Patent Description:
When drilling a wellbore, the drill bit may be turned by a rotation of the drill string or by a downhole motor. The downhole motor may be used to rotate the drill bit while the drill string is stationary. In such a drill string, the bottom hole assembly (BHA), located at the end of the drill string, may include the downhole motor, the drill bit, and a bearing section. The bearing section couples between the motor sub and the drill bit and houses the drive shaft which couples between the drill bit and the downhole motor. The bearing section couples to the drive shaft through one or more bearings to allow rotation of the drive shaft as the bearing section remains generally stationary within the wellbore.

The present invention provides for an offset shaft bearing assembly for a downhole tool according to the claims.

The present disclosure also provides for a method according to the respective claims and defined by them.

The present invention is best understood from the following detailed description when read with the accompanying figures.

It is to be understood that the following disclosure provides many different embodiments, or examples of the invention, for implementing different features of various embodiments. Specific examples of components and arrangements are described below to simplify. These are, of course, merely examples and are not intended to be limiting.

In some embodiments as depicted in <FIG>, <FIG>, a bottom hole assembly (BHA) may include offset shaft bearing assembly <NUM>. Offset shaft bearing assembly <NUM> may include outer housing <NUM>. Outer housing <NUM> may be generally tubular. Outer housing <NUM> may include one or more tubular subunits or subs to, for example and without limitation, facilitate assembly of offset shaft bearing assembly <NUM>. One having ordinary skill in the art with the benefit of this disclosure will understand that the specific sub arrangement of outer housing <NUM> depicted and described herein is merely exemplary and is not intended to limit the scope of this disclosure. Outer housing <NUM> may include coupler <NUM>. Coupler <NUM> may be adapted to couple to additional subs (not shown) of the BHA, including, for example and without limitation, a housing of a downhole motor such as a mud motor. Coupler <NUM> may rigidly couple outer housing <NUM> to the rest of the BHA. In some embodiments, outer housing <NUM> may be prevented from rotating within the wellbore. In some embodiments, outer housing <NUM> may include one or more external stabilizers <NUM> to, for example and without limitation, position offset shaft bearing assembly <NUM> within the wellbore. External stabilizers <NUM> may be, for example and without limitation, one or more radial protrusions, depicted in cross section in <FIG>, <FIG>. External stabilizers <NUM> may be positioned and have a selected diameter depending on the wellbore in which offset shaft bearing assembly <NUM> is to be used.

Offset shaft bearing assembly <NUM> may further include drive shaft <NUM>. Drive shaft <NUM> extends through inner bore <NUM> of outer housing <NUM>. Drive shaft <NUM> may include shaft coupler <NUM>. Shaft coupler <NUM> may mechanically couple to the output shaft of a downhole motor at a second end of drive shaft <NUM>. In some embodiments, shaft coupler <NUM> may mechanically couple to the output shaft of a mud motor through a transmission shaft. In some embodiments, shaft coupler <NUM> may include a constant velocity joint adapted to allow the output shaft of the motor to couple to drive shaft <NUM>. Drive shaft <NUM> may further include bit coupler <NUM> at a first end of drive shaft <NUM>. Bit coupler <NUM> may mechanically couple to a drill bit by, for example and without limitation, a box and pin joint.

In some embodiments, drive shaft <NUM> may be coupled to outer housing <NUM> by one or more bearings 111a, b. In some embodiments, bearings 111a, b may be radiused conical bearings, also referred to in the art as angle, taper, or cup/cone bearings. Radiused conical bearings, as depicted in <FIG>, may include cup portion <NUM> and cone portion <NUM>. Cup portion <NUM> and cone portion <NUM> may be generally annular and adapted to contact at bearing surfaces <NUM> and <NUM> respectively. Bearing surfaces <NUM> and <NUM> may be generally frustoconical in shape, allowing bearings 111a, b to resist longitudinal or thrust loading as well as radial loading between cup portion <NUM> and cone portion <NUM> while allowing relative rotation between cup portion <NUM> and cone portion <NUM>. Bearing surfaces <NUM>, <NUM> may be radiused such that bearing surfaces <NUM>, <NUM> are in contact. In some embodiments, bearing surfaces <NUM>, <NUM> may remain in contact despite angular misalignment between cup portion <NUM> and cone portion <NUM>, allowing bearings 111a, b to function with an angle between drive shaft <NUM> and outer housing <NUM>. Furthermore, the ability of bearings 111a, b to function through continuous angular offsets allows the same bearings 111a, b to be utilized as a part of offset shaft bearing assembly <NUM> with any desired angular offset as discussed below. Bearings 111a, b may thus act as both thrust and radial bearings. In some embodiments, bearing surfaces <NUM> and <NUM> may include one or more bearing elements <NUM> adapted to reduce wear on cup portion <NUM> and cone portion <NUM>. In some embodiments, bearing elements <NUM> may be polycrystalline diamond compacts.

In some embodiments, bearings 111a, b may include generally cylindrical outer surface <NUM> and generally cylindrical inner surface <NUM>. Outer surface <NUM> may serve to couple between or align bearings 111a, b with outer housing <NUM> and inner surface <NUM> may serve to couple between or align bearings 111a, b with drive shaft <NUM>. In some embodiments, bearing surfaces <NUM> and <NUM> may be curved or radiused such that bearing surfaces <NUM> and <NUM> remain in contact despite angular misalignment between cup portion <NUM> and cone portion <NUM>, thus allowing rotation of drive shaft <NUM> relative to outer housing <NUM> while drive shaft <NUM> is at an angle thereto.

As depicted in <FIG>, <FIG>, in some embodiments, the cup portion <NUM> of each bearing 111a, b may be coupled to outer housing <NUM> and the cone portion <NUM> may be coupled to drive shaft <NUM>. As understood by one having ordinary skill in the art with the benefit of this disclosure, cup portions <NUM> may instead be coupled to drive shaft <NUM> and cone portions <NUM> may be coupled to outer housing <NUM> without deviating from the scope of this disclosure. Bearings 111a, b may be positioned such that they retain drive shaft <NUM> both longitudinally and radially. In some embodiments, bearings 111a, b may thus be oriented in opposing directions. Although described herein as utilizing two bearings 111a, b, one having ordinary skill in the art with the benefit of this disclosure will understand that any number of bearings 111a, b may be utilized without deviating from the scope of this disclosure.

In some embodiments, one or more of bearings 111a, b may be offset from the housing centerline α of outer housing <NUM>, designated as α. <FIG>, <FIG> depict bearing 111b as being offset (<FIG>, <FIG>) and bearing 111a as being centered (<FIG>, <FIG>). One having ordinary skill in the art with the benefit of this disclosure will understand that both bearings 111a, b or bearing 111a alone may be offset without deviating from the scope of the present disclosure.

In other embodiments, as depicted in <FIG>, <FIG>, <FIG>, bearing 111b may be formed eccentrically. In such an embodiment, outer surface <NUM> of bearing 111b may be parallel to but nonconcentric with inner surface <NUM>. In such an embodiment, bearing mount <NUM> may be concentric with the housing centerline α of outer housing <NUM>.

In some embodiments, as depicted in <FIG>, <FIG>, <FIG>, outer surface <NUM>' of bearing 111b may be concentric with inner surface <NUM>'. Bearings 111b may be coupled to outer housing <NUM> by offset bearing mount <NUM>'. Offset bearing mount <NUM>' may be formed eccentrically such that the centerline of bearing 111b is offset from housing centerline α of outer housing <NUM>, thus positioning drive shaft <NUM> (defining shaft centerline β) at an angle to housing centerline α. Bearings 111a, b may thus be formed as standard radiused conical bearings including no eccentricity. In some embodiments, offset bearing mount <NUM>' may be formed such that inner surface <NUM>' is parallel to but nonconcentric with outer surface <NUM>'. In some embodiments, offset bearing mount <NUM>' may be formed such that inner surface <NUM>' is at an angle to outer surface <NUM>'.

As depicted in <FIG>, <FIG>, by offsetting bearing 111b, drive shaft <NUM>, having shaft centerline β, extends at an angle to housing centerline α of outer housing <NUM>. When operated, the drill bit coupled to drive shaft <NUM> is pointed in the direction of shaft centerline β, causing the wellbore drilled thereby to deviate or build in the direction of offset of shaft centerline β from housing centerline α, referred to herein as the build direction. In some embodiments, the angle between housing centerline α and shaft centerline β may be between <NUM>° and <NUM>°, between <NUM>° and <NUM>°, or between <NUM>° and <NUM>°.

In some embodiments, as depicted in <FIG>, both bearing 111b and bearing mount <NUM>" may be offset. As depicted in <FIG>, cup portion <NUM>" may be offset as previously discussed. One having ordinary skill in the art with the benefit of this disclosure will understand that cone portion <NUM> may be coupled to bearing mount <NUM>" and may be the offset portion of bearing 111b. In some embodiments, cup portion <NUM>" may be rotatably positionable within bearing mount <NUM>". In some embodiments, one or more rotational retention features including, for example and without limitation, cup portion <NUM>" may include an external spline and bearing mount <NUM>" may include an internal spline at coupling interface <NUM> which may, for example, allow cup portion <NUM>" to be engaged into bearing mount <NUM>" in various rotational positions. By positioning cup portion <NUM>" such that the offset aligns with the offset of bearing mount <NUM>" as depicted in <FIG>, the angle of drive shaft <NUM> as previously discussed may be increased. Likewise, by positioning cup portion <NUM>" such that the offset opposes that of bearing mount <NUM>" as depicted in <FIG>, the angle of drive shaft <NUM> may be decreased or eliminated. Furthermore, by varying the angle between the offset of cup portion <NUM>" and bearing mount <NUM>", the angle of drive shaft <NUM> may be varied.

In some embodiments, one or both of bearing mount <NUM>" and cup portion <NUM>" may be rotatable relative to outer housing <NUM>. In some embodiments, one or both of bearing mount <NUM>" and cup portion <NUM>" may be mechanically coupled to one or more motors such as, for example and without limitation, electric motors, gearing systems, ratcheting valve systems, ramps, solenoids, pistons, or other power transmission mechanisms. The motor or motors may rotate bearing mount <NUM>" and/or cup portion <NUM>" to, for example and without limitation, vary the angle of drive shaft <NUM>. In some embodiments, the motor or motors may be operable while offset shaft bearing assembly <NUM> is positioned in the wellbore.

In some embodiments, shaft centerline β may intersect housing centerline α of outer housing <NUM> at crossover point <NUM>. In some embodiments, crossover point <NUM> may be positioned at an end of offset shaft bearing assembly near or at bit coupler <NUM>. By locating crossover point <NUM> near the drill bit, the drill bit may remain generally centered during a rotation of the drill string. By reducing eccentricity of the drill bit, wobble or eccentric movement during rotation of the drill string may be reduced. Reducing wobble may, for example and without limitation, reduce damage to the wellbore or drill bit. Additionally, by forming outer housing <NUM> as a straight housing, the drill string may be capable of rotating at a higher rate than a drill string utilizing a bent sub to achieve the build angle as, for example and without limitation, eccentric rotation of bent components is eliminated, reducing damage to the wellbore and stresses imposed on the drill string. Furthermore, due to reduced stresses, rotation of the drill string may be achieved utilizing less power and lower pressure to run a mud pump to power drive shaft <NUM>. In some embodiments, rotation rates nearly equal to straight bottom hole assemblies may be achieved without additional damage to the drill string or wellbore. For example and without limitation, the drill string including offset shaft bearing assembly <NUM> may be capable of reliable rotation up to <NUM> RPM.

In some embodiments, inner bore <NUM> of outer housing <NUM> may be angled relative to housing centerline α of outer housing <NUM> such that inner bore <NUM> is concentric with shaft centerline β.

In some embodiments, offset shaft bearing assembly <NUM> may include mandrel catcher <NUM> to, for example and without limitation, prevent drive shaft <NUM> from exiting outer housing <NUM>.

In some embodiments, in order to, for example and without limitation, assist in cooling of bearing elements <NUM>, flow path <NUM> may be formed between drive shaft <NUM> and outer housing <NUM>. In some embodiments, flow restrictor <NUM> may be positioned between drive shaft <NUM> and outer housing <NUM> to, for example and without limitation, limit the flow of fluid between drive shaft <NUM> and outer housing <NUM> and reduce or prevent washout of components of offset shaft bearing assembly <NUM> caused by high speed fluid flow through flowpath <NUM>. In some embodiments, bearings 111a, 111b may, as depicted in <FIG>, include parent surface <NUM> between bearing elements <NUM>. Parent surface <NUM> may, for example and without limitation, be formed from a material softer than bearing elements <NUM> and may be positioned to erode when exposed to high velocity fluid, avoiding damage to bearing elements <NUM>. In some embodiments, parent surface <NUM> may be hardened by, for example and without limitation, a carbide coating.

In some embodiments, preload spacer <NUM> may be positioned between preloading shoulders <NUM>, <NUM> positioned on outer housing <NUM> and drive shaft <NUM> respectively. Preload spacer <NUM> may be positioned to preload bearings 111a, b. As an example, because of the weight on the drill bit, the bearing providing thrust resistance in the direction of the drill bit, depicted in <FIG>, <FIG> as bearing 111b, must resist a greater thrust force than the other bearing (111a). Preload spacer <NUM> may generally equalize loading between bearings 111a, b preventing, for example and without limitation, uneven wear between bearings 111a, b and uneven frictional characteristics. One having ordinary skill in the art with the benefit of this disclosure will understand that although depicted at a specific location along offset shaft bearing assembly <NUM>, preload spacer <NUM> and preloading shoulders <NUM>, <NUM> may be positioned between any components of offset shaft bearing assembly <NUM> capable of inducing the preloading as described without deviating from the scope of this disclosure. Other exemplary locations at which preload spacer <NUM> may be positioned include, for example and without limitation, between outer housing <NUM> and bearings 111a, b (denoted as <NUM>' in <FIG>) or between drive shaft <NUM> and bearings 111a, b (denoted as <NUM>" in <FIG>).

In some embodiments, offset shaft bearing assembly <NUM> may include an indication of the offset direction of shaft centerline β from housing centerline α. The indication may, for example and without limitation, allow an operator to identify the build direction or toolface of the BHA including offset shaft bearing assembly <NUM>. In some embodiments, offset shaft bearing assembly <NUM> may include one or more scribe lines <NUM>.

In some embodiments, the build rate of offset shaft bearing assembly <NUM> may be further increased by positioning a bent housing as understood in the art between the motor and offset shaft bearing assembly. As depicted in <FIG>, B, offset shaft bearing assembly <NUM> may include bent outer housing <NUM>. Bent outer housing <NUM> may, for example and without limitation, include bent portion <NUM>. Bent portion <NUM> may be adapted to couple to the rest of the drill string to, for example and without limitation, further increase the build angle of drive shaft <NUM>. In some embodiments, bent portion <NUM> may include a bend angle between <NUM>° and <NUM>°, between <NUM>° and <NUM>°, or between <NUM>° and <NUM>°. <FIG> depicts the centerline of drill string as drill string centerline γ, offset from both housing centerline α and shaft centerline β. Bent portion <NUM> may be fixed or adjustable.

In some embodiments, bent outer housing <NUM> may couple to inner housing <NUM>. Inner housing <NUM> may include inner bore <NUM> formed at an angle to housing centerline α as previously described which defines shaft centerline β. Inner housing <NUM> may be coupled to bearings 211a, b. In some embodiments, inner housing <NUM> may couple to bent outer housing <NUM> by threaded coupler <NUM>. In order to align or clock the bend of bent outer housing <NUM> with the build angle of inner housing <NUM>, timing spacer <NUM> may be positioned between bent outer housing <NUM> and inner housing <NUM> in threaded coupler <NUM>. In some embodiments, timing spacer <NUM> may be a ring or washer of a specific width such that when inner housing <NUM> is coupled onto bent outer housing <NUM>, the bend of bent outer housing <NUM> and build angle of inner housing <NUM> are aligned while maintaining a tight threaded coupling therebetween. In some embodiments, timing spacer <NUM> may be one or more annular spacers, bushings, washers, or Belleville springs.

In some embodiments, offset shaft bearing assembly <NUM> may include bearing pad <NUM>. Bearing pad <NUM> may be positioned on the exterior of bent outer housing <NUM> at a location opposite the toolface of offset shaft bearing assembly <NUM>. Bearing pad <NUM> may, for example and without limitation, prevent rotation of offset shaft bearing assembly <NUM> within the wellbore and reduce wear on offset shaft bearing assembly <NUM> during drilling operations.

With reference to <FIG>, <FIG>, in order to form offset shaft bearing assembly <NUM>, inner bore <NUM> may be formed in inner housing <NUM>. Inner bore <NUM> may be formed by any method including, for example and without limitation, milling, boring, turning, or combinations thereof. Inner bore <NUM> may be formed at an angle to the housing centerline α of inner housing <NUM> to form shaft centerline β as discussed hereinabove. Drive shaft <NUM> and bearings 211a, b may be coupled to inner housing <NUM>. As previously discussed, because of the radius of the bearing surfaces of bearings 211a, b, the same bearings 211a, b, may be utilized despite the selected angle between housing centerline α and shaft centerline β. Inner housing <NUM> may then be coupled to an outer housing, either a straight outer housing such as outer housing <NUM> as depicted in <FIG>, <FIG> or bent outer housing <NUM> as depicted in <FIG>, B. In some embodiments, inner housing <NUM> may be coupled to bent outer housing <NUM> utilizing a threaded coupler <NUM> having timing spacer <NUM> as described hereinabove. Timing spacer <NUM> may be selected such that its width allows the bend of bent outer housing <NUM> to align with the angle between housing centerline α and shaft centerline β.

In some embodiments, as depicted in <FIG>, offset shaft bearing assembly <NUM> may include bit box stabilizer <NUM>". Bit box stabilizer <NUM>" may be positioned on an outer surface of offset shaft bearing assembly <NUM> at bit coupler <NUM>. In some embodiments, bit box stabilizer <NUM>" may, for example and without limitation, position offset shaft bearing assembly <NUM> within the wellbore. Bit box stabilizer <NUM>" may be, for example and without limitation, one or more radial protrusions. Bit box stabilizer <NUM>" may have a selected diameter depending on the wellbore in which offset shaft bearing assembly <NUM> is to be used.

In some embodiments, as depicted in <FIG>, external stabilizers <NUM> may include one or more pistons <NUM>'. Pistons <NUM>' may, for example and without limitation, be extendable from an outer surface of external stabilizers <NUM>. Pistons <NUM>' may, in some embodiments, be driven hydraulically. In some embodiments, pistons <NUM>' may be controlled by one or more valves (not shown) and may extend from offset shaft bearing assembly <NUM> to contact the surrounding wellbore. In some embodiments, pistons <NUM>' may be used to vary the angle between centerline α of outer housing <NUM> and a centerline of the wellbore.

Claim 1:
An offset shaft bearing assembly (<NUM>, <NUM>) for a downhole tool comprising:
an outer housing (<NUM>, <NUM>), the outer housing (<NUM>, <NUM>) having a housing centerline;
a drive shaft (<NUM>), the drive shaft (<NUM>) extending through the outer housing (<NUM><NUM>), the drive shaft (<NUM>) being generally tubular and having a shaft centerline; and
two or more radiused conical bearings (111a, 111b, 211a, 211b) positioned to couple the drive shaft (<NUM>) to the outer housing (<NUM>, <NUM>), each radiused conical bearing (111a, 111b, 211a, 211b) having:
an outer surface (<NUM>, <NUM>'), the outer surface (<NUM>, <NUM>') being generally cylindrical, wherein the outer surface (<NUM>, <NUM>') is coupled to the outer housing (<NUM>, <NUM>) and aligned with the housing centerline;
an inner surface (<NUM>, <NUM>'), the inner surface (<NUM>, <NUM>') being generally cylindrical, wherein the inner surface (<NUM>, <NUM>') is coupled to the drive shaft (<NUM>) and aligned with the shaft centerline such that the inner surface (<NUM>, <NUM>') and outer surface (<NUM>, <NUM>') are concentric
a first bearing surface (<NUM>, <NUM>), the first bearing surface (<NUM>, <NUM>) coupled to the outer surface (<NUM>, <NUM>') of the radiused conical bearing (111a, 111b, 211a, 211b); and
a second bearing surface (<NUM>, <NUM>), the second bearing surface (<NUM>, <NUM>) coupled to the inner surface (<NUM>, <NUM>') of the radiused conical bearing (111a, 111b, 211a, 211b), the bearing surfaces (<NUM>, <NUM>) radiused such that the bearing surfaces (<NUM>, <NUM>) remain in contact despite angular misalignment between the outer surface (<NUM>, <NUM>') and the inner surface (<NUM>, <NUM>');
characterised in that
the inner surface (<NUM>, <NUM>') of at least one radiused conical bearing (111a, 111b, 211a, 211b) is offset from the housing centerline in a direction perpendicular to the housing centerline such that the shaft centerline is at an angle to the housing centerline.