RU2549620C1 - Threaded connection of drill pipes - Google Patents

Abstract

FIELD: mining.

SUBSTANCE: surface area of a thrust face of a coupling of a threaded connection in a maximum worn-out state is equal to surface area of a critical section of a nipple, which is multiplied by a coefficient of optimum stress of pre-tightening and at the same time, the surface area of the thrust face of the nipple, due to which optimum values of the main parameters of the connection are provided.

EFFECT: improving reliability and efficiency of functioning of a drill column both at drilling and during performance of lowering and lifting operations.

3 dwg, 1 tbl, 1 ex

Description

The invention relates to drilling equipment and relates mainly to drill pipes used in high-frequency diamond drilling with a removable core receiver.

There is the closest analogue adopted for the prototype. This is a threaded joint for NRQ drill pipes from Boart Longyear / 2 /.

A design feature of such a threaded connection is the presence of two, external and internal, thrust joints, and in a new, worn-out joint, the area of the inner joint is always less than the area of the outer and the tension from the preliminary tightening is determined by the area of the thrust end of the nipple.

The main disadvantage of the threaded connection developed by Boart Longyear as a prototype is the irrational ratio of the areas of the thrust ends of the coupling, nipple and the dangerous section of the latter, which leads to insufficient preliminary tightening of the connection, and, as a result, to a decrease in its endurance and torque limit.

The endurance limit is most accurately assessed by the alternating alternating bending moment (M _before ), and depends on the pre-tension of the threaded connection / 4 /. Figure 1 presents a graph of the dependence of the coefficient of influence on the endurance limit of the tension of the pre-tightening. (K _VPZ ) from the coefficient K _s , which is determined by the expression / 3 /:

$$K_{\mathrm{at}Ps}=f\left(K_s\right),(\mathrm{one})$$

where K _z = σ _z / σ _t is the stress coefficient of the preliminary tightening of the connection;

σ _s - pre-tension in a dangerous section of the nipple;

σ _t - yield strength of the nipple material.

This graph shows that the value of K _VPS increases from the value at which the compound had a _fatigue limit without preliminary tightening (the position on the graph corresponds to zero) to the maximum value of K _VPS = 2.80 at K _s = 0.66, after which it begins to decrease .

In the NRQ drill pipe threaded joint, the area of the dangerous section of the nipple is 450 mm ² and, provided that the stress in the thrust end of the nipple is equal to the yield strength, according to the schedule, its area should be 450 · 0.66 = 297 mm ² . In fact, it is equal to 203 mm ² , i.e. 46% less than necessary to ensure the maximum value of M _before .

At the same time, the area of the persistent end of the coupling in the extremely worn state is 242 mm ² , which is 19% more than the area of the persistent end of the nipple. This excess area is not realized in any way, but it cannot be realized, since the tension from the tightening is determined by the smaller area of the thrust end of the nipple, which indicates the irrational use of the total cross-sectional area of this threaded connection.

In addition, the too small area of the persistent end of the nipple and the persistent end of the worn coupling of the threaded connection, lead to known cases of their deformation when placing the candle on the candlestick during lifting or on the coupling of the top of the column during descent. Cases of cone-shaped deformation of the end face of the nipple are also frequent, leading to the overlap of the internal connection channel and an emergency situation due to the impossibility of passing the core-receiving pipe both during descent and, which is especially dangerous, when removing it filled with core, i.e. when lifting after the end of the next drilling trip.

Insufficient torque of the threaded connection limits the achievement of significant drilling depths and also deprives the possibility of reliable operation at shallow depths, but differing in complex geological and technical conditions associated with increased power consumption for rotation and, accordingly, high torques.

The objective of the invention is to create a threaded connection with the optimal ratio of geometric parameters, providing maximum values of torque and endurance limit of the connection, higher strength of its thrust ends for reliable operation of the drill string during drilling and hoisting operations.

To solve this problem, in a threaded joint of a drill pipe, consisting of a nipple and a coupling, with a tapered thread and two, external and internal, thrust joints, at given values of the external and internal diameters of the connection, its outer diameter in the extremely worn state, thread length, height of its profile at the nipple and the coupling, the area of the persistent end of the coupling in the extremely worn state is equal to the area of the dangerous section of the nipple, multiplied by the coefficient of the optimal pre-tension voltage and simultaneously the area persistent end of the nipple.

The invention is illustrated by drawings (figure 2), which shows: 1 - coupling; 2 - nipple; 3 - persistent end face of the coupling; 4 - persistent end of the nipple; 5 - wear part of the body of the connection along the outer diameter.

Note that the plane of dangerous sections of the nipple and the coupling are located near the plane of the outer and inner thrust joints (hereinafter, joints), respectively. For the convenience of calculations, we assume that the plane of the dangerous section of the nipple coincides with the plane of the outer joint, and the plane of the dangerous section of the coupling with the plane of the inner joint.

The claimed invention allows to solve the problem.

Indeed, we have the following initial parameters of the threaded connection:

D and d are the outer and inner diameters of the threaded connection;

D _and - the outer diameter of the threaded connection in extremely worn condition;

t _m and t _n - the height of the thread profile, respectively, of the coupling and nipple;

L is the length of the thread.

We also have two conditions for optimizing the remaining parameters of the threaded connection. The first condition:

$$S_{\mathrm{at}tm}=S_{\mathrm{about}\mathrm{from}n}\cdot K_s(2)$$

where S _utm - the area of the persistent end face of the coupling in extremely worn condition;

S _main area of the dangerous section of the nipple;

K _s - stress coefficient of the preliminary tightening of the threaded connection The second condition:

$$S_{\mathrm{at}tm}=S_{\mathrm{at}tn},(3)$$

where S _utm - the area of the persistent end of the nipple.

It is required to determine the following parameters of the threaded connection taking into account the specified conditions for their optimization:

D _rns - the outer diameter of the thread of the coupling in the plane of the outer joint;

D _RVS - the outer diameter of the thread of the coupling in the plane of the inner joint;

d _rns - the inner diameter of the thread of the nipple in the plane of the outer joint;

d _RVS - the inner diameter of the thread of the nipple in the plane of the inner joint;

K _p - the taper of the thread.

We assume that t _m + t _n = a . Then, according to condition (2), we have the following equality

After transformations of equality (4), we obtain the value of D _rns from the following equation

$$D_{R\mathrm{and}\mathrm{from}}=B/2+{\left|{\left(B/2\right)}^2-C\right|}^{0,5},(5)$$

where B = 2 a K _s / (K _s +1);

Having determined from the expression (5) the outer diameter of the thread of the coupling in the plane of the outer joint, we find the internal diameter of the thread of the nipple in the same plane

To determine the inner diameter of the thread of the nipple in the plane of the inner joint, we first find the expression of the area of the thrust end of the nipple

$$S_{\mathrm{at}tn}=\left(d_{R\mathrm{at}\mathrm{from}}^2-d^2\right)0.785(7)$$

and according to condition (3) we have

$$\left(d_{R\mathrm{at}\mathrm{from}}^2-d^2\right)0.785=\left(D_{\mathrm{and}}^2-D_{Rn\mathrm{from}}^2\right)\mathrm{0.785,}(8)$$

where do we find the inner diameter of the thread of the nipple in the plane of the inner joint

$$d_{R\mathrm{at}\mathrm{from}}={\left(D_{\mathrm{and}}^2-D_{Rn\mathrm{from}}^2+d^2\right)}^{0,5}(9)$$

Since the outer diameters of the thread of the nipple are determined in the planes of the external and internal joints, we determine the taper of the thread

$$K_R=\left(d_{Rn\mathrm{from}}-d_{R\mathrm{at}\mathrm{from}}\right)/L(10)$$

Finally, having an expression of taper, we determine the outer diameter of the external thread in the plane of the internal joint

$$D_{R\mathrm{at}\mathrm{from}}=D_{Rn\mathrm{from}}-L{K}_R=D_{Rn\mathrm{from}}-\left(d_{Rn\mathrm{from}}-d_{R\mathrm{at}\mathrm{from}}\right)\cdot L/L=D_{Rn\mathrm{from}}-d_{Rn\mathrm{from}}+d_{R\mathrm{at}\mathrm{from}}(\mathrm{eleven})$$

Thus, all the desired thread parameters are defined in general, i.e. in letter form, taking into account the source data and the given conditions for solving the problem. Since the geometrical parameters of the threaded connection are also determined taking into account the given ratio of the areas of the thrust ends of the nipple coupling and its dangerous section, which ensures the optimum pre-tension of the connection, the torque and its endurance limit must have maximum values. You can verify this when solving the problem in numerical form for the proposed threaded connection and compare the obtained parameters with the connection parameters adopted for the prototype, as shown in the example implementation of the invention.

An example implementation of the invention.

For example, we take the initial parameters of the threaded connection adopted for the prototype, i.e. NRQ drill pipe connections:

D = 69.90 mm; d = 60.30 mm; D _and = 69.00 mm; L = 41.99 mm; t _m = 0.90 mm; t _n = 0.95 mm; yield strength of steel σ _t = 1000 MPa; temporary resistance σ _in = 1200 MPa. We take K _s = 0.66.

To determine the outer diameter of the thread of the coupling in the plane of the outer joint, we calculate the following quantities included in equation (5):

a = 0.90 + 0.95 = 1.85 mm;

B = 2 · 1.85 · 0.66 / (0.66 + 1) = 1.47;

C = {0.66 (1.85 ² -60.30 ² ) -69.00 ² } / (0.66 + 1) = - 4312.4

Substituting these quantities into equation (5) we have

D _rns = 1.47 / 2 + | (1.47 / 2) ² +4312.4 | ^0.5 = 66.40 mm

The inner diameter of the nipple in the plane of the outer joint according to (6)

d _rns = D _rns -1.85 = 64.55 mm.

From expression (9) we find the inner diameter of the thread of the nipple in the plane of the inner joint

d _RVS = (69.0 ² -66.4 ² +60.3 ² ) ^0.5 = 63.15 mm

Thread taper from expression (10)

K _p = (64.55-63.15) / 41.99 = 0.0334 (1: 29.94)

Having taper, determine the outer diameter of the thread of the coupling in the plane of the inner joint

D _RVS = 66.40-41.99.0334 = 65.00 mm

Having obtained the main parameters of the threaded connection, we calculate their derivatives: the area and wall thicknesses of the external and internal joints and dangerous sections of the nipple and the coupling, the moments of bending resistance of these sections and their wall thicknesses, the tightening torques of the threaded connection and the endurance limits of the joints depending on their preliminary tightening and taking into account the schedule in figure 1.

All these parameters for the new compound (option No. 1) and two so-called control variants (No. 2 and No. 3) of compounds in comparison with the same parameters of the compound adopted as a prototype are shown in Table 1.

Table 1 Name of the parameters of the threaded connection Threaded connection values Prototype (NRQ) New and control options * ¹ Number 2 No. 1 Number 3 1. The diameters of the threaded connection, mm: outer 69.90 69.90 69.90 69.90 interior 60.30 60.30 60.30 60.30 2. The stock of wear on the outer diameter, mm * ² 0.9 0.9 0.9 0.9 3. The outer diameter of the thread of the coupling, mm: in the plane of the outer joint 66.73 66.50 66.40 66.30 in the plane of the inner joint 64.26 64.90 65.00 65.11 middle in the middle of the thread length 65.5 65.7 65.7 65.7 4. The internal diameter of the thread of the nipple, mm: in the plane of the outer joint 64.95 64.65 64.55 64.45 in the plane of the inner joint 62.55 63.05 63.15 63.26 5. Thread taper 1:17 1: 26.25 1: 29.94 1: 35.28 6. The area of the persistent end of the coupling, mm ² : new 340 364 374 385 in extreme wear condition 242 266 275 287 7. Wall thickness of the coupling end face, mm: new 1,58 1.70 1.75 1.80 in extreme wear condition 1.14 1.25 1.30 1.35 8. The area of the persistent end of the nipple, mm ² : from the condition of optimum tension 297 282 275 268 actually 203 266 275 287 9. Wall thickness of the persistent end of the nipple, mm: from the condition of optimum tension 1,50 1.45 1.40 1.35 actually 1.05 1.38 1.40 1.48 10. The area of the dangerous section, mm ² : nipple 450 427 416 406 couplings of the new coupling 545 527 519 508 worn out 447 431 421 410 11. Wall thickness of the dangerous section, mm: nipple 2,32 2.18 2.12 2.08 couplings new 2.75 2,50 2.45 2.40 worn couplings 2,30 2.05 2.00 1.95 12. The moment of resistance of the dangerous section during bending, 10 ³ mm ³ : nipple 6.9 6.6 6.4 6.3 couplings new 9.8 8.8 8.7 8.4 worn couplings 8.1 7.1 7.0 6.8 13. Ultimate alternating bending moment (M _before ), Nm: nipple (connections without preliminary tightening) * ³ : 385 368 357 349 couplings new 1680 508 1490 1440 worn couplings 1388 1217 1200 1166 14. The voltage coefficient of the preliminary tightening of the threaded connection, K _s 0.45 0.62 0.66 0.71 15. The coefficient of influence of the tension of the pre-tightening on the endurance limit of the threaded connection K _VPZ 2.22 2.66 2.80 2.66 16. The alternating alternating bending moment of the connection with the preliminary tightening of the thread (M _before ), Nm: 855 980 1000 940 17. The ultimate torque of the tightening of the threaded connection from the condition of reaching the yield strength of the material in the thrust end of the nipple, kNm ^{* 4} 2.64 3.49 3.57 3.52 18. The maximum depth of the well, at which the torque in the upper end of the drill string reaches the maximum torque, m * ⁵ 2450 3500 3700 3600 19. Ultimate tensile load at which the stress in the dangerous section of the joint reaches the yield strength, kN * ⁶ 447 427 416 406 Notes: * ¹ The main one is option No. 1, since it is calculated according to the given conditions (2) and (3). Control options No. 2 and No. 3 are distinguished by the fact that the outer diameter of the coupling thread in the plane of the outer joint was not calculated, but was adopted for OD mm larger and smaller, respectively, than basically, and then other parameters were calculated. Comparison of their parameters with the parameters of the main option allows us to conclude that the latter is optimal for a given size of a threaded connection. * ² Boart Longyear does not recommend this parameter in its / 1 / directory. The value of the maximum wear on the outer diameter of the joint was adopted based on the data of Russian Drilling Company, which has been operating NRQ drill pipes for many years. At the same time, the average resource of a drill pipe in rocks of the VI-VII categories for drillability and average abrasiveness is about 6000 meters or 2000 hours of pure drilling at an average rotational speed of the drill string of 1000 rpm. and a mechanical speed of 3 m / h. According to the * ^3/6 / smooth specimen endurance limit for steel with a strength σ _in = 1200 MPa is σ _-1 = 1200 · 0.40 = 480 MPa, and fatigue strength reduction factor for the coupling due to stress concentration on its surface / 4 / is the value of (K _σ ) d = 2,8. As a result, the endurance limit, expressed in the ultimate bending moment, for example, for a new NRQ pipe threaded coupling, will be 480: 2.8 · 9.8 · 10 ³ = 1680 · 10 ³ Nmm = 1680 Nm, where 9.8 · 10 ³ mm ³ - the moment of resistance of the dangerous section of the coupling in bending. In all considered variants of connections, a thread with a pitch of 8.466 mm of a trapezoidal profile with a negative angle of its working side is adopted. Based on field tests of threaded joints carried out by Drilling Equipment Plant OJSC, for a thread of this profile, the value (K _σ ) d = 8.6. (for threads with a triangular profile and rounded cavities, it is 6.3 / 5 /). Therefore, for example, for a nipple, i.e. the connection without pre-tightening the NRQ pipe, the ultimate bending moment will be 480: 8.6 · 6.9 = 385 Nm, and for the same connection, but with the preliminary tightening - 385 · K _VPZ = 385 · 2.22 = 855 Nm. Here, the nipple is underloaded due to the small value of K _VPS . In the control version of the connection No. 2, the nipple, when tightened, is on the contrary overloaded (K _s = 0.71 instead of 0.66). Therefore, it is advisable to take the tightening force and, accordingly, the torque for this connection not according to the actual area (287 mm ² ) of the thrust end of the nipple, as shown in the table, but according to the area (268 mm ² ) calculated from the optimum tightening voltage. Then the coefficient K _VBZ = 2.8 and, accordingly, M _pre = 349 · 2.8 = 977 instead of 940 Nm. For all compared variants of connections, the value of M _before the dangerous section of the coupling, both new and worn, is significantly higher than that of the dangerous section of the nipple, which is confirmed by practice - breaks in the column almost always occur along the dangerous section of the nipple. * ⁴ Tightening torque is determined from the known dependencies / 1 /. It includes three components: moments of resistance to friction forces in the thread, external and internal thrust joints. For example, for the threaded connection of the NRQ pipe, the sum of these components is 1.333 + 0.690 + 0.617 = 2.64, and for the proposed 1.807 + 0.933 + 0.833 = 3.57 kNm. * ⁵ This parameter was obtained for the following drilling conditions: The well is vertical, its diameter, taking into account the development coefficient, is 83.6 mm (76 · 1.10 = 83.6). The rotation speed is 1000 rpm, the axial load on the diamond drill bit is 19.6 kN. First, the consumed power for the rotation of the drill string at a given depth of the well was determined using the Kardysh-Okmyansky formula / 7 /, and then the rotation torque corresponding to it at this depth: Well depth, m 1000 2000 3000 4000 Power consumption, kW 143 238 322 399 Torque of rotation, kNm 1.36 2.27 3.08 3.81 Figure 3 presents a graph of the dependence of the torque of the rotation of the drill string from the depth of the borehole in the given drilling conditions. * ⁶ The ultimate tensile load was determined by the minimum area of dangerous cross sections of the nipple and sleeve at a given yield strength of the material of the drill pipe. For example, to connect the NRQ pipe, the clutch section area in the worn state is minimal. Therefore, the ultimate tensile load will be 447 mm ² · 1000 N / mm ² = 447000 N = 447 kN.

From the data given in Table 1, it follows that a threaded connection made in accordance with two predetermined initial positions (2) and (3) has an optimal combination of geometric parameters and, as a result, the limiting torque increases by 35%, the limiting (in specified drilling conditions) the depth of the well, as a result, is 48%, and the endurance limit is higher by 17%. The area of the persistent end of the nipple is larger by 33, and the couplings in extremely worn condition by 14%, which contributes to a more reliable functioning of the drill string using a removable core receiver during tripping with the drill string.

It should be noted that as a result of the unbalanced geometric parameters of the thread, the ultimate tensile load at the joint of the NRQ drill pipe turned out to be 7% higher than the proposed one, which is insignificant, since it is practically not realized.

Indeed, this load naturally arises at the moment of the beginning of the rise of the drill pipe string from the maximum depth of the borehole (pos. 18, Table 1) and will actually be equal to the mass of the string (for a vertical borehole, it can be assumed that the buoyancy force of the flushing fluid is balanced by the resistance to friction against the walls wells). For an NRQ column, the maximum depth of the well is 2450 m. With a specific gravity of 7.8 kg / m, the mass of the column at this depth is 19 110 kg or 187 kN, which is 42% of its ultimate tensile load and, therefore, an advantage of 7% for ultimate tensile load does not play any role here.

For a drill pipe with the proposed threaded connection, the maximum depth of the well is 3700 m with a total mass of the string of 28860 kg or 283 kN, while the ultimate tensile load is 416 kN, which is quite enough.

The considered implementation example showed that as a result of solving the task, the threaded connection of drill pipes due to the optimal combination of geometric parameters has advantages over the prototype in terms of maximum torque and endurance limit, it has more durable thrust ends, which in general provides more reliable and efficient functioning of the drill string.

Literature

1. Birger I.A. Calculation of threaded connections. M .: State. ed. defense. prom., 1959, 252 p.

2. Drill and casing pipes. Consolidated product catalog. BOART LONGYEAR ™. .

3. Lachinyan L.A., Ugarov S.A. Design, calculation and operation of drill exploration pipes and their compounds. M .: Nedra, 1975, 232 p.

4. Lachinyan L.A. The work of the drill string. - 2nd ed., Revised. and add. - M .: Nedra, 1992, - 214 p., Ill.

5. Saroyan A.E. Theory and practice of the drill string. - M .: Nedra, 1990 .-- 263 p., Ill.

6. Resistance of materials, Kinasoshvili RS Ch. ed. Physical and mathematical literature ed. “Science”, 1968, 384 pp.

7. Handbook of an engineer for drilling exploration wells: in 2 volumes / Edited by prof. Kozlovsky. - Volume 2. - M .: Nedra, 1984, 437 p.

Claims (1)

A threaded joint of a drill pipe consisting of a nipple and a sleeve with a tapered thread and two external and internal thrust joints for given values of the external and internal diameters of the joint, its outer diameter in extremely worn condition, the length of the thread, the height of its profile at the nipple and couplings, characterized in that the area of the persistent end of the coupling in the extremely worn state is equal to the area of the dangerous section of the nipple, multiplied by the coefficient of the optimal pre-tension voltage and simultaneously the end face of the nipple, which ensures optimal values of the main parameters of the connection, including the outer diameter of the thread of the coupling in the plane of the external stop joint, determined from the expression:
$$D_{Rn\mathrm{from}}=B/2+{\left|{\left(B/2\right)}^2-C\right|}^{0,5}$$

,
where B = 2aK _s (K _s +1);
$$C=\left|K_s\left(a^2-d^2\right)-D_{\mathrm{and}}|/\left(K_s+\mathrm{one}\right)\right|$$

;
a = t _m + t _n - the sum of the heights of the thread profile, respectively, of the coupling and nipple;
K _s = σ ₃ / σ _t = 0,66 - the coefficient of the optimal voltage of the preliminary tightening of the connection;
σ _s - pre-tension in a dangerous section of the nipple;
σ _t - yield strength of the compound material;
d is the inner diameter of the compound;
D _and - the outer diameter of the connection in extremely worn condition, as well as the inner diameter of the thread of the nipple in the same plane d _pbc = D _rns - D, the inner diameter of the thread of the nipple in the plane of the internal thrust joint $$d_{Rn\mathrm{from}}={\left(D_{\mathrm{and}}^2-D_{Rn\mathrm{from}}^2+d^2\right)}^{0,5}$$

, the taper of the thread, determined from the expression (d _rns -d _rvs ) / L, where L is the length of the thread, and the outer diameter of the thread of the coupling in the plane of the inner joint D _rvs = D _rns -d _rns + d _rvs .

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