PROPULSION DEVICE FOR A STEP ISE MOVABLE PIG
This invention regards a propulsion device for a stepwise movable pig of the type used in downhole operations, typically in connection with petroleum production.
When carrying out measurements, inspection, cleaning and other operations internally in pipes of the type in question, tools and instruments are normally led into the pipe by means of a so-called driving pig. A driving pig is designed to be displaced back and forth in a pipe. In some operations where the position of the pig in the longitudinal direction of the pipe must be determined accurately, the pig may be equipped with a suitable measuring device for accurate positioning. In order to perform other tasks, the pig must be constructed to exert great force. Thus the pig is adapted to the operations to be performed.
Pigs that need to exert great force in the axial direction of the pipe or carry great loads are often constructed as a piston-like body in which seals are provided between the pig
and the pipe wall. Thus the pig may be propelled in the pipe through hydraulic differential pressure, e.g. by means of drill fluid. Such hydrostatic propulsion commonly achieves a relatively high propulsion speed. However, seals used in this type of pig are subjected to a lot of wear, while at the same time being impaired by the temperatures that exist e.g. in a petroleum well. Pigs of this type are not suited for use in pipes in which pipe diameter reductions occur. It is normally not possible to perform other operations in a well while using this type of pig.
Pigs that are to be used for more accurate and complex operations are often fitted with powered wheels/tracks that are designed to displace the pig back and forth in the pipe when forced against the internal pipe wall. Relatively complex and sensitive devices for propulsion and control of wheel-going/tracklaying pigs limit the applications to mainly time consuming and complicated operations.
The object of the invention is to remedy the disadvantages of known techniques .
The object is achieved in accordance with the invention by the characteristics stated in the undermentioned specification and in the appended claims.
A telescopic pig is provided with a gripping/locking device at the outer end portions of each of its two, relative to each other telescoping main bodies, which device is designed to releasably connect the end portions of the pig to the pipe wall. A tension spring extends between the two telescoping main bodies, and is designed to displace the two main bodies
of the pig in a direction away from each other. The telescoping main body facing into the pipe is designated the front portion, while the other main body is designated the rear portion.
The pig is further equipped with contraction means designed to overcome the spring tension, thereby pulling the two telescoping main bodies together.
In a preferred embodiment, the gripping/locking device at each end portion of the pig comprises at least one over centre locking arm. On their projecting end faces, the locking arms are provided with gripping teeth or other friction extention means. The gripping teeth of the locking arm are pressed against the inside of the pipe by a retaining spring, and are rotatably supported in a manner such that the gripping teeth of the locking arm slide against the pipe wall when the pig is moved in one direction, while they grip and lock against the pipe wall when an attempt is made to move the pig in the opposite direction. The locking/release action of the locking arm is known per se, and is termed an over centre function.
The contraction means comprise a multi-notch block and pulley device in which one set of pulleys is rotatably connected to the front portion of the pig, while another set of pulleys is connected to the rear portion of the pig. One free rope part is connected to one of the pig portions, while the other free rope part is led up to a suitable capstan arrangement at the surface.
When the pig is to be guided into a pipe, it is lowered by
gravity as far as possible. The free rope part (in this context, rope represents any type of rope, wire rope, cable or other elongated object) extends out through the rear portion of the pig, up to said capstan. On the rope being tensioned, the locking arms of the front portion grip the pipe wall, thus creating an anchor for the rope pulleys connected to the front portion. By pulling the free rope part up further, the two sets of pulleys are displaced towards each other, whereby the front portion is pulled into the rear portion in a telescoping manner while the tension spring is compressed. After the two main bodies have been brought together, wholly or in part, the free rope part can be paid out. The compressed tension spring moves the main bodies apart. The locking arms coupled to the rear portion thereby lock against the pipe wall, whereby the rear portion takes over the anchor function. Thus the front portion is displaced further down/into the pipe until the tension spring has reached its initial position. The free rope end may now be pulled up, whereby the front portion takes over the anchor function, and the rear portion is pulled further down/into the pipe.
By repeatedly pulling up and paying out rope, the pig will be displaced further down/into the pipe. A disengaging apparatus that is known per se, possibly in the form of an eccentrically supported shaft, may be used to hold the gripping arms in a retracted, inactive position, so as to allow the pig to be pulled back by means of the free rope part. Alternatively, the gripping arms may be equipped with shear pins that are sheared at a predetermined force, whereby the gripping arms assume an inactive position.
The pig may if so desired be constructed in a manner such that the tension spring moves the main bodies together, while the block and pulley device moves them apart.
The following describes a non-limiting example of a preferred embodiment illustrated in the accompanying drawings, in which:
Figure 1 is a sectional, schematic view of the pig according to the invention in the initial position;
Figure 2 is a sectional, schematic view of the pig of Figure 1, but here the pig has been partly pushed together;
Figure 3 is a sectional, schematic view of the pig of Figure 1, but here the pig has been pushed together fully;
Figure 4 is a section I-I of the pig of Figure 1;
Figure 5 is a sectional, schematic view of the pig of Figure 1, but here the pulley is single-notch;
Figure 6 is a sectional, schematic view of an alternative embodiment in which the locking arms are equipped with unidirectional rotary wheels;
Figure 7 is a sectional, schematic view of a further embodiment in which the contraction device comprises a rack and pinion device in the initial position; and
Figure 8 is a sectional, schematic view of the pig of Figure
7 pushed together.
In the drawings, reference number 1 denotes a pig comprising a front portion 4 and a rear portion 6, where the rear portion 6 is telescopingly supported in guides 8, 8'. The pig 1 is designed to be displaced in a pipe 2.
The front portion 4 comprises a telescoping pipe member 10 equipped with a projecting flange 12 and a guide holder 14 for the guide 8, which holder projects to the pipe member 10. By its projecting free end portion 16, the front portion 4 is provided with at least one over centre supported locking arm 18 rotatably supported about a shaft 20, and where the projecting end face 22 of the locking arm is provided with gripping teeth/grooves/serrations. The end face 22 is designed to be pressed releasably against the inner wall of the pipe 2. The locking arm 18 is pressed against the inner wall of the pipe 2 by a retaining spring 26. The free end portion 16 of the front portion 4 is equipped with a mounting socket 24.
The rear portion 6 comprises a penetrated end piece 28 and an outer casing 30 fixed to the end piece 28. The outer casing 30 is fitted with an inward projecting flange 31 and an inward projecting flange-like guide holder 32 for the guide 8'. Near the end piece 28, the rear portion 6 is equipped with at least one locking arm 18' having an equivalent construction and function to the locking arm 18.
A tension spring 34 extends between the flange 12 of the front portion 4 and the flange 31 of the rear portion 6, and is designed to move the front 4 and rear 6 portions of the
pig 1 apart. A multi-notch block and pulley device 36 comprises a rope 38 and one or more pulleys 40, 40', 40''' and 40'''. The pulleys 40 and 40' are rotatably connected to the pipe member 10 of the front portion 4, while the pulleys 40'' and 40''' are rotatably connected to the outer casing 30 of the rear portion 6. The free end portion 42 of the rope is fixed to the front portion 4. The other free end portion 44 of the rope is led over deflecting wheels 46 and 46' and out through the bore 48 of end piece 28, and further to a capstan (not shown) .
When the free end portion 44 of the rope 38 is pulled in the direction out of the rear portion 6, see Fig. 1, the whole pig moves a short distance in the direction of the free end portion 44 of the rope 38. The movement causes the end faces 22 of the locking arms 18, which are braced against the inside of the pipe 2 by retaining spring 26, to rotate about the shaft 20 at their over centre support, whereby the gripping teeth of the locking arms are brought into fixed engagement with the inner wall of the pipe 2 with great force. By pulling the rope 38 further out of the pig 1, see Figs. 2 and 3, the distance between those pulleys 40, 40' of the multi-notch block and tackle device 36 that are connected to the front portion 4 and those pulleys 40'', 40''' that are connected to the rear portion 6 is shortened, whereby the pig 1 and thereby the tension spring 34 are compressed. The locking arms 18' of the rear portion 6 are displaced in this direction of displacement along the inner wall of the pipe 2 without gripping the wall .
After the pig 1 has been fully or partly brought together, the rope end portion 44 can be paid out. The force from the
compressed tension spring 34 moves the main bodies 4, 6 of the pig 1 apart. The direction of force causes the locking arms 18' of the rear portion 6 to grip the inner wall of the pipe 2 as described above, while the locking arms 18 of the front portion 4 are displaced in a non-locking manner along the inner wall of the pipe 2. The front portion 4 of the pig 1 is then displaced further down/into the pipe 2. By repeatedly pulling up and paying out rope, the pig 1 can be made to move into the pipe 2 in a stepwise manner.
In an alternative embodiment, see Fig. 6, the locking arms 18, 18' are provided with unidirectional rotary wheels 50. The wheels 50 are equipped with a free-wheel locking device of a type that is known per se.
In a further embodiment, see Fig. 7, the front portion 4 is provided with a rotatably supported rope reel 52. A pinion 56 that meshes with a rack 54 is concentrically coupled to the rope reel 52. The rack 54, which is fixed to the rear portion 6, is moved in a guide 58 connected to the front portion 4. When the rope 38 is pulled out of the rope reel 52, the rope reel 52 and the pinion 56 rotate. The teeth of the pinion 56 grip the rack 54, which is displaced in such a manner relative to the front portion 4 that the front portion 4 is displaced into the rear portion 6, along with the rope reel 52 and the pinion 56. In this embodiment, the rope reel 52 may be associated with a helical spring designed to replace the tensioning function of the tension spring 34.
A pig according to the invention is simple and reliable in comparison with known pigs. It can carry relatively great loads, and the influence of the existing pressure and
temperature is insignificant. The pig may be applied to tasks regardless of whether liquid is being pumped through the pipe.