Purely mechanical rotary drilling tool and method suitable for horizontal and horizontal branch drilling

Abstract

The present invention relates to a pure mechanical rotary guide drilling tool and method suitable for horizontal and horizontal branch drilling, belonging to the field of drilling tool development, including a drill string, a weight-biasing mechanism and a single-bend screw drill tool connected in sequence, the weight-biasing mechanism including a connecting bearing, a weight-biasing mechanism housing and a weight block; the drill string is connected to the inside of the connecting bearing, the outside of the connecting bearing is fixedly connected to the upper end of the weight-biasing mechanism housing, and a sealing ring is provided at the connection between the connecting bearing and the weight-biasing mechanism housing; the lower end of the weight-biasing mechanism is fixedly connected to the stator of the single-bend screw drill tool, and the lower end of the single-bend screw drill tool is provided with a bend angle, which is always kept biased toward the high side of the wellbore, and is used to balance the downward inclination trend of the wellbore trajectory caused by the deadweight of the drill tool. The present invention is a pure mechanical device with high reliability and simple manufacturing. It can avoid the failure problem of electronic components of deep-layer high-temperature rotary guide systems and reduce the cost of drilling unconventional oil and gas horizontal wells; at the same time, the drill string is in a fully rotating state, which solves the problem of large friction torque in long horizontal section horizontal well drilling.

Description

Technical Field

[0001] The invention relates to a pure mechanical rotary guide drilling tool and method suitable for horizontal and horizontal branch drilling, belonging to the technical field of drilling tool development. Background Art

[0002] As the difficulty of oil and gas exploration and development increases, directional drilling technology can adjust the drilling trajectory profile while drilling, thereby achieving refined drilling monitoring and control, and plays an irreplaceable and important role in the exploration and development of high-difficulty oil and gas reservoirs and complex fault block oil and gas reservoirs. At present, the core technology of rotary steering is still mastered by foreign countries, and only a small number of domestically developed rotary steering systems have passed the test and been applied to field operations. Due to the failure to master the core technology, they are basically localized by imitating the advanced foreign rotary steering systems, so the pace is slow.

[0003] Domestic rotary steering systems are mainly divided into push-type rotary steering systems and pointing-type rotary steering systems. The push-type rotary steering system achieves guidance by applying a bias force to the sleeve near the drill bit, while the pointing-type rotary steering system gives a bias force to the mandrel at a certain distance from the drill bit, so that the drill bit and the center line of the sleeve form an angle. The guiding tool has a mechanical structure inside that can offset the drill bit, thereby making the drill bit drill in the preset direction.

[0004] Chinese patent document CN202011124111.5 includes an upper housing, a mandrel, a lower housing and a drill bit. The start and stop of the inner eccentric barrel and the outer eccentric barrel are controlled by a tooth-type electromagnetic clutch, thereby changing the drilling direction of the drill bit. No additional device is required to provide power for guidance, which causes less damage to the well wall and can ensure better wellbore quality. However, due to the complexity of the internal control system, the probability of accident risks during the operation of the equipment underground is increased.

[0005] Chinese patent document CN202211289084.6 discloses a fully mechanical rotary steerable drilling tool, including a spindle, a bearing assembly, a lower bearing seat, a push piston, a piston seat, a lower torsion spring, an upper bearing seat, an upper spindle joint, a displaced ring, an axial piston, an upper joint, a limit ring, a filter ring, an upper spring, a weight block, an outer cylinder, an impeller, an upper disc valve and a lower disc valve. It solves the problems of insufficient high temperature resistance of existing rotary steerable drilling tools and failure of drilling tools caused by easy damage of electronic components, and can meet the drilling needs under high temperature and high pressure conditions in deep wells. However, the coordination between the disc valves is unstable, and there is a risk of failure of the drilling tools downhole when the system is working.

[0006] Through the above analysis, the current domestically developed rotary steerable system is more inclined to the overall optimization of electromechanical control devices. The main drawback is that the complex electromechanical devices are prone to failure in the high temperature and high pressure environment underground, resulting in high production and development costs and short equipment life. Nowadays, all major oil fields are facing the difficulty of long horizontal section horizontal drilling. The development of a set of low-cost rotary steerable drilling tools is urgent for various oil fields to overcome the difficulty of long horizontal section horizontal wells. Summary of the invention

[0007] In view of the technical deficiencies, the present invention provides a pure mechanical rotary guide drilling tool and method suitable for horizontal and horizontal branch drilling to solve the current problems of large friction torque, slow drilling speed or pressure in long horizontal section horizontal well drilling. The present invention does not use electronic components, is simple to manufacture, has extremely low cost, and is convenient to use. It can effectively solve the failure problem of electronic components in deep high-temperature rotary guide systems and reduce the loss caused by the burial of rotary guide systems for unconventional oil and gas horizontal well drilling. The present invention adds a weight-biasing mechanism, which can keep the screw tool face of the single-bend screw stable while rotating the drill string, saving the manufacturing cost of the drilling tool. It can be used in various oil fields to drill long horizontal section horizontal wells and branch wells, has good application and promotion value, and has great market potential.

[0008] The technical solution of the present invention is as follows:

[0009] On the one hand, the present invention provides a purely mechanical rotary guide drilling tool suitable for horizontal and horizontal branch drilling, including a drill string, an eccentric weight mechanism and a single-bend screw drill tool connected in sequence from top to bottom, the eccentric weight mechanism including a connecting bearing, an eccentric weight mechanism housing and an eccentric weight block; the drill string is connected to the inside of the connecting bearing, the outside of the connecting bearing is fixedly connected to the upper end of the eccentric weight mechanism housing, and a sealing ring is provided at the connection between the connecting bearing and the eccentric weight mechanism housing; the lower end of the eccentric weight mechanism is fixedly connected to the stator of the single-bend screw drill tool, such as by welding or buckling, and the lower end of the single-bend screw drill tool is provided with a bend angle, and the bend angle always remains biased toward the high side of the wellbore, which is used to balance the downward inclination trend of the wellbore trajectory caused by the deadweight of the drill tool. The angle between the gravity stabilization surface of the eccentric weight mechanism and the screw tool surface of the single-bend screw needs to be set at a relative angle according to different working modes when connected.

[0010] Preferably, the cross-section of the eccentric weight block is symmetrical on both sides and has a fan-shaped structure. The eccentric weight block and the outer shell of the eccentric weight mechanism are rigidly connected. The eccentric weight block and the outer shell of the eccentric weight mechanism can be integrally processed with rigid material, or the two materials (the eccentric weight block has a larger specific gravity) can be processed separately and then rigidly connected. The fan-shaped area where the eccentric weight block is located can also be poured with high-density material (such as lead) so that the eccentric weight block and the outer shell of the eccentric weight mechanism always remain relatively still when the gravity is in dynamic balance.

[0011] The center of the eccentric weight mechanism is a tubular structure to ensure that the drilling fluid flows through the drill string, the connecting bearing, the eccentric weight mechanism and the single-bend screw drilling tool to reach the drill bit.

[0012] Preferably, the connecting bearing is used to transmit the axial force generated by the drill string, and the sealing ring can be a sealing ring of commonly used standard specifications, such as an O-ring, an X-ring, a U-ring, etc.

[0013] Preferably, the bending angle of the lower end of the single-bent screw drill, that is, the angle δ between the axes of the left and right sections of the bent screw drill is preferably 1.5°.

[0014] On the other hand, the present invention provides a working method of the above-mentioned pure mechanical rotary guide drilling tool suitable for horizontal and horizontal branch drilling, wherein the longitudinal section of the eccentric weight mechanism is a gravity stable surface α, the surface where the single-bend screw drill tool and the bend angle are located is a screw tool surface β, and the lower end of the eccentric weight mechanism is fixedly connected to the stator of the single-bend screw drill tool to ensure the consistency between the screw tool surface and the gravity stable surface of the eccentric weight mechanism; when in the drilling working condition, the eccentric weight mechanism housing and the eccentric weight block remain relatively stationary in the radial direction, and the rotation of the drill string drives the connecting bearing to rotate, thereby applying a positive (counterclockwise) torque to the eccentric weight mechanism housing; the drilling fluid flows in sequence The rotor and drill bit of the single-bend screw drill are driven to rotate through the drill string, connecting bearings, eccentric weight mechanism and single-bend screw drill to achieve drilling. The rock breaking of the drill bit will apply reverse torque to the stator of the single-bend screw drill and transmit it upward to the housing of the eccentric weight mechanism. The eccentric weight block applies positive torque to the housing of the eccentric weight mechanism under the action of its own weight. Since the housing of the eccentric weight mechanism is fixedly connected to the stator of the single-bend screw drill, the screw tool face β is kept stable under the combined action of the positive torque applied to the housing of the eccentric weight mechanism, the reverse torque applied to the stator of the single-bend screw drill and the positive torque applied to the housing of the eccentric weight mechanism under the action of its own weight.

[0015] The main function of the eccentric weight block in the present invention is to increase the weight of the lower half of the eccentric weight mechanism, so that the center of gravity of the entire eccentric weight mechanism is at a lower position, the lower part is heavier, and the overall stability is improved. The purpose of the eccentric weight block is that when the drill string rotates clockwise to generate a clockwise torque on the lower drilling tool assembly, the eccentric weight block gives the eccentric weight mechanism a counterclockwise torque under the action of its own weight, thereby maintaining the stability of the gravity stability plane α where the eccentric weight mechanism is located.

[0016] The rotor and the stator of the single-bend screw drill in the present invention are both structures inside the single-bend screw drill, and belong to the existing conventional structure.

[0017] Further preferably, in the present invention, after the bend angle of the single-bend screw drill bit is balanced by the eccentric weight mechanism, the screw tool face β does not change with the rotation of the drill string and always remains stable; in the prior art, during horizontal drilling in a long horizontal section, due to the influence of the drill bit's own weight, the wellbore trajectory always maintains a downward trend in inclination. During horizontal drilling in a long horizontal section, the present invention maintains the screw tool face β in the high-side direction, and utilizes the mutual balance between the inclination-increasing effect caused by the upward bend of the bend angle in the single-bend screw drill bit and the inclination-reducing effect caused by the screw's own weight, so that the well inclination angle can be maintained at 90° during horizontal well drilling.

[0018] Since the main function of the single-bend screw drill bit when drilling a long horizontal section horizontal well is to balance the inclination-increasing effect caused by the upward bend of the single-bend screw with the inclination-reducing effect caused by the deadweight of the lower drill bit assembly, the requirements for curved wells are not high; single-bend screw drill bits usually select a small bend angle, such as 1.5°, which is suitable for relatively straight wells with low requirements for curved drilling. This design makes the screw easier to operate in straight well sections; at the same time, the rotation of the drill string itself can effectively prevent the accumulation of cuttings during horizontal drilling of long horizontal sections, which causes problems such as large friction torque, slow drilling speed or support pressure.

[0019] Further preferably, under horizontal branch drilling conditions, the single-bend screw drill tool is swung to different angles (the single-bend screw drill tool is rigidly connected to the eccentric weight mechanism, and the screw tool face of the single-bend screw drill tool is kept stable by utilizing the combined effect of the eccentric weight mechanism's own torque and the additional torque of the drill string and drill bit), and the angle between the gravity stability plane α and the screw tool face β is θ. When θ is less than 90° or greater than 270°, the drilling presents the wellbore trajectory of a branch well.

[0020] For any details not provided in the present invention, please refer to the prior art.

[0021] The beneficial effects of the present invention are:

[0022] The present invention provides a purely mechanical rotary guide drilling tool and method suitable for horizontal and horizontal branch drilling, which solves the problems of large friction torque, slow drilling speed or support pressure in horizontal well drilling with long horizontal sections; in addition, the present invention is a purely mechanical device with simple manufacturing, extremely low cost and high reliability, which can avoid the failure of electronic components of deep high-temperature rotary guide systems and reduce the high losses caused by the burial of traditional rotary guide systems in unconventional oil and gas horizontal well drilling. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The drawings in the specification, which constitute a part of the present application, are used to provide further understanding of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0024] Figure 1 It is a schematic diagram of the overall structure of a pure mechanical rotary drilling tool suitable for horizontal and horizontal branch drilling of the present invention;

[0025] Figure 2 is a cross-sectional view of the weight-biasing mechanism of the present invention;

[0026] Figure 3 It is a flow diagram of drilling fluid in the weight-biased mechanism of the present invention;

[0027] Figure 4 A wellbore trajectory diagram generated by the deadweight of a drilling tool in the prior art;

[0028] Figure 5 A wellbore trajectory diagram generated by the single-bend screw drilling tool of the present invention;

[0029] Figure 6 The drilling state when θ is less than 90° in the present invention;

[0030] Figure 7 It is the drilling state when θ is greater than 270°;

[0031] Figure 8 This is an imaging diagram of the branch well in the present invention;

[0032] In the figure, 1-drill string, 2-connecting bearing, 3-sealing ring, 4-excursion weight mechanism housing, 5-excursion weight block, 6-connecting buckle, 7-stator of single-bend screw drilling tool, 8-drill bit, 9-drilling fluid circulation channel, 10-drill bit rotation direction, 11-drill string rotation output torque direction, 12-drill string rotation direction, 13-gravity direction of the whole device, 14-movement trajectory one of the whole device, 15-direction of the single-bend screw drilling tool to maintain the high side of the wellbore, 16-movement trajectory two of the whole device, 17-gravity stability surface α, 18-screw tool surface β. DETAILED DESCRIPTION

[0033] The present invention is further described in detail by the following examples, but the embodiments of the present invention are not limited thereto. For researchers in the field, the present invention may have various changes and variations, and any modification, equivalent replacement or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

[0034] Example 1

[0035] A purely mechanical rotary drilling tool suitable for horizontal and horizontal branch drilling, such as Figure 1 As shown, it includes a drill string 1, a weight-biasing mechanism and a single-bend screw drill tool connected in sequence from top to bottom, and the weight-biasing mechanism includes a connecting bearing 2, a weight-biasing mechanism housing 4 and a weight block 5; the drill string 1 is connected to the inside of the connecting bearing 2, and the outside of the connecting bearing 2 is fixedly connected to the upper end of the weight-biasing mechanism housing 4, such as through a connecting buckle 6, and a sealing ring 3 is provided at the connection between the connecting bearing 2 and the weight-biasing mechanism housing; the lower end of the weight-biasing mechanism is fixedly connected to the stator 7 of the single-bend screw drill tool, and the lower end of the single-bend screw drill tool is provided with a bend angle, which is always kept biased toward the high side of the wellbore to balance the downward inclination trend of the wellbore trajectory caused by the deadweight of the drill tool. The angle between the gravity stabilizing surface of the weight-biasing mechanism and the screw tool surface of the single-bend screw needs to be set at a relative angle according to different working modes when connected.

[0036] like Figure 2As shown, the cross-section of the eccentric weight 5 is symmetrical on the left and right and has a fan-shaped structure. The eccentric weight 5 and the eccentric weight mechanism shell 4 are rigidly connected. The eccentric weight and the eccentric weight mechanism shell can be integrally processed with rigid material, or the two materials (the eccentric weight has a larger specific gravity) can be processed separately and then rigidly connected. The fan-shaped area where the eccentric weight is located can also be poured with high-density material (such as lead) so that the eccentric weight and the eccentric weight mechanism shell always remain relatively still when the gravity is in dynamic balance.

[0037] The center of the eccentric weight mechanism is a tubular structure to ensure that the drilling fluid flows through the drill string 1, the connecting bearing 2, the eccentric weight mechanism and the single-bend screw drill to reach the drill bit 8. Figure 3 The drilling fluid circulation channel 9.

[0038] The connecting bearing 2 is used to transmit the axial force generated by the drill string 1, and the sealing ring 3 is an O-ring.

[0039] The bending angle of the lower end of the single-bent screw drill, that is, the angle δ between the axes of the left and right sections of the bent screw drill is preferably 1.5°.

[0040] Example 2

[0041] A working method of a purely mechanical rotary drilling tool suitable for horizontal and horizontal branch drilling in embodiment 1, such as Figure 6 As shown, a local coordinate system is established with the center of the lower end of the eccentric weight mechanism as the origin, the vertical direction is the Y-axis direction, the direction perpendicular to the Y-axis and the axial direction of the drill string is the X-axis direction, the longitudinal section of the eccentric weight mechanism is the gravity stability plane α 17, that is, the plane where the Y-axis and the drill string are located, the plane where the single-bend screw drill tool and the bend are located is the screw tool surface β 18, and the lower end of the eccentric weight mechanism is fixedly connected to the stator of the single-bend screw drill tool to ensure the consistency of the screw tool surface and the gravity stability surface of the eccentric weight mechanism; when in drilling working conditions, the eccentric weight mechanism housing and the eccentric weight block remain relatively stationary in the radial direction, and the rotation of the drill string 1 drives the connecting bearing 2 to rotate, thereby applying a positive (counterclockwise) torque to the eccentric weight mechanism housing 4; the drilling fluid flows through the drill string 1, the connecting bearing 2, the eccentric weight mechanism and the single-bend screw drill tool in turn, driving the rotor and the drill bit 8 of the single-bend screw drill tool Rotation is used to achieve drilling, and the drill bit 8 breaking the rock will apply reverse torque to the stator of the single-bend screw drill and transmit it upward to the housing 4 of the eccentric weight mechanism; the eccentric weight block 5 applies positive torque to the housing of the eccentric weight mechanism under the action of its own weight; since the housing of the eccentric weight mechanism is fixedly connected to the stator of the single-bend screw drill, the combined action of the positive torque applied to the housing of the eccentric weight mechanism, the reverse torque applied to the stator of the single-bend screw drill and the positive torque applied to the housing of the eccentric weight mechanism under the action of its own weight will keep the screw tool surface β stable.

[0042] In this embodiment, the drill string 1, the housing 4 of the eccentric weight mechanism and the connecting bearing 2 cooperate, and the connecting bearing 2 disperses the radial force generated by the rotation of the drill string. By relying on the internal structure of the connecting bearing, the radial force caused by the rotation of the drill string can be dispersed through the rolling of the rolling element inside the bearing, and under the combined effect of the torque of the eccentric weight mechanism itself and the additional torque of the drill string 1 and the drill bit 8, the housing 4 of the eccentric weight mechanism and the eccentric weight block 5 are kept relatively still in the radial direction. Based on the counterclockwise torque of the drill string 1, the sealing ring 3 is used to seal the connection between the drill string 1 and the eccentric weight mechanism to prevent leakage of drilling fluid.

[0043] The main function of the eccentric weight block 5 in the present invention is to increase the weight of the lower half of the eccentric weight mechanism, so that the center of gravity of the entire eccentric weight mechanism is at a lower position, the lower part is heavier, and the overall stability is improved. The purpose of the eccentric weight block is that when the drill string rotates clockwise to generate a clockwise torque on the lower drilling tool assembly, the eccentric weight block gives the eccentric weight mechanism a counterclockwise torque under the action of its own weight, thereby maintaining the stability of the gravity stability plane α where the eccentric weight mechanism is located.

[0044] The fixed connection between the lower end of the eccentric weight mechanism and the stator of the single-bend screw ensures the consistency between the screw tool surface and the eccentric weight mechanism stable surface. Figure 1 The drill string rotates in the direction 12, and the drill string 1 drives the connecting bearing 2, which will apply a clockwise torque to the weight-biased mechanism housing 4, such as Figure 1 The drill string rotates to produce torque direction 11, and the drilling fluid drives the screw to rotate. Through the counter-torque of the drill bit 8, a torque is also applied to the stator 7 of the single-bend screw drill. The weight block of the weight mechanism also applies a torque to the weight mechanism housing 4 under the action of its own weight. Since the weight mechanism housing 4 is fixedly connected to the stator 7 of the single-bend screw drill, the combined action of the three torques will keep the screw tool surface stable. Figure 1 The drill bit rotation direction is 10, wherein the rotor and stator of the single-bend screw drill are both structures inside the single-bend screw drill, which belongs to the existing conventional structure.

[0045] Example 3

[0046] A working method of a purely mechanical rotary guide drilling tool suitable for horizontal and horizontal branch drilling, after the bending angle of a single-bend screw drill is balanced by a weight-biased mechanism, the screw tool surface β does not change with the rotation of the drill string and always remains stable; in the prior art, when drilling in a long horizontal section, due to the influence of the deadweight of the drill tool, such as Figure 4 As shown in the gravity direction 13 of the overall device, the wellbore trajectory always maintains a downward trend, such as Figure 4 The overall device motion trajectory is 14. In this embodiment, when drilling horizontally in a long horizontal section, the screw tool face β is kept in the high side direction, and the inclination effect caused by the upward bend of the bend angle in the single-bend screw drilling tool is utilized, such as Figure 5The single-bend screw drill bit maintains the direction of the high side of the wellbore by 15 degrees, balancing the wellbore trajectory deflection caused by the deadweight of the drill bit, so that the wellbore inclination angle can be maintained at 90 degrees during the horizontal well drilling process. Figure 5 The motion trajectory of the overall device is 216.

[0047] Since the main function of the single-bend screw drill bit when drilling a long horizontal section horizontal well is to balance the inclination-increasing effect caused by the upward bend of the single-bend screw with the inclination-reducing effect caused by the deadweight of the lower drill bit assembly, the requirements for curved wells are not high; single-bend screw drill bits usually select a small bend angle, such as 1.5°, which is suitable for relatively straight wells with low requirements for curved drilling. This design makes the screw easier to operate in straight well sections; at the same time, the rotation of the drill string itself can effectively prevent the accumulation of cuttings during horizontal drilling of long horizontal sections, which causes problems such as large friction torque, slow drilling speed or support pressure.

[0048] Example 4

[0049] A working method of a purely mechanical rotary guide drilling tool suitable for horizontal and horizontal branch drilling, under the condition of horizontal branch drilling, a single-bend screw drill tool is swung to different angles (the single-bend screw drill tool is rigidly connected to a weight-biasing mechanism, and the screw tool face of the single-bend screw drill tool is kept stable by the combined effect of the torque of the weight-biasing mechanism itself and the additional torque of the drill string and the drill bit), and the angle between the gravity stable surface α 17 and the screw tool face β 18 is θ. When θ is less than 90° or greater than 270°, as Figure 6 , Figure 7 As shown in Figure 2, the drilling presents a wellbore trajectory of a branch well, such as Figure 8 shown.

[0050] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A purely mechanical rotary drilling tool suitable for horizontal and horizontal branch drilling, characterized in that: It comprises a drill string, a weight-biasing mechanism and a single-bend screw drill tool which are sequentially connected from top to bottom, the weight-biasing mechanism comprises a connecting bearing, a weight-biasing mechanism housing and a weight-biasing block; the drill string is connected to the inside of the connecting bearing, the outside of the connecting bearing is fixedly connected to the upper end of the weight-biasing mechanism housing, and a sealing ring is provided at the connection between the connecting bearing and the weight-biasing mechanism housing; the lower end of the weight-biasing mechanism is fixedly connected to the stator of the single-bend screw drill tool, and the lower end of the single-bend screw drill tool is provided with a bend angle for balancing the downward inclination trend of the wellbore trajectory caused by the deadweight of the drill tool; The cross section of the eccentric weight block is bilaterally symmetrical and has a fan-shaped structure. The eccentric weight block and the housing of the eccentric weight mechanism are rigidly connected, and the eccentric weight block and the housing of the eccentric weight mechanism always remain relatively stationary. The center of the eccentric weight mechanism is a tubular structure to ensure that the drilling fluid flows through the drill string, connecting bearings, eccentric weight mechanism and single-bend screw drilling tool to reach the drill bit; The longitudinal section of the eccentric weight mechanism is the gravity stable surface α, the surface where the single-bend screw drill tool and the bend angle are located is the screw tool surface β, and the lower end of the eccentric weight mechanism is fixedly connected to the stator of the single-bend screw drill tool to ensure the consistency of the screw tool surface and the gravity stable surface of the eccentric weight mechanism; when in drilling working conditions, the eccentric weight mechanism housing and the eccentric weight block remain relatively stationary in the radial direction, and the rotation of the drill string drives the connecting bearing to rotate, thereby applying a positive torque to the eccentric weight mechanism housing; the drilling fluid flows through the drill string, the connecting bearing, the eccentric weight mechanism and the single-bend screw drill tool in turn, driving The rotor and drill bit of the single-bend screw drill rotate to achieve drilling, and the drill bit breaking the rock will apply reverse torque to the stator of the single-bend screw drill and transmit it upward to the housing of the eccentric weight mechanism; the eccentric weight block applies positive torque to the housing of the eccentric weight mechanism under the action of its own weight; because the housing of the eccentric weight mechanism is fixedly connected to the stator of the single-bend screw drill, the combined action of the positive torque applied to the housing of the eccentric weight mechanism, the reverse torque applied to the stator of the single-bend screw drill and the positive torque applied to the housing of the eccentric weight mechanism under the action of its own weight will keep the screw tool face β stable; Under the condition of long horizontal section drilling, the screw tool face β is kept in the high side direction, and the inclination-increasing effect caused by the upward bend of the bend angle in the single-bend screw drilling tool and the inclination-reducing effect caused by the screw's own weight are balanced with each other, so as to always keep the well inclination angle at 90°.

2. The purely mechanical rotary drilling tool suitable for horizontal and horizontal branch drilling according to claim 1, characterized in that: The connecting bearing is used to transmit the axial force generated by the drill string, and the sealing ring adopts an O-type sealing ring, an X-type sealing ring or a U-type sealing ring.

3. The purely mechanical rotary drilling tool suitable for horizontal and horizontal branch drilling according to claim 2, characterized in that: Under the condition of horizontal branch drilling, the single-bend screw drill bit is swung to different angles, and the angle between the gravity stable surface α and the screw tool surface β is set to θ. When θ is less than 90° or greater than 270°, the drilling presents the wellbore trajectory of the branch well.

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