Coal seam consolidation and refracturing method, coal bed gas exploitation method and application thereof

Abstract

The application discloses a coal seam consolidation refracturing method, a coal seam gas exploitation method and application thereof. The coal seam consolidation refracturing method can comprise the following steps: fracturing a target coal seam to open fractures; injecting a consolidation material into the target coal seam to realize consolidation of the consolidation material and the target coal seam; cleaning a well shaft after the consolidation material is solidified; and perforating and fracturing the consolidated target coal seam again to realize fracturing reconstruction of the target coal seam. The method overcomes the shortcoming of short fracturing cracks caused by the development of a coal seam fracture system, low elastic modulus and high Poisson's ratio, especially the short fracturing cracks caused by direct fracturing of broken coal in the prior art. Meanwhile, compared with roof fracturing, the method overcomes the shortcoming that roof fracturing is difficult to communicate with a coal seam. Furthermore, the method is applicable to all coal seams with broken coal development, has a wide popularization range and great application value.

Description

Technical Field

[0001] This invention relates to the field of coalbed methane development technology, and in particular to a coal seam consolidation and re-fracturing method, a coalbed methane extraction method, and their applications. Background Technology

[0002] When extracting coalbed methane (CBM) from coal seams, the low permeability of CBM reservoirs necessitates efficient fracturing for high-efficiency development. The size of the fracturing volume directly determines the well's production. Due to well-developed fractures, low elastic modulus, and high Poisson's ratio in coal seams, short fracturing fractures during fracturing can easily lead to poor fracturing results. Furthermore, the varying tectonic stresses experienced by coal seams result in significant differences in their structure. Specifically: for native coalbed methane, the high elastic modulus allows for longer fracturing fractures, easily forming fracture networks. However, native coalbed methane also exhibits more developed fractures compared to other rock formations (such as mudstone), resulting in generally lower fracturing effectiveness compared to oil and gas formation. Conversely, for fragmented coal and mylonite, the low elastic modulus and high Poisson's ratio result in shorter fracturing fractures, making it difficult to form fracture networks, leading to lower CBM well production and poor gas production. Meanwhile, for coal reservoirs that have undergone hydraulic fracturing, even if they were originally native coal, they have become granular coal, mylonite, etc. after fracturing. Therefore, if they are to be re-modified, they must be treated as granular coal.

[0003] Existing technologies include indirect roof fracturing methods for fractured coal seams, which involve fracturing the roof of coal seams with well-developed fractured coal. This fully utilizes the advantages of the sandstone and mudstone roof of the coal seam, such as high Young's modulus, high brittleness, and ease of fracturing. Fracturing is performed on the roof to form long fractures, control a larger area, and increase the production of a single well. Summary of the Invention

[0004] The inventors discovered that the aforementioned methods for fracturing the coal seam roof are not applicable to large-area roofs with high clay content or water-bearing roofs, resulting in poor fracturing effects. Therefore, there is an urgent need for pre-treatment of fragmented coal seams to increase their Young's modulus and brittleness, and to directly form complex fracture networks within the coal seam for coalbed methane extraction. In view of the above problems, this invention is proposed to provide a coal seam consolidation and re-fracturing method, a coalbed methane extraction method, and their applications, which overcome or at least partially solve the aforementioned problems.

[0005] In a first aspect, embodiments of the present invention provide a coal seam consolidation and re-fracturing method, which may include:

[0006] Fracturing is performed on the target coal seam to open fractures;

[0007] A consolidation material is injected into the target coal seam to achieve consolidation between the consolidation material and the target coal seam;

[0008] After the consolidation material has solidified, clean the well casing;

[0009] The consolidated target coal seam is perforated and re-fractured to achieve fracturing and transformation of the target coal seam.

[0010] Optionally, before fracturing the target coal seam to open fractures, the procedure may further include:

[0011] Identify the coal body structure of the target coal seam to determine the distribution of broken coal sections in the target coal seam;

[0012] Accordingly, the broken sections of the target coal seam are subjected to hydraulic fracturing to open fractures;

[0013] A consolidation material is injected into the pulverized coal section to achieve consolidation between the consolidation material and the pulverized coal in the pulverized coal section.

[0014] Optionally, the identification of the coal body structure of the target coal seam may include:

[0015] Based on the logging curves of the gas production wells corresponding to the target coal seam, and the comparison relationship between the core samples from the pre-constructed parameter wells and the logging curve parameters at the corresponding locations, the coal body structure of the target coal seam is identified.

[0016] The pre-constructed correlation between the core samples from the parameter wells and the corresponding logging curve parameters is based on the pre-constructed correlation between the core samples from the parameter wells and the logging curve parameters in the area where the target coal seam is located.

[0017] Optionally, the coal body structure corresponding to the core sample taken from the parameter well includes primary coal, fractured coal, granular coal, and mylonite.

[0018] Optionally, injecting consolidating material into the pulverized coal section may include:

[0019] Consolidation material is injected into the pulverized coal section using either a slug injection method or a one-time injection method.

[0020] Optionally, injecting consolidating material into the pulverized coal section may include:

[0021] Consolidating material is injected into the crushed coal section until the injection pressure reaches the target coal seam for fracturing and then injection is stopped.

[0022] Optionally, injecting consolidating material into the pulverized coal section may include:

[0023] The consolidating materials are injected into the crushed coal section in sequence, according to their density from smallest to largest.

[0024] Optionally, after injecting the consolidating material into the crushed coal section, the process may further include: injecting clean water into the well to completely replace the consolidating material in the wellbore with the crushed coal section.

[0025] Optionally, before perforating and re-fracturing the consolidated target coal seam, the process may further include:

[0026] The gas production wells corresponding to the target coal seam were tested again to determine the consolidation effect of the target coal seam after consolidation.

[0027] Based on the consolidation effect of the target coal seam after consolidation, the perforation location is determined.

[0028] Optionally, the fracturing of the pulverized coal section to open fractures may include:

[0029] Determine whether the coal crushing section has undergone fracturing operations;

[0030] If so, then perform pre-fracturing based on the perforation holes used in the previous fracturing;

[0031] Otherwise, perforate the coal crushing section first, and then fracturing the coal crushing section.

[0032] Optionally, the fracturing discharge rate when fracturing a coal crushed section that has not undergone fracturing is larger than the fracturing discharge rate when fracturing a coal crushed section that has already undergone fracturing.

[0033] Secondly, embodiments of the present invention provide an application of the coal seam consolidation and re-fracturing method described in the first aspect in the coalbed methane extraction process.

[0034] Thirdly, embodiments of the present invention provide a method for coalbed methane extraction, which may include:

[0035] The target coal seam is subjected to fracturing based on the coal seam consolidation and re-fracturing method described in the first aspect.

[0036] The beneficial effects of the above-mentioned technical solutions provided in the embodiments of the present invention include at least the following:

[0037] This invention provides a coal seam consolidation and re-fracture method, a coalbed methane extraction method, and their applications. The aforementioned coal seam consolidation and re-fracture method involves injecting consolidation material into fractured coal seams, allowing it to solidify, and then perforating and fracturing with sand, significantly increasing the drainage area of ​​the broken coal and thus improving the gas production of coalbed methane wells. This method is an important means to increase the production of coalbed methane wells in broken coal seams, overcoming the disadvantages of well-developed coal seam fracture systems, low elastic modulus, and high Poisson's ratio leading to short fracturing fractures, especially the short fractures formed by directly fracturing broken coal seams in the past. Simultaneously, compared to roof fracturing, it overcomes the disadvantage of roof fracturing's difficulty in connecting the coal seam. Furthermore, the method provided in this invention is applicable to all coal seams with well-developed broken coal seams, with a wide range of applications and significant value.

[0038] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings.

[0039] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0040] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0041] Figure 1 This is a schematic flowchart of the coal seam consolidation and re-fracturing method provided in an embodiment of the present invention;

[0042] Figure 2 This is a schematic flowchart of the coal seam consolidation and re-fracturing method for fractured coal sections provided in an embodiment of the present invention;

[0043] Figure 3 This is a detailed flowchart illustrating the coal seam consolidation and re-fracturing method provided in this embodiment of the invention. Detailed Implementation

[0044] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0045] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," "outer," "far," "near," "front," and "rear," etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0046] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; 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; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0047] This invention provides a coal seam consolidation and re-fracture method. This method is designed to treat coal seams with well-developed fractures, especially to consolidate and re-fracture fragmented sections, in order to improve their Young's modulus and brittleness, and directly form a complex fracture network in the coal seam, laying the foundation for subsequent coalbed methane extraction.

[0048] Reference Figure 1 As shown, the method may include the following steps:

[0049] S11. Perform hydraulic fracturing on the target coal seam to open fractures.

[0050] S12. Inject consolidation material into the target coal seam to achieve consolidation between the consolidation material and the target coal seam.

[0051] S13. After the solidification material has solidified, clean the well shaft.

[0052] S14. Perforate and re-fracturing the consolidated target coal seam to achieve fracturing transformation of the target coal seam.

[0053] In this embodiment of the invention, the inventors, taking into account the abundant development of fractures in coal seams, consolidate and then fracturize the target coal seam to provide a fracturing effect for the consolidated coal seam, making the fractured cracks more conducive to coalbed methane extraction.

[0054] In another optional embodiment, it is preferable to perform consolidation and re-fracture treatment on pulverized coal segments such as fine coal and mylonite, referring to... Figure 2 As shown, the method may include the following steps:

[0055] Step S21: Identify the coal body structure of the target coal seam to determine the distribution of broken coal sections in the target coal seam.

[0056] This step involves identifying the coal body structure of the target coal seam to determine the primary coal section, broken coal section, etc., of the target coal seam. In this embodiment of the invention, the broken coal section includes, but is not limited to, the following coal sections: granular coal section and mylonite coal section, etc.

[0057] Step S22: Fracturing the broken coal sections in the target coal seam to open fractures.

[0058] This step involves small-scale fracturing of the pulverized coal section to open fractures and prepare for the injection of consolidation materials.

[0059] Step S23: Inject consolidation material into the crushed coal section to achieve consolidation between the consolidation material and the crushed coal in the crushed coal section.

[0060] Step S24: After the solidified material has solidified, clean the wellbore. This step involves cleaning the wellbore after the solidified material has solidified to meet the requirements for subsequent pumping.

[0061] Step S25: Perforate and re-fracturing the consolidated target coal seam to achieve fracturing and stimulation of the target coal seam. This step involves large-scale, high-volume fracturing of the target coal seam to achieve fracturing and stimulation of the target coal seam and meet the needs of coalbed methane extraction.

[0062] The above-described method for consolidating and re-fracturing pulverized coal seams provided in this invention involves injecting consolidating material into the pulverized coal seam, allowing it to solidify, and then perforating and fracturing with sand, significantly increasing the drainage area of ​​the pulverized coal seam, thereby increasing the gas production of the coalbed methane well. This method is an important means to improve the production of coalbed methane wells in pulverized coal seams, overcoming the technical drawback of short fractures formed by directly fracturing pulverized coal in the past; at the same time, compared with roof fracturing, it overcomes the disadvantage of roof fracturing being difficult to connect with the coal seam. Furthermore, the above-described method provided in this invention is also applicable to all pulverized coal seams, with a wide range of applications and great value.

[0063] In a detailed embodiment, refer to Figure 3 As shown, the method for consolidating and re-fracturing pulverized coal may include the following steps:

[0064] Step S301: Perform well logging on the gas production well corresponding to the target coal seam. This step involves logging the gas production well to obtain its logging curve, preparing for subsequent steps to determine the fractured coal sections of the target coal seam. In this embodiment, the fractured coal sections are preferably consolidated for granular and mylonite sections. For primary or fractured coal sections, consolidation treatment can be omitted, and fracturing operations can be performed directly.

[0065] Step S302: Based on the logging curves of the gas production wells corresponding to the target coal seam, and the pre-constructed comparison relationship between the core samples from parameter wells and the corresponding logging curve parameters, identify the coal body structure of the target coal seam. The pre-constructed comparison relationship between the core samples from parameter wells and the corresponding logging curve parameters is based on the pre-constructed comparison of core samples from parameter wells in the area where the target coal seam is located.

[0066] The coal body structure corresponding to the above-mentioned parameter well cores (coal cores) in the embodiments of the present invention includes primary coal, fractured coal, granular coal, and mylonite.

[0067] In this step, the coal body structure of the target coal seam can be determined based on the logging curve of the target coal seam; the correspondence between the primary coal, fractured coal, granular coal, mylonite and logging parameters is determined in advance by comparing the core sampling results of the parameter well with the measured parameters, and the coal body structure of the target seam is determined based on the established correspondence; then the broken coal sections are determined based on the divided coal body structure, so as to consolidate the broken coal sections.

[0068] Step S303: Determine whether the coal pulverized section has undergone fracturing operations; if yes, proceed to step S304; otherwise, proceed to step S305. This step is to determine whether the coal pulverized section has undergone fracturing operations before performing small-scale fracturing.

[0069] Step S304: Perform pre-fracturing hydraulic fracturing based on the perforation holes used in the previous fracturing. In this step, the already fractured coal seam is directly subjected to small-scale fracturing. Small-scale fracturing mainly involves pre-fracturing hydraulic fracturing, generally without proppant-carrying fluid or proppant, and the fracturing flow rate can be relatively small.

[0070] Step S305: First, perforate the pulverized coal section, and then perform fracturing on the pulverized coal section. In this step, for coal seams that have not been fracturing, the pulverized coal section needs to be perforated first, and then small-scale fracturing should be performed. The fracturing displacement is generally larger.

[0071] Comparing the fracturing discharge rates in steps S304 and S305 above, the fracturing discharge rate when fracturing a coal section that has not undergone fracturing is greater than the fracturing discharge rate when fracturing a coal section that has already undergone fracturing again.

[0072] Step S306: Using a slug injection method or a one-time injection method, inject consolidation material into the pulverized coal section until the injection pressure reaches the target coal seam for fracturing and then stop the injection.

[0073] In this step, the consolidating material is injected into the crushed coal in a liquid state, solidifying with it to increase the elastic modulus of the coal and enhance its brittleness. It can be a cement slurry, chemical agent, or other material capable of phase transformation. The injection of the consolidating material can be done using a slug injection method, where a certain amount of consolidating material is injected first, then injection is stopped, the pump is stopped for a period of time, and then another certain amount of consolidating material is injected; alternatively, it can be injected all at once until the injection pressure reaches the level required for fracturing the coal seam and then injection is stopped.

[0074] In the injection process, the low-density consolidating material has low viscosity and can be injected further into the fracture; the high-density consolidating material has higher viscosity and can be injected closer to the fracture, but it has a good cementing effect around the well. Therefore, in this step, the consolidating materials are injected into the crushed coal section in order of increasing density.

[0075] Step S307: Inject clean water into the well to completely displace the solidified material inside the well shaft into the crushed coal section. In practice, clean water is used to replace one well volume to ensure that all the solidified material inside the well shaft is replaced inside the crushed coal section, preventing the solidified material from solidifying on the sidewalls of the well shaft, which would prevent the pump or pipe from being lowered in subsequent steps.

[0076] Step S308: After the solidification material has solidified, clean the well shaft.

[0077] This step is a routine cleaning of the wellbore to prepare for subsequent pumping and drainage.

[0078] Step S309: Test the gas well corresponding to the target coal seam again to determine the consolidation effect of the target coal seam after consolidation.

[0079] The purpose of this second test is to select the coal seam section with the best coal consolidation effect for perforation, so that more regular fractures can be generated during hydraulic fracturing.

[0080] Step S310: Determine the perforation location based on the coal body structure of the consolidated target coal seam.

[0081] Step S311: Perforate and re-fracturing the consolidated target coal seam to achieve fracturing and transformation of the target coal seam. This step uses pre-fracturing fluid, proppant-carrying fluid, and displacement fluid during fracturing, generally employing large-volume, large-scale fracturing.

[0082] This invention involves injecting a consolidating agent into a coal seam with well-developed pulverized coal, allowing it to solidify, and then performing hydraulic fracturing after the consolidating material has solidified with the pulverized coal. This creates a large-scale fracture network, significantly increasing the drainage area of ​​the pulverized coal and thus improving the gas production of coalbed methane wells. It is an important method for increasing the production of coalbed methane wells with pulverized coal, overcoming the shortcomings of previous methods such as directly fracturing pulverized coal resulting in short fractures and difficulty in connecting the coal seam using roof fracturing. It is applicable to all coal seams with well-developed pulverized coal, has a wide range of applications, and significant practical value.

[0083] In a specific example, well F-1 extracts only No. 3 coal seam, with a coal thickness of 7.8 meters, a burial depth of 672.9 meters, and a gas content of 20.9 cubic meters per ton. After one fracturing operation, the highest output was 500 cubic meters, and the overall output was relatively low. Analysis suggests that the coal seam structure of this well is poor, resulting in poor fracturing effect. It is recommended to perform coal crushing and consolidation before fracturing.

[0084] 1) According to the logging curves, the deep lateral resistivity is 2000 Ω·m and the shallow lateral resistivity is 500 Ω·m. Both are low and the difference between them is large. The acoustic transit time is 390s, which is also low. All of these indicate that the overall coal structure is fragmented coal with local mylonite development.

[0085] 2) Conduct small-scale fracturing to open the fracture. Inject 50 cubic meters of pre-fracturing fluid at a flow rate of 5-6 m³ / min to reopen the fracture.

[0086] 3) Inject consolidation material, replacing one well volume with clean water. The injection density is 1.1-1.2 g / cm³. 3 5 cubic meters of cement were applied to the well, with a displacement of 1.5-2.0 m³. 3 / min; injection density is 1.3-1.4 g / cm³ 3 The cementing cement used is 20-25 cubic meters, with a displacement of 2.0 m³. 3 / min or higher; inject displacement fluid to displace the cement slurry in the wellbore into the formation.

[0087] 4) After shutting in the well for more than 48 hours, clean the wellbore to meet the requirements for pumping out the pump.

[0088] 5) Deep penetration perforation holes are made in the coal seam section with the best coal structure, with a perforation section of 674-676m.

[0089] 6) Perform hydraulic fracturing. Fluid volume 1500 cubic meters, quartz sand 1200 cubic meters, discharge rate 12 cubic meters / min or higher.

[0090] 7) Measure the pressure drop 30 minutes after pressure is applied. After measuring the pressure drop, return the fracturing fluid and continuously release it. Measure the amount of return fluid with the goal of returning the maximum amount of fracturing fluid.

[0091] 8) After the blowout is complete, flush the sand to the bottom of the artificial well and then pump the well to complete the well.

[0092] This example demonstrates how consolidation and re-fracturing of the aforementioned pulverized coal section significantly increases coalbed methane production, thereby realizing the economic benefits of the gas well and the target coal seam.

[0093] Based on the same inventive concept, this embodiment of the invention also provides an application of the above-mentioned coal seam consolidation and re-fracturing method in coalbed methane extraction technology.

[0094] Based on the same inventive concept, this embodiment of the invention also provides a coalbed methane extraction method, which may include: fracturing the target coal seam based on the above-mentioned coal seam consolidation and re-fracturing method.

[0095] The beneficial effects and specific implementations of the embodiments of the present invention can be referred to in the detailed description of the above-described method for consolidating and re-fracturing crushed coal, and will not be repeated here.

[0096] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. This disclosure is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this disclosure is limited only by the appended claims. Thus, if these modifications and variations of the invention fall within the scope of the claims of the invention and their equivalents, the invention is also intended to include these modifications and variations.

Claims

1. A method for coal seam consolidation and re-fracturing, characterized in that, include: Based on the logging curves of the gas production wells corresponding to the target coal seam, and the pre-constructed correlation between the core samples from parameter wells and the logging curve parameters at the corresponding locations, the coal body structure of the target coal seam is identified to determine the distribution of the broken coal sections in the target coal seam; wherein, the pre-constructed correlation between the core samples from parameter wells and the logging curve parameters at the corresponding locations is based on the pre-constructed correlation between the core samples from parameter wells and the logging curve parameters in the area where the target coal seam is located. The broken sections of the target coal seam are subjected to hydraulic fracturing to open fractures; A consolidation material is injected into the crushed coal section to achieve consolidation between the consolidation material and the crushed coal section; After the consolidation material has solidified, clean the well casing; The consolidated target coal seam is perforated and re-fractured to achieve fracturing and transformation of the target coal seam.

2. The method according to claim 1, characterized in that, The coal body structure corresponding to the core samples taken from the parameter wells includes primary coal, fractured coal, granular coal, and mylonite.

3. The method according to claim 1, characterized in that, The injection of consolidating material into the crushed coal section includes: Consolidation material is injected into the pulverized coal section using either a slug injection method or a one-time injection method.

4. The method according to claim 3, characterized in that, The injection of consolidating material into the crushed coal section includes: Consolidating material is injected into the crushed coal section until the injection pressure reaches the target coal seam for fracturing and then injection is stopped.

5. The method according to claim 1, characterized in that, The injection of consolidating material into the crushed coal section includes: The consolidating materials are injected into the crushed coal section in sequence, according to their density from smallest to largest.

6. The method according to claim 1, characterized in that, After injecting the consolidating material into the crushed coal section, the method further includes: injecting clean water into the well to completely replace the consolidating material in the wellbore into the crushed coal section.

7. The method according to claim 1, characterized in that, Before perforating and re-fracturing the consolidated target coal seam, the process also includes: The gas production wells corresponding to the target coal seam were tested again to determine the consolidation effect of the target coal seam after consolidation. Based on the consolidation effect of the target coal seam after consolidation, the perforation location is determined.

8. The method according to any one of claims 1 to 7, characterized in that, The method of fracturing the broken sections of the target coal seam to open fractures includes: Determine whether the coal crushing section has undergone fracturing operations; If so, then perform pre-fracturing based on the perforation holes used in the previous fracturing; Otherwise, perforate the coal crushing section first, and then fracturing the coal crushing section.

9. The application of the coal seam consolidation and re-fracturing method as described in any one of claims 1 to 8 in the coalbed methane extraction process.

10. A method for coalbed methane extraction, characterized in that, include: The target coal seam is subjected to fracturing based on the coal seam consolidation and re-fracturing method according to any one of claims 1 to 8.

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