Sealing waterproof method and system for coal mine ground fracturing vertical well

Abstract

The invention relates to the technical field of coal mine thick and hard rock stratum roof fracturing weakening, in particular to a sealing and water resisting method and system for a coal mine ground fracturing vertical well. The sealing waterproof method comprises the step of carrying out sectional type plugging on a fractured vertical well, and comprises the following steps: S1, determining the mounting position of a bridge plug in the fractured vertical well according to fractured sectional stratum characteristics, and putting the bridge plug into a specified position; s2, according to the volume in the fracturing vertical well between the bridge plug of the current fracturing section and the bridge plug of the subsequent fracturing section, calculating the theoretical injection amount of cement paste of each fracturing section; and S3, cement paste is injected into the current fracturing section, and fracturing fluid is discharged. According to the method, the fracturing vertical well is divided into a plurality of fracturing sections for plugging, dynamic evaluation and adjustment can be conducted on the cement paste injection amount of the single fracturing section, the obtaining difficulty of the cement paste design dosage is lowered, the plugging effect of each fracturing section can be evaluated in time, and the plugging efficiency of each fracturing section is improved. And the problems of high construction cost, low construction efficiency and the like of the conventional drilling plug and plugging process after fracturing are solved.

Description

Technical Field

[0001] The invention relates to the technical field of fracturing and weakening of thick hard rock strata roofs in coal mines, and in particular to a sealing and water-isolating method and system for fracturing vertical wells on the ground of coal mines. Background Art

[0002] At present, ground hydraulic fracturing technology is applied to the field of fracturing and weakening of the roof of thick hard rock formations in coal mines, and vertical fracturing wells are one of the main well layout methods for ground fracturing. Vertical fracturing wells are drilled from the ground to the roof of the coal seam, and the casing cementing, perforation and staged fracturing processes are completed in sequence, and finally a large number of complex hydraulic fracture networks radiating from the well axis to the surrounding formations are formed. On the one hand, these fracture networks achieve the weakening of the target thick hard rock formations, and on the other hand, they fully communicate different aquifers in the formation and strengthen the hydraulic connection of the formation. At the same time, these formation waters flow continuously to the underground mining space and working face with the wellbore as the main water flow channel, posing a great threat and challenge to the safety and drainage capacity of underground operations.

[0003] In the prior art, the pumping bridge plug and perforation joint process mainly used in vertical well fracturing construction realizes backward fracturing by inserting soluble bridge plugs at the lower boundary of each fracturing segment. However, the soluble bridge plugs will gradually dissolve over time and lose their plugging effect. In addition, this method has serious problems such as extremely high engineering cost, long construction time, high risk of drilling and plugging, and large amount of filtration of injected cement slurry through hydraulic fractures. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the related art. To this end, the present invention proposes a sealing and water-isolating method and system for vertical wells in coal mine ground fracturing, so as to overcome the defects of the existing grouting well sealing technology, and achieve the purpose of preventing the formation aquifer from flowing into the underground mining space after the vertical well fracturing in the coal mine, optimizing the well sealing process after fracturing and saving costs.

[0005] In a first aspect, the present invention provides a sealing and water-isolating method for a vertical well of a coal mine surface fracturing, which performs segmented plugging of the vertical well of the fracturing, comprising: S1. Determine the installation position of the bridge plug in the fracturing vertical well according to the formation characteristics of the fracturing segment, and lower the bridge plug into the designated position; S2, calculating the theoretical injection volume of cement slurry for each fracturing segment according to the volume in the fracturing vertical well between the bridge plug of the current fracturing segment and the bridge plug of the subsequent fracturing segment; S3. Inject cement slurry into the current fracturing segment to displace and discharge the fracturing fluid.

[0006] According to a sealing and water-isolating method for a vertical well of ground fracturing in a coal mine provided by the present invention, a theoretical injection volume of cement slurry is divided into several times according to a proportion and injected into the vertical well of fracturing.

[0007] According to a sealing and water-isolating method for a vertical well in a coal mine surface fracturing provided by the present invention, the number of intervals for injecting cement slurry is determined according to the length of the fracturing segment and the perforation parameters.

[0008] According to a sealing and water-isolating method for a vertical well of a coal mine surface fracturing provided by the present invention, the discharge volume and rate of the fracturing fluid are obtained and compared with the injection volume and rate of the cement slurry. When the discharge volume and rate of the fracturing fluid gradually balance with the injection volume and rate of the cement slurry, the injection of the cement slurry is stopped; then steps S1, S2 and S3 are repeated to seal the next fracturing segment until the cement slurry fills the vertical well of the fracturing. Cement slurry is injected into the bottom of the wellbore of the vertical well through a hose. Since the density of cement slurry is greater than that of fracturing fluid and there is no physical or chemical reaction between the two, the wellbore is in a pressurized closed state at this time, and the cement slurry can be lifted from bottom to top to displace the fracturing fluid and be discharged.

[0009] According to a sealing and waterproofing method for ground fracturing vertical wells in coal mines provided by the present invention, the fracture loss rate of the fracturing vertical well is obtained according to the difference between the discharge rate of the fracturing fluid and the injection rate of the cement slurry, and the fracture loss volume of the fracturing vertical well is obtained according to the difference between the discharge volume of the fracturing fluid and the injection volume of the cement slurry, and the cement slurry injection rate is reduced by real-time control of the fracture loss rate and volume.

[0010] According to a sealing and water-isolating method for a vertical well in a coal mine surface fracturing provided by the present invention, the fracture filtration loss of the vertical well is obtained according to the difference between the discharge volume of the fracturing fluid and the injection volume of the cement slurry, and the cement slurry injection volume is increased when the fracture filtration loss is greater than 20%.

[0011] According to a sealing and water-isolating method for ground fracturing vertical wells in coal mines provided by the present invention, when the discharge volume and rate of the fracturing fluid gradually balance the injection volume and rate of the cement slurry, the injection of the cement slurry is stopped, and the perforating gun and the bridge plug are started to be lowered to complete the sealing and perforating of the next fracturing stage.

[0012] In a second aspect, the present invention further provides a sealing and water-isolating system for a vertical well of a coal mine surface fracturing, using any of the sealing and water-isolating methods for a vertical well of a coal mine surface fracturing as described above. The sealing and waterproofing system includes: A fracturing pump truck is provided with a fracturing fluid high-pressure injection pipeline connected to a fracturing vertical well, and is used to supply fracturing fluid to the fracturing vertical well; A mud pump truck is provided with a cement slurry high-pressure injection pipeline connected to the fracturing vertical well, and is used to supply cement slurry to the fracturing vertical well; A fracturing fluid flowback pool is provided with a fracturing fluid flowback pipeline connected to the fracturing vertical well, and is used to recover the fracturing fluid discharged from the fracturing vertical well; Wherein, a cement slurry injection hose is arranged in the vertical fracturing well, and the cement slurry injection hose is hoisted at the wellhead of the vertical fracturing well and extends downward.

[0013] According to a sealing and waterproofing system for a vertical well in a coal mine surface fracturing provided by the present invention, a cement slurry injection meter is connected in series in the cement slurry high-pressure injection pipeline to obtain the cement slurry injection volume.

[0014] According to a sealing and water-isolating system for a vertical well of ground fracturing in a coal mine provided by the present invention, a fracturing fluid return flow meter is connected in series in the fracturing fluid return pipeline to obtain the discharge volume of the fracturing fluid.

[0015] The above one or more technical solutions in the present invention have at least one of the following technical effects: The sealing and water-isolating method can efficiently and cost-effectively solve the problem of water damage to the underground working space caused by the conduction of the aquifer in the overlying rock strata of the coal seam due to the inability to seal the entire section of the vertical well. It can also overcome the problems of complex process steps of grouting and sealing the entire section after traditional drilling and plugging, multiple types of machinery and equipment, must be implemented after the completion of full-well fracturing, high engineering costs, long operation cycle time, construction failure risks caused by deformation of the casing after drilling and plugging, and difficulty in estimating the designed amount of cement slurry and timely evaluating the sealing effect. It innovatively realizes the "immediate pressure and plugging" of a single fracturing segment, which not only ensures the water layer sealing effect, but also greatly improves the operating efficiency. It can also dynamically evaluate and adjust the amount of cement slurry injected into the fracturing crack of a single fracturing segment; it is conducive to improving the implementation efficiency of ground fracturing wells, fundamentally eliminating the problem of water damage caused by the formation of vertical water guide channels by ground vertical well fracturing, and avoiding the impact on the recovery progress of the underground working face.

[0016] In addition to the technical problems solved by the present invention, the technical features of the technical solutions constituted, and the advantages brought about by the technical features of these technical solutions described above, other technical features of the present invention and the advantages brought about by these technical features will be further explained in conjunction with the accompanying drawings or will be understood through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the drawings required for use in the embodiments or related technical descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 A schematic structural diagram of a sealing and waterproofing system for a vertical well in a coal mine surface fracturing provided by an embodiment of the present invention.

[0019] Reference numerals: 1. Fracturing pump truck; 2. Fracturing fluid high-pressure injection pipeline; 3. Mud pump truck; 4. Cement slurry injection meter; 5. Cement slurry high-pressure injection pipeline; 6. Cement slurry injection hose; 7. Fracturing fluid return flow meter; 8. Fracturing fluid return pipeline; 9. Wellhead; 10. Fracturing fluid return pool; 11. Casing; 12. Perforation cluster; 13. Fracturing segment; 14. Formation stabilization; 15. Bridge plug; 16. Cement slurry; 17. Fracturing fluid. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] In the description of the embodiments of the present invention, it should be noted that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limitations on the embodiments of the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0022] In the description of the embodiments of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" 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. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present invention can be understood according to specific circumstances.

[0023] In the embodiments of the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0024] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. 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 embodiment of the present invention. In this specification, the schematic representations 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 one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0025] In an embodiment of the present invention, a sealing and water-isolating method for a vertical well in a coal mine surface fracturing is introduced.

[0026] like Figure 1 As shown, the sealing and water-proofing system of the vertical well of the ground fracturing in the coal mine is introduced. The system is integrated and installed at the wellhead 9 of the vertical well of the fracturing. In addition to the conventional devices and pipelines, the wellhead 9 is also connected with the high-pressure injection pipeline 2 of the fracturing fluid, the high-pressure injection pipeline 5 of the cement slurry and the return pipeline 8 of the fracturing fluid.

[0027] The fracturing fluid high-pressure injection pipeline 2, the cement slurry high-pressure injection pipeline 5 and the fracturing fluid return pipeline 8 are respectively provided with check valves in series to make the pipelines conductive in one direction.

[0028] The fracturing fluid high pressure injection pipeline 2 and the cement slurry high pressure injection pipeline 5 are unidirectional injection pipelines. The fracturing fluid return pipeline 8 is a unidirectional return pipeline.

[0029] The other end of the fracturing fluid high pressure injection pipeline 2 is connected to the fracturing pump truck 1. The fracturing pump truck 1 is equipped with an opening control valve for controlling the opening and closing of the fracturing fluid high pressure injection pipeline 2, thereby controlling the injection of fracturing fluid 17 into the well.

[0030] The other end of the cement slurry high pressure injection pipeline 5 is connected to the mud pump truck 3. The mud pump truck 3 is equipped with an opening control valve and a cement slurry injection meter 4, which are used to inject cement slurry 16 into the well according to the designed amount.

[0031] In addition, the sealing and water-isolating system is also provided with a cement slurry injection hose 6. The cement slurry injection hose 6 extends from the wellhead 9 of the fracturing vertical well and is hoisted in the wellbore. A hanging weight is provided at the bottom of the cement slurry injection hose 6 to ensure that the cement slurry injection hose 6 remains in an extended state in the wellbore.

[0032] The sealing and water-isolating method adopts the method of performing segmented plugging on the fractured vertical well. The fractured vertical well has been installed with a sealing and water-isolating system. In addition, the bridge plugs 15 in the present invention are all solid insoluble bridge plugs 15.

[0033] Take a fracturing segment 13 in a fracturing vertical well as an example for explanation. The specific steps include: S1, determine the installation position of the bridge plug 15 in the fracturing vertical well according to the fracturing segment 13, and lower the bridge plug 15 into the designated position; S2, calculate the theoretical cement slurry injection volume of each fracturing segment 13 according to the volume in the fracturing vertical well between the bridge plug 15 of the current fracturing segment 13 and the bridge plug 15 of the subsequent fracturing segment 13; S3, inject cement slurry 16 into the current fracturing segment 13, and discharge the fracturing fluid 17.

[0034] Specifically, firstly, based on the hydrogeological data of the coal mine strata, the logging data after drilling, etc., the lithology porosity, water richness and integrity of the strata encountered are analyzed. The dense and complete strata with high stratum strength, good integrity, low porosity and permeability, and less crack development and thick muddy aquiclude are selected as the plugging target positions of bridge plug 15.

[0035] The bridge plug 15 is lowered into the position through the perforating tool string and ignited to form a stable permanent seal in the wellbore. At the same time, the perforating operation of the fracturing segment 13 is completed. The perforating bullet penetrates the casing 11 of the fracturing vertical well and the cement ring arranged on the outer periphery of the casing 11 to form a perforation cluster 12.

[0036] After that, the fracturing operation is started, and the fracturing pump truck 1 is controlled to start the fracturing fluid injection operation, and the fracturing fluid 17 is injected into the fracturing segment 13 through the fracturing fluid high-pressure injection pipeline 2 .

[0037] After the fracturing operation of the fracturing segment 13 is completed, the fracturing pump truck 1 is controlled to stop supplying the fracturing fluid 17. The theoretical injection amount of cement slurry in the fracturing segment 13 is calculated. The specific calculation method is: theoretical injection amount of cement slurry = circular cross-sectional area of ​​casing 11 × length of fracturing segment 13 × surplus coefficient (1.5-3.5) considering the leakage amount.

[0038] During the process of injecting cement slurry 16, the hanging weight is suspended on the upper part of the solid insoluble bridge plug 15 of the fracturing segment 13 according to the well depth of the fracturing vertical well.

[0039] The other end of the fracturing fluid return pipeline 8 is connected to the fracturing fluid return tank 10. The fracturing fluid return pipeline 8 is installed with an opening control valve, a check valve and a fracturing fluid return flow meter 7. The fracturing fluid return flow meter 7 is used to measure the flow of the fracturing fluid in the fracturing fluid return pipeline 8.

[0040] The fracturing fluid high-pressure injection pipeline 2 unidirectionally injects fracturing fluid 17 into the wellbore through the wellhead 9 of the fracturing vertical well. The cement slurry high-pressure injection pipeline 5 unidirectionally injects cement slurry 16 into the wellbore through the wellhead 9 of the fracturing vertical well. Under the lifting effect of the cement slurry 16, the fracturing fluid in the wellbore flows unidirectionally to the fracturing fluid return pipeline 8 through the wellhead 9, and is discharged to the fracturing fluid return tank 10 through the fracturing fluid return pipeline 8.

[0041] This is because the density of the cement slurry 16 is much greater than that of the fracturing fluid, and the cement slurry 16 does not undergo physical or chemical reactions with the fracturing fluid, and will gradually sink and lift the fracturing fluid out of the wellbore.

[0042] On the basis of the above-mentioned embodiment, in another embodiment of the present invention, a sealing and water-isolating method for a vertical well of ground fracturing in a coal mine is introduced.

[0043] After the theoretical injection volume of cement slurry for each fracturing segment 13 is calculated, the theoretical injection volume of cement slurry is divided into several times according to a proportion and injected into the fracturing vertical well.

[0044] Furthermore, the number of intervals for setting the cement slurry 16 injection process is determined according to the length of the fracturing segment 13 and the perforation parameters.

[0045] Taking the conventional construction process as an example, the calculation method is listed as follows: the inner diameter of the casing 11 is 124.26 mm, the designed height of the fracturing segment 13 is 40 m, the redundancy coefficient is 1.5, and the theoretical cement slurry injection volume is calculated to be π (124.26×10-3)2×40×2.5=4.85 m 3 The injection procedure of cement slurry 16 is designed. Taking the fracturing segment 13 with a length of 40m and two perforation clusters and a cluster spacing of 20m as an example, the cement slurry 16 is injected below the bottom boundary of the first perforation cluster 12 for the first time, injected between the two perforation clusters 12 for the second time, and injected above the top boundary of the second perforation cluster 12 for the third time. The theoretical injection amount of cement slurry is divided into three injections according to the proportion, and 25%, 50%, and 25% of the theoretical injection amount of cement slurry are injected in sequence. The interval time between each injection is the initial strength time of cement rapid setting.

[0046] In addition, the discharge volume and rate of the fracturing fluid are obtained. The discharge volume and rate of the fracturing fluid are compared with the injection volume and rate of the cement slurry 16. When the discharge volume and rate of the fracturing fluid gradually balance with the injection volume and rate of the cement slurry 16, the injection of the cement slurry 16 is stopped, and the perforating gun and the bridge plug are started to complete the next fracturing stage setting and perforation.

[0047] Then, the next fracturing segment 13 is plugged. When plugging the next fracturing segment 13, steps S1, S2 and S3 are repeated until the cement slurry 16 is filled into the vertical fracturing well; the cement slurry is injected into the bottom of the wellbore of the vertical fracturing well through a hose. Since the density of the cement slurry 16 is greater than that of the fracturing fluid 17, and there is no physical or chemical reaction between the two, the wellbore is in a pressurized closed state at this time, and the cement slurry 16 can be lifted from bottom to top to replace the fracturing fluid 17 for discharge.

[0048] On the basis of the above-mentioned embodiment, in another embodiment of the present invention, a sealing and water-isolating method for a vertical well of ground fracturing in a coal mine is introduced.

[0049] The fracture loss rate of the fractured vertical well is obtained according to the difference between the discharge rate of the fracturing fluid and the injection rate of the cement slurry 16. The fracture loss volume of the fractured vertical well is obtained according to the difference between the discharge volume of the fracturing fluid 17 and the injection volume of the cement slurry 16. The injection rate of the cement slurry 16 is reduced by real-time control of the fracture loss rate and volume.

[0050] Furthermore, the fracture fluid loss of the fractured vertical well is obtained according to the difference between the discharged volume of the fracturing fluid and the injected volume of the cement slurry 16, and the injection volume of the cement slurry 16 is increased when the fracture fluid loss is greater than 20%.

[0051] The specific implementation method is as follows: after the fracturing pump truck 1 stops supplying the fracturing fluid, the wellbore is now in a pressurized closed state, and the only liquid passage is the perforation cluster 12 and the fracturing cracks. At this time, the pressure in the wellbore is relatively stable or slightly reduced. When the residual pressure in the wellbore drops below 2MPa, the injection procedure of the cement slurry 16 is started. The high-pressure injection pipeline 2 for fracturing fluid is kept open, the high-pressure injection pipeline 5 for cement slurry is opened, cement slurry 16 is supplied according to the injection procedure, and the fracturing fluid return pipeline 8 is gradually opened. Among them, the injection rate of cement slurry 16 is less than the maximum allowable flow rate of the fracturing fluid return pipeline 8. The cement slurry 16 is injected from the cement slurry high-pressure injection pipeline 5 to the cement slurry injection hose 6. The cement slurry injection hose 6 is suspended above the bridge plug 15.

[0052] The density of cement slurry 16 is much greater than that of fracturing fluid and no physical or chemical reaction occurs. It will gradually sink and displace the fracturing fluid. Cement slurry 16 flows out from cement slurry injection hose 6 and pushes the fracturing fluid at the bottom of the wellbore upward and flows back. The fracturing fluid flows upward from the wellbore to the wellhead 9 through the fracturing fluid return pipeline 8 and is discharged to the fracturing fluid return pool 10. During the return process, the flow rate of the fracturing fluid is measured by the fracturing fluid return flow meter 7 to analyze the plugging effect by comparing the injection amount of cement slurry 16.

[0053] The method for analyzing the plugging effect is as follows: the fracture loss rate of the fractured vertical well is obtained by the difference between the injection flow rate of the cement slurry 16 and the discharge flow rate of the fracturing fluid; the fracture loss amount of the fractured vertical well is obtained by the difference between the injection volume of the cement slurry 16 and the discharge volume of the fracturing fluid. Among them, the injection rate of the cement slurry 16 is reduced in real time by observing the fracture loss rate to reduce the pressure in the well and reduce the fracture loss amount of the cement slurry 16. After a single cement slurry 16 injection stage is completed, the cement slurry 16 displacement effect of this stage is evaluated according to the fracture loss amount. If the discharge amount of the fracturing fluid is not less than 80% of the injection amount of the cement slurry 16, it is considered that the sealing effect is good, otherwise the injection amount of the cement slurry 16 is increased.

[0054] When the discharge rate of the fracturing fluid and the injection rate of the cement slurry 16 are about to reach equilibrium, the injection of the cement slurry 16 is stopped, and the perforating gun and the solid bridge plug 15 are started to complete the setting and perforation of the bridge plug 15 of the next fracturing segment 13.

[0055] Each fracturing segment 13 repeats the above steps to complete the plugging of each fracturing segment 13 in turn until the top fracturing segment 13 is completely plugged.

[0056] In addition, the present invention also provides a sealing and water-isolating system for vertical wells in coal mine surface fracturing. The sealing and water-isolating system adopts the sealing and water-isolating method described in any of the above embodiments.

[0057] like Figure 1 As shown, the sealing and water-isolating system is integrated and installed at the wellhead 9 of the fracturing vertical well. In addition to conventional devices and pipelines, the wellhead 9 is also connected with a fracturing fluid high-pressure injection pipeline 2, a cement slurry high-pressure injection pipeline 5 and a fracturing fluid return pipeline 8.

[0058] The fracturing fluid high pressure injection pipeline 2, the cement slurry high pressure injection pipeline 5 and the fracturing fluid return pipeline 8 are respectively provided with a check valve in series to make the pipelines unidirectional. The fracturing fluid high pressure injection pipeline 2 and the cement slurry high pressure injection pipeline 5 are unidirectional injection pipelines. The fracturing fluid return pipeline 8 is a unidirectional return pipeline.

[0059] In addition, the other end of the fracturing fluid high-pressure injection pipeline 2 is connected to the fracturing pump truck 1. The fracturing pump truck 1 is equipped with an opening control valve for controlling the opening and closing of the fracturing fluid high-pressure injection pipeline 2, thereby controlling the injection of fracturing fluid 17 into the well. The other end of the cement slurry high-pressure injection pipeline 5 is connected to the mud pump truck 3. The mud pump truck 3 is equipped with an opening control valve and a cement slurry injection meter 4, which are used to inject cement slurry 16 into the well according to the designed amount.

[0060] The sealing and water-isolating system is also provided with a cement slurry injection hose 6. The cement slurry injection hose 6 extends from the wellhead 9 of the fracturing vertical well and is hoisted in the wellbore. A hanging weight is provided at the bottom of the cement slurry injection hose 6 to ensure that the cement slurry injection hose 6 remains in an extended state in the wellbore.

[0061] The high-pressure injection pipeline 2 for fracturing fluid is used to inject fracturing fluid 17 into the wellbore during fracturing construction. The high-pressure injection pipeline 5 for cement slurry and the cement slurry injection hose 6 are used to inject cement slurry 16 according to the designed amount to plug the fracturing segment 13 after fracturing. The fracturing fluid return pipeline 8 is used to return the fracturing fluid and measure the discharge amount of the fracturing fluid.

[0062] Furthermore, the fracturing pump truck 1 is provided with a high-pressure injection pipeline 2 for fracturing fluid connected to the fracturing vertical well. The mud pump truck 3 is provided with a high-pressure injection pipeline 5 for cement slurry connected to the fracturing vertical well. The fracturing fluid return pool 10 is provided with a fracturing fluid return pipeline 8 connected to the fracturing vertical well. Among them, a cement slurry injection hose 6 is provided in the fracturing vertical well, and the cement slurry injection hose 6 is hoisted at the wellhead 9 of the fracturing vertical well and extended downward.

[0063] The fracturing fluid high-pressure injection pipeline 2, the cement slurry high-pressure injection pipeline 5 and the fracturing fluid return pipeline 8 are respectively provided with check valves in series to make the pipelines conductive in one direction.

[0064] In addition, a cement slurry injection meter 4 is connected in series to the cement slurry high pressure injection pipeline 5 to obtain the injection amount of the cement slurry 16. A fracturing fluid return flow meter 7 is connected in series to the fracturing fluid return pipeline 8 to obtain the discharge amount of the fracturing fluid.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A sealing and water-isolating method for vertical wells in coal mine surface fracturing, characterized in that: Staged plugging of fractured vertical wells, including: S1. Determine the installation position of the bridge plug in the fracturing vertical well according to the formation characteristics of the fracturing segment, and lower the bridge plug into the designated position; S2, calculating the theoretical injection volume of cement slurry for each fracturing segment according to the volume in the fracturing vertical well between the bridge plug of the current fracturing segment and the bridge plug of the subsequent fracturing segment; S3. Inject cement slurry into the current fracturing segment to displace and discharge the fracturing fluid.

2. The sealing and water-isolating method for vertical well fracturing on the ground of a coal mine according to claim 1, characterized in that: The theoretical injection volume of cement slurry is divided into several times according to the proportion and injected into the fracturing vertical well.

3. The sealing and water-isolating method for vertical well fracturing on the ground of a coal mine according to claim 2, characterized in that: The number of intervals for injecting cement slurry is determined according to the length of the fracturing segment and the perforation parameters.

4. The sealing and water-isolating method for a vertical well of ground fracturing in a coal mine according to any one of claims 1 to 3, characterized in that: Obtain the discharge volume and rate of the fracturing fluid and compare them with the injection volume and rate of the cement slurry. When the discharge volume and rate of the fracturing fluid gradually balance with the injection volume and rate of the cement slurry, stop injecting the cement slurry. Then repeat steps S1, S2 and S3 to plug the next fracturing segment until the cement slurry fills the fractured vertical well. Cement slurry is injected into the bottom of the wellbore of the vertical well through a hose. Since the density of cement slurry is greater than that of fracturing fluid and there is no physical or chemical reaction between the two, the wellbore is in a pressurized closed state at this time, and the cement slurry can be lifted from bottom to top to displace the fracturing fluid and be discharged.

5. The sealing and water-isolating method for vertical well fracturing on the ground of a coal mine according to claim 4, characterized in that: The fracture loss rate of the fractured vertical well is obtained according to the difference between the discharge rate of the fracturing fluid and the injection rate of the cement slurry. The fracture loss volume of the fractured vertical well is obtained according to the difference between the discharge volume of the fracturing fluid and the injection volume of the cement slurry. The cement slurry injection rate is reduced by real-time control of the fracture loss rate and volume.

6. The sealing and water-isolating method for vertical well fracturing on the ground of a coal mine according to claim 5, characterized in that: The fracture loss of the fractured vertical well is obtained based on the difference between the discharged volume of the fracturing fluid and the injected volume of the cement slurry. When the fracture loss is greater than 20%, the cement slurry injection volume is increased.

7. The sealing and water-isolating method for vertical well fracturing on the ground of a coal mine according to claim 6, characterized in that: When the discharge volume and rate of the fracturing fluid gradually balance the injection volume and rate of the cement slurry, stop injecting the cement slurry, and start lowering the perforating gun and bridge plug to complete the next fracturing stage sealing and perforating.

8. A sealing and water-proofing system for vertical wells in coal mine surface fracturing, characterized in that: The sealing and water-isolating method for a vertical well in coal mine surface fracturing is adopted as claimed in any one of claims 1 to 7. The sealing and waterproofing system includes: A fracturing pump truck is provided with a fracturing fluid high-pressure injection pipeline connected to a fracturing vertical well, and is used to supply fracturing fluid to the fracturing vertical well; A mud pump truck is provided with a cement slurry high-pressure injection pipeline connected to the fracturing vertical well, and is used to supply cement slurry to the fracturing vertical well; A fracturing fluid flowback pool is provided with a fracturing fluid flowback pipeline connected to the fracturing vertical well, and is used to recover the fracturing fluid discharged from the fracturing vertical well; Wherein, a cement slurry injection hose is arranged in the vertical fracturing well, and the cement slurry injection hose is hoisted at the wellhead of the vertical fracturing well and extends downward.

9. The sealing and water-isolating system for vertical well fracturing on the ground of a coal mine according to claim 8, characterized in that: A cement slurry injection meter is connected in series in the cement slurry high-pressure injection pipeline to obtain the cement slurry injection volume.

10. The sealing and water-isolating system for vertical wells in coal mine surface fracturing according to claim 8, characterized in that: The fracturing fluid return pipeline is connected in series with a fracturing fluid return flow meter for obtaining the discharge volume of the fracturing fluid.

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