DEVICE AND METHOD FOR UNDERREAMING A BOREHOLE

Abstract: A borehole underreamer device comprises a downhole motor having a rotor part which carries by means of a pivot (2) an elongate clapper body (1) in which a series of abrasive teeth (8) are embedded. In use the device is pulled in upward direction through the borehole while the clapper body describes an orbital motion inside the borehole thereby forcing the teeth to penetrate into the surrounding side wall of the borehole so as to underream the hole.

Description: The invention relates to a borehole underreamer device for underreaming a borehole penetrating through a subsurface earth formation. A borehole underreamer is used to increase the diameter of a borehole, for example prior to setting a casing inside the borehole or to install a gravel packing in the production zone of an oil production well. US-A-3 472 553 discloses a borehole underreamer device comprising a downhole motor having a rotor part which can be rotated relative to a stator part, the rotor part carrying pivot means, the pivot means carrying a clapper body in which a series of abrasive teeth are embedded, the pivot means allowing the clapper body to describe in use an orbital motion inside a borehole, thereby inducing the abrasive teeth to penetrate into the wall of the borehole. In the known underreamer, the clapper body is a ball provided with projections, which ball is connected to the rotor part by means of a chain. During normal operation the projections directed away from the rotor slide along the borehole wall and thereby excavate the borehole, while the projections directed toward the rotor do not contribute to the excavating action. Therefore, the known device is inefficient in use and requires maintenance at short time intervals due to increased wear of the projections directed away from the rotor. It is an object of the invention to provide an underreamer device which is more efficient in use than the known device. It is a further object of the invention to provide an underreamer device which can be used for scaling out production liners without causing damage to the liner itself. To this end the underreamer device according to the invention is characterized in that the pivot means comprises a universal joint. The rotation of the rotor part is transmitted to the clapper body by the universal joint, which clapper body thereby rolls and slides along the borehole wall. Thus, it is achieved that all abrasive teeth of the clapper body contribute to the excavating action. US-A-1 485 615 discloses a borehole underreamer device comprising a pivot means arranged at the lower end of a drill string which carries a clapper body provided with abrasive teeth, wherein the pivot means allows the clapper body to describe in use an orbital motion inside a borehole, thereby inducing the abrasive teeth to penetrate into the wall of the borehole. This publication is not relevant to the present invention as the pivot means does not include a universal joint. US-A-4 229 296 discloses a downhole motor for driving a conventional drill bit. This publication, however, does not relate to underreaming a borehole drilled in an underground formation. FR-A-2 370 163 and FR-A-2 275 633 disclose devices suitable to be used in a borehole, which devices are provided with expandable stabilizer means that can be adjusted to various borehole widths. The invention will now be explained in more detail with reference to the accompanying drawings, in which Fig. 1 is a partly elevational and partly vertical-sectional view of the lower part of an underreamer device according to the invention, and Fig. 2 shows the underreamer of Fig. 2 with expanded stabilizer blades. In Figs. 1 and 2 is shown an underreamer device comprising a clapper body 26 which is carried via a universal joint 27 by an output shaft 25 of a hydraulically driven downhole motor 24. The motor comprises a housing 23 which is stabilized in a borehole 5 by stabilizer blades 20. The motor housing 23 is connected at the upper end thereof to a pipe string (not shown) which carries the underreamer device and through which a driving fluid is pumped into the motor housing 23 thereby inducing a rotor mounted inside the housing to rotate the output shaft 25 and clapper body 26. The output shaft 25, universal joint 27 and clapper body 26 comprise an axial fluid passage (not shown) and the driving fluid is discharged from the housing via said fluid passage and a series of nozzles 29 into the borehole so as to cool the abrasive teeth 45 mounted the clapper body 26 and to remove drill cuttings therefrom. When after lowering the underreamer device into a pilot hole 21 the output shaft 25 of the motor 24 is rotated the clapper body 26 starts orbiting in the pilot hole 21. This orbiting motion generates a centrifugal force as a result of which the teeth 28 penetrate the side wall 1 of the pilot hole 21 in lateral direction. The teeth 45 are distributed circumpherentially on a frustoconical section 30 of the clapper body 26. Said frustoconical section 30 is located between a hard faced nose section 41 and a tubular section 42 of the clapper 26 which latter sections serve to ensure that during operations the clapper 26 is oriented at a selected angle a relative to a central axis I of the borehole 21 and to avoid that the borehole would be underreamed to an undesired large extend. The underreaming process can be monitored at the surface by measuring the pressure of the driving fluid which is injected via a standpipe into the pipestring carrying the underreamer device. Since at a given rotary speed of the clapper 26 there is a clear relation between the standpipe pressure and power consumption of the clapper 26 and since there is a clear relationship between the power consumption of the clapper and the hole size, the measured standpipe pressure can be used to control the speed of pulling the underreamer device through the borehole during operation thereof. If desired the universal joint 27 may comprise a fluid passage which restricts the amount of fluid flow into the clapper body 26 with a progressing tilt angle α. In that case standpipe pressure changes generated as a result of the varying flow restriction in the universal joint may be used as a means for controlling the pulling speed of the device through the borehole during underreaming operations. Alternatively the universal joint 27 may be provided with a by-pass valve (not shown) having a fluid passage which is controlled by the tilt angle α of the clapper body 26. It will be understood that during underreaming operations the pipe string and motor housing 23 may be rotated or be kept non-rotating and that if the device is lowered into or retrieved from the pilot hole 21 the whole assembly is kept non-rotating so as to ensure that the clapper body 26 is kept in a longitudinal orientation in the pilot hole. There is shown the lower part of an underreamer device provided with hingeable stabilizer blades 20 which can be expanded so as to centralize the underreamer device in boreholes of various widths. A device of this type is able to make more passes to ream the hole to the ultimate diameter. In Fig. 1 the device is shown in a small diameter pilot hole 21 with the stabilizer blades 20 in the contracted position, whereas in Fig. 2 the device is shown in a widened hole 22 in which the stabilizer blades 20 are located in an expanded thereof. As can be seen the underreamer device comprises a motor housing 23 which carries near the lower end thereof the stabilizer blades 20. The motor comprises a hollow output shaft 25 which carries a clapper body 26 via a universal joint 27. The motor is a hydraulic motor, such as a Moineau motor which is driven by a driving fluid which is injected into the motor via a pipe string (not shown) which is connected to the upper end of the motor housing 23. The driving fluid is discharged (see arrows II) from the motor housing 23 into the hollow output shaft 25 via orifices 28 at the upper end of said shaft 25. The driving fluid subsequently flows via the interior of the output shaft 25, universal joint 27 and clapper body towards a series of nozzles 29 which are circumpherentially distributed on a frustoconical section 30 of the clapper body 26. At the lower end of the motor housing there is mounted an annular piston 31 which is slidably arranged in an annular-shaped piston housing 32. The piston housing 32 is coupled in fluid communication with the interior 34 of the motor housing 23 via an axial fluid passage 33. In this manner the pressure of the driving fluid inside the motor housing 34 exerts a downward force to the piston 31 thereby inducing a smoothly curved noze section 36 of the piston to push away in lateral direction inwardly curved lower portions 37 of the stabilizer blades 20, thereby forcing the stabilizer blades 20 towards an expanded position thereof. The piston 31 may be forced back into the retracted position by spring means (not shown) if no driving fluid is pumped through the motor so as to enable axial movement of the device through the borehole during insertion and retrieval while the stabilizer blades are kept in a retracted position. The clapper body 26 is provided with hard faced cylindrical section 39 located above the frustoconical section 30 in which the abrassive teeth 40 are inserted. The cylindrical section 39 serves to limit the hole diameter increase per pass. The final borehole diameter is limited by the arrangement of a smooth hard faced nose section 41 at the lower end of the clapper body 26. The underreamer device according to the invention may be used for any conventional underreaming operation such as for underreaming of boreholes, for example prior to setting a casing or prior to setting a gravel packing. The underreamer device according to the invention is furthermore particularly suitable for scaling out of at least partly plugged production liners. The smooth nose section of the clapper body prevents damage to the liner itself and the underreamer is able to operate properly in liner sections with various degrees of scaling. During operation of the underreamer device according to the invention there is no risk of stalling of the downhole motor driving the clapper body because the cutting action of said body becomes less pronounced with decreasing rotary speed. It will be understood that the orbital movement of the clapper in the borehole generates a centrifugal force as a result of which the teeth penetrate into the borehole wall in lateral direction and that the teeth will generally simultaneously have a tangential speed relative to the borehole wall as a result of which the teeth will scrape the rock from the wall. As the lateral force exerted to the teeth and the tangential speed thereof relative to the borehole wall may vary along the length of the clapper body the size, the orientation and distribution of teeth may also vary along the length of the clapper. If it is desired that the teeth have no tangential speed relative to the borehole wall during operation of the device, then the frustoconical section may be shaped such that the top of a mathematical cone enveloping the frustoconical section is located in the pivot centre of the universal joint. Alternatively the teeth may also be embedded in a spherical section of the clapper body. If desired part of the spherical surface of said section may be oriented tangential to a mathematical cone having its top located at the pivot centre of the universal joint. In that case at least some of the teeth have no tangential movement relative to the borehole wall during operation of the device. The abrasive teeth may be made of any wear resistant material such as diamond, tungsten carbide or sintered diamond or boron nitrite particles which are secured to a tungsten carbide substratum. The teeth may further have a triangular, disk, or any other suitable shape. It will further be understood that, if desired, the universal joint which interconnects in the examples shown in the drawings the output shaft of the motor and the clapper body may be replaced by any suitable other type of pivot means, such as a flexible conduit section.

Claims: Borehole underreamer device comprising a downhole motor (24) having a rotor part which can be rotated relative to a stator part, the rotor part carrying pivot means (27), the pivot means (27) carrying a clapper body (26) in which a series of abrasive teeth (40) are embedded, the pivot means (27) allowing the clapper body (26) to describe in use an orbital motion inside a borehole (5), thereby inducing the abrasive teeth (40) to penetrate into the wall of the borehole (5), characterized in that the pivot means (27) comprises a universal joint. The underreamer device of claim 1, wherein the motor (24) is a hydraulically driven motor and comprises a motor housing (23) which forms the stator part of the motor (24) and which is suitable to be connected to the lower end of a pipe string through which a driving fluid can be injected into the motor (24), the motor (24) further comprising a rotor part comprising a hydraulically driven rotor and an output shaft (25) protruding from the lower end of the motor (24) and being connected at the upper end thereof to said rotor and at the lower end thereof to said pivot means (27) carrying the clapper body (26). The underreamer device of claim 2, wherein the motor (24) is of the Moineau type. The underreamer device of claim 2, wherein the clapper body (26) comprises a tubular section (39) which is connected via said pivot means (27) to said output shaft (25) and a frustoconical section (30) in which said abrasive teeth (40) are embedded, said frustoconical section (30) having an outer diameter which increases in a direction away from said pivot means (27), the clapper body (26) further comprising a nose section (41) located at the lower end of the frustoconical section (30). The underreamer device of claim 4, wherein said output shaft (25) and clapper body (26) comprise a fluid passage via which driving fluid can flow from the motor housing (23) into a series of fluid nozzles (29) which are arranged in the frustoconical section (30) of the clapper body (26). The underreamer device of claim 2, wherein the motor housing (23) comprises expandable stabilizer means (20) for centralizing the motor housing (23) inside the borehole (5), which stabilizer means (20) can be adjusted to various borehole widths. The underreamer device of claim 4, wherein said fluid passage in the output shaft (25) and clapper body (26) comprises flow restriction means which impose an increasing flow restriction to the fluid flow through said passage in response to an increasing tilt angle of the clapper body (26) relative to the output shaft (25).

Inventors: ZIJSLING, DJURRE HANS
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1988
Main classification: E21B7
IPC codes: E21B10, E21B4, E21B7, E21B44