A core precise cleaning method and solvent formula based on crude oil component characteristics

Abstract

This invention relates to the field of core analysis technology in the exploration and development of oil and gas, and discloses a precise core cleaning method based on crude oil component characteristics, including the following steps: S1, obtaining the salt content information of the drilling core sample to be cleaned; if the salt content information is salt-containing, then proceed to S2 and S4; S2, obtaining the crude oil component characteristic information of the drilling core sample to be cleaned, and determining the ratio of toluene to methanol in the oil washing solvent according to the crude oil component characteristic information and a preset decision rule; using the oil washing solvent to extract and clean the core sample; S4, monitoring the cleaning process, and determining that cleaning is complete when the extraction solvent reaches a colorless, transparent, and stable state and the fluorescence detection result of the core sample is no fluorescence or weak fluorescence; and the solvent formulation for implementing this method. This invention optimizes the organic solvent formulation for oil and salt washing for different types of rock samples, further improving core cleaning efficiency.

Description

Technical Field

[0001] This invention relates to the field of core analysis technology in the process of oil and gas exploration and development, specifically to a precise core cleaning method and solvent formulation based on crude oil component characteristics. Background Technology

[0002] To obtain various rock parameters, such as porosity and permeability, it is necessary to first remove oil and salt from the inside of the core sample to ensure the accuracy of the parameters and reduce damage to the core measurement equipment.

[0003] Currently, the mainstream core cleaning methods in the industry are solvent extraction and carbon dioxide pressure cleaning. Among them, solvent extraction is more traditional and has advantages such as simple core cleaning equipment, convenient operation, non-destructive to core samples, and high cleaning quality. Figure 1 However, the industry currently mainly uses chloroform, benzene, or toluene as single solvents. This method is usually time-consuming, with an average oil washing cycle of 1 to 2 weeks, which restricts the overall timeliness of core analysis.

[0004] The carbon dioxide pressurized cleaning method involves dissolving carbon dioxide in organic solvents such as toluene and injecting it under pressure into the core sample. As the pressure is released, the carbon dioxide expands, carrying the organic solvent and crude oil out of the core. However, this method operates at high pressures, up to 7 MPa. For weakly consolidated rock samples, such as loose sandstone, this can easily cause significant structural damage, thus affecting the accuracy of subsequent core test results.

[0005] It is evident that in the process of cleaning core oil, it is difficult to balance cleaning efficiency with low destructive force. There is an urgent need for a cleaning method that can improve the efficiency of core cleaning and can be applied to different types of rock samples. Summary of the Invention

[0006] The purpose of this invention is to provide a core cleaning method and solvent formulation based on the characteristics of crude oil components, so as to solve the technical problem that high cleaning efficiency and low cleaning destructive force cannot be achieved at the same time in the prior art.

[0007] To solve the above-mentioned technical problems, the present invention specifically provides the following technical solution:

[0008] This invention provides a method for precise core cleaning based on crude oil composition characteristics, comprising the following steps:

[0009] S1. Obtain the salt content information of the drill core sample to be cleaned;

[0010] If the salt content information indicates salt content, then execute S2 and S4;

[0011] If the salt content information is salt-free, then execute S3 and S4;

[0012] S2. Obtain the crude oil component characteristic information of the drilling core sample to be cleaned, and based on the crude oil component characteristic information, determine the ratio of toluene to methanol in the washing solvent according to the preset decision rules.

[0013] The core sample is extracted and cleaned using the aforementioned washing oil solvent, which can specifically clean the crude oil components of the core sample.

[0014] S3. Use toluene or benzene to extract and clean the core sample;

[0015] S4. Monitor the cleaning process. When the extraction solvent reaches a colorless, transparent, and stable state, and the fluorescence detection result of the core sample is no fluorescence or weak fluorescence, the cleaning is considered complete.

[0016] As a preferred embodiment of the present invention, in the salinity information, the standard for salinity is that the mineralization of the formation water in the sample is ≥10000 mg / L.

[0017] In a preferred embodiment of the present invention, in step S2, the crude oil component characteristics include at least asphaltenes, gums, and waxes.

[0018] In a preferred embodiment of the present invention, in step S2, the decision rule is as follows: in the wash oil solvent, the proportion of toluene increases with the increase of the content of asphaltenes, gums and waxes in the crude oil components, based on the volume ratio.

[0019] In a preferred embodiment of the present invention, in step S2, the decision rule is:

[0020] a) When the crude oil does not contain asphaltenes, gums, or waxes, the ratio of toluene to methanol in the wash oil solvent is 1:1;

[0021] b) When the crude oil contains any one of asphaltenes, gums, or waxes, the ratio of toluene to methanol in the wash oil solvent is 2:1.

[0022] c) When the crude oil contains any two of the following: asphaltenes, gums, and waxes, the ratio of toluene to methanol in the wash oil solvent is 3:1.

[0023] d) When crude oil contains asphaltenes, gums and waxes, the ratio of toluene to methanol in the wash oil solvent is 4:1.

[0024] As a preferred embodiment of the present invention, in the decision rule, the standard for gum content is gum content ≥8% in crude oil, the standard for asphalt content is asphalt content ≥3% in crude oil, and the standard for wax content is wax content ≥5% in crude oil.

[0025] As a preferred embodiment of the present invention, in step S4, the criterion for determining the colorless, transparent, and stable state is: after heating is stopped, the core sample is soaked in the washing oil solvent at room temperature for at least 8 hours, and the solvent system remains colorless, transparent, turbid, and free of precipitates.

[0026] In a preferred embodiment of the present invention, in step S2, the method for obtaining the crude oil component characteristic information includes:

[0027] The core samples were analyzed using gas chromatography or liquid chromatography.

[0028] This invention provides a solvent formulation, wherein the washing solvent is a mixture of toluene and methanol in a specific ratio; the specific ratio is determined based on the crude oil composition characteristics of the core sample to be washed, according to a decision rule.

[0029] The decision-making rule is as follows:

[0030] a) When the crude oil does not contain asphaltenes, gums, or waxes, the ratio of toluene to methanol in the wash oil solvent is 1:1;

[0031] b) When the crude oil contains any one of asphaltenes, gums, or waxes, the ratio of toluene to methanol in the wash oil solvent is 2:1.

[0032] c) When the crude oil contains any two of the following: asphaltenes, gums, and waxes, the ratio of toluene to methanol in the wash oil solvent is 3:1.

[0033] d) When crude oil contains asphaltenes, gums and waxes, the ratio of toluene to methanol in the wash oil solvent is 4:1.

[0034] As a preferred embodiment of the present invention, the ratio of toluene to methanol is 1:1, 2:1, 3:1 or 4:1.

[0035] Compared with the prior art, the present invention has the following advantages:

[0036] This invention optimizes pure solvents by adjusting the organic solvent formulations for washing oil and salt based on the salt content characteristics of rock samples and crude oil composition. Without maintaining the "destructive effect", the traditional two-week washing time is reduced to three to five days, improving efficiency by about 60% to 85%. This quantitatively and significantly improves the cleaning efficiency of rock cores, and the fluorescence of the liquid in the core chamber is weaker, indicating more thorough cleaning and better cleaning effect.

[0037] This invention provides a wash solvent containing both toluene and methanol, which can specifically clean the crude oil components in rocks, quantitatively and significantly improving the cleaning efficiency of rock cores. Attached Figure Description

[0038] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0039] Figure 1 A simplified diagram of the instrument structure for the solvent extraction method is provided for this invention;

[0040] Figure 2 This invention provides a schematic flowchart of a precise core cleaning method based on crude oil composition characteristics. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] After comparing the cleaning results of hundreds of oil-bearing cores, such as Figure 2 As shown, this invention provides a method for precise core cleaning based on crude oil component characteristics and a solvent formulation, comprising the following steps:

[0043] S1. Obtain the salt content information of the drill core sample to be cleaned;

[0044] If the salt information indicates salt content, then execute S2 and S4;

[0045] If the information indicates that there is no salt, then execute S3 and S4;

[0046] S2. Obtain the crude oil component characteristic information of the drill core sample to be cleaned, and determine the ratio of toluene to methanol in the washing solvent based on the crude oil component characteristic information and according to the preset decision rules.

[0047] Core samples were extracted and cleaned using a washing oil solvent;

[0048] S3. Use toluene or benzene to extract and clean the core sample;

[0049] S4. Monitor the cleaning process. When the extraction solvent reaches a colorless, transparent, and stable state, and the fluorescence detection result of the core sample is no fluorescence or weak fluorescence, the cleaning is considered complete.

[0050] The extraction solvent is either a wash oil solvent or toluene (benzene) used after cleaning the drill core sample.

[0051] Because core samples are located underground for extended periods, they are highly susceptible to salinity due to the influence of groundwater; therefore, salinity preparation is typically required. In this method, the standards for salinity are: formation water salinity ≥ 10000 mg / L; for resin content, the standard is resin content in crude oil ≥ 8%; for asphaltene content, the standard is asphaltene content in crude oil ≥ 3%; and for wax content, the standard is wax content in the original material ≥ 5%.

[0052] This method can optimize the organic solvent formulation for washing oil and salt for different types of rock samples, further improving the core cleaning efficiency. This helps to obtain various core parameters more quickly, providing strong support for the calculation of resource quantities in new oilfields and the formulation of production improvement measures for old oilfields.

[0053] Furthermore, in step S2, the crude oil component characteristics include at least asphaltenes, gums, and waxes.

[0054] The crude oil components in the sample were mainly divided into four categories:

[0055] (1) Conventional light and medium hydrocarbons: The main components of light crude oil are mainly alkanes and cycloalkanes with fewer than 17 carbon atoms;

[0056] (2) Asphaltenes: These are high-molecular-weight non-hydrocarbon polymers in crude oil that are insoluble in n-pentane / n-heptane but soluble in strong polar organic solvents such as toluene, chloroform, and carbon tetrachloride. They are polycyclic aromatic hydrocarbon condensates containing S, N, and O heteroatoms and enriched with heavy metals (Ni, V, Fe). They have extremely high molecular weights (3,000~100,000) and belong to the high-molecular-weight portion of the heavy polar components in crude oil.

[0057] (3) Gum: It is a weakly polar non-hydrocarbon polymer in crude oil that is soluble in organic solvents such as petroleum ether (60~90℃), toluene, and chloroform, but insoluble in n-pentane / n-heptane. It is a polycyclic aromatic hydrocarbon derivative containing S, N, and O heteroatoms, with a medium molecular weight (500~3000). It belongs to the low molecular weight part of the heavy polar components in crude oil.

[0058] (4) Wax: A mixture of all solid n-alkanes and small amounts of isoalkanes and cycloalkanes in crude oil at room temperature, with C as the core. 17 High carbon number n-alkanes (C1 and above) 17 ~C 35 Mainly C, with a small amount of C 35 The above-mentioned high molecular weight waxes are heavy saturated hydrocarbons in crude oil hydrocarbon components, and contain no heteroatoms (only C and H).

[0059] In step S2, the preferred decision rule is: in the wash oil solvent, the proportion of toluene increases with the increase of the content of asphaltenes, gums and waxes in the crude oil components, based on volume ratio.

[0060] Based on the oil content of the core samples, this invention optimizes the pure solvent and the mixing ratio of toluene and methanol, achieving a better core sample cleaning effect than previous organic solvent cleaning methods, and resulting in weaker fluorescence display of the liquid in the core chamber.

[0061] Specifically, the decision-making rule is as follows:

[0062] a) When the crude oil does not contain asphaltenes, gums, or waxes, the ratio of toluene to methanol in the wash oil solvent is 1:1;

[0063] b) When the crude oil contains any one of asphaltenes, gums, or waxes, the ratio of toluene to methanol in the wash oil solvent is 2:1.

[0064] c) When the crude oil contains any two of the following: asphaltenes, gums, and waxes, the ratio of toluene to methanol in the wash oil solvent is 3:1.

[0065] d) When crude oil contains asphaltenes, gums and waxes, the ratio of toluene to methanol in the wash oil solvent is 4:1.

[0066] The present invention further provides an embodiment, which is implemented according to the following steps:

[0067] (1) If the core sample does not contain salt, methanol is not required in the solvent; toluene is sufficient.

[0068] (2) If the crude oil in the core does not contain asphalt, a mixture of toluene and methanol in a ratio of 1:1 is prepared as the wash oil solvent. If it contains asphalt, the ratio of toluene and methanol in the solvent is 2:1.

[0069] (3) If the crude oil in the core does not contain gum, maintain the previous toluene to methanol ratio; otherwise, increase the toluene ratio by 1 part. If the crude oil contains asphaltenes and gum, the toluene to methanol ratio in the solvent is 3:1; if the crude oil does not contain asphaltenes but contains gum, the toluene to methanol ratio in the solvent is 2:1; if the crude oil contains neither asphaltenes nor gum, the toluene to methanol ratio in the solvent is 1:1.

[0070] (4) If the crude oil composition of the core does not contain wax, then maintain the previous toluene to methanol ratio; otherwise, increase the toluene ratio by 1 part. If the crude oil contains asphaltenes, gums, and resins, the ratio of toluene to methanol in the solvent is 4:1; if the crude oil does not contain asphaltenes but contains gums and waxes, the ratio of toluene to methanol in the solvent is 3:1; if the crude oil does not contain asphaltenes or gums but contains waxes, the ratio of toluene to methanol in the solvent is 2:1; if the crude oil does not contain asphaltenes, gums, or waxes, the ratio of toluene to methanol in the solvent is 1:1.

[0071] (5) After preparing the solvent ratio of toluene and methanol according to the crude oil composition, core cleaning is carried out.

[0072] (6) Confirmation of cleaning results:

[0073] The heating process can be stopped when the solvent used in the core chamber becomes colorless and completely transparent. After soaking for eight hours or longer, the liquid in the core chamber should be carefully observed. If the liquid remains colorless and transparent at this time, without any turbidity, precipitation, or discoloration, the subsequent fluorescence identification steps can be performed. A weak fluorescence test result showing no fluorescence or weak fluorescence indicates that organic contaminants on the core surface and in the pores have been effectively removed, and the core sample can be considered clean. A weak fluorescence test result showing medium or strong fluorescence requires repeated cleaning until no fluorescence or weak fluorescence is achieved.

[0074] The proposed rapid fluorescence detection method mentioned in this invention is mainly used for qualitative determination of oil content and can quickly confirm whether the core cleaning quality meets the standards.

[0075] Cleaning equipment such as Figure 1 As shown.

[0076] This embodiment specifies in detail the detection sequence of crude oil component characteristics.

[0077] Compared to solvents such as benzene, toluene, and chloroform used in traditional extraction methods, the toluene / methanol mixed solvent used in this method can reduce the traditional oil washing time of 2 weeks to 3-5 days, significantly improving the core cleaning efficiency.

[0078] In the washing oil solvent, the ratio of toluene to methanol is selected from any of the following: 1:1, 2:1, 3:1 or 4:1.

[0079] In step S4, the criteria for determining the colorless, transparent, and stable state are: after heating is stopped, the core sample is soaked in the washing oil solvent at room temperature for at least 8 hours, and the solvent system remains colorless, transparent, turbid, and free of precipitates.

[0080] In step S2, the crude oil component characteristic information can be obtained by either phase chromatography or liquid chromatography.

[0081] Gas chromatography can obtain the hydrocarbon group composition of crude oil (such as n-alkanes, isoalkanes, cycloalkanes, aromatics, etc.), thus enabling detailed classification of crude oil components. Liquid chromatography can separate crude oil into four components (saturated hydrocarbons, aromatics, gums, and asphaltenes), allowing for the classification of crude oil components into major categories.

[0082] In practice, "determining the composition of crude oil" requires prior liquid chromatography analysis of the crude oil in the reservoir. The data can be from previously completed data from adjacent wells or from newly obtained data from coring wells.

[0083] The following are examples:

[0084] Example 1:

[0085] Extractor selection: Use a Soxhlet extractor with a volume of 1000 mL, wherein the outer diameter of the extraction tube is about 68 mm and the length of the extraction Soxhlet tube is about 230 mm.

[0086] 1. A plunger core sample from an oilfield was cut into two equal pieces. Analysis of the crude oil composition in this section revealed a formation water salinity of 13635.2 mg / L, an asphaltene content of 5.25%, a resin content of 20.33%, and a wax content of 4.3%.

[0087] 2. Based on the judgment criteria, it was determined to be an oil-bearing core containing salt, bituminous material, and resin. A solvent with a toluene and methanol ratio of 3:1 was prepared. The solvent and one of the samples were placed in the extractor, with the amount of solvent enough to submerge the sample. The mixture was heated to boiling (or kept at 130-150℃). After boiling, the solvent will automatically circulate and extract the sample.

[0088] 3. When the solvent used in the core chamber becomes colorless and completely transparent, the heating operation can be stopped. The fluorescence detection result is no fluorescence, and the cleaning is complete.

[0089] Comparative Example 1:

[0090] Another sample from Example 1 above was selected. The same instruments and operations were used, except that the oil was first cleaned with toluene and then the salt was cleaned with methanol.

[0091] The cleaning times are compared below, and the results are shown in Table 1:

[0092] Table 1

[0093]

[0094] Example 2:

[0095] Extractor selection: Use a Soxhlet extractor with a volume of 1000 mL, wherein the outer diameter of the extraction tube is about 68 mm and the length of the extraction Soxhlet tube is about 230 mm.

[0096] 1. A plunger core sample from an oilfield was cut into two equal pieces. Analysis of the crude oil composition in this section revealed a formation water salinity of 17285 mg / L, an asphaltene content of 1.18%, a resin content of 1.95%, and a wax content of 8.9%.

[0097] 2. Based on the judgment criteria, it was determined to be an oil-bearing core containing salt and wax. A solvent with a toluene and methanol ratio of 2:1 was prepared. The solvent and one of the samples were placed in the extractor. The amount of solvent was enough to submerge the sample. The sample was heated to boiling (or kept at 130-150℃). After the solvent boiled, it would automatically circulate and extract the sample.

[0098] 3. When the solvent used in the core chamber becomes colorless and completely transparent, the heating operation can be stopped. The fluorescence detection result is no fluorescence, and the cleaning is complete.

[0099] Comparative Example 2:

[0100] Another sample from Example 2 above was selected. The same instruments and operations were used, except that the oil was first cleaned with toluene and then the salt was cleaned with methanol.

[0101] The cleaning times are compared below, and the results are shown in Table 2:

[0102] Table 2

[0103]

[0104] Example 3:

[0105] Following the method described in Example 1, 10 plunger core samples from a certain oilfield were cut into two pieces on average and divided into two batches for comparative analysis using conventional and this method respectively.

[0106] Analysis of the crude oil composition of this layer revealed the following information on the oil and salt content of the 10 samples (see Table 3, which compares the oil and salt content and cleaning efficiency of the 10 samples). The core samples were identified as oil-bearing cores containing salt, asphaltene, and resin. A solvent of toluene and methanol in a ratio of 3:1 was prepared.

[0107] Comparative Example 3 involved washing the oil with toluene only, followed by washing the salt with methanol.

[0108] Table 3

[0109]

[0110] Results Analysis: A comparison of Example 1 and Comparative Example 1 shows that, for the same piece of rock cuttings, the core cleaning time of this method was reduced by 60%. A comparison of Example 2 and Comparative Example 2 shows that, for the same piece of rock cuttings, the core cleaning time of this method was reduced by 43.75%. In Example 3, numerous experiments were conducted, demonstrating that this method is adaptable to various types of rock cuttings, and that the cleaning efficiency is significantly improved in all cases.

[0111] The present invention further discloses a core cleaning solvent for implementing the above method. The core cleaning solvent is composed of toluene and methanol mixed in a specific ratio. The specific ratio is determined based on the crude oil composition characteristics of the core to be cleaned, according to the above decision rules.

[0112] The selection and ratio of the two reagents in the core cleaning oil solvent were determined through extensive verification through numerous examples.

[0113] Based on the above method, a precision core cleaning system can also be implemented, including:

[0114] The information input module is used to receive or input crude oil component characteristic information from core samples;

[0115] The intelligent decision-making module stores the aforementioned preset decision rules, which are used to automatically calculate and output the recommended ratio of toluene to methanol based on the characteristics of crude oil components.

[0116] The solvent preparation and delivery module is used to automatically prepare the cleaning solvent according to the recommended ratio and deliver it to the cleaning device.

[0117] The cleaning execution module includes a solvent extraction device for cleaning core samples using a washing oil solvent.

[0118] Based on the above method, a computer-readable storage medium storing a computer program can also be implemented. When the program is executed by a processor, it implements the above decision rules to output a recommended ratio of toluene to methanol based on the input crude oil component characteristic information.

[0119] The above embodiments are merely exemplary embodiments of this application and are not intended to limit this application. The scope of protection of this application is defined by the claims. Those skilled in the art can make various modifications or equivalent substitutions to this application within its substance and scope of protection, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of this application.

Claims

1. A method for precise core cleaning based on crude oil composition characteristics, characterized in that, The steps include the following: S1. Obtain the salt content information of the drill core sample to be cleaned; If the salt content information indicates salt content, then execute S2 and S4; If the salt content information is salt-free, then execute S3 and S4; S2. Obtain the crude oil component characteristic information of the drilling core sample to be cleaned, and based on the crude oil component characteristic information, determine the ratio of toluene to methanol in the washing solvent according to the preset decision rules. The core sample is extracted and cleaned using the aforementioned washing solvent, which can specifically clean the crude oil components of the core sample. S3. Use toluene or benzene to extract and clean the core sample; S4. Monitor the cleaning process. When the extraction solvent reaches a colorless, transparent, and stable state, and the fluorescence detection result of the core sample is no fluorescence or weak fluorescence, the cleaning is considered complete.

2. The method for precise core cleaning based on crude oil composition characteristics according to claim 1, characterized in that, In the salinity information, the standard for salinity is that the mineralization of the formation water in the sample is ≥10000 mg / L.

3. The method for precise core cleaning based on crude oil composition characteristics according to claim 1, characterized in that, In step S2, the crude oil component characteristics include at least asphaltenes, gums, and waxes.

4. The method for precise core cleaning based on crude oil composition characteristics according to claim 3, characterized in that, In step S2, the decision rule is: in the wash oil solvent, the proportion of toluene increases by volume as the content of asphaltenes, gums and waxes in the crude oil components increases.

5. The method for precise core cleaning based on crude oil composition characteristics according to claim 4, characterized in that, In step S2, the decision rule is: a) When the crude oil does not contain asphaltenes, gums, or waxes, the ratio of toluene to methanol in the wash oil solvent is 1:1; b) When the crude oil contains any one of asphaltenes, gums, or waxes, the ratio of toluene to methanol in the wash oil solvent is 2:

1. c) When the crude oil contains any two of the following: asphaltenes, gums, and waxes, the ratio of toluene to methanol in the wash oil solvent is 3:

1. d) When crude oil contains asphaltenes, gums and waxes, the ratio of toluene to methanol in the wash oil solvent is 4:

1.

6. The method for precise core cleaning based on crude oil composition characteristics according to claim 4, characterized in that, In the decision-making rules, the standard for gum content is gum content ≥8% in crude oil, the standard for asphalt content is asphalt content ≥3% in crude oil, and the standard for wax content is wax content ≥5% in crude oil.

7. The method for precise core cleaning based on crude oil composition characteristics according to claim 4, characterized in that, In step S4, the criterion for determining the colorless, transparent, and stable state is: after heating is stopped, the core sample is soaked in the washing oil solvent at room temperature for at least 8 hours, and the solvent system remains colorless, transparent, free of turbidity, and free of precipitates.

8. The method for precise core cleaning based on crude oil composition characteristics according to claim 4, characterized in that, In step S2, the method for obtaining the crude oil component characteristic information includes: The core samples were analyzed using gas chromatography or liquid chromatography.

9. A core cleaning solvent for implementing the method according to any one of claims 1-7, characterized in that, The washing oil solvent is a mixture of toluene and methanol in a specific ratio; The specific ratio is determined based on the crude oil composition characteristics of the core sample to be cleaned, according to the decision rule described in claim 3 or 4.

10. The washing oil solvent according to claim 9, characterized in that, The ratio of toluene to methanol is 1:1, 2:1, 3:1 or 4:1.

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