JP2002022070A - Oil well pipe screw joint excellent in external pressure resisting performance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oil well pipe joint excellent in sealing property to external pressure in a coupling type oil well pipe fitting for fastening a male screw pin to a short pipe having both boxed ends and an integral type oil well tube fitting consisting of a pair of pins and a box. SOLUTION: This oil well pipe screw joint excellent in external pressure resisting performance comprises a pin having a run-out type taper male thread with buttress thread arranged at the tube end and a seal part formed of a smooth taper surface and a tip shoulder part, which is arranged on the extension line of the male thread; and the box having a taper female thread with buttress thread arranged on the pin inner surface so as to be fitted thereto and a shoulder abutting on the smooth taper surface and the pin tip, which is arranged on the deep side thereof. The inner side is swollen over the whole area of at least the male thread complete screw part and the non-threaded seal part to enhance the radial displacement resistance to external pressure of the male thread.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coupling type oil country tubular joint in which a male pipe pin is fastened to a short pipe whose both ends are box-processed, and an integral type oil country pipe joint comprising a pair of pins and a box. The present invention relates to an oil country tubular good having excellent sealing performance against external pressure.

[0002]

2. Description of the Related Art It has been pointed out that with regard to the sealing performance of oil country tubular goods, it has been emphasized that the internal fluid does not leak out of the steel pipe, and that there has been little interest in external pressure performance.
However, recently, in order to improve the productivity of an oil and gas layer that is likely to be depleted, an enhanced recovery method for cracking the formation and improving the flow of oil and gas has been frequently used.
In this enhanced recovery method, a high internal pressure acts on the pipe to send high-pressure water to the stratum, and in order to balance this, pressure is applied from the outer surface of the pipe. If the internal pressure drops during formation or the internal pressure drops during production, the same situation occurs when the external pressure acts on the pipe alone, and the joint situation is exposed to high external pressure, leading to destruction and leakage of oil and gas. There is.

FIG. 1 shows a partial cross-sectional view of a conventional oil country tubular good joint having a metal contact portion at the tip of a male screw. In FIG. 1, the leakage of oil and gas into the joint due to the external pressure of the joint is as follows. First, the external fluid enters the screw fitting portion, and the male screw 1 is displaced inside and the female screw 2 is displaced outward by the fluid pressure. try to. These displacements work to pry open the contact portion 3 of the metal contact portion disposed at the screw tip, and when the radial displacement of the screw portion becomes larger as the amount of contact of the metal contact portion provided in advance becomes larger, the external fluid Will leak oil and gas into the joint through the metal contact 3 as well.

There are several factors that are considered to be effective for external resistance even with the current oil country tubular goods threaded joints. First, even if external pressure enters between the male screw and the female screw, for example, the side of the screw thread 4 shown in FIG. and acute angle theta _1, a male screw is to difficult away from the female screw, the second, the nose tip of the metal contact 3 threads similarly as acute theta _2, Ya the metal contact 3 is less likely to埀離The third is to insert a resin packing 6 such as a Teflon (registered trademark) seal ring between the screws. But,
In the first and second methods, if an acute angled inclined surface yields due to the action of tension in both directions of tension and compression, a gap is created there, and the external thread displaces the external thread radially inward due to external pressure. There is a problem that the blocking effect is considerably lost. Further, in the third method, an external pressure sealing effect can be expected, but there is a problem that trouble frequently occurs due to a failure in inserting the resin packing at the site, and the user side is avoided. Therefore, development of an oil country tubular good with high sealing performance against external pressure that solves these problems is desired.

[0005]

SUMMARY OF THE INVENTION The present invention provides an oil country tubular good with high sealing performance against external pressure, which solves the above-mentioned problems.

[0006]

SUMMARY OF THE INVENTION The present invention relates to an oil country tubular good tapered threaded joint having a threaded portion and a stepped metal contact portion at the tip of the threaded portion. Because taper processing is given to
Increased resistance to deformation of the external thread, which has become thinner and easily contracted by external pressure, inward in the radial direction, and designed to prevent the stair-shaped metal contact part provided at the distal end of the external thread from being pryed open. This is a threaded oil well pipe threaded joint, the gist of which is as follows.

According to the present invention, there is provided a pin having a run-out type tapered male screw with a buttress thread at a pipe end, and a pin having a seal portion formed of a smooth tapered surface and a tip shoulder on an extension of the run-out tapered screw. In an oil country tubular good threaded joint consisting of a box in which a buttress threaded tapered female thread on the inner surface of the pin and a shoulder in contact with the smooth tapered surface and the tip of the pin are arranged at the inner portion, at least a male thread completely threaded portion and a threadless seal portion are formed. Over the entire inner surface,
Preferably, for the tubing for coupling type and integral type casings, an inner wall thickness increasing portion is provided on the extension line of the external thread in parallel with the pipe axis, and the inner side is expanded to increase radial displacement resistance against external pressure of the external thread. An oil country tubular good threaded joint having excellent external pressure resistance, and the inner surface thickening portion forming means on the extension of the external thread is swaged, and the outer surface taper after the swaging is made parallel to the screw taper. The inner wall thickened portion is also parallel to the tapered screw, and the tapered screw portion has excellent external pressure resistance for casing and tubing for coupling and integral type casings in which the cross-sectional thickness approximates the wall thickness of the entire pipe over the entire screw. Oil well pipe threaded joint.

In the swaging, the present invention is characterized in that, in the swaging, the diameter of the steel pipe serving as the mother pipe is at most 6 mm larger than the diameter of the API standard casing steel pipe, and the inner diameter of the steel pipe is also increased by a corresponding increase. By performing the swaging to the inner diameter that can guarantee the minimum standard inner diameter specified by the standard, the range of the inner surface portion of the inner surface under the screw and the inner surface without the screw as it is swaged is lengthened, thereby increasing the thickness of the tapered screw processing portion. It is to ensure as thick as possible, and in the swaging process,
Coupling type in which the part corresponding to the threaded part after the swage processing is made parallel to the screw taper using the upper and lower half molds, and the extra part on the inner surface is minimized by further loosening the tapered part. It is an oil well pipe threaded joint with excellent external pressure resistance for integral type casing and tubing.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In a coupling type and integral type oil country tubular screw joint for casing and tubing, in order to increase the radial deformation resistance of the external thread against external pressure, the thickness of the thinned external thread is increased. In the present invention, it is intended to achieve me by increasing the thickness inside. Until now, there was an example of increasing the thickness of the inside of an oil well pipe, but this was due to the use of a drill type, round shank tubing pipe shading heating inside and outside upset molding, and these were means to secure the joint strength. It was used in. However, it is not necessary to perform inner upset processing on tubing and casing oil country tubular goods in which run-out type buttress screws such as 4 (c) shown in FIG. Did not.

In addition, this type of joint is not hot-worked,
Although there is something that has been inflated inward by cold swaging, the purpose is to secure the cutting allowance to keep the thickness of the metal contact part constant, or if the metal contact part is thin This is to increase the thickness of the part inward, and there is no example of swelling under the screw.
Some parallel screws have a screw fastening structure in which the thickness of the thread part is clearly thinner than the pipe body, so there is an example in which the inside of the male screw is swaged by swaging, but this is to compensate for the weakness of the parallel screw However, since the run-out taper screw originally aims to compensate for the weakness of the joint strength of the parallel screw, it is considered that it is not necessary to swage or upset in a form that completely covers the inside of the male screw, Such oil well casing, tubing has not been found in the past. This is presumably because there was no need in the past to increase the thickness of the male screw to suppress the radial displacement in response to the external pressure that entered the screw fitting portion. The following equation (1) is an equation for calculating the amount of displacement U of the outer surface in the radial direction when an external pressure p acts on the cylinder.

U = pr ² / (Et) (1) where r is the radius of the center of the wall thickness of the pipe, E is Young's modulus, t
Is thick. Thus, the radial displacement of the cylindrical outer surface is proportional to the square of the radius and inversely proportional to the wall thickness. P, r, and E are parameters that cannot be changed. The only thing that can be devised in the joint design is the wall thickness: t. The phenomenon of the thickness (t) of the male screw portion directly affects the radial displacement. For example, if the thickness of the screw portion is 20% smaller than that of the mother tube portion, the displacement in the radial direction is 1.25 times the reciprocal of 0.8. Now, pipe radius: 120 mm, wall thickness: 12 mm, load external pressure: 70
Assuming 0 atm and Young's modulus: 21000 kg / mm ² ,
Radial displacement: U is 0.4 mm. Assuming that the wall thickness is reduced by 20% by the threading, the radial displacement amount: U
Needs to be reduced to 560 atm to maintain 0.4 mm. That is, if the sealing function of the metal contact portion against the external pressure of the joint was maintained until the radial displacement of the screw portion became 0.4 mm, the thinning of the thread portion by 80% reduced the sealing performance from 700 atm to 560 atm. It is equal to having fallen.

As can be seen from the above examples, the effect of increasing the wall thickness under the screw for improving the external pressure sealing resistance of the joint is remarkable.
Here, the point devised in the present invention is the thickness increasing means and the shape in which the thickness is increased. There are two types of thickening means, hot working and cold working. First, the cold swaging method with low working cost will be described. The larger the inner wall thickness, the better. Therefore, in order to obtain the maximum wall thickness of the inner surface under the screw, it is preferable to swage the pipe end along the outer edge profile of the external thread taper as shown in FIG. By doing so, the depth and thickness of the thickened portion on the inner surface of the pipe can be maximized. That is, in FIG. 2, 7 (a) is a pipe end shape before swaging,
7 (b) shows the pipe end shape after swaging. The inner surface taper of the swage mold should be slightly larger than the screw taper so that the tube end outer surface taper after swaging is the same as the screw taper. If the taper is too large, the depth of the thickened part after threading becomes short, and it is not possible to increase the thickness of the entire inner surface of the complete screw. Conversely, if the taper is too small, the depth of the thickened part after threading can be secured but increased Department will be short.

[0013] The inner-wall-increased portion does not pass the inner-surface drift inspection with its shape as it is, so it is necessary to bore it to a required inner diameter. The machined part can penetrate the defined mandrel bar with little clearance. In practice, it is sufficient if the diameter of the mandrel is +1 mm. The combination of the cold tube swaging and the inner surface boring described above makes it possible to minimize the radial displacement of the distal end portion of the male screw against external pressure. this is. As shown in FIG. 2, where the thickness under the screw: t ′ becomes thinner due to the tapered thread as it progresses toward the tip of the male screw, the swaging was optimally performed.
_This is because it could be approximated to _zero .

As shown in FIG. 2, it is impossible to apply the current API standard steel pipe in order to leave the range of the swage as far as the tip of the tapered screw and to keep the thickness of the screw portion thick. The reason is that in the current API standard (steel tube inner diameter -3.18m
m), it is necessary to pass through the drift mandrel, and when the pipe end is swaged along the thread taper, the thread length: 100 m
In the case of m, taper: 1/16, the inner diameter becomes smaller by 6.25 mm, so that this drift inspection cannot be satisfied. Therefore, in order to satisfy the drift inspection and increase the swage range as shown in FIG. 2, it is preferable to increase the outer diameter of the steel pipe. However, when the outer diameter of the steel pipe is increased, there is a concern that the outer diameter standard may be violated.However, considering the application of oil country tubular goods, the inner diameter passes through the inner surface of the pipe so that the bit cannot be used unless it complies with the standard. Since the outer diameter is determined in consideration of the clearance between the outer wall and the pit wall in which the steel pipe is buried, the standard value has a margin, and a slight increase in the diameter is practically accepted. Heretofore, there is an example of an oversized casing for a steel pipe having an outer diameter larger than the API standard.
In this case, it is necessary to pass a steel pipe as large as possible through the inner surface of the steel pipe, or to cover a disadvantage that the inner diameter is reduced by forming a thick steel pipe. The improvement according to the invention is:
The motivation of the invention is to swage the end of the pipe in order to increase the thickness of the tapered thread portion and to use the pipe as much as possible.

There are two methods for the cold swaging described above, each having advantages and disadvantages. The first method is, as shown in FIG. 3, a method in which a pipe end is pushed into a cup-shaped die whose inner surface is tapered. This method is suitable when swaging deeply as in the present invention. The second method is, as shown in FIG. 4, a method in which the upper and lower molds are pressed in half, and this feature makes it possible to make the pipe end profile after swaging not a uniform profile but a combined taper. By doing so, even if the shape of the final product is the same, it is possible to reduce the inner surface cutting allowance at the time of bore processing, as compared with the uniform taper swage, and it is possible to improve productivity. However, a drawback is that since the mold is a half-split mold, it is easy to form an uneven thickness and shape portion at the boundary. Screw under thickness by any of the methods: mother tube wall thickness of t: swaging to approximate to t ₀ is possible.

This is because the cold swaging can increase the radial deformation resistance of the threaded portion from the viewpoint of strengthening the material, and the swage working increases the compressive strength in the circumferential direction. This is useful as an effect of preventing the male thread portion from being easily compressed and yielded by the action of tightening of the tapered screw and external pressure. That is, swaging not only has the effect of increasing the wall thickness but also has the effect of strengthening the pipe end in terms of material. However, in a corrosive environment containing hydrogen sulfide, the cold swaged material has increased stress corrosion cracking susceptibility. In this case, it is necessary to perform stress relief annealing after the cold swaged work, but work hardening cannot be performed.

Next, the inner surface thickening method by the hot upset method will be described. Although the pipe end wall thickness cannot be made larger than the original wall thickness by cold swaging, the wall thickness can be increased by the hot upset method. Therefore, the upset shape of the lower portion of the screw as shown in FIG. 5 can be made parallel to the pipe axis, and the thickness of the male screw terminal portion: t
Can be thicker than the mother tube wall thickness: t ₀ . Therefore, the resistance to the radial displacement of the external thread portion due to the external pressure can be made larger than that of cold swaging. However, the disadvantage is that it is more expensive than cold swaging. Hot upset processing is performed using a punch as shown in FIG.
This is performed by forging a pipe end heated to 0 ° C. One heat and two blows are a general method, and two heats and three blows may be applied at the time of heavy upset. As in the present invention,
When applied to casings and tubing, the upset amount is about 2 to 4 mm, so one heat and two blows are sufficient.

[0018]

FIG. 7 (a) shows an embodiment of a run-out casing type tapered threaded joint in which the inner surface under the screw and the inner surface without the screw are swaged to expand the inner surface. The steel pipe has an outer diameter of 139.7 mm (5.5 inches) and a wall thickness of 9.17.
mm API standard oil well tube. An API standard buttress with a taper: 1/16 was machined at the tip of the steel pipe 1, and an interference margin: 0.5 mm was provided on an extension 3 of the steel pipe 1 with a taper: 1/10 and the corresponding female screwless portion. It is a metal seal part. The end of the male screw has an end face tapered concavely inward so that the tip of the male screw does not contract inward when external pressure enters the screw fitting portion. Swage processing of steel pipe 1
At the time of screw fitting, it was designed to be bent 1.79 ° inward from the position corresponding to the complete screw termination position: Tp. The inner surface was bored before threading. The bore diameter was set to 119.8 mm, which was 2.18 mm smaller than the inner diameter. The reason is that the drift mandrel defined by the API standard can be passed without any problem. As a result, the bore depth was 34 mm. By performing swaging in this way, the above-mentioned bore depth of 34 is obtained.
The mm section could be made thicker by 1.09 mm inside the tube. The remaining 35 mm is also temporarily thick. That is, when swaging at an angle of 1.79 ° as described above, a thickening with a depth of 69 mm can be obtained for the first time. The wall thickness increasing effect of 1.09 mm is 15% from the above-mentioned equation (1) because the wall thickness increase is about 15% at the center of the complete screw.
This means that the external pressure sealing performance is increased by about%.

FIG. 7 (b) shows an external pressure resistant joint that makes full use of the above-mentioned swage shape.
The point is that by making the outer diameter slightly larger than that of the API standard steel pipe, the inner surface portion under the screw which is cut by the bore is reduced as much as possible. By doing this,
A joint is obtained in which the thread thickness does not change along the taper while the taper thread is being cut on the outer surface of the pipe. As described above, the joint according to the present invention is characterized in that the outer diameter of the steel pipe also plays a role in order to maximize the resistance to external pressure.

In the embodiment of the present invention, the outer diameter is set to 3.9.7 mm (5.5 inches) in comparison with the API standard.
It is 43.1 mm (5.63 inches) larger by 4 mm. Increasing outer diameter allows screw inclination: 1.79 °
Can be obtained over an area of 54 mm. Thus, in FIG. 7B of the present invention, the length is 19 mm longer than in FIG. 7A. The bore diameter is 119.18 m, which is the same as in FIG.
m. Since the bore diameter is determined by the outer diameter of the bit passing through the inner surface of the pipe during excavation, the degree of freedom for change is small. On the other hand, the outer diameter of the steel pipe including the joint is determined by the clearance between the steel pipe and the pit wall, and is usually about 1.5 inches (38 mm) that does not hinder the cementing work.

That is, there is a relatively large margin in the outer diameter of the steel pipe, and there is no actual harm even if the diameter of the pipe and the coupling is 3.4 mm larger than that of the ordinary steel pipe / joint as in this embodiment. In this embodiment, the reason why the diameter of the coupling is increased up to the swage-independent coupling diameter is that a critical section (male screw SP, female screw S
C) is intended to make the male screw and the female screw almost equal. The oil well tube casing is often applied with an API buttress type 1/16 taper screw. FIG.
In order to make the joint shown in (b) compatible with various sizes of the API standard casing, since the complete screw length changes from about 50 mm to 90 mm, it is 3.4 mm to 5.6 mm larger when converted to the outer diameter. A steel pipe with a diameter is required. By the way, when the joint as shown in FIG. 7B is used, the thickness at the center position of the completely threaded portion is about 21 compared with the joint without swaging.
%, The external pressure resistance performance is increased by 21%. FIG. 7 (b) shows the upper limit for increasing the outer diameter. Therefore, when the outer diameter cannot be increased due to the clearance with the pit wall, if the outer diameter is increased as much as possible, FIG.
A factory having an external pressure resistance intermediate between that of FIG. 7A and that of FIG. 7B can be expected. Even in such a case, it is best to make the inclination angle of the swage parallel to the screw taper.

[0022]

As described above, the oil country tubular good joint according to the present invention increases the radial deformation resistance at the transition from the threaded portion to the threadless metal contact portion, and makes the metal contact seal portion less likely to bend against external pressure. By doing so, it became possible to obtain an oil country tubular good with excellent external pressure resistance.

[Brief description of the drawings]

FIG. 1 is a partial sectional view of a conventional oil country tubular good.

FIG. 2 is a partially enlarged cross-sectional view of a male screw subjected to optimum swaging according to the present invention.

FIG. 3 is an enlarged sectional view of a pipe end swaged by a push-in type pipe end according to the present invention.

FIG. 4 is an enlarged sectional view of a pipe end by a half mold according to the present invention.

FIG. 5 is a partially enlarged cross-sectional view of a male screw subjected to optimal inner upset processing according to the present invention.

FIG. 6 is a view showing a tube end inner surface heating upset process according to the present invention.

7 (a) is a partially enlarged sectional view of an oil country tubular good having excellent sealing resistance, FIG. 7 (a) is a view showing a conventional steel pipe size swage, and FIG. 7 (b) is a large diameter steel pipe size swage. FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Male screw (pin) 2 ... Female screw (coupling) 3 ... Metal contact seal part 4 (a) ... Buttress screw 4 (b) ... Buttress screw with inclined load flank surface 4 (c) ... Runout screw 5 ... Inner concave taper shoulder 6 Teflon seal ring 7 (a) ... pipe end shape before swaging 7 (b) ... pipe end shape after swage 8 ... inner surface thickening part by swage 9 ... bore diameter 10 ... inner surface thickening section 11 ... heating inner surface thickening section by upsetting 12 ... cup swaging die 13 ... mold half swaging dies 14 ... upset containers 15 ... upset punch 16 ... upset before steel L ... full thread portion g ... incomplete thread portion t ₀ ... tube Body thickness t ': Thread thickness without swage t: Thread thickness with swage Tp: Boundary between complete screw and incomplete screw Sp: Dangerous cross section of steel pipe Sc Danger cross-sectional area of the coupling

Continued on the front page (72) Inventor Eiji Tsuru 20-1 Shintomi, Futtsu-shi, Chiba F-term in Nippon Steel Corporation Technology Development Division (reference) 3H013 JA02

Claims (5)

[Claims] 1. A pin having a run-out type tapered male screw with a buttress screw thread at a pipe end and a seal portion composed of a smooth tapered surface and a tip shoulder portion on an extension of the run-out tapered male screw. In an oil country tubular good threaded joint comprising a tapered female thread with a buttress thread on the inner surface and a box having a smooth tapered surface and a shoulder in contact with the tip of the pin at the back thereof, at least the entire inner surface of the completely threaded male threaded part and the threadless seal part An oil-well pipe thread joint with excellent external pressure resistance, characterized in that the inner side is inflated to increase the radial displacement resistance of the external thread against external pressure. 2. An oil country tubular good threaded joint having excellent external pressure resistance according to claim 1, wherein an inner wall thickening portion is provided on the extension line of the external thread in parallel with the pipe axis. 3. The internal-wall-thickening portion forming means on the extension line of the male screw is swaged, and the external-surface taper after the swaging is made parallel to the screw-taper so that the internal-wall-thick portion also becomes parallel to the taper screw. The threaded joint of an oil country tubular good having excellent external pressure resistance according to claim 1, wherein the tapered thread portion cross-sectional thickness is made to be close to the thickness of the mother pipe over the entire screw. 4. In the swaging process, the diameter of a steel pipe serving as a mother pipe is made up to 6 mm larger than the diameter of an API standard casing steel pipe and the inner diameter of the steel pipe is also increased by an amount corresponding to the maximum diameter. By performing the swage processing to the inner diameter that can guarantee that, the range of the inner surface portion of the inner surface under the screw and the inner surface without the screw as it is swaged is lengthened, thereby securing the thickness of the tapered screw processed portion as thick as possible. The threaded oil country tubular good with excellent external pressure resistance according to claim 3. 5. In the swaging process, a portion corresponding to the threaded portion is made parallel to the thread taper using a half-upper die and a portion corresponding to the threaded portion, and the non-threaded portion is further tapered so that the inner surface is formed. The threaded oil country tubular good with excellent external pressure resistance according to claim 3 or 4, wherein excess overhang is minimized.