A test method for simulating coal dust discharge in coalbed methane wellbore

Abstract

The present invention belongs to the technical field of coal dust settling in coalbed methane wellbores, and in particular relates to a method for testing coal dust discharge in a simulated coalbed methane wellbore, comprising a coal dust input system and a gas input system connected to the top of a simulated wellbore, and a water injection system arranged at the bottom of the simulated wellbore. A coal dust drainage strength test system is provided in the simulated wellbore, and also comprises a recovery system located at the top of the simulated wellbore. The device can test the minimum discharge volume and coal dust migration state of the wellbore under different flow states such as single-phase water flow and gas / water two-phase flow, different coal dust particle sizes, different clay contents, different concentrations, etc., so as to provide a theoretical basis for the water injection amount of an on-site water reinjection device.

Description

Technical Field

[0001] The invention belongs to the technical field of coal dust settling in a coalbed methane wellbore, and in particular relates to a test method for simulating coal dust discharge in a coalbed methane wellbore. Background Art

[0002] Coalbed methane wells produce gas by draining water from the reservoir. When the coal is relatively broken, water, gas, coal powder and other multiphase fluids often coexist in the wellbore during drainage. If the coal powder in the wellbore is not discharged, the friction resistance of the pump rod will increase after settlement. In severe cases, the pump rod will break, causing shutdown and production, affecting the gas production of the coalbed methane well. In order to prevent the coal powder in the wellbore from agglomerating and settling, coalbed methane workers have developed a water reinjection device. By reinjecting water into the wellbore, the amount of water discharged from the wellbore is increased, the coal powder content in the wellbore is reduced, and the coal powder in the wellbore is kept in a suspended state as much as possible and discharged to the ground with the outflow of gas and water in the wellbore. However, it is currently impossible to give an accurate answer to how large the coal powder particles are and how much drainage intensity is required to allow the coal powder to be discharged with the migration of gas and water. It is more adjusted based on field experience and lacks scientific basis. Some scientific and technological workers judge whether the coal dust in the wellbore has settled seriously according to the change of current during drainage. Through the water injection device on the ground, water is injected into the annulus at a certain displacement, so that the settled coal dust in the wellbore is suspended, and a circulation system is formed with the drainage water in the production casing, and the coal dust is produced by water. If the current change cannot be discovered in time, or the water injection device is not drained in time, the sucker rod is likely to break, which increases the number of well repair operations and causes great damage to the reservoir. In order to better guide on-site production, it is urgent to develop a device that can test the minimum displacement test device for the appropriate discharge of coal dust in the wellbore under different flow states such as single-phase water flow stage, gas / water two-phase flow, different coal dust particle sizes, different clay mineral contents, and different concentrations, so as to provide theoretical guidance for the appropriate discharge of coal dust under different on-site conditions. Summary of the invention

[0003] The purpose of the present invention is to provide a method for testing the discharge of coal powder in a simulated coalbed methane wellbore, in order to address the problem that coal dust sedimentation in coalbed methane wellbore is serious and water reinjection relies more on experience, which cannot effectively ensure the timely discharge of coal dust in the wellbore and may cause oil rod breakage. The device can test the minimum discharge volume and coal dust migration state of coal dust in the wellbore under different flow states such as single-phase water flow and gas / water two-phase flow, different coal dust particle sizes, different clay contents, and different concentrations, so as to provide a theoretical basis for the water injection volume of the on-site water reinjection device.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is:

[0005] A method for testing the discharge of coal dust in a simulated coalbed methane wellbore, wherein the testing device comprises a coal dust input system and a gas input system connected to the top of the simulated wellbore, and a water injection system arranged at the bottom of the simulated wellbore, wherein a coal dust drainage strength testing system is arranged in the simulated wellbore, and further comprises a recovery system located at the top of the simulated wellbore, and the device achieves the minimum discharge volume and coal dust migration state of the coal dust in the wellbore under different flow states, different coal dust particle sizes, different clay contents, different concentrations and the like through mutual coordination between various systems, so as to provide a theoretical basis for the water injection volume of the on-site water injection device; the testing method comprises the following steps:

[0006] 1) Preparation of experimental coal powder samples: Prepare coal powder of required particle size according to the actual coal powder situation in the wellbore;

[0007] 2) Assemble the experimental device and conduct airtightness test;

[0008] 3) Experimental test of moderate coal powder discharge: According to the experimental plan, experimental tests are carried out under conditions of different coal powder particle sizes, different contents, single-phase water or single-phase gas or gas / water two-phase flow;

[0009] 4) Data collection: The computer is connected with the pressure sensor, flow meter, water injection pump, mass flow meter and PID valve to monitor the pressure and flow values ​​in each system in real time, and collect the discharged coal powder at a certain time interval for data analysis;

[0010] 5) Coupling analysis: Analyze the experimental data to obtain the minimum water flow and gas flow of pulverized coal under different conditions.

[0011] Furthermore, the coal powder input system includes a blower, a coal powder tank connected to the blower outlet, a detachable screen and a mass flow meter are provided on the coal powder tank outlet pipeline, the coal powder tank outlet is connected to the simulated wellbore top through a pipeline, a valve and a safety valve are also provided on the blower outlet pipeline, a pressure relief valve, a buffer and a one-way valve are provided on the coal powder tank outlet pipeline, and a pressure sensor is provided at the bottom of the coal powder tank. The coal powder input system is mainly used to simulate the production of coal powder in the formation and provide coal powder with different particle sizes / different contents and coal powder with different mineral contents for the wellbore coal powder drainage strength test device.

[0012] Furthermore, the water injection system includes a water tank, which is connected to the holes at the bottom of the simulated wellbore through a water supply pipeline. A water injection pump, a rotor flowmeter and a slow-flow component are sequentially arranged on the water supply pipeline. A safety valve and a one-way valve are also arranged on the water supply pipeline. The water injection system is mainly used to simulate formation water supply and provide water source and water power for single-phase / multi-phase flow migration in the wellbore coal powder drainage intensity monitoring system.

[0013] Furthermore, the gas input system includes a high-pressure gas cylinder, which is connected to the hole at the bottom of the simulated wellbore through a gas pipeline. The gas pipeline is provided with a safety valve, a PID valve, a flow meter, a pressure relief valve, a flow slow-down device and a one-way valve in sequence. The gas input system provides gas for the wellbore coal powder extraction intensity test and simulates the flow of gas in the wellbore.

[0014] Furthermore, the coal powder drainage intensity testing system includes a simulated wellbore, a valve and a pressure relief valve are provided at the top of the simulated wellbore, and a coal powder concentration testing component is arranged inside the simulated wellbore. The coal powder concentration testing component includes an infrared signal transmitter and an infrared signal receiver relatively arranged along the inner wall of the simulated wellbore, and an infrared signal processor that controls the infrared signal transmitter and the infrared signal receiver.

[0015] Furthermore, the recovery system includes a diversion pipeline, the inlet of the diversion pipeline is connected to the solution of the simulated wellbore, the outlet of the diversion pipeline is connected to the recovery water tank, the diversion pipeline is provided with a density tester, a mass flow meter and a filter from the inlet to the outlet, a coal powder transport pipeline is provided at the filter screen, the coal powder transport pipeline is powered by a fan, a coal powder recovery box is provided at the end of the coal powder transport pipeline, the inner walls of the coal powder recovery box and the recovery water tank are provided with pressure sensors, and a pressure relief valve is provided at the outlet end of the coal powder transport pipeline.

[0016] Furthermore, the pressure sensor, flow meter, water injection pump, mass flow meter, and PID valve are all electrically connected to and controlled by a computer.

[0017] The present invention has the advantages that:

[0018] 1. The present invention can simulate the migration and output rules of coal powder under different drainage stages (single-phase water flow, single-phase air flow, gas / water two-phase flow including different gas-water ratios), different particle sizes (including whether clay minerals are contained), and different output rates;

[0019] 2. Through the simulation experiment research on coal powder transportation and output in different mining stages, the coal powder output conditions under different conditions can be obtained, providing a theoretical basis for the formulation of the optimal mining work system on site. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the structure of the present invention. DETAILED DESCRIPTION

[0021] like Figure 1As shown, a test device for coal powder discharge in a simulated coalbed methane wellbore includes a coal powder input system and a gas input system connected to the top of the simulated wellbore, and a water injection system arranged at the bottom of the simulated wellbore. The simulated wellbore is provided with a coal powder drainage strength test system, and also includes a recovery system located at the top of the simulated wellbore. The device coordinates with each other between various systems to achieve the minimum discharge volume and coal powder migration state of the coal powder discharged in the wellbore under different flow states, different coal powder particle sizes, different clay contents, different concentrations, etc., so as to provide a reference for the injection of the on-site water reinjection device. The water volume provides a theoretical basis; the pulverized coal input system includes a blower 1, a pulverized coal tank 4 connected to the outlet of the blower 1, a detachable screen 6 and a mass flow meter 29 are arranged on the outlet pipeline of the pulverized coal tank 4, the outlet of the pulverized coal tank 4 is connected to the top of the simulated wellbore 27 through a pipeline, a valve 2 and a safety valve 3 are also arranged on the outlet pipeline of the blower 1, a pressure relief valve 7, a buffer 8 and a one-way valve 9 are arranged on the outlet pipeline of the pulverized coal tank 4, wherein the buffer 8 strengthens and thickens the pipeline (steel can be used according to actual needs), plays a buffering and protective role on the pipeline, and reduces damage to the pipe wall. The pressure relief valve 7 releases the gas blown in by the fan to prevent interference with the wellbore coal powder drainage intensity monitoring system; a pressure sensor 5 is provided at the bottom of the coal powder tank 4 to measure the weight of the added coal powder and minerals. The coal powder tank 4 is also provided with a sand adding port 26 for simulating the use of sand and gravel in the actual wellbore. The coal powder input system is mainly used to simulate the production of coal powder in the formation and provide coal powder with different particle sizes / different contents and coal powder with different mineral contents for the wellbore coal powder drainage intensity testing device; the water injection system includes a water tank 24, which is connected to the hole 17 at the bottom of the simulated wellbore 27 through a water supply pipeline 23. A water injection pump 22, a rotor flowmeter 30 and a slow flow component 19 are arranged on the water supply pipeline in sequence. A safety valve and a one-way valve are also provided on the water supply pipeline. The water injection system is mainly used to simulate the formation water supply and provide a single The water tank 24 mainly provides water for experimental testing. When injected, the water is pressurized by the water tank 24 and the water injection pump 22 to obtain the fluid transport motive force. The water is passed through the pipeline through the water flow meter (because the injected clean water does not contain solid phase substances, the rotor flow meter can be used as the water flow meter to measure the injected water flow); the flow valve can be controlled to adjust the displacement; the safety valve plays a flow limiting role to prevent the excessive pressure of the water injection pump from causing damage to the subsequent devices; the one-way valve prevents the liquid from flowing back due to the height difference of the liquid column on both sides; the slow flow part is a large inner diameter pipeline with a built-in guide plate, which is used to increase the water flow area, slow down the fluid flow rate, control the water injection pressure, and prevent the excessive flow rate from causing agitation to the mixed liquid composed of coal powder and water / gas in the wellbore, and interfere with the migration and sedimentation of coal powder (its length can be extended according to actual needs). The computer connects the water injection pump and the flow meter, records the flow through the pipeline in real time, and directly controls the injection pressure of the water injection pump through computer adjustment, and adjusts the displacement of the injected water in real time according to needs.The gas input system includes a high-pressure gas cylinder 18, which is connected to the hole at the bottom of the simulated wellbore 27 through a gas pipeline. The gas pipeline is provided with a safety valve, a PID valve 16, a flow meter 12, a pressure relief valve, a slow flow piece and a one-way valve in sequence. The gas input system provides gas for the wellbore coal powder drainage intensity test and simulates the flow of gas in the wellbore. The coal powder drainage strength test system includes a simulated wellbore 27, and a glass tube 28 with an inner diameter of R 89mm×H0.5m is used as the simulated wellbore (its length can be extended according to actual needs). The lower part is installed on a fixed base 20 and fixed by bolts 21 to play a stabilizing role. A valve and a pressure relief valve are provided on the top of the simulated wellbore 27, and also includes a coal powder concentration test component arranged inside the simulated wellbore 27. The coal powder concentration test component includes an infrared signal transmitter 31 and an infrared signal receiver 32 that are relatively arranged along the inner wall of the simulated wellbore 27, and an infrared signal processor 10 that controls the infrared signal transmitter 31 and the infrared signal receiver 32. The coal powder concentration test component is connected to a computer 25 to monitor the change of coal powder content in the simulated test device in real time. There are pressure relief valves and pressure sensors at the top of the wellbore to prevent the pressure in the wellbore from being too high, which may cause safety hazards. The recovery system includes a diversion pipeline, the inlet of which is connected to the solution of the simulated wellbore 27, and the outlet of which is connected to the recovery water tank 15. The diversion pipeline is provided with a density tester 11, a mass flow meter and a filter 13 from the inlet to the outlet. Since the return fluid is a multiphase flow, a mass flow meter is used to measure the drainage flow rate, and to assist in measuring the drainage intensity and flow rate. The wellbore is made of transparent glass, and the coal powder migration and sedimentation in the wellbore can be directly observed from the outside. A coal powder migration pipeline is provided at the filter screen of the filter 13. The coal powder migration pipeline is powered by a fan. A coal powder recovery box 14 is provided at the end of the coal powder migration pipeline. The inner walls of the coal powder recovery box 14 and the recovery water tank 15 are provided with pressure sensors, and a pressure relief valve is provided at the outlet of the coal powder migration pipeline. The pressure sensor, flow meter, water injection pump, mass flow meter and PID valve are all electrically connected to and controlled by a computer.

[0022] A test method for simulating a coal dust discharge test device in a coalbed methane wellbore, comprising the following steps:

[0023] (1) Preparation of experimental coal powder samples

[0024] The methods for collecting and preparing coal powder samples are as follows: ① Filter and dry the return flow water samples collected on site to obtain coal powder samples; ② Use coal powder salvaged from on-site sand dredging operations; ③ Use block coal samples to manually crush them into coal powder, and use sieves of different mesh sizes to sieve them to produce coal powder with the required particle size. (A certain amount of clay minerals can be added as needed) and set aside.

[0025] Preparation of clay mineral particles: crush and grind minerals such as montmorillonite, kaolinite, illite, etc., and then screen them with sieves of different mesh sizes to produce clay minerals with the required particle size.

[0026] (2) Assemble the experimental device and test its airtightness

[0027] Connect various instruments with pipelines, turn on the high-pressure gas cylinder switch, and test the air tightness of the device.

[0028] (3) Experimental test on moderate coal powder discharge

[0029] According to the experimental plan, experimental tests are carried out under conditions of different coal powder particle sizes, different contents, single-phase water or single-phase gas or gas / water two-phase flow.

[0030] For example: the prepared coal powder is passed through national standard sieves of 50 mesh (300 μm), 70 mesh (212 μm) and 140 mesh (106 μm), and the coal powders of four particle sizes of less than 50 mesh, 50-70 mesh, 70-140 mesh and greater than 140 mesh are sieved for use.

[0031] Experiments were conducted on single-phase water flow, single-phase air flow, and gas / water two-phase flow (the two-phase flow stage was divided into three gas-water ratios: gas:water displacement ratio of 2:1, 5:1, and 7:1).

[0032] Under the above experimental conditions, experiments can be conducted with coal powder containing no clay minerals and with the ratio of clay minerals to coal powder being 1:1, 1:3, 1:5, etc. The same experiment is conducted three times to avoid experimental errors caused by operating errors and other reasons.

[0033] (4) Data collection

[0034] The computer is connected to the pressure sensors, flow meters, density meters, etc. in each device to monitor the pressure value, flow value and other data in each device in real time, and collects the discharged coal powder at a certain time interval for data analysis.

[0035] (5) Coupling analysis

[0036] The experimental data were analyzed to obtain the minimum water flow rate, gas flow rate, etc. of pulverized coal output under different conditions.

Claims

1. A method for testing coal dust in a simulated coalbed methane wellbore, characterized in that: The test device includes a coal powder input system and a gas input system connected to the top of the simulated wellbore, and a water injection system arranged at the bottom of the simulated wellbore. The simulated wellbore is provided with a coal powder drainage strength test system and also includes a recovery system located at the top of the simulated wellbore. The test method includes the following steps: 1) Preparation of experimental coal powder samples: Prepare coal powder of required particle size according to the actual coal powder situation in the wellbore; 2) Assemble the experimental device and conduct airtightness test; 3) Experimental test of moderate coal powder discharge: According to the experimental plan, experimental tests are carried out under conditions of different coal powder particle sizes, different contents, single-phase water or single-phase gas or gas / water two-phase flow; 4) Data collection: The computer is connected with the pressure sensor, flow meter, water injection pump, mass flow meter and PID valve to monitor the pressure and flow values ​​in each system in real time, and collect the discharged coal powder at a certain time interval for data analysis; 5) Coupling analysis: Analyze the experimental data to obtain the minimum water flow and gas flow of pulverized coal under different conditions.

2. The method for testing the discharge of coal dust in a simulated coalbed methane wellbore according to claim 1, characterized in that: The pulverized coal input system includes a blower, a pulverized coal tank connected to the blower outlet, a detachable screen and a mass flow meter are provided on the pulverized coal tank outlet pipeline, the pulverized coal tank outlet is connected to the top of the simulated wellbore through a pipeline, a valve and a safety valve are also provided on the blower outlet pipeline, a pressure relief valve, a buffer and a one-way valve are provided on the pulverized coal tank outlet pipeline, and a pressure sensor is provided at the bottom of the pulverized coal tank.

3. The method for testing the discharge of coal dust in a simulated coalbed methane wellbore according to claim 2, characterized in that: The water injection system includes a water tank, which is connected to the hole at the bottom of the simulated wellbore through a water pipeline. A water injection pump, a rotor flowmeter and a slow flow component are arranged in sequence on the water pipeline. A safety valve and a one-way valve are also arranged on the water pipeline.

4. The method for testing the discharge of coal dust in a simulated coalbed methane wellbore according to claim 3, characterized in that: The gas input system includes a high-pressure gas cylinder, which is connected to the hole at the bottom of the simulated wellbore through a gas pipeline. A safety valve, a PID valve, a flow meter, a pressure relief valve, a flow slowing member and a one-way valve are sequentially arranged on the gas pipeline.

5. The method for testing the discharge of coal dust in a simulated coalbed methane wellbore according to claim 4, characterized in that: The coal powder drainage intensity testing system includes a simulated wellbore, a valve and a pressure relief valve are provided at the top of the simulated wellbore, and a coal powder concentration testing component is arranged inside the simulated wellbore. The coal powder concentration testing component includes an infrared signal transmitter and an infrared signal receiver arranged relatively along the inner wall of the simulated wellbore, and an infrared signal processor that controls the infrared signal transmitter and the infrared signal receiver.

6. The method for testing the discharge of coal dust in a simulated coalbed methane wellbore according to claim 5, characterized in that: The recovery system includes a diversion pipeline, the inlet of the diversion pipeline is connected to the solution of the simulated wellbore, the outlet of the diversion pipeline is connected to the recovery water tank, the diversion pipeline is provided with a density tester, a mass flow meter and a filter from the inlet to the outlet, a coal powder transport pipeline is provided at the filter screen, the coal powder transport pipeline is powered by a fan, a coal powder recovery box is provided at the end of the coal powder transport pipeline, the inner walls of the coal powder recovery box and the recovery water tank are provided with pressure sensors, and a pressure relief valve is provided at the outlet end of the coal powder transport pipeline.

7. The method for testing the discharge of coal dust in a simulated coalbed methane wellbore according to claim 6, characterized in that: The pressure sensor, flow meter, water injection pump, mass flow meter and PID valve are all electrically connected to the computer and controlled by the computer.

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