METHOD FOR ANALYZING LIGHT N-ALKANE COMPONENTS AND CARBON ISOTOPES IN DEEP AND ULTRA-DEEP SOURCE ROCK

Abstract

A method for analyzing light n-alkane components and carbon isotopes in deep and ultra-deep source rocks includes: (S1) subjecting a 5 A molecular sieve column to aging; (S2) pyrolyzing a source rock; and allowing a pyrolysis product to enter the 5 A molecular sieve column; where n-alkanes are adsorbed and retained by the 5 A molecular sieve column; allowing an outflow to pass through a dividing plate and an empty column or a weak polarity column to be discharged; and (S3) performing programmed heating such that the n-alkanes adsorbed on the 5A molecular sieve column are successively desorbed according to molecular weight, and then pass through the dividing plate and the HP-5 or DB-5 column to enter a mass spectrometer for composition analysis or isotopic analysis.

Claims

1. A method for analyzing light n-alkane components and carbon isotopes in deep and ultra-deep source rocks, comprising: (S1) subjecting a 5 A molecular sieve column to aging; (S2) subjecting a source rock to pyrolysis to obtain a pyrolysate, and allowing the pyrolysate to pass through the 5 A molecular sieve column, wherein n-alkane components in the pyrolysis product are adsorbed by the 5 A molecular sieve column and retained in the 5 A molecular sieve column; allowing an outflow from the 5 A molecular sieve column to pass through a dividing plate; opening a first valve to allow the outflow to flow through an empty column or a weak polarity column; and continuing to perform helium purging until the source rock is completely pyrolyzed and the pyrolysis product other than the n-alkane components is completely purged; and (S3) turning on a programmable heating system to subject the 5 A molecular sieve column and a chromatographic column to programmed heating, wherein the n-alkane components adsorbed on the 5 A molecular sieve column are successively desorbed according to molecular weight and boiling point; and allowing the n-alkane components to pass through the dividing plate and the chromatographic column for separation, and to enter a mass spectrometer for composition analysis or carbon isotopic analysis.

2. The method of claim 1, wherein in step (S1), the aging is performed with helium as carrier gas to remove volatile organic components adsorbed on the 5 A molecular sieve column; and the aging is programmed as follows: 40 C. for 5-10 min; rising to 290-320 C. at 1 C./min; and 290-320 C. for 40-60 min.

3. The method of claim 1, wherein in step (S2), the pyrolysis is performed in a pyrolysis furnace, and is programmed as follows: initial temperature: 40 C.; rising to 290 C. at 20-30 C./min; and 290 C. for 5-10 min.

4. The method of claim 1, wherein in step (S2), after flowing through the empty column or the weak polarity column, the outflow is discharged or detected by a flame ionization detector.

5. The method of claim 1, wherein in step (S3), the programmed heating is performed as follows: 30-35 C. for 5 min; rising to 80 C. at 1-2 C./min; rising to 290 C. at 3-4 C./min; and 290 C. for 25-30 min.

6. The method of claim 1, wherein in step (S3), the mass spectrometer is a triple quadrupole mass spectrometer or an isotope ratio mass spectrometer; when the pyrolysis in step (S2) is performed in the presence of an internal standard, the n-alkane components are subjected to absolute quantitation by using the triple quadrupole mass spectrometer; or when the pyrolysis in step (S2) is performed in the absence of the internal standard, the n-alkane components are subjected to relative quantitation by using the triple quadrupole mass spectrometer to obtain biomarkers of the source rock, or analyzed by the isotope ratio mass spectrometer to obtain isotopic values of the n-alkane components.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] FIG. 1 is a chromatogram showing light hydrocarbon components in pyrolysis products of three kinds of source rocks (Green River shale; Minqin oil shale obtained from Minqin county, China; Hua'an carbonaceous shale obtained from Hua'an county, China) at 290 C.;

[0038] FIG. 2 is a flow chart of light n-alkane composition and isotopic analysis of the source rock; and

[0039] FIG. 3 shows MS comparison of pyrolysates of Hua'an carbonaceous shale obtained by two different strategies, where the upper mass spectrum reveals the composition of a pyrolysate produced by thermal desorption and on-line separation and purification by a 5 A molecular sieve gas chromatography column; and the lower mass spectrum reveals the composition of a pyrolysate produced by Soxhlet extraction and offline separation and purification by the 5 A molecular sieve packed column.

DETAILED DESCRIPTION OF EMBODIMENTS

[0040] The disclosure will be described in detail below in conjunction with the embodiments. It should be understood that the following embodiments are merely illustrative, and are not intended to limit the disclosure.

Embodiment 1

[0041] Provided herein is a system for analyzing light n-alkane components and carbon isotopes in deep and ultra-deep source rocks, including a source rock pyrolysis device and a column box. The column box is equipped with a programmable heating system, and the source rock pyrolysis device is a pyrolysis furnace.

[0042] The column box is provided with a 5 A molecular sieve column, a dividing plate, a first chromatographic column, and a second chromatographic column in the interior. The pyrolysis device is connected to an inlet of the 5 A molecular sieve column, and an outlet of the 5 A molecular sieve column is connected with an inlet of the dividing plate. A first outlet of the dividing plate is connected with the first chromatographic column through a first pipeline, and a second outlet of the dividing plate is connected with the second chromatographic column through a second pipeline. The first outlet of the dividing plate is provided with a first valve, and the second outlet of the dividing plate is provided with a second valve. The first chromatographic column is an empty column or a weak polarity column. In an embodiment, an outlet of the first chromatographic column is connected with a blow-down pipe or a flame ionization detector (FID). The second chromatographic column is HP-5 column. An outlet of the HP-5 column is connected to a mass spectrometer. The mass spectrometer is a 7000B triple quadrupole mass spectrometer or a Delta Plus XP isotope ratio mass spectrometer.

[0043] If only the n-alkanes are analyzed, the first chromatographic column is the empty column. An outflow from the 5 A molecular sieve column is directly discharged from the column box through the empty column. According to the need, the outflow from the 5 A molecular sieve column can also be separated using the weak polarity column, and then aromatic and non-hydrocarbon components can be detected by FID. The obtained test results can also be used to evaluate source rocks and compare oil sources.

Embodiment 2

[0044] Provided herein was a method for analyzing light n-alkane components and carbon isotopes in deep and ultra-deep source rocks. [0045] (S1) The 5 A molecular sieve column was aged. The aging was programmed as follows: 40 C. for 10 min; rising to 290 C. at 1 C./min; and 290 C. for 60 min. The aging was performed with helium as carrier gas to remove volatile organic components adsorbed on the 5 A molecular sieve column, thereby ensuring complete pyrolysis of the residual components in the 5 A molecular sieve column. [0046] (S2) 1-5 mg of the source rocks were added to the pyrolysis furnace for pyrolysis to obtain a pyrolysate. The pyrolysis was performed in a pyrolysis furnace, and was programmed as follows: initial temperature: 40 C.; rising to 290 C. at 30 C./min; and 290 C. for 5 min. The pyrolysate passed through the 5 A molecular sieve column. N-alkanes in the pyrolysis product were adsorbed by the 5 A molecular sieve column and retained therein. An outflow from the 5 A molecular sieve column passed through the dividing plate. The first valve of the dividing plate was opened, and the second valve of the dividing plate was closed, thereby allowing the outflow to flow through the first column to discharge or detect by FID. The first column was the empty column or the weak polarity column. Helium was continued to purge until the source rock was completely pyrolyzed and kept for 30 min, thereby ensuring that pyrolysis product such as isomeric alkanes, aromatic hydrocarbons and non-hydrocarbon components on the surface of the 5 A molecular sieve column were completely purged. [0047] (S3) The first valve of the dividing plate was closed, the second valve of the dividing plate was opened, and then the programmable heating system was turned on and the column box with the 5 A molecular sieve column and the second column was heated. The programmed heating was performed as follows: 30 C. for 5 min; rising to 80 C. at 2 C./min; rising to 290 C. at 3 C./min; and 290 C. for 25-30 min. The n-alkanes adsorbed on the 5 A molecular sieve column were successively desorbed according to molecular weight and boiling points thereof, then passed through the dividing plate and HP-5 chromatographic column for separation, as shown in FIG. 2. The first and second chromatographic columns used were Agilent HP-PLOT 5 A molecular sieve gas column (30 m0.53 mm50 um) and Agilent HP-5 conventional gas column (30 m0.32 mm0.25 um). The programmable heating system was an oven.

Embodiment 3

[0048] In this embodiment, Hua'an carbonaceous shale was used. The desorption temperature was set to 290 C., and the optimal temperature for pyrolysis of the source rock was 290 C. At this temperature, the adsorbed hydrocarbons can be completely desorbed, and will not undergo pyrolysis. The analysis experiments were carried out using the method in Embodiment 2, and the analysis results were compared with those of the extract obtained by Soxhlet extraction (as shown in FIG. 3).

[0049] In this embodiment, low-temperature pyrolysis and 5 A molecular sieve column on-line purification analysis technology were used, not only the C.sub.9-C.sub.16 saturated hydrocarbon light component and its carbon isotopic values were extracted, but also the alkane component with high molecular weight and its carbon isotopic values in C.sub.17-C.sub.33 were obtained. The alkane carbon isotope values obtained by the method of this application were close to Soxhlet extraction, as shown in Table 1. The experimental error was less than 5% % within the experimental error range.

TABLE-US-00001 TABLE 1 Comparison of alkane carbon isotope values of Hua'an carbonaceous shale obtained by two methods Isotope value (.sup.13C) Soxhlet Thermal extraction- desorption- offline online separation and separation and purification purification using a 5A using a 5A Isotope value molecular molecular (.sup.13C) sieve packed sieve GC Soxhlet Thermal No. Component column column No. Component extraction analysis 1 n-Nonane 32.2 15 n-Eicosane 34.3 34.7 (n-C.sub.9H.sub.20) (n-C.sub.20H.sub.42) 2 n-Decane 33.3 16 n-Heneicosane 35.8 35.5 (n-C.sub.10H.sub.22) (n-C.sub.21H.sub.44) 3 n-Undecane 31.6 17 n-Docosane 34.5 34.7 (n-C.sub.11H.sub.24) (n-C.sub.22H.sub.46) 4 n-Dodecane 32.3 18 n-Tricosane 34.9 35.0 (n-C.sub.12H.sub.26) (n-C.sub.23H.sub.48) 5 n-Tridecane 33.3 33.5 19 n-Tetracosane 35.2 35.0 (n-C.sub.13H.sub.28) (n-C.sub.24H.sub.50) 6 n-Tetradecane 34.8 34.7 20 n-Pentaccosane 33.7 34.1 (n-C.sub.14H.sub.30) (n-C.sub.25H.sub.52) 7 nor-Pristane 37.5 37.9 21 n-Hexacosane 33.6 34.3 (i-C.sub.14H.sub.30) (n-C.sub.26H.sub.54) 8 n-Pentadecane 33.7 33.9 22 n-Heptacosane 33.1 33.9 (n-C.sub.15H.sub.32) (n-C.sub.27H.sub.56) 9 n-Hexadecane 33.5 34.0 23 n-Octacosane 33.5 33.3 (n-C.sub.16H.sub.34) (n-C.sub.28H.sub.58) 10 n-Heptadecane 33.6 33.7 24 n-Nonacosane 35.7 35.2 (n-C.sub.17H.sub.36) (n-C.sub.29H.sub.60) 11 Pristane 37.9 37.6 25 n-Triacontane 35.8 (i-C.sub.19H.sub.40) (n-C.sub.30H.sub.62) 12 n-Octadecane 32.3 32.4 26 n-Hentriacontane 36.4 (n-C.sub.18H.sub.38) (n-C.sub.31H.sub.64) 13 Phytane 39.5 39.2 27 n-Dotriacontane 36.2 (i-C.sub.20H.sub.42) (n-C.sub.32H.sub.66) 14 n-Nonadecane 34.9 34.7 28 n-Tritriacontane 34.6 (n-C.sub.19H.sub.40) (n-C.sub.33H.sub.68) Note: indicates not detected.

[0050] In addition, this application not only obtains light hydrocarbon biomarkers, but also obtains a complete range of large molecular weight n-alkane biomarker compounds that are consistent with the composition of the Soxhlet extract. The distribution characteristics of the Pristane and Phytane are very similar, as shown in Table 2. Table 2 shows that the low-temperature pyrolysis products of the source rocks and the corresponding extraction products are basically consistent in the parameters related to the sedimentary environment of the source rocks, such as pristane-phytane ratio (Pr/Ph), the pristane/n-C.sub.17 (Pr/n-C.sub.17), and the phytosane/n-C.sub.18 (Ph/n-C.sub.18). Therefore, the above results indicate that the low-temperature pyrolysis and 5 A molecular sieve column on-line purification analysis technology is an effective method for quantify light hydrocarbon components and their monomer carbon isotope analysis in source rocks.

TABLE-US-00002 TABLE 2 Comparison of biomarker parameters obtained by two methods Method (A: thermal desorption-online separation and purification using 5A molecular sieve gas chromatography column; B: Soxhlet extraction-offline separation and purification using a 5A molecular sieve Pr/ Pr/ Ph/ Sample packed column Ph C.sub.17 C.sub.18 Green River A 0.45 0.74 8.19 shale B 0.45 0.70 8.39 Minqin oil A 1.06 1.62 1.90 shale B 0.90 1.68 2.26 Hua'an A 3.00 0.50 0.15 carbonaceous B 3.36 0.75 0.19 shale

[0051] In Table 1, the mass spectrometer was Finnigan Delta Plus XP isotope ratio mass spectrometer, and temperature in the oxidation furnace was 930 C.

[0052] In Table 2, the mass spectrometry detector was Agilent 7000B triple quadrupole mass spectrometer. The mass spectrometry ion source was EI, the ion source temperature was 230 C., the ion source ionization energy was 70 eV, and the interface temperature was 280 C. The acquisition method is full scanning, and the mass range is 10-550 amu.

[0053] In this embodiment, in the absence of an internal standard, Table 1 revealed isotope values of individual components, and Table 2 showed relative quantitation results of the components. If internal standards were added during pyrolysis of source rocks, the mass spectrometry detector can also be used to quantify the absolute values of each component.

[0054] Described above are merely preferred embodiments of the disclosure, which are not intended to limit the disclosure. It should be understood that any modifications and replacements made by those skilled in the art without departing from the spirit of the disclosure should fall within the scope of the disclosure defined by the appended claims.