Steering tool

Abstract

A steering tool for use in drilling a borehole, including a tubular housing, a tool actuating device movably supported within the housing, a plurality of hydraulically actuated steering devices circumferentially spaced about the housing, and a hydraulic control system interposed between the tool actuating device and the steering devices for converting an actuating movement of the tool actuating device to independent actuation of the steering devices.

Description

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the invention will now be described with reference to the accompanying drawings, in which:

FIGS. 1( a)-1(c) are schematic drawings of a portion of a drill string depicting three different configurations of a steering tool according to the invention.

FIG. 2 is an end view of a steering tool according to a preferred embodiment of the invention corresponding to FIG. 1(a), looking from the upper end of the housing of the steering tool toward the lower end of the housing of the steering tool.

FIGS. 3( a)-3(h) are a longitudinal section assembly drawing of the steering tool of FIG. 2 taken along section line III-III, in which FIG. 3(b) through FIG. 3(h) are continuations of FIG. 3(a) through 3(g) respectively.

FIG. 4( a)-4(c) are a partial longitudinal section assembly drawing of the steering tool of FIG. 2 taken along section line IV-IV, in which FIG. 4(b) is a continuation of FIG. 4(a) and FIG. 4(c) is a continuation of FIG. 4(b).

FIG. 5 is an end view of components of the hydraulic control system for the steering tool of FIG. 2.

FIG. 6 is a longitudinal section assembly drawing of components of the hydraulic control system for the steering tool of FIG. 2, taken along section line VI-VI of FIG. 5.

FIG. 7 is a longitudinal section assembly drawing of components of the hydraulic control system for the steering tool of FIG. 2, taken along section line VII-VII of FIG. 5.

FIG. 8 is a longitudinal section assembly drawing of components of the hydraulic control system for the steering tool of FIG. 2, taken along section line VIII-VIII of FIG. 5.

FIG. 9 is a longitudinal section assembly drawing of components of the hydraulic control system for the steering tool of FIG. 2, taken along section line IX-IX of FIG. 5.

FIG. 10 is a longitudinal section assembly drawing of components of the hydraulic control system for the steering tool of FIG. 2, taken along section line X-X of FIG. 5.

FIG. 11 is a longitudinal section assembly drawing of components of the hydraulic control system for the steering tool of FIG. 2, taken along section line XI-XI of FIG. 5.

FIG. 12 is a longitudinal section assembly drawing of components of the hydraulic control system for the steering tool of FIG. 2, taken along section line XII-XII of FIG. 5.

FIG. 13 is a schematic drawing of components of the hydraulic control system for the steering tool of FIG. 2 in which the hydraulic control system is a single-acting hydraulic system.

FIG. 14 is a schematic drawing of components of an alternate embodiment of hydraulic control system for use in the steering tool of FIG. 2 in which the hydraulic control system is a double-acting hydraulic system.

FIG. 15 is a schematic side view of the swash plate pump for the steering tool of FIG. 2.

FIG. 16 is a partial pictorial view of the swash plate pump for the steering tool of FIG. 2.

FIG. 17 is a pictorial bottom view of the aluminum core of one of the steering blades for the steering tool of FIG. 2.

FIG. 18 is a pictorial top view of the aluminum core of one of the steering blades for the steering tool of FIG. 2.

FIG. 19 is a pictorial top view of one of the steering blade covers for the steering tool of FIG. 2.

DETAILED DESCRIPTION

Referring to FIG. 1, a steering tool (20) according to the invention is depicted in three different exemplary configurations incorporated within a drill string (22). In all three exemplary configurations, a drill bit (24) is located at a distal end of the drill string (22).

In FIG. 1(a), the steering tool (20) is configured as a component of a drilling motor (26) having a motor housing (28) and a motor drive shaft (30). This configuration is described in detail below as a preferred embodiment of the invention.

In FIG. 1(b), the steering tool (20) is configured as a component of a rotary steerable drilling system (32) of the type in which a steering mechanism is rotatably connected with the drill string (22). In this configuration, the drill string (22) extends through the steering tool (20) and the steering tool (20) includes a borehole engaging device (34) for inhibiting the steering tool (20) from rotating in a borehole (not shown) when the drill string (22) is rotated.

In FIG. 1(c), the steering tool (20) is configured as a component of a fully rotating rotary steerable drilling system (32) of the type in which a steering mechanism is connected with the drill string (22) so that the steering mechanism rotates with the drill string (22). In this configuration, the steering tool (20) is fixedly connected within the drill string (22).

The principles of the invention are applicable to all of the configurations of the steering tool (20). A preferred embodiment of the invention in which the steering tool (20) is configured as a component of a drilling motor (26) is now described. In the preferred embodiment, the steering tool (20) is configured to maintain the drilling motor (26) in a vertical orientation as a target orientation. In other words, in the preferred embodiment the steering tool (20) is configured as a vertical steering tool.

In the preferred embodiment, the drilling motor (26) is comprised of a rotary motor so that the motor drive shaft (30) rotates relative to the motor housing (28) during operation of the drilling motor (26).

Referring to FIG. 3 and FIG. 4, longitudinal section views are provided of the steering tool (20) configured as a component of a drilling motor (26), taken along the section lines indicated in FIG. 2. As depicted in FIG. 3 and FIG. 4, the steering tool (20) is incorporated into the drilling motor (26) below the transmission section (not shown) of the drilling motor (26).

The steering tool is comprised of a tubular housing (36), a tool actuating device (38), a plurality of hydraulically actuated steering devices (40), and a hydraulic control system (42). The housing (36) has an upper end (44) and a lower end (46).

The upper end (44) of the housing (36) is adapted to provide a lower continuation of the motor housing (28). The housing (36) may be comprised of a single piece, but in the preferred embodiment the housing (36) is comprised of a plurality of sections connected together. The housing (36) may be formed with the motor housing (28) or may be otherwise connected with the motor housing (28).

In FIG. 3, the upper end (44) of the housing (36) is depicted as providing a threaded connection to the motor housing (28). The motor housing (28) is not depicted in FIG. 3.

The housing (36) has an interior (48), an exterior (50), and defines a housing bore (52). A shaft (54) extends through the housing bore (52) from the upper end (44) to the lower end (46) of the housing (36). The shaft (54) is adapted to provide a lower continuation of the motor drive shaft (30). The shaft (54) may be formed with the motor drive shaft (30) or may be otherwise connected with the motor drive shaft (30).

In FIG. 3, the shaft (54) at the upper end (44) of the housing (36) is depicted as providing a threaded connection to the motor drive shaft (30). The motor drive shaft (30) is not depicted in FIG. 3.

The shaft (54) extends from the lower end (46) of the housing (36). A drill bit (24) is connected to the shaft (54) adjacent to the lower end (46) of the housing (36).

The shaft (54) defines a shaft bore (55) for conducting drilling fluid (not shown) through the steering tool (20). A small amount of drilling fluid may also pass through the housing bore (52) in order to provide lubrication for some components of the steering tool (20). Portions of the interior (48) of the housing (36) are isolated from the exterior (50) of the housing (36) and from the housing bore (52) by seals positioned along the length of the housing (36).

The interior (48) of the housing (36) defines two compartments which are also isolated from each other. A first compartment (56) contains the tool actuating device (38). A second compartment (58) provides the hydraulic control system (42).

The tool actuating device (38) is comprised of a pendulum (60). The first compartment (56) is therefore comprised of a pendulum chamber (62). A proximal end (64) of the pendulum (60) is pivotably supported in the interior (48) of the housing (36) by a universal joint (66) which comprises two hinges located in perpendicular planes. The pendulum (60) pivots about the universal joint (66) in order to provide a pivoting movement as an actuating movement for actuating the steering devices (40).

In the preferred embodiment, the pendulum (82) is supported concentrically within the housing (36) so that the axis of the pendulum (36) is parallel with the axis of the housing (36) when the housing (36) is at a vertical orientation.

The pendulum (60) is comprised of a tubular member which is contained in the interior (48) of the housing so that it surrounds the housing bore (52). A plurality of carbide rings (68) are mounted on the pendulum (60) adjacent to a distal end (70) of the pendulum. The carbide rings (68) provide additional weight for the pendulum (60) to shift its center of gravity toward the distal end (70) and to increase an actuating force which is associated with the pivoting movement of the pendulum (60).

The pendulum chamber (62) is filled with a viscous medium (not shown) which provides viscous damping of the pivoting movement of the pendulum (60). In the preferred embodiment the viscous medium is comprised of a relatively high viscosity hydraulic oil such as, for example, Mobil (™) SHC 639 lubricant.

The purpose of the hydraulic control system (42) is to convert the actuating movement of the pendulum (60) to independent actuation of the steering devices (40) between a retracted position and an extended position. The hydraulic control system (42) is comprised of a pressurization device (72), a reservoir (74) and a plurality of valve mechanisms (76).

The steering tool (20) is further comprised of a hydraulic fluid (not shown) for use in the hydraulic control system (42) in order to actuate the steering devices (40). In the preferred embodiment the hydraulic fluid is comprised of a relatively low viscosity hydraulic oil such as, for example, Mobil (™) SHC 624 lubricant.

Details of aspects of the hydraulic control system (42), including the pressurization device (72), the reservoir (74) and the valve mechanisms (76), are depicted in FIG. 3. Further details of aspects of the hydraulic control system (42) are also depicted in FIGS. 6-12, which provide longitudinal section views taken along the section lines indicated in FIG. 5.

The number of valve mechanisms (76) is equal to the number of steering devices (40) so that each of the valve mechanisms (76) is associated with the pendulum (60) and with one of the steering devices (40).

In the preferred embodiment the steering tool (20) includes four steering devices (40) and thus also includes four valve mechanisms (76). The four steering devices (40) are circumferentially spaced evenly about the exterior of the housing (36) so that their centerlines are separated by ninety degrees.

Referring to FIG. 3 and FIG. 6, each of the valve mechanisms (76) is comprised of a valve (78) and a mechanical valve actuator (80). Each of the mechanical valve actuators (80) is comprised of an actuating lever (82). The actuating levers (82) are located in the interior (48) of the housing (36), are circumferentially spaced evenly about the interior (48) of the housing (36) so that their centerlines are separated by ninety degrees, and are located adjacent to the distal end (70) of the pendulum (60) so that they may be moved by the pivoting movement of the pendulum (70).

Although the centerlines of the actuating levers (82) are separated by ninety degrees, the actuating levers (82) each extend circumferentially about the interior of the housing (36) for about sixty degrees, with the result that a space of about thirty degrees separates the peripheral edges of the actuating levers (82) in the preferred embodiment.

Referring to FIG. 3 and FIG. 6, the actuating levers (82) pivot about a pivot point (84). In the preferred embodiment the actuating levers (82) are constructed of aluminum to reduce their weight and to minimize the centrifugal forces which are generated by the actuating levers (82) during rotation of the steering tool (20). The actuating levers (82) also include a counterweight (86) so that the actuating levers (82) are substantially balanced about the pivot point (84), thus reducing the tendency for the actuating levers (82) to pivot during rotation of the steering tool (20).

The actuating levers (82) are capable of being moved by the pendulum (70) between a first actuator position and a second actuator position. When the actuating levers (82) are in the first actuator position, their associated steering devices (40) are actuated to the retracted position. When the actuating levers (82) are in the second actuator position, their associated steering devices (40) are actuated to the extended position.

When the housing (36) is at a vertical orientation, with the result that the pendulum (70) is oriented so that its axis is parallel with the axis of the housing (36), the actuating levers (82) are all in the first actuator position. As a result, when the housing (36) is at a vertical orientation, all of the steering devices (40) are actuated to the retracted position.

When the housing (36) is at an orientation which deviates from the vertical orientation, with the result that the pendulum (70) is oriented so that its axis is not parallel with the axis of the housing (36), one or two of the actuating levers (82) are moved from the first actuator position toward the second actuator position. As a result, when the housing (36) is at an orientation which deviates from the vertical orientation, one or two of the steering devices (40) is actuated to the extended position.

In the preferred embodiment, a deviation of the housing (36) of at least about 0.183 degrees from a vertical orientation will result in one or two of the actuating levers (82) being moved to the second actuator position, thus causing full actuation of the steering tool (20).

The steering devices (40) and their associated mechanical valve actuators (80) are circumferentially offset from each other by substantially 180 degrees, with respect to the centerlines of the steering devices (40) and the mechanical valve actuators (80).

Movement of one of the actuating levers (82) from the first actuator position toward the second actuator position results in the operation of its associated valve (78) in order to provide communication between the pressurization device (72) and the steering device (40) which is associated with the particular valve mechanism (76).

In the preferred embodiment, the hydraulic control system (42) is a “single-acting” hydraulic system which includes only a single communication path between the valve (78) and its associated steering device (40). As a result, the steering devices (40) in the preferred embodiment of the hydraulic control system (42) are actively actuated to the extended position but are passively actuated back to the retracted position.

As depicted in FIG. 3 and FIG. 6, each valve (78) is a single shuttle valve which includes a valve body (98) which reciprocates between seating against a pressurized hydraulic fluid port (100) and a reservoir port (102) in response to movement of the mechanical valve actuator (80). When the mechanical valve actuator (80) is in the first actuator position, the valve body (98) is seated against the pressurized hydraulic fluid port (100) so that the steering device (40) communicates via a steering device port (104) only with the reservoir (74) via the reservoir port (102). When the mechanical valve actuator (80) is in the second actuator position, the valve body (98) is seated against the reservoir port (102) so that the steering device (40) communicates via the steering device port (104) only with the pressurization device (72) via the pressurized hydraulic fluid port (100). When the mechanical valve actuator (80) is between the first actuator position and the second actuator position, the valve body (98) is not seated against either port (100,102), with the result that the steering device (40) communicates via the steering device port (104) with both the reservoir (74) and the pressurization device (72).

Grooves or channels in the components of the housing (36) provide conduits between the ports (100,102,104) and the pressurization device (72), the reservoir (74) and the steering devices (40) respectively.

The hydraulic control system (42) of the preferred embodiment is depicted schematically in FIG. 13. In FIG. 14, an alternate embodiment of the hydraulic control system (42) is depicted schematically.

In the alternate embodiment of the hydraulic control system (42) depicted in FIG. 14, the hydraulic control system (42) is a “double-acting” hydraulic system which includes two communication paths between the valve (78) and its associated steering device (40). As a result, the steering devices (40) in the alternate embodiment of the hydraulic control system (42) are actively actuated to both the extended position and the retracted position.

In the alternate embodiment of the hydraulic control system (42) depicted in FIG. 14, each valve (78) is preferably comprised of a valve with four ports, such as a single spindle valve, in which the valve body (98) reciprocates between positions in which different combinations of pairs of ports are in communication with each other in response to movement of the mechanical valve actuator (80).

In the alternate embodiment, when the mechanical valve actuator (80) is in the first actuator position, the steering device (40) communicates via a first steering device port (110) with the reservoir (74) via a reservoir port (112) and the steering device (40) communicates via a second steering device port (114) with the pressurization device (72) via a pressurized hydraulic fluid port (116). When the mechanical valve actuator (80) is in the second actuator position, the steering device (40) communicates via the first steering device port (110) with the pressurization device (72) via the pressurized hydraulic fluid port (116) and the steering device (40) communicates via the second steering device port (114) with the reservoir (74) via the reservoir port (112).

Grooves or channels in the components of the housing (36) provide conduits between the ports (110,114) and the steering devices (40) and between the ports (112,116) and the reservoir (74) and the pressurization device (72) respectively.

In all embodiments of the hydraulic control system (42), each of the valves (78) is preferably comprised of a device which is not pressure dependent in its operation. For example, a shuttle valve, in which the ends of the valve body engage the ports in order to seat the valve body, may be advantageous due to its simplicity. However, a shuttle valve is also pressure dependent in its operation because the pressures at the pressurized hydraulic fluid port (100) and the reservoir port (102) act on the valve body (98) in directions which are parallel to the reciprocation of the valve body (98).

In contrast, a spindle valve, in which the ports are arranged along the sides of the valve body and the valve body includes one or more grooves or necks to allow fluid to pass by the valve body, is not pressure dependent in its operation because the pressures at the pressurized hydraulic fluid port (100) and the reservoir port (102) act on the valve body (98) in directions which are perpendicular to the reciprocation of the valve body (98). As a result, although shuttle valves are depicted as the valves (78) in the preferred embodiment, spindle valves may be more preferred if pressure dependency of the valves (78) is to be avoided.

Referring to FIG. 3 and FIG. 6, each of the valve mechanisms (76) is further comprised of a valve mechanism biasing device (120) for biasing the mechanical valve actuator (80) toward the first actuator position. In the preferred embodiment the valve mechanism biasing device (120) is comprised of a spring (122) which is associated with the shuttle valve.

Referring to FIG. 3 and FIG. 6, each of the valve mechanisms (76) is further comprised of a mechanical actuator dampening mechanism (130) for dampening the movement of the mechanical valve actuator (80). In the preferred embodiment, the mechanical actuator dampening mechanism (130) is comprised of a fluid metering device (132) which is operably connected with the mechanical valve actuator (80). The fluid metering device (132) is comprised of a dampening cylinder (134) and a metering piston (136) reciprocably contained in the dampening cylinder (134) so that the dampening cylinder (134) is divided into a first chamber (138) and a second chamber (140). The metering piston (136) is undersized relative to the dampening cylinder (134) so that a restricted flowpath (142) is provided between the first chamber (138) and the second chamber (140) as the metering piston (136) reciprocates relative to the dampening cylinder (134) as a result of movement of the mechanical valve actuator (80).

The pressurization device (72) draws the hydraulic fluid from the reservoir (74) in order to provide a supply of pressurized hydraulic fluid. As a result, the reservoir (74) is designed to have a reservoir pressure which is lower than a pressure of the pressurized hydraulic fluid which is provided by the pressurization device (72).

In the preferred embodiment, the pressurization device (72) is comprised of a swash plate pump (150). Referring to FIGS. 3-4 and FIGS. 15-16, the swash plate pump (150) is comprised of a swash plate (152) and a cylinder (154) which are associated with the shaft (54) and the housing (36) respectively.

The swash plate (152) is connected with the shaft (54) so that the swash plate (152) rotates with the shaft (54). As depicted in FIGS. 3-4 and FIG. 16, the swash plate (152) is fixedly connected with the shaft (54) so that the swash plate (152) moves axially with the shaft (54). More preferably, however, the swash plate (152) is connected with the shaft (54) using splines (not shown) so that the swash plate (152) can move axially relative to the shaft (152) in order to compensate for wear in the steering tool (20) which may cause the shaft (54) to move axially relative to the cylinder (154).

The cylinder (154) is fixed to the housing (36) so that the swash plate (152) rotates relative to the cylinder (154) as the shaft (54) rotates. The cylinder (154) is comprised of an array of piston assemblies (156) which are spaced circumferentially around the cylinder (154). Each of the piston assemblies (156) is comprised of a piston (158) and a reciprocable actuator surface (160) which is associated with the piston (158) for causing reciprocation of the piston (158).

Referring to FIGS. 3-4 and FIGS. 6-7, each of the pistons (158) is contained in a pumping chamber (162) so that the piston (158) may reciprocate in the pumping chamber (162) in order to pressurize the hydraulic fluid and provide the pressurized hydraulic fluid. A spring (163) is provided in the pumping chamber (162) to bias the piston (158) and the actuator surface (160) toward the swash plate (152).

The swash plate pump (150) is further comprised of a pump inlet (164) which communicates with the reservoir (74) and a pump outlet (166) which communicates with the valve (78) via the pressurized hydraulic fluid port (100). A filter (168) is provided at the pump outlet (166) to filter the hydraulic fluid which is delivered by the swash plate pump (150) to the pressurized hydraulic fluid port (100). The pump inlet (164) and the pump outlet (166) are both provided with pump check valves (170) which are biased toward a seated position by springs.

Referring to FIGS. 3-4 and FIGS. 15-16, the swash plate (152) is comprised of an angled profile. The swash plate pump (150) is further comprised of a stationary plate (172) which is rotatably and pivotably connected by a bearing (174) with the angled profile on the swash plate (152). The stationary plate (172) is connected with the housing (36) so that the stationary plate (174) does not rotate relative to the housing (36).

The stationary plate (174) defines a plurality of engagement surfaces (176) for engaging the actuator surfaces (160) as the actuator surfaces (160) are biased toward the stationary plate (174). In the preferred embodiment the engagement surfaces (176) are comprised of dimples or depressions which are complementary to the actuator surfaces (160).

During rotation of the swash plate (152) with the shaft (54), the stationary plate (172) does not rotate, but pivots as it follows the angled profile of the swash plate (152). The actuator surfaces (160) remain in engagement with the engagement surfaces (176) on the stationary plate, causing the pistons (158) to reciprocate in the pumping chambers (162), thus causing the hydraulic fluid to be drawn from the reservoir (74) and pressurized by the swash plate pump (150) to provide the pressurized hydraulic fluid.

The swash plate (152), the stationary plate (172) and the bearing (174) are lubricated by drilling fluid which passes through the housing bore (52) between the housing (36) and the shaft (54).

Referring to FIG. 7 and FIG. 8, the hydraulic control system (42) is further comprised of a first pressure relief valve (180) which is set using a first biasing spring (182) at a first threshold pressure and a second pressure relief valve (184) which is set using a second biasing spring (186) at a second threshold pressure. The pressure relief valves (180,182) are located between the swash plate pump (150) and the valves (78) and communicate with the reservoir (74) when their threshold pressures are exceeded due to excessive resistance or blockage between the swash plate pump (150) and the steering devices (40). In the preferred embodiment the pressure relief valves (180,184) are set at a pressure of about 850 psi (or about 5860 kPa) and about 1250 psi (or about 8620 kPa).

Referring to FIG. 4, in the preferred embodiment each of the steering devices (40) is comprised of four steering pistons (190) which hydraulically communicate with each other so that the steering pistons (190) are simultaneously actuatable in order to actuate the steering device (40) between the retracted position and the extended position.

Referring to FIGS. 3-4 and FIGS. 6-12, in the preferred embodiment the steering pistons (190) are hydraulically connected with the valve (78) via a conduit comprising grooves or channels formed in the housing (36).

Referring to FIG. 4, each of the steering pistons (190) is contained in a steering piston cylinder (192) so that the steering pistons are hydraulically connected with the valve (78) via the steering piston cylinders (192). Since the hydraulic control system (42) in the preferred embodiment is comprised of a single-acting hydraulic system, only one side of the steering pistons (190) is hydraulically connected with the valve (78).

Consequently, movement of one of the mechanical valve actuators (80) from the first actuator position to the second actuator position results in its associated steering pistons (190) communicating with the pressurized hydraulic fluid via the steering piston cylinders (192), which in turn results in the steering pistons (190) extending outward from the housing (36) as the steering piston cylinders (192) fill with the pressurized hydraulic fluid from the swash plate pump (150). Conversely, movement of the mechanical valve actuator (80) from the second actuator position to the first actuator position results in the steering pistons (190) communicating with the reservoir (74), which in turn results in the steering pistons (190) retracting inward toward the housing (36) as the pressurized hydraulic fluid drains from the steering piston cylinders (192) back to the reservoir (74).

In the preferred embodiment, and referring to FIG. 4, each of the steering devices (40) is comprised of a steering device biasing mechanism (194) which biases the steering devices (40) toward the retracted position. Each steering device biasing mechanism (194) is comprised of steering device biasing springs (196) which are contained in the steering piston cylinders (192) and which engage the steering pistons (190) to urge them inward.

Referring to FIG. 14, in the alternate embodiment in which the hydraulic control system (42) is a double-acting hydraulic system, both sides of the steering pistons (190) are hydraulically connected with the valve (78) via separate conduits comprising grooves or channels in the housing (36).

Consequently, movement of one of the mechanical valve actuators (80) from the first actuator position to the second actuator position results in the steering pistons (190) extending outward from the housing (36) as the steering piston cylinders (192) on a first side of the steering pistons (190) fill with the pressurized hydraulic fluid from the swash plate pump (150) and the steering piston cylinders (192) on a second side of the steering pistons (190) drain the pressurized hydraulic fluid back to the reservoir (74). Conversely, movement of the mechanical valve actuator (80) from the second actuator position to the first actuator position reverses the process so that the steering piston cylinders (192) on the first side of the steering pistons (190) drain the pressurized hydraulic fluid back to the reservoir (74) while the steering piston cylinders (192) on the second side of the steering pistons (190) fill with pressurized hydraulic fluid from the swash plate pump (150).

In the preferred embodiment each of the steering devices (40) is further comprised of a steering blade (198). Referring to FIGS. 17-19, each of the steering blades (198) is comprised of a steering blade core (200) having a honeycomb structure and constructed of aluminum and each of the steering blades (198) is further comprised of a steering blade cover (202) constructed of hard-faced steel. The steering blade cover (202) fits over the steering blade core (202) in order to protect the steering blade core (202).

The steering blade core (200) and the steering blade cover (202) are both connected with each of the steering pistons (190) by bolts which are accessible from the exterior (50) of the housing (36) without disassembling the steering tool (20).

The steering blades (198) are retained in a steering blade cavity (204) which is formed in the exterior (50) of the housing (36) by two blade stop members (206) which are located at both ends of the steering blade (198). Each of the blade stop members (206) is connected with the housing by a bolt which is accessible from the exterior (50) of the housing (36) without disassembling the steering tool (20).

Referring to FIG. 3, the hydraulic control system (42) is further comprised of a hydraulic fluid pressure balancing mechanism (220) for transmitting a first ambient pressure to the hydraulic fluid at a first pressure balancing position (222) on the exterior (50) of the housing (36). The hydraulic fluid pressure balancing mechanism (220) is comprised of a hydraulic fluid balancing piston (224) contained in a hydraulic fluid balancing cylinder (226). A hydraulic fluid balancing port (228) is located in the exterior (50) of the housing (36) at the first pressure balancing position (222).

Also referring to FIG. 3, the steering tool (20) is also further comprised of a viscous medium pressure balancing mechanism (230) for transmitting a second ambient pressure to the viscous medium contained in the pendulum chamber (62) at a second pressure balancing position (232) on the exterior (50) of the housing (36). The viscous medium pressure balancing mechanism (230) is comprised of a viscous medium balancing piston (234) contained in a viscous medium balancing cylinder (236). A viscous medium balancing port (238) is located in the exterior (50) of the housing (36) at the first pressure balancing position (232).

In the preferred embodiment, the first pressure balancing position (222) and thus the hydraulic fluid balancing port (228) are located between the steering devices (40) and the lower end (46) of the housing (36). The second pressure balancing position (232) and thus the viscous medium balancing port (238) are located between the upper end (44) of the housing (36) and the steering devices (40).

The first ambient pressure at the first pressure balancing position (222) is likely to be greater than the second ambient pressure at the second pressure balancing position (232) during the operation of the steering tool (20). In addition, in the event that the steering devices (40) effectively “pack-off” a borehole during use of the steering tool, a large pressure spike may occur at the first pressure balancing position (222).

In the preferred embodiment, the hydraulic control system (42) is therefore further comprised of an emergency relief valve (240) which is connected between the hydraulic control system (42) and the pendulum chamber (62) such that the hydraulic control system (42) communicates with the pendulum chamber (62) when the emergency relief valve (240) is in an open position., thereby releasing an amount of the hydraulic fluid from the hydraulic control system (42) to the pendulum chamber (62). In the preferred embodiment the emergency relief valve (240) is set to about 2000 psi or about 13800 kPa.

Referring to FIG. 3, in the preferred embodiment, the steering tool (20) is further comprised of a stabilizer (250) on the exterior (50) of the housing (36). In the preferred embodiment, the stabilizer (250) is located between the upper end (44) of the housing (36) and the steering devices (40).

The stabilizer (250) is comprised of a plurality of stabilizer blades (252) circumferentially spaced about the exterior (50) of the housing (36). The stabilizer blades (252) are removable from the housing (36) without disassembling the steering tool (20).

Each of the stabilizer blades (252) is retained in a stabilizer blade cavity (254) in the exterior (50) of the housing (36) by a stabilizer retaining ring (256) which is positioned at one end of the stabilizer blade (252). Each of the stabilizer blades (252) is further retained in the stabilizer blade cavity (254) by a combination, at the other end of the stabilizer blade (252), of an undercut (258) formed in the stabilizer blade (252) and an overcut (260) formed in the stabilizer blade cavity (254).

The stabilizer blades (252) are installed in the steering tool (20) by first inserting each of the stabilizer blades (252) in their respective stabilizer blade cavities (254) so that the undercuts (258) engage the overcuts (260), and then the stabilizer retaining ring is tightened over all of the stabilizer blades (252) to hold the stabilizer blades (252) in the stabilizer blade cavity (254).

Referring to FIG. 3, the steering tool (20) is further comprised of a thrust bearing assembly (270) for transmitting axial loads from the drill bit (24) and the shaft (54) to the housing (36) so that the axial loads do not pass through the rotor (not shown) of the drilling motor (26). In embodiments of the steering tool (20) in which the steering tool (20) is adapted to be connected with the drilling motor (26) as a separate tool or component, the thrust bearing assembly (270) may be provided by the drilling motor (26). The thrust bearing assembly (270) is lubricated by drilling fluid which passes through the housing bore (52) between the housing (36) and the shaft (54).

Referring to FIG. 3, the steering tool (20) is also further comprised of an upper radial bearing (272), an intermediate radial bearing (274) and a lower radial bearing (276) for radially supporting the shaft (54) within the housing (36). In the preferred embodiment, the radial bearings (272,274,276) are relatively close fit bearings which allow very little radial movement of the shaft (54) relative to the housing (36), thus maximizing the effectiveness of the steering devices (40) in pushing the housing (36) back toward the target orientation when the steering devices are actuated to the extended position. The radial bearings (272,274,276) are lubricated by drilling fluid which passes through the housing bore (52).

In order to provide adequate flow of drilling fluid past the radial bearings (272,274,276), the radial bearings are comprised of helical flutes (not shown) which provide helical channels for drilling fluid to pass through, while still providing for close contact between the bearings (272,274,276) and the shaft (54). The helical design of the flutes ensures contact between the bearings (272,274,276) and the shaft (54) regardless of the relative positions of the shaft (54) and the bearings (272,274,276), since the flutes are sequentially and continuously moving into and out of contact with the shaft (54).

In the preferred embodiment, the mating surfaces of the radial bearings (272,274,276) are comprised of press fit carbide sleeves which provide a long wear life and which are also easily replaceable. In the preferred embodiment, the helical flutes are configured as left hand helixes in order to prevent contaminates contained in the drilling fluid from threading into the flutes during rotation of the shaft (54) and thereby causing torque or damage to the steering tool (20) or seizure of the shaft (54).

In use of the preferred embodiment, the steering tool (20) is incorporated into the drill string (22) so that the steering tool (20) is between the power section (not shown) of the drilling motor (26) and the drill bit (24).

In the preferred embodiment, the drill string (22), including the steering tool (20) and the drilling motor (26), are not typically rotated during drilling. Instead, the drill bit (24) is rotated by the drilling motor (26).

The axis of the pendulum (60) will remain substantially parallel with the axis of the housing (36) as long as the housing (36) remains in a vertical orientation as the target orientation. As a result, the four actuating levers (82) remain in the first actuator position and the steering devices (40) remain in the retracted position.

Minor pivoting movement of the pendulum (60) due to vibration or transient deviations of the housing (36) is dampened by the viscous medium contained in the pendulum chamber (62) and by the mechanical actuator dampening mechanism (130).

If the housing (36) begins to deviate from the vertical orientation, the pendulum (60) will pivot in the pendulum chamber (62), thus providing an actuating movement in the direction of the pivoting movement. The actuating movement is accompanied by an actuating force due to the weight of the pendulum (60).

The distal end (70) of the pendulum (60) will engage one or two of the four actuating levers (82) and the actuating movement will move the engaged actuating levers (82) from the first actuator position toward the second actuator position once the actuating force is sufficient to overcome any resistance to movement of the engaged actuating levers (82) due to friction and/or due to the valve mechanism biasing device (120).

Movement of the engaged actuating levers (82) toward the second actuator position will cause operation of the valves (78) which are associated with the engaged actuating levers (82).

In the preferred embodiment as depicted in FIG. 3 and FIG. 6 where the valves (78) are shuttle valves, the valve bodies (98) will remain seated in the pressurized hydraulic fluid ports (100) as long as the engaged actuating levers (82) remain in the first actuator position, with the result that the steering devices (40) associated with the engaged actuating levers (82) are in communication only with the reservoir (74). Slight movement of the engaged actuating levers (82) toward the second actuator position will unseat the valve bodies (98) from the pressurized hydraulic fluid ports (100), thereby establishing some communication between the pressurized hydraulic fluid provided by the swash plate pump (150) and the steering devices (40), while maintaining some communication between the reservoir (74) and the steering devices (40). Pivoting movement of the pendulum (60) which reflects a deviation of the housing (36) from the vertical orientation of about 0.183 degrees or more will provide an actuating movement which is sufficient to move the engaged actuating levers (82) to the second actuator position. At the second actuator position, the valve bodies (98) of the shuttle valve will seat in the reservoir ports (102) of the valves (78), thereby eliminating communication between the reservoir (74) and the steering devices (40) while establishing full communication between the pressurized hydraulic fluid provided by the swash plate pump (150) and the steering devices (40).

The steering devices (40) will be actuated to the extended position due to the communication between the pressurized hydraulic fluid provided by the swash plate pump (150) and the steering devices (40). In the preferred embodiment where the valves (74) are shuttle valves, the steering devices (40) will become actuated to the extended position as the actuating levers (82) are moved closer to the second actuator position, as the communication between the pressurized hydraulic fluid and the steering devices (40) becomes proportionately greater and the communication between the reservoir (74) and the steering devices (40) becomes proportionately less, due to movement of the valve bodies (98) between the pressurized hydraulic fluid port (100) and the reservoir port (102).

When the engaged actuating levers (82) are relatively close to the first actuator position, the steering devices (40) may remain actuated at the retracted position. When the engaged actuating levers (82) are relatively close to the second actuator position, the steering devices (40) may become actuated tot the extended position relatively quickly. The actuation of the steering devices (40) to the extended position will be opposed by the biasing forces provided by the steering device biasing mechanisms (194) and by any external forces which may be exerted on the steering devices (40) by the borehole or some other source.

The swash plate pump (150) operates continuously as long as the shaft (54) is rotating due to operation of the drilling motor (26). As a result, where the pumping rate of the swash plate pump (150) exceeds the extent to which the pressurized hydraulic fluid may be communicated to the steering devices (40), the pressurized hydraulic fluid is returned to the reservoir (74) via one or both of the pressure relief valves (180,184).

The engaged actuating levers (82) and their associated steering devices (40) are offset by substantially 180 degrees. As a result, pivoting of the pendulum (60) toward the “low side” of the steering tool (20) will result in the steering devices (40) at the “high side” of the steering tool to become actuated to the extended position in order to push the housing (36) back toward the vertical orientation.

As the housing (36) moves back toward the vertical orientation, the pendulum (60) pivots back toward the position where the axis of the pendulum (60) is substantially parallel to the axis of the housing (36). An actuating movement of the pendulum (60) is therefore generated which allows the engaged actuating levers (82) to move back toward the first actuator position.

As the engaged actuating levers (82) move back toward the first actuator position, the communication between the pressurized hydraulic fluid and the steering devices (40) lessens and communication between the reservoir (74) and the steering devices (40) is established and/or is increased. As the engaged actuating levers (82) move closer to the first actuator position, the steering devices (40) will become actuated to the retracted position, assisted by the biasing force of the steering device biasing mechanism (194) and by any external forces exerted on the steering devices (40).

As a result, it may be seen that the steering tool (20) in the preferred embodiment is configured so that inadvertent actuation of the steering devices (40) to the extended position is minimized, due to the dampening effect of the viscous medium in the pendulum chamber (62), the dampening effect of the mechanical actuator dampening mechanism (130), the biasing effects of the steering device biasing mechanisms (194), and the configuration of the actuating levers (82) and the valves (74), which configuration effectively limits actuation of the steering devices (40) to the extended position unless the actuating levers (82) are moved significantly toward the second actuator position.

In the event that the drill string (22) is rotated in order to perform rotary drilling with the drill string (22), the steering devices (40) will be inhibited from actuating or moving to the extended position due to their reduced weight (which limits centrifugal forces), due to the biasing effects of the steering device biasing mechanisms (194), and due to the relative light weight and substantial balancing of the actuating levers (82).

In addition, in the preferred embodiment the actuating levers (82) each extend circumferentially about the interior of the housing (36) for about sixty degrees, with the result that a space of about thirty degrees separates the peripheral edges of the actuating levers (82). As a result, during rotation of the drill string (22) during rotary drilling, the actuating levers (82) are in the second actuator position for less than half of each rotation of the drill string (22), regardless of the orientation of the housing (36). The steering devices (40) therefore have more opportunity to move to the retracted position than to the extended position during rotation of the drill string (22).

Referring to FIG. 1(b), in a second configuration the steering tool (20) is adapted as a component of a rotary steerable drilling system (32). In this second configuration, the housing (36) may be connected with a drill string (22) with suitable bearings (not shown) so that the drill string (22) provides the shaft (54). The pressurization device (72) may be comprised of the swash plate pump (150), which may be associated with both the drill string (22) and the housing (36) in a similar manner as in the preferred embodiment. Alternatively, the pressurization device (72) may be comprised of a different type of pump or may be comprised of a system for using the pressure of drilling fluid in order to actuate the steering devices (40).

In the second configuration, a borehole engaging device (34) may be associated with the housing (36) in order to inhibit the housing (36) from rotating with the drill string (22) as the drill string (22) during drilling. In the second configuration, drilling fluid may be passed through the drill string (22) in order to circulate the drilling fluid through the steering tool (20), and a small amount of drilling fluid may be permitted to pass between the drill string (22) and the housing (36) in order to lubricate components of the steering tool (20).

The second configuration of the steering tool (20) may otherwise be configured and operated in a similar manner as the steering tool (20) described in the preferred embodiment.

Referring to FIG. 1(c), in a third configuration the steering tool (20) is adapted as a component of a fully rotating rotary steerable drilling system (32) of the type in which a steering mechanism is connected with the drill string (22) so that the steering mechanism rotates with the drill string (22) during rotary drilling.

In this third configuration, the tool actuating device (38), the steering devices (40) and the hydraulic control system (42) are configured so that the steering devices (40) are capable of actuating between the retracted position and the extended position in synchronization with the rotation of the drill string (22) so that the steering devices (40) are actuated substantially at the same rotational position during rotation of the drill string (22) in order to move the housing (36) back toward the target orientation.

In this third configuration, a shaft (54) may or may not be provided for the steering tool (20). A shaft (54) may be provided by a drilling motor (not shown) which is incorporated into the drill string (22) or by a member (not shown) which is contained within the housing bore (52). The purpose of the shaft (54) may be to provide a rotary movement to power a pump in similar manner as described in the preferred embodiment. Alternatively, the pressurization device (72) may be comprised of a different type of pump or may be comprised of a system for using the pressure of drilling fluid in order to actuate the steering devices (40).

Drilling fluid may be passed through the housing bore (52) in order to circulate the drilling fluid through the steering tool (20). Alternatively or additionally, if a shaft (54) is provided in the steering tool (20), the drilling fluid may be passed through the shaft bore (55).

In the third configuration, it may be necessary to provide modifications to the preferred embodiment of the steering tool (20) so that the steering devices (40) are capable of being actuated quickly enough to provide synchronization with the rotation of the drill string (22). As a first example, the dampening effects of the viscous medium in the pendulum chamber (62) and the mechanical actuator dampening mechanism (130) may be reduced. As a second example, the flowrates of hydraulic fluid to and from the steering devices (40) may be increased by increasing the size of the conduits amongst the pressurization device (72), the reservoir (74), and the steering devices (40). As a third example, the pumping rate of the pressurization device (72) may be increased. As a fourth example, a double-acting hydraulic system may be utilized. As a fifth example, a tool actuating device (38) which has a shorter natural frequency than the pendulum (60) of the preferred embodiment may be used.

Finally, in any of the configurations of the steering tool (20), the steering tool (20) may provide a vertical orientation as the target orientation or may provide some other orientation as the target orientation. If the target orientation is not a vertical orientation, the orientation of the tool actuating device (38) in the housing (36) may be altered to reflect the target orientation. Alternatively or additionally, the mechanical valve actuators (80) may be configured so that the first actuator position and the second actuator position are provided with reference to the target orientation.

If the target orientation is not a vertical orientation, the steering tool (20) or the drill string (22) may be further comprised of a surveying system (not shown) for determining the orientation of the steering tool (20) relative to a reference orientation so that the target orientation of the steering tool (20) has a reference.

Furthermore, in any of the configurations of the steering tool (20), the drill string (22) may be further comprised of any suitable drilling equipment and drilling tools for use in association with the drill string (22) and/or in association with any components of the drill string (22), including the steering tool (20).

Claims

1. A steering tool for use in drilling a borehole, comprising: (a) a tubular housing, the housing having an interior, an exterior, and defining a housing bore;(b) a tool actuating device movably supported within the interior of the housing, the tool actuating device being capable of an actuating movement relative to the housing;(c) a plurality of hydraulically actuated steering devices circumferentially spaced about the exterior of the housing, the steering devices being independently actuatable between a retracted position and an extended position as a result of the actuating movement of the tool actuating device; and(d) a hydraulic control system contained within the interior of the housing and operably interposed between the tool actuating device and the steering devices, for converting the actuating movement of the tool actuating device to independent actuation of the steering devices between the retracted position and the extended position.

2. The steering tool as claimed in claim 1, further comprising a hydraulic fluid for use in the hydraulic control system in order to actuate the steering devices, wherein the hydraulic fluid is isolated from other fluids.

3. The steering tool as claimed in claim 2 wherein the hydraulic fluid is comprised of a hydraulic oil.

4. The steering tool as claimed in claim 2 wherein the hydraulic control system is comprised of a pressurization device for pressurizing the hydraulic fluid to provide a supply of pressurized hydraulic fluid.

5. The steering tool as claimed in claim 4 wherein the steering tool is configured so that each of the steering devices is actuated to the retracted position when the housing is at a target orientation.

6. The steering tool as claimed in claim 4, further comprising a shaft extending through the housing bore, the shaft being capable of a drilling movement relative to the housing.

7. The steering tool as claimed in claim 6 wherein the shaft defines a shaft bore for conducting a drilling fluid through the steering tool.

8. The steering tool as claimed in claim 7 wherein the pressurization device is comprised of a pump and wherein the pump is associated with both the housing and the shaft.

9. The steering tool as claimed in claim 8 wherein the drilling movement of the shaft is a rotary movement and wherein the pump is comprised of a swash plate pump.

10. The steering tool as claimed in claim 4 wherein the hydraulic control system is comprised of a plurality of valve mechanisms, wherein each of the valve mechanisms is associated with the tool actuating device and with one of the steering devices, and wherein each of the valve mechanisms is capable of selectively providing communication of its associated steering device with the pressurized hydraulic fluid as a result of the actuating movement of the tool actuating device.

11. The steering tool as claimed in claim 10 wherein each of the valve mechanisms is comprised of a mechanical valve actuator for the valve mechanism, wherein the mechanical valve actuators are located in the interior of the housing, wherein the mechanical valve actuators are circumferentially spaced about the interior of the housing, and wherein the mechanical valve actuators are located adjacent to the tool actuating device so that they may be moved by the actuating movement of the tool actuating device.

12. The steering tool as claimed in claim 11 wherein the mechanical valve actuators are capable of movement by the tool actuating device between a first actuator position and a second actuator position and wherein the steering tool is configured so that each of the steering devices is actuated to the retracted position when its associated mechanical valve actuator is in the first actuator position and so that each of the steering devices is actuated to the extended position when its associated mechanical valve actuator is in the second actuator position.

13. The steering tool as claimed in claim 12 wherein the hydraulic control system is further comprised of a reservoir for the hydraulic fluid and wherein the reservoir has a reservoir pressure which is lower than a pressure of the pressurized hydraulic fluid.

14. The steering tool as claimed in claim 13 wherein each of the steering devices is in communication only with the reservoir when its associated mechanical valve actuator is in the first actuator position and wherein each of the steering devices is in communication only with the pressurized hydraulic fluid when its associated mechanical valve actuator is in the second actuator position.

15. The steering tool as claimed in claim 13 wherein the pressurization device draws the hydraulic fluid from the reservoir in order to provide the supply of the pressurized hydraulic fluid.

16. The steering tool as claimed in claim 13 wherein the steering tool is configured so that each of the mechanical valve actuators is at the first actuator position when the housing is at the target orientation.

17. The steering tool as claimed in claim 16 wherein each of the valve mechanisms is further comprised of a valve mechanism biasing device for biasing the mechanical valve actuator toward the first actuator position.

18. The steering tool as claimed in claim 12 wherein each of the valve mechanisms is further comprised of a mechanical actuator dampening mechanism for dampening the movement of the mechanical valve actuator.

19. The steering tool as claimed in claim 18 wherein the mechanical actuator dampening mechanism is comprised of a fluid metering device operably connected with the mechanical valve actuator.

20. The steering tool as claimed in claim 19 wherein the fluid metering device is comprised of: (a) a dampening cylinder;(b) a metering piston reciprocably contained within the dampening cylinder so that the dampening cylinder is divided into a first chamber and a second chamber; and(c) a restricted flowpath between the first chamber and the second chamber for permitting a restricted flow of a fluid between the first chamber and the second chamber as the metering piston reciprocates relative to the dampening cylinder as a result of movement of the mechanical valve actuator.

21. The steering tool as claimed in claim 12 wherein each of the mechanical valve actuators is comprised of an actuating lever.

22. The steering tool as claimed in claim 21 wherein each of the actuating levers is comprised of a pivot point and wherein each of the actuating levers is substantially balanced about the pivot point.

23. The steering tool as claimed in claim 12 wherein each of the steering devices and their associated mechanical valve actuators are circumferentially offset from each other by substantially 180 degrees.

24. The steering tool as claimed in claim 4 wherein the tool actuating device is comprised of a pendulum pivotably supported within the interior of the housing and wherein the actuating movement is a pivoting movement relative to the housing in order to maintain a vertical orientation of the pendulum.

25. The steering tool as claimed in claim 24 wherein the pendulum is comprised of a tubular member which is located within the interior of the housing such that the pendulum surrounds the housing bore.

26. The steering tool as claimed in claim 25 wherein the pendulum is pivotably supported within the housing by a universal joint.

27. The steering tool as claimed in claim 26 wherein the pendulum is contained in a viscous medium so that the pivoting movement of the pendulum is subject to viscous damping.

28. The steering tool as claimed in claim 27, further comprising a pendulum chamber for containing the pendulum and the viscous medium.

29. The steering tool as claimed in claim 28 wherein the viscous medium is comprised of a hydraulic oil.

30. The steering tool as claimed in claim 28 wherein the pendulum chamber is isolated from the hydraulic control system so that the viscous medium is isolated from the hydraulic fluid.

31. The steering tool as claimed in claim 30 wherein the hydraulic control system is further comprised of a hydraulic fluid pressure balancing mechanism for transmitting to the hydraulic fluid a first ambient pressure at a first pressure balancing position on the exterior of the housing.

32. The steering tool as claimed in claim 31, further comprising a viscous medium pressure balancing mechanism for transmitting to the viscous medium a second ambient pressure at a second pressure balancing position on the exterior of the housing.

33. The steering tool as claimed in claim 32 wherein the housing has an upper end and a lower end, wherein the steering devices are located between the upper end and the lower end, and wherein the second pressure balancing position is between the upper end of the housing and the steering devices.

34. The steering tool as claimed in claim 33 wherein the first pressure balancing position is between the steering devices and the lower end of the steering tool.

35. The steering tool as claimed in claim 34 wherein the hydraulic control system is further comprised of an emergency relief valve and wherein the hydraulic control system communicates with the pendulum chamber when the emergency relief valve is in an open position, thereby releasing the hydraulic fluid into the pendulum chamber.

36. The steering tool as claimed in claim 24 wherein the pendulum is comprised of a proximal end and a distal end, wherein the proximal end of the pendulum is pivotably supported within the housing, and wherein the mechanical valve actuators are located adjacent to the distal end of the pendulum.

37. The steering tool as claimed in claim 36 wherein the pendulum has a center of gravity and wherein the center of gravity of the pendulum is located closer to the distal end of the pendulum than to the proximal end of the pendulum.

38. The steering tool as claimed in claim 37 wherein the pendulum is comprised of at least one weighting ring for adding weight to the pendulum and wherein the weighting ring is located closer to the distal end of the pendulum than to the proximal end of the pendulum.

39. The steering tool as claimed in claim 38 wherein the weighting ring is comprised of a carbide ring.

40. The steering tool as claimed in claim 36 wherein each of the mechanical valve actuators is comprised of an actuating lever.

41. The steering tool as claimed in claim 40 wherein each of the actuating levers is comprised of a pivot point and wherein each of the actuating levers is substantially balanced about the pivot point.

42. The steering tool as claimed in claim 24 wherein each of the steering devices and their associated mechanical valve actuators are circumferentially offset from each other by substantially 180 degrees.

43. The steering tool as claimed in claim 4 wherein the steering tool is comprised of four steering devices which are circumferentially spaced from each other by ninety degrees.

44. The steering tool as claimed in claim 4 wherein each of the steering devices is comprised of at least one steering piston which is actuatable between the retracted position and the extended position.

45. The steering tool as claimed in claim 44 wherein each of the steering devices is comprised of a plurality of steering pistons which are simultaneously actuatable between the retracted position and the extended position.

46. The steering tool as claimed in claim 45 wherein each of the steering devices is further comprised of a steering blade connected with the steering pistons.

47. The steering tool as claimed in claim 46 wherein each of the steering devices is further comprised of a steering device biasing mechanism for biasing the steering device toward the retracted position.

48. The steering tool as claimed in claim 46 wherein the steering blades may be replaced without disassembling the steering tool.

49. The steering tool as claimed in claim 4 wherein the housing has an upper end and a lower end, wherein the steering tool is further comprised of a stabilizer associated with the housing, and wherein the stabilizer is located between the upper end of the housing and the steering devices.

50. The steering tool as claimed in claim 49 wherein the stabilizer is comprised of a plurality of stabilizer blades and wherein the stabilizer blades may be replaced without disassembling the steering tool.

51. The steering tool as claimed in claim 4 wherein the steering tool is adapted to be configured as a component of a drilling motor having a motor housing and a motor drive shaft such that the housing of the steering tool is connected with the motor housing and such that the motor drive shaft extends through the housing bore.

52. The steering tool as claimed in claim 4 wherein the steering tool is adapted such that a drill string may extend through the housing bore and such that the housing of the steering tool may be rotatably connected with the drill string.

53. The steering tool as claimed in claim 52, further comprising a borehole engaging device associated with the housing for engaging a borehole in order to inhibit the steering tool from rotating in the borehole when the drill string is rotated.

54. The steering tool as claimed in claim 4 wherein the steering tool is adapted such that the housing of the steering tool may be fixedly connected with a drill string so that the housing of the steering tool rotates when the drill string is rotated.