Method for detecting carbon isotope composition of light hydrocarbon monomer hydrocarbon in semi-open system thermal simulation product

Abstract

The invention discloses a method for detecting light hydrocarbon monomer hydrocarbon carbon isotope composition in a semi-open system thermal simulation product, and belongs to the technical field of oil gas geology. According to the method, a liquid nitrogen freezing enrichment light hydrocarbon device is added into a semi-open system thermal simulator, liquid nitrogen is kept at the position of 2 / 3 or above of a 10 ml glass collection bottle through an optimization method, the reading of a temperature detector is kept at-100 DEG C to-130 DEG C, C5-C8 light hydrocarbon collection is completed after 60 s to 90 s, and C1-C4 with the capacity larger than 300 ml is obtained through collection at the same time. The obtained two parts of hydrocarbon compounds can well meet the requirements of subsequent experiments. According to the technical scheme, the conventionally obtained solid, liquid and gas (C1-C4) products are not affected, C5-C8 light hydrocarbons enriched in the gas are also carried, scientific research on the geochemical characteristics of the hydrocarbon source rock thermal simulation products can be enriched, and double benefits are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas geology, and in particular relates to a method for detecting the carbon isotope composition of light hydrocarbon monomers in a thermal simulation product of a semi-open system. Background Art

[0002] Light hydrocarbons (C5 + ) plays a vital role in natural gas exploration. However, the enrichment and analysis of C5 + Light hydrocarbons do present certain difficulties.

[0003] The current improvements in the existing technology are mainly aimed at C5 + The enrichment and analysis of hydrocarbon compounds. Natural gas is obtained from places where proven reserves have been found. However, when characterizing the research results based on the information of proven reserves of natural gas in the same basin, and inferring other possible reserves nearby or around, there are often errors. This is because lateral migration is a key and complex step in the process of oil and gas accumulation. When hydrocarbons migrate laterally, C5 + The composition and isotopes of natural gas vary greatly, and the distance between the discovered oil and gas storage sites and the possible new reserves may be tens of kilometers. Therefore, in addition to analyzing the proven reserves of natural gas, researchers will also use the potential source rocks of different strata in the basin for thermal simulation experiments.

[0004] Thermal simulation experiments are divided into three types according to the closedness of the system: open system thermal simulation experiment, closed system thermal simulation experiment, and semi-open (semi-closed) system thermal simulation experiment.

[0005] In closed thermal simulation experiments, the gold tube is an important experimental container. It uses the chemical inertness and plasticity of gold to use the closed gold tube as a container for pyrolysis reactions of samples containing organic matter to generate hydrocarbons.

[0006] In the prior art, the entire gold tube is usually immersed in an organic solution of dichloromethane, and then the container containing dichloromethane is placed in liquid nitrogen. The gold tube is pierced in the dichloromethane to allow hydrocarbon compounds to dissolve in the dichloromethane, completing the separation of all liquid hydrocarbons (including C1-C 13 ) collection. Because the gold tube itself has a certain volume, and the amount of dichloromethane required is more, generally the amount of dichloromethane used for a single use is more than 50 ml. Dichloromethane is a Class 2A carcinogen and is not friendly to experimental operators. In addition, the gold tube cannot be reused after being punctured and needs to be reprocessed. The method is time-consuming and laborious.

[0007] However, when using the gold tube thermal simulation method to prepare light hydrocarbons, a small amount of crude oil and heavy hydrocarbon gas in the closed system cannot be discharged and cracked to form low molecular weight gas (mainly methane). Therefore, in addition to collecting light hydrocarbons in the thermal simulation gas, the gold tube also mixes a large amount of thermal simulation liquid and residual hydrocarbons in the internal pores of solid residues. This is quite different from the information in actual exploration.

[0008] The ideal is to collect only the light hydrocarbons in the thermal simulation gas and compare them with the light hydrocarbons in natural gas, that is, the gas-to-gas ratio, rather than the gas-to-oil ratio.

[0009] The subsequent operation of the experiment is to quickly transfer the 'methylene chloride dissolved with hydrocarbon compounds' into a glass bottle, and then inject the methylene chloride liquid dissolved with hydrocarbon compounds into the injection port of a gas chromatograph (GC) for gas chromatography analysis.

[0010] This C1-C4 and C5 + It is difficult to determine the exact injection volume when analyzing mixed hydrocarbon compounds that are not differentiated directly by gas chromatography. + The content of is more than 2 orders of magnitude higher. If they are mixed together for injection, the following situations will often occur:

[0011] ① The injection volume is too large, and the C5 peak at the back + Although the peaks are good, the peaks C1-C4 in front are prone to "peak truncation".

[0012] ② The injection volume is too small, and all peaks do not show truncation. However, because the injection volume is too small, many C5 + The compound has no peak because its content is too low.

[0013] Therefore, it is necessary to separate the C1-C4 and C5 + Separate.

[0014] The semi-open system hydrocarbon generation simulation experimental system is often used to simulate the hydrocarbon generation and expulsion process of source rocks under high temperature and high pressure conditions in deep basins. It has the advantages of large sample capacity, many thermal simulation products, flexible application of fluid pressure that conforms to geological reality, and adding or intermittent discharge of fluid to the system during the test phase. It can simulate episodic hydrocarbon expulsion, that is, simulate the intermittent discharge process of oil and gas caused by pressure changes underground. The gas, liquid hydrocarbons, water and solid residues generated in the semi-open system thermal simulation experiment are collected and analyzed separately, which can be used for related research.

[0015] However, after the semi-open system thermal simulation experiment, the products are all placed in the open, the solid residue is retained in the sample chamber of the heating furnace, and the liquid product is retained in the solid-liquid separator, completely exposed to the air. In the subsequent conventional experiments, it continues to be exposed to the air and undergoes the heating and separation process. Therefore, the liquid and solid products are finally obtained as C 14 + The gaseous products collected in the semi-open system include C1-C 13 + In the subsequent gas component and isotope composition analysis experiments conducted at room temperature and pressure, the main focus is on the analysis of C1-C4, and the C5 with low content, high volatility and no special enrichment treatment + Not only can the detection and analysis results not be obtained, but it will also evaporate and dissipate during the experiment.

[0016] If the thermal simulation gas of the semi-open system is specially tested for C5 + When enriching C1-C4, the gas will be wasted, which means that two experiments need to be done to simultaneously study hydrocarbon compounds with different components. 13 C5 + , it is necessary to introduce other cumbersome and complicated devices and steps, which is time-consuming and labor-intensive.

[0017] In addition, the C of the gaseous part of the thermal simulation product of the semi-open system 5-13 Low light hydrocarbon content (mostly between 10ppm and 10 3 ppm), and its isotope content is below the normal detection limit of the mass spectrometer, which brings difficulties to analytical testing. Summary of the invention

[0018] In order to overcome at least one shortcoming of the prior art, a first aspect of the present invention provides a semi-open system thermal simulator with a light hydrocarbon C5-C8 collection function.

[0019] The second aspect of the present invention provides a method for detecting the carbon isotope composition of light hydrocarbon monomers in a thermal simulation product of a semi-open system.

[0020] The technical solution adopted by the present invention is:

[0021] As a first aspect of the present invention, a semi-open system thermal simulator with a light hydrocarbon C5-C8 collection function is provided, wherein the semi-open system thermal simulator is added with a liquid nitrogen freezing and enriching light hydrocarbon device 2; the liquid nitrogen freezing and enriching light hydrocarbon device 2 is arranged between the gas-liquid collector a9 of the semi-open system thermal simulator 1 and the thermal simulation gas collection device 3;

[0022] The liquid nitrogen freezing and enriching light hydrocarbon device 2 comprises a collecting bottle 23 and a liquid nitrogen insulation cup 26, wherein the collecting bottle 23 is arranged in the liquid nitrogen insulation cup 26, and a stainless steel bottle cap 24 is arranged on the collecting bottle 23, and three holes are opened on the stainless steel bottle cap 24, and an air inlet pipe, an air outlet pipe and a temperature detector are respectively connected to the collecting bottle 23 through one of the holes, an air inlet valve 21 is arranged on the air inlet pipe, and an air outlet valve 22 is arranged on the air outlet pipe, and the temperature detector 25 comprises a detection head and a temperature sensor capable of displaying readings, and the detection head and the temperature sensor are connected by an electric wire, and the detection head is deeply inserted into the collecting bottle 23, and the temperature sensor is arranged outside the collecting bottle 23; the liquid nitrogen insulation cup 26 is filled with an appropriate amount of liquid nitrogen;

[0023] The air inlet pipe of the liquid nitrogen freezing and enriching light hydrocarbon device 2 is connected to the gas-liquid collector a9 of the semi-open system thermal simulator 1, and the air outlet pipe is connected to the thermal simulation gas collecting device 3 (ie a13).

[0024] In some embodiments, the collection bottle 23 has a capacity of 10 ml and is made of glass.

[0025] In some embodiments, the collecting bottle 23 is at least 2 cm away from the bottom of the liquid nitrogen insulation cup 26 .

[0026] In some embodiments, the thermal simulation gas collection bottle 34 has a capacity greater than 300 ml and is made of glass.

[0027] In some of the embodiments, the thermal simulated gas collecting device 3 includes a drainage gas collecting device and a thermal simulated gas metering storage collecting device.

[0028] In some embodiments, the drainage and gas collecting device includes a first measuring cylinder 31, a second measuring cylinder 32 and a funnel 33, wherein the first measuring cylinder 31 is connected to the top of the second measuring cylinder 32 from its bottom, and the bottom of the second measuring cylinder 32 is connected to the funnel 33, and the funnel includes a funnel tube and a funnel body, the funnel tube is connected to the small mouth of the funnel body, and the funnel is open and directly connected to the outside atmosphere.

[0029] In some of the embodiments, the thermal simulated gas metering, storage and collection device includes a thermal simulated gas collection bottle 34, a container 35 filled with a saturated saline solution and a tube 36; wherein the thermal simulated gas collection bottle 34 is inverted in the container 35 filled with a saturated saline solution, one end of the tube 36 is inserted into the thermal simulated gas collection bottle 34, and the other end is connected to the first measuring cylinder 31 of the drainage and gas collecting device, and a valve is provided at the position where the tube 36 is connected to the first measuring cylinder 31.

[0030] As a second aspect of the present invention, a method for detecting the carbon isotope composition of light hydrocarbon monomers in a semi-open system thermal simulation product is provided, comprising the following steps:

[0031] Step A: The semi-open system thermal simulator 1 described in any of the above items is subjected to vacuum treatment, and a source rock of not less than 50 g and a diameter of 3-10 mm is placed in the semi-open system thermal simulator 1 for a thermal simulation experiment. After the thermal simulation experiment is completed, liquid nitrogen is added to the liquid nitrogen thermos cup 26, and the measuring cylinder of the drainage and gas collection device is filled with a saturated salt water solution. The valve between the first measuring cylinder 31 and the pipe 36 is closed, and the hydrocarbon discharge valve of the gas-liquid collector a9 is opened. The gas inlet valve 21 and the gas outlet valve 22 of the liquid nitrogen freezing and enriching light hydrocarbon device 2 are opened in sequence, so that the gas of the thermal simulation product diffuses into the glass collection bottle 2 with a capacity of 10 ml in the liquid nitrogen freezing and enriching light hydrocarbon device 2. 3, C5-C8 light hydrocarbons in the enriched gas product are collected, and liquid nitrogen is manually added so that the liquid level of the liquid nitrogen is maintained at or above the position just covering 2 / 3 of the collecting bottle 23, and the reading of the temperature detector 25 is observed at the same time, so that the reading is maintained at -100°C to -130°C. After 60s-90s, the C5-C8 light hydrocarbons are collected, and the reading of the temperature detector 25 is continued to be controlled to be less than or equal to -80°C. The collecting bottle 23 is unscrewed from the stainless steel bottle cap 24, and the collecting bottle 23 is tightened and sealed with a new bottle cap to obtain gas I, and then the collecting bottle 23 is transferred to an environment equal to or lower than -18°C for storage for use in the carbon isotope composition analysis of C5-C8 light hydrocarbons;

[0032] The remaining hydrocarbon gas II entering the thermal simulated gas collection device 3 is measured for gas production by the first measuring cylinder 31 of the drainage gas collection device, and then the valve between the first measuring cylinder 31 and the pipe 36 is opened to transfer the gas II to the thermal simulated gas collection bottle 34 for geochemical analysis of the C1-C4 thermal simulated gas;

[0033] In some embodiments, in step A, the source rock is selected from core or cutting samples obtained during drilling, and the lithology of the sample includes shale, marl or coal.

[0034] In some embodiments, in step A, the thermal simulation gas collection bottle 34 is made of glass and has a capacity greater than 300 ml.

[0035] In some embodiments, the collecting bottle 23 is at least 2 cm away from the bottom of the liquid nitrogen insulation cup 26 .

[0036] The beneficial effects of the present invention are:

[0037] The present invention uses a semi-open system hydrocarbon generation thermal simulation experimental system that best meets geological reality to perform thermal simulation on source rocks, adds a liquid nitrogen freezing and enriching light hydrocarbon device to the semi-open system thermal simulator, and maintains the liquid nitrogen at or above the 2 / 3 position of the 10ml collection bottle through an optimization method, so that the reading of the temperature detector is maintained at -100°C to -130°C, completes the collection of C5-C8 light hydrocarbons after 60s-90s, and collects C1-C4 with a capacity of more than 300ml at the same time. The obtained two parts of hydrocarbon compounds can well meet the needs of subsequent experiments.

[0038] The technical solution of this application uses a semi-open system to conduct thermal simulation experiments on source rocks. In addition to the conventionally obtained 'solid, liquid, gas (C1-C4)' products being unaffected, the C5-C8 light hydrocarbons in the 'gas' are also enriched, which can enrich the scientific research on the geochemical characteristics of the thermal simulation products of source rocks, killing two birds with one stone. This technical solution avoids the introduction of other cumbersome and complicated devices and steps to collect C5-C8 light hydrocarbons separately, as well as doing additional repeated experiments (the cost of each thermal simulation temperature point exceeds RMB 1,500); at the same time, it also saves the amount of precious source rock samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a schematic diagram of a semi-open system high-temperature and high-pressure thermal simulator (WYMN-3 high-temperature and high-pressure hydrocarbon generation simulator).

[0040] Figure 2 This is a flow chart of the method for testing the carbon isotope composition of light hydrocarbon monomers of thermal simulation products of a semi-open system according to the present invention.

[0041] Figure 3 This is the liquid nitrogen freezing and enrichment of light hydrocarbons device of the present invention.

[0042] Figure 4 This is the thermal simulation gas collecting device of the present invention.

[0043] Figure 5 This is the carbon isotope ratio spectrum of light hydrocarbon monomers in the thermal simulation gas of the source rock in Example 1. DETAILED DESCRIPTION

[0044] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0045] The semi-open system high temperature and high pressure thermal simulator used in the present invention is a WYMN-3 high temperature and high pressure hydrocarbon generation simulator, which is produced by Nantong Huaxing Petroleum Instrument Co., Ltd. Figure 1The device diagram is a schematic diagram of a semi-open system thermal simulator (original factory state). Figure 1 Among them, a0 is the computer system, a1 is the high-pressure pump; a2 is the intermediate container of the high-pressure pump; a3 is the pneumatic valve of the high-pressure pump; a4 is the pressure transmitter; a5 is the thermocouple and the heating furnace; a6 is the high-pressure autoclave body (with a sample chamber inside); a7 is the hydraulic pump control system; a8 is the hydraulic cylinder; a9 is the gas-liquid collector (with a cold trap on the outer jacket); a10 is the cooling water circulation machine; a11 is the vacuum gauge; a12 is the vacuum pump; and a13 is the thermal simulation gas collection device.

[0046] The whole system is connected through stainless steel pipelines. The vacuum pump a12 is one to N. Many pipes are connected in parallel from the air inlet. Each pipe is equipped with a switch valve. These N pipes can be connected to any opening of the stainless steel pipeline of the whole system. When a position needs to be vacuumed, just open the switch valve of that pipe.

[0047] The working process of the WYMN-3 high temperature and high pressure hydrocarbon generation simulator is mainly:

[0048] Sample preparation: First, the organic sample to be studied (such as coal, oil shale, sediment, etc.) is placed in the sample chamber (autoclave body a6).

[0049] Seal the sample chamber: Make sure the sample chamber is sealed to prevent gas leakage during the experiment.

[0050] Setting parameters: Set the required temperature and pressure parameters through the control panel of the computer system a0, which should simulate the natural conditions deep underground.

[0051] Vacuum treatment: Vacuum the pipes of the entire system.

[0052] Heating: Start the heating system, such as the thermocouple and the heating furnace a5, to gradually heat the sample chamber to the set temperature.

[0053] Pressurization: Ultrapure water is injected into the sample chamber of the autoclave body a6 through the high-pressure pump a1, the high-pressure pump intermediate container a2, the high-pressure pump pneumatic valve a3, and the pressure transmitter a4 to increase the fluid pressure in the system to the set value.

[0054] Monitoring: Use a temperature sensor (a small probe, set in the sample chamber of the autoclave body a6) and a pressure sensor (a small probe, set in the sample chamber of the autoclave body a6) to monitor the temperature and pressure in the sample chamber in real time to ensure the stability of the experimental conditions.

[0055] Data acquisition: The temperature, pressure and possible other parameters during the entire experiment are recorded by the data acquisition system of the computer system a0.

[0056] Reaction: Under the set temperature and pressure, the organic matter in the sample undergoes pyrolysis and cracking reactions to generate hydrocarbon compounds. The hydrocarbon compounds are intermittently discharged and continuously enter the gas-liquid collector a9. The high-temperature and high-pressure gas-liquid mixture from the thermal simulator is separated in the gas-liquid collector a9 (tank), with the liquid remaining at the bottom of the tank and the gas at the top of the tank. The gas-liquid collector is covered with an aluminum metal heat-conducting shell (i.e., cold trap).

[0057] Product collection: After the experiment, the temperature of the sample chamber is lowered by closing the a5 thermocouple and the heating furnace, and then the hydrocarbon exhaust valve of the gas-liquid collector (separator) a9 is opened, the gas will escape, and the generated hydrocarbon compounds are collected by the thermal simulation gas collection device a13.

[0058] Safety measures: During the whole process, the safety valve (set between the hydraulic cylinder a8 and the gas-liquid collector a9) ensures that the system can automatically release the pressure when the pressure is too high, protecting the safety of the experimenters and equipment. During the whole process, the cooling water circulation machine a10 cools the system.

[0059] End of the experiment: turn off the heating and pressure systems, open the gas-liquid collector a9 to take out the liquid part, open the sample chamber in the autoclave body a6 to take out the solid sample for subsequent analysis.

[0060] like Figure 2 As shown, the improvement of the present invention is that a liquid nitrogen freezing and enriching light hydrocarbon device 2 is added to enrich C5-C8 in the thermal simulation gas. The liquid nitrogen freezing and enriching light hydrocarbon device 2 is arranged in the gas-liquid collector ( Figure 1 a9) and the thermal simulation gas collection device 3 ( Figure 1 between a13) in .

[0061] like Figure 2 and Figure 3 As shown, a semi-open system thermal simulator with a light hydrocarbon C5-C8 collection function is provided, wherein the semi-open system thermal simulator is added with a liquid nitrogen freezing and enriching light hydrocarbon device 2; the liquid nitrogen freezing and enriching light hydrocarbon device 2 is arranged in a gas-liquid collector ( Figure 1 a9) between the thermal simulation gas collecting device 3;

[0062] The liquid nitrogen freezing and enriching light hydrocarbon device 2 comprises a collecting bottle 23 and a liquid nitrogen insulation cup 26, wherein the collecting bottle 23 is arranged in the liquid nitrogen insulation cup 26, and a stainless steel bottle cap 24 is arranged on the collecting bottle 23, and three holes are opened on the stainless steel bottle cap 24, and an air inlet pipe, an air outlet pipe and a temperature detector are respectively connected to the collecting bottle 23 through one of the holes, an air inlet valve 21 is arranged on the air inlet pipe, and an air outlet valve 22 is arranged on the air outlet pipe, and the temperature detector 25 comprises a detection head and a temperature sensor capable of displaying readings, and the detection head and the temperature sensor are connected by an electric wire, and the detection head is deeply inserted into the collecting bottle 23, and the temperature sensor is arranged outside the collecting bottle 23; the liquid nitrogen insulation cup 26 is filled with an appropriate amount of liquid nitrogen;

[0063] The gas inlet pipe of the liquid nitrogen freezing and enriching light hydrocarbon device 2 and the gas-liquid collector of the semi-open system thermal simulator 1 ( Figure 1 a9) is connected, and the air outlet pipe is connected to the hot simulated gas collecting device 3.

[0064] Figure 2 Other components include: solid phase microextraction device 4, gas chromatograph 5, monomer hydrocarbon compound 6, combustion furnace 7, dehydration device 8, dried CO29, isotope ratio mass spectrometer 10, liquid nitrogen LN2. The relevant experimental method is: insert the solid phase microextraction head of the solid phase microextraction device 4 into the collection bottle 23 (gas I) of the liquid nitrogen freezing enrichment light hydrocarbon device 2 to enrich and extract light hydrocarbons. The enriched and extracted light hydrocarbons are separated into monomer hydrocarbon compounds 6 by gas chromatograph 5. The monomer hydrocarbon compound 6 is transferred to the combustion furnace 7, and the obtained gas is passed through the dehydration device 8 to obtain dried CO29, and finally the carbon isotope composition in the monomer hydrocarbon is determined by the isotope ratio mass spectrometer 10.

[0065] Preferably, the collecting bottle 23 has a capacity of 10 ml and is made of glass.

[0066] Preferably, the collecting bottle 23 is at least 2 cm away from the bottom of the liquid nitrogen thermos cup 26. If the height is less than this, the collecting bottle is likely to be directly attached to the bottom of the liquid nitrogen thermos cup, which may cause bumps during the experimental operation, or the collecting bottle 23 may be easily attached to the bottom of the liquid nitrogen thermos cup 26 in a liquid nitrogen environment.

[0067] Preferably, the opening of the liquid nitrogen thermos cup 26 should not be too large, and a 10 ml collection bottle can be placed therein, and liquid nitrogen can be easily added thereto. Because liquid nitrogen will vaporize at room temperature, a liquid nitrogen thermos cup with a slightly smaller caliber is preferred.

[0068] Preferably, the capacity of the liquid nitrogen thermos cup 26 is 300-400 ml. More preferably, the capacity of the liquid nitrogen thermos cup 26 is 300-350 ml.

[0069] Preferably, the thermal simulated gas collecting device 3 includes a drainage gas collecting device and a thermal simulated gas metering storage collecting device. Figure 4 shown.

[0070] Preferably, the drainage and gas collecting device includes a first measuring cylinder 31, a second measuring cylinder 32 and a funnel 33, wherein the first measuring cylinder 31 is connected to the top of the second measuring cylinder 32 from its bottom, and the bottom of the second measuring cylinder 32 is connected to the funnel 33, and the funnel includes a funnel tube and a bucket body, the funnel tube is connected to the small mouth of the bucket body, and the funnel is open and directly connected to the outside atmosphere.

[0071] Preferably, the thermal simulation gas metering storage and collection device comprises a thermal simulation gas collection bottle 34, a container 35 filled with a saturated salt water solution and a tube 36; wherein the thermal simulation gas collection bottle 34 is inverted in the container 35 filled with a saturated salt water solution, one end of the tube 36 is inserted into the thermal simulation gas collection bottle 34, and the other end is connected to the first measuring cylinder 31 of the drainage gas collection device, and a valve is provided at the position where the tube 36 is connected to the first measuring cylinder 31. When the valve is opened, when the gas diffuses from the first measuring cylinder 31 of the drainage gas collection device through the tube 36 into the thermal simulation gas collection bottle 34, the saturated salt water solution in the thermal simulation gas collection bottle 34 is discharged, and the gas in the thermal simulation gas collection bottle 34 will gradually accumulate.

[0072] Preferably, the capacity of the thermal simulation gas collection bottle 34 is greater than 300 ml and is made of glass.

[0073] The specific operation of collecting thermal simulation gas is as follows:

[0074] (1) A thermal simulation experiment was conducted using a semi-open system high temperature and high pressure thermal simulator (WYMN-3 high temperature and high pressure hydrocarbon generation simulator) 1 until the end of the experiment. During this process, the hydrocarbon discharge valve of the gas-liquid collector a9 was kept in a closed state.

[0075] (2) Close the valve between the tube 36 and the first measuring cylinder 31, and fill the two measuring cylinders 31 and 32 with saturated salt water through the rightmost funnel 33 to completely remove the air inside; and evacuate the pipe behind the gas-liquid collector a9 of the semi-open thermal simulator, place the vacuumed collection bottle 23, and check and ensure that the air inlet valve 21 and the air outlet valve 22 are in the closed state.

[0076] (3) Pour liquid nitrogen into the liquid nitrogen thermos cup 26 so that the liquid nitrogen level is maintained at a position just above 2 / 3 of the collecting bottle 23, and at the same time observe the temperature detector reading so that the temperature detector 25 reading is maintained at -100°C to -130°C.

[0077] (4) Open the hydrocarbon exhaust valve of the gas-liquid collector a9 of the semi-open system high-temperature and high-pressure thermal simulator 1. At this time, the high-temperature and high-pressure thermal simulation gas diffuses to the vicinity of the intake valve 21 through the pipeline.

[0078] (5) Open the air inlet valve 21 and the air outlet valve 22 in sequence; the high temperature and high pressure simulated gas diffuses into the collection bottle 23 through the air inlet valve 21 and fills the entire collection bottle 23. In this process, C5-C8 can be well enriched (frozen), and the excess high temperature and high pressure thermal simulated gas (mainly C1-C4) is discharged through the air outlet valve 22, and further enters the first measuring cylinder 31 of the thermal simulated gas collection device 3 through the pipeline, and discharges the saturated salt water solution SSS in the first measuring cylinder 31; the product collected in the collection bottle 23 is recorded as gas I, which is mainly liquid C5-C8, and inevitably contains a small amount of gaseous C1-C4; the gas collected in the first measuring cylinder 31 is recorded as gas II, which is mainly C1-C4.

[0079] C9-C 13 The content of C5-C8 is generally very low, at least one or two orders of magnitude lower than that of C5-C8, and below the detection line of the isotope ratio mass spectrometer. Therefore, it is no longer within the scope of consideration of the technical solution of this application. In addition, the program running time of the isotope ratio mass spectrometer set in this application is 25-32 minutes, and the main collected substances are C5-C8. The extremely small amount of C9-C 13 Generally, the peak appears after 35 minutes, so it is excluded here.

[0080] (6) Keep the reading of the temperature detector 25 at -100°C to -130°C for 60-90 seconds; if the temperature drops rapidly, liquid nitrogen can be added manually.

[0081] The operation of limiting this step is mainly related to the boiling point of gaseous hydrocarbons such as methane (the boiling point of methane is -162℃, and that of ethane is -90℃, and the boiling point gradually increases as the carbon number increases). Controlling the temperature in the 10ml small collection bottle at -100℃ to -130℃ can ensure that the methane gas is still in gaseous state at this time, and will not be liquefied and fixed to the inner wall of the small collection bottle with other C5-C8 light hydrocarbons (the content of methane usually accounts for 90% to 99.9% of hydrocarbon gases in natural gas and thermal simulation gas, so the purpose of liquid nitrogen freezing here is mainly to exclude methane). The time of 60-90S is to allow the C5-C8 light hydrocarbons sufficient time to liquefy and fix to the inner wall of the small collection bottle.

[0082] The temperature of -100°C to -130°C and the time of 60-90S can keep the C1-C4 gases such as methane in gaseous state and will not be frozen by liquid nitrogen. The continuously generated C1-C4 gases are discharged into the first measuring cylinder 31 through the gas outlet valve 22, and no less than 300ml of C1-C4 can be obtained in the time. Of course, it is inevitable that a small amount of C1 methane gas will still be contained in the 10ml collection bottle, but because methane accounts for a large proportion of the total gas, this little loss of methane has little effect on the subsequent carbon isotope value results of C1-C4 such as methane, which is within the error range. Through this operation, a sufficient amount of C5-C8 can be obtained in the 10ml collection bottle 23, and a volume of C1-C4 greater than 300ml can be obtained. The two parts of hydrocarbon compounds obtained can well meet the needs of subsequent experiments.

[0083] (7) Close the air inlet valve 21 and the air outlet valve 22 in sequence.

[0084] At this time, closing the valve is long enough to ensure that C5-C8 are frozen and the gas discharged from C1-C4 can reach the requirement of 300ml.

[0085] (8) Control the reading of the temperature detector 25 to be less than or equal to -80°C, quickly unscrew the collection bottle 23 from the (specially made) stainless steel bottle cap 24, and seal the collection bottle 23 with a brand new bottle cap with a rubber gasket, and then immediately transfer it to an environment equal to or lower than -18°C for storage; the gas collected in the collection bottle 23 is recorded as gas I, which is mainly C5-C8. The gas of C5-C8 can be stored for up to 3 months in an environment equal to or lower than -18°C. The C5-C8 is used for the carbon isotope composition analysis of light hydrocarbons.

[0086] (9) After properly storing the gas I obtained above in an environment of -18°C, transfer the gas II obtained in the first measuring cylinder 31 of the drainage gas collection device to the thermal simulation gas collection bottle 34. Specifically, the thermal simulation gas collection bottle 34 is inverted in a container 35 filled with a saturated saline solution to ensure that the opening of the thermal simulation gas collection bottle 34 is completely immersed in the saturated saline solution. Open the valve between the first measuring cylinder 31 and the hose 36. Slightly raise the liquid level of the funnel on the far right, and use the gravity of water to press the gas II in the first measuring cylinder into the 500ml thermal simulation gas collection bottle 34. After sealing with a rubber stopper, keep it inverted to prevent leakage. The gas is C1-C4, which is used for conventional thermal simulation gas geochemical analysis.

[0087] A method for detecting the carbon isotope composition of light hydrocarbon monomers in a semi-open system thermal simulation product comprises the following steps:

[0088] Step A: Put no less than 50g of source rock with a diameter of 3-10mm into the semi-open system thermal simulator 1 to conduct a thermal simulation experiment. After the thermal simulation experiment is completed, collect the thermal simulation gas. The method for collecting the thermal simulation gas is as described above.

[0089] Step B: The gas I stored at a temperature equal to or lower than -18°C is enriched with hydrocarbon compounds by using solid phase microextraction 4.

[0090] Step C: Separating hydrocarbon compounds into monomeric hydrocarbons 6 using gas chromatography 5 .

[0091] Step D: Using an isotope ratio mass spectrometer 10 to measure the carbon isotope composition in the monomeric hydrocarbons.

[0092] Among them, hydrocarbon compounds are a general term for hydrocarbons, which are compounds composed of carbon and hydrogen atoms, mainly including alkanes, cycloalkanes, alkenes, alkynes, and aromatic hydrocarbons.

[0093] Monomer hydrocarbons mainly refer to individual hydrocarbon compounds in petroleum fractions, especially normal alkanes, isoalkanes, olefins, cycloalkanes and aromatics in gasoline fractions.

[0094] The temperature of liquid nitrogen is generally 77K (-200°C). This application sets up a liquid nitrogen freezing and enriching light hydrocarbon device, and uses liquid nitrogen to cool the collecting bottle (10ml in capacity, made of glass) of the light hydrocarbon enriching device. Since the liquid nitrogen is cooled through the glass collecting bottle, due to the limitations of factors such as heat conduction efficiency and the thermal properties of the glass bottle, the temperature inside the glass bottle can generally be stabilized between -100°C and 150°C.

[0095] The inventors found in their research that the temperature inside the glass collection bottle of the liquid nitrogen freezing and enriching light hydrocarbon device can be measured by the height of the collection bottle covered by liquid nitrogen. The higher the height of the collection bottle, the lower the temperature inside the glass collection bottle. When the bottle is completely covered, the temperature inside the glass collection bottle can reach a minimum of -150°C; the less the liquid nitrogen is covered, the higher the temperature inside the glass collection bottle.

[0096] The present application is provided with manual filling of liquid nitrogen so that the liquid nitrogen level is maintained at a position just above 2 / 3 of the collecting bottle, so that the temperature in the collecting bottle can be maintained at -100°C to -130°C. Within this range, the light hydrocarbons C5-C8 can be frozen well. "Freezing" means using low temperature to turn the light hydrocarbons C5-C8 into liquid, so that the light hydrocarbons C5-C8 are adsorbed on the inner wall of the glass bottle and separated from the C1-C4 gases such as methane (the boiling point is too low and the liquid nitrogen cannot freeze it). If there is too little liquid nitrogen in the liquid nitrogen thermos cup, the refrigeration temperature in the collecting bottle may not meet the requirements, and the light hydrocarbons C5-C8 cannot be frozen; if it is too full, the liquid nitrogen is easy to splash out and cause frostbite on the operator's hand skin, and affect the operational stability of the experimenter when screwing the bottle cap later.

[0097] In some embodiments, the gas I (in liquid form) in the collection bottle 23 obtained in step A is transferred to an environment equal to or lower than -18°C for storage. The purpose is:

[0098] At a low temperature of -18°C, C5-C8 will adhere to the inner wall or bottom of the collection bottle 23 (10ml) in liquid form. This can ensure that C5 + The light hydrocarbons will not leak out of the bottle slowly. The collected gas I can be used for the following steps B, C, and D immediately or later according to the experimental arrangement.

[0099] The remaining hydrocarbon gas (gas II) refers to the gas not frozen by liquid nitrogen, mainly C1-C4 gas dominated by methane. Since the boiling point of methane is -161°C, it will not be frozen by liquid nitrogen and can be kept in the gas phase. Finally, after the gas output is measured by the large cylinder 31 of the drainage gas collection device, it is transferred and collected into a 500ml glass thermal simulation gas collection bottle 34.

[0100] The chromatographic columns used are HP-PONA columns or HP-AL / KCL columns. These two chromatographic columns can retain C5-C8 well.

[0101] More preferably, the chromatographic column used is a HP-PONA column.

[0102] In some preferred embodiments, the source rock sample particles are core or cutting samples obtained during drilling, and the lithology includes shale, marl and coal, with a diameter of 3 to 10 mm.

[0103] In some preferred embodiments, the amount of the thermal simulated gas collected in the thermal simulated gas collection bottle is greater than 300 ml (gas II).

[0104] In addition to C5-C8, the subsequent uses of conventional products obtained from semi-open systems include:

[0105] 1. Solid residue: used for determination of source rock maturity (Ro), residual oil extraction and biomarker compound analysis, solid residue organic carbon isotope composition analysis;

[0106] 2. Liquid (discharged oil): analysis of total oil generation rate, analysis of biomarker compounds of each component in the oil (saturated, aromatic, non-aromatic, bituminous), analysis of organic carbon isotope composition of whole oil and normal alkanes;

[0107] 3. Gas (C1-C4), also known as gas II collected by thermal simulation gas collection device 3: determination of total gas yield (used to determine the gas generation potential of the source rock), determination of gas components, determination of organic carbon isotope composition of methane and ethane in the gas (used to determine the genetic type and maturity of the thermal simulation gas).

[0108] The above is a further detailed description of the present invention, which should not be regarded as a limitation on the specific implementation of the present invention. For ordinary technicians in the technical field to which the present invention belongs, simple deduction or replacement without departing from the concept of the present invention is within the protection scope of the present invention.

[0109] The experimental methods in the following examples of the present invention without specifying specific conditions are usually carried out under conventional conditions or under conditions recommended by the manufacturers. The various commonly used chemical reagents used in the examples are all commercially available products.

[0110] Example 1

[0111] A method for detecting the carbon isotope composition of light hydrocarbon monomers in a semi-open system thermal simulation product comprises the following steps:

[0112] (1) 300 g of a gray-black shale core sample with a total organic carbon content greater than 2% from a certain well was taken and crushed into particles with a diameter of 3.0 to 10.0 mm. 50.0 g of the crushed gray-black shale sample was accurately weighed and loaded into the sample chamber in the autoclave body a6 of a semi-open system high-temperature and high-pressure thermal simulator, and the sample chamber was filled and sealed with matching baffles, gaskets, copper rings, graphite rings and other accessories;

[0113] (2) Install the sample chamber containing the gray-black shale sample in the heating furnace a5 of the thermal simulator according to the standard operating steps. According to the actual simulated formation pressure parameters of the sample, apply the corresponding static rock pressure (81.6MPa), surrounding rock pressure (137.0MPa) and fluid pressure (34.0MPa) to the sample with the help of the hydraulic control system, and ensure that the entire system is leak-proof;

[0114] (3) Turn on the heating furnace and maintain a heating rate of 7.5°C / h. After continuously heating to 350°C, maintain the constant temperature for 72 hours. During the heating and constant temperature process, the computer preset program and the electronically controlled valve are used to discharge hydrocarbons and adjust the fluid pressure in the system so that the fluid pressure in the system is maintained between 30.6 MPa and 40.8 MPa;

[0115] (4) After the 72-hour constant temperature is reached, the exhaust valve of the gas-liquid collector a9 of the semi-open system thermal simulator is opened, and the C in the gas product is enriched by the liquid nitrogen freezing and enrichment light hydrocarbon device 2 specially made in the present application. 5- After the C8 component light hydrocarbons are collected, they are tightly sealed with a new bottle cap with a polyethylene gasket, and then immediately transferred to a freezer (less than -18°C) for storage in the next step. 5- Used for carbon isotope composition analysis of C8 light hydrocarbons;

[0116] (5) The remaining hydrocarbon gas, mainly C1 (methane), is collected into a 500 ml thermal simulated gas collection bottle 34 after the gas production is measured by the drainage gas collection device (first measuring cylinder 31), sealed with a rubber stopper and kept upside down to prevent gas leakage, and used for conventional thermal simulated gas geochemical analysis. The carrier gas volume of the thermal simulated gas collection bottle 34 is maintained between 300 ml and 350 ml;

[0117] (6) Use a needle of one size larger to pierce the rubber pad in the center of the bottle cap of the collection bottle 23 in step (4) so ​​that the SPME needle 4 will not damage the extraction wire when passing through the rubber stopper. Take a carbon molecular sieve / polydimethylsiloxane (CAR / PDMS) manual solid phase microextraction head 4 that has been activated at 300°C for 3 hours, insert the extraction head 4 into the collection bottle 23 for light hydrocarbon enrichment extraction, the equilibrium time is 30 minutes, the temperature is room temperature 20°C, and the pressure is one standard atmosphere;

[0118] (7) After the equilibrium time is reached, the solid phase microextraction head 4 is pulled out from the collection bottle 23 and immediately inserted directly into the injection port of the gas chromatograph 5. The injection port temperature is 280° C., and the extraction head 4 is kept in the injection port for 2 minutes to allow the light hydrocarbons adsorbed on the extraction head 4 to be fully thermally desorbed;

[0119] (8) After separation by the chromatographic column of the gas chromatograph 5, the C 5- C8 component, and C 5- The C8 component hydrocarbon mixture is separated into monomer hydrocarbon compounds 6 (such as n-heptane, methylcyclohexane, toluene and other compounds);

[0120] (9) The separated monomer hydrocarbon compounds 6 flow out of the gas chromatograph 5 and enter the combustion furnace 7 in sequence to undergo oxidation-reduction reactions and are converted into CO2 and H2O;

[0121] (10) The CO2 and H2O obtained by the above redox reaction are driven by a carrier gas, and then the water is removed by a drying device 8 to obtain the corresponding CO29, which is introduced into an isotope ratio mass spectrometer 10;

[0122] (11) The dried CO29 is ionized into three different isotope isomer ions with mass-to-charge ratios (m / z) of 44, 45 and 46 in the ion source of the isotope ratio mass spectrometer 10. The three charged ion flows with different mass-to-charge ratios (m / z) are separated after passing through the magnetic field, and then the signals are received by the Faraday cup. The system calculates and determines the carbon isotope ratio.

[0123] Figure 5This is the carbon isotope ratio spectrum of light hydrocarbon monomer hydrocarbons in the thermal simulation gas of the gray-black shale sample of Example 1 at a preset heating temperature of 350°C. The carbon isotope composition characteristics of light hydrocarbon monomer hydrocarbons in the thermal simulation product of gray-black shale are determined by Figure 5 Analyze and obtain. Figure 5 The peak numbers in the graph correspond to the following monomer hydrocarbon compounds: 1) isopentane; 2) n-pentane; 3) 2,2-dimethylbutane; 4) cyclopentane; 5) 2-methanepentane; 6) 3-methylpentane; 7) n-hexane; 8) 2,2-dimethylpentane; 9) methylcyclopentane; 10) 2,4-dimethylpentane; 11) 2,2,3-trimethylbutane; 12) benzene; 13) 3,3-dimethylpentane; 14) cyclohexane; 15) 2-methylhexane; 16) 2,3-dimethylpentane; 17) 1,1-dimethylcyclopentane; 18) 3-methylhexane; 19) 1,cis-3-dimethylcyclopentane; 20) 1,trans-3-dimethylcyclopentane; 21) 1,trans-2-dimethylcyclopentane; 22) n-heptane; 23) methylcyclohexane; 24) toluene.

[0124] The preset heating temperatures in step (3) in Example 1 were adjusted to 400° C., 450° C., and 500° C., respectively, and the other reaction parameters were the same as in Example 1, to obtain Examples 2-4.

[0125] The carbon isotope composition results of light hydrocarbon monomers of the gray-black shale thermal simulation products at each preset thermal simulation temperature (350° C. to 500° C.) in Examples 1-4 are shown in Table 1.

[0126] Table 1

[0127]

[0128] Note: 13 C (VPDB / ‰) refers to the organic carbon isotope composition of the corresponding compound, and the standard is VPDB (Vienna PDB); 3-MC5 refers to 3-methyl-pentane, n-C6 refers to n-hexane, Benz. refers to benzene, CC6 refers to cyclohexane, 3-MC6 refers to 3-methyl-hexane, n-C7 refers to n-heptane, MCC6 refers to methylcyclohexane, Tol. refers to toluene, iC5 refers to isopentane, and nC5 refers to n-pentane.

[0129] If this technical solution is adjusted, the light hydrocarbon enrichment device ( Figure 2 and Figure 3), directly collect all the gases collected by the thermal simulation gas collection device, including C1-C4 and C5-C8, use solid phase microextraction (the chromatographic column used is HP-PONA column or HP-AL / KCL column) to enrich C5-C8, and use gas chromatography to separate hydrocarbon compounds into monomer hydrocarbons; and use isotope ratio mass spectrometry to determine the carbon isotope composition of monomer hydrocarbons. Many 'humus source rocks (tend to produce dry gas (i.e. methane), and produce less C5 during pyrolysis. + In the process of determining the organic carbon isotope composition by 'isotope ratio mass spectrometry', many C5 + The peak height of the compound is too low to obtain accurate isotope values ​​of individual hydrocarbons. Figure 5 The peaks that originally have relatively low peaks (height) are more obviously lower, or even absent. Therefore, the technical solution of this application can better enrich C5-C8.

[0130] In summary, the use of curtain-type hydrocarbon expulsion of the semi-open system thermal simulation experimental device of the present application to simulate the hydrocarbon generation process of in-situ mining of oil shale under actual geological conditions will produce more accurate results. In addition to retaining the liquid, solid residues and C1-C4 partial products obtained in the original semi-open system thermal simulation, the technical solution of the present application can also collect and obtain C5-C8 light hydrocarbons in its gas products. The C5-C8 portion of the thermal simulation gas production of the semi-open system obtained by the technical solution of the present application can be compared with the C5-C8 portion of the natural gas in the natural gas, and the obtained data analysis and experimental results will be more intuitive and convincing. This technology can directly serve natural gas exploration and is of great significance.

Claims

1. A semi-open system thermal simulator with light hydrocarbon C5-C8 collection function, characterized in that: The semi-open system thermal simulator is provided with a liquid nitrogen freezing and light hydrocarbon enrichment device (2); the liquid nitrogen freezing and light hydrocarbon enrichment device (2) is arranged between the gas-liquid collector and the thermal simulation gas collection device (3) of the semi-open system thermal simulator (1); The liquid nitrogen freezing and enriching light hydrocarbon device (2) comprises a collecting bottle (23) and a liquid nitrogen insulation cup (26), wherein the collecting bottle (23) is arranged in the liquid nitrogen insulation cup (26), a stainless steel bottle cap (24) is arranged on the collecting bottle (23), three holes are opened on the stainless steel bottle cap (24), an air inlet pipe, an air outlet pipe and a temperature detector are respectively connected to the collecting bottle (23) through one of the holes, an air inlet valve (21) is arranged on the air inlet pipe, an air outlet valve (22) is arranged on the air outlet pipe, and the temperature detector (25) comprises a detection head and a temperature sensor capable of displaying a reading, the detection head and the temperature sensor are connected by an electric wire, the detection head is deeply inserted into the collecting bottle (23), and the temperature sensor is arranged outside the collecting bottle (23); the liquid nitrogen insulation cup (26) is filled with an appropriate amount of liquid nitrogen; The air inlet pipe of the liquid nitrogen freezing and enriching light hydrocarbon device (2) is connected to the gas-liquid collector of the semi-open system thermal simulator (1), and the air outlet pipe is connected to the thermal simulation gas collecting device (3).

2. The semi-open system thermal simulator according to claim 1, characterized in that: The collecting bottle (23) has a capacity of 10 ml and is made of glass.

3. The semi-open system thermal simulator according to claim 1, characterized in that: The collecting bottle (23) is at least 2 cm away from the bottom of the liquid nitrogen insulation cup (26).

4. The semi-open system thermal simulator according to claim 1, characterized in that: The thermal simulated gas collecting device (3) comprises a drainage gas collecting device and a thermal simulated gas metering storage collecting device.

5. The semi-open system thermal simulator according to claim 4, characterized in that: The drainage gas collecting device comprises a first measuring cylinder (31), a second measuring cylinder (32) and a funnel (33), wherein the first measuring cylinder (31) is connected to the top of the second measuring cylinder (32) from its bottom, the bottom of the second measuring cylinder (32) is connected to the funnel (33), the funnel (33) comprises a funnel tube and a funnel body, the funnel tube is connected to the small mouth of the funnel body, and the funnel is open and directly connected to the outside atmosphere.

6. The semi-open system thermal simulator according to claim 4, characterized in that: The thermal simulated gas metering, storage and collection device comprises a thermal simulated gas collection bottle (34), a container (35) filled with a saturated salt water solution and a tube (36); wherein the thermal simulated gas collection bottle (34) is inverted in the container (35) filled with the saturated salt water solution, one end of the tube is inserted into the thermal simulated gas collection bottle (34), and the other end is connected to a first measuring cylinder (31) of the drainage and gas collection device, and a valve is provided at the position where the tube (36) is connected to the first measuring cylinder (31).

7. The semi-open system thermal simulator according to claim 6, characterized in that: The capacity of the thermal simulation gas collection bottle (34) is greater than 300 ml and is made of glass.

8. A method for detecting the carbon isotope composition of light hydrocarbon monomers in a semi-open system thermal simulation product, characterized in that: The following steps are involved: Step A: The semi-open system thermal simulator (1) system according to any one of claims 1 to 7 is subjected to vacuum treatment, and a source rock sample of not less than 50 g and a diameter of 3 to 10 mm is placed in the semi-open system thermal simulator (1) for a thermal simulation experiment. After the thermal simulation experiment, the measuring cylinder of the drainage and gas collection device is filled with a saturated salt water solution, the valve between the first measuring cylinder (31) and the tube (36) is closed, liquid nitrogen is added to the liquid nitrogen insulation cup (26), the hydrocarbon discharge valve of the gas-liquid collector is opened, and the gas inlet valve (21) and the gas outlet valve (22) of the liquid nitrogen freezing and enriching light hydrocarbons device (2) are opened in sequence, so that the gas of the thermal simulation product diffuses into the glass collecting cup with a capacity of 10 ml in the liquid nitrogen freezing and enriching light hydrocarbons device (2). In the collecting bottle (23), C5-C8 light hydrocarbons in the enriched gas product are collected, and liquid nitrogen is manually added to maintain the liquid level of the liquid nitrogen at a position just above 2 / 3 of the collecting bottle (23) or above, and the reading of the temperature detector (25) is observed at the same time, so that the reading is maintained at -100°C to -130°C. After 60s-90s, the collection of C5-C8 light hydrocarbons is completed, and the reading of the temperature detector (25) is continuously controlled to be less than or equal to -80°C. The collecting bottle (23) is unscrewed from the stainless steel bottle cap (24), and the collecting bottle (23) is tightened and sealed with a new bottle cap to obtain gas I, and then the collecting bottle (23) is transferred to an environment equal to or lower than -18°C for storage, and used for carbon isotope composition analysis of C5-C8 light hydrocarbons; The remaining hydrocarbon gas II entering the thermal simulated gas collection device (3) is measured for gas production by the first measuring cylinder (31) of the drainage gas collection device, and then the valve between the first measuring cylinder (31) and the pipe (36) is opened to transfer the gas II to the thermal simulated gas collection bottle (34) for geochemical analysis of C1-C4 thermal simulated gas; Step B: enriching the C5-C8 hydrocarbon compounds in the gas I stored at a temperature equal to or lower than -18°C by solid phase microextraction (4); Step C: Separating the C5-C8 hydrocarbon compounds into monomeric hydrocarbons (6) using gas chromatography (5); Step D: The carbon isotope composition is determined by using an isotope ratio mass spectrometer (10), wherein the program running time of the isotope ratio mass spectrometer (10) is set to 26-32 minutes to obtain the isotope composition results of C5-C8 light hydrocarbon monomer hydrocarbons.

9. The method according to claim 8, characterized in that In step A, the source rock is selected from core or rock cutting samples obtained during drilling, and the lithology of the sample includes shale, marl or coal.

10. The method according to claim 8, characterized in that The chromatographic column used in the gas chromatography of step C is a HP-PONA column or a HP-AL / KCL column.

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