Method for measuring true density of coal rock

Abstract

According to the method for measuring the true density of the coal rock, provided by the invention, different evolution stages experienced by the coal rock in a complex geological history can be efficiently and accurately identified. The stages cover the initial diagenesis to the later metamorphism, and each stage is accompanied by significant changes of physical and chemical properties of the coal rock. Besides, the method also has excellent distinguishing capability, the carbonaceous mudstone can be clearly and effectively distinguished from other types of coal rocks, and the carbonaceous mudstone is used as a special sedimentary rock, has complex components, often contains relatively high organic matters, and has significant difference from conventional coal rocks in multiple aspects. Therefore, the method not only contributes to deepening the understanding of the formation cause and the evolution process of the coal rock, but also provides important technical support and scientific basis for the fields of exploration and development of coal resources, environmental protection and the like.

Description

Technical Field

[0001] This invention relates to the field of testing technology for the true density of common reservoir rocks such as coal, shale, and sandstone, and particularly to the determination of the true density of coal. Background Technology

[0002] Density, as one of the core indicators for evaluating the physical properties of coal and rock, occupies a crucial position in coal petrology research. It not only reflects the compactness, porosity, and density of the internal structure of coal and rock, but also serves as an important basis for predicting the reservoir performance, permeability, and gas content of coal and rock. In the geologically complex southern deep region of the Songliao Basin, numerous fault depressions and complex stratigraphic structures have been formed due to multiple phases of tectonic movement. These geological features provide favorable conditions for coal seam development, resulting in a region with multi-layered coal seams and abundant resource reserves. However, this complex geological background also increases the difficulty and risk of coal exploration, making the accurate evaluation of coal and rock properties a critical task. Precise measurement and analysis of coal and rock density can further reveal the reservoir performance, fluid migration patterns, and mining potential of coal and rock, providing a scientific basis and technical support for the effective exploration and development of deep coal and rock resources in the southern Songliao Basin. This is of great significance for the accurate evaluation of coal and rock properties.

[0003] The prior art CN103439238A discloses a method for measuring closed porosity in coal shale, which obtains the volume of open pores by testing true density and apparent density, and then obtains the volume of closed pores by methane experiment, thereby accurately calculating closed porosity and making the total porosity test result closer to the true value of coal shale underground. The true density of the sample is obtained as dr by the method for determining the true density of coal and rock GB / T23561.2-2009. However, this method cannot deepen the understanding of the genesis and evolution process of coal and rock.

[0004] Existing technology CN 109269938 A discloses a method for testing the true density of coal and rock. This invention discloses a method for testing the true density of coal and rock, including determining the formation temperature and pressure of the sample, testing the mass and volume of the sample container under no-load conditions, testing the mass and volume of the sample and sample container under test conditions, calculating the mass and volume of the sample under formation temperature and conditions, and calculating the true density of the sample under formation temperature and conditions. This testing method can minimize damage to the sample during sample preparation and reflects the true density of coal and rock under formation temperature and pressure conditions, but it lacks in-depth research on the genesis and evolution of coal and rock. Summary of the Invention

[0005] To achieve the above objectives, the technical solution protected by this invention is as follows:

[0006] S1. Sample pretreatment

[0007] Take a representative sample of 250-350g, grind it into powder, sieve it, and dry it.

[0008] S2. Boil the distilled water and cool it to room temperature;

[0009] S3. Take the specific gravity bottle, wash it with distilled water, and fill it with one-third distilled water;

[0010] S4. Accurately weigh 2-3g (M) of coal powder analysis sample with a particle size of less than 0.2mm, and transfer it all into a specific gravity bottle through a neckless funnel;

[0011] S5. Pour 3-4 mL of a 2% sodium dodecylbenzenesulfonate or sodium dodecyl sulfate solution into the specific gravity bottle, let it stand to allow the sample to soak through, and then add 25 mL of distilled water along the bottle wall.

[0012] S6. Place the specific gravity bottle in a water bath or sand bath and boil for 20-30 minutes to remove the adsorbed gas;

[0013] S7. Remove the specific gravity bottle and add pure water cooled to room temperature; then place it in a thermostat and keep it at that temperature for 1–3 hours.

[0014] S8. Add a certain amount of room temperature pure water to the bottle mouth, and put on the bottle stopper to ensure that there are no air bubbles in the specific gravity bottle and capillary tube;

[0015] S9. Dry the specific gravity bottle and weigh the specific gravity bottle after adding the sample, M1.

[0016] S10. Correct the specific gravity bottle and weigh the water in the bottle to obtain M2;

[0017] S11. Calculate the true density of the sample.

[0018] Furthermore, in step S1, the sample is pulverized into small pieces using a pulverizer, then ground into powder using a grinding mill, and all of it is passed through a 0.2 mm sieve. Iron filings mixed in with the coal powder are removed using a magnet. The prepared coal sample is dried at 105℃~110℃ for 24 hours, then removed and placed in a desiccator to cool to room temperature.

[0019] Furthermore, step S4 is accurate to ±0.001g.

[0020] Further, in step S5, 3 mL of a 2% sodium dodecylbenzenesulfonate or sodium dodecyl sulfate solution is injected into the specific gravity bottle using a graduated cylinder, taking care to flush any coal particles adhering to the bottle wall into the bottle. The specific gravity bottle is then gently rotated and left to stand for 15 minutes to allow the sample to soak through. Then, 25 mL of distilled water is added along the bottle wall.

[0021] Furthermore, in step S7, the specific gravity bottle is removed, freshly boiled distilled water is added until the water level is about 1 cm below the bottle opening, and then cooled to room temperature; then it is placed in a thermostat at (20 ± 0.5) °C or slightly below room temperature and kept at that temperature for 1 hour (or it can be left at room temperature for more than 3 hours, or preferably overnight if sodium dodecyl sulfate solution is used), and the room temperature is recorded.

[0022] S8. Use a straw to add boiled 20°C or room temperature distilled water to the bottle mouth along the neck of the bottle, and put the bottle stopper on, so that the excess water overflows from the capillary tube on the bottle stopper (at this time there should be no air bubbles in the bottle or the capillary tube, otherwise water should be added and the bottle stopper should be put back on).

[0023]

[0024] In the formula:

[0025] d—True density of the sample, in grams per cubic centimeter (g / cm³) 3 );

[0026] M—Sample mass, in grams (g);

[0027] M1—Combined weight of specific gravity bottle, coal sample, lubricant and distilled water, in grams (g);

[0028] M2 — The combined weight of the specific gravity bottle and the full bottle of distilled water, in grams (g);

[0029] d s —The density of distilled water at room temperature, expressed in grams per cubic centimeter (g / cm³). 3 ), d s ≈1g / cm 3 .

[0030] Perform two parallel determinations and take the arithmetic mean. Round the result to three significant figures. If the difference between the two determinations exceeds 0.02 g / cm³, the determination is considered complete. 3 It should be redone.

[0031] Furthermore, in step S10, the correction M2 of the specific gravity bottle in this invention is accurate to 0.001g. Its calculation is as follows:

[0032]

[0033] In the formula:

[0034] T1—Correction temperature;

[0035] T2—Calculation temperature;

[0036] M2 — The total weight of water in the bottle at temperature T2, in grams (g);

[0037] M2 ’—The total weight of the water in the bottle at temperature T1 (m2) ’ Weigh three times and take the arithmetic mean, in grams (g);

[0038] M4 - The mass of the specific gravity bottle at temperature T1 (weighed three times after being washed with distilled water, dried and cooled to room temperature, and the arithmetic mean is taken), in grams (g).

[0039] d s1 —The density of water at temperature T1, expressed in grams per cubic centimeter (g / cm³). 3 );

[0040] d s2 —The density of water at temperature T2, expressed in grams per cubic centimeter (g / cm³). 3 );

[0041] ε γ —Coefficient of glass expansion and contraction, ε γ =2.4×10 -5 C -1 .

[0042] If the test is conducted under constant temperature conditions, the specific gravity bottle should be calibrated accordingly when the test temperature changes.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] The method provided by this invention can efficiently and accurately identify the different evolutionary stages of coal and rock in their complex geological history. These stages cover the period from initial diagenesis to later metamorphism, each accompanied by significant changes in the physical and chemical properties of the coal and rock. Furthermore, this method possesses excellent distinguishing ability, effectively differentiating carbonaceous mudstone from other types of coal and rock. As a special type of sedimentary rock, carbonaceous mudstone has a complex composition, often containing high levels of organic matter, and differs significantly from conventional coal and rock in many aspects. Based on a series of rigorous and detailed experimental data statistical patterns, this invention found that the true relative density of coal and rock samples collected in the experimental area generally ranges from 1.4 to 2.0 g / cm³. 3 Within this range, the density not only reveals the physical properties of the coal and rock samples but also indirectly reflects the diversity of their geological origin and composition. Therefore, the implementation of this invention not only helps to deepen the understanding of the genesis and evolution of coal and rock but also provides important technical support and scientific basis for the exploration, development, and environmental protection of coal resources. Detailed Implementation

[0047] Furthermore, the technical features involved in the different embodiments of this disclosure described below can be combined with each other as long as they do not conflict with each other.

[0048] The main instruments and equipment used in this invention are as follows:

[0049]

[0050]

[0051] The main reagents involved in this invention are as follows:

[0052] Sodium dodecylbenzenesulfonate (C 18 H 29 NaSO3), analytical grade, 2% aqueous solution.

[0053] Sodium dodecyl sulfate (C 12 H 25 NaSO4), analytical grade, 2% aqueous solution.

[0054] Example 1

[0055] S1. Sample pretreatment

[0056] Take a representative sample of 300g, crush it into small pieces using a pulverizer, then grind it into powder using a grinder, ensuring that all of it passes through a 0.2mm sieve. Use a magnet to remove any iron filings mixed in with the coal powder. Dry the prepared coal sample at 105℃~110℃ for 24h, then remove it and cool it to room temperature in a desiccator.

[0057] S2. Boil the distilled water and cool it to room temperature;

[0058] S3. Take a 50mL specific gravity bottle with a neck and stopper that match, wash it with distilled water, fill it with one-third distilled water, and wipe the outer surface of the bottle dry.

[0059] S4. Accurately weigh 2g of coal powder analysis sample with a particle size of less than 0.2mm (accurate to ±0.001g), and carefully transfer it all into the specific gravity bottle through a neckless funnel.

[0060] S5. Using a graduated cylinder, pour 3 mL of a 2% sodium dodecylbenzenesulfonate or sodium dodecyl sulfate solution into the specific gravity bottle, taking care to flush any coal particles adhering to the bottle wall into the bottle. Gently rotate the specific gravity bottle and let it stand for 15 minutes to allow the sample to soak through. Then add 25 mL of distilled water along the bottle wall.

[0061] S6. Move the specific gravity bottle to a water bath or sand bath and boil for 20 minutes to remove the adsorbed gas.

[0062] S7. Remove the specific gravity bottle, add freshly boiled distilled water until the water level is about 1 cm below the bottle opening, and cool to room temperature. Then place it in a thermostat at (20 ± 0.5) °C or slightly below room temperature, keep it at that temperature for 1 hour, and record the room temperature.

[0063] S8. Use a straw to add boiled 20°C or room temperature distilled water along the neck of the bottle to the mouth, then put the stopper on the bottle and let the excess water overflow from the capillary tube on the stopper (at this time, there should be no air bubbles in the bottle or the capillary tube; otherwise, water should be added and the stopper should be put back on).

[0064] S9. Quickly dry the specific gravity bottle and immediately weigh the specific gravity bottle containing the coal powder sample, lubricant, and water, M1.

[0065] S10. Calibrate the specific gravity bottle, weigh the water in the bottle to obtain M2, accurate to 0.001g.

[0066] Depending on the specific experimental conditions, any of the following methods can be selected to calibrate the specific gravity bottle:

[0067] If the test volume is small, the calibration can be performed once during each test, and the combined weight of the bottle and water can be calculated.

[0068] If the experiment involves a large number of samples, the specific gravity bottle can be calibrated twice a year, in spring and autumn, when the room temperature is around 20°C. The total weight of the water in the bottle at each temperature should be calculated and listed for future reference. The calculation is as follows:

[0069]

[0070] In the formula:

[0071] M2 — The total weight of water in the bottle at temperature T2 (calculated temperature), in grams (g);

[0072] M2 ’ —The total weight of the water in the bottle at temperature T1 (corrected temperature) (m2) ’ Weigh three times and take the arithmetic mean, in grams (g);

[0073] M4 - The mass of the specific gravity bottle at temperature T1 (it should be washed with distilled water, dried and cooled to room temperature, weighed three times, and the arithmetic mean should be taken), in grams (g).

[0074] d s1 —The density of water at temperature T1, expressed in grams per cubic centimeter (g / cm³). 3 );

[0075] d2 — The density of water at temperature T2, expressed in grams per cubic centimeter (g / cm³) 3 );

[0076] ε γ : — Coefficient of glass expansion and contraction, ε γ=2.4×10 -5 C -1 .

[0077] If the test is conducted under constant temperature conditions, the specific gravity bottle should be calibrated accordingly when the test temperature changes.

[0078] Calculation formula:

[0079]

[0080] In the formula:

[0081] d—True density of the sample, in grams per cubic centimeter (g / cm³) 3 );

[0082] M—Sample mass, in grams (g);

[0083] M1—Combined weight of specific gravity bottle, coal sample, lubricant and distilled water, in grams (g);

[0084] M2 — The combined weight of the specific gravity bottle and the full bottle of distilled water, in grams (g);

[0085] d s —The density of distilled water at room temperature, expressed in grams per cubic centimeter (g / cm³). 3 ),

[0086] d s ≈1g / cm 3 .

[0087] Perform two parallel determinations and take the arithmetic mean. Round the result to three significant figures. If the difference between the two determinations exceeds 0.02 g / cm³, the determination is considered complete. 3 It should be redone.

[0088] Experimental results:

[0089]

[0090] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for determining the true density of coal and rock, characterized in that, Includes the following steps: S1. Sample pretreatment: Take a representative sample, crush and grind it into powder, sieve it, and dry it; S2. Boil the distilled water and cool it to room temperature; S3. Take the specific gravity bottle, wash it with distilled water, and fill it with distilled water; S4. Accurately weigh the coal powder analysis sample and transfer it entirely into the specific gravity bottle through a neckless funnel; S5. Pour sodium dodecylbenzenesulfonate or sodium dodecyl sulfate solution into the specific gravity bottle, let it stand to allow the sample to soak through, and then add distilled water along the bottle wall; S6. Move the specific gravity bottle to a water bath or sand bath and boil it to remove the adsorbed gas; S7. Remove the specific gravity bottle and add pure water cooled to room temperature; then place it in a thermostat and keep it at that temperature for 1–3 hours. S8. Add a certain amount of room temperature pure water to the bottle mouth, and put on the bottle stopper to ensure that there are no air bubbles in the specific gravity bottle and capillary tube; S9. Wipe the specific gravity bottle dry and weigh the specific gravity bottle after adding the sample, M1. S10. Correct the specific gravity bottle, weigh the specific gravity bottle and the combined weight of water to obtain M2; S11. Calculate the true density of the sample.

2. The method according to claim 1, characterized in that, In step S11, the calculation formula is as follows: In the formula: d—True density of the sample, g / cm³ 3 ; M—Sample mass, g; M1—Combined weight of specific gravity bottle, coal sample, lubricant and distilled water, in g; M2 — Total weight of the hydrostatic bottle and the full bottle of distilled water, in g; d s —Density of distilled water at room temperature, g / cm³ 3 d s ≈1g / cm 3 .

3. The method according to claim 1, characterized in that, In step S1, the sample is crushed into small pieces by a pulverizer, then ground into powder by a grinding mill, and all of it is made to pass through a 0.2 mm sieve; iron filings mixed in with the coal powder are removed by a magnet; the prepared coal sample is dried at 105℃~110℃ for 24 hours and then placed in a desiccator to cool to room temperature.

4. The method according to claim 1, characterized in that, In step S1, a representative sample of 250-350g is used.

5. The method according to claim 1, characterized in that, The accuracy of step S4 is ±0.001g.

6. The method according to claim 1, characterized in that, In step S5, 3-4 mL of a 2% sodium dodecylbenzenesulfonate or sodium dodecyl sulfate solution is injected into the specific gravity bottle using a graduated cylinder, and left for 15 minutes to allow the sample to soak through; then 25 mL of distilled water is added along the bottle wall.

7. The method according to claim 1, characterized in that, In step S7, the specific gravity bottle is removed, and boiled distilled water is added until the water level is 1 cm below the bottle opening. The bottle is then cooled to room temperature. The bottle is then placed in a thermostat at 20 ± 0.5 °C or slightly below room temperature for 1 hour, and the room temperature is recorded.

8. The method according to claim 7, characterized in that, Let it stand overnight in sodium dodecyl sulfate solution.

9. The method according to claim 1, characterized in that, Step S8: Use a straw to add boiled 20°C or room temperature distilled water to the bottle mouth along the neck of the bottle, and put on the stopper so that the excess water overflows from the capillary tube on the stopper.

10. The method according to claim 1, characterized in that, The calculation formula for step S10 is as follows: In the formula: T1—Correction temperature; T2—Calculation temperature; M2—The total weight of the water in the bottle at temperature T2, in grams; M2 ’ —The total weight of the water in the bottle at temperature T1, in grams; M4 - Mass of the hydrometer bottle at temperature T1, in g; d s1 —The density of water at temperature T1, in g / cm³ 3 ; d s2 —The density of water at temperature T2, in g / cm³ 3 ; ε γ —Coefficient of glass expansion and contraction, ε γ =2.4×10 -5 C -1 .

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