Gas extraction method based on graded hole distribution type sieve tube

Abstract

The invention discloses a gas extraction method based on a graded hole distribution type screen pipe. The method comprises the steps that a drill hole used for gas extraction is drilled in a coal rock stratum; the distribution condition of cracks on the coal core is obtained, and the crack surface density of each segment in the drill hole is calculated according to the distribution condition of the cracks on the coal core; according to the fracture surface density of each segment, determining the hole arrangement grade and the connection sequence of the screen pipe corresponding to each segment; according to the connection sequence, the hole distribution type screen pipes corresponding to all the segments are sequentially connected; the hole distribution type screen pipe corresponding to each segment is correspondingly fed into each segment of the drill hole to form a screen pipe pipeline; and connecting the sieve pipe pipeline to a gas extraction main pipeline for gas extraction. According to the method, the graded sieve holes are matched with the crack distribution in each section of the gas drill hole, so that the gas extraction efficiency can be effectively improved, the strength and the service life of the sieve pipe can be greatly ensured, and the gas extraction benefit is further improved.

Description

Technical Field

[0001] The invention relates to the technical field of gas extraction, and in particular to a gas extraction method based on a graded hole-distribution screen pipe. Background Art

[0002] Carrying out coal seam gas extraction is the most fundamental measure to prevent and control coal mine gas disasters. By lowering the gas extraction screen into the coal seam borehole, a migration channel is established for the gas in the coal seam, so that the coal seam gas can enter the gas extraction pipeline through the screen. This method can not only reduce the gas content of the coal seam, but also facilitate the use of the extracted gas as a clean energy. Chinese patent application CN111608721A proposes a full-hole movable negative pressure adjustment gas extraction device and extraction method, which improves the gas extraction efficiency through the extraction method of full-hole movable adjustment; Chinese patent application CN117211859A discloses a variable diameter large-diameter borehole gas extraction support screen and its use method, which uses the method of changing the diameter of the screen to protect the borehole and thus improve the gas extraction efficiency.

[0003] The above patents all ignore the important role of the sieve holes. It is particularly important to note that the sieve holes, as a component of the sieve pipe, are also a bridge connecting the gas and the sieve pipe. The arrangement of the sieve holes seriously affects the gas extraction efficiency of the sieve pipe. In actual engineering applications, in order to ensure the gas extraction efficiency, a unified sieve hole arrangement is often used. On the one hand, the gas extraction effect cannot be improved. On the other hand, blindly inserting a large-diameter sieve pipe increases unnecessary material costs, which seriously affects the gas extraction efficiency. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems in the related art to a certain extent. To this end, the first purpose of the present invention is to propose a gas extraction method based on a graded hole screen pipe, which can effectively improve the gas extraction efficiency by matching the graded screen holes with the crack distribution in each segment of the gas drilling hole, and can also greatly ensure the strength and service life of the screen pipe, thereby further improving the gas extraction efficiency, and further solving the problem of high gas extraction cost and difficulty in improving gas extraction efficiency.

[0005] To achieve the above-mentioned purpose, the first embodiment of the present invention proposes a gas extraction method based on a graded perforated screen pipe, the method comprising: drilling a borehole in a coal rock layer for extracting gas; obtaining the distribution of cracks on the coal core, and calculating the fracture surface density of each segment in the borehole according to the distribution of cracks on the coal core; determining the hole arrangement level and connection sequence of the screen pipe corresponding to each segment according to the fracture surface density of each segment; connecting the perforated screen pipe corresponding to each segment in sequence according to the connection sequence; sending the perforated screen pipe corresponding to each segment into each segment of the borehole to form a screen pipe pipeline; connecting the screen pipe pipeline to the gas extraction main pipeline for gas extraction.

[0006] According to the gas extraction method based on the graded perforated screen pipe of the embodiment of the present invention, a borehole for extracting gas is drilled in the coal rock layer; the distribution of cracks on the coal core is obtained, and the fracture surface density of each segment in the borehole is calculated according to the distribution of cracks on the coal core; the hole distribution level and connection sequence of the screen pipe corresponding to each segment are determined according to the fracture surface density of each segment; the perforated screen pipe corresponding to each segment is connected in sequence according to the connection sequence; the perforated screen pipe corresponding to each segment is sent to each segment of the borehole to form a screen pipe pipeline; the screen pipe pipeline is connected to the gas extraction main pipeline for gas extraction. Therefore, this method can not only effectively improve the gas extraction efficiency by matching the graded screen holes with the fracture distribution in each segment of the gas borehole, but also greatly ensure the strength and service life of the screen pipe, thereby further improving the gas extraction efficiency.

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

[0008] According to one embodiment of the present invention, the fracture surface density of each segment in the borehole is calculated based on the distribution of fractures on the coal core, including: obtaining the fracture apparent 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 fracture apparent 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 in the borehole is calculated according to the following formula:

[0010]

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

[0012] According to one embodiment of the present invention, the hole arrangement level of the screen pipe corresponding to each segment is determined according to the fracture surface density of each segment, including: when the fracture surface density at the segment in the borehole is less than 0.3, the hole arrangement level of the screen pipe is a first hole arrangement level; when the fracture surface density at the segment in the borehole is greater than or equal to 0.3 and less than or equal to 0.6, the hole arrangement level of the screen pipe is a second hole arrangement level; when the fracture surface density at the segment in the borehole is greater than 0.6, the hole arrangement level of the screen pipe is a third hole arrangement level; wherein the third hole arrangement level is greater than the second hole arrangement level, and the second hole arrangement level is greater than the first hole arrangement level; when the segment in the borehole is in a rock formation, the screen pipe is not perforated.

[0013] According to an embodiment of the present invention, a plurality of rows of sieve holes corresponding to the hole arrangement levels are arranged on the tube wall of each section of the sieve tube.

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

[0015] According to one embodiment of the present invention, the hole arrangement level is determined according to the following formula:

[0016] λ=l / 1000

[0017] Wherein, λ is the hole arrangement level, and l is the row spacing of the sieve holes.

[0018] According to one embodiment of the present invention, a perforated screen pipe corresponding to each segment is sent into each segment of the borehole to form a screen pipe pipeline, comprising: after connecting multiple sections of the perforated screen pipe in sequence according to the connection sequence, the multiple sections of the perforated screen pipe are sent into each segment of the borehole corresponding to the fracture surface density by a drilling rig in sequence until the screen pipe extends out of the borehole to form the screen pipe pipeline.

[0019] According to one embodiment of the present invention, the method further comprises: fixing the screen pipe 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 present invention has the following beneficial effects:

[0022] 1. The present invention can achieve segmented matching of the gas extraction screen pipe and the gas extraction borehole by arranging the sieve holes in a graded manner on the gas extraction screen pipe, that is, more sieve holes are arranged to extract gas at places where cracks are developed, and the corresponding number of sieve holes is reduced at places where cracks are not developed, thereby improving the overall gas extraction efficiency of the screen pipe. By statistically analyzing the gas extraction volume for 3 months, the gas extraction efficiency of this method is at least 24% higher than that of the conventional screen pipe.

[0023] 2. The gas extraction screen pipe of the present invention has a more reasonable pressure-bearing design than the traditional uniform hole screen pipe. The surrounding pressure is low in places with high crack density, which is suitable for screen pipes with more screen holes and low strength; in places with low crack density, screen pipes with fewer screen holes and high strength are used; thus ensuring that the screen pipe has good anti-deformation ability at different positions of the gas extraction drilling hole, greatly improving the efficiency of gas drilling. According to the statistics of the gas drilling efficiency after 3 months, when conventional screen pipes are used for gas extraction, the gas drilling efficiency drops from 90% to 70%, while the gas drilling efficiency using this method drops 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 of re-drilling and screen purchase due to gas drilling failure, and further improve the gas extraction efficiency while shortening the time to meet gas extraction standards.

[0025] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a flow chart of a gas extraction method based on a graded hole-distributed screen pipe according to an embodiment of the present invention;

[0027] Figure 2 A schematic diagram of a gas drilling and a graded hole arrangement type gas extraction screen according to an embodiment of the present invention;

[0028] Figure 3 A schematic diagram showing a comparison of gas extraction volumes of different screen tubes according to an embodiment of the present invention;

[0029] Figure 4 It is a schematic diagram comparing the effective numbers of different screen tube drilling holes according to an embodiment of the present invention. DETAILED DESCRIPTION

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

[0031] The following describes a gas extraction method based on a graded perforated screen pipe according to an embodiment of the present invention with reference to the accompanying drawings.

[0032] Figure 1 The present invention is a flow chart of a gas extraction method based on a graded perforated screen pipe according to an embodiment of the present invention.

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

[0034] S1, drilling holes in coal rock for extracting gas.

[0035] Specifically, when drilling into coal rock formations, a directional drill can be used to drill a hole with a preset length (such as 86 meters) and a preset inclination (such as 23°) in the coal rock formation according to the drilling design standards. The hole is flushed with clean water to ensure that the hole wall is smooth, and then a drilling peep device is used to record the internal deformation of the hole and the rupture of the hole wall.

[0036] S2, obtaining the distribution of cracks on the coal core, and calculating the crack surface density of each segment in the borehole according to the distribution of cracks on the coal core.

[0037] According to one embodiment of the present invention, the fracture surface density of each segment in the borehole is calculated according to the distribution of fractures on the coal core, including: obtaining the fracture apparent area of ​​each segment according to the distribution of fractures on the coal core; and calculating the fracture surface density of each segment in the borehole according to the fracture apparent 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 in the borehole is calculated according to the following formula:

[0039]

[0040] Where η is the crack surface density, S f is the apparent area of ​​the crack (in m2) 2 , R is the radius of the coal core, in m.

[0041] Specifically, after drilling through the coal seam, the coal cores of each segment are obtained after drilling, and the radius R, length and other size parameters of each segment coal core are recorded. Then, the apparent crack area S is obtained according to the distribution of cracks on the coal core. f , the radius R of each segmented coal core, the apparent fracture area S f Substituting the above formula, the fracture surface density of each segment in the borehole can be calculated in turn.

[0042] S3, according to the fracture surface density of each segment, determine the hole arrangement level and connection sequence of the screen pipe corresponding to each segment. Figure 2 As shown, each section of the sieve pipe is a hollow tube body that can be connected front to back, and a plurality of rows of sieve holes corresponding to the hole arrangement levels are arranged on the tube wall of each section of the sieve pipe, and the shape of the sieve holes is circular or polygonal.

[0043] According to an embodiment of the present invention, the hole arrangement level of the screen pipe corresponding to each segment is determined according to the fracture surface density of each segment, including: when the fracture surface density at the segment in the borehole is less than 0.3, the hole arrangement level of the screen pipe is the first hole arrangement level; when the fracture surface density at the segment in the borehole is greater than or equal to 0.3 and less than or equal to 0.6, the hole arrangement level of the screen pipe is the second hole arrangement level; when the fracture surface density at the segment in the borehole is greater than 0.6, the hole arrangement level of the screen pipe is the third hole arrangement level; wherein the third hole arrangement level is greater than the second hole arrangement level, and the second hole arrangement level is greater than the first hole arrangement level; when the segment in the borehole is in the rock formation, the screen pipe is not perforated. wherein the first hole arrangement level may be 10, the second hole arrangement level may be 15, and the third hole arrangement level may be 20.

[0044] Specifically, if Figure 2 As shown in the figure, the confining pressure is low in the segment with larger fracture density, which is suitable for screen pipes with more mesh and lower strength; the confining pressure is high in the segment with smaller fracture density, so screen pipes with fewer mesh and higher strength are used. This ensures that the screen pipes have good anti-deformation ability at different positions of the gas extraction borehole, greatly improving the efficiency of gas drilling.

[0045] According to one embodiment of the present invention, the hole arrangement level is determined according to the following formula:

[0046] λ=l / 1000

[0047] Among them, λ is the hole arrangement level, l is the row spacing of the sieve holes, and the unit is mm.

[0048] S4, connecting the perforated screen pipes corresponding to each segment in sequence according to the connection sequence.

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

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

[0051] Further, according to an embodiment of the present invention, after the screen pipe is formed, the method further comprises: fixing the screen pipe at the borehole opening.

[0052] Specifically, after connecting the corresponding perforated screen pipes of each segment in sequence according to the connection order, multiple sections of screen pipes are sent into each segment of the gas borehole corresponding to the fracture surface density through a drilling rig, and are sent in sequence until the screen pipes are completely extended out of the entire borehole. Afterwards, the screen pipes are further fixed near the mouth of the gas borehole by clamps, hoop, etc. to prevent the screen pipes from falling out of the hole.

[0053] S6, connecting the screen pipe to the gas extraction main 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, exit the drilling rig, install a gas meter on the screen pipe, and connect the graded perforated screen pipe pipeline to the gas extraction main pipeline for gas extraction.

[0056] The gas extraction volume of conventional gas screens and graded perforated screens in three months was statistically analyzed. Figure 3 As shown in the figure, the maximum gas extraction capacity of the graded perforated screen pipe is 9.34m 3 / min and the maximum gas extraction capacity of conventional gas screen is 8.26m 3 / min. When using graded perforated screen pipes, the gas extraction volume began to decline to a minimum of 6.04m on the 53rd day. 3 / min; when using conventional perforated screen pipes, the gas extraction volume began to decline to a minimum of 4.46m on the 44th day. 3 / min.

[0057] Further, if Figure 4 As shown, by counting the effective numbers of gas holes drilled by different screens, in the case of a total of 145 gas holes constructed, after 3 months, the effective number of holes drilled by the conventional screen was 101, and the effective number of holes drilled by the graded hole screen was 123.

[0058] In summary, according to the gas extraction method based on the graded perforated screen pipe according to the embodiment of the present invention, a borehole for extracting gas is drilled in the coal rock layer; the distribution of cracks on the coal core is obtained, and the fracture surface density of each segment in the borehole is calculated according to the distribution of cracks on the coal core; the hole distribution level and connection sequence of the screen pipe corresponding to each segment are determined according to the fracture surface density of each segment; the perforated screen pipe corresponding to each segment is connected in sequence according to the connection sequence; the perforated screen pipe corresponding to each segment is sent to each segment of the borehole to form a screen pipe pipeline; the screen pipe pipeline is connected to the gas extraction main pipeline for gas extraction. Therefore, this method can not only effectively improve the gas extraction efficiency by matching the graded screen holes with the fracture distribution in each segment of the gas borehole, but also greatly ensure the strength and service life of the screen pipe, thereby further improving the gas extraction efficiency.

[0059] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0060] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0061] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0062] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A gas extraction method based on a graded perforated screen pipe, characterized in that: The method comprises: Drilling holes in coal formations for extracting gas; Obtaining the distribution of cracks on the coal core, and calculating the crack surface density of each segment in the borehole according to the distribution of cracks on the coal core; Determine the hole arrangement level and connection sequence of the screen pipe corresponding to each segment according to the fracture surface density of each segment; Connect the perforated screen pipes corresponding to each segment in sequence according to the connection sequence; Sending a perforated screen pipe corresponding to each segment into each segment of the borehole to form a screen pipe line; The screen pipe is connected to the main gas extraction pipeline for gas extraction.

2. The gas extraction method based on the graded hole screen pipe according to claim 1 is characterized in that: Calculating the fracture surface density of each segment in the borehole according to the distribution of fractures on the coal core includes: Obtaining the apparent fracture area of ​​each segment according to the distribution of fractures on the coal core; The fracture surface density of each segment in the borehole is calculated based on the fracture apparent area of ​​each segment and the radius of the coal core.

3. The gas extraction method based on the graded hole screen pipe according to claim 2 is characterized in that: The fracture surface density of each segment in the borehole is calculated according to the following formula: Where η is the crack surface density, S f is the apparent area of ​​the fracture, and R is the radius of the coal core.

4. The gas extraction method based on the graded hole screen pipe according to claim 1 is characterized in that: The hole arrangement level of the screen pipe corresponding to each segment is determined according to the fracture surface density of each segment, including: When the fracture surface density at the segment in the borehole is less than 0.3, the hole arrangement level of the screen pipe is the first hole arrangement level; When the fracture surface density at the segment in the borehole is greater than or equal to 0.3 and less than or equal to 0.6, the hole arrangement level of the screen pipe is the second hole arrangement level; When the fracture surface density at the segment in the borehole is greater than 0.6, the hole arrangement level of the screen pipe is a third hole arrangement level; wherein the third hole arrangement level is greater than the second hole arrangement level, and the second hole arrangement level is greater than the first hole arrangement level; In the case where the section in the borehole is within the rock formation, the screen is not perforated.

5. The gas extraction method based on the graded hole screen pipe according to claim 4 is characterized in that: The tube wall of each section of the sieve tube is arranged with sieve holes of multiple hole arrangement levels.

6. The gas extraction method based on the graded hole screen pipe according to claim 5 is characterized in that: The shape of the sieve holes is circular or polygonal.

7. The gas extraction method based on the graded hole screen pipe according to claim 5 is characterized in that: The hole arrangement level is determined according to the following formula: λ=l / 1000 Wherein, λ is the hole arrangement level, and l is the row spacing of the sieve holes.

8. The gas extraction method based on the graded perforated screen pipe according to claim 1, characterized in that: The perforated screen pipe corresponding to each segment is sent into each segment of the borehole to form a screen pipe line, including: After connecting multiple sections of perforated screen pipes in sequence according to the connection sequence, multiple sections of the screen pipes according to one embodiment of the present invention are sequentially sent into each section of the borehole corresponding to the fracture surface density by a drilling rig until the screen pipes extend out of the borehole to form the screen pipe pipeline.

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

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

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