RU2488092C1 - Method of determining gas concentration in liquid - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method involves determining gas concentration in a liquid by degassing a sample of the liquid and measuring the amount of released gas using a chemical indicator. The existing analysis scheme is supplemented with a gas-collecting chamber which collects a gas-air mixture obtained when extracting the desired gas. A residual amount of gas is determined in the degassed liquid sample and a considerably smaller portion of the gas-air mixture is collected for analysis from the chamber with the gas-air mixture. Gas concentration in the liquid sample is determined using a formula based on the entire gas released from the sample taking into account the volume fraction of the gas-air mixture taken for physical-chemical analysis.

EFFECT: high accuracy of determining gas concentration in a liquid and low cost of analysis by saving indicator pipes.

2 cl, 3 dwg

Description

The invention relates to methods for measuring the quantitative content of dissolved gas in an oilfield fluid and can be used in the search, production, preparation and transportation of oil and water.

A well-known global method for determining the content of gas dissolved in a liquid is to extract gas from a liquid by sparging and measure the amount of gas released using an indicator tube (Drader-Tube / CMS Reference: Reference Guide for Measurements in the Analysis of Soil, Water and Air, and technical gases, 12th edition, p.2.14, p. 42. - Lubeck, 2003. - 294 p.). This technique is designed to place a large volume of water samples in a calibrated extraction bottle - up to 200 ml, therefore, with an increased concentration of gas in the liquid, a large number of measuring tubes will be required for analysis. The second drawback is that the gas-air mixture (DHW) enters the measuring tubes in portions of the same volume (pump displacement), but the content of the desired gas in each portion is variable. The maximum gas content in the first portion of the hot water supply leads to the fact that at the set speed for pumping the hot water supply through the tube, the desired gas passes through the measuring tube, not completely reacting with the chemical substance of the tube. This leads to an overestimation of the gas content in the liquid sample.

A similar drawback has a technique based on various applications of the device for determining the concentration of gas in a liquid according to the patent of the Russian Federation for invention No. 2181882 (publ. 04/27/2002, bull. No. 12). In contrast to the Drader extraction method using the last device, it is possible to analyze a sample of a small volume liquid - up to 1 ml, dilute this volume with an inert liquid (water, kerosene) to the required volume (7 ÷ 40 ml) and also extract the desired gas from it . Numerous studies of oil samples with a high content of hydrogen sulfide (up to 1000 mg / l or more) using the device according to patent No. 2181882 showed that the content of H ₂ S in the DHW flow at the beginning of extraction is so high that the standard indicator tube H ₂ S - 0, 0066 is painted at an uneven and rooted pace. This leads to a certain overestimation of the gas concentration in the liquid. In addition, several expensive indicator tubes are required for the analysis.

An object of the invention is to improve the accuracy of analyzes by gas extraction from a liquid sample while reducing the cost of one analysis. This problem is solved by a known method for determining the concentration of gas in a liquid by extracting gas from a liquid and passing the gas-air mixture (DHW) through an indicator tube so that the DHW is first collected in a gas sampling chamber, the residual amount of gas in the liquid sample is determined, and the amount of gas is significantly determined in a smaller part of the hot water supply in the gas sampling chamber, and the concentration of gas in the liquid is determined by the formula:

$$\mathrm{FROM}=\frac{\mathrm{TO}}{V_{\mathrm{well}}}\left(n_{\mathrm{about}\mathrm{from}t}+n_{\mathrm{but}n}\cdot \frac{V_{G\mathrm{AT}\mathrm{FROM}}}{V_{\mathrm{but}n}}\right),\left(\mathrm{one}\right)$$

where C is the concentration of gas in the liquid;

K is the complex constant, depending on the properties of the gas and the temperature of the medium;

n _ost - the residual amount of gas in the liquid sample after gas extraction;

V _DHW - the volume of the gas-air mixture in the gas sampling chamber;

V _en - the volume of hot water from the gas sampling chamber taken for analysis (V _en << V _{hot water} );

n _en - the amount of gas in the volume of V _en .

For analysis from the gas sampling chamber, such a volume V _en is selected that would ensure representativeness of the analysis, in particular, by colorimetric assessment, the indication from the indicator tube should be taken in its second half.

In figure 1; 2 and 3 give the sequence of the proposed method according to the invention.

Figure 1 shows the process of extraction (extraction) of gas from a liquid sample and the collection of the resulting hot water supply in the sampling chamber. In the drawing: 1 - degassing chamber with a sample of liquid; 2 - stopcocks; 3 - a pump with a built-in domestic hot water meter; 4 - gas sampling chamber of an acceptable design.

Figure 2 shows the verification of the presence of residual gas content in the liquid sample after its long degassing using indicator tube 5.

Figure 3 shows the selection process from the chamber 4 with a volume of V _dhw for analysis through a tube 5 of a significantly smaller volume of dhw - V _en .

The method for determining the concentration of gas in a liquid is implemented by the following processes.

1. In a degassing chamber 1 take a sample of liquid volume V _g .

всего объема газовоздушной смеси.2. Using the pump 3 through its built-in counter, a gas-air mixture of volume V _{DHW is} pumped into a previously empty gas sampling chamber 4. Earlier in the application, it was noted that the first portions of hot water supply contain a high concentration of the desired gas, and the last portions do not contain it. In the chamber 4, a gas-air mixture is formed from air and the desired gas with one and constant concentration at all points of the chamber. On this well-known law of the state of ideal and real gases, the novelty and essence of the invention are built: for the chemical (colorimetric) analysis, it is enough to select the smaller and known part $$\left(\frac{V_{\mathrm{but}n}}{V_{G\mathrm{AT}\mathrm{FROM}}}\right)$$

the total volume of the gas mixture.

3. Determine the residual amount of gas n _OST in the liquid sample, for example, using the indicator tube 5 (figure 2) by further continuing the extraction of gas until the gas is completely degassed by the desired gas. As a rule, after diluting a liquid sample with a high concentration of the desired gas and degassing the resulting sample solution with a volume of 7 ÷ 10 ml using inert gas (air) with a volume of 1000 ml (1 liter), the desired gas, in particular hydrogen sulfide, is completely absent in the test sample. e. n _ost = 0. Such a procedure is necessary in order to ensure that all gas from the liquid sample from the degassing chamber 1 is transferred to the gas sampling chamber 4.

4. Pump 3 for analysis, for example, through an indicator tube 5, from the chamber 4, a significantly smaller part of the _{domestic hot water supply} V is taken, but such that the result is representative, in particular, for the indicator tube, the colorimetric reading n _en should be evaluated in the second half of the tube .

5. To determine the total amount of gas sought in chamber 4, it is necessary to multiply n _en by V _dhw / v _en (rule of proportions).

6. The value of the gas concentration in the liquid is determined by the formula (1).

The essence of the technical solution is as follows. In the gas sampling chamber 4, the DHW with a different concentration of the desired gas enters, but after filling the chamber 4 the hot water supply becomes homogeneous in composition. It is important that the concentration of the desired gas in the composition of the hot water supply in chamber 4 becomes significantly lower than in the first portion of hot water taken for analysis, in particular through an indicator tube, according to the existing method.

According to the invention, a double beneficial effect is achieved. Firstly, the accuracy of the analysis increases, in particular, in the indicator tube there is a qualitative and complete staining of the substance in the tube due to a decrease in the concentration of the desired gas in the hot water supply. Secondly, for one analysis of the sample, only two indicator tubes will be required: the first to evaluate the indicator n _ost , the second to determine n _AN . When analyzing such a sample according to the existing methodology (working with the device according to the patent of the Russian Federation No. 2181882), it is necessary to pass the entire volume of hot water through indicator tubes. Depending on the concentration of gas in the fluid, the tubes will require up to 10 or more. For comparison, we evaluate the content of hydrogen sulfide in oil in the existing way and proposed on request.

Initial data:

1. The content of H ₂ S in the oil sample according to GOST R 50802 - 740 mg / l (822 ppm).

2. The volume of the sample of oil V _W - 1,0 ml.

3. Pump for degassing - aspirator AM-5.

4. The volume of the pass DHW for 1 roll AM-5-100 ml.

5. The temperature of the sample and the medium T _p = 293 K (20 ° C).

6. The complex constant K = 1.41.

$$K=\frac{M}{V_{\mathrm{but}}}\cdot \frac{T_o}{T_P},$$

where M is the molar weight of H ₂ S; M = 34 g / mol;

V _a is the volume of 1 mol of gas at T ₀ = 273 ⁰ K (0 ⁰ C); V _a = 22.4 liters.

For analysis according to the existing method, 9 H ₂ S indicator tubes were spent - 0.0066: 8 full to the 66 mark and the ninth to the 42 mark. The total reading is n = 8 × 66 + 42 = 570 g.

$$C=K\cdot \frac{n}{V_{\mathrm{well}}}=\frac{1.41\cdot 570g}{\mathrm{one}ml}=804g/ml$$

For analysis according to the proposed method, 2 indicator tubes H ₂ S were spent - 0.0066: for the first n _ost = 0, for the second n _en = 50 g, and V _dhw = 1000 ml; V _en - 100 ml (1 quality AM-5). By the formula (1) we have:

$$C=\frac{1.41}{\mathrm{one}ml}\left(0+\mathrm{fifty}g\cdot \frac{1000ml}{\mathrm{one\; hundred}ml}\right)=705g/ml$$

Relative discrepancies (analysis error) between the existing method and GOST R 50802 8.6% $$\left(\mathrm{one\; hundred}\%\cdot \frac{804-740}{740}\right).$$

The relative differences between the proposed method and GOST R 50802 is equal to 4.7% $$\mathrm{one\; hundred}\%\cdot \frac{740-705}{740}$$

For ease of comparison, the results are summarized in a table:

Parameter The existing method according to patent No. 2181882 Proposed method one The concentration of H ₂ S in the oil sample (mg / l), (the result according to GOST R 50802: C = 740 mg / l is accepted as true) 804 705 2 The number of indicator tubes per analysis, pieces 9 2 3 The cost of one analysis, rub. (the price of one tube is 25 rubles.) 225 fifty four Time for one analysis, min 12 12 5 Analysis error (relative discrepancies with the result according to GOST R 50802) 8.6 4.7

The results indicate that the proposed method for assessing H ₂ S in a sample of a liquid with a high content solves the technical problem posed - the accuracy of the analysis increases while the cost of one analysis is reduced. Note that an increase in the accuracy of the analysis was achieved by reducing the concentration of hydrogen sulfide in the volume of NSA taken for analysis. This leads to a qualitative reaction of the chemical in the indicator tube, namely, the tube is painted evenly and completely.

The cost of the analysis is ensured by the fact that only a fixed part of the gas-air mixture obtained by extraction of the desired gas from the liquid sample is passed through the indicator tube.

Claims (2)

1. A method of determining gas concentrations in a liquid, comprising a gas extraction from the fluid sample and pass the resulting gas mixture through the test tube, characterized in that the gas-air mixture volume - V _{hot water} is collected in a gas sampling chamber defined residual amount of gas in the liquid sample - n _ost also determine the amount of gas in a much smaller part of the hot water supply in the gas sampling chamber - V _en , and the gas concentration in the liquid is determined by the formula:
$$C=\frac{K}{V_{\mathrm{well}}}\left(n_{\mathrm{about}\mathrm{from}t}+n_{\mathrm{but}n}\frac{V_{g\mathrm{at}\mathrm{from}}}{V_{\mathrm{but}n}}\right),$$

where C is the concentration of gas in the liquid;
K is the complex constant;
V _W - the volume of the sample fluid;
n _ost - the residual amount of gas in the sample after bubbling;
V _DHW - the volume of the gas-air mixture (DHW) in the gas sampling chamber;
V _en - the volume of hot water from the gas sampling chamber, taken for analysis;
n _en - the amount of gas in the analyzed volume V _en . 2. The method according to claim 1, characterized in that for the analysis from the gas sampling chamber take such a volume of hot water - V _en , which will ensure representativeness of the analysis in terms of n _en , in particular, the indication on the indicator tube by colorimetric assessment should be taken in its second half.

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