JPH07119376A - Oil well pipe - Google Patents

Abstract

PURPOSE:To prevent an oil-well pipe from being broken with frictional force caused by settlement of ground. CONSTITUTION:An oil-well pipe is constituted of an oil-well pipe main body 1 and a sliding layer 2 of ethylene acetic acid vinyl copolymer resin coated on the peripheral surface of the oil-well pipe main body 1. When frictional force is acted on the oil-well pipe, the sliding layer 2 is pulled downward by residual negative friction and is deformed. Frictional force acted on the oil-well pipe main body 1 is decreased by deforming the sliding layer 2, so that the oil-well pipe is not broken. In addition, during the conveyance, or in the case of execution, damage in the oil-pipe main 1 body 1 and sliding layer 2 is prevented by forming a protection layer 3 on the peripheral surface of the sliding layer 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oil country tubular good for casing which is not destroyed by ground subsidence and which is excellent in fracture resistance.

[0002]

2. Description of the Related Art An oil well for collecting crude oil is formed by a tubing which is an oil well pipe for pumping crude oil from an oil layer to the ground and a casing which is an oil well pipe for protecting the tubing. Most of the oil wells are dug almost vertically, and the casing oil well pipes (hereinafter simply referred to as “oil well pipes”) are subjected to a frictional force that is pulled downward due to ground subsidence associated with the collection of crude oil.

However, in the conventional oil well, the above-mentioned frictional force acting on the oil well pipe is not necessarily large, and therefore, the probability that the oil well pipe is destroyed due to the frictional force is not always high. No means have been applied.

[0004]

On the other hand, in deep-deep oil wells, the problem of destruction due to ground subsidence of oil well pipes has recently become remarkable. In other words, a large underground pressure is applied to an oil well pipe buried in a deep depth, so that the frictional force acting on the oil well pipe is large and the situation in which the oil well pipe is destroyed cannot be ignored. Therefore, it has been desired to develop an oil well pipe that reduces the frictional force acting between the ground and the oil well pipe and is not destroyed even when the ground sinks.

The present invention has been made in order to solve the above-mentioned problems of the prior art. By reducing the frictional force acting on the oil well pipe, an oil well pipe that is less likely to be damaged by ground subsidence is provided. It is intended to be provided.

[0006]

The oil well pipe according to the present invention has an oil well pipe main body and a slip layer outside the oil well pipe main body.

The slipping layer has a stiffness coefficient S (t) after a lapse of one year or more at the operating temperature of the oil country tubular good.
Is made of a material within the range of 10 ⁻⁵ to 10 ³ N / m ² .

The sliding layer is made of a material mainly containing asphalt. Further, the sliding layer is made of a material mainly composed of polyethylene having a density of 0.930 g / cm ³ or less.

The slip layer has a density of 0.930.
It is made of a material mainly composed of maleic acid-modified polyethylene of g / cm ³ or less.

The sliding layer is made of a material mainly composed of ethylene vinyl acetate copolymer resin.

The sliding layer is made of a material mainly composed of a mixture of an ethylene vinyl acetate copolymer resin and a malein-modified polyethylene resin. Further, the content ratio of vinyl acetate in the ethylene-vinyl acetate copolymer resin forming the sliding layer is set to 5 to 60% by weight.

The sliding layer is made of a material mainly containing a maleic acid-modified ethylene vinyl acetate copolymer resin.

Further, the content ratio of vinyl acetate in the maleic acid-modified ethylene vinyl acetate copolymer resin constituting the sliding layer is set to 5 to 60% by weight.

The slip layer is formed by extrusion coating. In addition, a protective layer is provided outside the sliding layer.

The protective layer is made of a material having a softening temperature exceeding the operating temperature of the oil country tubular good.

The protective layer is formed by extrusion coating.

[0017]

[Operation] When a frictional force due to ground subsidence acts on an oil well pipe vertically embedded in the ground, the viscous sliding layer that coats the outside of the oil well pipe is dragged downward by the frictional force and deforms. The frictional force acting on the tube body is reduced.

That is, as shown in the schematic diagram of FIG. 3, when a constant shear stress (frictional force) τ due to ground subsidence acts on the upper surface of the sliding layer 21 having a thickness h and exhibiting viscous behavior, after t seconds. Shear deformation (viscous behavior) occurs as shown by the broken line in the figure.

The relationship between the amount of slip deformation d (t) after t seconds and the frictional force τ is expressed by equation (1) using the stiffness coefficient S (t) of the slip layer and the thickness h of the slip layer. Can be represented. τ = S (t) · d (t) / 3h (1) From equation (1), it can be seen that the frictional force τ can be reduced by using a material having a small stiffness coefficient S (t) for the sliding layer. .

The present inventors conducted a model experiment and found that the frictional force τ should be set to 2 × 10 ³ N / m ² or less in order to prevent the oil country tubular good from being destroyed by ground subsidence. Furthermore, it has been found that by setting the frictional force τ to 2 × 10 ² N / m ² or less, it is possible to almost completely prevent breakage.

From these results, the thickness h of the slip layer is 2
mm, the slip amount d (t) of the slip layer after one year is 20 mm,
When the frictional force of 2 × 10 ³ N / m ² continues to act, the stiffness coefficient S of the slip layer where the oil country tubular good is not broken
As (t), 10 ³ N / m ² was obtained.

That is, the stiffness coefficient S after one year has passed
When (t) is 10 ³ N / m ² or less, the oil country tubular goods are less likely to be broken, and when the frictional force corresponds to 2 × 10 ² N / m ² or less, the stiffness coefficient S (t) is 10 ² N
It has been found that the oil well tube is not substantially destroyed at a pressure of less than / m ² .

In other words, the material having a stiffness coefficient S (t) of more than 10 ³ N / m ² after one year has insufficient deformability of the slipping layer, so that the frictional force cannot be reduced and the oil country tubular good is destroyed. The probability is high.

The stiffness coefficient S after one year has passed
It was also found that when (t) is less than 10 ^-5 N / m ² , the slip layer is softened and eluted.

The stiffness coefficient S (t) of the material according to the present invention gradually decreases for less than one year, but after the lapse of one year, it hardly changes after the lapse of one year. The range of the stiffness coefficient S (t) is the same after one year has passed.

As described above, the oil country tubular goods according to the present invention are intended to reduce the frictional force between the submerged ground and the oil country tubular goods body and prevent the destruction of the oil country tubular goods due to the viscous behavior of the slip layer. Yes, the material of the slip layer is selected according to the temperature at which the oil country tubular good is used.

That is, as a matter of course, the material used for the sliding layer needs to exhibit a desired viscous behavior in a desired temperature range.

Therefore, for example, when used in the temperature range of 100 to 130 ° C. where the breakage of oil country tubular goods is currently a problem, the stiffness coefficient S (t) after one year has passed as the material of the slip layer. , By selecting a material in the range of 10 ⁻⁵ to 10 ³ N / m ² in the temperature range of 100 to 130 ° C., and more preferably a material in the range of 10 ⁻⁵ to 10 ² N / m ² . The destruction of the oil country tubular good can be prevented.

Of course, even outside this temperature range,
It goes without saying that it is desirable to satisfy this condition, that is, a material that satisfies the above-mentioned range of the stiffness coefficient S (t) in a temperature range as wide as possible.

At present, the temperature to which the oil country tubular goods are exposed is 130 ° C. or lower, but as a result of various investigations on materials satisfying the above-mentioned conditions, it was found that some materials can be used for the sliding layer.

First, asphalt is prepared by mixing straight asphalt and hot asphalt at a predetermined ratio so that the stiffness coefficient S (t) after one year in the temperature range of 40 to 100 ° C. is 10 ⁻⁵ to 10 ³ N. / M ²
It is possible to obtain materials falling within the range. These asphalts can contain additives such as resins, oils and fats, rubbers, pigments and fillers.

Polyethylene can also be used. The softening point of polyethylene can be changed depending on the density.
For example, when used in the range of 100 ° C to 130 ° C, the above-mentioned stiffness coefficient S (t) in this temperature range.
To satisfy the range of 0.930 g / cm ³
The following polyethylenes should be selected.

Polyethylene having a density of more than 0.930 g / cm ³ has a stiffness coefficient S (t) of 10 ³ N / m ² or more after one year at 100 ° C. and is not sufficiently softened, and is used as a slip layer. It is not possible to exert the function of.
On the other hand, polyethylene having a density of 0.930 g / cm ³ or less has a softening temperature of less than 100 ° C.
The stiffness coefficient S (t) after one year at 10 ³ N /
Since it is m ² or less, the function as a slip layer can be exhibited.

In the case of low density polyethylene having a density of 0.930 g / cm ³ or less, the stiffness coefficient S (t) after one year at 130 ° C. is 10 ⁻⁵ N / m.
The lower limit of the density need not be specified because it satisfies the condition of ² or more.

Maleic acid-modified polyethylene can also be used. The maleic acid-modified polyethylene can also change the softening point depending on the density. For example, 100 ° C to 1
When used at 30 ° C., it is necessary to select a maleic acid-modified polyethylene having a density of 0.930 g / cm ³ or less in order to satisfy the above range of the stiffness coefficient S (t) in this temperature range.

The maleic acid-modified polyethylene having a density of more than 0.930 g / cm ³ has a stiffness coefficient S (t) of 10 ³ N / m ² or more after one year at 100 ° C. and is not sufficiently softened, It does not function as a slipping layer. On the other hand, the density is 0.930 g / c
The maleic acid-modified polyethylene of m ³ or less has a softening temperature of less than 100 ° C., and the stiffness coefficient S (t) after one year at 100 ° C. is 10 ³ N / m ² or less. It can exert its function.

In the case of low-density maleic acid-modified polyethylene having a density of 0.930 g / cm ³ or less, 130
Since the stiffness coefficient S (t) after 1 year at 0 ° C. satisfies the above condition of 10 ⁻⁵ N / m ² or more, the lower limit of the density need not be specified. Since maleic acid-modified polyethylene has a polar group called maleic acid, it has good adhesion to the steel of the oil country tubular good.

By selecting the optimum composition of the ethylene-vinyl acetate copolymer resin, a material satisfying the above range of the stiffness coefficient S (t) can be obtained in the intended temperature range. That is, since vinyl acetate has a lower softening temperature than the ethylene component, it is possible to freely select the stiffness coefficient S (t) within a certain range by changing the blending ratio.

In order to satisfy the above range of the stiffness coefficient S (t) in the range of 40 to 130 ° C., the content ratio of vinyl acetate in the ethylene vinyl acetate copolymer resin should be 5 to 60% by weight. Good.

Further, the ethylene vinyl acetate copolymer resin may be reacted with maleic acid to prepare a maleic acid-modified ethylene vinyl acetate copolymer resin to form a sliding layer. In this case, since maleic acid is a polar group, the adhesion of the oil country tubular goods body to the steel becomes good.

For the same reason, the sliding layer may be formed by adding maleic acid-modified polyethylene to an ethylene-vinyl acetate copolymer resin.

Additives and the like can be mixed with the above resins, if necessary. Examples of additives include pigments, antioxidants, weathering stabilizers, fillers, and the like. In pigments, antioxidants, weathering stabilizers, a maximum of about 2% may be added, and in a filler, a maximum of about 10% may be added. . Such a slip layer can be formed on the outer peripheral surface of the oil country tubular goods body by, for example, extrusion coating.

Next, the reason for providing the protective layer will be described. The protective layer has a function of preventing damage to the sliding layer and the body of the oil country tubular goods when the oil country tubular goods are transported or buried. The present invention also includes a case where a protective layer is provided as necessary.

For the protective layer, a material that does not soften under the environment in which the oil country tubular good is used is used. That is, when the upper limit of the operating temperature is 130 ° C, a material having a softening point of more than 130 ° C may be used.

As such a material, there is a polyolefin resin such as polypropylene or ethylene propylene block copolymer, and particularly, the softening temperature is from 140 to 140.
170 ° C. polypropylene or ethylene propylene block copolymer is preferred.

When the ethylene-propylene block copolymer is coated on the sliding layer made of maleic acid-modified polyethylene, the adhesion between the two is good and they are mutually preferable materials. As with the sliding layer, additives and the like can be mixed in the protective layer, if necessary.

The protective layer made of resin can be formed on the outer peripheral surface of the sliding layer by, for example, extrusion coating. On the other hand, metals such as mild steel are also useful as the protective layer. For example,
A mild steel strip can be spirally wound to form a protective layer. Of course, the presence or absence of the protective layer does not affect the frictional force acting on the oil country tubular good.

[0048]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The oil country tubular goods which are the embodiments of the present invention will be described with reference to FIGS. Figure 1 is a cross-sectional view of this oil country tubular good,
Reference numeral 1 is an oil country tubular goods body, 2 is a slip layer, and 3 is a protective layer.

FIG. 2 is an explanatory view showing one manufacturing method of an oil country tubular good. In this oil country tubular goods, the outer peripheral surface of the oil country tubular body main body 1 is extrusion-coated with the slip layer 2 by the slip layer extruder 4, and the outer peripheral surface of the slip layer 2 is extrusion coated with the protective layer 3 by the protective layer extruder 5. Manufactured by.

The steel pipe used has an outer diameter of 177.8 mm and a wall thickness of 2
It is an oil well pipe having a length of 3.8 mm and a length of 12,000 mm, and asphalt, polyethylene, maleic acid modified polyethylene, ethylene vinyl acetate copolymer resin, maleic acid modified vinyl acetate copolymer, which is heated and melted on the outer peripheral surface by the slide layer extruder 4. A resin or a mixture of an ethylene vinyl acetate copolymer resin and a maleic acid-modified polyethylene resin was extruded to form a slip layer 2. The thickness of the sliding layer is as in Example 10,
13 and 15 and Comparative Examples 1 and 2 are 1 mm, and others are 2 mm.

The protective layer 3 was formed by extruding polyethylene, polypropylene or an ethylene-propylene block copolymer heated and melted by the protective layer extruder 5 on the outer peripheral surface of the sliding layer 2. The thickness of the protective layer is 4 m in Example 10.
m and others are 3 mm. Also, 0.3 mmt, 200 m
We also manufactured an oil country tubular good that also has a protective layer made of m-width mild steel strip wound spirally. Of course, examples and comparative examples having no protective layer were also manufactured. Of these, Examples 1 to 15
Comparative Examples 1 to 4 are shown in Table 1, and Examples 16 to 44 are shown in Table 2.
In addition, Examples 45 to 60 are shown in Table 3.

Examples 1 to 60 and Comparative Examples 1 to 1 described above
4 wells, 40 ℃, 50 ℃, 60 ℃, 70
Stiffness coefficient S (t) of the slip layer after 1 year at ℃, 80 ℃, 90 ℃, 100 ℃, 110 ℃, 120 ℃ and 130 ℃, and the protective layer after left in a furnace at the same temperature for 1 hour Was investigated for stability. These results are shown in Table 4 ~
6 shows.

[0053]

[Table 1]

[0054]

[Table 2]

[0055]

[Table 3]

[0056]

[Table 4]

[0057]

[Table 5]

[0058]

[Table 6]

The oil country tubular goods of Examples 1 to 60 can be used in a temperature range in which the stiffness coefficient S (t) after one year is in the range of 10 ^-5 to 10 ³ N / m ² , and this temperature range There is little possibility that the oil country tubular good will be destroyed by subsidence. Further, the stiffness coefficient S (t) 10 ⁻⁵ to 10
^It is extremely safe when used in the temperature range of ² N / m ² .

On the contrary, Comparative Examples 1 and 2 are 120 ° C. or lower, and Comparative Examples 3 and 4 have a stiffness coefficient S (t) of 10 ³ N / m ² after one year in any temperature range. It is clear that the oil well pipe has a large frictional force and is easily broken by ground subsidence.

In addition, the protective layer of the oil country tubular goods of Examples 1 to 60 has no abnormality in a wide temperature range, and it is necessary to prevent damage to the sliding layer and the body of the oil country tubular goods not only when the oil country tubular goods are transported but also when the oil country tubular goods are buried. You can

As described above, the oil country tubular good having a sliding layer mainly made of asphalt, polyethylene, maleic acid modified polyethylene, ethylene vinyl acetate copolymer resin or maleic acid modified vinyl acetate copolymer resin, or a mixture thereof is When used in the temperature range from room temperature to 130 ° C, it is extremely safe from damage due to ground subsidence.

[0063]

EFFECTS OF THE INVENTION According to the present invention, it is possible to prevent the oil well pipe from being broken due to subsidence, and also to prevent the slip layer and the oil well pipe main body from being damaged not only when the oil well pipe is transported but also when the oil well pipe is buried.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an oil country tubular good according to an embodiment of the present invention.

FIG. 2 is an explanatory view showing a method for manufacturing an oil country tubular good according to an embodiment of the present invention.

FIG. 3 is a schematic diagram illustrating the viscous behavior of a slip layer.

[Explanation of symbols]

 1 Oil well pipe body 2 Sliding layer 3 Protective layer 4 Sliding layer extruder 5 Protective layer extruder

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shoichi Osuga Marunouchi 1-2-2 Marunouchi, Chiyoda-ku, Tokyo Inside Steel Pipe Co., Ltd. (72) Toshiyuki Kurosawa 1-2-1 Marunouchi Chiyoda-ku, Tokyo Main Steel Pipe Co., Ltd.

Claims (14)

[Claims] 1. An oil country tubular good characterized by having a sliding layer on the outside of the pipe body. 2. The stiffness coefficient S (t) of the sliding layer after a lapse of one year or more at the operating temperature of the oil country tubular good is
The oil country tubular good according to claim 1, which is made of a material in the range of 10 ^-5 N / m ² to 10 ³ N / m ² . 3. The oil country tubular good according to claim 1, wherein the sliding layer is made of a material mainly containing asphalt. 4. The sliding layer has a density of 0.930 g /
The oil country tubular good according to claim 1 or 2, which is made of a material mainly composed of polyethylene having a cm ³ or less. 5. The sliding layer has a density of 0.930 g /
The oil country tubular good according to claim 1 or 2, which is made of a material mainly composed of maleic acid-modified polyethylene having a cm ³ or less. 6. The oil country tubular good according to claim 1, wherein the sliding layer is made of a material mainly composed of an ethylene vinyl acetate copolymer resin. 7. The oil country tubular good according to claim 1, wherein the sliding layer is made of a material mainly composed of a mixture of an ethylene vinyl acetate copolymer resin and a malein-modified polyethylene resin. 8. The content ratio of vinyl acetate in the ethylene vinyl acetate copolymer resin constituting the sliding layer is 5 to 60.
The oil country tubular good according to claim 6 or claim 7, wherein the oil well pipe is defined as wt%. 9. The oil country tubular good according to claim 1, wherein the sliding layer is made of a material mainly containing a maleic acid-modified ethylene vinyl acetate copolymer resin. 10. The oil country tubular good according to claim 8, wherein the content ratio of vinyl acetate in the maleic acid-modified ethylene vinyl acetate copolymer resin constituting the sliding layer is 5 to 60% by weight. 11. The oil country tubular good according to any one of claims 1 to 10, wherein the slip layer is formed by extrusion coating. 12. The oil country tubular good according to any one of claims 1 to 11, further comprising a protective layer outside the sliding layer. 13. The oil country tubular good according to claim 12, wherein the protective layer is made of a material having a softening temperature exceeding the operating temperature of the oil country tubular good. 14. The oil country tubular good according to claim 12, wherein the protective layer is formed by extrusion coating.