Radial bearing apparatus for use with side forces

Abstract

A radial bearing apparatus including a housing with a housing bore defining a radial bearing housing surface, a shaft extending through the housing bore and defining a radial bearing shaft surface, and a radial bearing contact interface between the radial bearing housing surface and the radial bearing shaft surface for bearing a variable side force applied to the shaft. The radial bearing contact interface includes an oblique section in which the radial bearing housing surface and the radial bearing shaft surface are oblique to each other when the side force is zero and progressively increase in contact in an axial direction in response to an increasing magnitude of the side force.

Claims

1. A radial bearing apparatus comprising: a housing comprising a first section and a second section of length shorter than the first section, and including a housing bore defining a radial bearing housing surface; a shaft extending through the housing bore and defining a radial bearing shaft surface, the shaft comprising a narrowing section defining a tapered portion in the radial bearing shaft surface; in the first section, the radial bearing housing surface and the radial bearing shaft surface being configured to define a first axial gap therebetween and extending from a first vertex in an axial direction within the housing bore along the length of the housing, a first angle being defined between the radial bearing housing surface and the radial bearing shaft surface at the first vertex, the first axial gap allowing the shaft to tilt relative to the housing in response to a variable side force applied to the shaft; wherein the radial bearing housing surface and the radial bearing shaft surface are configured to be oblique to each other when the side force is zero and progressively increase in contact in the axial direction and become less oblique to each other as the first angle decreases within a first angular range along the first section in response to an increasing magnitude of the side force; the second section comprising an expanding section defining a flared portion in the radial bearing housing surface, the flared portion and the radial bearing shaft surface defining a second axial gap therebetween and the flared portion extending from a second vertex in the axial direction within the housing bore, the second vertex being between the first vertex and a side force axial position, a second angle being defined between the flared portion and the radial bearing shaft surface at the second vertex and being larger than the first angle; wherein the flared portion and the radial bearing shaft surface are oblique to each other in the axial direction along the second section when the side force is zero and become less oblique to each other as the second angle decreases within a second angular range along the second section in response to the increasing magnitude of the side force.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) Embodiments will now be described with reference to the accompanying drawings, in which:

(2) FIG. 1 is a pictorial view of a drilling motor for use in drilling a borehole.

(3) FIG. 2 is a pictorial view of a rotary steerable drilling apparatus for use in drilling a borehole.

(4) FIG. 3 is a simplified schematic side view of a first exemplary embodiment of an apparatus including a radial bearing apparatus, wherein a single oblique section of the radial bearing contact interface is provided by a relative tilt between the radial bearing housing surface and the radial bearing shaft surface, and wherein a relatively large side force has been applied to the shaft.

(5) FIG. 4 is a schematic side view of a second exemplary embodiment of an apparatus including a radial bearing apparatus, wherein a first oblique section of the radial bearing contact interface is provided by a relative tilt between the radial bearing housing surface and the radial bearing shaft surface, and wherein a second oblique section of the radial bearing contact interface is provided by the relative tilt between the radial bearing housing surface and the radial bearing shaft surface and by a flare at the distal end of the radial bearing housing surface.

(6) FIGS. 5A-5C provide views schematically depicting modeling of the second exemplary embodiment of the radial bearing apparatus as a component of a drilling motor during a sliding mode of operation, a rotary mode of operation, and a mode in which the shaft experiences a reverse-bend respectively, wherein the deflection profiles of the shaft are exaggerated for illustration purposes.

(7) FIG. 6 is a graph depicting a modeled relationship of side force to bearing surface contact area for the second exemplary embodiment of the radial bearing apparatus as a component of a drilling motor during the modes of operation depicted in FIGS. 5A-5C.

(8) FIG. 7 is a schematic side view of a third exemplary embodiment of an apparatus including a radial bearing apparatus, wherein a first oblique section of the radial bearing contact interface is provided by a relative tilt between the radial bearing housing surface and the radial bearing shaft surface and by a taper of the radial bearing shaft surface, and wherein a second oblique section of the radial bearing contact interface is provided by the relative tilt between the radial bearing housing surface and the radial bearing shaft surface, by the taper of the radial bearing shaft surface, and by a flare at the distal end of the radial bearing housing surface.

(9) FIG. 8 is a schematic side view of a fourth exemplary embodiment of an apparatus including a radial bearing apparatus, wherein a single oblique section of the radial bearing contact interface is provided by a taper of the radial bearing shaft surface.

(10) FIG. 9 is a schematic side view of a fifth exemplary embodiment of an apparatus including a radial bearing apparatus, wherein a first oblique section of the radial bearing contact interface is provided by a taper of the radial bearing shaft surface, and wherein a second oblique section of the radial bearing contact interface is provided by the taper of the radial bearing shaft surface and by a flare at the distal end of the radial bearing housing surface.

(11) FIG. 10 is a schematic longitudinal section view of a second exemplary embodiment of an apparatus for use in drilling a borehole, wherein the apparatus comprises a reduced stiffness section located along the length of the apparatus between a power section and a bearing assembly, an increased diameter structure located between the reduced stiffness section and a distal end of the apparatus, and at least one radial bearing apparatus as a component of the apparatus.

(12) FIG. 11 is a schematic longitudinal section view of a first exemplary embodiment of an apparatus for use in drilling a borehole, wherein the apparatus comprises a reduced stiffness section located along the length of the apparatus between a power section and a bearing assembly, a first increased diameter structure located between the reduced stiffness section and a distal end of the apparatus, a second increased diameter structure located between a proximal end of the apparatus and the reduced stiffness section, and at least one radial bearing apparatus as a component of the apparatus.

DETAILED DESCRIPTION

(13) FIGS. 1-11 are exemplary only. The radial bearing apparatus described herein may be used in any suitable apparatus and in any suitable application.

(14) In the description of the exemplary embodiments which follows, features which are identical or generally equivalent in the exemplary embodiments may be identified with the same reference numbers.

(15) Referring to FIG. 1, an exemplary drilling motor (20) comprises a power section (22) and a bearing section (26). The bearing section (26) is axially distal to the power section (22). One or more sections of the drilling motor (20) may be axially located between the power section (22) and the bearing section (26). As depicted in FIG. 1, the drilling motor (20) further comprises a transmission section (24) which is axially located between the power section (22) and the bearing section (26). These sections of the drilling motor (20) constitute components of a powertrain which utilizes fluid energy to rotate a drill bit (28).

(16) A drill string (70) is connected with a proximal end of the power section (22). As depicted in FIG. 1, the drill string (70) includes a drill string communication system (72) such as a measurement-while-drilling system.

(17) The drilling motor (20) comprises a tubular housing (30) for containing components of the sections (22, 24, 26) of the drilling motor (20). The housing (30) may comprise a plurality of housing components which together provide the housing (30), or the housing (30) may be a unitary housing (30) which is formed from a single power housing component.

(18) As depicted in FIG. 1, the housing (30) comprises a plurality of housing sections connected together with threaded connections, including a tubular power housing (32) for the power section (22), a tubular transmission housing (34) for the transmission section (24), and a tubular bearing housing (36) for the bearing section (26).

(19) The power housing (32) may comprise a plurality of power housing components which together provide the power housing (32), or the power housing (32) may be a unitary power housing (32) which is formed from a single power housing component.

(20) The transmission housing (34) may comprise a plurality of transmission housing components which together provide the transmission housing (34), or the transmission housing (34) may be a unitary transmission housing (34) which is formed from a single transmission housing component.

(21) The bearing housing (36) may comprise a plurality of bearing housing components which together provide the bearing housing (36), or the bearing housing (36) may be a unitary bearing housing (36) which is formed from a single bearing housing component.

(22) The power section (22) of the drilling motor (20) comprises a stator (50) and a rotor (52). The stator (50) is fixedly connected with the power housing (32), and the rotor (52) is rotatable within the stator (50) in response to fluid circulating through the power section (22).

(23) As depicted in FIG. 1, the power section (22) is a Moineau-type power section in which the stator (50) and the rotor (52) are lobed. The rotor (52) has one fewer lobe than the stator (50), and rotates eccentrically within the stator (50).

(24) The transmission section (24) accommodates and converts the eccentric movement of the rotor (52) to concentric rotation of a driveshaft (54) within the bearing section (26). The transmission section (24) also transmits rotational drive energy from the power section (22) to the bearing section (26).

(25) As depicted in FIG. 1, the transmission section (24) comprises the transmission housing (34) and a transmission shaft (60) which is connected between the rotor (52) and the driveshaft (54) such that eccentric rotation of the rotor (52) results in concentric rotation of the driveshaft (54). The transmission shaft (60) may be a flexible shaft, the transmission shaft (60) may be interposed between two universal joints, or the eccentric rotation of the rotor (52) may be converted to concentric rotation of the driveshaft (54) via the transmission shaft (60) in some other suitable manner (not shown).

(26) As depicted in FIG. 1, the bearing section (26) comprises the bearing housing (36), the driveshaft (54), and a bearing assembly (not shown in FIG. 1) comprising one or more thrust bearings and one or more radial bearings which rotatably support the driveshaft (54) within the housing (30). One or more radial bearings in the bearing assembly may comprise, consist of, or consist essentially of the radial bearing apparatus described herein.

(27) As depicted in FIG. 1, the bearing section (26) also comprises a stabilizer (62) which is attached to or integral with the exterior of the bearing housing (36). The stabilizer (62) has a larger nominal diameter than the nominal diameter of the drilling motor (20). As a result, the stabilizer (62) may be considered to be an increased diameter structure as described herein.

(28) As depicted in FIG. 1, the drill bit (28) is connected with the driveshaft (54) so that rotation of the driveshaft (54) causes rotation of the drill bit (28).

(29) The drilling motor (20) has a primary axis (80) and the driveshaft (54) has a driveshaft axis (82). As depicted in FIG. 1, the driveshaft axis (82) is oblique to the primary axis (80) so that the driveshaft (54) is tilted relative to the primary axis (80) in a shaft tilt direction (84). The tilt of the driveshaft (54) may be provided by a bend in the exterior of the housing (30), by a bend in the interior of the housing (30), by an articulation of the driveshaft (54) within the housing (30), or in any other suitable manner. The tilt of the driveshaft (54) may be fixed (i.e., non-adjustable) or may be adjustable.

(30) Referring to FIG. 2, an exemplary rotary steerable drilling apparatus (90) comprises a housing (92) having an exterior surface (94). A shaft (96) extends through the housing (92). The shaft (96) is rotatable relative to the housing (92).

(31) In the exemplary rotary steerable drilling apparatus (90), a drill bit (98) is connected with a distal end of the shaft (96), and a drill string (100) is connected with a proximal end of the shaft (96). As depicted in FIG. 2, the drill string (100) includes a drill string communication system (102) such as a measurement-while-drilling system.

(32) In the exemplary rotary steerable drilling apparatus (90), an anti-rotation device (104) is connected with or integrated into the housing (92) adjacent to a proximal end of the housing (92), and a near-bit stabilizer (106) is connected with or integrated into the housing (92) adjacent to a distal end of the housing (92). The anti-rotation device (104) and the near-bit stabilizer (106) each have a nominal diameter which is larger than the nominal diameter of the rotary steerable drilling apparatus (90). As a result, the anti-rotation device (104) and the near-bit stabilizer (106) may be considered to be increased diameter structures as described herein.

(33) In the exemplary rotary steerable drilling apparatus (90), a deflection mechanism (108) is contained within the housing (92), which may be actuated to cause radial deflection of a portion of the shaft (96) within the housing (92).

(34) The deflection mechanism (108) may be comprised of any structure, device, or apparatus which is capable of causing the radial deflection of the portion of the shaft (96) within the housing (92). The radial deflection of the portion of the shaft (96) may result in bending of the shaft (96) within the housing (92). Additionally or alternatively, the radial deflection of the portion of the shaft (96) may result in articulation of the shaft (96) within the housing (92), if the shaft (96) is comprised of a joint (not shown) which facilitates such articulation. In either case, the radial deflection of the shaft (96) may cause the shaft (96) to tilt relative to the housing (92) in a shaft tilt direction (110).

(35) In the exemplary embodiment of the rotary steerable drilling apparatus (90), a bearing assembly (not shown in FIG. 2) is contained within the housing (92), comprising one or more thrust bearings and one or more radial bearings which rotatably support the shaft (96) within the housing (92). One or more radial bearings in the bearing assembly may comprise, consist of, or consist essentially of the radial bearing apparatus described herein.

(36) Referring to FIGS. 3-5 and 7-9, exemplary embodiments of a radial bearing apparatus (120) are depicted. The exemplary embodiments of the radial bearing apparatus (120) may be configured and/or adapted as a component of an apparatus such as, without limitation, an apparatus (122) for use in a borehole, including as non-limiting examples the drilling motor (20) depicted in FIG. 1 and/or the rotary steerable drilling apparatus (90) depicted in FIG. 2.

(37) FIG. 3 depicts a first exemplary embodiment of the radial bearing apparatus (120). FIG. 4 depicts a second exemplary embodiment of the radial bearing apparatus (120). FIG. 7 depicts a third exemplary embodiment of the radial bearing apparatus (120). FIG. 8 depicts a fourth exemplary embodiment of the radial bearing apparatus (120). FIG. 9 depicts a fifth exemplary embodiment of the radial bearing apparatus (120).

(38) In the description that follows, features which are common to some or all of the exemplary embodiments are first described, followed by descriptions of other features of the particular exemplary embodiments. In the description that follows, features which are common to some or all of the exemplary embodiments may be indicated by the same reference numbers.

(39) In the exemplary embodiments, the radial bearing apparatus (120) comprises a housing (124) and a shaft (126). In the exemplary embodiments, the housing (124) may be a component or section of the housing (30) of a drilling motor (20), the housing (124) may be a component or section of the housing (92) of a rotary steerable drilling apparatus (90), or the housing (124) may be connected with the housing (30) of a drilling motor (20) or with the housing (92) of a rotary steerable drilling apparatus (90). In the exemplary embodiments, the shaft (126) may be a driveshaft (54) of a drilling motor (20) or may be connected with a driveshaft (54) of a drilling motor (20), or the shaft (126) may be a shaft (96) of a rotary steerable drilling apparatus (100) or may be connected with a shaft (96) of a rotary steerable drilling apparatus (100).

(40) In the exemplary embodiments, the housing (124) defines a housing bore (128) and comprises a radial bearing housing surface (132) within the housing bore (128). The shaft (126) extends through the housing bore (128) and comprises a radial bearing shaft surface (134) on an exterior of the shaft (126). In the exemplary embodiments, the radial bearing housing surface (132) and the radial bearing shaft surface (134) both comprise plain bearing surfaces which are provided as sleeves or as a coating on the housing bore (128) and the exterior of the shaft (126) respectively.

(41) FIGS. 3-5 and 7-9 each depict a side force (138) which has been applied to the shaft (126) at a side force axial position (140) and in a side force direction (142). The side force (138), the side force axial position (140), and/or the side force direction (142) may be constant or may vary for a particular apparatus (122), depending upon such non-limiting factors as the configuration of the apparatus (122), the mode of use of the apparatus (122), and the environment surrounding the apparatus (122) during use.

(42) The side force (138) may tend to move the shaft (126) transversely within the housing bore (128) in the side force direction (142).

(43) The apparatus (122) has a primary axis (146). In the exemplary embodiments, the primary axis (146) of the apparatus (122) is the “principal” or “main” axis of the apparatus (122), which may be the axis of the apparatus (122) at or adjacent to the proximal end of the apparatus (122).

(44) The shaft (126) of the apparatus (122) has a shaft axis (148). The shaft axis (148) of the apparatus (122) may be substantially parallel to the primary axis (146) of the apparatus (122). Alternatively, the shaft axis (148) of the apparatus (122) may be oblique to the primary axis (146) of the apparatus (122).

(45) If the apparatus (122) is a straight drilling motor (20) or if the apparatus (122) is a rotary steerable drilling apparatus (100) in which the deflection mechanism is not actuated, the shaft axis (148) of the apparatus (122) may be substantially parallel to the primary axis (146) of the apparatus (122).

(46) If the shaft axis (148) of the apparatus (122) is substantially parallel to the primary axis (146) of the apparatus (122), the side force direction (142) may be dependent upon the orientation and positioning of the apparatus (122) in the borehole environment (not shown in FIGS. 3-5 and 7-9) surrounding the apparatus (122). As a result, the side force direction (142) relative to the housing (124) and the housing bore (128) of the radial bearing apparatus (120) may vary as the orientation of the apparatus (122) in the surrounding borehole environment changes.

(47) If the apparatus (122) is a bent drilling motor (20) or if the apparatus (122) is a rotary steerable drilling apparatus (100) in which the deflection mechanism is actuated, the shaft axis (148) of the apparatus (122) may be oblique to the primary axis (146) of the apparatus (122) so that the shaft (126) is tilted relative to the primary axis (146) in a shaft tilt direction (150).

(48) If the shaft (126) is tilted relative to the primary axis (146) in the shaft tilt direction (150), a side force (138) may be exerted against the tilt of the shaft (126) by the borehole environment (not shown in FIGS. 3-5 and 7-9) surrounding the apparatus (122) such that the shaft tilt direction (150) is opposite to the side force direction (142). As a result, the side force direction (142) may be fixed or constant relative to the housing (124) and the housing bore (128) of the radial bearing apparatus (120).

(49) A radial bearing contact interface (154) is provided between the radial bearing housing surface (132) and the radial bearing shaft surface (134) for bearing the side force (138) which is applied to the shaft (126) in the side force direction (142). Since the side force (138) will tend to move the shaft (126) transversely in the housing bore (128) in the side force direction (142), the radial bearing contact interface (154) will typically be on an opposite side of the shaft (126) (i.e., 180 degrees around the circumference of the shaft (126)) from the location of application of the side force (138), assuming that the side force (138) is a pushing force.

(50) If the side force direction (142) is expected to be fixed or constant relative to the housing bore (128), then the circumferential location of the radial bearing contact interface (154) may potentially also be fixed or constant relative to the housing bore (128), with the result that the radial bearing housing surface (132) may potentially be required to be provided around only a portion of the circumference of the housing bore (128). In such circumstances, the radial bearing contact interface (154) may be configured to be circumferentially asymmetrical within the housing bore (128).

(51) If the side force direction (142) is expected to vary relative to the housing bore (128), then the circumferential location of the radial bearing contact interface (154) may potentially also vary around the circumference of the housing bore (128), with the result that the radial bearing housing surface (132) may potentially be required to be provided around the entire circumference of the housing bore (128). In such circumstances, the radial bearing contact interface may be configured to be circumferentially symmetrical within the housing bore (128).

(52) Referring to FIGS. 3-5 and 7-9, in the exemplary embodiments, the radial bearing contact interface (154) extends in an axial direction (156) for an interface length (158) within the housing bore (128) between a first interface end (160) and a second interface end (162). The interface length (158) is the maximum length of contact between the radial bearing housing surface (132) and the radial bearing shaft surface (134).

(53) In the exemplary embodiments, the radial bearing contact interface (154) also extends circumferentially for an interface width (not shown) within the housing bore (128). The interface width is the maximum width of contact between the radial bearing housing surface (132) and the radial bearing shaft surface (134), and is defined by the shape, dimensions, and configuration of the radial bearing surfaces (132, 134). In the exemplary embodiments, the housing bore (128) and the shaft (126) are both cylindrical so that the radial bearing surfaces (132, 134) are cylindrically shaped and the interface width is a circumferential arc of contact between the radial bearing surfaces (132, 134).

(54) The radial bearing contact interface (154) facilitates a contact area (164) between the radial bearing surfaces (132, 134). The interface length (158) multiplied by the interface width represents a maximum contact area between the radial bearing housing surface (132) and the radial bearing shaft surface (134) when the radial bearing housing surface (132) and the radial bearing shaft surface (134) are in contact with each other along the entire interface length (158) and the entire interface width.

(55) The radial bearing contact interface (154) may comprise, consist of, or consist essentially of a single or unitary interface section between the radial bearing housing surface (132) and the radial bearing shaft surface (134), or the radial bearing contact interface (154) may comprise a plurality of interface sections between the radial bearing housing surface (132) and the radial bearing shaft surface (134). An interface section may be an oblique section or may be a non-oblique section.

(56) In the exemplary embodiments, the radial bearing contact interface (154) comprises at least one oblique section (170) along which the radial bearing housing surface (132) and the radial bearing shaft surface (134) are arranged to be oblique to each other in the axial direction (156) when the side force (138) is zero. The radial bearing housing surface (132) and the radial bearing shaft surface (134) are arranged to become generally less oblique to each other within a range along the oblique section (170) as the side force (138) increases from zero.

(57) In the exemplary embodiments, the oblique section (170) has a vertex (172) which is defined by an axial location of maximum convergence of the radial bearing housing surface (132) and the radial bearing shaft surface (134) along the oblique section (170). In the exemplary embodiments, the gap between the radial bearing housing surface (132) and the radial bearing shaft surface (134) at the vertex (172) may be zero, minimal, or substantial, depending upon the configuration of the oblique section (170). In the exemplary embodiments, the oblique section (170) extends from the vertex (172) toward the side force axial position (140).

(58) A bearing interface angle (174) is defined between the radial bearing housing surface (132) and the radial bearing shaft surface (134) at the vertex (172) of the oblique section (170). The bearing interface angle (174) is generally larger than zero when the side force (138) is zero. The bearing interface angle (174) may tend generally to decrease within an angular range as the side force increases from zero.

(59) Consequently, in the exemplary embodiments, as the side force (138) increases from zero, the radial bearing housing surface (132) and the radial bearing shaft surface (134) may become generally less oblique to each other within a range and the bearing interface angle (174) may tend generally to decrease within an angular range. As the radial bearing housing surface (132) and the radial bearing shaft surface (134) become generally less oblique to each other and/or as the bearing interface angle (174) decreases, the contact area between the radial bearing surfaces (132, 134) may increase, may be maintained, or may be shifted within the radial bearing contact interface (154).

(60) In the first exemplary embodiment of the radial bearing apparatus (120) depicted in FIG. 3 and the fourth exemplary embodiment of the radial bearing apparatus (120) depicted in FIG. 8, the radial bearing contact interface (154) comprises a single oblique section (170) having a vertex (172) and a bearing interface angle (174).

(61) Referring to FIG. 3, in the first exemplary embodiment, the single oblique section (170) of the radial bearing contact interface (154) is provided by a relative tilt between the radial bearing housing surface (132) and the radial bearing shaft surface (134). In the first exemplary embodiment, the relative tilt of the bearing surfaces (132, 134) is achieved by configuring the housing (124) and the shaft (126) so that the bearing surfaces (132, 134) are oblique relative to each other. In the first exemplary embodiment, the radial bearing surfaces (132, 134) along the oblique section (170) are substantially straight surfaces. In the first exemplary embodiment, the shaft axis (148) of the apparatus (122) is oblique to the primary axis (146) of the apparatus (122) so that the shaft (126) is tilted relative to the primary axis (146) in a shaft tilt direction (150).

(62) In FIG. 3, the radial bearing apparatus (120) is depicted in an exaggerated manner with a relatively large side force (138) applied to the shaft (126) so that the shaft (126) has pivoted, tilted, or bent around the vertex (172) of the oblique section (170), with the result that the radial bearing housing surface (132) and the radial bearing shaft surface (134) have become less oblique to each other and the bearing interface angle has decreased to the extent that the radial bearing surfaces (132, 134) are substantially parallel to each other along the oblique section (170).

(63) Referring to FIG. 8, in the fourth exemplary embodiment, the single oblique section (170) of the radial bearing contact interface (154) is provided by a taper (176) of the radial bearing shaft surface (134). In the fourth exemplary embodiment, the radial bearing surfaces (132, 134) along the oblique section (170) are substantially straight surfaces. In the fourth exemplary embodiment, the shaft axis (148) of the apparatus (122) is substantially concentric with and/or substantially parallel to the primary axis (146) of the apparatus (122).

(64) In FIG. 8, the radial bearing apparatus (120) is depicted with a relatively small side force (138) applied to the shaft (126) so that the bearing surfaces (132, 134) continue to be significantly oblique to each other along the oblique section (170) and so that the bearing interface angle (174) remains relatively large.

(65) In the second exemplary embodiment of the radial bearing apparatus (120) depicted in FIG. 4, the third exemplary embodiment of the radial bearing apparatus (120) depicted in FIG. 7, and the fifth exemplary embodiment of the radial bearing apparatus (120) depicted in FIG. 9, the oblique section (170) is a first oblique section (190) and the radial bearing contact interface (154) further comprises a second oblique section (200). The first oblique section (190) has a first vertex (192), a first bearing interface angle (194) and a first oblique section length (196). The second oblique section (200) has a second vertex (202), a second bearing interface angle (204), and a second oblique section length (206).

(66) In the second exemplary embodiment, the third exemplary embodiment, and the fifth exemplary embodiment, the radial bearing housing surface (132) and the radial bearing shaft surface (134) are arranged to be generally oblique to each other in the axial direction along each of the first oblique section (190) and the second oblique section (200) when the side force (138) is zero.

(67) In the second exemplary embodiment, the third exemplary embodiment, and the fifth exemplary embodiment, the radial bearing housing surface (132) and the radial bearing shaft surface (134) are arranged to become generally less oblique within a first range along the first oblique section (190) as the side force (138) increases from zero, and the radial bearing housing surface (132) and the radial bearing shaft surface (134) are arranged to become generally less oblique within a second range along the second oblique section (200) as the side force (138) increases from zero.

(68) In the second exemplary embodiment, the third exemplary embodiment, and the fifth exemplary embodiment, the first bearing interface angle (194) may decrease within a first angular range as the side force (138) increases from zero, and the second bearing interface angle may decrease within a second angular range when the side force (138) increases from zero.

(69) In the second exemplary embodiment, the third exemplary embodiment, and the fifth exemplary embodiment, the first oblique section (190) extends from the first vertex (192) toward the side force axial position (140), the second oblique section (200) extends from the second vertex (202) toward the side force axial position, the second vertex (202) is between the first vertex (192) and the side force axial position (140), the first bearing interface angle (194) is smaller than the second bearing interface angle (204), and the first oblique section length (196) is greater than the second oblique section length (206).

(70) Referring to FIG. 4, in the second exemplary embodiment, the first oblique section (190) of the radial bearing contact interface (154) is provided by a relative tilt between the radial bearing housing surface (132) and the radial bearing shaft surface (134), and the second oblique section (200) of the radial bearing contact interface (154) is provided by the relative tilt between the radial bearing housing surface (132) and the radial bearing shaft surface (134) and by a flare (210) at the distal end of the radial bearing housing surface (132). The relative tilt of the bearing surfaces (132, 134) may be achieved by arranging one or both of the bearing surfaces (132, 134) to be tilted relative to the other bearing surface (132, 134) when the side force (138) is zero. In the second exemplary embodiment, the radial bearing surfaces (132, 134) along both the first oblique section (190) and the second oblique section (200) are substantially straight surfaces. In the second exemplary embodiment, the shaft axis (148) of the apparatus (122) is oblique to the primary axis (146) of the apparatus (122) so that the shaft (126) is tilted relative to the primary axis (146) in a shaft tilt direction (150).

(71) In FIG. 4, the radial bearing apparatus (120) is depicted with a relatively small side force (138) applied to the shaft (126) so that the bearing surfaces (132, 134) continue to be significantly oblique to each other along both the first oblique section (190) and the second oblique section (200) and so that the first bearing interface angle (194) and the second bearing interface angle (204) remain relatively large.

(72) Referring to FIG. 7, in the third exemplary embodiment, the first oblique section (190) of the radial bearing contact interface (154) is provided by a relative tilt between the radial bearing housing surface (132) and the radial bearing shaft surface (134) and by a taper (176) of the radial bearing shaft surface (134), and the second oblique section (200) of the radial bearing contact interface (154) is provided by the relative tilt between the radial bearing housing surface (132) and the radial bearing shaft surface (134), by the taper (176) of the radial bearing shaft surface (134), and by a flare (210) at the distal end of the radial bearing housing surface (132). The relative tilt of the bearing surfaces (132, 134) may be achieved by arranging one or both of the bearing surfaces (132, 134) to be tilted relative to the other bearing surface (132, 134) when the side force (138) is zero. In the third exemplary embodiment, the radial bearing surfaces (132, 134) along both the first oblique section (190) and the second oblique section (200) are substantially straight surfaces. In the third exemplary embodiment, the shaft axis (148) of the apparatus (122) is oblique to the primary axis (146) of the apparatus (122) so that the shaft (126) is tilted relative to the primary axis (146) in a shaft tilt direction (150).

(73) In FIG. 7, the radial bearing apparatus (120) is depicted with a relatively small side force (138) applied to the shaft (126) so that the bearing surfaces (132, 134) continue to be significantly oblique to each other along both the first oblique section (190) and the second oblique section (200) and so that the first bearing interface angle (194) and the second bearing interface angle (204) remain relatively large.

(74) Referring to FIG. 9, in the fifth exemplary embodiment, the first oblique section (190) of the radial bearing contact interface (154) is provided by a taper (176) of the radial bearing shaft surface (134), and the second oblique section (200) of the radial bearing contact interface (154) is provided by the taper (176) of the radial bearing shaft surface (134) and by a flare (210) at the distal end of the radial bearing housing surface (132). The relative tilt of the bearing surfaces (132, 134) may be achieved by arranging one or both of the bearing surfaces (132, 134) to be tilted relative to the other bearing surface (132, 134) when the side force (138) is zero. In the fifth exemplary embodiment, the radial bearing surfaces (132, 134) along both the first oblique section (190) and the second oblique section (200) are substantially straight surfaces. In the fifth exemplary embodiment, the shaft axis (148) of the apparatus (122) is substantially concentric with and/or substantially parallel to the primary axis (146) of the apparatus (122).

(75) In FIG. 9, the radial bearing apparatus (120) is depicted with a relatively small side force (138) applied to the shaft (126) so that the bearing surfaces (132, 134) continue to be significantly oblique to each other along both the first oblique section (190) and the second oblique section (200) and so that the first bearing interface angle (194) and the second bearing interface angle (204) remain relatively large.

(76) FIGS. 5A-5C schematically depict modeling of the second exemplary embodiment of the radial bearing apparatus (120) in different modes of operation of the apparatus (122), wherein the apparatus (122) is a drilling motor (20).

(77) FIG. 5A depicts the second exemplary embodiment of the radial bearing apparatus (120) during a sliding mode of operation of the drilling motor (20). Sliding mode occurs when the housing (30) of the drilling motor (20) is not rotated relative to the borehole, but the driveshaft (54) of the drilling motor (20) is rotated by the power section (22) of the drilling motor (20). Sliding mode may be predicted to apply a low to moderate side force (138) to the drilling motor (20) and the radial bearing apparatus (120). In sliding mode, the contact between the radial bearing housing surface (132) and the radial bearing shaft surface (134) may be expected to be predominantly toward the first vertex (192) of the first oblique section (190).

(78) FIG. 5B depicts the second exemplary embodiment of the radial bearing apparatus (120) during a rotary mode of operation of the drilling motor (20). Rotary mode occurs when the housing (30) of the drilling motor (20) is rotated relative to the borehole and the driveshaft (54) is or may be simultaneously rotated by the power section (22) of the drilling motor (20). Rotary mode may be predicted to apply a moderate to high side force (138) to the drilling motor (20) and the radial bearing apparatus (120). In rotary mode, the contact between the radial bearing housing surface (132) and the radial bearing shaft surface (134) may be expected to be along a significant portion of the first oblique section (190).

(79) FIG. 5C depicts the second exemplary embodiment of the radial bearing apparatus (120) during a mode of operation of the drilling motor (20) in which the driveshaft (54) of the drilling motor (20) experiences a reverse-bend. A reverse-bend occurs when a side force (138) is applied to the drilling motor (20) and the radial bearing apparatus (120) is sufficiently large to cause the driveshaft (54) of the drilling motor (20) to bend in a direction opposite to the shaft tilt direction (84). During reverse-bend mode, the contact between the radial bearing housing surface (132) and the radial bearing shaft surface (134) may be expected to be along the distal end of the first oblique section (190) and/or along all or a portion of the second oblique section (200).

(80) FIG. 6 is a graph depicting a modeled relationship of side force (138) to bearing surface contact area for the second exemplary embodiment of the radial bearing apparatus (120) as a component of a drilling motor (20) during the modes of operation depicted in FIGS. 5A-5C.

(81) The modeled relationship depicted in FIG. 6 suggests that the contact area between the radial bearing surfaces (132, 134) may tend generally to increase within a range or to be maintained as the side force (138) increases during either the sliding mode or rotary mode of operation, may tend to decrease within a range or to be maintained during a transition to reverse-bend mode, and may tend generally to increase within a range as the side force (138) increases during the reverse-bend mode.

(82) A variation in contact area and location of contact between the radial bearing surfaces (132, 134) as modeled in FIGS. 5A-5C and FIG. 6 may assist in distributing loads along the radial bearing contact interface (154), which may in turn assist in reducing wear and/or failure of the radial bearing apparatus (120). A variation in contact area and location of contact between the radial bearing surfaces (132, 134) as modeled in FIGS. 5A-5C and FIG. 6 may also potentially assist in reducing wear at the proximal end of the radial bearing contact interface (154), which may prevent or delay a reduction in the driveshaft tilt angle which may result from wear of the radial bearing surfaces (132, 134).

(83) FIG. 10 schematically depicts a first exemplary embodiment of an apparatus (220) for use in drilling a borehole (222). FIG. 11 schematically depicts a second exemplary embodiment of an apparatus (220) for use in drilling a borehole (222).

(84) In the exemplary embodiments, the apparatus (220) has a proximal end (224), a distal end (226), a length (228), a nominal diameter (230), and a primary axis (232). The distal end (226) of the apparatus (220) comprises a drill bit (not shown in FIGS. 10-11). The proximal end (224) of the apparatus (220) is connectable with a drill string (not shown in FIGS. 10-11).

(85) In the exemplary embodiments, the apparatus (220) comprises a shaft (234). The shaft (234) of the apparatus (220) may be tilted relative to the primary axis (232) of the apparatus (220) in a shaft tilt direction (not shown). Alternatively, the shaft (234) of the apparatus (220) may be substantially concentric with and/or substantially parallel to the primary axis (232) of the apparatus (220).

(86) In the exemplary embodiments, a portion of the length (228) of the apparatus (220) comprises a reduced stiffness section (240). The reduced stiffness section (240) flexes or bends preferentially relative to other portions of the length (228) of the apparatus (220) in response to a force or moment which is applied to the apparatus (228). In the exemplary embodiments, the reduced stiffness section (240) is provided as a reduced diameter section of the apparatus (220).

(87) In the exemplary embodiments, the apparatus (220) comprises a drilling motor (250). The drilling motor (250) comprises a power section (252), a transmission section (254), and a bearing section (256). In the exemplary embodiments, the transmission section (254) is axially located along the length (228) of the apparatus (220) between the power section (252) and the bearing section (256). In the exemplary embodiments, the reduced stiffness section (240) is axially located along the length (228) of the apparatus (220) at the drilling motor (250). In the exemplary embodiments, the reduced stiffness section (240) is more particularly axially located along the length (228) of the apparatus (220) at the transmission section (254) of the drilling motor (250).

(88) The bearing section (256) of the drilling motor (250) comprises a bearing assembly (258). In the exemplary embodiments, the bearing assembly (258) comprises a proximal radial bearing (260), a distal radial bearing (262), and one or more thrust bearings (264). In the exemplary embodiments, the bearing section (256) and the bearing assembly (258) of the drilling motor (250) are axially located along the length (228) of the apparatus (220) between the reduced stiffness section (240) and the distal end (226) of the apparatus (220).

(89) At least one of the proximal radial bearing (260) and the distal radial bearing (262) may comprise a radial bearing apparatus (120) as previously described. In the exemplary embodiments, at least the distal radial bearing (262) comprises a radial bearing apparatus (120) as previously described. As depicted in FIGS. 10 and 11, the distal radial bearing (262) is a first radial bearing apparatus (266) and the proximal radial bearing (260) is a second radial bearing apparatus (268), so that both the proximal radial bearing (260) and the distal radial bearing (262) comprise a radial bearing apparatus (120) as previously described. In the exemplary embodiments, the one or more thrust bearings (264) in the bearing assembly (258) are axially located along the length (228) of the apparatus (220) between the first radial bearing apparatus (266) and the second radial bearing apparatus (268).

(90) In the exemplary embodiments, the apparatus (220) comprises an increased diameter structure (280), which has a larger nominal diameter (282) than the nominal diameter (230) of the apparatus (220).

(91) In the first exemplary embodiment, the increased diameter structure (280) is a stabilizer. In the first exemplary embodiment, the increased diameter structure (280) is axially located along the length (228) of the apparatus (220) between the reduced stiffness section (240) and the distal end (226) of the apparatus (220).

(92) In the second exemplary embodiment, the increased diameter structure (280) is a first increased diameter structure (284) and the apparatus (220) further comprises a second increased diameter structure (286). In the second exemplary embodiment, both the first increased diameter structure (284) and the second increased diameter structure (286) are stabilizers. In the second exemplary embodiment, the first increased diameter structure (284) is axially located along the length (228) of the apparatus (220) between the reduced stiffness section (240) and the distal end (226) of the apparatus (220). In the second exemplary embodiment, the second increased diameter structure (286) is axially located along the length (228) of the apparatus (220) between the proximal end (224) of the apparatus (220) and the reduced stiffness section (240). In the second exemplary embodiment, the reduced stiffness section (240) is axially located along the length (228) of the apparatus (220) between the first increased diameter structure (284) and the second increased diameter structure (286). In the second exemplary embodiment, the second increased diameter structure (286) is more particularly axially located along the length (228) of the apparatus (220) at the power section (252) of the drilling motor (250).

(93) The combination of the apparatus (220) comprising the reduced stiffness section (240), at least one increased diameter structure (280, 284, 286), and at least one radial bearing apparatus (120) may assist in reducing, controlling and/or managing stresses exerted on the apparatus (220), and may result in a longer service life of the apparatus (220). The reduced stiffness section (240) may assist in relieving stresses from the apparatus (220). The at least one increased diameter structure (280, 284, 286) may assist in controlling the sections of the apparatus (220) upon which stresses are exerted. The at least one radial bearing apparatus (120) may assist in reducing and/or postponing wear which might otherwise be experienced by radial bearings in the apparatus (220).

Additional Disclosures

(94) The following are non-limiting, specific embodiments of a radial bearing apparatus and of an apparatus comprising the radial bearing apparatus:

(95) Embodiment A. A radial bearing apparatus comprising:

(96) a housing including a housing bore defining a radial bearing housing surface;

(97) a shaft extending through the housing bore and defining a radial bearing shaft surface; and

(98) a radial bearing contact interface between the radial bearing housing surface and the radial bearing shaft surface for bearing a variable side force applied to the shaft, the radial bearing contact interface including an oblique section in which the radial bearing housing surface and the radial bearing shaft surface are oblique to each other when the side force is zero and progressively increase in contact in an axial direction in response to an increasing magnitude of the side force.

(99) Embodiment B. The radial bearing apparatus of Embodiment A wherein the radial bearing housing surface and the radial bearing shaft surface become less oblique to each other within a range along the oblique section as the side force increases from zero.

(100) Embodiment C. The radial bearing apparatus of Embodiment B wherein the radial bearing shaft surface is on an exterior of the shaft, wherein the side force is applied to the shaft in a side force direction, wherein the radial bearing contact interface extends in the axial direction within the housing bore, and wherein the radial bearing housing surface and the radial bearing shaft surface are oblique to each other in the axial direction along the oblique section.

(101) Embodiment D. A radial bearing apparatus comprising:

(102) a housing defining a housing bore and comprising a radial bearing housing surface within the housing bore;

(103) a shaft extending through the housing bore, wherein the shaft comprises a radial bearing shaft surface on an exterior of the shaft; and

(104) a radial bearing contact interface between the radial bearing housing surface and the radial bearing shaft surface for bearing a side force which is applied to the shaft in a side force direction, wherein the radial bearing contact interface extends in an axial direction for an interface length within the housing bore, wherein the radial bearing contact interface comprises an oblique section, wherein the radial bearing housing surface and the radial bearing shaft surface are oblique to each other in the axial direction along the oblique section of the radial bearing contact interface when the side force is zero, and wherein the radial bearing housing surface and the radial bearing shaft surface become less oblique to each other within a range along the oblique section as the side force increases from zero.

(105) Embodiment E. The radial bearing apparatus any one of Embodiments A through D, further comprising a side force axial position where the side force is applied, wherein the oblique section has a vertex, and wherein the oblique section extends from the vertex toward the side force axial position.

(106) Embodiment F. The radial bearing apparatus of any one of Embodiments A through E wherein a bearing interface angle is defined between the radial bearing housing surface and the radial bearing shaft surface at the vertex of the oblique section and wherein the bearing interface angle decreases within an angular range as the side force increases from zero.

(107) Embodiment G. The radial bearing apparatus of any one of Embodiments A through F wherein the radial bearing apparatus is a component of an apparatus having a primary axis and comprising a shaft, wherein the shaft of the apparatus is tilted relative to the primary axis of the apparatus in a shaft tilt direction, and wherein the shaft tilt direction is opposite to the side force direction.

(108) Embodiment H. The radial bearing apparatus of any one of Embodiments A through G wherein the oblique section is a first oblique section, wherein the radial bearing contact interface further comprises a second oblique section, wherein the radial bearing housing surface and the radial bearing shaft surface are oblique to each other in the axial direction along the second oblique section when the side force is zero, wherein the radial bearing housing surface and the radial bearing shaft surface become less oblique to each other within a first range along the first oblique section as the side force increases from zero, and wherein the radial bearing housing surface and the radial bearing shaft surface become less oblique to each other within a second range along the second oblique section as the side force increases from zero.

(109) Embodiment I. The radial bearing apparatus of Embodiment H, further comprising a side force axial position where the side force is applied, wherein the first oblique section has a first vertex, wherein the first oblique section extends from the first vertex toward the side force axial position, wherein the second oblique section has a second vertex, wherein the second oblique section extends from the second vertex toward the side force axial position, and wherein the second vertex is between the first vertex and the side force axial position.

(110) Embodiment J. The radial bearing apparatus of Embodiment I wherein a first bearing interface angle is defined between the radial bearing housing surface and the radial bearing shaft surface at the first vertex and wherein the first bearing interface angle decreases within a first angular range as the side force increases from zero.

(111) Embodiment K. The radial bearing apparatus of Embodiment I or J wherein a second bearing interface angle is defined between the radial bearing housing surface and the radial bearing shaft surface at the second vertex, wherein the second bearing interface angle decreases within a second angular range as the side force increases from zero, and wherein the first bearing interface angle is smaller than the second bearing interface angle.

(112) Embodiment L. The radial bearing apparatus of any one of Embodiments H through K wherein the radial bearing apparatus is a component of an apparatus having a primary axis and comprising a shaft, wherein the shaft of the apparatus is tilted relative to the primary axis of the apparatus in a shaft tilt direction, and wherein the shaft tilt direction is opposite to the side force direction.

(113) Embodiment M. The radial bearing apparatus of any one of Embodiments H through L wherein the first oblique section has a first oblique section length in the axial direction, wherein the second oblique section has a second oblique section length in the axial direction, and wherein the first oblique section length is greater than the second oblique section length.

(114) Embodiment N. An apparatus for use in a borehole comprising a radial bearing apparatus as described in any one of Embodiments A through M.

(115) Embodiment O. The apparatus of Embodiment N wherein the apparatus has a length and a distal end, wherein a portion of the length of the apparatus comprises a reduced stiffness section, and wherein the radial bearing apparatus is axially located along the length of the apparatus between the reduced stiffness section and the distal end of the apparatus.

(116) Embodiment P. The apparatus of Embodiment O wherein the apparatus further comprises an increased diameter structure, and wherein the increased diameter structure is axially located along the length of the apparatus between the reduced stiffness section and the distal end of the apparatus.

(117) Embodiment Q. The apparatus of Embodiment P wherein the apparatus comprises a bearing assembly comprising the radial bearing apparatus and one or more thrust bearings, wherein the bearing assembly is axially located along the length of the apparatus between the reduced stiffness section and the distal end of the apparatus, and wherein the increased diameter structure is axially located along the length of the apparatus at one of the one or more thrust bearings.

(118) Embodiment R. The apparatus of any one of Embodiments N through Q wherein the radial bearing apparatus is a first radial bearing apparatus and wherein the apparatus further comprises a second radial bearing apparatus as described in any one of Embodiments A through J.

(119) Embodiment S. The apparatus of Embodiment R wherein the one or more thrust bearings are axially located along the length of the apparatus between the first radial bearing apparatus and the second radial bearing apparatus.

(120) Embodiment T. The apparatus of any one of Embodiments N through S wherein the apparatus comprises a drilling motor.

(121) Embodiment U. The apparatus of any one of Embodiments P through T wherein the increased diameter structure is a first increased diameter structure, wherein the apparatus further comprises a second increased diameter structure, and wherein the reduced stiffness section is axially located along the length of the apparatus between the first increased diameter structure and the second increased diameter structure.

(122) Embodiment V. The apparatus of Embodiment U wherein the apparatus comprises a drilling motor, wherein the drilling motor comprises a power section and wherein the second increased diameter structure is axially located along the length of the apparatus at the power section.

(123) Embodiment W. The apparatus of any one of Embodiments N through V wherein the apparatus comprises a transmission section and wherein the reduced stiffness section is axially located along the length of the apparatus at the transmission section.

(124) In this document, the word “comprising” is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the elements is present, unless the context clearly requires that there be one and only one of the elements.