Symmetric screw rotation directional drilling pipe string and its construction method

Abstract

The application provides a symmetrical screw rod rotary directional drilling pipe string, which comprises a positive screw rod drilling tool, a reverse screw rod drilling tool, a middle pipe column connected between the positive screw rod drilling tool and the reverse screw rod drilling tool, a pressure sensing throttling system arranged in the middle pipe column, wherein the positive screw rod drilling tool and the reverse screw rod drilling tool are symmetrically distributed relative to the middle pipe column, the reverse screw rod drilling tool can balance the reverse torque of the positive screw rod drilling tool, and the torque of the reverse screw rod drilling tool can follow the change of the positive screw rod drilling tool in real time under the action of the pressure sensing throttling system to keep balance, so that the tool face of the positive screw rod drilling tool is kept stable to carry out sliding directional drilling, and the torque generated by the reverse screw rod drilling tool is greater than the reverse torque of the positive screw rod drilling tool by increasing the rotation speed of the drill string to carry out composite drilling. The application also provides a construction method for directional drilling by using the pipe string.

Description

Technical Field

[0001] This invention belongs to the field of drilling tool technology, specifically relating to symmetrical screw rotary directional drilling string and its construction method, which is particularly suitable for long horizontal wells and offshore extended reach wells commonly used in unconventional oil and gas field development. Background Technology

[0002] Currently, directional and horizontal wells primarily utilize screw drill strings for wellbore trajectory control. During sliding drilling, the drill string does not rotate to ensure the stability of the screw drill string tool face. However, this results in significant axial friction between the drill string and the wellbore, especially in long horizontal sections and extended reach wells. This high axial friction leads to poor pressure on the drill string (PBT) transmission and low rate of drilling (RWD). To address the low RWD of screw drill strings in directional drilling, various technologies have been developed both domestically and internationally. The main approach is to rotate the drill string to reduce friction and thus increase the RWD. Advanced rotary steerable tools can rotate the drill string while effectively controlling the wellbore trajectory, overcoming the shortcomings of sliding steerable technology. This results in smooth PBT transmission, high RWD, and good wellbore quality. However, existing rotary steerable tools are electromechanical-hydraulic integrated devices, leading to high operating and maintenance costs, which hinders the reduction of drilling costs.

[0003] Existing technologies utilize large-angle screw drill bits, which, while maintaining wellbore trajectory control, reduce the proportion of sliding rigs and increase drilling speed through large-angle screw composite drilling technology. By applying screw-guided drill bit configuration tools and measures such as variable-diameter stabilizers, the performance of conventional directional drill bits can be improved as much as possible. However, the failure frequency of fractures and wear increases during large-angle screw drill bit composite drilling, and the increase in the proportion of composite drilling is limited. Another approach involves modifying the top drive program. During sliding drilling, the top drive first rotates forward a certain number of times, then reverses by the same number of times, continuously repeating this process. A certain length of the drill string is subjected to continuous forward and reverse oscillation, which can reduce the friction between the drill string and the wellbore. The number of forward and reverse rotations must be limited within a certain range, but the oscillation length is limited, and there is a risk of disconnection.

[0004] Chinese patent document CN201620363357.0 discloses a downhole tubing rotation control switch, which is installed approximately 300m above the screw drill string. The switch can be activated by drilling fluid, allowing the drill string to rotate using the frictional force of the approximately 300m length of the drill string to overcome the counter-torque of the screw drill string, thus achieving the purpose of rotating the drill string during directional drilling. However, this downhole tubing rotation control switch has certain drawbacks. Its reliance on the gravity of the drill string to generate friction is significantly affected by the motion state, potentially leading to instability of the screw drill string and preventing rotation of the approximately 300m length of the drill string. This reduces the rotation ratio of the drill string and affects the effect of friction reduction and speed increase.

[0005] Chinese patent document CN201220454297 discloses an up-and-down drilling friction and torque reduction tool, which uses an up-and-down control method, resulting in severe axial vibration during actual drilling. This up-and-down drilling friction and torque reduction tool suffers from control difficulties and basically does not involve the design of the transmission part. For the short section that bears an axial force of about 100KN, it will wear out quickly, thus its practicality is poor. Summary of the Invention

[0006] To address the technical problems described above, this invention aims to propose a symmetrical screw rotary directional drilling string and its construction method. Based on the screw drill string, it can rotate the drill string in the forward direction during sliding drilling to smoothly transmit drilling pressure and effectively control the tool face. It can effectively solve problems such as pressure drag and low mechanical drilling speed during sliding drilling.

[0007] Therefore, according to a first aspect of the present invention, a symmetrical screw rotary directional drilling string is provided, comprising: a forward screw drill string, the forward screw drill string including a forward screw stator and a forward screw rotor, the lower end of the forward screw drill string being connected to a drill bit; a reverse screw drill string disposed at the upper end of the forward screw drill string, the reverse screw drill string including a reverse screw stator and a reverse screw rotor, the upper end of the reverse screw drill string being connected to an upper drill pipe; and a central string connected between the forward screw drill string and the reverse screw drill string, the forward screw drill string and the reverse screw drill string being positioned relative to the central string. The tubing string is symmetrically distributed; and a pressure-sensitive throttling system is installed within the middle tubing string; wherein the reverse screw drill bit is configured to balance the counter-torque of the forward screw drill bit, and under the action of the pressure-sensitive throttling system, the torque of the reverse screw drill bit follows the changes of the forward screw drill bit in real time to maintain balance, so as to keep the tool face of the forward screw drill bit stable, thereby enabling the forward screw drill bit to perform sliding directional drilling, and by increasing the drill string speed, the torque generated by the reverse screw drill bit is greater than the counter-torque of the forward screw drill bit, thereby performing compound drilling.

[0008] In one embodiment, the central string includes a central drill rod and a non-magnetic drill rod connected to the lower end of the central drill rod, the reverse screw drill tool is connected to the upper end of the central drill rod, and the forward screw drill tool is connected to the lower end of the non-magnetic drill rod.

[0009] In one embodiment, an annular cavity is provided inside the central drill pipe, and the pressure-sensitive throttling system is installed in the annular cavity. The pressure-sensitive throttling system is configured to automatically adjust the torque of the reverse screw drill bit.

[0010] In one embodiment, a wireless measurement-while-drilling instrument is installed inside the non-magnetic drill pipe.

[0011] In one embodiment, the pressure-sensitive throttling system includes:

[0012] A slot adjuster is installed within the annular cavity, the slot adjuster having an L-shaped connecting portion; a piston cylinder is fixedly connected to the inner wall of the annular cavity, and a constant pressure air bladder is provided inside the piston cylinder; a piston is adapted to be installed inside the piston cylinder, the piston being connected to the L-shaped connecting portion; wherein, a pressure transmission hole is provided on the inner wall of the annular cavity, the pressure fluctuation generated by the change in counter-torque during the drilling process of the forward screw drill bit can transmit pressure to the piston, so that the piston can reciprocate along the piston cylinder under the action of body pressure and the constant pressure air bladder, thereby driving the slot adjuster to move axially, so as to adjust the size of the throttling gap formed between the lower end face of the reverse screw rotor and the upper end face of the slot adjuster in real time, thereby adjusting the torque of the reverse screw drill bit in real time.

[0013] In one embodiment, the piston cylinder is configured as an annular cylinder, and the inner wall of the annular cylinder is provided with an annular connecting portion extending radially inward, the annular connecting portion being fixedly connected to the inner wall of the annular cavity.

[0014] In one embodiment, the axial outer end of the piston is connected to the connecting portion via a coupling.

[0015] In one embodiment, the forward screw drill is a curved shell type drill, and the reverse screw drill is a straight screw drill.

[0016] In one embodiment, the reverse screw drill bit and the forward screw drill bit use the same outer diameter, screw stage, and screw head number.

[0017] According to a second aspect of the present invention, a method for directional drilling using a symmetrical screw rotating directional drilling string as described above is provided, comprising the following steps:

[0018] The symmetrical screw rotary directional drilling tubing string is assembled into the drilling string and lowered to the bottom of the well;

[0019] Drilling operations are carried out according to the wellbore trajectory requirements. During the drilling process, the wellbore trajectory is adjusted and controlled in real time by rotating the directional drilling string with the symmetrical screw.

[0020] Specifically, when sliding directional drilling is required, the drilling pressure is adjusted to a predetermined drilling pressure so that the torque of the reverse screw drill bit balances the counter-torque of the forward screw drill bit, thereby keeping the tool face of the forward screw drill bit stable. When combined drilling is required, the drill string speed is increased so that the torque generated by the reverse screw drill bit is greater than the counter-torque of the forward screw drill bit, thereby performing combined drilling operations.

[0021] Compared with the prior art, the advantages of this application are:

[0022] The symmetrical screw rotary directional drilling string of the present invention, based on a screw drill string, can rotate the drill string during sliding drilling to smoothly transmit drilling pressure and effectively control the tool face, keeping it stable and solving problems such as pressure buildup and low mechanical drilling speed in sliding drilling. When sliding directional drilling is required, the torque of the reverse screw drill string can balance the counter-torque of the forward screw drill string, thereby keeping the tool face of the forward screw drill string stable and significantly reducing axial friction, thus greatly increasing the mechanical drilling speed. When combined drilling is required, by increasing the drill string rotation speed, the torque generated by the reverse screw drill string is greater than the counter-torque of the forward screw drill string, causing the upper drill string to drive both the reverse and forward screw drill strings to rotate together, significantly increasing the mechanical drilling speed. Using this symmetrical screw rotary directional drilling string can significantly improve drilling efficiency and enhance drilling performance. Attached Figure Description

[0023] The present invention will now be described with reference to the accompanying drawings.

[0024] Figure 1 The schematic diagram illustrates the symmetrical screw rotary directional drilling string structure according to the present invention.

[0025] Figure 2 yes Figure 1 Enlarged view of section A.

[0026] Figure 3 yes Figure 2 A sectional view along line BB.

[0027] In this application, all drawings are schematic and are used only to illustrate the principles of the invention, and are not drawn to scale. Detailed Implementation

[0028] The invention will now be described with reference to the accompanying drawings.

[0029] In this application, it should be noted that the end of the symmetrical screw rotary directional drilling string that is lowered into the wellbore and is furthest from the wellhead is defined as the front end or a similar term, and the end furthest from the wellhead is defined as the rear end or a similar term.

[0030] Figure 1 The diagram schematically illustrates the structure of a symmetrical screw-driven directional drilling string 100 according to the present invention. For example... Figure 1As shown, the symmetrical screw rotary directional drilling string 100 includes, from top to bottom, an upper drill pipe 1, a reverse screw drill string 2, a middle string 3, a forward screw drill string 5, and a drill bit 6, connected sequentially. A pressure-sensitive throttling system 4 is installed within the middle string 3. The reverse screw drill string 2 is configured to balance the counter-torque of the forward screw drill string 5, and under the action of the pressure-sensitive throttling system 4, the torque of the reverse screw drill string 5 follows the changes in the forward screw drill string 5 in real time to maintain balance, thereby stabilizing the tool face of the forward screw drill string 5. This allows the forward screw drill string 5 to perform sliding directional drilling operations. Furthermore, by increasing the drill string rotation speed, the symmetrical screw rotary directional drilling string 100 can make the torque generated by the reverse screw drill string 2 greater than the counter-torque of the forward screw drill string 5, thus enabling combined drilling operations. The symmetrical screw rotary directional drilling string 100 of the present invention can rotate the drill string to smoothly transmit drilling pressure during sliding drilling and can effectively control the tool face, thus effectively solving problems such as pressure drag and low mechanical drilling speed during sliding drilling.

[0031] like Figure 1 As shown, the forward screw drill 5 is a curved-shell type screw drill 5, including a forward screw stator 51 and a forward screw rotor 52 adapted and installed within the forward screw stator 51. The drill bit 6 is connected to the lower end (output end) of the forward screw drill 5, used to drive the drill bit 6 to rotate, outputting speed and torque, thereby driving the drill bit 6 to break rock and convert the fluid energy of the drilling fluid into mechanical energy. The lower end of the forward screw drill 5 is connected to the drill bit 6 through a connecting assembly formed by a universal joint 8, a curved shell 9, a stabilizer 10, and a thrust bearing 11. The upper end of the universal joint 8 is connected to the forward screw rotor 52, and the curved shell 9 is connected to the forward screw stator 51.

[0032] In practical applications, when drilling in the directional section, the forward screw drill bit 5 uses a 1.5° bent outer shell screw, while when drilling in the horizontal section, the forward screw drill bit 5 uses a 1.25° bent outer shell screw.

[0033] According to the present invention, such as Figure 1 As shown, the reverse screw drill bit 2 includes a reverse screw stator 21 and a reverse screw rotor 22. The upper end of the reverse screw drill bit 2 is connected to the upper drill rod 1, and the upper drill string (not shown) is connected through the upper drill rod 1. The reverse screw drill bit 2 is a straight screw drill bit and is used in reverse arrangement.

[0034] The reverse screw drill string 2 is connected to the forward screw drill string 5 via an intermediate tubing string 3. The intermediate tubing string 3 includes a central drill pipe 31 and a non-magnetic drill pipe 32 connected to the lower end of the central drill pipe 31. The reverse screw drill string 2 is connected to the upper end of the central drill pipe 31, and the forward screw drill string 5 is connected to the lower end of the non-magnetic drill pipe 32. The reverse screw drill string 2 and the forward screw drill string 5 are symmetrically distributed relative to the intermediate tubing string 3, and the reverse screw stator 21 (reverse screw drill string housing) of the reverse screw drill string 2 is connected to the forward screw stator 51 (reverse screw drill string housing) of the forward screw drill string 5. The main function of the intermediate drill string 3 is to generate frictional torque with the wellbore. When the torques of the reverse screw drill string 2 and the forward screw drill string 5 are not completely balanced, the frictional torque can provide auxiliary balancing. When drilling with water-based drilling fluid, the length of the middle drill pipe 31 can be about 60 meters, and when drilling with oil-based drilling fluid, the length of the middle drill pipe 31 can be about 120 meters.

[0035] A wireless measurement-while-drilling (MWD) instrument (not shown) is installed inside the non-magnetic drill rod 32.

[0036] According to the present invention, the pressure-sensitive throttling system 4 is disposed within the middle drill pipe 31 and located at the ends of the reverse screw stator 21 and the reverse screw rotor 22 of the reverse screw drill tool 2. The lower end of the reverse screw drill tool 2 is connected to the middle drill pipe 31. During drilling operations, the middle drill pipe 31 drives the reverse screw drill tool 2 to rotate, making the reverse screw drill tool 2 a driven component. When the reverse screw rotor 22 rotates, it drives the liquid to flow downward, and under the action of the pressure-sensitive throttling system 4, outputs high-pressure drilling fluid, thereby converting mechanical energy into drilling fluid energy.

[0037] like Figure 2 As shown, an annular cavity is provided inside the central drill rod 31, and a pressure-sensitive throttling system 4 is installed inside the annular cavity. The pressure-sensitive throttling system 4 is configured to automatically adjust the torque of the reverse screw drill bit 2. The central drill rod 31 is cylindrical, and a step with its end face facing upward is provided on the inner wall of its upper end. The annular cavity is formed inside the upper side wall of the central drill rod 31, and its upper end extends to the step surface. The lower end face of the reverse screw rotor 22 of the reverse screw drill bit 2 extends correspondingly to a position above the annular cavity.

[0038] According to the present invention, such as Figure 2As shown, the pressure-sensitive throttling system 4 includes an adjuster 41, a piston cylinder 42, a normal pressure airbag 43, and a piston 44 adapted to be installed in the piston cylinder 42, all installed within the annular cavity. The adjuster 41 is constructed to include a cylindrical body, and an L-shaped connecting portion is provided on the lower end face of the cylindrical body of the adjuster 41. The inner and outer surfaces of the adjuster 41 form a sliding seal with the inner and outer walls of the annular cavity, respectively. The piston cylinder 42 is constructed as an annular cylinder, and the inner wall of the annular cylinder has a radially inwardly extending annular connecting portion, which is fixedly connected to the inner wall of the annular cavity. The piston cylinder 42 is fixedly connected to the inner wall of the annular cavity through the annular connecting portion. The normal pressure airbag 43 is located at the bottom of the piston cylinder 42. Figure 2 (Left end of the piston). Piston 44 is fitted inside piston cylinder 42, and piston 44 and the inner wall of piston cylinder 42 form a sliding seal fit. Atmospheric pressure air bladder 43 is located inside piston 44. The axial outer end of piston 44 is connected to L-shaped connecting part through coupling 45.

[0039] like Figure 2 and Figure 3 As shown, the piston cylinder 42 is constructed as an annular cylinder, including an outer cylinder, an inner cylinder concentrically arranged within the outer cylinder, and a connecting base plate connecting the upper ends of the outer and inner cylinders. The connecting base plate is annular, and its inner side extends radially inward, thereby forming a radially inwardly extending annular connecting portion on the inner wall of the inner cylinder of the annular cylinder. An annular cavity is formed between the cylindrical body of the adjusting device 41 and the L-shaped connecting portion. The piston cylinder 42 is arranged within the annular cavity, and the axial outer end of the piston 44 is connected to the L-shaped connecting portion via a coupling 45. This causes the piston 44 and the adjusting device 41 to move together. The adjusting device 41 is arranged within the annular cavity, and the upper end face of the adjusting device 41 is opposite to the lower end face of the anti-screw rotor 22, thereby forming a throttling gap 40 between the upper end face of the adjusting device 41 and the lower end face of the anti-screw rotor 22.

[0040] A pressure-transmitting hole 46 is provided on the inner wall of the annular cavity, thereby connecting the internal channel of the central drill rod 31 with the annular cavity where the piston cylinder 42 is arranged. Preferably, the pressure-transmitting hole 46 is located on the axial inner side of the annular connecting part of the piston cylinder 42. During the drilling process of the forward screw drill 5, the counter torque is affected by the rock-breaking torque of the drill bit 6, the drilling pressure, and the rock, resulting in pressure fluctuations. The pressure-transmitting hole 46 can transmit the pressure to the piston 44, which then acts on the axial outer end face of the piston 44. Figure 2 The piston 44 is positioned at the right end of the piston cylinder 42 under the action of liquid pressure and atmospheric pressure air bladder 43. This causes the piston 44 to reciprocate along the piston cylinder 42, thereby driving the adjusting device 41 to move axially through the connecting shaft 45 and L-shaped connection to adjust the size of the throttling gap 40 in real time. The throttling gap 40 affects the liquid pressure of the reverse screw drill 2, thereby achieving real-time adjustment of the torque of the reverse screw drill 2.

[0041] The automatic adjustment process of the pressure-sensitive throttling system 4 is as follows: when the counter-torque of the forward screw drill bit 5 increases due to the influence of the drill bit 6, the liquid pressure of the forward screw drill bit 5 increases, and the pressure is transmitted to the piston 44 through the pressure transmission hole 46, acting on the axial outer end face of the piston 44. Figure 2 The piston 44 (at the right end of the piston cylinder 42) compresses the atmospheric pressure air bladder 43, causing it to move to the left along the piston cylinder 42 to reduce the throttling gap 40. This throttling effect increases the fluid pressure of the reverse screw drill bit 2, thereby increasing its torque. Conversely, when the reverse torque of the forward screw drill bit 5 decreases, the above process is reversed, thus reducing the torque of the reverse screw drill bit 2.

[0042] According to the present invention, the reverse screw drill bit 2 and the forward screw drill bit 5 adopt the same outer diameter, screw stage, and screw head specifications. During normal drilling, while the forward screw drill bit 5 outputs clockwise torque, it also generates counterclockwise torque on the forward screw stator 51 (the housing of the forward screw drill bit). Under the clockwise drive of the intermediate drill string 3, the high-pressure liquid inside the reverse screw drill bit 2 acts on the reverse screw rotor 22 to generate counterclockwise torque, which is balanced with the clockwise torque of the intermediate drill string 3. At the same time, it generates clockwise torque on the reverse screw stator 21, which is balanced by the counterclockwise torque of the intermediate drill string 31, the non-magnetic drill string 32, and the forward screw drill bit housing.

[0043] Since the counter-torque of the forward screw drill bit casing depends on the rock-breaking torque of the drill bit 6, it is a variable affected by drilling pressure and rock conditions. The torque of the reverse screw drill bit casing depends on the rotational speed of the drill pipe and mandrel, as well as the throttling area of ​​the pressure-sensitive throttling system 4. These two parameters can be designed based on the counter-torque of the forward screw drill bit casing and the drilling process. For example, the drill pipe rotational speed designed for torque balance can be set to 40 revolutions per minute. During drilling operations, the pressure-sensitive throttling system 4 effectively solves the problem of lag in adjusting rotational speed on the surface due to the variable counter-torque of the forward screw drill bit casing, and also addresses the issue of frequent rotational speed adjustments affecting normal drilling processes.

[0044] According to the present invention, during normal drilling, the drill pipe, anti-screw rotor 22, positive screw rotor 52 and drill bit 6 of the symmetrical screw rotary directional drilling string 100 are in a rotating state, while the anti-screw stator 21, intermediate drill string 3 and positive screw stator 51 are in a non-rotating state.

[0045] The present invention also provides a method for directional drilling using a symmetrical screw rotating directional drilling string 100, comprising the following steps:

[0046] The symmetrical screw rotary directional drilling string 100 is assembled into the drilling string and lowered to the bottom of the well.

[0047] Afterwards, drilling operations were carried out according to the wellbore trajectory requirements. During the drilling process, the wellbore trajectory was adjusted and controlled in real time by rotating the directional drilling string 100 with symmetrical screws.

[0048] During operation, when sliding directional drilling is required, the rotary table is activated, and the drill string speed is adjusted to the design speed to adjust the drilling pressure to the predetermined drilling pressure. This allows the torque of the reverse screw drill string 2 to balance the counter-torque of the forward screw drill string 5, thereby stabilizing the tool face of the forward screw drill string 5. At this time, the drill string of the symmetrical screw rotary directional drilling string with a diameter of 100mm or more is in a rotating state under the drive of the rotary table, greatly reducing axial friction and significantly increasing the mechanical drilling speed.

[0049] When combined drilling is required, the drill string speed is increased so that the torque generated by the reverse screw drill bit 2 is greater than the counter-torque of the forward screw drill bit 5, thereby enabling combined drilling operations. At this time, the upper drill string will drive the reverse screw drill bit 2 and the forward screw drill bit 5 to rotate together, significantly increasing the mechanical drilling speed of the drill string.

[0050] The following example, using the application of a symmetrical screw rotary directional drilling string 100 to a 215.9mm wellbore, illustrates the symmetrical screw rotary directional drilling string 100 and its construction method according to the present invention. First, a screw drill string with an outer diameter of 172mm and 7 / 8 heads is selected. The forward screw drill string 5 has a 1.25° bent outer shell 9 and a stabilizer 10, while the reverse screw drill string 2 is a straight screw, and a pressure-sensitive throttling system 4 is added to the reverse screw drill string 2. When torque is balanced, the drill string rotation speed is 40 revolutions per minute. For water-based drilling fluid, a central string of approximately 63 meters is formed between the reverse screw drill string 2 and the forward screw drill string 5 using six central drill pipes 31 and one non-magnetic drill pipe 32. Thus, the specific configuration of the symmetrical screw rotary directional drilling string 100 is as follows:

[0051] After assembling the symmetrical screw rotary directional drilling string 100 and lowering it to the bottom of the well, it follows the wellbore trajectory requirements. If wellbore trajectory adjustment is needed, the tool face angle range is determined based on calculations. The drill pipe speed is adjusted to 40 revolutions per minute, and the drilling pressure is gradually increased to the design drilling pressure. At this point, the torque of the reverse screw drill bit balances the reverse torque of the forward screw drill bit, stabilizing the tool face of the forward screw drill bit. If the tool face angle range is not the calculated range, the speed is adjusted to 41-43 revolutions per minute, slowly rotating the forward screw drill bit. When the tool face reaches the design range, the drill pipe speed is reduced to 40 revolutions per minute. At this point, the tool face is stable and remains within the design range. When the reverse torque of the forward screw drill bit changes due to formation or other factors, the pressure-sensitive throttling system 4 automatically operates, causing the torque of the reverse screw drill bit to follow the changes in the forward screw drill bit, thereby coordinating with the friction torque of the intermediate drill string to achieve a real-time balance effect.

[0052] Once the experience trajectory adjustment is complete and it is time to enter the composite drilling stage, adjust the drill rod speed to 60-80 rpm so that the torque of the reverse screw drill bit is greater than the reverse torque of the forward screw drill bit. At this time, the upper drill string will drive the reverse screw drill bit and the forward screw drill bit to rotate together, thus entering the composite drilling mode.

[0053] The symmetrical screw rotary directional drilling string 100 of the present invention, based on a screw drill string, can rotate the drill string during sliding drilling to smoothly transmit drilling pressure and effectively control the tool face, keeping it stable and solving problems such as pressure buildup and low mechanical drilling speed during sliding drilling. When sliding directional drilling is required, the torque of the reverse screw drill string 2 can balance the counter-torque of the forward screw drill string 5, thereby keeping the tool face of the forward screw drill string 5 stable and greatly reducing axial friction, significantly increasing the mechanical drilling speed. When combined drilling is required, by increasing the drill string rotation speed, the torque generated by the reverse screw drill string 2 is greater than the counter-torque of the forward screw drill string 5, causing the upper drill string to drive the reverse screw drill string 2 and the forward screw drill string 5 to rotate together, significantly increasing the mechanical drilling speed of the drill string. Using this symmetrical screw rotary directional drilling string 100 can significantly improve drilling efficiency and enhance drilling performance.

[0054] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0055] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0056] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0057] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A symmetrical screw-driven directional drilling string, comprising: A forward screw drill bit (5) is provided, comprising a forward screw stator (51) and a forward screw rotor (52), with a drill bit (6) connected to the lower end of the forward screw drill bit. A reverse screw drill (2) is provided at the upper end of the forward screw drill, the reverse screw drill includes a reverse screw stator (21) and a reverse screw rotor (22), and the upper end of the reverse screw drill is connected to the upper drill rod (1). A central tubing string (3) connecting the forward screw drill bit and the reverse screw drill bit, wherein the forward screw drill bit and the reverse screw drill bit are symmetrically distributed relative to the central tubing string; and The pressure-sensing throttling system (4) is installed in the middle tube column. The central tubing includes a central drill pipe (31), and an annular cavity is provided inside the central drill pipe (31). The pressure-sensing throttling system (4) is installed in the annular cavity. The pressure-sensitive throttling system (4) includes: The seam adjuster (41) installed in the annular cavity has a connecting part with an L-shaped cross-section. A piston cylinder (42) is fixedly connected to the inner wall of the annular cavity, and a normal pressure air bladder (43) is provided inside the piston cylinder. A piston (44) is adapted to be installed inside the piston cylinder, and the piston is connected to the L-shaped connecting part; The annular cavity has a pressure transmission hole (46) on its inner wall. During drilling, the forward screw drill experiences pressure fluctuations due to changes in counter-torque. The pressure transmission hole transmits the pressure to the piston, allowing the piston to reciprocate along the piston cylinder under the influence of liquid pressure and the atmospheric pressure airbag. This, in turn, drives the slot adjuster to move axially, thereby adjusting the size of the throttling gap (40) formed between the lower end face of the reverse screw rotor and the upper end face of the slot adjuster in real time. This allows for real-time adjustment of the torque of the reverse screw drill. The reverse screw drill bit is configured to balance the counter-torque of the forward screw drill bit, and under the action of the pressure-sensitive throttling system, the torque of the reverse screw drill bit follows the changes of the forward screw drill bit in real time to maintain balance, so as to keep the tool face of the forward screw drill bit stable, thereby enabling the forward screw drill bit to perform sliding directional drilling. Furthermore, by increasing the drill string speed, the torque generated by the reverse screw drill bit can be made greater than the counter-torque of the forward screw drill bit, thereby enabling compound drilling.

2. The symmetrical screw rotary directional drilling string according to claim 1, characterized in that, The central drill string includes a non-magnetic drill rod (32) connected to the lower end of the central drill rod, the reverse screw drill tool is connected to the upper end of the central drill rod, and the forward screw drill tool is connected to the lower end of the non-magnetic drill rod.

3. The symmetrical screw rotary directional drilling string according to claim 2, characterized in that, A wireless measurement-while-drilling instrument is installed inside the non-magnetic drill rod.

4. The symmetrical screw rotary directional drilling string according to claim 2, characterized in that, The piston cylinder is configured as an annular cylinder, and the inner wall of the annular cylinder is provided with an annular connecting part extending radially inward, the annular connecting part being fixedly connected to the inner wall of the annular cavity.

5. The symmetrical screw rotary directional drilling string according to claim 2, characterized in that, The outer axial end of the piston is connected to the connecting part via a coupling (45).

6. The symmetrical screw rotary directional drilling string according to claim 1, characterized in that, The forward screw drill is a curved shell type drill, and the reverse screw drill is a straight screw drill.

7. The symmetrical screw rotary directional drilling string according to claim 1 or 6, characterized in that, The reverse screw drill bit and the forward screw drill bit have the same outer diameter, screw stage, and screw head.

8. A method for directional drilling using a symmetrical screw rotary directional drilling string according to any one of claims 1 to 7, comprising the following steps: The symmetrical screw rotary directional drilling tubing string is assembled into the drilling string and lowered to the bottom of the well; Drilling operations are carried out according to the wellbore trajectory requirements. During the drilling process, the wellbore trajectory is adjusted and controlled in real time by rotating the directional drilling string with the symmetrical screw. Specifically, when sliding directional drilling is required, the drilling pressure is adjusted to a predetermined drilling pressure so that the torque of the reverse screw drill bit balances the counter-torque of the forward screw drill bit, thereby keeping the tool face of the forward screw drill bit stable. When combined drilling is required, the drill string speed is increased so that the torque generated by the reverse screw drill bit is greater than the counter-torque of the forward screw drill bit, thereby performing combined drilling operations.

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