Method for detecting gas content and chemical components in open hole and closed hole of coal rock

Abstract

The invention discloses a method for detecting gas contents and chemical components of open pores and closed pores of coal rock, and belongs to the field of coal bed gas resource development, the method comprises the following steps: carrying out first water bath heating on a coal sample, completing desorption of the open pores, determining the desorption amount through a drainage gas collection method, and determining the gas chemical components through a gas chromatography; performing crushing and secondary water bath heating on the coal sample subjected to open hole desorption to complete closed hole desorption, determining the gas desorption amount by a water drainage and gas collection method, and determining the chemical components of the gas by a gas chromatographic method; both the open hole desorption and the closed hole desorption are completed under a closed condition. The hole sealing gas is obtained by adopting a coal rock crushing method, and the crushing time is controlled to ensure that the hole sealing gas is fully released; volume measurement and chemical component detection are carried out on desorbed gas of the open hole and the closed hole, and reference is provided for comprehensive evaluation of the coal bed gas content by accumulating the alkane gas content of the open hole and the closed hole.

Description

Technical Field

[0001] The invention belongs to the field of coal bed gas resource development, and in particular relates to a method for detecting gas content and chemical composition of open pores and closed pores of coal rocks. Background Art

[0002] Coalbed methane is a hydrocarbon gas with methane as the main component. It exists in coal seams mainly by adsorption on the surface of coal matrix pores. Coal is a heterogeneous organic rock with a complex pore structure. The pores in coal can be divided into two categories: open pores and closed pores based on pore connectivity. Open pores have good connectivity with the external environment, while closed pores are not connected to the outside world. Closed pores in coal account for a large part of the pore volume. However, previous coalbed methane resource evaluations often ignored the proportion of closed pore gas. With the advancement of mining and fracturing technology, the gas in the closed pores in coal seams will be effectively developed and utilized, thereby improving coalbed methane mining capacity and economic benefits.

[0003] In the past, the coalbed methane content was determined by conducting natural desorption and residual gas desorption experiments. However, the desorption time of these two experiments is often as long as several days or even dozens of days, and the above experiments are difficult to accurately evaluate the content of closed pore gas in the coal seam. Summary of the invention

[0004] The purpose of the present invention is to provide a method for detecting the gas content and chemical composition of open pores and closed pores of coal rocks to solve the problems existing in the above-mentioned prior art. The water bath heating method is used to accelerate the test of coalbed methane production, greatly improving the detection efficiency, and measuring the volume and chemical composition of desorbed gas from open pores and closed pores. The measurement results can be used as one of the indicators for comprehensively judging the gas production capacity of coalbed methane.

[0005] A method for detecting the gas content and chemical composition of open pores and closed pores of coal rock, comprising the following steps: heating the coal sample in a water bath for the first time to complete open pore desorption, determining the desorption amount by a water drainage gas collection method, and determining the gas chemical composition by gas chromatography; crushing the coal sample that has completed open pore desorption and heating it in a water bath for a second time to complete closed pore desorption, determining the gas desorption amount by a water drainage gas collection method, and determining the gas chemical composition by gas chromatography; the open pore desorption and closed pore desorption are both completed under closed conditions.

[0006] The present invention accelerates the desorption rate of coalbed methane by water bath heating, which greatly saves detection time; controls the pulverization time to ensure that the particle size of different samples is consistent and the gas in closed pores is fully released; measures the volume of desorbed gas by the water drainage gas collection method to preliminarily judge the gas production capacity of closed pores and open pores of coalbed methane; and determines the composition of the chemical components of coalbed methane by gas chromatography, so as to more clearly judge the mining value of coalbed methane.

[0007] Preferably, the open-hole desorption comprises the following steps: quickly loading the whole coal core with gangue removed into the desorption tank, filling the remaining space with broken coal samples, quickly tightening the tank cover, measuring the mass of the coal sample, checking the air tightness, and then immersing the desorption tank in water for the first water bath heating.

[0008] More preferably, the temperature of the first water bath heating is 100°C.

[0009] More preferably, the water bath heating is stopped when the open pore desorption continues until the desorption amount within 1 hour is less than 0.1 mL / g.

[0010] Preferably, the closed pore desorption comprises the following steps: placing the coal core that has completed the open pore desorption into a ball mill crushing tank, pulverizing it after vacuuming, and immersing the ball mill crushing tank in water during the pulverizing process for secondary water bath heating.

[0011] More preferably, the temperature of the secondary water bath heating is 100°C.

[0012] More preferably, the crushing time is 10 hours.

[0013] More preferably, the water bath heating is stopped when the closed pore desorption continues until the desorption amount within 1 hour is less than 0.1 mL / g.

[0014] Preferably, the drainage and gas collection method uses a saturated salt water solution.

[0015] Compared with the prior art, the present invention has the following advantages and technical effects:

[0016] The present invention accelerates the coalbed methane desorption rate by water bath heating, greatly shortening the time for coalbed methane content evaluation test. Considering that there are a large number of hydrocarbon gases in the closed pores, the present invention adopts the method of crushing coal rock to obtain closed pore gas, and controls the crushing time to ensure that the closed pore gas is fully released; the present invention measures the volume and detects the chemical composition of the desorbed gas from the open pores and closed pores, and provides a reference for the comprehensive evaluation of the coalbed methane content by accumulating the alkane gas content of the open pores and closed pores; the present invention has a concise detection process, simple operation, scientific principle, high measurement efficiency, good measurement effect, and provides a simple and fast testing method for studying the chemical composition of coalbed methane open pore and closed pore gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0018] Figure 1 A flow chart of a method for detecting gas content and chemical composition in open pores and closed pores of coal rock provided by the present invention;

[0019] Figure 2 The graphs for measuring the gas desorption amount of open pores and closed pores of coal rock samples 1-4 in Example 1;

[0020] Figure 3 The open pore and closed pore gas desorption volume ratio diagram of coal rock samples 1-4 in Example 1;

[0021] Figure 4 The coal rock crushing particle size distribution diagram of coal rock samples 1-4 in Example 1;

[0022] Figure 5 The gas chemical composition determination diagrams of the open pores and closed pores of the coal rock samples 1-4 in Example 1, wherein (a) is the gas chemical composition determination diagram of the open pores, and (b) is the gas chemical composition determination diagram of the closed pores;

[0023] Figure 6 This is a graph showing the determination of the alkane gas content of coal bed methane in coal rock samples 1-4 in Example 1;

[0024] Figure 7 The coal rock crushing particle size distribution diagrams of the coal rock sample 1 after grinding in Example 1, Comparative Example 1 and Comparative Example 2, wherein (a) is the coal rock crushing particle size distribution diagram of the coal rock sample 1 after grinding in Example 1 and Comparative Example 2, and (b) is the coal rock crushing particle size distribution diagram of the coal rock sample 1 after grinding in Comparative Example 1;

[0025] Figure 8 The graph is a comparison of the gas chemical composition determination of the closed pores of coal rock sample 1 in Example 1, Comparative Example 1 and Comparative Example 2, wherein (a) is alkane gas, (b) is nitrogen, (c) is chlorine, and (d) is carbon dioxide;

[0026] Fig. 9 Schematic diagram of a device for collecting desorbed gas from a ball mill crushing tank in an embodiment of the present invention, wherein 1 is a ball mill crushing tank, 2 is a water bath heating tank, 3 is a check valve one, 4 is a check valve two, 5 is a check valve three and 6 is a check valve four, 7 is a liquid collecting barrel, 8 is a measuring cylinder, and 9 is a gas collecting device. DETAILED DESCRIPTION

[0027] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0028] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0029] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0030] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to the skilled artisan. The present invention description and examples are exemplary only.

[0031] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0032] The embodiment of the present invention provides a method for detecting the gas content and chemical composition of open pores and closed pores of coal rock, comprising the following steps: rapid determination of the desorbed gas content of open pores, rapid determination of the desorbed gas content of closed pores, and detection of the chemical composition of open pore and closed pore gases. Among them, the rapid determination of the desorbed gas content of open pores comprises: using a water bath heating method to rapidly desorb the coal core from which gangue is removed in the coring of drilling, collecting the gas of the open pores through a drainage gas collection device and determining its content, and the rapid determination of the desorbed gas content of closed pores comprises: using a ball mill to crush the coal core after rapid desorption for 10 hours, heating the coal core in a water bath, collecting the gas of the closed pores through a drainage gas collection device and determining its content. The detection of the chemical composition of open pore and closed pore gases comprises: performing gas chromatography component determination on the collected open pore and closed pore gases respectively, obtaining the chemical composition of the open pore and closed pore gases, and providing a reference for the comprehensive evaluation of the coalbed methane content by accumulating the closed pore and open pore alkane gas contents. Figure 1 The present invention provides a flow chart of a method for detecting the gas content and chemical composition of open pores and closed pores in coal and rock. The specific operations are as follows:

[0033] Step 1. Rapid determination of open pore desorbed gas content:

[0034] 1) After drilling out the coal core, quickly put the whole coal core without gangue into the desorption tank, and then fill the remaining space with broken coal samples to ensure that the remaining space in the desorption tank does not exceed 5% of the total space. Quickly tighten the tank cover, measure the mass of the coal sample, and then immerse it in a saturated NaCl solution to check the air tightness;

[0035] 2) Immerse the desorption tank in water and heat it in a water bath at 100°C;

[0036] 3) Collect desorbed gas using the drainage gas collection method and measure the desorbed gas volume using a saturated salt water solution;

[0037] 4) When the desorption amount within 1 hour is less than 0.1 mL / g, the open hole desorption is terminated.

[0038] The present invention adopts water bath heating to increase the gas migration rate, accelerates the desorption of open-hole coalbed methane, and greatly saves detection time.

[0039] Step 2. Rapid determination of closed pore desorption gas content:

[0040] 1) Put the desorbed coal core into the ball mill crushing tank and crush it after vacuuming;

[0041] 2) During the pulverizing process, immerse the ball mill pulverizing tank in water and heat it in a water bath at 100°C;

[0042] 3) Collect desorbed gas using the drainage gas collection method, measure the desorbed gas volume, and use saturated salt water solution to prevent microbial activity in the air from affecting the alkane gas content.

[0043] 4) When the desorption amount within 1 hour is less than 0.1 mL / g, the closed pore desorption is terminated;

[0044] 5) After desorption, extract the powder for laser particle size analysis.

[0045] Since the closed pores are not connected to the outer surface of the coal, the gas in them must be released by means of crushing, and the crushing particle size is closely related to the release of the closed pores. The longer the crushing time, the finer the crushing particle size, and the more closed pores are released. Based on this rule, the present invention sets the crushing time to 10 hours, and judges whether the crushing meets the standard by finally analyzing the crushing particle size.

[0046] Step 3. Detection of chemical composition of open pore and closed pore gases:

[0047] 1) Turn on the gas source, start the gas chromatograph and chromatographic workstation and set the parameters. When all parameters reach the set values, start sampling and analysis;

[0048] 2) Dry the gases in the open and closed pores and pass them into the gas chromatograph respectively, and use the chromatographic column to separate the different gas components;

[0049] 3) During continuous ventilation, the chromatographic column is maintained at 25°C to prevent some hydrocarbon gases from cooling and liquefying and hindering gas flow;

[0050] 4) Use the instrument’s data processing system to obtain the chemical composition of open-pore and closed-pore gases and the proportion of each component.

[0051] The present invention releases the gas in the open pores and closed pores by the above-mentioned water bath heating, thereby greatly shortening the detection time; at the same time, mechanically crushing the coal rock provides a simple and quick testing method for studying the closed pore gas, and provides a reference for the comprehensive evaluation of the coalbed methane content by accumulating the alkane gas content in the open pores and closed pores.

[0052] Fig. 9 Schematic diagram of a device for collecting desorbed gas from a ball mill crushing tank in an embodiment of the present invention, wherein 1 is a ball mill crushing tank, 2 is a water bath heating tank, 3 is a check valve 1, 4 is a check valve 2, 5 is a check valve 3 and 6 is a check valve 4, 7 is a liquid collecting bucket, 8 is a measuring cylinder, and 9 is a gas collecting device; the specific operation method is: the ball mill crushing tank 1 and the measuring cylinder 8 are connected to each other through a guide pipe, the interface is well sealed, the check valve 3 5 and the check valve 4 6 are closed, and then vacuuming is started with a vacuum pump. After the vacuuming is completed, Close the check valve 1 3, open the check valve 3 5, start to power on and water-bath heat the ball mill pulverizing tank 1, and the closed-hole gas analyzed by water-bath heating enters the measuring cylinder 8, so that the liquid in the measuring cylinder 8 is discharged into the liquid collecting barrel 7; when the measurement is completed or the measuring range of the measuring cylinder 8 is insufficient, close the check valve 3 5, record the single closed-hole analyzed gas volume, then open the check valve 4 6, inject water from the mouth of the check valve 2 4, so that the gas flows into the gas collecting device 9, collect and record the single collected gas sample volume, then repeat the drainage and gas collection process or end the experiment.

[0053] In the embodiment of the present invention, the method for collecting the desorbed gas from the desorption tank is as follows: Fig. 9 As shown, the ball mill crushing tank 1 is replaced with a desorption tank, the desorption tank and the measuring cylinder 8 are connected to each other through a gas-liquid conduit, the interface is sealed, and the check valve four 6 is closed. Then, the gas production of the open hole is measured, so that the gas analyzed by water bath heating enters the measuring cylinder 8, and the liquid in the measuring cylinder 8 is discharged into the liquid collecting bucket 7; when the measurement is completed or the range of the measuring cylinder 8 is insufficient, the check valve three 5 is closed, and the volume of the gas analyzed by a single open hole is recorded, and then the check valve four 6 is opened, and water is injected from the mouth of the check valve two 4 to make the gas flow into the gas collecting device 9. After the collection is completed, the volume of the gas sample collected once is recorded, and then the drainage and gas collection process is repeated or the experiment is ended.

[0054] The gas chromatography conditions in the embodiment of the present invention are as follows: instrument model TRACE 1300 Mainframe 230V, injection port temperature of 50-60°C, column temperature of 25°C, helium as carrier gas, and flow rate of 40 mL / min.

[0055] The embodiment of the present invention tests four coal rock samples collected from a coal field in Guizhou.

[0056] Example 1

[0057] S1. Rapid determination of open pore desorption gas content:

[0058] 1) After drilling and taking out the coal core from the coal rock sample 1, quickly put the whole coal core without the gangue into the desorption tank, and then fill the remaining space with the broken coal sample to ensure that the remaining space of the desorption tank does not exceed 5% of the total space, quickly tighten the tank cover, measure the mass of the coal sample, and then immerse it in a saturated NaCl solution to check the air tightness of the desorption tank;

[0059] 2) Immerse the desorption tank with good airtightness in water and heat it in a water bath at 100°C;

[0060] 3) Pass the desorbed gas into a measuring cylinder filled with saturated saline solution, and measure the desorbed gas volume by observing the descending liquid level in the measuring cylinder;

[0061] 4) When the desorption amount within 1 hour is less than 0.1 mL / g, the open hole desorption is terminated.

[0062] S2. Rapid determination of closed pore desorption gas content:

[0063] 1) Put the desorbed coal core into the ball mill crushing tank, remove the gas in the ball mill crushing tank by vacuuming, and crush it for 10 hours to fully release the gas in the closed pores;

[0064] 2) During the pulverizing process, immerse the ball mill pulverizing tank in water and heat it in a water bath at 100°C;

[0065] 3) Pass the desorbed gas into a measuring cylinder filled with saturated saline solution, and measure the desorbed gas volume by observing the descending liquid level in the measuring cylinder;

[0066] 4) When the desorption amount within 1 hour is less than 0.1 mL / g, the closed pore desorption is terminated;

[0067] 5) Extract the powder from the ball mill crushing tank and perform laser particle size analysis.

[0068] Samples 2-4 were tested using the same procedure as sample 1.

[0069] Figure 2The open pore and closed pore gas desorption measurement diagram of coal rock samples 1-4 in Example 1, Figure 2 It can be seen that the open pore desorption gas content is 11.32-18.23 mL / g, and the open pore desorption gas of sample 3 is the least. The closed pore desorption gas content is 6.99-9.60 mL / g, and the closed pore desorption gas of sample 3 is the most.

[0070] Figure 3 The open pore and closed pore gas desorption volume ratio diagram of coal rock samples 1-4 in Example 1; Figure 3 It can be seen that the closed pore desorption gas accounts for up to 45.89% of the total gas production and the lowest is 29.61%. Ignoring the closed pore gas content will seriously underestimate the gas production capacity of the coal seam. The detection method provided by the present invention calculates the content of closed pore desorption gas, which is conducive to a more reasonable evaluation of the coalbed methane production.

[0071] Figure 4 The coal rock crushing particle size distribution diagram of coal rock samples 1-4 in Example 1 is shown in FIG. Figure 4 It can be seen that the main peak of the particle size distribution is approximately 30-50μm, which on the one hand indicates that the degree of coal rock crushing is basically the same, and on the other hand indicates that the coal rock is fully crushed and the closed pore gas is fully released.

[0072] S3. Detection of chemical composition of open pore and closed pore gas:

[0073] 1) Turn on the gas chromatograph and chromatographic workstation and set the parameters. When all parameters reach the set values, start to introduce gas for analysis;

[0074] 2) The gases in the open pores and the closed pores are dried and introduced into the gas chromatograph respectively, and the different gas components are separated by the chromatographic column;

[0075] 3) During continuous ventilation, the chromatographic column is maintained at 25°C to prevent some hydrocarbon gases from cooling and liquefying and hindering gas flow;

[0076] 4) Use the instrument’s built-in data processing system to analyze the chemical composition of open-pore and closed-pore gases and calculate the proportion of each component.

[0077] Figure 5 The gas chemical composition determination diagrams of the open pores and closed pores of the coal rock samples 1-4 in Example 1, wherein (a) is the gas chemical composition determination diagram of the open pores, and (b) is the gas chemical composition determination diagram of the closed pores. Figure 5It can be seen that the gas composition of the open pores is mainly alkane gas, and the gas released by the closed pores is mainly alkane gas and nitrogen, which proves that there is a difference in the composition of the gas adsorbed by the closed pores and the open pores, and the nitrogen concentration in the closed pores is higher. In addition, except for sample 3, the argon and carbon dioxide concentrations in the closed pores of the other samples are also significantly higher than those in the open pores.

[0078] Figure 6 This is a graph showing the determination of alkane gas content in coal bed methane of coal rock samples 1-4 in Example 1. Figure 6 It can be seen that the closed pore alkane gas content of each sample is 5.43-7.61mL / g, and the closed pore alkane gas content of sample 3 is the largest, accounting for the largest proportion in the total alkane gas production, reaching 41.73%. If the closed pore gas can be used in the current low-gas-yield coalbed methane wells, it will greatly increase the production capacity.

[0079] Comparative Example 1

[0080] Taking sample 1 as an example, comparative example 1 is set, and the specific operation is the same as that of example 1, except that the crushing time in the rapid determination of the desorbed gas content of the S2 closed pore is 6 hours.

[0081] Comparative Example 2

[0082] Taking sample 1 as an example, comparative example 2 is set. The specific operation is the same as that of example 1, except that the crushing time in the rapid determination of the desorbed gas content of the S2 closed pore is 14 hours.

[0083] Figure 7 The coal rock crushing particle size distribution diagrams of the coal rock sample 1 after grinding in Example 1, Comparative Example 1 and Comparative Example 2, wherein (a) is the coal rock crushing particle size distribution diagram of the coal rock sample 1 after grinding in Example 1 and Comparative Example 2, and (b) is the coal rock crushing particle size distribution diagram of the coal rock sample 1 after grinding in Comparative Example 1;

[0084] Figure 8 This is a comparative diagram of the gas chemical composition determination of the closed pores of coal rock sample 1 in Example 1, Comparative Example 1 and Comparative Example 2, wherein (a) is alkane gas, (b) is nitrogen, (c) is chlorine, and (d) is carbon dioxide.

[0085] from Figure 7 and Figure 8It can be seen that the particle size distribution of comparative example 1 is around 100 μm, and the alkane gas produced after 6 hours of crushing is 4.090 mL / g, which is far from 6.593 mL / g after 10 hours of crushing. The particle size distribution of comparative example 2 is 30-40 μm, which is close to the particle size of 10 hours of crushing, and the alkane gas measured after 14 hours of crushing is 6.852 mL / g, which is very close to 6.593 mL / g after 10 hours of crushing. Therefore, the present invention sets 10 hours as the crushing time, which ensures that the sample is fully crushed, the closed pore gas is fully released, and the crushing time is not too long to reduce the experimental efficiency.

[0086] The above are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for detecting the gas content and chemical composition of open pores and closed pores in coal and rock, characterized in that: The following steps are involved: The coal sample is heated in a water bath for the first time to complete open pore desorption, the desorption amount is determined by the water drainage gas collection method, and the chemical composition of the gas is determined by gas chromatography; the coal sample that has completed open pore desorption is crushed and heated in a water bath for a second time to complete closed pore desorption, the gas desorption amount is determined by the water drainage gas collection method, and the chemical composition of the gas is determined by gas chromatography; both the open pore desorption and the closed pore desorption are completed under closed conditions.

2. The method for detecting gas content and chemical composition of open pores and closed pores of coal and rock according to claim 1, characterized in that: The open hole desorption comprises the following steps: quickly loading the whole coal core after removing the gangue into the desorption tank, filling the remaining space with the broken coal sample, quickly tightening the tank cover, measuring the coal sample mass, checking the air tightness, and then immersing the desorption tank in water for the first water bath heating.

3. The method for detecting gas content and chemical composition of open pores and closed pores of coal and rock according to claim 2, characterized in that: The temperature of the first water bath heating is 100°C.

4. The method for detecting gas content and chemical composition of open pores and closed pores of coal and rock according to claim 2, characterized in that: The water bath heating was stopped when the open pore desorption continued until the desorption amount within 1 hour was less than 0.1 mL / g.

5. The method for detecting gas content and chemical composition of open pores and closed pores of coal and rock according to claim 1, characterized in that: The closed pore desorption comprises the following steps: The coal sample after the open pore desorption is placed in a ball mill pulverizing tank, and the ball mill pulverizing tank is evacuated and then pulverized. During the pulverizing process, the ball mill pulverizing tank is immersed in water and heated in a water bath for a second time.

6. The method for detecting gas content and chemical composition of open pores and closed pores of coal and rock according to claim 5, characterized in that: The temperature of the secondary water bath heating is 100°C.

7. The method for detecting gas content and chemical composition of open pores and closed pores of coal and rock according to claim 5, characterized in that: The crushing time is 10 hours.

8. The method for detecting gas content and chemical composition of open pores and closed pores of coal and rock according to claim 5, characterized in that: The water bath heating is stopped when the closed pore desorption continues until the desorption amount is less than 0.1 mL / g within 1 hour.

9. The method for detecting gas content and chemical composition of open pores and closed pores of coal and rock according to claim 1, characterized in that: The drainage gas collection method adopts a saturated salt water solution.

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