Simple Rotary Steerable Drilling System

Abstract

A steering collar for deflecting a drill string in a borehole to cause the borehole to be drilled in a different direction. The steering collar surrounds a hollow drive shaft which is driven by the drill string. During normal drilling operations, the steering collar does not rotate with the drive shaft. The steering collar has three sets of pistons operated by the pressure of the drilling fluid, one set of which is pressure relieved. Drill fluid that is pumped down the drill string flows into the hollow drive shaft and through ports to activate the pistons which thereby force corresponding pads outwardly into contact with the sidewall of the borehole. Since the one set of pistons is pressure relieved, it does not force its pad against the borehole sidewall with as much pressure as the other two sets of pistons force their pads against the sidewall of the borehole. Accordingly, the steering collar is deflected laterally in the borehole so that the drill bit is also steered laterally to cause drilling in a different direction. In order to reorient the steering collar in the borehole, the steering collar can be locked to the drive shaft so that when the drill string is rotated, the steering collar is also rotated so that it is moved to a new angular position in the borehole.

Claims

1. A rotary drilling system of the type having a drill string that rotates and drives a drill bit to provide directional control in the formation of a borehole, comprising: a bottom hole assembly connected to the drill string, said bottom hole assembly comprising: a steering collar; a drive shaft that is coupled to the drill string and to said drill bit, said drive shaft passing through a said steering collar; said steering collar being lockable to said drive shaft in response to a first pressure of said drilling fluid coupled down the drill string, whereby the steering collar rotates with the drill string to position said steering collar at a desired angular location in the borehole; at least one pressure relieved piston responsive to a second pressure of the drilling fluid for operating a respective thrust pad against a sidewall of the borehole to push said steering collar in an opposite direction; at least two spaced apart non-pressure relieved pistons, each responsive to the second pressure of the drilling fluid for operating respective thrust pads against the sidewall of the borehole to push the steering collar in directions different from that of said pressure relieved piston; and a drilling fluid pump for pumping the drilling fluid at desired flow rates to operate lock said drive shaft to said steering collar, and said second drilling fluid pressure to operate said pistons.

2. The rotary drilling system of claim 1, wherein said pressure relieved piston, and said two non-pressure relieved pistons are located about 120 degrees apart around said steering collar.

3. The rotary drilling system of claim 1, where each said thrust pad is attached to said steering collar with hinged links that allow said thrust pads to extend radially outwardly from an outer surface of said steering collar.

4. The rotary drilling system of claim 1, wherein said pressure relieved piston includes an orifice that controls the pressure of the drilling fluid applied thereto.

5. The rotary drilling system of claim 1, wherein said steering collar includes a hollow body with said drive shaft extending thereto, said drive shaft having an axial bore extending therethrough, and pressurized drilling fluid passes through the axial bore and through a lateral bore in said drive shaft to an annulus located between an outer cylindrical surface of said drive shaft and an inner cylindrical surface of a body of said steering collar.

6. The rotary drilling system of claim 5, wherein each said pressure relieved piston and each said non-pressure relieved piston is operated by the pressurized drilling fluid in said annulus.

7. The rotary drilling system of claim 1, wherein said steering collar includes cutting edges on a back side thereof to allow the steering collar to cut material when withdrawn by said drill string from the borehole.

8. The rotary drilling system of claim 3, wherein each said pad includes a fin that is pushed into a sidewall of the borehole to prevent said steering collar from rotating when the borehole is drilled by said drill bit.

9. The rotary steering system of claim 1, further including a flow restriction which under drill fluid flowing conditions permits the development a differential pressure between the inside of the steering collar and the outside of the steering collar so as to permit the operation of a locking mechanism between the drive shaft and the steering collar and also to actuate the pistons of the steering collar.

10. A rotary drilling system of the type having a drill string that rotates and drives a drill bit to provide directional control in the formation of a borehole, comprising: a bottom hole assembly that includes; a drive shaft driven by the drill string, said drive shaft having an axial bore therethrough to couple drilling fluid therethrough from the drill string to the drill bit; a steering collar having an axial bore therethrough through which said drive shaft extends, said steering collar being lockable to said drive shaft in response to a first pressure of a drilling fluid coupled down said drill string, whereby said steering collar rotates with said drill string to position said steering collar at a desired angular location in said borehole; said steering collar having: at least one pressure relieved piston responsive to a second pressure of the drilling fluid for moving axially outwardly from said steering collar; a first pad that moves in response to the movement of said pressure relieved piston, said first pad for engaging a sidewall of the borehole; at least one non-pressure relieved piston responsive to the second pressure of the drilling fluid for moving axially outwardly from said steering collar in a direction different from said pressure relieved piston; and a second pad that moves in response to the movement of said non-pressure relieved piston, said second pad for engaging a sidewall of the borehole; whereby when the drilling fluid is pumped down the drill string, said pressure relieved piston is forced against the sidewall of the borehole with less force than said non-pressure relieved piston, thereby forcing said steering collar, said drive shaft and said drill bit in a lateral direction in said borehole to thereby deviate the direction of drilling the borehole.

11. The rotary drilling system of claim 10, wherein said steering collar is rotatable around said drive shaft, and further including a peg for locking said steering collar to said drive shaft so that when said drill string is rotated, said steering collar rotates therewith.

12. The rotary drilling system of claim 11, further including a locking piston for moving said peg to lock said steering collar to said drive shaft, said locking piston responsive to a pressure of the drilling fluid to move said peg to lock said steering collar to said drive shaft.

13. The rotary drilling system of claim 10, further including a respective guide vane attached to each said first and second pad, said guide vanes engaging within the sidewall of the borehole to prevent rotation of said steering collar while said steering collar is pushed forwardly during drilling of the borehole.

14. The rotary drilling system of claim 10, further including an annulus between said steering collar and said drive shaft, said annulus for carrying pressurized drilling fluid that is coupled to said pressure relieved piston and to said non-pressure relieved piston for operation thereof.

15. The rotary drilling system of claim 14, wherein there is a drill string annulus between the drill string and the borehole, and wherein pressurized drilling fluid is coupled to said pressure relieved piston for operation thereof and then released into the drill string annulus to thereby reduce the force by which said pressure relieved piston is extended radially outwardly.

16. The rotary drilling system of claim 15, wherein the path of the borehole deviates in a direction related to the sidewall of the borehole acted upon by said pressure relieved piston.

17. A rotary drilling system of the type having a drill string that rotates and drives a drill bit to provide directional control in the formation of a borehole, comprising: a bottom hole assembly that includes; a drive shaft driven by the drill string, said drive shaft having an axial bore therethrough to couple drilling fluid therethrough from the drill string to the drill bit; a steering collar having an axial bore therethrough through which said drive shaft extends, an annular space between said steering collar and said drive shaft defining an annulus for carrying pressurized drilling fluid, said steering collar further including: at least two pistons responsive to the pressure of the drilling fluid coupled through the annulus between said steering collar and said drive shaft, said at least two pistons for moving axially outwardly from said steering collar to push said steering collar laterally in the borehole, said two pistons located less than 180 degrees apart around a circumference of said steering collar; a respective pad moved by each of said two pistons for engaging respective portions of a sidewall of the borehole; and a peg movable by a piston in response to a pressure of the drilling fluid, said peg for locking said steering collar to said drive shaft so that movement of the drill string is effective to rotate said steering collar to a desired angular orientation within said borehole; whereby when the pistons of the steering collar are deployed, the steering collar is displaced laterally in the borehole to thereby deviate the path of the borehole, and for so long as said pistons are deployed the steering collar does not rotate but slides within the borehole during drilling to continue deviating the path of the borehole.

18. The rotary drilling system of claim 17, wherein said peg is moved into a locking position in response to a first pressure of the drilling fluid, and said two pistons are moved outwardly by a drilling fluid pressure of a greater pressure.

19. The rotary drilling system of claim 17, further including a third piston movable outwardly from said steering collar to engage the sidewall of the borehole via a pad, said third piston being pressure relieved so as to exhibit a force less than a force presented by said two pistons, whereby said steering collar moves to the sidewall of the borehole adjacent the pressure relieved piston.

20. A method of controlling the direction of drilling of a borehole, comprising: forcing a steering collar surrounding a portion of a drill string upstream from a drill bit laterally toward a sidewall of the borehole to deviate the path of the borehole; using a first pressure of a drilling fluid pumped down the drill string to activate a locking mechanism to lock the steering collar and prevent relative rotary movement between the steering collar and the drill string; rotating the drill string to thereby rotate the steering collar in a desired angular position within the borehole to cause the path of the borehole to deviate in a desired direction; forcing the steering collar laterally by using a second pressure of said drilling fluid to move one or more pistons radially away from the steering collar to cause engagement with the sidewall of the borehole and push the steering collar away from the part of the borehole sidewall engaged; and disengaging the locking mechanism so that the drill string can rotate the drill bit and drill the borehole in the deviated path, while preventing the steering collar from rotating for so long as it is desired to deviate the path of the borehole.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Further features and advantages will become apparent from the following and more particular description of the preferred embodiment of the invention, as illustrated in the accompanying drawings in which like reference characters generally refer to the same parts, components or elements throughout the views, and in which:

[0046] FIG. 1 illustrates the steering collar tool being used to push the bit laterally to achieve directional control;

[0047] FIG. 2 illustrates the steering collar tool being used to point the bit to achieve directional control;

[0048] FIG. 3 illustrates a transverse section of the steering collar tool with various longitudinal section positions;

[0049] FIG. 4 illustrates a longitudinal section of the steering collar tool through the set of pressure relieved pistons;

[0050] FIG. 5 illustrates a longitudinal section of the steering collar tool through one set of the two sets of non-pressure relieved pistons;

[0051] FIG. 6 illustrates a detailed section of one of the three pressure relieved pistons;

[0052] FIG. 7 illustrates a transverse section of the steering collar tool with the locking mechanism; and

[0053] FIG. 8 illustrates the locking mechanism in detail.

DETAILED DESCRIPTION OF THE INVENTION

[0054] FIG. 1 illustrates a horizontal borehole (1) in which a drill string (2) lies on the bottom thereof until deflected by the steering collar (3). The steering collar (3) enables the transmission of the rotating motion of the drill string from its right hand side (as shown) to an extended part of the drill string (4) on its left hand side, and then to the drill bit (5) itself. Because the steering collar (3) laterally deflects the drill string (4) and the bit (5), the latter cuts a deviated path and will continue to do so in the desired path (6). In this form, the steering collar (3) is being used to push the bit (5) sideways to effect a directional change of the borehole (1). It should be appreciated that the steering collar (3) may be used in this mode to push in any lateral direction in the borehole (1) to change the alignment of the borehole (1).

[0055] FIG. 2 illustrates the borehole (1) in which the drill string (2) lies on the bottom of the borehole (1) in the right side of the drawing. It is deflected by a steering collar (3) and the drill string (4) continues to the left side up to the location of a drill centraliser (7) and thence as (8) to the drill bit (5). The sideways thrust of the steering collar (3) within the borehole (1) forces the drill string sections (2) and (4) to effectively bend. The centraliser (7) acts as a fulcrum pointing the extended part of the drill string (8) and the drill bit (5) to drill a projected path (6). This mode is a point the bit system. As can be appreciated, both modes of operation utilize the same steering collar (3).

[0056] FIG. 3 illustrates a section of the steering collar (3) in schematic form. The body of the steering collar (3) is shown pushed laterally upwardly off centre within the borehole (1). Through the steering collar body (3) passes a drive shaft (21) which transmits rotating motion, torque and thrust from the drill string (2) to the drill bit (5). Between the steering collar body (3) and the drive shaft (21) is an annulus (19) which carries drilling fluid at a pressure which is higher than that existing in the borehole annulus between the steering collar body (3) and the borehole (1). The drilling fluid in the drive shaft annulus (19) is derived from drilling fluid that is carried through a central bore (36) formed within the drive shaft (21). Three thrust pads (7), (8) and (9), each located about one hundred twenty degrees apart on the steering collar (3), are pushed toward or into contact with the sidewall of the borehole (1) by three respective groups or sets of pistons (10), (11) and (12). In practice, each group of pistons (10), (11) and (12) is comprised of one or several pistons. The set of pressure-relieved pistons (12) is constructed differently from the non-pressure relieved sets of pistons (10) and (11). These pistons are driven outward by the difference in the drilling fluid pressure between the drive shaft annulus (19) and the borehole annulus located outside of the steering collar body (3). Piston sets (10) and (11) are simple pistons which carry respective elastomeric seals (13) and (14). Drilling fluid is supplied to the base of the piston cylinders (in which the pistons (10) and (11) are located) via respective ports (16) and (17). The base of piston (12) is supplied with fluid via a metering port (18). The piston (12) carries an elastomeric seal (15) and also carries a pressure relief system that is shown in more detail in FIG. 6. At lower drilling fluid flow rates and pressures, all pistons (10), (11) and (12) bear outwardly against the thrust pads (7), (8) and (9) which bear outwardly against the sidewall of the borehole (1) with equal force. When the pressure in the drive shaft annulus (19) rises above a certain level, the piston (12) vents into the annulus within the borehole (1), thus limiting the differential pressure across the piston (12). The replenishment of the drilling fluid to the base of the piston (12) is limited by the metering port (18). Each of the three sets of pistons (10), (11) and (12) is equipped with respective shoes or thrust pads (7), (8) and (9) that push against the sidewall of the borehole (1) to move the collar (3) to an off-centre position. The thrust pads (7), (8) and (9) carry respective fins (66), (67) and (68) that bear against the sidewall of the borehole (1) to minimise rotation of the steering collar body (3) while drilling ahead. The effect of differing pressures applied to the pads (7) and (8) as compared to pad (9) is that the steering collar (3) tends to be forced to the side of the borehole (1) adjacent the piston equipped with the pressure relief system (12). This is illustrated in FIG. 3 where the top of the borehole (1) is adjacent the pressure relief piston (12), and the steering collar (3) is forced to the top of the borehole (1). The higher the drilling fluid pressure in the central bore (36) of the drive shaft (21), compared to that in the annulus between the steering collar body (3) and the borehole (1), the greater this net side force is. This pressure differential is controlled by the rate at which the drilling fluid is pumped through an orifice (37) located within the central bore (36) of the drive shaft (21).

[0057] FIG. 4 illustrates section A-A of the steering collar (3) of FIG. 3. Here, all three pressure relieved pistons of the set (12) are shown. In the right side of the drawing is a drive sub (20) that screws into the upstream drill string pipe section (not shown). This transmits thrust and torque to the drive shaft (21) via a threaded connection (38). The threaded connection (38)-bears against the internal end of the drive sub (20) via an adjustment shim (22). Also on this threaded connection (38) is a locking assembly (23). This contains cutters (24) that enable the assembly to cut its way backwards out of the borehole (1) should the borehole (1) collapse or otherwise become blocked. As noted above, the drive shaft (21) passes through the body of the steering collar (3). The left hand side of the drive shaft (21) extends beyond the body (3) and contains a downstream threaded connection (27) which can transmit thrust and torque to the drill string section (4) (in FIG. 1 or 2) which is screwed into it. At the base of the threaded connection (27) is a plate containing the orifice (37) which causes a fluid pressure drop as drilling fluid is pumped from right to left. The drive shaft (21) is supported within the steering collar body (3) by bearings (25) and (26) so that the drive shaft (21) can rotate and transmit torque downstream without rotating the steering collar (3). These bearings (25) and (26) are preferably of an angular contact ball race construction. To make up the steering collar (3), the drive shaft (21) is inserted through the bearings (26) and (25), and the locking assembly (23) is then screwed onto the drive shaft threads (38). The drive sub (20) is then tightened against the end of the drive shaft (21) via the adjustment shim (22). The locking assembly (23) is then tightened against the drive sub (20) to lock the drive sub onto the threads of connection (38).

[0058] FIG. 4 also illustrates a section through the thrust shoe or pad (9) associated with the set of pistons (12) that act upon it. A fin (68) attached to the thrust pad (9) extends outwardly to contact the borehole wall to inhibit rotation of the steering collar while the thrust pad (9) is in the extended position. The three pressure relieved pistons (12) of the set underlie the elongated thrust pad (9). The thrust pad (9) is attached on each end thereof to respective links (29) and (30) via pin and bush assemblies (32) and (33). These links (29) and (30) are in turn recessed in the outer surface of the steering collar body (3) by pin and bush assemblies (31) and (34). The bushes within the pin and bush assemblies (31 to 34) are made of an elastomer that permits the pad (9) and link (29 and 30) assembly to extend outwardly when it is pushed away from the body (3) by the set of pistons (12). The elastomeric bushes also pull the pad (9) and link (29 and 30) assembly back into the steering body (3) when the set of pistons (12) are no longer energised. Also shown is the position of the locking peg assembly (28). This assembly (28) locks the drive shaft (21) to the steering collar body (3) for orientation purposes when a fluid pressure difference between the outside of the collar body (3) and that in the drive shaft annulus (19) is low. Drilling fluid is conveyed from the inside of the drive shaft (21) via port (35) to the drive shaft annulus (19) around the drive shaft (21) and thence via the ports 18 (FIG. 3) to the set of pistons (12). The other two sets of pistons (10) and (11) receive pressurized drill fluid in a similar manner via respective ports (16) and (17) (FIG. 3).

[0059] FIG. 5 illustrates section B-B of the steering collar (3) of FIG. 3. Here, all three non-pressure relieved pistons of the set (10) are shown. The other set of non-pressure relieved pistons of the set (11) is similarly constructed. In particular, illustrated is the thrust pad (7) and associated links (39 and 40) and pin and elastomeric bush assemblies (41 to 44) in section. In this view, the set of pistons (10) are shown extended from the steering body (3) by fluid pressure delivered to the inner end of the set of pistons (10). In this extended condition the thrust pad (7) pushes against the sidewall of the borehole (1) thus deflecting the body of the steering collar (3) in the opposite direction within the borehole (1).

[0060] FIG. 6 illustrates an enlarged sectional view of one pressure relieved piston of the set (12) of FIGS. 3 and 4. The piston (12) is located in a cylindrical bore which is fed at its base by drilling fluid via port (18). The pressurised drilling fluid pushes the set of pistons outwardly against the thrust pad (9) via the threaded and ported component (56). When the fluid pressure exceeds a certain design value, the pin (53) lifts within the piston body (50), thus opening the piston (50) to the through flow of the drilling fluid. This occurs via port (51) in the base of the piston around the centralisers (54), which do not occlude fluid flow. The drilling fluid continues flowing past the spring (55) and out via port (52) located within component (56) into the space between the top of the piston body (50) and the pad (9). The force on the piston (12) is thus limited by the dimension of port (18) and the pressure relief characteristics of the piston assembly. The spring (55) functions to return the pin (53) to the downward position when the drilling fluid pressure is lowered.

[0061] FIG. 7 is section D-D of the steering collar (3) of FIG. 4. In this drawing, the peg (61) of the locking peg assembly (28) is shown engaged in a notch (45) formed within the drive shaft (21). With the peg (61) in this position, the drive shaft (21) may be rotated clockwise to turn the steering collar body (3) clockwise within the borehole (1). When the peg (61) is engaged in the shaft notch (45), the rotation of the drive shaft (21) with the drill string (2) is effective to relocate the steering collar (3) in the borehole (1) so that the pistons (9), (10) and (11) and corresponding thrust pads (7), (8) and (9) are positioned to deviate the drilling in a desired direction. When fluid is flowing through the drive shaft (21) it will be at a higher pressure than the fluid outside the steering collar (3) and within the annulus of the borehole (1). When a sufficient flow rate is reached, the differential fluid pressure will raise the locking peg (61) against the spring (64) and out of the notch (45), allowing the drive shaft (21) to rotate freely of the steering collar body (3).

[0062] FIG. 8 illustrates the locking peg assembly (28) in more detail. The peg (61), which is contained within the cylindrical bore (62), is shown engaged in the notch (45) formed in the drive shaft (21). It is held in this position by the spring (64) that pushes against the bottom cap (63) which is screwed into the steering collar body (3). The cap (63) contains a port (65) which is in communication with the drilling fluid outside of the steering collar body (3). When the differential pressure between the drive shaft annulus (19) and the outside of the body (3) exceeds the compressive resistance of the spring (64), the peg (61) is pushed out the notch (45) in the drive shaft (21), thus enabling the drive shaft (21) to rotate within the steering collar body (3). In this mode normal drilling can take place.

[0063] From the foregoing, it should be understood that while the preferred embodiment of the invention has been described in connection with three pistons constituting a set, other numbers of pistons can be employed as a set. Also, the embodiment of the invention is described with three sets of pistons located about one hundred and twenty degrees around the rotary collar, it is understood that the angular positions of the sets of pistons could be other than one hundred and twenty degrees. Further, while the preferred embodiment contemplates the use of a pressure relieved piston and non-pressure relieved pistons to move the steering collar laterally within the borehole, those skilled in the art may prefer to omit the pressure relieved piston and utilize only the non-pressure relieved pistons to move the steering collar sideways in the borehole to modify the direction of drilling.

[0064] While the preferred embodiment of the invention has been disclosed with reference to a specific steerable collar, it is to be understood that many changes in detail may be made as a matter of engineering choices without departing from the spirit and scope of the invention, as defined by the appended claims.

[0065] Unless the context clearly requires otherwise, throughout the description and the claims, the words comprise, comprising, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of including, but not limited to.