Patent Grant
9482223
This application, pursuant to 35 U.S.C. §120, claims benefit to U.S. patent application Ser. No. 13/300,446, filed Nov. 18, 2011, which claims priority to UK Patent Application No. 1019614.5 filed on Nov. 19, 2010, which are herein incorporated by reference in their entirety. It is also related to PCT/US11/61499, filed Nov. 18, 2011, which is herein incorporated by reference in its entirety.
Embodiments disclosed herein relate to apparatus and methods for controlling or limiting the position of a rotor relative to a stator in a moving cavity motor or pump. In another aspect, embodiments disclosed herein relate to apparatus and methods for controlling or limiting the position of a rotor relative to a stator in a mud motor.
Moving cavity motors or pumps, sometimes known as positive displacement motors or pumps, or progressive or progressing cavity motors or pumps, work by trapping fluid in cavities. The cavities are formed in spaces between the rotor and the stator, and the relative rotation between these components is the mechanism which causes the cavities to progress and travel axially along the length of the device from the input end to the output end. If the rotor is forced to rotate, fluid is drawn along in the cavities and the device will be a pump. If the fluid is pumped into the input end cavity at a higher pressure than that at the outlet end, the forces generated on the rotor cause it to rotate and the device will be a motor.
In order that the rotor can rotate within the stator and generate cavities that will progress in an axial direction, the profiles of both components must take specific forms. Typically, the rotor (2) will be a helically shaped shaft with a sectional shape similar to those shown in
One of the surfaces, often that of the stator (4), is flexible so that seals (6) can be maintained between the points of contact of the rotor (2) and the stator (4). The seals (6) define a plurality of cavities (8) between the rotor (2) and the stator (4) and still allow for relative rotation between the rotor (2) and stator (4). The rotor (2) and stator (4) sections typically remain the same along the length of the motor or pump (10), but progressively rotate to result in a helical profile. A section through a diametral plane of part of a motor or pump (10) is shown in
The rotor (2) does not have to be of a fixed length. The chosen length is often defined in stages where one stage consists of a complete rotation of the helix of the stator (4). The cavities (8) are formed between the stator (4) and the rotor (2).
It will be apparent from the sections in
The torque that is generated in the rotor (2) in the case of the device being a motor, or required in the rotor (2) in the case of the device being a pump, is a complex combination of the pressure forces acting in the cavities (8) and the reaction forces between the points of contact between the stator (4) and the rotor (2). This has the effect of trying to turn the rotor (2) in the case of a motor or resisting rotation in the case of a pump. In both cases there is also a net lateral force that acts to push the rotor (2) into the stator (4). The direction of this force rotates as the rotor (2) turns. There is also a centrifugal force generated by the orbital motion of the rotor. And in the case of a motor, such as a mud motor, there may be a lateral component of the thrust carried by the transmission.
It has been found that a consequence of the forces acting on a rotor and the pushing of the rotor into the stator is that the flexible surface of the stator can deform and allow a gap to form on one side of the device. If this happens, then fluid can pass along the device between the fluid cavities. The effect of this is to reduce the flow rate and maximum pressure for a pump and to reduce the rotary speed and limit the developed torque in the case of a motor.
Embodiments disclosed herein may be used to overcome some of the limitations of known mud pumps and other moving cavity motors or pumps, or at least to provide an alternative to known mud pumps and other moving cavity motors or pumps.
According to a first aspect of embodiments disclosed herein, there is provided a moving cavity motor or pump comprising: a rotor, a stator and apparatus for controlling or limiting the movement of the rotor relative to the stator.
As discussed, a surface of the rotor or the stator may be made of a flexible material to permit a seal to form between contacting surfaces of the rotor and the stator, and in one or more embodiments the movement of the rotor relative to the stator is controlled or limited to minimise deformation of the flexible material and the consequential opening of gaps between the contacting surfaces of the rotor and the stator.
In one or more embodiments, the rotor is constrained to follow a desired rotational and positional movement.
In one or more embodiments, the rotor is constrained by a precession device constructed such that rotor rotation can be made dependent on rotor position.
In one or more embodiments, the precession device consists of a lobed wheel, connected to the rotor shaft that follows a lobed track connected to the stator.
In one or more embodiments, the ratio of the number of lobes on the wheel to the number of lobes on the track is the same as the ratio of the number of lobes on the rotor to the number of lobes on the stator.
In one or more embodiments, the lobed wheel has a compliant layer on the outside surface that mates with the track. Alternatively or additionally, the lobed track has a compliant layer on the surface that mates with the lobed wheel.
In one or more embodiments, the radial movement of the rotor relative to the stator is controlled or limited.
In one or more embodiments, the movement of a geometric centre of the rotor is limited to a predetermined path in use of the motor or pump.
In one or more embodiments, there is provided a wheel assembly at one or more locations to control or limit the movement of the rotor within, or around, the stator.
In one or more embodiments, the wheel assembly comprises a wheel mounted on a shaft of the rotor, the wheel being configured to run around an inner surface of the stator.
In one or more embodiments, the outside diameter of the wheel is equal to the diameter of the inner surface of the stator minus twice the predetermined maximum offset of the rotor from its geometric centreline.
Alternatively, the wheel assembly may comprise a wheel mounted on a shaft of the stator, the wheel being configured to permit the rotor to run around an outer surface of the stator. One skilled in the art would readily understand that in such an embodiment the inner component is fixed (thus being the stator or stationary member) while the outer component of the motor or pump rotates (the rotor or rotating member).
In one or more embodiments, the outside diameter of the wheel is equal to that of the inner surface of the rotor minus twice the predetermined maximum offset of the rotor from its geometric centreline.
In one or more embodiments, the wheel assembly is located at a position in the motor or pump where the profile of the rotor and the stator are substantially circular.
In one or more embodiments, the wheel assembly further comprises a bearing to permit relative rotation between the wheel and the rotor. The bearing may conveniently be a needle bearing.
In one or more embodiments, the wheel has apertures to permit the flow of fluid therethrough.
In one or more embodiments, engaging surfaces of the rotor and the stator are substantially rigid in the area of the wheel assembly.
In one or more embodiments, there is provided a fixed insert at one or more locations to control or limit the movement of the rotor within, or around, the stator.
In one or more embodiments, the fixed insert is mounted within an outer member of the rotor-stator pair and has a central aperture through which a shaft of an inner member of the rotor-stator pair can pass, the diameter of the central aperture being sized to limit the radial motion of the rotor relative to the stator.
In one or more embodiments, the fixed insert has a further plurality of apertures to permit the flow of fluid therethrough.
In one or more embodiments, the fixed insert is located at a position in the motor or pump where the profiles of the rotor and/or stator are substantially circular.
In one or more embodiments, the central aperture is substantially circular such that the shaft of the rotor can run around the central aperture, or the rotor and fixed insert can run around the stator.
In one or more embodiments, there is provided a drive shaft assembly at one or more locations to control or limit the movement of the rotor within, or around, the stator.
In one or more embodiments, the drive shaft assembly comprises: a driver shaft and a driven shaft, such that rotation may be transmitted when the two shafts are not parallel; and a mechanism for limiting the angle between the driver shaft and the driven shaft such that the movement of the rotor relative to the stator is limited.
In one or more embodiments, the mechanism for limiting the angle of the driver shaft and the driven shaft is a buffer ring.
In one or more embodiments, there is provided a rotatable insert at one or more locations to control or limit the movement of the rotor within the stator.
In one or more embodiments, the rotatable insert is mounted within the stator and has an aperture through which a shaft of the rotor can pass, the aperture being offset from the centre of the rotatable insert such that movement of the rotor is limited to a predetermined path.
In one or more embodiments, the rotatable insert is free to rotate within the stator.
In one or more embodiments, the rotor is free to rotate within the rotatable insert.
In one or more embodiments, a bearing is provided to facilitate rotation of the rotatable insert and/or rotor.
In one or more embodiments, the rotatable insert comprises a further plurality of apertures to permit the flow of fluid therethrough.
In one or more embodiments, there is provided a piston assembly at one or more locations to control or limit the movement of the rotor within, or around, the stator.
In one or more embodiments, the piston assembly comprises a plurality of inward facing pistons spaced around the outer member of the rotor-stator pair to control the movement of the rotor relative to the stator. The pistons may conveniently be evenly spaced around the outer member of the rotor-stator pair.
In one or more embodiments, the pistons are mounted into an insert which is itself mounted onto the outer member of the rotor-stator pair.
In one or more embodiments, the outer member of the rotor-stator pair is locally thickened in the regions where the pistons are mounted.
In one or more embodiments, the insert is provided with a plurality of apertures to permit the flow of fluid therethrough.
According to a second aspect of embodiments disclosed herein, there is provided a method for improving the performance of a moving cavity motor or pump, comprising the step of controlling or limiting the movement of the rotor relative to the stator to minimise the opening of gaps between the rotor and stator.
In one or more embodiments, the control or limitation of the movement of the rotor relative to the stator is in addition to any restrictions caused by contact with the stator or by connections made to the end of the rotor.
In one or more embodiments, the radial movement of the rotor is controlled or limited relative to the stator.
In one or more embodiments, the rotor is controlled to follow a predetermined combination of path and rotation using a precession device.
In one or more embodiments, the movement of a geometric centre of the rotor is limited to a predetermined path.
In one or more embodiments, a wheel is provided between the rotor and the stator to limit the movement therebetween.
In one or more embodiments, a fixed insert is provided between the rotor and the stator to limit the movement therebetween.
In one or more embodiments, a drive shaft is connect to the rotor to limit the relative movement between the rotor and the stator.
In one or more embodiments, a rotatable insert is provided between the rotor and the stator, the insert having an aperture offset from its centre through which a shaft of the rotor extends, to limit the relative movement between the rotor and the stator.
In one or more embodiments, a piston arrangement is provided between the rotor and the stator to limit the movement therebetween.
In another aspect, embodiments disclosed herein are related to a method of drilling a wellbore through a subterranean formation. The method may include: passing a drilling fluid through a mud motor assembly, the mud motor assembly comprising a moving or progressive cavity motor having a proximal end and a distal end, the motor comprising: a stator and a rotor, wherein a surface of the stator is made of a flexible material to permit a seal to form between contacting surfaces of the rotor and the stator; at least one apparatus disposed proximate at least one of the proximal end and the distal end, the at least one apparatus constraining the radial and/or tangential movement of the rotor relative to the stator; and drilling the formation using a drill bit directly or indirectly coupled to the rotor.
In another aspect, embodiments disclosed herein relate to a mud motor assembly comprising a moving or progressive cavity motor having an inlet end and an outlet end. The motor may include: a stator and a rotor, wherein a surface of the stator is made of a flexible material to permit a seal to form between contacting surfaces of the rotor and the stator; at least one apparatus disposed proximate at least one of the inlet end and the outlet end, the at least one apparatus constraining the radial and/or tangential movement of the rotor relative to the stator.
In another aspect, embodiments disclosed herein relate to a drilling assembly. The drilling assembly may include: a mud motor assembly comprising a moving or progressive cavity motor having a proximal end and a distal end, including: a stator and a rotor, wherein a surface of the stator is made of a flexible material to permit a seal to form between contacting surfaces of the rotor and the stator; at least one apparatus disposed proximate at least one of the proximal end and the distal end, the at least one apparatus constraining the radial and/or tangential movement of the rotor relative to the stator; and a motor output shaft directly or indirectly coupled to the distal end of the rotor; and a drill bit directly or indirectly couple to a distal end of the motor output shaft.
In another aspect, embodiments disclosed herein relate to a moving or progressive cavity motor or pump assembly having an inlet end and an outlet end. The motor or pump may include: an inner member disposed within an outer member, one comprising a stator and the other a rotor, wherein a surface of the rotor or the stator is made of a flexible material to permit a seal to form between contacting surfaces of the rotor and the stator; at least one apparatus disposed proximate at least one of the inlet end and the outlet end, the at least one apparatus constraining the radial and/or tangential movement of the rotor relative to the stator.
In another aspect, embodiments disclosed herein relate to a method of manufacturing a moving or progressive cavity motor or pump having an inlet end and an outlet end, the method comprising: disposing an inner member within an outer member, one comprising a stator and the other a rotor; the inner member having a section having a profiled helical outer surface; the outer member comprising a first section having a profiled helical inner surface and at least one second section having a circular inner surface, the at least one second section being proximate at least one of the inlet end and the outlet end and concentric with the first section; operatively connecting at least one apparatus for constraining the radial and/or tangential movement of the rotor relative to the stator to at least one of the inner member and the outer member along a length of the respective at least one second section.
In another aspect, embodiments disclosed herein relate to a method of manufacturing an outer member of a moving or progressive cavity motor or pump, such as a stator for a mud motor, the method comprising: aligning a tubular outer member with a moulding, machining, and/or spray coating device, wherein the centreline of the tubular outer member and the centreline of the device may be the same or different; moulding, machining, and/or spray coating a first inner portion of the outer member to have a profiled helical inner surface and at least one second inner portion having an inner surface of approximately constant inner diameter and concentric with the first inner portion, the second inner portion being configured to house an apparatus for constraining the radial and/or tangential movement of an inner member disposed therein.
In another aspect, embodiments disclosed herein relate to a mud motor assembly including a moving or progressive cavity motor having a proximal end and a distal end, the motor having: a stator and a rotor; and at least one apparatus disposed proximate at least one of the proximal end and the distal end, the at least one apparatus constraining the radial and/or tangential movement of the rotor relative to the stator; wherein the stator comprise a contact surface formed from a rigid material.
In another aspect, embodiments disclosed herein relate to a steering head, an adjustable bend housing, a bottom hole assembly, or a stabilizer comprising a mud motor assembly as described above, including a moving or progressive cavity motor having a proximal end and a distal end, the motor having: a stator and a rotor; and at least one apparatus disposed proximate at least one of the proximal end and the distal end, the at least one apparatus constraining the radial and/or tangential movement of the rotor relative to the stator; wherein the stator comprise a contact surface formed from a rigid material.
In another aspect, embodiments disclosed herein relate to a method of drilling a wellbore through a subterranean formation, the method including: passing a drilling fluid through a mud motor assembly as described above, and including a moving or progressive cavity motor having a proximal end and a distal end, the motor having: a stator and a rotor; and at least one apparatus disposed proximate at least one of the proximal end and the distal end, the at least one apparatus constraining the radial and/or tangential movement of the rotor relative to the stator; wherein the stator comprise a contact surface formed from a rigid material. In yet other aspects, embodiments disclosed herein relate to a method of drilling a wellbore through a subterranean formation, the method including: passing a drilling fluid through a steering head, an adjustable bend housing, a bottom hole assembly, or a stabilizer including such a mud motor assembly. The formation is then drilled using a drill bit directly or indirectly coupled to the rotor.
In another aspect, embodiments disclosed herein relate to a drilling assembly including a mud motor assembly as described above and including a moving or progressive cavity motor having a proximal end and a distal end, the motor having: a stator and a rotor; and at least one apparatus disposed proximate at least one of the proximal end and the distal end, the at least one apparatus constraining the radial and/or tangential movement of the rotor relative to the stator; wherein the stator comprise a contact surface formed from a rigid material. In yet other aspects, embodiments disclosed herein relate to a drilling assembly including a steering head, adjustable bend housing, bottom hole assembly, or stabilizer including such a mud motor assembly.
In another aspect, embodiments disclosed herein relate to a mud motor assembly comprising a moving or progressive cavity motor, the motor including: a stator and a rotor; wherein the stator and the rotor comprise a contact surface formed from a rigid material
The motors and pumps disclosed herein will now be described, purely by way of example, with reference to the accompanying drawings, in which:
Embodiments of the motors or pumps disclosed herein constrain the rotor to maintain a prescribed motion, in other words, they limit the path for the geometric centre of the rotor, and in some cases, lock the rotation to that path. Although various embodiments are illustrated, it will be appreciated that other systems for controlling or limiting the radial and/or tangential movement of the rotor relative to the stator could also be conceived within the scope of the present disclosure. Movement of a rotor relative to a stator is generally limited only by the inherent resilience of the materials used to form the rotor and stator (e.g., deflection/compression of the rubber lining of the stator, etc.). As used herein, constraining the movement of the rotor relative to the stator refers to restricting or limiting the movement to a greater extent than would otherwise result or be permitted by the inherent resilience of the materials used to form the rotor and stator during use.
It should be understood that although the illustrated embodiments have the rotor as a component that revolves within the stator, and indeed most pumps and motors are arranged this way, the embodiments will work equally as well if the inside component is fixed and the outside component rotates.
Referring firstly to
A bearing wheel (26) is supported onto the rotor shaft (22) through a needle bearing (28), although another suitable bearing could also be used, such as roller bearings or journal bearings. In some embodiments, the bearings (28) are journal bearings comprising silicon carbide, tungsten carbide, silicon nitride or other similarly wear resistant materials. The bearing wheel may be manufactured with steel or other materials suitable for the intended environment. The outside surface of the bearing wheel (26) is designed to slide or roll around the inside surface of the stator body (24) at a position where the profile is approximately circular. The difference in the radius of the bearing wheel (26) and the inside surface of the stator body (24) defines the maximum offset of the rotor axis from the stator axis. The bearing wheel (26) has passages (27) incorporated to increase the area for fluid to flow along the device, where the passages may be of any number or shape, with the proviso that they be large enough to pass any solids that may be in the power fluid or pumped fluid. The stator body (24) has a circular profile where the bearing wheel (26) makes contact, such that the rotor shaft (22) centreline will be constrained to remain approximately within a circle of fixed radius and this helps to prevent the opening of gaps between the rotor (22) and stator (24) surfaces.
In some embodiments, the bearing wheel (26) may slide or roll in contact with the interior surface of the stator cylinder itself. In other embodiments, the bearing wheel (26) may slide or roll in contact with a coating placed on the interior surface of the stator cylinder. During manufacture of some stators, the interior surface of a cylinder, such as a pipe or tube, is lined, such as by pouring or injecting a liner material onto the interior surface of the cylinder. However, due to the complexity of the stator manufacturing process, concentricity of the resulting stator with the stator cylinder itself cannot be guaranteed. Thus, during manufacture, the resulting stator liner (90) may be offset from the centreline (92) of the stator cylinder (94), such as illustrated in
As noted above, the difference in the radius of the bearing wheel (26) and the inside surface of the stator body (24) defines the maximum offset of the rotor axis from the stator axis. Additionally, for proper function, the bearing wheel (26) must maintain a sliding and/or rolling relationship with the inner surface of the stator so as to constrain the rotor through the entire rotation, i.e., maintaining contact over 360°. Due to the eccentric rotation of the rotor, the relative diameter of the bearing wheel (26) to that of the interior surface of the stator (90) is an important variable, where an improper ratio may result in irregular contact of the bearing wheel with the inner surface of the stator, i.e., a non-rolling or non-sliding relationship.
In addition to diameter, the length of the bearing wheel (26) must also be sufficient to maintain the side loads imparted due to the wobble of the rotor. Bearing wheel (26) should be of sufficient axial dimensions to address the structural considerations. The length of bearing wheel (26) may thus depend upon the number of lobes, motor/pump torque, and other variables readily recognizable to one skilled in the art, and may also be limited by the available space between the rotor and the drive shaft.
The bearing wheel (26) limits the extent of the wobble imparted by the eccentric motion of the rotor. This, in turn, may limit the formation of flow gaps along the length of the motor/pump by limiting the compression or deflection in the stator lining, such as a rubber or other elastic material. In some embodiments, the bearing wheel may limit the deflection of the stator lining by less than 0.64 mm (0.025 inches); by less than 0.5 mm (0.02 inches) in other embodiments; and by less than 0.38 mm (0.015 inches) in yet other embodiments. Similar deflection limits may also be attained using other embodiments disclosed herein.
Bearing wheel (26), as described above, radially constrains the position of the rotor, keeping the rotor in contact with the stator (i.e., providing an offset contact force without preventing the generation of torque). The resulting reduced normal force at the point of contact between the rotor and stator may reduce the drag forces, improving compression at the contact points, minimizing leakage paths. By limiting the formation of flow gaps (leakage paths) along the length of the rotor, pressure losses may be decreased, increasing the power output of the motor. Additionally, constraining the position of the rotor may reduce stator wear, especially proximate the top of the lobes, where tangential velocities are the highest.
Referring now to
Similar to the embodiments of
A third embodiment of an apparatus (40) for controlling or limiting the movement of a rotor (42) relative to a stator (44) is illustrated in
A fourth embodiment of an apparatus (50) for controlling or limiting the movement of a rotor (52) relative to a stator (54) is shown in
A fifth embodiment of an apparatus (60) for controlling or limiting the movement of a rotor (62) relative to a stator (64) is illustrated in
As described above, the embodiments illustrated in and described with respect to
In addition to the relatively circular means for constraining radial movement as illustrated in
Precession apparatus (70) controls the rotor (74) such that it will move on a prescribed path and with a prescribed rotation relative to stator (78). This type of restraint may effectively lock the rotation of the rotor to its orbit position. The lobed wheel (72) engages with lobed track (76) such that the relative profiles of the lobed wheel (72) and track (76) fix the path and rotation of the rotor (74) to prescribed values.
The lobed wheel (72) is connected to the rotor shaft (75) in a substantially fixed way. The ratio of the number of lobes on the wheel (72) to the number of lobes on the track (76) is limited to the same ratio as the number of lobes on the rotor (74) to the number of lobes on the stator (78). The profiles of the lobes on the wheel (72) and on the track (76) will determine the extent to which the rotor (74) can deform the sealing surface of the stator (78) and therefore limits the opening of gaps between them.
To allow some rotational compliance, the surface of the lobed wheel (72) or the track (76) may have a flexible layer added of, for example, rubber. The lobed wheel (72) and track (76) could have parallel sides or incorporate a helix angle to allow for some small axial movement and accommodate manufacturing tolerances.
The profile and composition (material of construction, compressibility, etc.) of lobed wheel (72) may be designed such that the deformation of the rubber in stator (78) is limited. In other embodiments, the profile and composition of lobed wheel (72) may be designed such that the deformation of the rubber in stator (78) is maintained to a fixed value. In this manner, the interaction between the rotor (74) and the rubber in stator (78) is used to maintain sealing, with the torque being generated largely on lobed wheel (72). This not only allows pressure loading up to the point where the seal would fail (a very high pressure) but it also ensures that the contact forces in the rubber can be kept substantially independent of pressure magnitude. This should reduce wear and fatigue failure in the rubber as well as improve motor/pump efficiency.
Motors according to embodiments disclosed herein may be used, for example, as a mud motor in a drilling assembly. Referring to
Forces imposed on the rotor (105) during operation include those due to the pressure differential across the motor (100) from inlet (proximal) end (102) to outlet (distal) end (104). The pressure differential may result in a pitching moment. There is also a downward force exerted on the drill string, commonly referred to as “weight on bit,” where this force is necessarily transmitted through the rotor-drive shaft-drill bit couplings. The orbital-axial relationship of the drive shaft coupling may result in angular and/or radial forces being applied to rotor (105). Rotation of rotor (105) also results in tangential forces.
Each of these forces may have an impact on the manner in which rotor (105) interacts with stator (114) (e.g., compressive forces generating seals along the edges of the resulting cavities, sliding, drag, or frictional forces between rotor (105) and stator (114) as the rotor rotates, etc.), and may cause a gap to form along the length of the motor (100), reducing motor efficiency. Additionally, the impact of these forces may be different proximate inlet end (102) and outlet end (104). The various apparatus disclosed herein for constraining the rotor as discussed above may be used to control or limit the movement of rotor (105) proximate inlet end 102, outlet end 104, or both.
Other examples of various motors (100) using constrained rotors as disclosed herein, such as for use in drilling operations, are illustrated in
When two or more constraints are used, such as in
Although
The multiple constraints (one or multiple at each end or both ends) should be selected and/or designed so as to complement each other, achieving the desired improvement in sealing (elimination of flow gaps) while not negatively impacting rotor operation or wear. For example, the constraints at the inlet and outlet ends may both act in the same direction or similar phases so as to not put opposing loads on the rotor and to avoid lock-up of the rotor due to conflicting forces. In this manner, the operation of the motor may be improved without fear of motor seizure.
The apparatuses disclosed herein may be used to constrain the radial and/or tangential movement of a rotor relative to a stator, decreasing, minimizing, or eliminating the flow gaps along the length of the motor, thereby improving motor efficiency. Apparatuses disclosed herein may also reduce stator wear.
Improvements in motor efficiency, such as sealing improvements and higher power output per length, as noted above, may be used, in some embodiments, to shorten the overall length of the motor while attaining a desired power output. A shortened power section may have numerous benefits and applications, as discussed below.
The limited overall axial length of the power section may allow for flow of solids, such a drilling mud including solid materials, through the motor without issue, even where both the rotor and stator have contact surfaces formed from rigid materials. The limited overall axial length may also provide flexibility in materials of construction that would otherwise be cost prohibitive.
In some embodiments, the rotor and/or the stator may be formed from a metal, composite, ceramic, PDC/diamond, hard plastic, or stiff rubber structural material. For example, both the rotor and stator may be formed from a metal, providing metal-to-metal contact along the length of the power section.
In other embodiments, the rotor and/or stator may be formed with a resilient layer (such as NBR rubber) and a hard layer, such as a hard rubber or plastic, ceramic, composite, or metal coating disposed as the contact surface on top of the resilient inner layer. For example, the rotor may be a metal, similar to currently produced rotors, and the stator may be a metal-coated rubber, where the metal layer is the layer contacting the rotor during operation of the motor. Similarly, a hard rubber or reinforced rubber layer may be provided as the innermost layer contacting the rotor. Typical “layered” stators disclosed in the prior art provide for a hard or reinforced inner elastomeric layer, opposite that of the present embodiments, to provide for the desired compression and sealing properties of the outer layer. However, due to the decreased axial length of the power sections, use of a rigid contact layer may be possible, improving wear properties of the motor (rotor, stator, or both) while providing the desired power output. While exemplified with a multi-layered stator, multi-layered rotors may also be used, such as a rotor having a metal core to provide torque capacity, an elastomeric material disposed on the core, and a metal shell. These embodiments are illustrated in
Where the corresponding contacting portions of the rotor and stator(s) are both rigid, such as a metal, hard plastic, composite, or ceramic, for example, it may be desirable to limit the friction, wear, and other undesirable interactions between the rotor and stator that may cause premature failure or seizure of the rotating component. The contact surfaces of the insert and/or the rotor may be coated or treated to reduce at least one of friction and wear. Treatments may include chroming, HVOF or HVAF coating, and diffusing during sintering, among others. Metal-to-metal (rigid-to-rigid) power sections may also provide sufficient clearance to be tolerant of debris, but tight enough to constrain the rotor motion close to ideal, achieving the above-noted benefits, without use of constraining devices.
Similarly, the relatively short contact length between the constraining devices and the rotor or stator may provide for flexibility in materials, and similar combinations of hard materials or hard-coated materials may be used for the constraining devices.
Alternatively, a resilient elastomer may be used as the contact surface on both the rotor and stator. The reduction in the otherwise high frictional loads attained by the constraining devices may provide for use of elastomeric stators and rotors in combination to attain a desired pump performance (power output, wear properties, etc.).
The benefits from use of constraining devices may also provide for alternative stator designs. For example, as illustrated in
One potential benefit of a constrained motor may be a reduction in vibrations associated with the mud motor. Constrained lateral forces may result in less wobble or a narrower orbital path as compared to an un-constrained motor. As a result of reduced vibrations, drilling may be improved, such as by resulting in one or more of a better hole quality, an even-gage hole, and improved steering.
A reduction in the axial length of the motor may also provide the ability to modify the drill string components to incorporate a motor. For example, an adjustable bend housing typically includes a transmission shaft to transmit torque generated from the power section of the drilling motor to a bearing section of the drilling motor. Due to the potential reduction in size of the motor due to the constraining devices disclosed herein, it may be possible to incorporate a motor into the bent housing along with the transmission shaft. Similarly, motors according to embodiments herein may advantageously be incorporated into a stabilizer, a steering head, or other various portions of the bottom hole assembly (BHA).
The decreased axial length may also facilitate disposal of wire through the motor and provide space for additional downhole instrumentation, such as instrumentation to monitor the motor and/or components below the motor. Instrumentation may beneficially monitor motor RPM, pressure drop, and other factors, possibly avoiding stalls and allowing operation of the motor at high efficiency or peak efficiency, each of which may result in improved drilling performance (increased rate of penetration, less downtime due to stalled motors, etc.).
While described above with respect to a constraining device being located proximate the rotor in a motor assembly, such as illustrated in
The embodiments illustrated herein are provided purely by way of example and it will be appreciated that other systems for controlling or limiting the movement of the rotor relative to the stator could also be conceived within the scope of the concepts disclosed herein.
It will also be understood that although the illustrated embodiments have the rotor as a component that revolves within the stator, and indeed most pumps and motors are arranged this way, the embodiments disclosed herein will work equally as well if the inside component is fixed and the outside component rotates.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1019614.5 | Nov 2010 | GB | national |
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| 2794498 | Dec 2000 | FR |
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| Number | Date | Country | |
|---|---|---|---|
| 20130048384 A1 | Feb 2013 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13300446 | Nov 2011 | US |
| Child | 13480080 | US |
