Oil Tool Release Joint

The present invention relates to the field of oil tool release joints and in particular to a tool which releases a downhole component from a drill string in response to changes in hydraulic pressure in the drill string.

In the drilling of oil wells, a drill bit and drill string is used to drill a well hole. After the well hole is drilled, a liner (or casing) may be run across the productive interval by using the drill pipe. With the liner in place, a cement slurry is pumped down through the drill pipe, through the liner, and into an annulus between the liner and a casing in the well hole to cement the liner in place and to keep production fluids in the liner.

Quite often well holes are not completely vertical. They can have substantial horizontal components. Wells with substantial horizontal components are called high angle extended reach wells. Running the liner through high angle extended reach well holes can be difficult because of friction between the liner and the well hole wall caused by the weight of the liner against the wall. Translational friction can be substantially reduced by rotating the liner while it is being run into the well hole.

The tools that have run liners into extended reach well holes have not generally rotated the liners while they were being run in due to the high torque required for rotation, although the tools permit liner rotations after run-in. Rotation is typically used to release the tools from the liners once the liners are in place. Consequently, it has not been possible to rotate the liners to reduce frictional drag when release-by-rotation tools are used.

U.S. patent application Ser. No. 418,510, filed Oct. 10, 1989, discloses a hydraulic release oil tool which avoids these problems with existing release tools. This application is assigned to the assignee of the present invention and is incorporated herein fully by this reference. The tool described in that application allows the liner to be rotated in either direction as it is run into the well hole, and it releases the liner upon application of hydraulic pressure in the drill string. It is preferred to provide a safety joint as a backup for the primary release joint. In the event that the primary release joint fails to operate, the safety joint can be used to separate the liner. The present invention is particularly suited for use as a backup safety joint in connection with the hydraulic release oil tool of U.S. patent application Ser. No. 418,510, filed Oct. 10, 1989, when rotation is desired. It can also be used independently or as a primary release tool in its own right.

The present invention provides a release tool for use with pipe strings. The tool translates rotational motion in either direction from a drill or other pipe string to the downhole components to which it is connected and releases upon application of one or more forces, such as hydraulic pressure and upward pulls. The forces can be combined, or used separately to release components of the tool.

In one embodiment, the invention encompasses a release tool with a top sub for coupling to a drill or other pipe string and a bottom sub for coupling to a downhole tool. The top and bottom subs have a longitudinal axis and bores substantially along the longitudinal axis. The bottom sub is connectable to the top sub so that the top and bottom sub bores are substantially aligned. The tool also has means on each sub for transmitting motion rotational about the longitudinal axis from the top sub to the bottom sub, and means for retaining the subs in connection with each other and for releasing the subs from each other upon the application of a force pulling the subs apart which is greater than a predetermined force. The means for transmitting rotational motion preferably includes a plurality of splines on one of the subs extending substantially parallel to the sub's longitudinal axis, and a plurality of slots on the other one of the subs extending substantially parallel to the same axis. The slots receive the splines when the subs are connected to transmit rotational motion. The means for retaining the subs preferably includes shear pins extending into the two subs, the shear pins shearing upon the application of hydraulic pressure greater than the predetermined pressure, or upon an upward pull on the drill string, or both.

The connected subs form a substantially straight axial bore which allows fluid, other tools and pressure to freely pass. The splines and slots allow rotational forces to be transmitted between the subs without unscrewing or releasing any portion of the release tool. Since the release tool releases upon the application of hydraulic pressure, an upward pull, or both, the tool can be rotated or released independent of other tools which respond to axial rotation.

These and other aspects of the invention will be more fully understood by referring to the following detailed description and the accompanying drawings wherein:

FIG. 1 shows an oil tool release joint exploded and in half-section;

FIG. 2 shows the release joint of FIG. 1 assembled and in half-section;

FIG. 3 illustrates schematically the use of the joint of the present invention; and

FIG. 4 shows an alternative oil tool release joint assembled and in half-section.

The oil tool release joint of the present invention is particularly well suited for use as a setting and release tool in running a liner down a well hole and will be described primarily in that context. However, it can also be used in many other drilling procedures. The release tool has a top sub or running head 10 with threads 12 at its uphole end for screwing the top sub onto a coupling, running tool, or a work string, and a bottom sub or setting assembly 14 with threads 16 for screwing the bottom sub onto some downhole duct-like segment or component, for example, a liner. Both subs are elongated along their own longitudinal axes and have longitudinal bores 18, 20 along those axes. The subs are constructed so that when the two subs are joined together there is an open passageway extending from the pipe string threads on the top sub down through the downhole component threads on the bottom sub. This is particularly important, for example, in running in a liner because it allows cement to flow through the pipe string, past the release tool, and into the liner. Preferably the longitudinal axes are substantially aligned coincident to each other when the subs are connected.

The top sub has a pin end 22 opposite the threads 12 which is insertable into an opening 24 in the bottom sub. The bottom sub opening is at the end of the bottom sub opposite the downhole component threads. The pin end of the top sub has a short, smaller-diameter section at its extreme end which extends into the opening and is adapted to meet a shoulder 26. When the top and bottom subs are pushed together this shoulder locates the top sub in its proper position within the opening of the bottom sub. Encircling the outside of the extreme end of the top sub is a packing, gasket or 0-ring 30 to prevent fluids from leaking between the inside and the outside of the open passageway. Past the packing 30, the pin end has a larger outside diameter main portion 32 with a discontinuous ring of eight recesses 34. These recesses are preferably spaced equidistant around the outer circumference of the top sub and are adapted to receive shear pins. Past the recesses are a set of slots 36. These slots are also spaced equidistant around the outer circumference of the pin end of the top sub. The number of slots and shear pins can be altered depending upon the particular application and the stresses involved.

The bottom sub 14 opening 24 is adapted to receive the pin end of the top sub 10 which extends into the opening in the bottom sub until it butt up against the shoulder 26. The shoulder allows the joint to withstand very high forces pushing the two subs together, i.e., compressive forces, without stressing the shear pins. Such compressive forces can arise from the weight of the upwell pipe string and in many other ways. The bottom sub has a set of splines 38 which fit into the slots 36 on the top sub. These splines have walls extending radially away from the center of the bottom sub, which butt against similar radially extending walls on the slots so that when the top sub is rotated, the walls of the slots push against the walls of the splines and force the bottom sub to rotate as well. The bottom sub can be rotated in either direction by rotating the top sub independent of tensile or compressive forces on the subs.

The shape of slots 36 and splines 38 can be altered. If the radial dimensions of each spline 38 are reduced, while maintaining the location of one of the slot abutting surfaces, rotation in one direction may be accomplished without relative rotation between bottom and top subs. Alternative mating shapes of splines 38 may include triangular and trapezoidal. These alternative shapes can allow uni- or bi-directional rotation if longitudinal separation of subs 10 and 14 is restrained.

Although alternative spline shapes may allow a portion of some rotational forces to contribute to rupturing the shear pins 47 (see FIG. 2), the majority of the force required to rupture the shear pins 47 must be supplied by axial forces if abutting surface angles with respect to the longitudinal axes are small. Typically, these are created by hydraulic pressure and by pulling on the pipe string. The splines and slots can also be provided with abutting horizontal surfaces at their ends. The splines and slots can then withstand compressive forces in the same way that the shoulder and pin end do.

The bottom sub also has a series of threaded holes 40 equidistantly spaced apart around its circumference. When the top sub is inserted into the bottom sub so that the pin end rests against the shoulder on the bottom sub, the holes are aligned with the recesses in the top sub. This allows threaded shear pins 47 (FIG. 2) to be screwed into the holes 40 and extend into the recesses 34 to hold the top and bottom subs together. The shear pins are shown with an Allen head, however, many different types of heads may be used to screw the pins into place. Because of the preferred shape and abutting location of splines and slots, rotational motion does not apply any stress to the shear pins. All of the rotational torque is transmitted through the splines and slots. The shear pins are stressed only by applying an axial force between the subs.

While the inside diameter of the opening of the bottom sub must be large enough to receive the pin end of the top sub, the remainder of the bottom sub preferably has an inside diameter which is substantially equal to that of the top sub. When the top and bottom subs are connected together, material moving through the two subs sees a smooth consistent inside diameter and does not hang up on the walls.

The bottom sub on its end opposite the threads 16 faces uphole when the tool has been run down a well and after the subs have been separated. In the illustrated embodiments, the ends of the splines 38 extend further uphole than any other portion of the bottom sub and present an upward pointing face around the rim of the opening to anything proceeding downhole, for example, wire lines, darts and tools. The faces 42 at the ends of the splines are preferably beveled at an angle toward the center of the bottom sub. This helps guide any materials in the well into the axial bore of the bottom sub. The rim of the bottom sub between the splines can also be similarly beveled.

The apparatus includes a guide ring 44. The guide ring is annular with an inside diameter large enough to encircle the bottom sub at the bottom sub opening. The guide ring is preferably welded in place around the bottom sub before the assembly is run downhole. The guide ring, like the rim of the opening of the bottom sub, has its own peripheral ring which faces uphole when the guide ring is in use and the top sub has been separated from the bottom sub. The uphole facing edge on this face is beveled like the edges of the splines toward the center of the longitudinal bore. This beveled face 46 combines with the beveled face 42 of the bottom sub to further guide tools into the axial bore of the bottom sub (FIGS. 2 and 4).

To assemble a pipe string using the release tool, the top sub pin end is inserted into the bottom sub so that it butts up against the shoulder within the opening of the bottom sub. The shear pins are then screwed into place through the holes 40 into the recesses 34 in the top and bottom subs, and the guide ring 44 is welded onto the bottom sub. The assembled release tool's top sub is then coupled to accompanying running assemblies or string and the bottom sub is screwed onto a downhole component, for example, a liner. Preferably, the top sub threads 12 are screwed onto a hydraulic release oil tool assembly such as that description in U.S. patent application Ser. No. 418,510, filed Oct. 10, 1989, which, in turn, is connected to a drill string so that the release tool of the present invention acts as a backup safety joint.

FIG. 3 shows the apparatus required in a typical application of the present invention for running in a liner. In FIG. 3 the running head or top sub 10 of the release tool is coupled to a string of drill pipe 50 without an additional release tool. The drill pipe at the top of the well connects to a top drive power swivel 52 which drives the drill string into the well hole and a rotating cement head 54 which supplies cement for cementing in the liner. The bottom sub 14 is connected to a liner hanger 56 which anchors the liner against the larger or previously set casing. This connects serially to a liner 58, a landing collar 60, a float collar 62 and a float shoe 64 at the bottom of the downhole componentry.

Typically, in use, the liner and release tool are run down the well using the drill pipe string by rotating the liner and allowing gravity to push downward, i.e., creating compressive forces. If the well has portions with a significant horizontal component, then rotating the pipe string at the well head with the power swivel helps to significantly reduce the friction of the liner and pipe string against the sides of the well. Because of the spline and slot arrangement, the downhole components threaded onto the bottom sub can easily be rotated without stressing the shear pins. Once the liner reaches the desired position, the liner may be anchored into the well using conventional techniques. The liner is then cemented into place by running cement down the pipe string through the axial bores of the two subs and the liner. The cement is followed by a wiper dart which travels also through the top and bottom subs and lodges at the bottom of the liner. Drilling mud (not shown) is pumped through the pipe string behind the wiper dart (not shown) to push the wiper dart down the hole and drive the cement out around the liner. Once the wiper dart is in position, the pressure of the drilling mud supplied by a pump (not shown) is increased to operate the release tool. If a primary hydraulic release tool is used in conjunction with the release tool of the present invention, a moderate increase in hydraulic pressure should anchor the liner and then release the primary coupling tool and allow the pipe string to be removed. The release tool of the present invention remains in the well together with the bottom sub of the primary release tool.

If the primary release tool does not operate properly, or if the present invention is used as a primary release tool, then the release tool of the present invention is used to separate the drill string from the liner. First, the hydraulic pressure is increased in the pipe string. This tends to push the liner away from the drill string or, in other words, it tends to push the bottom sub axially away from the top sub. With enough hydraulic pressure the shear pins will shear and the top sub will be released from the bottom sub. A wiper dart can be used to seal off the pipe string below the release tool. This can aid in increasing the hydraulic pressure; however, it is not required. As the top and bottom subs separate further, the seal provided by the gasket 30 is broken and fluid leaks out toward the formation. This drop in hydraulic fluid pressure signals that the top and bottom subs have released and the top sub, together with the drill string, can be removed from the well. If adequate hydraulic pressure is not available, the hydraulic pressure can be complemented by pulling the top sub upwards. This can be done either by jarring or with a consistent upward pull. The bottom may be an anchored liner to increase the effectiveness of the pull. Alternatively, the inertia of the pipe string or its friction against the well hole can be relied upon to shear the shear pins and release the two subs. The top and bottom subs can also be released by pulling the top sub upwards in cases where an increase in hydraulic pressure is not desired, or possible. Once the top sub is removed, the guide ring together with the bottom sub guide any substances coming from uphole down into the bottom sub and from there into the liner (see FIG. 2).

FIG. 4 shows a second embodiment of a hydraulic release oil tool which incorporates a tie back sleeve. In this embodiment the top sub 10 and guide ring 44 are the same as those shown in FIG. 1. The bottom sub 114 is substantially elongated to include a tie back sleeve. While in the first embodiment the bottom sub has an opening with a larger inside diameter which is followed by a smaller diameter inside bore, the bottom sub 114 of FIG. 4 has no shoulder and no narrower passageway. The large inside diameter bore 120 of the bottom sub continues through to its very end where it has threads 116 to connect to a smaller diameter pin 48. The top sub must be positioned into the opening of the bottom sub without benefit of the shoulder; however, once the shear pins have been screwed into place, the top sub is securely positioned. The larger diameter tie back sleeve portion 49 of the bottom sub provides a surface into which a stinger can be stabbed in the event that a second liner is to be hung above the first liner using techniques known in the art.

The present invention has been described with reference to certain preferred embodiments. The scope of the attached claims, however, should not necessarily be limited to the described embodiments. The hydraulic release tool of the present invention can be used in a variety of different contexts. It is not limited strictly to running in a liner, but can be used in a drill string for variety of purposes. For example, during drilling if the leading end of the drill string were to get stuck in a well, the release tool can be used to remove the drill string. The splines and slots can be reversed so that the splines are carried on the top sub or so that the splines and slots are inside the bores of the subs. The pin and opening can be reversed also so that the bottom sub is inserted into the top sub. The guide ring can be eliminated, if desired.