Deep coal seam combined penetration method and system

Abstract

The application relates to the technical field of coal seam permeability improvement, and provides a deep coal seam combined permeability improvement method and system. The combined permeability improvement method comprises the following steps: according to obtained coal seam parameters of a target coal seam, drilling two empty holes and a fracturing hole in the target coal seam; the two empty holes and the fracturing hole are located in the same horizontal coal seam; performing three times of grouting and hole sealing on the target coal seam; after the hole sealing is completed, performing once of hydraulic fracturing on the target coal seam, so that new fractures are generated in the target coal seam after the hydraulic fracturing; and adopting an air gun to cyclically perform high-pressure air pulse on the target coal seam to expand the fractures. Therefore, the development scale of the fractures is better increased, the gas enrichment area and the extraction blank area are reduced, the permeability improvement effect of the coal seam is better, the range is larger, and gas extraction is more thorough.

Description

Technical Field

[0001] This application relates to the field of coal seam permeability enhancement technology, and in particular to a combined permeability enhancement method and system for deep coal seams. Background Technology

[0002] Due to the complex structure, poor permeability, high gas content, and the fact that most of them are coal and gas outburst seams, gas control in bottom permeable coal seams has always affected their mining.

[0003] Traditionally, single-seam permeability enhancement techniques are mainly used to improve the permeability of coal seams. However, the permeability enhancement effect of existing single-seam permeability enhancement techniques is not ideal. For example, hydraulic fracturing technology can achieve large-scale coal seam permeability enhancement, but hydraulic fracturing pollutes the environment and consumes too much fresh water. Moreover, hydraulic fracturing activities can also trigger earthquakes. High-pressure air pulse technology can increase the scale of fracture development and reduce gas-rich areas and drainage gaps, but the fracturing range of high-pressure air pulses is limited.

[0004] Therefore, there is an urgent need to provide a technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0005] The purpose of this application is to provide a method and system for combined permeability enhancement in deep coal seams, so as to solve or alleviate the problems existing in the prior art.

[0006] To achieve the above objectives, this application provides the following technical solution:

[0007] This application provides a method for enhancing the permeability of deep coal seams, comprising: step S101, drilling two cavities and one fracturing hole in the target coal seam according to the obtained coal seam parameters; wherein the two cavities and the fracturing hole are located in the same horizontal coal seam; step S102, performing three grouting injections to seal the target coal seam; step S103, after sealing the hole, performing one hydraulic fracturing operation on the target coal seam to generate new fractures after the hydraulic fracturing, and using an air gun to cyclically apply high-pressure air pulses to the target coal seam to expand the fractures.

[0008] Preferably, in step S101, the fracture hole is enlarged to the bottom plate of the target coal seam.

[0009] Preferably, in step S102, during the three grouting and sealing operations, the interval between each grouting operation is 12 hours, and 48 hours after the third grouting operation, the target coal seam is subjected to hydraulic fracturing once.

[0010] Preferably, step S102 includes: inserting the casing and grouting pipe into the fractured hole to the bottom of the borehole, sealing the borehole opening, fixing the casing with cement grout, then opening the control valve of the grouting pipe to release the cement grout, and starting the first grouting; after the first grouting is completed, after 12 hours of solidification, a second grouting operation is performed, releasing the cement grout in the grouting pipe until the cement grout returns to the hydraulic fracturing pipe at the bottom of the hole, at which point the second grouting is completed; after the first grouting is completed, after 12 hours of solidification, a third grouting operation is performed, releasing the cement grout in the grouting pipe to the bottom of the hole, and sealing the hole to the designed layer.

[0011] Preferably, in step S103, the hydraulic fracturing of the target coal seam includes: injecting water into the fracturing hole of the target coal seam, with the injection pressure not lower than the coal seam fracturing pressure and the injection volume sufficient; after the water is injected until the backflow of the fracturing hole, the water injection is stopped, and the drainage continues until the natural fractures in the target coal seam are exposed; after the natural fractures in the target coal seam are saturated, fracturing fluid is added to the fracturing hole, and the addition of fracturing fluid is stopped after the target coal seam forms a fracture, and the fracturing fluid is pressure-maintained using a pressure device.

[0012] Preferably, according to the formula:

[0013]

[0014] Determine the total water injection pressure and total filter vector ;

[0015] in, For crack propagation pressure, This refers to the static pressure within the seam. The crack is located at the center of the cross-section of the borehole along the axial, horizontal radial, and vertical radial directions of the borehole, respectively. Viscosity; Inject fracturing fluid flow rate; The average seam width; The average crack height;

[0016] To achieve the overall filtration loss coefficient, The time it takes for the crack front to reach the filtration point. For filtration time, The entire length of the crack; The height of the crack; These are the total crack length variable and the filtration time variable, respectively.

[0017] Preferably, in step S103, the hydraulic fracturing pressure is greater than the coal seam initiation pressure, so that new fractures are generated in the target coal seam after hydraulic fracturing.

[0018] Preferably, according to the formula:

[0019]

[0020] Determine the fracturing pressure of the coal seam ;

[0021] in, Poisson's ratio of the coal seam; This refers to the vertical pressure exerted on the coal seam. This refers to the pore pressure of the coal seam.

[0022] This application embodiment also provides a deep coal seam combined permeability enhancement system, including: a drilling unit configured to drill two empty holes and one fracture-inducing hole in the target coal seam according to the obtained coal seam parameters; wherein the two empty holes and the fracture-inducing hole are located in the same horizontal coal seam; a grouting and sealing unit configured to perform three grouting and sealing operations on the target coal seam; and a fracture generation unit configured to perform one hydraulic fracturing operation after the sealing operation is completed, so that new fractures are generated in the target coal seam after the hydraulic fracturing, and to use an air gun to circulate high-pressure air pulses on the target coal seam to expand the fractures.

[0023] Beneficial effects:

[0024] The deep coal seam permeability enhancement method provided in this application involves, firstly, drilling two cavities and one fracturing hole in the target coal seam based on the obtained coal seam parameters, with the two cavities and the fracturing hole located at the same horizontal level. Then, based on the correspondence between hydraulic pressure and coal seam fracture propagation, the target coal seam is grouted and sealed three times. After sealing, hydraulic fracturing is performed once to generate new fractures in the target coal seam, and high-pressure air pulses are circulated through the target coal seam using an air gun to propagate the fractures. Finally, 15-30 minutes after fracturing is completed, the fracturing effect is evaluated, and gas concentration is tested and gas extraction is performed. This method aims to better increase the scale of fracture development, reduce gas-rich areas and extraction blank zones, resulting in better and wider permeability enhancement of the coal seam, and more thorough gas extraction. Attached Figure Description

[0025] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. Wherein:

[0026] Figure 1This is a schematic flowchart of a combined permeability enhancement method for deep coal seams provided according to some embodiments of this application;

[0027] Figure 2 This is a schematic diagram illustrating the effect of hydraulic fracturing in deep coal seams according to some embodiments of this application;

[0028] Figure 3 This is a schematic diagram illustrating the combined permeability enhancement effect in deep coal seams according to some embodiments of this application;

[0029] Figure 4 This is a schematic diagram of a combined permeability enhancement system for deep coal seams provided according to some embodiments of this application. Detailed Implementation

[0030] The present application will now be described in detail with reference to the accompanying drawings and embodiments. Various examples are provided by way of explanation and not by way of limitation. In fact, those skilled in the art will understand that modifications and variations can be made to the present application without departing from the scope or spirit of the present application. For example, a feature shown or described as part of one embodiment may be used in another embodiment to produce yet another embodiment. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention should fall within the scope of protection of the embodiments of the present invention.

[0031] To address the problems of poor permeability enhancement, poor extraction efficiency, and long extraction time associated with single-seam permeability enhancement technologies used to improve coal seam permeability, this application proposes a combined deep coal seam permeability enhancement method. This method involves drilling holes according to various parameters of the target coal seam, and employing a three-stage grouting sealing technique and a single-stage hydraulic fracturing technique based on the correlation between hydraulic pressure and coal seam fracture expansion. This induces new fractures in the target coal seam. High-pressure air pulses are then applied using an air cannon, with compressed air delivered into the borehole through pipelines. The high pressure then releases the air, generating significant energy that expands surrounding fractures and creates new ones. This pulse process is repeated to increase the scale of fracture development. Through the combined effect of hydraulic fracturing and high-pressure air pulses, gas enrichment zones and extraction dead zones are reduced, resulting in better and wider permeability enhancement and more thorough gas extraction.

[0032] like Figures 1 to 3 As shown, the combined permeability enhancement method for deep coal seams includes:

[0033] Step S101: Based on the obtained coal seam parameters of the target coal seam, drill two empty holes and one fracturing hole in the target coal seam.

[0034] The coal seam parameters obtained include: in-situ stress, formation pressure, coal seam hardness, natural fracture density, natural fracture occurrence, and hydraulic fracturing parameters.

[0035] In this application, the coal seam parameters obtained mainly include: coal seam in-situ stress (maximum horizontal principal stress, minimum horizontal principal stress, and vertical stress), formation pressure, coal seam hardness, natural fracture density, natural fracture occurrence (natural fracture dip angle and natural fracture inclination), and fracturing construction parameters (borehole diameter, borehole depth, construction angle, coal seam thickness, and burial depth).

[0036] Based on the various parameters of the target coal seam to enhance permeability, the coal seam thickness determines the borehole diameter, the coal seam burial depth determines the borehole depth, and the coal seam dip angle determines the drilling angle. The borehole spacing is determined according to the density and occurrence of natural fractures in the coal seam. Drilling and flushing are carried out in the target coal seam, creating two empty boreholes and one fracturing borehole. The depth of the fracturing borehole is the bottom plate of the target coal seam, followed by borehole enlargement. The two empty boreholes and the fracturing borehole are located in the same horizontal coal seam. Empty boreholes are set on both sides of the fracturing borehole so that the shock waves and stress waves generated by the subsequent pulses are reflected when they reach the boundary of the empty boreholes. The shock waves and stress waves repeatedly superimpose around the empty boreholes, thereby increasing the fracture damage range and enhancing the fracturing effect.

[0037] Step S102: Perform three grouting and sealing operations on the target coal seam.

[0038] As the pressure in the perforated section increases, the pore water pressure in the coal seam also increases. Once it reaches a certain level, it forces the coal seam to fracture. Three grouting injections are performed through the fracture-inducing holes in the target coal seam to effectively improve the sealing effect. Each grouting injection is spaced 12 hours apart. After the third grouting injection, hydraulic fracturing can be performed 48 hours later. This ensures that the grout fully hardens, guaranteeing the airtightness of the pores and the stability of the structure.

[0039] Specifically, during the third grouting sealing process, after inserting the casing and grouting pipe into the fractured hole to the bottom of the borehole, the borehole opening is sealed. Cement grout is used to fix the casing, and then the control valve of the grouting pipe is opened to release the cement grout, starting the first grouting. Wooden plugs and cotton yarn, grouting plugs, cement-based grouting materials, or epoxy resin grouting materials can be used to seal the borehole opening to achieve better waterproofing, corrosion resistance, wear resistance, and pressure resistance.

[0040] After the first grouting is completed, and after 12 hours of solidification, the second grouting operation is carried out to release the cement grout in the grouting pipe until the cement grout returns to the hydraulic pressure pipe at the bottom of the hole, at which point the second grouting is completed; after another 12 hours of solidification, the third grouting operation is carried out to release the cement grout in the grouting pipe to the bottom of the hole, and then the hole is sealed to the designed layer.

[0041] Step S103: After sealing the borehole, perform hydraulic fracturing to create new fractures in the target coal seam. Use an air gun to circulate high-pressure air pulses to the target coal seam to expand the fractures.

[0042] Forty-eight hours after the third grouting, once the grout has fully hardened, a hydraulic fracturing operation will be performed. Specifically, firstly, downhole pressure will be assessed through downhole pressure testing to ensure accurate calculation of hydraulic parameters before the hydraulic fracturing operation. This includes the total hydraulic pressure at different locations along the fracture. for:

[0043]

[0044] in, For crack propagation pressure (constant). The net pressure inside the seam. Determine the geometric dimensions of the crack, such as its height and width; The positions of the cracks relative to the center of the borehole cross-section are defined along the axial, horizontal radial, and vertical radial directions of the borehole, respectively. Viscosity; Inject fracturing fluid flow rate; The average seam width; The average crack height is obtained by measuring with a crack inclinometer. Here, a coordinate system is established with the center of the cross-section at the crack inlet as the reference, extending inward along the axial direction of the crack inlet. The positive axis, perpendicular to the radial direction of the fracture hole, is upward. The positive axis, along the horizontal radial direction of the fracture hole is Axial direction. This represents the relative coordinate position of the crack and the origin.

[0045] Total filtration loss for:

[0046]

[0047] in, To achieve the overall filtration loss coefficient, The time it takes for the crack front to reach the filtration point. For filtration time, The entire length of the crack; The height of the crack; These are the total crack length variable and the filtration time variable, respectively.

[0048] Then, water is injected into the fracture-initiating holes of the target coal seam, with the injection pressure not lower than the fracturing pressure of the coal seam. While ensuring sufficient water volume to saturate the coal seam, the injection pressure should not be too high. Typically, the injection pressure is [insert pressure here]. To avoid damaging the borehole, water is injected until the fracture hole is drained back, then water injection is stopped, and drainage continues until the natural fractures in the target coal seam are exposed. Once the natural fractures in the target coal seam are saturated, fracturing fluid is added to the fracture hole, and the coal seam fracturing pressure is calculated and adjusted according to the on-site coal seam mechanical parameters.

[0049] Specifically, according to the formula:

[0050]

[0051] Determine the coal seam fracturing pressure ;in, The Poisson's ratio of the coal seam. This refers to the vertical pressure exerted on the coal seam. This refers to the pore pressure of the coal seam. The pressure of the fracturing fluid added to the fracture hole must be greater than or equal to the determined coal seam fracturing pressure. To improve construction quality and effectively ensure the formation of hydraulic fractures in the coal seam, fracturing fluid is added after fractures are formed in the target coal seam, and pressure is maintained using a pressure device.

[0052] In this application, the hydraulic fracturing pressure is greater than the coal seam initiation pressure, so that after the target coal seam is hydraulically fracturing and new fractures are generated, a high-pressure air pulse (pressure range is...) is applied. To enhance fracture propagation, an air cannon is used to deliver compressed air through a pipeline into the borehole. Then, the air is released under high pressure, generating enormous energy that expands the surrounding fractures and creates new fractures.

[0053] Compressed air is piped into the borehole, where it is then released under high pressure, generating tremendous energy and a shock wave. This shock wave performs work on the coal seam, disrupting its structure, while its energy attenuates as it diminishes, and the remaining energy is transmitted to more distant locations. In the area surrounding the borehole, the amplitude of the generated shock wave exceeds the compressive strength of the coal seam, directly causing it to fracture and further expanding the original fractures.

[0054] 15-30 minutes after fracturing of the target coal seam is completed, the fracturing effect of the target coal seam can be evaluated, and gas concentration testing and extraction can be carried out. Gas extraction of the target coal seam is carried out by connecting the fracturing borehole to a dedicated pipeline and using extraction equipment to extract the gas in the coal seam to the surface. The concentration of the extracted gas is measured by a gas analyzer. The longer the extraction time and the slower the gas concentration decreases with the extraction time, the better the fracturing effect.

[0055] In this application, new fractures are generated in the target coal seam through three-stage grouting and sealing technology and one-stage hydraulic fracturing technology. High-pressure air pulses are generated using an air gun. Compressed air is delivered into the borehole through a pipeline and then released under high pressure, generating enormous energy to expand the surrounding fractures and generate new fractures. This pulse process is repeated to increase the scale of fracture development, reduce the gas enrichment zone and the drainage blank zone, and make the coal seam more permeable and the range larger, and the gas drainage more thorough.

[0056] like Figure 4 As shown in the embodiment of this application, a deep coal seam combined permeability enhancement system is also provided, including: a drilling construction unit 401, a grouting and sealing unit 402, and a fracture generation unit 403. The drilling construction unit 401 is configured to drill two empty holes and one fracture-inducing hole in the target coal seam according to the obtained coal seam parameters, with the two empty holes and the fracture-inducing hole located in the same horizontal coal seam; the grouting and sealing unit 402 is configured to perform three grouting and sealing operations on the target coal seam; the fracture generation unit 403 is configured to perform one hydraulic fracturing operation after the sealing is completed, so that new fractures are generated in the target coal seam after hydraulic fracturing, and to use an air gun to circulate high-pressure air pulses to the target coal seam to expand the fractures.

[0057] The deep coal seam combined permeability enhancement system provided in this application embodiment can realize the steps and processes of the deep coal seam combined permeability enhancement method described in any of the above embodiments, and achieve the same technical effect, which will not be repeated here.

[0058] In the description of this invention, 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 indicated technical features. 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.

[0059] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which 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. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0060] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for enhancing permeability in deep coal seams, characterized in that, include: Step S101: Based on the obtained coal seam parameters of the target coal seam, drill two voids and one fracture hole in the target coal seam; wherein the two voids and the fracture hole are located in the same horizontal coal seam; Step S102: Perform three grouting and sealing operations on the target coal seam; Step S103: After sealing the borehole, perform hydraulic fracturing on the target coal seam to generate new fractures in the target coal seam after hydraulic fracturing. Use an air gun to circulate high-pressure air pulses on the target coal seam to expand the fractures.

2. The method for combined permeability enhancement of deep coal seams according to claim 1, characterized in that, In step S101, The fracture hole is enlarged to a depth reaching the bottom plate of the target coal seam.

3. The method for combined permeability enhancement in deep coal seams according to claim 1, characterized in that, In step S102, During the three grouting and sealing operations, the interval between each grouting operation is 12 hours, and 48 hours after the third grouting operation, the target coal seam is subjected to hydraulic fracturing.

4. The method for combined permeability enhancement of deep coal seams according to claim 3, characterized in that, Step S102 includes: After inserting the casing and grouting pipe into the fracture hole to the bottom of the borehole, the borehole opening is sealed, and the casing is fixed with cement grout. Then, the control valve of the grouting pipe is opened to release the cement grout and the first grouting begins. After the first grouting is completed, and after 12 hours of solidification, the second grouting operation is carried out to release the cement slurry in the grouting pipe. The second grouting is completed when the cement slurry returns to the hydraulic fracturing pipe at the bottom of the hole. After the first grouting is completed and 12 hours have passed since solidification, the third grouting operation is carried out to release the cement slurry in the grouting pipe to the bottom of the hole and seal the hole to the designed layer.

5. The method for combined permeability enhancement of deep coal seams according to claim 3, characterized in that, In step S103, performing hydraulic fracturing on the target coal seam once includes: Water is injected into the fracture pores of the target coal seam, and the injection pressure is not lower than the coal seam fracture pressure; After water is injected to the backflow of the fracture-inducing hole, water injection is stopped, and drainage continues until the natural fractures in the target coal seam are exposed. After the natural fractures in the target coal seam are saturated, fracturing fluid is added to the fracturing hole, and the addition of fracturing fluid is stopped after the target coal seam forms a fracture. The fracturing fluid is then pressurized using a pressure device.

6. The method for combined permeability enhancement of deep coal seams according to claim 5, characterized in that, According to the formula: Determine the total water injection pressure and total filter vector ; in, For crack propagation pressure, This refers to the static pressure within the seam. The crack is located at the center of the cross-section of the borehole along the axial, horizontal radial, and vertical radial directions of the borehole, respectively. Viscosity; Inject fracturing fluid flow rate; The average seam width; The average crack height; To achieve the overall filtration loss coefficient, The time it takes for the crack front to reach the filtration point. For filtration time, The entire length of the crack; The height of the crack; These are the total crack length variable and the filtration time variable, respectively.

7. The method for combined permeability enhancement of deep coal seams according to claim 1, characterized in that, In step S103, the hydraulic fracturing pressure is greater than the coal seam initiation pressure, so that new fractures are generated in the target coal seam after hydraulic fracturing.

8. The method for combined permeability enhancement of deep coal seams according to claim 7, characterized in that, According to the formula: Determine the fracturing pressure of the coal seam ; in, Poisson's ratio of the coal seam; This refers to the vertical pressure exerted on the coal seam. This refers to the pore pressure of the coal seam.

9. A deep coal seam combined permeability enhancement system, characterized in that, include: The drilling unit is configured to drill two boreholes and one fracture hole in the target coal seam based on the obtained coal seam parameters; wherein the two boreholes and the fracture hole are located in the same horizontal coal seam. The grouting and sealing unit is configured to perform three grouting and sealing operations on the target coal seam. The fracture generation unit is configured to perform hydraulic fracturing after the borehole is sealed, so that new fractures are generated in the target coal seam after the hydraulic fracturing. High-pressure air pulses are circulated on the target coal seam using an air gun to expand the fractures.

Images