Comparison experiment method for gas extraction and concentration of coal seam with external plugging and internal pressure

Abstract

The invention discloses an external-plugging internal-pressure coal seam gas extraction concentration contrast experiment method which comprises the following steps: S1, dividing into two regions, setting the region I as a reference group, and setting the region II as an experiment group; s2, a first blocking material and a second blocking material are sequentially and evenly sprayed to the coal wall of the second area and the junction of the coal wall of the second area and the coal wall of the other side through spraying equipment; the plugging material I comprises a polyurethane prepolymer, isocyanate, a thickening agent and a propylene glycol solvent, and the weight of the thickening agent is 1 / 40 of the weight of a mixture of the polyurethane prepolymer and the isocyanate; the second plugging material is prepared from, by mass, 30% of fine sand, 30% of quartz powder and 40% of sodium silicate; s3, drilling is conducted, and then a fracturing pipe column is fed into the bottom of a hole through a drilling machine for fracturing; and S4, the fracturing pipe column is taken out, and gas extraction operation is conducted. The method has the advantages of being high in gas extraction efficiency, high in gas extraction concentration, good in coating leakproofness, low in air permeability and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of coal seam gas drainage, and particularly relates to a method for contrast experiments on the concentration enhancement of coal seam gas drainage with external plugging and internal pressure. Background Art

[0002] The gas problem has always been one of the main reasons affecting coal mine exploitation. High-concentration gas not only easily causes explosions, leading to miner casualties, but also may cause serious consequences such as poisoning and asphyxiation. When the gas concentration exceeds the standard, the air quality in the mine drops rapidly, and miners are extremely vulnerable to threats without effective protection. In addition, the accumulation of gas will lead to accidents such as roof falls and collapses, seriously affecting the safe production of coal mines and the lives of miners. Various gas disasters not only cause huge economic losses, but also have a long-term impact on the surrounding environment of the mining area. Therefore, the monitoring and drainage of gas are particularly important to ensure safe exploitation and protect the lives and health of miners.

[0003] In engineering practice, due to the small permeability of the coal seam and serious air leakage, the efficiency of in-seam gas drainage in the mine is low, resulting in the gas drainage concentration dropping to an unusable value in a short time, and it can only be forced to be discharged into the atmosphere. This low-efficiency drainage status not only pollutes the environment, but also cannot effectively reduce the gas content in the coal seam, causing potential safety hazards for coal mine production; moreover, there is currently a lack of both a coal seam gas drainage method with external plugging and internal pressure in the market and an experimental method for the specific selection of different coal roadway gas drainage methods, resulting in the inability to maximize the benefits of gas drainage. Summary of the Invention

[0004] The present invention aims to provide a method for contrast experiments on the concentration enhancement of coal seam gas drainage with external plugging and internal pressure, to solve the problems that the current coal seam has small permeability and serious air leakage, resulting in the gas drainage concentration dropping to an unusable value in a short time, and that there is currently a lack of both a coal seam gas drainage method with external plugging and internal pressure in the market and an experimental method for the specific selection of different coal roadway gas drainage methods, resulting in the inability to maximize the benefits of gas drainage.

[0005] For this purpose, the technical solution adopted by the present invention is as follows: A method for contrast experiments on the concentration enhancement of coal seam gas drainage with external plugging and internal pressure, comprising the following steps:

[0006] Step S1, divide two areas that meet the operation requirements. Area 1 is set as the reference group, and Area 2 is set as the experimental group. Then, determine the layout of the fracturing holes, the fracturing spacing, and the number of times of the overall fracturing operation in the two areas respectively;

[0007] Step S2: Use a spraying device to evenly spray Sealing Material 1 on the coal wall in Area 2 and at the junctions with other side coal walls in sequence. After standing still, evenly spray Sealing Material 2, and then let it stand still until a solidified sealing coating is formed.

[0008] The Sealing Material 1 includes polyurethane prepolymer, isocyanate, thickening agent, and propylene glycol solvent. Among them, the mass ratio of polyurethane prepolymer to isocyanate is 3:1, and the weight of the thickening agent is 1 / 40 of the weight of the mixture of polyurethane prepolymer and isocyanate; the Sealing Material 2 consists of 30% fine sand, 30% quartz powder, and 40% sodium silicate by mass percentage.

[0009] Step S3: Drill holes according to the designed drill points in the two areas respectively. Then send the fracturing string into the bottom of the hole through the drilling rig for fracturing, and use the method of withdrawing the drill for fracturing, so as to form a uniform fracture network in the hole.

[0010] Step S4: Take out the fracturing string, re - place it with a gas drainage pipeline, and conduct gas drainage operations. Finally, compare the gas drainage flow data of the two areas.

[0011] As an optimization of the above solution, in Step S2, the spraying device includes a material tank, a nozzle, and a connecting rubber hose. The material tank is used to evenly mix Sealing Material 1 or Sealing Material 2 with water. Adding an appropriate amount of water can facilitate the flow of the sealing material. The connecting rubber hose connects the material tank and the nozzle and is equipped with a flow meter. The structural design is reasonable. The sealing material can be sprayed flexibly through the flow meter, and the thickness of the sprayed coating can be adjusted according to requirements.

[0012] Further preferably, in Step S2, after spraying Sealing Material 1, let it stand still for 30 min - 40 min. Only when its surface is slightly solidified but not completely dry can Sealing Material 2 be sprayed continuously. After spraying Sealing Material 2, let it stand still for more than 23 hours, waiting for the sprayed material on the coal wall to fully solidify to form a stable sealing coating. The time design is reasonable.

[0013] Further preferably, the dosage of propylene glycol solvent in the Sealing Material 1 is positively correlated with the spraying thickness, and the design is reasonable.

[0014] Further preferably, in Step S3, the front end of the fracturing string is provided with a whipstock, a packer, a water pressure conversion valve, a restrictor, and a check valve. The drilling rig is sequentially connected with a fracturing pump and a water tank along the reverse direction of the water supply. After reaching the target position, start the fracturing pump. The whipstock can effectively prevent the front end from being stuck by the rough hole wall when the fracturing string is sent into the hole. The water in the water tank is injected under high pressure. Under the action of high pressure, the packer expands to form a sealed area between the packers. As the injection pressure of the high - pressure water flow continuously rises until it reaches the coal body fracture limit, a complex fracture network is generated in the coal body near the fracturing area, increasing the permeability of the coal body.

[0015] More preferably, in step S3, fracturing is carried out every 15 m to 20 m retreat in the hole, and each fracturing time lasts for 20 min to 30 min to ensure the fracturing effect and the uniformity of the fissures in the fracturing hole.

[0016] Beneficial effects of the present invention:

[0017] (1) Compared with the current situation where the coal seam permeability is small and air leakage is serious, and the extraction efficiency of the cross-measure gas in the mine is low, this scheme adopts the method of external plugging and internal pressure. By spraying the sealing material one and the sealing material two on the coal wall in sequence, a closed coating is formed, which not only effectively avoids the air in the roadway from entering the coal seam during the gas extraction process due to air leakage in the coal wall, affecting the gas extraction efficiency and the gas extraction concentration, but also increases the internal permeability of the coal seam through hydraulic fracturing operations, making the gas in the coal seam easier to be extracted, greatly improving the operation efficiency.

[0018] (2) The isocyanate in the sealing material one reacts with the hydroxyl group (-OH) in the polyurethane prepolymer to form a polyurethane structure. The reaction between the isocyanate and the polyurethane prepolymer can enhance the strength, hardness and durability of the material. The role of the thickener is to increase the viscosity of the formulation, making the mixture have better rheology, facilitating coating and molding operations. Propylene glycol is used as a solvent, mainly playing the role of dilution and dissolution, helping other components to be evenly dispersed, and the polyurethane prepolymer can also react with sodium silicate in the sealing material two to form a cross-linked structure. This cross-linking significantly improves the strength and durability of the material. The three-dimensional structure formed by the cross-linked products tightly wraps the fine sand and quartz powder in the subsequently sprayed sealing material two, generally forming a dense structure, which can effectively seal the coal wall and reduce the air leakage volume. At the same time, the presence of fine sand and quartz powder not only improves the sealing effect but also reduces the cost.

[0019] (3) The method of spraying the sealing material one and the sealing material two separately before and after is because the isocyanate and sodium silicate will coagulate relatively quickly after mixing. If they are sprayed together, it is easy to block the spraying equipment. Therefore, the isocyanate is first sprayed on the roadway wall, and under the action of the thickener, it will not slide off the coal wall surface and can initially maintain a uniform wall-hanging state. At this time, when sodium silicate is sprayed, it can quickly react and solidify into a sealing layer, and can also ensure the uniformity of the thickness of the sealing layer, further ensuring the sealing effect.

[0020] (4) Considering that the mining conditions of each coal roadway are inconsistent, the gas concentration content and the degree of coal seam fissures are inconsistent in the coal seam. Therefore, according to the different characteristics of the coal roadway, by first setting the gas extraction flow data of the control group and the experimental group for comparison, the degree of gas extraction efficiency increase is obtained, and then a simple calculation is carried out with the cost of the additional process, so as to obtain which gas extraction method can maximize the gas extraction benefit in this coal roadway, and then this method can be continuously used for extraction in this coal roadway, with high practical value.

[0021] In summary, the present invention has the advantages of high gas drainage efficiency, high gas drainage concentration, good coating tightness, low air permeability, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic structural diagram of the spraying equipment of the present invention.

[0023] Figure 2 It is a schematic structural diagram of step S3 of the present invention.

[0024] Figure 3 It is a comparison chart of gas concentrations in two areas.

[0025] Figure 4 It is a comparison chart of the pure gas amounts in two areas.

[0026] Figure 5 It is a comparison chart of gas leakage amounts in two areas. DETAILED DESCRIPTION OF THE INVENTION

[0027] The present invention will be further described below through embodiments in conjunction with the drawings:

[0028] Combined with Figure 1 — Figure 5 As shown, a comparative experimental method for enhancing the concentration of coal seam gas by external plugging and internal pressure is as follows:

[0029] Step S1: Divide two areas that meet the operation requirements. Area 1 is set as the reference group, and Area 2 is set as the experimental group. Then, determine the layout of the fracturing holes, the fracturing spacing, and the number of times of the overall fracturing operation in the two areas respectively.

[0030] Step S2: Sequentially and evenly spray the first plugging material on the coal wall of Area 2 and the junction with other side coal walls through the spraying equipment 1. After standing, evenly spray the second plugging material, and then stand until a solidified sealing coating is formed.

[0031] The first plugging material includes polyurethane prepolymer, isocyanate, thickener, and propylene glycol solvent, wherein the mass ratio of polyurethane prepolymer to isocyanate is 3:1, and the weight of the thickener is 1 / 40 of the weight of the mixture of polyurethane prepolymer and isocyanate; the second plugging material is composed of 30% fine sand, 30% quartz powder, and 40% sodium silicate by mass percentage.

[0032] In step S2, the spraying equipment 1 is composed of a material tank 11, a nozzle 12, and a connecting rubber hose 13.

[0033] The material tank 11 is used to uniformly mix the first plugging material or the second plugging material with water.

[0034] The parameters of the relevant spraying materials can be directly operated and set on the system screen of the nozzle 12. The materials required for the plugging material one or the plugging material two are evenly mixed in the dedicated material tank 11, and then an appropriate amount of water is added, which is convenient for direct spraying on the coal wall.

[0035] The connecting hose 13 connects the material tank 11 and the nozzle 12, and a flow meter 14 is installed.

[0036] In step S2, after spraying the plugging material one, it is left standing for 30 min to 40 min, and after spraying the plugging material two, it is left standing for more than 23 hours.

[0037] The dosage of the propylene glycol solvent in the plugging material one is positively correlated with the spraying thickness.

[0038] Step S3: Drill holes according to the designed drill points in two areas respectively, and then send the fracturing string 2 to the bottom of the hole through the drill rig 3 for fracturing, and use the method of withdrawing the drill to carry out fracturing, so as to form a uniform fracture network in the hole.

[0039] In step S3, the front end of the fracturing string 2 is provided with a whipstock 21, a packer 22, a water pressure conversion valve, a restrictor 23, and a check valve 24. The water pressure conversion valve is used to install the fracturing string 2 on the drill rig 3. The restrictor 23 is located between the two packers 22, and the whipstock 21 is located at the outermost end, which is used to prevent the front end of the fracturing string 2 from being stuck by the rough hole wall when it is sent into the hole.

[0040] The drill rig 3 is sequentially connected with a fracturing pump 5 and a water tank 4 along the reverse direction of the water supply.

[0041] Precisely move the drill rig to the predetermined hole-opening position. The installation of the drill rig needs to be fixed strictly according to the specified angle to ensure that the drilling direction is accurate. Once the machine moving and positioning are completed, the hole-opening and hole-expanding operations can be started.

[0042] The hydraulic fracturing construction adopts the operation mode of short-hole fracturing. Several fracturing sections are set in one hole, and the packers are corresponding to the areas by the way of removing the drill pipes when withdrawing the drill. When designing the hole layout method and the fracturing sections, the fracturing radius should be strictly referred to to ensure the overall increase of the coal body permeability.

[0043] Under the action of high pressure, the packer 22 expands, forming a closed area between the packers 22. As the injection pressure of the high-pressure water flow continuously rises until it reaches the coal body fracture limit, a complex fracture network is generated in the coal body near the fracturing area, increasing the permeability of the coal body.

[0044] In step S3, fracturing is carried out once every 15 m to 20 m in the hole, and each fracturing lasts for 20 min to 30 min.

[0045] Step S4: Remove the fracturing string 2, reinstall it into the gas drainage pipeline, and conduct gas drainage operations. Finally, compare the gas drainage flow rate data of the two areas.

[0046] The gas drainage pipeline enables the gas in the coal-rock fractures to be effectively sucked into the collection container under the action of the pressure gradient, thus completing the entire gas drainage operation process.

[0047] As Figure 3 shown in the comparison of the gas drainage concentration data of the two areas, it can be seen that the attenuation rate of the average gas concentration in Area 2 is slower, while the average gas concentration in Area 1 decays faster. Therefore, the gas drainage effect after spraying and plugging the cracks in the coal wall is significantly better than that without plugging. Whether it is the initial concentration or the downward trend, it can reflect that plugging the cracks is more beneficial to gas drainage.

[0048] As Figure 4 shown in the comparison of the gas drainage flow rate data of the two areas; the net gas drainage volume is an important parameter to characterize the gas drainage effect and can directly reflect the gas flow rate during the borehole drainage process. Therefore, by sorting out the net gas drainage volume data of the two test areas, the influence on the net gas drainage volume data before and after plugging can be analyzed.

[0049] Judging from the data, the average net gas drainage volume in the plugging test area is higher. For Area 1, from the overall downward trend of the net gas drainage volume, most of the fluctuation ranges do not exceed 0.2 m 3 / min, which indicates that the attenuation rate of the net gas drainage volume in the non-plugging test area is relatively fast, and air seepage is one of the reasons for this phenomenon. The initial net gas drainage volume in Area 2 is higher than that in Area 1, which is 1.4 m 3 / min. Through the comparison of the average net gas drainage volume data of the two areas, the same conclusion as that after the above average concentration comparison can still be obtained, that is, spraying and plugging the cracks in the coal wall in Area 2 can effectively improve the gas drainage effect.

[0050] As Figure 5 shown in the comparison of the gas leakage volume data of the two areas, the counted gas leakage volume is the total content of non-gas gases in the gas of the drainage boreholes. The gas leakage volume can intuitively reflect the quality of the plugging effect in different test areas. The gas leakage volumes and change trends of the two areas are clear at a glance. The gas leakage volume in Area 2 is significantly smaller than that in Area 1. Therefore, plugging the cracks in Area 2 has a good improvement effect on gas drainage.

[0051] Finally, based on the data comparison, simply calculate the degree of gas drainage efficiency improvement and the cost of additional processes, so as to obtain whether the ordinary gas drainage method or the external plugging and internal pressure drainage method can maximize the gas drainage benefits in this coal roadway, and then continue to use this method for drainage in this coal roadway.

Claims

1. A comparative experimental method for coal seam gas extraction and concentration with external plugging and internal pressure, characterized in that: The following steps are involved: Step S1, dividing two areas that meet the operation requirements, area one is set as a reference group, and area two is set as an experimental group, and then the arrangement layout of the fracturing holes, the fracturing spacing, and the number of times the overall fracturing operation needs to be performed are determined in the two areas respectively; Step S2, using the spraying device (1) to uniformly spray the plugging material 1 on the coal wall of the second area and the interface with the other side coal wall, and then uniformly spray the plugging material 2 after standing, and then stand until a solidified sealing coating is formed; The first plugging material comprises a polyurethane prepolymer, an isocyanate, a thickener, and a propylene glycol solvent, wherein the weight ratio of the polyurethane prepolymer to the isocyanate is 3:1, and the weight of the thickener is 1 / 40 of the weight of the mixture of the polyurethane prepolymer and the isocyanate; the second plugging material comprises 30% fine sand, 30% quartz powder, and 40% sodium silicate according to the weight percentage; Step S3, drilling holes in the two areas according to the designed drilling points, and then sending the fracturing pipe string (2) to the bottom of the hole through the drilling rig (3) for fracturing, and fracturing by withdrawing the drill, so as to form a uniform fracture network in the hole; Step S4, taking out the fracturing string (2), reinserting it into the gas extraction pipeline, and performing gas extraction operations, and finally comparing the gas extraction flow data of the two areas.

2. According to the external plugging and internal pressure coal seam gas extraction and concentration comparison experimental method of claim 1, it is characterized by: In step S2, the spraying equipment (1) comprises a material tank (11), a nozzle (12) and a connecting hose (13); the material tank (11) is used to evenly mix the plugging material 1 or the plugging material 2 with water; the connecting hose (13) connects the material tank (11) and the nozzle (12) and is provided with a flow meter (14).

3. The comparative experimental method for coal seam gas extraction and concentration with external plugging and internal pressure according to claim 1 is characterized in that: In the step S2, the first plugging material is sprayed and then left to stand for 30 to 40 minutes, and the second plugging material is sprayed and then left to stand for more than 23 hours.

4. The method for comparative experiment of coal seam gas extraction and concentration with external plugging and internal pressure according to claim 3 is characterized in that: The amount of propylene glycol solvent used in the plugging material 1 is positively correlated with the spraying thickness.

5. The method for comparative experiment of coal seam gas extraction and concentration with external plugging and internal pressure according to claim 1 is characterized in that: In step S3, the front end of the fracturing pipe string (2) is provided with a guide deflector (21), a packer (22), a water pressure conversion valve, a throttle (23), and a one-way valve (24), and the drilling rig (3) is connected to a fracturing pump (5) and a water tank (4) in sequence along the reverse direction of water supply.

6. The method for comparative experiment of coal seam gas extraction and concentration with external plugging and internal pressure according to claim 1, characterized in that: In step S3, fracturing is performed every 15m to 20m of retreat in the hole, and each fracturing lasts for 20min to 30min.

Images