Drilling speed increasing device

A drilling speed-enhancing device has an outer cylinder a rotary main shaft arranged in an inner chamber of the outer cylinder and configured to rotate around its own axis; an output main shaft arranged below the rotary main shaft and configured to be driven by the rotary main shaft to rotate around its own axis, a lower end of the output main shaft extending out of the inner chamber of the outer cylinder for connecting with a drilling bit of a dual-drive drilling tool; and a percussion generator arranged between the output main shaft and the outer cylinder. The percussion generator can drive the outer cylinder and the rotary main shaft to move upward relative to the output main shaft, so that under action of WOB, the rotary main shaft and the outer cylinder move downward to generate impact on the output main shaft.

CROSS REFERENCE OF RELATED APPLICATION

This application is a U.S. national stage entry of PCT International Application No. PCT/CN2020/114861, filed on Sep. 11, 2020, which claims the priority of Chinese patent application No. 201911294230.2, entitled “Drilling Speed Increasing Device,” and filed on Dec. 16, 2019, the entire content of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to the technical field of oil and gas well drilling, in particular to a drilling speed-enhancing device.

TECHNICAL BACKGROUND

With the rapid development of the oil industry, people's demand for oil is ever growing. The exploration and exploitation of oil and gas resources are gradually developing toward deep formations, so that the drilling speed enhancement in deep/ultra-deep wells has always been a technical problem confronted in the developments of well drilling technology. Rotary percussion drilling technology uses various percussive tools to generate high-frequency impacting loads, which can result in volumetric fracture of rocks and thus improve the rock-breaking effect.

Research shows that with a combination of the dual-drive drilling technology and the rotary percussion drilling technology can achieve volumetric fracture of rocks under high-frequency impact and high-speed rotary cutting, so that the speed-enhancing effect will be more obvious.

SUMMARY OF THE INVENTION

In view of the above problem, the present invention proposes a drilling speed-enhancing device, which can be arranged on a dual-drive drilling tool to generate high-frequency impacting loads by the drilling bit, resulting in volumetric fracture of rocks to improved rock-breaking efficiency.

According to the present invention, a drilling speed-enhancing device is proposed, comprising: an outer cylinder; a rotary main shaft arranged in an inner chamber of the outer cylinder and configured to rotate around its own axis; an output main shaft arranged below the rotary main shaft and configured to be driven by the rotary main shaft to rotate around its own axis, a lower end of the output main shaft extending out of the inner chamber of the outer cylinder for connecting with a drilling bit of a dual-drive drilling tool; and a percussion generator arranged between the output main shaft and the outer cylinder, and configured to drive the outer cylinder and the rotary main shaft to move upward relative to the output main shaft, so that under action of WOB, the rotary main shaft and the outer cylinder move downward to generate impact on the output main shaft.

In one embodiment, the percussion generator comprises: an upper cam arranged around an outer wall of the output main shaft in a clearance fit, and fixed relative to the outer cylinder in an axial direction and a circumferential direction, a lower end of the upper cam being provided with driven teeth; and a lower cam arranged around the outer wall of the output main shaft, and provided at an upper end thereof with driving teeth, which form with the driven teeth a conjugate set of cam teeth. During rotation of the output main shaft the lower cam is driven to rotate, and the driving teeth act on the driven teeth to enable that the upper cam moves reciprocally in the axial direction and acts on the outer cylinder.

In one embodiment, a lower cam seat is fixedly arranged around the output main shaft, and an outer wall of the lower cam seat is provided with engaging teeth protruding therefrom, each clamping tooth extending radially outward in a respective one of engaging slots formed on a wall of the lower cam, an upper end face of the lower cam seat abutting against a first step surface formed in an inner chamber of the lower cam.

In one embodiment, a lower end face of the lower cam extends axially over a lower end face of the lower cam seat to abut against a damping assembly arranged around the output main shaft, a lower end face of the damping assembly being in contact with a limiting sleeve arranged on the output main shaft.

In one embodiment, the damping assembly comprises two retaining rings axially spaced from each other, and a disc spring arranged between said two retaining rings, an upper one of the retaining rings abutting against the lower end face of the lower cam while a lower one of the retaining rings abutting against the limiting sleeve.

In one embodiment, the outer cylinder is of a combined structure, and comprises an upper joint and a cylindrical body connected to a lower end of the upper joint via thread, an outer wall of the upper cam being sandwiched between a lower end face of the upper joint and a second step surface formed on the cylindrical body, and an upper end face of the upper cam being connected with the lower end face of the upper joint via teeth.

In one embodiment, an upper end of the output main shaft extends into an inner chamber of the rotary main shaft and forms a circumferential snap-fit connection therebetween. An upper end face of the output main shaft is opposite to a third step surface formed on an inner side of the rotary main shaft, wherein an axially extending limiting groove is arranged on an outer wall of the output main shaft, and a limiting key is fixed on the rotary main shaft to extend radially into the limiting groove.

In one embodiment, a wall of the rotary main shaft is provided with a step hole passing therethrough, the limiting key radially extending in the step hole to be clamped therewith. A ferrule radially abutting against the limiting key is fixed on the outer wall of the rotary main shaft.

In one embodiment, a tungsten carbide (“TC”) bearing assembly is provided between the outer cylinder and the output main shaft. An inner ring of the TC bearing assembly is connected with the output main shaft in an interference fit, a bearing shell of the TC bearing assembly is fixedly arranged on the lower end of the outer cylinder, and an inner-ring locking nut of the TC bearing assembly is fixedly arranged around the output main shaft, and located above the inner ring of the TC bearing assembly.

In one embodiment, a first seal is provided between the outer cylinder and the rotary main shaft, and a second seal is provided between the inner ring and the bearing shell of the TC bearing assembly. Lubricating oil is filled in a spaced defined by the first seal, the second seal, the outer cylinder, the rotary main shaft and the output main shaft.

Compared with the prior arts, the present invention has the advantages as follows. The drilling speed-enhancing device can be arranged in a drilling tool, such as a dual-drive drilling tool. Under the action of the percussion generator, the output main shaft will be subjected to axial impact, which can be transmitted to the drilling bit arranged at the lower end of the a output main shaft, so that the drilling bit can generate impact on the formation. This compound action facilitates to break up the formation rapidly, thus increasing drilling efficiency and reducing drilling cost.

In the drawings, the same reference numerals are used to indicate the same components. The drawings are not drawn to actual scale.

DETAILED DESCRIPTION OF EMBODIMENTS

The present invention will be further described below in conjunction with the accompanying drawings.

FIG.1schematically shows one embodiment of a drilling speed-enhancing device100according to the present invention. The drilling speed-enhancing device100can be applied to a dual-drive drilling tool to generate high-frequency impact for improving rock-breaking efficiency. Specifically, the drilling speed-enhancing device100includes an outer cylinder, a rotary main shaft4, an output main shaft7, and a percussion generator. The outer cylinder1is cylindrical and connected with a housing of a downhole power motor of the dual-drive drilling tool, mainly for connection and force transmission. The rotary main shaft4is arranged in an inner chamber of the outer cylinder1, and connected with a rotating shaft of the downhole power motor of the dual-drive drilling tool to be driven to rotate around its own axis, for transmitting rotational power. The output main shaft7is arranged at a lower end of the rotary main shaft4, and configured to rotate around its own axis when being driven by the rotary main shaft4, for transmitting rotational power to a drilling bit arranged at a lower end of the output main shaft7. The percussion generator is provided between the output main shaft7and the outer cylinder. The percussion generator can actuate the center of gravity (i.e., neutral point) of a combination consisting of the outer cylinder, the rotary main shaft4, and the upper drilling string fixedly connected therewith (collectively referred to as driven assembly) to move upward relative to the output main shaft7, that is, enable the neutral point of the whole drilling string to move upward. And under the action of the WOB, the center of gravity of the driven assembly (that is, the neutral point of the drilling string) moves down to impact on the output main shaft7, so as to form an instantaneously high “percussive WOB”, like “churn drilling”, and further provide impact energy for the drilling bit. Therefore, the drilling speed-enhancing device100of the present invention can be applied to the dual-drive drilling tool to generate high-frequency reciprocating percussive WOB on the formation while driving the drilling bit to rotate in a high speed by the dual-drive power. This compound action facilitates to break up the formation rapidly, thus increasing drilling efficiency and reducing drilling cost.

In one embodiment, the percussion generator has an upper cam8, a lower cam9, and a lower cam seat10. As shown inFIGS.5A and5B, the upper cam8per se is cylindrical, and arranged around an outer wall of the output main shaft7with a gap. The upper cam8is fixed relative to the outer cylinder in an axial direction and a circumferential direction. As shown inFIGS.7A and7B, the lower cam seat10per se is cylindrical, and fixedly arranged around the output main shaft7. For example, the lower cam seat10is screwed on the output main shaft7by a left-handed trapezoidal thread. Moreover, on the threaded connection area between the lower cam seat10and the output main shaft7, the lower cam seat10and the output main shaft7are engaged with each other through step surfaces, so that the output main shaft7can restrict the axial position of the lower cam seat10. Further, as shown inFIGS.6A and6B, the lower cam9per se is cylindrical, and arranged around an outer wall of the lower cam seat10. The outer wall of the lower cam seat10is provided with engaging teeth27-2radially protruding out. At the same time, the wall of the lower cam9is provided with engaging slots27-1. Upon assembly, each of the engaging teeth27-2extends radially into a corresponding one of the engaging slots27-1, thus forming a snap-fit connection between the lower cam9and the lower cam seat10in the circumferential direction. Therefore, the output main shaft7can drive the lower cam seat10into rotation through the engagement between step surfaces, while the rotation of the lower cam seat10can drive the lower cam9into rotation through the snap-fit connection. For example, a plurality (say, three, four, or five, etc.) of the engaging teeth27-2may be arranged at intervals in the circumferential direction, in order to achieve uniform transmission of torque. In addition, a first step surface91is arranged in an inner chamber of the lower cam9to abut against an upper end face of the lower cam seat10, so that the downward axial movement of the lower cam9can be restricted by the lower cam seat10. At the same time, during the movement of the upper cam8pushed by the lower cam9, the lower cam9presses against the lower cam seat10, so that the axial force received by the lower cam9will be transmitted downward through the lower cam seat10to the output main shaft7, and finally to the drilling bit. The above structure adopts the lower cam9and the lower cam seat10that are separate from each other, so that the structure is simple, the processing is convenient, the installation and replacement are easy, and the use cost is reduced.

The outer cylinder consists of two parts, i.e., an upper joint1and a cylindrical body14disposed at a lower end of the upper joint1. The upper joint1is directly connected with the housing of the downhole power motor of the dual-drive drilling tool. An upper end of the cylindrical body14is arranged around the outer wall of the upper joint1, and connected therewith by means of inclined threaded surfaces. A second step surface25is arranged on an inner wall of the cylindrical body14in a manner of opposite to a lower end face of the upper joint1extending into the inner chamber of the cylindrical body14. The outer wall of the upper cam8at the lower end thereof is provided with a fourth step surface81, so that the upper cam8radially extends to be partially sandwiched between the lower end face of the upper joint1and the second step surface25. Accordingly, the second step surface25and the fourth step surface81together forms an axial locking structure. With the above arrangement, the axial position of the upper cam8can be restricted by the outer cylinder. Moreover, the upper end face of the upper cam8and the lower end face of the upper joint1are engaged with each other through teeth. Specifically, multiple sector-shaped teeth24circumferentially spaced from each other extend from the upper end face of the upper cam8, and multiple sector-shaped slots (not shown) circumferentially spaced from each other are formed in the lower end face of the upper joint1. Each tooth24can be inserted into a corresponding one of the sector-shaped slots to form a snap-fit connection. With the above arrangement, the rotation of the upper cam8can be restricted by the upper joint1. In the above arrangement, the upper cam8makes full use of its axial engagement with the upper joint1and the cylinder body14to provide a compact structure, so that the axial length of the drilling speed-enhancing device100is shortened, and the upper cam8can be restricted in the axial direction and also prevented from dropping-off.

Driven teeth82are arranged on the lower end of the upper cam8, and each have a tooth surface substantially facing downward. Correspondingly, driving teeth92are arranged on the upper end of the lower cam9, and each has a tooth surface substantially facing upward. Upon assembly, the driven teeth82and the driving teeth92are opposite and engaged with each other to form a conjugate set of cam teeth. Each of the driven teeth82and the driving teeth92may be generally configured as a wave-like shape as shown inFIGS.5A and6B. In operation, the lower cam9starts to rotate clockwise when being driven by the output main shaft7. A pushing-up stroke will start when troughs of the driven teeth82face toward peaks of the driving teeth92. Since the upper cam8is axially sandwiched between the upper joint1and the cylinder body14and also circumferentially locked with the upper joint1, the upper cam8can actuate the center of gravity of a combination consisting of the outer cylinder, the rotary main shaft4, and the upper drilling string fixedly connected therewith and located below the neutral point (collectively referred to as driven assembly) to move upward relative to the lower cam9. When the peaks of the driven teeth82face toward the peaks of the driving teeth92while the troughs of the driven teeth82face toward to the troughs of the driving teeth92, the center of gravity of the combination consisting of the upper cam82, the outer cylinder, the rotary main shaft4, and the upper drilling string fixedly connected therewith and located below the neutral point (collectively referred to as driven assembly) reaches its highest point. At this time, the axial distance between the peaks of the upper cam8and the troughs of the lower cam9is D, and that between the upper end face of the output main shaft7and the third step surface41(described in detail later) of the rotary main shaft4is C, wherein D>C. After that, the center of gravity of the driven assembly (that is, the neutral point of the drilling string) suddenly moves downward, that is, the driven assembly impacts downward under the action of the WOB. Since D>C, the impact acts on the upper end face of the output main shaft7, so that impact energy will be transmitted to the downstream drilling bit through the output main shaft7, thus forming an instantaneously high “percussive WOB”, like “churn drilling”, and further providing the impact energy for the drilling bit. In this manner, the drilling bit can impact downward on the formation during rotating-while-drilling. Subsequently, a new stage of engaging-rotating-pushing begins between the teeth of the upper cam8and the lower cam9, and the WOB returns to its normal value. That is, the neutral point of the drilling string returns to its original position, so that a next stage of lifting stroke begins. In this manner, a periodic change of the WOB is repeated in cycle.

In a preferred embodiment, each of the wave-like driven teeth82and driving teeth92comprises an upward tooth segment and a downward tooth segment connected thereto. As shown inFIG.6A, the upward tooth segment of each of the driving teeth92is inclined in the direction opposite to the rotational direction of the lower cam9, while the downward tooth segment of each of the driving teeth92is inclined downward in said direction opposite to the rotational direction of the lower cam9. The inclination of the upward tooth segment is relatively gentle, and for example, can be designed according to the required height of the stroke, and is by no means limited in the present invention. By contrast, the inclination of the downward tooth segment is relatively steep, and for example, can be a vertical surface, so that the upper cam8can move towards the lower cam9with a relatively high speed. The driving teeth92rotates clockwise with a certain rotational speed, which ensures that the downward tooth segment of the driven teeth82would not touch the downward tooth segment of the driving teeth92, thus further ensuring that the movement of the upper cam8towards the lower cam9is a free fall movement. That is, the upper cam8can move upstream relative to the lower cam9at a relatively slow speed, but move downward at a relatively fast speed. In the circumferential direction, a plurality of driven teeth82and a plurality of driving teeth92can be provided as required, and at the area where the downward tooth segment and the upper tooth segment of each driven tooth82are connected and at the area where the lower tooth segment and the upper tooth segment of each driving tooth92are connected, a transition fillet is provided for eliminating stress concentration and also buffering the movement between the upper cam8and the lower cam9.

A damping assembly is arranged around the output main shaft7. The lower end face of the lower cam9extends axially over the lower end face of the lower cam seat10to abut against the damping assembly. The lower end face of the damping assembly abuts against a limiting sleeve arranged on the output main shaft7. It should note that the limiting sleeve is mainly used to limit the damping assembly axially. However, in order to optimize the structure, it is not necessary to provide an additional limiting sleeve on the output main shaft; in this case, an inner ring nut of a TC bearing fixedly arranged on the output main shaft7can serve as the limiting sleeve. That is to say, in the axial direction, the damping assembly is located between the lower cam9and the limiting sleeve. After one single impact is completed, the upper cam8will exert an impact force to the lower cam9at the moment when the upper tooth segment of the driven teeth82touches and meshes with the upper tooth segment of the driving teeth92. By arranging the damping assembly, the impact force exerted on the lower cam9is transmitted to the damping assembly. That is, the damping assembly can absorb the energy received by the lower cam9, and slow down the hard impact between the upper cam8and the lower cam9, so as to protect the upper cam8and the lower cam9and prolong the service life of both.

In a preferred embodiment, the damping assembly includes two retaining rings11axially spaced from each other, and a disc spring12arranged between said two retaining rings11. An upper retaining ring11is in contact with the lower end face of the lower cam9, while a lower retaining ring11is in contact with the limiting sleeve. For example, the disc spring12is a Mubeu disc spring, in a form of pairing two single pieces together. The disc spring12has a pre-compressed amount initially set as N mm, which corresponds to a pre-tightening force of T kN. That is, when the impact force F received by the lower cam9is in the range of 0-T, the teeth of the upper cam8and the lower cam9will not be damaged.

A third step surface41is arranged on the inner surface of the rotary main shaft4, so that the size of the inner chamber of the rotary main shaft4is increased at the lower end thereof. During installation, the upper end of the output main shaft7extends axially upward into the inner chamber of the rotary main shaft4, so that the upper end face thereof is opposite to the third step surface41. A circumferential snap-fit connection is formed between the output main shaft7and the rotary main shaft4. Specifically, as shown inFIGS.4A and4B, the portion of the output main shaft7extending into the rotary main shaft4is shaped as a polygonal column, e.g., an octagonal column. Correspondingly, the inner chamber of the lower end of the rotary main shaft4below the third step surface41is configured as having a polygonal cross section. Therefore, the above arrangement realizes a positive connection between the rotary main shaft4and the output main shaft7, so that the rotary main shaft4can drive the output main shaft7in rotation. This arrangement can also ensure that the rotary main shaft4and the output main shaft7can move relative to each other in the axial direction, thereby ensuring that the rotary main shaft4can impact the output main shaft7to provide rock-breaking impact force. It should note that in order to avoid stress concentration, in the octagonal column where the inner wall of the rotary main shaft4is in engagement with the outer wall of the output main shaft7, adjacent sides of the octagonal column are connected with each other with a rounded corner, thus ensuring smooth connection.

Of course, the axial position of the output main shaft7relative to the rotary main shaft4should be further restricted, in order to prevent the output main shaft7from dropping-off during tripping operations. Specifically, a limiting groove22extending axially is arranged on the outer wall of the output main shaft7. For example, multiple pairs (e.g., one pair, two pairs, three pairs or four pairs) of limiting grooves22may be arranged in the circumferential direction, and two limiting grooves22of each pair are distributed relative to each other in order to ensure force balance. Correspondingly, a step hole42passing through the rotary main shaft4is provided on the rotary main shaft4, and has a diameter of the radially outer portion larger than that of the radially inner portion. The limiting key5is arranged in the step hole42. Correspondingly, as shown inFIGS.3A and3B, the main body of the limiting key5is elongated and extends along the axial direction, so as to improve the shear strength. In the radial direction, the limiting key5is formed as a step. For example, a radially outer portion of the limiting key5is an A-type ordinary flat key, and a radially inner portion thereof is a step key formed by expanding said A-type ordinary flat key outward. Accordingly, the cross-sectional size of the radially outer portion is larger than that of the radially inner portion. Therefore, the limiting key5is arranged in the step hole42, with the radially outer portion having a large cross-sectional size being clamped at the step hole while the radially inner portion extending radially inward into the limiting groove22. A ferrule3is fixed on the outer wall of the rotary main shaft4. The ferrule3can radially restrict the limiting key5to prevent it from falling out from the step hole42. During the axial movement of the output main shaft7relative to the rotary main shaft4, the limiting key5can move axially within the limiting groove22to a limited extent, so as to restrict the further relative movement of the output main shaft7. For example, during tripping operations, the output main shaft7drives the lower cam9or the like to fall down relative to the rotary main shaft4or the like, so that a groove wall surface at the upper end of the limiting groove22is received on the limiting key5. In this manner, the limiting key5can realize an anti-drop effect.

As shown inFIGS.2A and2B, the inner surface of the ferrule3has two portions of different inner diameters, wherein the portion with a relatively large inner diameter is provided with thread to form a fixed connection with the rotary main shaft4. A step surface connecting said two portions forms a snap-fit connection with the rotary main shaft4. A downward inclined slope of 60 degrees is provided between the step surface connecting said two portions and the inner wall surface of the portion of the ferrule3with a relatively small inner diameter. In this manner, when the ferrule3is mounted, the screwing depth of the thread can be limited, and the ferrule3can be better matched with the rotary main shaft4via the step surface, thus preventing structural interference.

It should note that when the output main shaft7is seated on the limiting key5during tripping operations, the driven teeth82and the driving teeth92will be separated from each other by a certain distance in the axial direction, thus ensuring that the driven teeth82cannot be in contact with the driving teeth92in blank rotation. In this manner, the safety of the teeth can be improved. Moreover, after correct installation, the inner end face of the limiting key5has a certain distance in the radial direction from the bottom wall of the limiting groove22of the output main shaft7, wherein the value of said distance should meet the requirement on the torsion angle of the output main shaft7, thus preventing the limiting key5from being sheared during rotation of the output main shaft7. This arrangement ensures the safety of the limiting key5in use, and increases its service life. Moreover, when the WOB is applied after the drilling tool touches the bottom of the well, the wall surface at the lower end of the limiting groove22will not contact the limiting key5during the upward movement of the output main shaft7relative to the rotary main shaft4. In this manner, the limiting key5is prevented from being impacted, thus improving its safety in use.

A TC bearing assembly is provided between the outer cylinder and the output main shaft7. An inner ring18of the TC bearing assembly is connected with the output main shaft7by an interference fit. A bearing shell15of the TC bearing assembly is located outside the inner ring18of the TC bearing assembly and engaged therewith, and fixedly arranged at the lower end of the outer cylinder. An inner-ring locking nut13of the TC bearing assembly is fixedly arranged around the output main shaft7, and located at an upper end of the inner ring18of the TC bearing assembly. This arrangement ensures a smooth rotation of the output main shaft7relative to the outer cylinder. In a specific embodiment, the bearing shell15of the TC bearing assembly and the cylindrical body14are connected with each other through drill-pipe joint threads arranged on inclined contact surfaces therebetween, so as to realize a fixed connection. An inner side of the inner-ring locking nut13of the TC bearing assembly is provided with a left-handed trapezoidal female thread, which is engaged with the left-handed trapezoidal male thread on the output main shaft7, for tightening the inner ring18of the TC bearing assembly located downstream.

A positioning sleeve19is provided at the lower end of the inner ring18of the TC bearing assembly. For example, the positioning sleeve19may have a conical cross-section. After the positioning sleeve19is arranged around the output main shaft7, the upper end of the positioning sleeve19is in contact with the inner ring18of the TC bearing assembly, while the lower end thereof is in contact with a fifth step surface71formed on the output main shaft7. The positioning sleeve19is used to axially press the inner ring18of the TC bearing assembly.

In one embodiment, a first seal is provided between the outer cylinder and the rotary main shaft4. The first seal can be a rotary seal ring2, e.g., a RDI profile rotary seal ring by Hunger DFE GmbH. Additionally, a second seal is provided between the inner ring18of the TC bearing assembly and the bearing shell15of the TC bearing assembly. Also, the second seal may be in the form of a double-pass seal, and specifically a GDSA profile piston seal16by Hunger DFE GmbH and a RODA profile rotary seal17by Hunger DFE GmbH located therebelow. A sealed chamber is formed in an area defined by a portion of the outer cylinder from the first seal and the second seal, the rotary main shaft4, and the output main shaft7. Lubricating oil is poured into the sealed chamber, in order to provide an oil-sealing environment for the upper cam8, the lower cam9, the disc spring12or the like arranged therein, thus greatly prolonging their service life. A third sealing ring6is further provided between the rotary main shaft4and the output main shaft7to achieve sealing therebetween. The third sealing ring6is located below the limiting groove22.

The specific working process of the drilling speed-enhancing device100according toFIGS.1to7Bis described in detail as follows.

First, the above-mentioned drilling speed-enhancing device100is arranged on a dual-drive drilling tool, wherein the outer cylinder1is connected with the housing of the downhole power motor of the dual-drive drilling tool, while the rotary main shaft4is connected with the rotating shaft of the downhole power motor of the dual-drive drilling tool. A drilling bit is arranged at the lower end of the output main shaft7.

Then, the dual-drive drilling tool provided with the drilling speed-enhancing device100is lowered into the well to be drilled. During this process, the output main shaft7, the lower cam9, the damping assembly, the inner-ring locking nut13and the inner ring18of the TC bearing assembly, the positioning sleeve19and the drilling bit move downward together relative to the outer cylinder, and further downward movement can be prevented since the output main shaft7is seated on the upper end face of the limiting key5. At this time, the teeth of the upper cam8are not in contact with the teeth of the lower cam9, so as to ensure that the teeth will not collide with each other.

When the drilling bit of the drilling tool touches the bottom of the well, the drilling tool is further lowered to apply the WOB, so that the output main shaft7drives the lower cam9or the like to move axially upward relative to the outer cylinder and the rotary main shaft4, until the lower cam9and the upper cam8are in cooperation. At this time, since the upward tooth segments of the driven teeth82of the upper cam and those of the driving teeth92of the lower cam are engaged with each other, there is a certain axial distance, which less than C, between the upper end face20of the output main shaft7and the third step surface41of the rotary main shaft4.

Then, drilling operation may start. The rotary main shaft4is rotated by the rotating shaft of the downhole power motor, so as to drive the output main shaft7in rotation to supply rotational power to the drilling bit arranged at the lower end of the output main shaft7. At the same time, the rotating output main shaft7drives the lower cam9to rotate together, which axially pushes up the upper cam8to lift the outer cylinder and the rotary main shaft4. After reaching the highest point, the outer cylinder and the rotary main shaft4will, under the action of the WOB, impact downward on the upper end face of the output main shaft7. The axial reciprocating impact acts on the output main shaft7, and is finally transmitted to the drilling bit. As a result, when the drilling bit rotates, reciprocating impact will be generated to improve rock-breaking efficiency, which provides new technical means for efficient drilling in hard and complex formations for ultra-deep oil wells, geothermal wells, and dry-hot rock wells.

In the present invention, it should be emphasized that the outer wall of the rotary main shaft4consists of three sections for axially positioning the ferrule3, while the inner wall of the rotary main shaft4consists of two sections, that is, includes the third step surface42so that the inner diameter of the upper section is smaller than that of the lower section. The inner chamber of the upper section is mainly used for conveying drilling fluid, while that of the lower section is mainly used for arranging the output main shaft7therein. The rotary main shaft with the above arrangement has an optimized structure, and ensures good transmission of power.

The outer wall of the output main shaft7consists of multiple sections from top to bottom, for example, eight sections. On the outer wall of the output main shaft7, the outer diameter of the output shaft7can be increased gradually from top to bottom through arranging step surfaces, which can engage and connect with different members. Specifically, from top to bottom, the diameter of the first segment is relatively small to ensure that the output main shaft7is guided to be inserted into the rotary main shaft4. The second section can guarantee to form a circumferential snap-fit connection with the rotary main shaft4for ensuring power transmission. The third section is used to arrange the upper cam8, the lower cam9and the lower cam seat10thereon, for achieving coaxial orientation. The fourth section is used to mount the lower cam seat10with the left-handed trapezoidal thread. The fifth section is used to arrange the damping assembly. The sixth section is used to mount the inner-ring locking nut13of the TC bearing assembly with the left-handed trapezoidal male thread. The seventh section is used to arrange the inner ring18of the TC bearing assembly and the locating sleeve19. The eighth section is provided in its inner chamber with thread for connection with the drilling bit. For example, transition slopes may be provided between the above adjacent sections.

Although the present invention has been described with reference to the preferred embodiments, various modifications may be made and equivalents may be substituted for components thereof without departing from the scope of the present invention. In particular, under the condition that there is no structural conflict, each technical feature mentioned in each embodiment can be combined in any manner. The present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.