WO2012056500A1

WO2012056500A1 - Screw connector for oil well pipe

Info

Publication number: WO2012056500A1
Application number: PCT/JP2010/006387
Authority: WO
Inventors: 鈴木　照明
Original assignee: 株式会社メタルワン
Priority date: 2010-10-29
Filing date: 2010-10-29
Publication date: 2012-05-03

Abstract

Provided is a screw connector for an oil well pipe, said connector equipped with a male screw (1) having a seal (5) formed as a convex surface and a shoulder (6) formed farther toward the tip than the seal (5), and with a female screw (2) having a tapered seal (7), with the contact portion of the seal (5) of the male screw and the seal (7) of the female screw being formed by pressure bonding, and the length of the male screw (5) from the tip of said male screw to the aforementioned contact portion in the direction parallel to the longitudinal direction of the male screw being set on the basis of the thickness of the oil well pipe (100).

Description

Screw joint for oil well pipe

The present invention relates to an oil well pipe screw joint.

In recent years, casings (made up of oil well pipes, oil well pipe screw joints, etc.) used in the drilling of oil and natural gas (hereinafter also referred to as mined materials) are plastically deformed due to the following circumstances, Mining may leak.

For example, when mining a large volume of mining material from a deep formation, the mining material is usually at high temperature and high pressure, and accordingly, the casing may be plastically deformed to cause a leak. .
In order to promote green energy policy, energy is generated by geothermal power generation. In geothermal wells excavated by geothermal power generation, the casing is exposed to high temperature by water vapor. There is a risk of causing plastic deformation and leakage.
Also, in response to the recent rise in oil prices, there is a movement to use heavy oil that has been difficult to make commercially profitable. However, in order to mine heavy oil, steam having a temperature higher than the ground (for example, about 350 degrees) is injected into heavy oil stored underground through the casing to reduce the viscosity and make it easier to mine. However, even at this time, since the casing is exposed to high temperature (water vapor), the casing may be plastically deformed to cause leakage.

Further, after the casing is lowered to the basement, in order to limit the movement of the casing in the longitudinal direction, a process of hardening the outer surface of the casing with concrete or the like is performed. Therefore, when the casing is exposed to a high temperature as described above, the casing tends to expand, but since the outer surface is solidified with concrete, the expansion is suppressed, so that a high compressive force is applied to the casing. It will be. Thereby, there exists a possibility that a casing may plastically deform and leak may arise.
Therefore, the casing is required to have high strength (plastic deformation resistance). However, since the joint portion connecting the oil well pipes in the casing is likely to leak, this joint portion. Various improvements have been made to improve the strength.

In such an improvement, the male screw (PIN) and the female screw (BOX) are pressed at the part where the seals abut against each other by the fitting force of the screw, so that the surface pressure generated at the corresponding part is increased. What was comprised is proposed (for example, refer patent document 1 and patent document 2).

Japanese Patent Laid-Open No. 61-6488 (for example, see page 1 and FIG. 1) JP-B-2-31271 (for example, see page 1 and FIG. 1)

The techniques described in Patent Document 1 and Patent Document 2 are configured such that a contact portion between a convex curved seal on the male screw side and a tapered seal on the female screw side is bonded to form a seal. Here, when a strong force for compressing the oil joint pipe joint is applied, a portion called an inner shoulder at the tip of the male screw and a thin butted portion of the female screw cause plastic deformation. If this plastic deformation reaches the contact portion between the male screw and the female screw, the surface pressure of the seal (main seal) decreases, and the mined product may leak.
Also, in the geothermal well or steam injection well, when the drilling of the mined material is temporarily stopped or the injection of steam is temporarily stopped and the temperature of the oil well pipe decreases, the above screw joint for the oil well pipe The tensile force opposite to the compressive force works, and the seal that has already undergone plastic deformation due to high compression caused by mining or injection of steam is further deformed, and mining is started again or steam is applied again. When it was injected, it caused a leak.

The present invention was made to solve the above-described problems, and suppresses plastic deformation to the contact portion between the male screw and the female screw, and the mined product leaks. It aims at providing the screw joint for oil well pipes which controls.

The screw joint for oil well pipe according to the present invention includes a seal formed in a convex curved surface shape, a male screw having a shoulder formed on the tip side from the seal, and a female screw having a taper-formed seal, In an oil well pipe screw joint constructed by crimping a contact portion between a male screw seal and a female screw seal, the male screw seal is based on the thickness of the oil well pipe in a direction parallel to the longitudinal direction of the male screw. The length from the tip of the male screw to the contact portion is set.

According to the oil well pipe screw joint according to the present invention, since the above-described configuration is provided, since the plastic deformation is suppressed to the contact portion between the male screw and the female screw, the mined product leaks. This can be suppressed.

This is to explain in which part plastic deformation that occurs in the vicinity of the seal tip occurs when a mined product having a predetermined pressure flows in the oil well pipe. It is sectional drawing in the surface parallel to the longitudinal direction of the screw joint for oil well pipes concerning embodiment of this invention. The tangent point of the screw joint for oil well pipes shown in FIG. 2 will be described. The shape of the seal of the male screw joint of the oil well pipe screw joint shown in FIG. 2 and the thickness of the tip of the male screw with respect to the seal length will be described. The magnitude | size of the seal surface pressure with respect to the distance from the front-end | tip of a male screw is demonstrated based on a simulation result. The size of the seal index relative to the shoulder surface tightening allowance will be described for each shoulder angle. This is to explain the decrease in the seal surface pressure with respect to the shoulder angle.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Embodiment.
FIG. 1 is a diagram for explaining in which part plastic deformation that occurs in the vicinity of the seal tip occurs when a drilled product having a predetermined pressure flows in the oil well pipe 200. In addition, in the following drawings including FIG. 1, the relationship of the size of each component may be different from the actual one. Further, in the following drawings including FIG. 1, a cross-section of a joint tip portion of the oil well pipe 200 is shown. Further, in the following drawings including FIG. 1, the cross-sectional view in the plane parallel to the longitudinal direction is described.

From FIG. 1, it can be seen in which part the plastic deformation occurred due to the pressure generated by the flow of the mined material in the oil well pipe 200 against the tip of the male screw 1 and the inner side of the female screw 2. Specifically, it can be seen that a large plastic deformation occurs in the tip portion of the male screw 1 and the portion of the female screw 2 facing the tip portion (see K in FIG. 1) (the darker the color, the more the plastic deformation amount). Is great). The portion indicated by K is called a seal (main seal), and if the seal and the vicinity of the seal are plastically deformed, it may cause a leak of mined material. This oil well pipe threaded joint 100 has been improved to suppress this leak.

[Configuration of male screw 1]
FIG. 2 is a cross-sectional view in a plane parallel to the longitudinal direction of the oil well pipe screw joint 100 according to the embodiment of the present invention. FIG. 3 explains tangent points of the oil well pipe screw joint 100 shown in FIG. FIG. 4 explains the shape of the male screw seal 5 of the oil well pipe screw joint 100 shown in FIG. 1 and the thickness of the tip of the male screw with respect to the seal length.

The configuration of the male screw 1 will be described with reference to FIGS. 2, 3, and 4.
The oil well pipe screw joint 100 is formed by fitting a male screw 1 (PIN) to a female screw 2 (BOX).
The male screw 1 has a screw thread 3 on the outer surface of the male screw 1 formed in a spiral shape. The screw thread 3 on the male screw side engages with the female screw 2. A seal 5 having a predetermined shape is formed on the distal end side of the male screw 1 in a direction substantially parallel to the longitudinal direction of the oil well pipe screw joint 100 (X-axis direction in FIG. 1). As shown in FIG. 2, the tip side corresponds to the back side of the female screw 2 when viewed from the female screw 2 side. The male screw seal 5 is crimped to the female screw seal 7 with “strong surface pressure” to suppress leakage of the mined material flowing through the oil well pipe screw joint 100. The “strong surface pressure” is a level corresponding to a surface pressure at which the mined material flowing through the oil well pipe screw joint 100 does not leak from the seal, and is about 3000 kgf / cm 2, for example.

As shown in FIG. 4A, the male screw seal 5 is formed with a convex curved surface protruding in a direction from the male screw 1 toward the female screw 2. In a cross section parallel to the longitudinal direction of the oil well pipe thread joint 100, the convex curved cross section is provided in a plane perpendicular to the longitudinal direction of the oil well pipe thread joint 100 through the end A of the male screw seal 5. The arc is centered on the point O. Needless to say, a curved surface that is convex in the positive direction of the Y axis, such as an elliptical arc, may be used instead of an arc. However, it is assumed that it is inclined in the negative direction of the Y axis as it goes in the positive direction of the X axis. In the following description, it is assumed that it is an arc.

Here, as shown in FIGS. 2, 3 and 4A, the length in the X-axis direction from the tip of the male screw seal 5 to the tangent point (see below) is based on the thickness of the oil well pipe. Is set.
Specifically, the length in the X-axis direction from the tip of the male screw seal 5 to the tangent point is 6.35 mm when the oil well pipe thickness WT is 12.7 mm (0.500 inches) or less. (0.250 inch) or more.
The length in the X-axis direction from the tip of the male screw seal 5 to the tangent point is such that the oil well pipe thickness WT is greater than 12.7 mm (0.500 inches) and 19.05 mm (0.750 inches) or less. In this case, it is preferable to set it to 7.62 mm (0.300 inch) or more.
Further, the length in the X-axis direction from the tip of the male screw seal 5 to the tangent point is 8.9 mm (0.00 mm) when the oil well pipe thickness WT is greater than 19.05 mm (0.750 inches). 350 inches) or more.
Since the seal thickness WT2 is set by the thickness WT of the oil well pipe, the length in the X-axis direction from the tip of the male screw seal 5 to the tangent point may be set from the seal thickness WT2. Needless to say. The seal thickness WT2 here is the thickness of the seal at the tangent point.
Thus, by setting the length in the X-axis direction from the tip of the male screw seal 5 to the tangent point based on the thickness WT of the oil well pipe, the plastic deformation of the seal causes the tip of the male screw seal 5 to Even if a length corresponding to the oil well pipe thickness WT (or seal thickness WT2) is generated in the negative direction of the X-axis from the portion, it is suppressed that plastic deformation reaches the tangent point. It is possible to prevent the mined material from leaking when mining the mined material with the oil well pipe 200 or when mining again after stopping the mining.

Here, as shown in FIGS. 3 and 4A, the tangent point is a portion where the male screw seal 5 and the female screw side seal 7 are in contact with each other and the corresponding contact portion is crimped. Actually, the male screw seal 5 and the female screw seal 7 are in contact with each other on the surface. However, the female screw seal 7 has a metaphysically perfect straight line so that the male screw seal 5 Is a complete arc, they touch at a certain point. This point of contact is called a tangent point.

In the male screw seal 5, the length in the X-axis direction from the tip to the tangent point is set based on the oil well pipe thickness WT, but from the tip of the male screw seal 5 to the tangent point. When the distance is increased, as shown in FIG. 4A, the thickness of the tip portion is reduced by that amount (see arrow F). That is, by increasing the length of the portion occupied by the arc in the seal 5 of the male screw, the thickness decreases toward the tip of the male screw 1 by that amount, so the tip of the male screw 1 is plastic. It becomes easy to deform | transform and will cause a leak.
In response, the male screw seal 5 is formed so that the cross-sectional arc shape is formed in a direction from the tangent point to the tip of the male screw seal 5 up to a maximum of 3 mm from the tangent point. In addition, a straight section L (FIG. 4B) is formed from the portion formed in the circular arc shape to the tip of the male screw 1.
The male screw seal 5 will be described on the assumption that the cross-sectional linear shape L is formed in a cross-sectional linear shape parallel to the X-axis, but it is not parallel to the X-axis unless the thickness is reduced. Also good.

Further, a shoulder 6 having a predetermined angle is formed at the tip of the male screw 1. This male threaded shoulder 6 acts to increase the surface pressure of the seal by the structure having a predetermined angle as described above when the mined material flows and compressive force is applied to the oil well pipe joint 100. Therefore, it is possible to prevent the mined product from leaking. As shown in FIG. 3, the angle θ2 of the shoulder 6 of the male screw is an angle formed clockwise with respect to the perpendicular direction (the negative direction of the Y axis) from the inner surface to the outer surface of the male screw. 5 degrees to 10 degrees. The reason for this will be described in the description of FIGS.

[Configuration of female screw 2]
The configuration of the female screw 2 will be described with reference to FIGS. 2, 3, and 4.
The female screw 2 has a screw thread 4 on the female screw side formed in a spiral shape so as to be engaged with the screw thread 3 on the male screw side. The screw thread 3 on the male screw side is connected to the screw thread 4 on the female screw side. It comes to fit. On the back side of the female screw 2, a female screw seal 7, which is a linear taper in a cross section of a surface substantially parallel to the longitudinal direction of the oil well pipe joint 100, is formed. As shown in FIG. 1, the back side corresponds to the front end side of the male screw 1 when viewed from the male screw 1 side. The female screw seal 7 is connected to the male screw seal 5 with a strong surface pressure to suppress leakage of the mined material flowing through the oil well pipe joint 100.

The female screw seal 7 has a predetermined angle θ1. As shown in FIG. 3, the predetermined angle θ1 is set to 5 degrees or less clockwise with respect to a direction parallel to the longitudinal direction of the oil well pipe joint 100 (the positive direction of the X axis). This is because not only the internal pressure caused by the mined material but also the tensile force is exerted on the oil well pipe 200 due to its own weight, and the tensile force may become so strong that the oil well pipe 200 is plastically deformed. is there. When such a tensile force is applied, the female screw seal 7 is elongated in the longitudinal direction of the oil well pipe 200, resulting in misalignment between the male screw seal 5 and the female screw seal 7. The surface pressure between the male screw seal 5 and the female screw seal 7 is reduced, which causes leakage. On the other hand, in the oil well pipe screw joint 100, even if the taper of the predetermined angle θ1 is formed on the female thread seal 7 and the oil well pipe 200 is elongated in the longitudinal direction, it contacts the male thread seal 5. Since the reduction of the surface pressure is suppressed, the leakage is suppressed (self-sealing effect).
The female threaded shoulder 8 has a predetermined angle similar to that of the male threaded shoulder 6, and the angle is such that the female threaded shoulder 8 and the male threaded shoulder 6 are crimped so that there is as little gap as possible. Good.

FIG. 5 illustrates the magnitude of the seal surface pressure with respect to the distance from the tip of the male screw 1 based on the simulation results. Specifically, FIG. 5 shows that an oil pipe is formed by fitting a male screw and a female screw of a predetermined shape, and a fluid (predetermined density, flow rate and other parameters) corresponding to a mined product is formed inside the oil well pipe 200. The result of verifying by simulation using the finite element method how the surface pressure of the male screw seal changes with respect to the distance from the tip of the male screw It is.

As shown in FIG. 5, in this simulation model, it can be seen that the surface pressure is generated from about 1.8 mm to 4.2 mm from the tip of the male screw. In other words, it can be seen that the male screw is a contact portion with the female screw between about 1.8 mm and 4.2 mm from the tip of the male screw. The length of the contact portion is referred to as “contact length”. Further, the value having the highest surface pressure in the “contact length” is referred to as “maximum surface pressure”. Further, a value obtained by integrating the value of the seal surface pressure at the contact portion is referred to as “seal index (seal performance)”. In addition, the “seal index (seal performance)” is, in other words, an index indicating that if the “contact length” of the seal is long and the “surface pressure” is large, the seal is difficult to leak.

FIG. 6 illustrates the size of the seal index with respect to the shoulder surface tightening allowance for each shoulder angle. FIG. 7 explains the decrease in the seal surface pressure with respect to the shoulder angle.
As shown in FIG. 6, it can be understood that as the size of the angle θ <b> 2 of the shoulder 6 is increased, the “seal index” is also increased, so that the sealing performance is improved. On the other hand, as shown in FIG. 7, when the size of the angle θ2 of the shoulder 6 is increased, when the drilled material flows and pressure is applied to the oil well pipe 200, the male screw seal 5 is connected to the female screw. It can be seen that the amount of plastic deformation is increased by the amount of pressing strongly against the seal 7 side.
Therefore, when the angle θ2 of the shoulder 6 is set to 5 degrees to 10 degrees by balancing the results of FIGS. 6 and 7, the plastic deformation amount can be suppressed while improving the sealing performance.

[Effects of oil well pipe screw joint 100]
The oil well pipe screw joint 100 sets the length in the X-axis direction from the tip of the male screw seal 5 to the tangent point based on the thickness WT of the oil well pipe. When compression is applied, it is possible to suppress plastic deformation to the contact portion between the male screw and the female screw, so that it is possible to suppress the leakage of the mined material. Therefore, it is possible to prevent the mined product from leaking when mining the mined product with the oil well pipe 200 or when mining again after stopping the mining.

In addition, the oil well pipe screw joint 100 has a cross-sectional arc shape in a direction from the tangent point toward the tip of the male screw seal 5 and has a maximum of 3 mm from the tangent point. Since the cross section of the male screw 1 is formed in a linear shape, it is possible to suppress plastic deformation to the contact portion between the male screw and the female screw when the oil well pipe joint 100 is highly compressed. . Therefore, it is possible to prevent the mined product from leaking when mining the mined product with the oil well pipe 200 or when mining again after stopping the mining.

Further, the oil well pipe thread joint 100 has a taper angle θ1 of the female thread seal 7 of 5 degrees or less clockwise with respect to a direction parallel to the longitudinal direction of the oil well pipe thread joint 100 (positive direction of the X axis). It is said. As a result, for example, in geothermal wells or steam injection wells, when the drilling of mining is temporarily stopped or steam injection is temporarily stopped, and the temperature of the oil well pipe decreases, the screw joint for the oil well pipe Even if a tensile force opposite to the compressive force acts to cause elongation in the longitudinal direction of the oil well pipe 200, the contact surface pressure with the male screw seal 5 is suppressed from decreasing. Therefore, it is possible to prevent the mined product from leaking when mining the mined product with the oil well pipe 200 or when mining again after stopping the mining.

Further, since the oil joint pipe screw joint 100 has the shoulder 6 having an angle θ2 of 5 degrees to 10 degrees, the amount of plastic deformation can be suppressed while improving the sealing performance. Therefore, it is possible to prevent the mined product from leaking when mining the mined product with the oil well pipe 200 or when mining again after stopping the mining.

1 male thread, 2 female thread, 3 male thread side thread, 4 female thread side thread, 5 male thread seal, 6 male thread shoulder, 7 female thread seal, 8 female thread shoulder, 100 oil well Screw joint for pipe, 200 oil well pipe, A seal end, O center.

Claims

A male screw having a seal formed in a convex curve shape and a shoulder formed on the tip side from the seal;
A female thread having a taper-formed seal,
In the oil joint pipe thread joint formed by pressing the contact portion between the male screw seal and the female screw seal,
The male screw seal is
In a direction parallel to the longitudinal direction of the male screw,
The length from the front-end | tip of the said male screw to the said contact part was set based on the thickness of the said oil well pipe. The screw joint for oil well pipes characterized by the above-mentioned.
When the thickness of the oil well pipe is 0.500 inch,
The length from the tip of the male screw to the contact portion is 0.250 inch or more,
When the thickness of the oil well pipe is larger than 0.500 inch and not larger than 0.750 inch,
The length from the tip of the male screw to the contact portion is 0.300 inch or more,
If the oil well pipe thickness is greater than 0.750 inches,
The length from the front-end | tip of the said external thread to the said contact part was 0.350 inch or more. The screw joint for oil well pipes of Claim 1 characterized by the above-mentioned.
The male screw seal is
In the direction parallel to the longitudinal direction of the male screw and toward the tip side,
The oil well pipe screw according to claim 1 or 2, wherein a portion from the contact portion to 3 mm is formed in a convex curved surface shape, and the portion from the convex curved surface shape to the tip of the male screw is formed in a straight cross-sectional shape. Fitting.
The taper angle θ1 of the female screw is
Based on the direction parallel to the longitudinal direction of the male screw and toward the tip,
The oil well pipe screw joint according to any one of claims 1 to 3, wherein the angle is set to 5 degrees or less in a clockwise direction.
The shoulder angle θ2 of the male screw is
On the basis of the perpendicular direction from the inner surface to the outer surface of the male screw,
The oil well pipe screw joint according to any one of claims 1 to 4, wherein the angle is set to 5 to 10 degrees clockwise.