Downhole Release Mechanism

Abstract

A downhole release mechanism for a drillstring. A first, uphole section and a second, downhole section comprise longitudinal bores and are rotationally locked together via a spline. A collet assembly is connected to the first section, with collet fingers extending into the bore of the second section when the first and second sections are joined. The collet fingers are biased outwardly, and an external shoulder on the collet fingers mates with an internal shoulder in the second section, locking the sections together. A piston is slidably disposed in a bore of the collet, and spring biased uphole. Fluid flow moves the piston to a downhole position, in which the collet fingers are held outwardly and the shoulders locked together. With fluid flow stopped, the piston moves uphole, and sufficient tension on the mechanism shears shear screws and snaps the collet fingers out the internal shoulder, releasing the mechanism.

Description

BACKGROUND—FIELD OF THE INVENTION

This invention relates to apparatus used in connection with the drilling and servicing of oil and gas wells.

Broadly speaking, many of such drilling and servicing operations employ some sort of downhole tool string, deployed into a wellbore on a tubular string, which may be drill pipe, a so-called “work string,” other types of tubing, etc. The tool string may comprise a number of downhole tools all connected to the tubular string or to one another.

By way of example only, one such downhole tool string may comprise a downhole “motor,” which provides rotation via fluid flow (pumped from the surface) through the tubular string. The motor may be a positive displacement motor (“PDM”) or a turbine. Both types are well known in the relevant art. By way of further example, below (downhole from) the motor may be a downhole cutting tool, such as a casing cutting and/or milling tool, which is in turn rotated by the motor and used to cut/mill casing or other tubulars. It is understood that this is by way of example only; a variety of downhole tools and combinations of same are known in the art.

One exemplary problem that is presented in such a downhole tool assembly arises when the tool or tools below the motor, for example the casing cutting tool, becomes stuck in the well. In the absence of some release mechanism positioned between the motor and the casing cutting tool, then not only is the cutting tool stuck, but so is everything else above it.

Prior art release mechanisms have generally employed a release ball which is dropped down the tubular, to rest in some sort of seat in the release mechanism and seal the bore of the tubular. Pressuring up on the tubular pushes the ball downward and activates the release, thereby separating that portion of the downhole string above the release mechanism, from that below.

However, it is impossible to pass a ball through a downhole motor in the tubular string, due to the rotor or similar mechanism in the motor; said another way, a ball cannot pass through the motor. In the past, a ball type release mechanism has at times been run above the motor. However, when actuated, this placement leaves the motor downhole, which is frequently the most expensive component in the string. The operator is then faced with going back into the hole with a fishing assembly to hopefully jar the motor and everything downhole from it loose for retrieval. Unfortunately, however, stuck tools below the motor frequently result in the loss of the entire downhole tool assembly, including the motor.

The known downhole release mechanisms, or other methods such as severing the tubular string via mechanical or chemical means, all present various issues, giving rise to a desire for an improved downhole release mechanism that addresses these issues.

SUMMARY OF THE INVENTION

The downhole release mechanism embodying the principles of the present invention can be run in a downhole tool string below a tool such as a downhole motor, which does not permit passage of a ball, yet still permits separation of or release of the tool string below the motor, in a controlled fashion. In one embodiment, the downhole release mechanism embodying the principles of the present invention comprises a main body, having first (upper or uphole) and second (lower or downhole) sections, each comprising tubular members and having a longitudinal bore therethrough. Connected to the first section is a collet assembly having a bore and a plurality of fingers (capable of some flexing) which are generally biased radially outward. When the first and second sections are joined or mated together, the collet assembly, namely the collet fingers, fits into the bore of the second section and an external shoulder profile on the collet fingers engages a matching internal shoulder profile within the bore of the second section. A slidable piston, itself having a bore therethrough and a jet disposed in the bore, for fluid passage, is positioned in the collet assembly bore, and is spring biased toward an uphole position.

The downhole release mechanism is assembled by inserting the collet assembly, namely the collet fingers, into the bore of the second section, the collet finger shoulder thereby engaging (“snapping in to”) the matching internal shoulder profile in the second (lower or downhole) section, thereby connecting the first and second sections. One or more shear screws are then inserted to further join the first and second sections together. It is understood that the piston is initially (under “no flow” conditions) in an uphole position, under the bias of the spring. The collet fingers can move radially inward when the piston is in its uphole position. In this position, the apparatus can be made up into a tool string and run into a well on the tubular string.

When fluid is being pumped down the tubular string and through the downhole release mechanism, the piston is moved to a lower (downhole) position, as a result of fluid flow through the jet and bore of the piston, with a lower nose of the piston positioned within the the collet assembly, more particularly within the collet finger assembly portion, and preventing the collet fingers from moving radially inward. In this position, the two sections of the release mechanism are positively locked together by engagement of the collet finger shoulder in the mating internal shoulder profile within the second section.

If the tool string becomes stuck and it is desired to actuate the downhole release mechanism, fluid flow is stopped, which permits the piston to move to its uphole position under the influence of the spring. In this position, the piston is not engaged with the collet fingers, which can then move radially inward as will be described.

Tension is then applied to the tubular string, and therefore to the downhole release mechanism. Sufficient tension is applied to yield a radially inward resulting force to the collet fingers, by virtue of the angle on the collet finger shoulders/internal shoulder profile, sufficient to move the collet fingers inward (the so-called “snap out” force), therefore disengaging the shoulder-to-shoulder connection. This force also shears the shear screws. The tubular string, with the lowermost component being the first (upper or uphole) section of the downhole release mechanism, can then be pulled out of the hole.

The second (lower or downhole) section preferably has an internal profile adapted to engage a fishing tool, such as a 3½″ GS internal profile. A fishing tool assembly can therefore be lowered into the wellbore, engaged with the internal profile in the second section, and fishing efforts (jarring, fluid circulation, etc.) be carried out in an effort to retrieve the second section and the tool string components below it.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general, exemplary view of a wellbore, showing positioning of a tubular string and downhole tool assembly in the well.

FIG. 2 is a cross section view of a downhole release mechanism embodying the principles of the present invention, under a no fluid flow position (piston in its first or uphole position).

FIG. 3 is a cross section view of a downhole release mechanism embodying the principles of the present invention, while fluid is flowing through the release mechanism (piston in its second or downhole position).

FIG. 4 is a cross section view of a downhole release mechanism embodying the principles of the present invention, in which the two sections of the release mechanism have been released from one another (third position).

DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENT(S)

While various downhole release mechanisms can embody the principles of the present invention, with reference to the drawings some of the presently preferred embodiments can be described.

By way of example, the downhole release mechanism may be beneficially used below a thru-tubing motor, run downhole on coiled tubing, as an emergency release mechanism. An exemplary application is in downhole casing cutting/milling, with a casing cutting/milling tool run on coiled tubing, and rotation of that tool provided by a downhole motor. As known in the relevant art, conventional coiled tubing release tools require a ball to be dropped to land in the release tool, which is not possible due to the downhole motor positioned above (uphole from) the release tool. A tension only release tool, for example using shear pins only, could prematurely shear due to the constantly fluctuating load on the tool string due to milling in tension, causing fatigue of the shear pins. The downhole release mechanism embodying the principles of the present invention utilizes a collet assembly, having a shoulder profiles on the collet fingers engaging an internal shoulder profile in a second (lower or downhole) section of the release mechanism, the collet fingers held in that position during fluid flow conditions by a movable piston, to hold the two sections of the release mechanism together. This arrangement prevents a premature disconnect due to fatiguing shear pins.

FIG. 1 shows of a exemplary, general setting in which the downhole release mechanism may be used. FIG. 1 is a general cross section view of a wellbore, showing positioning of a tubular string and downhole tool string or assembly in the well, comprising a downhole motor, the downhole release mechanism, and a downhole casing cutting/milling tool. By way of example, the tubular string may be coiled tubing, and the downhole tools below the downhole motor may comprise a casing cutting/milling tool or any other type of tool. Common casing cutting/milling tools utilize cutting elements which extend outwardly when actuated by a fluid-actuated internal piston, and the cutting/milling tool is then rotated by the downhole motor. As is known in the relevant art, such cutting/milling tools at times become stuck in the well. It is in such cases that the release mechanism, positioned between the downhole motor and the cutting/milling tool, permits disconnection of the tool string below the downhole motor, thereby permitting the motor to be retrieved from the well, while (at least for a while) leaving the remaining downhole tool components in the well, for later fishing efforts. Typically, the downhole motor is the most expensive component in the overall string, hence its retrieval is important. It is understood that the downhole release mechanism described herein may be run on coiled tubing or any other type of jointed tubular.

Referring to FIGS. 2-4, the downhole release mechanism in three different positions can be described.

First Position (No Fluid Flow Through the Downhole Release Mechanism)

FIG. 2 shows the downhole release mechanism in a first position, without fluid flow down the tubular string and through the release mechanism, such as when running in the hole with the tool. Release mechanism 10 comprises a first (upper or uphole) section 22 and a second (lower or downhole) section 24. Both first and second sections 22 and 24 are tubular members and have a longitudinal bore 26 therethrough. Suitable connections 100, typically threaded connections, may be provided to connect release mechanism 10 into a tubular string. The “uphole” and “downhole” directions are noted in the figures.

Attached to first section 22, for example disposed within bore 26, is a collet assembly 30, which is typically threadably connected to first section 22 within bore 26. As can be seen in FIG. 4, collet assembly 30 extends from first section 22 when the first and second sections of the apparatus are separated. Collet assembly 30 has a plurality of collet fingers 32, which are (in an unstressed position) generally positioned as shown in FIGS. 2 and 4, but which are flexible and may be flexed radially inward to a degree, as is described in more detail herein. Collet fingers 32 are biased radially outward by virtue of the flexibility of the fingers. Collet assembly 30 has a longitudinal bore 38.

Piston 40 is disposed within bore 38 of collet assembly 30, as can be seen in the figures. In FIG. 3, which shows the release mechanism 10 with no fluid flow therethrough, spring 50 biases piston 40 toward a first, uphole position. A jet 44 (which may be a removable jet, to permit change for various flow conditions or other criteria, by changing the jet flow area) is preferably positioned in bore 45 of piston 40, which permits fluid flow therethrough. Slots 46 may be provided to permit fluid flow into and out of the chamber in which spring 50 is positioned.

Shear screws 200, as can be seen in the figures, further join first and second sections 22 and 24. In the embodiment shown, shear screws 200 extend through the wall of second section 22 and into collet assembly 30; however, it is understood that other placements are possible. The number of shear screws and shear strength screw can be varied to suit particular needs. In the position shown in FIG. 2, tension forces on downhole release mechanism 10 may be borne, in part, by shear screws 200. Tension is also borne by shoulders 34 on collet fingers 32, engaging a mating internal shoulder profile 28 within second section 24. In the position shown in FIG. 2, collet fingers 32 are held radially in place (that is, radially outward) by only their inherent spring force, and are able to move radially inward under a resultant radial force from tensile forces between shoulders 28 and 34 (that is, when downhole release mechanism 10 is put in tension). As will be described further below, shoulders 28 and 34 are angled so as to provide a desired “snap out” force; said another way, collet fingers will move radially inward only when a sufficient and desired tension is placed on downhole release mechanism 10.

Second Position (Fluid Flow Through the Release Mechanism)

FIG. 3 shows the release mechanism under fluid flow conditions. In this position, fluid flow through the tubular string, through bore 26 of release mechanism 10, and through jet 44 and bore 45 in piston 40, moves piston 40 in a downhole direction. Piston 40 moves in a downhole direction until tapered piston nose 42 seats in a mating profile 36 within collet fingers 32. In this position, collet fingers 32 are prevented from moving radially inward due to the positioning of piston 40, more particularly piston nose 42, thereby effectively locking collet fingers 32 in place with collet shoulders 34 engaged in mating profile or internal shoulder 28 in second section 24. Tensile loads could therefore be borne by collet assembly 30. For example, if shear screws 200 were to part while release mechanism is in the position shown in FIG. 3, the release mechanism 10 would remain connected and capable of withstanding a high tensile load.

Third Position (Released)

FIG. 4 shows release mechanism 10 in a released or separated position. Sufficient tension has been applied to release mechanism 10 to generate a sufficient inward radial resulting force on collet fingers 32 from the interaction between shoulders 34 and 28, to move collet fingers 32 radially inward, out of engagement with internal shoulder profile 28. This is known as the “snap out” force, which by way of example may be on the order of 3,000-4,000 lbs. This relatively high value avoids imparting tension loads to shear screws 200 until the collet fingers have moved radially inward and released or are out of engagement with shoulder 28. It will be recognized by those having skill in the relevant art that the angles of shoulders 34 and 28 are not 90 degree or right angles, but slightly angled as can be seen in the drawings, so as to create a radially inward force to move collet fingers 32 inward, when a tension load is placed on release mechanism 10. The degree of angulation is of course a matter of design choice, and factors include the desired “snap out” force, the resilience of collet fingers 32, etc.

Continued tension shears shear screws 200, thereby permitting first and second sections 22 and 24 to separate and upper section 22 to move uphole, pulling collet assembly 30 out of second section 24, as shown in FIG. 4. The tubular string (that is, everything down through first section 22) can then be pulled from the wellbore.

FIG. 4 clearly shows one side 29A of spline connection 29, namely on the uphole end of second (lower or downhole) section 24. It can be readily understood that a mating spline section 29B is on the lowermost end of first (upper or uphole) section 22. It can further be readily understood that when first and second sections 22 and 24 are joined, the mating and interacting fingers of spline connection 29 transmit torque loads through the first and second sections 22 and 24.

Once the two sections of release mechanism 10 have been separated, and the tubular string with first section 22 attached thereto has been pulled out of the wellbore, a fishing assembly can be run into the well if desired in an effort to recover second section 24 and the downhole tool string below it. Preferably, release mechanism 10 comprises a suitable fishing tool profile, for example an internal profile 25 within second section 24, adapted to engage a fishing tool, which in currently envisioned tool sizes may be a 3½″ GS internal profile. It is understood that other dimensions of fishing tool profiles are possible.

Other Elements of a Present Embodiment of the Downhole Release Mechanism

As can be seen in FIGS. 2-4, a burst disk or pressure relief disk 60 is disposed in the main body of the release mechanism 10, in the illustrated embodiment in second section 24. Pressure relief disk 60 will rupture at a set pressure differential, for example 2000 psi, between bore 26 and an annulus surrounding release mechanism 10. In the event that the tool string becomes plugged below downhole release mechanism 10, and fluid flow down the tubular string ceases, a risk is that the downhole release tool is effectively “pumped off,” or pushed off as a result of a downward pressure differential between bore 60 and the annulus surrounding release mechanism 10, and a resulting force (longitudinally) across release mechanism 10. Pressure relief disk 60 will rupture and prevent this pressure differential from developing. It is understood that pressure relief disk 60 may be selected to yield a desired pressure differential resistance value.

Guide members 47, for example made of teflon or similar low-friction material, may be provided around piston 40, to reduce friction forces between piston 40 and the structure surrounding piston 40.

Piston 40 may have a reduced outer diameter section 40A near nose 42, to minimize binding, etc., which may arise from possible deformation from nose 42 contacting collet taper 36.

It is understood that the downhole release mechanism may comprise various seal elements, threaded connections, etc. as will be understood by those having skill in the relevant art. Further, downhole release mechanism 10 may be fabricated from materials well known in the relevant art, such as high strength steel, alloys, and where applicable non-metallic materials may be used for seals and other components.

Benefits and Attributes of the Downhole Release Mechanism

The release mechanism embodying the principles of the present invention allows for downhole apparatus above the release mechanism, by way of example the downhole “thru-tubing” motor, to be recovered in the event that the tool string below the release mechanism, for example a casing cutting/milling tool, becomes stuck in the borehole.

Various attributes of the release mechanism protect the shear screws from shearing during fluid flow conditions. When fluid flow ceases (no circulation), the release mechanism shifts to a release position, allowing the collet fingers to “snap in” and shear pins to be sheared, when the appropriate tension is placed on release mechanism 10.

The release mechanism 10 reliably transmits tensile loads (via the collet and mating internal shoulder) and torque loads (via the spline fingers) to downhole tools below the release mechanism, without prematurely shearing the shear screws.

The release mechanism shear load is adjustable, by varying the number of shear screws and/or the shear strength per shear screw. The lower section of the release mechanism (and any tools below it) are easily fishable, via an internal GS fishing neck profile or other suitable profiles, preferably positioned in the bore of the second (lower or downhole) section 24.

As described above, the downhole release mechanism preferably comprises an internal rupture or pressure relief disc; if any tools downhole from the release mechanism were to become clogged, the pressure relief disc would rupture due to the increase in pressure between the bore of the release mechanism and the annulus surrounding it. This would prevent the downhole release mechanism from separating due to the sudden increase in pressure coupled with no flow (the high differential pressure would both “snap out” the collet fingers and shear the shear pins due to the no flow condition). The downhole release mechanism 10 does not rely on hydrostatic force or any electronics for operation.

CONCLUSION

While the preceding description contains many specificities, it is to be understood that same are presented only to describe some of the presently preferred embodiments of the invention, and not by way of limitation. Changes can be made to various aspects of the invention, without departing from the scope thereof.

Therefore, the scope of the invention is to be determined not by the illustrative examples set forth above, but by the appended claims and their legal equivalents.

Claims

1. A downhole release mechanism, comprising: a first, uphole section and a second, downhole section, said first and second sections comprising tubular members with longitudinal bores, and a spline connection rotationally locking said first and second sections together when said first and section sections are joined;a collet assembly attached to said first section and having a plurality of flexible collet fingers extending into said second section when said first and second sections are joined, said collet fingers comprising an external shoulder, said collet fingers being biased radially outward;said second section comprising an internal shoulder in said longitudinal bore, said internal shoulder shaped so as to receive said external shoulder of said collet fingers;a piston slidably disposed in a bore of said collet assembly and spring biased toward a first, uphole position, said piston movable to a second, downhole position within said collet fingers by fluid flow through a bore of said piston, whereby when said first and second sections are joined and said collet is positioned within said second section, and said piston is in said second, downhole position, said collet fingers are held radially outward such that said external shoulder on said collet fingers and said internal shoulder in said second section are engaged, thereby locking said first and second sections together.

2. The downhole release mechanism of claim 1, further comprising one or more shear screws joining said first and second sections.

3. The downhole release mechanism of claim 1, wherein said piston comprises a removable jet in said bore of said piston.

4. The downhole release mechanism of claim 1, wherein said second section comprises an internal profile adapted to engage a fishing tool.

5. The downhole release mechanism of claim 1, further comprising a pressure relief disk permitting fluid flow from said bore of said downhole release mechanism to an annulus around said downhole release mechanism, once a desired pressure differential across said pressure relief disk has been attained.

6. The downhole release mechanism of claim 2, wherein said piston comprises a removable jet in said bore of said piston.

7. The downhole release mechanism of claim 6, wherein said second section comprises an internal profile adapted to engage a fishing tool.

8. The downhole release mechanism of claim 7, further comprising a pressure relief disk permitting fluid flow from said bore of said downhole release mechanism to an annulus around said downhole release mechanism, once a desired pressure differential across said pressure relief disk has been attained.

9. The downhole release mechanism of claim 2, wherein when fluid flow through said piston stops, said piston moves under said spring bias to said first, uphole position out of engagement with said collet fingers, and with sufficient tension on said downhole release mechanism said collet fingers move radially inward and said external shoulder on said collet fingers snaps out of engagement with said internal shoulder in said second section, said shear screws shear and said first and second sections separate.

10. A downhole release mechanism, for placement in a drillstring, comprising: a first, uphole section and a second, downhole section, said first and second sections comprising tubular members with longitudinal bores, and a spline connection rotationally locking said first and second sections together when said first and section sections are joined, said second section comprising an internal profile adapted to engage a fishing tool;one or more shear screws joining said first and second sections;a collet assembly attached to said first section and having a plurality of flexible collet fingers extending into said second section when said first and second sections are joined, said collet fingers comprising an external shoulder, said collet fingers being biased radially outward;said second section comprising an internal shoulder in said longitudinal bore, said internal shoulder shaped so as to receive said external shoulder of said collet fingers;a piston slidably disposed in a bore of said collet assembly and spring biased toward a first, uphole position, said piston movable to a second, downhole position within said collet fingers by fluid flow through a bore of said piston, said piston further comprising a removable jet in the bore thereof, whereby when said first and second sections are joined and said collet is positioned within said second section, and said piston is in said second, downhole position, said collet fingers are held radially outward such that said external shoulder on said collet fingers and said internal shoulder in said second section are engaged, thereby locking said first and second sections together; anda pressure relief disk permitting fluid flow from said bore of said downhole release mechanism to an annulus around said downhole release mechanism, once a desired pressure differential across said pressure relief disk has been attained.

11. The downhole release mechanism of claim 10, wherein said external shoulder on said collet fingers and said internal shoulder in said second section are angled so as to withstand a desired tension between said first and second sections before said collet fingers move radially inward.

12. The downhole release mechanism of claim 11, wherein when fluid flow through said piston stops, said piston moves under said spring bias to said first, uphole position out of engagement with said collet fingers, and with sufficient tension on said downhole release mechanism said collet fingers move radially inward and said external shoulder on said collet fingers snaps out of engagement with said internal shoulder in said second section, said shear screws shear and said first and second sections separate.

13. The downhole release mechanism of claim 11, wherein said piston comprises an angled nose at its downhole end, shaped to engage a mating profile within said collet fingers, and wherein said piston comprises a reduced outer diameter section proximal said angled nose.

14. The downhole release mechanism of claim 13, wherein said piston further comprises guide members of a low-friction material, positioned on an outer surface thereof.