A two-phase mixed-source gas quantitative analysis method based on natural gas inclusion Raman technology

Abstract

This invention discloses a method for quantitatively analyzing two-phase mixed-source gas based on Raman analysis of natural gas inclusions, relating to the field of geological exploration technology. The technical solution comprises the following steps: S1: selecting typical gas reservoir veins as two-phase natural gas inclusion samples and subjecting them to Raman analysis; S2: calculating the relative concentrations and ratios of the components in the two-phase natural gas inclusion samples based on the Raman data measured in step S1; and S3: establishing a quantitative analysis method for mixed-source gas based on the principle of material balance to calculate the contribution of natural gas injections from different phases to the present-day gas reservoir. This invention quantitatively reveals the contribution of natural gas injections from different phases to the present-day gas reservoir, thereby resolving the difficult problem of quantitatively calculating the contribution of natural gas from different geological periods.

Description

Technical Field

[0001] The present invention relates to the field of geological exploration technology, and in particular to a two-phase mixed-source gas quantitative analysis method based on natural gas inclusion Raman technology. Background Art

[0002] Natural gas, due to its clean, low-carbon, stable, flexible, and economical characteristics, will ensure a safe, sustainable, and reliable energy supply to meet energy needs. Vigorously developing natural gas will become an inevitable trend in future energy development. Natural gas molecules are extremely small, requiring extremely high caprock conditions, and mixing of natural gas from different injection phases is highly likely. Existing evaluation techniques can reveal the origin / source of natural gas (terrestrial or marine; different kerogen types; or kerogen and crude oil cracking gas), but there is currently no quantitative method to calculate the relative contribution of natural gas injection from different phases. However, the contribution of natural gas from different phases has a significant impact on natural gas exploration. When the contribution of early-stage natural gas injection is relatively small, oil and gas exploration should focus on traps with good late-stage caprock conditions, while traps with good early-stage caprock sealing conditions but later-stage damage should not be explored. When the contribution of late-stage natural gas injection is relatively small, oil and gas exploration should focus on traps with good early-stage caprock conditions, while traps with good late-stage caprock sealing conditions suffer from limited natural gas injection. Therefore, high-quality traps developed after the main injection period should not be explored. Obviously, the relative contribution of natural gas injected at different injection stages directly affects the effectiveness of traps and their recoverability assessment.

[0003] Existing technologies for measuring natural gas component content are relatively mature, primarily including gas chromatography, Fourier transform infrared spectroscopy, and Raman spectroscopy. Gas chromatographs require carrier gas, resulting in lengthy analysis times and inability to monitor natural gas in real time. While infrared spectroscopy, as a non-destructive analytical technique, offers advantages such as high efficiency, pollution-free operation, and rapid analysis speed, it cannot detect homonuclear diatomic molecules such as nitrogen and hydrogen. Therefore, infrared absorption spectroscopy does not fully meet the requirements for natural gas composition testing. Raman spectroscopy, on the other hand, offers unique advantages: it requires only a single laser source to simultaneously measure all components in a gas sample, with rapid detection speed (within 30 seconds) and high sensitivity. Key methods for quantitatively analyzing mixed gas compositions using laser Raman spectroscopy include peak height, area, kurtosis, and pure substance spectral decomposition. Among them, predecessors proposed a Raman spectrum automatic decomposition algorithm based on the Lorentz function, defining natural gas as consisting of seven pure substances: methane (CH4), ethane (C2H6), propane (C3H8), carbon dioxide (CO2), nitrogen (N2), hydrogen (H2), carbon monoxide (CO) and C4 + The mixture of alkane components, on the premise of obtaining the Raman spectra of 7 pure substances, introduced the Lorentz function group to fit the C4+ The Raman spectra of the alkane components are then decomposed using a nonlinear least squares algorithm to obtain a complete peak distribution of the different components, effectively eliminating the influence of possible overlapping peaks. Therefore, how to quantitatively analyze natural gas injection phases based on the quantitative testing of natural gas components using Raman spectroscopy is an urgent problem to be solved. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: in response to the current problem of lack of quantitative analysis and evaluation technology for mixed-source gas reservoirs, a mixed-source gas quantitative analysis method with simple operation, easy instrument acquisition, high accuracy and strong feasibility is provided. The method will quantitatively reveal the contribution of natural gas charging in different periods to the current gas reservoir, thereby solving the problem of quantitative calculation of the contribution of natural gas in different geological historical periods.

[0005] The technical solution of the present invention is:

[0006] The two-phase mixed-source gas quantitative analysis method based on natural gas inclusion Raman technology includes the following steps:

[0007] S1 selected typical vein bodies in gas reservoirs as two-phase natural gas inclusion samples and conducted Raman tests on them;

[0008] S2 calculates the relative concentrations and ratios of the components in the two phases of natural gas inclusion samples based on the Raman data measured in step S1;

[0009] Based on the principle of material balance, S3 establishes a quantitative analysis method for mixed-source gas to calculate the contribution of natural gas injected at different stages to the current gas reservoir.

[0010] Preferably, in step S1, when selecting samples, vein samples that directly reflect natural gas injection events are selected, preferably calcite or quartz veins. The geochemical characteristics of the natural gas inclusions contained in these veins represent the geochemical composition of the natural gas injection during the corresponding geological period (the relative content and ratio characteristics of the natural gas components). Therefore, the veins must develop within a gas reservoir or along a path that must pass through a gas reservoir, and must also contain two phases of natural gas inclusions (which can be determined by the development of brine inclusions during the same period). Natural gas inclusions in quartz secondary over-rims or calcite authigenic minerals, as used in traditional methods, are not acceptable. Furthermore, the vein samples are prepared into thin slices approximately 0.08 mm thick to prepare for the next step of testing the Raman characteristics of the natural gas inclusions using confocal laser Raman microscopy.

[0011] Preferably, in step S2, the calculation formula for the relative concentration and ratio of methane and ethane in the two phases of natural gas inclusion samples is as follows:

[0012]

[0013]

[0014] Where C ij —The relative content of the i-th component of the j-th natural gas inclusion sample, where j=1 represents the first-phase natural gas inclusion, j=2 represents the second-phase natural gas inclusion, j=3 represents the mixed source gas of the two-phase natural gas injection, i=1 represents the methane component, and i=2 represents the ethane component (the present invention mainly uses the first two hydrocarbon gases with the highest content in natural gas, namely methane and ethane); S ij —The peak area of ​​the i-th component of the j-th natural gas inclusion sample; K i —The coefficient when the peak area of ​​the i-th component in the Raman spectrum is converted into relative concentration. When i=1, it represents the methane component, and when i=2, it represents the ethane component; m, n, p and q—the ratio of the relative concentrations of the corresponding components.

[0015] The direct application condition of formula (IV) is that the sizes of the natural gas inclusions in the two phases are similar (i.e., the total molar amount of each component of the natural gas and the sum of the peak areas are the same), otherwise the peak area S ij All need to be replaced by the relative area S ij 'Use, for example (at this time It is the sum of the peak areas of all gas components, namely methane, ethane, propane, carbon dioxide, nitrogen, hydrogen, carbon monoxide and C 4+ alkanes).

[0016] The coefficient K values ​​when the peak areas of the components of the natural gas inclusions in the Raman spectrum are converted into relative concentrations are shown in Table 1. The coefficient K values ​​are constant coefficients summarized in this field.

[0017] Table 1

[0018]

[0019] Preferably, in step S3, the calculation formula for the contribution of natural gas injected in different phases to the current gas reservoir is as follows:

[0020]

[0021] Where, f is the relative contribution ratio of the first-stage natural gas inclusions to the current gas reservoir.

[0022] Preferably, the relative contribution rate of the first-phase natural gas inclusions is α=f×100%, and the relative contribution rate of the second-phase natural gas inclusions is 1-α, and the following judgment relationship exists: if 50%<α≤100%, it means that the contribution of the first-phase natural gas inclusions is dominant; if α=50%, it means that the contributions of the two-phase natural gas inclusions are the same; if 0%≤α<50%, it means that the contribution of the second-phase natural gas inclusions is dominant; if α<0% or α>100%, it means that there may be interference from the contribution of unknown natural gas inclusion sources.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. This invention primarily analyzes the relative concentrations and ratios of methane and ethane in natural gas inclusions from two phases and natural gas produced from a gas reservoir (i.e., the current reservoir natural gas formed by a mixture of the aforementioned two phases of natural gas inclusions). Using Raman spectra from the two phases of natural gas inclusions, the relative concentrations and ratios of methane and ethane in natural gas from different phases are quantitatively calculated. This establishes a quantitative analysis method for mixed sources of natural gas from gas reservoirs, reveals the relative contributions of natural gas from different phases, and thus guides future natural gas exploration activities and promotes increased energy reserves and production.

[0025] 2. The two-phase natural gas inclusion Raman analysis and natural gas composition analysis of the present invention are basic oilfield data and are easy to obtain. The relevant ratios can be directly calculated by simply screening the natural gas inclusion characteristics in the vein body, without the need for additional experiments. Even for new area exploration, the equipment used in the present invention is easy to obtain in actual research. Most universities, research institutes, and oilfield research institutes in the industry have the relevant testing equipment, making it convenient and fast.

[0026] 3. This invention proposes for the first time a method for quantitatively analyzing mixed-source gas by directly using natural gas inclusions that can reflect the characteristics of natural gas during the charging period and through Raman analysis. This method reduces the tedious steps of finding and identifying end-element gases and achieves higher accuracy, thus filling a gap in the field of natural gas research in the quantitative analysis of natural gas charging quantities at different stages.

[0027] 4. The method of the present invention does not require absolute quantitative calculation of natural gas component concentrations; instead, it only requires calculating relative component contents and obtaining ratios. Compared to traditional component quantification methods, which require the addition of standard samples and calibration, the present method avoids the cumbersome process of absolute concentration quantification. Furthermore, the instrument's measurement of relative contents and calculation of ratios is more sensitive than first calculating absolute concentrations and then calculating ratios, resulting in more accurate mixed-source gas quantitative analysis results. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1These are the observation results of the occurrence of veins and natural gas inclusions in the natural gas production layer of Well G1 in Example 1, where 1(a) is the reflected light characteristic of the calcite vein, 1(b) is the cathodoluminescence characteristic of the calcite vein, 1(c) is the identification of two phases of calcite veins under cathodoluminescence, 1(c1) is the identification of natural gas inclusions in calcite vein 1 (fluorescence), 1(c2) is the identification of natural gas inclusions in calcite vein 2 (transmitted light), and 1(d) is the characteristic of the calcite vein hand specimen.

[0029] Figure 2 is the homogenization temperature of the brine inclusion during the two-phase natural gas charging of the gas reservoir in Example 1, and N in the figure is the total number of test points of the corresponding vein body.

[0030] Figure 3 These are the Raman spectra of the two phases of natural gas inclusions in Example 1, where (a) is the Raman spectrum and (b) is the Raman spectrum after the overlapping peaks are resolved. DETAILED DESCRIPTION

[0031] This invention uses the mixed-source analysis of natural gas from the G1 well in the PL region of northern Jiangxi Province, located in the middle and lower reaches of the Yangtze River, as an example, and illustrates the specific implementation scheme and application effects of the invention with reference to the accompanying drawings. It should be understood that the specific implementation scheme described here is merely a small, typical example, intended to illustrate the invention and is not intended to limit the invention.

[0032] The technical solution of the present invention is further described below in conjunction with specific embodiments.

[0033] Example 1

[0034] The two-phase mixed-source gas quantitative analysis method based on the natural gas inclusion Raman technology of this embodiment includes the following steps:

[0035] S1 selected typical gas reservoir veins as two-phase natural gas inclusion samples and performed Raman testing on them

[0036] The natural gas in the PL area is mainly produced from the Permian system. The thickness of its related source rocks is 50-300m, with high organic matter abundance (mainly TOC>2%) and maturity mainly in the overmature stage (Ro>2%), indicating that the area is mainly in the peak stage of natural gas generation and has strong natural gas exploration potential.

[0037] The natural gas production veins in Well G1 include two phases of calcite veins. Figure 1 Presented a calcite vein hand specimen ( Figure 1 (d)) and calcite vein reflected light ( Figure 1 (a)), cathode luminescence ( Figure 1 (b)) characteristics, the same vein body appears in two red colors in the cathode luminescence photograph (the surrounding rock does not emit red light): the first phase calcite appears reddish brown ( Figure 1(c) "Calcite vein 1"), in close contact with the surrounding rock, reflects the calcite authigenic cementation during the first phase of natural gas inclusion filling; the other phase appears orange-red ( Figure 1 (c) "Calcite vein 2" shows that although some parts are in close contact with the surrounding rock, some parts are contained in dark red calcite, indicating that the orange-red calcite was formed later than the reddish-brown calcite, indicating that calcite was authigenic cemented during the second phase of natural gas inclusion filling. Both phases of calcite have a large number of natural gas inclusions, which appear blue-white under fluorescence ( Figure 1 (c1)), appears black under transmitted light ( Figure 1 (c2)), consistent with its overmature thermal evolution.

[0038] This result is also verified by the homogenization temperature of brine inclusions developed during the same period, such as Figure 2 As shown, brine inclusions coeval with natural gas inclusions record formation temperatures during the natural gas charging period. Combined with burial history, these inclusions exhibit temporal differences: lower homogenization temperatures indicate an earlier charging period, while higher temperatures indicate a later period. The homogenization temperatures of coeval brine inclusions in calcite vein 1 range from 145-175°C, with a dominant high-frequency peak at 155-160°C. The homogenization temperatures of coeval brine inclusions in calcite vein 2 range from 155-200°C, with a dominant high-frequency peak at 180-185°C, indicating distinct two phases of fluid activity. Calcite vein 1 formed earlier than calcite vein 2, consistent with the order of development determined by cathodoluminescence analysis of the calcite veins. This suggests that the gas reservoir contains contributions from both phases of natural gas inclusions. Therefore, quantitative analysis of mixed-source gas was conducted using this reservoir as an example.

[0039] S2 calculates the relative concentration and ratio of methane and ethane in the two phases of natural gas inclusion samples based on the Raman data measured in step S1

[0040] First, the Raman spectra of two phases of natural gas inclusions in the calcite vein were measured using a JY / Horiba LabRam HR800 Raman spectrometer. The instrument model used was a JY / Horiba LabRam HR800 (Raman system: frequency-doubled Nd, YAG laser, 532.06nm laser, output laser power of 400-500mW). The laser used 10×, 20×, and 50× Olympus objectives (with long working distance) with a numerical aperture of 0.5. The electronically cooled detector was set to -70°C and a 520.7cm -1 Apply Raman peak correction to polished silicon wafer strips before each experiment. -1 The composition of the gas-containing fluid was detected at the confocal aperture, and the grating and aperture were set to 200 μm; the center of the grating was set to 2650 cm-1 The total acquisition time range was 0-50 seconds, and each spectrum was recorded 200-500 times to improve the signal-to-noise ratio. In particular, the spectrum of impurities was subtracted using the Galactic software to minimize background fluorescence. In the Raman spectrum of natural gas inclusions tested by confocal laser Raman microscopy, compounds of different components of natural gas will appear at specific Raman shifts (cm -1 ) produces a response peak, and the peak area is a response to the relative content of its different components.

[0041] like Figure 3 As shown in (a), in the Raman spectra of the two phases of natural gas inclusions in the calcite vein measured in this embodiment, the left side has a Raman shift of ~490cm -1 The peak at the right is the surrounding rock peak, and the Raman shift on the right is ~2917cm -1 The peak is the methane peak in the natural gas inclusion, with a Raman shift of ~2954 cm -1 The peak at the left is the ethane peak in the natural gas inclusion. Since the ethane and methane peaks partially overlap, the "Lorentzian line-shaped Raman spectrum automatic decomposition algorithm" commonly used in this field is introduced to split the overlapping peaks, and the following is obtained: Figure 3 The Raman shift shown in (b) is 2917 cm -1 The methane peak and Raman shift are 2954 cm -1 ethane peak.

[0042] The peak area is then obtained by integration. Based on the peak area ratio of the methane peak and the ethane peak, the following formula (I) can be used to obtain a methane to ethane ratio of 11.02 (i.e., m = 11.02) for the first phase natural gas inclusion. Similarly, the formula (II) is used to calculate a methane to ethane ratio of 3.48 (i.e., n = 3.48) for the second phase natural gas inclusion. The formula (IV) is used to calculate a ethane ratio of the second phase natural gas inclusion to the ethane of the first phase natural gas inclusion, which is 3.87 (i.e., q = 3.48). The relative concentration ratio of methane to ethane in the natural gas produced from well G1 was then analyzed by gas chromatography. The instrument and process used were as follows: the instrument used was an LX3000 chromatograph (other chromatographs were also acceptable) equipped with a TCD detector with a sensitivity of >6000 mV·mL / mg (n-hexadecane / iso-octane). The carrier gas used was He (99.999% purity). Calibration was performed using a natural gas standard. The methane to ethane ratio calculated according to formula (III) was 7.39 (i.e., p = 3.48).

[0043] This test method is a routine test in this field. The instrument can be replaced by other models, and the calculation results remain basically unchanged.

[0044]

[0045] S3 uses the material balance principle as a basis to establish a quantitative analysis method for mixed-source gas to calculate the contribution of natural gas injected at different stages to the current gas reservoir. The calculation formula is as follows:

[0046]

[0047] According to formulas (I), (II), (III), (IV), and (VI), we can obtain:

[0048]

[0049] Where, f is the relative contribution ratio of the first-stage natural gas inclusions to the current gas reservoir.

[0050] Substituting the previously calculated values ​​of m, n, p, and q into formula (V) yields f = 0.807. Therefore, the relative contribution rate of the first-phase natural gas inclusions is α = f × 100% = 80.7%, and the relative contribution rate of the second-phase natural gas inclusions is 19.3%. The calculated results for each parameter are shown in Table 2:

[0051] Table 2

[0052]

[0053] This result is basically consistent with the geological conditions of low gas production and relatively small injection volume in the late overmature stage (corresponding to maturity of 3.5%), which shows that the quantitative analysis method of the present invention has high reliability and accuracy.

Claims

1. A two-phase mixed-source gas quantitative analysis method based on natural gas inclusion Raman technology, characterized by: The following steps are involved: S1 selected typical vein bodies in gas reservoirs as two-phase natural gas inclusion samples and conducted Raman tests on them; S2 calculates the relative concentrations and ratios of the components in the two phases of natural gas inclusion samples based on the Raman data measured in step S1; S3 uses the material balance principle to establish a quantitative analysis method for mixed-source gas and calculates the contribution of natural gas injected at different stages to the current gas reservoir. In step S2, the calculation formulas for the relative concentrations and ratios of methane and ethane in the two phases of natural gas inclusion samples are as follows: (I) (II) (III) (IV) Where C ij —The relative content of the i-th component of the j-th natural gas inclusion sample, where j = 1 represents the first-phase natural gas inclusion, j = 2 represents the second-phase natural gas inclusion, j = 3 represents the mixed source gas of the two-phase injection natural gas, i = 1 represents the methane component, and i = 2 represents the ethane component; S ij —The peak area of ​​the i-th component of the j-th natural gas inclusion sample; K1, K2—The coefficients when the peak areas of methane and ethane in the Raman spectrum are converted into relative concentrations; m, n, p and q—The ratios of the relative concentrations of the corresponding components.

2. The two-phase mixed-source gas quantitative analysis method based on natural gas inclusion Raman technology according to claim 1, characterized in that: In step S1, calcite veins or quartz veins are selected as two-phase natural gas inclusion samples.

3. The two-phase mixed-source gas quantitative analysis method based on natural gas inclusion Raman technology according to claim 1, characterized in that: In step S3, the calculation formula for the contribution of natural gas injected in different phases to the current gas reservoir is as follows: (V) Where, f —Relative contribution of the first-phase natural gas inclusions to the current gas reservoir.

4. The two-phase mixed-source gas quantitative analysis method based on natural gas inclusion Raman technology according to claim 3, characterized in that: The relative contribution rate of the first-phase natural gas inclusions is α=f×100%, and the relative contribution rate of the second-phase natural gas inclusions is 1-α. The following judgment relationship exists: if 50%<α≤100%, it means that the contribution of the first-phase natural gas inclusions is dominant; if α=50%, it means that the contributions of the two phases of natural gas inclusions are equal; if 0%≤α<50%, it means that the contribution of the second-phase natural gas inclusions is dominant; if α<0% or α>100%, it means that there is interference from the contribution of unknown natural gas inclusion sources.

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