Special-shaped PDC (Polycrystalline Diamond Compact) tooth well bottom periphery grooving pressure relief drill bit and optimization design method thereof

Abstract

The invention provides a special-shaped PDC tooth shaft bottom periphery grooving pressure relief drill bit and an optimization design method thereof. The drill bit comprises a drill bit body, an upper connector, a drilling fluid flow channel, a nozzle assembly, main PDC cutting teeth and at least one impact unloading cutting assembly. The impact unloading cutting assembly is composed of a special-shaped PDC cutting tooth, a tooth matrix, an elastic connecting piece and a hydraulic differential pressure driving mechanism and is controlled by hydraulic differential pressure and fluctuation of the hydraulic differential pressure established by drilling fluid circulation. According to the optimization design method, by establishing a quantifiable evaluation index system of grooving capacity, invasion capacity, cutting capacity and overall rock breaking efficiency, the optimal tooth shape and tooth arrangement parameters are matched under the working conditions of different rock strengths, formation pressures and the like. External power is not needed, stress redistribution is induced through preferential grooving on the periphery of the well bottom, rock breaking is strengthened in combination with impact, the surrounding rock constraint of a deep high ground stress stratum is remarkably weakened, the rock breaking difficulty is reduced, the rock breaking efficiency of the PDC drill bit is effectively improved, the service life of the PDC drill bit is effectively prolonged, and the deep well drilling requirement is met.

Description

Technical Field

[0001] This invention relates to the field of bottom hole rock breaking technology, and more specifically, to a non-circular PDC tooth bottom hole peripheral groove pressure relief drill bit and its optimized design method. Background Technology

[0002] In recent years, the depth of oil and gas drilling has continued to increase. In the Tarim Basin, a total of 191 deep wells with a depth of 8,000 meters have been completed, and the proven reserves of ultra-deep oil and gas are 24.1×10^8 tons. The Deep Earth Takor 1 well, which was completed on January 5, 2025, reached a depth of 10,910 meters, making it the deepest vertical well in Asia and the second deepest in the world, marking the entry of related drilling into the "10,000-meter era".

[0003] However, as drilling depth increases, the encountered rocks become stronger, more abrasive, and less drillable, leading to a significant decrease in drill bit rock-breaking efficiency and lifespan. Taking the Tako-1 well as an example, compared to the third section (5856-7856m), the fifth section (9889-10910m) required 10 more drilling runs, resulting in a 79.23% decrease in footage per drill bit and a 75.69% decrease in mechanical drilling rate. Research has found that the high-pressure environment in deep formations is the main cause of these phenomena. On the one hand, the mechanical properties of rock change significantly with increasing confining pressure: experiments show that for every 10MPa increase in confining pressure, the corresponding rock compressive strength increases by 20.15%-75.75%, while the failure mode shifts from brittle to ductile. On the other hand, geostress directly affects the stress state and damage evolution characteristics of the rock surrounding the cutting teeth, leading to a decrease in rock-breaking efficiency. When the in-situ stress increases from 10 MPa to 40 MPa, the penetration depth and rock breaking efficiency of a single PDC tooth decrease by 9.38% and 7.79%, respectively, under the same drilling pressure.

[0004] To address the challenge of rock breaking in high-stress environments at deep strata, scholars both domestically and internationally have conducted research from two perspectives: weakening rock strength and enhancing drill bit performance. The former primarily utilizes various drill bit structure optimization modes, such as dual-stage PDC drill bits and differential pressure drill bits, to pre-break parts of the rock, forming an outwardly convex / inwardly concave well bottom, thereby achieving stress unloading and reducing the mechanical strength of the rock. Field applications show that different drill bit structures can achieve a combined speed increase of 30%-336%. However, at the same time, the pre-breaking structure of the drill bit requires a large amount of mechanical and hydraulic energy to operate under the initial high-temperature and high-pressure environment at the well bottom. Therefore, the overall drill bit design is complex, and if the structure and energy distribution are not properly optimized, the desired effect cannot be achieved.

[0005] In terms of enhancing drill bit performance, numerous researchers have significantly improved rock-breaking efficiency, aggressiveness, and wear resistance by optimizing PDC tooth shape and cobalt removal processes. However, for the challenge of peripheral rock breaking under the coupled constraints of high ground stress and high confining pressure at depth, simply "improving tooth strength or aggressiveness" is often insufficient to address issues such as strong peripheral lateral constraints, limited crack propagation, discontinuous peripheral damage, and repeated breaking caused by rock cuttings trapped at the bottom of the well. Especially for technologies like "bottom-hole peripheral grooving and unloading," although existing structures can achieve a certain degree of grooving, the grooving capacity, penetration capacity, cutting capacity, and overall rock-breaking efficiency of different tooth shapes vary significantly under different rock strengths, formation pressures, hydrostatic pressures, and drilling speeds. Without quantifiable tooth shape evaluation and selection criteria, issues such as insufficient grooving formation, unstable unloading effects, mismatched energy utilization, and limited drilling speed can easily arise, thus affecting the adaptability and stability of the technical solution.

[0006] Therefore, there is an urgent need to propose a technical solution that can effectively improve the rock-breaking boundary conditions at the bottom of the well, enhance the rock-breaking efficiency of PDC drill bits, and possess formation adaptability under the constraints of high ground stress in deep wells. This solution addresses the problems of difficulty in fracturing the surrounding rock at the bottom of the well under the combined effects of in-situ ground stress and high confining pressure, as well as the strong lateral constraints on the outer perimeter. Summary of the Invention

[0007] The purpose of this invention is to provide a non-circular PDC tooth bottom hole groove pressure relief drill bit and its optimized design method, which addresses the shortcomings of the prior art and solves the problems mentioned in the background.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A non-circular PDC tooth bottom hole peripheral grooving pressure relief drill bit includes a drill bit body, an upper connector located at the top of the drill bit body, a drilling fluid flow channel opened inside the drill bit body, at least one nozzle assembly located on the lower end face of the drill bit body and communicating with the drilling fluid flow channel, and multiple PDC main cutting teeth arranged on the lower end face of the drill bit body. It also includes at least one set of impact unloading cutting components. The drill bit body has a receiving cavity for accommodating the impact unloading cutting components. The lower end of the impact unloading cutting components extends to the outside of the drill bit body and reciprocates along the axial direction of the receiving cavity to impact the rock in the outer peripheral ring of the bottom hole. The power of the impact unloading cutting components comes from the hydraulic pressure difference formed between the drilling fluid flow channel and the annular return channel.

[0009] Furthermore, the impact unloading cutting assembly includes a shaped PDC cutting tooth, a tooth body, an elastic connector, and a hydraulic differential pressure drive mechanism. The shaped PDC cutting tooth is disposed inside or around the drill bit body via the tooth body. The tooth body is connected to the hydraulic differential pressure drive mechanism via the elastic connector, forming an elastic support structure that allows the shaped PDC cutting tooth to move axially along the receiving cavity. The hydraulic differential pressure drive mechanism is located inside the drilling fluid flow channel and is sealed against the inner wall of the upper connector, used to convert the hydraulic pressure difference into driving force and transmit it to the shaped PDC cutting tooth.

[0010] Furthermore, the hydraulic differential pressure drive mechanism includes a pressure-bearing component and a support block. One side of the support block is slidably connected to the side wall of the pressure-bearing component, and the end of the toothed body is connected to the support block via an elastic connector. The elastic connector supports the pressure-bearing component, allowing it to abut and seal against the inner wall of the upper connector. Under pressure, the pressure-bearing component moves downward, connecting the internal space of the upper connector with the drilling fluid flow channel.

[0011] Furthermore, the elastic connector is a disc spring, which is used to store elastic potential energy when subjected to force and release it when unloaded, so as to realize the reciprocating motion of the irregular PDC cutting teeth.

[0012] Preferably, it also includes a pulse jet nozzle, which is disposed on the outer periphery of the bottom of the drill bit body, located on one side of the impact unloading cutting assembly, and is used to output pulse jets to clean the chip carrier.

[0013] Furthermore, when there are multiple unloading cutting components, they are spaced apart axially along the bottom end of the drill bit body.

[0014] Furthermore, the tooth shape of the irregular PDC cutting teeth is a conical tooth, an axe-shaped tooth, or a conventional cylindrical tooth and combination thereof. The tooth shape is selected and determined based on the evaluation index system of grooving ability, intrusion ability, cutting ability and overall rock breaking efficiency.

[0015] An optimized design method for a non-circular PDC tooth bottom hole peripheral groove pressure relief drill bit, applicable to the aforementioned drill bit, includes the following steps: S1. Establish a quantifiable evaluation index system for the grooving ability, penetration ability, cutting ability and overall rock breaking efficiency of irregular PDC cutting teeth; S2. Under different rock strength, formation pressure, hydrostatic column pressure and drilling speed conditions, the candidate tooth profiles are comprehensively sorted and matched; S3. Based on the sorting and matching results, determine the preferred tooth profile and the corresponding tooth inclination angle, cutting depth and tooth arrangement parameter combination of the impact unloading cutting component; S4. During drilling operations, the drilling fluid circulation forms a hydraulic pressure difference ΔP and its fluctuations, which drive the irregularly shaped PDC cutting teeth of the impact unloading cutting assembly to reciprocate axially periodically, applying an impact-cutting composite load to the rock around the bottom of the well, forming a circumferential stress unloading groove around the bottom of the well.

[0016] The evaluation formula for the tank-forming capacity in step S1 is:

[0017] In the formula, For the groove depth, The average width of the groove. , The contribution of different geometric parameters to stress unloading, This represents the theoretical contact area of ​​the irregularly shaped PDC cutting teeth. The brittle rock-breaking characteristics of the tooth, i.e., the actual cutting area versus the theoretical value. The ratio; actual grooving area The formula is:

[0018] In the formula, The mass of rock cuttings in the rock breaking experiment. For density, For cutting speed, For time.

[0019] In step 1, the formula for evaluating intrusion capability is:

[0020] In the formula, A and These represent the effective contact area and the average vertical force, respectively.

[0021] The formula for evaluating cutting capability in step S1 is:

[0022] In the formula, This represents the effective contact area between the irregularly shaped PDC cutting teeth and the rock. This represents the average cutting force.

[0023] In step S1, the overall rock-breaking efficiency is quantifiable using the MSE (Mean Separation Efficiency) method to evaluate the overall rock-breaking efficiency of different types of PDC (Programmable Dental Cavity) teeth. The formula is as follows:

[0024] In the formula, and These represent the lateral and vertical displacements of the tooth between the two sampling points, respectively. The volume of rock crushing is determined based on the number and corresponding dimensions of the crushing units. and These are two consecutive horizontal cutting force sampling points. and For two consecutive vertical intrusion force sampling points,n This represents the total number of sampling points. i For a single sampling point.

[0025] The present invention has at least the following advantages or beneficial effects: 1. This invention utilizes the hydraulic pressure difference ΔP naturally formed by the drilling fluid circulation and its fluctuations as a driving source, directly converting it into the axial reciprocating impact load of the irregular PDC cutting teeth. It does not require the introduction of additional external power or complex control devices, has a relatively simple structure, is easy to implement in engineering, and can be adapted to complex drilling environments such as deep wells and ultra-deep wells.

[0026] 2. The irregular PDC cutting teeth preferentially form continuous or semi-continuous circumferential stress unloading grooves on the outer periphery of the well bottom, transforming the well bottom edge from a strongly constrained boundary to a weakly constrained boundary, thus promoting stress redistribution at the well bottom. After the grooves are formed, the constraint on the outer periphery of the well bottom changes from being dominated by in-situ geostress to being dominated by drilling fluid column pressure (the fluid column pressure is usually significantly less than the geostress), further reducing the effective normal stress and lateral confining pressure on the outer and near-outer periphery, significantly improving the conditions for main cutting tooth intrusion and crack propagation, reducing rock breaking load and energy consumption, and increasing mechanical drilling speed.

[0027] 3. Axial reciprocating impact can generate higher load peak and contact stress peak at the moment the cutting teeth contact the rock, which is more likely to induce the initiation, propagation and local spalling of microcracks in the surrounding rock, significantly improve the grooving forming speed and the effectiveness of the unloading structure, and improve the rock breaking environment in the main cutting zone more quickly.

[0028] 4. By arranging irregularly shaped PDC cutting tooth units along the axial direction in the outer peripheral area of ​​the same blade, an alternating cutting mechanism is formed. Even if a single tooth wears or fails locally, the continuity of the cutting groove and the stability of the unloading effect can still be maintained, ensuring the continuous and efficient rock breaking process.

[0029] 5. This invention establishes a quantifiable evaluation index system for trenching capability, intrusion capability, cutting capability, and overall rock breaking efficiency. Under different rock strength, formation pressure, hydrostatic column pressure, and drilling speed conditions, it can match the optimal tooth shape and tooth layout parameter combination to ensure stable and reliable trenching and unloading effect, further improving the adaptability of the drill bit to different formations and its engineering application value.

[0030] 6. Without significantly increasing drilling pressure and rotation speed, this invention reduces the difficulty of rock breaking and the risk of cutting tooth wear and failure through multiple effects such as stress unloading, impact enhancement, rock clearing efficiency improvement and tooth shape adaptation. It achieves simultaneous improvement in rock breaking efficiency and drill bit service life, providing an efficient solution for drilling in deep high-stress formations. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of the structure of a non-circular PDC tooth well bottom peripheral groove pressure relief drill bit provided by the present invention; Figure 2 A schematic diagram of a customized drill bit for deep formations, including bottom perimeter grooving and stress unloading methods. Figure 3 A cross-sectional view of an irregularly shaped PDC tooth bottom peripheral groove pressure relief drill bit provided by the present invention; Figure 4 The diagram shows the grooving capacity, cutting capacity, penetration capacity, and rock-breaking efficiency of different PDC teeth.

[0033] Icons: 1. Irregular PDC cutting teeth; 2. Drill body; 3. Cutting blade; 4. PDC main cutting teeth; 5. Nozzle assembly; 6. Pulse jet nozzle; 7. Groove; 8. Support block; 9. Elastic connector; 10. Tooth body; 11. Upper connector; 12. Pressure-bearing component. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0035] Please refer to Figures 1 to 3As shown, a non-circular PDC tooth bottom-hole peripheral groove pressure relief drill bit includes a drill bit body 2, an upper connector 11 located at the top of the drill bit body 2, a drilling fluid flow channel opened inside the drill bit body 2, at least one nozzle assembly 5 located on the lower end face of the drill bit body and communicating with the drilling fluid flow channel, and multiple PDC main cutting teeth 4 arranged on the lower end face of the drill bit body 2. The drill bit body 2 is the core load-bearing component, and its upper part is fixedly connected to the drill string through the upper connector 11 to realize the transmission of drill string torque and drilling pressure. The drilling fluid flow channel runs through the drill bit body 2 and the upper connector 11 and communicates with the drilling fluid channel in the drill string. The nozzle assembly 5 communicates with the drilling fluid flow channel. The drilling fluid passes through the drill string, the upper connector 11 and the drill bit body 2 in sequence and is sprayed onto the bottom of the well through the nozzle assembly 5 to achieve lubrication and heat exchange at the bottom of the drill bit body 2; the drilling fluid is disturbed from the bottom of the well and rises along the annular return channel, carrying rock cuttings out of the well. The main PDC cutting teeth are evenly arranged on the working end face of the cutter blade 3 of the drill bit body, distributed along the rotation trajectory of the drill bit, and are used to perform conventional shearing and rock breaking.

[0036] In addition, the drill bit includes at least one set of impact unloading cutting components. A receiving cavity is provided within the drill bit body 2 to accommodate the impact unloading cutting components. The lower end of the impact unloading cutting components extends to the outer side of the cutter blades 3 of the drill bit body 2. The impact unloading cutting components reciprocate along the axial direction of the receiving cavity to impact the rock in the outer periphery of the well bottom. The power for the impact unloading cutting components comes from the hydraulic pressure difference ΔP formed between the drilling fluid flow channel and the annular return channel. When there are multiple unloading cutting components, at least one is configured for each cutter blade, arranged at intervals along the axial direction of the bottom end of the drill bit body to form an alternating cutting structure.

[0037] like Figure 2 As shown in (a), the in-situ in-situ stress of the rock surrounding the bottom of the deep formation is shown in (a). σh Under the triaxial constraint of high confining pressure, the lateral confining pressure is high and the crack propagation is limited. Conventional stable cutting modes are not easy to form a continuous and effective failure structure at the bottom periphery of the well, which makes it difficult to release the peripheral constraint and increases the difficulty of rock breaking.

[0038] like Figure 2 As shown in (b), this invention forms a circumferential stress-unloading groove 7 around the bottom of the well through peripheral impact-cutting, creating a low-constraint fracture zone around the bottom of the well and causing stress redistribution. This weakens the lateral constraint of the surrounding rock on the central region of the well bottom, improves the entry and crack propagation boundary conditions of the PDC main cutting teeth 4, and achieves efficient rock breaking under stress-induced unloading conditions. After the groove 7 is formed, the peripheral constraint boundary at the bottom of the well gradually changes from being dominated by in-situ geostress to being dominated by the drilling fluid pressure at the bottom of the well. Ph Dominantly, since the liquid column pressure is usually significantly lower than the geostress level, the equivalent constraint at the outer and near-outer periphery is further reduced, thereby further improving the overall rock breaking efficiency.

[0039] Specifically, the impact unloading cutting assembly includes a shaped PDC cutting tooth 1, a tooth housing 10, an elastic connector 9, and a hydraulic differential pressure drive mechanism. The shaped PDC cutting tooth 1 is disposed within or around the drill bit body 2 via the tooth housing 10. The tooth housing 10 is connected to the hydraulic differential pressure drive mechanism via the elastic connector 9, forming an elastic support structure that allows the shaped PDC cutting tooth 1 to move axially along the receiving cavity. The hydraulic differential pressure drive mechanism is located within the drilling fluid flow channel and is sealed against the inner wall of the upper connector through the elastic potential energy of the elastic connector 9, used to convert the hydraulic pressure difference ΔP into a driving force and transmit it to the shaped PDC cutting tooth. The hydraulic differential pressure drive mechanism includes a pressure-bearing component 12 and a support block 8. One side of the support block 8 is slidably connected to the side wall of the pressure-bearing member 12. The end of the tooth matrix 10 is connected to the support block 8 through the elastic connector 9. The support block 8 is also located in the receiving cavity. The side wall of the support block 8 fits against the cavity wall of the receiving cavity. The support block 8 is used to provide guidance support and limit for the tooth matrix 10 and the irregular cutting tooth 1, so as to ensure its axial movement is stable and avoid off-center loading and jamming.

[0040] During the drilling process, the pressure-bearing component 12, under the elastic potential energy of the elastic connector 9, has its sidewall abutting and sealing against the inner wall of the upper connector 11. The internal space of the upper connector 11 is not connected to the drilling fluid flow channel opened inside the drill bit body 2. As the drilling fluid enters the internal space of the upper connector 11, the pressure on the pressure-bearing component 12 gradually increases. When the pressure reaches a certain value, it pushes the pressure-bearing component 12 downward, further compressing the elastic connector 9. The tooth matrix 10 moves along the axis of the receiving cavity under the tension of the elastic connector 9, pushing the irregular PDC cutting tooth 1 to act on the outer periphery of the bottom of the well. At the same time, the pressure-bearing component 12 separates from the upper connector 11, the drilling fluid enters the drilling fluid flow channel, the pressure at the upper end of the pressure-bearing component 12 decreases rapidly, the elastic potential energy of the elastic connector 9 is released, and the pressure-bearing component 12 rebounds. Then, it is pressurized again, and the cycle repeats. During this process, the tooth matrix 10 is driven to reciprocate, achieving rock breaking by impact.

[0041] The tooth shape of the irregular PDC cutting tooth 1 is a conical tooth, an axe-shaped tooth, or a conventional cylindrical tooth and a combination thereof. The tooth shape is selected and determined based on the evaluation index system of grooving ability, intrusion ability, cutting ability and overall rock breaking efficiency.

[0042] During drilling operations, drilling fluid circulation is established. The drilling fluid enters the nozzle assembly 5 through the internal flow channels of the drill bit and is then ejected after being throttled, acting on the bottom of the well. Due to factors such as nozzle throttling, changes in the flow field at the bottom of the well, and cuttings disturbance, a pressure difference ΔP = P1 is formed between the pressure P1 inside the hydraulic chamber of the drill bit and the pressure P2 on the annulus side near the nozzle outlet. P2, accompanied by differential pressure fluctuations of a certain amplitude (periodic changes in hydraulic energy). The differential pressure ΔP and its fluctuations act on component 8 and transmit energy to the tooth matrix 10 through the elastic element 9, generating a driving force along the axial direction of the receiving cavity, causing the tooth matrix 10 to push the PDC profiled cutting tooth 1 towards the bottom of the well. During this process, the elastic element 9 is compressed. When the hydraulic cavity is depressurized through the drill bit's return / relief channel (this channel is already provided in the existing drill bit and is connected to the drilling fluid flow channel inside the drill bit body 1) or when the nozzle assembly 5 discharges, causing ΔP to decrease in stages, the elastic connector releases the stored energy, and component 8 rebounds at this time, pulling the profiled cutting tooth back to its original position. Thus, under the coupled effect of "differential pressure drive - differential pressure fall - elastic reset", the shaped cutting teeth form a periodic axial reciprocating acceleration motion and apply alternating impact-cutting composite load to the rock around the bottom of the well. The reciprocating impact preferentially acts on the outermost rock at the bottom of the well, causing microcracks to initiate and expand, local peeling, and gradually forming the circumferential stress unloading groove 7 around the bottom of the well.

[0043] Preferably, the elastic connector 9 is a disc spring, which is used to store elastic potential energy when subjected to force and release it when unloaded, so as to realize the reciprocating motion of the irregular PDC cutting teeth.

[0044] Preferably, the drill bit also includes a jet nozzle 6, which is located on the outer periphery of the bottom of the drill bit body 2, on one side of the impact unloading cutting assembly. The pulse jet generated by the pulse jet nozzle 6 assists in rock breaking and close-range flushing and removal of cuttings in the cutting area, reducing the risk of cuttings accumulation and mud packing, and minimizing repeated crushing and secondary grinding. This ensures that the cutting stability and unloading effect remain consistent even with a single blade and single irregular tooth configuration. The specific flow channel structure design of the jet nozzle 6 is determined by considering drilling depth, mechanical drilling rate, and on-site pumping capacity; specific designs can refer to existing methods.

[0045] Please refer to Figure 4 As shown, to address the problem of "difficulty in matching the cutting tooth shape and fluctuation in groove stability" under different formation and drilling parameter conditions, this invention also provides an optimized design method for a non-circular PDC tooth bottom hole peripheral grooving pressure relief drill bit, applicable to the aforementioned drill bit, comprising the following steps: S1. Establish a quantifiable evaluation index system for the grooving ability, penetration ability, cutting ability and overall rock breaking efficiency of irregular PDC cutting teeth; Grooving capability evaluation: The theoretical contact area is obtained based on the geometric characteristics of the tooth shape, and the actual grooving area is obtained by combining rock breaking experiments. The grooving characteristic parameters are calculated by formula (1): (1) In the formula, For the groove depth, The average width of the groove. , The contribution of different geometric parameters to stress unloading, This represents the theoretical contact area of ​​the irregularly shaped PDC cutting teeth. The brittle rock-breaking characteristics of the tooth, i.e., the actual cutting area versus the theoretical value. The ratio; actual grooving area The formula is: (2) In the formula, The mass of rock cuttings in the rock breaking experiment. For density, For cutting speed, For time.

[0046] Cutting capability evaluation: The cutting capability index is calculated using formula (3). C : (3) In the formula, This represents the effective contact area between the irregularly shaped PDC cutting teeth and the rock. This represents the average cutting force. When the torque provided during actual drilling is constant, this value is... C The larger the value, the larger the corresponding tooth-rock interaction area and the higher the mechanical drilling speed.

[0047] Intrusion capability assessment: Intrusion capability index is calculated using formula (4). P : (4) In the formula, A and These represent the effective contact area and the average vertical force, respectively. In actual drilling operations, when the available drilling pressure is constant (such as in horizontal wells with constant tooth bearing capacity), the corresponding tooth-rock interaction area changes with... P As the value increases, the mechanical drilling speed is less restricted by the drilling pressure.

[0048] Overall rock-breaking efficiency evaluation: MSE was used to evaluate the overall rock-breaking efficiency of different types of PDC teeth. However, unlike the conventional rock-breaking calculation method, the cutting teeth fluctuate continuously in the vertical direction under constant intrusion force. Therefore, this factor is considered when calculating MSE, as shown in formula (5):

[0049] In the formula, and These represent the lateral and vertical displacements of the tooth between the two sampling points, respectively. The volume of rock crushing is determined based on the number and corresponding dimensions of the crushing units. and These are two consecutive horizontal cutting force sampling points. and For two consecutive vertical intrusion force sampling points, n This represents the total number of sampling points. i For a single sampling point.

[0050] S2. Under different rock strength, formation pressure, hydrostatic column pressure and drilling speed conditions, the candidate tooth profiles are comprehensively sorted and matched; S3. Based on the sorting and matching results, determine the preferred tooth profile and the corresponding tooth inclination angle, cutting depth and tooth arrangement parameter combination of the impact unloading cutting component; S4. During drilling operations, the drilling fluid circulation forms a hydraulic pressure difference ΔP and its fluctuations, which drive the irregularly shaped PDC cutting teeth of the impact unloading cutting assembly to reciprocate axially periodically, applying an impact-cutting composite load to the rock around the bottom of the well, forming a circumferential stress unloading groove around the bottom of the well.

[0051] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A non-circular PDC tooth bottom-hole peripheral groove pressure relief drill bit, comprising a drill bit body, an upper connector located at the top of the drill bit body, a drilling fluid flow channel opened inside the drill bit body, at least one nozzle assembly located on the lower end face of the drill bit body and communicating with the drilling fluid flow channel, and a plurality of PDC main cutting teeth arranged on the lower end face of the drill bit body, characterized in that, It also includes at least one set of impact unloading cutting components. The drill bit body has a cavity for accommodating the impact unloading cutting components. The lower end of the impact unloading cutting components extends to the outside of the drill bit body and reciprocates along the axial direction of the cavity to impact the rock in the outer circumferential zone of the bottom of the well. The power of the impact unloading cutting components comes from the hydraulic pressure difference formed between the drilling fluid flow channel and the annular return channel.

2. The irregularly shaped PDC tooth bottom peripheral groove pressure relief drill bit according to claim 1, characterized in that, The impact unloading cutting assembly includes a shaped PDC cutting tooth, a tooth body, an elastic connector, and a hydraulic differential pressure drive mechanism. The shaped PDC cutting tooth is disposed inside or around the drill bit body via the tooth body. The tooth body is connected to the hydraulic differential pressure drive mechanism via the elastic connector, forming an elastic support structure that allows the shaped PDC cutting tooth to move axially along the receiving cavity. The hydraulic differential pressure drive mechanism is located inside the drilling fluid flow channel and is sealed against the inner wall of the upper connector, used to convert the hydraulic pressure difference into driving force and transmit it to the shaped PDC cutting tooth.

3. The irregularly shaped PDC tooth bottom peripheral groove pressure relief drill bit according to claim 2, characterized in that, The hydraulic differential pressure drive mechanism includes a pressure-bearing component and a support block. One side of the support block is slidably connected to the side wall of the pressure-bearing component. The end of the toothed body is connected to the support block through an elastic connector. The elastic connector is used to support the pressure-bearing component, so that the pressure-bearing component abuts and seals against the inner wall of the upper connector. The pressure-bearing component moves downward under pressure, so that the internal space of the upper connector is connected to the drilling fluid flow channel.

4. The irregularly shaped PDC tooth bottom peripheral groove pressure relief drill bit according to claim 2, characterized in that, The elastic connector is a disc spring, which is used to store elastic potential energy when subjected to force and release it when unloaded, so as to realize the reciprocating motion of the irregular PDC cutting teeth.

5. The irregularly shaped PDC tooth bottom peripheral groove pressure relief drill bit according to claim 1, characterized in that, It also includes a pulse jet nozzle, which is located on the outer periphery of the bottom of the drill body, on one side of the impact unloading cutting assembly. The pulse jet nozzle relies on the fluid pressure fluctuation inside the drill cavity to output a pulse jet to clean the chips.

6. The irregularly shaped PDC tooth bottom peripheral groove pressure relief drill bit according to claim 1, characterized in that, When there are multiple unloading cutting components, they are spaced apart axially along the bottom end of the drill bit body.

7. The irregularly shaped PDC tooth bottom peripheral groove pressure relief drill bit according to claim 1, characterized in that, The tooth shape of the irregular PDC cutting tooth is a conical tooth, an axe-shaped tooth, or a conventional cylindrical tooth and combination thereof. The tooth shape is selected and determined based on the evaluation index system of grooving ability, intrusion ability, cutting ability and overall rock breaking efficiency.

8. An optimized design method for a non-circular PDC tooth bottom-hole peripheral groove pressure relief drill bit, applicable to the drill bit described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Establish a quantifiable evaluation index system for the grooving ability, penetration ability, cutting ability and overall rock breaking efficiency of irregular PDC cutting teeth; S2. Under different rock strength, formation pressure, hydrostatic column pressure and drilling speed conditions, the candidate tooth profiles are comprehensively sorted and matched; S3. Based on the sorting and matching results, determine the preferred tooth profile and the corresponding tooth inclination angle, cutting depth and tooth arrangement parameter combination of the impact unloading cutting component; S4. During drilling operations, the drilling fluid circulation forms a hydraulic pressure difference ΔP and its fluctuations, which drive the irregularly shaped PDC cutting teeth of the impact unloading cutting assembly to reciprocate axially periodically, applying an impact-cutting composite load to the rock around the bottom of the well, forming a circumferential stress unloading groove around the bottom of the well.

9. The optimized design method for a non-circular PDC tooth bottom-hole peripheral groove pressure relief drill bit according to claim 8, characterized in that, The evaluation formula for the tank-forming capacity in step S1 is: In the formula, For the groove depth, The average width of the groove. , The contribution of different geometric parameters to stress unloading, This represents the theoretical contact area of ​​the irregularly shaped PDC cutting teeth. The brittle rock-breaking characteristics of the tooth, i.e., the actual cutting area versus the theoretical value. The ratio; actual grooving area The formula is: In the formula, The mass of rock cuttings in the rock breaking experiment. For density, For cutting speed, For time; In step 1, the formula for evaluating intrusion capability is: In the formula, A and These represent the effective contact area and the average vertical force, respectively.

10. The optimized design method for a non-circular PDC tooth bottom-hole peripheral groove pressure relief drill bit according to claim 8, characterized in that, The formula for evaluating cutting capability in step S1 is: In the formula, This represents the effective contact area between the irregularly shaped PDC cutting teeth and the rock. This represents the average cutting force. In step S1, the overall rock-breaking efficiency is quantifiable using the MSE (Mean Separation Efficiency) method to evaluate the overall rock-breaking efficiency of different types of PDC (Programmable Dental Cavity) teeth. The formula is as follows: In the formula, and These represent the lateral and vertical displacements of the tooth between the two sampling points, respectively. The volume of rock crushing is determined based on the number and corresponding dimensions of the crushing units. and These are two consecutive horizontal cutting force sampling points. and For two consecutive vertical intrusion force sampling points, n This represents the total number of sampling points. i For a single sampling point.

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