A trident type coal underground gasification furnace and a construction and gasification method thereof

Abstract

The application discloses a trident type coal underground gasification furnace and a construction and gasification method. The coal underground gasification furnace is designed and constructed by using one gas inlet channel to realize stable production of two working faces. The main body of the gasification furnace is composed of four wells, three of which are directional (horizontal) wells, and one of which is a vertical well. The four wells are mutually connected to form a trident type furnace body structure. In the three directional wells, the middle well is a gas inlet well and an ignition well, and the two side wells are gas outlet wells; the vertical well is an auxiliary ignition well and an auxiliary gas production well. The distance (furnace width) between the gas inlet directional well and the two side gas outlet directional wells is designed based on the empirical relationship between the coal seam thickness and the gasification working face width. The application saves the construction cost of the furnace body by using the "one-to-two" directional well structure, and can ensure successful ignition and smooth gasification channel in the initial production stage by using the auxiliary vertical well.

Description

Technical Field

[0001] This invention belongs to the field of directional well underground coal gasification engineering technology, specifically involving a "trident" type underground coal gasifier, the construction of the gasifier, and a coal seam gasification method. Background Technology

[0002] For a long time, coal production has relied on underground and open-pit mining methods, resulting in a series of problems such as ground subsidence, landslides, mudslides, surface desertification, and atmospheric dust pollution. Furthermore, my country's coal consumption structure is characterized by diversified users and low utilization rates; over 80% of coal is directly burned, and 80% of soot and 90% of SO2 originate from coal combustion. Underground coal gasification and its integrated full-chain utilization technology store combustion ash underground, significantly reducing surface subsidence and eliminating solid emissions. The gas from underground gasification outlets can be centrally purified, removing harmful substances such as tar, sulfur, and dust. It can even separate CO2 from surface-mounted CO2 using separation or absorption technologies for storage or backfilling into the gasification space, thus obtaining clean coal gas.

[0003] Coal-smoke pollution caused by fuel structure accounts for about 70% of all air pollution, with coal-fired pollution, mainly sulfur dioxide, carbon dioxide, and soot, becoming increasingly serious. If the energy structure does not undergo a strategic transformation, these structural contradictions will not be significantly improved. This means that my country must accelerate industrial structural reforms, urgently change traditional coal production and consumption methods, and develop clean, harmless, and environmentally friendly production technology systems. Underground coal gasification technology can effectively solve this problem.

[0004] Underground coal gasification technology can recover various coal resources abandoned in old mines, thin coal seams that are difficult to mine underground or have poor economic or safety conditions, coal seams under pressure from underground sources, and coal seams with high sulfur, high ash, and high gas content. In addition, it can also be used for deep coal seams (below 1000m). Underground coal gasification can effectively utilize various resources and improve resource utilization efficiency.

[0005] With advancements in drilling technology, multi-row gasifiers have emerged. However, due to limitations in gasifier ignition technology, they only support single ignition. If ignition fails, subsequent work is difficult to advance quickly. Furthermore, traditional multi-row gasifiers typically connect a directional well to a vertical well, requiring the construction of multiple vertical wells to increase gas production, which is costly. Summary of the Invention

[0006] The present invention aims to provide a trident-type underground coal gasification furnace and its construction and gasification method, which can achieve multiple ignition, save construction costs and improve economic benefits.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A trident-type underground coal gasification furnace includes a first directional well, a second directional well, a third directional well, and a vertical well;

[0009] The first directional well and the third directional well are located on both sides of the second directional well. The second directional well is a gas intake and ignition well, while the first directional well and the third directional well are both gas outlet wells.

[0010] The vertical well is simultaneously connected to the ends of the first directional well, the second directional well, and the third directional well, and the connection point is located in the coal seam to be gasified. The vertical well serves as an auxiliary ignition well and an auxiliary gas production well. The first directional well and the third directional well are arranged symmetrically about the line connecting the second directional well and the vertical well.

[0011] Furthermore, the first directional well, the second directional well, and the third directional well include a vertical section and a horizontal section, wherein the horizontal section is located in the coal seam to be gasified.

[0012] Alternatively, the horizontal section of the second directional well is located in the coal seam for a length of 200–450 m.

[0013] Alternatively, the wellheads of the first directional well, the second directional well, and the third directional well are distributed on a straight line, and the straight line is perpendicular to the line connecting the wellhead of the second directional well and the wellhead of the vertical well.

[0014] Alternatively, the distance between the wellheads of the first and second directional wells, and the distance between the wellheads of the second and third directional wells, are both 30 to 40 meters.

[0015] Alternatively, the angle between the first directional well and the second directional well, and the angle between the second directional well and the third directional well, are all 15 to 20°.

[0016] As an alternative, the first, second, and third directional wells are all equipped with support casings that serve as coiled tubing, with screen pipes used for coal seam sections and casings used for non-coal seam sections.

[0017] A method for constructing a trident-type underground coal gasification furnace includes the following steps:

[0018] Step 1: Construct a vertical well, a second directional well as an intake directional well, and a first and third directional well as exhaust directional wells in sequence.

[0019] Step 2: Use a mechanical drilling rig to connect the first directional well, the second directional well, the third directional well, and the vertical well in the coal seam to be gasified;

[0020] Step 3: Screen pipe completion is used for the coal seam sections corresponding to the first, second, and third directional wells, and casing completion is used for the non-coal seam sections.

[0021] Furthermore, in step one, the vertical well is drilled to a final depth of 20m below the coal seam to be gasified, and the well is completed using casing from the top of the coal seam to the wellhead.

[0022] A coal seam gasification method using the aforementioned trident-type underground coal gasifier includes an ignition step, wherein a second directional well or a vertical well is used as the ignition well.

[0023] Compared with existing technologies, this invention provides a design and construction method for an underground coal gasification furnace that enables stable production on two working faces using a single air intake channel. The gasification furnace consists of four wells: three directional (horizontal) wells and one vertical well, which are interconnected to form a "trident" furnace structure. Of the three directional wells, the middle well serves as both the air intake and ignition well, while the two side wells are the gas output wells; the vertical well serves as both an auxiliary ignition and auxiliary gas production well. Based on the empirical relationship between coal seam thickness and the width of the gasification working face, the spacing (furnace width) between the air intake directional well and the two side gas output directional wells is designed.

[0024] In the construction of the gasifier of this invention, a vertical well is constructed first, followed by sequential construction of an intake directional well and an outlet directional well. All three directional wells are connected to the vertical well within the coal seam to be gasified. The three directional wells utilize screen pipe completion in the coal seam section and casing completion in the non-coal seam section. The vertical well is drilled to a final depth of 20m below the coal seam to be gasified, and casing completion is used from the top of the coal seam to the wellhead. The furnace structure of this invention, through a "one-to-two" directional well structure, saves on furnace construction costs; the use of the auxiliary vertical well ensures successful ignition and smooth gasification channels during the initial production phase. Attached Figure Description

[0025] Figure 1 This is a three-dimensional schematic diagram of the trident-type underground coal gasification furnace in this invention;

[0026] Figure 2 This is a plan view of the trident-type underground coal gasification furnace in this invention;

[0027] Figure 3 This is a schematic elevation view of the trident-type underground coal gasification furnace in this invention.

[0028] In the picture:

[0029] 1—First directional well; 2—Second directional well; 3—Third directional well; 4—Vertical well. Detailed Implementation

[0030] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, it should not be construed that the scope of the subject matter of the present invention is limited to the following embodiments. All modifications, substitutions and alterations made based on ordinary technical knowledge and common practices in the art without departing from the above-described technical concept of the present invention are included within the scope of the present invention.

[0031] like Figures 1-3 As shown, the trident-type underground coal gasification furnace of the present invention includes a first directional well 1, a second directional well 2, a third directional well 3, and a vertical well 4. All three directional wells are connected to the vertical well 4 in the coal seam to be gasified, forming a "one-to-two" directional well structure, which saves on furnace construction costs. The three directional wells and the vertical well 4 together form a "trident" type furnace. The auxiliary vertical well 4 ensures successful ignition and smooth gasification channels during the initial production phase.

[0032] Of the three directional wells, the second directional well (2), which serves as the intake well, has an outlet well symmetrically distributed on each side, namely the first directional well (1) and the third directional well (3). The wellheads of the three directional wells are distributed in a straight line, with a distance of 30-40 meters between adjacent wellheads. The included angle between adjacent directional wells (which can be understood as...) Figure 2 The acute angle between adjacent horizontal directional drilling sections is 15-20°, and the drilling distance of the gas well in the coal seam is 200-450m. The connected vertical well 4 is used as an auxiliary ignition well and auxiliary gas production. All three directional wells are equipped with support casing as coiled tubing. Screen pipe completion is used for the coal seam section, and casing completion is used for the non-coal seam section.

[0033] The trident-type underground coal gasification furnace is built in the target coal seam and includes the following construction steps:

[0034] Step 1: First, construct a vertical well No. 4, drilling to a final depth of 20m below the coal seam to be gasified, and complete the well using casing from the top of the coal seam to the wellhead;

[0035] Step 2: Construct a second directional well along the dip of the target coal seam to be gasified, which will be the second directional well 2. The horizontal section of the second directional well 2 will be 200-450m apart. The coal seam section will be completed using screen pipes, and the section from the top of the coal seam to the wellhead will be completed using casing pipes. A mechanical drilling rig will be used to connect and connect it with the vertical well 4.

[0036] Step 3: Then, construct two outlet directional wells (first directional well 1 and third directional well 3) symmetrically on both sides of the intake directional well (second directional well 2) for 30-40m. The line connecting the wellheads of the two outlet wells should be as perpendicular as possible to the line connecting the wellheads of the intake directional well (second directional well 2) and the vertical well 4.

[0037] Step four: Use a mechanical drilling rig to connect the gas-producing directional wells (first directional well 1 and third directional well 3) with the vertical well 4. Use screen pipe for well completion in the coal seam section and casing pipe for well completion from the top of the coal seam to the wellhead. All the constructed wells form a "trident" type furnace.

[0038] After the trident-type underground coal gasification furnace is constructed, ignition can be performed using either the intake directional well (second directional well 2) or the vertical well 4. Both ignition methods can greatly improve the ignition success rate.

[0039] Example 1:

[0040] like Figure 1 , Figure 2 and Figure 3 As shown, the trident-type underground coal gasification furnace includes a first directional well 1 and a third directional well 3 as gas outlet directional wells, a second directional well 2 as gas inlet directional wells, and a vertical well 4 as an auxiliary ignition / gas production well. The horizontal sections of the first directional well 1, the second directional well 2, and the third directional well 3 are all within the coal seam and are completed using screen pipes; above the coal seam, they are completed using casing pipes. The vertical well 4 is drilled to a depth of 20m below the coal seam, and all three directional wells are connected to the vertical well 4 via a mechanical drilling rig.

[0041] The construction method of the trident-type underground coal gasification furnace includes the following steps:

[0042] Step 1: First, construct a vertical well No. 4, drilling to a final depth of 20m below the coal seam to be gasified, and complete the well using casing from the top of the coal seam to the wellhead;

[0043] Step 2: Construct a second directional well along the dip of the target coal seam to be gasified, which will be the second directional well 2. The horizontal section of the second directional well 2 is 270m long. The coal seam section will be completed using screen pipe, and the section from the top of the coal seam to the wellhead will be completed using casing. A mechanical drilling rig will be used to connect and connect it with the vertical well 4.

[0044] Step 3: Then, construct two symmetrical directional wells (first directional well 1 and third directional well 3) 30m on both sides of the intake directional well (second directional well 2), and the line connecting the wellheads of the two directional wells should be as perpendicular as possible to the line connecting the wellhead of the intake directional well (second directional well 2) and the wellhead of the vertical well 4.

[0045] Step 4: Use a mechanical drilling rig to connect the gas-producing directional wells (first directional well 1 and third directional well 3) with the vertical well 4. Use screen pipes for well completion in the coal seam section and casing pipes for well completion from the top of the coal seam to the wellhead. All the construction wells form a "trident" type furnace.

[0046] (e) Inject 50% medium-rich oxygen-enriched gas through the gas-intake directional well (second directional well 2) using coiled tubing, and ignite it using the ignition system of the coiled tubing. If the first ignition fails, a second ignition can be performed using the vertical well 4 to ensure that the ignition success rate is greatly improved.

[0047] (f) Once the coal seam is ignited, the gasifying agent is injected through the continuous tubing in the intake well (second directional well 2). The continuous tubing can directly inject the gasifying agent into the vicinity of the combustion zone, and can intelligently adjust the intake volume to control the expansion and movement of the fire zone until the entire gasifier is burned out. Finally, the furnace is closed for management as required.

[0048] The present invention provides a method for constructing a trident-type underground coal gasification furnace, in which three directional wells are connected to a vertical well 4 in the coal seam to be gasified. The furnace structure is constructed using a "one-to-two" directional well structure, which saves on furnace construction costs. The use of the auxiliary vertical well 4 ensures successful ignition and smooth gasification channels in the early stages of production, thereby reducing production costs and improving the success rate and economic benefits.

[0049] Obviously, the above embodiments are merely illustrative examples for clear explanation and to limit the implementation methods. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exemplify all implementation methods here. However, any obvious or derivative variations derived therefrom are still within the scope of protection of this invention.

Claims

1. A trident-type underground coal gasification furnace, characterized in that: Including the first directional well (1), the second directional well (2), the third directional well (3), and the vertical well (4); The first directional well (1) and the third directional well (3) are located on both sides of the second directional well (2). The second directional well (2) is an air intake and ignition well, while the first directional well (1) and the third directional well (3) are both air outlet wells. The vertical well (4) is connected to the ends of the first directional well (1), the second directional well (2) and the third directional well (3), and the connection position is located in the coal seam to be gasified. The vertical well (4) serves as an auxiliary ignition well and an auxiliary gas production well. The first directional well (1) and the third directional well (3) are arranged symmetrically about the line connecting the second directional well (2) and the vertical well (4). 50% oxygen-enriched gasifying agent is injected through the second directional well (2) using coiled tubing. The ignition system of the coiled tubing is used for ignition. If the first ignition fails, a second ignition can be performed using the vertical well (4) to ensure the success rate of ignition. Once the coal seam is ignited, gasifying agent is injected through the coiled tubing in the second directional well (2). The coiled tubing can directly inject the gasifying agent near the combustion zone, and the expansion and movement of the fire zone can be controlled by adjusting the amount of gas intake.

2. The trident-type underground coal gasification furnace according to claim 1, characterized in that: The first directional well (1), the second directional well (2) and the third directional well (3) include a vertical section and a horizontal section, wherein the horizontal section is located in the coal seam to be gasified.

3. The trident-type underground coal gasification furnace according to claim 2, characterized in that: The horizontal section of the second directional well (2) is located in the coal seam and has a length of 200-450m.

4. The trident-type underground coal gasification furnace according to claim 1, characterized in that: The wellheads of the first directional well (1), the second directional well (2) and the third directional well (3) are distributed on a straight line, and the straight line is perpendicular to the line connecting the wellhead of the second directional well (2) and the wellhead of the vertical well (4).

5. A trident-type underground coal gasification furnace according to claim 1, characterized in that: The distance between the wellhead of the first directional well (1) and the wellhead of the second directional well (2), and the distance between the wellhead of the second directional well (2) and the wellhead of the third directional well (3) are all 30 to 40 m.

6. A trident-type underground coal gasification furnace according to claim 1, characterized in that: The angle between the first directional well (1) and the second directional well (2), and the angle between the second directional well (2) and the third directional well (3) are all 15 to 20°.

7. A trident-type underground coal gasification furnace according to claim 1, characterized in that: The first directional well (1), the second directional well (2), and the third directional well (3) are all equipped with support casings as continuous tubing, with screen pipes used for coal seam sections and casings used for non-coal seam sections.

8. A method for constructing a trident-type underground coal gasification furnace, characterized in that: The method for constructing the trident-type underground coal gasification furnace as described in claim 1 includes the following steps: Step 1: Construct the vertical well (4), the second directional well (2) which serves as the gas intake directional well, and the first directional well (1) and the third directional well (3) which serve as the gas outlet directional wells, respectively. Step 2: Using a mechanical drilling rig, the first directional well (1), the second directional well (2), the third directional well (3), and the vertical well (4) are connected in the coal seam to be gasified; Step 3: The first directional well (1), the second directional well (2), and the third directional well (3) are completed using screen pipes for the coal seam sections and using casing pipes for the non-coal seam sections.

9. The method for constructing a trident-type underground coal gasification furnace according to claim 8, characterized in that: In step one, the vertical well (4) is drilled to a final hole 20m below the coal seam to be gasified, and the well is completed from the top of the coal seam to the wellhead using casing.

10. A coalbed gasification method using the trident-type underground coal gasifier as described in claim 1, comprising an ignition step, characterized in that: The second directional well (2) or the vertical well (4) is used as the ignition well.

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