Patent Publication Number: US-11639663-B2

Title: Regulating flow to a mud pulser

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from U.S. Provisional Application Ser. No. 62/916,092 filed Oct. 16, 2019 the full disclosure of which is incorporated by reference herein in its entirety and for all purposes. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present disclosure relates to communicating downhole and uphole with pressure pulses in a flow of drilling fluid. More specifically, the present disclosure relates to regulating a flow of drilling mud to a mud pulser. 
     2. Description of Prior Art 
     One type of measurement while drilling (“MWD”) senses conditions within the wellbore, and transmits data representing the sensed conditions to surface. One type of data sensed is the inclination and azimuth of the wellbore being formed. Mud pulse telemetry is one way to transmit the data from within the wellbore to surface, and where pressure pulses (commonly referred to as mud pulses) are generated within drilling fluid in a drill string. The mud pulses are monitored by sensors disposed in a flow of the drilling fluid returning to surface. Decisions for steering the drill bit are often based on information obtained from decoding the monitored mud pulses. 
     Mud pulses (also referred to as pressure pulses) are typically generated with mud pulsers that are disposed within the drill string and in the path of drilling fluid flowing through the drill string. One well known manner of producing mud or pressure pulses is to selectively alter the cross sectional area of the drilling fluid flow path with internally located valves. The valves typically employ a reciprocating piston or a rotating shear valve. Mud pulsers with either type of valve are operable within a limited range of drilling fluid flowrate, and are sometimes ineffective above or below certain flowrates. 
     SUMMARY OF THE INVENTION 
     Disclosed is an example of a system for use in wellbore operations having a drill string, and a mud pulser in the drill string. The mud pulser includes a stator having an outer surface with one or more channels that project along an axis of the drill string and that are spaced angularly apart from one another about the axis of the drill string, a rotor having one or more slots that selectively move into and out of registration with outlets of the channels with rotation or oscillation of the rotor, and a plug assembly that selectively defines a barrier to a flow of the drilling fluid through a designated channel. The plug assembly may selectively define either a total or partial barrier to the flow of the drilling fluid through the designated channel. When the plug assembly defines a total barrier to the flow of drilling fluid through a designated channel, the drilling fluid flowing through the one or more channels other than the designated channel is at a velocity of sufficient magnitude to generate pressure pulses in the drilling fluid by selectively moving the one or more slots into and out of registration with the one or more outlets. When the plug assembly defines a partial barrier to the flow of drilling fluid through the only channel of the stator, the drilling fluid that can still flow through the channel is at the velocity of sufficient magnitude. When the plug assembly defines a partial barrier to the flow of drilling fluid through a designated channel and the stator has multiple channels, the drilling fluid that can still flow through the designated channel together with the drilling fluid flowing through the one or more channels other than the designated channel is at the required velocity. The plug assembly optionally includes a disk having slots that register with less than all of the channels. In one example the plug assembly includes an elongated body that is disposed axially the designated channel. An opening is optionally provided that extends axially through the body. In an alternative, the opening defines a passage through which drilling fluid flows. The opening optionally defines a bore that selectively receives a fastener. In an embodiment, the fastener engages a receptacle formed in the channel and the plug assembly further includes an annular stop sleeve circumscribing the fastener and coupled to the body, and a C-ring coupled to the fastener between the stop sleeve and receptacle, so that when the fastener is uncoupled and pulled away from the receptacle, the body is removable from the channel by interfering contact of the C-ring with the stop sleeve. A cross sectional area of the body can vary with respect to a length of the body. In one embodiment, the plug assembly is laterally expandable into sealing contact with the channel. In an example embodiment, the plug assembly includes spaced apart leaf members, a wedge that is selectively drawn into a space between the leaf members, and a fastener coupled with the wedge and the leaf members. Optionally included in the system is a sensor in communication with the drilling fluid that monitors pressure pulses in the drilling fluid, and a controller in communication with the sensor. 
     An alternate example of a system for use in wellbore operations is described and that includes a stator selectively disposed in a path of fluid flowing in a drill string with a body having an outer surface with axially extending channels that are spaced apart from one another, a rotor having slots that selectively register and unregister with the channels, and a plug assembly for regulating a flow of the fluid to a velocity having a magnitude sufficient so that pressure pulses generated in the fluid from interaction between the fluid and the slots are at a magnitude so that the pressure pulses are detectable. The system optionally further includes a sensor in communication with the fluid downstream of the stator and rotor, and that selectively detects the pressure pulses. In one example, a flowrate of the fluid is at a magnitude so that a pressure pulse is not detectable that is generated by fluid flowing past the stator and rotor at a velocity without the plug assembly. 
     An example method of wellbore operations is also disclosed, and that includes flowing fluid within a wellbore, generating a pressure pulse in the flowing fluid that is at a threshold level of detection by controlling a velocity of the fluid in which the pressure pulse is being generated, and detecting the pressure pulse. Embodiments exist where the step of generating a pressure pulse includes introducing a localized pressure increase in the fluid by blocking a flow of the fluid for a discrete time period. Optionally included with the method is encoding data into the fluid by generating a plurality of pressure pulses in the flowing fluid. Controlling a velocity of the fluid optionally includes reducing a cross sectional area of the flowing fluid. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which: 
         FIG.  1    is a partial side sectional view of an example of a wellbore being formed with a drilling system having a mud pulser. 
         FIG.  2    is a side partial sectional view of an example of the mud pulser of  FIG.  1   . 
         FIGS.  3 A- 3 C and  4    are perspective views of embodiments of stators for use with the mud pulser of  FIG.  2   . 
         FIG.  3 D  is a side sectional view of an example of a plug for use with stators of  FIGS.  3 A- 3 C . 
         FIGS.  3 E and  3 F  are perspective views of alternate examples of plugs for use with stators of  FIGS.  3 A- 3 C . 
         FIG.  5    is a perspective view of an example of a pulser assembly with a flow control system and for use with the mud pulser of  FIG.  1   . 
         FIG.  6    is a side sectional view of the pulser assembly of  FIG.  5   . 
         FIG.  6 A  is a perspective view of an example of a disk assembly for use with the pulser assembly of  FIGS.  5  and  6   . 
         FIGS.  7 A and  7 C  are perspective views of an example of an alternate embodiment of a pulser assembly with a plug assembly and for use with the mud pulser of  FIG.  1   . 
         FIG.  7 B  is a side sectional view of a portion of the pulser assembly and plug assembly of  FIG.  7 A . 
         FIGS.  8 A and  8 B  are perspective and exploded views of the plug assembly of  FIG.  7 A . 
         FIG.  9    is a perspective view of an alternate example of the stator of  FIG.  2   . 
         FIG.  10 A  is a side sectional view of an example of a plug assembly coupled with the stator of  FIG.  9   . 
         FIG.  10 B  is a perspective view of the plug assembly of  FIG.  10 A . 
     
    
    
     While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF INVENTION 
     The method and system of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The method and system of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout. In an embodiment, usage of the term “about” includes +/−5% of the cited magnitude. In an embodiment, usage of the term “substantially” includes +/−5% of the cited magnitude. In an embodiment, usage of the term “generally” includes +/−10% of the cited magnitude. 
     It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. 
     Shown in a partial side sectional view in  FIG.  1    is an example of a drilling system  10  forming a wellbore  12  in a formation  14 . A drill string assembly  16  is included with drilling system  10 , and which is rotated by a drive system  18  depicted mounted on a surface rig  20  which is outside of wellbore  12 . For the purposes of discussion, an axis A DS  of the drill string  16  is represented that extends along a length of drill string  16 . A derrick  22  is included with surface rig  20  and which mounts over an opening to wellbore  12 . A wellhead assembly  24  mounts over wellbore  12  and provides pressure control of fluids within wellbore  12 . Illustrated on an upper surface of wellhead assembly  24  is a blowout preventer (“BOP”)  26 . Drill string  16  is made up of a length of drilling collars or joints threaded together to form an elongated pipe string  28 . In this example, an upper end of pipe string  28  is disposed in a bore that axially intersects BOP  26 . A drill bit  30  is on a lower end of pipe string  28 , and when forced into rotation against the formation  14  excavates rock and other materials making up the formation to form the wellbore  12 . 
     Drilling fluid, which for the purposes of illustration herein is also referred to as drilling mud DM, is introduced into the pipe string  28 . In the example of  FIG.  1   , drilling mud DM exits from nozzles (not shown) on a lower surface of drill bit  30 , and recirculates back to surface within an annulus  32  between the pipe string  16  and sidewalls of the wellbore  12 . Optional functions provided by the drilling mud DM include pressure control in the formation  14 , cooling of the drill bit  30 , and removing cuttings (not shown) that result from excavating within formation  14 . Integrated within the pipe string  28  is a measurement while drilling (“MWD”) module  34 , which in a non-limiting example of operation and as described in more detail below generates mud pulses MP in the drilling mud DM that travel uphole with the drilling mud DM flowing upward in annulus  32  to surface. As described in more detail below, in an example the mud pulses MP are generated by fluctuating pressure at a location or locations in the wellbore  12  and the mud pulses MP that propagate in the drilling mud DM are subsequently sensed at a different location or locations. In an embodiment, the mud pulses MP are at or above a designated magnitude detectable by a sensor  36 . Examples of placement of the sensor  36  include locations that are in communication with the drilling mud DM; such as but not limited to the wellhead assembly  24 , blowout preventer  26 , and the string  16  (including portions inside and outside the wellbore  12  and above the blowout preventer  26 ). 
     In an embodiment, the drilling system  10  includes a controller  38 , which is schematically illustrated outside the wellbore  12 ; and is in communication with sensor  36  via communication means  40 . Optionally, controller  38  is in communication with other devices of drilling assembly  10  and also with that remote to the wellbore  12 . In an example, controller  38  includes an information handling system (IHS); which optionally controls generation of pulses as well as controlling the subsequent recording of the pulses or signal(s) resulting from the pulses. In an embodiment, recorded data is stored in the IHS, and optionally in the IHS data is transformed into a readable format. Example locations of the IHS include at the surface, in the wellbore, or partially above and below the surface. Further optionally, the IHS includes a processor, memory accessible by the processor, nonvolatile storage area accessible by the processor, and logics for performing some or all of the steps above described. In an example of transmission to the surface data is encoded pursuant to a selected communication protocol. Examples of communication protocols for communicating data through a pulse series include frequency-shift keying (“FSK”), phase-shift keying (“PSK”), amplitude-shift keying (“ASK”), combinations of the above, and other known or later developed communication protocols. 
     Shown in a side partial sectional view in  FIG.  2    is an example portion of the drill string  28  having the MWD module  34 . In this embodiment a pulser assembly  42  is disposed within the MWD module  34  and which includes a stator  44  and rotor  46 . Arrows A represent a direction of a flow of the drilling mud DM within the drill string  28  and in the annulus  32 , and in the illustrated example the drilling mud DM reaches stator  44  before reaching rotor  46 . For the purposes of discussion herein, a direction opposite that of arrows A is referred to as upstream, and in the direction of arrows A is referred to as downstream. Rotor  46  is selectively rotated about axis A MP  and as reflected by arrow A R . In the illustrated example, rotation of rotor  46  is provided by motor  48  which is schematically illustrated upstream of stator  44  and within string  28 . In the example of  FIG.  2   , an elongated shaft  50  is shown having opposing ends respectively connected to the motor  48  and rotor  46  and provides a mechanical coupling between motor  48  and rotor  46 ; as shown a portion of shaft  50  is disposed within stator  44 . In alternatives, motor  48  directly couples to rotor  46  either mechanically or electro-magnetically. Yet further alternatives exist in which rotor  46  is actuated by means such as mechanical, hydraulic, pneumatic, electrical, electro-magnetic, and combinations thereof. 
     Stator  44  of  FIG.  2    includes a generally frusto-conical body  52 , and which in an alternative is generally hollow within. Vanes  54  in this example are formed along an outer surface of body  52  with lengths L V  that are aligned generally axially along the body  52 . Widths W V  of vanes  52  extend circumferentially around body  52 . The vanes  54  also have thicknesses, shown oriented radially to the body  52 . The widths W V  increase with distance proximate to rotor  46 . The vanes  54  are shown spaced apart angularly with respect to one another about a circumference of the body  52 , and where channels  56  are defined between adjacent vanes  54 . The channels  56  in this example also extend generally axially along the length of body  52 , and whose widths are complementary to that of the vanes  54 . A flow path FP is shown that schematically illustrates an example course or route of drilling mud DM flowing within the pipe string  28  and within the channels  56  intersecting the body  52 , and in alternatives the flow path FP continues past the downhole or lower ends of the channels  56  distal from motor  48 . In this example, the flow path FP is in an open configuration. In an alternate example stator  44  includes a single vane  54  and a single channel  56  intersecting the vane  54 ; in this alternate example a portion of a length of flow path FP is contained within the single channel  56 . Embodiments exist with the one or more channels  56  of the stator  44  extending axially along and/or radially across the body  52 . That in an example allows the drilling fluid to flow from an uphole to a downhole direction as indicated by arrow A. In a non-limiting example, the one or more channels  56  are in a twisted or helical configuration and extending radially as they extend axially. In a further non-limiting example, one or more channels  56  of the stator  44  extend axially, while other channels  56  extend both axially and radially. Inlets  58  are defined within the channels  56  proximate an end of stator  44  distal from rotor  46 . Outlets  60  are defined within channel  56  at an end of stator  44  proximate to rotor  46 . As the vanes  54  have increasing widths W V  with distance proximate to rotor  46 , the outlets  60  have widths that are less than those of the inlets  58 . Alternate embodiments exist where the vanes  54 , and thus channels  56  as well, have widths that are substantially constant along a length of the body  52 , are undulating, or larger distal from rotor  46 . 
     Further included in the example of  FIG.  2    is an annular sleeve  62  shown circumscribing pulser assembly  42  and in close contact with an inner surface of the pipe string  28 . In an example, a flow barrier is between sleeve  62  and string  28  so that all drilling mud DM flowing downhole within the string  28  flows through pulser assembly  42 . In the illustrated example, a portion of the body  52  is frusto-conically shaped with a diameter D that narrows with distance from motor  48 . Further illustrated in this example is that a thickness of the sidewall of sleeve  62  increases, which decreases the inner diameter of sleeve  62  to accommodate dimensional changes of body  52 ; and which maintains a close contact between the outer periphery of stator  44  with an inner surface of sleeve  62  along substantially an entire length of the stator  44 . In an embodiment, sleeve  62  spans across the space between adjacent vanes  54  to define a flow barrier along the outer radial surface of the channels  56 . Alternatively, sleeve  62  is in sealing contact with the outer radial surfaces of vanes  54  and all drilling mud DM flowing into each inlet  58  remains within the respective channel  56  until reaching the corresponding outlet  60 . 
     Still referring to  FIG.  2   , rotor  46  of this example includes a rotor body  64  with a frusto-conical cross section, and an outer radial surface profiled oblique to axis A MP  that depends towards stator  44  with distance from axis A MP . Further included with rotor  46  is a planar base element  66  mounted on a side of rotor body  64  facing stator  44 ; as shown base element  66  is substantially perpendicular with axis A MP . In an example, an outer diameter of the base element  66  is spaced radially inward from the outer circumference of the vanes  54 . Slots  68  are shown formed axially through the outer periphery of the base element  66  at selected angular positions around the axis A MP  of the pulser assembly  42 . Rotating rotor  46  revolves or orbits slots  68  about axis A MP  and into and out of registration with the outlets  60 . In a non-limiting example of operation, rotating rotor  46  at a designated angular velocity moves slots  68  and outlets  60  in and out of registration with one another; and during the time when the outlets  60  are not in registration with slots  68 , the drilling mud DM flowing through one or more of channels  56  is blocked by a portion or portions of the base element  66  disposed angularly between adjacent slots  68 . In an embodiment, the blocking contact between the drilling mud DM and the solid portion of the base element  66  introduces a discreet and localized increase of pressure within the drilling mud DM that in turn generates one or more mud pulse MP in the drilling mud DM. Further in this example, strategically rotating rotor  46  generates mud pulses MP in the drilling mud DM that are of a designated length and/or sequence, where the sequence of mud pulses MP define signals that represent data. In another non-limiting example mud pulses MP are generated in the drilling mud DM by oscillating rotor  46 ; such as by rotating rotor  46  an angular distance about axis A MP  in an angular direction (e.g. clockwise), then rotating rotor  46  another angular distance about axis A MP  in a reverse angular direction (e.g. counter-clockwise), alternatives include the angular distances of the clockwise and counter-clockwise being the same or different and at differing angular velocities. Optionally mud pulses MP that are of a designated length and/or sequence is achieved by strategically oscillating rotor  46 . Further non-limiting examples of the generation of mud pulses MP in the drilling mud DM that are of a designated length and/or sequence include strategically rotating rotor  46  in two directions, and alternatively at different speeds in one direction. In an embodiment of operation, data signals are encoded in the drilling mud DM by the mud pulses MP. In a further alternative to this example, the data signals are then monitored by sensor  36  ( FIG.  1   ) to obtain information about the operation of the drilling assembly  10 . Example data includes azimuth and/or orientation of the string  16 , which in one example provides a basis and guidance for adjusting an orientation of the wellbore  12  during drilling. Example configurations of the body  64  are not limited to the frusto-conical shape depicted, but include cylindrical, ovoid, an inverted frusto-conical shape, and any configuration for generating pulses across the pulser assembly  42 . 
     Referring now to  FIGS.  3 A through  3 D , alternate embodiments of stators  44 A,  44 B,  44 C are illustrated having elongate lengths extending respectively along axes A SA , A SB , A SC . Stator  44 A illustrated in perspective view in  FIG.  3 A  has a generally cylindrically-shaped body  52 A and axially extending channels  56 A in the body  52 A. Each channel  56 A of  FIG.  3 A  has an outer radius spaced radially inward from an outer surface of body  52 A. Further illustrated is an example of a plug assembly  70 A that is selectively inserted into one of the channels  56 A for blocking flow through that channel  56 A. In a non-limiting example of operation, an area of one of the channels  56 A is blocked or reduced without adjusting a total flow rate of the drilling mud DM flowing through stator  44 A that increases velocity of drilling mud DM flowing through the remaining channels  56 A, and which puts the flow path FP ( FIG.  2   ) in a restricted configuration. The increase in velocity correspondingly increases magnitudes of pressure variations in the mud pulses MP formed when the higher velocity drilling mud DM impinges on the upstream surface of a rotor  46  ( FIG.  2   ) after exiting channel  56 A. The example plug assembly  70 A of  FIG.  3 A  includes a plug body  72 A having a wedge-like cross-section formed complementary to a cross-section of channel  56 A. The body  72 A has a length L B ; examples exist where length L B  is the same, greater than, or less than respective lengths of the channels  56 A. It is believed it is within the capabilities of those skilled in the art to determine a velocity of a fluid, i.e. drilling mud, being directed through a mud pulser that is sufficient (a sufficient velocity) for creating pressure pulses in the flow of drilling mud DM that are of adequate magnitude to be detectable downstream of the channel(s)  56 A. Moreover, it is further understood it is within the capabilities of those skilled in the art to determine which of the one or more of the channels  56 A to be blocked for creating the sufficient velocity. 
     Alternate examples of the stator  44 B,  44 C are illustrated in perspective view respectively in  FIGS.  3 B and  3 C . In the example of  FIG.  3 B , stator  44 B is shown having channels  56 B with lateral sides that are spaced apart angularly from one another about axis A SB , lateral sides follow a generally curved path along their respective radial and axial directions. In the example of  FIG.  3 B  the channels  56 B extend radially outward to the outer surface of body  52 B, and in the example shown widths of the channels  56 B decrease in a direction away from the inlets  58 B and towards the outlets  60 B. An example of a plug assembly  70 B is illustrated with a shape and contour that is substantially complementary to that of the channels  56 B, and when selectively inserted into a one of the channels  56 B blocks most of or all flow through that particular channel  56 B. In the example of  FIG.  3 C , the body  72 C of plug assembly  70 C has a height H B  along a direction radial to axis A SC  and that increases with respect to the length L B  of body  72 C. The increasing height of the body  72 C largely matches an increase in height of the channel  56 B along a length of the stator  44 C. As described above, installing plug assemblies  70 A,  70 B,  70 C into one or more of respective channels  56 A,  56 B,  56 C blocks a flow of drilling mud DM through the channels  56 A,  56 B,  56 C having plug assemblies  70 A,  70 B,  70 C and diverts the drilling mud DM into channels  56 A,  56 B,  56 C without plug assemblies  70 A,  70 B,  70 C (“unplugged channels  56 A,  56 B,  56 C”). In examples in which a flowrate of drilling mud DM is substantially maintained and a plug assembly  70 A,  70 B,  70 C is inserted into one or more of the channels  56 A,  56 B,  56 C increases a flowrate and velocity of the drilling mud DM flowing through the unplugged channels  56 A,  56 B,  56 C and also the stators  44 A,  44 B,  44 C. In a non-limiting example of operation, plug assemblies  70 A,  70 B,  70 C are strategically inserted into one or more of respective channels  56 A,  56 B,  56 C to adjust velocity of the drilling mud DM through the stators  44 A,  44 B,  44 C so that pressure pulses generated in the drilling mud DM are at a threshold level of detection so that the pressure pulses are detectable and recordable by sensor  36  ( FIG.  1   ). In an alternative, pressure pulses in the drilling mud DM that are at a threshold level of detection are at a magnitude that when detected and recorded by sensor  36 , the recorded signals are discernable so that substantially all of the data encoded into the fluid by the mud pulser  42 A,  42 B,  42 C is obtained by decoding the detected pressure pulses. With further reference to  FIG.  3 A , in a non-limiting example plug assembly  70 A is employed one or multiple times to selectively block, either totally or partially, one or more channels  56 A of the stator  44 A. A single plug assembly  70 A is optionally used to partially or totally block a single channel  56 A, leaving the three remaining channels shown unblocked. In another alternative two plug assemblies  70 A are employed, blocking two of the four channels  56 A. In this example, an option exists with both plug assemblies  70 A either partially or totally blocking the two channels  56 A, or the first plug assembly  70 A partially blocking one channel  56 A with the second plug assembly  70 A totally blocking one of the remaining channels  56 A. With further reference to  FIGS.  3 B and  3 C , plug assemblies  70 B and  70 C are optionally employed in a manner similar to that of plug assembly  70 A as described above. Examples exist with the axial length of a plug assembly  70 A,  70 B or  70 C ranges from a portion, a substantial portion or a whole of the axial length of a channel  56 A,  56 B or  56 C in the respective stator body  52 A,  52 B or  52 C; or any length(s) between. In an example, two or more plug assemblies are used within a stator body having axial lengths that are the same or different. Alternatively the stator has one, two, three, or four or more channels. In an embodiment of an open configuration the rotor has the same number of open slots as the stator channels. In an alternative embodiment when a channel is plugged the number of rotor slots is equal to the number of remaining open channels. In another example, the rotor has one, two, three, or four or more slots. In a non-limiting example of operation, rotating or rotation of the rotor includes oscillating or oscillation of the rotor. Examples of a restricted configuration includes the cases wherein at least one channel of the stator body is either partially or totally closed, by either the insertion of a plug assembly into the channel, or by the plug assembly defining a barrier outside the channel to the drilling fluid. 
     An alternate example of a plug assembly  70 D is depicted in side sectional view in  FIG.  3 D . In this example body  72 D includes forward and aft sections S F , S A  that are separate and spaced apart from one another. A bore  74 D axially intersects both the forward and aft sections S F , S A  and which receives a fastener  76 D that couples together the forward and aft sections S F , S A . An elastomeric seal  78 D is sandwiched between the forward and aft sections S F , S A  and intersected by the fastener  76 D. In this example, tightening fastener  76 D draws together the two sections of body  72 D to axially compress the seal  78 D and also cause a mid-portion of the seal  78 D to bulge radially outward; which when installed in a channel (not shown) creates a sealing interface along a portion of the channel to block flow through that channel. 
     Shown in perspective view in  FIGS.  3 E and  3 F  are alternate examples of plug assemblies  70 E,  70 F with plug bodies  72 E,  72 F that in examples of use block a portion of a cross-section within a channel  56 ,  56 A-D,  56 F when installed therein. In the example of  FIG.  3 E  a passage  80 E extends axially through the length of the body  72 E. Fluid, such as drilling mud, is selectively directed to and flows through passage  80 E, and in an example inserting body  72 E into a channel (not shown) reduces flow area without blocking all flow through passage  80 E. Similarly, illustrated in  FIG.  3 F  is an example of a plug assembly  70 F that is made up of a body  72 F that occupies a portion of a cross-sectional area of channel  56 F formed axially through a stator  44 F. 
     An alternate example of selectively limiting flow through a stator is illustrated in  FIG.  4   , where plug assembly  70 G includes a plug body  72 G that is a generally planar disk-like member and includes passages  80 G that project axially through the plug body  72 G. The plug assembly  70 G in this example is constructed for assembly with an example of stator  44 G shown with channels  56 G that project axially through the stator  44 G. In this example the quantity of passages  80 G is less than that of channels  56 G. In the example of  FIG.  4   , a portion of a flow area through the stator  44 G is selectively blocked by coaxially coupling the plug assembly  70 G to an end of stator  44 G so that all or a portion of the passages  80 G are aligned with channels  56 G. Similar to the example described above for encoding pressure pulses with data signals, selective rotation or oscillation of plug body  72 G moves passages  80 G out of registration with channels  56 G when drilling mud DM or other fluid is flowing through the passages  80 G to generate a localized increase in pressure in the fluid against plug body  72 G, and rotating plug body  72 G so that the channel  56 G having the fluid with the localized increase in pressure is in registration with a passage  80 G, and the fluid with the localized increase in pressure flows past the body  72 G. 
     Referring now to  FIG.  5   , shown in a perspective view is an example of a pulser assembly  42 H. In this example a disk assembly  82 H is included with the pulser assembly  42 H and which is coaxially disposed between stator  44 H and rotor  46 H. Disk assembly  82 H of  FIG.  5    includes a plate  84 H and a disk  86 H coaxially coupled to a side of the plate  84 H that faces stator  44 H. Plate  84 H and disk  86 H are each substantially planar members with generally circular outer perimeters. Plate  84 H as shown is axially thicker than disk  86 H. In the embodiment illustrated, slots  88 H are provided along an outer periphery of the disk assembly  82 H that extend axially through the disk assembly  82 H at selected angular locations about a circumference of disk assembly  82 H. In this example, the number of slots  88 H is less than the number of channels  56 H within stator  44 H. In the illustrated example, the disk assembly  82 H defines a barrier to a flow of fluid in at least one of the channels  56 H to downstream of the disk assembly  82 H, and reduces a cross-sectional area for fluid flow across the pulser assembly  42 H that would otherwise be available if all flow through channels  56 H were not impeded by disk assembly  82 H, and increases a flow velocity of fluid within the unblocked channels  56 H. Similar to the pulsing operations described above, one or more mud pulses MP ( FIG.  2   ) are generated in drilling mud DM flowing across pulser assembly  42 H by selectively rotating or oscillating rotor  46 H to move the slots  68 H in and out of registration with channels  56 H. 
     Illustrated in a side sectional view in  FIG.  6    is an example of pulser assembly  42 H with sleeve  62 H shown circumscribing stator  44 H and extending axially past rotor  46 H. In this example, a disk-like cap  90 H is provided on an axial end of rotor  46 H and coupled to the body  64 H of rotor  46 H Further illustrated in  FIG.  6    is an annular clamp ring  94 H that is generally coaxial with disk assembly  82 H and that provides a way of coupling disk assembly  82 H to stator  44 H. An outer circumference of the clamp ring  94 H is profiled radially inward to define a shoulder and against which an inner circumference of disk  86 H is shown in interfering contact. A portion of clamp ring  94 H upstream of shoulder projects axially past the disk  86 H and couples inside of an end of a bore  96 H that is within stator  44 H; in the example shown the coupling is via threads, alternatives exist having other coupling means. As shown in perspective view in  FIGS.  6  and  6 A , tabs  98 H project axially from a surface of disk  86 H adjacent stator  44 H and insert into recesses  100 H formed on a surface of stator  44 H facing rotor  46 H. In this example, disk  86 H is rotationally coupled to stator  44 H by interfering contact between tabs  98 H and recesses  100 H. Indentations  102 H are shown provided along an inner surface of the clamp ring  94 H, and which provide flat surfaces for tools to engage clamp ring  94  for decoupling from stator  44 H. 
     Shown in perspective view in  FIG.  7 A  is an alternate example of a plug assembly  70 I for use in blocking flow through a channel  56 I in stator  44 I. Shown in more detail in a side sectional view in  FIG.  7 B  and in perspective view in  FIG.  8 A , plug assembly  70 I includes a wedge  104 I which is shown having a length L WE , and width W WE  that changes with respect to length L WE . In this example wedge  104 I is a substantially solid member. Also included in plug assembly  70 I is a clip member  106 I which is made up of a base  108 I configured complementary to channel  56 I and planar leaf members  110 I on opposing lateral sides of base  108 I shown depending axially away from base  108 I and adjacent sidewalls of channel  56 I. In one example of installation provided in  FIGS.  7 B and  8 A  wedge  104 I is being drawn towards clip member  106 I and between leaf members  110 I. In this example, leaf members  110 I include an elastic material that retains its structural integrity without yielding as the wedge  104 I is drawn in a space between leaf members  110 I. A front plate  112 I is included with the illustrated embodiment, and which is on a side of base  108 I opposite from leaf members  110 I. A gasket  114 I, optionally formed from an elastomeric material, is sandwiched between the front plate  112 I and base  108 I. In this example, each of the base  108 I, front plate  112 I, and gasket  114 I have an outer periphery with a generally frusto-conical shape and substantially complementary to channel  56 I. In an example, a sealing interface is formed between the plug assembly  70 I and inner surfaces of channel  56 I when plug assembly  70 I is assembled. Further included in the example of the plug assembly  70 I is an elongated fastener  116 I shown extending generally along axis A F . Fastener  116 I projects into a bore  118 I that intersects each of wedge  104 I, clip member  106 I, and gasket  114 I. 
     Referring back to  FIG.  7 B , a pin  120 I is disposed within a bore  122 I that intersects the front plate  112 I and base  108 I of clip member  106 I. Pin  120 I provides a way of coupling together front plate  112 I with clip member  106 I to reduce unnecessary movement between these members. In one example of operation of installing the plug assembly  70 I within channel  56 I of stator  44 I, continued rotation of fastener  116 I draws wedge  104 I towards the base  108 I, and with the portion of wedge  104 I having the larger width W WE  between leaf members  110 I, urges the opposing disposed leaf members  110 I away from each other and against sidewalls of channel  56 I. As illustrated in an example of  FIG.  7 C , an end of wedge  104 I is proximate base  108 I and gasket  114 I is expanded radially outward and into sealing contact with sidewalls of channel  56 I. In an example, gasket  114 I when expanded is in sealing contact with an inner surface of sleeve (not shown) and blocks flow of fluid through channel  56 I. The plug assembly  70 I is shown in an exploded view in  FIG.  8 B  depicting gasket  114 I as a generally annular member that circumscribes the lateral surfaces of a platform  124 I shown projecting axially from on a surface of the front plate  112 I facing base  108 I, and having a lateral surface set radially inward from that of front plate  112 I and base  108 I. 
     Referring now to  FIG.  9   , shown in a perspective view in is another alternate example of a stator  44 J where a receptacle  126 J is formed within a raised projection  128 J set within channel  56 J. Receptacle  126 J includes threads and faces towards a downstream end of stator  44 J. Channel  56 J is shown in side sectional view in  FIG.  10 A , and with a portion of an alternate embodiment of a plug assembly  70 J inserted in channel  56 J. Plug assembly  70 J in this example includes an elongated body  72 J with an axial bore  130 J having a diameter that changes at various locations along its length. Bore  130 J is shown in registration with the receptacle  126 J, also shown is an elongated fastener  116 J that projects through bore  130 J and having an end that couples within receptacle  126 J; coupling in the example shown is with threads, options include other coupling means. As shown in  FIG.  10 A  and in perspective view in  FIG.  10 B , the plug assembly  70 J also includes an annular stop sleeve  132 J that circumscribes a portion of fastener  116 J distal from receptacle  126 J. A slot  134 J is shown formed radially through the sidewall of stop sleeve  132 J and along a portion of its axial length. The stop sleeve  132 J in the example of  FIG.  10 A  is inserted within bore  130 J so that slot  134 J is on a side of sleeve  132 J facing away from receptacle  126 J. A hole  136 J shown extending radially through a sidewall of body  72 J and adjacent slot  134 J, a pin  138 J inserted into hole  136 J extends into slot  134 J. Fastener  116 J is axially movable within the stop sleeve  132 J. Further illustrated in the embodiment of  FIG.  10 A  is a C-ring  140 J that is set into a groove  142 J that circumscribes fastener  116 J at a location that is between stop sleeve  132 J and receptacle  126 J. The outer surface of bore  130 J projects radially inward at a location proximate the C-ring  140 J to define a shoulder  144 J that faces away from receptacle  126 J. An outer radius of C-ring  140 J exceeds an inner radius of stop sleeve  132 J, so that a force applied to fastener  116 J to slide it and C-ring  140 J against a lateral end of stop sleeve  132 J also transfers that force, via slot  134 J and pin  138 J, to body  72 J. Accordingly, the addition of the stop sleeve  132 J and C-ring  140 J provide a means for removing the plug assembly  70 J from within receptacle  56 J. 
     The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. For example, alternatives exist in which any of the above described stators include a single channel that selectively receives a plug assembly that when inserted into the single channel blocks less than all of the cross-sectional area of the single channel to define a reduced cross-sectional area in the single channel, and fluid selectively flows through the reduced cross-sectional area in the single channel. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.