CN115114790B - Drill string double-shoulder joint shoulder optimization design method - Google Patents

Abstract

The invention provides an optimal design method for a double-shoulder joint shoulder of a drill string, which comprises the following steps: firstly, determining a double-shoulder joint of a drill string to be calculated, and recording the material mechanical parameters and the structural parameters of the double-shoulder joint of the drill string; then determining the type of drilling tool in the double shoulder joint of the drill string; the corresponding strength calculation method is used according to different drilling tool types, the strength of the drilling tool and the deformation of the inner shoulder and the outer shoulder are calculated according to mechanical parameters and structural parameters, and the make-up torque of the double-shoulder joint of the drill string is calculated through a double-shoulder Frer formula; finally, according to the calculated deformation of the inner shoulder and the outer shoulder and the buckling torque of the double shoulders, the optimal design parameter combination of the gap design size of the inner shoulder and the buckling torque is obtained; the invention effectively solves the problems of difficult observation of shoulder plastic deformation, difficult determination of make-up torque and the like in the process of making-up and breaking-out on the threaded joint of the drill string with the torque shoulder, and realizes the efficient and accurate design of the make-up torque of the threaded joint of the drill string.

Description

A shoulder optimization design method for double shoulder joint of drill string

Technical Field

The invention relates to the technical field of drill tool joints, and in particular to a shoulder optimization design method for a drill column double-shouldered joint.

Background Art

During the oil drilling process, drill pipes are needed to provide high-pressure mud to enter the channel, transmit tension and torque, and apply drilling pressure to the drill bit through partial gravity of the drill collar to ensure that the pressure neutral surface is on the drill collar under compression to withstand alternating stress, reduce the vibration, swing and jump of the drill bit, make the drill pipe work smoothly and control the well inclination. The drill pipe and drill collar are composed of multiple sections, and the tightness of the two-section threaded connection needs to be ensured. During the drilling process of the drill bit, drilling pressure needs to be provided by the drill collar. The drill pipe and drill collar transmit torque, and sufficient strength must be ensured at the threaded connection. The main failure forms of the joint are excessive deformation, fracture and surface damage. The first two failure forms are related to the elastic-plastic properties of the threaded connection.

In order to meet the increasingly demanding drilling conditions, double-shouldered drill pipe joints with an internal shoulder structure are currently widely used. The internal shoulder structure has the function of assisting the buckle positioning and bearing part of the load, which can reasonably improve the stress distribution of the joint and enhance the torsion resistance of the joint. In the tolerance design of the double-shouldered joint of the drilling tool, the design must be completed based on the independent principle of tolerance design, the maximum entity principle, and the inclusion principle, combined with actual experience judgment, and the tolerance design experience often needs to be combined with a lot of actual engineering experience to make progress.

In actual tolerance calculation, it is necessary to make a comprehensive judgment based on factors such as the mechanical properties of different materials and the feasibility of processing technology. However, before this invention, there has been no systematic design method for the double shoulder clearance of drilling tools. This invention designs a method that can quickly obtain the shoulder clearance and its make-up torque, so that the clearance at the shoulder joint is more reasonable. Compared with the previous design, the defects can be found:

① The design of shoulder clearance is complex. In actual design, it is necessary to clarify the actual functional requirements. According to the functions and applications, previous designs made extensive use of finite element analysis to obtain the deformation, and the established models were not universal. It also required a high level of design skills on the part of designers to ensure the calculation accuracy of the model, and no complete design method was formed.

② Different designers have different design ideas, which will lead to inconsistent design standards and inconvenience in later maintenance.

Summary of the invention

In view of the above problems, the present invention provides a shoulder optimization design method for a double-shouldered joint of a drill string. By using tolerance deformation data, the basic structural dimensions, bending strength ratio of the drill collar, make-up torque, joint tolerance and deformation optimization design in the design of the double-shouldered joint of the drill tool are achieved.

The present invention adopts the following technical solutions:

A drill string double shoulder joint shoulder optimization design method specifically comprises the following steps:

Step 1: Determine the drill string double shoulder joint to be calculated, and record the material mechanical parameters and structural parameters of the drill string double shoulder joint;

Step 2: Determine the type of drill tool in the double shoulder joint of the drill string in step 1; use the corresponding strength calculation method according to different drill tool types, and calculate the drill tool thread strength according to the mechanical parameters and structural parameters in step 1;

Step 3: According to the strength parameters calculated in step 2, a theoretical analysis is performed to calculate the deformation of the double shoulder, wherein the double shoulder includes an inner shoulder and an outer shoulder, and then the make-up torque of the double shoulder is calculated by the Farr formula of the double shoulder;

Step 4: Based on the deformation of the outer shoulder and the inner shoulder and the make-up torque of the double shoulder calculated in step 3, the optimal design parameter combination of the clearance design size and the make-up torque of the outer shoulder and the inner shoulder is obtained.

Furthermore, the material mechanical parameters and structural parameters of the drill string double shoulder joint input in step one include thread type, inner and outer shoulder distance, inner shoulder angle, inner and outer diameters, base thread pitch diameter, box boring diameter, box to end face length, pin length, pin big and small end diameters, number of threads per inch, thread taper, thread bottom truncation height, thread non-truncation height and thread profile half-angle angle.

Furthermore, the strength calculation in step 2 includes the torque strength calculation of the drill string threaded connection, and the torque strength calculation of the drill string threaded connection includes the torsional strength of the inner shoulder and the outer shoulder, and the torsional strength is calculated by the double shoulder Farr's formula.

Furthermore, when the drilling tool is determined to be a drill rod in step 2, it is necessary to calculate the tensile strength, internal pressure resistance and torque strength of the drill rod thread.

Furthermore, when the drilling tool is determined to be a drill collar in step 2, it is necessary to calculate the bending strength ratio of the drill collar, the tensile strength at the thread of the drill collar, the internal pressure strength and the torque strength.

Further, step three is specifically as follows: according to the strength data calculated in step two, the stress _S1 value of the first buckle of the pin is set, and the deformation of the double shoulders is first calculated. When the buckle is just in contact with the inner shoulder, the outer shoulder deformation ΔL is generated, and the inner shoulder has not yet generated a contact force. The deformation ΔL near the outer shoulder includes the deformation _ΔL1 generated at the root of the pin, the deformation _ΔL2 generated by the thread at the outer shoulder at 3P of the pin, the deformation _ΔL3 generated at the end of the box, and the deformation _ΔL4 generated by the thread at the outer shoulder at 3P of the box;

The calculation formula of the external shoulder deformation is as follows:

ΔL＝ΔL ₁ +ΔL ₂ +ΔL ₃ +ΔL ₄ (5)

After the make-up is continued, the inner shoulder deformation ΔL′ is generated, including the deformation ΔL ₅ of the pin nose tip, the deformation ΔL ₆ of the inner shoulder thread at the root of the pin 3P, the deformation ΔL ₇ of the box root, and the deformation ΔL ₈ of the inner shoulder thread at the box 3P. The calculation formula of the inner shoulder deformation is as follows:

ΔL′＝ΔL ₅ +ΔL ₆ +ΔL ₇ +ΔL ₈ (10)

The specific calculation formula is as follows:

When the calculated stress S ₅ at the nose of the pin exceeds the yield strength of the material, the stress S ₁ of the first pin is reduced and the operation is repeated until the yield strength of the material is met. Finally, the make-up torque of the drill string threaded joint is calculated by the double shoulder Farr formula.

Furthermore, the make-up torque in step 3 is calculated by the double-shoulder Farr formula, which is as follows:

Inner shoulder make-up torque calculation formula:

External shoulder make-up torque calculation formula:

Total Makeup Torque:

_Tn = T + T' (30).

A high-voltage connector, characterized in that the high-voltage connector is provided with a male buckle and a female buckle designed by the gap calculation method.

Furthermore, the pin and box of the joint are high-strength thread seals; thread seals are achieved by deformation of the pin and box, and the thread seals can be used in high-pressure working conditions.

The beneficial effects of the present invention are:

The design method of the present invention can quickly obtain the tolerance range, make the gap at the shoulder joint more reasonable, and improve the strength and service life of the double shoulder joint of the drill string; it overcomes the inevitable defects of the conventional and complex empirical design method, is convenient for unified design, and is beneficial to later maintenance and replacement; the design method of the present invention is simple and clear, easy to use, has the advantages of high universality and low cost, and is conducive to wide use.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings of the embodiments will be briefly introduced below. Obviously, the drawings in the following description only relate to some embodiments of the present invention, but are not intended to limit the present invention.

Fig. 1 is a block diagram of the module structure of the present invention;

FIG2 is a schematic diagram of the deformation of the outer shoulder of the present invention;

FIG3 is a schematic diagram of the deformation of the inner shoulder of the present invention;

FIG4 is a schematic diagram of the basic structural dimensions of a male buckle of the present invention;

FIG5 is a schematic diagram of the basic structural dimensions of the female buckle of the present invention;

FIG6 is a schematic diagram of a threaded connection according to the present invention;

FIG7 is a schematic diagram of threaded connection dimensions of the present invention;

DETAILED DESCRIPTION

The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

As shown in FIGS. 1 to 7 , the present invention provides a technical solution: a drill string double shoulder joint shoulder optimization design method, specifically comprising the following steps:

Step 1: Determine the double shoulder joint of the drill string to be calculated, record the thread type, inner and outer shoulder distance, inner shoulder angle, inner and outer diameters, base thread pitch diameter, box boring diameter, box to end face length, pin length, pin big and small end diameters, number of threads per inch, thread taper, thread bottom truncation height, thread non-truncation height and thread profile half angle of the double shoulder joint of the drill string, and provide basic calculation parameters.

Step 2: According to the parameters in step 1, the thread torque strength of the double shoulder, i.e., the inner shoulder and the outer shoulder, is calculated. The thread torque strength includes the inner shoulder axial force _Fn and the outer shoulder axial force _Fw . The thread torque strength calculation formula is:

A＝min(A _p ,A _b ) (33)

From formulas (31)-(33), we get:

_Fw ＝ _YpA (34)

D _S =C-(L _pc -(B ₁ +B ₂ ))×t _pr (35)

From formulas (35)-(37), we get:

_Fn ＝ _{YpAs '} (38)

Wherein, _bp is the thread bottom diameter at 3/4in from the shoulder, in units of in; _bc is the box bottom diameter at 3/8in from the shoulder, in units of in; _Yp is the yield strength of the shoulder material, in units of psi; _Fw is the axial force of the external shoulder, in units of lbf; _Lpc is the length of the pin, in units of in; _B1 is the distance between the base and the middle diameter of the external shoulder, in units of in; _B2 is the length of the nose end of the internal shoulder joint, in units of in; _tpr is the taper, in units of in/ft; _Fn is the axial force of the external shoulder, in units of lbf;

The calculation formula for the torque strength of the external shoulder is:

The calculation formula for the torque strength of the inner shoulder is:

The calculation formula for the average intermediate radius _Rt of the thread and the average radius _Rs of the shoulder is:

The total torsional strength of the double shoulder is:

_Tn ＝T+T′ (43)

Wherein, _Tn is the total torsional strength of double shoulders, in lbf.ft; T is the torsional strength of the outer shoulder, in lbf.ft; T′ is the torsional strength of the inner shoulder, in lbf.ft; _YP is the yield strength, in psi; A is the minimum of _Ab and _AP , in ² ; θ is the thread profile half angle, in degrees; _Rt is the average intermediate radius of the thread, in in; _Rs is the average shoulder radius, in in; f is the friction coefficient of the contact surface of the thread shoulder, dimensionless; α is the inner shoulder angle, in degrees;

When the drilling tool type is determined to be a drill pipe, the drill pipe strength needs to be calculated;

Drill pipe tensile strength calculation formula:

F _c =7.854×10 ^-7 ·Y _p ·(D_out ² -(D_out-2T) ² ) (44)

Drill pipe internal pressure strength calculation formula:

Drill pipe torque strength calculation formula:

Wherein, B is the bending strength ratio, dimensionless; Z _B is the section modulus of the box, in ³ ; Z _P is the section modulus of the pin, in ³ ; H is the height of the thread without truncation, in ; b is the diameter of the root of the box at the end of the pin, in ; R is the root diameter of the pin at 3/4 in from the shoulder of the pin, in ; Q _c is the boring diameter of the box, in ;

The calculation methods of tensile strength, internal pressure resistance and torque strength of drill collar are the same as those of drill pipe;

The bending strength of the drill tool joint is calculated by the bending strength ratio when the drill collar is selected as the drill tool type. After analyzing a large number of examples of drill collar thread damage by organizations such as API, it was concluded that when the bending strength ratio is 2.50:1, the fatigue strength of the male and female buckles are roughly equal. According to the recommendation of API RP7G, the range allowed by drilling conditions can vary from 3.20:1 to 1.90:1. However, since the outer diameter of the box buckle wears much faster than the inner diameter of the pin buckle, the bending strength ratio will be reduced accordingly. When the bending strength ratio drops to 2.00:1, it is easy to cause the internal thread to expand or crack, disengage, and break the root of the thread. Therefore, after calculation, if the bending strength ratio of the drill collar is not within the range recommended by the API RP7G standard, the design parameters must be adjusted appropriately;

The calculation formula of drill collar bending strength ratio is:

Step 3: Calculate the make-up torque when the length difference between the pin and the box is determined and the inner shoulder just contacts. When the inner shoulder is just contacted, the inner shoulder has not yet generated contact force, the outer shoulder has already contacted and the outer shoulder deformation ΔL generated near the outer shoulder includes the following four deformations: deformation _ΔL1 generated at the root of the pin, deformation _ΔL2 generated by the thread of the pin close to the outer shoulder, deformation _ΔL3 generated at the end of the box, and deformation _ΔL4 generated by the thread of the box close to the outer shoulder;

The deformation ΔL ₁ generated at the root of the pin: The stress is the stress at the first pin of the pin. If the stress at this point is assumed to be known, the deformations at the other three points can be obtained through the stress at this point;

The deformation ΔL ₂ of the thread near the external shoulder of the pin: due to its small cross-sectional area, the stress here is assumed to be consistent with the stress at the first thread of the pin;

Deformation ΔL ₃ generated at the end of the box buckle: The tension generated at the root of the pin buckle is balanced with the pressure generated at the end of the box buckle. The stress at this location can be calculated based on its cross-sectional area.

Deformation ΔL ₄ of the thread of the box near the outer shoulder: only considering the length of the third thread, these four deformations all make ΔL smaller, that is, the nose of the pin is closer to the inner shoulder of the box;

Continue to make-up on the basis of the previous step, determine the make-up torque when the first buckle of the pin buckle yields or the pin buckle nose yields, and the inner shoulder deformation ΔL′ will be generated near the inner shoulder after the inner shoulder contacts, including the following four deformations: deformation of the pin buckle nose ΔL ₅ , deformation of the pin buckle thread near the inner shoulder ΔL ₆ , deformation of the box buckle root ΔL ₇ and deformation of the box buckle thread near the inner shoulder ΔL ₈ ;

Based on the above definition of ΔL ₁ -ΔL ₈ , the given stress value S ₁ at the first thread of the pin can be used. The stress at the pin near the external shoulder thread is assumed to be consistent with the stress at the first thread of the pin, and the value of ΔL ₂ can be calculated. On the basis of S ₁ , since the external shoulder is only affected by the external shoulder force, but the cross-sectional area is different, the value of S ₃ can be calculated. In the second stage of calculation, the shoulder force at the nose of the pin can be calculated using formula (38), and the stress S ₅ at the nose of the pin can be calculated. On the basis of S ₅ , since the shoulder force at the internal shoulder is also affected, and only the cross-sectional area is different, the specific values of S ₆ -S ₈ can be calculated according to the definition of ΔL ₆ -ΔL _8. According to the constitutive equation of the material, the deformation can be calculated according to the stress, so the results _{of ΔL 1 -ΔL 8 can be calculated} .

The calculation formula of the external shoulder deformation is as follows:

ΔL＝ΔL ₁ +ΔL ₂ +ΔL ₃ +ΔL ₄ (5)

The calculation formula of inner shoulder deformation is as follows:

ΔL′＝ΔL ₅ +ΔL ₆ +ΔL ₇ +ΔL ₈ (10)

The specific calculation formula is as follows:

By setting the stress at the first buckle of the pin, ΔL and ΔL′ can be calculated, and then the stress at the nose tip of the pin can be calculated from ΔL′. It can then be determined whether the first buckle of the pin yields first or the nose tip of the pin yields first. After obtaining the stress at the two locations, the double shoulder make-up torque can be calculated according to the double shoulder Farr formula. The calculation formula is as follows:

Inner shoulder make-up torque calculation formula:

External shoulder make-up torque calculation formula:

Total Makeup Torque:

_Tn ＝T+T′ (52)

When the calculated stress at the nose of the pin exceeds the yield strength of the material, the stress of the first pin of the pin is reduced, and the operation is repeated until the yield strength of the material is met;

The calculated deformation of the outer shoulder and the deformation of the inner shoulder are multiplied by the safety factor to obtain the clearance and make-up torque of the double shoulder joint of the drill string that we need to design. The make-up torque safety factor of the drill pipe is 0.52, and the make-up torque safety factor of the drill collar is 0.6.

The drill string is processed according to the calculated clearance of the double shoulder joint of the drill string, and then the make-up is performed according to the calculated make-up torque to obtain the optimal design parameter combination.

The high-pressure joint can be designed by calculating the shoulder of the double-shouldered joint of the drill string. The designed high-pressure joint can be used for sealing under high-pressure working conditions. The thread sealing is achieved through the thread deformation designed by the gap at the joint, which is easy to use.

Example:

This embodiment provides a drill string double shoulder joint shoulder optimization design method, taking the calculation of the torsional strength of the NC46 drill collar with a diameter of 82.55 as an example:

Step 1: Input the drill bit type, thread type, inner and outer shoulder distance, inner shoulder angle, inner and outer diameter size, base thread pitch diameter, box boring diameter, pin length, number of threads, taper, thread bottom cut height, thread non-cut top height and thread profile half angle of the drill collar;

Step 2: Use the parameters in step 1 to obtain the data in Table 1 of the drill collar, which are the mechanical strength of the drill collar NC46 joint and the strength ratio of the inner and outer shoulders to be calculated. Table 2 is the basic structural parameters of the drill collar NC46 joint. The torque strength of the outer shoulder, the torque strength of the inner shoulder and the torsional strength of the double shoulder, as well as the shoulder force of the inner and outer shoulders are calculated by formulas (31)-(43). Table 3 is the calculation result of the drill joint. Step 3: According to the calculation results of Table 3, the tolerance design calculation parameters of the double shoulder joint of the drill tool are calculated by formulas (1)-(27) as shown in Table 4. Step 4: Output the calculation results of the deformation and interference of the inner and outer shoulders of the drill tool as shown in Table 5. Finally, the drill collar is processed according to the calculated deformation and interference of the inner and outer shoulders, and the make-up torque is calculated.

Table 1 Mechanical strength of drill collar joint

Table 2 Basic structural dimension parameters

Table 3 Calculation results of drill joints

Table 4 Tolerance design calculation parameters of double shoulder joint of drilling tool

Table 5 Calculation results of deformation and interference of inner and outer shoulders of drilling tools

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims (7)

1. The method for optimally designing the double-shoulder joint shoulder of the drill string is characterized by comprising the following steps of:

step one: determining a double-shoulder joint of the drill string to be calculated, and recording the material mechanical parameters and the structural parameters of the double-shoulder joint of the drill string;

step two: determining the type of drilling tool in the double-shoulder joint of the drill string in the first step; using corresponding strength calculation methods according to different drilling tool types, and calculating the thread strength of the drilling tool according to the mechanical parameters and the structural parameters in the first step;

Step three: according to the strength parameters calculated in the second step, theoretical analysis is carried out to calculate the deformation of the double shoulders, wherein the double shoulders comprise an inner shoulder and an outer shoulder, and then the buckling torque of the double shoulders is calculated through a double-shoulder Frer formula;

Step four: according to the deformation of the outer shoulder and the inner shoulder and the buckling torque of the double shoulders calculated in the step three, the optimal design parameter combination of the gap design size and the buckling torque size of the outer shoulder and the inner shoulder is obtained;

the third step is as follows: setting the stress S ₁ of the first pin according to the intensity data calculated in the second step, firstly calculating the deformation of the double shoulder, and generating the deformation delta L of the outer shoulder when the upper shoulder is just contacted with the inner shoulder, wherein the deformation delta L near the outer shoulder does not generate contact force, and the deformation delta L near the outer shoulder comprises the deformation delta L ₁ generated at the root of the pin, the deformation delta L ₂ generated at the thread at the outer shoulder at the position of the pin 3P, the deformation delta L ₃ generated at the end of the box and the deformation delta L ₄ generated at the thread at the position of the outer shoulder at the position of the box 3P;

the calculation formula of the deformation of the outer shoulder is as follows:

ΔL＝ΔL₁+ΔL₂+ΔL₃+ΔL₄ (5)

The deformation delta L' of the inner shoulder after the connection comprises the deformation delta L5 of the nose tip of the pin, the deformation delta L6 of the thread at the inner shoulder at the root of the pin 3P, the deformation delta L7 of the root of the box and the deformation delta L8 of the thread at the inner shoulder of the box 3P; the calculation formula of the deformation of the inner shoulder is as follows:

ΔL′＝ΔL₅+ΔL₆+ΔL₇+ΔL₈ (10)

Wherein E is the elastic modulus of the material, and the unit is psi; p is thread pitch, and the unit is in; s ₁ is stress at the first buckle root of the male buckle, and the unit is psi; s ₃ is the box stress in psi; s ₅ is stress at the nose tip of the pin thread, and the unit is psi; s ₆ is root stress at the pin 3P, and the unit is psi; s ₇ is the root stress of the box, and the unit is psi; s ₈ is stress at the outer shoulder of the female buckle 3P, and the unit is psi; l ₁ is the length of the first buckle root of the male buckle, and the unit is in; l ₃ is the length of the female buckle, and the unit is in; l ₅ is the length of the nose tip of the pin, and the unit is in; l ₇ is the root length of the female buckle, and the unit is in;

the specific calculation formula is as follows:

Wherein h ₁ is the height from the buckling root to the base surface, and the unit is in; a ₂ is the annular area of the root of the first pin, the unit is in ²;A₂₁, the area of the root of the box at the position A ₂, the unit is in ²;A₅, the area of the root of the pin 3P, the unit is in ²;A₆, the unit is in ²;A₇, the area of the root of the box, the unit is in ²;A₈, the area of the box 3P, and the unit is in ²; c is the diameter of a basal plane thread pitch circle, and the unit is in; l _p is the length of the male buckle, and the unit is in; d ₅ is the outer diameter of the nose tip of the pin, and the unit is in; d ₆ is the outer diameter of the male buckle 3P, and the unit is in; d ₇ is the external diameter of the root of the female buckle, and the unit is in; d ₀ is the outer diameter of the joint in; d ₁ is the inner diameter of the joint, in; f _w is the external shoulder axial force in psi; f _n is the internal shoulder axial force in psi;

When the stress S ₅ at the nose of the male buckle exceeds the yield strength of the material, reducing the stress S ₁ of the first buckle of the set male buckle, repeating the operation until the yield strength of the material is met, and finally calculating the buckling torque of the threaded joint of the drill string through a double-shoulder Frer formula;

The torque of the button-up in the third step is calculated by a double-shoulder Frer formula, and the calculation formula is as follows:

the calculation formula of the torque of the inner shoulder button-up comprises the following steps:

the calculation formula of the torque of the outer shoulder button-up is as follows:

Total make-up torque:

T_n＝T+T′ (30)

Wherein T _n is the total torsional strength value of the double shoulders, and the unit is lbf.ft; t is the torsional strength value of the outer shoulder, and the unit is lbf.ft; t' is the torsion strength value of the inner shoulder and is expressed as lbf.ft; y _P is the yield strength in psi; a is the minimum value of A _b and A _P, and the unit is in ²; θ is the thread form half angle in degrees; r _t is the mean median radius of the thread in; r _s is the average radius of the shoulder in; f is the friction coefficient of the contact surface of the thread shoulder, and is dimensionless; alpha is the angle of the inner shoulder in degrees.

2. The method of claim 1, wherein the mechanical parameters and structural parameters of the drill string double shoulder joint input in the first step include thread type, internal and external shoulder distance, internal shoulder angle, internal and external diameter, base thread pitch diameter, box bore diameter, box to face length, pin size end diameter, threads per inch, thread taper, thread root height, thread non-truncated height, and thread half angle.

3. The method of optimizing the design of the double-shoulder joint shoulder of the drill string according to claim 1, wherein the strength calculation in the second step comprises calculation of the strength of the threaded connection torque of the drill string, the calculation of the strength of the threaded connection torque of the drill string comprises calculation of the torsional strength of the inner shoulder and the outer shoulder, and the torsional strength is calculated through a double-shoulder fire formula.

4. The method of optimizing the design of the double shoulder joint shoulder of the drill string according to claim 3, wherein when the drilling tool is determined to be the drill rod in the second step, the calculation of the tensile strength, the calculation of the internal pressure resistance and the calculation of the torque strength at the thread of the drill rod are required.

5. The method for optimizing the design of the double-shoulder joint shoulder of the drill string according to claim 3, wherein when the drilling tool is determined to be the drill collar in the second step, calculation of the bending strength ratio of the drill collar, calculation of the tensile strength at the thread of the drill collar, calculation of the internal pressure resistance strength and calculation of the torque strength are required.

6. A high voltage joint, characterized in that it is provided with a pin and a box designed by the clearance calculation method according to any of the preceding claims.

7. The high pressure fitting of claim 6 wherein the pin and box of the fitting are high strength threaded seals.