Method for measuring and calculating maximum water storage capacity and water storage coefficient of coal mine underground reservoir

Abstract

The invention discloses a method for measuring and calculating the maximum water storage capacity and the maximum water storage coefficient of a coal mine underground reservoir, and belongs to the technical field of coal mining and water conservancy projects. The method comprises the following steps: firstly, selecting a coal mine underground reservoir with preset closed conditions, setting observation points, and recording initial pressure and temperature of the observation points of the reservoir; then gas medium intervention operation of gas injection or gas extraction is carried out on the reservoir capacity occupied by the reservoir gas, the gas medium flow and the current pressure and the current temperature of an observation point are recorded, and then a pressure change value and a temperature change value are obtained; calculating the gas storage capacity; and finally, summing the gas storage capacity and the known water storage capacity to obtain the total storage capacity of the coal mine underground reservoir, namely the maximum water storage capacity. The water storage coefficient can be further measured and calculated based on the ratio of the total storage capacity to the total space volume related to water storage and gas storage of the reservoir. The method does not need long-term testing, is short in measurement period and low in cost, and can break through water level limitation to realize measurement and calculation of the maximum water storage capacity and the total water storage coefficient.

Description

Technical Field

[0001] This invention belongs to the field of coal mining and water conservancy engineering technology, specifically relating to a method for calculating the maximum water storage capacity of underground reservoirs in coal mines. This invention also relates to a method for calculating the water storage coefficient of underground reservoirs in coal mines. Background Technology

[0002] Western my country, as a core coal-producing region, already suffers from a fragile ecological environment and faces inherent challenges such as drought, low rainfall, and insufficient water resources. Coal mining operations consume significant amounts of water to ensure production, and these activities themselves disrupt and damage existing groundwater systems, further exacerbating the imbalance between water supply and demand in the west and placing significant pressure on local ecological and economic sustainable development. Therefore, how to ensure the rational development of coal resources while effectively protecting water resources has become a critical issue that urgently needs to be addressed in the western energy development sector.

[0003] To address this issue, academia and industry have previously proposed water-conserving coal mining technologies such as height-restricted mining, backfilling mining, and zoned avoidance mining. These methods reduce disturbance to the coal seam overburden structure and aquifers by optimizing mining processes, thus alleviating water resource damage to some extent. However, they also have limitations such as low mining efficiency and low coal resource recovery rate, making it difficult to simultaneously meet the dual needs of ecological protection and energy development.

[0004] To overcome this predicament, researchers have innovatively proposed a solution: constructing underground water reservoirs in coal mines. By building a multi-functional underground water conservancy system that integrates water storage, purification, use, and protection, the damage to groundwater caused by mining activities can be minimized without reducing coal mining efficiency or affecting resource utilization. Furthermore, it allows for the recycling and reuse of mine water resources, effectively addressing the coal mining enterprises' own water needs and forming a virtuous cycle of "energy development—water resource protection—recycling."

[0005] Determining the capacity and storage coefficient of underground coal mine reservoirs is crucial for their construction. Currently, the capacity and storage coefficient of underground coal mine reservoirs are primarily estimated through theoretical methods and pumping tests. While rock strata movement theory and experimental measurement data can provide approximate estimates of the reservoir's capacity and storage coefficient, the error is significant. Pumping tests can measure the reservoir's capacity and storage coefficient, but this process is time-consuming and costly, typically requiring more than six months. For underground reservoirs constructed with narrow coal pillar dams, safety considerations dictate that the water level is usually limited to 6-8 meters. Therefore, traditional pumping test-based methods can only measure the capacity and storage coefficient within a 6-8 meter elevation range, making it difficult to assess the overall capacity (maximum storage) and storage coefficient of the entire underground coal mine reservoir. Summary of the Invention

[0006] The purpose of this invention is to provide a method for calculating the maximum water storage capacity of underground reservoirs in coal mines, which has the advantage of a short testing cycle.

[0007] The technical solution adopted in this invention is a method for calculating the maximum water storage capacity of underground reservoirs in coal mines, comprising the following steps: Step 1: Select a coal mine underground water reservoir with preset closed conditions, set up observation points in the reservoir, and record the initial pressure and temperature at the observation points; Step 2: Perform gas medium intervention operation on the reservoir capacity occupied by gas. After completion, record the gas medium flow rate and the current pressure and temperature at the observation point. Step 3: Calculate the pressure and temperature changes at the observation points, and calculate the gas capacity of the reservoir based on the gas flow rate. Step 4: Calculate the total capacity of the underground water reservoir in the coal mine, i.e., the maximum water storage capacity, based on the gas storage capacity and the water storage capacity of the reservoir.

[0008] The invention is further characterized by: In step 1, the observation points are set on the water-near side of the artificial dam, the water-near side of the coal pillar dam, the water-near side of the reservoir bottom plate, or the water-near side of the reservoir top plate.

[0009] If the observation point is occupied by water, record the water pressure and water temperature at that point; otherwise, record the air pressure and air temperature at that point.

[0010] Step 2 involves gas medium intervention operations, including gas injection into the goaf or gas extraction from the goaf.

[0011] After the gas injection operation in step 2, the current pressure is (1.1~2.0) times the initial pressure, and after the gas extraction operation, the current pressure is (0.1~0.9) times the initial pressure.

[0012] In step 3, the gas storage capacity is calculated according to formula (1). (1) in, For gas storage capacity, Q This refers to the total flow rate of the injected or extracted gas. Temperature influence coefficient , The initial pressure at the observation point, The initial temperature at the observation point, The pressure at the observation point after gas injection or extraction. The temperature at the observation point after gas injection or extraction. In step 4, the total reservoir capacity is calculated according to formula (2). (2) in, The total capacity of the reservoir The water volume of the reservoir.

[0013] Multiple observation points were selected for testing, and the average of the total storage capacity calculated from the multiple test points was taken as the final total storage capacity.

[0014] The second technical solution adopted in this invention is a method for calculating the water storage coefficient of underground reservoirs in coal mines, calculated according to formula (3). (3) in, R The water storage coefficient, It is the total storage capacity of the reservoir. It refers to the total spatial volume related to the water and gas storage space of the reservoir.

[0015] The second technical solution of the present invention is further characterized by: Calculated according to equation (4), (4) in, It is the total space length related to water and gas storage space. It refers to the total space width related to water and gas storage space. It refers to the total spatial height related to water and gas storage space.

[0016] The beneficial effects of this invention are: The method of this invention is based on the compressibility of gas. Within a confined, enclosed space, the pressure changes rapidly with the gas flow rate after gas is injected or extracted. By recording the initial and subsequent pressure, temperature, and gas flow rate, the gas reservoir capacity can be directly calculated using a formula. Combined with the known water reservoir capacity, the total reservoir capacity is obtained. The entire process revolves around changes in the gas state, resulting in a rapid response. In contrast, existing water injection and pumping tests rely on the water infiltration and filling process. This requires slowly injecting or pumping water into the reservoir, waiting for the water to fully infiltrate and stabilize in rock fissures and mined-out areas before the reservoir capacity can be calculated from changes in water volume. This process is greatly affected by the rock permeability coefficient and spatial connectivity, requiring long-term monitoring of the water level and volume. Therefore, the method of this invention significantly shortens the measurement cycle. Attached Figure Description

[0017] Figure 1 This is a flowchart of the method of the present invention; Figure 2 This is a schematic diagram of an implementation scenario of Embodiment 1 of the present invention; In the diagram: 1. Coal pillar, 2. Artificial dam, 31. Pressure sensor one, 32. Pressure sensor two, 33. Pressure sensor three, 4. Ventilation pipeline. Detailed Implementation

[0018] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0019] This invention provides a method for calculating the maximum water storage capacity of underground reservoirs in coal mines. This method is based on the principles of gas injection and gas compressibility. Taking the gas injection process as an example, it mainly includes the following steps: Figure 1 As shown: Step 1: Before injecting gas, record the initial water level in the reservoir. h Record the initial pressure at the observation point. and temperature ; The initial water level is calculated based on the lowest point of the reservoir. Observation points are set at any of the following locations: the water-side of the artificial dam, the water-side of the coal pillar dam, the water-side of the reservoir floor, or the water-side of the reservoir roof. If an observation point is occupied by water, the water pressure at that point is recorded. and water temperature If the observation point is occupied by air, record the air pressure at the observation point. and temperature .

[0020] Step 2: Select either method 1 or method 2. Method 1: Inject gas into the goaf of the reservoir and record the pressure at the observation point during the gas injection process. and temperature ,when Stop injecting gas and calculate the total flow rate of injected gas. Q ( Q This refers to the flow rate under converted standard conditions); Method 2: Extract gas from the goaf and record the pressure at the observation points during the extraction process. and temperature ,when Stop pumping gas and calculate the total flow rate of the pumped gas. Q ( Q This refers to the converted flow rate under standard conditions.

[0021] Preferably, a compressor is used to inject air into the goaf, and the flow rate is controlled by a valve; a high-pressure, high-flow-rate pump is used to inject air into the goaf of the reservoir, and the pumped gas flow rate is converted into the gas flow rate under standard conditions. Q .

[0022] Step 3: Calculate the storage capacity occupied by the gas according to equation (1). (1) in, For gas storage capacity, Q This refers to the total flow rate of the injected or extracted gas. Temperature influence coefficient , The initial pressure at the observation point, The initial temperature at the observation point, The pressure at the observation point after gas injection or extraction. The temperature at the observation point after gas injection or extraction.

[0023] Equation (1) is derived from the ideal gas law. If the temperature change during the gas injection process is within 10℃, the temperature influence coefficient is... It can be approximated as 1.

[0024] Step 4: Based on the reservoir capacity occupied by gas calculated in Step 3, combine it with the reservoir capacity occupied by water. The total capacity of the underground reservoir in the coal mine is calculated according to formula (2), which is the maximum water storage capacity of the reservoir. (2) Reservoir capacity occupied by water It is a known quantity; the total capacity of a coal mine underground reservoir refers to the maximum volume of water that the reservoir space can hold.

[0025] The above method for calculating the maximum water storage capacity of underground reservoirs in coal mines is based on the principle of gas injection. According to the principle of gas compressibility, injecting gas into a confined space will cause the gas pressure to increase, and the volume of the space can be calculated using the gas law. Alternatively, the principle of gas extraction can also be used. The calculation formula based on the gas extraction principle is the same as that based on the gas injection principle. According to the principle of gas compressibility, pumping out gas into a confined space will cause the gas pressure to decrease, and the volume of the space can be calculated using the gas law.

[0026] This invention also provides a method for calculating the water storage coefficient of underground reservoirs in coal mines, calculated according to formula (3). (3) in, R The water storage coefficient, It is the total storage capacity of the reservoir. This refers to the total spatial volume (including the total volume of solids and water) related to the reservoir's water and gas storage space. The total spatial volume related to the reservoir's water and gas storage space is the volume of the coal mine goaf. , This refers to the total length of the space related to water and gas storage, determined based on on-site measurements. It is the total space width related to the water and gas storage space, determined by measurement. It is the total space height related to the water and gas storage space, determined by measurement.

[0027] Furthermore, this formula can also be used to calculate the water storage coefficient of the gas region in the reservoir. and water storage coefficient of water body area , ,in, It is the storage capacity occupied by gas. It is the total spatial volume related to the gas storage space (including the total spatial volume of solids and gases), according to , It is the total space length related to the gas storage space, determined based on on-site measurements. It is the total width of the space related to the gas storage space, determined by measurement. It is the total space height related to the gas storage space, determined by measurement; ,in, It is the reservoir capacity occupied by water bodies. That is, the volume of water already stored. It is the total spatial volume related to the water storage space (including the total spatial volume of solids and water), according to , It is the total length of the space related to the water storage space, determined based on on-site measurements. It is the total width of the space related to the water storage space, determined by measurement. It is the total height of the space related to the water storage space, determined by measurement; Example 1 The method for calculating the maximum water storage capacity of underground reservoirs in coal mines provided in this embodiment is used to calculate the storage capacity of the underground reservoir in the No. 52 coal seam of the Daliuta Coal Mine. (The Daliuta Coal Mine underground reservoir is shown in the image.) Figure 2 As shown, the reservoir has the following characteristics: (1) the fissure zone in the reservoir area is not connected to the ground; (2) the fissure zone in the reservoir area is not connected to the fissure zone in the adjacent basin area; and (3) the fissure zone in the reservoir area is not connected to the fissure zone in the adjacent reservoir or has poor connectivity.

[0028] Preparations before gas injection include: Pipeline and pump station setup: Ventilation ports are installed on the artificial dam 2 or coal pillar 1, and water injection ports can be used as ventilation ports. Ventilation pipeline 4 is connected to a centrifugal compressor, which is located in the ground or underground roadway. Air is injected into the reservoir or extracted from the reservoir through the centrifugal compressor and ventilation pipeline 4.

[0029] Install flow and pressure sensors: Install a flow meter and a pressure gauge on the ventilation pipe 4. Install pressure gauges on the water-near side of the dam body around the reservoir, that is, install 3-5 pressure gauges on the water-near side of the artificial dam body (or coal pillar dam body, roof, and floor) to measure water pressure or air pressure. In this embodiment, pressure sensor 31 and pressure sensor 32 are installed at the bottom and top of the artificial dam body, respectively, and pressure sensor 33 is installed at the top of the coal pillar dam body.

[0030] The reservoir capacity test using the air injection method mainly includes the following steps: Step 1: Select the top of the artificial dam, i.e., the location of pressure sensor 32, as the observation point. This observation point is occupied by air. Record the initial pressure of pressure sensor 32 before air injection. The pressure is 0.101 MPa (standard atmosphere), and the temperature at this location is measured. It is 25℃, or 298K.

[0031] Step 2: Inject air into the reservoir through the ventilation pipe 4 and monitor the flow rate.

[0032] By using ground pumping stations and air compressors to pump air into the reservoir, the existing water diversion pipelines of the reservoir can be used as air transmission pipelines, which can shorten the measurement cycle and reduce construction costs.

[0033] In this embodiment, the gas injection flow rate is set to 10000 m³ / h. 3 / h, in the first stage, after 10 hours of continuous pumping, the pressure of pressure sensor 32 is... The pressure is 0.111 MPa, and the gas injection rate is 100,000 m³. 3 Temperature after gas injection It is 28℃, or 301K.

[0034] calculate , Step 3: Based on the calculated storage capacity occupied by the gas, = =1140000m 3 .

[0035] Step 4: The reservoir's water volume is known. 160,000m 3 Combined with the storage capacity occupied by the aforementioned gases Calculate the total storage capacity of underground reservoirs in coal mines. , =1140000m 3 +160000m 3 =1300000m 3 in, This is the volume of the goaf in this coal mine; its length was measured on-site. It is 3000m wide It is 200m high. It is 20m. m 3 .

[0036] Furthermore, the overall water storage coefficient of the reservoir is calculated. , =0.108.

[0037] Example 2 Based on Example 1, this example uses the same centrifugal compressor as in the first stage, maintaining a stable flow rate of 10,000 m³ / s under standard conditions. 3 At a rate of / h, the second stage of gas injection begins, continuing for 10 hours, with a total injection volume of 200,000 cubic meters. At this point, the pressure at the observation point... The pressure is 0.121 MPa, and the temperature after gas injection is... It is 28℃, or 301K.

[0038] Based on the second-stage gas injection data and the above formulas (1)-(4), the reservoir capacity and water storage coefficient are calculated again: Temperature influence coefficient , Storage capacity occupied by gas = =1080000m 3 , Calculate the total storage capacity of underground water reservoirs in coal mines = =1080000m 3 +160000m 3 =1240000m 3 , Overall water storage coefficient =0.103.

[0039] Example 3 Based on Example 1, the top of the coal pillar dam was selected as the observation point, i.e., the location of pressure sensor 33. Initially, this observation point was occupied by air. Using the same equipment and pipeline as in Example 1, the reservoir capacity was tested in the air extraction mode. Record the initial pressure of pressure sensor 333 before evacuation. The pressure is 0.101 MPa (standard atmosphere), and the temperature at this location is measured. The temperature is 25℃ (298K). Under standard conditions, the extraction flow rate is stably controlled at 8000 m³ / s. 3 / h, continuous evacuation for 12 hours, the total evacuation volume (volume of gas removed) under standard conditions is 96000 m³ / h. 3 After the evacuation is complete, stabilize for 10 minutes and record the data at the observation points: The pressure is 0.092 MPa, and the temperature after gas injection is... It is 24℃ (297K).

[0040] The calculation is as follows: Temperature influence coefficient , Storage capacity occupied by gas =1080000m 3 , Total reservoir capacity =1080000m 3 +160000m 3 =1240000m 3 , Overall water storage coefficient =0.103.

[0041] Example 4 Based on Example 3, the top of the coal pillar dam was selected as the observation point, and the reservoir capacity was tested using the air extraction mode: Record the initial pressure of pressure sensor 33. The pressure is 0.101 MPa (standard atmosphere), and the temperature at this location is measured. The temperature is 25℃ (298K). Under standard conditions, the extraction flow rate is stably controlled at 8000 m³ / s. 3 / h, continuous pumping for 24 hours, the total pumping volume under standard conditions is 192000m³. 3 After the evacuation is complete, stabilize for 10 minutes and record the data at the observation points: The pressure is 0.083 MPa, and the temperature after gas injection is... It is 25℃ (298K).

[0042] The calculation is as follows: Temperature influence coefficient , Storage capacity occupied by gas =1080000m 3 , Total reservoir capacity =1080000m 3 +160000m 3 =1240000m 3 , Overall water storage coefficient =0.103.

[0043] Example 5 Based on Example 1, the bottom of the artificial dam was selected as the observation point, i.e., the location of pressure sensor 31. An air injection test was conducted to measure water pressure and temperature. The observation point was initially occupied by water. Using the same equipment and piping as in Example 1, the reservoir capacity was tested in air injection mode. Record the initial pressure of pressure sensor 31 The pressure is 0.12 MPa; measure the temperature at that location. The temperature was 22℃ (295K). Because the observation point was located at the bottom of the artificial dam, it was necessary to ensure that the outlet of the ventilation pipeline was higher than the initial water level to prevent backflow. A waterproof valve was also installed in the pipeline. Gas was continuously injected into the reservoir's mined-out area for 9 hours, with the injection flow rate consistently controlled at 10,000 m³ / h under standard conditions. 3 / h, with a total gas injection volume of 90,000 m³ under standard conditions. 3 After the gas injection is completed and the system has been stable for 10 minutes, the data at the observation points are recorded. The pressure is 0.13 MPa, and the temperature after gas injection is... It is 22℃ (295K).

[0044] The calculation is as follows: Temperature influence coefficient , Storage capacity occupied by gas =1080000m 3 , Total reservoir capacity =1080000m 3 +160000m 3 =1240000m 3 , Overall water storage coefficient =0.103.

[0045] Example 6 This embodiment, based on five sets of independently calculated data from embodiments 1-5, reduces the random errors of single observation points and single test modes by calculating the arithmetic mean of the total reservoir capacity and water storage coefficient, thereby improving the engineering reference accuracy of key parameters of the underground water reservoir in the No. 52 coal seam of Daliuta Coal Mine. All calculations are based on the same total spatial volume and water reservoir capacity of the goaf. Average total storage capacity (maximum water storage) =1252000m 3 .

[0046] Calculated based on the average total storage capacity = =0.104, Based on the direct averaging of water storage coefficients in each embodiment .

[0047] The results from both methods were consistent, verifying the accuracy of the calculation.

[0048] Based on field experience, the water-bearing area is located in a rock collapse zone, where the water storage coefficient is relatively large, typically greater than 0.1. Above the road crossing is a fracture zone, where the water storage coefficient is relatively small, typically less than 0.1. The local water storage coefficient of the already-stored area can be obtained using pumping and injection methods, but the pumping and injection cycle is usually quite long.

[0049] The above description is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention. Structures, devices, and operating methods not specifically described or explained in this invention are implemented according to conventional methods in the art unless otherwise specified or limited.

Claims

1. A method for calculating the maximum water storage capacity of a coal mine underground reservoir, characterized in that, The method comprises the following steps: Step 1, selecting a coal mine underground reservoir under preset closed conditions, setting an observation point of the reservoir, and recording initial pressure and temperature of the observation point; Step 2, performing a gas medium intervention operation on the reservoir capacity occupied by the gas, and recording the gas medium flow and the current pressure and current temperature at the observation point after the operation is completed; Step 3, calculating the pressure change value and temperature change value at the observation point, and calculating the gas capacity of the reservoir in combination with the gas medium flow; Step 4, calculating the total capacity of the coal mine underground reservoir, i.e. the maximum water storage capacity, according to the gas capacity and in combination with the water capacity of the reservoir.

2. The method for calculating the maximum water storage capacity of a coal mine underground reservoir according to claim 1, characterized in that, The observation point in step 1 is set on the near-water side of an artificial dam body, the near-water side of a coal pillar dam body, the near-water side of a reservoir bottom plate or the near-water side of a reservoir top plate.

3. The method for calculating the maximum water storage capacity of a coal mine underground reservoir according to claim 1, characterized in that, If the observation point is occupied by water, the water pressure and water temperature at the point are recorded, otherwise the air pressure and air temperature at the point are recorded.

4. The method for calculating the maximum water storage capacity of a coal mine underground reservoir according to claim 1, characterized in that, The gas medium intervention operation in step 2 comprises gas injection operation of injecting gas into a goaf or gas extraction operation of extracting gas from the goaf.

5. The method for calculating the maximum water storage capacity of a coal mine underground reservoir according to claim 4, characterized in that, After the gas injection operation in step 2, the current pressure is (1.1-2.0) times the initial pressure, and after the gas extraction operation, the current pressure is (0.1-0.9) times the initial pressure.

6. The method for calculating the maximum water storage capacity of a coal mine underground reservoir according to claim 4, characterized in that, The gas capacity in step 3 is calculated according to formula (1), （1） wherein, is the gas reservoir capacity, Q is the total gas flow rate of injection or extraction, is the temperature influence coefficient , is the initial pressure of the observation point, is the initial temperature of the observation point, is the pressure of the observation point after gas injection or extraction, is the temperature of the observation point after gas injection or extraction.

7. The method for calculating the maximum water storage capacity of a coal mine underground reservoir according to claim 1, characterized in that, The total capacity of the reservoir in step 4 is calculated according to formula (2), （2） wherein, the total reservoir capacity of the reservoir, is the water body reservoir capacity of the reservoir.

8. The method of claim 1, wherein, Multiple observation points are tested, and the average value of the total capacities calculated from multiple test points is taken as the final water capacity.

9. A method of calculating a water storage coefficient of a coal mine underground reservoir, characterized by, The formula (3) is used for calculation, （3） wherein, R is the water storage coefficient, is the total reservoir capacity, is the total volume of space associated with the water storage reservoir.

10. The method for calculating the storage coefficient of a coal mine underground reservoir according to claim 9, characterized in that, The According to calculation of formula (4), （4） wherein, Ltot is the total space length associated with the water and gas storage space, Wtot is the total space width associated with the water and gas storage space, Htot is the total space height associated with the water and gas storage space.

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