A gas extraction method based on a hierarchical hole distribution type screen pipe

Abstract

The application discloses a gas extraction method based on a hierarchical hole distribution type screen pipe, and the method comprises the following steps: drilling a borehole for extracting gas in a coal rock stratum; obtaining the distribution of cracks on a coal rock core, and calculating the crack surface density of each section in the borehole according to the distribution of cracks on the coal rock core; determining the hole distribution order and connection sequence of the screen pipe corresponding to each section according to the crack surface density of each section; connecting the hole distribution type screen pipe corresponding to each section in sequence according to the connection sequence; sending the hole distribution type screen pipe corresponding to each section into each section of the borehole to form a screen pipe pipeline; and connecting the screen pipe pipeline to a main gas extraction pipeline for gas extraction. The method can effectively improve the gas extraction efficiency, greatly guarantee the strength and service life of the screen pipe, and further improve the gas extraction benefit by matching the hierarchical screen hole with the crack distribution in each section of the gas borehole.

Description

Technical Field

[0001] This invention relates to the field of gas extraction technology, and in particular to a gas extraction method based on a graded perforated screen. Background Technology

[0002] Coal seam gas drainage is the most fundamental measure to prevent coal mine gas disasters. By lowering gas drainage screens into coal seam boreholes, a transport channel is established for the gas within the coal seam, allowing it to enter the gas drainage pipeline. This method not only reduces the gas content in the coal seam but also facilitates the utilization of the extracted gas as a clean energy source. Chinese patent application CN111608721A proposes a fully movable negative pressure regulating gas drainage device and method, improving gas drainage efficiency through fully movable and adjustable drainage. Chinese patent application CN117211859A discloses a variable diameter large-diameter borehole gas drainage support screen and its usage method, which improves gas drainage efficiency by changing the screen diameter to protect the borehole.

[0003] The aforementioned patents all overlook the crucial role of the screen apertures. It is particularly important to note that while the screen apertures are a component of the screen pipe, they also serve as a bridge connecting the gas and the screen pipe. The arrangement of the screen apertures significantly impacts the gas extraction efficiency of the screen pipe. In practical engineering applications, to ensure gas extraction efficiency, a uniform screen aperture arrangement is often adopted. This not only fails to improve gas extraction effectiveness but also leads to unnecessary material costs due to the indiscriminate installation of large-diameter screen pipes, thus severely impacting gas extraction benefits. Summary of the Invention

[0004] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, the first objective of this invention is to propose a gas extraction method based on a graded perforated screen. By matching the graded screen holes with the crack distribution within each segment of the gas borehole, not only can the gas extraction efficiency be effectively improved, but the strength and service life of the screen can also be greatly guaranteed, thereby further enhancing the gas extraction benefits and solving the problems of high gas extraction costs and difficulty in improving gas extraction efficiency.

[0005] To achieve the above objectives, a first aspect of the present invention proposes a gas extraction method based on a graded perforated screen pipe. The method includes: drilling a borehole for gas extraction in a coal and rock stratum; obtaining the distribution of fractures on the coal core and calculating the fracture surface density of each segment within the borehole based on the fracture surface density of the coal core; determining the perforation level and connection sequence of the screen pipe corresponding to each segment based on the fracture surface density of each segment; sequentially connecting the perforated screen pipes corresponding to each segment according to the connection sequence; inserting the perforated screen pipes corresponding to each segment into each segment of the borehole to form a screen pipe pipeline; and connecting the screen pipe pipeline to a main gas extraction pipeline for gas extraction.

[0006] According to an embodiment of the present invention, a gas extraction method based on a graded perforated screen pipe involves drilling a borehole for gas extraction in a coal and rock stratum; obtaining the distribution of fractures in the coal core and calculating the fracture surface density of each segment within the borehole based on the fracture surface density; determining the perforation level and connection sequence of the screen pipe corresponding to each segment based on the fracture surface density; sequentially connecting the perforated screen pipes corresponding to each segment according to the connection sequence; inserting the perforated screen pipes corresponding to each segment into each segment of the borehole to form a screen pipe pipeline; and connecting the screen pipe pipeline to the main gas extraction pipeline for gas extraction. Thus, by matching the graded perforated screen with the fracture distribution within each segment of the gas borehole, this method not only effectively improves gas extraction efficiency but also greatly ensures the strength and service life of the screen pipe, thereby further enhancing the gas extraction benefits.

[0007] In addition, the gas extraction method based on a graded perforated screen tube according to the above embodiments of the present invention may also have the following additional technical features:

[0008] According to one embodiment of the present invention, calculating the fracture surface density of each segment in the borehole based on the distribution of fractures on the coal core includes: obtaining the apparent fracture area of ​​each segment based on the distribution of fractures on the coal core; and calculating the fracture surface density of each segment in the borehole based on the apparent fracture area of ​​each segment and the radius of the coal core.

[0009] According to one embodiment of the present invention, the fracture surface density of each segment within the borehole is calculated using the following formula:

[0010]

[0011] Where η is the crack surface density, S f R represents the apparent area of ​​the fracture, and R is the radius of the coal core.

[0012] According to one embodiment of the present invention, determining the perforation level of the screen pipe corresponding to each segment based on the fracture surface density of each segment includes: when the fracture surface density at the segment within the borehole is less than 0.3, the perforation level of the screen pipe is a first perforation level; when the fracture surface density at the segment within the borehole is greater than or equal to 0.3 and less than or equal to 0.6, the perforation level of the screen pipe is a second perforation level; when the fracture surface density at the segment within the borehole is greater than 0.6, the perforation level of the screen pipe is a third perforation level; wherein the third perforation level is greater than the second perforation level, and the second perforation level is greater than the first perforation level; when the segment within the borehole is located within a rock stratum, the screen pipe is not perforated.

[0013] According to one embodiment of the present invention, each section of the screen tube has multiple rows of screen holes corresponding to the number of hole levels arranged on its tube wall.

[0014] According to one embodiment of the present invention, the shape of the sieve holes is circular or polygonal.

[0015] According to one embodiment of the present invention, the number of aperture levels is determined according to the following formula:

[0016] λ = l / 1000

[0017] Wherein, λ is the number of aperture levels, and l is the row spacing of the sieve apertures.

[0018] According to one embodiment of the present invention, the perforated screen pipe corresponding to each segment is sent into each segment of the borehole to form a screen pipe pipeline, including: after connecting multiple perforated screen pipes in sequence according to the connection order, sending multiple perforated screen pipes into each segment of the borehole corresponding to the crack surface density by a drilling machine until the screen pipes extend out of the borehole to form the screen pipe pipeline.

[0019] According to one embodiment of the present invention, the method further includes fixing the screen tube at the borehole opening.

[0020] According to one embodiment of the present invention, a gas meter is installed on the screen pipe.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1. This invention achieves segmented matching between the gas extraction screen and the gas extraction borehole by grading the screen holes on the gas extraction screen. That is, more screen holes are arranged in areas with developed fractures to extract gas, while the number of screen holes is reduced in areas without developed fractures, thereby improving the overall gas extraction efficiency of the screen. According to the statistical analysis of gas extraction volume over 3 months, the gas extraction efficiency of this method is at least 24% higher than that of conventional screens.

[0023] 2. Compared to traditional uniformly perforated screens, the gas extraction screen of this invention features a more rational pressure-bearing design. It exhibits lower confining pressure in areas with high fracture density, making it suitable for screens with many perforations and low strength. Conversely, in areas with low fracture density, screens with fewer perforations and higher strength are used. This ensures that the screen maintains good deformation resistance at different locations within the gas extraction borehole, significantly improving the borehole's efficiency. Statistical analysis of the borehole efficiency after three months shows that when using conventional screens for gas extraction, the efficiency decreased from 90% to 70%, while the efficiency using this method decreased from 90% to 85%.

[0024] 3. The gas extraction screen and method of the present invention can effectively avoid the use of large-diameter screens, greatly reduce the costs incurred by re-drilling and purchasing screens due to gas borehole failure, and further improve the efficiency of gas extraction while shortening the time to achieve gas extraction standards.

[0025] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0026] Figure 1 A flowchart of a gas extraction method based on a graded perforated screen tube according to an embodiment of the present invention;

[0027] Figure 2 This is a schematic diagram of a gas drilling and graded perforated gas extraction screen according to an embodiment of the present invention.

[0028] Figure 3 This is a schematic diagram comparing the gas extraction rates of different screen tubes according to an embodiment of the present invention;

[0029] Figure 4 This is a schematic diagram comparing the effective number of boreholes in different screen tubes according to an embodiment of the present invention. Detailed Implementation

[0030] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0031] The following description, with reference to the accompanying drawings, describes a gas extraction method based on a graded perforated screen tube proposed in an embodiment of the present invention.

[0032] Figure 1 This is a flowchart of a gas extraction method based on a graded perforated screen tube according to an embodiment of the present invention.

[0033] like Figure 1 As shown, the gas extraction method based on a graded perforated screen tube according to an embodiment of the present invention may include the following steps:

[0034] S1, drilling boreholes in the coal and rock strata for gas extraction.

[0035] Specifically, when drilling into coal and rock strata, a directional drilling rig can be used to drill holes with a preset length (e.g., 86 meters) and a preset inclination angle (e.g., 23°) in the coal and rock strata according to the drilling design standards. The holes are then rinsed with clean water to ensure that the hole walls are smooth. Finally, a drilling inspection device is used to record the internal deformation and hole wall cracking of the holes.

[0036] S2, obtain the distribution of cracks on the coal core, and calculate the crack surface density of each segment in the borehole based on the distribution of cracks on the coal core.

[0037] According to one embodiment of the present invention, calculating the fracture surface density of each segment in the borehole based on the distribution of fractures on the coal core includes: obtaining the apparent fracture area of ​​each segment based on the distribution of fractures on the coal core; and calculating the fracture surface density of each segment in the borehole based on the apparent fracture area of ​​each segment and the radius of the coal core.

[0038] According to one embodiment of the present invention, the fracture surface density of each segment within the borehole is calculated using the following formula:

[0039]

[0040] Where η is the crack surface density, S f The apparent area of ​​the crack is in meters. 2 R is the radius of the coal core, in meters.

[0041] Specifically, after drilling through the coal seam, the coal core samples obtained from each segment are collected and their dimensional parameters, such as radius R and length, are recorded. Then, the apparent area S of the fractures is obtained based on the distribution of fractures on the coal core samples. f The radius R and the apparent fracture area S of each segment of coal core are determined. f Substituting into the above formula, the surface density of the cracks in each segment of the borehole can be calculated sequentially.

[0042] S3, determine the number of aperture levels and connection sequence of the screen tubes corresponding to each segment based on the crack surface density of each segment. For example, Figure 2 As shown, each sieve tube is a hollow tube that can be connected front to back. The tube wall of each sieve tube is arranged with multiple rows of sieve holes corresponding to the number of hole levels. The shape of the sieve holes is circular or polygonal.

[0043] According to one embodiment of the present invention, determining the perforation level of the screen pipe corresponding to each segment based on the fracture surface density of each segment includes: when the fracture surface density at the segment within the borehole is less than 0.3, the perforation level of the screen pipe is a first perforation level; when the fracture surface density at the segment within the borehole is greater than or equal to 0.3 and less than or equal to 0.6, the perforation level of the screen pipe is a second perforation level; when the fracture surface density at the segment within the borehole is greater than 0.6, the perforation level of the screen pipe is a third perforation level; wherein the third perforation level is greater than the second perforation level, and the second perforation level is greater than the first perforation level; when the segment within the borehole is located within a rock stratum, the screen pipe is not perforated. The first perforation level can be 10, the second perforation level can be 15, and the third perforation level can be 20.

[0044] Specifically, such as Figure 2 As shown, sections with higher fracture density have lower confining pressure, making them suitable for screen pipes with more perforations and lower strength; sections with lower fracture density have higher confining pressure, requiring screen pipes with fewer perforations and higher strength. This ensures that the screen pipe has good deformation resistance at different locations in the gas drainage borehole, greatly improving the efficiency of the gas drilling.

[0045] According to one embodiment of the present invention, the number of aperture levels is determined according to the following formula:

[0046] λ = l / 1000

[0047] Where λ is the number of aperture levels and l is the row spacing of the sieve apertures, in mm.

[0048] S4, connect the perforated screen tubes corresponding to each segment in sequence according to the connection order.

[0049] S5, the perforated screen pipe corresponding to each segment is sent into each segment of the borehole to form a screen pipe pipeline.

[0050] According to one embodiment of the present invention, the perforated screen pipe corresponding to each segment is sent into each segment of the borehole to form a screen pipe pipeline, including: after connecting multiple perforated screen pipes in sequence according to the connection order, the multiple screen pipes are sent into each segment of the borehole corresponding to the crack surface density by a drilling machine until the screen pipes extend out of the borehole to form a screen pipe pipeline.

[0051] Furthermore, according to an embodiment of the present invention, after the screen pipe pipeline is formed, the above method further includes fixing the screen pipe at the borehole opening.

[0052] Specifically, after connecting the perforated screen pipes corresponding to each segment in the connection sequence, the drilling rig sends multiple screen pipes into each segment of the gas borehole corresponding to the fracture surface density. The screen pipes are sent in sequence until they completely extend out of the entire borehole. Then, the screen pipes are further fixed near the gas borehole opening using clamps, clamps, etc., to prevent the screen pipes from coming out of the hole.

[0053] S6, connect the screen pipe to the main gas extraction pipe for gas extraction.

[0054] According to one embodiment of the present invention, a gas meter is installed on the screen pipe.

[0055] Specifically, after fixing the screen pipe, the drilling rig is removed, a gas meter is installed on the screen pipe, and the graded perforated screen pipe pipeline is connected to the gas extraction main pipeline for gas extraction.

[0056] Statistical analysis was conducted on the gas extraction volumes of conventional gas screens and graded perforated screens over a three-month period. Figure 3 As shown, the maximum gas extraction capacity of the graded perforated screen is 9.34 m³. 3 The maximum gas extraction rate of the conventional gas screen is 8.26 m³ / min. 3 / min. With the use of graded perforated screens, the gas extraction rate began to decline to a minimum of 6.04 m³ / min on day 53. 3 / min; with conventional perforated screens, the gas extraction rate began to decline to a minimum of 4.46m³ on day 44. 3 / min.

[0057] Furthermore, such as Figure 4 As shown, by statistically analyzing the effective number of gas boreholes for different screen pipes, with a total of 145 gas boreholes constructed, after 3 months, the effective number of boreholes for conventional screen pipes was 101, and the effective number of boreholes for graded perforated screen pipes was 123.

[0058] In summary, the gas extraction method based on graded perforated screen pipes according to embodiments of the present invention involves drilling a borehole for gas extraction in a coal and rock stratum; obtaining the distribution of fractures in the coal core and calculating the fracture surface density of each segment within the borehole based on the fracture surface density; determining the perforation level and connection sequence of the screen pipes corresponding to each segment based on the fracture surface density; sequentially connecting the perforated screen pipes corresponding to each segment according to the connection sequence; inserting the perforated screen pipes corresponding to each segment into each segment of the borehole to form a screen pipe pipeline; and connecting the screen pipe pipeline to the main gas extraction pipeline for gas extraction. Therefore, by matching the graded perforated screen holes with the fracture distribution within each segment of the gas borehole, this method not only effectively improves gas extraction efficiency but also greatly ensures the strength and service life of the screen pipes, thereby further enhancing the gas extraction benefits.

[0059] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0060] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0061] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0062] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A gas extraction method based on a graded perforated screen tube, characterized in that, The method includes: Drill boreholes in coal and rock strata for gas extraction; The distribution of fractures on the coal core is obtained, and the fracture surface density of each segment in the borehole is calculated based on the distribution of fractures on the coal core. The number of pore sizes and the connection sequence of the screen tubes corresponding to each segment are determined based on the crack surface density of each segment. Connect the perforated sieve tubes corresponding to each segment in sequence according to the connection order; Each segment of the perforated screen pipe is inserted into each segment of the borehole to form a screen pipe pipeline. The screen pipe is connected to the main gas extraction pipe for gas extraction.

2. The gas extraction method based on a graded perforated screen tube according to claim 1, characterized in that, The fracture surface density of each segment within the borehole is calculated based on the distribution of fractures in the coal core, including: The apparent area of ​​the fractures in each segment is obtained based on the distribution of fractures on the coal core. The fracture surface density of each segment within the borehole is calculated based on the apparent fracture area of ​​each segment and the radius of the coal core.

3. The gas extraction method based on a graded perforated screen tube according to claim 2, characterized in that, The fracture surface density of each segment within the borehole is calculated using the following formula: in, The surface density of the crack. The apparent area of ​​the crack. The radius of the coal core is given.

4. The gas extraction method based on a graded perforated screen tube according to claim 1, characterized in that, The number of aperture levels for each segment is determined based on the crack surface density of each segment, including: When the surface density of the cracks at the segment within the borehole is less than 0.3, the pore size of the screen tube is the first pore size. When the surface density of the cracks at the segment within the borehole is greater than or equal to 0.3 and less than or equal to 0.6, the pore size of the screen tube is the second pore size. When the crack surface density at the segment within the borehole is greater than 0.6, the pore size of the screen tube is the third pore size; wherein the third pore size is greater than the second pore size, and the second pore size is greater than the first pore size. When the section within the borehole is located within a rock stratum, the screen tube is not perforated.

5. The gas extraction method based on a graded perforated screen tube according to claim 4, characterized in that, Each section of the screen tube has multiple rows of screen holes arranged on its tube wall.

6. The gas extraction method based on a graded perforated screen tube according to claim 5, characterized in that, The sieve holes are circular or polygonal in shape.

7. The gas extraction method based on a graded perforated screen tube according to claim 5, characterized in that, The number of aperture levels is determined according to the following formula: in, The number of aperture levels is... The spacing between the rows of the sieve holes is denoted as .

8. The gas extraction method based on a graded perforated screen tube according to claim 1, characterized in that, Each segment of the perforated screen pipe is inserted into each segment of the borehole to form a screen pipe pipeline, including: After connecting multiple perforated screen pipes in sequence according to the connection order, the perforated screen pipes are sequentially fed into the corresponding sections of the borehole with the corresponding crack surface density by a drilling machine until the screen pipes extend out of the boreholes to form the screen pipe pipeline.

9. The gas extraction method based on a graded perforated screen tube according to claim 8, characterized in that, After forming the screen tube pipeline, the method further includes: The screen tube at the borehole opening is fixed.

10. The gas extraction method based on a graded perforated screen tube according to claim 1, characterized in that, A gas meter is installed on the screen pipe.

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