A high-temperature and high-pressure rock mass in-situ borehole sealing and hydraulic fracturing experiment method

Abstract

This application provides a method for in-situ drilling sealing and hydraulic fracturing experiments in high-temperature and high-pressure rock masses, comprising the following steps: Step S1, placing the drill bit device at the rock sample drilling position, and coaxially placing the drill bit sleeve at the tail of the drill bit device; Step S2, starting the drill bit device to drill; simultaneously, the drill bit sleeve extends into the borehole; Step S3, when the drill bit device reaches the designated position, extending the drill bit sleeve to the bottom of the hole; Step S4, assembling the hollow water injection fracturing steel pipe; Step S5, withdrawing the drill bit device, retaining the drill bit sleeve; Step S6, coaxially placing the fracturing steel pipe sleeve inside the drill bit sleeve; pushing the fracturing steel pipe sleeve to the bottom of the hole; Step S7, removing the drill bit sleeve; Step S8, sealing with a nut, connecting a high-pressure pump for hydraulic fracturing operations. The method provided by this application is simple and convenient to operate, and can achieve rapid and mechanized sealing between the hydraulic fracturing pipe and the borehole wall after completing in-situ drilling of large-size rock masses under high temperature and high pressure.

Description

Technical Field

[0001] This application relates to the field of hydraulic fracturing test technology for large-size rock masses, and in particular to a method for in-situ drilling sealing and hydraulic fracturing test of high-temperature and high-pressure rock masses. Background Technology

[0002] In fields such as deep geothermal energy development and oil and gas exploration, conducting in-situ hydraulic fracturing tests on large-scale rock masses under high temperature and high pressure environments is crucial for studying rock mass fracture mechanisms, assessing reservoir fracturability, and evaluating the integrity of engineering barriers. These tests typically involve inserting fracturing tubing into a pre-set borehole and injecting high-pressure fluid under simulated deep environments (high temperature and high pressure) to induce fracture propagation.

[0003] Current hydraulic fracturing experiments on large-size specimens typically employ a procedure of "sealing at room temperature after drilling, then installing in the testing machine before fracturing." This process is cumbersome, and traditional sealing materials (such as ordinary rubber seals or incompletely cured cement) are prone to seal failure under high temperature and pressure, leading to high-pressure fluid leakage or flow along the pipe wall. Furthermore, experimental data obtained after fracturing with a properly sealed casing differ significantly from the in-situ characteristics of large-size rock masses under high temperature and pressure. Additionally, existing fracturing pipes also suffer from the following drawbacks:

[0004] (1) The sealing effect depends on the tight fit between the rubber ring and the connecting pipe, and between the airbag and the hole wall. If there is local expansion or contraction of the borehole or unevenness of the hole wall, the rubber ring cannot completely fill the gap. After the airbag expands, local uneven stress is likely to occur. During fracturing, the fluid is likely to leak from the gap. Under high temperature and high pressure, the rigid spring may be over-compressed and fail, and cannot block the flow of high pressure fluid. There are many parts and they are closely related, and the operation time is long.

[0005] (2) Whether using a triple-seal or double-seal perforator, the structure is relatively complex, containing multiple components. During downhole installation, precise installation and connection of each component is required, making the operation cumbersome and difficult. Installation errors or component damage are common, affecting the sealing effect and construction progress. Furthermore, the perforation capsule has limitations; after actual use, it may be damaged or have foreign matter adhering to it, leading to further damage during recycling and affecting its reuse efficiency. The PVC pipe and variable diameter section in the perforator need to be well-fitted to the borehole. Uneven borehole diameter or localized expansion or contraction will affect the installation and sealing effect of the perforator.

[0006] (3) The elastic material of the airbag is prone to thermal aging at high temperature, which leads to a decrease in expansion performance and even local rupture; the protective shell is a rigid structure, and its thermal expansion coefficient is very different from that of the airbag at high temperature, which can easily squeeze the airbag and cause cracks, and cannot meet the long-term sealing requirements of high temperature conditions; the protective shell is heavy and its sliding depends on the guide rod groove. If there is a slight bend or diameter fluctuation in the drill hole, the protective shell is easy to get stuck on the hole wall and cannot move, which increases the difficulty of installation.

[0007] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0008] In view of the shortcomings of the prior art, the purpose of this invention is to provide a simple and convenient experimental device and method for achieving rapid and mechanized sealing between the hydraulic fracturing pipe and the borehole wall after in-situ drilling of large-sized rock masses under high temperature and high pressure, so as to solve or alleviate the problems existing in the prior art.

[0009] To achieve the above objectives, this application provides the following technical solution:

[0010] This application provides a method for sealing in-situ boreholes in high-temperature and high-pressure rock masses. The improvement is that the borehole sealing method includes the following steps: Step S1, placing the drill bit device 1 at the drilling position of the rock mass sample, and placing the drill bit sleeve 2 coaxially at the tail of the drill bit device 1.

[0011] The drill bit device 1 includes a hydraulic drill bit 1-2; the end of the hydraulic drill bit 1-2 is connected to the hydraulic drill rod 1-3; the top of the front end of the hydraulic drill bit 1-2 is provided with spikes 1-1; and the front circumferential side of the hydraulic drill bit 1-2 is provided with a retractable hydraulic side cutting edge 1-4.

[0012] Step S2: Start the drill bit device 1 to drill; while the drill bit device 1 is drilling, the drill bit sleeve 2 extends into the borehole simultaneously.

[0013] Step S3: When the drill bit device 1 has drilled to the designated position, the drill bit sleeve 2 is inserted into the bottom of the hole;

[0014] Step S4, assembling the hollow water injection fracturing steel pipe, including: placing the hollow water injection fracturing steel pipe in the fracturing steel pipe sleeve 3, and placing the sealing material and graphite gasket at equal intervals;

[0015] Step S5: Remove the drill bit assembly 1, leaving the drill bit sleeve 2.

[0016] Step S6: The fracturing steel pipe sleeve 3 of the assembled hollow water injection fracturing steel pipe is coaxially installed inside the drill bit sleeve 2; the fracturing steel pipe sleeve 3 of the assembled hollow water injection fracturing steel pipe is pushed to the bottom of the hole using an alloy push rod.

[0017] Step S7, remove drill sleeve 2;

[0018] Step S8: Seal the sealing material and graphite gasket with an annular metal washer and an external thread nut. After the sealing material and graphite gasket have stabilized, connect the high-pressure pump to carry out hydraulic fracturing operations.

[0019] Preferably, the retractable hydraulic side blade 1-4 is disposed on the outer wall of the hydraulic drill bit 1-2; the retractable hydraulic side blade 1-4 includes a cutting edge disposed parallel to the axial direction of the hydraulic drill bit 1-2 and added along the circumference of the outer wall of the hydraulic drill bit 1-2.

[0020] Preferably, the hydraulic drill bit 1-2 includes:

[0021] Slider 13 is located at the center of the hydraulic drill bit 1-2 and near the front end of the hydraulic drill bit.

[0022] Link 14 includes a telescopic rod; one end of link 14 is connected to slider 13, and the other end of link 14 is connected to the blade of telescopic hydraulic side blade 1-4.

[0023] The hydraulic drill bit 1-2 also includes: a spring 12, one end of which is connected to the slider 13, and the other end of which is connected to the front end of the hydraulic drill bit 1-2;

[0024] The hydraulic drill bit 1-2 also includes a slider blocking ring 11, which is located at the upper end of the central pipe and is an annular protrusion integrated with the hydraulic drill bit.

[0025] Preferably, step S3 further includes: when the drill bit device 1 reaches the designated position, blowing away the debris in the hole; the drill bit sleeve 2 further includes a press-in air duct arranged symmetrically on both sides inside the drill bit sleeve 2; the diameter of the press-in air duct matches the width of the retractable hydraulic side cutting edge 1-4 when it is fully extended.

[0026] Preferably, the hollow water injection fracturing steel pipe is a hollow steel pipe, and an axially added thread is provided on the outer wall of the hollow water injection fracturing steel pipe as an anti-slip texture; a protrusion is provided at the bottom of the hollow water injection fracturing steel pipe, and two radial through holes are symmetrically provided inside the protrusion.

[0027] Preferably, step S4 further includes: cross-fitting the sealing material 5 and the graphite gasket 6 onto the hollow water injection fracturing steel pipe; the sealing material 5 includes a sleeve-shaped object; the graphite gasket 6 includes a ring.

[0028] Preferably, step S7 includes: step S7-1, confirming that the fracturing steel pipe sleeve 3 has been pushed to the bottom of the hole and is stable; step S7-2, placing a receiving tray at the borehole opening to collect the debris that falls during the removal process.

[0029] Preferably, step S8 further includes step S8-1, installation of the annular metal washer, including:

[0030] S8-1-1 Before installation, ensure that the annular metal gasket is smooth, undamaged, and free of debris, and that the sealing material and graphite gasket are properly fitted together according to the design spacing, with the graphite gasket at the bottom.

[0031] S8-1-2, Align the high-temperature resistant metal push rod axially with the outer wall of the annular metal washer, and fit the cracked steel pipe sleeve 3 with the annular metal washer;

[0032] S8-1-3, using a high-temperature resistant metal push rod, pushes the annular metal washer toward the sealing material;

[0033] S8-1-4, take out the high-temperature resistant metal push rod, measure the distance between the annular metal washer and the borehole wall with a ruler, and confirm that the hollow water injection fracturing steel pipe is in the center of the borehole; at the same time, gently push the sealing material with a thin metal rod to check whether the sealing material is tight and whether it is loose or displaced.

[0034] Preferably, step S8 further includes step S8-2, in which the external thread nut is installed using a special installation tool: one end of the external thread nut is an extended hexagonal outer contour, and it is installed using a hexagonal external thread nut installation sleeve that is adapted to the outer contour;

[0035] Step S8-2-1: Before installation, ensure that the external thread nut is undamaged and free of debris, and that the sealing material 5, graphite washer 6, and annular metal washer 7 are installed in place as designed.

[0036] Step S8-2-2: Align the grooved end of the male thread nut mounting sleeve with the extended hexagonal outer wall of the male thread nut, and insert it axially to ensure that the male thread nut mounting sleeve and the extended hexagonal outer contour of the male thread nut are completely fitted; ensure that the male thread nut and the hollow water injection fracturing steel pipe are coaxial by visual inspection or ruler calibration.

[0037] Step S8-2-3: Use a torque wrench to rotate the male thread nut installation sleeve, thereby driving the male thread nut. During the process, observe the position of the male thread nut in real time to ensure that it is in close contact with the annular metal washer below to form the final support.

[0038] Step S8-2-4: Remove the male thread nut installation sleeve and gently push the male thread nut with a thin metal rod to check the tightness of the male thread nut.

[0039] This application also relates to a hydraulic fracturing test method, the improvement of which is that the hydraulic fracturing test method includes the following steps:

[0040] Step S1: Place the rock mass sample into the high-temperature and high-pressure fracturing chamber and check the experimental equipment.

[0041] Step S2: Apply confining pressure, axial pressure and high temperature to the rock sample to bring the core to an in-situ high temperature and high pressure state.

[0042] Step S3: Drill holes in the rock mass sample and seal them using the method described above;

[0043] Step S4: Conduct a hydraulic fracturing experiment.

[0044] Compared with the closest prior art, the technical solution of this application has the following beneficial effects:

[0045] (1) By using sealing materials, the sealing shape and expansion pressure can be dynamically adjusted according to different borehole wall conditions and sealing requirements, thereby improving the reliability and durability of the seal. In addition, sealing materials can be recycled and reused, reducing material waste during construction and providing environmental benefits.

[0046] (2) The graphite gaskets used have extremely low creep relaxation rate, which can maintain sufficient sealing specific pressure for a long time and ensure the durability of the seal. At the same time, they have excellent high temperature and high pressure resistance and corrosion resistance, which can ensure continuous fracturing operations, improve efficiency and save costs.

[0047] (3) The side edge of the hydraulic drill bit used is retractable and can be directly pulled out through the sleeve after drilling is completed, so as to avoid the drill bit getting stuck and affecting the experiment when the sample breaks.

[0048] (4) The sleeve used can not only blow out the debris, but also ensure the safe extraction of the drill bit. At the same time, the sleeve maintains the high temperature and high pressure of the sample in situ. If the large-sized rock sample is a soft rock, the sleeve can better maintain the in situ state and enhance the accuracy of the test.

[0049] (5) The use of annular metal washers and external threaded nuts not only provides bottom support for the sealing material, but also ensures that the hollow water injection fracturing steel pipe is always in the center of the borehole. At the same time, it avoids the problem of the sealing material expanding too much and blocking the outlet, thus ensuring smooth hydraulic fracturing operations.

[0050] (6) The hollow water injection fracturing steel pipe adopts a three-hole structure design on the opposite side and bottom, which can increase the effect of hydraulic fracturing at specific locations. It can also make the sealing material more uniformly stressed during the expansion process, thereby better filling the gap between the borehole and the steel pipe and effectively preventing water leakage. At the same time, the smooth hollow water injection fracturing steel pipe can increase the fit and sealing effect between the hollow water injection fracturing steel pipe and the sealing material, effectively preventing the hollow water injection fracturing steel pipe from bursting out and leaking during the water injection process.

[0051] (7) The present invention has fewer main components, and each component has a clear function. The installation process is simple and reduces the safety hazards caused by installation. Attached Figure Description

[0052] 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:

[0053] Figure 1 This is a schematic diagram of the hydraulic drill bit involved in this application;

[0054] Figure 2 This is a schematic diagram of the internal structure of the hydraulic drill bit involved in this application.

[0055] Figure 3 This is a schematic diagram of the hydraulic drill pipe involved in this application;

[0056] Figure 4 This is a schematic diagram of the sleeve involved in this application;

[0057] Figure 5 This is a schematic diagram of the drill bit side cutting edge protrusion and the drill bit sleeve covering the drill bit involved in this application;

[0058] Figure 6 This is a schematic diagram illustrating the drilling to the designated location involved in this application;

[0059] Figure 7 This is a schematic diagram of the drill bit side edge contraction involved in this application;

[0060] Figure 8 A schematic diagram showing the connection of the drill bit sleeve to the fracturing steel pipe sleeve after the sealing device is installed in the sleeve involved in this application;

[0061] Figure 9 This is a schematic diagram of the hollow water injection fracturing steel pipe involved in this application;

[0062] Figure 10 A schematic diagram showing the sealing device involved in this application pushed to the bottom of the hole;

[0063] Figure 11 This is a schematic diagram illustrating the completed sealing process involved in this application;

[0064] Figure 12 This is a schematic diagram of the external thread nut structure involved in this application;

[0065] Figure 13 This is a schematic diagram of the water injection fracturing experiment involved in this application;

[0066] Explanation of reference numerals in the attached figures:

[0067] 1. Drill bit assembly; 1-2. Hydraulic drill bit; 1-3. Hydraulic drill rod; 1-4. Telescopic hydraulic side cutting edge; 2. Drill bit sleeve; 3. Fracturing steel pipe sleeve; 4. Hollow water injection fracturing steel pipe; 5. Sealing material; 6. Graphite washer; 7. Annular metal washer; 8. External thread nut; 9. Hollow water injection fracturing steel pipe; 10. Forced-in air duct; 11. Slider blocking ring; 12. Spring; 13. Slider; 14. Connecting rod. Detailed Implementation

[0068] 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 recognize that modifications and variations can be made to the present application without departing from the scope or spirit thereof. For example, a feature shown or described as part of one embodiment may be used in another embodiment to produce yet another embodiment. Therefore, it is desirable that the present application encompass such modifications and variations that fall within the scope of the appended claims and their equivalents.

[0069] In the following description, the terms "first / second / third" are used merely to distinguish similar objects and do not represent a specific order of objects. It is understood that "first / second / third" may be interchanged in a specific order or sequence where permitted, so that the embodiments of this application described herein can be implemented in an order other than that illustrated or described herein.

[0070] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used herein is for the purpose of describing embodiments of this disclosure only and is not intended to limit this disclosure.

[0071] In the description of this application, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," and "bottom," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and do not require that this application be constructed and operated in a specific orientation, and therefore should not be construed as limiting this application. The terms "connected," "linked," and "set up" used in this application should be interpreted broadly. For example, they can refer to fixed connections or detachable connections; direct connections or indirect connections through intermediate components; wired connections, radio connections, or wireless communication signal connections. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0072] This application relates to a sealing method for hydraulic fracturing pipes, the improvement of which is that the sealing method includes the following steps:

[0073] Step S1: Place the drill bit device 1 at the drilling position of the large-size rock sample, and place the drill bit sleeve 2 coaxially at the tail of the drill bit device 1.

[0074] Step S2: Start the drill bit device 1 and rotate the drill bit device 1 to drill a hole; while the drill bit device 1 is drilling, the drill bit sleeve 2 extends into the hole simultaneously.

[0075] Preferred, such as Figure 1 As shown, the drill bit device 1 includes a hydraulic drill bit 1-2; the end of the hydraulic drill bit 1-2 is connected to the hydraulic drill rod 1-3; the top of the front end of the hydraulic drill bit 1-2 is provided with spikes 1-1; the front circumferential side of the hydraulic drill bit 1-2 is provided with a retractable hydraulic side blade 1-4, which extends and retracts by hydraulic control.

[0076] The retractable hydraulic side blade 1-4 is set on the outer wall of the hydraulic drill bit 1-2; the retractable hydraulic side blade 1-4 includes a cutting edge that is set parallel to the axis of the hydraulic drill bit 1-2 and added along the circumference of the outer wall of the hydraulic drill bit 1-2; the number of cutting edges is set according to the actual situation.

[0077] like Figure 2 As shown, the front of the hydraulic drill bit 1-2 is a receiving cavity for housing the retractable hydraulic side cutting edge 1-4; the rear of the hydraulic drill bit 1-2 is a solid structure with a central pipe. The hydraulic drill bit 1-2 includes:

[0078] The slider 13 is located at the center of the hydraulic drill bit 1-2 and near the front end of the hydraulic drill bit.

[0079] Link 14 includes a telescopic rod-like component. One end of link 14 is connected to slider 13, and the other end is connected to the cutting edge of telescopic hydraulic side blade 1-4. The number of link 14 is determined based on the number of cutting edges, ensuring that each link 14 connects to one cutting edge. The telescopic rod-like component comprises two connected, relatively sliding rods, thereby enabling the extension and retraction of link 14. Preferably, the telescopic rod-like component consists of two coaxially connected sleeves, with the first sleeve capable of sliding within the second sleeve.

[0080] The hydraulic drill bit 1-2 also includes a spring 12, one end of which is connected to the slider 13, and the other end of which is connected to the front end of the hydraulic drill bit 1-2.

[0081] The hydraulic drill bit 1-2 also includes a slider blocking ring 11, which is located at the upper end of the central pipe. It is a ring-shaped protrusion directly cut out during the machining of the hydraulic drill bit and is integrated with the hydraulic drill bit. When the work is finished, the slider blocking ring 11 can stop the slider 13 to prevent the slider from falling out.

[0082] Among them, such as Figure 3As shown, one end of the hydraulic drill rod 1-3 has an external thread that connects to the hydraulic drill bit 1-2, for use during drilling. The other end of the hydraulic drill rod 1-3 has an internal thread. When the drilling depth is relatively deep, the length of the first drill rod is insufficient to continue drilling, requiring the connection of subsequent drill rods. The external thread ends of the latter two drill rods are connected to the internal thread end of the former drill rod. The hollow hydraulic drill rod 1-3 is used to deliver hydraulic pressure, enabling the extension and retraction of the retractable hydraulic side cutting edge 1-4. Specifically, the hydraulic system injects hydraulic fluid into the hydraulic drill bit through the hydraulic drill rod 1-3, pushing the slider 13, which in turn drives the connecting rod 14 to push the cutting edge until it is fully extended. When the work is finished, the hydraulic system releases the hydraulic pressure and returns the hydraulic fluid. The spring 12 pushes the slider 13 back, and simultaneously pulls the side cutting edge to retract via the connecting rod 14.

[0083] Among them, such as Figure 4 As shown, the drill bit sleeve 2 is a hollow tube, and its diameter matches the diameter of the hydraulic drill bit 1-2. Preferably, the drill bit sleeve 2 is made of a high-temperature resistant alloy. An internal thread is provided inside the drill bit sleeve 2, and an external thread is provided on the outer wall of the hydraulic drill bit 1-2, connecting the drill bit sleeve 2 to the hydraulic drill bit 1-2 via a threaded connection. This ensures that the drill bit sleeve 2 does not detach from the hydraulic drill bit 1-2 during drilling.

[0084] Step S3, as follows Figures 5 to 7 As shown, when the drill bit device 1 drills to the designated position, the drill bit sleeve 2 is inserted into the bottom of the hole.

[0085] Specifically, step S3 includes: when the drill bit device 1 reaches the designated position, blowing away debris from the hole. The hydraulic device stops and pumps back the hydraulic fluid, and after the retractable hydraulic side cutting edge 1-4 retracts, the drill bit sleeve 2 extends into the bottom of the hole. When the hydraulic system releases the hydraulic fluid and the hydraulic fluid returns, the spring 12 pushes the slider 13 back, and at the same time, the connecting rod 14 pulls the side cutting edge to retract, thus achieving the retraction of the retractable hydraulic side cutting edge 1-4. The slider blocking ring 11 can also block the slider 13 to prevent the slider from dislodging.

[0086] Preferably, to handle debris inside the hole, pressurized air ducts are installed on both symmetrical sides of the drill sleeve 2. These ducts provide air cooling for the hydraulic drill bit 1-2 and simultaneously clean drill chips from the drill bit 1-2. A metal mesh is installed at the air outlet of the ducts to block large pieces of debris. An air compressor can be connected to the free end of the drill sleeve 2 to provide high-pressure airflow. The high-pressure airflow cools the hydraulic drill bit 1-2 through the pressurized air ducts. The pressurized air ducts are made of the same material as the sleeve and are welded symmetrically to both sides inside the sleeve. The diameter of the pressurized air duct matches the width when the hydraulic side cutting edge is fully extended; the length of the pressurized air duct matches the length of the drill sleeve 2.

[0087] Step S4, as follows Figures 8 to 10As shown, assembling a hollow water injection fracturing steel pipe includes: placing the hollow water injection fracturing steel pipe in the fracturing steel pipe sleeve 3, and placing sealing material and graphite gaskets at equal intervals.

[0088] Specifically, the hollow water injection fracturing steel pipe is a smooth, hollow steel pipe, which increases the adhesion between it and the sealing material, preventing leakage and pipe breakage during subsequent water injection. Preferably, the hollow water injection fracturing steel pipe has an axial through-hole, and a protrusion is provided at the bottom. Two radial through-holes are symmetrically arranged inside the protrusion, forming a hollow water injection fracturing steel pipe and a three-hole structure at the bottom. This design enhances the hydraulic fracturing effect at specific locations. It also allows the sealing material to be stressed more evenly during expansion, thus better filling the gap between the borehole and the steel pipe and effectively preventing leakage.

[0089] The sealing material 5 and graphite gasket 6 are cross-fitted onto the hollow water injection fracturing steel pipe. The sealing material 5 is a sleeve-shaped material made of high-temperature and high-pressure resistant material; the graphite gasket 6 is a ring. The dimensions of both the sealing material 5 and the graphite gasket 6 are set according to actual conditions, with their inner diameters matching the diameter of the hollow water injection fracturing steel pipe; their outer diameters are smaller than the inner diameter of the fracturing steel pipe sleeve 3.

[0090] The sealing material can be considered as the primary sealing material, which expands under certain temperature and pressure conditions to enhance the sealing effect. The graphite gasket is considered as the secondary sealing material, which is tightly bonded to the hollow water injection fracturing steel pipe to reinforce the sealing material, prevent it from bursting out, and provide a fixed seal.

[0091] Step S5: Remove drill bit assembly 1, retaining drill bit sleeve 2. Specifically, when removing drill bit assembly 1, the hydraulic pressure must be completely released via the hydraulic device to ensure the retractable hydraulic side cutting edge is fully retracted, preventing the side cutting edge from scraping the borehole wall or the inner wall of the drill bit sleeve, which could cause damage to the borehole wall or deformation of the side cutting edge or sleeve. High-pressure airflow must be continuously supplied through a pressurized air duct to clean debris from the borehole until all debris is blown out. The removal process must be smooth to prevent loosening of the threaded connection between the hydraulic drill rod and the hydraulic drill bit.

[0092] Step S6: The fracturing steel pipe sleeve 3 of the assembled hollow water injection fracturing steel pipe is coaxially installed inside the drill bit sleeve 2; the fracturing steel pipe sleeve 3 of the assembled hollow water injection fracturing steel pipe is pushed to the bottom of the hole using an alloy push rod.

[0093] Specifically, when advancing the fracturing steel pipe casing 3 using an alloy pusher, it is necessary to push at a uniform speed to avoid excessive impact force that could cause the graphite gasket inside the fracturing steel pipe casing 3 to detach from the fracturing steel pipe, or cause abnormal engagement between the external thread of the casing and the internal thread of the drill bit sleeve 2. Before advancing the fracturing steel pipe casing 3, it is necessary to confirm that the sealing material 5 and the graphite gasket 6 are properly and cross-fitted onto the hollow water injection fracturing steel pipe at the designed spacing, without any looseness or misalignment; at the same time, check whether the inner wall of the fracturing steel pipe casing 3 is smooth and without protrusions to prevent scratching the sealing material during advancement, which would affect the sealing performance.

[0094] Step S7: Remove the drill bit sleeve 2. Specifically, in step S7-1, before removing the drill bit sleeve 2, check whether the fracturing steel pipe sleeve 3 has been pushed to the bottom of the hole and is stable. This is to prevent the fracturing steel pipe sleeve from shifting during the removal of the drill bit sleeve due to its lack of fixation, which could lead to misalignment of the sealing material. At the same time, wear high-temperature resistant gloves when removing the drill bit sleeve 2 to avoid direct contact with the high temperature of the sleeve. In step S7-2, place a receiving tray at the borehole opening to collect any debris that may fall during the removal process.

[0095] Step S8, as follows Figure 11 As shown, the sealing material is sealed with an annular metal washer 7 and an external thread nut 8. After the sealing material stabilizes, a high-pressure pump is connected to carry out hydraulic fracturing operations.

[0096] The annular metal washer, considered the third sealing material, is made of high-temperature resistant material and is directly pushed in using a high-temperature resistant metal push rod. It is used to tighten the first and second sealing materials and achieve a sealing effect. The external threaded nut, considered the fourth sealing material, is installed using a special installation tool and tightened onto the external testing device to complete the final seal.

[0097] Step S8-1, installation of the annular metal washer, includes: Step S8-1-1, before installing the annular metal washer, ensure that the annular metal washer is smooth, undamaged, and free of debris, and that the sealing material and graphite washer are properly fitted in a cross-fitting manner according to the design spacing, with the graphite washer at the bottom. Step S8-1-2, align the high-temperature resistant metal push rod axially with the outer wall of the annular metal washer, ensuring that the fracturing steel pipe sleeve 3 is fully fitted with the annular metal washer; at this time, the annular metal washer needs to be aligned with the hollow water injection fracturing steel pipe, and the annular metal washer and the steel pipe are ensured to be coaxial by visual inspection or a ruler calibration. Step S8-1-3, push the annular metal washer towards the sealing material using the high-temperature resistant metal push rod, observing the position of the annular metal washer in real time during the pushing process to ensure that it is in close contact with the sealing material below. Step S8-1-4: Take out the high-temperature resistant metal push rod, measure the distance between the annular metal washer and the borehole wall with a ruler, and confirm that the hollow water injection fracturing steel pipe is in the center of the borehole; at the same time, gently push the sealing material with a thin metal rod to check whether the sealing material is loose or displaced.

[0098] In step S8-2, the external threaded nut is installed using a special installation tool, including: one end of the external threaded nut is an extended hexagonal outer contour, which is installed using a special hexagonal installation sleeve adapted to the outer contour. Specifically, as shown... Figure 12 As shown, the externally threaded nut has a through hole at its center and includes an integrally formed hexagonal outer contour and a cylindrical protrusion. The outer diameter of the cylindrical protrusion matches the borehole diameter, and external threads are provided on the outer wall of the cylindrical protrusion for easy installation with the borehole. The length of the cylindrical protrusion is designed according to actual experimental needs. The diameter of the hexagonal outer contour is larger than the borehole diameter, expanding the contact range with the outside of the borehole and making the hollow water injection fracturing steel pipe seal more tightly. Step S8-2-1: Before installation, ensure the threads are undamaged and free of debris, and that the first, second, and third sealing materials are installed in place as designed. Step S8-2-2: Align the grooved end of the installation sleeve with the extended hexagonal outer wall of the externally threaded nut and insert it axially, ensuring the installation sleeve and the extended hexagonal outer contour of the externally threaded nut are completely fitted; verify visually or with a ruler that the externally threaded nut is coaxial with the hollow water injection fracturing steel pipe. Step S8-2-3: Rotate the mounting sleeve with a torque wrench to move the external threaded nut. During the process, observe the position of the external threaded nut in real time to ensure that it is in tight contact with the annular metal washer below, forming the final support. Step S8-2-4: Remove the mounting sleeve and gently push the external threaded nut with a thin metal rod to check whether the external threaded nut is tight and whether it is loose or displaced.

[0099] This application also includes a hydraulic fracturing test method, such as Figure 13 As shown, firstly, cubic rock mass samples (100-200mm in length) are subjected to high-pressure hydraulic loading and high-temperature loading. Then, the in-situ high-temperature and high-pressure state is maintained, followed by drilling, sealing, and fracturing experiments. Specifically, the hydraulic fracturing test method includes the following steps:

[0100] Step SⅠ involves placing the rock mass sample into the high-temperature, high-pressure fracturing chamber and checking the experimental equipment. Specifically, the equipment check and preparation includes: SⅠ-1, placing the rock mass sample into the high-temperature, high-pressure fracturing chamber. Perform an airtightness check without heating or pressurization. SⅠ-2, selecting clean water or a special fracturing fluid as the fracturing fluid medium according to experimental requirements, ensuring no air bubbles in the fluid pipeline. SⅠ-3, calibrating and zeroing the pressure sensors, temperature sensors, displacement sensors, etc. SⅠ-4, setting an appropriate sampling frequency to capture the instantaneous signals of fracture initiation and propagation.

[0101] Step SⅡ involves applying confining pressure, axial pressure, and high temperature to the rock sample to bring the core to an in-situ high-temperature and high-pressure state. Specifically, the experimental loading and simulation include: SⅡ-1, applying confining pressure via a hydraulic servo device to subject the core to uniform lateral pressure until the preset in-situ stress conditions are reached. SⅡ-2, applying axial pressure to the core via a piston to create a preset true triaxial stress state. SⅡ-3, activating the heating system to slowly heat the fracturing chamber and core to the target temperature. Maintaining the temperature and stress stable for a period allows the core to reach thermal and stress equilibrium, achieving the in-situ high-temperature and high-pressure state.

[0102] Step SⅢ involves drilling and sealing the rock mass sample using the method mentioned above.

[0103] Step SⅣ, conduct the hydraulic fracturing experiment. Specifically, the hydraulic fracturing experiment includes: SⅣ-1, after installing and sealing all equipment, connect the hollow water injection fracturing steel pipe to the injection pump, start the injection pump, and inject fracturing fluid (water) at the preset pressure and flow rate into the sample. Simultaneously record the pressure and flow rate data at the start of the experiment. SⅣ-2, monitor the sample temperature change in real time using a temperature sensor, and monitor the pressure change within the core in real time using a pressure sensor, and record the data. SⅣ-3, when the experiment reaches the preset target or fracturing cannot continue, stop the injection and turn off the injection pump; the experiment ends.

[0104] 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 sealing a borehole drilled in-situ in a high-temperature high-pressure rock mass, characterized in that, The borehole sealing method includes the following steps: Step S1, place the drill bit device (1) at the rock sample drilling position and place the drill bit sleeve (2) coaxially at the tail of the drill bit device (1); The drill bit device (1) includes a hydraulic drill bit (1-2); the end of the hydraulic drill bit (1-2) is connected to the hydraulic drill rod (1-3); the top of the front end of the hydraulic drill bit (1-2) is provided with spikes (1-1); and the front circumferential side of the hydraulic drill bit (1-2) is provided with a retractable hydraulic side blade (1-4). Step S2: Start the drill bit device (1) to drill; while the drill bit device (1) is drilling, the drill bit sleeve (2) extends into the hole simultaneously. Step S3: When the drill bit device (1) drills to the designated position, the drill bit sleeve (2) is inserted into the bottom of the hole; Step S4, assembling the hollow water injection fracturing steel pipe, including: placing the hollow water injection fracturing steel pipe in the fracturing steel pipe sleeve (3), and placing the sealing material and graphite gasket at equal intervals; Step S5: Remove the drill bit assembly (1) and retain the drill bit sleeve (2). Step S6: The fracturing steel pipe sleeve (3) of the assembled hollow water injection fracturing steel pipe is coaxially set inside the drill bit sleeve (2); the fracturing steel pipe sleeve (3) of the assembled hollow water injection fracturing steel pipe is pushed to the bottom of the hole using an alloy push rod; Step S7, remove the drill sleeve (2); Step S8: Seal the sealing material and graphite gasket with an annular metal washer and an external thread nut. After the sealing material and graphite gasket are stable, connect the high-pressure pump to carry out hydraulic fracturing operation. Step S4 further includes: cross-fitting the sealing material (5) and the graphite gasket (6) onto the hollow water injection fracturing steel pipe; the sealing material (5) includes a sleeve-shaped object; the graphite gasket (6) includes a ring.

2. The in-situ drilling sealing method for high-temperature and high-pressure rock masses as described in claim 1, characterized in that, A retractable hydraulic side cutting edge (1-4) is provided on the outer wall of the hydraulic drill bit (1-2); the retractable hydraulic side cutting edge (1-4) includes a cutting edge that is arranged parallel to the axial direction of the hydraulic drill bit (1-2) and is added along the circumference of the outer wall of the hydraulic drill bit (1-2).

3. The in-situ drilling sealing method for high-temperature and high-pressure rock masses as described in claim 1, characterized in that, Hydraulic drill bits (1-2) include: The slider (13) is located at the center of the hydraulic drill bit (1-2) and close to the front end of the hydraulic drill bit; Link (14) includes a telescopic rod; one end of link (14) is connected to slider (13), and the other end of link (14) is connected to the blade of telescopic hydraulic side blade (1-4); The hydraulic drill bit (1-2) also includes: a spring (12), one end of which is connected to the slider (13), and the other end of which is connected to the front end of the hydraulic drill bit (1-2); The hydraulic drill bit (1-2) also includes a slider blocking ring (11), which is located at the upper end of the central pipe and is an annular protrusion integrated with the hydraulic drill bit.

4. The in-situ drilling sealing method for high-temperature and high-pressure rock masses as described in claim 1, characterized in that, Step S3 further includes: when the drill bit device (1) reaches the designated position, blow away the debris in the hole; the drill bit sleeve (2) further includes a press-in air duct arranged symmetrically on both sides inside the drill bit sleeve (2); the diameter of the press-in air duct matches the width of the retractable hydraulic side blade (1-4) when it is fully extended.

5. The in-situ drilling sealing method for high-temperature and high-pressure rock masses as described in claim 1, characterized in that, The hollow water injection fracturing steel pipe is a hollow steel pipe. An axially added thread is provided on the outer wall of the hollow water injection fracturing steel pipe as an anti-slip texture. A protrusion is provided at the bottom of the hollow water injection fracturing steel pipe, and two radial through holes are symmetrically arranged inside the protrusion.

6. The in-situ drilling sealing method for high-temperature and high-pressure rock masses as described in claim 1, characterized in that, Step S7 includes: Step S7-1, confirming that the fracturing steel pipe sleeve (3) has been pushed to the bottom of the hole and is stable; Step S7-2, placing a receiving tray at the borehole opening to collect the debris that falls during the removal process.

7. The in-situ drilling sealing method for high-temperature and high-pressure rock masses as described in claim 1, characterized in that, Step S8 also includes step S8-1, installation of the annular metal washer, including: S8-1-1 Before installation, ensure that the annular metal gasket is smooth, undamaged, and free of debris, and that the sealing material and graphite gasket are properly fitted together according to the design spacing, with the graphite gasket at the bottom. S8-1-2, Align the high-temperature resistant metal push rod axially with the outer wall of the annular metal washer, and fit the cracked steel pipe sleeve (3) with the annular metal washer; S8-1-3, using a high-temperature resistant metal push rod, pushes the annular metal washer toward the sealing material; S8-1-4, take out the high-temperature resistant metal push rod, measure the distance between the annular metal washer and the borehole wall with a ruler, and confirm that the hollow water injection fracturing steel pipe is in the center of the borehole; at the same time, gently push the sealing material with a thin metal rod to check whether the sealing material is tight and whether it is loose or displaced.

8. The in-situ drilling sealing method for high-temperature and high-pressure rock masses as described in claim 1, characterized in that, Step S8 also includes step S8-2, in which the external thread nut is installed using a special installation tool: one end of the external thread nut is an extended hexagonal outer contour, and it is installed using a hexagonal external thread nut installation sleeve that is adapted to the outer contour; Step S8-2-1: Before installation, ensure that the external thread nut is undamaged and free of debris, and that the sealing material (5), graphite washer (6), and annular metal washer (7) are installed in place as designed. Step S8-2-2: Align the grooved end of the male thread nut mounting sleeve with the extended hexagonal outer wall of the male thread nut, and insert it axially to ensure that the male thread nut mounting sleeve and the extended hexagonal outer contour of the male thread nut are completely fitted; ensure that the male thread nut and the hollow water injection fracturing steel pipe are coaxial by visual inspection or ruler calibration. Step S8-2-3: Use a torque wrench to rotate the male threaded nut installation sleeve to drive the male threaded nut. During the process, observe the position of the male threaded nut in real time to ensure that it is in close contact with the annular metal washer below to form the final support. Step S8-2-4: Remove the male thread nut installation sleeve and gently push the male thread nut with a thin metal rod to check the tightness of the male thread nut.

9. A hydraulic fracturing experimental method, characterized in that, The hydraulic fracturing experimental method includes the following steps: Step S1: Place the rock mass sample into the high-temperature and high-pressure fracturing chamber and check the experimental equipment. Step S2: Apply confining pressure, axial pressure and high temperature to the rock sample to bring the core to an in-situ high temperature and high pressure state. Step S3: Drill holes in the rock mass sample and seal them using the method described in any one of claims 1-8; Step S4: Conduct a hydraulic fracturing experiment.

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