Coil springs for cable support

TECHNICAL FIELD

This invention relates in general to a method and apparatus for installing and supporting an electrical submersible pump cable, and in particular to helically wound coil springs affixed to an electrical submersible pump cable for engaging an inside wall of coiled tubing.

BACKGROUND ART

Electrical submersible pumps (ESP) are normally installed on jointed production tubing and powered by an ESP cable attached to the outside of production tubing. All produced fluids are pumped up the production tubing to the surface.

Oil well completions are being developed to deploy ESPs on the bottom of continuous coiled tubing where the power cable is placed inside the coiled tubing. In these installations, produced fluids are pumped up the annulus between the coiled tubing and the production tubing, or well casing or liner. Many advantages are gained through the use of coiled tubing such as faster deployment, the elimination of a need for large workover rigs, and less frictional pumping losses.

Because ESP cable cannot support its total vertical weight, cable support must be provided by the coiled tubing at regular intervals. Various proposals have been made to provide support, such as the use of mechanical anchors. A need exists for anchors which can be used in fairly small diameter coiled tubing, which will accommodate movement associated with thermal expansion and which will accommodate bending of coiled tubing.

DISCLOSURE OF INVENTION

This invention discloses a new method for installing and supporting an ESP cable in a coiled tubing while allowing slight side-to-side or reciprocal movement of the electrical power cable with respect to the tubing as may occur during handling and service. Helically wound coil springs are wrapped around and attached to a cable at regular intervals. The upper section of each coil spring or support spring is affixed to the cable armor by a connecting section such as a cable clamp. A remainder of each spring is formed in a long open helix facing downward when the tubing is installed in a well. The open helix section experiences frictional engagement between the spring and the coiled tubing during installation. The entire surface of the spring may be knurled to increase friction between the spring and the coiled tubing. Additionally, the spring may be provided with a square cross-section to increase the surface area in contact with the coiled tubing. The open helix terminates in a free end. Preferably, the free end is sharpened and hardened for frictional engagement with the inner surface of the tubing.

In one embodiment, the open helix portion of the spring is divided into two sections. The first and longest section is referred to as the undersized section and has a diameter just slightly smaller than the inside of the coiled tubing. The second section located at the very bottom of the helical spring is designed to be slightly larger than the inside diameter of the coiled tubing and is referred to as the oversized section.

A sufficient number of support springs are placed on the cable prior to installation in the tubing. Preferably, the cable is installed in the tubing by pulling the cable in a direction toward the connecting section of the spring. When each spring enters the tubing, the open helix portion of each spring engages the inside diameter of the tubing wall, causing a dragging force. This force stretches the spring, causing the oversized open helix section of the spring to increase in length and decrease in diameter until the stretched spring slides inside the tubing. The process is repeated with each spring support as the entire cable is pulled into the tubing.

When the coiled tubing and cable assembly is placed in a vertical position during installation, the cable is pulled downward by gravity. The outside diameter of the spring, which is preferably knurled, engages the inner surface of the tubing. Movement of the cable in the downward direction with respect to the tubing causes the support springs to compress or shorten due to frictional forces between the spring and the inside surface of the tubing wall. As the helical springs are compressed, the outside diameter of the springs expand to cause a self regulating locking action between the tubing and the spring while preventing the cable from moving downward. The locking action increases with an increased downward force on the cable so as to make a “fail safe” attachment between the cable and the tubing. It has been found that vibration of the coiled tubing, such as may occur during installation, may cause the springs to initially slip within the coiled tubing. However, after the initial slippage, equilibrium is achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is an elevational view, partially in cross section of two spring supports of the invention supporting a cable within a tubing string.

FIG. 2

is an enlarged view of the upper support spring of

FIG. 1

shown during installation.

FIG. 3

is a cross sectional view of the cable and tubing string of

FIG. 1

taken along the line

3

—

3

of FIG.

1

.

FIG. 4

is an enlarged view of the upper support spring of

FIG. 1

shown being compressed by the weight of the cable.

BEST MODE OF INVENTION

Referring to

FIGS. 1-4

, tubing

10

is shown encompassing a cable

12

such as a power cable or a cable conductor. A cutaway view of tubing

10

is shown in

FIGS. 1

,

2

and

4

. In the preferred embodiment, cable

12

consists of three conductors

14

to provide power to an electrical submersible pump, each of which is surrounded by conductor insulation

16

. However, other types of apparatus may be used with the invention. Conductors

14

and conductor insulation

16

are surrounded by cable jacket

18

which is surrounded by cable armor

20

. Armor

20

comprises a strip of metal wound around jacket

18

.

To support cable

12

within tubing

10

, a plurality of support springs

22

are provided. Support springs

22

have a connecting section or clamp

24

that affixes support spring

22

to cable

12

.

Support springs

22

additionally have a helical section

26

for engaging inside surface

28

of tubing

10

. In an alternate embodiment, helical section

26

includes an undersized section which has an outside diameter that is initially smaller than an inside diameter of tubing

10

prior to installation. In the alternate embodiment, support spring

22

also has an oversized section which has an initial outside diameter that is larger than an inside diameter of tubing

10

prior to installation. Support spring

22

may have a square cross section to increase the surface area in contact with the inside surface

28

of tubing

10

.

Helical section

26

can be seen in an uncompressed or non-load-bearing state in

FIGS. 1 and 2

. Support spring

22

terminates at free end

33

. Free end

33

is preferably sharpened and hardened for engagement with inside surface

28

of tubing

10

. Other methods of increasing friction between free end

33

and inside surface

28

of tubing

10

may be used including providing a serrated free end

33

. Preferably, the entire surface of spring

22

is knurled to increase friction between spring

22

and inside surface

28

of tubing

10

.

A plurality of support springs

22

are affixed to power cable

12

prior to installing cable

12

within tubing

10

. Cable

12

and support springs

22

are pulled into tubing

10

using a previously inserted line. When each support spring

22

is pulled within tubing

10

, the clamped end of spring

22

enters first. Then, the helical section

26

of each support spring

22

engages inside surface

28

of tubing

10

, causing a dragging force as shown in

FIGS. 1 and 2

. The dragging force stretches spring

22

causing the helical section

26

of spring

22

to increase in length and decrease in diameter until the spring slides inside of tubing

10

. This process is repeated with each support spring

22

until the entire power cable

12

is pulled into tubing

10

.

In practice, tubing

10

is continuous coiled tubing that is extended into casing or production tubing in a well bore. An electrical submersible pump or other apparatus (not shown) is affixed to a lower end of tubing

10

. Cable

12

, within tubing

10

, may be used for delivering power from a power source to the electrical submersible pump.

When tubing

10

and cable

12

are placed in a vertical position during installation, cable

12

is pulled downward by gravity. The outside diameter of the helical section

26

of spring

22

and free end

33

engages inside wall

28

of tubing

10

to provide frictional contact between spring

22

and inside surface

28

of tubing

10

. Downward movement of cable

12

relative to tubing

10

results in a shortening of support springs

22

and a firm engagement of the entire length of helical section

26

with inside surface

28

due to frictional forces between the spring and the inside surface

28

of tubing

10

as shown in FIG.

4

. This engagement causes a self-regulating locking action between tubing

10

and spring

22

, while preventing the cable from moving downward. In practice, vibration of the coiled tubing may result in initial slippage of the spring relative to the coiled tubing. However, after an initial slippage, equilibrium and locking action are achieved.

Because the springs are formed in an open helix in helical section

26

below clamp

24

, slight movement in either direction relative to the tubing

10

, such as may be imparted to the cable during coiling and uncoiling is easily accommodated. The spring supports

22

can also accommodate movement associated with thermal expansion of the cable

12

due to conductor heat rise during service. Additionally, the open helix design of support springs

22

provides a passageway for fluids to be pumped through the tubing

10

through the annulus between the cable

12

and the inside surface

28

of tubing

10

. Further, since support springs

22

are flexible, they are unlikely to be damaged by bending action of the tubing

10

as it passes from a reel, over a gooseneck and into the well.

Other advantages of this invention include the advantage of requiring very little space for the support springs

22

, making it possible to use a smaller diameter coiled tubing than is possible with certain other support methods in use today. The support springs

22

of the invention are economical and easy to install. The support springs

22

also keep the cable

12

centered within the coiled tubing

10

, thereby minimizing relative motion of the cable

12

with respect to the tubing

10

during bending. Further, and perhaps most importantly, the cable

12

can be removed for inspection and/or replacement of either the cable

12

or the tubing string

10

by pulling the cable

12

from the tubing

10

in the same direction that it was installed.

While the invention is shown in only one of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention.