A coal drilling type coal underground gasification furnace, a gasification furnace construction method, and a coal seam gasification method

Abstract

The application discloses a coal drilling type coal underground gasification furnace, a gasification furnace construction method and a coal seam gasification method. A gas outlet well is connected with a gas injection well through a horizontal section at the top of a coal seam to form a U-shaped gasification furnace structure. The coal seam is excavated at the joint of the gas injection well, so that the coal seam collapses, stress is redistributed, the cavity is enlarged, the coal seam below the pocket section of the gas injection well is ignited, the coal seam is positively advanced, and the effective synthesis gas is discharged to the ground through the gas outlet well. The application can well develop and utilize tectonic coal, and has the advantages of environmental protection, safety and good economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of underground coal gasification engineering technology, specifically relating to a method for drilling underground coal gasification of structural coal, a gasifier, and a method for constructing the gasifier. Background Technology

[0002] Tectonic coal is coal whose structure has been disrupted by tectonic processes, resulting in a powdery texture that crumbles easily when squeezed by hand. It has extremely low permeability, making it prone to collapse, blockage, and obstruction when constructing gasification furnace channels in the coal seam during drilling-type underground coal gasification. This hinders the progress of underground coal gasification.

[0003] Under normal circumstances, well-drilled underground coal gasification requires selecting coal seams with good coal body structure, easy-to-construct gasification channels that do not collapse or become blocked, and constructing double-horizontal gasification channels in the lower part of the coal seam (20cm from the bottom of the coal seam), using a coiled tubing retraction ignition gasification method. However, structural coal has a fragmented, powdery structure that crumbles easily when squeezed by hand. Constructing gasification channels within the coal seam is prone to collapse and blockage, which is detrimental to underground gasification of structural coal. Under a dual-carbon background, this is also unfavorable for the development and utilization of structural coal. Summary of the Invention

[0004] The present invention aims to provide a structural coal drilling underground coal gasification furnace, a gasification furnace construction method and a coal seam gasification method, so as to enable structural coal to be well developed and utilized, with good environmental protection, safety and economic benefits.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A coal drilling-type underground coal gasification furnace includes,

[0007] The gas injection well sequentially penetrates the upper rock strata of the coal seam, the coal seam, and extends to the lower rock strata of the coal seam for a certain distance;

[0008] The gas well is a directional well and includes a vertical section, an inclined section and a horizontal section. The gas well is connected to the gas injection well through the horizontal section located at the top of the coal seam to form a U-shaped gasifier structure.

[0009] Furthermore, the gas injection well includes a vertical well and a directional well. The vertical well consists of a first-stage gas injection well section and a second-stage gas injection well section connected in sequence with gradually decreasing diameters. The second-stage gas injection well section penetrates the roof of the coal seam. The directional well is a third-stage gas injection well section that penetrates the coal seam and extends a distance into the lower rock strata of the coal seam.

[0010] The gas well comprises, in sequence, a first opening section, a second vertical opening section, a second directional drilling, stabilization, and inclination enhancement section, and a second horizontal section at the top of the coal seam. The borehole diameter of the first opening section is larger than that of the second vertical opening section, the second directional drilling, stabilization, and inclination enhancement section, and the second horizontal section at the top of the coal seam. The second horizontal section at the top of the coal seam is located at the top of the coal seam and includes a fiberglass casing. The gas well is connected to the injection well through the second horizontal section at the top of the coal seam.

[0011] Furthermore, the third well section of the gas injection well also includes a pocket section formed in the coal seam.

[0012] The method for constructing the aforementioned underground coal drilling gasification furnace includes the following steps:

[0013] Step 1: Construct the first, second, and third well sections of the gas injection well sequentially, where:

[0014] The opening diameter of the first section of the gas injection well is φD1. After the hole depth is sufficient to penetrate a certain distance into the bedrock and ensure that there is no lost layer, a casing with an outer diameter of φD2 is installed, where φD2 < φD1, and cement grout is used for sealing.

[0015] In the second section of the gas injection well, a drill bit with an outer diameter of φD3 is used to drill through the roof of the gasifiable coal seam, and a casing with an outer diameter of φD4 is installed for cementing. φD4 < φD3 < φD2, and the cement slurry is returned to the surface.

[0016] The third section of the gas injection well uses a drill bit with an outer diameter of φD5 to drill through the gasifiable coal seam to a certain distance below the coal seam and complete the well with an open hole, where φD5 < φD4.

[0017] Step two involves sequentially constructing the first well section of the gas well, the second vertical well section of the gas well, the second inclined section of the gas well (including the inclination building, stabilization, and inclination enhancement sections), and the second horizontal section at the top of the coal seam of the gas well, wherein:

[0018] After drilling through the lost circulation zone with a drill bit of φD6 outer diameter in the first well section of the gas well, it entered the first bedrock section of Julu and ran in a casing of φD7 (φD7 < φD6) for sealing.

[0019] The second vertical section of the gas well, the second inclined section of the gas well (including the inclination building, stabilization, and inclination enhancement sections) and the horizontal section at the top of the coal seam of the second gas well are drilled with a drill bit of φD8 outer diameter. After drilling through the gasifiable coal seam, the drill bit lands and then connects with the third section of the gas injection well at the top of the coal seam of the second gas well. φD8 < φD7. For the second vertical section of the gas well, the inclination building, stabilization, and inclination enhancement sections, the part above the gasified coal seam is fitted with a steel casing of φD9 outer diameter, and the part below the gasified coal seam is fitted with a fiberglass casing of φD9. φD9 < φD8. Half of the well is cemented. The horizontal section at the top of the coal seam of the second gas well is not cemented.

[0020] Furthermore, in step one, the third well section of the gas injection well adopts cavern completion to form a pocket section.

[0021] Furthermore, in step two, a drill bit with an outer diameter of φD8 is used to drill through the gasifiable coal seam and land, and a grading hoop is installed in a stable stratum above the landing position.

[0022] Furthermore, in steps one and two, φD1 = φD6, φD2 = φD7, and φD5 = φD8.

[0023] The coalbed gasification method using the aforementioned underground coal drilling gasifier includes,

[0024] A gasification channel is constructed at the top of the coal seam and a forward combustion method is adopted. The coal seam is completed by a cavern well through a gas injection well, which redistributes the stress of the coal seam and forms a cavern cavity. The syngas after forward combustion returns to the surface through the gasification channel at the top of the coal seam.

[0025] Tectonic coal (mylonite) is produced by tectonic processes that disrupt the coal seam structure. It is powdery, easily crumbled by hand, and has extremely low permeability. When drilling underground coal gasification, it is prone to collapse and blockage when constructing gasification furnace channels in the coal seam, which can hinder the progress of underground coal gasification.

[0026] Therefore, this invention utilizes a U-shaped well to construct a gasifier through forward combustion. The gasification channel is constructed by drilling a vertical well at an angle into the top of the coal seam and then horizontally drilling along the top of the coal seam to connect with the injection well. After connection, the injection well cavits into the coal seam, causing it to collapse, redistributing stress, and enlarging the cavity. The coal seam is ignited through the three-section well with pockets in the injection well, and the gas is advanced forward. The effective syngas reduced to its original state is discharged to the surface through the second section of the gas well (angle-building, stabilization, and angle-increasing sections), the second section of the gas well (vertical section), and the first section of the gas well (opening section).

[0027] Compared with existing technologies, this invention provides a structural coal drilling-type underground coal gasification furnace, a gasification furnace construction method, and a coal seam gasification method. This invention employs forward combustion for structural coal, constructing a U-shaped gasification furnace at the top of the coal seam. Through injection wells, a cavernous completion method is used to redistribute stress within the coal seam, facilitating the formation of cavernous cavities. Forward combustion allows syngas to be recovered from the top of the coal seam via a channel (the horizontal section at the top of the second section of the gas well), through the second section of the gas well's inclined shaft, stabilization section, and vertical section, back to the surface. This enables the effective development and utilization of structural coal, resulting in better environmental protection, safety, and economic benefits.

[0028] The coal drilling-type underground coal gasifier, gasifier construction, and coal seam gasification method described in this invention have the following advantages:

[0029] (1) It can make full use of the coal structure to produce syngas through underground coal gasification, improve the energy structure, and has low cost and good benefits.

[0030] (2) Constructing a gasification channel on the upper part of the coal can ensure that the gasification process is not blocked, which is conducive to the gasification process.

[0031] (3) The fiberglass casing used in the horizontal section of the top of the coal seam in the second gas well can protect the hole in the early stage. It does not melt during the gasification process, and it is easy to ash at high temperature (not exceeding 20 meters). It also ensures that the gasification channel is easy to open and not blocked. Attached Figure Description

[0032] Figure 1 This is a cross-sectional view of the underground coal gasification furnace constructed in an embodiment of the present invention;

[0033] Figure 2 This is a structural diagram of the gas injection well in an embodiment of the present invention;

[0034] Figure 3 This is a structural diagram of the gas well in an embodiment of the present invention;

[0035] In the picture:

[0036] 1-Gas injection well; 11-Gas injection well first opening section; 12-Gas injection well second opening section; 13-Gas injection well third opening section; 14-Connecting target point; 2-Gas production well; 21-Gas production well first opening section; 22-Gas production well second opening vertical section; 23-Gas production well second opening section for inclination building, stabilization, and inclination enhancement; 24-Gas production well second opening coal seam landing point; 25-Gas production well second opening horizontal section at the top of the coal seam; 3-Coal seam; 4-Upper strata of the coal seam; 5-Lower strata of the coal seam. Detailed Implementation

[0037] 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.

[0038] like Figures 1-3 As shown, Figure 1 , Figure 2 , Figure 3 As shown, this embodiment provides a structure for a coal drilling-type underground coal gasification gasifier, including a vertically oriented injection well 1 and an outlet well 2. The injection well 1 and the outlet well 2 are connected by a horizontal section 25 at the top of the coal seam through the outlet well. The connection point between the two wells (injection well 1 and outlet well 2) is the connection target point 14. The injection well 1 includes a three-section well 13 in the coal seam 3, which adopts a cavern completion method.

[0039] Specifically, the gas outlet well 2 is connected to the gas injection well 1 via a horizontal section located at the top of the coal seam 3 to form a U-shaped gasifier structure.

[0040] Among them, gas injection well 1 includes a vertical well and a directional well. The vertical well consists of two sections, 11 and 12, which are connected in sequence with gradually decreasing diameters. Section 12 penetrates the roof of coal seam 3. The directional well is section 13, which penetrates coal seam 3 and extends to a distance into the lower rock strata 5. Figure 1 The 60m marked in the diagram refers to the drilling depth of section 13 of the third section of the gas injection well (meaning the third section extends to the bottom of the borehole). Section 13 of the third section of the gas injection well uses cavern completion to form a pocket section. Gas injection well 1 corresponds to the pocket section below coal seam 3, which is the coal seam cavern completion section. The pocket section of coal seam 3 is formed through cavern completion technology.

[0041] The gas well 2 includes a gas well opening section 21, a gas well opening vertical section 22, a gas well opening skew section 23 for skew building, stabilizing, and increasing skewness, and a gas well opening horizontal section 25 at the top of the coal seam, which are connected in sequence. The diameter of the opening section 21 is larger than that of the gas well opening vertical section 22, the gas well opening skew section 23 for skew building, stabilizing, and increasing skewness, and the gas well opening horizontal section 25 at the top of the coal seam. The gas well opening horizontal section 25 at the top of the coal seam is located at the top of the coal seam 3 and includes a fiberglass casing. The gas well 2 is connected to the gas injection 1 through the gas well opening horizontal section 25 at the top of the coal seam.

[0042] Gas injection well 1 typically adopts a three-section structure, as detailed below:

[0043] The opening diameter of the first section (section 11 of the gas injection well) is φ444.5mm. A casing with a diameter of φ339.7mm is installed. The hole depth is generally not less than 10mm into the bedrock. After ensuring that there is no leakage layer, a guide pipe with a diameter of φ339.7mm is installed and sealed with cement grout.

[0044] In the second section (section 12 of the gas injection well), a φ222.25mm drill bit was used to drill through the roof of the gasifiable coal seam 3, and a 177.8mm casing was run in for cementing. Cement slurry was returned to the surface.

[0045] The third section (section 13 of the gas injection well) was drilled through a 60-meter-thick gasifiable coal seam 3 using a φ155.6mm drill bit, completing the well in open hole. This facilitates docking with the top horizontal section 25 of the second section of the coal seam in the gas production well, and also facilitates coal extraction from the tunnel. During the tunnel completion process of coal seam 3, a pocket-like bottom was formed. During the tunnel completion process, a cavity larger than the diameter of the drilled section was excavated at the bottom. Its main functions are to facilitate docking with the directional well and to catch rock cuttings falling during drilling, which is conducive to the smooth implementation of cementing and gasification processes. The cavity in coal seam 3 is the pocket. The size of the pocket determines the ease of docking between the two wells (gas injection well 1 and gas production well 2) of the gasifier, as well as the efficiency of gasification ignition and stable propulsion. Therefore, it is necessary to control the size of the pocket.

[0046] Gas well 2 typically adopts a two-section structure, as detailed below:

[0047] First opening (Gas well section 21): After the φ444.5mm drill bit penetrates the lost circulation zone, it enters the bedrock for no less than 10 meters, and then runs in a φ339.7mm casing for sealing.

[0048] The second section (22, vertical section of the second gas well; 23, inclination building, stabilization, and inclination enhancement section of the second gas well; 24, coal seam landing point of the second gas well; 25, horizontal section at the top of the coal seam of the second gas well) uses a φ155.6mm drill bit to drill through the gasifiable coal seam 3 and land at the target point 14, completing the drilling after connection. Above the gasifiable coal seam 3, in the vertical section 22 of the second gas well and the inclination building, stabilization, and inclination enhancement section 23 of the second gas well, a φ114.3mm steel casing is installed (the deformation of the steel casing is limited, similar to...). Figure 1 The arc segment and the straight segment are tangent. A φ114.3mm fiberglass casing is installed in section 3 of the coal seam. Above landing point 24 of the second coal seam of the gas well, a stable formation is selected to install a graded hoop (a cementing tool that is effective for lost formations and achieves layered formation sealing. Here, a support ring can be used in conjunction with the graded hoop to achieve temporary pipeline sealing and achieve the purpose of half-way cementing). Half-way cementing (i.e., no cementing in coal seam 3, or it can be understood as no cementing in the top horizontal section 25 of the second coal seam of the gas well). No cementing in the top horizontal section 25 of the second coal seam of the gas well in coal seam 3.

[0049] The trajectory of the gas well 2 adopts a structural design of "22 vertical well section of the second gas well opening, 23 inclined, stabilizing and increasing inclination section of the second gas well opening, 25 horizontal section at the top of the coal seam of the second gas well opening, and 14 connecting target point as docking position".

[0050] 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 coal seam gasification method for constructing a coal well-type underground coal gasification furnace, characterized in that: The aforementioned underground coal drilling-type coal gasification furnace includes... The gas injection well (1) passes through the upper rock strata (4) and the coal seam (3) in sequence and extends to the lower rock strata (5) of the coal seam for a distance. Gas well (2), which is a directional well and includes a vertical section, an inclined section and a horizontal section. The gas well (2) is connected to the gas injection well (1) through the horizontal section located at the top of the coal seam (3) to form a U-shaped gasifier structure. The gas injection well (1) includes a vertical well and a directional well. The vertical well consists of a first-stage gas injection well section (11) and a second-stage gas injection well section (12) connected in sequence with gradually decreasing diameter. The second-stage gas injection well section (12) penetrates the roof of the coal seam (3). The directional well is a third-stage gas injection well section (13). The third-stage gas injection well section (13) penetrates the coal seam (3) and extends to a distance into the lower rock strata (5) of the coal seam. The gas well (2) includes a gas well opening section (21), a gas well opening vertical section (22), a gas well opening skew section (23) for stabilizing and increasing skewness (23), and a gas well opening horizontal section at the top of the coal seam (25) connected in sequence. The diameter of the gas well opening section (21) is larger than that of the gas well opening vertical section (22), the gas well opening skew section (23), and the gas well opening horizontal section at the top of the coal seam (25). The gas well opening horizontal section at the top of the coal seam (25) is located at the top of the coal seam (3) and includes a fiberglass casing. The gas well (2) is connected to the gas injection well (1) through the gas well opening horizontal section at the top of the coal seam (25). The three-section well section (13) of the gas injection well also includes a pocket section formed in the coal seam (3); The coalbed gasification method includes... A gasification channel is constructed at the top of the coal seam (3) and a forward combustion method is adopted. The stress of the coal seam (3) is redistributed through the injection well (1) and a cavern completion method is adopted to form a cavern cavity. The syngas after forward combustion returns to the ground through the gasification channel at the top of the coal seam (3). The construction method of the aforementioned underground coal drilling gasification furnace includes the following steps. Step 1: Construct the first well section (11), the second well section (12), and the third well section (13) of the gas injection well in sequence, wherein: The opening diameter of the first section (11) of the gas injection well is φD1. The hole depth is sufficient to enter the bedrock for a certain distance. After ensuring that there is no leakage layer, the casing with an outer diameter of φD2 is lowered. φD2 < φD1 and cement grout is used for sealing. In the second section (12) of the gas injection well, a drill bit with an outer diameter of φD3 is used to drill through the roof of the gasifiable coal seam (3), and a casing with a diameter of φD4 is installed for cementing. φD4 < φD3 < φD2, and the cement slurry is returned to the surface. In the third section of the gas injection well (13), a drill bit with an outer diameter of φD5 is used to drill through the gasifiable coal seam (3) until a distance of rock strata (5) below the coal seam. The well is completed with an open hole, and φD5 < φD4. Step 2: Construct the first well section (21), the second vertical well section (22), the second inclined section (23), and the second horizontal section at the top of the coal seam (25) in sequence, where: After drilling through the lost circulation zone with a drill bit with an outer diameter of φD6 in the first well section (21), the well enters the bedrock for a distance and then runs in a casing with an outer diameter of φD7 (φD7 < φD6) for sealing. The second vertical section (22), the second inclined, stabilizing, and increasing section (23), and the second horizontal section at the top of the coal seam (25) of the gas well are drilled through the gasifiable coal seam (3) with a drill bit of φD8 outer diameter and landed. Then, the second horizontal section at the top of the coal seam (25) of the gas well is connected to the third section (13) of the gas injection well and the drilling is completed. φD8 < φD7. The second vertical section (22), the second inclined, stabilizing, and increasing section (23) of the gas well are drilled with steel casing with an outer diameter of φD9 in the part above the gasified coal seam and fiberglass casing with an outer diameter of φD9 in the part below the gasified coal seam. φD9 < φD8. Half of the well is cemented. The second horizontal section at the top of the coal seam (25) of the gas well is not cemented.

2. The coal seam gasification method of the underground coal gasification furnace of the coal drilling type according to claim 1, characterized in that: In step one, the three-stage well section (13) of the gas injection well adopts cave completion to form a pocket section.

3. The coalbed gasification method of the underground coal gasification furnace of the coal drilling type according to claim 1, characterized in that: In step two, a drill bit with an outer diameter of φD8 is used to drill through the gasifiable coal seam (3) and land, and a graded hoop is installed in a stable stratum above the landing position.

4. The coal seam gasification method of the underground coal gasification furnace of the coal drilling type according to claim 1, characterized in that: In steps one and two, φD1=φD6, φD2=φD7, and φD5=φD8.

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