Patent Publication Number: US-10760339-B2

Title: Eliminating threaded lower mud motor housing connections

Description:
BACKGROUND 
     Mud motors are a type of progressive cavity motor. Mud motors are used to supplement drilling operations by converting fluid power into mechanical torque and applying this mechanical torque to a drill bit. Mud motors operate under very high pressure and high torque conditions, and mud motors can fail in predictable ways at identifiable stress points. Ongoing efforts are directed to improving fatigue endurance and lowering the cost of servicing mud motors. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a drilling system according to some embodiments. 
         FIG. 2A  is an exploded view of a portion of a mud motor as can be used in some available systems for purposes of comparison to mud motors of some embodiments. 
         FIG. 2B  is an exploded view of a portion of a mud motor in accordance with some embodiments. 
         FIG. 3  is a perspective view of a portion of a mud motor with a section cut away to reveal a continuous power section stator housing in accordance with some embodiments. 
         FIG. 4  is a perspective view of a portion of a mud motor with a section cut away to reveal welding in a continuous power section stator housing in accordance with some embodiments. 
         FIG. 5  is a flowchart showing an embodiment of a method for operating a mud motor in accordance with some embodiments. 
         FIG. 6  is a flowchart showing an embodiment of a manufacturing method in accordance with some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     To address some of the challenges described above, as well as others, some embodiments of a mud motor are described herein. 
       FIG. 1  illustrates a drilling system  100  in which some embodiments can be implemented. A drilling rig  102  is located at the surface  104  of a well  106 . A drilling platform  103  is equipped with a derrick  107 . The drilling rig  102  provides support for a drill string  108 . The drill string  108  may include a bottom hole assembly  110 , perhaps located at the lower portion of the drill pipe  112 . 
     The bottom hole assembly  110  may include drill collars  114 , a downhole tool  116 , and a drill bit  118 . The drill bit  118  may operate to create the borehole  120  by penetrating the surface  104  and the subsurface formations  122 . The downhole tool  116  may comprise any of a number of different types of tools including measurement-while-drilling (MWD) tools, logging-while-drilling (LWD) tools, and others. 
     The drill collars  114  may be used to add weight to the drill bit  118 . The drill collars  114  may also operate to stiffen the bottom hole assembly  110 , allowing the bottom hole assembly  110  to transfer the added weight to the drill bit  118 , and in turn, to assist the drill bit  118  in penetrating the surface  104  and subsurface formations  122 . 
     During drilling operations, a mud pump  124  may pump drilling fluid (sometimes known by those of ordinary skill in the art as “drilling mud”) from a mud pit  126  through a hose  128  into the drill pipe  112  and down to the drill bit  118 . The drilling fluid can flow out from the drill bit  118  and be returned to the surface  104  through an annular area  130  between the drill pipe  112  and the sides of the borehole. The drilling fluid may then be returned to the mud pit  126 , where such fluid is filtered. In some embodiments, the drilling fluid can be used to cool the drill bit  118 , as well as to provide lubrication for the drill bit  118  during drilling operations. Additionally, the drilling fluid may be used to remove subsurface formation cuttings created by operating the drill bit  118 . 
     During drilling operations, the drill string  108  (perhaps including the Kelly  132 , the drill pipe  112 , and the bottom hole assembly  110 ) may be rotated by the rotary table  134 . In addition, or alternatively, the bottom hole assembly  110  may be rotated by a progressive cavity motor  136  (e.g., a mud motor) that is located downhole. The mud motor  136  can be a positive displacement motor (PDM) assembly, which can include a SperryDrill® or SperryDrill® XL/XLS series PDM assembly available from Halliburton of Houston, Tex. The mud motor  136  can include a multi-lobed stator (not shown in  FIG. 1 ) with an internal passage within which is disposed a multi-lobed rotor (not shown in  FIG. 1 ). The PDM assembly operates according to the Moineau principle whereby when pressurized fluid is forced into the PDM assembly and through the series of helically shaped channels formed between the stator and rotor, the pressurized fluid acts against the rotor causing nutation and rotation of the rotor within the stator. Rotation of the rotor generates a rotational drive force for the drill bit  118 . 
     Directional drilling may also be performed by rotating the drill string  108  while contemporaneously powering the mud motor  136 , thereby increasing the available torque and drill bit  118  speed. The drill bit  118  may take on various forms, including diamond-impregnated bits and specialized polycrystalline-diamond-compact (PDC) bit designs, such as the FX and FS Series™ drill bits available from Halliburton of Houston, Tex., for example. 
     The mud motor  136  must be able to withstand loads that arise in two drilling operational modes: “on-bottom” loading, and “off-bottom” loading. On-bottom loading corresponds to the operational mode during which the drill bit  118  is boring into a subsurface formation under vertical load from the weight of the drill string  108 , which in turn is in compression; in other words, the drill bit  118  is on the bottom of the wellbore. Off-bottom loading corresponds to operational modes during which the drill bit  118  is raised off the bottom of the wellbore and the drill string  108  is in tension (i.e., when the bit is off the bottom of the wellbore and is hanging from the drill string  108 , such as when the drill string  108  is being “tripped” out of the wellbore, or when the wellbore is being reamed in the uphole direction). Tension loads are also induced when circulating drilling fluid with the drill bit  118  off-bottom, due to the pressure drop across the drill bit  118  and bearing assembly (not shown in  FIG. 1 ). 
     Mud motors  136  in accordance with various embodiments can withstand the above-described loads without experiencing premature fatigue failures.  FIG. 2A  is an exploded view of a portion of a mud motor  136  as can be used in some available systems for purposes of comparison with example embodiments.  FIG. 2B  is an exploded view of a portion of a mud motor  136  in accordance with some embodiments. 
     As shown in  FIG. 2A , a currently available mud motor  136  includes a power section stator  240 . The power section stator  240  can connect to a flex housing  242  through, for example, threading. The flex housing  242  can further be connected to a bearing pack  244 . The power section rotor  246  can be coupled to the drill bit  118  via the drivetrain  248  driveshaft  250  and drill bit  118  such that the eccentric power from the power section rotor  246  is transmitted as concentric power to the drill bit  118 . In this manner, the mud motor  136  can provide a drive mechanism for the drill bit  118  which is at least partially and, in some instances, completely independent of any rotational motion of the drill string  108  ( FIG. 1 ). 
     The drill bit  118  is coupled to the end of the driveshaft  250  according to methods understood by those of ordinary skill in the art to perform, for example, any of the drilling operations described earlier herein with reference to  FIG. 1 , or other drilling and exploration operations. The power section rotor  246 , drivetrain  248 , and driveshaft  250  are assembled inside the power section stator  240 , flex housing  242 , and bearing pack  244 . The mud motor  136  can further include a saver subassembly  243  coupled at the first end of the power section stator  240  and a rotor catcher  245 . Adjustable bend mud motors  136  may have additional interfaces beneath the housing interface which may be called upon to carry the appropriate loads. 
     Failure of any of the above-described threaded connections will result in an unserviceable mud motor  136 . Even more frequently, failures such as fatigue damage can occur in segments where the mud motor  136  is subjected to bending. Motor fleet operations utilizing fixed bend or adjustable bend housing arrangements continue to have fatigue related problems with the threaded connections in the housings, particularly in high dogleg severity conditions where rotating through bends places very high cyclical loads on these critical threaded joints. 
     Mud motors  136  in accordance with some embodiments can allow operators to perform according to time- and cost-competitive strategies by reaching target depths in shale plays in one run without tripping and at high rotation speeds, through high dogleg bends without fatigue failures. In order to address these and other challenges, embodiments illustrated in  FIG. 2B  eliminate housing connections, which are predictable sources of fatigue failure, below the top end of a power section stator housing  241 . 
     The power section stator housing  241  includes a first (e.g., “uphole”) end, a second (e.g., “downhole”)  256  end, and a cavity passing therethrough. The power section rotor  246  includes rotor lobes  247  to cooperate with one or more stator lobes ( 308  in  FIGS. 3 and 4 ) of the power section stator housing  241 . 
     In embodiments, the drivetrain  248  is operably coupled to the power section rotor  246 , and bearing set  252 , and the bearing set  252  has a driveshaft partially enclosed therein (not shown in  FIG. 2B ). The power section rotor  246 , drivetrain  248 , bearing set  252 , and driveshaft portion are preassembled into a loadable rotor assembly  254  to be fed into a downhole end  256  of the power section stator  240  and fully encased in the internal cavity of the power section stator housing  241 . The bearings in the bearing set  252  can include roller-type bearings, although embodiments are not limited thereto. Further, the bearings can include polycrystalline diamond (PCD) materials although embodiments are not limited to PCD materials. 
     A tonging area  258  and tool joint  260  portion of the driveshaft  250  are outside of the power section stator housing  241 . The tonging area  258  is an area that is accessible to a set of tongs or wrench jaws that can grip the driveshaft  250  immediately above the tool joint  260  for the purposes of tightening or loosening the tool joint. In some embodiments, the tongs can also grip at the tool joint  260  depending on whether the thread above or below the tool joint  260  is to be broken out. The drill bit  118  is coupled to the bottom of the driveshaft  250 . The connection  262  between the drill bit  118  and driveshaft  250  can include an American Petroleum Institute (API) drill string rotary shouldered connection with a tapered end. 
     The rotor assembly  254  is retained within the power section stator housing  241  such that the power section rotor  246 , drivetrain  248  and bearing set  252  with driveshaft can reliably carry power section torque and react to drilling loads within the power section stator housing  241 . 
     The power section stator housing  241  can be constructed in various ways in accordance with different embodiments.  FIG. 3  is a perspective view of a portion of a mud motor  136  with a section cut away to reveal a continuous power section stator housing  241  in accordance with some embodiments. 
     With reference to  FIG. 3 , in some embodiments, one form of a mud motor  136  apparatus includes a continuously formed power section stator housing  241 . For the purposes of this document, “continuously formed” means formed as a unitary piece, or from unitary pieces that are permanently joined (e.g., by welding) to become an integral piece that requires destructive disassembly to separate the original unitary pieces. “Unitary” means a single piece of material that is integral, undivided, and not formed from separate pieces. A “unitary combination” also means a single piece of material that is integral, undivided, and not formed from separate pieces, but may be described as a combination of separate (albeit undivided) elements as a matter of convenience. It is the unitary combination of (a) the stator lobes and (b) the transition portion (and in some embodiments (c) part or all of the housing portion, as well) making up the mud motor  136  that provides increased fatigue life and reliability. However, embodiments are not limited to the combination of the illustrated elements of a mud motor  136  in a continuously formed, unitary fashion. On the contrary, other elements, or housings of other elements of a drilling system, diagnostics system or other system, for example housings for sensors, power system elements, communication elements, etc., can be combined in a unitary combination in a manner similar to other embodiments described herein. 
     According to at least the embodiment illustrated in  FIG. 3 , the mud motor  136  includes a continuously formed power section stator housing  241  having a first end  255 , a second end  256 , and an internal cavity  304  comprising a series of stator lobes  308  and a housing portion  310  passing therethrough. The stator lobes  308  extend from the first end  255  of the power section stator housing  241  until a first end  312  of a transition portion  314 . The housing portion  310  extends from a second end  316  of the transition portion  314  until the second end  256  of the power section stator housing  241 . The transition portion  314  forms a unitary combination  318  with the stator lobes  308 . 
     The mud motor  136  further includes a rotor assembly  254  as described earlier herein with reference to  FIG. 2B , including a power section rotor  246  having rotor lobes  247  to be disposed completely within the internal cavity  304 . The rotor lobes  247  to cooperate with one or more of the stator lobes  308  to rotate the rotor assembly  254  when a drilling fluid under pressure passes through the internal cavity  304 . 
     The embodiment illustrated in  FIG. 3  permits the manufacture of the power section stator housing  241  with large fillet features or gentle coning of the even profile steel power section stator housing  241  into a smooth inside diameter. However, machining processes may become complicated due to the extended length of the power section stator housing  241 . These complications can be mitigated for manufacturers that build the profiles with plates or for manufacturers that hydroform the profile directly into the power section stator housing  241 . 
     In some embodiments, the transition portion  314  forms a unitary combination with the stator lobes  308  and at least part of the housing portion  310  opposite the second end  256  of the power section stator housing  241 . In some embodiments, the continuously formed power section stator housing  241  includes the stator lobes  308 , the transition portion  314 , and the housing portion  310  as a unitary assembly. 
     In some embodiments, the housing portion  310  maintains an unchanging housing cavity profile from the second end  316  of the transition portion  314  to the second end  256  of the power section stator housing  241 . However, in other embodiments the housing portion  310  may include plural profiles (not shown in  FIG. 3 ) along the housing portion  310  length. At least one of the plural profiles may correspond to a threaded junction at the second end  256  of the power section stator housing  241  to enable length extension of the housing portion  310  using a threaded tubular housing element (not shown in  FIG. 3 ). 
     The transition portion  314  can take various forms, profiles, or shapes, some of which can have further fatigue-mitigating effects. For example, in embodiments, the transition portion  314  can be formed as a linear progression (e.g., a linear transition) from the first end  312  of the transition portion  314  to the second end  316  of the transition portion  314 , resulting in a conical profile of the transition portion  314 . In other embodiments, the transition portion  314  can be formed as a concave or convex fillet progression from the first end  312  of the transition portion  314  to the second end  316  of the transition portion  314 , resulting in a curved profile of the transition portion  314 . The transition portion  314  can be formed in even more complex ways, such as progressing smoothly from individual peaks and valleys at the end of the stator lobes  308 , to a circular profile at the beginning of the housing portion  310 , resulting in a multi-concave, lobed profile of the transition portion  314  from the first end  312  to the second end  316  of the transition portion  314 . 
     A continuously formed power section stator housing  241  may be formed as a welded (e.g., via friction welding or other permanent joining) combination of the transition portion  314  and the housing portion  310 . In some embodiments, one or more conduit elements (not shown in  FIG. 3 ) can be disposed in at least one of the housing portion  310  or in material making up the power section stator housing  241  and surrounding the housing portion  310 . These conduit elements can include wire, optical fiber, hydraulic, and other conduit elements for communications with, for example, a processor at the surface system  138 , to communicate with sensors on the drill bit  118  ( FIG. 1 ). Additionally, the conduit elements can be used for providing power hydraulically, electrically, or otherwise to the drill bit  118  ( FIG. 1 ) or any other tool or device at the lower end of the mud motor  136 . This can allow batteries or a turbine to be placed above (uphole from) the mud motor  136  to power sensors in the drill bit  118  or lower end of the mud motor  136 . 
       FIG. 4  is a perspective view of a portion of a mud motor  136  with a section cut away to illustrate a welded construction of a continuous power section stator housing  241  in accordance with some embodiments. A continuously formed power section stator housing  241  can include welding  320  in the housing portion  310  to join portions of the housing portion  310  into one single unitary piece. 
       FIG. 5  is a flowchart showing an embodiment of a method  500  for operating a mud motor  136 . The example method  500  is described herein with reference to elements shown in  FIGS. 1-4 . Some operations of example method  500  can be performed in whole or in part by a mud motor  136  or any component of system  100  ( FIG. 1 ), although embodiments are not limited thereto. 
     The example method  500  begins with operation  502  by coupling the mud motor  136  to a drill string  108  and a drill bit  118 . As described earlier herein with reference to  FIGS. 1 and 2B , the mud motor  136  includes a continuously formed power section stator housing  241  having a first end  255 , a second end  256 , and an internal cavity  304  comprising a series of stator lobes  308  and a housing portion  310  passing therethrough. The stator lobes  308  extend from the first end  255  of the power section stator housing  241  until a first end  312  of a transition portion  314 . The housing portion  310  extends from a second end  316  of the transition portion  314  until the second end  256  of the power section stator housing  241 . The transition portion  314  forms a unitary combination  318  with the stator lobes  308 . 
     The mud motor  136  further includes a rotor assembly  254  as described earlier herein with reference to  FIG. 2B , including a power section rotor  246  having rotor lobes  247  to be disposed completely within the internal cavity  304 . The rotor lobes  247  to cooperate with one or more of the stator lobes  308  to rotate the rotor assembly  254  when a drilling fluid under pressure passes through the internal cavity  304 . 
     The example method  500  continues with operation  504  by forcing the drilling fluid through the internal cavity  304  with sufficient pressure to cause the rotor assembly  254  to rotate relative to the power section stator housing  241  to provide a torque force to the drill bit  118  to make a borehole  120  in a geological formation  122 . In some embodiments, the method  500  includes performing a bench test of the mud motor  136  prior to coupling the mud motor  136  to the drill string  108 , and subsequent to coupling the mud motor  136  to the drill bit  118 . In some embodiments, the method  500  includes drilling a borehole from a surface  104  of the Earth to target depth, past a dogleg (not shown in the Figures) in the borehole  120 , in one continuous run. 
       FIG. 6  is a flowchart showing an embodiment of a manufacturing method  600 . The example method  600  is described herein with reference to elements shown in  FIGS. 1-4 . Some operations of example method  600  can be performed in whole or in part by a mud motor  136  or any component of system  100  ( FIG. 1 ), although embodiments are not limited thereto. 
     The example method  600  begins with operation  602  by forming a power section stator housing  241  having a first end  255 , a second end  256 , and an internal cavity  304  comprising a series of stator lobes  308  and a housing portion  310  passing therethrough. The transition portion  314  forms a unitary combination  318  with the stator lobes  308 . 
     The example method  600  continues with operation  604  by forming a housing portion  310  of the internal cavity  304  as a unitary combination with the stator lobes  308  and the transition portion  314 , or as a continuously formed assembly of a unitary combination of the stator lobes  308  and the transition portion  314  with the housing portion  310 . The stator lobes  308  extend from the first end  255  of the power section stator housing  241  until a first end  312  of a transition portion  314 , and the housing portion  310  extends from a second end  316  of the transition portion  314  until the second end  256  of the power section stator housing  241 . 
     The example method  600  can further include forming the rotor assembly  254  ( FIG. 2B ) including a power section rotor  246  having rotor lobes  247  which, when assembled with the power section stator housing  241  for operation, are disposed completely within the internal cavity  310 . The rotor lobes  247  are formed to cooperate with one or more of the stator lobes  308  to rotate the rotor assembly  254  when a drilling fluid under pressure passes through the internal cavity  310 . 
     The example method  600  can further include forming the transition portion  314  according to various shapes or profiles as described earlier herein with reference to  FIGS. 3 and 4 . For example, the transition portion  314  can be formed with one of a linear transition or a curved transition from the first end  312  of the transition portion  314  to the second end  316  of the transition portion  314 . The example method  600  can further include forming a wiring channel in the power section stator housing to hold conduits for communication with, for example, a processor of the surface system  138 . 
     Referring again to  FIG. 1 , the system  100  can further include a surface system  138  for storage, processing, and analysis of measurements taken by tools on the bottom hole assembly  110  or for providing control to the mud motor  136  or drill bit  118 . The surface system  138  may be provided with electronic equipment, for example a processor, for various types of signal processing, which may be implemented by any one or more of the components of the bottom hole assembly  110 . Formation evaluation data may be gathered and analyzed during drilling operations (e.g., during LWD operations, and by extension, sampling while drilling). The surface system  138  can include a workstation  140  with a display  142 . 
     Any of the above components, for example the mud motor  136 , etc., may all be characterized as “modules” herein. The illustrations of mud motor  136  power section and drill bit  118  components and system  100  are intended to provide a general understanding of the structure of various embodiments, and they are not intended to serve as a complete description of all the elements and features of apparatus and systems that might make use of the structures described herein. It should be noted that the methods described herein do not have to be executed in the order described, or in any particular order. Moreover, various activities described with respect to the methods identified herein can be executed in iterative, serial, or parallel fashion. 
     In summary, using the apparatus, systems, and methods disclosed herein may provide access to serviceable components of mud motors while enhancing fatigue endurance of the housing and lowering the cost of service life of the mud motor and of the housing. Embodiments provide for an extended power section stator housing  241  for the purpose of eliminating threaded connections at the position of very high bending loads. Example embodiments eliminate connections within the power section stator housing  241 , thereby reducing or eliminating sources of fatigue at connections and extending the life of the mud motor  136  generally. These advantages can significantly enhance the value of the services provided by an operation/exploration company, while at the same time controlling time-related costs. 
     Further examples of apparatuses, methods, a means for performing acts, systems or devices include, but are not limited to: 
     Example 1 is a motor (e.g., a progressive cavity motor such as a mud motor) or other apparatus comprising a continuously formed power section stator housing having a first end, a second end, and an internal cavity comprising a series of stator lobes and a housing portion passing therethrough, wherein the stator lobes extend from the first end of the power section stator housing until a first end of a transition portion, wherein the housing portion extends from a second end of the transition portion until the second end of the power section stator housing, and wherein the transition portion forms a unitary combination with the stator lobes; and a rotor assembly including a power section rotor having rotor lobes to be disposed completely within the internal cavity, the rotor lobes to cooperate with one or more of the stator lobes to rotate the rotor assembly when a drilling fluid under pressure passes through the internal cavity. 
     Example 2 may include or use, or may optionally be combined with the subject matter of Example 1 to include wherein the transition portion forms a unitary combination with the stator lobes and at least part of the housing portion opposite the second end of the power section stator housing. 
     Example 3 may include or use, or may optionally be combined with the subject matter of any of Examples 1-2, wherein the continuously formed power section stator housing comprises the stator lobes, the transition portion, and the housing portion as a unitary assembly. 
     Example 4 may include or use, or may be optionally combined with the subject matter of any of Examples 1-3, wherein the housing portion maintains an unchanging housing cavity profile from the second end of the transition portion to the second end of the power section stator housing. 
     Example 5 may include or use, or may be optionally combined with the subject matter of any of Examples 1-3, wherein the housing portion comprises plural profiles along a length of the housing portion. 
     Example 6 may include or use, or may optionally be combined with the subject matter of any of Examples 1-5, wherein the transition portion comprises a linear transition from the first end of the transition portion to the second end of the transition portion. 
     Example 7 include or use, or may optionally be combined with the subject matter of any of Examples 1-5, wherein the transition portion comprises a curved transition from the first end of the transition portion to the second end of the transition portion. 
     Example 8 may include or use, or may optionally be combined with the subject matter of any of Examples 1-5, wherein the transition portion comprises a lobed transition from the first end of the transition portion to the second end of the transition portion. 
     Example 9 may include or use, or may be optionally combined with the subject matter of any of Examples 1-8, wherein the continuously formed power section stator housing is formed as a welded combination of the transition portion and the housing portion. 
     Example 10 may include or use, or may optionally be combined with the subject matter of any of Examples 1-9, to include one or more conduit elements disposed in at least one of the housing portion or in material making up the power section stator housing and surrounding the housing portion. 
     Example 11 may include or use, or may optionally be combined with the subject matter of any of Examples 1-10, to include wherein a shoulder is formed as a welded combination of an inner profile portion and the power section stator housing. 
     Example 12 is a system, which can include portions of any of Examples 1-11, comprising a drill string; a mud motor coupled to the drill string through a rotary shouldered connection, the motor including a continuously formed power section stator housing having a first end, a second end, and an internal cavity comprising a series of stator lobes and a housing portion passing therethrough, wherein the stator lobes extend from the first end of the power section stator housing until a first end of a transition portion, wherein the housing portion extends from a second end of the transition portion until the second end of the power section stator housing, and wherein the transition portion forms a unitary combination with the stator lobes, and a rotor assembly including a power section rotor having rotor lobes disposed completely within the internal cavity, the rotor lobes to cooperate with one or more of the stator lobes to rotate the rotor assembly when a drilling fluid under pressure passes through the internal cavity; and a drill bit coupled to the rotor assembly. 
     Example 13 can include the subject matter of Example 12, and optionally further including a processor to communicate with sensors on the drill bit via one or more conduit elements disposed in the housing portion. 
     Example 14 can include the subject matter of any of Examples 12-13, and further optionally including a processor to control the motor and the drill bit. 
     Example 15 is a method of operating a mud motor, the method comprising operations wherein any of Examples 1-14 can include means for performing the method of Example 25, and wherein the method of Example 15 comprises coupling the mud motor to a drill string and a drill bit, the mud motor comprising a continuously formed power section stator housing having a first end, a second end, and an internal cavity comprising a series of stator lobes and a housing portion passing therethrough, wherein the stator lobes extend from the first end of the power section stator housing until a first end of a transition portion, wherein the housing portion extends from a second end of the transition portion until the second end of the power section stator housing, and wherein the transition portion forms a unitary combination with the stator lobes, and a rotor assembly including a power section rotor having rotor lobes disposed completely within the internal cavity, the rotor lobes to cooperate with one or more of the stator lobes to rotate the rotor assembly when drilling fluid under pressure passes through the internal cavity; and forcing the drilling fluid through the internal cavity with sufficient pressure to cause the rotor assembly to rotate relative to the power section stator housing to provide a torque force to the drill bit to make a borehole in a geological formation. 
     Example 16 includes the subject matter of Example 15, further optionally including performing a bench test of the mud motor prior to coupling the mud motor to the drill string, and subsequent to coupling the mud motor to the drill bit. 
     Example 17 includes the subject matter of any of Examples 15-16, and further optionally including drilling a borehole from a surface of the Earth to target depth, past a dogleg in the borehole, in one continuous run. 
     Example 18 is a manufacturing method, the method comprising operations wherein any of Examples 1-14 can include means for performing the method of Example 18, and wherein the method of Example 18 comprises forming a power section stator housing having a first end, a second end, and an internal cavity comprising a series of stator lobes and a housing portion passing therethrough, the stator lobes forming a unitary combination with the transition portion; and forming a housing portion of the internal cavity as a unitary combination with the stator lobes and the transition portion, or as a continuously formed assembly of a unitary combination of the stator lobes and the transition portion with the housing portion, wherein the stator lobes extend from the first end of the power section stator housing until a first end of a transition portion, and wherein the housing portion extends from a second end of the transition portion until the second end of the power section stator housing. 
     Example 19 includes the subject matter of Example 18, and further optionally comprising forming a rotor assembly including a power section rotor having rotor lobes which, when assembled with the power section stator housing for operation, are disposed completely within the internal cavity, the rotor lobes formed to cooperate with one or more of the stator lobes to rotate the rotor assembly when a drilling fluid under pressure passes through the internal cavity. 
     Example 20 includes the subject matter of any of Examples 18-19, and further optionally comprising forming the transition portion with one of a linear transition or a curved transition from the first end of the transition portion to the second end of the transition portion. 
     Example 21 includes the subject matter of any of Examples 18-20, and further optionally comprising forming a wiring channel in the power section stator housing. 
     The accompanying drawings that form a part hereof, show by way of illustration, and not of limitation, specific embodiments in which the subject matter may be practiced. The embodiments illustrated are described in sufficient detail to enable those skilled in the art to practice the teachings disclosed herein. Other embodiments may be utilized and derived therefrom, such that structural and logical substitutions and changes may be made without departing from the scope of this disclosure. This Detailed Description, therefore, is not to be taken in a limiting sense, and the scope of various embodiments is defined only by the appended claims, along with the full range of equivalents to which such claims are entitled. 
     Such embodiments of the inventive subject matter may be referred to herein, individually and/or collectively, by the term “invention” merely for convenience and without intending to voluntarily limit the scope of this application to any single invention or inventive concept if more than one is in fact disclosed. Thus, although specific embodiments have been illustrated and described herein, it should be appreciated that any arrangement calculated to achieve the same purpose may be substituted for the specific embodiments shown. This disclosure is intended to cover any and all adaptations or variations of various embodiments. Combinations of the above embodiments, and other embodiments not specifically described herein, will be apparent to those of skill in the art upon reviewing the above description. 
     Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement that is calculated to achieve the same purpose may be substituted for the specific embodiments shown. Various embodiments use permutations or combinations of embodiments described herein. It is to be understood that the above description is intended to be illustrative, and not restrictive, and that the phraseology or terminology employed herein is for the purpose of description. Combinations of the above embodiments and other embodiments will be apparent to those of ordinary skill in the art upon studying the above description.