EA042230B1 - METHOD FOR QUANTITATIVE DETERMINATION OF ORGANIC ACID CONTENT IN CRUDE OIL - Google Patents

Description

The field of technology to which the invention belongs

The present invention relates to a method for the quantitative determination of organic acids in crude oil.

State of the art

The total acid number (TAN) is a measure of acidity in crude oil and is defined as the amount of potassium hydroxide, expressed in milligrams, that is required to neutralize the acids contained in 1 g of oil. Although the OCT value provides information about the acidity of the crude oil, this value does not provide information about the types of organic acids (usually carboxylic acids) contained in the crude oil.

Therefore, it would be preferable to develop a method that quantifies the content of representatives of types or classes of organic acids in samples of different crude oils and obtains the chemical characterization of the crude oil. Thus, the content of representatives of types and classes of organic acids in crude oil produced from different fields may be different. It is also believed that the contents of representatives of types and classes of organic acids in crude oil extracted from the field may change over time. In addition, the levels of representatives of types and classes of organic acids in crude oil can be different if advanced oil recovery (EAP) is used to extract crude oil from the field, for example, by low salinity water flooding. Accordingly, changing the content of representatives of different types and classes of organic acids in crude oil extracted from the field can provide information about the effectiveness of the DCM methods.

Brief summary of the invention

The first object of the present invention is a method for analyzing crude oil, designed to determine the amount of at least one organic acid contained in crude oil, including the extraction of organic acids from a sample containing a known amount of crude oil, obtaining an extract containing organic acids, and determining the amount extracted organic acids;

dissolving the extract in a given volume of at least one polar solvent to obtain a solution of the extracted organic acids in the polar solvent(s);

introducing a sample containing a predetermined volume of the extracted organic acid solution into an instrument including a reverse phase liquid chromatography (LC) column and a mass spectrometer (MS) (hereinafter: LC-MS instrument) arranged in series, where the column for The reverse phase LC contains a hydrophobic sorbent and the mobile phase for the LC column contains a polar organic solvent;

separation of organic acids in the LC column of the LC/MS instrument and continuous feeding of the separated organic acids leaving the LC column to the MS of the LC/MS instrument to ionize the organic acids and obtain a chromatogram with mass spectroscopic data over time for ionized organic acids;

determining the area under at least one peak in the isolated ion chromatogram obtained from the mass spectroscopic data assigned to at least one organic acid;

determining the amount of organic acid in the sample solution of the extracted organic acids by comparing the area of the peak(s) assigned to the organic acid(s) with the area under the peak in the isolated ion chromatogram assigned to a given amount of the standard organic acid; and extrapolating from the amount of organic acid in the sample solution of extracted organic acids to obtain the total amount of organic acid in the extract.

Other features and advantages of the present invention will become apparent from the following description of the preferred embodiments of the present invention, which are presented by way of example only, with reference to the accompanying drawings.

Brief description of the drawings

In FIG. 1 is a chromatogram for a solution of organic acids extracted from a crude oil sample, showing the relative content (intensities) of ionized organic acids (mass spectroscopic data) over time;

fig. 2 is derived from the results shown in FIG. 1 and is a mass spectrum showing the relative abundance of all ions having m/z values (where m is mass and z is charge) ranging from 150 to 1100, during the time period during which the organic acids eluted from the LC column included in the LC-MS instrument;

in fig. 3 is an isolated ion chromatogram (IIC) for a solution of three standard carboxylic acids (dodecanoic acid, hexadecanoic acid and octadecanoic acid) in methanol and IIC for a solution of an additional standard carboxylic acid (cyclohexylpentanoic acid) in methanol. Dodecanoic acid, hexadecanoic acid, and octadecanoic acid all have a double bond equivalent number (EDC) value of 1, while cyclohexylpentanoic acid has an ED value of 2 (EDC is defined below);

in fig. 4 shows relative abundances (calibration curves) (area under the peaks in the isolated ion chromatograms shown in FIG. 3) versus concentration, expressed in parts per million (ppm) for four standard carboxylic acids (dodecanoic acid, hexadecanoic acid, octadecanoic acid and cyclohexylpentanoic acid);

in fig. 5 shows the areas under the peaks for individual organic acids belonging to the group of compounds having EKDS values of 1 in the m/z range from 0 to 800. Three samples of crude oil were extracted and three different extracts were obtained, with analysis of the solution of each extract using liquid chromatography - mass spectrometry was repeated three times. The results shown in FIG. 5 show that the method of the present invention has good reproducibility.

Definitions.

In the description below, the following terms have the following meanings:

Organic acids means compounds contained in a crude oil sample that are Bronsted acids (donors of hydrogen atoms), including carboxylic acids (particularly fatty acids and naphthenic acids) and organic sulfonic acids.

Ionized organic acids means organic acids that have been ionized in the mass spectrometer included in the LC-MS instrument with minimal fragmentation of the ionized compounds.

The extract includes organic acids that are selectively isolated from the crude oil sample.

Chromatogram means a representation of data obtained by mass spectrometry, where the x-axis indicates the time and the y-axis indicates the total signal intensity of the ion. This data representation can be used for mass spectrometry data obtained using a liquid chromatography-mass spectrometry (LC-MS) instrument. Liquid chromatography separates mixtures of organic compounds, while mass spectrometry determines formulas for individual organic molecules. Accordingly, the x-axis indicates the retention time in the LC column included in the LC-MS instrument. In the case of an isolated ion chromatogram (IIC), one or more m/z values relating to one or more molecules of interest isolated from the full set of data presented in the chromatogram.

The equivalent number of double bonds (ECDS) is a means of expressing the degree of unsaturation of an organic compound and is described in more detail below.

A carboxylic acid standard solution is a solution containing a standard carboxylic acid of known chemical composition at a precisely known concentration obtained by dissolving a carboxylic acid of known mass in a given volume of a polar solvent.

A standard carboxylic acid is a carboxylic acid of known chemical composition that is used to make a standard solution.

Recovery acid means an organic acid, usually a carboxylic acid, which is added to an oil sample in a known amount to determine the yield (also known as recovery) of the acids produced in the extraction step of the method of the present invention.

Acid recovery means the ratio of the amount of acid to determine the degree of extraction contained in the extract to the amount of acid to determine the degree of recovery added to the oil sample.

m/z means the ratio of mass (m) to charge (z) for ionized compounds for which the spectrum is obtained.

High Resolution Mass Spectrometry (HRMS) refers to a mass spectrometry analysis technique that produces a spectrum of mass-to-charge ratio (m/z) values of ionizable compounds, determined to four decimal places.

Liquid chromatography - mass spectrometry means a method of analysis using mass spectrometry using an instrument that includes a liquid chromatography (LC) column located before the mass spectrometer (MS), and where in the LC column, the components contained in the sample are separated based on a certain parameter ( e.g. polarity or size) before introducing the separated components into the MS.

Detailed description of the invention

The method proposed in the present invention includes determining the amount of one or more individual organic acids contained in the extract, which is extracted from a sample of crude oil. Thus, samples of crude oil produced from different fields contain different amounts or types of organic acids, such as carboxylic acids. In addition, the quantity or

- 2 042230 types of organic acids, in particular carboxylic acids, contained in crude oil extracted from a field may vary depending on the extraction technique used for this field, for example, they may vary due to oil recovery by improved methods (ANM), such as flooding low salinity water.

Preferably, organic acids are selectively extracted from a sample containing a known amount of crude oil to obtain an extract containing organic acids by:

(i) diluting a sample containing a known amount of crude oil with an organic solvent;

(ii) passing the diluted crude oil sample through an adsorption column or cartridge containing pulverized weakly alkaline sorbent (solid phase sorbent) to adsorb organic acids from the dilute crude oil sample;

(iii) passing an eluent containing at least one volatile polar organic solvent having a lower boiling point than the boiling points of organic acids through a column or cartridge to elute adsorbed organic acids from the sorbent and withdrawing from the column or cartridge an effluent stream containing the solution organic acids in a volatile polar organic solvent; and (iv) separating the extract containing organic acids from the eluent by evaporating the volatile polar organic solvent(s) and quantifying the extract.

The dilution step (i) may be omitted if the crude oil is a light (low viscosity) oil.

Typically, the known amount of crude oil is the known mass (or weight) of the crude oil.

The minimum mass of a crude oil sample (for quantifying the content of a particular organic acid or members of a particular class of homologous organic acids) depends on the organic acid content of the crude oil, with the minimum mass decreasing as the organic acid content increases. As mentioned above, the OCT value can be used as an indicator of the content of organic acids in crude oil. Accordingly, the minimum mass of a crude oil sample decreases as the crude oil OCT value increases. Typically, the minimum weight of a crude oil sample is in the range of 0.1 to 1 g, with the minimum amount decreasing as the TOC value of the crude oil increases. Typically, a crude oil sample has a weight in the range of 0.5 to 5 g, preferably 0.5 to 2 g, such as 1 to 2 g, although larger crude oil samples can also be used.

Preferably, the crude oil sample is diluted with an organic solvent selected from the following: aliphatic organic solvents, aromatic organic solvents such as toluene or xylene, tetrahydrofuran, diethyl ether, and halogenated aliphatic organic solvents. Typically, the ratio of the volume of organic solvent to the volume of crude oil in a dilute crude oil sample is in the range of 1:1 to 10:1, preferably 1:1 to 3:1.

The organic acids are then extracted from the dilute crude oil samples using solid phase extraction (SPE) by passing the dilute crude oil samples through a column or cartridge containing a solid phase sorbent that selectively adsorbs the organic acids from the dilute crude oil sample. Preferably, the solid phase sorbent includes a slightly alkaline sorbent. Preferably, the solid phase sorbent comprises silica particles that are functionalized with an amino group, such as the -O-Si(CH ₃ ) ₂ (CH ₂ ) _n -NH ₂ group, in which n is an integer from 1 to 10, preferably 2 to 8, more preferably 2 to 5, particularly preferably 3. SPE cartridges containing amine-functionalized silica sorbent include Mega BE-NH2 available from Agilent Technologies having a tube volume of 6 ml, and a sorbent weight of 1 g. Alternatively, the solid phase sorbent may include silica particles that are functionalized with a quaternary amino group. A suitable SPE cartridge containing a quaternary amine-functionalized silica sorbent is the SAX quaternary amine ion exchange cartridge available from International Sorbent Technology, which has a sorbent weight of 10 g. organic acids and the adsorption capacity of the column or cartridge. Accordingly, larger or smaller columns or cartridges can also be used. Typically, larger columns or cartridges are used for large crude oil samples, especially if the crude oil has a high TOC value. They are used because the adsorption capacity of the column or cartridge must be sufficient to adsorb all of the organic acids contained in the crude oil sample.

The organic acids are then eluted from the sorbent using an eluent containing a mixture of volatile polar organic solvents having lower boiling points than those of the adsorbed organic acids. Preferably, the eluent contains a larger proportion of the first polar solvent selected from the following:

- 3 042230 a C1-C3 alcohol, tetrahydrofuran and diethyl ether, preferably methanol or diethyl ether, and a minor part of a C1-C3 carboxylic acid solvent, preferably formic acid or acetic acid. Typically, the carboxylic acid solvent is present in the eluent in an amount of up to 15% by volume, preferably in an amount in the range of 1.5 to vol%, more preferably 2 to 7.5% by volume, particularly preferably from 2 to 5 vol.%.

The column or cartridge effluent is collected and the eluent containing a mixture of volatile polar organic solvents is removed, for example by evaporation, to give an extract containing organic acids. The weight of the extract can then be determined. The effluent from the sorbent column is usually collected in a vessel of known mass, and the vessel is reweighed after the volatile polar organic solvent has been completely evaporated (to obtain an extract containing organic acids). The difference between the mass of the vessel after evaporation of the volatile polar organic solvent and the mass of the vessel is the mass of the extract.

The organic acids contained in the extract typically include linear aliphatic carboxylic acids, branched aliphatic carboxylic acids, monocyclic naphthenic acids, bicyclic naphthenic acids, polycyclic naphthenic acids, aromatic acids, bicyclic aromatic acids, and polycyclic aromatic acids. The extract can then be dissolved in a given volume of at least one polar organic solvent to form a solution of the extract (ie, a solution of the extracted organic acids) in the polar organic solvent(s). Preferably, the polar organic solvent is selected from among the following: halogenated organic solvents, alcohol solvents, and mixtures thereof. Preferably, the extract is first dissolved in a given volume of a halogenated organic solvent and then the resulting solution is diluted with a given volume of an alcoholic solvent to obtain a solution of the extracted organic acids in a mixture of a halogenated organic solvent and an alcoholic solvent. The ratio of the volume of halogenated organic solvent to the volume of alcoholic solvent in the extracted organic acid solution is typically from about 1:1 to about 1:2. Preferably, if the halogenated organic solvent is a chlorinated organic solvent, dichloromethane is particularly preferred. Preferably, if the alcoholic solvent is a C1-C3 alcohol, methanol or ethanol is particularly preferred, methanol is more preferred.

The extract solutions (containing organic acids) are then analyzed by a reverse phase liquid chromatography-mass spectrometry technique using a high resolution mass spectrometer (HRMS) as a detector. Thus, a predetermined volume of the extracted organic acid solution is injected into the mobile phase, which is continuously passed through a liquid chromatography (LC) column included in the LC-MS instrument.

Preferably, the LC column included in the LC-MS instrument contains a solid phase sorbent (stationary phase) that separates organic acids based on polarity due to the different distribution between the liquid mobile phase and the stationary phase. In the liquid chromatography step of the method of the present invention, reverse phase liquid chromatography can be used, where the stationary phase is more hydrophobic (less polar) than the mobile phase. Preferably, the stationary phase contains alkylsilyl-modified silica particles, wherein the alkyl group of the alkylsilyl has a chain length of 8 to 20 carbon atoms, preferably 8 or 18 carbon atoms, and the alkylsilyl is bonded to the silica particles via a silyl group. Preferably, the alkylsilyl-modified silica particles have a size in the range of about 1 to 10 µm, more preferably 2 to 5 µm, particularly preferably 2.5 to 3 µm.

The mobile phase used in an LC column is usually a polar solvent or a mixture of polar solvents. Preferably, the composition of the mobile phase used in the LC column can be changed during the period of time that the organic acids are eluting from the LC column. The polar solvent used as the mobile phase may initially contain a mixture of water and a C1-C3 alcohol, preferably methanol. Typically, in the polar solvent used as the mobile phase, the ratio of alcohol to water is initially in the range of 8:1 to 9.5:1. The amount of water in the polar solvent can then be gradually or stepwise reduced until the polar solvent contains 100% alcohol by volume, i.e. using a gradient mode program. Preferably, a carboxylate (preferably acetate) can be added to the polar solvent as a modifier to improve the separation of organic acids in the LC column included in the LCMS instrument. Preferably, the carboxylate is an ammonium salt, such as ammonium acetate. The concentration of carboxylate in the polar solvent may be in the range of 5 to 15 mM, preferably 7.5 to 12.5 mM.

The rate of introduction of the mobile phase (carrier liquid) is usually in the range from 0.2 to

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0.5 ml/min, for example equals about 0.3 ml/min.

Extracted organic acids (eg, extracted carboxylic acids) typically contain at least one hydrophilic functional group (eg, carboxylate group) and at least one hydrophobic or lipophilic (hydrocarbyl) group. The more hydrophobic molecules contained in the mobile phase (eg, those containing more hydrophobic hydrocarbyl groups) preferentially tend to adsorb to the relatively hydrophobic stationary phase, with the more hydrophilic carboxylic acids tending to elute first from the LC column. Accordingly, the order in which organic acids elute from the LC column depends on their hydrophilic-lipophilic balance (HLB) values.

In addition to a liquid chromatography (LC) column and a mass spectrometer (MS), the LC-MS instrument used in the method of the present invention may include an intermediate device that effectively transfers the separated organic acids eluted from the column for LC to the ionization source included in the MS. This intermediate device is required if the LC and MS column are incompatible. While the mobile phase in an LC column is a pressurized liquid, MS analyzers typically operate under vacuum (about 10 ^-6 Torr). Thus, it may not be possible to pump the eluate from the LC column directly to the ion source in the MS. From a mechanical point of view, the intermediate device is a common component of an LC/MS instrument that removes a significant portion of the mobile phase used in the LC column and transports the organic acids to the ionization source in the MS, where the compounds are ionized. An intermediate device is not necessary if the ionization source is at a temperature high enough for the mobile phase to vaporize before the separated organic acids enter the MS analyzer. Typically, when using the Orbitrap MS (see below), no intermediate device is required.

The MS is a high resolution mass spectrometer (HRMS). The resolution of the HRMS can be expressed as (m/Am), where Am denotes the width of the peak at a height that is a given fraction of the maximum peak height. A common standard, well known to those skilled in the art, is based on the definition of Aw as full peak width at half maximum (FWHM). The high resolution mass spectrometer used in the present invention typically has a resolution greater than 50,000 fshm, preferably greater than 100,000 fshm, at a m/z value of, for example, 400. Preferably, if the mass spectrum for the separated organic acids can be obtained with using one of the following mass spectrometers (analyzers): Fourier transform ion cyclotron resonance mass spectrometers (MS-ICR-FP), time-of-flight mass spectrometers (TFR-MS) and ion trap mass spectrometers (MS-IL), such as mass spectrometer Orbitrap.

Preferably, the ionization technique used in the MS included in the LCMS instrument is one that involves ionizing organic acids, such as carboxylic acids, to produce charged molecules (organic ions) while minimizing fragmentation of these ions.

Preferably, the LC-MS instrument uses atmospheric pressure ionization (API) techniques such as electrospray ionization in negative ion mode (EPI-) or atmospheric pressure photoionization in negative ion mode (PIAD-).

All the different ionization techniques used give different mass spectra that are characteristic of the crude oil extract. In one embodiment of the present invention, when analyzing a sample solution of extracted organic acids using liquid chromatography-mass spectrometry, a single ionization technique is used, preferably if that single ionization technique is ESI(-).

For ESI(-), the voltage difference at the entrance to the mass spectrometer is set in such a way that the separated organic acids leaving the LC column included in the LC/MS instrument, when injected into the ionization source, become ionized, but do not undergo significant fragmentation . The value of the voltage in the HRMS, which provides ionization while minimizing fragmentation, is well known to a person skilled in the art.

Ionization according to the FIAD(-) method proceeds according to a different mechanism. Usually, the separated organic acids (molecules) exiting the LC column included in the LC-MS instrument are irradiated with UV light, which causes the molecules to become excited and lose electrons from the molecules, resulting in the formation of radical cations. Ions can also be obtained indirectly by excitation of an additive, such as toluene, which can be added to the solution of the extracted acids.

MS (eg Orbitrap MS) typically records the m/z values for organic acids as they elute from the LC column and are ionized in the MS. With the help of HRMS, it is extremely

- 5 042230 accurately determines the mass-to-charge ratio (m/z) of organic ions, this makes it possible to assign unique compositions of elements to the peaks associated with each m/z value. Thus, the peaks in the isolated ion chromatogram of the crude oil extract are assigned to specific ionized organic acids. You can then determine the area under the peaks in the selected ion chromatogram, assigned to one or more specific ionized organic acids.

The area under the peak in the extracted ion chromatogram of a crude oil extract assigned to a specific organic acid can be compared with the area under the peak in the extracted ion chromatogram obtained from a sample containing a specific volume of a standard solution of one or more standard organic acids. Such standard solutions are often referred to in the art as external standards. The standard solution may contain standard organic acid(s) at known concentration(s) in a polar solvent, typically a C1-C3 alcohol, preferably methanol. The standard organic acid may be a carboxylic acid, such as a C1o-C2o fatty acid (alkanoic acid), preferably dodecanoic acid, hexadecanoic acid or octadecanoic acid having an EKDS value of 1, or cyclohexylalkanoic acid or cyclopentylalkanoic acid having an EKDS value of 2, preferably cyclohexylpentanoic acid. It is also possible to use standard carboxylic acids with higher DR values if the peak is assigned to a specific organic acid(s) with a DR greater than 2.

Preferably, results for these standard solutions are obtained using the same LC/MS instrument as used to analyze the extracted organic acid solution sample.

Preferably, isolated ion chromatograms are obtained for several standard solutions having given volumes, having different precisely known concentrations of at least one standard organic acid. It is possible to plot the calibration dependences of the relative contents, determined from the peaks in the isolated ion chromatograms, assigned to standard organic acids, from the known concentrations of the standard organic acid in standard solutions. Usually these calibration dependences are linear. You can use linear regression analysis and derive an equation that relates the areas under the peaks in the isolated ion chromatograms (referred to the standard organic acid) with the concentrations of the standard organic acid in the standard solutions. You can get different equations for different standard organic acids.

It is contemplated that each standard solution may have an accurately known concentration of one standard organic acid, or known concentrations of several standard organic acids. If the standard solutions contain several standard organic acids, then the concentration of each standard organic acid can be changed independently. Equations can be derived (as described above) that relate the areas under the peak(s) in the isolated ion chromatograms assigned to the standard organic acid(s) to the concentrations of the standard organic acid(s).

The concentrations of standard organic acid(s) in standard solutions are generally chosen to cover a concentration range of 0.01 to 10 ppm (mg/l). To determine the concentration of a particular organic acid in an extract sample, one or more equations can be used involving the area under the peak (in the isolated ion chromatogram obtained from a sample solution of extracted organic acids) assigned to a particular organic acid.

Generally, a standard organic acid(s) (i.e. an acid having a known chemical composition) is selected that has a composition similar to the individual organic acid(s) assigned to the peak(s) in the isolated ion chromatogram obtained from a sample solution. extracted organic acids. For example, if the peak in the isolated ion chromatogram obtained from a sample solution of extracted organic acids is assigned to a saturated straight chain fatty acid, then a straight chain fatty acid can be used as a standard organic acid. If the peak in the mass spectrum is assigned to monocyclic naphthenic acid, then cyclopentylalkanoic acid or cyclohexylalkanoic acid can be used as the standard organic acid.

In addition, it is contemplated that a known amount of a standard organic acid (referred to in the art as an internal standard) can be added to the solution of the extracted organic acids. In this case, the peak for the internal standard should not overlap (coincide) with the peaks of the organic acids obtained from the extract.

The method proposed in the present invention can be used to determine the amounts of one or more specific (individual) organic acids contained in the extract.

- 6 042230

The method proposed in the present invention can also be used to determine the number of representatives of one or more classes or series of homologous organic acids contained in the extract. Thus, the method of the present invention can be used to determine the amounts of organic acids assigned to peaks for members of classes or series of homologous organic acids in an isolated ion chromatogram. The total amount (concentration) of organic acids included in classes or series of homologous organic acids can be obtained by summing the values obtained for the amounts (concentrations) of specific organic acids included in classes or series of homologous organic acids, for example, using a calibration curve. In addition, it is contemplated that the areas under the peaks assigned to members of the homologous organic acid classes or series can be summed, and then the total area can be used to establish the amount (concentration) of organic acids included in the homologous organic acid classes or series, for example, using calibration dependence.

Preferably, the series or classes of homologous organic acids are classes or series of carboxylic acids having a particular EKDS value, preferably EKDS values of 1 or 2 (or EKDS values of both 1 and 2). It has been found that the concentrations of representatives of classes or series of homologous carboxylic acids having an EKDS value of 1 may differ for different crude oil samples, for example by at least ± 2.5%, in particular by at least ± 5%. It has also been found that the concentrations of members of classes or series of homologous carboxylic acids having an EKDS value of 2 may remain substantially constant across crude oil samples, e.g. concentrations may vary by less than ± 1.0%, in particular by less than ±0.50%.

The class of homologous carboxylic acids may be selected from among the following:

1) a class of homologous compounds of the general formula C _x H _y O _n , in which x is an integer ranging from 5 to 100, preferably from 8 to 75, more preferably from 8 to 60, particularly preferably from 10 to 45, y is an integer < 2x + 2, and n is an integer ranging from 1 to 10, preferably 1 to 5, more preferably 1 to 3, particularly preferably 2;

2) a class of homologous compounds of the general formula CxHyOn (having EKDS values from 1 to 5) in which x, y and n are as defined above;

3) a class of homologous compounds of the general formula C _x H _y O _n (ECDS =1, 2 or both 1 and 2), in which x, y and n are as defined above;

4) a class of homologous compounds of the general formula C _x H _y O ₂ (ECDS =1, 2 or both 1 and 2), in which x and y are as defined above.

For a person skilled in the art it should be obvious that EKDS is a means of expressing the degree of unsaturation of an organic compound. Assigning the ECDS values to each of the formulas derived from the numerical values of m/z on the mass spectrum is a common method of analysis. The value of EKDS equal to 1 means either the presence of one π-bond (C=C bond or C=O bond), or one closed fully saturated ring. It can be seen that saturated aliphatic monocarboxylic acids have an EKDS value of 1; monocyclic naphthenic acids containing one carboxylate functional group and not containing ethylenically unsaturated groups have an EKDS value of 2; benzoic acid and phenylacetic acid have an EKDS value of 5.

For a person skilled in the art it should be obvious that members of the class of homologous compounds are described by the same general formula, but may be different in structure. For a person skilled in the art it should also be obvious that the homologous series included in the class of homologous compounds means a group of compounds that differ only in the number of CH ₂ units contained in their main carbon chain (for branched carbon chains) or in their single carbon chain (for unbranched carbon chains). It should also be apparent to one of ordinary skill in the art that crude oil contains many different classes of homologous organic acids.

An acid may optionally be added to the crude oil sample to determine recovery (ie, organic acid) at a known concentration. Preferably, the recovery acid is added to the crude oil sample as a dilute solution in an organic solvent (hereinafter referred to as the recovery acid standard solution). The recovery acid standard solution may have a recovery acid concentration of 0.5 to 5 mg/l, preferably 0.5 to 2 mg/l, particularly preferably about 1 mg/l. The amount of standard acid recovery solution added to the crude oil sample is typically in the range of 2.5 to 10 µl, preferably 2.5 to 0.75 µl, eg 5 µl.

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An example of a suitable acid for determining recovery is 1 adamantane carboxylic acid. 1-Adamantanecarboxylic acid contains 4 linked cyclohexane rings and therefore has a high EKDS value (see below).

At least a portion of the acid is recovered from the extract obtained from the crude oil sample for determining recovery. Accordingly, isolated ion chromatograms of solutions of extracted organic acids in polar organic solvent(s) contain an isolated peak assigned to the acid to determine recovery.

Preferably, recovery (RI) is determined by taking the same amount of acid recovery standard solution (as added to a crude oil sample) and diluting this solution with polar organic solvent(s) as used to prepare an extract solution containing extracted organics. acids in a polar organic solvent(s). Preferably, the resulting acid solution for determining the degree of recovery in the polar organic solvent(s) has the same volume as the solution of the extract in the polar organic solvent(s). The acid solution is then analyzed for recovery by liquid chromatography-mass spectrometry in the same manner as the extracted organic acid solution.

The area under the peak (referred to acid for recovery) in the isolated ion chromatograms obtained for each of the extracted organic acid solutions is then compared with the area under the peak (referred to acid for recovery) in the isolated ion chromatogram obtained for the acid solution. to determine the degree of extraction. Recovery (SI) can be defined as the ratio of the area under the peak (referred to acid to determine recovery) in the isolated ion chromatogram obtained from an extracted organic acid solution to the area under the peak (referred to acid to determine recovery) in the isolated ion chromatogram obtained for the acid solution to determine the degree of extraction. Alternatively, recovery (SI) can be defined as the area under the peak (referred to acid to determine recovery) in the isolated ion chromatogram obtained from an extracted organic acid solution, expressed as a percentage of the area under peak (referred to acid to determine recovery). ) on the isolated ion chromatogram obtained from the acid solution to determine the degree of extraction.

The amounts contained in the extract, determined for each specific organic acid (or for members of a class or series of organic acids), can then be recalculated using the degree of extraction and obtain the amount of a particular organic acid or members of a class or series of organic acids contained in a sample of crude oil.

Crude oil samples may be analyzed at the production facility, or they may be analyzed at a laboratory located at a distance from the production facility. To reduce the likelihood of any change in the chemical composition of the samples, the samples can be cooled prior to analysis (for example, they can be cooled to a temperature equal to below 10°C, preferably in the range from 3 to 5°C). The likelihood of any change in the chemical composition of the samples can be further reduced by ensuring that oxygen is removed from the samples. In particular, samples can be stored in an inert atmosphere such as nitrogen. Preferably, samples of produced oil are stored for less than 1 month, more preferably less than 2 weeks, particularly preferably less than 1 week, prior to analysis.

The present invention is illustrated with reference to the following examples.

Experimental section

Crude oil, which was analyzed using the method proposed in the present invention, had the values of OCT shown in table. 1.

Table 1

OCT values and masses of crude oil samples

Raw oil Total Acid Number (mg/(g KOH)) Weight of crude oil sample (g) 1 1.8 0.500 2 0.34 1,000 3 1.05 0.500

Materials.

A 1 mg/mL solution of 1-adamantanecarboxylic acid (recovery acid) in dichloromethane (DCM) was prepared.

A mixture of diethyl ether and formic acid (2 vol.% formic acid) was prepared for use as eluent for a solid phase extraction (SPE) column.

Crude oil samples were placed in sample vials (one sample vial was used for each crude oil sample) at the amounts shown in Table 1. 1. Each crude oil sample was then diluted with 3 ml of hexane, followed by the optional addition of 5 µl of a 1 mg/ml solution of 1-adamantanecarboxylic acid.

extraction procedure.

Solid phase extraction (SPE) cartridges (Mega BE-NH2, 1 g, 6 ml), one cartridge for each crude oil sample, were mounted vertically in a vacuum filtration unit. Each cartridge contained a label.

The vacuum filtration unit included a vacuum pump to pump liquid through the cartridges. A 25 ml glass collection vessel was placed under each cartridge to collect the effluent from each cartridge.

The vacuum pump included in the filtration unit was turned on to provide a pressure of about 2 inches Hg. Art. (50.8 Torr).

The cartridges were then conditioned with 20 to 30 ml of hexane solvent until the hexane level reached the top of the sorbent beds.

The vacuum pump was turned off and the hexane effluent was removed from each collection vessel.

The glass vessels under the cartridges were replaced and the vacuum pump was turned on.

The diluted crude oil samples were then placed on top of the cartridges. Then, each glass vial was washed with a small amount of hexane (0.25 to 1 ml) and the hexane, together with trace amounts of crude oil dissolved in it, was placed on top of the SPE cartridges and the solvent was eluted from the sorbent bed contained in each cartridge.

Each cartridge was then eluted with 20 to 25 ml dichloromethane (DCM) until the level of DCM reached the top of the sorbent bed.

The vacuum pump was turned off and the DCM effluent was removed from the collection vessels.

The 25 ml glass vials under the cartridges were replaced and the vacuum pump was turned on.

The cartridges were eluted with 10 ml diethyl ether (until the solvent level reached the top of the sorbent layers).

The vacuum pump was turned off and the diethyl ether effluent was removed from the collection vessels.

Clean 25 ml glass collection vials were then labeled, weighed and placed under the cartridges.

The vacuum pump was turned on and each cartridge was eluted with 10 ml of a mixture of diethyl ether and formic acid (until the level of the solvent mixture reached the top of the cartridges).

The vacuum pump was turned off.

The vials (each containing a solution of the eluted acids in a mixture of diethyl ether and formic acid) were then removed from the vacuum filtration unit.

Then the solvent (eluent - a mixture of diethyl ether and formic acid) was removed by evaporation using a bath of granules (or water) and received an extract containing the extracted organic acids.

After evaporation of the solvent, each vessel was reweighed and the mass of extracted organic acids was determined, i.e. mass of acids = (mass of collection vessel + extracted acids) - mass of empty collection vessel.

The collection vessels were capped and the extracts containing organic acids were stored for analysis by liquid chromatography-mass spectrometry.

Obtaining standard solutions of standard carboxylic acids intended for analysis using liquid chromatography - mass spectrometry.

Standard carboxylic acids were used to generate calibration curves to quantify the amount of organic acids extracted from each crude oil sample.

4 stock solutions were prepared, which were solutions of standard carboxylic acids (1 mg/l) in methanol. These stock solutions were solutions of: (a) dodecanoic acid (C ₁₂ fatty acid), (b) hexadecanoic acid (C ₁₆ fatty acid), (c) octadecanoic acid (C ₁₈ fatty acid), and (d) cyclohexylpentanoic acid. For each stock solution, the mass of the standard carboxylic acid and the mass of methanol were carefully determined, which made it possible to accurately determine the concentration of the standard carboxylic acid in each stock solution. Then different volumes of the stock solutions were mixed with different volumes of methanol and DCM to form a series of standard solutions (containing each of the standard carboxylic acids) for analysis by liquid chromatography-mass spectrometry.

The amount of each stock solution and the amounts of methanol and DCM used to make the standard solutions are shown in the table below. 2.

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table 2

Standard solutions

Fatty acid concentration (ppm) Amount of each stock solution (µl) Methanol (µl) DXM (µl) OD 0.1 666.6 333 0.5 0.5 665.0 333 1.0 1.0 663.0 333 h, o h, o 655.0 333 5.0 5.0 647.0 333 7.0 7.0 639.0 333 10.0 10.0 627.0 333

Obtaining samples of solutions of extracted acids intended for analysis using liquid chromatography - mass spectrometry.

Using a 1000 µl pipette, 1 ml of DCM was added to each collection vessel containing the extract containing the extracted organic acids. A 50 µl portion of the resulting solution of the extracted organic acids in DCM was taken with a 100 µl pipette and this portion of the solution was added to a 2 ml glass vessel equipped with an injector nozzle. Then, 100 µl of methanol (MeOH) was added to a glass vessel using a 100 μl pipette to obtain a solution of the extracted organic acids in a mixture of DCM and methanol. Then the glass vessel was closed with a lid and the solution was stirred, for example, by shaking.

Obtain an optional acid recovery sample for analysis by liquid chromatography-mass spectrometry.

To an empty labeled glass vial was added 5 μl of a 1 mg/ml solution of 1-adamantanecarboxylic acid (acid for recovery) in dichloromethane and the volume was adjusted to 1 ml with a mixture of DCM and methanol, the resulting solution had a DCM:methanol volume ratio of 333:667. Then the vessel was closed with a lid and the sample was mixed, for example, by shaking.

Liquid chromatography (LC) conditions.

The LC-MS instrument included a liquid chromatography (LC) column having a size of 2.1 x 100 mm and containing a stationary phase of octylsilyl modified silica particles having a size of 2.7 μm. The following mobile phases were used on the LC column:

mobile phase A: H ₂ O:MeOH, 9:1 v/v + 10 mM ammonium acetate; and mobile phase B: MeOH+10 mM ammonium acetate.

The LC column was supplied with eluent directed directly to the ESI source of the mass spectrometry (MS) system. The initial elution conditions were then chosen (mobile phase B: 80 vol.%; mobile phase A: 20 vol.%; 0.3 ml/min.). The amount of mobile phase A was then reduced to zero over 2 min, so that the mobile phase was 100% of mobile phase B.

With the LC system pump turned on, extracted organic acid samples, standard carboxylic acid solution samples, and recovery acid solution samples were injected into the LC system column in a predetermined order using an injection volume of 5 μl. Standard carboxylic acids were added in order of increasing carboxylic acid concentration. Preferably, the samples are analyzed in triplicate.

Data processing - standard carboxylic acids.

The concentrations of standard carboxylic acids (C ₁₂ , C ₁₆ and C ₁₈ fatty acids and cyclohexylpentanoic acid) were calculated in each standard solution.

Then, for each standard solution, the relative content was determined from the peaks in the isolated ion chromatograms assigned to the four standard carboxylic acids.

Calibration dependences of the relative content, determined from the peaks in the isolated ion chromatograms obtained for standard solutions, assigned to standard carboxylic acids, were obtained from known concentrations (in ppm) of carboxylic acids in the standard solution. Four calibration curves were built (one for each standard carboxylic acid standard), all of which were linear relationships. For each carboxylic acid standard, best fit relationships were determined having R ² (determination coefficient) values of at least 0.99. Then, for each calibration dependence, equations were obtained for the dependences of the best fit.

Data Processing - Samples of extracted organic acids.

The relative content was determined from the peaks located on the isolated ion chromatograms obtained for each sample of the solution of extracted acids, assigned to representatives of the class of carboxylic acids with EKDS values equal to 1 (for m/z ranging from 0 to 800). Each sample of the extracted acid solution was analyzed three times by liquid chromatography-mass spectrometry with good reproducibility.

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Data Processing - Acid to Determine Recovery.

Optionally, it is possible to determine (triple) the relative abundance from the extracted ion chromatograms obtained for each sample solution of extracted acids (which contains an optional acid to determine the degree of recovery) of the peak assigned to the acid to determine the degree of extraction (1-adamantanecarboxylic acid).

It is also possible to determine (triple) the relative abundance from the peak assigned to the recovery acid (1-adamantanecarboxylic acid) of the control acid to determine the recovery (obtained as described above). This provides an estimate of the amount of organic acids extracted from each crude oil sample, since when extracting 100% organic acids from crude oil samples, the relative content of 1-adamantanecarboxylic acid, determined from the isolated ion chromatograms obtained for the extract sample and for the control sample, should be the same .

Results.

Three different crude oil samples were extracted (crude oil 1, 2 and 3) having the OCT values shown in Table 1. 1 (in the absence of an optional acid to determine the degree of recovery), and received three different extracts (extracts 1, 2 and 3). These extracts were prepared for analysis by liquid chromatography-mass spectrometry as described above, and each extract was analyzed three times and thus 9 data sets were obtained. The amount (mass) of C11-C ₄₃ carboxylic acids having an EKDS value of 1 in each sample of the extracted acid solution was determined by the area under the peaks for these acids in the isolated ion chromatograms and using a calibration dependence for a standard C ₁₈ fatty acid. From these results it was then possible to obtain the wt % amount of these compounds in the total acid extract and the wt % amount of these compounds in the crude oil sample. The results are presented in table. 3.

Table 3

Extract weight (mg) Total amount of crude oil (wt.%) Mass of connections possessing EKDS=1 (µg) Compounds Sp-C ₄ h with EKDS=1 in acid extract (wt.%) Compounds Sts-C ₄ s with EKDS=1 in crude oil (wt.%) Extract 1.8 0.18% 75.49 4.19 0.0076 Extract 1 2 76.71 4.26 0.0077 Extract 1 3 72.52 4.03 0.0073 Extract 2 1 1.8 0.18% 75.20 4.18 0.0073 Extract 78.24 4.35 0.0076 Extract 2 3 79.19 4.40 0.0077 Extract 0.14% 77.65 5.55 0.0078 Extract 3 2 78.77 5.63 0.0079 Extract 3 3 76.21 5.44 0.0076

CLAIM

Claims (14)

CLAIM 1. A crude oil analysis method for determining the amount of at least one organic acid contained in crude oil, comprising extracting organic acids from a sample containing a known amount of crude oil to obtain an extract containing organic acids, and determining the amount of extracted organic acids , wherein the extraction of organic acids from a dilute crude oil sample includes: (i) diluting a sample containing a known amount of crude oil with an organic solvent to obtain a sample of diluted crude oil; (ii) passing the diluted crude oil sample through an adsorption column or cartridge containing a slightly alkaline solid phase sorbent to adsorb organic acids from the dilute crude oil sample; (iii) passing an eluent containing at least one volatile polar organic solvent having a lower boiling point than the boiling points of organic acids through a column or cartridge to elute the adsorbed organic acids from the sorbent and withdraw from the column or cartridge an effluent stream containing the solution organic acids in a volatile polar organic solvent; and (iv) separating the extract containing organic acids from the eluent by evaporating the volatile polar organic solvent(s) and quantifying the extract; dissolving the extract in a given volume of at least one polar solvent to obtain a solution of the extracted organic acids in the polar solvent(s); introducing a sample containing a predetermined volume of a solution of extracted organic acids in a polar solvent(s) into an instrument comprising a reverse phase liquid chromatography (LC) column and a mass spectrometer (MS) (LC-MS instrument) in series, where the column for reverse phase LC contains a hydrophobic sorbent and the mobile phase for the LC column contains a polar organic solvent; - 11 042230 Separation of organic acids in the LC-MS column of the LC-MS instrument and continuous feeding of the separated organic acids exiting the LC-MS column of the LC-MS instrument to ionize the organic acids and obtain a chromatogram with mass spectroscopic data over time time for ionized organic acids; determining the area under the peak(s) in the isolated ion chromatogram obtained from the mass spectroscopic data assigned to the organic acid(s); determination of the amount of organic acid(s) in a sample solution of extracted organic acids by comparing the area under the peak(s) in the isolated ion chromatogram assigned to organic acid(s) with the area under the peak in the isolated ion chromatogram assigned to a given amount of standard organic acid ; and extrapolating from the amount of organic acid(s) in the sample solution of extracted organic acids to obtain the total amount of organic acid(s) in the extract. 2. The method according to claim 1, characterized in that the sample of crude oil is diluted with an organic solvent selected from among the following: aliphatic organic solvents, aromatic organic solvents, tetrahydrofuran, diethyl ether and halogenated aliphatic organic solvents, with the ratio of the volume of organic solvent to the volume of crude oil, ranging from 1:1 to 10:1. 3. The method according to claim 1, characterized in that the eluent containing a larger part of the first volatile polar solvent selected from among the following: C ₁ -C ₃ alcohol and diethyl ether, and a small part of the second volatile polar organic solvent selected from a group comprising C ₁ -C ₃ carboxylic acid solvents is passed through a SPE column or cartridge; the solution of organic acids in the eluent is removed from the column or cartridge, and the eluent is removed from the solution by evaporation to obtain an extract containing organic acids. 4. The method according to any of the preceding claims, characterized in that the extract containing organic acids is dissolved in a given volume of a mixture of polar organic solvents containing a halogenated organic solvent and an alcohol solvent, and a solution of the extracted organic acids in a mixture of polar organic solvents is obtained. 5. The method according to any of the preceding claims, characterized in that the mobile phase containing at least one polar solvent is passed through the LC column of the LC/MS instrument at a flow rate of 0.2 to 0.5 ml/min . 6. The method according to any one of the preceding claims, characterized in that the LC column contains a stationary phase comprising alkylsilyl-modified silica particles, wherein the alkylsilyl is bonded to the silica particles via a silyl group and the alkyl group of the alkylsilyl has a chain length of 8 to 20 carbon atoms, and that the alkylsilyl-modified silica particles have a particle size ranging from 1 to 10 μm. 7. The method according to any one of the preceding claims, characterized in that the MS contains an ionization source selected from the following: an atmospheric pressure ionization source (API), an electrospray ionization source in negative ion mode (NER-), or an atmospheric pressure photoionization source in mode of negative ions (FIAD-). 8. Method according to any one of the preceding claims, characterized in that the MS LC/MS instrument records m/z values, where m is the mass and z is the charge for organic acids as they are eluted from the LC column and ionized in the source MS. 9. The method according to any of the preceding claims, characterized in that the amount of organic acid or the number of representatives of the class of homologous organic acids in a sample solution of extracted organic acids is determined using the calibration dependence of the areas under the peaks in the selected ion chromatograms obtained for several standard solutions of at least one standard carboxylic acid, from the amounts of at least one standard carboxylic acid in several standard solutions. 10. The method according to claim 9, characterized in that the class of homologous organic acids can be selected from among the following: (a) a class of homologous compounds of general formula C _x H _y O _n having an equivalent number of double bonds equal to 1, 2, or both 1 and 2, where x is an integer ranging from 5 to 100, y is an integer number < 2x + 2 and n is an integer ranging from 1 to 10; or (b) a class of homologous compounds of general formula C _x H _y O ₂ having an equivalent double bond value of 1, 2, or both 1 and 2, where x and y are as defined above. 11. The method according to claim 10, characterized in that the area under the peaks on the selected ion chromatogram, assigned to representatives of the class of organic acids, having a value of the equivalent number of double bonds equal to 1, is determined and compared with the area under the peak on the selected ion chromatogram obtained for a standard distribution having a given volume - 12 042230 solution, having a known concentration of one or more C ₁₀ -C ₂₀ fatty acids with a value of the equivalent number of double bonds equal to 1; or determine the area under the peaks in the isolated ion chromatogram, assigned to members of the class of organic acids having an equivalent number of double bonds equal to 2, and compare with the area under the peak in the isolated ion chromatogram obtained for a standard solution with a given volume, having a known concentration of cycloalkylalkanoic an acid having a double bond equivalent value of 2. 12. A method according to any one of the preceding claims, characterized in that a known volume of organic acid standard solution is added to the oil sample to determine the recovery, and the recovery (SI) for the extracted organic acids is determined by comparing the area under the acid-related peak to determine the recovery on the isolated ion chromatogram obtained from the solution of extracted organic acids, with the area under the peak assigned to the acid to determine the degree of extraction on the isolated ion chromatogram obtained from the standard acid solution to determine the degree of extraction. 13. The method according to any of the preceding claims, characterized in that oil samples are extracted over a period of time from an oil field that uses improved oil recovery methods to study changes in the amount of at least one organic acid or the number of representatives of at least one class organic acids in crude oil samples over time. 14. The method according to claim 1, characterized in that the weakly alkaline solid sorbent is contained in a cartridge for solid phase extraction (SPE).