A method for judging the migration direction by the change characteristics of the content of fatty acid compounds in crude oil

Abstract

The present invention relates to the technical field of petroleum geological exploration, and specifically relates to a method for judging the migration direction by the content change characteristics of fatty acid compounds in crude oil. The method comprises the following steps: selecting crude oil samples generated from the same set of hydrocarbon source rocks; detecting the relative contents of fatty acid compounds with different carbon numbers in the crude oil samples; respectively taking X and Y carbon atoms as the critical values, and calculating the ratio A of the total relative content of fatty acids with more than X carbon atoms to the total relative content of fatty acids with less than or equal to X carbon atoms; calculating the ratio B of the total relative content of fatty acids with more than Y carbon atoms to the total relative content of fatty acids with less than or equal to Y carbon atoms; analyzing the correlation between the two groups of ratios A and B. If A and B are correlated, then according to the change rules of the A and B values of different samples, the petroleum migration direction is determined. The method of the present invention has the advantages of detecting fewer compound types, less time consumption, simple steps and high accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of petroleum geological exploration, and particularly relates to a method for judging the migration direction by the change characteristics of the content of fatty acid compounds in crude oil. Background Technique

[0002] The organic matter in the source rock forms petroleum after experiencing thermal evolution. The generated petroleum migrates along permeable sand bodies, faults, unconformities and other conduction channels under the action of power, and then accumulates in suitable traps to form oil and gas reservoirs.

[0003] The determination of the petroleum migration direction can be used to trace the migration path of petroleum, find the location of petroleum accumulation, which is beneficial to the discovery of new oil fields and has important significance in oil and gas exploration. Using geochemical means to determine the petroleum migration direction is the main way in the process of oil and gas exploration. Petroleum will leave traces during its migration in the conduction layer. At the same time, the migration process will change the geochemical characteristics of petroleum such as its physical properties and chemical composition.

[0004] Compounds with different molecular weights, different molecular polarities, and different stereochemical structures have different adsorption capacities during the process of passing through the conduction layer. During the migration process, the content of compounds with strong adsorption capacity will decrease with the increase of the migration distance. In addition to physical adsorption, the acidic substances in petroleum can also chemically react with the minerals in the conduction layer. The organic acids in petroleum have complex structures and various types. According to their structural characteristics, they are mainly divided into fatty acids, naphthenic acids, aromatic acids, etc. (Jiang Qigui et al., 2014). There are significant differences in the water solubility characteristics and decarboxylation ability of different types of organic acids, so there are also significant differences in their ability to dissolve minerals. Therefore, for petroleum derived from the same set of source rocks, the characteristics of its organic acids should change regularly during the migration process, and the migration direction of petroleum can be judged based on this.

[0005] Fourier transform ion cyclotron resonance mass spectrometry, also known as high-resolution mass spectrometry, has extremely high resolution and sensitivity compared with ordinary mass spectrometry. It is a mass spectrometry made on the basis of an ordinary cyclotron resonance analyzer using the Fourier transform ion cyclotron resonance principle, and can accurately identify the content of elements such as C, H, O, N, S and their combined compounds.

[0006] Chinese invention patent CN105987946B discloses a method for tracing the direction of oil migration, which includes the following steps: 1) Collect at least two oil samples of homologous oil from the same hydrocarbon source rock; 2) Sample analysis, perform Fourier transform ion cyclotron resonance mass spectrometry analysis; 3) Data processing, extract the carbon number, abundance and DBE structure information of N1S1 compounds, and obtain the abundance intensities of three types of N1S1 compounds with DBE = 14, DBE = 15, and DBE = 17; 4) Determine the direction of oil migration: According to the abundance intensities of the three types of N1S1 compounds with DBE = 14, DBE = 15, and DBE = 17, calculate the percentage of the abundance intensity of each type of compound respectively, and then perform graph analysis on the abundance percentages of the three types of compounds. The increasing direction of the abundance percentage of the N1S1 compound with DBE = 15 is the direction of oil migration. This method starts from the perspective of physical effects, analyzes the relative changes caused by the different adsorption abilities of different types of compounds to the conducting layer during the migration process, and then judges the migration direction.

[0007] Existing indicators for tracing the direction of oil migration mostly consider the changes in the compound composition caused by adsorption, steric hindrance and other effects during the oil migration process, and the steps are relatively complex. A simpler judgment method is needed. Summary of the Invention

[0008] The main object of the present invention is to provide a method for judging the migration direction by the change characteristics of the content of fatty acid compounds in crude oil. The present invention constructs a tracer parameter for the oil migration direction by analyzing the change in the compound composition caused by the chemical reaction between the oil and the minerals in the conducting layer during the oil migration process, that is, the change in the relative content of fatty acids with different carbon numbers, and determines the oil migration direction. The method of the present invention has fewer types of compounds to be detected, less time consumption, simple steps and high accuracy.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] The present invention provides a method for judging the migration direction by the change characteristics of the content of fatty acid compounds in crude oil, which includes the following steps: Select crude oil samples generated from the same set of hydrocarbon source rocks; Detect the relative content of fatty acid compounds with different carbon numbers in the crude oil samples; Respectively take X and Y carbon atom numbers as critical values, and calculate the ratio A of the total relative content of fatty acids with more than X carbon atom numbers to the total relative content of fatty acids with less than or equal to X carbon atom numbers; Calculate the ratio B of the total relative content of fatty acids with more than Y carbon atom numbers to the total relative content of fatty acids with less than or equal to Y carbon atom numbers; Analyze the correlation between the two groups of ratios A and B. If A and B are correlated, then determine the oil migration direction according to the change rules of the A and B values of different samples.

[0011] Furthermore, a Fourier transform ion cyclotron resonance mass spectrometer is used to detect the relative contents of fatty acid compounds with different carbon numbers in the crude oil sample. Among them, the storage time of ions in the hexapole ion source is 0.1 - 0.15 s.

[0012] Even further, all ions are focused by a quadrupole in a hexapole collision cell filled with argon, and the storage time is 1 - 3 s.

[0013] Furthermore, if A and B are not correlated, the critical value is re - determined until the two sets of ratios are correlated.

[0014] Furthermore, the direction in which both the values of A and B increase is the direction of oil migration.

[0015] Furthermore, carbon atom numbers 20 - 25 and 30 - 35 are respectively selected as the critical values.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] The method of the present invention starts from a chemical perspective. By constructing a tracer parameter for the oil migration direction based on the change in the compound composition, that is, the change in the relative content of fatty acids with different carbon numbers, which is caused by the chemical interaction with the minerals in the carrier bed during the oil migration process, the oil migration direction is determined. The method of the present invention involves fewer types of compounds. The method of the present invention only involves fatty acid compounds. The relative change of compounds during the migration process is clearer, and the data processing process is simpler. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a specific implementation flowchart of the present invention for judging the migration direction according to the change characteristics of the fatty acid compound content in the crude oil;

[0019] Figure 2 is a schematic diagram of the relative contents of compounds with different element compositions determined by a Fourier transform ion cyclotron resonance mass spectrometer;

[0020] Figure 3 is the relative content of different types of compounds in the representative samples determined by the present invention;

[0021] Figure 4 is the relative content of compounds with different DBE numbers in the O2 - type compounds of the typical samples of the present invention;

[0022] Figure 5 is the relative content of fatty acid compounds with different carbon numbers in the typical samples of the present invention;

[0023] Figure 6 is ∑(C 26+ ) / ∑(C 25- ) and ∑(C 31+) / ∑(C 30- )Correlation analysis diagram of two parameters;

[0024] Figure 7 It is a schematic diagram for judging the migration direction of crude oil in the research example area selected for the present invention. In the legend, parameter A and parameter B are ∑(C 26+ ) / ∑(C 25- ) and ∑(C 31+ ) / ∑(C 30- ), respectively. Specific implementation manners

[0025] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0026] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, and / or combinations thereof.

[0027] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0028] Example 1

[0029] As Figure 1 shown, the method for judging the migration direction by the change characteristics of the content of fatty acid compounds in crude oil includes the following steps:

[0030] Step 1: Collect crude oil samples from the same set of source rocks in the research area;

[0031] Step 2: Analyze the crude oil samples using a Fourier transform ion cyclotron resonance mass spectrometer. For each crude oil sample, take 10 mg and dissolve it in 1 mL of toluene to prepare a solution with a concentration of 10 mg / mL. Take 25 μL of this solution and dilute it to 1 mL with a toluene-methanol solution with a volume ratio of 1:1. Then add 15 μL of ammonium hydroxide with a concentration of 28% and mix well. Use an injection pump to inject the solution into the Fourier transform ion cyclotron resonance mass spectrometer through an ionization source for analysis. Conduct the test in negative ion mode. The ion formation polarization voltage is 4.0 kV, the inlet and outlet voltages of the capillary column are 4.5 kV and -320 V respectively, the storage time of ions in the hexapole ion source is 0.1 s, and all ions are focused by the quadrupole and gathered in a hexapole collision cell filled with argon, with a storage time of 1 s.

[0032] Step 3: Process and analyze the experimental data obtained in Step 2 to determine the relative contents of different types of compounds ( Figure 3 ), for O2-type compounds, determine the relative contents of compounds with different DBE numbers ( Figure 4 ), select DBE = 1-type compounds and determine the relative contents of compounds with different carbon numbers ( Figure 5 ).

[0033] Step 4: Respectively take the carbon number equal to 25 and the carbon number equal to 30 as the critical values, and calculate the ratios of ∑(C 26+ ) / ∑(C 25- ), ∑(C 31+ ) / ∑(C 30- ) in each sample.

[0034] Step 5: Draw a scatter plot and fit ∑(C 26+ ) / ∑(C 25- ) and ∑(C 31+ ) / ∑(C 30- ) to determine the correlation of the two parameters ( Figure 6 ). The two parameters have a good correlation, indicating that they can be used as effective migration tracer parameters.

[0035] According to the migration direction tracer parameters determined in Step 5, project the tracer parameters of different crude oil samples onto a plane graph. Since during the migration of petroleum, fatty acids with fewer carbon atoms are more likely to react with minerals in the conducting layer than fatty acids with larger carbon atoms, therefore, along the migration direction, ∑(C 26+ ) / ∑(C 25- ) and ∑(C 31+ ) / ∑(C 30-)As the two parameters gradually increase, based on the above principle, the migration direction of petroleum can be determined by the variation law of the parameters of different samples on the plane. In this example, the petroleum first migrates to SL1, and then successively migrates to SL2, SL3, and SL4. After that, it migrates along two directions. One direction is from SL4 to SL7, and the other direction is from SL4 to SL5, SL6, and SL8 successively. The result is as Figure 7 shown.

[0036] The above embodiments are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A method for judging the migration direction by the change characteristics of the content of fatty acid compounds in crude oil, characterized in that, Select crude oil samples generated from the same set of source rocks; detect the relative contents of fatty acid compounds with different carbon numbers in the crude oil samples; respectively use X and Y carbon atom numbers as critical values, and calculate the ratio A of the total relative content of fatty acids with more than X carbon atoms to the total relative content of fatty acids with less than or equal to X carbon atoms; calculate the ratio B of the total relative content of fatty acids with more than Y carbon atoms to the total relative content of fatty acids with less than or equal to Y carbon atoms; analyze the correlation between the two sets of ratios A and B. If A and B are correlated, then determine the petroleum migration direction according to the variation rules of the A and B values of different samples.

2. The method according to claim 1, characterized in that Use a Fourier transform ion cyclotron resonance mass spectrometer to detect the relative contents of fatty acid compounds with different carbon numbers in the crude oil samples. Among them, the storage time of ions in the hexapole ion source is 0.1 - 0.15 s.

3. The method according to claim 2, wherein All ions are focused by the quadrupole in the argon-filled hexapole collision cell, and the storage time is 1 - 3 s.

4. The method according to claim 1, characterized in that, If A and B are not correlated, then re-determine the critical values until the two sets of ratios are correlated.

5. The method according to claim 1, wherein The direction in which both the A and B values increase is the petroleum migration direction.

6. The method according to claim 1, wherein Respectively select carbon atom numbers 20 - 25 and 30 - 35 as the critical values.

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