Method for evaluating oil and gas maturity inside inclusion by infrared spectrum

Abstract

The present application belongs to the field of petroleum geology, and particularly relates to a method for evaluating oil and gas maturity in a fluid inclusion by using infrared spectrum. First, a fluid inclusion slice prepared from a stratum rock sample in a sedimentary basin is obtained; a filling sequence of diagenetic minerals in the stratum rock is determined; different occurrences of oil and gas are judged by petrographic characteristics under a microscope and fluorescence spectrum characteristics of the rock slice; infrared spectrum testing is performed on the oil and gas inclusions with different occurrences, and infrared spectrum characteristics of inclusions in different stages are obtained; a required spectrum range peak area is extracted from a spectrum diagram and brought into a formula; and an effective parameter for evaluating oil and gas maturity in the inclusions is obtained by using the formula and is sorted. The instrument used in the present application eliminates the requirement and limitation of traditional infrared spectrum on the size of the inclusions, and can measure and evaluate most oil and gas inclusions with smaller size.

Description

Technical Field

[0001] This invention belongs to the field of petroleum geology, specifically relating to a method for evaluating the maturity of oil and gas inside inclusions using infrared spectroscopy. Background Technology

[0002] The study of hydrocarbon maturity is of great significance in the evaluation of hydrocarbon resources in sedimentary basins. It is closely related to hydrocarbon generation, formation hydrocarbon expulsion pressure, and the tracing of source rocks, and can directly indicate the extraction strategy and exploration direction. Commonly used methods for evaluating hydrocarbon maturity include fluorescence spectroscopy, vitrinite reflectance, and rock pyrolysis analysis.

[0003] To date, methods such as vitrinite reflectance, rock pyrolysis, fluorescence spectroscopy, and stereoisomerization of biomarkers all rely on the changes in related substances with temperature to infer the original formation temperature during rock deposition, and then indirectly infer hydrocarbon maturity through formation temperature. Fluorescence spectroscopy provides relatively limited information about hydrocarbons and loses its effectiveness in some basins containing low-maturity hydrocarbons. Furthermore, the changes in fluorescence spectroscopy, vitrinite reflectance, rock pyrolysis, and stereoisomerization of biomarkers are not solely determined by temperature; the duration of temperature change also significantly impacts these parameters. For example, rock pyrolysis results may not accurately reflect the actual evolutionary process under certain scenarios and temperatures. In studies of type III kerogen pyrolysis, when the Tmax value exceeds 500℃, it fails to reflect the true sedimentary basin conditions. Therefore, in the assessment of hydrocarbon maturity in some basins, rock pyrolysis simulation experiments cannot accurately reflect hydrocarbon maturity. Because these methods are not controlled by a single temperature factor, indirectly determining hydrocarbon maturity through calculation presents certain problems.

[0004] Oil and gas inclusions can directly capture the most primordial fluids and seal them within mineral fractures. These fractures act like a space tunnel, directly isolating the fluid inclusions from external material exchange. As the most direct natural geological sample capable of recording primordial crude oil, the chemical composition and physical properties of the crude oil are best preserved by the minerals, allowing for direct study of the original crude oil components in sedimentary basins. Therefore, using primordial crude oil within fluid inclusions to assess oil and gas maturity and development potential is entirely advisable. Whether considering the purity of the crude oil or the non-destructive nature of the process, inclusions can serve as an effective resource for evaluating oil and gas maturity.

[0005] After being captured, fluid inclusions may undergo secondary evolution under changing stratigraphic conditions. Although fluid inclusions are closest to crude oil in physicochemical composition, their internal materials still possess a certain degree of evolutionary potential. Furthermore, the same mineral may capture inclusions of different ages, originating from different source rocks, and possessing completely different physicochemical properties. Therefore, the analysis of fluid inclusions requires consideration of the specific geological context. Consequently, using fluid inclusions to evaluate hydrocarbons often introduces certain biases, directly leading to insufficient accuracy in crude oil geochemical data.

[0006] In terms of methods for studying inclusions, scanning laser electron microscopy (SEM) has the advantages of high resolution and fast analysis speed, but its ability to observe the internal composition of inclusions and the process of compositional changes is limited. Laser ablation requires eroding away the mineral surface to open the closed system inside the inclusion and study its internal substances, which inevitably leads to contamination of internal components. Laser Raman spectroscopy can effectively measure tiny inclusions in a non-destructive and efficient manner, but it is susceptible to fluorescence interference from organic matter, resulting in poor signal quality. Synchrotron radiation has good accuracy, but the experiment takes a long time and the sample is easily affected during the process. Inductively coupled plasma mass spectrometry (ICP-MS) is usually used for the study of ore-forming fluids and is less commonly used for hydrocarbon fluids.

[0007] Previously, the use of infrared spectroscopy for hydrocarbon inclusions was limited by the small size of fluid inclusions, resulting in poor spectral quality. However, with advancements in Fourier transform infrared (FTIR) spectrometers and analytical software, most hydrocarbon inclusions can now be measured and analyzed. Furthermore, because infrared spectroscopy is effective in identifying organic functional groups, it has become widely used in the study of oil and gas inclusions. Fourier transform infrared spectroscopy significantly improves the convenience of experiments, providing an efficient and non-destructive new method for analyzing oil and gas inclusions. From the perspective of analyzing organic functional groups, its principle is feasible and offers better resolution.

[0008] From the perspective of experimental results and time requirements, scanning electron microscopy (SEM) and Raman spectroscopy are currently the most common and mature methods for indirectly studying inclusion maturity. However, both have different limitations in studying hydrocarbons. SEM is expensive and time-consuming compared to spectroscopic analysis, and it is less effective at analyzing the internal composition of inclusions and observing changes in composition. Raman spectroscopy is easily affected by fluorescence interference, resulting in poor imaging results. Synchrotron radiation is time-consuming and may face the challenge of not being able to replicate the results. Laser ablation may alter the composition of hydrocarbons due to high temperatures, thus affecting the accuracy of evaluating hydrocarbon maturity. Rock pyrolysis is also expensive and requires a large number of experiments, and the results may be limited depending on the type of kerogen in sedimentary basins. Vitrin reflectance is expensive and requires multiple samples for experiments, making a single sample set costly, and its experimental results for kerogen are worse than those for fluid inclusions. Summary of the Invention

[0009] To overcome the problems existing in the prior art, this invention provides a method for evaluating the maturity of hydrocarbons within hydrocarbon inclusions using infrared spectroscopy. This method involves acquiring hydrocarbon inclusions in sedimentary basin reservoirs, measuring the maturity of hydrocarbons within these inclusions using infrared spectroscopy, and then correcting for the maturity by considering the specific geological conditions and background of the oil-bearing basin. The resulting hydrocarbon maturity is directly assessed based on the functional group characteristics and internal properties of the hydrocarbons themselves. This method eliminates the need for indirect paleothermal assessment of hydrocarbon maturity, facilitating a more comprehensive study of hydrocarbon generation, expulsion, and storage by oil and gas exploration and development companies, ultimately contributing to oil and gas exploration in sedimentary basins.

[0010] To achieve the above objectives, the present invention includes the following steps:

[0011] S1. Collect rock samples, prepare fluid inclusion thin sections, and determine the filling sequence of diagenetic minerals in the fluid inclusion thin sections.

[0012] S2. By conducting microscopic observation and fluorescence microscopy on fluid inclusions, and by comprehensively analyzing and judging the petrographic characteristics of fluid inclusions, the petrographic characteristics of fluid inclusions are determined, including the size, shape, structure, occurrence, phase combination and phase volume ratio characteristics, internal material composition, and fluid inclusion stages.

[0013] S3. Determine the minerals and types of inclusions based on the petrographic characteristics of the thin sections, as well as the occurrence and fluorescence characteristics of the inclusions.

[0014] S4. Select hydrocarbon inclusions from different phases that meet the experimental conditions. Use a single polarizing microscope, fluorescence microscope, and Raman laser method combined with petrographic characteristics to determine the host minerals of the hydrocarbon inclusions. Quartz is the preferred host mineral for hydrocarbon inclusions. At the same time, use isotope dating, X-ray diffraction, petrographic characteristics, organic element analysis, nuclear magnetic resonance, and inclusion fluid chemistry to determine the geological history of the hydrocarbon inclusions and distinguish different phases. The selection principle for hydrocarbon inclusions is to select hydrocarbon inclusion groups of different phases and maturity. Within the hydrocarbon inclusion group, hydrocarbon inclusions of the same phase are selected based on the criteria of large number, large grain size, and single phase.

[0015] S5. Using a Fourier transform infrared spectrometer, tests were conducted on hydrocarbon inclusions of different phases to obtain the infrared spectral characteristics of methyl, methine, and hydroxyl groups in hydrocarbon inclusions of different phases. The infrared spectra of hydrocarbon inclusions were plotted using OPUS and Origin software, and the ratio of the peak areas of methine and methyl infrared spectra and the ratio of the peak areas of hydroxyl and methyl were calculated to evaluate the oil and gas maturity of the inclusions.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] (1) Provides new parameters to more comprehensively evaluate the maturity of oil and gas inside inclusions; improves the original method of evaluating oil and gas inside inclusions to enhance the evaluation effect; the instrument used in this invention removes the requirements and limitations of traditional infrared spectroscopy on the size of inclusions, and can measure and evaluate most common oil and gas inclusions with smaller sizes.

[0018] (2) By combining the two parameters R1 and R2 obtained from the infrared spectrum of the inclusions, the maturity of oil and gas inside the inclusions can be more clearly classified. The improved evaluation parameter R1 makes greater use of the advantages of Fourier transform infrared spectroscopy, while the new evaluation parameter R2 makes up for the shortcomings of previous studies that relied on a single parameter to evaluate the maturity of oil and gas inside inclusions, resulting in poor evaluation results. This invention introduces the ratio of hydroxyl content to methyl content inside the inclusions as a parameter to reflect the maturity of oil and gas, based on the original method of judging oil and gas maturity using carbon chain length. This allows for a more comprehensive and objective evaluation of oil and gas maturity using two parameters.

[0019] (3) This method can simply, quickly, efficiently, and non-destructively classify the maturity of hydrocarbons within inclusions to determine the specific hydrocarbon accumulation stages, maturity evolution characteristics, and even reflect formation temperature to a certain extent, thereby guiding subsequent hydrocarbon accumulation and development work. Fluid inclusion records can effectively determine hydrocarbon types in different geological periods by documenting the original fluids during reservoir diagenesis. This invention provides a new approach and method for the study of hydrocarbon maturity in sedimentary basin strata. Attached Figure Description

[0020] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0021] Figure 1 This is a schematic diagram of a process for obtaining evaluation data from testing inclusions using a Fourier transform infrared spectrometer, as provided by the present invention.

[0022] Figure 2 The preferred mineral map required for this invention and the reasons thereof;

[0023] Figure 3 This is a flowchart illustrating the specific experimental procedure for evaluating the maturity of inclusions in hydrocarbons using Fourier transform infrared spectroscopy (FTIR).

[0024] Figure 4 Typical oil and gas inclusions selected according to the selection criteria of this invention;

[0025] Figure 5 This refers to the specific location of the Fourier transform infrared spectroscopy measurement in this invention;

[0026] Figure 6 This document shows the range of functional groups selected for infrared spectroscopy of oil and gas inclusions in this invention, as well as the infrared spectra of typical oil and gas inclusion samples. Detailed Implementation

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] Taking a specific work area in a depression within the Gulf Basin as an example, the scheme of this application will be explained in conjunction with the attached drawings. Figure 1 As shown, the present invention provides a method for evaluating the maturity of oil and gas inside inclusions using infrared spectroscopy, the specific implementation steps of which are as follows:

[0029] S1. Collect rock samples and prepare fluid inclusion thin sections. The preparation method can be followed (Petroleum Industry Standard: SY / T5913-2004). Determine the filling sequence of diagenetic minerals in the fluid inclusion thin sections.

[0030] S2. By observing and analyzing fluid inclusions under microscopic and fluorescence microscopes, and by comprehensively analyzing and judging the petrographic characteristics of fluid inclusions, we can determine the size, shape, structure, occurrence, phase combination and phase volume ratio characteristics, internal material composition, and fluid inclusion stages of fluid inclusions.

[0031] S3. Using transmission light and fluorescence microscopy, fluid inclusion assemblages were studied. The morphology, structure, phase combination, internal composition, and stage of fluid inclusions were observed to preliminarily determine the types of hydrocarbon inclusions. Two selection principles were followed: first, it was necessary to ensure that the hydrocarbon inclusions had not undergone reequilibrium, as reequilibrium could alter the internal composition of inclusions, affecting the accuracy of the experimental data; second, inclusions with varying fluorescence colors under fluorescence microscopy were preferred. While fluorescence color cannot be the sole criterion for evaluating hydrocarbon maturity, it can serve as valid evidence for distinguishing inclusions at different stages under certain circumstances. Further screening of hydrocarbon inclusions was required to ensure the accuracy of the final spectral data.

[0032] The host minerals of oil and gas inclusions also need further clarification, such as... Figure 2 As shown, because different minerals absorb infrared spectra to different degrees in different bands, the interference of some minerals on the spectral data of oil and gas inclusions is too severe, making them unusable. Calcite, one of the most common minerals in sedimentary basins, is unsuitable as the primary mineral for practical application in this invention due to its strong absorption of the infrared spectrum across the entire wavelength range. Fluorite has weaker absorption of the infrared spectrum, but it is relatively rare in sedimentary basins, although it may be found in volcanic reservoirs; therefore, hydrocarbon inclusions within fluorite minerals can be considered as a backup option. Halite, as an ionic compound, has almost no absorption of the infrared spectrum, and due to its inherent transparency, it can serve as an excellent carrier for infrared spectroscopy studies of hydrocarbon inclusions. However, because halite crystals are relatively rare compared to the seven major rock-forming minerals under natural conditions, and naturally occurring halite crystals with hydrocarbon inclusions are even scarcer in sedimentary basins, halite is not the primary experimental mineral for this invention. Quartz, one of the seven major rock-forming minerals, is very common in terrestrial sedimentary basins and sandstone reservoirs, and it also contains a large number of hydrocarbon inclusions. Furthermore, quartz minerals are smooth and transparent under a microscope, exhibiting better light transmission, and quartz exhibits good absorption of the infrared spectrum at 2000 cm⁻¹. -1There is almost no interference within the above range; the infrared spectral band required by this invention is in the range of 2800 cm⁻¹. -1 ~3000cm -1 Therefore, quartz was selected as the preferred mineral for the experiments required by this invention.

[0033] S4. Select hydrocarbon inclusions that meet the experimental conditions for measurement using Fourier transform infrared spectroscopy.

[0034] The minerals hosting the inclusions were determined using a combination of methods including single-polarization microscopy, fluorescence microscopy, and Raman laser analysis, along with petrographic characteristics. Isotope dating, X-ray diffraction, petrographic features, organic elemental analysis, nuclear magnetic resonance (NMR), and fluid chemistry of the inclusions were then used to determine the geological history of the inclusions' capture and differentiate between different phases. The selection principles were: to choose hydrocarbon inclusion assemblages of multiple phases and different maturity levels, with a greater number of inclusions corresponding to the same phase within each assemblage being preferred; to choose inclusions with larger grain sizes, as larger inclusions facilitate observation and measurement; and to choose oil inclusions of a single phase to minimize the influence of the gas phase on the infrared spectrum. After selecting the hydrocarbon inclusion samples, they were summarized and classified for Fourier transform infrared spectroscopy (FTIR) measurements. Figure 3 As shown, by identifying the different phases and characteristics of inclusions and combining them with geological history, the differences in inclusion maturity can be preliminarily determined. Figure 4 Typical oil and gas inclusion samples that meet the screening criteria of this invention are the most ideal subjects for experiments. Figure 5 This is a diagram showing the center points of oil and gas inclusions measured by Fourier transform infrared spectroscopy.

[0035] S5. Fourier transform infrared spectroscopy was used to test oil and gas inclusions of different phases to obtain the infrared spectral characteristics of methyl, methine, and hydroxyl groups in oil and gas inclusions of different phases. The infrared spectra of oil and gas inclusions were plotted using OPUS and Origin software, and the ratio of the peak areas of the characteristic infrared spectra of methine and methyl groups and the ratio of the peak areas of hydroxyl and methyl groups were calculated to evaluate the maturity of oil and gas inclusions. During this process, oil and gas inclusion samples with poor signals and abnormal spectra need to be removed.

[0036] The specific process is as follows: Based on experimental analysis, this invention selects the vibrational segments of methyl and methine functional groups and the vibrational segments of methyl and hydroxyl functional groups in oil and gas inclusions as methods for evaluating oil and gas maturity. The two sets of data complement each other, thus providing a more comprehensive and complete evaluation of oil and gas maturity. The following explains the specific vibrational segments of the functional groups, their principles, and the specific calculation method for evaluating oil and gas maturity in this invention:

[0037] (1) Functional group vibration region and principle:

[0038] In infrared spectroscopy, methyl (-CH3), methine (-CH2), and hydroxyl (-OH) groups all show good performance. Methyl (-CH3) and methine (-CH2) are important functional groups in hydrocarbon carbon chains, while hydroxyl (-OH) usually represents the presence of water. It is well known that longer carbon chains typically contain more methine (-CH2) groups, while shorter carbon chains contain more methyl (-CH3) groups. Furthermore, because less mature oil and gas contain more heavy hydrocarbons, their carbon chains are generally longer, and they are mainly produced in the early stages of hydrocarbon generation; more mature oil and gas contain more light hydrocarbons, and their carbon chains are generally shorter, and they are mainly produced in the later stages of hydrocarbon generation. Therefore, this invention aims to propose a method for evaluating the maturity of oil and gas within inclusions by using the ratio of methine (-CH2) to methyl (-CH3) groups, based on the length of the carbon chains within the inclusions.

[0039] The hydroxyl group (-OH), as a functional group that reflects the presence of water, is highly likely to be captured by oil and gas during transport, forming a "microemulsion"-like oil-water mixture under high-temperature and complex geological conditions. Therefore, within a specific region at the same geological time, hydroxyl groups (-OH) are co-encapsulated with oil and gas by minerals, forming oil and gas inclusions of the same phase. The number of hydroxyl groups (-OH) within these inclusions can serve as one indicator of oil and gas maturity. The principle is based on chemical bond lengths. Shorter hydroxyl (-OH) bonds require greater energy and higher temperatures to break; conversely, the most dominant carbon-hydrogen (CH) bonds in oil and gas are shorter, requiring less energy and lower temperatures to break. From the perspective of energy required to break chemical bonds, oil and gas inclusions with more hydroxyl groups (-OH) tend to have lower maturity, while those with higher hydroxyl (-OH) content tend to have higher maturity. From the perspective of molecular weight and molecular structure, lighter oils with higher maturity have smaller molecular structures. Due to the immiscibility of oil and water, theoretically, oil and gas molecules separate from water molecules in the formation, with the oil and gas floating above the water layer in a suspended state, resulting in fewer hydroxyl (-OH) groups within the oil and gas. Conversely, heavier oils with lower maturity, due to their larger molecular weight and more complex structure, may form viscous emulsion-like fluids with water molecules for co-transport. In this state, the fluid properties are stable, the flow rate is slow, and it contains more hydroxyl (-OH) groups. Therefore, considering both the oil-water mixing and transport state and chemical bond energies, this invention proposes a method for evaluating the maturity of oil and gas within fluid inclusions by using the ratio of hydroxyl (-OH) to methyl (-CH3) groups in the fluid inclusions of crude oil.

[0040] In summary, this invention aims to evaluate oil and gas maturity by using the ratio of methine (-CH2) to methyl (-CH3), and then to constrain the maturity of oil and gas within oil and gas inclusions by adding hydroxyl (-OH) and methyl (-CH3), in order to more accurately classify oil and gas maturity.

[0041] Infrared absorption frequencies and their relative intensities are used to determine the type and concentration of functional groups. Specifically, the CH stretching vibration region of n-alkanes is distributed between 3100 and 2700 cm⁻¹. -1 Within a given range, the relative intensity of the spectrum depends on the concentration of the substance and the nature of the chemical bonds themselves. However, chemical bonds with the same functional group have consistent absorption intensities. The peak value of the methylene bond (CH2) is typically distributed around 2927 cm⁻¹. -1 (υ) 反对称 ) and 2856cm -1 (υ) 对称 The spectral peak of methyl (CH3) is typically located at 2959 cm⁻¹. -1 (υ) 反对称 ) and 2873cm -1 (υ) 对称 Due to the overlapping of spectral bands, determining the boundary of the calculated area is a difficult task. Therefore, the specific method for determining the spectral bands of each functional group, as shown in the figure, relies on manual constraints.

[0042] like Figure 6 As shown, based on the distribution range of methyl and methine groups in the Fourier transform infrared spectrum proposed by Pironon, 2800~2869 cm⁻¹ -1 Methionine (CH) 2s ) group in υ 对称 Absorption range, 2869~2883 cm -1 Methyl (CH) 3s ) group in υ 对称 Absorption range, 2883~2947 cm -1 Methionine (CH) 2a ) group in υ 反对称 Absorption range: 2947~3000cm -1 Methyl (CH) 3a ) group in υ 反对称 Absorption range; while carbon-hydrogen bond (CH) groups are located at 2800~3000 cm⁻¹. -1 The specific range of the hydroxyl (OH) functional group depends on the host mineral and the state of water within the mineral. Given that the mineral in this study is quartz and the oil-water mixture is in an emulsion state, the peak range for the hydroxyl (OH) group is 3400-3600 cm⁻¹. -1 .

[0043] (2) Specific calculation method for evaluating oil and gas maturity:

[0044] The calculation of the peak area in an infrared spectrum depends on Beer-Lambert's law: A = εlc.

[0045] Where ε is the molar absorptivity, which directly depends on the properties of the substance and the wavelength of the incident light, and is a constant; l is the optical path length, which is the distance the infrared spectrum passes through the substance, i.e., the length of the light passing through the entire substance; and c is the molar concentration, which directly reflects the content of the substance in a single system.

[0046] Area A (CH) 3a ) and area A (CH 3s ) is used to represent the methyl group in υ 反对称 and υ 对称 The area of ​​absorption, area A (CH 2a ) and area A (CH 2s ) is used to represent the methine group in υ 反对称 and υ 对称 The area of ​​absorption.

[0047] The Fourier transform infrared principle formula is as follows:

[0048]

[0049] Where B(ν) is the final spectral intensity, which is a function of the wave number ν; I(δ) is the measured interferogram signal; I(∞) is the center burst intensity of the interferogram signal; ∫…dδ represents the integration over the optical path difference δ.

[0050] The original spectrum after Fourier transform needs to be further processed into a common absorption spectrum by calculating transmittance T or absorbance A. The methods for calculating transmittance and absorbance are as follows:

[0051]

[0052]

[0053] I represents the light intensity after passing through the sample; denoted as , where is the light intensity incident on the sample; T is the transmittance; and A is the absorbance.

[0054] The final spectrum is usually obtained in terms of wavenumber (cm). -1 Plot the spectrum with transmittance (T) or absorbance (A) on the x-axis and transmittance (T) or absorbance (A) on the y-axis. The peak area of ​​the infrared spectrum is generally calculated using absorbance (A). Based on the fact that methyl and methine groups are located at 2800 cm⁻¹... -1 up to 3000cm -1The region contains both vibrational and anti-vibrational peaks, and both exhibit good spectral signals within quartz minerals. Therefore, both types of data can be used to evaluate the maturity of hydrocarbon inclusions. Because antisymmetric spectral features are clearer and more pronounced, with relatively larger peak areas, they reflect more significant organic information within the hydrocarbon inclusions. Therefore, the antisymmetric peak area coefficient is set at 0.65, and the symmetric peak area coefficient at 0.35. Finally, the ratio of the infrared spectral peak areas of methylene and methyl is used as the first parameter for evaluating the maturity of hydrocarbon inclusions.

[0055]

[0056] Where R1 is the peak area ratio; α is the antisymmetric peak area coefficient, denoted as 0.65; A(CH 2a ) is a methine group in υ 反对称 Absorption area; A(CH) 3a ) is a methyl group in υ 反对称 The area of ​​absorption; β is the area coefficient of the symmetric peak; A(CH 2s ) is a methine group in υ 对称 Absorption area; A(CH) 3s ) is a methyl group in υ 对称 The area of ​​absorption.

[0057] Because of the hydroxyl group (OH) and the methyl group (CH) 3a Both peaks showed good signals in the infrared spectrum, so these two peak areas were chosen based on the hydroxyl (OH) and methyl (CH) groups. 3a The ratio of peak areas determines the second parameter for evaluating the maturity of hydrocarbon inclusions.

[0058]

[0059] R2 is a hydroxyl group (OH) and a methyl group (CH). 3a The ratio of A(OH) to A(OH) is the second parameter for evaluating the maturity of hydrocarbon inclusions; A(OH) is the peak area of ​​the hydroxyl group.

[0060] like Figure 6 As shown, the present invention selects 2800~2869cm. -1 Methionine (CH) 2s ) group in υ 对称 Absorption range, 2869~2883 cm -1 Methyl (CH) 3s ) group in υ 对称 Absorption range, 2883~2947 cm -1 Methionine (CH) 2a ) group in υ 反对称 Absorption range: 2947~3000cm -1 Methyl (CH)3a ) group in υ 反对称 The absorption range is determined by integrating the wavenumber ranges corresponding to the functional groups mentioned above, obtaining the peak areas of the corresponding functional groups, and then calculating the parameter R1. The peak range for the hydroxyl (OH) group is then selected as 3400-3600 cm⁻¹. -1 and 2947~3000cm -1 Methyl (CH) 3a ) group in υ 反对称 The absorption range is calculated by integrating the wavenumber ranges corresponding to these two functional groups to obtain the peak area of ​​the corresponding functional group, and then calculating the parameter R2.

[0061] This invention specifies that when parameter R1 is less than 1 and parameter R2 is less than 40, the oil and gas maturity within the inclusion is high maturity; when parameter R1 is greater than 1 and less than 2, and parameter R2 is greater than 40 and less than 67, the oil and gas maturity within the inclusion is medium maturity; and when parameter R1 is greater than 2 and parameter R2 is greater than 67, the oil and gas maturity within the inclusion is low maturity. For example, as shown in Table 1, the peak areas of the methyl antisymmetric peak, methine antisymmetric peak, methyl symmetric peak, and methine symmetric peak of hy-1 used in this experiment are 31.30, 41.64, 9.31, and 32.95, respectively, and its hydroxyl peak area is 102.21. Therefore, the parameter R1 of hy-1 sample is calculated to be 2.10, and the parameter R2 is 31.30, indicating that the oil and gas maturity inside its inclusions is classified as medium maturity. The peak areas of the methyl antisymmetric peak, methine antisymmetric peak, methyl symmetric peak, and methine symmetric peak of hy-7 are 20.41, 9.42, 1.44, and 1.49, respectively, and its hydroxyl peak area is 167.25. Therefore, the parameter R1 of hy-7 sample is calculated to be 0.66, and the parameter R2 is 20.41, indicating that the oil and gas maturity inside its inclusions is classified as high maturity.

[0062] Table 1. Maturity of Oil and Gas Inclusions in Different Samples

[0063]

[0064] In summary, Fourier transform infrared spectroscopy is an effective research method for studying oil and gas inclusions. This method utilizes the different characteristics of oil and gas under infrared spectra to show the relative content of hydrocarbon molecules and hydroxyl functional groups, and then uses the different peak characteristics of the corresponding spectra to determine the degree of oil and gas evolution. Finally, the maturity of oil and gas inclusions is comprehensively evaluated by calculating two parameters.

[0065] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the protection scope of the claims and specification of the present invention.

Claims

1. A method for evaluating the maturity of hydrocarbons inside inclusions using infrared spectroscopy, characterized in that, Includes the following steps: S1. Collect rock samples, prepare fluid inclusion thin sections, and determine the filling sequence of diagenetic minerals in the fluid inclusion thin sections; S2. By conducting microscopic observation and fluorescence microscopy on fluid inclusions, and by comprehensively analyzing and judging the petrographic characteristics of fluid inclusions, the petrographic characteristics of fluid inclusions are determined, including the size, shape, structure, occurrence, phase combination and phase volume ratio characteristics, internal material composition, and fluid inclusion stages. S3. Determine the minerals and types of inclusions based on the petrographic characteristics of the thin sections, as well as the occurrence and fluorescence characteristics of the inclusions; S4. Select hydrocarbon inclusions of different phases that meet the experimental conditions, and use single-polarized light microscope, fluorescence microscope, and Raman laser method combined with petrographic characteristics to determine the minerals hosting the hydrocarbon inclusions; at the same time, use isotope dating, X-ray diffraction, petrographic characteristics, organic element analysis, nuclear magnetic resonance, and inclusion fluid chemistry to determine the geological history of the inclusions and distinguish different phases; select hydrocarbon inclusion groups of different phases and maturity, and select hydrocarbon inclusions of the same phase within the hydrocarbon inclusion group based on the criteria of large number, large grain size, and single phase. S5. Using a Fourier transform infrared spectrometer, test experiments were conducted on hydrocarbon inclusions of different phases to obtain the infrared spectral characteristics of methyl, methine, and hydroxyl groups in hydrocarbon inclusions of different phases. Infrared spectra of hydrocarbon inclusions were plotted, and the ratio of the peak areas of methine and methyl infrared spectra and the ratio of the peak areas of hydroxyl and methyl were calculated to evaluate the oil and gas maturity of the inclusions.

2. The method for evaluating the maturity of hydrocarbons inside inclusions using infrared spectroscopy according to claim 1, characterized in that, Quartz is the preferred mineral for containing hydrocarbon inclusions.

3. The method for evaluating the maturity of hydrocarbons inside inclusions using infrared spectroscopy according to claim 1, characterized in that, In step S5, the infrared spectrum of the hydrocarbon inclusions is plotted using OPUS and Origin software.

4. The method for evaluating the maturity of hydrocarbons inside inclusions using infrared spectroscopy according to claim 1, characterized in that, In step S5, the formula for calculating the ratio R1 of the infrared spectral characteristic peak areas of methine and methyl is as follows: ； Where α is the antisymmetric peak area coefficient, denoted as 0.65; A(CH 2a ) is a methine group in υ 反对称 Absorption area; A(CH) 3a ) is a methyl group in υ 反对称 The area of ​​absorption; β is the area coefficient of the symmetric peak; A(CH 2s ) is a methine group in υ 对称 Absorption area; A(CH) 3s ) is a methyl group in υ 对称 The area of ​​absorption; The formula for calculating the ratio R2 of the peak areas of hydroxyl and methyl groups is as follows: ； Wherein, R2 is a hydroxyl group (OH) and a methyl group (CH). 3a The ratio of A(OH) to A(OH) is the peak area of ​​the hydroxyl group.

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