High ground stress hard rock stratum three-core stepped reaming drilling tool and advance drilling method

Abstract

The invention relates to the technical field of deep engineering geological exploration, and particularly discloses a high-ground-stress hard rock stratum three-core stepped reaming drilling tool and an advanced drilling method. The working process of the three-core stepped drill for the high-crustal-stress hard rock stratum comprises the following steps that after a first-stage reaming drilling tool drills to the bottom, slurry is circulated, the drilling tool is rotated, a lower drilling tool conducts advanced reaming drilling firstly, and a low-stress working environment is provided for an internal second-stage reaming drilling tool; the secondary reaming drilling tool performs secondary reaming on the basis, the surrounding rock stress is further released, and the hole wall is trimmed; and finally, finish machining is completed through the three-stage reaming drilling tool, and the final size precision and the hole wall quality of a drilled hole are ensured. By adopting the design of step-by-step reaming of the three-core stepped reaming drilling tool structure, preliminary reaming and stress release are changed into precise forming, violent vibration and tool eccentric wear caused by single-time large-diameter drilling are avoided, and the effects of high drilling precision, good hole wall quality, long drilling tool service life and stable drilling process are achieved.

Description

Technical Field

[0001] This application relates to the field of deep engineering geological exploration technology, and more specifically, it relates to a three-center stepped borehole drilling tool and advanced drilling method for high-stress hard rock formations. Background Technology

[0003] Exploring deep-buried tunnels in challenging areas such as high-altitude mountainous regions and deeply incised river valleys presents complex and harsh geographical conditions. Vertical borehole drilling rigs are difficult to transport or even impossible to move, necessitating the use of horizontal or high-angle directional drilling to reach the target strata. While wireline coring is commonly used, encountering high-stress, hard, and fractured strata with core samples that are disc-shaped or sheet-like leads to rapid stress release, a rapid increase in drilling torque, and a sharp rise in pump pressure, causing the drill bit to jam and preventing further drilling. Therefore, it is necessary to develop a method that utilizes existing wireline coring drill rods connected to a three-core stepped reaming diamond drill bit. This allows for staged, segmented reaming drilling in high-stress strata, minimizing the risk of stuck drill bits due to rapid stress release. Summary of the Invention

[0004] To address the problem of drill bit jamming caused by the use of wireline coring in drilling, this application provides a three-core stepped reaming drill bit and an advanced drilling method for high-stress hard rock formations.

[0005] Firstly, this application provides a three-core stepped reaming drill bit for high-stress hard rock formations, employing the following technical solution: A three-core stepped reaming drill bit for high-stress hard rock formations, characterized in that it includes a first-stage reaming drill bit, a second-stage reaming drill bit inside the first-stage reaming drill bit, a third-stage reaming drill bit inside the second-stage reaming drill bit, a return spring three on the sidewall of the first-stage reaming drill bit, an eccentric block one on the outside of the first-stage reaming drill bit, one end of the return spring three on the sidewall of the eccentric block one, a return spring one on the sidewall of the second-stage reaming drill bit, an eccentric block two on the outside of the second-stage reaming drill bit, one end of the return spring one on the sidewall of the eccentric block two, a return spring two on the sidewall of the third-stage reaming drill bit, an eccentric block three on the outside of the third-stage reaming drill bit, and the return spring two on the sidewall of the eccentric block three.

[0006] By adopting the above technical solution, the drill string is connected to the wireline coring drill rod, eliminating the need for other types of drill rods and avoiding the problem of stacking multiple types of drill rods on site. During drilling, the upper reaming drill string, i.e., the third-stage reaming drill string, adopts a double-core structure design with geometric dimensions consistent with the outer diameter of the original drill string, thus not affecting the drilling string's descent. At this time, after the first-stage reaming drill string reaches the bottom, the mud is circulated, the drill string is rotated, and the lower drill string advances ahead to ream the hole, providing a low-stress operating environment for the internal second-stage reaming drill string. The second-stage reaming drill string then performs secondary reaming on this basis, further releasing the surrounding rock stress and trimming the rock. The borehole wall is ultimately finished by a three-stage reamer to ensure the final dimensional accuracy and quality of the borehole wall. A return spring three is installed at the eccentric position of the first-stage reamer. This allows the eccentric block one to be adjusted under the action of the return spring three when it is worn and deflected. Similarly, the second-stage reamer has a return spring one at its eccentric position, and the third-stage reamer has a return spring two at its eccentric position. Eccentric blocks two and three are adjusted using the same principle, ultimately preventing the drill bit from deflecting to one side, thereby improving the stability of the drilling process and the service life of the drill bit.

[0007] Preferably, the secondary reaming drill bit has an internally fixedly connected outer shell, an externally fixedly connected drive motor, an output end of the drive motor connected to a transmission screw, an externally threaded transmission ring connected to the transmission screw, an externally fixedly connected connecting block to the transmission ring, an internal shell fixedly connected to one end of the connecting block, the external of the internal shell being inside the outer shell, a slider fixedly connected to the side wall of the internal shell, the external of the slider being slidably connected to the internal of the outer shell, the external of the internal shell being fixedly connected to the external of the primary reaming drill bit, and the external of the outer shell being positioned outside the primary reaming drill bit.

[0008] By adopting the above technical solution, the drive motor is first started to drive the transmission screw to rotate inside the outer shell. Then, the transmission ring moves upward along the transmission screw under the drive of the transmission screw. Since the transmission ring is fixedly connected to the connecting block, the connecting block moves synchronously under the drive of the transmission ring. The inner shell is fixedly connected to the connecting block, and then the inner shell slides inside the outer shell under the drive of the connecting block. Subsequently, the slider slides inside the outer shell under the drive of the inner shell. The slider is used to limit the sliding range of the inner shell to prevent the inner shell from detaching from the inside of the outer shell. Therefore, the extension and retraction of the first-stage reaming drill bit are adjusted, avoiding wear on the first-stage reaming drill bit in hard geological environments, thereby extending the service life of the first-stage reaming drill bit.

[0009] Secondly, this application provides an advanced drilling method for a three-center stepped reaming drill bit in high-stress hard rock formations, employing the following technical solution: The advanced drilling method of the three-center stepped reaming drill bit in high-stress hard rock formations includes the following steps: S1. Pre-drilling preparation and formation pretreatment: Surface cleaning and positioning marking are carried out on the high-stress hard rock formation, and the formation surface is pretreated with low-pressure water jet to reduce surface hardness and stress concentration. S2. Drill tool installation and initial drilling: Connect the drill tool to the drilling rig through the connector and carry out initial drilling. Control the drilling pressure to be 50-100kN, the rotation speed to be 30-60rpm, and the drilling speed to be 0.5-2.0m / h. S3, First-stage reaming: Start the first-stage reaming drill string to ream the hole, and inject drilling fluid at the same time; S4, Secondary Reaming: Start the secondary reaming drill bit to perform secondary reaming; S5, Third-stage reaming: Start the third-stage reaming drill to perform final reaming; S6. Retract the drill bit: Gradually withdraw the drill bit and check the stability of the borehole wall.

[0010] By adopting the above technical solution, this method weakens the microstructure of the rock surface in advance through the low-pressure water jet pretreatment in step S1, laying the foundation for reducing energy consumption and tool wear in subsequent drilling. In step S2, the drilling pressure of 50-100kN and the rotation speed of 30-60rpm are set to overcome the initial resistance of hard rock with sufficient axial force, while controlling the rotation speed to avoid excessive centrifugal force that could cause premature damage to the drill bit. At this time, the slow drilling speed of 0.5-2.0 meters per hour is to ensure the verticality and positional accuracy of the initial pilot hole. The stepped reaming process from S3 to S5 is a stage of stress release and precise hole diameter formation. The drilling fluid flow rate, reaming pressure and time parameters associated with each stage of reaming serve the specific engineering goals of effectively carrying cuttings, fully cooling the drill bit and providing immediate support to the hole wall under the current hole diameter. Finally, by monitoring the roundness error and vibration amplitude, the quality of the hole is ensured to meet the long-term stability requirements under high stress environment.

[0011] Preferably, before step S1, a periodic pressure fluctuation is applied to the borehole area using a hydraulic rock-splitting device. The pressure range is 10–20 MPa, the fluctuation frequency is 1–5 Hz, and the duration is 10–30 min.

[0012] By adopting the above technical solution, this pretreatment step utilizes the fatigue damage mechanism of rock under cyclic loads to pre-generate a network of microcracks inside the rock mass before drilling begins; applying pressure fluctuations of 10-20 MPa, which are strong enough to overcome the tensile strength threshold of the rock but avoid instantaneous crushing, while the fluctuation frequency of 1-5 Hz simulates low-frequency impact loads, promoting the stable propagation and connection of microcracks; and maintaining the action time for 10-30 minutes to ensure the accumulation of damage inside the rock. The above adjustments transform the intact hard rock into a rock mass containing a large number of microdefects, thereby reducing the mechanical specific energy and tool wear during the drilling stage.

[0013] Preferably, in step S2, a drill bit coolant is added. The coolant is an aqueous emulsion, and it is added at the beginning of drilling, at a rate of 0.5 to 2.0 L per meter of borehole.

[0014] By adopting the above technical solution, water-based emulsion is added as a coolant during the initial drilling stage. The heat absorbed by the vaporization of the liquid is promptly carried away from the heat generated by the friction between the drill bit and the rock, preventing the drill bit cutting teeth from hardening or developing thermal cracks due to overheating. At the same time, the high thermal conductivity and fluidity of the water-based emulsion ensure that the cooling effect can quickly reach the friction interface. Furthermore, setting the addition amount to 0.5 to 2.0 L per meter of borehole not only meets the cooling requirements but also avoids altering the basic properties of the drilling fluid due to excessive addition. In addition, the emulsion can also reduce the adhesion of rock cuttings to the drill bit to a certain extent, playing an auxiliary lubricating role.

[0015] Preferably, in step S3, the diameter of the primary reaming drill bit is 60mm, it has an eccentric structure with an eccentricity of 1mm, and the reaming diameter is 62mm.

[0016] By adopting the above technical solution, the use of a 60mm diameter primary reaming drill bit, combined with an eccentric structure with an eccentricity of 1mm, enables the drill bit to generate controllable radial movement during rotation, thereby gradually breaking the rock and releasing ground stress. At the same time, the eccentric structure helps to reduce the contact area between the drill bit and the borehole wall, reducing frictional resistance. Therefore, a stable primary reaming process is obtained, providing guidance and a low-stress foundation for secondary reaming.

[0017] Preferably, in step S4, the outer diameter of the secondary reaming drill bit is 75mm, the eccentricity is 2mm, the angle between the eccentric axis and the lower eccentric line is 120°, and the reaming diameter is 79mm.

[0018] By adopting the above technical solution, the use of a two-stage reaming drill bit with an outer diameter of 75mm increases the eccentricity to 2mm, and the eccentric axis forms a 120° angle with the lower eccentric line. This geometric configuration ensures a uniform distribution of reaming force. At the same time, the 120° angle design causes the stress release directions to be staggered, avoiding concentrated crack propagation. The reaming diameter increases from 62mm to 79mm, with the increment based on drilling stability specifications to prevent sudden changes in hole diameter from causing hole wall instability. Therefore, a uniform secondary reaming effect is obtained, effectively smoothing the hole wall and further reducing stress.

[0019] Preferably, in step S4, a polymer lubricant is added at the beginning of hole enlargement, and the amount added is 1% to 5% of the total volume of drilling fluid.

[0020] By adopting the above technical solution, polymer lubricant is added at the beginning of the second-stage reaming stage. This reduces the coefficient of friction between the drill string and the borehole wall, as well as between the stepped drill bit and the rock. The polymer molecules can form a lubricating film on the metal and rock surfaces, which not only reduces the torque and power consumption required for rotating the drill bit, but also suppresses the drill bit's vibration tendency and stick-slip phenomenon, improving the stability of the drilling process. Since the contact area between the drill bit and the formation increases during the second-stage reaming stage, the friction problem is more serious, so polymer lubricant is added at this time. The amount of lubricant added is controlled at 1% to 5% of the total volume of drilling fluid. This concentration can meet the lubrication requirements, while excessive addition will reduce the rheological properties of the drilling fluid.

[0021] Preferably, in step S5, the outer diameter of the three-stage reaming drill bit is 98mm, the eccentricity is 2mm, the angle between the eccentric axis and the central eccentric line is 120°, and the intersection angle of the three-stage eccentric axes is 120°.

[0022] By adopting the above technical solution, a three-stage reaming drill bit with an outer diameter of 98mm is used, maintaining an eccentricity of 2mm, and the intersection angle of the three eccentric axes is 120°. The symmetrical layout minimizes the roundness error of the final hole diameter. The 120° intersection angle ensures stress balance and release at each reaming stage, preventing local overcutting. Each stage of the drill bit is a double-center drill bit, with its geometric center not on the same line as the rotary drilling center, hence it is called a three-center drill bit. Therefore, a high-precision final borehole is obtained, with a smooth hole wall that meets engineering requirements.

[0023] Preferably, before step S6, a hole wall reinforcement step is also included: injecting cement-based grout through the drill string, with a water-cement ratio of 0.4 to 0.6, an injection pressure of 2 to 8 MPa, and a duration of 10 to 30 minutes.

[0024] By adopting the above technical solution, an additional borehole wall reinforcement step is added before drill string withdrawal to consolidate the borehole after multi-stage reaming and prevent stress recovery in high-stress hard rock formations from causing borehole wall shrinkage or collapse. Specifically, a cement-based grout with a water-cement ratio between 0.4 and 0.6 is injected through the drill string. This ratio ensures the grout has both high fluidity and final strength. The injection pressure is controlled at 2-8 MPa to allow the grout to penetrate into the micro-fractures around the borehole wall while avoiding excessive pressure that could cause hydraulic fracturing. Injection continues for 10-30 minutes to ensure sufficient time for the grout to diffuse and initially solidify, thus providing a long-term stable support structure for the newly formed borehole after drill string withdrawal.

[0025] In summary, this application has the following beneficial effects: 1. This application adopts a three-core stepped reaming drill bit structure for step-by-step reaming design. Since each stage of the drill bit undertakes different reaming tasks, from initial reaming and stress release to precision shaping, it avoids the severe vibration and tool wear caused by a single large-diameter drilling, reduces stress interference during drilling, and thus prevents the drill bit from getting stuck. This results in high drilling accuracy, good hole wall quality, long drill bit life, and stable drilling process.

[0026] 2. In this application, each stage of the drilling tool is a dual-center drilling tool, and the geometric center and the rotary drilling center are not on the same line. Therefore, the hole-reaming drilling tool is a three-center drilling tool. During the drilling process, since each stage of the drilling tool is designed with a certain eccentricity, the drill bit makes eccentric movements to ream the hole. This causes the hole drilled by each stage of the drilling tool to be larger than the volume of the drill bit, thereby achieving the effect of enlarging the borehole, facilitating subsequent exploration work, further preventing the drilling tool from getting stuck, and improving the drilling rate.

[0027] 3. The method of this application starts the drive motor to drive the transmission screw to rotate, then the transmission ring moves upward under the drive of the transmission screw, then the connecting block moves synchronously under the drive of the transmission ring, then the inner shell slides under the drive of the connecting block, and then the slider slides under the drive of the inner shell. Therefore, the extension and retraction of the first-stage reaming drill bit is adjusted, avoiding wear on the first-stage reaming drill bit in hard geological environments, thereby extending the service life of the first-stage reaming drill bit.

[0028] 4. In this application, a return spring three is provided at the eccentric position of the first-stage reaming drill bit. This allows the eccentric block one to be adjusted under the action of the return spring three when it is worn and deflected. Similarly, a return spring one is provided at the eccentric position of the second-stage reaming drill bit, and a return spring two is provided at the eccentric position of the third-stage reaming drill bit. The eccentric block two and eccentric block three are adjusted in the same way, which ultimately prevents the drill bit from deflecting to one side, prevents the borehole from deviating and affecting subsequent exploration, thereby improving the stability of the drilling process and the service life of the drill bit. Attached Figure Description

[0029] Figure 1 This is a three-dimensional structural diagram of the three-center stepped reaming drill bit for high-stress hard rock formations proposed in this application; Figure 2 This is a partial structural diagram of the drive motor of the three-center stepped borehole drill bit for high-stress hard rock formations proposed in this application; Figure 3 This is a cross-sectional schematic diagram of the internal structure of the shell of the three-center stepped reaming drill bit for high-stress hard rock formations proposed in this application; Figure 4 This is a flowchart of the advanced drilling method for the three-center stepped borehole reamer in high-stress hard rock formations proposed in this application; Figure 5This is a partial structural diagram of the three-stage reaming drill bit for high-stress hard rock formations proposed in this application.

[0030] The components include: 1. Three-stage reaming drill bit; 2. Two-stage reaming drill bit; 3. One-stage reaming drill bit; 4. Return spring one; 5. Return spring two; 6. Eccentric block one; 7. Eccentric block two; 8. Eccentric block three; 9. Return spring three; 10. Outer shell; 11. Drive motor; 12. Transmission screw; 13. Transmission ring; 14. Connecting block; 15. Inner shell; 16. Slider. Detailed Implementation

[0031] The present application will be further described in detail below with reference to the accompanying drawings and embodiments.

[0032] Example 1 This embodiment provides a method for advanced drilling using a three-center stepped reaming drill bit in high-stress hard rock formations, comprising the following steps: S1. Pre-drilling preparation and formation pretreatment: Surface cleaning and positioning marking are carried out on high-stress hard rock formations, and low-pressure water jet pretreatment is used to reduce surface hardness and stress concentration.

[0033] Prior to step S1, a periodic pressure fluctuation is applied to the borehole area using a hydraulic rock-splitting device. The pressure is 10 MPa, the fluctuation frequency is 1 Hz, and the duration is 10 min.

[0034] S2. Drill tool installation and initial drilling: Connect the drill tool to the drilling rig through connector 5 and start the initial drilling. Control the drilling pressure to 50kN, the rotation speed to 30rpm, and the drilling speed to 0.5m / h.

[0035] In step S2, a drill bit coolant is added. This coolant is an aqueous emulsion and is added at the beginning of drilling at a rate of 0.5L per meter of borehole.

[0036] S3, First-stage reaming: Start the first-stage reaming drill bit 3 to ream the hole, and inject drilling fluid at the same time.

[0037] In step S3, the first-stage reaming drill bit 3 has a diameter of 60mm, an eccentric structure, an eccentricity of 1mm, and a reaming diameter of 62mm.

[0038] S4, Secondary Reaming: Start the secondary reaming drill bit 2 to perform secondary reaming.

[0039] In step S4, the outer diameter of the secondary reaming drill bit 2 is 75mm, the eccentricity is 2mm, the angle between the eccentric axis and the lower eccentric line is 120°, and the reaming diameter is 79mm.

[0040] In step S4, a polymer lubricant is added at the beginning of the reaming process, at a rate of 1% of the total drilling fluid volume.

[0041] S5, Third-stage reaming: Start the third-stage reaming drill 1 to perform final reaming.

[0042] In step S5, the outer diameter of the three-stage reaming drill bit 1 is 98mm, the eccentricity is 2mm, the angle between the eccentric axis and the central eccentric line is 120°, and the intersection angle of the three-stage eccentric axes is 120°.

[0043] S6. Retract the drill bit: Gradually withdraw the drill bit and check the stability of the borehole wall.

[0044] Before step S6, there is a hole wall reinforcement step: cement-based grout is injected through drill string 4, the water-cement ratio of the grout is 0.4, the injection pressure is 2MPa, and the duration is 10min.

[0045] Example 2 This embodiment provides a method for advanced drilling using a three-center stepped reaming drill bit in high-stress hard rock formations, comprising the following steps: S1. Pre-drilling preparation and formation pretreatment: Surface cleaning and positioning marking are carried out on high-stress hard rock formations, and low-pressure water jet pretreatment is used to reduce surface hardness and stress concentration.

[0046] Prior to step S1, a periodic pressure fluctuation is applied to the borehole area using a hydraulic rock-splitting device. The pressure is 15 MPa, the fluctuation frequency is 3 Hz, and the duration is 20 min.

[0047] S2. Drill tool installation and initial drilling: Connect the drill tool to the drilling rig through connector 5 and start the initial drilling. Control the drilling pressure to 75kN, the rotation speed to 45rpm, and the drilling speed to 1.25m / h.

[0048] In step S2, a drill bit coolant is added. This coolant is an aqueous emulsion and is added at the beginning of drilling at a rate of 1.25L per meter of borehole.

[0049] S3, First-stage reaming: Start the first-stage reaming drill bit 3 to ream the hole, and inject drilling fluid at the same time.

[0050] In step S3, the first-stage reaming drill bit 3 has a diameter of 60mm, an eccentric structure, an eccentricity of 1mm, and a reaming diameter of 62mm.

[0051] S4, Secondary Reaming: Start the secondary reaming drill bit 2 to perform secondary reaming.

[0052] In step S4, the outer diameter of the secondary reaming drill bit 2 is 75mm, the eccentricity is 2mm, the angle between the eccentric axis and the lower eccentric line is 120°, and the reaming diameter is 79mm.

[0053] In step S4, a polymer lubricant is added at the beginning of the reaming process, at a rate of 3% of the total drilling fluid volume.

[0054] S5, Third-stage reaming: Start the third-stage reaming drill 1 to perform final reaming.

[0055] In step S5, the outer diameter of the three-stage reaming drill bit 1 is 98mm, the eccentricity is 2mm, the angle between the eccentric axis and the central eccentric line is 120°, and the intersection angle of the three-stage eccentric axes is 120°.

[0056] S6. Retract the drill bit: Gradually withdraw the drill bit and check the stability of the borehole wall.

[0057] Before step S6, there is a hole wall reinforcement step: cement-based grout is injected through drill string 4, the water-cement ratio of the grout is 0.5, the injection pressure is 5MPa, and the duration is 20min.

[0058] Example 3 This embodiment provides a method for advanced drilling using a three-center stepped reaming drill bit in high-stress hard rock formations, comprising the following steps: S1. Pre-drilling preparation and formation pretreatment: Surface cleaning and positioning marking are carried out on high-stress hard rock formations, and low-pressure water jet pretreatment is used to reduce surface hardness and stress concentration.

[0059] Prior to step S1, a periodic pressure fluctuation is applied to the borehole area using a hydraulic rock-splitting device. The pressure is 20 MPa, the fluctuation frequency is 5 Hz, and the duration is 30 min.

[0060] S2. Drill tool installation and initial drilling: Connect the drill tool to the drilling rig via connector 5 and perform initial drilling. Control the drilling pressure to 100kN, the rotation speed to 60rpm, and the drilling speed to 2.0m / h.

[0061] In step S2, drill bit coolant is added. This coolant is an aqueous emulsion and is added at the beginning of drilling at a rate of 2.0L per meter of borehole.

[0062] S3, First-stage reaming: Start the first-stage reaming drill bit 3 to ream the hole, and inject drilling fluid at the same time.

[0063] In step S3, the first-stage reaming drill bit 3 has a diameter of 60mm, an eccentric structure, an eccentricity of 1mm, and a reaming diameter of 62mm.

[0064] S4, Secondary Reaming: Start the secondary reaming drill bit 2 to perform secondary reaming.

[0065] In step S4, the outer diameter of the secondary reaming drill bit 2 is 75mm, the eccentricity is 2mm, the angle between the eccentric axis and the lower eccentric line is 120°, and the reaming diameter is 79mm.

[0066] In step S4, a polymer lubricant is added at the beginning of the reaming process, at a rate of 5% of the total drilling fluid volume.

[0067] S5, Third-stage reaming: Start the third-stage reaming drill 1 to perform final reaming.

[0068] In step S5, the outer diameter of the three-stage reaming drill bit 1 is 98mm, the eccentricity is 2mm, the angle between the eccentric axis and the central eccentric line is 120°, and the intersection angle of the three-stage eccentric axes is 120°.

[0069] S6. Retract the drill bit: Gradually withdraw the drill bit and check the stability of the borehole wall.

[0070] Before step S6, there is a hole wall reinforcement step: cement-based grout is injected through drill string 4, the water-cement ratio of the grout is 0.6, the injection pressure is 8MPa, and the duration is 30min.

[0071] Comparative Example 1 The comparative example refers to the content of Example 1, except that in step S3, the diameter of the first-stage reaming drill 3 is 84mm, the eccentricity is 1mm, and the reaming diameter is 86mm. The rest of the content is the same as in Example 1.

[0072] Comparative Example 2 The comparative example refers to the content of Example 1, except that in step S3, the diameter of the first-stage reaming drill 3 is 60mm, the eccentricity is 1.4mm, and the reaming diameter is 62.8mm. The rest of the content is the same as in Example 1.

[0073] Comparative Example 3 The comparative example refers to the content of Example 1, except that in step S4, the outer diameter of the secondary reaming drill 2 is 105mm, the eccentricity is 2mm, the angle between the eccentric axis and the lower eccentric line is 120°, and the reaming diameter is 109mm. The rest of the content is the same as in Example 1.

[0074] Comparative Example 4 The comparative example refers to the content of Example 1, except that in step S4, the outer diameter of the secondary reaming drill 2 is 75mm, the eccentricity is 2.8mm, the angle between the eccentric axis and the lower eccentric line is 120°, and the reaming diameter is 80.6mm. The rest of the contents are the same as in Example 1.

[0075] Comparative Example 5 The comparative example is the same as that in Example 1, except that in step S4, the amount of polymer lubricant added is 1.4% of the total volume of drilling fluid, and the timing of addition is when the hole enlargement begins. The rest of the content is the same as that in Example 1.

[0076] Comparative Example 6 The comparative example refers to the content of Example 1, except that in step S5, the outer diameter of the three-stage reaming drill 1 is 137.2 mm, the eccentricity is 2 mm, the angle between the eccentric axis and the central eccentric line is 120°, and the intersection angle of the three-stage eccentric axes is 120°. The rest of the content is the same as in Example 1.

[0077] Performance testing Sample preparation: High-stress granite rock masses with uniform geomechanical properties were selected as test objects. All specimens were from adjacent areas of the same quarry to ensure basic consistency in mineral composition, grain size and initial stress state. Subsequently, drilling operations were carried out on the respective rock mass specimens according to the steps, parameters and materials detailed in Examples 1-3 and Comparative Examples 1-6. Each scheme was repeated three times, and a total of 27 drilled samples were finally prepared for subsequent performance testing.

[0078] Drilling diameter accuracy inspection: After drilling is completed and the hole is completely cleaned and dried, the sensor probe of the measuring instrument is inserted into the hole at a uniform speed. A measuring section is set every 100 mm along the drilling axis, and two diameter values ​​are measured perpendicularly at each section. The diameter data of all measuring sections are recorded, and then the average value and standard deviation are obtained. The smaller the standard deviation, the better the cylindricity and diameter consistency of the hole, that is, the higher the drilling accuracy. Refer to the measurement principle of lining thickness uniformity in the national standard "GB / T17457-2022 Cement Mortar Lining of Ductile Iron Pipes and Fittings", as well as the general method for detecting the accuracy of machined hole diameter.

[0079] Borehole wall surface roughness inspection: A representative core sample is taken from the borehole sample and fixed on the inspection platform; the probe of the profilometer is scanned along the axial direction of the core surface at a constant speed to record the micro-undulation profile curve of the surface; the arithmetic mean deviation Ra value of the profile is calculated by analysis software. The lower the Ra value, the smoother the borehole wall and the less surface damage caused by vibration and tool wear during drilling; refer to the international standard "ISO 4287:1997 Product geometry technical specifications surface structure: profilometry terminology, definitions and surface structure parameters".

[0080] Wear detection of key parts of the drilling tool: Before and after each drilling operation, a high-precision 3D laser scanner is used to completely scan the carbide cutting teeth of each level of the reaming drill bit to obtain its 3D model; by comparing the data of the model before and after the operation with software, the volume loss of each cutting tooth is accurately calculated, and the average value is taken as the wear of the drill bit for that operation; the smaller the wear, the better the protection effect of the method on the drill bit and the longer the service life of the drill bit; the measurement method of tool wear is referred to the industry standard "JB / T10006-2020 Technical Conditions for Carbide Indexable Inserts".

[0081] Vibration and torque stability testing during drilling: Throughout the drilling process, sensors continuously record instantaneous data of vibration acceleration and driving torque of the drilling system. After data processing, the root mean square values ​​of vibration acceleration and torque data are calculated respectively. These values ​​can effectively characterize the average energy level of vibration and torque. The lower the value and the smaller the fluctuation range, the smoother the drilling process. The dynamic performance testing is tested in accordance with the relevant specifications of the national standard GB / T13823-2022 "Calibration Method for Vibration and Shock Sensors" and GB / T18400.6-2022 "Inspection Conditions for Machining Centers Part 6: Feed Rate, Speed ​​and Interpolation Accuracy".

[0082] Post-drilling borehole wall stability observation: After drilling and borehole wall reinforcement, a high-definition industrial endoscope is used to penetrate deep into the borehole to record and photograph the borehole wall panoramically. The focus is on observing for obvious cracks, spalling, or chipping. Simultaneously, the borehole sample is placed under laboratory conditions for 48 hours, and then examined again using the endoscope to compare changes before and after, thus assessing the short-term stability of the borehole wall. A more intact borehole wall with no obvious damage indicates less stress interference to the formation and better borehole quality.

[0083] Table 1:

[0084] Example Conclusion: As can be seen from Examples 1-3 and Comparative Example 1, and Table 1, when the diameter of the first-stage reaming drill bit is too large, it will increase the resistance and vibration during drilling, leading to borehole deviation and increased borehole wall roughness. This indicates that setting the initial diameter of the first-stage reaming drill bit appropriately is the basis for achieving smooth introduction and guidance, which in turn affects the accuracy and stability of subsequent reaming processes.

[0085] As can be seen from Examples 1-3 and Comparative Example 2, and Table 1, an increase in the eccentricity of the first-stage reaming drill bit leads to an increase in the instability of its rotation trajectory, which in turn causes increased drill bit vibration and abnormal wear of the cutting teeth. This confirms that controlling the eccentricity within a small and precise range can reduce tool wear and provide a guarantee for obtaining a smooth hole wall and extending the life of the drill bit.

[0086] Based on Examples 1-3 and Comparative Example 3, and in conjunction with Table 1, it can be seen that increasing the outer diameter of the two-stage reaming drill bit results in an excessively large single-stage reaming amount, which increases the cutting load and the severity of formation stress release, causing significant torque fluctuations and out-of-roundness of the hole. This indicates that the optimized stepped reaming design should ensure that the reaming amount of each stage is moderate in order to achieve stable stress release and a smooth load transition.

[0087] Based on Examples 1-3 and Comparative Example 4, and in conjunction with Table 1, it can be seen that increasing the eccentricity of the secondary reaming drill bit amplifies the impact effect during its rotary cutting, worsens the motion state of the drill bit within the hole, and thus exacerbates hole wall damage and tool wear. This comparison corroborates that controlling the eccentricity of each stage of the drill bit can affect the dynamic balance of the drilling process and reduce stress interference.

[0088] As can be seen from Examples 1-3 and Comparative Example 5, and Table 1, insufficient addition of polymer lubricant will reduce the lubrication and slag-carrying performance of drilling fluid, increase the frictional resistance between the drill string and the borehole wall and the cutting temperature, and ultimately result in increased torque and accelerated drill string wear. This demonstrates that sufficient and efficient lubrication can reduce workload and ensure smooth drilling.

[0089] As can be seen from Examples 1-3 and Comparative Example 6, and Table 1, the excessive increase in the final size of the three-stage reaming drill bit will cause the drill bit to reach its bearing limit, resulting in severe vibration and a sharp increase in torque, which will affect the quality of hole wall formation and threaten the safety of the drill bit. This ultimately verifies the synergy of the three-center stepped parameter combination of this application, that is, the precise matching of the size of each stage of the drill bit with the eccentric structure, which together achieves a stable drilling effect with high precision, low damage and long service life.

[0090] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A three-core stepped reaming drill bit for high-stress hard rock formations, characterized in that, The device includes a primary reaming drill bit (3), a secondary reaming drill bit (2) inside the primary reaming drill bit (3), a tertiary reaming drill bit (1) inside the secondary reaming drill bit (2), a return spring three (9) on the side wall of the primary reaming drill bit (3), an eccentric block one (6) on the outside of the primary reaming drill bit (3), one end of the return spring three (9) on the side wall of the eccentric block one (6), a return spring one (4) on the side wall of the secondary reaming drill bit (2), an eccentric block two (7) on the outside of the secondary reaming drill bit (2), one end of the return spring one (4) on the side wall of the eccentric block two (7), a return spring two (5) on the side wall of the tertiary reaming drill bit (1), an eccentric block three (8) on the outside of the tertiary reaming drill bit (1), and the outside of the return spring two (5) on the side wall of the eccentric block three (8).

2. The three-core stepped reaming drill bit for high-stress hard rock formations according to claim 1, characterized in that, The secondary reaming drill bit (2) is internally fixedly connected to a shell (10), and the outer side of the shell (10) is fixedly connected to a drive motor (11). The output end of the drive motor (11) is connected to a transmission screw (12), and the outer thread of the transmission screw (12) is connected to a transmission ring (13). The outer side of the transmission ring (13) is fixedly connected to a connecting block (14), and one end of the connecting block (14) is fixedly connected to an inner shell (15). The outer side of the inner shell (15) is inside the shell (10), and the side wall of the inner shell (15) is fixedly connected to a slider (16). The outer side of the slider (16) is slidably connected to the inside of the shell (10), and the outer side of the inner shell (15) is fixedly connected to the outside of the primary reaming drill bit (3). The outer side of the shell (10) is located outside the primary reaming drill bit (3).

3. A method for advanced drilling using a three-center stepped reaming drill bit in high-stress hard rock formations, characterized in that... The three-core stepped reaming drill string for high-stress hard rock formations as described in any one of claims 1-2 comprises the following steps: S1. Pre-drilling preparation and formation pretreatment: Surface cleaning and positioning marking are carried out on the high-stress hard rock formation, and the formation surface is pretreated with low-pressure water jet to reduce surface hardness and stress concentration. S2. Drill tool installation and initial drilling: Connect the drill tool to the drilling rig through the connector (5) and carry out initial drilling. Control the drilling pressure to be 50-100kN, the rotation speed to be 30-60rpm, and the drilling speed to be 0.5-2.0m / h. S3, First-stage reaming: Start the first-stage reaming drill bit (3) to ream the hole, and inject drilling fluid at the same time; S4, Secondary reaming: Start the secondary reaming drill (2) to perform secondary reaming; S5, Third-stage reaming: Start the third-stage reaming drill (1) to perform final reaming; S6. Retract the drill bit: Gradually withdraw the drill bit and check the stability of the borehole wall.

4. The advanced drilling method for a three-center stepped reaming drill bit in high-stress hard rock formations according to claim 3, characterized in that, Before step S1, periodic pressure fluctuations are applied to the borehole area using a hydraulic rock-splitting device. The pressure range is 10–20 MPa, the fluctuation frequency is 1–5 Hz, and the duration is 10–30 min.

5. The advanced drilling method for a three-center stepped reaming drill bit in high-stress hard rock formations according to claim 3, characterized in that, In step S2, a drill bit coolant is added. This coolant is an aqueous emulsion and is added at the beginning of drilling at a rate of 0.5 to 2.0 L per meter of borehole.

6. The advanced drilling method for a three-center stepped reaming drill bit in high-stress hard rock formations according to claim 3, characterized in that, In step S3, the diameter of the first-stage reaming drill (3) is 60 mm, with an eccentric structure and an eccentricity of 1 mm, and the reaming diameter is 62 mm.

7. The advanced drilling method for a three-center stepped reaming drill bit in high-stress hard rock formations according to claim 3, characterized in that, In step S4, the outer diameter of the secondary reaming drill bit (2) is 75 mm, the eccentricity is 2 mm, the angle between the eccentric axis and the lower eccentric line is 120°, and the reaming diameter is 79 mm.

8. The advanced drilling method for a three-center stepped reaming drill bit in high-stress hard rock formations according to claim 3, characterized in that, In step S4, a polymer lubricant is added at the beginning of reaming, at a rate of 1% to 5% of the total drilling fluid volume.

9. The advanced drilling method for a three-center stepped reaming drill bit in high-stress hard rock formations according to claim 3, characterized in that, In step S5, the outer diameter of the three-stage reaming drill bit (1) is 98mm, the eccentricity is 2mm, the angle between the eccentric axis and the central eccentric line is 120°, and the intersection angle of the three-stage eccentric axes is 120°.

10. The advanced drilling method for a three-center stepped reaming drill bit in high-stress hard rock formations according to claim 3, characterized in that, Before step S6, a hole wall reinforcement step is also included: cement-based grout is injected through the drill string (4), the water-cement ratio of the grout is 0.4 to 0.6, the injection pressure is 2 to 8 MPa, and the duration is 10 to 30 minutes.

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