Quantitative characterization method of heavy components of reservoir crude oil based on three-dimensional fluorescence decomposition spectrum

Abstract

The application discloses a kind of reservoir crude oil heavy component quantitative characterization method based on three-dimensional fluorescence decomposition spectrum, first using dichloromethane to rock powder sample extraction to extract liquid without fluorescence signal;Respectively prepare series concentration standard solution of colloid and asphaltene, collect three-dimensional fluorescence spectrum, establish respective standard curve;Then the three-dimensional fluorescence spectrum of extract liquid is collected, and the fluorescence intensity of colloid and asphaltene characteristic peak position is read;Again, the fluorescence intensity of characteristic peak position is substituted into standard curve to calculate the concentration of colloid and asphaltene in extract liquid, and is converted into the content in unit mass rock;Finally, the content of colloid, asphaltene and total heavy component is output.The application does not need SARA column chromatography separation, and can directly realize fast, accurate quantification of colloid and asphaltene in rock, with the advantages of short time consumption, small sample consumption, good repeatability, high quantitative precision, suitable for complex reservoir heavy component fast detection and evaluation of shale oil, tight sandstone oil and the like.

Description

Technical Field

[0001] This invention belongs to the field of reservoir fluid chemical analysis technology in oil and gas exploration and development, specifically relating to a quantitative characterization method for heavy components of crude oil in reservoirs based on three-dimensional fluorescence spectroscopy decomposition technology. Background Technology

[0002] In the evaluation of complex reservoirs such as shale oil and tight sandstone oil, accurately determining the content of heavy crude oil components (colloids and asphaltenes) in the rock is crucial for identifying "sweet spots" and assessing mobility. Current mainstream methods include: 1. Column chromatography (SARA separation): The extract is separated into four components: saturated hydrocarbons, aromatics, resins and asphaltenes, and weighed and quantified. SARA separation is time-consuming (2-3 days per sample), requires a large sample volume (>100mg), and the separation boundary between fractions depends on manual operation, resulting in poor repeatability. The results of different operators can vary by 10% to 15%, ultimately leading to large errors in the results.

[0003] 2. Conventional fluorescence spectroscopy (one-dimensional / synchronous fluorescence): It can only provide information on total fluorescence intensity or intensity at a specific wavelength. The fluorescence emission peaks of light and heavy components overlap significantly. One-dimensional fluorescence cannot distinguish components with different aromatic ring numbers / structures, and its quantitative ability for heavy components is poor. It lacks standard material calibration, and existing fluorescence analysis mostly outputs "relative intensity" rather than "absolute concentration", which cannot achieve accurate quantification. Summary of the Invention

[0004] This invention addresses the existing problems of how to directly quantify the content of resins and asphaltenes from extracts without SARA column separation, and how to establish a quantitative relationship between fluorescence signal and absolute concentration to achieve accurate quantification of heavy components. Its purpose is to provide a quantitative characterization method for heavy components of crude oil in reservoirs based on three-dimensional fluorescence spectroscopy decomposition technology.

[0005] This invention is achieved through the following technical solution: A quantitative characterization method for heavy components in reservoir crude oil based on three-dimensional fluorescence decomposition spectroscopy includes the following steps: S1. Use dichloromethane to perform multiple ultrasonic-assisted extractions on the rock powder sample until there is no fluorescent signal in the extract, and then collect the extract. Specifically, the following steps are included: S11. Add 20 mL of dichloromethane (CH2Cl2, chromatographic or analytical grade) to 2.0 g of sample. S12. After sealing, place in an ultrasonic cleaner and perform ultrasonic extraction for 20 minutes (ultrasonic power: 200W~300W, frequency: 40kHz). S13. After sonication, centrifuge at 4000 rpm for 10 min, take the supernatant as the extraction solution, and use the remainder for repeated extraction in step S14. S14. Add 20 mL of fresh dichloromethane to the remaining portion after separation and extraction, and repeat the ultrasonic extraction and centrifugation operations. S15. Repeat step S14 until the extract is detected by a fluorescence spectrophotometer. If there is no significant fluorescence signal (fluorescence intensity < 3 times the detection limit), the extraction is considered complete. S16. Combine all extracts and bring the volume up to 100 mL with dichloromethane or record the total volume.

[0006] S2. Prepare a series of standard solutions of resin and asphaltene at different concentrations, collect the characteristic three-dimensional fluorescence spectra of resin and asphaltene, and establish their respective standard curves; Specifically, the following steps are included: S21. Separate and purify resin and asphaltene standards from crude oil in the target reservoir according to industry standards (such as SY / T5119-2016); S22. Weigh out the resin and asphalt standard samples respectively, dissolve them in dichloromethane, and prepare a series of resin and asphalt standard solutions of different concentrations. The concentrations of the standard solutions are 0.1 mg / L, 0.5 mg / L, 1 mg / L, 5 mg / L, 10 mg / L, 20 mg / L, 50 mg / L, and 100 mg / L. S23. Use a fluorescence spectrophotometer (such as Horiba FluoroMax or Agilent Cary Eclipse) to acquire the optimal fluorescence emission spectrum and EEM; The parameters of the fluorescence spectrophotometer were set as follows: excitation wavelength (Ex) range: 240nm~600nm, step size 5nm; emission wavelength (Em) range: 250nm~700nm, step size 2nm; excitation / emission slit width: 5nm / 5nm; scan speed: 1500nm / min. S24. Collect the optimal emission spectrum and EEM for each concentration of the colloidal standard solution and the asphaltene standard solution; S25. Based on the fluorescence emission spectra, determine the characteristic emission wavelengths of the resin and asphaltene, read the fluorescence intensity F of the standard solutions of resin and asphaltene at various concentrations, and plot the concentration-fluorescence intensity standard curve: The characteristic excitation-emission peak positions of the colloidal material are Ex / Em = 320~380 / 400~500 nm; The characteristic excitation-emission peak positions of asphaltenes are Ex / Em = 280~350 / 420~600nm; The expression for the concentration-fluorescence intensity standard curve is:

[0007]

[0008] In the formula: The fluorescence intensity of the gel; The fluorescence intensity of the asphaltene; This represents the mass concentration of the colloidal standard solution, expressed in mg / L. This represents the mass concentration of the asphaltene standard solution, expressed in mg / L. The slope of the linear regression curve of the concentration-fluorescence intensity standard curve of the colloid; The slope of the linear regression of the standard curve of asphaltene concentration-fluorescence intensity; The linear correlation coefficient R of the concentration-fluorescence intensity standard curve 2 >0.99, ensuring quantitative accuracy.

[0009] S3. Collect the three-dimensional fluorescence spectrum of the extract obtained in step S2, combine Gaussian function decomposition to fit the composite fluorescence peak, and read the fluorescence intensity of the characteristic peak positions of the resin and asphaltenes. Specifically, the following steps are included: S31. Take the extract collected in step S1 and use the same acquisition parameters as in step S2 to obtain the three-dimensional fluorescence spectrum of the extract. If the concentration of the extract is too high and exceeds the range of the standard curve, it should be appropriately diluted with dichloromethane. S32. Using the characteristic three-dimensional fluorescence spectra of asphaltenes and gums obtained in step S2 as a reference, the three-dimensional fluorescence spectra of the extract obtained in step S31 are divided into regions to qualitatively distinguish gums and asphaltenes in the extract. S33. Obtain the fluorescence intensity F of the resin and asphaltenes at the characteristic peak positions corresponding to the three-dimensional fluorescence spectrum of the extract. 胶质1 and F 沥青质1 S34. Use Gaussian function to split and fit the composite peaks in the three-dimensional fluorescence spectrum of the extract, and obtain the characteristic peaks of resin and asphaltenes based on the best fitting index parameters. Specifically, the process involves: first, baseline correction and appropriate smoothing of the original spectrum; then, setting the initial number of peaks and initial parameters based on the peak shape characteristics and potential shoulder peaks; subsequently, continuously optimizing the parameters of each peak through nonlinear fitting to make the fitted curve as close as possible to the original experimental data; the peak separation effect is mainly judged based on the degree of agreement between the fitted curve and the original data, combined with R... 2 The quality of the fit is evaluated by residuals and related statistical indicators; S35. Based on S34, obtain the percentage of the corresponding area of ​​gum and asphaltenes in the three-dimensional fluorescence spectrum after fitting the extract, and use this as the internal standard. S36, the fluorescence intensity F of the resinous and asphaltene obtained in S33. 胶质1 and F 沥青质1 Multiply by the percentage of the corresponding areas of resins and asphaltenes in S35 to obtain the corrected fluorescence intensity F after peak fitting of resins and asphaltenes. 胶质2 and F 沥青质2 This is used for subsequent content calculations.

[0010] S4. Correct the fluorescence intensity F of the characteristic peak positions of the resins and asphaltenes obtained in step S36. 胶质2 and F 沥青质2 Substitute the standard curve established in step S2 into the solution to calculate the concentrations of resins and asphaltenes in the extract and convert them to the content per unit mass of rock; output the contents of resins, asphaltenes, and total heavy components.

[0011] The formula for converting the content to a unit mass of rock is:

[0012]

[0013] In the formula: This represents the mass concentration of colloids in the extract, expressed in mg / L. This represents the mass concentration of asphaltenes in the extract, expressed in mg / L. The volume of the extract obtained in step S1 is in liters (L). The mass of the rock sample is expressed in grams.

[0014] The beneficial effects of this invention are: This invention provides a method for qualitative identification and accurate quantitative analysis of heavy components (asphaltene and resin) in reservoir heavy crude oil using fluorescence spectral decomposition and fitting processing and asphaltene / resin standard curve quantification. Using the characteristic three-dimensional fluorescence emission spectra of asphaltene and resin as references, the superimposed fluorescence spectra of multiple components of crude oil are divided into regions to establish a three-dimensional fluorescence spectrum for qualitative differentiation of resin and asphaltene. By using Gaussian functions and other peak shapes to decompose and fit composite peaks, the superimposed fluorescence spectra of multiple components of crude oil are decomposed. Using the percentage of corresponding areas occupied by resin and asphaltene as internal standards, the intensity at the wavelengths corresponding to resin and asphaltene in the extracted crude oil fluorescence spectrum is decomposed to obtain fitted fluorescence intensity data for resin and asphaltene. By establishing standard curves for resin and asphaltene respectively, the absolute concentrations of resin and asphaltene can be calculated from the fluorescence peak intensity of the extract. Attached Figure Description

[0015] Figure 1 These are the fluorescence emission spectra of the resin and asphaltenes in this invention (the left side is the resin; the right side is the asphaltenes). Figure 2This is the standard curve diagram of the gelatinous substance in this invention; Figure 3 This is the asphaltene standard curve diagram in this invention; Figure 4 These are three-dimensional fluorescence spectra of the gum, asphaltenes, and extract in this invention (a is gum, b is asphaltenes, c is extract). Figure 5 This is the fluorescence decomposition spectrum of the extract in this invention.

[0016] For those skilled in the art, other related figures can be obtained from the above figures without any creative effort. Detailed Implementation

[0017] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0018] Example 1

[0019] A quantitative characterization method for heavy components in crude oil reservoirs based on three-dimensional fluorescence spectroscopy decomposition technology includes the following steps: S1. Sample and Extraction: Take 2.0035g of shale oil core powder, add 20mL of dichloromethane, sonicate for 20min (power 240W, frequency 40kHz), centrifuge and take the supernatant; repeat the extraction and centrifugation of the remaining part 3 times, combine the extracts, and make up to 100mL with dichloromethane. S2. Establishing the standard curve: Prepare colloidal standard solutions with concentrations of 0.5 mg / L, 1 mg / L, 5 mg / L, 10 mg / L, 20 mg / L and 50 mg / L; Prepare asphaltene standard solutions with concentrations of 0.2 mg / L, 0.5 mg / L, 1 mg / L, 2 mg / L, 5 mg / L and 10 mg / L; Determination of fluorescence emission spectra of resins and asphaltenes (e.g.) Figure 1 ); Fluorescence intensity of each concentration of colloidal standard solution was read at Ex / Em = 360 / 410 nm, and the linear fitting calibration curve was... R 2 =0.9902 (e.g.) Figure 2 ).

[0020] Fluorescence intensity of asphaltene standard solutions of various concentrations was read at Ex / Em = 310 / 448 nm, and the linear fitting calibration curve was... R 2 =0.9926 (e.g.) Figure 3 ).

[0021] S3, Sample Measurement: Characteristic peak identification: The difference in fluorescence red shift between resins and asphaltenes (resin blue-green, asphaltenes orange-red) is used to distinguish their spectra. Three-dimensional fluorescence spectra of resins, asphaltenes, and extract (e.g.) Figure 4 As shown), the fluorescence decomposition spectrum of the extract (e.g.) Figure 5 The decomposition results of the fluorescence decomposition spectrum (as shown in the figure) are shown in Table 1.

[0022] Table 1: Results of Fluorescence Decomposition Spectra

[0023] The measurement results are as follows: Substituting the fluorescence intensity of the extract at Ex / Em = 360 / 410 nm into the colloidal standard curve, we obtain C. 胶质 =9.82 mg / L Substituting the fluorescence intensity of the extract at Ex / Em = 310 / 448 nm into the asphaltene standard curve, we obtain C. 沥青质 =2.86mg / L S4. Calculation of cement and bituminous content in unit mass of rock: Gum content = (9.82 mg / L × 0.02 L) / 2.0035 g = 0.098 mg / g Asphalt content = (2.86 mg / L × 0.02 L) / 2.0035 g = 0.028 mg / g.

[0024] This invention employs a dual standard curve method for quantification, establishing separate standard curves for resins and asphalt to achieve independent quantification of the two heavy components, rather than a general "heavy component"; it utilizes characteristic peak identification, taking advantage of the difference in fluorescence redshift between resins and asphalt (resin is blue-green, asphalt is orange-red), to achieve spectral differentiation between the two; and it uses mixed spectrum decomposition and fitting for quantification, using the percentage of corresponding areas of resins and asphalt as internal standards to obtain fitted fluorescence intensity data for resins and asphalt, and then uses the dual standard curve method to calculate the resin concentration.

[0025] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for quantitative characterization of heavy components in reservoir crude oil based on three-dimensional fluorescence decomposition spectroscopy, characterized in that: Includes the following steps: S1. Extract rock powder samples with dichloromethane until the extract shows no fluorescence signal, and collect the extract. S2. Prepare a series of standard solutions of resin and asphalt at different concentrations, collect characteristic three-dimensional fluorescence spectra of resin and asphalt, determine the characteristic excitation-emission peak positions of resin and asphalt, and establish standard curves for resin and asphalt respectively. S3. Collect the three-dimensional fluorescence spectrum of the extract obtained in step S1, combine Gaussian function decomposition to fit the composite fluorescence peak, and read the fluorescence intensity of the characteristic peak positions of the resin and asphaltenes. S4. Substitute the fluorescence intensity of the characteristic peaks of the resin and asphaltene read in step S3 into the standard curve, calculate the concentration of resin and asphaltene in the sample extract, convert it into the content per unit mass of rock, and output the content of resin, asphaltene and total heavy components.

2. The method for quantitative characterization of heavy components in reservoir crude oil based on three-dimensional fluorescence decomposition spectroscopy according to claim 1, characterized in that: The extraction in step S1 is performed with ultrasound assistance; the extraction is repeated no less than 3 times.

3. The method for quantitative characterization of heavy components in reservoir crude oil based on three-dimensional fluorescence decomposition spectroscopy according to claim 1, characterized in that: The standard for no significant fluorescence signal in step S1 is that the fluorescence intensity of the extract is less than 3 times the detection limit.

4. The method for quantitative characterization of heavy components in reservoir crude oil based on three-dimensional fluorescence decomposition spectroscopy according to claim 1, characterized in that: In step S1, the ratio of dichloromethane to rock powder sample is (1~20) mL:1g.

5. The method for quantitative characterization of heavy components in reservoir crude oil based on three-dimensional fluorescence decomposition spectroscopy according to claim 1, characterized in that: The linear correlation coefficient R of the standard curve in step S2 2 >0.

99.

6. The method for quantitative characterization of heavy components in reservoir crude oil based on three-dimensional fluorescence decomposition spectroscopy according to claim 1, characterized in that: In step S2, the characteristic excitation-emission peak positions of the resin are 320nm~380nm / 400nm~500nm, and the characteristic excitation-emission peak positions of the asphaltene are 280nm~350nm / 420nm~600nm.

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