Adjustable bend assembly for a downhole motor

A downhole motor for directional drilling includes a driveshaft assembly including a driveshaft housing and a driveshaft rotatably disposed within the driveshaft housing. In addition, the downhole motor includes a bearing assembly including a bearing housing and a bearing mandrel rotatably disposed within the bearing housing. The bearing mandrel has a first end directly connected to the driveshaft with a universal joint and a second end coupled to a drill bit. Further, the downhole motor includes an adjustment mandrel configured to adjust an acute deflection angle θ between the central axis of the bearing housing and the central axis of the driveshaft housing. The adjustment mandrel has a central axis coaxially aligned with the bearing housing, a first end coupled to the driveshaft housing, and a second end coupled to the bearing housing.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

Not applicable.

BACKGROUND

1. Field of the Disclosure

The disclosure relates generally to downhole motors used to drill boreholes in earthen formations for the ultimate recovery of oil, gas, or minerals. More particularly, the disclosure relates to downhole motors including adjustable bend assemblies for directional drilling.

2. Background of the Technology

In drilling a borehole into an earthen formation, such as for the recovery of hydrocarbons or minerals from a subsurface formation, it is conventional practice to connect a drill bit onto the lower end of a drillstring formed from a plurality of pipe joints connected together end-to-end, and then rotate the drill string so that the drill bit progresses downward into the earth to create a borehole along a predetermined trajectory. In addition to pipe joints, the drillstring typically includes heavier tubular members known as drill collars positioned between the pipe joints and the drill bit. The drill collars increase the vertical load applied to the drill bit to enhance its operational effectiveness. Other accessories commonly incorporated into drill strings include stabilizers to assist in maintaining the desired direction of the drilled borehole, and reamers to ensure that the drilled borehole is maintained at a desired gauge (i.e., diameter). In vertical drilling operations, the drillstring and drill bit are typically rotated from the surface with a top dive or rotary table.

During the drilling operations, drilling fluid or mud is pumped under pressure down the drill string, out the face of the drill bit into the borehole, and then up the annulus between the drill string and the borehole sidewall to the surface. The drilling fluid, which may be water-based or oil-based, is typically viscous to enhance its ability to carry borehole cuttings to the surface. The drilling fluid can perform various other valuable functions, including enhancement of drill bit performance (e.g., by ejection of fluid under pressure through ports in the drill bit, creating mud jets that blast into and weaken the underlying formation in advance of the drill bit), drill bit cooling, and formation of a protective cake on the borehole wall (to stabilize and seal the borehole wall).

Recently, it has become increasingly common and desirable in the oil and gas industry to drill horizontal and other non-vertical or deviated boreholes (i.e., “directional drilling”), to facilitate greater exposure to and production from larger regions of subsurface hydrocarbon-bearing formations than would be possible using only vertical boreholes. In directional drilling, specialized drill string components and “bottomhole assemblies” (BHAs) are often used to induce, monitor, and control deviations in the path of the drill bit, so as to produce a borehole of the desired deviated configuration.

Directional drilling is typically carried out using a downhole or mud motor provided in the bottomhole assembly (BHA) at the lower end of the drillstring immediately above the drill bit. Downhole motors typically include several components, such as, for example (in order, starting from the top of the motor): (1) a power section including a stator and a rotor rotatably disposed in the stator; (2) a drive shaft assembly including a drive shaft disposed within a housing, with the upper end of the drive shaft being coupled to the lower end of the rotor; and (3) a bearing assembly positioned between the driveshaft assembly and the drill bit for supporting radial and thrust loads. For directional drilling, the motor often includes a bent housing to provide an angle of deflection between the drill bit and the BHA. The deflection angle is usually between 0° and 5°. The axial distance between the lower end of the drill bit and bend in the motor is commonly referred to as the “bit-to-bend” distance.

To drill straight sections of borehole with a bent motor, the entire drillstring and BHA are rotated from the surface with the drillstring, thereby rotating the drill bit about the longitudinal axis of the drillstring; and to change the trajectory of the borehole, the drill bit is rotated exclusively with the downhole motor, thereby enabling the drill bit to rotate about its own central axis, which is oriented at the deflection angle relative to the drillstring due to the bent housing. Since the drill bit is skewed (i.e., oriented at the deflection angle) when the entire drillstring is rotated while drilling straight sections, the downhole motor is subjected to bending moments which may result in potentially damaging stresses at critical locations within the motor.

BRIEF SUMMARY OF THE DISCLOSURE

These and other needs in the art are addressed in one embodiment by a downhole motor for directional drilling. In an embodiment, the downhole motor comprises a driveshaft assembly including a driveshaft housing and a driveshaft rotatably disposed within the driveshaft housing. The driveshaft housing has a central axis, a first end, and a second end opposite the first end. The driveshaft has a central axis, a first end, and a second end opposite the first end. In addition, the downhole motor comprises a bearing assembly including a bearing housing and a bearing mandrel rotatably disposed within the bearing housing. The bearing housing has a central axis, a first end comprising a connector, and a second end opposite the first end. The bearing mandrel has a central axis coaxially aligned with the central axis of the bearing housing, a first end directly connected to the second end of the driveshaft with a universal joint, and a second end coupled to a drill bit. Further, the downhole motor comprises an adjustment mandrel configured to adjust an acute deflection angle θ between the central axis of the bearing housing and the central axis of the driveshaft housing. The adjustment mandrel has a central axis coaxially aligned with the central axis of the bearing housing, a first end, and a second end opposite the first end. The first end of the adjustment mandrel is coupled to the second end of the driveshaft housing and the second end of the adjustment mandrel is coupled to the first end of the bearing housing.

These and other needs in the art are addressed in another embodiment by a downhole motor for directional drilling. In an embodiment, the downhole motor comprises a driveshaft assembly including a driveshaft housing and a driveshaft rotatably disposed within the driveshaft housing. The driveshaft housing has a central axis, a first end, and a second end opposite the first end. The driveshaft has a central axis, a first end, and a second end opposite the first end. In addition, the downhole motor comprises a bearing assembly including a bearing housing and a bearing mandrel coaxially disposed within the bearing housing. The bearing housing has a central axis, a first end, and a second end opposite the first end. The bearing mandrel has a first end pivotally coupled to the second end of the driveshaft and a second end coupled to a drill bit. The first end of the bearing mandrel extends from the bearing housing into the driveshaft housing. Further, the downhole motor comprises an adjustment mandrel having a first end coupled to the second end of the driveshaft housing and a second end coupled to first end of the bearing housing. Rotation of the adjustment mandrel relative to the driveshaft housing is configured to adjust an acute deflection angle θ between the central axis of the driveshaft housing and the central axis of the bearing housing.

These and other needs in the art are addressed in another embodiment by a downhole motor for directional drilling. In an embodiment, the downhole motor comprises a driveshaft assembly including a driveshaft housing and a driveshaft rotatably disposed within the driveshaft housing. The driveshaft housing has a central axis, a first end, and a second end opposite the first end. The driveshaft has a central axis, a first end, a second end opposite the first end, and a receptacle extending axially from the second end of the driveshaft. In addition, the downhole motor comprises a bearing assembly including a bearing housing and a bearing mandrel rotatably disposed within the bearing housing. The bearing housing has a central axis, a first end, and a second end opposite the first end. The bearing mandrel has a first end pivotally coupled to the driveshaft and a second end coupled to a drill bit. The first end of the bearing mandrel is disposed within the receptacle of the driveshaft. The central axis of the driveshaft housing is oriented at an acute deflection angle θ relative to the central axis of the bearing housing.

Embodiments described herein comprise a combination of features and advantages intended to address various shortcomings associated with certain prior devices, systems, and methods. The foregoing has outlined rather broadly the features and technical advantages of the invention in order that the detailed description of the invention that follows may be better understood. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description, and by referring to the accompanying drawings. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . . ” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection via other devices, components, and connections. In addition, as used herein, the terms “axial” and “axially” generally mean along or parallel to a central axis (e.g., central axis of a body or a port), while the terms “radial” and “radially” generally mean perpendicular to the central axis. For instance, an axial distance refers to a distance measured along or parallel to the central axis, and a radial distance means a distance measured perpendicular to the central axis. Any reference to up or down in the description and the claims is made for purposes of clarity, with “up”, “upper”, “upwardly”, “uphole”, or “upstream” meaning toward the surface of the borehole and with “down”, “lower”, “downwardly”, “downhole”, or “downstream” meaning toward the terminal end of the borehole, regardless of the borehole orientation.

Referring now toFIG. 1, a system10for drilling for drilling a borehole16in an earthen formation is shown. In this embodiment, system10includes a drilling rig20disposed at the surface, a drill string21extending downhole from rig20, a bottomhole assembly (BHA)30coupled to the lower end of drillstring21, and a drill bit90attached to the lower end of BHA30. A downhole mud motor35is provided in BHA30for facilitating the drilling of deviated portions of borehole16. Moving downward along BHA30, motor35includes a hydraulic drive or power section40, a driveshaft assembly100, and a bearing assembly200. The portion of BHA30disposed between drillstring21and motor35can include other components, such as drill collars, measurement-while-drilling (MWD) tools, reamers, stabilizers and the like.

Power section40converts the fluid pressure of the drilling fluid pumped downward through drillstring21into rotational torque for driving the rotation of drill bit90. Drive shaft assembly100and bearing assembly200transfer the torque generated in power section40to bit90. With force or weight applied to the drill bit90, also referred to as weight-on-bit (“WOB”), the rotating drill bit90engages the earthen formation and proceeds to form borehole16along a predetermined path toward a target zone. The drilling fluid or mud pumped down the drill string21and through motor30passes out of the face of drill bit90and back up the annulus18formed between drill string21and the wall19of borehole16. The drilling fluid cools the bit90, and flushes the cuttings away from the face of bit90and carries the cuttings to the surface.

Referring now toFIGS. 2 and 3, hydraulic drive section40comprises a helical-shaped rotor50, preferably made of steel that may be chrome-plated or coated for wear and corrosion resistance, disposed within a stator60comprising a cylindrical stator housing65lined with a helical-shaped elastomeric insert61. Helical-shaped rotor50defines a set of rotor lobes57that intermesh with a set of stator lobes67defined by the helical-shaped insert61. As best shown inFIG. 3, the rotor50has one fewer lobe57than the stator60. When the rotor50and the stator60are assembled, a series of cavities70are formed between the outer surface53of the rotor50and the inner surface63of the stator60. Each cavity70is sealed from adjacent cavities70by seals formed along the contact lines between the rotor50and the stator60. The central axis58of the rotor50is radially offset from the central axis68of the stator60by a fixed value known as the “eccentricity” of the rotor-stator assembly. Consequently, rotor50may be described as rotating eccentrically within stator60.

During operation of the hydraulic drive section40, fluid is pumped under pressure into one end of the hydraulic drive section40where it fills a first set of open cavities70. A pressure differential across the adjacent cavities70forces the rotor50to rotate relative to the stator60. As the rotor50rotates inside the stator60, adjacent cavities70are opened and filled with fluid. As this rotation and filling process repeats in a continuous manner, the fluid flows progressively down the length of hydraulic drive section40and continues to drive the rotation of the rotor50. Driveshaft assembly100shown inFIG. 1includes a driveshaft discussed in more detail below that has an upper end coupled to the lower end of rotor50. The rotational motion and torque of rotor50is transferred to drill bit90via driveshaft assembly100and bearing assembly200.

In this embodiment, driveshaft assembly100is coupled to an outer housing210of bearing assembly200with a bend adjustment assembly300that provides an adjustable bend301along motor35. Due to bend301, a deflection angle θ is formed between the central axis95of drill bit90and the longitudinal axis25of drill string21. To drill a straight section of borehole16, drillstring21is rotated from rig20with a rotary table or top drive to rotate BHA30and drill bit90coupled thereto. Drillstring21and BHA30rotate about the longitudinal axis of drillstring21, and thus, drill bit90is also forced to rotate about the longitudinal axis of drillstring21.

Referring again toFIG. 1, with bit90disposed at deflection angle θ, the lower end of drill bit90distal BHA30seeks to move in an arc about longitudinal axis25of drillstring21as it rotates, but is restricted by the sidewall19of borehole16, thereby imposing bending moments and associated stress on BHA30and mud motor35. In general, the magnitudes of such bending moments and associated stresses are directly related to the bit-to-bend distance D—the greater the bit-to-bend distance D, the greater the bending moments and stresses experienced by BHA30and mud motor35.

In general, driveshaft assembly100functions to transfer torque from the eccentrically-rotating rotor50of power section40to a concentrically-rotating bearing mandrel220of bearing assembly200and drill bit90. As best shown inFIG. 3, rotor50rotates about rotor axis58in the direction of arrow54, and rotor axis58rotates about stator axis68in the direction of arrow55. However, drill bit90and bearing mandrel220are coaxially aligned and rotate about a common axis that is offset and/or oriented at an acute angle relative to rotor axis58. Thus, driveshaft assembly100converts the eccentric rotation of rotor50to the concentric rotation of bearing mandrel220and drill bit90, which are radially offset and/or angularly skewed relative to rotor axis58.

Referring now toFIG. 4, driveshaft assembly100includes an outer housing110and a one-piece (i.e., unitary) driveshaft120rotatably disposed within housing110. Housing110has a linear central or longitudinal axis115, an upper end110acoupled end-to-end with the lower end of stator housing65, and a lower end110bcoupled to housing210of bearing assembly200via bend adjustment assembly300. As best shown inFIG. 1, in this embodiment, driveshaft housing110is coaxially aligned with stator housing65, however, due to bend301between driveshaft assembly100and bearing assembly200, driveshaft housing100is oriented at deflection angle θ relative to bearing assembly200and drill bit90.

In this embodiment, driveshaft housing110is formed from a pair of coaxially aligned, generally tubular housings connected together end-to-end. Namely, driveshaft housing110includes a first or upper housing section111extending axially from upper end110aand a second or lower housing section116extending axially from lower end110bto upper housing section111. Upper housing section111has a first or upper end111acoincident with end110aand a second or lower end111bcoupled to lower housing section116. Upper end110a,111acomprises a threaded connector112and lower end111bcomprises a threaded connector113. Threaded connectors112,113are coaxially aligned, each being concentrically disposed about axis115. In this embodiment, connector112is an externally threaded connector or pin end, and connector113is an internally threaded connector or box end.

Referring now toFIGS. 4 and 5, lower housing section116has a first or upper end116acoupled to upper housing section111and a second or lower end116bcoincident with end110b. Upper end116acomprises a threaded connector117and lower end110b,116bcomprises a threaded connector118. Threaded connector117is coaxially aligned with connectors112,113and concentrically disposed about axis115, however, threaded connector118is concentrically disposed about an axis118aoriented at a non-zero acute angle α relative to axis115. In this embodiment, connector117is an externally threaded connector or pin end, and connector118is an internally threaded connector or box end. Thus, axis118ais the central axis of the threaded inner cylindrical surface of lower housing section116at end116b. Accordingly, connector118may be described as being “offset.” Angle α is preferably greater than 0° and less than or equal to 2°.

Externally threaded connector112of upper housing section111threadably engages a mating internally threaded connector or box end disposed at the lower end of stator housing65, and internally threaded connector113of upper housing section111threadably engages mating externally threaded connector117of lower housing section116. As will be described in more detail below, lower end110b,116bof lower housing section116, and in particular internally threaded offset connector118, threadably engages a mating externally threaded component of bend adjustment assembly300.

Driveshaft housing110has a central through bore or passage114extending axially between ends110a,110b. Bore114defines a radially inner surface119within housing110that includes a first or upper annular recess119aand a second or lower annular recess119baxially spaced below recess119a. In this embodiment, upper recess119ais disposed along upper housing section111and lower recess119bis disposed along lower housing section116. Recesses119a,119bare disposed at a radius that is greater than the remainder of inner surface119and provide sufficient clearance for the movement (rotation and pivoting) of driveshaft120.

Referring again toFIG. 4, driveshaft120has a linear central or longitudinal axis125, a first or upper end120a, and a second or lower end120bopposite end120a. Upper end120ais pivotally coupled to the lower end of rotor50with a driveshaft adapter130and universal joint140, and lower end120bis pivotally coupled to an upper end220aof bearing mandrel220with a universal joint140. In this embodiment, upper end120aand one universal joint140are disposed within driveshaft adapter130, whereas lower end120bcomprises an axially extending counterbore or receptacle121that receives upper end220aof bearing mandrel220and one universal joint140. Thus, upper end120amay also be referred to as male end120a, and lower end120bmay also be referred to as female end120b.

Driveshaft adapter130extends along a central or longitudinal axis135between a first or upper end130acoupled to rotor50, and a second or lower end130bcoupled to upper end120aof driveshaft120. Upper end130acomprises an externally threaded male pin or pin end131that threadably engages a mating female box or box end at the lower end of rotor50. A receptacle or counterbore132extends axially (relative to axis135) from end130b. Upper male end120aof driveshaft120is disposed within counterbore132and pivotally coupled to adapter130with one universal joint140disposed within counterbore132.

Universal joints140allow ends120a,120bto pivot relative to adapter130and bearing mandrel220, respectively, while transmitting rotational torque between rotor50and bearing mandrel220. Specifically, upper universal joint140allows upper end120ato pivot relative to upper adapter130about an upper pivot point121a, and lower universal joint140allows lower end120bto pivot relative to bearing mandrel220about a lower pivot point121b. Upper adapter130is coaxially aligned with rotor50(i.e., axis135of upper adapter and rotor axis58are coaxially aligned). Since rotor axis58is radially offset and/or oriented at an acute angle relative to the central axis of bearing mandrel220, axis125of driveshaft120is skewed or oriented at an acute angle relative to axis115of housing110, axis58of rotor50, and the central axis225of bearing mandrel220. However, universal joints140accommodate for the angularly skewed driveshaft120, while simultaneously permitting rotation of the driveshaft120within housing110. Ends120a,120band corresponding universal joints140are axially positioned within recesses119a,119b, respectively, of housing110, which provide clearance for end120b,130bas driveshaft120simultaneously rotates and pivots within housing110.

In general, each universal joint (e.g., each universal joint140) may comprise any joint or coupling that allows two parts that are coupled together and not coaxially aligned with each other (e.g., driveshaft120and adapter130oriented at an acute angle relative to each other) limited freedom of movement in any direction while transmitting rotary motion and torque including, without limitation, universal joints (Cardan joints, Hardy-Spicer joints, Hooke joints, etc.), constant velocity joints, or any other custom designed joint.

As previously described, adapter130couples driveshaft120to the lower end of rotor50. During drilling operations, high pressure drilling fluid or mud is pumped under pressure down drillstring21and through cavities70between rotor50and stator60, causing rotor50to rotate relative to stator60. Rotation of rotor50drives the rotation of adapter130, driveshaft120, the bearing assembly mandrel, and drill bit90. The drilling fluid flowing down drillstring21through power section40also flows through driveshaft assembly100and bearing assembly200to drill bit90, where the drilling fluid flows through nozzles in the face of bit90into annulus18. Within driveshaft assembly100and the upper portion of bearing assembly200, the drilling fluid flows through an annulus150formed between driveshaft housing110and driveshaft120, and between driveshaft housing110and bearing mandrel220of bearing assembly200.

Referring now toFIGS. 4 and 6, bearing assembly200includes bearing housing210and one-piece (i.e., unitary) bearing mandrel220rotatably disposed within housing210. Bearing housing210has a linear central or longitudinal axis215, a first or upper end210acoupled to lower end110bof driveshaft housing110with bend adjustment assembly300, a second or lower end210b, and a central through bore or passage214extending axially between ends210a,210b. Bearing housing210is coaxially aligned with bit90, however, due to bend301between driveshaft assembly100and bearing assembly200, bearing housing210is oriented at deflection angle θ relative to driveshaft housing110.

In this embodiment, bearing housing210is formed from a pair of generally tubular housings connected together end-to-end. Namely, housing210includes a first or upper housing section211extending axially from upper end210aand a second or lower housing section216extending axially from lower end210bto housing section211. Upper housing section211has a first or upper end211acoincident with end210aand a second or lower end211bcoupled to lower housing section216. Upper end210a,211acomprises a threaded connector212and lower end comprises a threaded connector213. Threaded connectors212,213are coaxially aligned, each being concentrically disposed about axis215. In this embodiment, connector212is an externally threaded connector or pin end and connector213is an internally threaded connector or box end.

Referring still toFIGS. 4 and 6, lower housing section216has a first or upper end216acoupled to upper housing section211and a second or lower end216bcoincident with end210b. Upper end216acomprises a threaded connector217coaxially aligned with axis215. In this embodiment, connector217is an externally threaded connector or pin end. Internally threaded connector213of upper housing section211threadably engages mating externally threaded connector217of lower housing section211. As will be described in more detail below, upper end210b,211aof upper housing section211, and in particular externally threaded connector212, threadably engages a mating internally threaded component of bend adjustment assembly300.

Referring still toFIGS. 4 and 6, bearing mandrel220has a central axis225coaxially aligned with central axis215of housing210, a first or upper end220a, a second or lower end220b, and a central through passage221extending axially from lower end220band terminating axially below upper end220a. Upper end220aof mandrel220extends axially from upper end210aof bearing housing210into passage114of driveshaft housing110. In addition, upper end220ais directly coupled to lower end120bof driveshaft via one universal joint140. In particular, upper end220ais disposed within receptacle121at lower end120bof driveshaft120and pivotally coupled thereto with one universal joint140. Lower end220bof mandrel220is coupled to drill bit90.

Mandrel220also includes a plurality of circumferentially-spaced, and axially spaced drilling fluid ports222extending radially from passage221to the outer surface of mandrel220. Ports222provide fluid communication between annulus150and passage221. During drilling operations, mandrel220is rotated about axis215relative to housing210. In particular, high pressure drilling mud is pumped through power section40to drive the rotation of rotor50, which in turn drives the rotation of driveshaft120, mandrel220, and drill bit90. The drilling mud flowing through power section40flows through annulus150, ports222and passage221of mandrel220in route to drill bit90.

As abrasive drilling fluid flows from annulus150into ports222, an uneven distribution of drilling fluid among ports222can lead to excessive erosion—in general, ports (e.g., ports222) that flow a greater volume of drilling fluid experience greater erosion than ports that flow a lesser volume of drilling fluid. However, in this embodiment, annulus150and ports222are sized, shaped, and oriented to facilitate a more uniform distribution of drilling fluid among the different ports222, thereby offering the potential to reduce excessive erosion of certain ports222. More specifically, each port222is oriented at an angle of 45° relative to axis225of mandrel220. Further, the radial width of annulus150decreases moving axially towards ports222. Namely, the portion of annulus150disposed about bearing mandrel220has three axially adjacent segments or sections that decrease in radial width moving axially towards ports222. Moving towards ports222, annulus150includes a first axial segment150ahaving a radial width W150ameasured radially from bearing mandrel220to housing110, a second axial segment150badjacent segment150ahaving a radial width W150bmeasured radially from bearing mandrel220to an adjustment mandrel310disposed within housing110, and a third axial segment150cadjacent segment150bhaving a radial width W150cmeasured radially from bearing mandrel220to adjustment mandrel310. Radial widths W150a, W150band W150cprogressively decrease moving axially towards ports222. Computational fluid dynamic (CFD) modeling indicates the angular orientation of ports222and stepwise decrease in radial width of annulus150moving axially towards ports222more uniformly distributes drilling fluid among the different ports222.

Referring again toFIG. 4, as previously described, in this embodiment, driveshaft120is a unitary, single-piece and bearing mandrel220is unitary, single-piece. In particular, end120aof driveshaft120is coupled to rotor50with a driveshaft adapter130and universal joint140, and end120bof driveshaft120is coupled to bearing mandrel220with receptacle121and universal joint140. However, between ends120a,120bcoupled to rotor50and bearing mandrel220, driveshaft adapter120is a single, unitary, monolithic structure devoid of joints (e.g., universal joints). Similarly, end220aof bearing mandrel220is coupled to driveshaft120via receptacle121and universal joint140, and end220bof bearing mandrel220is coupled to a drill bit. However, between ends220a,220bcoupled to driveshaft120and the drill bit, bearing mandrel220is a single, unitary, monolithic structure devoid of joints (e.g., universal joints). Consequently, between rotor50and the drill bit, only two universal joints140are provided along the drivetrain comprising driveshaft120and bearing mandrel220. Further, only one universal joint is provided between driveshaft120and bearing mandrel220. Providing only a single universal joint140between driveshaft120and mandrel220eliminates any intermediary universal joints, which may increase the strength of the coupling between driveshaft120and mandrel220, as well as facilitate a further reduction in the bit-to-bend distance D. In other embodiments, the driveshaft (e.g., driveshaft120) and/or the bearing mandrel (e.g., bearing mandrel220) may contain a varying number of universal joints (e.g., universal joints140).

Referring still toFIGS. 4 and 6, housing210has a radially inner surface218that defines through passage214. Inner surface218includes a plurality of axially spaced apart annular shoulders. Specifically, inner surface218includes a first annular shoulder218aand a second annular shoulder218bpositioned axially below first shoulder218a. Shoulders218a,218bface each other. First annular shoulder218ais formed along inner surface218in upper housing section211, and second annular shoulder218bis defined by end216aof lower housing section216. Mandrel220has a radially outer surface223including an annular shoulder223aaxially aligned with shoulder218b

As best shown inFIG. 6, a plurality of annuli are radially positioned between mandrel220and housing210. In particular, a first or upper annulus250is axially positioned between housing shoulder218aand end210a, a second or intermediate annulus251is axially positioned between shoulder218aand shoulders223,218b, and a third or lower annulus252is axially positioned between shoulders223a,218band end210b. An upper radial bearing260is disposed in upper annulus250, a thrust bearing assembly261is disposed in intermediate annulus251, and a lower radial bearing262is disposed in lower annulus252.

Upper radial bearing260is disposed about mandrel220and axially positioned above thrust bearing assembly261, and lower radial bearing262is disposed about mandrel220and axially positioned below thrust bearing assembly261. In general, radial bearings260,262permit rotation of mandrel220relative to housing210while simultaneously supporting radial forces therebetween. In this embodiment, upper radial bearing260and lower radial bearing262are both sleeve type bearings that slidingly engage cylindrical surfaces on the outer surface223of mandrel220. However, in general, any suitable type of radial bearing(s) may be employed including, without limitation, needle-type roller bearings, radial ball bearings, or combinations thereof. Annular thrust bearing assembly261is disposed about mandrel220and permits rotation of mandrel220relative to housing210while simultaneously supporting axial loads in both directions (e.g., off-bottom and on-bottom axial loads). In this embodiment, thrust bearing assembly261generally comprises a pair of caged roller bearings and corresponding races, with the central race threadedly engaged to bearing mandrel220. Although this embodiment includes a single thrust bearing assembly261disposed in one annulus251, in other embodiments, more than one thrust bearing assembly (e.g., thrust bearing assembly261) may be included, and further, the thrust bearing assemblies may be disposed in the same or different thrust bearing chambers (e.g., two-shoulder or four-shoulder thrust bearing chambers).

In this embodiment, radial bearings260,262and thrust bearing assembly261are oil-sealed bearings. In particular, an upper seal assembly270is radially positioned between upper end210aof housing210and mandrel220, and a lower seal assembly271is radially positioned between lower end210bof housing210and mandrel220. Seal assemblies270,271provide annular seals between housing210and mandrel220at ends210a,210b, respectively. Thus, seal assemblies270,271isolate radial bearings260,262and bearing assembly261from drilling fluid in annulus150and drilling fluid in borehole16, respectively. A pressure compensation system is preferably utilized in connection with oil-sealed bearings260,262,261. Examples of pressure compensation systems that can be used in connection with bearings260,262,261are disclosed in U.S. Patent Application No. 61/765,164, which is herein incorporated by reference in its entirely. As previously described, in this embodiment, bearings260,261,262are oil-sealed. However, in other embodiments, the bearings of the bearing assembly (e.g., bearing assembly200) are mud lubricated. For example, referring now toFIG. 11, an embodiment of a mud motor35′ is shown. Mud motor35′ is the same as mud motor35previously described with the exception that bearing assembly200′ includes mud-lubricated radial bearings260′,262′ and thrust bearing261′, seal assemblies270,271are omitted to allow a portion of drilling mud flowing through annulus150to access bearings260′,261′,262′, and bearing mandrel220′ includes a plurality of circumferentially-spaced mud return ports222′ proximal lower end220bfor retuning drilling mud flowing through bearings260′,261′,262′ to central passage221. Each port222′ extends radially from central passage221to the outer surface of mandrel220′. Thus, in this embodiment, a portion of the drilling fluid flowing through annulus150bypasses ports222and lubricates bearings260′,261′ and262′ prior to returning to central passage221via ports222′.

Referring now toFIGS. 1, 4, and 6, as previously described, bend adjustment assembly300couples driveshaft housing110to bearing housing210, and introduces bend301and deflection angle θ along motor35. Axis115of driveshaft housing110is coaxially aligned with axis25and axis215of bearing housing210is coaxially aligned with axis95, thus, deflection angle θ also represents the angle between axes115,215when mud motor35is in an undeflected state (e.g., outside borehole16). Due to the deflection of motor35in borehole16, the angle between axes115,215will typically be less than deflection angle θ. As will be described in more detail below, deflection angle θ can be adjusted, as desired, with bend adjustment assembly300.

As best shown inFIG. 6, in this embodiment, bearing adjustment assembly300includes an adjustment mandrel310and an adjustment lock ring320. Adjustment mandrel310is disposed about mandrel220and ring320is disposed about adjustment mandrel310. As will be described in more detail below, ring320enables the rotation of adjustment mandrel310relative to driveshaft housing110to adjust deflection angle θ between a maximum and a minimum.

Referring now toFIGS. 6-8, adjustment mandrel310has a central or longitudinal axis315, a first or upper end310a, a second or lower end310bopposite end310a, and a central through bore or passage311extending axially between ends310a,310b. Axis315is coaxially aligned with axis215of bearing housing210.

Upper end310acomprises a threaded connector312and lower end310bcomprises a threaded connector313. Threaded connector313is coaxially aligned with axis315, and concentrically disposed about axis315, however, threaded connector312is concentrically disposed about an axis312aoriented at a non-zero acute angle relative to axis315. In this embodiment, connector312is an externally threaded connector or pin end, and connector313is an internally threaded connector or box end. Thus, axis312ais the central axis of the threaded outer cylindrical surface of adjustment mandrel310at end310a. Accordingly, connector312may be described as being “offset.” Angle β is preferably greater than 0° and less than or equal to 2°, and preferably the same as angle α.

As best shown inFIGS. 6 and 8, externally threaded offset connector312of mandrel310threadably engages mating internally threaded offset connector118of lower housing section116, and internally threaded connector313of mandrel310threadably engages mating externally threaded connector212of bearing housing210. When connectors118,312are threaded together and connectors212,313are threaded together, axes118a,312aare coaxially aligned, axes215,315are coaxially aligned, and axes215,315are oriented at deflection angle θ relative to axis115, thereby inducing bend301along motor35. Depending on the rotational position of mandrel310relative to lower housing section116, deflection angle θ can be adjusted to an intermediate angle between a minimum deflection angle θminequal to the difference of angles α, β (i.e., 0° if α=β) and a maximum deflection angle θmaxequal to the sum of angles α, β.

Referring now toFIGS. 6 and 7, the outer cylindrical surface of mandrel310includes a plurality of circumferentially-spaced elongate semi-cylindrical recesses319positioned proximal lower end310b. Recesses319are oriented parallel to axis315. As will be described in more detail below, each recess319receives a mating, elongate cylindrical spline330. Although splines330slidingly engage recesses319in this embodiment, in other embodiments, a plurality of circumferentially-spaced splines can extend radially from and be integrally formed with the adjustment mandrel (e.g., mandrel310).

Referring now toFIGS. 6, 9, and 10, annular adjustment lock ring320is axially positioned between lower end116bof lower housing section116and an annular shoulder211con the outer surface of upper housing section211, and is disposed about upper end211aof upper housing section211and lower end310bof adjustment mandrel310. Lock ring320has a central or longitudinal axis325, a first or upper end320a, a second or lower end320bopposite end320a, and a through bore or passage321extending axially between ends320a,320b. Passage321defines a cylindrical inner surface322extending between ends320a,320b. Inner surface322includes a plurality of circumferentially-spaced semi-cylindrical recesses323, each recess323is oriented parallel to axis325and extends from upper end320ato lower end320b. As best shown inFIG. 7, when lock ring320is mounted to mandrel310, each recess323is circumferentially aligned with a corresponding recess319, and one spline330is disposed within each set of aligned recesses319,323. Splines330allow lock ring320to move axially relative to mandrel310, but prevent lock ring320from moving rotationally relative to mandrel310. Thus, by rotating lock ring320about axis315, mandrel310is rotated about axis315.

Referring now toFIGS. 9 and 10, adjustment ring320further includes a plurality of circumferentially spaced teeth326at upper end320a. Teeth326are sized and shaped to releasably engage a mating set of circumferentially spaced teeth327at lower end116bof lower housing section116. As shown inFIG. 9, engagement and interlock of mating teeth326,327prevents lock ring320from rotating relative to lower housing section116, however, as shown inFIG. 10, when lock ring320is axially spaced from lower housing section116and teeth326,327are disengaged, lock ring320can be rotated relative to lower housing section116. It should also be appreciated that teeth326,327can releasably engage and interlock while accommodating bend301at the junction of lock ring320and housing110.

Referring now toFIGS. 1 and 4, prior to lowering BHA30downhole, the deflection angle θ is adjusted and set based on the projected or targeted profile of borehole16to be drilled with system10. In general, the deflection angle θ can be adjusted and set at any angle between 0° and the sum of angles α, β by rotating annular adjustment ring320relative to housing110. Deflection angle θ is controlled and varied via bend adjustment assembly300. In particular, mandrel310is rotated relative to housing110via lock ring320and splines330to adjust and set deflection angle θ. As previously described, engagement of teeth326,327prevents lock ring320from being rotated relative to housing110, and thus, to enable rotation of lock ring320(and hence rotation of mandrel310) relative to housing110, teeth326,327are disengaged. Thus, bearing housing210is unthreaded from mandrel310to create an axial clearance between lock ring320and shoulder211c. With a sufficient axial clearance between lock ring320and shoulder211c, lock ring320is slid axially downward away from housing110via sliding engagement of splines330and recesses323until teeth326,327are fully disengaged. With teeth326,327fully disengaged, torque is applied to adjustment ring320to rotate ring320and mandrel310(via splines330) relative to housing110. Rotation of mandrel310relative to housing110causes offset connector312of mandrel310to rotate relative to offset connector118of housing110.

The full range in variation of deflection angle θ can be achieved by rotating mandrel310between 0° and 180° relative to housing110, with the 0° angular position of mandrel310relative to housing110providing the minimum deflection angle θminequal to the difference between angles α, β (i.e., 0° if α=β), and the 180° angular position of mandrel310relative to housing110providing the maximum deflection angle θmaxequal to the sum of angles α, β. In general, deflection angle θ varies non-linearly moving between the 0° and 180° angular positions of mandrel310relative to housing110. Thus, an incremental deflection angle θ between minimum deflection angle θminand maximum deflection angle θmaxcan be set. The specific incremental values of deflection angle θ that can be selected depend on the quantity and spacing of teeth326,327and the values of angles α, β. In this embodiment, the radially outer surfaces of lock ring320and housing110at ends320a,110b, respectively, are marked/indexed to provide an indication of the deflection angle θ for various angular positions of lock ring320, and hence mandrel310, relative to housing110between 0° and 180°.

Once mandrel310has been rotated sufficiently to provide the desired deflection angle θ, ring320is axially moved towards housing110to engage teeth326,327, which prevent relative rotation of lock ring320and mandrel310relative to housing110, thereby locking in the desired deflection angle θ. Next, the bearing housing210is threaded into mandrel310until shoulder211caxially abuts lock ring320, thereby preventing lock ring320from moving axially away from housing110and disengaging teeth326,327.

In the manner described herein, an adjustable bend motor assembly is provided for use in drilling boreholes having non-vertical or deviated sections. As compared to most conventional bent motor assemblies, embodiments described herein provide a substantially reduced bit-to-bend distance via a bend positioned immediately above the bearing housing and axial overlap of the bend adjustment assembly with the bearing assembly mandrel. The reduced bit-to-bend distance offers the potential to enhance durability and build rates. In particular, for a given deflection angle, the magnitude of the bending moments and stresses experienced by downhole mud motors are directly related to the bit-to-bend distance (i.e., the greater the bit-to-bend distance, the greater the bending moments). Consequently, the maximum deflection angle of a downhole mud motor is typically limited by the magnitude of the stresses resulting from the bending moments. Therefore, by decreasing the bit-to-bend distance for a given deflection angle, embodiments described herein offer the potential to reduce bending moments and associated stresses experienced by the downhole mud motor. In addition, a shorter bit-to-bend distance decreases the minimum radius of curvature (i.e., a sharper bend) of the borehole path that can be excavated by the drill bit at a given deflection angle provided by the bent housing. For a borehole having a deviated section that includes a desired radius of curvature, by decreasing the bit-to-bend distance, a smaller deflection angle of the bent housing can be used in order to produce a borehole section at that desired radius. Thus, a downhole motor having a relatively short bit-to-bend distance may both reduce stresses imparted to the motor at a given deflection angle and allow for the use of a smaller deflection angle to drill a borehole having a desired radius of curvature.

Moreover, in conventional mud motors, the threaded connection between the upper end of the bearing mandrel and an adapter threaded thereon and coupled to the lower end of the driveshaft with a universal joint is particularly susceptible to failure or fracturing when excessive bending moments and stresses are applied to the motor. However, in embodiments described herein, that threaded connection is eliminated. In particular, as previously described, upper end220aof bearing mandrel220is disposed in receptacle121provided at lower end120bof driveshaft120and coupled to driveshaft120with universal joint140. In other words, no adapter is threaded onto upper end220aof bearing mandrel220in this embodiment.

Although embodiments of mud motor35described herein include an adjustable bend301, potential advantageous features of mud motor35can also be used in connection with fixed bend mud motors. For example, a mud flow annulus having a decreasing radial width moving towards the mud inlet ports of the mandrel can be employed in fixed bend mud motors to more uniformly distribute drilling fluid amongst the inlet ports. As another example, a bearing mandrel having an upper end coupled to the lower end of a driveshaft without a threaded connection can be employed in fixed bend mud motors to enhance durability.