Abstract:
A system and method of drilling. The method may generally include providing a drilling system including a rotary motor operable to rotationally drive a drill bit and providing a supply of compressible drill fluid, the supply producing an operating volumetric flow rate of fluid in a normal operating condition. The rotary motor operates at a rotational operating speed under a first volumetric flow rate of fluid, and the supply provides a volumetric flow rate of fluid greater than the first volumetric flow rate of fluid. The method further includes supplying the first volumetric flow rate of fluid from the supply to the rotary motor, and diverting a portion of fluid flow from the supply through a jet sub.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. provisional patent application 61/408,441 filed 29 Oct. 2010, the entire contents of the disclosure of which is hereby incorporated by reference. 
     
    
     FIELD 
       [0002]    The present invention relates to a down-the-hole (DTH) drill and, more particularly, a DTH drill for directional drilling. 
       BACKGROUND 
       [0003]    In some aspects, the present system and method are related to directional (e.g., horizontal, angled, non-vertical) drilling and/or to continuous drilling (e.g., the drilling operation does not need to be periodically ceased to allow drilling fluid (air) to clear the bore hole). In some existing directional drilling systems, incompressible drill fluid, such as thick mud with polymers, is used to drive a rotary motor. With such a system, cuttings are suspended in the incompressible drill fluid. However, incompressible drill fluid tends to plug pores in the wall of the bore hole such that hydrocarbons cannot drain into the well. 
         [0004]    A compressible drill fluid (e.g., air) does not plug the pores in the wall so that hydrocarbons are able to drain into the well. Because air is compressible, the compressible drill fluid does not suspend the cutting chips which can settle on the low side of the bore hole due to gravity. In order to remove chips and debris, jet subs may be located along the drill string to boost the removal force of the compressible drill fluid. 
         [0005]    A drilling system with a rotary air motor and down-the-hole (DTH) air percussion drill may provide improved drilling. A DTH (percussion) drill cannot operate on incompressible drill fluid because of the expansion cycle of the hammer; air or another gas is necessary for expansion cycle of the hammer. A DTH drill may provide a rate of progress (ROP) that is about 2 to 3 times faster than the ROP for most rotary drill operations using incompressible mud drilling fluid. 
       SUMMARY 
       [0006]    The disclosed system and method relate to earth drilling operations, particularly “underbalanced” drilling, in which the pressure of the drilling fluid, (e.g., a compressible fluid, such as air or a “mist” of air (or nitrogen or natural gas) and water) is lower than the pressure of fluid contained in the drilled formation(s). 
         [0007]    The ability to clear rock cuttings and formation fluid affects drilling productivity, especially when using a rotary air motor and down-the-hole (DTH) air percussion drill. Cuttings and fluid must be effectively and continuously transported up the bore hole (away from the drill face) to avoid increasing borehole (or back) pressure. Back pressure reduces the power output of both rotary motors and DTH drills, which reduces the ROP. This effect may be particularly problematic in directional drilling applications due to the tendency of the solid and liquid components of the ejecta to separate from the air component and collect via gravity on the low side of an angled (non-vertical) or horizontal borehole. Current practice is to periodically cease drilling and allow air to remove the debris from the borehole, which hampers overall productivity of drilling operations. 
         [0008]    In the present system and method of underbalanced drilling, supplemental air is introduced into the ejecta stream to facilitate removal of fluids and solids such that back pressure is reduced at the drill face. This may reduce or eliminate the need to stop drilling to clear debris from the borehole, to thereby improve the productivity of the drill assembly. 
         [0009]    While the present system and method is directed at underbalanced drilling with DTH, this system and method may also be employed with conventional air rotary drilling. This method may also be applicable for other compressible motive drilling fluids, such as nitrogen and natural gas, and may be compatible with drilling foams. The illustrated jet subs are not necessarily intended for use with incompressible drilling fluids, but the system and method can be employed with suitable equipment. 
         [0010]    In one independent embodiment, a method of directional drilling is provided. The method may generally include providing a drilling system including a rotary motor operable to rotationally drive a drill bit and a hammer operable to impart percussive force on the drill bit, providing a supply of compressible drill fluid, the supply producing an operating volumetric flow rate of fluid in a normal operating condition. The rotary motor operates at a rotational operating speed under a first volumetric flow rate of fluid, and the supply provides a volumetric flow rate of fluid greater than the first volumetric flow rate of fluid. The method further includes supplying the first volumetric flow rate of fluid from the supply to the rotary motor, and diverting a portion of fluid flow from the supply through a jet sub. 
         [0011]    In another independent aspect, a method of down-the-drill (DTH) percussive drilling is provided. The method may generally include providing a drilling system including a rotary motor operable to rotationally drive a drill bit and a hammer operable to impart percussive force on the drill bit, providing a supply of compressible drill fluid, the supply producing an operating volumetric flow rate of fluid in a normal operating condition. The rotary motor operates at a rotational operating speed under a first volumetric flow rate of fluid. The method further includes supplying the first volumetric flow rate of fluid from the supply to the rotary motor, and diverting a portion of fluid flow from the supply through a jet sub to facilitate removal of debris from the bore hole. 
         [0012]    Independent aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a schematic illustration of a directional drilling system including a jet sub. 
           [0014]      FIG. 2  is a schematic illustration of a vertical drilling system including a jet sub. 
           [0015]      FIG. 3A  is a cross-sectional side view of a jet sub. 
           [0016]      FIG. 3B  is a cross-sectional side view of the jet sub shown in  FIG. 3A  and illustrating the seal member in the open position 
           [0017]      FIG. 4  is a side view of an alternative jet sub, such as a stabilizer jet sub. 
           [0018]      FIG. 5  is a schematic side view of a portion of a hammer mechanism. 
           [0019]      FIG. 6  is a schematic side view of a portion of an alternative hammer mechanism. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    Before any independent embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other independent embodiments and of being practiced or of being carried out in various ways. 
         [0021]      FIG. 1  illustrates a drilling system  10  for earth drilling operations, particularly “underbalanced” drilling, in which the pressure of the drilling fluid is lower than the pressure of fluid contained in the drilled formation(s). The drilling system  10  generally includes a drilling rig  14  connected to a drill string including a series of pipes  18 , typically in thirty foot ( 30 ′) sections, in a well bore or bore hole H. The illustrated system  10  is used for directional (e.g., horizontal, angled, non-vertical) drilling and includes a vertical section  22 , a non-vertical or lateral section  26 , and a curved section  30  connected between the sections  22 ,  26 .  FIG. 2  illustrates a similar drilling system  10 ′ for vertical drilling operations including only a vertical section  22 ′. 
         [0022]    A bottom hole assembly (BHA)  34  is connected to the remote or bottom end  39  of the drill string. The BHA  34  generally includes a sequence of devices at bottom such as a drill bit B, a hammer or air hammer  100  (shown in greater detail in  FIGS. 5 and 6 ) for percussive driving of the drill bit B, a rotary motor or air motor  110  for rotational driving of the drill bit B, a collar, a stabilizer, a measurement-while-drilling device, etc. One example of a hammer and bit that may be utilized is described in U.S. Pat. No. 5,085,284 to Fu, issued Feb. 4, 1992, the entire contents of the disclosure of which is hereby incorporated by reference. 
         [0023]    In the illustrated construction, the BHA  34  includes an air motor, such as a Moyno® motor manufactured by Moyno, Inc., Springfield, Ohio. The air motor is generally tubular and includes a rubber stator with lobes arranged in a helix and a metal rotor with a helical vane. There is generally one less vane on the rotor or lobe on the stator to facilitate a progressing cavity action in the motor. As motive drilling fluid is supplied to the motor, the rotor turns within the stator. The continuous seal line between the helical vane on the rotor and the helical lobes on the stator keeps the rotor moving steadily at a generally fixed rate proportional to the flow rate of the drilling fluid. In the illustrated system, air flows through the air motor, to the hammer and out of the system (generally at or near the bottom of the bore hole H). U.S. Pat. No. 5,417,281, to Wood et al., issued May 23, 1995, the entire contents of the disclosure of which are hereby incorporated by reference, illustrates an example of a motor that could be utilized. While U.S. Pat. No. 5,417,281 illustrates a mud-operated motor, an air motor has a similar construction. The motor may be connected similarly to the motor connection in U.S. Pat. No. 5,417,281. 
         [0024]    As shown in  FIG. 1 , the system  10  includes in-line jet subs  38  spaced along the length of the drill string. One or more pipes  18  may be provided before each jet sub  38 . One or more jet subs  38  may be provided between adjacent pipes  18  in the drill string. The jet subs  38  may be an integral part of a down-the-hole (DTH) drill or an accessory attached to the DTH. The jet sub  38  may be constructed and manufactured in a manner similar to the device described in U.S. Pat. No. 7,665,549 to Lyon, issued Feb. 23, 2010, which is incorporated by reference in its entirety in this application. 
         [0025]      FIGS. 3A and 3B  illustrate a jet sub  38  in more detail. The illustrated jet sub  38  includes a body  42  defining a central bore  46  and one or more radial passage  50  communicating between the central bore  46  and the outer surface of the body  42 . A threaded portion  54  with an API thread connects to the adjacent component (e.g., a pipe  18 ). 
         [0026]    An annular orifice plate  58  is positioned on the body  42  proximate to and covering the radial passage(s)  50 . The orifice plate  58  is generally a ring and defines a number of discharge ports or jet orifices  62  about the circumference. Each jet orifice  62  is angled to eject flow in a direction toward the upper end of the bore hole H (e.g., in a direction away from the BHA  34 ). The jet orifices  62  are arranged about the circumference of the orifice plate  58  such that, in a directional drilling arrangement (see  FIG. 1 ) and on the lateral section  26  and the curved section  30 , a jet orifice will be on the low side and the high side of the jet sub  38  during rotation of the pipes  18 . The jet orifices  62  are sized for the particular drilling application. 
         [0027]    A check seal  66  is provided for each radial passage  50 . In the illustrated construction, the radial passages  50  are all at the same axial position in the body  42 , and the check seal  66  is in the form of an O-ring extending about the circumference of the body  42  at the axial position of the radial passages. As a result, the single O-ring check seal  66  covers all the radial passages  50  at that axial position. The body  42  defines a recess or groove  70  receiving the check seal  66  in a closed position, in which the check seal  66  resists flow through the radial passages  50 . An annular space  74  is formed between the outer surface of the body  42  and the inner surface of the orifice plate  58 . A relief area or recess  78  is provided in the orifice plate  58 . The check seal  66  is movable toward and into the recess  78  to an open position, in which the radial passages  50  are uncovered such that fluid can flow from the central bore  46 , to the annular space  74  and out through the jet orifices  62 . 
         [0028]    A retainer arrangement  82  is provided between the body  42  and the orifice plate  58  to axially retain the orifice plate  58  on the body  42  at least during assembly. In the illustrated construction, the retainer arrangement  82  includes an O-ring between the body  42  and the orifice plate  58  providing a retaining force to hold the orifice plate  58  on the body  42 . The O-ring may also provide a sealing arrangement between the body  42  and the orifice plate  58 . When the jet sub  38  is assembled with an adjacent component (e.g., a drill pipe  18 , the BHA  34 ), the orifice plate  58  is axially captured between a shoulder  86  on the body  42  and an axial end surface  90  of the adjacent component. 
         [0029]    The jet sub  38  shown in  FIG. 3  is generally adapted for installation at a desired distance above the DTH.  FIG. 4  illustrates a stabilized version of a jet sub  38 ′ which is normally placed immediately above the bottom hole assembly (BHA)  34 . In this construction, the jet sub  38 ′ also includes stabilizing ribs or blades  94  which are engageable with the sides of the bore hole H to generally stabilize, center, straighten, etc., the jet sub  38  and adjacent component(s) (e.g., the BHA  34 , a drill pipe  18 ). The blades  94  are arranged in a “thread-like” manner about the body  42 ′ to provide 360° support against the wall of the bore hole H and to provide a passage for debris and chips. The blades  94  may also transmit debris through the “thread” and auger the material chips toward the top of the bore hole H. 
         [0030]    Each jet sub  38 ,  38 ′ is generally manufactured by forming the body  42  and forming the radial passage(s)  50  with the desired size, shape, etc. The check seal  66  is positioned on the body  42  (in the groove  70 ). The check seal  66  can prevent the introduction of debris to the inside of the drill string when air flow stops. The orifice plate  58  is then positioned over the check seal  66 . The retainer O-ring provides a frictional force to hold the orifice plate  58  in position on the body  42 . The assembled jet sub  38 ,  38 ′ may then be assembled to the adjacent components (e.g., drill pipe  18 , BHA  34 , etc.). 
         [0031]    The drilling system  10  also includes a supply  98  of motive fluid or drilling fluid. In the present system and method, the drilling fluid is a compressible drilling fluid, such as air or a “mist” of air (or nitrogen or natural gas) and water. The supply  98  generally includes one or more compressors (not shown) and is operable under normal operating conditions to supply drilling fluid at a volumetric flow rate. The flow rate of the supply  98  depends on the conditions of the drilling operation/bore hole H. In an example of a 6¼″ bit B/bore hole H, the supply  98  provides a volumetric flow rate between 1200 cfm to 3510 cfm. The supply  98  has sufficient capacity of motive fluid for DTH and the jet subs  38 . 
         [0032]    The air motor of the BHA  34  is operated under normal operating conditions at a rotational operating speed. The speed depends on the size of the bit B, and, in the example of the 6¼″ bit B/bore hole H, the rotational speed of the air motor is generally between 45 rpm to 55 rpm (e.g., 48 rpm). In order to achieve this speed, the supply  98  supplies about 1100 cfm to the air motor. 
         [0033]    If the motor is operated at a higher speed (e.g., by an increased fluid supply), the rotor may rotate too fast causing an increase in friction/heat which could damage the motor (e.g., melt rubber stator). In the illustrated construction, rather than throttling down the supply  98  to supply fluid at this lower volumetric flow rate (of only about 1100 cfm) to the air motor, the fluid supply  98  is operated to supply its higher volumetric flow rate (e.g., 1200 cfm to 3510 cfm), and the excess motive fluid (bypass flow) is used with/diverted through the jet sub(s)  38 . Typically, the flow pressure is greater than a pressure needed to operate the motor and hammer. The increased flow is bypassed through the jet sub(s) to increase up hole (or bailing) velocity in the borehole annulus to more reliably remove drilled solids and fluid from the hole. According to one example, the flow pressure is 350 psi. Because the supply  98  has sufficient capacity of motive fluid for DTH and the jet subs  38 , additional booster compressors (providing 700 psi to 1100 psi) are not required in the drilling system  10 , potentially resulting in equipment and fuel savings. 
         [0034]    One or more jet subs may always be open whenever air is flowing. Typical operating pressures range from 200 psi to 1000 psi or higher, depending on downhole conditions. Most drilling is done around 300 to 500 psi. The jet sub(s) may be adjusted for flow at the expected pressures by changing the diameters of the holes  62 . The holes are often supplied as partially drilled, with a desired diameter being drilled on site when a job is set up. As air is bypassed through successive jet subs, the pressure will drop based on the remaining flow in the drill string. 
         [0035]    The bypass flow through each jet sub  38  may be between 300 cfm to 1100 cfm, depending on the number of jet subs  38  and the flow rate of the supply  98 . In some constructions, the bypass flow may be equally divided between the jet subs  38 . In other constructions, the bypass flow may be higher for certain jet sub(s)  38  than others based on the requirements of the drilling system  10 . The bypass flow through the jet sub(s)  38  will usually be selected/determined when the drill string is set up. 
         [0036]    In the drilling system  10 , the hammer, when activated, will typically consume about 1100 cfm at 350 psi. The hammer flow is discharged through the system  10  generally at or near the bottom of the bore hole H. With the compressible drill fluid, this discharged flow may not be sufficient to clean the bore hole H. The fluid supply through the jet subs  38  compensates for reduced fluid flow at the bottom of the bore hole H through the BHA  34  to facilitate removal of debris from the bore hole H. 
         [0037]      FIGS. 5 and 6  illustrate an example of a hammer that may be utilized. The hammer  100  includes a casing  104 . The casing surrounds the other elements of the hammer, which include a cylinder  106 . A piston  108  is arranged within the cylinder. The upper half of  FIGS. 5 and 6  illustrates the cylinder in a drilling position while the lower half illustrates an off, bottom position. The hammer also includes an air distributor  110 . 
         [0038]    When the hammer is inactivated, for example, when the bit B is disengaged from the bottom of the bore hole H, the flow  103  bypasses the hammer. In this condition, there is an instantaneous change in the fluid flow resulting in a significant drop in the pressure (e.g., of about 250 psi (from 350 psi to 100 psi)) in the system  10 . This change can cause an instantaneous increase in the rotational speed of the rotary air motor, potentially damaging the motor. In order to limit the change in air pressure (e.g., of about 50 psi (from 350 psi to about 300 psi)) in the system  10 , the hammer bypass port or orifice  102  (see  FIG. 6 ) is reduced in size (when compared to the hammer bypass port  102 A shown in  FIG. 5 ) to restrict the flow bypassing the hammer. This restriction arrangement on the hammer bypass may improve operation and durability of the air motor. 
         [0039]    Incompressible liquid, such as water, is generally not compatible with an air hammer. The drilling system  10  also includes a hydro-cyclone or water separator (not shown) operable to remove and expel incompressible liquid (e.g., water) from the compressible drilling fluid (e.g., air) before the air goes through hammer of the BHA  34 . A suitable water separator for the drilling system  10  is shown and described in U.S. Pat. No. 5,862,957, attached the entire contents of which are hereby incorporated by reference. 
         [0040]      FIG. 1  schematically illustrates the general arrangement of the drilling system  10  applied to the directionally-drilled well bore hole. In this arrangement, the jet subs  38  are placed in the lateral section  26  and the curved section  30  of the bore hole H. Conveniently, the jet sub  38  deployed nearest the bottom hole assembly (BHA)  34  can be of the stabilized variety (jet sub  38 ′) to maintain the drill string centered in the bore hole H for drilling accuracy. The stabilizer blades  94  are a type providing 360 degrees of contact with the sides of the bore hole H, but any suitable stabilizer configuration can be used. 
         [0041]    In the illustrated drilling system  10 , the jet subs  38 ,  38 ′ are placed at approximately equal intervals and in sufficient number to prevent significant accumulation of drilled solids on the lower wall of the lateral section  26  and/or curved section  30  of the bore hole H. In certain situations, two or more jet subs  38  may be deployed in close proximity to maximize removal of ejecta at critical points in the trajectory of the bore hole H (e.g., where debris is most prone to accumulating or where the shape and size of the bore hole H causes excessive pressure drop). The size and/or number of the discharge ports or jet orifices  62  may also be increased to provide a greater flow. Similarly, where there is not a need to maximize removal of ejecta, fewer jet subs, fewer discharge ports or jet orifices, and/or discharge ports or jet orifices having smaller diameters could be employed. The shape of the discharge ports or jet orifices  62  could also be adjusted. The jet sub orifice holes typically are sized for expected ranges of bypass requirements for different basic sizes of drills. The maximum bypassed flow may be controlled by the set of holes at the base of the pin thread in the jet sub body. The minimum flow bypassed and flow rates lower than the maximum may be controlled by the size and number of holes drilled in the orifice plate. The size, shape, number of discharge ports or jet orifices may be adjusted such that air flow in excess of the flow needed to run the motor and hammer may be diverted into the hole annulus for clearing drilled solids and fluids. 
         [0042]    According to one embodiment for drilling a 6.25″ hole, the jet subs include six holes. The size of each hole is 0.19″ and the bypass flow at 350 psi is 750 scfm. According to another embodiment for drilling a 8.875″ hole, the jet subs include six holes. The size of each hole is 0.31″ and the bypass flow at 350 psi is 1800 scfm. According to a third exemplary embodiment for drilling 12.25″ hole, the jet subs include eight holes. The size of each hole is 0.44″ and the bypass flow at 350 psi is 4500 scfm. 
         [0043]      FIG. 2  schematically illustrates the general arrangement of the drilling system  10 ′ applied to a vertical well bore hole H′. The jet subs  38 ,  38 ′ are assembled into the drill string at selected locations and intervals, determined by such factors as hole depth, formation fluid intrusion zones, the amount of drilling fluid (e.g., air) available to operate the DTH and bypass through the jet subs  38 ,  38 ′. Generally, the jet subs  38 ,  38 ′ will be placed at approximately equal intervals in the drill string, and the number of jet subs  38 ,  38 ′ deployed is determined by the condition of the well bore. Under testing in vertical bore, the drilling system  10 ′ with the DTH and the jet subs provides a 10% improvement in drilling performance. 
         [0044]    In the present method of underbalanced drilling, supplemental air is introduced into the drill string and through the jet subs  38 ,  38 ′ into the ejecta stream to facilitate removal of fluids and solids such that back pressure is reduced at the drill face. This may reduce or eliminate the need to stop drilling to clear debris from the borehole, to thereby improve the productivity of the drill assembly  10 ,  10 ′. 
         [0045]    While the present system and method are directed at underbalanced drilling with DTH, the system and method may also be employed with conventional air rotary drilling. Compressible motive drilling fluids other than air, such as nitrogen, natural gas, etc., and drilling foams may also be used. 
         [0046]    Thus, the invention may generally provide, among other things, a directional drilling system and method including a DTH drill and jet subs through which excess compressible drill fluid from the supply is diverted. The invention may also generally provide, among other things, a directional drilling system and method including a DTH drill and jet subs through which compressible drill fluid from the supply is diverted to facilitate removal of debris from the bore hall. Various independent features and independent advantages of the invention are set forth in the claims.