Patent Publication Number: US-2015075870-A1

Title: System and method for horizontal directional drilling and product pulling through a pilot bore

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application for patent claims priority under 35 U.S.C. §119(e) to, and incorporates by reference the entire contents of, U.S. provisional application entitled “SYSTEM AND METHOD FOR HORIZONTAL DIRECTIONAL DRILLING AND PRODUCT PULLING THROUGH A PILOT BORE,” filed on Mar. 14, 2013 and assigned application Ser. No. 61/781,211. 
    
    
     BACKGROUND 
     The present invention relates to horizontal directional drilling (“HDD”) and, more particularly, to improved drill bits and improved pulling systems to be used in HDD processes. 
     Horizontal directional drilling (“HDD”), also termed “slant drilling,” is the practice of drilling non-vertical bores. A common application for HDD is for the installation of utility products such as underground wiring, small bore piping, cable bundles, and the like. The HDD process typically begins with drilling a pilot bore along a desired underground path. Next, the pilot hole is enlarged to a desired diameter and its walls conditioned by passing a larger cutting tool, sometimes termed a “back reamer,” back through the pilot hole. As one of ordinary skill in the art understands, selection of a back reamer may depend on the product that will ultimately be installed in the bore. Finally, the product is installed in the enlarged hole by way of being pulled behind the reamer as the drill string is retracted from the reamed bore. 
     An HDD process may include the use of a viscous fluid known as drilling fluid. Drilling fluid is typically a mixture of water and either bentonite or a polymer that is continuously pumped to the drill bit located at the very end of a drill string in the down-the-hole (“DTH”) assembly. The drilling fluid is blown through ports in the drill bit to facilitate the removal of cuttings, stabilize the bore hole, cool the drill bit cutting head, and lubricate the passage of the product. The drilling fluid may be recycled through a machine called a reclaimer which removes the drill cuttings and maintains the proper viscosity of the fluid. Advantageously, drilling fluids hold the cuttings in suspension to prevent them from clogging the bore, thereby alleviating pressure on the drill bit that could slow the boring process. 
     BRIEF SUMMARY OF THE INVENTION 
     Various embodiments, aspects and features of the present invention encompass a system and/or a method employed in a horizontal directional drilling (“HDD”) process. 
     An exemplary embodiment includes a drill bit with thirteen (13) or more splines for improved orientation of the drill bit relative to the orientation of a bent sub. 
     Another exemplary embodiment includes a drill bit configured for receipt of a pulling device so that the drill bit may be used in a back reaming step to pull a product back through a pilot bore. 
     Another exemplary embodiment includes a pulling device for mounting to a drill bit. The pulling device, in some embodiments, may include one or more pins for diverting and channeling air and/or fluid through the drill bit to lubricate a hammer assembly and/or the product being pulled as the drill string to which the drill bit is attached is retracted back through the pilot bore. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIGS. 1A-1B  depict a method for aligning or “clocking” the orientation of a drill bit relative to the orientation of a bent sub. 
         FIG. 2  depicts an exemplary embodiment of a drill bit with thirteen splines. 
         FIGS. 3A-3B  is a non-limiting example of a drill bit and pulling device, according to an embodiment of the invention. 
         FIG. 4  is a non-limiting example of a blow hole pin that may be included in some embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments and aspects of the present invention provide solutions to various needs in the art by providing a drill bit with thirteen (13) or more splines. Further embodiments and aspects of the present invention provide solutions to various needs in the art by providing a drill bit and pulling system for converting a drill bit to a back reamer suitable for pulling product back through a pilot bore. 
     A typical DTH drill assembly is screwed onto the bottom of the drill string and may include any number of components including, but not necessarily limited to, a sonde assembly, a bent sub, a hydraulic motor assembly, a chuck and a drill bit. 
     The sonde assembly may include various instrumentation and transmitters for measuring various data such as angle of the string, rotation, direction of the bore, temperature and the like. The data measured by the sonde assembly is transmitted to the surface and used to adjust the drilling direction, as is understood by one of ordinary skill in the art. Location and guidance of the drilling is an important part of the drilling operation, as the drill bit is under the ground while drilling and, in most cases, not visible from the ground surface. Uncontrolled or unguided drilling can lead to substantial destruction, which can be eliminated by properly locating and guiding the drill bit. 
     The sonde assembly provides the means by which the drill bit may be located and guided through use of a “walk-over” locating system. The data collected by the sonde assembly is encoded into an electro-magnetic signal and transmitted through the ground to the surface to be received by the walk-over system. At the surface, when a receiver (usually a hand-held locator) is positioned over the sonde, the signal is decoded and steering directions are subsequently relayed to the bore machine operator. 
     The bent sub portion of the DTH assembly, sometimes termed the adjustable kickoff sub, is a small segment of the drill string with a body portion that is bent at an angle rather than being straight. In some embodiments of a DTH assembly, the bent sub may be located above the drill bit and below the motor assembly, although such is not required in all embodiments of a DTH assembly. As one of ordinary skill in the art recognizes, the inclusion of a bent sub in the drill string makes it possible to steer the bore as needed by pushing off the side of the bore to produce a sideways force on the drill bit. The specific bend angle of a bent sub is application specific, as one of ordinary skill in the art understands. An exemplary bent sub, however, may include a lower thread portion that is inclined 1°-3° from the axis of the bent sub body. 
     The hydraulic motor, chuck and drill bit components of a DTH assembly work together to operate like a mini jackhammer that breaks hard rock into small flakes and dust. The debris of flakes and dust is subsequently blown clear of the drill bit by exhausted air. The percussion mechanism, i.e. the hydraulic motor, is located directly behind the drill bit. The pipes that form the drill string transmit the necessary feed force and rotation to hydraulic motor and drill bit as well as the compressed air and/or drilling fluid. As understood by one of ordinary skill in the art, the drill pipes are added to the drill string successively behind the DTH assembly as the bore is drilled. A piston in the hydraulic motor strikes the impact surface of the drill bit directly, while the bent sub and hydraulic motor casing work together to provide straight and stable guidance of the drill bit. Advantageously, the impact energy generated in a DTH does not have to pass through the joints of the drill string and, as such, energy is not lost in the various joints. 
     Once the pilot bore is completed in an HDD process, the pilot bore is back reamed. In the back reaming step of a HDD process, the pilot bore may be expanded to a desired diameter and the walls of the bore conditioned for receipt of a product. Back reaming is a part of almost every horizontal directional drilling operation. Typically, to begin the back reaming step, the DTH assembly, or some portion of the DTH assembly, must be decoupled from the drill string so that a back reaming tool may be attached in its place. As described above, the back reaming tool may be pulled back through the pilot bore to enlarge the bore and condition its walls. In many HDD operations, the product to be installed may be pulled back through the bore during the back reaming step by attaching the product to a swivel which is mounted to the back reamer tool. 
     Current systems and methods for horizontal directional drilling are in need of improvement. Returning to the pilot boring step in an HDD process, for example, the accuracy at which the DTH assembly may be steered is not just dependent on the data taken from the sonde assembly but also the accuracy at which the various components of the DTH are connected (i.e., “clocked”) relative to one another. 
     In current HDD systems and methods, one or more sensor/transmitter instruments in the sonde housing is/are orientated relative to the bent sub. As described above, a hydraulic motor (i.e., a “hammer”) is attached to the opposite end of the bent sub. On the opposite side of the hammer from the bent sub, a “slant bit” drill bit is clocked relative to the orientation of the bent sub. Notably, the accuracy at which the drill bit is positioned relative to the bent sub directly affects the steering accuracy during the HDD process. 
     Current drill bits used in HDD systems and methods include 12 or less splines. Notably, because the number of splines on current drill bits is inadequate to accurately clock the orientation of the drill bit on one end of a hammer to the orientation of a bent sub on the other end of the hammer, shims inserted between the chuck and the hammer are often used as spacers to accommodate any misalignment. As one of ordinary skill in the art understands, the use of spacer shims to make up for the inaccuracy at which a drill bit that includes 12 or less splines can be clocked to a bent sub in a DTH assembly can be a tedious and time consuming task because the drill bit must be repeatedly removed, replaced and measured relative to the bent sub until the correct amount of shims is determined. 
     As one of ordinary skill in the art understands, orientation of a drill bit to a bent sub is critical in an HDD process for at least the reason that the sonde sensor/transmitter instrument is clocked to the bent sub and provides data back to the surface that is used to steer the DTH assembly. Notably, therefore, if the drill bit is not accurately clocked to the bent sub, the data associated with the bent sub that is collected by the sonde will not be an accurate representation of the direction at which the drill bit is moving. For example, in a typical HDD process, the information transmitted by the sonde is represented by a “clock” such that “12 o&#39;clock” represents vertically upward, “3 o&#39;clock” represents a right direction, “6 o&#39;clock” represents a downward direction, and “9 o&#39;clock” represents a left direction. In the exemplary system, one of ordinary skill in the art understands that “1 o&#39;clock” represents an upward direction and slightly to the right. Notably, other information measured and transmitted by the sonde may include, but is not limited to including, information representative of relative depth, temperature, battery strength, signal strength, pitch and the like. 
     Returning to the exemplary application of an HDD process, a typical bore length may be 600 feet in distance. If the drill bit is inaccurately clocked relative to the bent sub, the steering of the DTH assembly over the 600 foot length of the bore may be unpredictable and in need of counter steering. For example, while the sonde is transmitting data measured relative to the bent sub that indicates that the bore direction is at 12 o&#39;clock, the inaccuracy at which the drill bit was clocked to the bent sub may be causing the bore direction to actually be more consistent with 1 o&#39;clock. In such a situation, over the 600 foot bore the direction may deviate to the right off of the desired path. To accommodate the misalignment in the exemplary application, the operator of the HDD system must essentially steer back to the left as if the desired bore direction were 9 o&#39;clock , all the while recognizing that the actual drilling direction (because of the misalignment of the bit to the bent sub) is closer to 10 o&#39;clock in order to overcome the directional deviation of the bore. 
     What is needed in the art, therefore, is a drill bit having thirteen (13) or more splines so that the drill bit may be accurately clocked in its position relative to a bent sub orientation. Advantageously, by including 13 or more splines on a drill bit, the need for shims may be reduced or alleviated as the resolution of the positioning of the drill bit relative to a bent sub orientation may be improved to such an extent that directional data associated with the bent sub (and collected by a sonde) may be used to steer a DTH assembly without significant counter steering. 
     Current systems and methods for horizontal directional drilling are also in need of improvement in the step of installing product through a bore. As described above, hammers and drill bits used in DTH assemblies for installing products of the utility industry must be removed from the drill string and replaced with a back reamer. To break the hammer (and drill bit) off the drill string to attach the back reamer may require the use of a back hoe, oil field tongs or other heavy piece of machinery. In some applications, the back reamer may include a swivel for attaching the product and “pulling” the product back through the bore during the back reaming step (the swivel prevents the product from rotating with the drill string during the back reaming step). In addition to pulling the product back through the bore, a back reamer may also be configured to mix fluid with the cuttings and lubricate the product. 
     What is needed in the art is a system and method for pulling product back through a pilot bore without having to replace the DTH assembly with a back reamer device. An embodiment of the invention is a pulling device configured to attach to a drill bit in the field at the exit pit of a pilot bore, thereby alleviating the need to replace the DTH assembly with a back reamer. Essentially, by attaching a pulling device according to an embodiment of the invention to a drill bit configured to receive the pulling device, the drill bit is converted to a back reamer suitable for pulling product sized to fit within the pilot bore. 
     An exemplary embodiment of a pulling device includes a plate component that covers the blow holes of the drill bit and a pair of bolts or pins that extend through the plate into the blow holes. Advantageously, the blow hole pins of the exemplary embodiment may divert drilling fluid and air forward of the drill bit as it is pulled back through the bore to lubricate the product being pulled. The diverted fluid and/or air may also lubricate the hammer assembly during the back boring step. An exemplary blow hole pin that is included in a given embodiment of a pulling device may include four keyway grooves cut on the outside radius of the pin from the bottom up toward the threads. Air forced through the blow holes of the drill bit would be diverted by the plate along the channel on the drill bit and blown back toward the hammer, thereby moving debris and lubricating the hammer as it is being pulled back through the bore. Certain embodiments of a blow hole pin may also have a hole drilled through its center so that air and fluid may be allowed to pass along toward the product being pulled, thereby lubricating the product. In some embodiments, the backside of the plate which mates with the drill bit may be milled to accommodate the contour of the drill bit including any wear buttons. It is further envisioned that certain embodiments may include a pulling eye and/or swivel component for extending from the plate and configured for pulling the product as the drill string is retracted from the bore. 
     Systems, devices and methods of the various inventions have been described using descriptions of embodiments thereof that are provided by way of example and are not intended to limit the scope of the disclosure. The described embodiments comprise different features, not all of which are required in all embodiments. Some embodiments utilize only some of the features or possible combinations of the features. Variations of embodiments that are described and embodiments that comprise different combinations of features noted in the described embodiments will occur to persons of the art. 
     Moreover, it will be appreciated by persons skilled in the art that systems, devices and methods of the inventions are not limited by what has been particularly shown and described herein and above. Therefore, although selected aspects have been illustrated and described in detail, it will be understood that various substitutions and alterations may be made therein without departing from the spirit and scope of the present invention. As such, the scope of the invention is limited only as it may be defined by a claim.