The invention relates to a motor/pump assembly for driving downhole tooling such as a drilling tool, wherein the motor assembly can be positioned in a casing.

Downhole tooling such as a drilling tool can be applied with the use of casing that is positioned into the ground from a drilling rig. Such tooling is often driven by a motor to which is also referred as a so-called mud motor.

Problems with conventional motors (or pumps) for driving downhole tooling are caused by the difficult conditions in relation to pressure and temperature, for example. Materials may expand thereby causing problems with friction, wear and/or leakage. This significantly reduces the operational window of the motor assembly and associated tooling.

The present invention aims to provide a motor or motor/pump assembly obviating or at least reducing the aforementioned problems and to provide a motor assembly with a larger operational window.

This is achieved with a motor or motor/pump assembly for driving the downhole tooling according to the present invention, with the motor or motor/pump assembly comprising:

- a metal rotor with a rotor thread and having a rotor-centerline;

- a metal stator housing comprising a rotatable metal stator having a stator-centerline; wherein the rotor-centerline and the stator-centerline are provided at an off-set.

The motor or motor/pump assembly according to the invention is provided with a metal rotor and a metal stator both having a separate centerline. According to the invention the rotor centerline and the stator centerline are provided at a(n) (mutual) offset, such that the rotor centerline and the starter centerline are placed at a (small) distance from each other. In fact, the offset provides an eccentricity between the stator and the rotor.

When the motor or motor/pump assembly is operated as a motor, an amount of pumping fluid is supplied to the motor. As a consequence thereof the motor starts rotating and can be used for driving a tool, such as a drill tool or drill bit. It will be understood that the motor/pump assembly according to the invention can also be applied as a pump when the rotor is driven by an external motor and fluid can be pumped with the assembly. In the context of this description will be referred to a motor assembly. It will be understood that this also encompasses a motor/pump assembly and that the motor or motor/pump assembly can also be operated as a pump.

The rotor is provided with a rotor thread that may comprise helical lobes. Preferably, the stator is provided with a stator thread that may comprise helical lobes. The thread or threads is/are designed to provide a space or chamber that allows fluid to flow from the entrance of the motor assembly to the exit of the motor assembly. Preferably, differences in threading are provided to assist the tooling with additional vibrations to overcome frictional forces, for example. Also, the threads of the stator and the rotor can be designed such that they rotate in a different direction when fluid is sent through the motor assembly. Also the number of threads on the rotor and stator can be different to further increase the frictional effect.

Providing the rotor and stator with separate centerlines that are provided at an offset reduces undesired eccentric movements and reduces wear. This enlarges the operational window, for example allowing for larger temperatures and/or higher pressures. Also, in addition or as an alternative, this may allow for larger time of operation between maintenance intervals.

Preferably, the stator and the rotor are formed by electrochemical machining (ECM). ECM is applied to structure the rotor contacting surfaces of the stator to achieve a sufficiently narrow clearance of negative interference fit with the rotor to form an efficient seal without seizing the progressive cavity section in use.

In a presently preferred embodiment of the invention the motor assembly further comprises a rotor bearing and a stator bearing.

Providing the rotor and stator with separate bearings enables both the stator and rotor to rotate independently. This provides additional flexibility to the motor assembly. In addition, by providing separate bearings the effect of side forces that act on the motor assembly are significantly reduced. In fact, tests with an embodiment of the motor assembly according to the invention have shown that the amount of damage or wear to the bearing is significantly reduced by providing both the rotor and stator with separate bearings as compared to a more conventional motor assembly.

In a preferred embodiment of the invention the offset is about half of the difference between a major diameter of the stator thread and a major diameter of the rotor thread.

A thread, or helical lobe, when provided on a shaft has a major diameter that corresponds to the largest diameter that defines the height of the thread profile as seen in a cross-sectional view of the thread. This defines the threading outside diameter (OD). A minor diameter of a thread is the minimal diameter seen in a cross section of the thread. The height of a thread is defined as half of the major diameter minus the minor diameter.

In the presently preferred embodiment of the invention the rotor centerline is substantially coaxial with the centerline of the stator housing.

Providing the rotor centerline substantially coaxial with the centerline of the stator housing, and therefore also providing the stator centerline with an offset to the centerline of the stator housing, a more stable motor assembly is achieved. Tests have shown that a more stable operation is achieved when providing such embodiment of the motor assembly in a casing with downhole tooling. This further contributes to enlarging the operational window of the motor assembly. In a further preferred embodiment of the invention, the metal rotor and metal stator provide a full-metal motor assembly.

A full metal motor assembly, such as a mud motor, no longer relies on other materials such as rubbers for sealing purposes, for example. Therefore, in such full metal motor assembly thermal expansion only involves the metal materials such that differences in thermal expansion between different materials are minimized or even nonexistent. This reduces adverse effect of large temperature differences on the operation of the motor assembly. As a result, the operational window for temperature and pressure is significantly increased. It is noted that the motor assembly can be applied at depths of up to about 10 km at temperatures of even above 180 °C or even above 200 °C, and even above 400 °C.

Also, the full metal mud-motor reduces problems caused by the use of rubber material and/or other suitable materials for sealing that are associated with interference. In such conventional case the interference causes friction between the rubber and stator. Also, in such conventional case problems are caused with respect to the clearance fit, relating to the gap between the stator and rotor, which may result in an ineffective seal. These problems are obviated by the full metal motor.

Furthermore, the full metal mud-motor is independent of the fluid type that is applied.

With conventional motors fluids may interact with rubber seals thereby reducing the choice for fluid types. With the full metal motor more possibilities for fluid type are available. This enables optimizing the fluid type at the desired conditions thereby improving the operational time between maintenance intervals. For example, a conventional motor assembly with rubber material may have a 40 to 200 hours maintenance interval. A similar type full metal motor according to the invention may have an improved interval of 500 to 1000 hour maintenance interval. This reduces costs and improves efficiency of the motor assembly.

In a further preferred embodiment of the invention the rotor comprises one or more rotor threads, wherein the rotor has less rotor threads as compared to the number of stator threads. In a presently preferred embodiment the amount of rotor threads is the amount of stator threads minus one.

The threads or helical lobes for the rotor preferably comprise a helical ridge that is wrapped around the core of the rotor. The number of threads can be 1, 2, 3, 4, or any other suitable number. In general, providing less rotor threads as compared to the number of stator threads provides a differential. By reducing the (relative) number of rotor threads the relative movement between the rotor and the rotatable stator is reduced. This reduces the amount of wear.

The pitch of a thread is the distance between the crest of one thread to the next. The lead is the distance along the axis that is covered by one complete rotation. In case of one thread (single start) the pitch and lead are equal. In case of two threads (double start) two of these ridges are wrapped around the core of the rotor.

In a presently preferred embodiment the rotor comprises four threads and the rotatable stator comprises five threads. Alternatively, the rotor comprises nine threads and the rotatable stator comprises ten threads. It will be understood that any other number of threads and differential (difference in number between rotor threads and stator threads) can be envisaged in accordance with the present invention.

In a further preferred embodiment of the invention the motor assembly comprises at least three stages, preferably at least four stages, more preferably at least five stages, and most preferably six stages.

A stage corresponds to the lead that is described earlier in this description. The offset between the stator centerline and rotor centerline provides a more constant metal-to metal sealing, especially in a mud-motor in a full metal embodiment. In addition, the sealing remains more constant in a wider operating range as compared to conventional motor assemblies. This means that it is possible to reduce the number of stages, thereby rendering the motor assembly easier to handle as compared to the conventional motors. This is especially advantageous when using the motor assembly in a casing for downhole tooling as maneuvering at these large depths is often difficult.

In a further preferred embodiment of the invention the stator of the motor assembly comprises electromagnetic stator means and/or electromagnetic rotor means, respectively.

Providing the (rotatable) stator with electromagnetic stator means enables the motor assembly to generate electrical energy when in use in a downhole situation. In use, when downhole fluid moves the motor assembly the motor starts rotating and can be used for driving a tool, such as a drill tool or drill bit. In addition, by providing electromagnetic means for the stator and/or the rotor, electrical energy can be generated in a downhole situation. This obviates or at least reduces the need for power supply to downhole measurement equipment, for example. In fact, this energy generation enables an effective (downhole) measurement system without requiring additional cables. In addition, this reduces the risk of malfunctioning of the downhole operation. A further advantage is that energy can be provided directly downhole at the respective operating conditions.

The motor assembly preferably comprises energy harvesting device and/or an electromagnetic generator and/or thermoelectric equipment and/or piezoelectric equipment. These tools further enhance the possibilities and operational window for the motor assembly.

Preferably, the stator is a rotatable stator and is provided with the electromagnetic stator means, more preferably with the means comprising one or more coils. In addition, or as an alternative, the electromagnetic rotor means comprise one or more coils. In the alternative it would be possible to apply the electromagnetic rotor means to a conventional motor assembly thereby providing similar effects that include the obviation or reduction of power cables to downhole measurement equipment.

In use, the coil or coils generate an alternating current, optionally in cooperating with (permanent) magnet(s). In a presently preferred embodiment, there is provided an electrical connector configured for operatively connecting the electromagnetic means to downhole measuring equipment. This enables providing power directly to the (downhole) measurement equipment. Optionally, the motor assembly further comprises a downhole battery. This battery is optionally provided in combination with the measurement equipment. The battery can be used for storing electrical energy. Preferably, the motor assembly further comprises a downhole AC-DC convertor. This enables converting alternating current into direct current. As an alternative to the battery or in addition thereto the motor assembly may comprise a capacitor and/or supercapacitor and/or any other suitable device to store energy.

The present invention further relates to a downhole tooling comprising a motor assembly in an embodiment according to the present invention.

The downhole tooling provides the same or similar effects and advantages as described in relation to the motor assembly according to the invention.

In a presently preferred embodiment the downhole tooling further comprises a drill bit, wherein the rotor is directly or indirectly coupled to the drill bit. More preferably, the rotor is directly coupled to the drill bit thereby obviating the need to apply so-called flexible shafts. This reduces the number of parts and associated costs. Furthermore, this reduces the risk of malfunctioning thereby contributing to a failsafe operation.

The invention further also relates to a drilling rig comprising a downhole tooling in an embodiment according to the present invention.

The drilling rig provides the same or similar effects and advantages as described in relation to the motor assembly and/or downhole tooling according to the present invention.

The invention further also relates to a method for manufacturing a rotor and rotatable stator of a motor assembly according to an embodiment of the present invention, with the method comprising the steps of:

- designing the rotor and stator, wherein the rotor-centerline and the stator-centerline have an off-set;

- providing a rough model for the rotor and stator; and

- performing an electrolytic process to form the stator involving electrochemical machining the surface of the stator.

The method according to the invention provides the same or similar effects and advantages as described in relation to the motor assembly, downhole tooling and/or drilling rig. One of the manufacturing processes that can be applied when performing the method according to the present invention is described in US 10, 676,992 B2 and may involve polishing, preferably electrochemical polishing and surface hardening as additional treatments.

Further advantages, features and details of the invention are elucidated on the basis of preferred embodiments thereof, wherein reference is made to the accompanying drawings in which:

Fig. 1 shows a cross sectional view of a motor assembly according to the invention; Fig. 2 shows another cross-sectional view in a transverse direction of the motor assembly of figure 1 ;

Fig. 3 shows the rotor of the motor assembly of figures 1 and 2;

Fig. 4 schematically shows a drilling rig with casing in which the motor assembly of figures 1-3 can be applied;

Fig. 5 shows an alternative embodiment for a motor assembly for driving downhole tooling and energy generation; and

Fig. 6 shows a schematic overview of the manufacturing process of the motor assembly of figures 1-3;.

Motor assembly 2 (figure 1) is shown in a cross-sectional view in a longitudinal direction. Motor assembly 2 comprises rotor 4 that is provided in rotatable stator 6. Rotatable stator 6 is provided in stationary housing 8 that is assembled from several parts. In the illustrated embodiments stationary housing 8 is assembled from first stator housing end 8a, stator housing middle section 8b and second stationary housing end 8c. It will be understood that another number of parts can also be envisaged in accordance to the present invention.

Rotor 4 is capable of rotating using first and second rotor bearings 10. Rotor 4 has rotor centerline 12. Rotatable stator 6 is rotatable with first and second stator bearings 14. Rotatable stator 6 comprises stator centerline 16. Between the rotor 4 and stator 6 there is provided sealing surface 18. Space or chamber 20 enables fluids to pass from one side to the other side of motor assembly 2.

Rotor 4 is provided with threads 22. Rotor thread 22 has maximum outer radius dl and minimum radius d2, wherein the difference dl minus d2 corresponds to the height of the thread d. The height of the rotor thread d relates to offset e between rotor centerline 12 and stator centerline 16, wherein offset e is preferably equal to half of the difference between the major diameter of the stator thread and the major diameter dl of the rotor thread. Stator 8 is provided with stator threading 24. In the illustrated embodiment sealing surface 18 is a metal -to-metal contact between rotor 4 and stator 6.

In the illustrated embodiment (figure 2) motor assembly 2 is provided with offset e in a direction that is illustrated in the vertical direction in figure 2. In the illustrated embodiment rotor 4 is provided with six separate helical ridges 22 a-f (figure 3). It will be understood that another number of ridges or threads can be envisaged in accordance with the present invention.

When the motor assembly is operated as a motor drive, fluid is pumped in the direction of the longitudinal axis of motor assembly 2, thereby starting to rotate rotor 4 relative to the rotatable stator housing 6. By connecting, directly or indirectly, a tooling such as drill bit, to rotor 4 the tooling can be operated. When operating motor assembly 2 of the invention as a pump, rotor 4 is rotated thereby “screwing” fluid along the axis of assembly 2.

In an application with motor assembly 2 (figure 4) application 102 involves (drilling) rig 106 that is positioned on surface 104. Casing 108 extends from rig 106 into the ground. A drill bit 110 is connected to mud-motor 2 thereby comprising downhole tooling 112. In the illustrated application 102 there is provided a blowout preventor (BOP) 114 as a safety measure and there is provided motor pump system 116 that is connected to mud-motor 2. It will be understood that other applications can also be envisaged in accordance to the present invention.

In an alternative embodiment, motor assembly 152 (figure 5) comprises rotor 154 and stator 156. In the illustrated embodiment stator 156 is a rotatable stator similar to stator 6 of motor assembly 2. Rotatable stator 156 is provided in stationary housing 158. Further, there is provided front flange 160 and rear flange 162. Stator 156 is provided with electromagnetic elements, preferably coils 164. Elements 164 cooperate with housing coils 166 and are capable of generating energy. Stator bearing 168 and rotor bearing 170 enable rotation of the respective parts. In the illustrated embodiment is schematically illustrated downhole measurement equipment 172 that receives and uses the generated energy thereby enabling downhole measurements. Optionally, measurement equipment 172 is provided with a (rechargeable) battery 172a and/or AC-DC convertor 172b. In this illustrated embodiment stator centerline 174 is provided at a distance from rotor centerline 176 similar to centerlines 12, 16 of motor assembly 2.

Manufacturing method 202 (figure 6) preferably starts with a design phase 204 resulting in design 206 of rotor 4, stator 6 and other components of motor assembly 2. Then, a rough model for the rotor 4 and stator 6 is prepared in modelling phase 208 resulting in a rough rotor and rough stator models 210. These rough models 210 are treated in electrochemical machine step 212 resulting in machined rotor and stator components 214. Components 214 are treated in an etching or polishing phase 216 resulting in final rotor and stator parts 218 that correspond to rotor 4 and stator 6. In assembling phase 220 the rotors 4, 6 are assembled to the final end product 222 that relates to motor assembly 2.

The present invention is by no means limited to the above-described preferred embodiments thereof. The rights sought are defined by the following claims within the scope of which many modifications can be envisaged.