Apparatus for Connecting A Rotating Drive Rod String To A Downhole Assembly

Abstract

A system for connecting and disconnecting a rod string from a downhole assembly in which a captured spline assembly is encased in a receiver attached to the downhole assembly and an on-off tool separating the rod string from the downhole assembly.

Description

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

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

BACKGROUND OF THE INVENTION

1. Field of the Invention

In a typical production well, a downhole assembly is lowered to a predetermined depth where it is immersed in the fluid deposit. The pump is driven by a power supply at the surface of the well, and a rod string spans the distance between the power supply and the pump in order to drive the pump.

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 run 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 in a receiver at the top of the downhole assembly.

This stab-in rod may have any one of several cross section configurations, among them a square, hex, spline or other cross section that figs 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 downhole assembly. The stab-in rod, via the drive rods, rotates the female receptacle, which is fixedly attached to the drive shaft that extends through the upper seal section. In the case of the GCP, the drive shaft is attached tot he input shaft of a speed increasing transmission, which, in turn, drives the centrifugal pump.

An important disadvantage to this system 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.

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

SUMMARY OF THE INVENTION

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 downhole assembly costs dearly.

With that understanding, it is clearly a great advantage of the present invention to the oil producer, to eliminate the prior art difficulties experienced when, as and if the female receptacle is in any way impaired, thereby increasing the difficulty in making the connection.

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 downhole assembly.

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.

It will quickly become apparent that all of the drawings are pictorial representations of the area in the production tubing wherein the downhole assembly is engaged by the rod string and disengaged as needed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a depiction of the upper portion of a downhole assembly with a short section of connecting tubing, in the area of the connection between a downhole assembly and a rod drive string, illustrating the mechanics of the connection in a prior art embodiment, wherein a female receptacle extends upwardly and away from the downhole assembly and is engaged by a depending drive rod and stab-in shaft;

FIG. 2 illustrates, pictorially, the prior art embodiment with the drive rod and stab-in shaft disengaged; leaving the female receptacle open for collection of debris;

FIG. 3 is a view similar to that of FIG. 1, the difference being the FIG. 3 embodiment illustrates the structure which characterizes the present invention, wherein the connection between the downhole assembly and the drive rod string is via a captured spline assembly fixed within the receiver component of the downhole assembly; wherein the drive rod string is engaged with a male receiver shaft extending upward from the captured spline assembly via an on-off tool;

FIG. 4 illustrates, pictorially, the present invention with the drive rod string disengaged from the captured spline assembly receiver shaft;

FIG. 5 is an enlarged detail of the receiver and the captured spline assembly as shown in FIGS. 3 and 4, sectioned in order to illustrate the detail within the assembly housing;

FIGS. 6a, b and c illustrate, pictorially, a sequence of downhole activity, when one employs the FIGS. 3 and 4 embodiment, in which the drive string is initially moved into position to engage and capture, via the on-off tool, the receiver shaft extending upwardly from the receiver captured spline assembly;

FIGS. 7a and b are expanded views of the structure of FIGS. 3 and 4, providing detail of the on-off tool currently in use in downhole oilfield production equipment.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The following detailed description discloses, to those skilled in the art, a novel system for engaging a downhole assembly with a rod drive string.

It will be observed in the prior art configuration in FIG. 1, which illustrates the current practice in the industry, various elements of a system to connect a downhole assembly 22 to a drive rod string are shown by numbers following by a prime sign. Drive rod 24′ is attached to splined stab-in rod 23″,which is inserted into the female spline receptacle 25′ in receiver 27′. Spline receptacle 25′ is mounted within the receiver 27′ via bearings 45′, such that rotation of the rod string 24′ will be transmitted by receptacle 25′ to the transmission drive shaft 51′, which is fixedly attached to receptacle 25′. The downhole assembly is thereby rotationally connected to the drive string 24′. Arrows A indicate the direction of fluid flow in the production tubing and downhole assembly.

This connection system functions satisfactorily until maintenance or repair calls for a disconnect and the stab-in rod is removed from the receiver 27′, as shown in FIG. 2, and the upwardly facing female splined receptacle 25′ is, thus, open to the capture of downward moving debris, shown by arrows B.

As shown in FIGS. 3 and 4, and in accordance with the present invention, the debris-clogging problem of the open female splined receptacle 26′ shown in FIG. 2, is eliminated by reversing the downhole rod-receiver elements of the connection and making the rod-end connector the female portion 47f of an on-off assembly 47, and the receiver connector the male portion 47m of the on-off assembly 47.

Accordingly, an exemplary embodiment is shown in FIG. 4, wherein the rod string 24 is withdrawn from engagement with the receiver 27, by disconnecting the on-off tool 47, and 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 27 where it will settle into the flow channels past the receiver and upper seal section and, most importantly, does not interfere with the connection between the rod 24 and the receiver extension shaft 54.

There are principal advantages to the present invention when operationally attaching a rod string to a downhole assembly, and, they are:

1) The rods can be run after the downhole assembly is installed;

2) The rod string is able to move vertically, freely, while still in torque transmitting connection with the downhole assembly;

3) The rod string can be detached and retrieved without requiring the retrieval of the downhole assembly.

Referring, once again, to FIGS. 3 and 4, a system is configured to show the structure of the present invention in its most basic form. The system consists of a receiver 27, which houses the captured spline assembly 25. Captured spline assembly 25 is connected rotationally and torsionally to the transmission input drive shaft 51 and to the drive rod string 24 via the receiver extension shaft 54 and the on-off tool 47, shown in FIG. 3 in its connected state.

The receiver extension shaft 54 extends into, and is rotationally connected to, the captured spline assembly 25, which, in turn, is rotationally connected to the transmission drive shaft 51.

The captured spline assembly 25 is shown in more detail in the partial cross section shown in FIG. 5. Extension shaft 54 has the freedom of some vertical movement within the splined assembly housing 49, while remaining in torsional and rotational connection to assembly housing 49. Receiver extension shaft 54 passes through a seal 52 to keep debris from entering the receiver 27. The splined assembly housing 49 is mounted in several shaft bearings 45 and is free to rotate within said bearings, but does not have the freedom of vertical movement within the receiver 27.

Referring to FIG. 5, the receiver extension shaft 54 is shown near the bottom of its possible vertical travel within the splined assembly housing 49, with the male splined portion 48 engaging the female splined bore 46 of the assembly housing 49. Cushioning spring 43, at the downhole end of the female splined assembly housing 49, is clearly shown. The upward vertical travel of extension shaft 54 is limited by collet 50, fixedly attached to shaft 54, which is larger in diameter than the diametric restriction 53 at the uphole end of assembly housing 49. Assembly housing 49 is mounted within the receiver 27 with bearings 45 that allow free rotation of the housing, but restrict its vertical movement within the receiver 27. The assembly housing 49 is rotationally and torsionally attached to transmission draft shaft 51.

The receiver captured spline assembly 25 provides a torsional connection between the drive rod string 24 and the transmission input drive shaft 51, while also allowing relative vertical movement between the drive shaft 24 and the receiver 27 required for connection, disconnection and vertical adjustment of the rod drive string position during rod string installation and normal operations.

FIGS. 6a, b and c show, pictorially, the steps followed during the installation and engagement of the drive rod shaft 24 and the receiver captured spline assembly described above. The downhole assembly is run in the hole on the production tubing T and set at the desired depth. The drive rods 24, with the female portion of the on-off tool 47f, are run near the expected depth of the connection with the male portion of the on-off tool 47m (FIG. 6a), and slowly eased down until the female half of the on-off tool 47f fully engages and locks with the male half 47m, and the receiver extension shaft 54 is at the bottom of its travel within the receiver captured splined assembly (FIG. 6b). 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 (not shown), and then pulled another approximately 1.5 feet and hung off (FIG. 6c). This will give the rods about 1.5 feet of relative downward travel and 1.5 feet of relative upward travel within the receiver captured spline assembly without either tagging the cushioning spring 43, or hitting the upward travel stop 50. This amount of freedom of vertical travel should be sufficient to accommodate any expected relative vertical movement between the drive rod string 24 and the receiver 27.

FIG. 7a shows a side view of the on-off tool 47, in its fully engaged state. FIG. 7b shows a side view of the on-off tool, with the female portion 47f disengaged from the male portion 47m.

Having now described the invention with particularity, those skilled in the art will be able to envision alternative elements to those described to accomplish essentially the same purpose as those originally set forth herein. It will be appreciated that such alternative devices are within the contemplation of the invention as hereinafter described in the claims, wherein:

Claims

1. In a well for the capture of subterranean fluids in which a power supply located at the surface of the well drives a downhole assembly for pumping the fluid in the well to the surface through a captured spline assembly,

a rod string depending from, and connected with, the power supply and engaged with the downhole assembly;

a system for the connection and release of said rod string from said downhole assembly, said downhole assembly having a receiver, said receiver standing upwardly therefrom, said receiver encasing a captured spline assembly to provide a torsional connection thereto.

2. The system of claim 1, wherein said captured spline assembly being mounted in bearings within said receiver to thereby permit rotation of said captured spline assembly.

3. The system of claim 1, wherein said captured spline assembly includes a stab-in rod;

a receptacle, said receptacle receiving said stab-in rod in rotational driving relation;

said receptacle directing rotational power to said downhole assembly;

said stab-in rod connected with said rod string for rotating said stab-in rod.

4. In a well for the capture of subterranean fluids in which a power supply located at the surface of the well dries a downhole assembly for pumping the fluid in the well to the surface,

a rod string depending from, and connected with, the power supply and engaged with the downhole assembly;

a system for the connection and release of a rod string from a downhole assembly, said downhole assembly having a receiver, said receiver standing upwardly therefrom, said receiver housing a captured spline assembly;

an on-off tool mounted in said rod string, said on-off tool being selectively separable to disengage said captured spline assembly from said power supply as needed.

5. The system of claim 1, wherein said receiver having an opening at the free end thereof, a cap, said cap covering said opening.

6. The system of claim 5, wherein an aperture in said cap, an extension shaft connected to said stab-in rod and passing through said aperture to connected with said drive string.

7. The system of claim 3, wherein said captured spline assembly being mounted in bearings within said receiver to thereby permit rotation of said captured spline assembly.

8. The system of claim 5, in which a power supply located at the surface of the well dries a downhole assembly for pumping the fluid in the well to the surface,

a rod string depending from, and connected with, the power supply and engaged with the downhole assembly;

a system for the connection and release of a rod string from a downhole assembly, said downhole assembly having a receiver, said receiver standing upwardly therefrom, said receiver housing a captured spline assembly;

an on-off tool mounted in said rod string, said on-off tool being selectively separable to disengage said captured spline assembly from said power supply as needed.

9. The system of claim 6, in which a power supply located at the surface of the well dries a downhole assembly for pumping the fluid in the well to the surface,

a rod string depending from, and connected with, the power supply and engaged with the downhole assembly;

a system for the connection and release of a rod string from a downhole assembly, said downhole assembly having a receiver, said receiver standing upwardly therefrom, said receiver housing a captured spline assembly;

an on-off tool mounted in said rod string, said on-off tool being selectively separable to disengage said captured spline assembly from said power supply as needed.