Tubing connector

Details Tubing connector Tubing connector

1998-12-16

2002-11-05

Luu, Teri Pham (Department: 3627)

Pipe joints or couplings

Deformed

Both members

C285S256000, C285S382000

Reexamination Certificate

active

06474701

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a tubing connector suitable for use with coiled tubing in oil and gas well operations.
BACKGROUND OF THE INVENTION
Coiled tubing is primarily used to perform maintenance tasks on completed oil and gas wells. The principle of coiled tubing maintenance or ‘workover’ is to attach a toolstring to the end of a reel of steel tubing. By reeling out the tubing, the toolstring may be lowered many thousands of feet into the well. By either reeling in or reeling out the tubing, the toolstring can be positioned and made to perform simple tasks downhole. The toolstring is retrieved by reeling in the tubing at the end of the task. Because the tubing is moderately rigid, in the same manner as drain rods, it is able to transmit torque and compression. This allows light drilling work and access to deviated sections where gravity alone would not be enough to convey the toolstring. Because coiled tubing is hollow, it is able to pass fluids. This feature may be used to place chemicals accurately at a given depth in the well. It may also be used to provide hydraulic power to the toolstring. The hydraulic power is typically used to activate tools and run hydraulic motors for example when drilling.
The tool string consists of a variable combination of individual tools screwed or otherwise locked together to form a working unit. A typical toolstring would comprise a tubing connector, non-return valves, accelerator, stem, upstroke jar and a running/pulling tool or motor and bit. The tubing connector joins the toolstring to the coiled tubing. Non-return or check valves are needed since the tubing passes through the wellhead seals. If the tubing broke at surface the non-return valves in the toolstring would shut and prevent escape of the well fluids. An accelerator stores energy in a spring system for use when hammering or ‘jarring’. The stem is lengths of dense tubing, the mass of which increases the momentum of the hammer blow when jarring. The upstroke jar is a latching slide hammer arranged so that the slide is latched closed until sufficient tension is applied to the toolstring via the tubing. The applied tension also compresses the springs in the accelerator, storing a measure of energy. When the jar latch releases, the jar rod and attached stem are accelerated by the stored energy. At the end of the jar rod travel the rod and stem are suddenly stopped giving a powerful hammer action. Setting the toolstring down after activating the upstroke jar pushes the jar rod back to the start of its travel and resets the latch. At the end of the toolstring there may be a running/pulling tool. This interfaces with equipment to be left in or retrieved from the well. In many cases a shear pin will need to be fractured to activate the running/pulling tool, thus the requirement for a hydraulically effect from the jar. Even if the running/pulling tool is hydraulically activated then, due to the arduous conditions of heat and contaminants downhole, mechanisms and interlocking parts can become jammed and require blows to free them. Alternatively, the coiled tubing tool string may end in a hydraulic motor and some form of drill bit or cutter. This equipment would be used for clearing obstructions or for deepening the well.
Another use for coiled tubing, especially in larger diameters, is as a permanent fixture in the well through which the oil or gas will be produced. This one-time deployment is often termed a hang-off. A coiled tubing hang-off is a fast and economical alternative to deploying screw-jointed tubulars. The tubing in the hang-off is suspended from and sealed to the existing well steelwork by a top connector. Typically the bottom tubing connector attaches filters, e.g. sand-screens or an electric submersible pump (ESP).
From the above descriptions it will be seen that the integrity of the connection between tubing and the tool string or hang-off components is of paramount importance. The tubing connector must be permanently secure when subject to large tensile, torque, shock and vibrational loadings. The connector must also allow a quick and foolproof assembly onto the tubing end as it hangs free from the tubing unit. Previous tubing connectors all present serious problems, either in security or assembly. These connectors may be divided into groups dependent upon their structure. Each group is described in turn below.
Grapple connectors, of which a typical example is shown in
FIG. 1
, use an externally tapered, internally serrated split sleeve to bite onto the coiled tubing and wedge into the connector body. The connector must be firmly assembled to the tubing before operations commence, this requiring large make up torques onto the free hanging tubing end. This is a difficult task. Large pull loads when in use will often cause the grapple to bite deeper onto the tubing and slip in its taper, so loosening the assembly thread which risks subsequent unscrewing and loss down hole. Since the grapple and tapered housing are outside the tubing this type of connector is ‘upset’ or ‘outline’ and the increased diameter of the assembly over the tubing diameter can pose an access problem in some wells. This connector is internally flush. The serrations inside the grapple
5
and the grapple location in the taper do not provide a good torque drive. When used for drilling this type of connector is normally enhanced with grub screws
3
through the connector body
1
top portion
4
biting into the tubing
2
.
Pinned end connectors, of which a typical example is shown in
FIG. 2
, use a number of radial pins
6
loaded in shear to maintain a hollow spigot in the end of the tubing. The tubing is cross drilled to accept the pins using a guide jig and a pistol drill. The connector is assembled by placing the spigot in the tubing and pushing the pins through the tubing drilling and into matching blind holes in the spigot. An external sleeve
7
maintains the pins
6
in the connector. The connector transmits torque and tension commendably well but is tricky to assemble because of the predrilling required and the insertion of the small loose pins. The connector is neither internally nor externally flush.
Dimple grub screw connectors, a typical example of which is shown in
FIG. 3
, are also neither externally nor internally flush. Here the tubing end
2
is plastically worked by a jig so that it presents local depressions or dimples
8
into which grubscrews
3
in the connector
1
can seat. The connector itself is a sleeve which fits over the tubing and is threaded for the grubscrews. The connector has good tensile and torque capability.
Roll-on connectors, a typical example of which is shown in
FIG. 4
, are externally flush or ‘inline’ connectors which use an internal spigot-type connector body
1
. In this case the spigot is retained by plastically deforming or ‘crimping’ the tubing into grooves
9
running around the spigot. The deformation is achieved with a manual pipe cutting tool in which the sharp cutting wheel is replaced by a radiused wheel to suit the grooves in the spigot. Some measure of torque transmission can be achieved by stopping one or more of the spigot grooves from being fully circumferential. This increases the difficulty of make up since the rolling tool cannot be run all the way round the tubing but must stop in accordance with the part grooves. The connector has limited tensile strength because of severe stress concentrations. Those, present around the full circumference of the tubing, are introduced by load transfer through the crimped profile.
It is an object of the present invention to overcome these disadvantages with a simple, remarkably robust, torque transmitting tubing connector of novel design that does not significantly diminish the tubing strength at the connection either in torque or in tension.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention there is provided a tubing connector non-releasably connected to a tube of tubing string for use downhole in oil and gas well operations, the connector compr

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