Patent Application
20140170011
Embodiments disclosed herein relate generally to Moineau pumps and motors, inclusive of positive displacement or progressive cavity motors and pumps. Embodiments disclosed herein relate to downhole motors and pumps used when drilling the bore of a subterranean well. More particularly, embodiments disclosed herein relate to improving motor or pump efficiency and reducing stator wear.
Boreholes are frequently drilled into the Earth's formation to recover deposits of hydrocarbons and other desirable materials trapped beneath the Earth's surface. Traditionally, a well is drilled using a drill bit attached to the lower end of what is known in the art as a drillstring. The drillstring is traditionally a long string of sections of drill pipe that are connected together end-to-end through rotary threaded pipe connections. The drillstring is rotated by a drilling rig at the surface thereby rotating the attached drill bit. Drilling fluid, or mud, is typically pumped down through the bore of the drillstring and exits through ports at the drill bit. The drilling fluid acts both to lubricate and cool the drill bit as well as to carry cuttings back to the surface. Typically, drilling mud is pumped from the surface to the drill bit through the bore of the drillstring, and is allowed to return with the cuttings through the annulus formed between the drillstring and the drilled borehole wall. At the surface, the drilling fluid is filtered to remove the cuttings and is often recycled.
In typical drilling operations, a drilling rig and rotary table are used to rotate a drillstring to drill a borehole through the subterranean formations that may contain oil and gas deposits. At the downhole end of the drillstring is a collection of drilling tools and measurement devices commonly known as a Bottom Hole Assembly (BHA). Typically, the BHA includes the drill bit, any directional or formation measurement tools, deviated drilling mechanisms, mud motors, and weight collars that are used in the drilling operation. A measurement while drilling (MWD) or logging while drilling (LWD) collar is often positioned just above the drill bit to take measurements relating to the properties of the formation as the borehole is being drilled. Measurements recorded from MWD and LWD systems may be transmitted to the surface in real-time using a variety of methods known to those skilled in the art. Once received, these measurements will enable those at the surface to make decisions concerning the drilling operation. For the purposes of this application, the term MWD is used to refer either to an MWD (sometimes called a directional) system or an LWD (sometimes called a formation evaluation) system. Those having ordinary skill in the art will realize that there are differences between these two types of systems.
A popular form of drilling is called “directional drilling.” Directional drilling is the intentional deviation of the wellbore from the path it would naturally take. In other words, directional drilling is the steering of the drill string so that it travels in a desired direction. Directional drilling can be advantageous offshore because it enables several wells to be drilled from a single platform. Directional drilling also enables horizontal drilling through a reservoir. Horizontal drilling enables a longer length of the wellbore to traverse the reservoir, which may increase the production rate from the well. A directional drilling system may also be beneficial in situations where a vertical wellbore is desired. Often the drill bit will veer off of a planned drilling trajectory because of the unpredictable nature of the formations being penetrated or the varying forces that the drill bit experiences. When such a deviation occurs, a directional drilling system may be used to put the drill bit back on course.
A traditional method of directional drilling uses a BHA that includes a bent housing and a positive displacement motor (PDM) or mud motor. The bent housing includes an upper section and a lower section formed on the same section of drill pipe, but are separated by a bend in the pipe. Instead of rotating the drillstring from the surface, the drill bit in a bent housing drilling apparatus is pointed in the desired drilling direction, and the drill bit is rotated by a mud motor located in the BHA.
A mud motor converts some of the energy of the mud flowing down through the drill pipe into a rotational motion that drives the drill bit. Thus, by maintaining the bent housing at the same azimuth relative to the borehole, the drill bit will drill in a desired direction. When straight drilling is desired, the entire drill string, including the bent housing, is rotated from the surface. The drill bit may angulate with the bent housing and drills a slightly overbore, but straight, borehole.
Positive displacement motor (PDM) power sections include a metal (typically steel) rotor and a stator. The stator is typically a steel tube with rubber molded in into a multi-lobed, helixed profile in the interior. The stator tube may be cylindrical inside (having a solid rubber insert of varying thickness), or may have a similar multi-lobed, helixed profile machined into the interior so that the molded-in rubber is substantially uniform thickness (i.e. “even wall”). Power sections, whether solid rubber or even-wall, are typically uniform throughout the length of the power section. That is, they are either all-rubber or all-even-wall over the entire length of the multi-lobed profile.
Motor failure during directional drilling can be a significant and undesirable event. One mode of motor failure is rubber chunking. Elastomeric materials in the mud motor provide a seal between the rotor and the stator. Without this seal, the motor does not operate efficiently and may fail altogether. In mud motors, as they currently exist, the elastomer sustains undesirable lateral forces between the rotor and the stator as the rotor turns. It may be desirable to determine a way to reduce or eliminate the excessive lateral forces sustained by the elastomer.
It has been observed that the majority of chunking happens on the down hole part of the rubber lining. The second main chunking occurrence is at the up and down hole portions on the same stator. Potential causes of this chunking have been hypothesized as aggressive differential pressures, motor stalling, junk damage, poor rotor/stator matching, and elastomer quality degradation.
These potential causes do not explain why most of the chunking happens or starts mainly on the bottom portion of the stator. One potential explanation for this pattern is the concentrated presence of side forces on the rubber at the downhole part followed by the uphole part of stator. Potential contributing factors for the concentrated side force at the bottom of the stator during drilling of curve section may include: side forces resulting from the bending of motor section to fit in the directional hole; side force resulting from the combined effect of hydraulic thrust on the rotor and the misalignment between the rotor axis and the transmission shaft; side force resulting from the combined effect of the torque on the rotor and the misalignment between the rotor axis and the transmission shaft; and side force resulting from inertial forces produced by the transmission shaft.
In one aspect, embodiments disclosed herein relate to a mud motor including a rotor and a stator. The stator has one or more inserts or gearing sections to limit a lateral movement of the rotor relative to the stator.
In another aspect, embodiments disclosed herein relate to a moving or progressive cavity motor or pump. The motor or pump may include a rotor and a stator, where the stator has: a first, helicoidal section that is a compliant material having a first compressibility; and a second section, helicoidal, non-helicoidal, or combination thereof, having a second compressibility, wherein the second compressibility is less than the first compressibility.
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 moving or progressive cavity motor may include: a rotor; and a stator, where the stator has: a power generating section; and a gearing section, the gearing section reacting the loads generated by the power generating section.
This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter. Other aspects and advantages will be apparent from the following description and the appended claims.
Embodiments disclosed herein relate generally to Moineau machines, i.e., Moineau pumps and motors, inclusive of positive displacement or progressive cavity motors and pumps. Embodiments disclosed herein relate to downhole motors and pumps used when drilling the bore of a subterranean well. More particularly, embodiments disclosed herein relate to improving motor or pump efficiency and reducing rotor and/or stator wear.
Moineau machines typically include a rotor and a stator. As used herein, “rotor” refers to the rotating portion of the motor or pump, which may be the shaft or the sheath. Similarly, “stator” refers to the stationary portion of the motor or pump, which may be the sheath or the shaft, respectively. While embodiments disclosed herein may be described with respect to a rotor (shaft) rotating within a stator (sheath), those skilled in the art should readily understand that embodiments disclosed herein may also apply where the rotor (sheath) is rotating about a stator (shaft). Additionally, those skilled in the art will appreciate that descriptions with respect to a motor, such as an output shaft, may similarly apply to pumps, such as a drive shaft. Accordingly, while portions of the description below may be discussed in relation to mud motors, embodiments herein are not limited to the described motors.
Positive displacement motors and pumps include a rotor and a stator. 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
As shown in
Due to their meshed multi-lobed profiles, the rotor/stator pair also serves as gears. The sealed cavities create a driving fluid force that is roughly perpendicular to the direction of rotor eccentricity at any given point in time. This force is reacted at the point where the rotor contacts the stator lobes. The two forces act as a couple, thus creating torque. The torque that is generated in the rotor in the case of the device being a motor, or required in the rotor in the case of the device being a pump, is a complex combination of the pressure forces acting in the cavities and the reaction forces between the points of contact between the stator and the rotor. This has the effect of trying to turn the rotor in the case of a motor or resisting rotation in the case of a pump. In both cases there is also a sideways force component that acts to push the rotor into the stator. The direction of this force rotates as the rotor 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 angular and/or radial components of the thrust carried by the transmission due to the angled relationship of the rotor and drive shaft axes.
To summarize the above, there are five primary functions that the stator must accomplish in order to generate power or to pump fluid: (1) create discrete cavities, (2) seal those cavities through compression of the rubber, (3) handle radial loads due to the centrifugal force of the rotor (i.e., act as a radial bearing), (4) gear the rotor so that it must rotate when acted upon by fluid forces, and (5) withstand (react) the forces from gearing.
For a typical (“traditional”) stator, the requirements of the sealing function are, in general, at odds with those of the bearing/gearing functions. To seal, the stator lobe must compress when contacted by the rotor, and thus must be flexible. To withstand loads, however, the stator lobe should be as rigid as possible to avoid excessive deflection, which may allow leakage between the individual chambers and reduce power section efficiency.
While elastomeric materials in mud motors may provide a seal between the rotor and the stator, such that the motor operates efficiently, a compression seal is not necessary. In other words, a Moineau machine does not require a compliant layer interface between the rotor and the stator; that is, the motor or pump does not require a physical interface between the shaft and the sheath. In fact, it has been found that limiting the interference between the rotor and stator, i.e., limiting the compression of the rubber, may minimize stator wear, chunking, and other failure modes. Additionally, a perfect Moineau machine may not benefit by the presence of more than a single stage. Further, the shorter the Moineau machine is, the easier it is to maintain a very tight tolerance on the mating profile of the shaft and the sheath (of the rotor and stator). Embodiments disclosed herein, providing minimal interference between the stator and rotor, or portions thereof, may provide for manufacture of essentially perfect, short Moineau machines that may be limited in length to a little more than one active full stage.
Moineau machines according to embodiments disclosed herein may include a rotor and a stator, where the stator includes a first, helicoidal section comprising a compliant material having a first compressibility and a second section, helicoidal, non-helicoidal, or combination thereof, having a second compressibility, wherein the second compressibility is less than the first compressibility. The second section may be formed from a hard plastic, rubber, composite, ceramic, or metal, providing a structural member within the stator, limiting deflection of the stator due to external loads and/or eliminating or limiting the interference between the first, compressible section of the stator and the rotor. In this manner, the sealing and structural functions of the stator may be separated, allowing the materials of each respective section to be optimized independently. The materials of the second section or sections (if more than one second section is used) may be optimized for handling mechanical loads, while the materials of the first section may be optimized for sealing, power generation, and fluid transport, including fluids that may contain solid particles, such as drilling muds.
The second section of the stator in embodiments of the motors and pumps disclosed herein may be integral with the power section, such as a section of reduced compressibility forming part of the same helicoidal profile as the first section. In other embodiments, the second section of the stator may be formed as a separate and distinct portion of the stator. Regardless of placement, the structural function of the second section may provide for limited lateral movement of the rotor relative to the stator, regardless of the relative angular position of the shaft (rotor) into the sheath (stator).
The second section, providing a structural function, may be an insert located along the length of the stator profile, where the insert provides a localized harder material to improve the durability and reliability of the Moineau machines. In other embodiments, the second section, providing the structural function, may be a separate and distinct portion of the stator, such as where the power generating function is provided by a first portion or length of the stator, and the structural, gearing function of the stator is provided by a second portion or length of the stator.
Moineau machines according to embodiments disclosed herein may include one or more relatively short (with respect to axial length of the stator) metal, composite, ceramic, or hard rubber inserts disposed at select points within the mud motor to constrain the movement of the rotor relative to the stator. This restraint may help to reduce the lateral movement of the rotor within the stator, thus reducing the undesirable lateral forces on the elastomeric materials of the stator. Because of this reduction, it may be possible to have a more efficient motor, thus reducing the length of the motor without reducing the power of the motor.
Referring now to
As illustrated in
Each insert 16 may have an inner surface 18 that is similar in profile to that of the inner surface 20 of the helicoidal section 14. For example, insert 16 may have a shape of a ring that is similar to an imaginary rubber ring cut from the rubber tube with planes perpendicular to the stator axis; this shape is a general guideline and not intended to limit the shape of the insert. In some embodiments, the inner surface 20 of helicoidal section 14 and the inner surface 18 of insert 16 may form a continuous helical profile. For example, as illustrated in
It would be appreciated by one of ordinary skill in the art that the length of the inserts is not necessarily as shown in
In some embodiments, such as where the corresponding contacting portions of the rotor and insert(s) are both a metal, 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. Further, the insert itself, or a surface portion thereof, may be formed from a hard, erosion and abrasion resistant material or combination of materials.
Drilling muds or other fluids processed through motors and pumps according to embodiments herein may contain solids or other materials. The limited overall axial length of the inserts may allow for flow of the solids through the assembly without issue. Alternatively, referring now to
It is also contemplated to constrain the lateral movement of the rotor within the stator by placing inserts on the rotor. Referring now to
As noted above, there may be little or no interference contact between the respective portions of the rotor and stator. The limited interference between the respective portions of the rotor and stator may limit the compression of the helicoidal section 14. For example, as noted above, inserts 16 may have a reduced profile providing for limited compression of the rubber helicoidal section. Additionally, rotor motion may result in bending or other movements that may also be limited by inserts. During operation, compression of the rubber in helicoidal section 14 may be less than about 100 microns; less than about 75 microns in other embodiments; less than about 50 microns in other embodiments; and less than about 25 microns in yet other embodiments.
Any acceptable manufacturing or fixing mechanism may be used to fix, dispose, or otherwise locate the insert in place to handle the downhole stresses and to provide proper seal to avoid mud induced wash out. The inserts may be machined with high speed milling, grinding, ECM, EDM, sintered net or near shape, cast, printed, injected, molded, or generated by a combination of these and other manufacturing methods. The inserts may be an integral part of the shaft or the sheath, or may be installed onto the shaft or the sheath by one or more of the following methods: press-fit, welding, brazing, threading, fusing, gluing, or various mechanical or pressure locking devices. Inserts according to embodiments disclosed herein may provide benefits to Moineau machines, and may be used with currently known manufacturing techniques, including conventional technology with a metallic shaft and a rubberized cylindrical sheath, and thin wall technology, where one or both of the shaft and sheath are rubberized by any method where the profiled shaft and/or sheath is made my any technique, such as cold forming, hot forming, casting, milling, grinding, broaching, ECM, EDM, injecting, molding, and metal-to-metal technology.
Further, inserts according to embodiments herein may be added as a modification on already existing stators. As an example, inserts may be disposed at the extremities (proximal end, distal end) after the stator and rotor have been manufactured, and may also be replaced as needed.
As described above, inserts used in embodiments of motors and pumps disclosed herein may support lateral forces between the metallic rotor and the stator, and ease the stress on the rubber portions of the motor or pump. Another potential advantage of these inserts, disposed on the rotor, the stator, or both, may be to limit lateral vibrations of the rotor against the stator, which may induce rapid deterioration of rubber once it starts. It is also possible by proper centralization of the rotor inside the stator that these inserts may help produce an even loading profile along the length of the stator and thus improve reliability and allow greater loading to be applied to the power section.
Another potential benefit as disclosed herein may be the increase in efficiency of the motors or pumps, such that, for example, a shorter motor may produce equivalent power of a traditional longer motor. There may be many potential advantages to a shorter motor. For example, shorter motors may be easier to manufacture and manufacturing of a shorter motor may lend itself to the use of advantageous manufacturing techniques that are not feasible in the manufacture of shorter motors. Further, decreasing the overall length of motors according to embodiments herein may provide advantages during the drilling process.
As noted above, the first, compressible section and the second, relatively incompressible section may be formed as distinct sections of the stator assembly, thus providing for both the desired structural and power generating functions. Embodiments of positive displacement motors and pumps according to embodiments disclosed herein may include a rotor and a stator, where the stator includes a first “power generating section,” where the stator is formed from a solid rubber of varying thickness, and a “gearing section,” where the stator is a structural member, for example a metal, composite, hard plastic, ceramic, or stiff rubber structural member, or alternatively an “even wall” stator. In other embodiments, the “power generating section” may be an “even wall” stator and the “gearing section” may be formed from a metal, composite, or ceramic; in general, the compressibility of the power generating section is less than the compressibility of the gearing section, similar to the inserts described with respect to
For example, an all-rubber stator does well sealing at low pressure and torque, but typically suffers from the heat generated by hysteresis due to deflection from interference, as well as from wear and tear from the mechanical loads (from centrifugal force and torque-reaction) imposed upon it. Further, the mechanical loads make the lobes deflect enough to create leakage between individual chambers, reducing efficiency. Conventional (relatively soft) rubber has good abrasion resistance, but poor structural properties. Hard rubber (HR) does a better job of handling mechanical loads, but is more prone to wear rapidly due to lower elastomer content. On the other hand, an all-even wall stator does well structurally, handling centrifugal and torque-reaction loads, but typically must be designed to run at lower rotor-stator interference, and thus loses power and efficiency more rapidly as the rubber wears. Motors and pumps according to embodiments herein may thus synergistically utilize the molded power generating section and the even wall gearing section to improve motor/pump performance.
Referring now to
In some embodiments, such as illustrated in
When separated by a hydraulic disconnect section B, the helical profile of the power generating section A may be the same or different than the helical profile of gearing section C. When different, the rotor should be configured to run properly in the respective sections, and may be formed as a continuous shaft or may include two sections coupled together, such as within the hydraulic disconnect section B. When it is desired to use a rotor of a continuous profile, the power generating section A and the gearing section C may form respective portions of a continuous helical profile (i.e., accounting for the hydraulic disconnect section B). In such an instance, the gearing section and power sections may have a similar profile, and should be aligned so that the rotor profile and helix are unchanged. In other embodiments, the power generating section A and the gearing section C may form a continuous helical profile, such as illustrated in
The power generating section may be a solid rubber profile 30, having a non-uniform thickness and a helical profile, disposed in or molded within a housing 12, such as illustrated in
In some embodiments, the gearing section may be an even wall rubber profile 32, including a metallic, ceramic, or composite profile section 34 and a rubber layer 36 having a relatively uniform thickness disposed in a housing 12, such as illustrated in
One example of a non-integral profile section is illustrated in
The gearing section may comprises a first rubber and the power section may comprises a second rubber, where the first rubber and the second rubber may be the same or different. In some embodiments, the first rubber (gearing section) is harder (i.e., stiffer, less compressible) than the second rubber (power generating section). As noted above, the power generating section may be formed using a relatively conventional rubber with typical interferences. For example, the conventional rubber widely used in mud motors may be on the order of 65 to 85 durometer on the Shore A hardness scale, with interference on the order of 0.005 inch to 0.040 inch, as conventionally measured on the diameter at room temperature, and as configured for typical drilling conditions. In contrast, the gearing section may comprise a hard rubber with low interference to a clearance. In this context, “hard” rubber may be on the order of 80 to 100 durometer on the Shore A hardness scale, “low” interference may be on the order of zero to 0.010 inch, and “clearance” may be on the order of zero to 0.025 inch. It should be noted that these values are taken at room temperature, and compensation is normally made for thermal expansion of rubber at downhole temperature. So, for example, a clearance of 0.025 inch at room temperature may be chosen to create zero interference at a high down hole temperature, for example 350 degrees Fahrenheit. Interference guidelines may be found from a variety of power section manufacturers, such as Dyna-Drill Technologies, Inc., available at dyna-drill.com. One skilled in the art would readily understand that “soft” and “hard” refer to the relative elasticity or compressibility (flexibility, brittleness, etc.) of the elastomeric (rubber) material used to form the inner contact surface of the stator, a harder rubber being less compressible than a softer rubber, for example. Elastomers that may be used in embodiments herein include, but are not limited to, compounds known in the industry as NBR, HNBR, and HSN. Further, it should be noted that as anticipated drilling environmental conditions, including the type of drilling mud and bottom hole temperature, are typically a factor in rubber selection criteria, the exact hardness values of the rubbers chosen are not as important as the difference between the two. For example, in a typical embodiment, the hardness of the rubber in the power generating section may be on the order of 10 to 25 Shore A hardness points softer than the hardness of the rubber in the structural gearing section. For example, the rubber in the power generating section may be a NBR rubber with 70 Shore A hardness and the rubber in the gearing section may be a NBR rubber with 85 Shore A hardness, where each may have deflection properties as follows.
The gearing section C may be axially and helically aligned with power generating section A. As one skilled in the art may readily appreciate, due to the complexity of the stator manufacturing process, concentricity of the resulting stator with the stator cylinder (housing) itself cannot be guaranteed. As such, steps should be taken during the process to manufacture the stator to ensure alignment between the various sections (gearing and power generating).
The ratio of the length of the power generating section to the length of the gearing section may be in the range from about 1:1 to about 400:1 in some embodiments; in the range from about 2:1 to about 30:1 in other embodiments; in the range from about 3:1 to about 20:1 in other embodiments; and in the range from about 2:1 to about 10:1 in yet other embodiments. For example, mud motors according to embodiments herein may have an overall length in the range from about 5 feet to about 30 feet, where in some embodiments the gearing section may have a length in the range from about 0.5 feet to about 5 feet, and in other embodiments in the range from about 1 foot to 3 feet.
In other embodiments, such as illustrated in
As illustrated in
Motor assemblies as described above separate the power section of the progressive cavity motor (or pump) into two sections, one of which is purpose-built to seal and generate power, while the other of which is purpose-built to handle the structural loads generated by the first. The function of the gearing section, such as in mud motors according to embodiments herein, for example, is to handle (1) the radial loads generated from centrifugal force of the rotor and from the radial component of rotor thrust, as reacted by the angled CV-Joint (coupling to the transmission or drive shaft), and (2) the tangential loads normally acting on the stator lobes, acting as a gear. Separating these functions allows the materials in each section to be optimized independently.
In some embodiments, the gearing section is located proximate the end of the rotor that is coupled to the transmission or drive shaft (i.e., the motor output end or the pump drive end). Forces proximate the drive shaft, for example, may be different than those at the opposite end of the rotor due to torque generation (input), pressure differentials, and other factors as noted above. Placement of a gearing section proximate the end of the rotor that is coupled to the transmission or drive shaft may thus advantageously handle the radial and tangential loads, minimizing the formation of flow gaps in the power generating section.
While the drive shaft may be attached to either end of a rotor, in some embodiments, the gearing section is located proximate the distal end of the rotor. As used herein, the distal end refers to the portion of the rotor that is coupled to the transmission or drive shaft (i.e., the motor output end or the pump drive end), and the proximal end of the rotor refers to the portion of the rotor not coupled to the transmission or drive shaft (i.e., the drive (drilling) fluid input end or the pump output end). Forces at the distal end of the rotor may be different than those at the proximal end of the rotor due to torque generation (input), pressure differentials, and other factors as noted above. Placement of a gearing section proximate the distal end may thus advantageously handle the radial and tangential loads, minimizing the formation of flow gaps in the power generating section.
In other embodiments, a gearing section is located proximate the proximal end of the rotor. Gearing section(s) may also be located intermediate the proximal and distal end of the rotor. For example, gearing sections disposed proximate the middle of the stator may be used to control rotor bending and motion as a predictable function of stator bending. With respect to rotor motion in the gearing section, in some embodiments the rotor pitch diameter may roll along the stator pitch diameter without slippage about the pitch diameters. Further, as a result of the gearing section(s), the rotor's longitudinal axis may remain parallel to the stator axis, eliminating rotor wobbling or tilting.
In yet other embodiments, motor assemblies according to embodiments disclosed herein may include a first gearing section located proximate the distal end of the rotor, a second gearing section located proximate the proximal end of the rotor, and a power generating section intermediate the first and second gearing sections. Such an arrangement may be advantageous where the forces acting on the proximal end of the rotor also contribute to the formation of flow gaps in the power generating section.
Embodiments disclosed herein also relate to a method of manufacturing an outer member of a moving or progressive cavity motor or pump, such as a stator. The method may include: disposing a layer of a first rubber having a substantially uniform thickness and a helical profile on an inner surface of a first section of the outer member; and disposing a second rubber having a non-uniform thickness and a helical profile on an inner surface of a second section of the outer member (i.e., the stator cylinder or housing).
The method may also include forming the outer member to have a first section comprising an inner surface having a helical profile. For example, forming the housing may include at least one of: stacking wafers in a housing to create an inner surface having a helical profile; molding, casting, or machining an insert comprising an inner surface having a helical profile and disposing the insert in a cylindrical housing; molding or casting an epoxy composite comprising an inner surface having a helical profile in a housing; machining or casting a housing comprising an integral section comprising an inner surface having a helical profile.
During the disposing steps, it may be desirable to form the power generating section and the gearing section as a continuous helical profile or a discontinuous helical profile. In embodiments forming a discontinuous helical profile, the method may also include spacing the layer of first rubber from the layer of second rubber to form a third section hydraulically disconnecting the first and the second sections. Additionally, the disposing steps may be performed via a continuous rubber injection process or may be performed during discrete rubber placement processes, such as spray coating of an even wall gearing section and injection molding of the solid rubber power generating section. The method may also include adjusting a location of the housing to align the helical profile of the first rubber layer with the helical profile of the second rubber layer.
The above described mud motor assemblies, including a stator having a power generating section and a gearing section, may be used in a drilling assembly for drilling a wellbore through a subterranean formation. The drilling assembly may include, for example, a mud motor assembly as described in any of the above embodiments, and including, among other components: a top sub, a power section including a progressive cavity motor having a stator and a rotor configured to rotate eccentrically when a drilling fluid is passed through the motor, a rotor catch device, and a device for constraining the motion of the rotor catch device. The drilling assembly may also include a motor output shaft configured to rotate concentrically, a first end of which is directly or indirectly coupled to the rotor, and a second end of which is coupled, indirectly or directly, to a drill bit.
In operation, a drilling fluid is passed through the mud motor assembly, eccentrically rotating the rotor as the drilling fluid passes through the progressive cavity motor. The motor output shaft transmits the eccentric rotor motion (and torque) to the concentrically rotating drill bit to drill the formation. The device for constraining the motion of the rotor or the rotor catch device imparts corrective forces to the rotor, constraining the movement of the rotor relative to the stator, improving the overall performance of the mud motor and the drilling assembly as a whole by counteracting the centrifugal forces and hydraulic pressure loading on the rotor, limiting, minimizing, or eliminating the formation of flow gaps along the length of the motor.
As the gearing section and power generating section are specifically designed to handle the different forces encountered along the length of the power generating section of the motor, improved sealing between the stator/rotor pair may result in the power generating section. A corresponding improvement in one or more of rotary speed output per gallon, developed torque, pressure drop, design centrifugal and torque loads, wear characteristics, as well as other motor properties as compared to a traditionally designed stators (all even wall or all rubber) of similar size and configuration (i.e., lobe count, diameter, materials of construction, length, helix angle, etc.) may be realized. The resulting increase in torque and/or rotary speed may, for example, allow for a greater force to be applied to the drill bit or for the drill bit to be rotated at a greater rotary speed, both of which may individually or collectively result in improved drilling performance (less time to drill a given depth, etc.). Alternatively, the resulting increase in torque and/or rotary speed may allow for a reduction in the length of the motor (rotor/stator pair length) to achieve the same desired performance. Further, as motor assemblies according to embodiments disclosed herein use a relatively short even wall section, the structural benefits of even wall stators may be realized at a significantly reduced cost (i.e., not having to machine the even-wall profile over the entire length of the stator tube).
Stators and rotors having inserts and/or gearing sections as described above may be described by one or more of the following embodiments:
Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures. It is the express intention of the applicant not to invoke 35 U.S.C. §112, paragraph 6 for any limitations of any of the claims herein, except for those in which the claim expressly uses the words ‘means for’ together with an associated function.
While the disclosure includes a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments may be devised which do not depart from the scope of the present disclosure. Accordingly, the scope should be limited only by the attached claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 13414043 | Mar 2012 | US | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US2012/028153 | 3/8/2012 | WO | 00 | 2/13/2014 |
| Number | Date | Country | |
|---|---|---|---|
| 61450239 | Mar 2011 | US |
