Two-stage mixed source gas quantitative analysis method based on natural gas inclusion Raman technology

Abstract

The invention discloses a two-stage mixed source gas quantitative analysis method based on a natural gas inclusion Raman technology, and relates to the technical field of geological exploration. According to the technical scheme, the method comprises the following steps: S1, selecting a typical vein of a gas reservoir as a two-stage natural gas inclusion sample, and carrying out Raman test on the two-stage natural gas inclusion sample; s2, calculating relative concentrations and ratios of components in the two-stage natural gas inclusion samples according to the Raman data measured in the step S1; and S3, establishing a mixed source gas quantitative analysis method on the basis of a material balance principle, and calculating the contribution of natural gas filling in different periods to the current gas reservoir. The contribution of natural gas filling in different periods to the current gas reservoir is quantitatively revealed, so that the problem of quantitative calculation of natural gas contribution in different geological historical periods is solved.

Description

Technical Field

[0001] The invention relates to the technical field of geological exploration, 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 is clean, low-carbon, stable, flexible and economical. It ensures that energy supply meets demand in a safe, sustainable and reliable manner. Vigorously developing natural gas will also become one of the inevitable trends in future energy development. Natural gas molecules are extremely small, and the cap rock conditions are extremely demanding. It is very easy to mix natural gas injected at different times. Existing evaluation technologies can reveal the origin / source of natural gas (terrestrial origin, marine origin; origin of different kerogen types; or origin of kerogen and crude oil cracking gas, etc.), but there is no relevant quantitative calculation method for the relative contribution of natural gas injection at different times. However, the contribution of natural gas at different times has an important impact on natural gas exploration. When the contribution of natural gas injected in the early stage is relatively small, it means that oil and gas exploration should seek traps with good cap rock conditions in the late stage, while traps with good cap rock sealing conditions in the early stage but damaged in the late stage should not be explored; when the contribution of natural gas injected in the late stage is relatively small, it means that oil and gas exploration should seek traps with good cap rock conditions in the early stage, while traps with good cap rock sealing conditions in the late stage suffer from limited natural gas injection, so traps with good quality developed after the main injection period should not be explored. Obviously, the relative contribution of natural gas injected in different injection periods will directly affect the effectiveness of the trap and its recoverability evaluation.

[0003] The existing technologies for testing the content of natural gas components are relatively mature, mainly including gas chromatography, Fourier infrared spectroscopy and Raman spectroscopy. Gas chromatographs require carrier gas to operate, and the analysis takes a long time, making it impossible to monitor natural gas in real time; infrared spectroscopy technology, as a non-destructive analysis technology, has the advantages of high analysis efficiency, no pollution, and fast analysis speed, but it cannot detect homonuclear diatomic molecules such as nitrogen and hydrogen. Therefore, infrared absorption spectroscopy technology does not fully meet the requirements of natural gas component detection; Raman spectroscopy detection has unique advantages: only a single laser source is needed to simultaneously measure all components in the gas sample, with fast detection speed (within 30 seconds) and high sensitivity. The main methods for quantitative analysis of mixed gas components using laser Raman spectroscopy include peak height method, area method, kurtosis method, and pure substance spectral decomposition method. Among them, predecessors proposed an automatic decomposition algorithm of Raman spectrum based on Lorentz function, defining natural gas as 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 spectrum of the alkane components and the nonlinear least squares algorithm are used to decompose the spectrum of the mixture to be tested, and the complete peak distribution of different components can be obtained, effectively eliminating the influence of possible overlapping peaks. Therefore, how to quantitatively analyze the natural gas injected at different times based on the quantitative test of natural gas components by Raman spectroscopy is an urgent problem to be solved nowadays. Summary of the invention

[0004] The technical problem to be solved by the present invention is: in view of the current lack of mixed-source quantitative analysis and evaluation technology for natural gas reservoirs, a mixed-source gas quantitative analysis method is provided which is simple to operate, easy to obtain instruments, highly accurate and highly feasible, which will quantitatively reveal the contribution of natural gas charging in different periods to the current gas reservoirs, 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 samples of natural gas inclusions in two phases 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] S3 is based on the material balance principle and 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, it is required to select vein samples that can directly reflect the natural gas charging event, preferably calcite veins or quartz veins, and the geochemical characteristics of the natural gas inclusions contained therein represent the geochemical composition information of the natural gas charging in the corresponding geological history period (relative content and ratio characteristics of natural gas components). Therefore, it is required that the vein develops in the gas reservoir or the necessary path of the gas reservoir, and it is required to develop two phases of natural gas inclusions (which can be judged by the brine inclusions developed in the same period), and the natural gas inclusions in the secondary enlarged edge of quartz or the calcite authigenic minerals in the traditional method cannot be selected. In addition, the vein sample is prepared into a thin slice with a thickness of about 0.08 mm, so as to prepare for the next step of using a confocal microscopic laser Raman spectrometer to test the Raman characteristics of the natural gas inclusions.

[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] In the formula, C ij —Relative content of the i-th component of the j-th natural gas inclusion sample, where j=1 represents the first-stage natural gas inclusion, j=2 represents the second-stage natural gas inclusion, j=3 represents the mixed source gas of the two-stage 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 natural gas inclusions in the two phases are similar (i.e., the total molar amount of each component of natural gas and the sum of 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 the art.

[0017] Table 1

[0018]

[0019] Preferably, in step S3, the calculation formula for the contribution of natural gas injected at different stages 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 there is the following judgment relationship: 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. The present invention takes the relative concentration and ratio of methane and ethane in two-phase natural gas inclusions and natural gas produced from gas reservoirs (i.e., the current gas reservoir natural gas formed by a mixture of the two-phase natural gas inclusions) as the main analysis objects, and quantitatively calculates the relative concentration and ratio of methane and ethane in natural gas of different phases through the Raman spectra of the two-phase natural gas inclusions, establishes a quantitative analysis method for mixed sources of natural gas in gas reservoirs, reveals the relative contribution of natural gas of different phases, thereby guiding future natural gas exploration activities and promoting energy reserves and production.

[0025] 2. The two-phase Raman analysis of natural gas inclusions and the natural gas component analysis of the present invention are basic data of oil fields, which are easy to obtain, and the relevant ratios can be directly calculated by only screening the characteristics of natural gas inclusions in the veins, 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, and most of the universities, research institutes and oilfield research institutes in the industry are equipped with relevant testing instruments, which is convenient and fast.

[0026] 3. The present invention proposes for the first time a method of directly using natural gas inclusions that can reflect the characteristics of natural gas during the charging period and performing quantitative analysis of mixed source gas through Raman analysis, which reduces the tedious steps of finding and determining end-element gases and has higher accuracy, thus filling the gap in the quantitative analysis of natural gas charging amounts at different periods in the field of natural gas research.

[0027] 4. The method of the present invention does not need to calculate the concentration of natural gas components by absolute quantification during execution. It only needs to calculate the relative content of the components and obtain the ratio. Compared with the traditional component quantification method, which requires adding standard samples and calculating calibration, the present invention avoids the cumbersome process of absolute concentration quantification. In addition, the instrument tests the relative content and calculates the ratio, which is more sensitive than calculating the absolute concentration first and then the ratio, and the corresponding mixed source gas quantitative analysis results will be more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1The results of observation of the occurrence of veins and natural gas inclusions in the natural gas producing layer of Well G1 in Example 1 are shown in Figure 1, where 1(a) is the reflected light characteristic of the calcite vein, 1(b) is the cathode luminescence characteristic of the calcite vein, 1(c) is the identification of two stages of calcite veins under cathode luminescence, 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 hand specimen of calcite veins.

[0029] Figure 2 is the homogenization temperature of the brine inclusion during the two-stage 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 Raman spectra of two phases of natural gas inclusions in Example 1, where (a) is a Raman spectrum and (b) is a Raman spectrum after the overlapping peaks are separated. DETAILED DESCRIPTION

[0031] The present invention takes the mixed source analysis of natural gas in the G1 well in the PL area in the middle and lower reaches of the Yangtze River in northern Jiangxi Province as an example, and illustrates the specific implementation scheme and application effect of the present invention in combination with the accompanying drawings. It should be understood that the specific implementation scheme described here is only a small typical case to explain the present invention, but is not used to limit the present 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 natural gas inclusion Raman technology of this embodiment includes the following steps:

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

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

[0037] The veins of the natural gas production layer in Well G1 include two phases of calcite veins. Figure 1 The calcite vein hand specimen is presented ( 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" is in close contact with the surrounding rock, reflecting the calcite authigenic cementation during the first phase of natural gas inclusion filling; the other phase is orange-red ( Figure 1 (c) "Calcite vein 2" has some parts in close contact with the surrounding rock, but some parts are contained in the dark red calcite, indicating that the orange-red calcite was formed later than the reddish-brown calcite, indicating the calcite authigenic cementation during the second phase of natural gas inclusion filling. A large number of natural gas inclusions are developed in both phases of calcite, showing blue-white fluorescence under fluorescence ( Figure 1 (c1)), and appears black under transmitted light ( Figure 1 (c2)), which is consistent with its overmature thermal evolution.

[0038] This result is also verified by the homogenization temperature of the brine inclusions developed during the same period, such as Figure 2 As shown in the figure, the salt water inclusions developed in the same period as the natural gas inclusions record the formation temperature during the natural gas charging period. Combined with the burial history, it is manifested as a time difference. The inclusions with lower homogenization temperatures indicate an earlier charging period, while those with higher homogenization temperatures indicate a later charging period. The homogenization temperatures of the salt water inclusions in the same period in calcite vein 1 are distributed between 145-175℃, and the main peak high-frequency temperature is 155-160℃; the homogenization temperatures of the salt water inclusions in the same period in calcite vein 2 are distributed between 155-200℃, and the main peak high-frequency temperature is 180-185℃, showing significant two-stage fluid activity. The formation time of calcite vein 1 is earlier than that of calcite vein 2, which is consistent with the order of development stages determined by the cathode luminescence of calcite veins. This indicates that the gas reservoir contains the contributions of these two periods of natural gas inclusions. Therefore, the quantitative analysis of mixed source gas was carried out using this gas 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 the two-phase natural gas inclusions in the calcite vein were tested by JY / Horiba LabRam HR800 Raman spectrometer. The instrument model used was 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 objective lenses (with long working distance), and the numerical aperture was 0.5. The electronic cooling detector was set to -70℃, and the ~520.7cm -1 Raman peak correction was applied to polished silicon wafer tape before each experiment. -1 The composition of the gas-containing fluid was detected at 1.5°. The grating and aperture of the confocal hole were set to 200 μm; the center of the grating was set to 2650 cm-1 ; The total acquisition time range is 0-50s, and each spectrum is recorded 200-500 times to improve the signal-to-noise ratio. In particular, the spectrum of impurities is subtracted by the software Galactic to minimize background fluorescence. In the Raman spectrum of natural gas inclusions in the test vein body by confocal microscopy laser Raman spectrometer, the compounds of different components of natural gas will be in a specific Raman shift (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-phase natural gas inclusions in the calcite vein measured in this example, 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 ~2954cm -1 The peak at the position is the ethane peak in the natural gas inclusion. Since the ethane and methane peaks partially overlap, the "Lorentzian line type 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] Then the peak area is obtained by integrating it. According to the peak area ratio of the methane peak and the ethane peak, the following formula (I) can be used to obtain that the ratio of methane to ethane in the first phase natural gas inclusion is 11.02 (i.e., m=11.02). Similarly, the formula (II) is used to calculate that the ratio of methane to ethane in the second phase natural gas inclusion is 3.48 (i.e., n=3.48). The formula (IV) is used to calculate that the ratio of ethane in the second phase natural gas inclusion to ethane in the first phase natural gas inclusion is 3.87 (i.e., q=3.48). Then, gas chromatography was used to analyze the relative concentration ratio of methane to ethane in the natural gas produced from the G1 well. The instrument and process used were as follows: the instrument used was an LX3000 chromatograph (other chromatographs may also be used), equipped with a TCD detector with a sensitivity of >6000mV·mL / mg (n-hexadecane / iso-octane), the carrier gas used was He (purity 99.999%), and 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 is based on the material balance principle and 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. 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 above calculated m, n, p and q parameter values ​​into formula (V), we can get f = 0.807. Therefore, the relative contribution rate of the first-stage natural gas inclusions is α = f × 100% = 80.7%, and the relative contribution rate of the second-stage natural gas inclusions is 19.3%. The calculation results of 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 filling volume in the late overmature stage (corresponding to a 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 in that: The following steps are involved: S1 selected typical vein bodies in gas reservoirs as samples of natural gas inclusions in two phases 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 is based on the principle of material balance and 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.

2. The two-phase mixed source gas quantitative analysis method based on natural gas inclusion Raman technology according to claim 1 is 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 is characterized in that: 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: In the formula, C ij —Relative content of the i-th component of the j-th natural gas inclusion sample, where j=1 represents the first-stage natural gas inclusion, j=2 represents the second-stage natural gas inclusion, j=3 represents the mixed source gas of the two-stage 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.

4. The two-phase mixed source gas quantitative analysis method based on natural gas inclusion Raman technology according to claim 3 is characterized in that: In step S3, the calculation formula of the contribution of natural gas injected at different stages to the current gas reservoir is as follows: Where, f is the relative contribution ratio of the first-stage natural gas inclusions to the current gas reservoir.

5. The two-phase mixed source gas quantitative analysis method based on natural gas inclusion Raman technology according to claim 4 is 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, and there is the following judgment relationship: if 50%<α≤100%, it means that the contribution of the first-phase natural gas inclusions is the main one; 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 the main one; 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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