Coal underground gasification horizontal well carbon dioxide fracturing device

Abstract

The invention discloses a carbon dioxide fracturing device for a coal underground gasification horizontal well. The device comprises an outer cylinder, a pressure pipe, a partition plate, a fracturing fluid outlet, a gasifying agent outlet and a flow distribution plate. Wherein the pressure pipe is arranged in the outer cylinder in a sliding manner; a plurality of partition plates are arranged in the outer cylinder and used for dividing the space formed by the outer cylinder and the pressure pipe into a plurality of sections, and a circle of fracturing fluid outlet is formed in the lower portion of each section of the outer cylinder. A circle of gasifying agent outlet is formed above the fracturing fluid outlet of each section of the outer cylinder; and the fracturing fluid outlet is separated from the gasifying agent outlet through a flow distribution plate. According to the device, through step-by-step injection of fracturing fluid, separate injection of the fracturing fluid and the gasifying agent and accurate segmented control, the permeability, the gasification efficiency and the gas production rate of the coal seam are improved, and meanwhile, the underground complex accident risk is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of coal mining, and in particular to a carbon dioxide fracturing device for underground coal gasification horizontal wells. Background Art

[0002] Underground coal gasification (UCG) is an important energy development technology that converts coal underground into crude gas. During this process, coal is heated, combusted, and reacts with a gasifying agent to produce crude gas containing combustible components such as methane, hydrogen, and carbon monoxide. To specifically improve gasification efficiency and coal seam permeability, a new type of equipment, CO2 fracturing equipment for UCG horizontal wells, has emerged.

[0003] Currently, underground coal gasification (UCG) typically doesn't involve fracturing the coal seams. Consequently, the coal-rock fracture system remains ineffective during the gasification process, resulting in a small contact area between the gasifier and the coal, hindering gasification reaction efficiency. Water-based fracturing fluids, commonly used in the oil and gas industry, increase the water content of coal seams. The injection of external water increases the ineffective heat supply, hindering coal combustion and gasification. Furthermore, existing horizontal well staged fracturing processes typically involve perforating and fracturing the entire coal seam at once. This can negatively impact the subsequent gasification process. Small coal fragments in the wellbore can cause obstruction during the retreat of the coiled tubing, making it difficult to accurately monitor and control the process and, in severe cases, potentially causing underground accidents.

[0004] Therefore, in order to overcome the shortcomings of existing process technologies in the fracturing process of underground coal gasification horizontal wells, a carbon dioxide fracturing device suitable for underground coal gasification horizontal wells was developed. Summary of the Invention

[0005] The present invention aims to provide a carbon dioxide fracturing device for underground coal gasification horizontal wells. The device improves coal seam permeability, gasification efficiency and gas production rate by injecting fracturing fluid step by step, injecting fracturing fluid and gasifying agent separately, and performing precise segmented control, while reducing the risk of complex accidents underground.

[0006] To achieve the above-mentioned object, the present invention provides a carbon dioxide fracturing device for underground coal gasification horizontal wells, the device comprising: an outer cylinder, a pressure pipe, a partition plate, a fracturing fluid outlet, a gasifying agent outlet, and a distribution plate;

[0007] Among them, the pressure tube is slidably arranged in the outer tube; a plurality of partition plates are provided in the outer tube for dividing the space formed by the outer tube and the pressure tube into multiple sections, and a circle of fracturing fluid outlets is provided at the lower part of each section of the outer tube; a circle of gasifying agent outlets is provided above the fracturing fluid outlet of each section of the outer tube; the fracturing fluid outlet and the gasifying agent outlet are separated by a distribution plate.

[0008] The technical effects and advantages of the present invention are as follows:

[0009] 1. Separately injecting the fracturing fluid and gasifying agent helps prevent adverse chemical reactions between the chemical components of the fracturing fluid and the gasifying agent, thereby avoiding changes in the gasifying agent composition and reduced gasification efficiency. Staged fracturing and separate injection of the gasifying agent simplify the management and monitoring of the gasification process, allowing operators to more precisely control the gasification reaction and make adjustments as needed.

[0010] 2. Carbon dioxide replaces water-based fracturing fluid. On the one hand, it can avoid the increase of water content in coal seams caused by water injection during the fracturing process, thereby reducing the consumption of additional heat. On the other hand, the raw coal gas produced by underground coal gasification contains carbon dioxide, which realizes the "local material" of fracturing fluid. The carbon dioxide injected into the formation during the fracturing process can participate in chemical reactions in the high temperature and high pressure environment underground or be buried in the coal seam, thereby achieving the purpose of reducing carbon dioxide production.

[0011] 3. By injecting fracturing fluid in stages, the coal seam is effectively fractured and a fracture system is created, increasing the permeability of the coal seam. Fracturing operations and the gradual injection of fracturing fluid help increase gas production. The injection of fracturing fluid improves the coal seam fracture system, allowing the gasifier to more effectively contact the coal seam and promote the gasification reaction, thereby increasing gas production. This helps achieve a more consistent gasification reaction, preventing localized excessive or low gasification rates, thereby improving gasifier utilization.

[0012] 4. By injecting a gasifier into the next rock formation, the fracturing process in the previous rock formation can be prevented from causing collapse of the next rock formation, helping to maintain the integrity of the horizontal wellbore. The design of active and passive plates can simplify the pressurization device, reducing equipment costs and maintenance complexity.

[0013] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a schematic diagram of the structure of a carbon dioxide fracturing device for underground coal gasification horizontal wells;

[0015] Figure 2 It is a structural diagram of the sealing block;

[0016] Figure 3 Schematic diagram of the structure of the upper wedge and the lower wedge;

[0017] Figure numerals: 1. outer cylinder; 2. pressure tube; 21. pressure hole; 3. partition plate; 4. fracturing fluid outlet; 5. sealing sleeve; 6. distribution plate; 7. gasifying agent outlet; 71. injection port; 8. connecting plate; 81. connecting groove; 9. sealing block; 91. sealing spring; 10. driven plate; 11. active plate; 12. connecting rod; 13. upper wedge; 14. lower wedge. DETAILED DESCRIPTION

[0018] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0019] It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for understanding and reading by those familiar with this technology, and are not used to limit the conditions for implementation of the present invention. Therefore, they have no substantial technical significance. Any modification of the structure, change in the proportional relationship, or adjustment of the size should still fall within the scope of the technical content disclosed by the present invention without affecting the efficacy and purpose that can be achieved by the present invention. At the same time, terms such as "upper", "lower", "left", "right", "middle" and "one" quoted in this specification are only for the convenience of description and are not used to limit the scope of implementation of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of implementation of the present invention without substantially changing the technical content.

[0020] The present invention discloses a carbon dioxide fracturing device for underground coal gasification horizontal wells. Figure 1 The device is explained in detail.

[0021] The device comprises: an outer cylinder 1, a pressure tube 2, a partition plate 3, a fracturing fluid outlet 4, a gasifying agent outlet 7, and a distribution plate 6.

[0022] The pressure tube 2 is slidably disposed within the outer tube 1. Multiple partition plates 3 are provided within the outer tube 1 to separate the outer tube 1 and the pressure tube 2 into multiple sections. A circle of fracturing fluid outlets 4 is provided at the lower portion of each section. A circle of gasifying agent outlets 7 is provided a distance above the fracturing fluid outlets 4. The fracturing fluid outlets 4 and the gasifying agent outlets 7 are separated by a distribution plate 6. The distribution plate 6 separates the fracturing fluid from the gasifying agent, allowing them to be injected separately. Separately injecting the gasifying agent prevents undesirable chemical reactions between certain fracturing fluid components and the gasifying agent, which could reduce gasification efficiency and even contaminate the produced gas. Separately injecting the gasifying agent simplifies the management and monitoring of the gasification process, allowing for more precise control of the gasification reaction.

[0023] A sealing sleeve 5 slides along the outer wall of the outer cylinder 1 at a location corresponding to each fracturing fluid outlet 4. Each sealing sleeve 5 is connected to a pull rope. When the sealing sleeve 5 seals the fracturing fluid outlet 4, the pressure pipe 2 injects fracturing fluid into the corresponding cavity, increasing the pressure of the fracturing fluid. When the corresponding pull rope is pulled to move the sleeve away from the fracturing fluid outlet 4, the fracturing fluid is ejected from the outlet 4 to fracture the rock mass.

[0024] A pressure hole 21 is formed in the sidewall of the pressure tube 2, and the distance between the pressure hole 21 and the bottom of the pressure tube 2 is greater than the distance between two adjacent partitions 3. In other words, by sliding the pressure tube 2 so that the pressure hole 21 is located at different heights of the fracturing fluid outlet 4, the fracturing fluid is injected step by step. Each sealing sleeve 5 opens at the correct time and pressure, which can better disperse the pressure of the fracturing fluid and ensure that the cracks in the coal seam expand evenly, thereby improving the fracturing effect and increasing the permeability of the coal seam. By gradually increasing the pressure, sudden high-pressure shocks can be avoided, reducing damage to the well wall and coal seam.

[0025] An active plate 11 is slidably mounted below the fracturing fluid outlet 4. A connecting rod 12 penetrating the partition plate 3 is fixed to the bottom of the active plate 11. The lower end of the connecting rod 12 is fixed to a driven plate 10. The driven plate 10 is slidably mounted above the gasifying agent outlet 7 of the next stage. In other words, when the fracturing fluid at the previous stage fracturing fluid outlet 4 is pressurized, it pushes the active plate 11 below it downward, thereby pressurizing the gasifying agent at the next stage gasifying agent outlet 7. This simplifies the pressurizing device and enables the injection of gasifying agent into the next stage rock formation before the previous stage fracturing fluid is fracturing, preventing the fracturing process of the previous stage rock formation from causing the collapse of the next stage rock formation and affecting the gasification effect.

[0026] Among them, a connecting plate 8 is provided above the gasifying agent outlet 7, and connecting grooves 81 are provided on both sides of the connecting plate 8. Two sealing blocks 9 are provided above the connecting plate 8, and the sealing blocks 9 can seal the connecting grooves 81. A sealing spring 91 is provided between the two sealing blocks 9, and the sealing spring 91 provides an elastic force to keep the two sealing blocks 9 away from each other. Under the action of the sealing spring 91, the two sealing blocks 9 are attached to the inner wall of the outer cylinder 1 and seal the connecting grooves 81. A one-way injection port 71 is provided on the side wall of the outer cylinder 1 above the sealing block 9. The gasifying agent can be injected into the space between the driven plate 10 and the sealing block 9 in advance through the injection port 71, as shown in FIG. Figure 2 shown.

[0027] Each sealing block 9 is fixed with a lower wedge 14 on both sides, and an upper wedge 13 is fixed to the corresponding position below the driven plate 10. That is, when the driven plate 10 compresses the gasifier until the upper wedge 13 and the lower wedge 14 are in contact, the two sealing blocks 9 are pushed closer to each other, so that the gasifier flows from the connecting groove 81 to the distribution plate 6 and is injected from the gasifier outlet 7, thereby ensuring the injection pressure of the gasifier. Figure 3 shown.

[0028] To better understand the present invention, the following explains the method of using the CO2 fracturing device for underground coal gasification horizontal wells, specifically as follows:

[0029] Before using the device, the following preparations are required: Ensure that all equipment and components have been inspected and maintained to ensure proper operation. Ensure that all fracturing fluids and gasification agents, as well as their storage equipment, are ready and meet requirements. Conduct a detailed assessment and planning of the horizontal well's geological conditions and gasification plan, and pre-inject the gasification agent into each stage's gasification agent chamber through the injection port 71.

[0030] Install and set up the device, ensuring its correct position and orientation in the horizontal well, and ensuring that the sealing sleeve, active plate, driven plate, and flow distribution plate are correctly installed and adjusted;

[0031] The fracturing fluid outlet 4 is sealed by the sealing sleeve 5. By sliding the pressure pipe 2, the position of the fracturing fluid outlet 4 at different heights can be controlled, and the fracturing fluid is injected step by step. The corresponding pull ropes are pulled from bottom to top to make the sleeve leave the fracturing fluid outlet 4. The fracturing fluid is injected from the fracturing fluid outlet 4 to fracture the rock mass.

[0032] When the fracturing fluid at the upper-stage fracturing fluid outlet 4 begins to be pressurized, it pushes the active plate 11 below it downward, thereby pressurizing the gasifying agent at the lower-stage gasifying agent outlet 7. The driven plate 10 compresses the gasifying agent until the upper wedge 13 and the lower wedge 14 fit together, pushing the two sealing blocks 9 closer to each other, so that the gasifying agent flows from the connecting groove 81 to the distribution plate 6 and is injected from the gasifying agent outlet 7, promoting the gasification reaction.

[0033] Throughout the operation, parameters such as pressure, temperature, and flow need to be constantly monitored and adjusted as needed to ensure that the operation proceeds as planned. In addition, the status of components such as the sealing sleeve, driven plate, and active plate need to be paid attention to to ensure their normal operation.

[0034] Once the predetermined operating target is achieved, the fracturing fluid injection and gasification agent injection can be stopped, and then the equipment can be cleaned and maintained to prepare for the next round of operation or to maintain the long-term stable operation of the equipment.

[0035] By following the above steps, the underground coal gasification horizontal well carbon dioxide fracturing device can be effectively utilized to improve gas production efficiency, ensure uniform distribution of gasification agents, and avoid adverse chemical reactions and pollution.

[0036] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A carbon dioxide fracturing device for underground coal gasification horizontal wells, characterized in that: The device comprises: an outer cylinder (1), a pressure tube (2), a partition plate (3), a fracturing fluid outlet (4), a gasifying agent outlet (7), and a flow distribution plate (6); The pressure tube (2) is slidably arranged in the outer tube (1); a plurality of partition plates (3) are provided in the outer tube (1) for dividing the space formed by the outer tube (1) and the pressure tube (2) into a plurality of sections, and a circle of fracturing fluid outlets (4) are provided at the lower part of each section of the outer tube (1); a circle of gasifying agent outlets (7) are provided above the fracturing fluid outlets (4) of each section of the outer tube (1); and the fracturing fluid outlets (4) and the gasifying agent outlets (7) are separated by a distribution plate (6).

2. The device according to claim 1, characterized in that A circle of sealing sleeve (5) is slidably provided on the outer wall of the outer cylinder (1) at a position corresponding to each circle of the fracturing fluid outlet (4).

3. The device according to claim 1, characterized in that A pressure hole (21) is provided on the side wall of the pressure tube (2), and the distance between the pressure hole (21) and the bottom of the pressure tube (2) is greater than the distance between two adjacent partition plates (3).

4. The device according to claim 1, characterized in that The device further comprises: an active plate (11), a driven plate (10), and a connecting rod (12); The active plate (11) is slidably arranged below the fracturing fluid outlet (4); a connecting rod (12) penetrating the partition plate (3) is fixedly arranged at the bottom of the active plate (11), and the lower end of the connecting rod (12) is fixedly connected to the driven plate (10); and the driven plate (10) is slidably arranged above the next gasifying agent outlet (7).

5. The device according to claim 4, characterized in that The device further comprises: a connecting plate (8) arranged above the gasifying agent outlet (7), and connecting grooves (81) provided on both sides of the connecting plate (8).

6. The device according to claim 5, characterized in that The device further comprises: two sealing blocks (9) arranged above the communicating plate (8) for sealing the communicating groove (81).

7. The device according to claim 6, characterized in that The device further comprises: a sealing spring (91); The sealing spring (91) is arranged between the two sealing blocks (9) and is used to provide an elastic force to move the two sealing blocks (9) away from each other.

8. The device according to claim 7, characterized in that The device further comprises: lower wedge blocks (14) respectively fixed on both sides above each sealing block (9) and an upper wedge block (13) fixedly arranged below the driven plate (10); The positions of the lower wedge block (14) and the upper wedge block (13) correspond to each other, and the upper wedge block (13) and the lower wedge block (14) are placed in opposite directions.

9. The device according to claim 8, characterized in that The device further comprises: an injection port (71); A one-way injection port (71) is provided on the side wall of the outer cylinder (1) above the sealing block (9) for pre-injecting a gasifying agent between the driven plate (10) and the sealing block (9).

10. The device according to claim 2, characterized in that Each sealing sleeve (5) is connected to a pull rope for controlling the opening and closing of the cracking fluid outlet (4).

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