Steerable drilling tool

Abstract

A downhole steering tool will steer the angle of the drill bit for drilling directional wells. The steering tool includes a steering housing which is mounted on the drill string above the drill bit. The steering housing can be held against rotation while the drill string rotates to cause the bit to drill in a desired direction. Guide members are mounted on the steering housing. The guide members may engage the borehole. The guide members can be turned about an axis which is perpendicular to the longitudinal axis of the steering housing. Turning the guide members causes the steering housing to rotate relative to the borehole in one direction or the other as the housing slides downward in the borehole. Reorienting the steering housing allows steering of the drill bit.

Description

BACKGROUND OF INVENTION

[0002] This invention relates in general to downhole steerable drilling tools for drilling directional wells.

[0003] Directional wells have curved or inclined portions. A variety of types of tools have been used in the past for drilling wells at a desired inclination and in the desired direction. One type, used particularly for highly deviated wells, utilizes a downhole drill or mud motor. While drilling a curved portion of the well, the downhole drill motor rotates the drill bit in response to the mud flow pressure being delivered from the surface. The drill string is not rotated, but slides downward while the drill bit extends the well in the desired direction and at the desired angle.

[0004] In one technique, the mud operated drill motor steers the drill string with the assistance of a bent housing. The lower portion of the housing is “bent” at an angle of a few degrees relative to the upper portion of the housing, typically about 0.4 to 2.5 degrees. Sensors above the housing sense the orientation of the housing and provide a signal to instruments at the surface. Typically, the orientation is sensed and signals sent by a measuring while drilling tool (MWD), which provides mud pulses or uses some other type of telemetry. When the operator wishes to change the direction, the operator stops rotating the drill pipe and orients the drill pipe so that the lower part of the bent housing and bit are pointed in the desired direction. The operator then operates the drill motor by pumping drilling fluid down the drill pipe while holding the bent housing and drill pipe stationary. Once a sufficient curve has been built, the operator then begins drilling straight by rotating the drill pipe. The bent housing, which always rotates with the drill pipe, causes the bit to orbit slightly. However, because the origin of the orbital path is coincident or almost coincident with the center of the hole, straight drilling can be performed. While this technique is satisfactory, there are disadvantages associated with using this technique. For example, the operator is unable to rotate the upper section of the drill string while building an angle. This reduces the efficiency of hole cleaning. Also, the mud operated drill motor is inefficient in energy consumption.

[0005] In another type of directional drilling tool, a straight housing is used. The axis of rotation of the drill bit can be changed relative to the housing because of articulated joints located within the housing. This type of tool also operates with a downhole drill motor. In still another type, a downhole drill motor is not utilized. Rather, eccentric cam sleeves and weights are employed in the housing. The eccentric cam sleeves can be selectively rotated to change the angle of the axis of rotation of the drill bit relative to the housing. The housing is held against rotation by stabilizer blades, in type wheels, while the drill string and drill bit rotate. This type of tool has its advantages, however it is expensive and complex. Also, it is difficult to completely restrain the housing from rotation while the drill pipe and drill bit are rotating.

SUMMARY OF INVENTION

[0006] In this invention, the drill pipe and drill bit can rotate relative to the steering housing. A downhole drill motor is typically not utilized, but may be used above the assembly. Preferably, the steering housing is of a bent housing type, with a lower portion at a slight angle relative to the upper portion. Alternately, the steering housing could be straight, with articulated connecting joints within it to vary the axis of rotation of the drill bit relative to the housing.

[0007] The steering housing has at least one guide member mounted to it. The guide member protrudes laterally from the steering housing for engaging the borehole wall while the drill pipe and drill bit are rotating relative to the steering housing. The guide member is mounted for selective turning movement about a steering axis. The steering axis is transverse to the length of the steering housing. Turning the guide member causes the steering housing to rotate about its longitudinal axis relative to the borehole as the housing slides downward in the borehole. Changing the orientation of the steering housing relative to the borehole changes the direction of the drill bit. As an analogy, the guide member operates similar to a short section of a screw thread of a self-tapping screw. The change in the angle of the protruding guide member behaves like a variable pitch screw thread.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 is a schematic view of a drill string and steerable drilling tool constructed in accordance with this invention.

[0009] FIG. 2 is an enlarged side elevational view of an upper portion of the steering housing of the steerable drilling tool of FIG. 1.

[0010] FIG. 3 is a sectional view of an upper portion of the housing of FIG. 2, taken along the line 3-3 of FIG. 2.

[0011] FIG. 4 is a sectional view of the steering housing of FIG. 2, taken along the line 4-4 of FIG. 3.

[0012] FIG. 5 is a partial sectional view similar to FIG. 4, but enlarged and showing one of the guide members in a retracted position.

[0013] FIG. 6 is a sectional view of an alternate embodiment of a guide member for the steering housing of FIG. 2.

[0014] FIG. 7 is a sectional view of the guide member of FIG. 6, taken along the line 7-7 of FIG. 6.

[0015] FIG. 8 is a sectional view of another alternate embodiment of the steering housing for the steering tool of FIG. 1.

[0016] FIG. 9 is a sectional view of the housing of FIG. 8, taken along the line 9-9 of FIG. 8.

[0017] FIG. 10 is an elevational view of a portion of the steering housing of FIG. 8.

[0018] FIG. 11 is an enlarged partial view of the guide member for the steering housing of FIG. 10, illustrating the cam slot which controls turning of the guide member.

[0019] FIG. 12 is a view of the guide member similar to FIG. 11, but showing the guide member rotated in one direction.

[0020] FIG. 13 is a view of the guide member similar to FIG. 12, but showing the guide member rotated in an opposite direction.

DETAILED DESCRIPTION OF THE INVENTION

[0021] Referring to FIG. 1, a deviated borehole 11 is shown schematically. A string 13 of drill pipe extends into borehole 11, terminating in a drill bit 15 at the lower end. A steering housing 17 is located a short distance above drill bit 15. Steering housing 17 in this embodiment is of a type referred to as a “bent housing”, suggesting it has an upper portion 17a and a lower portion 17b which are inclined a few degrees relative to each other. The angle of inclination in the drawing is exaggerated. A mandrel 19 extends rotatably through steering housing 17, being supported within steering housing 17 by bearings (not shown). Mandrel 19 may be considered a part of drill string 13 because it always rotates with drill string 13. Mandrel 19 has a passage 20 (FIG. 3) within it for the passage of drilling fluid being pumped down drill string 13 to bit 15. The axis of rotation of bit 15 will be at a slight angle relative to the upper portion 17a because of the bend in steering housing 17. Consequently, by first orienting steering housing 17 in a particular direction and position in borehole 11, and then holding it stationary, bit 15 will drill in a desired direction. Alternately, a straight housing with articulated joints between bit 15 and drill string 13 could be used, such as shown and described in U.S. Pat. No. 4,895,214, which is intended to be incorporated herein by reference.

[0022] A plurality of stabilizer blades 21 assist in allowing drill string 13, mandrel 19 and drill bit 15 to rotate relative to steering housing 17. Stabilizer blades 21 are longitudinally extending blades on upper portion 17a or lower portion 17b, or both, for engaging the sidewall 11a defining borehole 11. In the preferred embodiment, each stabilizer blade 21 has a guide member 23 mounted to it, although a single guide member 23 could suffice. As shown more clearly in FIGS. 2-4, each guide member 23 has a protuberance 23a which may be a sharp thin disk or blade for engaging the sidewall 11a of borehole 11. Guide members 23 are “angulatable” which, for purposes of this application, means the guide member(s) 23 can be rotated, moved or turned relative to the longitudinal axis of steering housing 17 to cause housing 17 to rotate slightly or for orientation in a desired direction. The turning movement of guide members 23, coupled with the downhole sliding movement of steering housing 17, is similar in effect to varying the pitch of a short section of a screw thread of a self-tapping screw.

[0023] Referring still to FIG. 1, the downhole assembly also includes a measuring while drilling (MWD) tool 25, which may be of conventional design. MWD tool 25 will sense various characteristics of the well, including the direction or bearing, referred to as the tool face, of drill bit 15 and the inclination of the borehole 11. MWD tool 25 provides signals to surface equipment by mud pulse telemetry (or alternate methods of telemetry) through the drilling mud flowing back through the annulus surrounding drill string 13. Also, the system preferably has bi-directional communication abilities between surface equipment and MWD tool 25, allowing commands to be sent by the operator at the surface to MWD tool 25. One method of communicating with MWD tool 25 is by manipulating mud pump pressure as explained in U.S. Pat. No. 5,979,570. For example, shutting off the mud pump (not shown) for a period of time may be sensed by the MWD tool 25, which interprets this event as an indication to move from straight drilling to curved drilling.

[0024] A clutch 27 is preferably mounted between steering housing 17 and MWD tool 25, which rotates with drill string 13. MWD tool 25 preferably always rotates with drill string 13, however, housing 17 may be disengaged from rotation with drill string 13. Clutch 27 may be of a generally conventional design which operates to selectively cause steering housing 17 to rotate with drill string 13 and, alternately, to allow drill string 13 and drill bit 15 to rotate relative to steering housing 17. For example, clutch 27 may include an actuator which is powered by a battery or generator in MWD tool 25. A signal may be provided from the surface to MWD tool 25, which sends an electrical signal to an actuator to cause clutch 27 to move between engaged and disengaged positions. Alternately, clutch 27 may be shifted between its positions by manipulating mud pump pressure, generally as shown in U.S. Pat. No. 4,895,214, which material is hereby incorporated by reference.

[0025] Referring now to FIGS. 2-4, in this embodiment each guide member 23 is located in a hole 29 extending through the sidewall of steering housing 17 and one of the stabilizer blades 21. Guide member 23 in this embodiment is a flat, thin blade 23a with a sharpened outer edge for engaging the sidewall of borehole 11. Guide member 23 is secured to and protrudes outward from a rotary member 33. Rotary member 33 is a cylindrical disk which is rotatable relative to steering housing 17 about a steering axis 34. Steering axis 34 is perpendicular to longitudinal axis 31 and intersects it in the preferred embodiment, as shown in FIG. 4. Rotary member 33 may be located within a retainer sleeve 35, which in turn is sealingly secured within housing sidewall hole 29. Rotary member 33 has seals on its sidewall which slidingly engage the inner diameter of retainer sleeve 35. A snap ring type retainer 36 fits within the inner diameter of retainer sleeve 35 to retain rotary member 33 within retainer sleeve 35.

[0026] Referring to FIG. 2, guide member 23 has a leading edge 37 and a trailing edge 39, considering the forward or downward movement of steering housing 17 during drilling. Leading edge 37 refers to the lower or forward edge, which is the edge of guide member 23 closest to drill bit 15. An imaginary line extending between leading edge 37 and trailing edge 39 may be referred to as a track 41. In the position shown in FIG. 2, track 41 is at a track angle 43 of about ten degrees negative relative to longitudinal axis 31. If steering housing 17 is moving downward while guide member 23 is in the position shown in FIG. 2, its engagement with the sidewall 11a of borehole 11 will tend to cause steering housing 17 to rotate counterclockwise, as viewed from above. On the other hand, if rotary member 33 is rotated clockwise about steering axis 34 to a position wherein track angle 43 is positive, or located on the opposite side of longitudinal axis 31, guide member 23 would tend to cause steering housing 17 to rotate clockwise in the borehole 11 as seen from above. Presently, a track angle 43 within the range of from negative fifteen degrees to positive fifteen degrees is a preferred working range for the track angle 43.

[0027] Various actuators may be employed to cause each of the guide members 23 to turn about its steering axis 34. Preferably, each of the guide members 23 are synchronized to turn in unison. One type of actuator comprises a plurality of stepper motors 45, shown in FIG. 4. A separate stepper motor 45 is coupled to each rotary member 33 by a right angle drive. Stepper motors 45 are located inside steering housing 17, preferably in an annulus 47 located between mandrel 19 and the sidewall of steering housing 17. Stepper motors 45 may be electrically powered by a battery or generator (not shown) located within MWD tool 25 (FIG. 1). Annulus 47 is filled with a dielectric fluid, such as oil. A pressure compensator (not shown) will equalize the pressure of the dielectric fluid with that of the drilling fluid pressure in the drill string 13 or alternately in the annulus of borehole 11.

[0028] Also, preferably, each guide member 23 is retractable along its steering axis 34 from a retracted position shown in FIG. 5 to an extended position, shown in FIGS. 3 and 4. In the retracted position, the outer edge of guide member 23 will be recessed within hole 29. Retraction and extension may be accomplished in a variety of manners. Preferably it is handled by a telescoping device which is biased to a retracted position. For example, this may include a hydraulic passage 48 leading to a hydraulic pump 49 incorporated within steering housing 17 and driven by an electrical motor supplied with power from MWD tool 25 (FIG. 1). Hydraulic pump 49 (FIG. 3) supplies pressure to a chamber on the interior side of rotary member 33, causing it to move to the extended position. A spring 50 (FIG. 5) urges guide member 23 to the retracted position when hydraulic pressure from hydraulic pump 49 is removed.

[0029] In the operation of the embodiment of FIGS. 1-5, the upper end of mandrel 19 will be connected to MWD tool 25 and the lower end to drill bit 15. Clutch 27 will be located on the upper end 17a of steering housing 17. MWD tool 25 will be secured to a string 13 of drill pipe. The entire assembly is lowered into the well. The default position for clutch 27 will be in an engaged position, locking steering housing 17 to drill string 13 for rotation therewith, and the default position for guide members 23 will be a retracted position. While in the default position, which is for drilling in a straight line, MWD tool 25 and housing 17 rotate in unison with drill string 13 and mandrel 19. Although bit 15 will orbit slightly relative to upper housing portion 17a, it will drill straight portions of borehole 11.

[0030] When it is desired to begin a curve to establish a new direction, the operator provides a signal to actuate clutch 27 to the released position and to move guide members 23 to the extended position shown in FIGS. 3 and 4. Guide members 23 will engage the side of borehole 11. The default orientation for guide members 23 may be in a neutral position, generally shown in FIG. 10, although a small track angle 43 (FIG. 2) may exist in the default position to accommodate for normal bit walk due to rotation of drill bit 15. MWD tool 25 will sense the angle of the tool face of steering housing 17 and signal stepper motors 45 to turn guide members 23 to a desired track angle 43, such as illustrated in FIG. 2, which is either preprogrammed in MWD tool 25 or signaled from the surface. Drill string 13 continues to rotate, which rotates MWD tool 25 and drill bit 15 through mandrel 19. Housing 17 will not rotate in unison with drill pipe 13 because of stabilizer blades 21 and guide members 23, however steering housing 17 will rotate slowly or turn about its longitudinal axis 31 due to seal and bearing friction between mandrel 19 and steering housing 17 and the track angle 43 (FIG. 2) set by guide members 23. As drill bit 15 drills forward, steering housing 17 slides forwardly or downwardly. The track angle 43 selected by guide members 23 will force steering housing 17 to rotate to a different orientation relative to borehole 11. Signals from MWD tool 25 will control stepper motor 45 to turn guide members 23 to various tracks 41. Guide members 23 will thus be able to rotate steering housing 17 clockwise or counterclockwise as desired to maintain a desired heading or bearing of drill bit 15 which is either preprogrammed or signaled from the surface. When a sufficient amount of the curve has been built, the operator again provides a signal to cause clutch 27 to actuate, placing steering housing 17 in an engaged mode with drill pipe 13 and retracting guide members 23. Signaling clutch 27 to engage and disengage could be automatic.

[0031] FIGS. 6 and 7 illustrate an alternate embodiment with similar components to those in the first embodiment being shown with a prime symbol. The only difference between the embodiment shown in FIG. 6 and the first embodiment is that rather than a stationary flat, thin blade for guide member 23, the embodiment of FIG. 6 has a circular guide member 23′ rotatably mounted to axle 52. Axle 52 is rigidly mounted to rotary member 33′ perpendicular to steering axis 34 (FIGS. 3 & 4). Guide member 23′ is thus a sharp circular disk which rolls as it engages the sidewall of borehole 11.

[0032] In the embodiment of FIGS. 8 and 9, guide member 23″ could be either a circular rolling disk/blade as in FIGS. 6 and 7 or a non-rotating blade as in FIGS. 1-5. The embodiment of FIGS. 8-12, however, utilizes a different mechanism for turning guide members 23 about the steerable axis. In this embodiment, similar components are shown with a double prime symbol. A cam sleeve 51 is mounted within annulus 47″ for axial movement along longitudinal axis 31″. Cam sleeve 51 has a cam slot 53 formed in its outer sidewall. A pin 55 is eccentrically mounted in rotary member 33″. Pin 55 engages slot 53, and slot 53 is curved to cause rotation of rotary member 33″ when cam sleeve 51 moves axially. An actuator (not shown), which may be of a variety of types, will engage cam sleeve 51 to cause it to move axially. The actuator may be a linear motor supplied by power from MWD tool 25. Alternately, the actuator might be a hydraulically driven piston supplied with hydraulic pressure from a hydraulic pump located within housing 17″. Preferably coil springs 57 and 59 urge cam sleeve 51 to a neutral position.

[0033] The neutral position is illustrated in FIGS. 10-11. In this position, guide member 23″ is substantially aligned on longitudinal axis 31″, however, it may be at a slight angle to resist normal bit walk. In the neutral position, guide member 23″ will thus resist any rotation of housing 17″ relative to the borehole. As shown in FIG. 11, cam slot 53 has an upper portion 53a which is inclined relative to axis 31″ and a central portion 53b which is parallel with axis 31″. A lower portion 53c joins central portion 53b and is inclined relative to axis 31″ at the same angle as upper portion 53a. When cam sleeve 51 has moved downward to the position shown in FIG. 12, pin 55 rotates rotary member 33″ counterclockwise to orient steering housing 17″ for clockwise movement when viewed from above. When the actuator moves cam sleeve 51 upward to the position shown in FIG. 13, it will cause pin 55 to rotate rotary member 33″ clockwise. This results in steering housing 17″ rotating counterclockwise when viewed from above.

[0034] The invention has significant advantages. It allows substantially real time steering by monitoring the angle of the tool face and orienting the steering housing relative to the borehole by use of the guide members. It is less complex than an eccentric cam tool. It does not require the use of a downhole drill motor. Drilling continues with the drill string rotating at all times.

[0035] While it has been shown in only a few of its forms, it should be apparent to those skilled in the art that it is not so limited, but susceptible to various changes without departing from the scope of the invention.

Claims

1. A steering apparatus for use in directional drilling a borehole with a drill string and a drill bit, comprising: a steering housing mounted on the drill string above the drill bit; a clutch connected between the drill string and the steering housing; and at least one angulatable guide member mounted to the steering housing, and having a protuberance from the steering housing.

2. The apparatus according to claim 1, wherein said protuberance comprises a blade for engaging a sidewall of the borehole.

3. The apparatus according to claim 1, wherein said at least one angulatable guide member includes a rotary member defining a steering axis which is approximately perpendicular to a longitudinal axis of the steering housing.

4. The apparatus according to claim 3, wherein said protuberance comprises a blade for engaging a sidewall of the borehole.

5. The apparatus according to claim 1, further comprising a motor mounted in the steering housing and coupled to said at least one angulatable guide member.

6. The apparatus according to claim 1, wherein said at least one angulatable guide member comprises an extensible and retractable, angulatable guide member.

7. The apparatus according to claim 1, further comprising at least one stabilizer blade connected to the steering housing having an outer diameter which is greater than an outer diameter of the steering housing and less than an outer diameter of said protuberance.

8. The apparatus according to claim 1, further comprising: an annular cam member mounted in the steering housing, said annular cam member having a cam slot; and a pin extending eccentrically from said at least one angulatable guide member into engagement with the cam slot.

9. The apparatus according to claim 1, wherein said at least one angulatable guide member comprises a plurality of angulatable guide members evenly spaced around a circumference of the steering housing.

10. The apparatus according to claim 1, wherein the steering housing has an upper portion and a lower portion, and the lower portion has a longitudinal axis which is at angle relative to a longitudinal axis of the upper portion.

11. A steering apparatus for use in directional drilling a borehole with a drill string and a drill bit, comprising: a steering housing mounted on the drill string above the drill bit; a means for allowing rotation of the drill string relative to the steering housing connected between the drill string and the steering housing; and a means for engaging a sidewall of the borehole mounted in the steering housing including a means for independently turning said means for engaging the sidewall of the borehole.

12. The apparatus according to claim 11, wherein said means for engaging a sidewall of the borehole comprises a plurality of blades.

13. The apparatus according to claim 11, wherein said means for independently turning comprises an angulatable guide member.

14. The apparatus according to claim 13, wherein said means for engaging a sidewall of the borehole comprises a plurality of blades.

15. The apparatus according to claim 11, wherein said means for independently turning comprises a plurality of motors mounted in the steering housing and operationally coupled to said means for engaging a sidewall of the borehole.

16. The apparatus according to claim 11, wherein said means for engaging the sidewall of the borehole comprises a plurality of extensible and retractable blades.

17. The apparatus according to claim 11, wherein said means for allowing rotation of the drill string relative to the steering housing comprises a clutch.

18. The apparatus according to claim 11, wherein the actuator compnses: an annular cam member mounted in the steering housing, said annular cam member having a cam slot; and a pin extending eccentrically from said means for independently turning into engagement with the cam slot.

19. The apparatus according to claim 11, wherein the steering housing has a lower portion and an upper portion, and the lower portion has a longitudinal axis which is inclined relative to a longitudinal axis of the upper portion.

20. The apparatus according to claim 19, wherein said means for engaging a sidewall of the borehole is located on the upper portion of the steering housing.

21. A method of steering a drill bit for directional drilling a well wherein the drill bit forms a borehole with a sidewall, comprising: (a) penetrating the sidewall of the borehole with a guide member; (b) rotating the drill string and the drill bit independent from the guide member; and (c) selectively angulating the guide member to change an orientation relative to the borehole.

22. The method according to claim 21, further comprising: retracting the guide member away from the sidewall of the borehole.

23. The method according to claim 22, further comprising selectively rotating the drill string and the drill bit together with the guide member.

24. The method according to claim 21, wherein said step of angulating the guide member in one direction causes the drill bit to rotate relative to the borehole in a counterclockwise direction, and angulating the guide member sufficiently in an opposite direction causes the drill bit to rotate relative to the borehole in a clockwise direction.