Abstract:
A drill bit assembly for boring including a drill bit and a bit sub. A front bit end has a plurality cutting elements at a forward face of the front bit end and a first fluid return passage extending through the drill bit to a rear bit end. The bit sub couples to the rear bit end. The bit sub includes a bore disposed at a front sub end sized and shaped to receive the rear bit end of the drill bit. A plurality of legs extends from a mid-sub region toward the front sub end between pairs of cutting elements. The plurality of legs has a fluid delivery passage disposed therein with the fluid delivery passage extending from the plurality of legs to a rear sub bit end. The bit sub has a second fluid return passage connecting the first fluid return passage to the rear sub bit end.

Description:
PRIORITY CLAIM 
     This application claims the benefit of and priority from U.S. Provisional Patent Application No. 61/548,037 filed on Oct. 17, 2011, that is incorporated in its entirety for all purposes by this reference. 
    
    
     FIELD 
     The present application relates to drill bits used for earth boring, such as water wells; oil and gas wells; injection wells; geothermal wells; monitoring wells, mining; and, other operations in which a well-bore is drilled into the Earth. 
     BACKGROUND 
     Specialized drill bits are used to drill well-bores, boreholes, or wells in the earth for a variety of purposes, including water wells; oil and gas wells; injection wells; geothermal wells; monitoring wells, mining; and, other similar operations. These drill bits come in two common types, roller cone drill bits and fixed cutter drill bits. 
     Wells and other holes in the earth are drilled by attaching or connecting a drill bit to some means of turning the drill bit. In some instances, such as in some mining applications, the drill bit is attached directly to a shaft that is turned by a motor, engine, drive, or other means of providing torque to rotate the drill bit. 
     In other applications, such as oil and gas drilling, the well may be several thousand feet or more in total depth. In these circumstances, the drill bit is connected to the surface of the earth by what is referred to as a drill string and a motor or drive that rotates the drill bit. The drill string typically comprises several elements that may include a special down-hole motor configured to provide additional or, if a surface motor or drive is not provided, the only means of turning the drill bit. Special logging and directional tools to measure various physical characteristics of the geological formation being drilled and to measure the location of the drill bit and drill string may be employed. Additional drill collars, heavy, thick-walled pipe, typically provide weight that is used to push the drill bit into the formation being drilled. Finally, drill pipe connects these elements, the drill bit, down-hole motor, logging tools, and drill collars, to the surface where a motor or drive mechanism turns the entire drill string and, consequently, the drill bit, to engage the drill bit with the geological formation to drill the well-bore deeper. 
     A standard roller cone drill bit  202  is shown in  FIG. 3 . In  FIG. 3 , the roller cone drill bit  202  is comprised of a body  300  having a shank  302  and a plurality of legs  304 . Although not shown in  FIG. 3 , the shank  302  has an external thread for connection to an adjacent drill string component. A bore  310  extends from the shank  302  through the body  300  of the roller cone bit  202 . The legs  304  extend towards the front of the roller cone bit  202  and have a roller cone  306  disposed at an end of the leg  304 . Although not illustrated, each roller cone  306  has at least one cutter disposed on an external surface of the roller cone  306  for degrading a formation. The cutters may be formed of a hardened material or have a coating of a hard material such as polycrystalline diamond. The roller cones  306  have a central axis about which they rotate, with the roller cone  306  being rotatably connected to the leg  304 . 
     As a bore hole is drilled, fluid, typically a water or oil based drilling fluid referred to as drilling mud, is pumped down the drill string through the drill pipe and any other elements present and through the drill bit. Other types of drilling fluids are sometimes used; including air, nitrogen, foams, mists, and other combinations of gases, fluids, and mixtures of gases and fluids, but for purposes of this application, drilling fluid and/or drilling mud refers to any type of drilling fluid, including gases, fluid, and combinations thereof. In other words, drill bits typically have a fluid channel within the drill bit to allow the drilling mud to pass through the bit and out one or more jets, ports, or nozzles. The purpose of the drilling fluid is to cool and lubricate the drill bit, to stabilize the well-bore from collapsing, to prevent fluids present in the geological formation from entering the well-bore, and to carry fragments or cuttings removed by the drill bit up the annulus and out of the well-bore. 
     In a standard roller cone bit, drilling fluid is pumped to a working face  308  of the roller cone bit  202  through the drill string to the roller cone drill bit  202 . The fluid flows through the bore  310  of the roller cone drill bit  202  to the roller cones  306  and around the roller cone bit  202 . The drilling fluid returns up an annulus (the space between the exterior of the drill pipe and the wall of the well-bore). As the drilling fluid flows from the working face  308  to the outside of the roller cone bit  202 , the drilling fluid carries cuttings from the formation away from the roller cone bit  202 . 
     It may be beneficial in some situations to reverse the circulation of the drilling fluid. In such situations the drilling fluid is pumped down the annulus of the well-bore, across the face of the drill bit, and into the inner fluid channels of the drill bit through and up into the interior of the drill string. Alternatively, the drill string may have at least one section of double-wall pipe. Double wall pipe has an inner passage defined by an inner surface of the inner wall of the pipe and an outer passage defined by the outer surface of the inner wall and the inner surface of the outer wall. The drilling fluid may then be pumped down the outer passage and exit the exterior of the drill string proximate the drill bit. The drilling fluid then returns through the inner passage. It is also possible for the fluid to be pumped down the inner passage and crossover to the outer passage prior to the drill bit where the drilling fluid exits the drill string. 
     In either situation, the drilling fluid being pumped down the annulus or the drilling fluid being pumped down the outer passage of the double wall pipe, the drilling fluid does not necessarily pass across the face of the drill bit. Often much of the drilling fluid bypasses the face of the drill bit and flows to the inner channels of the drill bit through other paths, such as between the legs in the roller cone bit. To direct more of the fluid to the face of the roller cone bit, extensions may be welded to the roller cone bit between each of the legs. However, the process of welding the extensions may heat the bearings and seals of the roller cones affecting the longevity of the drill bit. Thus there is a need for a way to direct more of the fluid to the face of an existing roller cone drill bit without detrimentally affecting the longevity of the drill bit. 
     SUMMARY 
     Embodiments of the present invention include a drill bit assembly for earth boring. The drill bit assembly includes a drill bit and a bit sub. The drill bit has a front bit end and a rear bit end. The front bit end has a plurality cutting elements at a forward face of the front bit end and a first fluid return passage extending through the drill bit to the rear end. The bit sub is disposed about the rear bit end and couples to the rear bit end. The bit sub includes a body with a front sub end, a rear sub end, and a bore disposed at the front sub end sized and shaped to receive the rear bit end of the drill bit. The rear sub end is adapted to connect to an adjacent downhole component, such as a drill pipe. A plurality of legs extends from a mid sub region toward the front sub end between pairs of cutting elements. The plurality of legs preferably have a fluid delivery passage disposed therein with the fluid delivery passage extending from the plurality of legs to the rear sub bit end. The bit sub has a second fluid return passage connecting the first fluid return passage to the rear sub bit end with the second fluid return passage preferably being isolated from the fluid delivery passage within the bit sub. 
     In another embodiment, a bit sub includes a body, a plurality of legs, and a fluid return passage. The body has a front end, a rear end, and a bore disposed at the front end sized and shaped to receive a drill bit. The rear end is adapted to connect to an adjacent downhole component. The plurality of legs extends from the front end and has a forward end. The plurality of legs is adapted to complement an outer surface of the drill bit. Each of the plurality of legs has a fluid delivery passage disposed therein with the fluid delivery passage extending from the forward end to the rear sub bit end. The fluid return passage connects to the bore sized and shaped to receive a drill bit and is isolated from the fluid delivery passage within the body. 
     In another embodiment, a method of fabricating a reverse circulation drill bit assembly from a standard drill bit includes providing a standard drill bit and a bit sub component. The standard drill bit includes a shank and the bit sub component has a plurality of legs extending from a front end of the bit sub component. The shank is inserted into bit sub component such that the plurality of legs extends past the shank to a working surface of the drill bit. The bit sub component is then secured to the drill bit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To further clarify the above and other advantages and features of the one or more present inventions, reference to specific embodiments thereof are illustrated in the appended drawings. The drawings depict only typical embodiments and are therefore not to be considered limiting. One or more embodiments will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
         FIG. 1  illustrates a schematic of a cross-section of a bore hole having a drill string compatible with embodiments of the present invention. 
         FIG. 2  illustrates a reverse flow bit assembly in accordance with an embodiment of the current invention. 
         FIG. 3  illustrates a cross section of a three cone roller cone bit used in reverse flow bit assembly of  FIG. 2 . 
         FIG. 4  illustrates a cross section of a skirt section used in the reverse flow bit assembly of  FIG. 2 . 
         FIG. 5  illustrates a cross section of the nut section used in the reverse flow bit assembly of  FIG. 2 . 
         FIG. 6  illustrates a cross section of a check valve section used in the reverse flow bit assembly of  FIG. 2 . 
         FIG. 7  illustrates a cross section of the reverse circulation drill bit assembly of  FIG. 2  showing the flow of drilling fluid. 
         FIG. 8  illustrates a reverse flow bit assembly in accordance with an embodiment of the current invention. 
         FIG. 9  illustrates a cross section of a skirt section used in the reverse flow bit assembly of  FIG. 8 . 
         FIG. 10  illustrates a cross section of the nut section used in the reverse flow bit assembly of  FIG. 8 . 
         FIG. 11  illustrates a cross section of the reverse circulation drill bit assembly of  FIG. 8  showing the flow of drilling fluid. 
     
    
    
     The drawings are not necessarily to scale. 
     DETAILED DESCRIPTION 
     As used herein, “at least one,” “one or more,” and “and/or” are open-ended expressions that are both conjunctive and disjunctive in operation. For example, each of the expressions “at least one of A, B and C,” “at least one of A, B, or C,” “one or more of A, B, and C,” “one or more of A, B, or C” and “A, B, and/or C” means A alone, B alone, C alone, A and B together, A and C together, B and C together, or A, B and C together. 
     Various embodiments of the present inventions are set forth in the attached figures and in the Detailed Description as provided herein and as embodied by the claims. It should be understood, however, that this Summary does not contain all of the aspects and embodiments of the one or more present inventions, is not meant to be limiting or restrictive in any manner, and that the invention(s) as disclosed herein is/are and will be understood by those of ordinary skill in the art to encompass obvious improvements and modifications thereto. 
     Additional advantages of the present invention will become readily apparent from the following discussion, particularly when taken together with the accompanying drawings. 
       FIG. 1  illustrates a schematic of a cross-section of a borehole  100  having a drill string  102  disposed therein. A derrick  104  connects the drill string  102  to the top surface of an earthen formation  106 . The drill string  102  is comprised of a plurality of down-hole tool components, such as pipe segments, measuring tools, and drill bits. The pipe segments have an inner bore providing a passageway for fluid to be transferred through the drill string. The pipe segments may be double walled providing two separate passages for fluid. An annulus  108  is formed between the drill string  102  and an inner wall of the borehole  100 . A drill bit  110  disposed at the bottom of the drill string  102 . Movement of the drill bit  110  degrades the formation  106  allowing the drill string  102  to proceed further into the formation  106 . 
       FIG. 2  illustrates an embodiment of a reverse circulation bit assembly  200 . The reverse circulation drill bit assembly  200  is generally comprised of a roller cone bit  202  and a skirt  204 . The reverse circulation bit assembly  200  further comprises a nut section  206  and a check valve section  208 . In the embodiment of  FIG. 2  the skirt  204 , the nut section  206 , and the check valve section  208  are shown as three distinct parts, but in some embodiments they may be combined with one another so as to have less than three distinct components. The skirt  204 , the nut section  206 , and the check valve section  208  are generally referred to as a bit sub, whether they are distinct components or combined. Furthermore, the skirt  204 , the nut section  206 , or the check valve section  208  may each be comprised of individual parts making up that component. 
       FIG. 3  illustrates the roller cone bit  202  of  FIG. 2  in more detail. The illustrated roller cone bit  202  is a standard three cone roller cone bit. However, other types of bits may be used in the reverse circulation bit assembly  200  and embodiments are not limited to three cone roller cone bits. The bits may be off the shelf parts and modified to become a reverse circulation bit assembly. 
     The operation of the roller cone bit of  FIG. 3  was previously described as a standard circulation drill bit. Using embodiments of the current invention, the roller cone bit of  FIG. 3  can be used as a reverse circulation drill bit. Embodiments of the current invention enable most drill bits to be used as a reverse circulation drill bit. 
       FIG. 4  illustrates a cross-section of the skirt  204 . The skirt  204  enables the standard roller cone bit  202  to be used as a reverse circulation bit. The skirt  204  has a plurality of legs  402  that extend towards the working face  308  of the roller cone bit  202 . Each leg  402  is sized and shaped to fit closely around and between the roller cone bit legs  304 . In some embodiments, the roller cone bit legs  304  may be modified to have a profile that is complementary to that of the skirt legs  402 , or in other embodiments the roller cone bit legs  304  may be unmodified and the skirt legs  402  may have been modified to complement the profile of the roller cone bit legs  304 . In some embodiments, a combination of modifying the roller cone bit legs  304  and the skirt legs  402  may be used. 
     At least one skirt leg  402  has a passageway  404  through which drilling fluid can be delivered. The passageway  404  exits the skirt leg  402  proximate the working face  308  of the roller cone bit  202 . Since the drilling fluid is provided at the working face  308 , the drilling fluid is more likely to flow across the working face  308  and then into the bore  310  of the roller cone bit  202 , as opposed to flowing closer to the roller cone bit legs  304  without the skirt  204 . 
     The skirt  204  is sized and shaped to slide over the roller cone bit  202  such that the skirt legs  402  are proximate the roller cones  306 . The skirt  204  has a central bore  406  sized and shaped to complement the outer surface of the bit body  300 . In some embodiments, the skirt  204  may press fit over the bit body  300 . 
       FIG. 5  illustrates a cross-sectional view of the nut section  206  of the reverse circulation bit assembly  200 . The nut section  206  secures the skirt  204  to the roller cone bit  202 . The nut section  206  includes an internal surface having an internal thread sized and shaped to complement the external thread of the roller cone bit shank  302 . As the roller cone shank  302  is threaded into internal thread of the nut section  206 , the nut section  206  advances towards the working face  308  of the roller cone bit  202 . The skirt  204  is unable to advance past the front of the roller cone bit  202  and forms a stop for the nut section  206 . When a rear surface of the skirt  204  contacts a forward surface  504  of the nut section  206 , the nut section  206  can advance no further. The skirt  204  is then constrained from forward movement by the roller cone bit  202  and rearward movement by the nut section  206 . 
     The nut section  206  includes a trough  506  disposed in the forward surface  504 . The trough  506  is annular and the forward surface forms an inner sealing surface  510  and an outer sealing surface  508  about the trough  506 . When the rear surface of the skirt  204  and the forward surface  504  of the nut section  206  contact one another, a seal is formed between the skirt  204  and the nut section  206  such that the trough  506  forms a front annular passageway. The through bores  404  from the legs  402  of the skirt  204  extend through the back of the skirt  204  such that the through bores  404  are fluidly connected with the trough  506  forming the front annular passageway. As the nut section  206  is threaded onto the roller cone bit  202  with the skirt  204  in place, the angular position of the nut assembly  206  relative to the skirt  204  is unimportant, as the through bores  404  will always line up with the trough  506  forming the front annular passageway. 
     The nut section  206  may have at least one side bore  512  through which a set screw or pin can be inserted to secure the nut section  206  to the roller cone bit  202 . A matching side bore can me be machined in the roller cone bit  202  to receive the set screw or pin to prevent the roller cone bit  202  from rotating relative to the nut section  206 . The matching side bore may be machined prior to the nut section  206  being threaded on the roller cone bit  202 , or the matching side bore may be machined after the nut section  206  is threaded on the roller cone bit  202 . In some embodiments, no matching side bore may be present and the set screw or pin may press into the shank  302  of the roller cone bit  202 . Other means of securing the nut section or the entire bit sub to the bit may be employed. 
     A rear end  514  of the nut section  206  includes a rear annular trough  516  and a center protrusion  518 . A nut section bore  520  extends from the forward surface  504  of the nut section  206  to the rear end  514  of the center protrusion  518 . The nut section bore  520  aligns with the bore  310  of the roller cone bit  204  and provides a passage for the return of drilling fluid. The rear annular trough  516  and the front annular trough  506  are connected by at least one through passage  522 . The through passage  522  enables fluid communication between the rear annular trough  516  and the forward annular trough  506 . 
       FIG. 6  illustrates a cross-sectional view of the check valve section  208 . The check valve section  208  is generally cylindrical with an outer diameter  602  similar to that of the nut section  206  and the skirt section  204 . The check valve section  208  has a central bore  604  that extends from a front face  606  of the check valve section  208  to the rear of the check valve section  208 . A wall  610  is formed between the central bore  604  and an outer surface  608  of the check valve section  208 . Disposed within the wall  610  is at least one check valve passageway  612  providing fluid communication to the front face  606  of the check valve section  208 . The rear of the check valve section  208  has an enlarged bore  614  that extends from the rear of the check valve section  208  to about mid-way the length of the check valve section  208 . 
     Disposed within the check valve passageway  612  is a check valve assembly  616 . The check valve assembly  616  inhibits drilling fluid from flowing up the check valve passageway  612 . Although different types of check valves assemblies are compatible with the present embodiments, the check valve assembly  616  of  FIG. 6  comprises a seat  618 , a biasing member  620 , and a piston  622 . The biasing member  620  biases the piston  622  into the seat  618  forming a seal. When a pressure differential across the seal is sufficient to overcome the bias of the biasing member  620 , the piston  622  moves against the bias, opening the valve. 
     The front face  606  of the check valve section  208  is coupled to the rear face of the nut section  206 . The front face  606  may be coupled by way of a welded connection or other connection means. The front face  606  seals to the rear annular trough  516  of the nut section  206  forming a rear annular passage. Like the relation between the nut assembly  206  and the skirt  202 , the angular position of the nut section  206  relative to the check valve section  208  is unimportant, as the check valve passageway  612  will always line up with the rear annular passageway. 
     As shown in  FIG. 7 , an inner tube flange  700  is disposed within the enlarged bore  614 . The inner tubular flange  700  may be threaded into the check valve section  208 . The inner tubular flange  700  has an outer surface, an inner surface, and a wall there between. The inner surface defines an inner tube flange bore that aligns with the central bore  604  of the check valve section  208  and provides fluid communication from the rear end of the check valve section  208  to the bore  502  of the nut section  206 . The outer surface and the enlarged bore together define an annular passageway fluidly connecting the rear of the check valve section  208  and the check valve passageway  612 . 
     The rear end of the check valve section  208  is adapted to be connected to a tool string. The tool string may be a double walled tool string having two separate fluid paths. The tool string connects to the rear end of the check valve section  208  and connects the two separate fluid paths to the annular passageway of the check valve section  208  and the central bore of the check valve section  208 . 
     Although the bit sub was described with relation to the skirt  204 , nut section  206 , and check valve section  208 , the check valve section  208  may be combined with the nut section  206 . In some embodiments, the check valve section  208  may not include a check valve assembly  616 . For example, in some instances a drill operator may not be concerned about back flow and the check valve assembly  616  may be eliminated. In such instances, it may be simpler to manufacture the nut section  206  and the check valve section  208  as a single component. 
     The operation of the reverse circulation drill bit will be explained in relation to  FIG. 7 , which is a cross section of the assembled reverse circulation drill bit assembly  200 . Drilling fluid is delivered to the annular passageway fluidly connecting the rear of the check valve section  208  and the check valve passageway  612 . The pressure of the drilling fluid generates a pressure differential across the check valve assembly  616 , causing the check valve assembly  616  to open. The drilling fluid flows from the check valve passageway  612  into the annular passageway formed by the rear annular trough  516 . The drilling fluid then flows from the rear annular trough  516  through the through passage  522  into the forward annular trough  506 . The forward annular trough  506  is in fluid communication with the skirt leg passage way  404  and the drilling fluid flows into the skirt leg passageway  404 . 
     From the skirt leg passageway  404 , the drilling fluid is delivered to the working face  308  of the roller cone bit  202 . The drilling fluid collects cuttings and other material and flows into the bore  310  of the roller cone bit  302 . The bore  310  of the roller cone bit  202  is in fluid communication with the inner tube flange bore through the nut section bore  502  and the check valve section bore  604 . The drilling fluid flows up the reverse flow bit assembly  200  and out of the inner tube flange bore. 
       FIG. 8  illustrates another embodiment of a reverse circulation drill bit assembly  800 . The reverse circulation drill bit assembly  800  comprises a roller cone bit  202 , a skirt section  804 , and a nut section  806 . In this embodiment, the drilling fluid is delivered to the annulus between the drill bit and the bore wall and not through the skirt as described in the previous embodiment. 
       FIG. 9  illustrates a cross-section of the skirt section  804  of the reverse circulation drill bit assembly  800 . The skirt section has a plurality of legs  902  extending toward the working face  308  of the roller cone bit  202 . Each leg  902  is sized and shaped to fit closely around and between the roller cone bit legs  304 . In some embodiments, the roller cone bit legs  304  may be modified to have a profile that is complementary to that of the skirt legs  902 , or in other embodiments the roller cone bit legs  304  may be unmodified and the skirt legs  902  may have been modified to complement the profile of the roller cone bit legs  304 . In some embodiments, a combination of modifying the roller cone bit legs  304  and the skirt legs  902  may be used. 
     Unlike the previous embodiment, the skirt legs  902  do not have a passageway for the delivery of drilling fluid. Instead drilling fluid is delivered to the annulus of the drill bit and the skirt legs  902  inhibit the drilling fluid from flowing into the bore  310  of the roller cone bit  202  between the roller cone bit legs  304 . Since the drilling fluid is inhibited from flowing into the bore until  310  it reaches the working face  308 , the drilling fluid is more likely to flow across the working face  308  and into the bore  310  of the roller cone bit  202 , as opposed to between the roller cone bit legs  304  without the skirt legs  902 . 
     The skirt  804  is sized and shaped to slide over the roller cone bit  202  such that the skirt legs  902  are proximate the roller cones  306 . The skirt  804  has a central bore  906  sized and shaped to complement the outer surface of the bit body  300 . In some embodiments, the skirt  804  may press fit over the bit body  300 . 
       FIG. 10  illustrates a cross-sectional view of the nut section  806  of the reverse circulation bit assembly  800 . The nut section  806  secures the skirt  804  to the roller cone bit  202  and provides a means for connecting the reverse circulation bit assembly  800  to the drill string. The nut section  806  includes an internal surface  908  having an internal thread sized and shaped to complement the external thread of the roller cone bit shank  302 . As the roller cone shank  302  is threaded into internal thread of the nut section  806 , the nut section  806  advances towards the working face  308  of the roller cone bit  202 . The skirt  804  is unable to advance past the front of the roller cone bit  202  and forms a stop for the nut section  806 . When a rear surface of the skirt  804  contacts a forward surface  910  of the nut section  806 , the nut section  806  can advance no further. The skirt  804  is then constrained from forward movement by the roller cone bit  202  and rearward movement by the nut section  806 . 
     The nut section  806  includes a shank  910  adapted to connect to a drill string. The shank  910  may have an external thread (not shown) for threading into a drill string. An internal bore  912  aligns with the bore  310  of the roller cone bit  202  and allows fluid to flow from the bore  310  of the roller cone bit  202  to a drill string bore. The nut section  806  may include a side bore  914  that may receive a set screw or pin that can be inserted to secure the nut section  806  to the roller cone bit  202 . A matching side bore can be machined in the roller cone bit  202  to receive the set screw or pin to prevent the roller cone bit  202  from rotating relative to the nut section  806 . The matching side bore may be machined prior to the nut section  806  being threaded on the roller cone bit  202 , or the matching side bore may be machined after the nut section  806  is threaded on the roller cone bit  202 . In some embodiments, no matching side bore may be present and the set screw or pin may press into the shank  302  of the roller cone bit  202 . Other means of securing the nut section or the entire bit sub to the bit may be employed. 
       FIG. 11  illustrates a cross section of the reverse circulation drill bit assembly  800  and will be used to describe the reverse circulation of the drilling fluid. The direction of the flow of fluid is represented by the arrows on the figure. The drill fluid initially is delivered to the annulus  1202  and flows around the roller cone drill bit  202 . Near the working face  308  the fluid is inhibited from flowing between the roller cone legs  304  by the skirt legs  902 . The drilling fluid flow across the working face  308  and into the central bore  310  of the roller cone drill bit  202 . The drilling fluid flows from the central bore  310  to the bore  912  of the nut section  904 . From there the drilling fluid flows into the bore of the drill string. 
     The forgoing reverse flow bit assemblies  200 ,  800  can be manufactured using a standard, off the shelf drill bit. Embodiments of the invention include a method of making a reverse flow circulation bit assembly. 
     The method includes providing a standard drill bit. The standard drill bit may be a roller cone bit as previously described, or it may include a fixed blade bit or any other type of drill bit. A skirt sized and shaped to complement the drill bit is provided. In some embodiments the standard drill bit may be modified to complement the size and shape of the skirt or the skirt may be modified to complement the size and shape of the standard drill bit. The skirt is placed over the shank of the drill bit. 
     A nut assembly is then provided and coupled to the standard drill bit. In some embodiments the nut assembly may have a female thread that complements the shank of the standard drill bit. In such embodiments the nut assembly is threaded onto the shank until the nut assembly contacts the skirt, securing the skirt in place. A set screw or pin may then be inserted into the nut assembly to hold the drill bit in place. After the nut is in place, a check valve section may then be coupled to the nut assembly. Such a coupling may be performed by welding, a threaded connection, or some other means of connection. In other embodiments, the check valve section may be coupled to the nut section prior to the nut section being coupled to the standard drill bit. In some embodiments, the check valve section and the nut may be single components that are coupled to the standard drill bit. 
     An inner tube flange is provided and coupled to the rear end of the check valve section. The inner tube flange may be coupled to the rear end of the check valve section prior to the check valve section being coupled to the nut section, or it may be coupled after. In some embodiments the inner tube flange is an integral part of the check valve section and is not removable. 
     The inner tube flange may be sized and shaped for connection to a specific type of drill string. For example, different inner tube flanges may be used to connect the reverse circulation bit assembly with different drill pipes. In this way a single reverse circulation drill bit assembly may be compatible with multiple types of drill pipe. 
     The foregoing discussion of the invention has been presented for purposes of illustration and description. The foregoing is not intended to limit the invention to the form or forms disclosed herein. In the foregoing Detailed Description for example, various features of the invention are grouped together in one or more embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the following claims are hereby incorporated into this Detailed Description, with each claim standing on its own as a separate preferred embodiment of the invention. 
     Moreover, though the description of the invention has included description of one or more embodiments and certain variations and modifications, other variations and modifications are within the scope of the invention, e.g., as may be within the skill and knowledge of those in the art, after understanding the present disclosure. It is intended to obtain rights which include alternative embodiments to the extent permitted, including alternate, interchangeable and/or equivalent structures, functions, ranges or steps to those claimed, whether or not such alternate, interchangeable and/or equivalent structures, functions, ranges or steps are disclosed herein, and without intending to publicly dedicate any patentable subject matter.