EA040027B1 - CONNECTING ELEMENT FOR CONNECTING DOWNHOLE PIPES - Google Patents

Description

The field of technology to which the invention belongs

The present invention generally relates to a curved profile thread for connecting a drill string, in particular, although not exclusively, a drill string used for rock percussive drilling.

State of the art

EP 1511911/US 8066307 describes a threaded connection for a drill string intended for rock percussive drilling, comprising male and female screw threads on elements to be connected to form a drill string, said threaded connection being characterized in that a male thread and a female the threads have a trapezoidal profile, wherein said threads run along a conical surface along the length of the thread with a taper angle of less than 7°, and the angles of the thread profile between the side surfaces of the turns and the tangent to the tops of the turns are less than 45°.

The tapered threads described in EP 1511911 are not optimal for evenly distributing the bending load along the length of the thread, and also the tapered threads do not provide reasonable connection and disconnection times. The wear resistance of the tapered threads described in EP 1511911 leaves much to be desired.

Thus, there is a need to provide an improved drill string thread for percussive rock drilling that does not suffer from the aforementioned disadvantages of tapered threads.

The essence of the invention

The present invention generally relates to a curved profile thread for a drill string connector, in particular, although not exclusively, a drill string used for rock percussion drilling. In one embodiment, a connecting element for connecting downhole pipes comprises a tubular body, a female connecting part, a male connecting part, and at least one of the following: a male screw thread made on the outer surface of said body, and a female screw thread made on the inner surface of said corps.

The specified at least one thread has a profile containing a ledge, a cavity and a pair of side surfaces. The protrusion and the cavity are bent along the corresponding first and second bending radii. Each bending radius is greater than the outer diameter of the connecting element.

Compared to the tapered threads described in EP 1511911, curved threads provide the advantage that they have improved connection characteristics and increased stiffness under bending loads. Curvilinear threads reduce connection and disconnection time. Threads with a curved profile more evenly distribute the bending load along the length due to the fact that the curvature of these threads is better aligned with the curvature of the bend. In addition, curved threads have improved wear resistance due to a more perpendicular direction of the contact force, thereby reducing sliding forces.

In one aspect of said embodiment, each side surface is straight and is connected to an adjacent ridge and/or trough by a corresponding arc.

In another aspect of said embodiment, the center line of the thread profile, perpendicular to the arc of each bend radius, is inclined relative to the longitudinal axis of the connecting element at a sharp and nearly perpendicular first angle adjacent to the start of said at least one thread and inclined at a second angle adjacent to the end. said at least one thread, wherein said second angle is less than said first angle.

In another aspect of said embodiment, each bend radius is at least five times the outside diameter of said connector. In another aspect of said embodiment, the thread profile has an asymmetrical shape. In another aspect of said embodiment, the thread profile is trapezoidal. In another aspect of said embodiment, the angle of curvature of said at least one thread is in the range of 1 to 10°. In another aspect of said embodiment, the trough and the ridge are concentric. In another aspect of said embodiment, the valley arc length and the protrusion arc length are equal. In another aspect of said embodiment, the valley arc length and the protrusion arc length are not equal.

In another aspect of said embodiment, the connection comprises a female connector having a female thread and a male connector having a male thread and screwed into the female thread. When the connecting parts are compressed, one of the side surfaces is a contact side surface and the other side surface is a non-contact side surface. Each side surface is straight. Each thread profile has a center line perpendicular to the arc of each respective bend radius. Each side surface is located at an angle, with an inclination relative to the corresponding center line. Each angle at which the contact side surface is located is greater than the corresponding angle at which the non-contact side surface is located.

- 1 040027

Alternatively, each angle at which the non-contact side surface is located is less than 45°.

Since according to EP 1511911 the thread profile angle is defined as being measured from the thread tip, it follows from EP 1511911 that thread profile angles are greater than 45°. Minimizing the angle at which the non-contact side surface is located simplifies separation and facilitates shock wave transmission during separation.

In another aspect of the specified variant of execution, each connecting part is made of metal or alloy. The male connecting part contains a section with an outer diameter, a section with a reduced diameter, having a male thread, and a shoulder connecting these two sections. The shoulder engages with the end of the female fitting to create a metal-to-metal seal.

In another aspect of said embodiment, a percussion drill rod comprises a body having a female fitting having a female thread and welded to a first end of the rod body and a male fitting having a male thread and welded to a second end of the rod body. Alternatively, the outer diameter of said connecting parts is in the range of 0.05 to 0.20 m and each bending radius is more than 1 m.

In another aspect of said embodiment, the drill string comprises a drill rod.

Brief description of the drawings

The following is a description of a particular embodiment of the present invention by way of example only and with reference to the accompanying drawings, in which: FIG. 1 depicts a drill stem comprising a male connector and a female connector, each connector having a curved profile screw thread in accordance with one embodiment of the present invention;

fig. 2A shows a curved helix for designing a curved thread;

fig. 2B shows curved thread parameters;

fig. 3A-3G contain formulas for a helix with a curved profile;

fig. 4 shows a male thread profile with a curved profile;

fig. 5A and 5B are enlarged parts of FIG. 4;

fig. 6 shows the profile of a female thread with a curved profile;

fig. 7A and 7B are enlarged fragments of FIG. 6;

fig. 8 shows male and female connectors screwed together.

Detailed description of the invention

In FIG. 1 shows a drill rod 1 comprising a female connector 2 and a male connector 4, each connector having a respective 2t, 4t screw thread with a curved profile, in accordance with one embodiment of the invention. The drill rod 1 may be made of metal or alloy, such as steel. The drill rod 1 can also be surface hardened, for example by carbon saturation. Each connecting element 2, 4 can be attached, for example welded, by means of a weld 5 to the intermediate body 3 of the rod to form the longitudinal ends of the rod 1. Each weld 5 can be smooth, for example obtained by friction welding. Rod 1 may have a flow channel passing through the specified rod, and can be made 6 m long.

A drill string (not shown) can be made by screwing together drill rods 1 (FIG. 8) with a drill bit at one end and a shank at the other end. The drill bit and shank can also have any of the 2t, 4t helical threads with a curvilinear profile. The drill string can be used for rock percussive drilling with a ground hammer (not shown) or a downhole hammer (not shown). In the case of using a DTH hammer, it can be made with each of the helical threads 2t, 4t with a curved profile for assembly as part of the said drill string.

Alternatively, the rod 1 may include a pair of male connectors 4 and a sleeve (not shown) containing a pair of female connectors 2 that can be used to connect the pair of drill rods to each other. Alternatively, 2t, 4t screw threads with curved profile can be used to connect other types of downhole tubing, such as oilfield drill string, oilfield casing or liners, oilfield production strings, or oilfield sucker rod.

The male connecting part 4 may comprise a tubular body, containing an upper section with an outer diameter for connection with the lower end of the rod body 3, a lower section with a reduced diameter, having an external male thread 4t, made on its outer

- 2 040027 surfaces, and a shoulder 4s fastening said upper and lower sections. The upper section of the male connecting part may have turnkey faces made on its outer surface.

The flow channel in the upper section may contain a guide element and a section of the narrowed element. The narrowed element can pass through the bead 4s and the bottom section.

The female connecting part 2 may comprise a tubular body with a lower section for connection with the upper end of the rod body 3 . The female connecting part 2 may have an internal female thread 2t made on the inner surface of said part adjacent to its flow channel. The flow channel can be made of a suitable size with the possibility of introducing into it a lower section with a reduced diameter of the male connecting part 4 of another drill rod (Fig. 8). The male connector 4 can be screwed into the female connector 2 until the bead 4s abuts the upper part 2p of the female connector, thus creating a metal-to-metal seal to isolate the flow channel and tie the two drill rods together. The flow channel of the female fitting 2 may include a diffuser located adjacent to the lower end of the female thread 2t.

Alternatively, the male fitting 4 can be connected to the upper end of the rod body 3 and the female fitting 2 can be connected to the lower end of the rod body. In this embodiment, the guiding element of the male fitting 4 can be a diffuser and the diffuser of the female fitting 2 can be a guiding element.

In FIG. 2A shows a helix 6 with a curved profile for making 2t, 4t threads with a curved profile. In FIG. 2B shows the parameters of 2t, 4t threads with a curved profile. In FIG. 3A-3G show the formulas for a helix 6 with a curved profile. To create 2t, 4t threads with a curved profile, one or more thread parameters can be selected, using the dimensions of the drill rod 1, for example, the initial diameter D ₀ , the final diameter D1 and the (linear) length L. After selecting the thread parameters, the radius R can be calculated _b bending using the formula shown in FIG. 3A. The bending radius R _b may extend from the center point C _P and may form male thread ridges 4t and female thread troughs 2t. The parameters of the threads can be chosen so that the radius _Rb of the bend is, for example, 5 or 10 times the outer diameter of the connecting parts 2, 4. The outer diameter of the connecting parts 2, 4 can be in the range from 0.05 to 0.20 m , and the radius R _b of the bend can be greater than 1 m, for example in the range from 1.05 to 1.7 m.

After calculating the bending radius _Rb, it is possible to calculate the curvature angle γ using the formula shown in FIG. 3b. The curvature angle γ may be in the range of 1 to 10°. When the curvature angle γ is calculated, it is possible to create a helix 6 with a curvilinear profile using the parametric formulas shown in FIG. 3C-3G. The helix 6 with a curved profile can be used to form the contour of the threads 2t, 4t with a curved profile. In parametric formulas, R(t) may be the radial coordinate of a helix with a curved profile around the longitudinal axis GL of the drill rod 1. The accepted coordinate directions for the formulas given in FIG. 3E-3G may be negative (as shown) for left hand threads and positive for right hand threads.

The female 2t and male 4t threads can be mating, for example the male thread of one drill rod 1 can be screwed into the female thread of another drill rod (FIG. 8). To simplify the make-up and break-out of the 2t, 4t, male 4t and female 2t threads may be similar but not identical mirror images of each other. The calculation process described above can be performed once for a 2t female thread and again for a 4t male thread. Each of the male 2t and female 4t threads may be a two-start thread.

Alternatively, 2t, 4t curved threads may be right hand threads. Alternatively, each of the 2t male and 4t male threads may be a single thread or a triple thread.

In FIG. 4 shows the profile 7m of a male thread 4t with a curved profile. In FIG. 5A and 5B are enlarged fragments of FIG. 4. After creating the contour of the 4t male thread, the 7m profile can be defined. Profile 7m can start at a given distance X ₀ from shoulder 4s. The profile 7m may end at the point where the protrusion of said profile intersects the axis G1 parallel to the longitudinal axis GL and is offset to the end diameter D1. The angle of curvature γ may form a continuation of the profile 7m in the form of an arc from the beginning to the end and may be in the range from 1 to 10°.

As shown in FIG. 5A, the thread profile 7m may have a first projection A1. Said thread profile may have a trapezoidal shape. The first protrusion A1 may be an arc with an (outer) bending radius _Rb and may extend to the second arc A2. The center line C _L can be inclined with respect to the displacement axis G1 at a sharp and almost perpendicular first angle δ ₀ . The second arc A2 may have a radius of less than one percent of the outer radius R _b of the bend. The second arc A2 may extend from the first protrusion A1 to the non-contact side surface E1. The second arc A2 may extend tangentially to the first projection A1 and the non-contact side surface E1.

The non-contact side surface E1 may be a straight line inclined under

- 3 040027 the first angle α of the thread profile relative to the center line C _L . Said first thread profile angle α may range from 35° to 55°, or said first thread profile angle may be less than 45°. The non-contact side surface E ₁ can extend from the second arc A2 to the third arc A ₃ . The third arc A ₃ may have a radius of less than one percent of the outer radius R _b of the bend. The third arc A3 can extend from the non-contact side surface E ₁ to the first cavity Ad. The third arc A3 can run tangentially to the non-contact side surface E ₁ and the first cavity Ad. The thread profile may have a height T between the first root A4 and the second shoulder A ₇ . The first trough A4 may be an arc with an inner bend radius R _b -T and may extend from the third arc A3 to the fifth arc A ₅ . The height T may be less than one percent of the outer bend radius R _b so that the inner bend radius R _b -T is also greater than the outer diameter of the male coupling 4 as described above for said bend radius. The first trough A4 may be concentric with the first ridge A ₁ . The center line C _L may be perpendicular to the arc of each radius R _b , R _b -T bend.

Said fifth arc A ₅ may have a radius of less than one percent of the outer radius R _b of the bend. The fifth arc A ₅ can extend from the first trough A4 to the contact side surface E2. The fifth arc A ₅ can extend tangentially to the first trough A4 and the contact side surface E2. The contact flank E2 may be a straight line inclined at a second angle β of the thread profile with respect to the center line C _L . Said second angle β of the thread profile may be in the range of 40 to 45°. Said first angle α of the thread profile may be less than the second angle β of the thread profile; this ensures an asymmetric profile shape. Said contact side surface E2 can extend from the fifth arc A ₅ to the sixth arc A6. The sixth arc A ₆ can extend from the contact side surface E2 to the second protrusion A7. The sixth arc A ₆ may extend tangentially to the contact side surface E2 and the second protrusion A ₇ . The second protrusion A ₇ may be an arc with an outer radius R _b of the bend.

The thread profile may have a pitch β (along the length of the arc) from the beginning of the profile 7m to the middle of the second shoulder A7. The first protrusion A ₁ may have an arc length X1 which may also be half the arc length of the second protrusion A7. The first trough A4 may also have an arc length equal to two arc lengths Xi.

Alternatively, said projections and depressions may have different arc lengths. Alternatively, said second thread profile angle may be less than 45°.

As shown in particular in FIG. 5B, due to the bending of the profile 7m at each bending radius R _b , R _b -T , the center line C _L of the thread profile adjacent to the end of the profile 7m can be inclined with respect to the displacement axis G ₁ at a second acute angle δ ₁ which is smaller than the first angle δ ₀ .

In FIG. 6 shows the profile 7t of a female thread 2t with a curved profile. In FIG. 7A and 7B are enlarged fragments of FIG. 6. After the female thread contour 2t has been created, the profile 7f can be defined. The profile 7f may start at a given distance X ₀ from the top 2p. The profile 7f may end at the point where the root of said profile intersects the axis G ₁ parallel to the longitudinal axis G _L and is displaced towards the final diameter D ₁ . The predetermined distance X ₀ of the female profile 7f may differ slightly from the predetermined distance of the male profile 7m. The angle of curvature γ may form a continuation of the profile 7f in the form of an arc from the beginning to the end and may be in the range from 1 to 10°.

As shown in particular in FIG. 7A, thread profile 7f may have a first root. A _b Said thread profile may have a trapezoidal shape. The first cavity A ₁ may be an arc with an outer bend radius R _b and may extend to the second arc A ₂ . The outer bending radius _Rb of the female profile 7f may differ slightly from the outer bending radius of the male profile 7m. The center line C _L can be inclined to the displacement axis G ₁ at a sharp and almost perpendicular first angle δ0. Said second arc A2 may have a radius of less than one percent of the outer radius _Rb of the bend. The second arc A ₂ may extend from the first cavity A ₁ to the non-contact side surface E ₁ . The second arc A2 may be tangential to the first root A ₁ and the non-contact flank E _b The non-contact flank E ₁ may be a straight line inclined at a first thread profile angle α with respect to the center line C _L . Each first thread profile angle α may range from 35° to 55°.

The non-contact side surface E ₁ can extend from the second arc A2 to the third arc A3. Said third arc A3 may have a radius of less than one percent of the outer radius _Rb of the bend. The third arc A3 may extend from said non-contact side surface E ₁ to the first protrusion A4. The third arc A3 may extend tangentially to the non-contact side surface E ₁ and the first protrusion A4. The thread profile may have a height T between the first shoulder A4 and the second root A7. The first protrusion A4 may be an arc with an inner bending radius R _b -T and may extend from said third arc A3 to the fifth arc A ₅ . The inner bending radius R _b -T of the female profile 7f may differ slightly from the inner bending radius of the male profile 7m. As shown by a pair of dotted lines extending from the end points of the first projection A4, the middle line C _L

- 4 040027 can pass through the midpoint of the first protrusion L4. The center line C _L may be perpendicular to the arc of each radius R _b , R _b -T bend. The height T may be less than one percent of the outer bend radius R _b so that the inner bend radius R _b -T is also greater than the outer diameter of the female connector 2 as described above for said bend radius.

Said fifth arc L ₅ may have a radius of less than one percent of the outer radius R _b of the bend. The fifth arc L ₅ can extend from the first ledge L4 to the contact side surface E2. The fifth arc L ₅ can run tangentially to the first ledge L ₄ and the contact side surface E2. The contact flank E2 may be a straight line inclined at a second angle β of the thread profile with respect to the center line C _L . Said second thread profile angle β may range from 45° to 45°. Said first angle α of the thread profile may be less than the second angle β of the thread profile; this ensures an asymmetric profile shape. Further, the asymmetric shape of the profile is illustrated using the projections of the side surfaces Ei, E2, crossing the offset point from the center line C _L . The second thread profile angle β of the female profile 7f may differ slightly from the second thread profile angle of the male profile 7m. The contact side surface E2 may extend from the fifth arc A ₅ to the sixth arc A6. The sixth arc A6 can extend from the contact side surface E2 to said second trough L ₇ . The sixth arc A6 may extend tangentially to the contact side surface E2 and the second trough L7. The second cavity L7 may be an arc with an outer bend radius Rb.

The thread profile may have a step β (along the length of the arc) from the beginning of the profile 7m to the middle of the second cavity L ₇ . The first cavity L ₁ may have an arc length X1, which may also be equal to half the length of the arc of the second cavity L7. The arc length Xi of the female profile 7f may differ from the specified arc length of the male profile 7m. The first protrusion L ₄ may also have an arc length two times less than the specified arc length X _i .

Alternatively, said valleys and protrusions may have the same arc length.

As shown in particular in FIG. 7B, due to the bending of the profile 7m around each bending radius R _b , R _b -T , the center line C _L of the thread profile adjacent to the end of the profile 7m can be inclined with respect to the displacement axis G ₁ at a second acute angle δ ₁ which is less the specified first angle δ ₀ .

Reference to contact surfaces E ₂ and non-contact surfaces E _i is given for drilling conditions when the drill string is compressed. When pulling the drill string out of the well and unscrewing the drill rod, the drill string is in a stretched state and the contact flanks E2 become the non-contact flanks and the non-contact flanks E ₁ become the contact flanks, as shown in FIG. 8.

In FIG. 8 shows a male 4 and female 2 connecting parts screwed together. Once the thread profiles 7m, 7f have been created, each profile can be adapted to the geometry of the corresponding curved profile threads 4t, 2t, for example by trimming said profiles. The curvature of the curved profile of each thread 2t, 4t along the longitudinal axis G _L can provide a frusto-ogival shape.

Claims (16)

CLAIM 1. A connecting element for connecting downhole pipes containing a tubular body; female connecting part (2); covered connecting part (4); and at least one of the following: a male screw thread (4t) provided on the outer surface of said body; and a female screw thread (2t) made on the inner surface of the specified body, and the specified at least one thread has a profile containing a protrusion (L ₁ , L ₄ , L ₇ ), a depression (L ₁ , L ₄ , L ₇ ) and a pair of side surfaces (E ₁ , E2), while each ledge (L1, L4, L7) and each cavity (L1, L4, L7) are located along curved thread profiles corresponding to the first and second radii (Rb, Rb-T), respectively , along the entire length of the thread profile; and each radius (Rb, Rb-T) of the bend is greater than the outer diameter of the connecting element. 2. The connecting element according to claim 1, in which each side surface (E ₁ , E2) is straight and connected to an adjacent protrusion (L ₁ , L4, L ₇ ) and/or depression (L ₁ , L4, L ₇ ) through corresponding arc (L ₂ , L ₃ , L ₅ , L ₆ ). 3. The connecting element according to claim 1 or 2, in which the middle line (C _L ) of the thread profile, perpendicular to the arc of each radius (R _b , R _b -T) of the bend, is located with an inclination relative to the longitudinal axis (GL) of the connecting element under the sharp and almost perpendicular to the first angle (δο) adjacent to the beginning of said at least one thread and with a slope at a second angle (δ1) adjacent to the end - 5 040027 specified at least one thread, and the second angle (δ1) is less than the specified first angle (δ ₀ ). 4. A connecting element according to any one of the preceding claims, in which each radius (R _b , R _b -T) bend is at least five times the outer diameter of the specified connecting element. 5. A connector according to any one of the preceding claims, wherein the thread profile has an asymmetric shape. 6. A connector according to any one of the preceding claims, wherein the thread profile is trapezoidal. 7. A connector according to any one of the preceding claims, wherein the angle (γ) of curvature of said at least one thread is in the range of 1 to 10°. 8. A connector according to any one of the preceding claims, wherein the trough (A1, A4, A ₇ ) and the lip (A1, A ₄ , A ₇ ) are concentric. 9. A connector according to any one of the preceding claims, wherein the length of the arc of the trough (A1, A4, A ₇ ) and the length of the arc of the protrusion (A1, A4, A ₇ ) are equal. 10. A connector according to any one of the preceding claims, wherein the valley arc length (A1, A4, A7) and the protrusion arc length (A1, A4, A ₇ ) are not equal. 11. Rod connection for downhole pipes, containing two connecting elements according to any one of claims 1 to 10, while the male thread (4t) of one of these connecting elements is screwed into the female thread (2t) of the other connecting element, and one of the side surfaces ( E1, E2) is the contact side surface (E2) and the other side surface is the non-contact side surface (E1) when the female and male connecting parts (2, 4) are compressed; each side surface is rectilinear; each thread profile has a center line (C _L ) perpendicular to the arc of each respective radius (R _b , R _b -T) bend; each side surface is located at an angle (α, β), with an inclination relative to the corresponding center line; and each angle (β) at which the contact side surface is located is greater than the corresponding angle (α) at which the non-contact side surface is located. 12. Rod connection according to claim 11, in which each angle under which the non-contact side surface is located is less than 45°. 13. Rod connection according to claim 12, in which each connecting element is made of metal or alloy, and the male connecting part (4) contains a section with an outer diameter, a section with a reduced diameter having a male thread, and a shoulder (4s) connecting these two sections, while the shoulder (4s) interacts with the end (2p) of the female connecting part (2) to create a metal-to-metal seal. 14. Drill rod (1) for percussive drilling, containing a body (3) and two connecting elements according to any one of claims 1 to 10, while the female connecting part (2) of one of these connecting elements, having a female thread (2t), is welded to the first end of the said body (3) of the rod, and the male connecting part (4) of another connecting element, having a male thread (4t), is welded to the second end of the said body (3) of the rod. 15. Drill rod according to claim 14, in which the outer diameter of said female and male connecting parts (2, 4) is in the range from 0.05 to 0.20 m, and each radius (Rb, Rb-T) of the bend is more 1m. 16. A drill string containing a drill rod (1) according to claim 14 or 15.