Variable-pitch all-metal screw drill with self-adaptive wear compensation function

Abstract

The invention discloses a variable-pitch all-metal screw drill with a self-adaptive wear compensation function. The variable-pitch all-metal screw drill comprises a stator, a rotor, a transmission mechanism, a self-adaptive compensation driving mechanism and a mechanical limiting mechanism which are made of all-metal materials. The inner cavity of the stator and the outer contour of the rotor are of a variable-cross-section cone conical spiral structure with a tiny taper angle, and the radial sealing gap between the stator and the rotor can be linearly adjusted through axial displacement of the rotor. The transmission mechanism is a long-stroke hollow porous spline transmission shaft and is used for realizing torque transmission and axial micro-sliding of the rotor; the self-adaptive compensation driving mechanism is of a belleville spring and hydraulic cooperative driving structure, is arranged in the universal shaft assembly and provides power for axial compensation of the rotor; the mechanical limiting mechanism is an adjustable limiting ring and is arranged at the tail end of the rotor or the transmission shaft to limit the maximum axial displacement of the rotor.

Description

Technical Field

[0001] This invention relates to the fields of oil and gas exploration and development and geothermal resource development, specifically to downhole power drilling tool technology, and more specifically to all-metal screw drilling tools and sealing gap control technology. Background Technology

[0002] In modern deep and ultra-deep oil and gas drilling and hot dry rock drilling, the bottom hole conditions are extreme, with temperatures often exceeding 180°C and even reaching 300°C. Traditional volumetric screw drills rely on the interference fit between the rubber bushing stator and the metal rotor for sealing. However, rubber materials suffer from severe hysteresis heat generation, aging, and brittleness under high-temperature conditions, and are prone to swelling in oil-based drilling mud. This results in extremely short lifespans for such drills, making them unsuitable for high-temperature deep well operations.

[0003] To overcome the temperature resistance bottleneck of rubber stators, the industry has developed all-metal screw drill bits, replacing the stator material with metal to create a metal-to-metal mating structure. Currently, existing all-metal screw drill bit technologies mainly fall into two categories: one uses a conventional all-metal structure with a high-precision micro-clearance fit, and the other uses a conical stator and rotor ground pump technology. The latter requires shutdown and manual adjustment of shims to restore the mating clearance after stator and rotor wear.

[0004] Existing all-metal screw drill bits still have many technical defects: First, the all-metal structure lacks an elastic compensation mechanism, and the increased gap after stator and rotor wear will quickly lead to high-pressure leakage and torque failure; Second, its micron-level fitting precision is extremely sensitive to temperature, and it is prone to expansion jamming or contraction leakage in the high-temperature environment downhole; Third, there are technical difficulties in axial clearance adjustment. Existing solutions mostly rely on manual adjustment, which cannot be completed downhole, while existing automatic adjustment solutions often cause rotor self-locking due to spline friction under high torque transmission, which cannot achieve effective clearance compensation. Summary of the Invention

[0005] To address the needs and problems mentioned in the background above, the present invention provides a variable pitch all-metal screw drill bit with adaptive wear compensation function, so as to at least partially solve the above problems.

[0006] This invention provides a variable pitch all-metal screw drill bit with adaptive wear compensation function, including an all-metal stator, rotor, transmission mechanism, adaptive compensation drive mechanism and mechanical limit mechanism; The inner cavity of the stator and the outer profile of the rotor are variable cross-section conical spiral structures with a small cone angle. The axial displacement of the rotor can linearly adjust the radial sealing gap between the stator and the rotor. The transmission mechanism is a long-stroke hollow multi-hole spline drive shaft, used to realize torque transmission and rotor axial micro-sliding; The adaptive compensation drive mechanism is a disc spring and hydraulic coordinated drive structure, which is set in the universal joint assembly to provide power for rotor axial compensation; The mechanical limiting mechanism is an adjustable limiting ring, which is set at the end of the rotor or transmission shaft to limit the maximum axial displacement of the rotor.

[0007] Preferably, the variable cross-section conical spiral structure transforms the uncontrollable radial wear between the stator and rotor into a controllable axial displacement of the rotor through geometric topological transformation. When the radial clearance increases due to wear, the rotor moves axially in the direction of increasing cone diameter to tighten the radial clearance and restore sealing performance.

[0008] Preferably, the effective spline engagement length of the long-stroke hollow multi-hole spline drive shaft covers the entire preset wear compensation stroke; the spline shaft is hollow inside and has radial guide holes at the root of the tooth surface, which can introduce drilling fluid or lubricating oil to the spline engagement surface to form a high-pressure fluid film and achieve hydrostatic lubrication; at the same time, the spline shaft can balance the internal and external fluid pressure and eliminate additional axial force interference.

[0009] Preferably, the disc spring assembly in the disc spring and hydraulic co-drive structure is made of high-temperature nickel-based alloy and is in a pre-compressed state to provide basic pre-tightening force; the hydraulic thrust is provided by the pressure difference generated by the drilling fluid flowing through the rotor, and the resultant force of the spring force and the hydraulic force is the power source for rotor axial compensation. When the contact reaction force between the stator and rotor decreases, the resultant force pushes the rotor to move axially.

[0010] Preferably, the adjustable limiting ring is a mechanical rigid limiting structure. When the rotor axial displacement reaches the preset limit value, the limiting ring physically blocks the rotor from continuing to descend. At this time, the riser pressure naturally decays or fluctuates, which can serve as a ground indication signal that the stator life has been exhausted.

[0011] Preferably, the long-stroke hollow multi-hole spline drive shaft can convert the dry friction between metals into fluid lubrication when the drill is working, so that the rotor can maintain an axial floating state while transmitting a large torque of thousands of Newton-meters, thus avoiding friction self-locking.

[0012] Preferably, the compensation triggering condition of the adaptive compensation drive mechanism is that the wear of the metal mating surfaces of the stator and rotor leads to an increase in radial clearance, a decrease in tool volumetric efficiency, and a reduction in the reaction force of the contact surface. At this time, the disc spring group releases potential energy and superimposes hydraulic thrust to drive the rotor to move axially.

[0013] Preferably, the drilling tool is designed with a pure metal structure, and its theoretical temperature resistance can reach more than 300℃. It can adapt to the high temperature and high pressure extreme bottom hole conditions of deep and ultra-deep oil and gas drilling and hot dry rock drilling, and is not affected by the swelling of oil-based mud.

[0014] Beneficial effects of the invention Compared with the prior art, this invention realizes the leap from passive wear resistance to active compensation in all-metal screw drills. Through the conical fit between the stator and rotor and the axial automatic propulsion mechanism, it ensures that the volumetric efficiency of the drill remains relatively constant throughout its entire life cycle, and completely solves the problem that traditional all-metal screw drills have high efficiency in the early stage but a sharp drop in efficiency due to wear in the later stage.

[0015] This invention adopts a pure metal structure and is combined with a disc spring assembly made of high-temperature resistant nickel-based alloy. The theoretical temperature resistance can reach over 300℃, effectively breaking through the thermal aging bottleneck of rubber stators. This enables it to adapt to the extreme working conditions of high temperature and high pressure in hot dry rock and ultra-deep well drilling, while also eliminating the swelling effect of oil-based mud on the drilling tools.

[0016] The long-stroke hollow multi-hole spline drive shaft of this invention utilizes the principle of hydrostatic lubrication to significantly reduce axial frictional resistance during high torque transmission, solving the engineering problem of rotor lock-up due to friction and inability to compensate for gaps. Combined with the design of a mechanical limit safety ring, it not only ensures the sensitivity of automatic gap compensation, but also effectively prevents the risk of rotor wedging or disengagement due to overcompensation, significantly improving the operational safety and reliability of the drilling tool.

[0017] Furthermore, by adjusting the preload of the disc spring and the stroke of the limiting ring, this invention can adapt to different well bottom conditions and drill string life requirements at different depths, significantly extending the effective operating cycle of the tool in deep, ultra-deep, and hot dry rock drilling. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the present invention; In the diagram: 1-Stator; 2-Rotor; 3-Universal shaft; 4-Intermediate connecting housing; 5-Drive main shaft; 6-Spring housing; 7-Disc spring assembly; 8-Limiting ring; 9-Annular gap; 10-Radial bearing; 11-Lower connector; 12-Power output end; 13-Central flow channel; 14-Radial guide hole. Detailed Implementation

[0019] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection.

[0020] This invention, through a variable cross-section conical stator and rotor profile design combined with an axial adaptive compensation mechanism, changes the rigid fit mode of traditional screw drills. Simultaneously, it introduces a long-stroke hollow multi-hole spline transmission structure, utilizing hydrostatic lubrication to break axial friction lock under high torque, transforming uncontrollable radial wear into controllable axial displacement. This achieves active real-time compensation of sealing gaps under all-metal operating conditions. Specific technical means are as follows: Variable cross-section conical stator and rotor profile design: Abandoning the traditional straight cylindrical design of screw with uniform cross-section, the inner cavity of the metal stator 1 and the outer contour of the metal rotor 2 are designed as a conical helical structure with a small cone angle. By using geometric topological transformation, the difficult-to-control radial wear of the stator and rotor is transformed into a controllable axial displacement of the rotor. When the radial clearance increases due to wear, the rotor moves axially in the direction of increasing cone diameter, thereby tightening the radial clearance and restoring the sealing effect.

[0021] Long-stroke hollow multi-hole spline drive spindle 5: A dedicated long-stroke hollow multi-hole spline drive shaft is designed as the transmission mechanism. The effective meshing length of the spline covers the entire preset wear compensation stroke. The spline shaft has a hollow internal structure and radial guide holes 14 are provided at the root of the tooth surface. Utilizing the principle of hydrostatic lubrication, drilling fluid or lubricating oil is introduced into the spline meshing surface to form a high-pressure fluid film between the metal contact surfaces, which greatly reduces the coefficient of friction and ensures that the rotor can still generate micro-slippage under axial thrust while transmitting thousands of Newton-meters of torque. This drive shaft can balance the fluid pressure inside and outside the spline shaft and eliminate the interference of additional axial force.

[0022] Disc spring and hydraulic combined drive: A disc spring and hydraulic combined drive structure is set in the universal joint assembly as the power source for automatic compensation. The structure uses a disc spring group 7 made of high temperature nickel-based alloy to provide basic preload, while the pressure difference generated by the drilling fluid flowing through the rotor provides auxiliary thrust. When the wear of the stator and rotor causes a gap and the contact reaction force decreases, the resultant force of the spring force and hydraulic force pushes the rotor downward until the gap is eliminated and the force is rebalanced.

[0023] Mechanical limit safety ring: An adjustable limit ring 8 is set at the end of the rotor or drive shaft. The maximum axial displacement of the rotor is preset. When the compensation stroke reaches the limit, that is, when the stator life is exhausted, the limit ring physically blocks the rotor from continuing to descend, preventing the rotor from wedging with the stator tapered surface or the rotor from slipping off, thus ensuring the safety of the drilling operation.

[0024] An embodiment of the present invention provides a variable pitch all-metal screw drill bit with adaptive wear compensation function. The core power components are a variable cross-section conical stator and rotor made of all-metal material. The mating surfaces of the two are designed with a slight taper along the axial direction, so that the axial displacement of the rotor can linearly adjust the radial sealing gap between the stator and rotor.

[0025] Specifically, the single-sided cone angle of the variable cross-section conical spiral structure ranges from 0.05° to 0.2°. The base material of the all-metal stator 1 and rotor 2 can be 17-4PH martensitic precipitation-hardening stainless steel or beryllium copper alloy. To cope with highly abrasive working conditions, their working surfaces are coated with a 0.1mm to 0.3mm thick tungsten carbide wear-resistant hard alloy layer using supersonic flame spraying technology. Furthermore, the variable pitch design and the variable cross-section cone are in synergy: the pitch of the stator and rotor gradually decreases at a uniform gradient from the fluid inlet to the outlet, with a reduction of 1% to 3% per lead. Because the rotor 2 is conical, the single-chamber volume undergoes a slight change when it moves towards the larger cone diameter to compensate for the gap. The gradient reduction in pitch can produce a progressive compression effect on the fluid, compensating for volume changes and eliminating cavitation effects at high temperatures, ensuring stable output torque.

[0026] To address the axial jamming problem of all-metal structures under high-torque transmission, the drill bit's transmission system incorporates a long-stroke hollow multi-hole spline shaft structure. This spline shaft has a through-flow fluid channel inside, and several micron-sized radial guide holes 14 are distributed axially at the root of the spline teeth. The drill bit's power compensation source is a disc spring assembly 7 made of high-temperature nickel-based alloy. This spring assembly is sleeved at the end of the spline shaft or independently encapsulated in a power sub-section, and is always in a pre-compressed state, capable of continuously applying a constant axial thrust to the rotor in the direction of the drill bit. At the same time, an adjustable mechanical limit ring 8 is provided at the end of the transmission shaft to limit the maximum axial compensation stroke of the rotor and prevent mechanical structure lock-up due to over-compensation.

[0027] Regarding specific structural parameters and dynamic design: (1) Transmission parameters: The effective engagement length of the long-stroke hollow multi-hole spline is set to 200mm to 400mm, and the axial compensation stroke range of the compatible rotor 2 is 20mm to 50mm. The diameter of its radial guide holes 14 is set to 1.5mm to 3.0mm, and they are distributed equidistantly in multiple rows along the bottom surface of the spline tooth groove. The distribution spacing between adjacent axial guide holes is 15mm to 30mm. The spline pair mating clearance is controlled at 0.05mm to 0.15mm.

[0028] (2) Power and hydraulic parameters: The disc spring assembly 7 is made of precipitation-hardening high-temperature nickel-based alloy, specifically Inconel 718 or Nimonic 90. The spring assembly consists of 20 to 60 single disc springs arranged in pairs and stacks, with an initial preload adjustment range of 10kN to 30kN. In the hydraulically coordinated drive structure, the hydrostatic lubricating fluid pressure introduced into the spline meshing surface is controlled at 2MPa to 5MPa, and the flow rate is precisely controlled by a throttling nozzle.

[0029] (3) Limiting structure: The adjustable limiting ring 8 adopts a structure combining fine thread adjustment and anti-loosening set screw. The inner wall of the limiting ring 8 is machined with fine thread to engage with the transmission spindle. Before the drill bit is lowered into the well, the preset maximum axial displacement of the rotor 2 is precisely set by rotating the limiting ring 8. The adjustment range of this displacement is set to 25mm to 40mm, and it is locked by radially tightening the anti-loosening set screw to ensure that it does not loosen under high vibration conditions.

[0030] The working process of this drill bit is as follows: After the high-pressure drilling fluid enters the drill bit from the upper connector, it drives the rotor 2 to rotate in the stator 1 to provide power for drilling operations. On the other hand, a portion of the high-pressure fluid is diverted into the inner cavity of the hollow spline shaft and sprayed through the radial guide hole 14 to the meshing tooth surfaces of the spline pair, forming a stable hydrostatic lubrication film on the spline contact surface. This transforms the dry friction between metals into fluid lubrication, allowing the rotor 2 to maintain an axial floating state even when transmitting a large torque of several thousand Newtons, thus avoiding friction self-locking.

[0031] As drilling continues, the metal mating surfaces of the stator and rotor gradually wear down, leading to an increase in the radial clearance between them and a decrease in the volumetric efficiency of the drill bit. At this point, due to the reduced reaction force on the stator and rotor contact surfaces, the pre-compressed disc spring assembly 7 releases its potential energy, which, combined with the hydraulic thrust borne by the rotor tip, overcomes the extremely low spline axial resistance, pushing the conical rotor to move slightly along the axial direction in the direction of increasing cone diameter. With the help of the conical geometry of the stator and rotor, this tiny axial movement can quickly tighten the radial clearance that has increased due to wear, allowing the stator and rotor mating surfaces to re-fit, restoring the sealing performance and output torque of the drill bit.

[0032] When the drill bit reaches the end of its designed lifespan, and the accumulated wear causes the rotor's axial movement distance to reach the preset limit, the shoulder of the rotor 2 or the drive spindle 5 will contact the mechanical limit ring 8. The limit ring 8 will physically prevent the rotor 2 from continuing to descend. At this time, the drill bit clearance can no longer be compensated, and the riser pressure will show a natural decay or fluctuation. This signal can indicate to the ground operator that the stator lifespan has ended and a tripping and replacement operation is required.

[0033] To further illustrate the engineering applicability and replicability of this invention, taking a commonly used Φ172mm all-metal screw drill bit as an example, its rated working torque is 6000 N·m to 10000 N·m, and its suitable displacement range is 20 L / s to 35 L / s. For different wellbore conditions, this invention can be adaptively adjusted as follows:

[0034] (1) Conventional deep well hard formation working conditions: When the ambient temperature is below 180℃, the thermal expansion effect of the material is within a controllable range; preferably, a medium initial preload of 15kN is applied and the maximum axial compensation stroke is set to 40mm, so as to maximize the pure drilling life of the drill bit.

[0035] (2) Extreme high temperature conditions in hot dry rock: When the ambient temperature reaches 300℃, the thermal expansion of all metals increases significantly. The disc spring assembly must use high temperature alloys such as Inconel 718 to prevent stress relaxation; the maximum compensation stroke should be limited to within 25mm to reserve sufficient thermal expansion safety margin to prevent the drill bit from seizing up due to thermal expansion under high temperature conditions; at the same time, replace the large-diameter throttling nozzle, increase the fluid flow rate of the radial guide hole, and strengthen the circulation cooling and static pressure support.

[0036] The design of this invention not only achieves automatic and seamless compensation of the sealing gap throughout the entire life cycle of the drilling tool, but also effectively avoids downhole safety accidents such as rotor detachment or wedging in the stator. It is applicable to fields such as ultra-deep oil and gas exploration, geothermal and hot dry rock resource development, and drilling in extremely hard formations.

[0037] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A variable pitch all-metal screw drill bit with adaptive wear compensation function, characterized in that, It includes a stator, rotor, transmission mechanism, adaptive compensation drive mechanism, and mechanical limit mechanism made entirely of metal. The inner cavity of the stator and the outer profile of the rotor are variable cross-section conical spiral structures with a small cone angle. The axial displacement of the rotor can linearly adjust the radial sealing gap between the stator and the rotor. The transmission mechanism is a long-stroke hollow multi-hole spline drive shaft, used to realize torque transmission and rotor axial micro-sliding; The adaptive compensation drive mechanism is a disc spring and hydraulic coordinated drive structure, which is set in the universal joint assembly to provide power for rotor axial compensation; The mechanical limiting mechanism is an adjustable limiting ring, which is set at the end of the rotor or transmission shaft to limit the maximum axial displacement of the rotor.

2. The variable pitch all-metal screw drill bit with adaptive wear compensation function according to claim 1, characterized in that, The variable cross-section conical spiral structure transforms the uncontrollable radial wear between the stator and rotor into a controllable axial displacement of the rotor through geometric topological transformation. When the radial clearance increases due to wear, the rotor moves axially in the direction of increasing cone diameter to tighten the radial clearance and restore sealing performance.

3. The variable pitch all-metal screw drill bit with adaptive wear compensation function according to claim 1, characterized in that, The effective spline engagement length of the long-stroke hollow multi-hole spline drive shaft covers the entire preset wear compensation stroke; the spline shaft is hollow inside and has radial guide holes at the root of the tooth surface, which can introduce drilling fluid or lubricating oil to the spline engagement surface to form a high-pressure fluid film and achieve hydrostatic lubrication; at the same time, the spline shaft can balance the internal and external fluid pressure and eliminate additional axial force interference.

4. The variable pitch all-metal screw drill bit with adaptive wear compensation function according to claim 1, characterized in that, The disc spring assembly in the hydraulic co-drive structure is made of high-temperature nickel-based alloy and is in a pre-compressed state to provide basic pre-tightening force. The hydraulic thrust is provided by the pressure difference generated by the drilling fluid flowing through the rotor. The resultant force of the spring force and the hydraulic force is the power source for rotor axial compensation. When the contact reaction force between the stator and rotor decreases, the resultant force pushes the rotor to move axially.

5. The variable pitch all-metal screw drill bit with adaptive wear compensation function according to claim 1, characterized in that, The adjustable limiting ring is a mechanical rigid limiting structure. When the rotor axial displacement reaches the preset limit value, the limiting ring physically blocks the rotor from continuing to descend. At this time, the riser pressure will naturally decay or fluctuate, which can serve as a ground indication signal that the stator life has been exhausted.

6. The variable pitch all-metal screw drill bit with adaptive wear compensation function according to claim 1, characterized in that, When the drill is working, the long-stroke hollow multi-hole spline drive shaft can convert the dry friction between metals into fluid lubrication, so that the rotor can maintain an axial floating state while transmitting torque and avoid friction self-locking.

7. The variable pitch all-metal screw drill bit with adaptive wear compensation function according to claim 1, characterized in that, The compensation trigger condition of the adaptive compensation drive mechanism is that the wear of the metal mating surfaces of the stator and rotor leads to an increase in radial clearance, a decrease in tool volumetric efficiency, and a reduction in the reaction force of the contact surface. At this time, the disc spring group releases potential energy and superimposes hydraulic thrust to drive the rotor to move axially.

8. The variable pitch all-metal screw drill bit with adaptive wear compensation function according to claim 1, characterized in that, The drilling tool is designed with a pure metal structure and can theoretically withstand temperatures of over 300℃. It can adapt to the high temperature and high pressure extreme bottom hole conditions of deep and ultra-deep oil and gas drilling and hot dry rock drilling, and is not affected by the swelling of oil-based mud.

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