RU2301409C2 - Mode of definition of quantitative contents of indicators in formation waters - Google Patents

Abstract

FIELD: the invention refers to measuring technique.

SUBSTANCE: the sample is cleared from mechanical admixtures, alkali is added in the received solution for quantitative definition of natrium fluorescein with the aid of luminescent method in accordance with predetermined calibration. The concentration of other indicators in the sample is defined with the aid of interpolation method according to the results of three combined spectrophotometric measurements on fixed lengths of the waves for each separate indicator. At that one of the measurements refers to cleared investigated sample and two others refer to model solutions prepared out of formation water of average mineralization in which besides corresponding reagents natrium fluorescein in quantity equal to the quantity measured in the sample and an attachment of the investigated indicator in such quantity that the signal of the spectrophotometer for one of the model solution would be more and for the other - less then the signal of the investigated sample.

EFFECT: increases accuracy of definition.

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Description

The invention relates to spectrophotometric methods of analysis and can be used in the oil and gas industry for the quantitative determination in reservoir waters specially injected into productive formations of various water-soluble, poorly sorbed rocks and environmentally friendly organic and inorganic compounds called indicators or tracers.

It is known (see Sokolovsky EV, Soloviev GB, Trenchikov Yu.I. Indicator methods for the study of oil and gas bearing layers. M: Nedra, 1986. 158 pp.) That sodium fluorescein is used as indicators in oil fields, ammonium thiocyanate, sodium chloride, nitrates, urea, thiourea and other substances. The most difficult stage of indicator research is the quantitative determination of a labeling substance (indicator) in formation fluids. This is due to the multicomponent composition of the reservoir fluids and their high contamination. Therefore, a sample of produced water is separated from the oil before measurement, filtered and appropriate reagents are added for analysis. For example, to determine the nitrate ion, a rivanol reaction in an acidic medium is used, which gives an orange or red color depending on the concentration of the soda, a urea with dimethylaminobenzaldehyde is used to determine the urea, a yellow-green color is obtained, thiourea is determined by the reaction with potassium iron-sulfide, etc. d.

There is also a known method for determining the concentrations of a four-component composition of indicators (sodium fluorescein, ammonium nitrate, urea, thiocarbamide) when they are together in reservoir waters using spectrophotometry and special calibration dependencies for each individual indicator (see Chernorubashkin A.I., Makeev G.A. ., Gavrilenko G.A., Shamkin V.N. // Oilfield business. VNIIOENG, 1980. No. 5. P.15-16).

However, the well-known methods for determining the content of both individual indicators and individual indicators when they are present together in formation waters, with the exception of sodium fluorescein by luminescence, have relatively low measurement accuracy due to unaccounted for calibration errors introduced by the composition of formation waters and a variable level the background of undetectable indicators on the measurement results.

Closest to the present invention in terms of essential features is a method for luminescent determination of sodium fluorescein in a four-component composition of indicators containing potassium rhodanide, carbamide and potassium nitrate in addition to fluorescein sodium in reservoir water, based on the use of a Fluorat 02-3M fluid analyzer from Lumex, St. -Petersburg (see Onuchak L.A., Sizonenko G.M., Kudryashov S.Yu., Arutyunov Yu.I., Deynega O.V. // Bulletin of SamSU, Natural Science Series, 2005, No. 5 (39 )))

In the known method, the test sample of produced water is separated from oil, purified from mechanical impurities and clarified by centrifugation. To increase the sensitivity and stability of the measurement, NaOH alkali is added to the purified solution to obtain a pH of nine. The quantitative content of fluorescein is determined by a previously performed calibration dependence using model mineralized solutions of distilled water with fixed additives of sodium fluorescein at pH 9.

The disadvantage of this method is the lack of spectrophotometric determination with acceptable accuracy of the content of urea, potassium thiocyanate and potassium nitrate in formation water with the simultaneous presence of sodium fluorescein due to the superposition of its absorption spectra on the spectra of the determined indicators at the used wavelengths.

The objective of the invention is to improve the accuracy of spectrophotometric determination of the concentration of multicomponent compositions of indicators in formation waters.

This problem is solved due to the fact that in the method for determining the quantitative content of indicators in produced waters containing sodium fluorescein in the presence of a multicomponent composition of indicators, which consists in separating the analyzed sample from oil, purification from mechanical impurities, clarification in a centrifuge, adding alkali to the resulting solution for the quantitative determination of sodium fluorescein by the luminescent method according to a previously performed calibration dependence, and the concentration of individual indicators in the sample is determined by interpolation on the cumulative results of three spectrophotometric measurements carried out at fixed wavelengths for each indicator. One of the measurements relates to a purified test sample with the addition of appropriate reagents. Two other measurements relate to model solutions prepared from the source formation water (without indicators), to which sodium fluorescein is added in an amount equal to that measured in the sample according to the calibration curve and the test indicator weighed in such an amount that the spectrophotometer signal for one of the model solutions is greater , and for another - less than the signal of the test sample.

When solving this problem, a technical result is created, which consists in the fact that the concentration of individual indicators, with the exception of sodium fluorescein, is measured by the interpolation method when they are present together in the formation water sample using the results of three cumulative measurements, one of which relates to the analysis of the test sample, and the other two - to model solutions of the source formation water with the addition of sodium fluorescein so that its concentration in the model solutions is equal to that measured in the sample, e.g. why, in each model solution, a portion of the indicator under investigation is added so that the signal of the spectrophotometer for one of the solutions becomes larger, and for the other, less than the signal of the analyzed sample. The addition of sodium fluorescein to model solutions reduces the measurement error associated with the superposition of the absorption spectra of sodium fluorescein and the studied indicators at the used wavelengths.

The interpolation measurement method allows to reduce the measurement error in the nonlinear region of the dependence of the signal on the concentration due to the linearization of the dependence plot at the measurement point between two fixed additives, one of which provides a larger and the other a lower concentration of the indicator, relative to its concentration in the test sample.

An example of a specific implementation of the method

The proposed method was performed using serial spectrophotometric analyzers, for example, Fluorate 02-3M (Lumex, St. Petersburg), KFK-3 and SF-26.

The method was carried out as follows. A sample of produced water from an oil refinery containing sodium fluorescein in the presence of a multicomponent composition of indicators, for example, potassium thiocyanate, potassium nitrate and urea, was previously separated from the oil in a separatory funnel, mechanical impurities were removed by filtration through a FOFS-17 blue ribbon paper filter. Then the sample was clarified by sedimentation of colloidal impurities using a coagulant FeCl ₃ in an alkaline medium. The resulting solution was poured together with the precipitate into centrifuge tubes and centrifuged at 8-10 thousand rpm until the sample became transparent (without visible opalescence).

Prepared by the method described above, formation water samples were subjected to additional operations to determine the concentration of individual indicators in case of their joint presence in the test sample:

- fluorescein sodium. A few drops of 2N were added to the sample. NaOH to obtain a solution with a pH of 9. This significantly increases the fluorescence intensity, the measurement of which using the Fluorat 02-3M device (fluorescence wavelength 525 nm) provides a determination of the concentration of sodium fluorescein in the test sample;

- potassium nitrate. An aqueous solution saturated with toluene and concentrated sulfuric acid were added to the sample. Sulfuric acid was added carefully with vigorous stirring, avoiding strong heating of the solution. After the solution was cooled, it was mixed again, and then photometric at a wavelength of 284 nm using an SF-26 spectrophotometer. The method is based on the reaction of potassium nitrate with toluene in the presence of sulfuric acid;

- potassium thiocyanate. 0.2 ml of HCl with a density of 1.125 g / ml and 0.2 ml of FeCl ₃ with a concentration of 0.12 g / ml were added to 10 ml of the prepared sample. In this case, Fe ⁺ ions in an acidic medium pH≤0.2 form complex compounds with thiocyanates colored in blood red. The solution was stirred and held for 10 minutes. Then, the absorbance, depending on the concentration, was measured with a KFK-3 instrument at a wavelength of 490 nm. It should be noted that during clarification during the preparation of the sample, the formation complex of rhodanidione with iron (III) is not formed, because coagulation of suspensions occurs in an alkaline environment;

- urea. To 10 ml of the obtained sample was added 10 ml of a solution of paradimethylaminobenzaldehyde (20 g of paradimethylaminobenzaldehyde dissolved in 100 ml of concentrated hydrochloric acid and diluted to 1000 ml with distilled water). Then, 10 ml of 98% acetic acid was added, and after 10 min the optical density was measured using a KFK-3 instrument at a wavelength of 434 nm. The method is based on the photocolorimetric reaction of urea with paradimethylaminobenzaldehyde, giving an intense yellow color.

An experimental evaluation of the implementation of the proposed and known methods for spectrophotometric determination of the concentrations of four different indicators (sodium fluorescein, potassium thiocyanate, potassium nitrate and urea) in formation waters was carried out using three mixtures of these indicators as an example. The first and second mixtures contained the minimum and maximum concentrations of the analyzed indicators, respectively, measured with the Fluorat 02-3M, KFK-3 SF-26 devices. The third mixture contained the average values of the indicator concentrations in the studied range of instrument measurement.

To determine the content of individual indicators in the analyzed mixture in a known manner used calibration dependencies of the form:

where y is the signal of the spectrophotometer; x is the concentration of the studied indicator C _i , g / ml, and a and b are the coefficients of the calibration dependence.

Calibration solutions were prepared using mineralized formation water with the addition of appropriate reagents for each individual indicator. When constructing calibration dependences to determine the content of potassium nitrate, carbamide, and potassium rhodanide, sodium fluorescein with an average concentration of 0.12 mg / L was additionally added to calibration solutions, which somewhat reduces its effect on the results of quantitative determination of other indicators due to the mutual superposition of absorption spectra at the used wavelengths.

The results of the calibration of devices for each indicator in the working range of measurements are presented in table 1.

Table 1 Instrument calibration results for a four-component indicator composition No.
p / p Name
indicator Linear
range
measuring
concentrations
mg / l Odds calibration dependence and confidence intervals their measurements a ± Δa b ± Δb one. Fluorescein sodium 0-0.2 0.003 ± 0.01 3.57 ± 0.08 2. Potassium thiocyanate 0-20,0 0.06 ± 0.012 0.009 ± 0.01 3. Urea 0-100.0 0.14 ± 0.005 5 · 10 ^-4 ± 1 · 10 ^-4 four. Potassium nitrate 0-20,0 0.33 ± 0.004 0.003 ± 0.0004

To determine the content of sodium fluorescein in the four-component composition of indicators in the analyzed mixture by the proposed method, as well as in the known method, a calibration dependence was used (see table 1, p. 1).

The concentration of other indicators (potassium nitrate, urea and potassium thiocyanate) was measured by the proposed method by the interpolation method according to the results of three cumulative measurements, one of which relates to the analysis of the test sample, and the other two to model solutions of the initial formation water with the addition of sodium fluorescein in an amount equal to its concentration in the test sample, measured by a fluorimeter using a calibration dependence. The corresponding reagents were added to each of the model solutions for spectrophotometric determination of individual indicators, as well as a sample of the analyzed indicator, so that the signal of the spectrophotometer for one of the model solutions becomes larger, and for the other, less than the signal of the test sample. The concentration of the corresponding indicator relative to two additives was calculated by the equation:

where C _i is the concentration of the i-th indicator in the test sample, mg / l; C ₁ and C ₂ are the concentrations of the i-th indicator additive in model solutions 1 and 2, J _i , J ₁ J ₂ are the spectrophotometer signals for the i-component in the test sample and in model solutions 1 and 2, respectively, with J ₁ < J _i <J ₂ .

The experimental results are summarized in table 2.

table 2 Comparative data of experimental verification of the known and proposed method Test mixtures Conc., Mg / l Known method The proposed method instrument signal J _i Conc. according to (1), mg / l δ *,% Instrument signal Conc. according to (2), mg / l δ *,% J ₁ J ₂ one Fluorescein sodium 0.04 0.142 0,039 2,5 - - 0,039 2,5 Potassium nitrate 2.0 0.335 1.77 11.5 0.33 0.34 2.06 3.0 Urea 20,0 0.148 16.84 15.8 0.14 0.16 19.14 4.3 Potassium thiocyanate 4.0 0,091 3.45 13.7 0.08 0.10 4.15 3.8 2 Fluorescein sodium 0.2 0.746 0.208 4.0 - - 0.208 4.0 Potassium nitrate 20,0 0.399 23.16 15.8 0.39 0.41 20.78 3.9 Urea 100.0 0,203 125.3 25.3 0.19 0.21 95.00 5,0 Potassium thiocyanate 20,0 0.272 23.54 17.7 0.26 0.28 19.04 4.8 3 Fluorescein sodium 0.12 0.446 0.124 3.3 - - 0.124 3.3 Potassium nitrate 11.0 0.366 11.9 8.2 0.36 0.38 11.5 4,5 Urea 60.0 0.167 53.6 10.7 0.16 0.18 57.06 4.9 Potassium thiocyanate 12.0 0.157 10.8 10.0 0.15 0.17 11.5 4.2 * Relative error in determining the concentration of the i-th indicator according to equations (1) and (2)

As can be seen from the data in table 2, the proposed method provides a significant increase in the accuracy of determining the quantitative content of potassium nitrate, urea and potassium thiocyanate in the presence of sodium fluorescein in the studied formation waters compared with the known method. So, for the test mixture 3, when the content of sodium fluorescein in the sample is equal to its average value in the working measurement range (0.12 mg / l), which was used in the formation water for the preparation of calibration solutions when constructing calibration dependences of other analyzed indicators, their relative error definitions decreased on average by half.

For mixture 1 with small values of the concentrations of the indicators being determined, the relative error decreased on average by more than three times, and for mixture 2 with large values of concentrations by almost four to five times, which, apparently, is due to the partial exclusion of the signal nonlinearity from the concentration by measurement results.

It should be noted that the error in the determination of sodium fluorescein in the studied mixtures, both by the known and the proposed method, is the same, since the measurement was carried out using the same calibration dependence.

The determined concentrations of potassium nitrate, urea and potassium thiocyanate in mixture 1 in a known manner are less than the set values by about 12-16%, and in mixture 2 more than the set values by 16-25%, which may be due to the influence of the absorption spectrum of sodium fluorescein on the spectra of other indicators at corresponding wavelengths.

Using the proposed method can improve the accuracy of determining the concentrations of multicomponent compositions of indicators in formation waters when conducting indicator studies in the oil fields by taking into account the non-linearity of the signal at the measurement point.

Claims (1)

A method for determining the quantitative content of indicators in produced water, in which a sample containing sodium fluorescein in the presence of a multicomponent composition of indicators is separated from oil, purified from mechanical impurities and clarified by centrifugation, alkali is added to the resulting solution to quantify sodium fluorescein using a luminescent method according to a previously performed calibration dependencies, characterized in that the concentration of individual indicators in the sample is determined by interpolation by the results of three aggregate spectrophotometric measurements at wavelengths fixed for each individual indicator, moreover, one of the measurements is carried out for a purified test sample with the addition of appropriate reagents, and the other two measurements are for model solutions prepared from the source formation water (without indicators) with the addition of fluorescein sodium in an amount equal to that measured in the sample according to the calibration dependence, and a portion of the indicator under investigation in such an amount that the signal of the spectrophotometer To one of the model solutions was greater, and for another - is less than the signal of a test sample.