0078] This comparative example provides a method for determining the source of source rocks, and the specific steps are as follows:

[0079] S1. Take each sample to be tested (tight sandstone gas sample), crush it, pass it through a 40-mesh sieve, place it in a quartz tube in a pyrolysis furnace, fill solid quartz rods on both sides of the quartz tube, and introduce argon with a purity of 99.999% for 10 min to remove the residual air in the quartz tube.

[0080] S2. Heat the pyrolysis furnace (heating condition: heat it to 180 °C at a heating rate of 20 °C / min and keep it for 60 min.) to desorb the hydrocarbon gases in the sample; use the combination of Thermo Scientific 253Plus IRMS and Thermo Scientific Trace 1310GC equipped with a capillary column (HP-PLOT Q 30 m×0.32 mm i.d.) to measure the monomer carbon isotope values, and the test results are shown in Table 7. The initial temperature of the gas chromatograph is 30 °C, the temperature is maintained for 10 min, and then it is raised to 180 °C at a speed of 20 °C / min and kept at this temperature for 2 min.

[0081] S3. Use the same steps as in steps S1-S2 to measure the monomer carbon isotope values in the desorbed gas of samples of different known source rock types ((J2x, J1s, J1b)) (the results are shown in Table 8).

[0082] Table 7 Monomer carbon isotope values in the desorbed gas of different tight sandstone gas samples

[0083]

[0084] Combined Figure 3 and Table 7 show that the δ 13 C values of hydrocarbons in the desorbed gas of tight sandstone gas samples increase with the increase of carbon number; the δ 13The C averages are -41.0, -27.8, -27.0, -25.8, -25.8, 25.8, and -24.6‰ respectively.

[0085] Table 8 Monomer carbon isotope values in the desorbed gas of samples of different known source rock types

[0086]

[0087]

[0088] Combined with Figure 4 and Table 8, it can be seen that: for the carbon isotope distribution of alkane gases in the desorbed gas of samples of different known source rock types, the overall trends of J10H, J702H-2, J10H-2, and J10H-3 are normal trends where the δ 13 C value increases with the increase in carbon number. Most samples show normal carbon isotope trends in propane-pentane (C3-C5). Some samples show an inversion of the carbon isotope sequence, that is, δ 13 C1 > δ 13 C2 > δ 13 C3, indicating that the gas and isotope compositions of methane (and possibly ethane) in the thermally desorbed gas of the source rock may have been altered by epigenetic processes.

[0089] The δ 13 C1 value of the thermally desorbed gas of the J2x source rock is significantly higher than that of the thermally desorbed gas of the J1s source rock, the thermally desorbed gas of the J1b source rock, and the tight sandstone gas ( Figure 5 in a). According to the δ 13 C1-Ro relationship of coal-derived gas, the equivalent Ro value of the thermally desorbed gas of J2x exceeds 2.5%, which is significantly inconsistent with the measured Ro value (average value of 0.8%) of the J2x source rock and cannot be discriminated.

[0090] In addition, most of the tight sandstone gas is almost located in the overlapping area of these two sets of source rocks, J2x and J1s. Relying solely on the overall δ 13 C3 value, the carbon isotope values of butane and pentane isomers cannot well explain the genetic origin of the source rock ( Figure 5 in b, c, d).

[0091] The above is only a preferred implementation of the present invention and is not used to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for discriminating the source of hydrocarbon source rocks by using carbon isotopes in propane molecules, characterized in that It includes the following steps: S1. Take the sample to be tested, crush it, sieve it, place it in a pyrolysis furnace, heat and desorb it to generate desorbed gas; S2. Separate propane in the desorbed gas using a gas chromatograph and measure the δ 13 C value; S3. Separate the desorbed gas through Gas Chromatography Column I, subject the separated propane to high-temperature decomposition, separate the heating decomposition products through Gas Chromatography Column II, and measure the δ 13 C terminal value; S4. Take a known hydrocarbon source rock sample and measure the δ 13 C value of propane and the δ 13 C terminal value in propane according to the same steps as in steps S1 - S3; S5. Using the propane δ 13 C value as the abscissa and the propane δ 13 C terminal value as the ordinate, mark the values of the sample to be tested and the known hydrocarbon source rock sample in a rectangular coordinate system, observe the degree of overlap of the values, and when there is a high degree of overlap, the hydrocarbon source rock origin of the sample to be tested can be determined.

2. The method according to claim 1, wherein The sample to be tested after sieving is placed in a quartz tube with solid quartz rods filled on both sides. Before pyrolysis, argon is used to purge the air in the quartz tube.

3. The method according to claim 2, wherein In step S1, the sieving mesh number is 20 - 60 meshes; the purity of argon is ≥99.999%, and the purging time is 8 - 12 min.

4. The method according to claim 1, wherein In step S1, the heating conditions of the pyrolysis furnace are as follows: heat at a heating rate of 20°C / min to 180°C and hold for 60 min.

5. The method according to claim 1, wherein In step S2, the parameters of the gas chromatograph are as follows: the initial temperature is 30°C, hold for 10 min, then increase the temperature to 180°C at a rate of 20°C / min and hold for 2 min.

6. The method according to claim 1, wherein In step S3, the separation conditions of gas chromatographic column Ⅰ are as follows: the initial temperature is 50°C, hold for 3 min, then increase the temperature to 200°C at a rate of 10°C / min and hold for 8 min.

7. The method according to claim 1, wherein In step S3, the high-temperature decomposition temperature is 790°C.

8. The method according to claim 1, wherein In step S3, the separation conditions of gas chromatographic column Ⅱ are as follows: the initial temperature is 50°C, hold for 25 min, then increase the temperature to 200°C at a rate of 20°C / min and hold for 5 min.

9. A pyrolysis desorption device for implementing the method according to any one of claims 1-8, characterized in that, The pyrolysis desorption device is sequentially connected by a control system, a pyrolysis desorption system, and a detection system through pipelines; Among them, the control system consists of an argon gas tank and a flow controller connected to the outlet, and is used to provide argon to remove the residual air in the quartz tube; The pyrolysis desorption system consists of a pyrolysis furnace and a quartz tube, and is used to place the sample in the quartz tube and then put it into the pyrolysis furnace for pyrolysis desorption; The detection system consists of a helium gas tank, a gas chromatograph, and an isotope ratio mass spectrometer, and is used to separate and detect the desorbed gas.

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