CN114113440B - System and method for capturing and analyzing volatile hydrocarbon in natural gas hydrate reservoir - Google Patents

Abstract

The invention provides a system and a method for trapping and analyzing volatile hydrocarbon in a natural gas hydrate reservoir, wherein the system comprises a volatilization device, a primary cold trap device, a secondary cold trap device, a temperature control device and a gas chromatography-mass spectrum; the volatilizing device comprises a sealed ball milling tank and a ball milling tank heating body, wherein the ball milling tank heating body is sleeved outside the sealed ball milling tank and used for heating the sealed ball milling tank; the sealed ball milling tank is respectively provided with an inlet and an outlet, and the inlet is communicated with the gas carrying bottle; the primary cold trap device comprises an ice-water bath device and a sample absorption bottle, the sample absorption bottle is filled with dichloromethane, the sample absorption bottle is positioned in the ice-water bath device, and the opening of the sample absorption bottle is communicated with the outlet of the sealed ball milling tank through a transmission pipeline; the secondary cold trap device comprises a liquid nitrogen thermos bottle and a U-shaped absorption tube, wherein an opening at one end of the U-shaped absorption tube is communicated with an opening of the sample absorption bottle; the gas chromatography-mass spectrometry is used for analyzing the composition and content of the trapped volatile hydrocarbon component.

Description

System and method for capturing and analyzing volatile hydrocarbons in natural gas hydrate reservoirs

technical field

The invention relates to a system and method for capturing and analyzing volatile hydrocarbons in natural gas hydrate reservoirs, and belongs to the technical field of natural gas hydrate analysis and testing.

Background technique

Natural gas hydrate (Natural gas hydrate/Gas hydrate), also known as combustible ice or hydrate, is an ice-like crystalline substance formed by natural gas and water under high pressure and low temperature conditions, and is mainly distributed in marine shelf sediments and permanent land areas. In the permafrost. The research on the source of hydrate gas and its cause has important theoretical and practical application value for guiding the exploration of hydrate resources, and has far-reaching significance for understanding the changes of climate and environment. The current understanding of the gas source and origin of hydrates is mainly based on CH ₄ content (such as C ₁ /(C ₁ +C ₂ )) and natural gas carbon (hydrogen) isotopes (δ ¹³ C and δD). Genetic gas and mixed genetic gas. The exploration and research of gas hydrates around the ocean and continental margin oil and gas basins have attracted attention in recent years in deep water areas such as the northern slope of the Gulf of Mexico, the South Falkland Basin of the Atlantic Ocean, and the Mackenzie Delta in Canada. The natural gas comes from deep hydrocarbon sources rock or oil and gas reservoir, and it is thermogenic gas or mixed genetic gas. Natural gas hydrate resources are abundant in the northern part of the South China Sea. The free and bound gas released from the hydrate samples in the deep water area of the Qiongdongnan Basin contains relatively rich C ₂ + heavy hydrocarbons (2.3-18.8%), and its carbon isotope value indicates that the thermogenic gas have contributed.

At present, the understanding of the source and cause of hydrate gas is deepening, but because the analysis methods and means are relatively single, most of them focus on the analysis of gas geochemistry, it is still difficult to effectively solve some key scientific problems in the study of hydrate accumulation, especially in deep The effectiveness and supply size of thermogenic oil and gas as gas source for gas hydrate reservoirs. Studies suggest that hydrocarbons formed by seepage in deep oil and gas reservoirs or thermal degradation of mature source rocks can migrate to the shallow surface layer through long-distance migration along faults, diapirs, or gas chimneys, among which gases and volatile components are more likely to reach the hydration zone. So far, light or volatile hydrocarbons (C ₅ ~C ₁₅ ) in hydrate reservoirs and their adjacent sediments have not been successfully extracted and analyzed. Experimental methods of separation and extraction from sediments (sedimentary rocks) by Soxhlet extraction often result in the loss of low-boiling volatile fractions, obtaining mainly medium-high boiling hydrocarbons such as _C15 + n-alkanes, steranes, aromatic Steroids and terpenes and polycyclic aromatic hydrocarbons (PAH), etc. In view of the large number and types of light hydrocarbons, such as normal alkanes, naphthenes, benzene series, adamantane series and monoterpenes, etc., and their rich geological significance, through the analysis of hydrates and light or volatile hydrocarbons in their reservoirs, The analysis will be very helpful to explore and study the composition, contribution and potential source rocks of thermogenic natural gas. Among them, volatile hydrocarbons can also be referred to as light distillate hydrocarbons or light hydrocarbons, which refer to low-boiling and volatile hydrocarbon components in sediments, sedimentary rocks, and petroleum. The carbon number distribution includes C ₅ -C ₁₃ . The boiling point is 30-235°C. The volatile hydrocarbons include various types of organic compounds such as normal alkanes, isoparaffins, cycloalkanes, aromatic hydrocarbons, adamantanes and monoterpenes, and the number of known compounds is more than 450.

Prior art relevant to the present invention one

The technical scheme of prior art one:

Chinese patent CN101900713A discloses a chromatographic and chromatographic-mass spectrometric online analysis device with airtight ball milling, heating analysis, helium purging, and cold trap trapping. One piece is weighed and put into a cleaned sealed jar, then the sealed jar is evacuated to 1Pa, and the sealed jar and the transfer line are heated to 300°C. Both ends of the transfer line are sampling needles for chromatography, which are respectively inserted into the sealed jar And the high-temperature-resistant silica gel pad of the chromatographic vaporization chamber, use the mass flow controller to set the flow rate of gaseous hydrocarbons entering the chromatogram through the transfer line, and adjust the pressure regulator valve to control the flow and pressure of helium into the sealed tank, and the gaseous hydrocarbons heated and vaporized in the sealed tank Carried by helium into the chromatograph, part of the flow enters the liquid nitrogen cold trap in the chromatographic box, so that the sample is trapped in the condensation at the front of the chromatographic column. After the gaseous hydrocarbons in the tank are fully carried into the cold trap, the liquid nitrogen is removed cup, close the furnace door, and start the chromatographic program to increase the temperature for analysis.

The shortcoming of prior art one:

(1) Since the natural gas hydrate is distributed at the depth of 0-200m in the seabed sediment/water interface, it is in the early stage of diagenesis, and the sample has the characteristics of high water content and weak soil quality, so the existing technology 1 cannot effectively remove water and light hydrocarbons enrichment analysis;

(2) During the heating process of the sample, the water vapor generated will condense in the transmission pipeline, causing the transmission pipeline to be easily blocked, so that the success rate of online analysis is not high.

Therefore, providing a novel system and method for capturing and analyzing volatile hydrocarbons in natural gas hydrate reservoirs has become an urgent technical problem in this field.

Contents of the invention

In order to solve the above shortcomings and deficiencies, an object of the present invention is to provide a system for capturing and analyzing volatile hydrocarbons in natural gas hydrate reservoirs.

Another object of the present invention is to provide a method for capturing and analyzing volatile hydrocarbons in natural gas hydrate reservoirs. The invention realizes the analysis of volatile hydrocarbons in deep-sea natural gas hydrate for the first time, helps to understand and understand the formation and distribution mechanism of natural gas hydrate, and provides new ideas and methods for searching for clean alternative energy and paying attention to climate and environmental effects.

In order to achieve the above objectives, on the one hand, the present invention provides a system for capturing and analyzing volatile hydrocarbons in natural gas hydrate reservoirs, wherein the system includes a volatilization device, a primary cold trap device, and a secondary cold trap device , temperature control device and gas chromatography-mass spectrometry;

Wherein, the volatilization device includes a sealed ball milling pot and a ball milling pot heating body, and the ball milling pot heating body is sleeved outside the sealed ball milling pot for heating the sealed ball milling pot; the sealed ball milling pots are respectively provided with inlets and an outlet, the inlet is communicated with the carrier gas bottle;

The primary cold trap device includes an ice-water bath device and a sample absorption bottle, the sample absorption bottle is filled with dichloromethane, and the sample absorption bottle is located in the ice-water bath device, and its opening is sealed with the described ice-water bath device through a transmission line. The outlet of the ball mill tank is connected;

The secondary cold trap device includes a liquid nitrogen thermos bottle and a U-shaped absorption tube, and one end opening of the U-shaped absorption tube communicates with the opening of the sample absorption bottle;

The gas chromatography-mass spectrometry is used to analyze the composition and content of the captured volatile hydrocarbon components;

The temperature control device is used for programmatically raising the temperature of the sealed ball milling tank through the ball milling tank heating body, for controlling the temperature of the transmission pipeline and for controlling the temperature of the ice-water bath device.

As a specific embodiment of the above-mentioned system of the present invention, wherein the carrier gas cylinder communicates with the inlet of the sealed ball mill tank through a pipeline sequentially via a pressure gauge and a mass flow meter.

As a specific embodiment of the above-mentioned system of the present invention, wherein, the transmission pipeline is covered with a pipeline heating insulation body.

As a specific embodiment of the system described above in the present invention, wherein, the opening of the sample absorption bottle is provided with a variable diameter tee, which is used to connect the outlet of the sealed ball mill jar and the opening of one end of the U-shaped absorption tube to the The opening of the sample absorption bottle is connected.

As a specific embodiment of the above-mentioned system of the present invention, wherein, the opening at one end of the U-shaped absorption tube is provided with a variable-diameter joint to connect the opening of the sample absorption bottle with the opening at one end of the U-shaped absorption tube .

In the present invention, the sealed ball milling tank, ball milling tank heating body, pipeline heating insulation body, carrier gas bottle, ice-water bath device, sample absorption bottle, liquid nitrogen thermos bottle, temperature control device, gas chromatography-mass spectrometry and other equipment and variable diameter Tee, variable diameter two-way pressure gauge, mass flow meter, transmission pipeline and other accessories are all conventional equipment or accessories in this field. For example, in some embodiments of the present invention, the ball mill tank heating body can be a heating furnace, and the pipeline heating insulation body can be a heating resistance wire.

On the other hand, the present invention also provides a method for capturing and analyzing volatile hydrocarbons in natural gas hydrate reservoirs, wherein the method uses the above-mentioned method for capturing volatile hydrocarbons in natural gas hydrate reservoirs. and analysis system, which includes the following steps:

(1) Put the hydrate sediment sample into the sealed ball mill tank and then seal and evacuate it, use the heating body of the ball mill tank to program the temperature of the sealed ball mill tank, and open the carrier gas bottle at the same time;

(2) During the temperature programming process, the light hydrocarbon components and water vapor are separated and carried into the sample absorption bottle by the carrier gas, and the light hydrocarbon components are absorbed by dichloromethane in the sample absorption bottle, and the two The temperature of methyl chloride is always kept at 0°C;

(3) The light hydrocarbon components that have not been absorbed by dichloromethane enter the U-shaped absorption tube, and the light hydrocarbon components are condensed in liquid nitrogen;

(4) Collect the light hydrocarbon components captured by the sample absorption bottle and the light hydrocarbon components captured by the U-shaped absorption tube respectively, and then mix the two and send them to gas chromatography-mass spectrometry for composition and content analysis.

As a specific embodiment of the method described above in the present invention, wherein, in step (1), the temperature programming includes:

First, the temperature is raised to 110-150°C at a heating rate of 2-5°C/min, during which moisture and some light hydrocarbon components with low boiling points are fully evaporated and precipitated, and then the temperature is raised to 300°C at a heating rate of 5-10°C/min At this time, a large amount of light hydrocarbon components are volatilized and precipitated.

As a specific embodiment of the method described above in the present invention, wherein, in step (1), the temperature programming includes:

First, the temperature is raised to 150°C at a heating rate of 3°C/min, during which moisture and some light hydrocarbon components with low boiling points are fully evaporated and precipitated, and then the temperature is raised to 300°C at a heating rate of 5°C/min. A large number of volatilization and precipitation.

As a specific embodiment of the method described above in the present invention, wherein the carrier gas is nitrogen.

As a specific embodiment of the method described above in the present invention, wherein, in step (2), light hydrocarbon components and water vapor are separated and carried by carrier gas through the transfer line into the sample absorption bottle, and the pipeline is used to heat the The heat preservation body heats the transfer pipeline and maintains the temperature at 120-150°C.

As a specific embodiment of the method described above in the present invention, wherein the hydrate sediment sample is taken from a place 1-200 m below the water/sediment interface of the deep seabed.

Different from the existing light hydrocarbon extraction and analysis methods for source rocks or rock samples, the natural gas hydrate samples targeted by the present invention, that is, the hydrate sediment samples have a large water content and appear in the form of ooze, and the easy Volatile hydrocarbons must remove or separate the water in them, so removing or separating the water in them is very critical, but the boiling point of water (100°C under normal pressure) is just at the boiling point of light hydrocarbon components, that is, volatile hydrocarbon components (30°C ~300° C.), when the sample is heated, the moisture in the sample will be separated simultaneously with the light hydrocarbon components. Therefore, when the present invention extracts light hydrocarbon components, it is necessary to simultaneously remove and separate the moisture contained therein. The basic process includes: a certain amount of hydrate sediment samples are heated to 300°C in a ball mill tank through temperature programming , water and light hydrocarbon components volatilize from the ball mill tank and then enter the transfer pipeline. In the sample absorption bottle, the light hydrocarbon components are absorbed by dichloromethane, water is condensed, and the light hydrocarbon components that are not absorbed by dichloromethane Enter the U-shaped absorption tube, and condense the light hydrocarbon components in liquid nitrogen, collect the light hydrocarbon components captured by the sample absorption bottle and the light hydrocarbon components captured by the U-shaped absorption tube, and then mix the two Sent to gas chromatography-mass spectrometry for analysis.

In summary, the system and method for capturing and analyzing volatile hydrocarbons in natural gas hydrate reservoirs provided by the present invention uses two-stage cold traps to separate and capture light hydrocarbon components, which can effectively separate the water contained in hydrate sediment samples , to reduce the loss of light hydrocarbons; at the same time, the temperature-programmed heating and sealing of the ball mill tank can effectively prevent the blockage of the transmission pipeline and improve the analysis efficiency.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings that need to be used in the description of the embodiments. Obviously, the accompanying drawings in the following description are some of the present invention. Embodiments, for those of ordinary skill in the art, other drawings can also be obtained based on these drawings without any creative effort.

Fig. 1 is a schematic structural diagram of a system for capturing and analyzing volatile hydrocarbons in natural gas hydrate reservoirs provided by Example 1 of the present invention.

Fig. 2 is a comparison diagram of the gas chromatogram obtained in the blank experiment and the gas chromatogram of the hydrate sediment sample in Experimental Example 2 of the present invention.

Fig. 3 is a total ion chromatogram of light hydrocarbon components in the hydrate sediment sample obtained in Example 2 of the present invention.

Fig. 4a is the mass spectrum of adamantane in the light hydrocarbon components contained in the hydrate sediment samples in the research area obtained in Example 2 of the present invention.

Fig. 4b is the mass spectrum of bisamantane in the light hydrocarbon components contained in the hydrate sediment sample in the research area obtained in Example 2 of the present invention.

Fig. 4c is the mass spectrum of triamantane in the light hydrocarbon components contained in the hydrate sediment sample in the research area obtained in Example 2 of the present invention.

Fig. 5a is a total ion chromatogram of light hydrocarbons obtained under constant temperature (300° C.) conditions in Comparative Example 1.

Figure 5b is a total ion chromatogram of light hydrocarbons obtained under programmed temperature conditions in Example 2 of the present invention.

Figure 5c-Figure 5d are the analysis results of the adamantane compound (m/z 135) obtained under the temperature-programmed condition in Example 2 of the present invention and the adamantane obtained under the constant temperature (300°C) condition in Comparative Example 1, respectively. Analysis results of alkanes (m/z135).

Figure 5e-Figure 5f are the analysis results of the adamantane compound (m/z 149) obtained under the temperature-programmed condition in Example 2 of the present invention and the adamantane obtained under the constant temperature (300°C) condition in Comparative Example 1, respectively. Analysis results of alkanes (m/z149).

Figure 5g-Figure 5h are the analysis results of the adamantane compound (m/z 163) obtained under the temperature-programmed condition in Example 2 of the present invention and the adamantane obtained under the constant temperature (300°C) condition in Comparative Example 1, respectively. Analysis results of alkanes (m/z163).

Explanation of main figures and symbols:

1. Pressure gauge;

2. Mass flow meter;

3. Ball mill tank heating body/temperature control heating body;

4. Sealed ball mill tank;

5-1. Entrance;

5-2. Export;

6. Grinding ball;

7. Pipeline heating insulation body;

8. Reducing tee;

9. Sample absorption bottle;

10. Ice water bath device;

11. Variable diameter coupler;

12. Liquid nitrogen vacuum flask;

13. U-shaped absorption tube;

14. Temperature control device.

detailed description

It should be noted that the terms "comprising" and any variations thereof in the specification and claims of the present invention and the above drawings are intended to cover non-exclusive inclusion, for example, processes, methods, A system, product or device is not necessarily limited to those steps or elements explicitly listed, but may include other steps or elements not explicitly listed or inherent to the process, method, product or device.

In the present invention, the orientation or positional relationship indicated by the terms "upper", "lower", "inner", "outer", "middle", etc. is based on the orientation or positional relationship shown in the drawings. These terms are mainly used to better describe the present invention and its embodiments, and are not intended to limit that the indicated device, element or component must have a specific orientation, or be constructed and operated in a specific orientation.

Moreover, some of the above terms may be used to indicate other meanings besides orientation or positional relationship, for example, the term "upper" may also be used to indicate a certain attachment relationship or connection relationship in some cases. Those skilled in the art can understand the specific meanings of these terms in the present invention according to specific situations.

Furthermore, the terms "setting", "connecting" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection, or an electrical connection; it can be a direct connection, or an indirect connection through an intermediary, or two devices, components or Internal connectivity between components. Those of ordinary skill in the art can understand the specific meanings of the above terms in the present invention according to specific situations.

The "ranges" disclosed herein are given in terms of lower limits and upper limits. There can be one or more lower bounds, and one or more upper bounds, respectively. A given range is defined by selecting a lower limit and an upper limit. Selected lower and upper limits define the boundaries of a particular range. All ranges defined in this manner are combinable, ie, any lower limit can be combined with any upper limit to form a range. For example, ranges of 60-120 and 80-110 are listed for a particular parameter, with the understanding that ranges of 60-110 and 80-120 are also contemplated. Additionally, if the minimum range values listed are 1 and 2, and the maximum range values listed are 3, 4, and 5, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~ 3, 2~4 and 2~5.

In the present invention, unless otherwise stated, the numerical range "a~b" represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in the present invention, and "0-5" is only an abbreviated representation of the combination of these values.

In the present invention, if there is no special description, all the embodiments and preferred embodiments mentioned in the present invention can be combined with each other to form a new technical solution.

In the present invention, if there is no special description, all the technical features and preferred features mentioned in the present invention can be combined with each other to form a new technical solution.

In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solution of the present invention will be described in detail below in conjunction with the following specific examples, but it should not be construed as limiting the scope of the present invention.

Example 1

This embodiment provides a system for capturing and analyzing volatile hydrocarbons in natural gas hydrate reservoirs. The schematic diagram of its structure is shown in Figure 1. Trap device, secondary cold trap device and gas chromatography-mass spectrometry;

Wherein, the volatilization device includes a sealed ball milling tank 4 filled with grinding balls 6 and a ball milling tank heater/temperature-controlling heater 3, and the ball milling tank heater/temperature-controlling heater 3 is sleeved on the sealed ball milling tank 4 Outside, it is used to heat the sealed ball milling tank 4; the sealed ball milling tank 4 is respectively provided with an inlet 5-1 and an outlet 5-2, and the carrier gas cylinder (not shown in the figure) passes through the pipeline successively through the pressure gauge 1, The mass flow meter 2 communicates with the inlet 5-1 of the sealed ball mill tank 4;

The first-stage cold trap device includes an ice-water bath device 10 and a sample absorption bottle 9, the sample absorption bottle 9 is filled with dichloromethane, the sample absorption bottle 9 is located in the ice-water bath device 10, and its opening passes through the transmission The pipeline communicates with the outlet 5-1 of the sealed ball mill tank 4; the transmission pipeline is covered with a pipeline heating insulation body 7;

The secondary cold trap device includes a liquid nitrogen thermos bottle 12 and a U-shaped absorption tube 13, and one end opening of the U-shaped absorption tube 13 communicates with the opening of the sample absorption bottle 9;

The gas chromatography-mass spectrometry is used to analyze the composition and content of the captured easily volatile hydrocarbon components.

In this embodiment, the opening of the sample absorbing bottle 9 is provided with a variable-diameter tee 8 for connecting the outlet 5-2 of the sealed ball milling tank 4 and the opening of one end of the U-shaped absorbing tube 13 to the sample absorbing bottle. The opening of 9 is connected.

In this embodiment, the openings at both ends of the U-shaped absorption tube 13 are provided with variable-diameter joints 11, and the variable-diameter joints 11 provided at one end opening are used to connect the opening of the sample absorption bottle 9 with the U-shaped The opening of this end of the absorption pipe 13 is connected, and the variable diameter joint 11 provided at the opening of the other end of the U-shaped absorption pipe 13 is used to communicate with the external pipeline to discharge the light hydrocarbon components condensed in the U-shaped absorption pipe 13;

In this embodiment, the system also includes a temperature control device 14, which is used to program the temperature of the sealed ball milling tank 4 through the ball milling tank heating body/temperature control heating body 3, and is also used to control the transmission through the pipeline heating insulation body 7. The temperature of the pipeline and the temperature used to control the ice-water bath device 10.

Example 2

This embodiment provides a method for capturing and analyzing volatile hydrocarbons in natural gas hydrate reservoirs, which is realized by using the system for capturing and analyzing volatile hydrocarbons in natural gas hydrate reservoirs provided in this embodiment. Said method comprises the following specific steps:

1) Weigh 15-20g of the hydrate sediment sample collected from 3-170m below the water/sediment interface and put it into a sealed ball mill tank. After sealing and vacuuming, put the sealed ball mill tank into the ball mill heating body;

2) Connect the carrier gas bottle, the carrier gas is nitrogen, controlled by the mass flow meter, insert one end of the pipeline connected to the outlet of the carrier gas bottle into the injection port (inlet) on the side of the ball mill tank with a Φ1 needle;

3) Insert one end of the transmission line into the injection port (outlet) of the ball mill tank, and insert the other end into the bottom of the sample absorption bottle containing a certain amount of methylene chloride sample, and place the sample absorption bottle in the ice-water bath device;

4) Connect the sample absorption bottle to one end opening of the U-shaped absorption tube, and place the U-shaped absorption tube in a liquid nitrogen thermos to freeze;

5) The temperature of the ball milling tank is programmed to rise in the ball milling tank heating body. When the ball milling tank is put into the ball milling tank heating body, the nitrogen bottle is opened, and the mass flow meter is set to 10ml/min. During the temperature programming process, light hydrocarbon components and water vapor are separated and carried into the sample absorption bottle through the transfer pipeline through the carrier gas. Condensation with light hydrocarbon components;

The temperature programming process includes: first, the temperature is raised to 150°C at a heating rate of 3°C/min, during which moisture and some low-boiling light hydrocarbon components are fully evaporated and precipitated; then, the temperature is raised to 300°C at a heating rate of 5°C/min , a large amount of light hydrocarbon components volatilized and precipitated. Water and light hydrocarbon components enter the sample absorption bottle through the insulated transfer line. Due to the high calorific value of the sample and water, methylene chloride will be vaporized, so the temperature of methylene chloride must be kept at or below 0°C during this process to facilitate the dissolution and absorption of light hydrocarbon components by methylene chloride ;

6) Due to the fast flow rate, the product stays in the sample absorption bottle for a short time, and the light hydrocarbon product not absorbed by the dichloromethane solution enters the U-shaped absorption tube, and performs secondary condensation and collection in the liquid nitrogen thermos;

7) After the extraction is completed, clean the pipeline, filter and separate the dichloromethane absorption liquid in the sample absorption bottle from water, and then concentrate it with nitrogen blowing method, then mix the obtained light hydrocarbon components with the light hydrocarbon components captured in the U-shaped absorption tube , enter gas chromatography-mass spectrometry (GC-MS) analysis composition and content;

Wherein, described gas chromatography-mass spectrometry (GC-MS) analysis used analysis equipment and analysis condition include:

The gas chromatography-mass spectrometry (GC-MS) adopts Agilent 6890GC-Agilent 5975i MS gas chromatography-mass spectrometry and is configured with a DB-5 capillary column (60m×0.25mm×0.25 μm);

Gas chromatographic conditions: the initial temperature of the non-heating program is 100°C, the temperature is raised to 320°C at a heating rate of 4°C/min, and then kept at a constant temperature for 20 minutes, the carrier gas is high-purity helium, and the split ratio is 20:1;

Mass spectrometry adopts full-scan mode, using EI ion source, electron bombardment energy is 70eV, mass number is 50-500aum.

The hydrate sediment sample was repeated three times according to this procedure, that is, the procedure shown in the above steps 1)-7), and the parallelism of the results was analyzed, and a blank control experiment was carried out. Among them, the difference between the blank control experiment and Example 2 is that step 1) was not performed, that is, no hydrate sediment sample was added.

The comparison chart of the gas chromatogram obtained in the blank experiment and the gas chromatogram of the hydrate sediment sample is shown in Figure 2.

Among them, the total ion chromatogram of the light hydrocarbon components in the hydrate sediment samples obtained by gas chromatography-mass spectrometry is shown in Fig. 3. It can be seen from Fig. Extraction of hydrocarbon components, the extracted light hydrocarbon components are mainly hydrocarbon components in the range of C ₈ -C ₁₅ , including n-paraffin series (C ₈ ~C ₁₅ ), toluene, xylene, trimethylbenzene And naphthalene series (C ₀ ~ C ₃ ), etc., and especially rich in adamantane series compounds.

The mass spectrograms of the adamantane series compounds in the light hydrocarbon components contained in the hydrate sediment samples in the study area are shown in Figure 4a-Figure 4c, where Figure 4a shows the light hydrocarbon components contained in the hydrate sediment samples in the study area. The mass spectrum of adamantane, Figure 4b is the mass spectrum of double adamantane, and Figure 4c is the mass spectrum of triamantane.

The specific composition information of the adamantane series compounds in the light hydrocarbon components contained in the hydrate sediment samples in the study area obtained according to Fig. 4a-Fig. 4c is shown in Table 1 below.

Table 1 Analysis and identification table of adamantane series compounds in light hydrocarbon components contained in hydrate sediment samples

From Figure 4a-Figure 4c and Table 1, it can be seen that the adamantane series compounds in the light hydrocarbon components contained in the hydrate sediment samples in the study area include adamantane, diadamantane and triamantane, and the adamantane content is dominant.

According to the analysis results of three parallel experiments, the parameters of four main types of compounds, such as methyladamantane, dimethyladamantane, methylnaphthalene and dimethylnaphthalene, were calculated. The calculated results are shown in Table 2 below. .

Table 2 Calculation table of parameters for three experiments of hydrate sediment samples

Note: The parameters* shown in Table 2 include adamantane parameters, such as MAI, EAI, and DMAI, and naphthalene parameters, such as DNR-1, MNR, and ENR. For the specific meanings and calculation formulas of these parameters, please refer to literature [1] and Literature [2].

Literature [1] Zhibin Wei, J.M.Moldowan, Shuichang Zhang, et al., 2007. Diamondoidhydrocarbons as a molecular proxy for thermal maturity and oil cracking: Geochemical models from hydrous pyrolysis. Organic Geochemistry 38, 227–249.

Literature [2] Radke, M., Willsch, H. and Leythaeuser, D., 1982. Aromatic components of coal: relation of distribution pattern to rank. Geochimica et Cosmochimica Acta, 46, 1831–48.

It can be seen from Table 2 that generally the higher the abundance, the better the parallelism. Among them, the relative standard deviation RSD of adamantane is basically less than 5%, and the relative standard deviation RSD of naphthalene series compounds is less than 10%.

Comparative example 1

This comparative example provides a method for trapping and analyzing volatile hydrocarbons in natural gas hydrate reservoirs, the only difference from Example 2 is that in step 5), the ball mill tank is kept at a constant temperature (300° C.) in the ball mill tank heating body , rather than temperature programming.

The total ion chromatograms of light hydrocarbons obtained under constant temperature (300°C) conditions in Comparative Example 1 and the total ion chromatograms of light hydrocarbons obtained under temperature-programmed conditions in Example 2 of the present invention are shown in Figure 5a and Figure 5b respectively .

The analysis results of different adamantane compounds obtained under the condition of programmed temperature increase in Example 2 of the present invention and the analysis results of different adamantane compounds obtained under constant temperature (300°C) conditions in Comparative Example 1 are shown in Figure 5c - shown in Figure 5h.

Comparing Fig. 5a and Fig. 5b, Fig. 5c and Fig. 5d, Fig. 5e and Fig. 5f, and Fig. 5g and Fig. 5h, it can be seen that a higher yield of light hydrocarbons can be obtained by using temperature programming in Example 2 of the present invention.

In the embodiment of the present invention, when the light hydrocarbon components are extracted, the water contained therein needs to be removed and separated at the same time. The basic process includes: a certain amount of hydrate sediment samples are heated to 300 °C in a ball mill tank through temperature programming. °C, water and light hydrocarbon components volatilize from the ball mill tank and then enter the transfer pipeline. In the sample absorption bottle, the light hydrocarbon components are absorbed by dichloromethane, water is condensed, and the light hydrocarbon components not absorbed by dichloromethane into the U-shaped absorption tube, and condense the light hydrocarbon components in liquid nitrogen, respectively collect the light hydrocarbon components captured by the sample absorption bottle and the light hydrocarbon components captured by the U-shaped absorption tube, and then mix the two Then sent to gas chromatography-mass spectrometry for analysis.

To sum up, the system and method for capturing and analyzing volatile hydrocarbons in natural gas hydrate reservoirs provided by the embodiments of the present invention adopts two-stage cold traps to separate and capture light hydrocarbon components, which can effectively separate the volatile hydrocarbons contained in hydrate sediment samples. Contains moisture to reduce the loss of light hydrocarbons; at the same time, it adopts temperature programming to heat and seal the ball mill tank, which can effectively prevent the blockage of the transmission pipeline and improve the analysis efficiency.

The above is only a specific embodiment of the present invention, and cannot limit the scope of the invention, so the replacement of its equivalent components, or the equivalent changes and modifications made according to the patent protection scope of the present invention, should still fall within the scope of this patent. category. In addition, the technical features and technical features, technical features and technical inventions, and technical inventions and technical inventions in the present invention can be used in free combination.

Claims (6)

1. A method for trapping and analyzing volatile hydrocarbons in natural gas hydrate reservoirs, characterized in that, the method is realized by a trapping and analyzing system for volatile hydrocarbons in natural gas hydrate reservoirs, and the system Including volatilization device, primary cold trap device, secondary cold trap device, temperature control device and gas chromatography-mass spectrometry; Wherein, the volatilization device includes a sealed ball milling pot and a ball milling pot heating body, and the ball milling pot heating body is sleeved outside the sealed ball milling pot for heating the sealed ball milling pot; the sealed ball milling pots are respectively provided with inlets and an outlet, the inlet is communicated with the carrier gas bottle; The primary cold trap device includes an ice-water bath device and a sample absorption bottle, the sample absorption bottle is filled with dichloromethane, and the sample absorption bottle is located in the ice-water bath device, and its opening is sealed with the described ice-water bath device through a transmission line. The outlet of the ball mill tank is connected; wherein, the transmission pipeline is covered with a pipeline heating insulation body; The secondary cold trap device includes a liquid nitrogen thermos bottle and a U-shaped absorption tube, and one end opening of the U-shaped absorption tube communicates with the opening of the sample absorption bottle; The gas chromatography-mass spectrometry is used to analyze the composition and content of the captured volatile hydrocarbon components; The temperature control device is used to program the temperature of the sealed ball milling tank through the ball milling tank heating body, to control the temperature of the transmission pipeline and to control the temperature of the ice-water bath device; The method comprises the steps of: (1) Put the hydrate sediment sample into the sealed ball milling tank, seal and evacuate it, use the heating body of the ball milling tank to program the temperature of the sealed ball milling tank, and open the carrier gas bottle at the same time; in step (1), the temperature programming includes: First, the temperature is raised to 110-150°C at a heating rate of 2-5°C/min, during which moisture and some light hydrocarbon components with low boiling points are fully evaporated and precipitated, and then the temperature is raised to 300°C at a heating rate of 5-10°C/min , at this time, a large amount of light hydrocarbon components are volatilized and precipitated; (2) During the temperature programming process, the light hydrocarbon components and water vapor are separated and carried into the sample absorption bottle by the carrier gas, and the light hydrocarbon components in the sample absorption bottle are absorbed by dichloromethane, and the two The temperature of methyl chloride is always kept at 0°C; In step (2), the light hydrocarbon components and water vapor are separated and carried by the carrier gas through the transfer pipeline into the sample absorption bottle. During this process, the pipeline heating insulation body is used to heat the transmission pipeline and maintain the temperature at 120 ~150℃; (3) The light hydrocarbon components not absorbed by dichloromethane enter the U-shaped absorption tube, and condense the light hydrocarbon components in liquid nitrogen; (4) Collect the light hydrocarbon components captured by the sample absorption bottle and the light hydrocarbon components captured by the U-shaped absorption tube respectively, and then mix the two and send them to gas chromatography-mass spectrometry for composition and content analysis. 2. The method according to claim 1, wherein the carrier gas is nitrogen. 3. The method according to claim 1 or 2, wherein the hydrate sediment sample is taken from 1-200m below the water/sediment interface of the deep seabed. 4. The method according to claim 1, characterized in that, the carrier gas bottle communicates with the inlet of the sealed ball mill tank through a pipeline sequentially via a pressure gauge and a mass flow meter. 5. according to the described method of claim 1 or 4, it is characterized in that, the opening of described sample absorbing bottle is provided with variable-diameter tee, in order to the outlet of described sealed ball mill jar and one end opening of U-shaped absorbing tube and The opening of the sample absorption bottle is connected. 6. The method according to claim 1 or 4, wherein the opening at one end of the U-shaped absorption tube is provided with a variable-diameter joint for connecting the opening of the sample absorption bottle to one end of the U-shaped absorption tube. The opening is connected.

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