Patent Publication Number: US-8985977-B2

Title: Asymmetric lobes for motors and pumps

Description:
BACKGROUND OF THE DISCLOSURE 
     1. Field of the Disclosure 
     This disclosure relates generally to moineau motors and pumps used for drilling wellbores. 
     2. Description of the Related Art 
     To obtain hydrocarbons such as oil and gas, boreholes or wellbores are drilled by rotating a drill bit attached to a drill string end. A substantial proportion of the current drilling activity involves directional drilling, i.e., drilling deviated and horizontal boreholes, to increase the hydrocarbon production and/or to withdraw additional hydrocarbons from the earth&#39;s formations. Modern directional drilling systems generally employ a drill string having a drill bit at the bottom that is rotated by a motor (commonly referred to in the oilfield as the “mud motor” or the “drilling motor”). 
     Positive displacement motors are commonly used as mud motors. A typical mud motor includes a power section which contains a stator and a rotor disposed in the stator. A stator typically includes a housing that is lined inside with a helically contoured or lobed elastomeric material. The rotor is usually made from a suitable metal, such as steel, and has an outer lobed surface. Pressurized drilling fluid is pumped into a progressive cavity formed between the rotor and stator lobes. The force of the pressurized fluid pumped into the cavity causes the rotor to turn in a planetary-type motion. A suitable shaft connected to the rotor via a flexible coupling compensates for eccentric movement of the rotor. The shaft is coupled to a bearing assembly having a drive shaft, which in turn rotates the drill bit attached thereto. 
     As noted above, both the rotor and stator are lobed. The rotor and stator lobe profiles are similar, with the rotor having one less lobe than the stator. The difference between the number of lobes on the stator and rotor results in an eccentricity between the axis of rotation of the rotor and the axis of the stator. The lobes and helix angles are designed such that the rotor and stator lobe pair seal at discrete intervals, which creates axial fluid chambers that are filled by the pressurized circulating fluid. The action of the pressurized circulating fluid causes the rotor to rotate and precess within the stator. 
     The present disclosure provides methods and devices for increasing the reliability, durability, and efficiency of the motors (or pumps), and other similar fluid pressure differential activated devices. 
     SUMMARY OF THE DISCLOSURE 
     In aspects, the present disclosure provides an apparatus for use in a wellbore. The apparatus may include a stator having a bore and a rotor disposed in the bore. The rotor may include a layer that has an asymmetrical material property profile along at least a portion of a circumference of the layer. In another embodiment, the apparatus may have a stator having a layer defining a bore and a rotor disposed in the bore. In this embodiment, the layer of the stator has an asymmetrical material property profile along at least a portion of a circumference of the layer. 
     In aspects, the present disclosure further provides an apparatus that has a stator and a rotor that cooperate to form at least one fluid chamber and at least one seal during relative rotation between the rotor and the stator. A layer forming at least a portion of the at least one fluid chamber and the at least one seal may have an asymmetrical material property profile. 
     Examples of certain features of the disclosure thus have been summarized rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the disclosure that will be described hereinafter and which will form the subject of the claims appended hereto. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For detailed understanding of the present disclosure, reference should be made to the following detailed description of the embodiment, taken in conjunction with the accompanying drawings, in which like elements have been given like numerals and wherein: 
         FIGS. 1A and 1B  show a longitudinal cross-section of a moineau device; 
         FIG. 2  illustrates a sectional end view of a stator and a rotor; and 
         FIG. 3  illustrates a fluid cavity and a seal formed during relative rotation between the  FIG. 2  stator and rotor. 
     
    
    
     DESCRIPTION OF THE DISCLOSURE 
     The present disclosure relates to methods for wellbore devices that utilize an asymmetric material property profile to enhance operation and service life of pumps and motors. As used herein, the term “asymmetric” refers to a non-uniformity, a discontinuity, or a variance in a value of a parameter or parameters. As discussed in greater detail below, the lobes of stators and/or rotors for such devices may incorporate asymmetric material properties of the used materials to enable certain different sections or sides of one component to perform different tasks. 
     While the teachings of the present disclosure may be advantageously applied to various types of wellbore equipment, for simplicity, the present teachings will be described in connection with moineau devices that are commonly utilized during the drilling oilfield wellbores. Generally, a moineau motor generates rotational power in response to an applied pressure differential and a moineau pump displaces fluid in response to an applied rotational power. While certain operating characteristics and configurations may vary between a pump and a motor, the present teachings may be advantageously applied to either device. For convenience, the term moineau devices encompass motors and pumps. 
     Referring initially to  FIGS. 1A-1B , there is shown a cross-sectional view of a positive displacement motor  10  having a power section  12  and a bearing assembly  14 . The power section  10  may contain a stator  16  that has a helically-lobed inner surface  18 , which may include a lining, coating or protection member  20 . The member  20  may be an elastomeric or metal lining, coating or layer configured to protect the inner surface  18  from corrosion, wear or other type of degradation. 
     The power section  10  may also include a rotor  22  that is configured to rotate inside the stator  16 . The rotor  22  may have a helically-lobed outer surface  24  that has contours that complements the contours of the helically-lobed inner surface  18  of the stator  16 . The rotor  22  and the stator  16  may have a different number of lobes, e.g., the rotor may have one less lobe than the stator  16 . The contours of the stator inner surface  18  and the rotor outer surface  24  and their helical angles are such that the rotor  22  and the stator  16  seal at discrete intervals as the rotor  22  rotates eccentrically inside the stator  16 . The sealing creates axial fluid chambers or closed cavities  30  that are filled by the pressurized drilling fluid  32 . The fluid is displaced along the length of the motor  10  while in the cavities  30 . The action of the pressurized circulating drilling mud  32  flowing from the top  34  to the bottom  36  of the power section  12  causes the rotor  22  to rotate within the stator  16 . The rotor  22  may be coupled to a flexible shaft  40 , which connects to a rotatable drive shaft  42  in the bearing assembly  14  that carries the drill bit (not shown). 
     Referring now to  FIG. 2 , there is shown a sectional view of the rotor  22  and the stator  16 . As discussed above, the helical structures and lobe design of the contours form closed chambers between rotor  22  and stator  16  that make the device  10  work like a “rotating hydraulic cylinder”. In operation, the lobes  50  of the rotor  22  and the lobes  52  of the stator  16  simultaneously create a closed chamber and seal. These closed chambers and seals are made and unmade cyclically as the rotor  22  rotates relative to the stator  16 . Referring briefly to  FIG. 3 , there are shown portions of the rotor lobe  50  engaging the stator lobe  52  to form a closed chamber  54  and a seal  56 . Therefore, both sides of the lobes  50 ,  52  fulfill different tasks. “Load sides”  58 ,  60  of the rotor lobe  50  and stator lobe  52 , respectively, form the closed chamber  54  and mainly support the rotor  22  and transfer all forces that arise from the generated torque to the stator  16 . On the other hand, the “sealing sides”  62 ,  64  of the rotor lobe  50  and the stator lobe  52  form the seal  56  and mainly ensure the sealing capacity of the power section. For the purposes of this discussion, the load sides  58 ,  60  and the sealing sides  62 ,  64  are the opposing sides of the rotor and stator lobes  50 ,  52 , respectively. Thus, these sides are positioned along the same radial distance but face opposing directions. 
     Embodiments of the present disclosure provide lobe features that are particularly suited each of these distinct functions. For example, the stator  16  has a layer  61  having a portion at a load side  58  and a portion at a sealing side  62 . Also, the rotor  22  has a layer  63  having a portion at a load side  60  and a portion at a sealing side  64 . The layers  61 ,  63  may each use one or more materials that having one or more properties specifically suited for each of these functions. The layer portion(s) at the load sides  58 ,  60  must support the forces generated by the pressurized drilling fluid in the closed chamber  54 . Generally speaking, materials that are relatively hard or inflexible are better suited for load bearing applications. Often, such materials exhibit relatively small elastic deformation. The layer portion(s) at the sealing sides  62 ,  64  must form, at least temporarily, a liquid tight seal between the contact surfaces of the rotor  22  and the stator  16 . Generally speaking, materials that are pliable are better suited for sealing applications. Such materials can elastically flow or deform to block fluid paths between two surfaces. 
     In arrangement suitable for this application, the lobes  50 ,  52  may each have one or more elastomeric layers. However, the modulus of elasticity of the elastomeric layers may be different in magnitude. For instance, the load sides  58 ,  60  may have an elastomer formulated to have a higher modulus of elasticity than the elastomer at the sealing sides  62 ,  64 . Suitable elastomers include, but are not limited to, natural rubber, synthetic rubber, polyisoprene, butyl rubber, polybutadiene, styrene-butadiene rubber, nitrile rubber, ethylene propylene rubber, epichlorohydrin rubber, polyacrylic rubber, silicone rubber, fluorosilicone rubber, thermoplastic elastomers, hydrogenated nitrile rubber, fluoroelastomer, perfluoroelastomer and polyurethane rubber. 
     Generally speaking, the material property of the layer forming the outer surface  24  of the rotor lobe  50  and the inner surface  18  of the stator lobe  52  may vary along at least along a portion of the circumference of the rotor  22  and the stator  16 . This circumferential change in a material property or properties will be referred to as “an asymmetrical material property profile.” 
     The variance in material properties along the circumferential profile may be formed using different formulations within the same type of materials. For example, the amount of “cross-linking” may be varied to cause differences in a polymers&#39; physical properties. The variance may also be formed by physically altering a material layer by using grooves or channels in areas to reduce material rigidity. Other ways to obtain asymmetry may include applying a coating or lining, treating a surface (e.g., with heat, friction, pressure, impact, etc.), or by embedding a secondary material into a material layer. For example, a relatively soft material layer may include embedded rigid plates, a filler material, beads, or rods. Thus, the asymmetrical material property profile may be formed in a variety of ways other than by chemically varying a material property. 
     The above discussion involved both the rotor  22  and the stator  16  having one or more lobes formed with a layer or layers with an asymmetric material property profile. Other arrangements may include a layer with asymmetric material properties on either the rotor lobe  50  or the stator lobe  52 , but not both. For example, the rotor lobes  50  may have lobes  50  formed with one or more layers having asymmetric material properties, but the stator lobes  52  may have lobes  52  with generally symmetric material properties, and vice versa. In still arrangements, the asymmetric material profile may be formed by using completely different materials. For example, the load sides  58 ,  60  may include a rigid or hard layer formed of a ceramic, plastic, a thermoplastic material, a duroplastic material or metal and the sealing sides  62 ,  64  may be formed of rubber. 
     It should be understood that the material properties other than the modulus of elasticity may be varied. Illustrative material properties that may be asymmetric include, but are not limited to: ductility, fatigue limit, flexural modulus, flexural strength, fracture toughness, hardness, indentation, plasticity, Poisson&#39;s ratio, shear modulus, shear strain, shear strength, specific modulus, specific weight, tensile strength, yield strength, and/or young&#39;s modulus. In some instances, such properties may also be referred to as mechanical properties. 
     It should also be understood that the asymmetric material property profile may also be selected to factors other than force transfer or sealing effectiveness. For example, the load sides  58 ,  60  are subjected to fluid pressure at a solid-liquid interface. The sealing sides  62 ,  64  are subjected to pressure at a solid-solid interface. Thus, the asymmetric material property may relate to wear resistance or resistance to degradation due to liquid surface contact or solid surface contact. In other arrangements, the asymmetric material property profile may be constructed to address different levels of surface abrasion, corrosion, or chemical reactivity encountered by the load side and the sealing side. 
     From the above, it should be appreciated that what has been disclosed includes an apparatus having a rotor disposed in a bore of a stator. The stator and the rotor cooperate to form at least one fluid chamber and at least one seal at substantially the same time during relative rotation between the rotor and the stator. A layer forming at least a portion of the at least one fluid chamber and portion of the at least one seal may have an asymmetrical material property profile. In some embodiments, the layer is formed on opposing sides of a lobe associated with the rotor and the asymmetrical material property profile is across a circumference of an outer surface of the rotor that includes the lobe. In other embodiments, the layer is formed on opposing sides of a lobe associated with the stator and the asymmetrical material property profile is across a circumference of an inner surface of the stator that includes the lobe. In still other embodiments, the rotor and the stator may each include a layer on opposing sides of a lobe and that has an asymmetrical material property profile 
     As used above, the term “layer” is used in a functional sense to refer to a portion or section of the lobe that is specifically shaped, constructed, and dimensioned to perform the tasks of forming the closed chambers or the seals. A “layer” may exist as a homogeneous body (e.g., a separate coating or lining). The layer may also be a substrate and a lining/coating or a material having embedded secondary materials (e.g., fillers). A layer may also be composed of two or more materials vary along the circumference. That is, the layer may be composed of two or more radially or circumferentially separated layers. Furthermore, the term “material property” refers to the behavior or response of the “layer” as a whole. If the layer is formed of one homogeneous material, then the “material property” is that of the one material. However, if the layer is formed of two or more materials, then the “material” property is the property of all the materials making up the layer acting collectively. In a general sense, even if the materials vary and 
     As is known, nearly all materials will have imperfections in manufacture and assembly that may cause variances in material properties. In the discussion above, the term “asymmetric” refers to disparities in material properties that are intentional and have been specifically engineered and calibrated to control behavior of a component in response to given operating condition. Thus, the term “an asymmetrical material property profile” refers to an intentional variance in a material property along a circumferential profile of a rotor or stator as opposed to an unintentional variance. 
     The foregoing description is directed to a particular embodiment of the present disclosure for the purpose of illustration and explanation. It will be apparent, however, to one skilled in the art that many modifications and changes to the embodiment set forth above are possible without departing from the scope and the spirit of the disclosure. It is intended that the following claims be interpreted to embrace all such modifications and changes.