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CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    Not Applicable  
         STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not Applicable  
         BACKGROUND OF THE INVENTION  
         [0003]    The present invention relates generally to downhole circulation subs. More particularly, this invention relates to the use of an electric motor to drive a downhole circulation sub.  
           [0004]    Retrieval of oil and other hydrocarbons from below ground typically includes drilling a borehole, also known as a wellbore, in the Earth. As drilling technology has advanced, these boreholes may be drilled off of vertical, sometimes even sideways or horizontal. In this way, an operator can reach a formation that contains the desired substance. Thus, the terms “upper” and “lower”, or “above” and “below” as used herein are made with respect to a position in the borehole, and may not necessarily reflect whether two elements are above or below each other in an absolute sense. FIG. 1 includes rock formation  100  surrounding a borehole  110 . Borehole  100  is formed by the cutting action of drill bit  125  attached to rotating drill string  120 . Drill string  120  also includes a circulating sub  170 .  
           [0005]    A variety of drill bits  125  are known, but a common feature is that each contains ports or nozzles on its face to direct drilling mud  130  (also known as drilling fluid) flowing through drill string  120 . The drilling mud  130  exits the drill bit as shown by arrows  160 . This mud not only cools the face of the drill bit, but also carries to the surface a substantial amount of shavings and cuttings  140  that result from the drilling action. These cuttings are carried up to the surface from downhole along an area between the drillstring and the borehole wall known as the annulus  150 . At the surface, the drilling mud is then cleaned, filtered and recycled for repeated use.  
           [0006]    One problem occurs when the ports or nozzles on the face of the drill bit  125  become blocked or otherwise impeded from spraying drilling mud out the face of the drill bit  160 . This prevents or substantially slows the flow of mud to the surface, resulting in the rock cuttings falling to the bottom of the wellbore. It also results in a pressure build-up in the mud contained in the drill string. The increase in pressure can damage equipment uphole such as pumps. To minimize this problem, it is known to provide a circulating sub  170  that provides an alternate route  165  for drilling mud flow when the mud is unable to exit drill bit  160  properly.  
           [0007]    Referring to FIG. 2, a known circulating sub  200  is called a ball-drop circulating sub. It includes a cylindrical valve sleeve  210  having holes or ports  220 . At its lower end is a lip  230  that reduces the inner diameter of the cylindrical valve sleeve  210 . The circulating sub housing surrounds valve sleeve  210  and also includes ports  225 . Shoulder  260  is positioned for abutment against the lower portion of valve sleeve  210 , as explained below. Between valve sleeve  210  and drill string  120  are o-rings  240 - 242  and a shear pin  250 . Ball  270  is shown falling in mid-travel from the surface before lodging in area formed by lip  230 .  
           [0008]    During normal operation (i.e., when mud is properly flowing  160  through the drill bit  125 ), drilling mud  130  flows through the center of circulating sub  200  as shown by arrows  280 . However, upon a blockage in the flow of mud, a ball  270  is shot from the surface down to ball-drop circulating sub  200 . Ball  270  lodges against lip  230 , preventing the flow of mud  130  along flow path  280 . Pressure built up in the mud column exerts itself against ball  270  and causes shear pin  250  to break. Valve sleeve  210  drops down until stopped by shoulder  260 . This aligns ports or holes  220  and  225 . Drilling mud  130  then escapes circulating sub  200  and follows mud path  165  (shown in FIG. 1) to the surface. This lifts the rock cuttings above the circulating sub  200  to the surface. However, the ball-drop circulating subs have a number of problems. For example, because the ball  270  originates at the surface, it can take up to thirty minutes from the time the mud flow stops through a drill bit to the time the circulating sub redirects the flow. In addition, this design is a one-time actuation and cannot be reset. Other circulating subs having various problems, such as U.S. Pat. No. 5,465,787, are also presently known.  
         SUMMARY OF THE INVENTION  
         [0009]    A preferred embodiment of the present invention features a downhole circulation sub having an electric motor associated with a valve poppet. The valve poppet moves from a first position to a second position in response to force from the electric motor, causing drilling fluid flowing through the circulation sub to switch its path of travel from a first route generally downhole to a second route generally uphole. In its second position, the valve sleeve may engage a valve plug. Further, the valve poppet may be placed back in its first position by operation of the electric motor. The circulation sub is designed so that this movement of the valve sleeve from its first to its second position, and back again, may be carried out repeatedly.  
           [0010]    Another aspect to the invention is a method of redirecting the flow of drilling fluid in a circulation sub. This aspect of the invention includes actuating an electric motor to apply force to a connected valve sleeve, moving the valve sleeve from a first position inside a housing to a second position by actuation of the electric motor, preventing by movement of the valve sleeve to the second position the flow of fluid past a lower end of the circulation sub, and directing by the movement of the valve sleeve to the second position the flow of fluid through ports positioned between die valve sleeve and an annulus. The first position is typically an upper position with respect to a wellbore, and the second position is a lower position.  
           [0011]    Thus, the present invention comprises a combination of features and advantages which enable it to overcome various problems of prior devices. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention, and by referring to the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    For a more detailed description of the preferred embodiment of the present invention, reference will now be made to the accompanying drawings, wherein:  
         [0013]    [0013]FIG. 1 illustrates the typical flow of drilling fluid in a borehole.  
         [0014]    [0014]FIG. 2 depicts the operation of a ball drop circulating sub.  
         [0015]    [0015]FIG. 3A and 3B is a cut-away view of the preferred embodiment of the invention.  
         [0016]    [0016]FIG. 4A is a cut-away view of the valve sleeve of the preferred embodiment in a closed position.  
         [0017]    [0017]FIG. 4B is taken along line A-A of FIG. 4A.  
         [0018]    [0018]FIG. 5 is a cut-away view of the valve sleeve of the preferred embodiment in an open position.  
         [0019]    [0019]FIG. 6 is a cut-away diagram of a second embodiment of the invention.  
         [0020]    [0020]FIG. 7 is a block diagram of a third embodiment of the invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]    [0021]FIGS. 3A and 3B generally show the operation of the preferred embodiment. A fluid circulating sub  300  according to the preferred embodiment is attached to drill string or other housing  320 . The circulating sub  300  includes a DC motor  310  with associated downhole circulating sub electronics  308 , the DC motor  310  being mechanically coupled to rotate threaded screw  330  in either direction. Nut  340  terminates in piston  335 . Nut  340  threadably affixes to screw  330 , and moves laterally as shown by arrow  345  upon the rotation of the screw by motor  310 . Chamber  350  terminates at its narrow end at piston  335  and at its wide end at piston  360 . Piston  360  connects to connecting rod  365 . Also shove in FIG. 3A are mud passage  305  around the perimeter of the circulating sub, oil compensation spring  355 , oil compensation piston  357 , and fail-safe spring  367 .  
         [0022]    [0022]FIG. 3B also illustrates drillstring  320  and connecting rod  365 . Additionally shown are valve sleeve  370 , also known as a valve poppet, formed to sealably engage valve seat  375 . Valve seat  375 , also called a valve plug, may be mounted by use of a screw, for example, and includes an o-ring  378  to form a seal with valve sleeve  270 . Holes  380  and  381  for mud flow  390  into the center of the circulating sub are formed in the upper portion of valve sleeve  370 . Holes  382  and  383  in valve sleeve  370  correspond to holes  384  and  385  in the housing and provide an alternate route for the drilling mud when the circulating sub is open and activated. The housing is a circulating sub housing that engages with the valve sleeve, but may be any appropriate housing such as a section of the drill string. In addition, many of the advantages of the preferred embodiment may still be obtained even where the valve poppet is not exactly like the configuration shown. The valve poppet can therefore be any of a variety of configurations.  
         [0023]    During operation, downhole circulating sub electronics  308  receive power from the surface. To facilitate power delivery, the system may be preferably part of a coiled tubing drillstring equipped with electric wiring. Alternatively, the system may be part of a slim-hole jointed drill pipe string, for example, or may be any other structure suitable to deliver power downhole. Real-time data communications from the surface are also sent to the downhole circulating sub electronics. In response, the electronics  308  control the operation of electric motor  310 . Electric motor  310  is preferably a DC motor, although this is not crucial to the invention. The electric actuation motor  310  is reversible and may turn screw  330  in either direction to repeatedly open and close the circulating sub  300 . As such, the circulating sub disclosed herein has a longer life span than circulating subs known in the prior art. It also does not require replacement when the drillstring is “tripped”, or removed from the well bore. It is therefore more economical than circulating subs known in the prior art.  
         [0024]    As electric motor  310  turns screw  330 , the nut  340  moves laterally  345  by force of threaded screw  330 . This moves piston  335  within chamber  350 . Chamber  350  includes both a smaller cross-sectional end for piston  335  and a larger cross-sectional end for piston  360 . As screw  330  is actuated (i.e., moves from left to right in FIG. 3B), it applies force to clean hydraulic fluid filling chamber  350 . This fluid transmits the force from piston  335  to piston  360 . What results is a hydraulic intensifier requiring less torque from, and thus less instantaneous current for, DC motor  310 . As force is applied to piston  360 , connecting rod  365  moves laterally in opposition to fail-safe spring  367 . In case of power failure, fail-safe spring returns the connecting rod  365 , and hence the circulating sub, to its unactuated and closed position.  
         [0025]    Surrounding chamber  350  is an oil compression spring to resist the collapsing force from the drilling mud under high pressure and traveling through passage  305 . Oil compensation piston  357  accounts for the expansion and contraction of the hydraulic fluid due to temperature variations.  
         [0026]    When valve sleeve is in its unactuated position as shown in FIG. 3B, drilling mud flows through holes  380  and  381  and follows mud path  390  past valve seat  375  and down to a drill bit, where it exits and travels up to the surface. The movement of connecting rod  365  from left to right opens the circulating sub by movement of valve sleeve  370 .  
         [0027]    When this occurs, valve sleeve  370  covers and seals with valve seat  375  by, for example, o-ring seal  378 . This movement of the valve sleeve aligns holes  383  and  385 , and holes  382  and  384 , respectively, to provide an alternate mud flow path to the annulus. This alternate mud flow path bypasses the downhole drill bit and provides direct access to the annulus for the drilling fluid. It would now be apparent to the artisan of ordinary skill that the valve plug need not necessarily engage within the valve sleeve exactly as shown, but rather that other appropriate geometries and structures could be used, so long as the valve sleeve engages to prevent flow of drilling fluid past the circulation sub.  
         [0028]    [0028]FIG. 4A includes a connecting rod  365  that connects to sliding sleeve valve  370 . Sleeve valve  370  resides in nozzle sub  420  and lower sub  320 . Valve body  470  includes a bypass chamber  410  and wire channel  520 , as well as containing plug valve  275 . Sleeve valve  370  prevents the flow of mud into the bypass chamber  410  and forces the flow of drilling mud  390  past valve plug  375  toward a downhole assembly. Wires in wire channel  520  supply power downhole. Thus, like FIG. 3, FIG. 4A depicts the valve assembly in a closed position. FIG. 4B is taken along line A-A of FIG. 4A.  
         [0029]    [0029]FIG. 5 shows the valve assembly in an open position. Connecting rod  365  attaches to sliding sleeve valve  370 . A seal between these two components is made by o-ring seal  378 . As can be seen, mud flow is prevented from going past valve plug  375  and instead is directed to bypass chamber  410  and out replaceable nozzles  430 . These nozzles  430  are angularly mounted with the centerline, creating a spiraling fluid stream that is effective to lift and transport cuttings out of the borehole for hole cleaning purposes. Further, because all bore fluid flow is cut off from the lower port of the bottomhole assembly, all of the drilling mud is forced to circulate to the annular region between the drillstring and the borehole wall. This results in the cuttings in the borehole above the circulating sub being circulated to the surface (where they can be cleaned from the drilling fluid) prior to the tripping or removal of the drill string from the borehole.  
         [0030]    [0030]FIG. 6 illustrates a second embodiment of the invention. This circulating sub  600  includes an electric motor  610  attached to a lead screw  630 . The lead screw  630  attaches to a valve sleeve  670 . Hence, this embodiment does not use hydraulic force amplification. Instead, this embodiment uses direct mechanical actuation involving the advancing and retracting of a lead screw  630  by the electric motor  610 , the lead screw opening and closing the valve sleeve  670 .  
         [0031]    [0031]FIG. 7 illustrates a third embodiment of this invention that does not include a connecting rod to associate the electric motor to the valve sleeve. An assembly inside a housing  720  includes an electric motor  710  associated with a valve poppet  770 . A translation means  730  applies from the electric motor  710  to the valve poppet  770 . Thus, a non-mechanical linkage, such as a hydraulic arrangement, may be used as the translation means  730  to open and close the downhole valve poppet  770  by operation of the electric motor  710 .  
         [0032]    While preferred embodiments of this invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit or teaching of this invention. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the system and apparatus are possible and are within the scope of the invention. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims.

Summary:
A preferred novel circulating sub includes an electric motor, hydraulic intensifier, connecting rod, valve sleeve, valve plug, and angled nozzles. Upon activation of the circulating sub the electric motor drives the valve sleeve over the valve plug, causing a flow of drilling fluid to exit the angled nozzles. Upon deactivation of the circulating sub, the electric motor removes the valve sleeve from the valve plug, allowing the flow of drilling fluid to once again flow to the drill bit. Because the electric motor is reversible, the circulating sub can be repeatedly activated and deactivated.