RU2783935C1 - Balanced threaded drill string connection - Google Patents

Abstract

FIELD: drill pipes.

SUBSTANCE: invention relates to a threaded connection of drill pipes, made with external and internal stops, including nipple and box ends with trapezoidal tapered thread, the pitch of which is 8.467 mm, the taper is 1:9.6, the profile angle is 90 degrees, characterized in that with in order to increase the maximum allowable torque of a threaded connection, provided that it is balanced in bending, the outer diameter is from 123.8 to 127 mm, the inner diameter is from 57.2 to 68.3 mm, the average thread diameter in the main plane is from 96.7 to 97.7 mm, and the inner stop of the nipple end has a cylindrical section adjacent to the thread and a conical section associated with it, the outer diameter of the end part of which is from 83 to 84 mm. An additional advantage of the lock is better maintainability compared to the prototype. For recutting the coupling part of the proposed lock, the loss of length is about 45 mm versus 80 mm for the closest analogue.

EFFECT: increase in the maximum allowable torque of the threaded connection of the lock with an outer diameter from 123.8 to 127 mm, provided that it is balanced in bending and there is a margin for wear along the outer diameter.

1 cl, 3 dwg

Description

The proposed invention relates to the field of mining, namely to threaded joints (locks) of drill pipes with an outer diameter of 123.8-127 mm, intended mainly for drilling, including horizontal and highly deviated wells.

In cases where this does not matter, in the present description, the lock will be referred to as both the nipple and the box. Maintainability will be evaluated by the length of the lock metal cut off when re-cutting a worn joint: the smaller this length, the more times the thread can be re-cut, the higher the maintainability of the joint. The maximum allowable torsional moment (torque) of a threaded connection (hereinafter - PC) of the lock in the present description is the torsional moment at which the yield strength is reached in the material of the lock.

Drill pipes are required to be able to transmit high torque to the bit, withstand axial tensile and compressive loads, and perform reliably in alternating bending conditions in horizontal and highly deviated wells. The latter requirement means that welded tool joints (hereinafter referred to as locks), with which the drill string is built up, must have not only strength commensurate with the strength of the body of the drill pipes, but also high fatigue resistance, or high fatigue strength. In addition, the lock connections must be resistant to bending loads, which is taken into account by the bending strength factor W _m / W _n , where W _m is the moment of resistance of the dangerous section of the lock coupling, and W _n is the moment of resistance of the dangerous section of the lock nipple. In foreign technical literature, this ratio is referred to as BSR - Bending Strength Ratio. In a stable lock connection, it should lie in the range from 2.05 to 2.7.

For example, the API RP 7G standard requires that the torsional strength of the lock, measured by the maximum allowable torsional moment, be no less than 80% of the torsional strength of the pipe body. At the same time, it is desirable that the tool joint has the minimum possible outer diameter and the maximum possible inner diameter in order to minimize hydraulic losses during pumping of the drilling fluid and wiring of geophysical instruments.

Lock joints must be resistant to seizing and wear, quickly assembled and disassembled, and easy to repair.

In order to obtain the minimum dimensions of interlocks while maintaining their strength, lock designers began to use designs with a small taper PC, which is not typical for standard locks with a taper of 1:4 or 1:6.

A well-known design of a double-shouldered locking PC with a trapezoidal thread, the pitch of which is 8.467 mm, the taper is 1:9.6, the profile angle is 90 degrees [RU 128912]. The slope angle of the conical outer surface of the thrust collar of the nipple corresponds to the slope angle of the thread surface. The well-known PC with a taper of 1:9.6 is optimally balanced in terms of bending, torsional and compressive strength. But it has limited application, since it is intended for locks with an outer diameter of 105.5 and 108.0 mm and an inner diameter of 51 mm, used in wells with a diameter of 120.6 and 151.0 mm, i.e. in small boreholes.

To connect the elements of the drill string when drilling larger diameter wells, a more powerful PC is needed.

Grant Prideco XT (Extreme Torque) double-shoulder interlocks are known, the thread profile of which has the following geometric parameters: taper - 0.75 inch / ft (corresponds to a taper of 1:16 mm / mm), thread pitch is 3.5 threads per inch (7.257 mm) and the height of the thread profile - 0.14 inches (3.556 mm), the angle at the top of the thread - 60 degrees. These parameters are given in the sketches of Grant Prideco [https://vdocuments.mx/drill-pipe-charts.html], intended for repairing tool joints of drill pipes in the field.

In particular, an XT39 joint with an outer lock diameter of 123.83 mm and an inner lock diameter of 61.91 to 68.3 mm is known, having a high maximum allowable torque of 47,850 to 52,200 N⋅m.

The weak element of this connection is the coupling, which is why it has a low bending strength factor (BSR from 1.5 to 1.67). Since the strength of the lock mainly depends on the outer diameter of the coupling, when the outer diameter of the lock decreases due to friction against the borehole walls during drilling, the strength properties of the lock joint will inevitably be lost. Due to the low coefficient of bending strength of the known connection is not balanced and is prone to the accumulation of fatigue damage to the coupling end.

A small taper of 1/16 is uncharacteristic of tool joints and requires special care when carrying out tripping operations. In particular, to avoid misalignment of the pin and box threads during make-up, it is necessary to use a guide funnel, the installation and removal of which takes additional time.

This taper requires 13 turns to fully make up, while standard API 7-2 1/6 taper connections require only 5 turns.

All this leads to an increase in the period of construction (repair) of the well and increases operating costs.

XT (Extreme Torque) type connections with a 1/16 taper have low maintainability, since when repairing (recutting) both the pin and box threads have to be cut off by 113 mm.

Also known are double-shouldered locking joints of the HLST type of Tekhnomash LLC (HILONG Super Torque) [RU 201674, RU 202565 and RU 203057] with a taper of 1:12, a thread pitch of 7.26 mm (3.5 turns per inch), a thread height of range from 3.4 to 3.6 mm (preferably 3.556 mm) and a thread angle of 60 degrees.

The thread profile of HLST type connections is practically the same as the thread profile of XT (Extreme Torque) type connections, except for the taper of the thread, which has increased from 1/16 to 1/12.

Due to this, the performance of the lock is slightly improved.

It takes 9.8 turns to fully make up a 1/12 taper HLST connection.

HLST type connections with a 1/12 taper also have low maintainability, since when repairing (re-cutting) both the pin and box threads have to be cut off at 85.3 mm.

The disadvantage of HLST connections with an outer diameter of the lock of 123.8 mm and an inner diameter of the lock of 61.9-68.3 mm is that in almost all of these connections the weak element is the coupling, which is worn out by friction against the borehole walls. These locks are not flex balanced and have BSR flex ratios from 1.63 to 1.81 units.

The closest to the claimed in terms of the totality of features is a double-shouldered PC drill pipe type Z2-99 with an outer diameter of the lock of a thick-walled drill pipe equal to 121 mm and an inner diameter of 71 mm, with a taper of 1/9.6, a thread pitch of 8.467 mm (3 threads per inch ), an angle at the top of the thread of 90 degrees and an internal stop of the nipple end, having a conical section adjacent to the thread, and a cylindrical section associated with it, the outer diameter of the end part of which is 82 mm [RU 181276]. In this case, the average diameter of the connection in the main plane is 95.8 mm.

According to the table in the patent description, the strength characteristics of the connection are:

- tensile load Qpc=2153 kN;

- torsion moment Mcr.rs=32.6 kN⋅m.

In the table and in the description of the patent, the moment of torsion Mcr.pc is the moment at which the yield strength is reached in the lock material, that is, the maximum allowable torque of the threaded lock.

Known connection is not well balanced in terms of bending strength. In it, the weak element is the sleeve, which is subject to wear from friction against the borehole walls during drilling, as a result of which the strength properties of the lock deteriorate relatively quickly. If, in an effort to increase the durability of the connection, the diameter of the coupling is increased, for example, to 123.8 or 127 mm, then the nipple will become the weak element of the Z2-99 connection. However, the level of the maximum allowable torque, which in this case depends only on the value of the inner diameter of the lock, will remain the same and will not increase.

The inner (second) stop of the nipple end of the Z2-99 connection has conical and cylindrical sections, and the conical section begins immediately after the end of the threaded section of the nipple, and the cylindrical section is closer to the butt end of the nipple nose stop. The disadvantage of the Z2-99 (121×71) connection is a too thin wall at the end of the internal stop (nose) of the nipple (only 5.5 mm), which will collapse under real loads on the lock connection. With a thin wall at the end of the nipple, the cylindrical shape of the stop is prone to collapse in the form of an inverse cone. The protruding metal of the crumpled end of the nipple can interfere with the screwing of the interlock.

Even with the inner diameter of the lock equal to 68.3 mm, the wall thickness at the end of the inner (second) stop of the nipple will be only 6.85 mm, which is also not enough to ensure strength.

Another disadvantage of the Z2-99 connection is its low maintainability due to the use of a boring on the coupling end in the form of a toroidal pocket designed to collect solid particles of sludge. The pocket reduces the maintainability of the lock, since when repairing (re-cutting) the threaded connection at the coupling end, it is necessary to cut off about 80 mm, which corresponds to almost the entire threaded section of the coupling.

In addition, solidified mud residues and cuttings particles will eventually fill the cavities of the toroidal pockets on all pipes of the drill string. It is safe to assume that drilling crew personnel will not be constantly cleaning these pockets of mud and cuttings residues during the drilling process. Attempting to clear these pockets while tripping the drillstring will cause hardened cuttings removed from the collar pocket to fall to the bottom of the drillstring and, if a downhole motor is used, will hinder its operation.

The objective of the present invention is to create a lock with an outer diameter of 123.8 to 127 mm, balanced in bending and having a sufficient margin for wear along the outer diameter without losing the strength properties of the lock. In other words, for the given dimensions of the lock, it is necessary to obtain the maximum value of the allowable torque PC of the lock, but in such a way that the nipple remains the weaker link of the connection.

The technical result of the claimed invention is an increase in the maximum allowable torque of the threaded connection of the lock with an outer diameter from 123.8 to 127 mm, provided that it is balanced in bending and there is a margin for wear along the outer diameter.

The technical result is achieved due to the fact that in the threaded connection of drill pipes, made with external and internal stops, including the nipple and box ends with a trapezoidal tapered thread, the pitch of which is 8.467 mm, the taper is 1:9.6, the profile angle is 90 degrees , the outer diameter is from 123.8 to 127 mm, the inner diameter is from 57.2 to 68.3 mm, the average thread diameter in the main plane is from 96.7 to 97.7 mm, the internal stop of the pin end has a cylindrical section, adjacent to the thread, and a conical section associated with it, and the outer diameter of the end of the conical section is from 83 to 84 mm.

Due to the fact that the outer diameter is increased to 123.8-127 mm, the durability of the connection is increased by creating a margin for wear of the outer part of the coupling.

Due to the fact that the average thread diameter in the main plane is from 96.7 to 97.7 mm and thereby increases the diameter of the larger base of the cone of the nipple end (from 100.5 to 101.5 mm), the PC strength is increased compared to the prototype, the greatest increase in the maximum permissible torque of the PC lock is achieved. At the same time, in locks with an outer diameter of 127 mm and an inner diameter of 57.2 to 68.3 mm, the nipple remains a weak element. In locks with an outer diameter of 123.8 mm and an inner diameter of 65.1 to 68.3 mm, the nipple also remains a weak element. This creates a reserve for wear of the outer diameter of the lock without losing its strength properties.

With a decrease in the average thread diameter in the main plane below 96.7 mm, the increase in the maximum allowable torque becomes insignificant, and with an increase in the average thread diameter in the main plane above 97.7 mm, the coupling becomes a weak element of the interlock connection and the connection becomes unbalanced according to the bending strength condition .

By giving the outer surface of the inner stop at the end of the threaded section of the nipple end of a cylindrical shape, turning into a conical shape with a taper equal to 1/9.6 at the end of the nipple, the maximum allowable torque PC of the lock increases due to an increase in the outer diameter and wall thickness of the stop, and , respectively, the surface area of the stop. The outer diameter of the inner stop of the nipple end lies in this case in the range from 83 to 84 mm. The reliability of the second stop of the nipple thus increases. Even if the second stop is damaged during careless operation of drill pipes, the metal protruding outward on the conical end of the nipple does not impede the screwing of the tool joint, which cannot be said about the cylindrical shape of the end of the nipple.

In addition, the conical shape of the end of the inner stop facilitates the centering of the drill pipe during the assembly of the string, thereby speeding it up.

An additional advantage of the proposed castle is the best maintainability compared to the prototype. For re-cutting the coupling part of the proposed lock, the loss of length is about 45 mm versus 80 mm for the prototype.

The essence of the invention is illustrated by drawings.

In FIG. 1 shows a partial longitudinal section of the nipple of the proposed utility model.

In FIG. 2 shows an enlarged view of the end section of the nipple.

In FIG. 3 shows a partial longitudinal section of the coupling of the proposed invention.

The nipple 1 of the proposed lock (Fig. 1) has an outer diameter D ₁ ranging from 123.8 to 127 mm (123.8≤D ₁ ≤127 mm). The inner diameter D _{2 of} the nipple ranges from 57.2 to 68.3 mm (57.2≤D ₂ ≤68.3 mm). The trapezoidal tapered thread 2 of the nipple 1 and the coupling 3 (Fig. 3) has a pitch of 8.467 mm, a taper of 1:9.6 and a profile angle of 90 degrees. The average thread diameter d _cp in the main plane indicated by line 4 is 96.7 to 97.7 mm (96.7≤d _cp ≤97.7 mm). Accordingly, with the given thread parameters, the outer diameter d _{1 of} the large base of the threaded cone of the nipple lies in the range from 100.5 to 101.5 mm (100.5≤d ₁ ≤101.5 mm). Distance L from the main plane to the plane of the thrust end of the interlock (15.875 mm) is standard according to GOST 28487-2018.

The outer surface of the inner stop of the nipple 1 has a cylindrical section 6 adjacent to the thread 2, conjugated with the end section 7 having a conical shape with a taper of 1:9.6 (Fig. 2). The larger diameter D _{3 of} the end portion of section 7 is in the range from 83 to 84 mm (83≤D ₃ ≤84 mm). This design increases the maximum allowable torque of the PC lock by increasing the outer diameter and wall thickness of the stop and, accordingly, the surface area of the stop.

The side wall 8 of the inner bore of the coupling 3 is made cylindrical. The diameter of the inner bore of the coupling D _past provides a guaranteed clearance of 0.8 to 1.6 mm between the bore surface and the diameter D _{4 of} the cylindrical part of the inner stop when assembling the joint.

The conical shape of the end section 7 of the internal stop facilitates the centering of the drill pipes during the assembly of the string, thereby speeding it up.

The claimed connection with the code name Z101 / 9.6, where 101 is the nominal size of the tool joint, and 9.6 is the taper of the thread, is applicable for use on drill pipes with an outer diameter of 88.9 and 101.6 mm, as well as on drilling collars, TBTs , subs and other elements of the drill string.

In particular:

- for drill pipes 88.9×9.35 of strength group S, the ratio of the torsion strength of the lock Z101/9.6 (123.8×65) to the torsion strength of the pipe body is 1.13; weak element - nipple, W _m /W _n =2.08;

- for drill pipes 88.9×9.35 of strength group S, the ratio of the torsion strength of the lock Z101/9.6 (127×68.3) to the torsion strength of the pipe body is 1.01; weak element - nipple, W _m /W _n =2.48;

- for drill pipes 101.6×8.38 of strength group S, the ratio of the torsion strength of the lock Z101/9.6 (127×62) to the torsion strength of the pipe body is 1.0; weak element - nipple, W _m /W _n =2.22;

- for drill pipes 88.9×9.35 of strength group S, the ratio of the torsion strength of the lock Z101/9.6 (127×68.3) to the torsion strength of the pipe body is 0.81; weak element - nipple, W _m /W _n =2.48;

- for drill pipes 88.9×9.35 of strength group S, the ratio of the torsion strength of the lock Z101/9.6 (127×57.2) to the torsion strength of the pipe body is 1.32; weak element - nipple, W _m /W _n =2.09;

- for drill pipes 101.6×8.38 of strength group S, the ratio of the torsion strength of the lock Z101/9.6 (127×57.2) to the torsion strength of the pipe body is 1.06; weak element - nipple, W _m / W _n = 2.09.

Connection Z101 / 9.6 with the same outer and inner diameters of the lock has a gain in the maximum allowable torque over the connection Z-99 from 6 to 12%.

For example:

1. Double-shoulder joint Z101/9.6 (123.8×62) with the same overall dimensions as the joint Z2-99 (123.8×62) specified in PM No. 181276 will have the following characteristics:

- tensile load Qpc=3300 kN; (against 3130 kN at lock Z2-99 according to PM No. 18176);

- torsion moment Мcr.rs=54.9 kN⋅m (against 51.5 kN⋅m at lock Z2-99 according to PM No. 18176).

The gain in tensile load compared to Z2-99 (123.8×62) is 5.5%.

The gain in torque compared to Z2-99 (123.8×62) is 6.6%.

2. Double-shoulder joint Z101/9.6 (123.8×68.3) with the same overall dimensions as the Z2-99 (123.8×68.3) joint specified in PM No. 181276 will have the following characteristics :

- tensile load Qpc=2770 kN (against 2600 kN for lock Z2-99 according to PM No. 18176);

- torsion moment Мcr.rs=45.5 kN⋅m (against 40.6 kN⋅m at lock Z2-99 according to PM No. 18176);

The gain in tensile load compared to Z2-99 (123.8×68.3) is 6.5%.

The gain in torque compared to Z2-99 (123.8×68.3) is 12%.

3. Double-shoulder joint Z101/9.6 (127×57.2) with the same overall dimensions as the Z2-99 (127×57.2) joint specified in PM No. 181276 will have the following characteristics:

- tensile load Qpc=3680 kN; (against 3490 kN at lock Z2-99 according to PM No. 18176);

- torsion moment Мcr.rs=60.0 kN⋅m. (against 58.8 kN⋅m at lock Z2-99 according to PM No. 18176);

The gain in tensile load compared to Z2-99 (127×57.2) is 5.4%.

The gain in torque compared to Z2-99 (123.8×57.2) is 3.4%.

An additional advantage of the proposed lock is the best maintainability compared to the prototype (less loss of length when re-cutting the connection).

Claims (1)

Threaded connection of drill pipes, made with external and internal stops, including nipple and socket ends with trapezoidal conical thread, the pitch of which is 8.467 mm, the taper is 1:9.6, the profile angle is 90 degrees, characterized in that the outer diameter is from 123.8 to 127 mm, inner diameter - from 57.2 to 68.3 mm, average thread diameter in the main plane - from 96.7 to 97.7 mm, internal stop of the pin end has a cylindrical section adjacent to the thread, and a conical section associated with it, the outer diameter of the end part of which is from 83 to 84 mm.

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