Apparatus for connecting and disconnecting a downhole assembly

[0001] This application claims the benefits of earlier filed provisional application Ser. No. 61/752,157, filed on Jan. 14, 2013.

[0002] The present invention relates, in a general sense, to oil and gas production wells and, more particularly, to improved apparatus for connecting and disconnecting a downhole assembly including, e.g., geared centrifugal pumps.

[0003] In a typical production well having a well casing extending to a fluid deposit, a downhole assembly is lowered to a predetermined depth from the earth's surface, where it is immersed in a target fluid deposit. The pump, as part of the downhole assembly is driven by a source of motive power, such as a power supply at the surface of the well. A rod string depends from the power source and spans the distance between the power supply and the pump where it is connected to the pump to drive it.

[0004] The geared centrifugal pump (GCP), among other devices, utilizes the rod string to rotationally drive a downhole pump. In the case of the GCP, this rod string is run inside the production tubing after the pump assembly has been lowered on said production tubing and set at the desired downhole location. The current method of connecting the rod string to the downhole assembly, so that rotational force can be transmitted to that assembly, is via a male stab-in rod attached to the end of the drive rod string that fits into a companion female receptacle facing upwardly, which is part of a receiver component at the top of the downhole pump assembly.

[0005] This stab-in rod, as will later appear in keeping with the invention, may have any one of several cross section configurations, among them a square, a hex, or other cross section that fits snugly into a like-shaped female receptacle in the receiver. The stab-in rod is not attached to the receptacle for tensional loads and is of such length as to permit free movement vertically to adjust to differential vertical movement between the rod string and the overshot assembly. The stab-in rod, via the drive rods, when engaged, rotates the female receptacle, which is fixedly attached to the drive shaft that extends from the receiver through the upper seal section. In the case of the GCP, the drive shaft is attached to the input shaft of a speed increasing transmission, which, in turn, drives a centrifugal pump.

[0006] An important disadvantage to prior art systems of a male stab-in shaft and a female receptacle is debris can, and usually will, collect in the female receptacle before the rod string is run, or when the rod string is removed for service, making it somewhere between difficult to impossible to re-engage the stab-in rod into the receiver.

[0007] The present invention addresses that problem by eliminating a female receiver that is open to the unwanted collection of receptacle clogging debris.

[0008] In the business of oil and gas production, time is literally money. It is readily understood, therefore, that any difficulty in connecting the rod string to the overshot assembly costs dearly, in both time and money.

[0009] With that understanding, it is clearly a great advantage of the present invention to the oil producer, to eliminate prior art difficulties experienced when, as and if the female receptacle is in any way impaired, so as to greatly increase the difficulty with which the rod string is engaged with the downhole assembly.

[0010] It is a further benefit of the present invention to provide a mechanism, and a method of operation, which enhances the ability of the producer to connect the rod string with the receiver component of the downhole pump assembly.

[0011] Other objects and advantages of the present invention will become apparent to those skilled in the art from a reading of the following Detailed Description Of The Preferred Embodiment when read in concert with the drawings.

[0012] It will quickly become apparent that all of the drawings are pictorial representations of the area in the production tubing, wherein the receiver component of the downhole pump assembly is engaged by the drive rod string, and disengaged as needed.

[0022] The following detailed description discloses, to those skilled in the art, a novel system 20 for engaging a downhole assembly 22 with a rod drive string 24. Arrows A [FIG. 1] indicate the direction of flow of fluid in the production tubing T and overshot assembly 31.

[0023] It will be observed that in FIG. 1, which illustrates the current practice in the industry, various elements of the connection system are shown by numbers followed by a prime sign. Drive rod string 24′ is attached to stab-in rod 25′, at its low end, which is inserted into a female receptacle in receiver 26′. The downhole assembly is thereby rotationally connected to the drive string 24′. This connection arrangement functions satisfactorily until the stab-in rod is removed from the female receiver, as shown in FIG. 2, when the upward facing female receptacle in receiver 26′ is open to the ingress of downward moving debris, shown by arrows B.

[0024] As shown in FIG. 3, and in accordance with the present invention, the debris-clogging problem inevitably resulting from an open female receptacle in receiver 26′ is virtually eliminated by reversing the downhole rod/receiver elements of the connection and making the overshot assembly 31 the female receiver, and the receiver 26 the male connection member.

[0025] Accordingly, with this FIG. 3 configuration, and as shown in FIG. 4, when the drive rod string 24 is withdrawn from engagement with the receiver 26, there is no open receptacle facing upwardly towards the surface into which the debris can collect, and the debris, shown as arrows B, falls harmlessly past the receiver 26 where it will settle into the flow channels of the receiver and upper seal section and does not interfere with the connection between the drive rod string 24 and the receiver 26.

[0026] There are three main requirements for operationally attaching a rod string to a downhole assembly, and they are:

• • [0027] 1. The rod string is lowered after the downhole assembly is installed;
  • [0028] 2. The rod string is able to move vertically, freely within a limited travel distance while remaining rotationally connected to the downhole assembly; and,
  • [0029] 3. The rod string can be withdrawn and then detached and retrieved without requiring the retrieval of the downhole assembly.

[0030] Referring to FIGS. 3 and 4, a novel connection system 20 is configured to show the structure of the present invention in its simplest form.

[0031] The system 20 consists of a drive rod-attached overshot assembly 31 and a male receiver shaft 33 attached to the downhole assembly 22. By definition, the overshot assembly 31 is essentially a long, or otherwise configured, female receiver, or coupling, attached at the up-hole end 35 to the drive rod string 24, and having an elongated longitudinal bore 39 terminating in a downwardly facing opening at its free end, with a short length of internal splines 34 opening to the down-hole end 37 to fit over the male receiver shaft 33.

[0032] The free downhole end opening is flared as at 41 to provide an entry guide during engagement with the male receiver shaft 33. In practice, the length of the travel distance portion of the overshot assembly 31 would be approximately three feet. This is enough length to accommodate any expected differential vertical movement between the drive rod string 24 and the downhole assembly 22 without becoming disengaged. The overshot assembly 31 would have the female internal portion 34 of the inner bore over only the last approximately two inches of the three feet of potential engagement length, the rest being a smooth bore. At the top of the smooth bore would be a cushioning spring 43 to avoid damage to the male receiver shaft 33, overshot assembly 31 or receiver 26, when the rods are run as far as possible during installation of the drive rod string 24, and the overshot assembly 31 “bottoms out” as the connector shaft hits the spring 43.

[0033] The male receiver shaft 33 extends about four feet above the uphole end of the receiver 26 for engagement with the overshot assembly 31. The entire length of the shaft above the receiver 26 is configured so that there would be torsional engagement with the overshot assembly 31 over the entire length of the shaft.

[0034] Referring again to FIGS. 3 and 4, the male receiver shaft 33 extends downward into the receiver 26, which is equipped with two or more shaft bearings 46 to locate the shaft securely in the receiver. There is a seal 44 on the male receiver shaft 33 at the top of the receiver to keep debris from entering the receiver 26. The male receiver shaft 33 is connected below the bearings to the main drive shaft that, in the case of the GCP, extends through the upper seal section and connects to the input shaft of the transmission.

[0035] FIGS. 5a, b, and c show pictorially the process of engaging the receiver 26 with the overshot assembly 31 described above. The bottom-hole equipment is run in the hole on the production tubing T and set at the desired depth. The rods, with the overshot assembly 31 attached to the downhole end, are run near the expected depth of the connection with the male receiver shaft 33 (FIG. 5a), and slowly eased down until the overshot assembly 31 fully engages the receiver shaft 33, and the cushioning spring 43 is compressed, so that part of the weight of the rods is carried by receiver shaft 33 (FIG. 5b). The rods are then pulled up just to the point where all of the weight of the rod string is carried by the installation equipment at the surface, and then another approximately 1.5 feet, and hung off (FIG. 5c). This will give the rods about 1.5 feet of relative downward travel and 1.5 feet of relative upward travel without either tagging the top of the overshot assembly 31, or becoming disengaged from the male receiver shaft 33, respectively.

[0036] FIG. 6a shows, pictorially, a side view, partial cross-section, of the overshot assembly 31, configured for connection with a male receiver shaft 33. Drive rod string 24 is shown with the coupling 25 detached from the overshot assembly 31 for clarity. Normally, the coupling 25 would fully engage the threaded pin 27 of the overshot assembly 31 for tensional and torsional connection to the drive rod string 24. Cushioning spring 43, the short female inner bore section 34, and flared downhole end opening 41 are clearly shown. FIG. 6b shows a cross-section of the overshot assembly 31 through I-I’.

[0037] FIG. 7a shows a side view of the male receiver shaft 33, showing tapered lead-in 36 at the uphole end of the shaft. FIG. 7b shows a cross-section through the male connector or receiver shaft 33.

[0038] FIG. 8a shows, pictorially, a side view, partial cross-section, of the overshot assembly 31, configured for connection with a female square cross-section receiver shaft 38. Drive rod string 24 is shown with the coupling 25 detached from the overshot assembly 31 for clarity. Cushioning spring 43, the short female square cross-section inner bore 38, and flared downhole end opening 41 are clearly shown. FIG. 8b shows a cross-section of the overshot assembly 31 through II-II’.

[0039] FIG. 9a shows a side view of the rectangular cross-sectioned portion of the male receiver shaft 33, showing the tapered lead-in 36 shape of the uphole end 35 of the shaft. FIG. 9b shows a cross-section through the square cross-sectioned portion of the male receiver shaft 33.

[0040] In openings, with the downhole assembly 22 in place, connection with the power supply at the surface of the earth is connected by lowering the drive rod string 24 slowly until it reaches the downhole assembly 22 with the stab-in rod extending upwardly in the receiver.

[0041] The receiver is open at the free end thereof, that being the end which, in space, is not connected to anything and is flared outwardly in order to essentially guide the stab-in rod into the centrally located opening in the receiver. As the receiver continues to descend on to the stab-in rod, with the configured portion of the stab-in rod engaged with those compatibly formed on the interior of the central bore of the receiver, resulting in a driving connection between the power supply on the surface and the overshot assembly 31.

[0042] A disconnection is achieved by reversing the process by drawing the drive rod string 24 upwardly, at which time it disconnects from the receiver.

[0043] While those skilled in the art will perceive some variation in the structural elements disclosed herein, it will be understood that the invention contemplates such variations which are within the contemplation of the claims,