Abstract:
A mud pulser controlled by a field applied to an electroactive fluid. The electroactive fluid is employed to act as a rapid-response brake to slow or interrupt the rotation of a mud motor or mud siren, thus creating pressure pulses in a circulating fluid. In certain embodiments, the electroactive fluid is used as a direct brake acting on a shaft rotating in a volume of electroactive fluid where the shaft is coupled to the mud motor or siren. The application of a field to the electroactive fluid impedes the rotation of the shaft, thus slowing the mud motor and creating a pressure pulse in the circulating fluid. In another embodiment, a Moineau pump circulating an electroactive fluid is coupled to the mud motor. The application of a field to the electroactive fluid slows the rotation of the pump, thus slowing the mud motor and creating a pressure pulse in the circulating fluid.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Not applicable. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not applicable.  
       BACKGROUND OF THE INVENTION  
       [0003]     The embodiments of the present invention relate generally to measurement while drilling data transmission technologies. More specifically, the embodiments relate to methods and apparatus for generating pressure pulse signals in a circulating drilling fluid. Still more specifically, the embodiments relate to methods and apparatus for using an electroactive fluid to create pressure pulse signals.  
         [0004]     Modern petroleum drilling and production operations demand a great quantity of information relating to parameters and conditions downhole. Such information typically includes characteristics of the earthen formations traversed by the wellbore, data relating to the size and configuration of the wellbore itself, and information as to tool orientation, location, and operating parameters. Techniques used to measure conditions in the wellbore, including the movement and location of the drilling assembly, during drilling operations are commonly known as measurement-while-drilling (MWD) or logging-while-drilling (LWD).  
         [0005]     These techniques often involve the use of a telemetry system that employs one or more sensors or transducers at the lower end of the drill string that collect data from the drill string or wellbore. These sensors relay the gathered information to an encoder that coverts the data to digital signals, which can be transmitted to receiving equipment at the surface. A commonly employed technique to relay signals from downhole to the surface is transmission of pressure pulses through the column of drilling mud that fills the borehole. These pulses are then received and decoded by a pressure transducer and computer at the surface.  
         [0006]     In typical prior art mud pressure pulse systems, the pressure pulses in the drilling mud are created by means of a valve and control mechanism, generally termed a pulser or mud pulser. Mud pressure pulses are generated by opening and closing a valve, normally near the bottom of the drill string, so as to momentarily restrict or increase the mud flow. Early MWD tools used a “negative” pressure pulse that was created in the fluid by temporarily opening a valve in the drill collar allowing direct communication between the high pressure fluid inside the drill string and the fluid at lower pressure returning to the surface via the wellbore annulus. Negative pressure pulse techniques proved less than ideal because a failure in the valve could result in an uncontrolled release of drill string fluid into the annulus.  
         [0007]     Alternatively, and often more preferably, a “positive” pressure pulse was created by temporarily restricting the flow of drilling fluid by partially blocking the fluid path in the drill string. Devices used to create these positive pressure pulses include poppets, sirens, and rotary pulsers.  
         [0008]     Poppet-type pulsers operate like unidirectional check valves by permitting the flow of fluid in only one direction. The poppet employs an axially moveable plug to open and close a fluid pathway that, when closed, causes a pressure rise in the drilling fluid.  
         [0009]     Sirens typically feature a stationary stator and a coaxially mounted, motor driven rotor. The stator and the rotor have a plurality of radially extending lobes such that when the lobes of the stator and the rotor are aligned, a fluid port is formed for the passage of fluid. As the rotor rotates, the flow of fluid is interrupted and pressure pulses are generated.  
         [0010]     A rotary pulser is similar to a siren but rather than being driven to produce a relatively continuous series of signals like a siren, the actuation of a rotary pulser is controlled to produce a desired sequence of pulses in the drilling fluid. Thus, instead of the constant rotation of a siren, a rotary pulser is intermittently rotated a small amount to open and close fluid pathways.  
         [0011]     Because all of these pulser designs operate by restricting the flow of drilling fluid through relatively small passageways, erosion and wear caused by the abrasive-laden drilling fluid is a serious concern. Drilling fluid normally contains some concentration of solid particles, which, at the pressure and flow rates typically encountered, tend erode the pulser components. Such erosion can lead to relatively short useful lives for many pulser components. Thus, there remains a need in the art for a pulser design exhibiting improved wear characteristics.  
         [0012]     Disclosed in U.S. Pat. No. 2,661,596, the entire disclosure of which is hereby incorporated by reference, are electroactive fluids whose viscosity, or resistance to flow, is modifiable by subjecting the fluid to a magnetic or electric field. Electroactive fluids that are responsive to an electrical field are known as electrorheological (ER) fluids, while those responsive to magnetic fields are known as magnetorheological (MR) fluids. Of these two, MR fluids have proved easier to work with because they are less susceptible to performance-degrading contamination, and are easily controllable using magnetic fields easily created with either permanent magnets or electromagnets.  
         [0013]     MR fluids can be formed by combining a low viscosity fluid, such as a type of oil, with magnetizable particles to form a viscous slurry. U.S. Pat. No. 2,661,596 used particles of iron on the order of 0.1 to 5 microns, with the particles comprising 20% or more by volume of the MR fluid. More recent work in MR fluids can be found, for instance, in U.S. Pat. No. 6,280,658, the entire disclosure of which is hereby incorporated herein by reference.  
         [0014]     When a magnetic field passes through an MR fluid, the magnetizable particles align with the field, limiting movement of the fluid due to the arrangement of the magnetizable particles. As the field increases, the MR fluid becomes increasingly solid, but when the field is removed, the fluid reassumes its liquid state again. MR fluids have been used in such areas as dampers, locks, brakes, and abrasive finishing and polishing. MR fluids can be commercially obtained from the Lord Corporation of Cary, N.C.  
         [0015]     The embodiments of the present invention are directed to methods and apparatus for generating a pressure pulse in drilling fluid using a pulser, controlled by an electroactive fluid, that seeks to overcome the limitations of the prior art.  
       SUMMARY OF THE PREFERRED EMBODIMENTS  
       [0016]     The preferred embodiments provide a mud pulser controlled by a field applied to an electroactive fluid. The electroactive fluid is employed to act as a rapid-response brake to interrupt the rotation of the rotor of a mud motor or mud siren, thus creating pressure pulses in the circulating fluid. In certain embodiments, the electroactive fluid is used as a direct brake, acting on a shaft rotating in a volume of electroactive fluid where the shaft is coupled to the rotor. The application of a field to the electroactive fluid impedes the rotation of the shaft, thus slowing the rotor and creating a pressure pulse in the circulating fluid. In another embodiment, a Moineau pump circulating electroactive fluid is coupled to the rotor. The application of a field to the electroactive fluid slows the rotation of the pump, thus slowing the rotor and creating a pressure pulse in the circulating fluid.  
         [0017]     In one embodiment, the pressure pulser comprises a first body rotated by flowing fluid and a second body rotatably coupled to the first body and at least partially disposed within an electroactive fluid. The pulser is actuated by applying a field to the electroactive fluid. The field causes the physical properties of the electroactive fluid to change, which affects the rotation of the second body.  
         [0018]     In certain embodiments, the first body is a mud motor. The second body may be a shaft rotating in the electroactive fluid or a pump rotor circulating the electroactive fluid through a flowline having an electroactive fluid valve. Alternate embodiments may also comprise a mud siren where the rotation of the siren rotor is controlled by an electroactive fluid.  
         [0019]     In an alternative embodiment, a method for generating a pressure pulse includes disposing a first body in a flowing fluid so as to rotate the first body, coupling the first body to a second body disposed in an electroactive fluid, and applying a field to the electroactive fluid. A magnetic field may be applied by applying a current to an electromagnetic coil or removing a shunt from a permanent magnet.  
         [0020]     Thus, the present invention comprises a combination of features and advantages that enable it to provide for a mud pulser actuated by the intermittent application of a field to an electroactive fluid. These and various other characteristics and advantages of the preferred embodiments will be readily apparent to those skilled in the art upon reading the following detailed description and by referring to the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     For a more detailed understanding of the preferred embodiments, reference is made to the accompanying Figures, wherein:  
         [0022]      FIG. 1  is a schematic view of one embodiment of an electroactive fluid controlled pulser;  
         [0023]      FIG. 2  is a schematic view of a second embodiment of an electroactive fluid controlled pulser;  
         [0024]      FIG. 3  is a schematic view of one embodiment of an electroactive fluid controlled mud siren; and  
         [0025]      FIGS. 4A-4C  are schematic views of alternative embodiments of permanent magnet circuits. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]     In the description that follows, like parts are marked throughout the specification and drawings with the same reference numerals, respectively. The drawing figures are not necessarily to scale. Certain features of the invention may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in the interest of clarity and conciseness. The present invention is susceptible to embodiments of different forms. There are shown in the drawings, and herein will be described in detail, specific embodiments of the present invention with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that illustrated and described herein. It is to be fully recognized that the different teachings of the embodiments discussed below may be employed separately or in any suitable combination to produce the desired results.  
         [0027]     In particular, various embodiments of the present invention provide a number of different methods and apparatus for using an electroactive fluid to generate a pressure pulse in fluid. The concepts of the invention are discussed in the context of a mud pulser, but the use of the concepts of the present invention is not limited to this particular application and may be applied in other, downhole rotating mechanisms. The concepts disclosed herein may find application in other downhole tool applications, as well as other hydraulically actuated components, both within oilfield technology and other technologies to which the concepts of the current invention may be applied.  
         [0028]     As used herein, an electroactive fluid is a fluid, gel, or other material having physical properties that change in response to a magnetic or electric field. Although the present invention is discussed relative to an MR fluid, an electrorheological (ER) or other electroactive fluid may be used without departing from the scope of this disclosure. It is understood that physical properties of an electroactive fluid can be changed by applying a magnetic field to an MR fluid or by applying an electrical field to an ER fluid.  
         [0029]     A Moineau pump is a positive displacement or progressive cavity pump that includes a helical rigid rotor which rotates inside an elastic helical stator. The geometry and dimensions of these components are designed so that a double string of sealed chambers (or cavities) are formed when the rotor turns relative to the stator. These volumes within these chambers effectively move from one end of the pump to the other as the rotor rotates. A Moineau pump can be used as a pump by rotating the rotor or can be used as a motor by forcing fluid through the chambers, with the rotating rotor acting as an output shaft. Moineau pumps are commonly known in drilling applications as mud motors.  
         [0030]     Referring now to  FIG. 1 , a pulser  10  is shown including a motor section  12  and a brake section  14 . In the preferred embodiments motor section  12  and brake section  14  are a component of a drill string or integrated into a drilling tool or sub. The motor section  12  includes a mud motor  16  rotated by flowing drilling fluid, represented by arrows  18 . Mud motor  16  is preferably a Moineau pump having a rubberized stator  20  and a metallic rotor  22  that rotates in response to pressurized fluid being applied to the pump. Brake section  14  includes a housing  24  containing a shaft  26  in a cavity  28  filled with an MR fluid  30 . The MR fluid  30  is isolated from the drilling fluid  18 , which flows through bypass ports  32  to motor section  12 . Shaft  26  of brake section  14  includes an electromagnet coil  34  wound around the shaft that, when energized, creates a magnetic field in the MR fluid  30 .  
         [0031]     The application of a magnetic field to the MR fluid  30  cause the characteristics of the fluid to change from a liquid to a near solid. The coil can be powered with batteries, a generator that extracts its power from the flow, such as a turbine, or a generator that produces its own power from stored chemical energy, such as a fuel cell. This phase-shift of MR fluid  30 , from viscous liquid to near-solid, increases the friction on the rotating shaft  26 , which reduces the rotational speed of the shaft  26  and the coupled mud motor  16 . The reduction in rotational speed of the mud motor  16  reduces the flow of drilling fluid  18  through the motor, causing a pressure increase in the drilling fluid that can be detected at the surface by conventional pressure pulse sensing and recording equipment.  
         [0032]     Referring now to  FIG. 2 , a pulser  36  is shown including an alternative braking section  38  coupled with motor section  12 . Braking section  38  includes a second Moineau pump  40  that is rotated by rotor  22 . Pump  40  circulates an MR fluid  42  through flowline  44  that includes an MR valve  46 . The MR fluid  42  is isolated from the drilling fluid  18 , which flows through bypass ports  48  to motor section  12 . MR valve  46  applies a magnetic field to the MR fluid  42  in flowline  44 , which changes the characteristics of the fluid from a liquid to a near solid. The change of the viscosity of fluid  42  causes pump  40  to slow or stop rotating, which in turn slows motor  16 , causing a pressure increase in the drilling fluid  18 .  
         [0033]     MR valve  46  operates by applying a magnetic field to a small area of flowline  44 . The MR fluid  42  within this portion of the flowline changes from a liquid to a near solid and effectively blocks flow through the flowline  44 . The magnetic field of MR valve  46  can be created by an electromagnet or a permanent magnet and many different MR valve designs are known in the art. A number of MR valve designs are disclosed in U.S. Patent Application No. ______ (2001-IP-004288), titled “Valve and Position Control using Magnetorheological Fluids,” which is hereby incorporated by reference for all purposes.  
         [0034]     Referring now to  FIG. 3 , one embodiment of a continuous wave telemetry system using a mud siren  50  controlled by an electroactive fluid is shown. Mud siren  50  includes a slotted rotor  52  and stator  54 , which restrict the mud flow in such a way as to generate a modulating positive pressure wave that travels to the surface. Rotor  52  is mounted on a shaft  60 , which rotates in a housing  58  containing an electroactive fluid  56 . Thus, the electroactive fluid  56  can be used as the method through which the rotation of the rotor  52  is modulated. Activating an electric field across housing  58  solidifies the fluid  56  and causes rotor  52  to slow, which changes the frequency and/or phase of the rotor and creates a corresponding change in the continuous pressure wave. In certain embodiments, rotor  52  self-rotates, powered by flowing mud, while in other embodiments, it is driven by an electric or hydraulic drive motor  59 . If rotor  52  is self-rotating, then fluid  56  acts as a brake. If rotor  52  is driven by drive motor  59 , then fluid  56  acts as a clutch between the drive motor and the rotor.  
         [0035]     As an alternative to electromagnet coil  34 , the magnetic field needed to activate MR fluid  30  may also be created by a permanent magnet. While the electromagnetic coil  34  creates a magnetic field when a current is applied, a permanent magnet creates a permanent magnetic field and a magnetic circuit is used to control the application of the field to the MR fluid. Power is required only to operate the magnetic circuit switching mechanism and not to apply the magnetic field to the fluid. Thus, although potentially of greater mechanical complexity, employing a permanent magnet may potentially reduce the power required to create pressure pulses.  
         [0036]     Referring now to  FIG. 4A , one embodiment of a magnetic circuit  62  is shown. Circuit  62  includes MR fluid path  64 , permanent magnet  66 , moveable ferromagnetic bar  68 , and flux path  70 . Permanent magnet  66  creates a magnetic field that is transferred through flux path  70  to fluid path  64 . To provide for an intermittent magnetic field, ferromagnetic bar  68  is placed across the flux path  70 , effectively shifting the magnetic field from the fluid path  64  to the bar  68 . Removing bar  68  allows the magnetic field to be applied to fluid path  64 . Moveable ferromagnetic bar  68  may preferably be a rotating or oscillating disk having ferromagnetic portions.  
         [0037]      FIG. 4B  shows an alternative permanent magnet circuit  72  including MR fluid path  74 , permanent magnet  76 , moveable member  78 , and flux path  80 . Permanent magnet  76  creates a magnetic field that is transferred through flux path  80  to fluid path  74 . To provide for an intermittent magnetic field, member  78  is used to complete flux path  70 , effectively completing the circuit to allow the magnetic field from magnet  76  to reach fluid path  74 . Removing member  78  breaks the circuit and prevents the magnetic field from being applied to fluid path  74 . Moveable member  78  may preferably be a rotating or oscillating disk having field transferring portions.  
         [0038]     In an alternative embodiment as shown in  FIG. 4C , a negative fluid pulser may be utilized including circuit  82 . Circuit  82  includes MR fluid path  84 , permanent magnet  86 , electromagnet  88 , and flux path  90 . The permanent magnet  86  generates a constant magnetic field that solidifies the MR fluid in fluid path  84  when the power to the electromagnet  86  is off. Once power is applied to the electromagnet  86 , the field generated by the electromagnet  86  cancels the field generated by the permanent magnet  84  and the MR fluid in fluid path  84  liquefies.  
         [0039]     While MWD telemetry is sometime thought of as producing a single pulse, it actually produces two pulses. A first pulse propagates directly from the pulse generator up the mud column to the surface. Another pulse propagates downward and then reflects off of the bit. These two pulses can cause confusion at the surface. Because the use of an electroactive fluid provides excellent response times for a pulse generator, a feedback control could be included so that the two pulses constructively interfered with each other. For example, if the frequency of the generator is such that the travel time for the downward pulse corresponds to one wavelength of the frequency, then, upon reflection, that pulse will constructively interfere with the upward pulse and the combined pulse will have a larger amplitude. The combination of a feedback controller and an electroactive fluid could ensure that the two pulses constructively interfere during changes in the drilling environment.  
         [0040]     The embodiments set forth herein are merely illustrative and do not limit the scope of the invention or the details therein. It will be appreciated that many other modifications and improvements to the disclosure herein may be made without departing from the scope of the invention or the inventive concepts herein disclosed. Because many varying and different embodiments may be made within the scope of the present inventive concept, including equivalent structures or materials hereafter thought of, and because many modifications may be made in the embodiments herein detailed in accordance with the descriptive requirements of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense.