Abstract:
A sonde assembly of the invention includes a sonde housing in the form of a nonmagnetic tube having windows therein for permitting a radio signal to be transmitted out the tube from the inside, means such as a device enclosing a front end of the tube, a sonde disposed inside the non-magnetic tube and closely fitting in a sonde cavity thereof in engagement with a front end plug. The sonde comprises a sensor and a transmitter connected to the sensor to transmit a directional signal based on sensor output, which sensor and transmitter are disposed inside a non-magnetic sonde cavity.

Description:
[0001]    This application is a continuation of U.S. patent application Ser. No. 12/653,282, filed Dec. 10, 2009, which claims priority of U.S. provisional application Ser. No. 61/1201,394 filed Dec. 10, 2008, and the entire contents of each are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to directional drilling systems, and more specifically to a sonde used to transmit information concerning a drill head used in directional drilling. 
       SUMMARY OF THE INVENTION 
       [0003]    The present invention is directed to a sonde assembly. The sonde assembly comprises a sonde housing comprising a non-magnetic tube, the tube forming a non-magnetic sonde cavity, a front plug for enclosing a front end opening of the non-magnetic sonde cavity, and a sonde slidingly disposed inside the non-magnetic sonde cavity. The sonde comprises a sensor and a radio transmitter connected to the sensor to transmit a directional sensor based on sensor input. The sonde assembly further comprises a rear end cap securable in a fixed position in a rear end opening of the non-magnetic sonde cavity. Upon securing the rear end cap in a rear end opening of the sonde housing, the sonde is secured in a fixed position relative to the sonde housing. 
         [0004]    The present invention is also directed to a second embodiment of a sonde assembly. The sonde assembly comprises a sonde housing in the form of a non-magnetic tube, the tube forming a non-magnetic sonde cavity, a means for enclosing a front end opening of the non-magnetic tube, and a sonde slidingly disposed inside the non-magnetic sonde housing. The sonde comprises a sensor and a radio transmitter connected to the sensor to transmit a directional sensor based on sensor input. The sonde assembly further comprises a means for enclosing the rear end opening of the non-magnetic sonde housing. Upon securing the rear end opening of the non-magnetic sonde housing, the sonde is secured in a fixed position relative to the non-magnetic sonde housing. 
         [0005]    The present invention is further directed to a third embodiment of the sonde assembly. The sonde assembly comprises a sonde housing in the form of a non-magnetic tube, a front plug for enclosing a front end opening of the non-magnetic tube, a sonde slidingly disposed inside the non-magnetic tube, and a rear end cap securable in a fixed position in a rear end opening of the non-magnetic tube. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a side view of a drill head having a sonde assembly of the invention. 
           [0007]      FIG. 2  is a lengthwise sectional view of the drill head of  FIG. 1  along the line  2 - 2  in  FIG. 1 . 
           [0008]      FIG. 3  is an enlarged view of the circled area  3  in  FIG. 2 . 
           [0009]      FIG. 4  is an enlarged view of the circled area  4  in  FIG. 2 . 
           [0010]      FIG. 5  is an enlarged view of the circled area  5  in  FIG. 4 . 
           [0011]      FIG. 6  is a partial side view of a sonde assembly of the invention. 
           [0012]      FIG. 7  is an end view of the rear end cap of the sonde assembly of  FIG. 6 . 
           [0013]      FIG. 8  is a top view of the sonde assembly of  FIG. 6 . 
           [0014]      FIG. 9  is a side view partly in section, of the sonde assembly of  FIG. 6 . 
           [0015]      FIG. 10  is an enlarged view of the circled area  10  in  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Horizontal directional drilling (“HDD”) has become an effective and efficient method of installing or rehabilitating utilities with minimal surface disruption. However, accurate placement of utilities in HDD tends to require accurate tracking of a drill head as it progresses along a borepath. Thus, several methods of tracking have developed over time. One such method of tracking is called “walkover tracking”. Walkover tracking uses a wireless signal beacon disposed underground proximate or within the drill head and an above-ground tracker used to detect a signal transmitted from the beacon. The signal is used to determine the location and orientation of the drill head. Another method of tracking the drill head utilizes a wireline transmitter. 
         [0017]    Wireline sondes (transmitters) are capable of reading the earth&#39;s magnetic field rather than gravity. These systems are capable of use underneath busy streets, rivers or other locations where a walkover transmitter may be imperiled by traffic, need for a boat, or the signal may be affected by the existence of steel rebar between the receiver and the transmitter. One potential drawback to the use of a wireline sonde is that they are generally required to be located at a distance (preferably at least about 10 feet) from any magnetic item, including alloy steel making up the housing or drill pipe. Steel alloys commonly used to make sonde housings are sufficiently magnetic to prevent the sonde from sensing the earth&#39;s magnetic field accurately. To remedy this, non-magnetic variations of stainless steel can be used. 
         [0018]    Non-magnetic variations of stainless steel, however, can be difficult to fabricate into tooling because they have a low machinability rating. Thus, end load housings have been developed because of their simplicity of design. As used herein “end load housing” means the drill stem may be disconnected from the housing to access the sonde for loading/unloading through the end of the housing. End load housings normally restrain and clock the sonde relative to the housing with a slot in the sonde to engage a tabbed feature within the housing. The sonde is then trapped from the opposite end with a plug which maintains the tab/slot engagement and therefore the clock orientation of the sonde relative to the housing. 
         [0019]    The action of finding and engaging the slot and the tab is risk prone as it cannot be inspected at the bottom of its blind bore, a bore possibly contaminated with dried mud. Should this engagement not be accomplished, the sonde will drift in clock position during operation and the drill head orientation signals from the sonde will be inaccurate. Inaccurate orientation readings may cause the drill head to deviate from the desired borepath. 
         [0020]    Turning now to the Figures, and more specifically  FIG. 1 , there is shown therein a sonde assembly  100  of the present invention. The sonde assembly  100  is constructed, as described herein, to reduce the risk of not engaging a housing tab into the sonde slot by rigidly bolting the sonde to a plug which threadedly retains the sonde within the housing. 
         [0021]    The sonde assembly  100  of  FIG. 1  comprises a drill bit  12  and a sonde housing  14 . The drill bit  12  may comprise a slant-faced steering bit. The slant-faced bit  12  may comprise a conventional flat bill made of non-magnetic steel. A plurality of bolts  15  are used to secure the bit  12  to the housing  14 . The bit  12  is used to bore through the ground; it should be appreciated that a variety of drill bits could be used with the current invention including drag bits, rotary bits and back reamers. 
         [0022]    The sonde housing  14  comprises a non-magnetic housing  17  having a cavity  18  ( FIG. 2 ). The cavity  18  is vented to the outside ground pressure through at least one window  16 . Window  16  permits a directional signal to be transmitted from inside the non-magnetic housing  17 . These windows  16  may be open, or they may be sealed with putty that will yield and leak should sufficient differential pressures develop between the cavity  18  and the adjacent soil. 
         [0023]    Wireline  19  is shown extending from the up hole end of housing  17  and may extend to the surface along the drill string (not shown). As shown in  FIG. 2 , the wireline  19  is connected to the sonde  34  and passes through a yet to be described rear end plug  32 . 
         [0024]    Turning to  FIG. 2 , the sonde assembly  100  of  FIG. 1  is shown in a longitudinal section view. The drill a bit adapter  20  is shown supporting dill bit  12  and connected to housing  17 . The bit adapter  20  is used to support the drill bit  12  relative to the housing. The bit adaptor  20  shown in  FIG. 2  comprises an angled face  21  for mounting the bit at an angle relative to a central axis  23  ( FIG. 1 ) of the housing  17  to facilitate steering. One skilled in the art will appreciate that the bit adaptor  20  may comprise a threaded portion (not shown) at its downhole end to facilitate the connection of a rotary bit or backreamer to the housing  17 . Alternatively, the bit adaptor  20  may have a drill bit  12  formed integrally therewith. 
         [0025]    The bit adapter  20  may comprise threads  22 , shown more clearly in  FIG. 3 , at its up hole end for connecting the bit adaptor to the housing  17 . The bit adapter  20  has a central fluid passage  24  and a discharge nozzle  26  to meter drilling fluid or mud from the downhole end of the adaptor  20 . Alternatively, one skilled in the art will appreciate passage  24  may be operatively connected to a fluid passage formed in the drill bit  12  such that said fluid is expelled from the bit itself. Both the bit adapter  20  and housing  17  are preferably made of a non-magnetic metal (steel) for use in the present invention. 
         [0026]    Continuing with  FIG. 2-5 , the housing  17  has at least one fluid passage  28  that direct the drill fluid or mud along the housing  17  to the bit adaptor  20  and around the cavity  18 . One such passage  28  is shown below the cavity  18  in  FIG. 2 . One skilled in the art will appreciate that a plurality of passages may be disposed about the housing without departing from the spirit of the present invention. Such passages may be arranged in a circular formation around the periphery of the cavity  18 . 
         [0027]    Cavity  18  is sealed from the flow of pressurized mud via a front plug  30  and a rear end cap  32 . The front plug  30  attaches to the front end opening  31  of the cavity  18  and encloses the front end opening. The rear end cap is securable within the rear end opening  33  of the cavity  18 . A sonde  34  is disposed within the cavity  18  and engages the front plug  30  and the rear end cap  32  at opposite ends. The sonde  34  comprises a sensor (not shown) and a transmitter (not shown) connected to the sensor. The sonde  34  may be formed inside of a non-magnetic tube  43 . The transmitter may comprise a radio signal transmitter adapted to transmit a directional signal based on a sensor output. The front plug  30 , shown more clearly in  FIG. 3 , comprises an O-ring  36  and an elastic isolator  38  to help seal and cushion the sonde  34  from shock. As shown in  FIG. 9 , the end plug comprises a non-ferrous component having a series of threads  60  for threading the plug into the cavity  18  of the housing  17 . An elastic isolator  38  is positioned between the sonde  34  and the plug  30  to absorb shock during drilling operations. A sleeve  62  is formed to support the isolator  38 , plug  30  and sonde  34 . The sleeve  62  comprises a cavity  64  formed to support the sonde  34  therein. 
         [0028]    The sensor may comprise an orientation sensor package adapted to detect the roll, pitch and/or yaw orientation of the sonde assembly. Accordingly, the sensor may comprise a sensor that senses the magnetic field of the earth such as a magnetometer. The sensor may alternatively comprise at least one accelerometer. The sensor generates an output signal indicative of an orientation component of the sonde  34  and housing  17  and transmits said output to the transmitter. The transmitter, in turn, embeds or encodes orientation information onto a communication signal that is transmitted above-ground. 
         [0029]    Referring now to  FIGS. 6-9  in addition to  FIGS. 2-5 , the rear end cap  32  is securable in a fixed position in the rear end opening  33  ( FIG. 4 ) of the cavity  18 . The rear end cap  32  comprises a rear plug  40 , a flange  42 , and a connector  44 . The rear plug  40  extends into the cavity  18  and creates a tight seal via threads  48  and an O-ring  50  ( FIG. 4 ) supported in an O-ring groove. The flange  42  is connected to the connector  44  and the sonde  34 . The flange  42  has a hole (not shown) therein used to connect the flange to the tube  43 . The non-magnetic tube  43  that houses the sensor and transmitter further comprises rearwardly opening holes (not shown) that align with the holes in the flange  42 . At least two bolts  52  ( FIGS. 6 &amp; 8 ) are used to secure the rear end cap  32  to the non-magnetic tube  43 . The bolts  52  are preferably located 180 degrees apart. Connection of the flange  42  to the non-magnetic tube  43  may seal the sonde  34  to prevent pressurized fluid from entering the sonde.  FIGS. 5 and 10  show the flange  42  connected to the tube  43 . As bolts  52  are tightened to bias the flange  42  toward the tube  43 , an O-ring  53  compressed to seal the sonde where the wireline  19  enters the sonde tube  43 . 
         [0030]    The attachment of the rear end cap  32  to the sonde  34  and cavity  18  is considered a semi-permanent installation, removable to service the cavity  18 , sonde  34 , or front plug  30 . The front plug  30  and rear plug  40  also seal a data transmission line wireline  19  ( FIG. 5 ) which extends from the rear of the sonde  34  and continues through the length of the drill stem up to the machine (not shown). The data transmission line  19  works to transmit the directional signal and other information from the sonde  34  up to the operator regarding the position, operation, and condition of the sonde assembly  100 . 
         [0031]      FIGS. 6-9  show the sonde  34  with front plug  30  and rear end cap  32  connected on opposite ends. As shown in  FIGS. 2-4 , the sonde  34  is secured within the housing  17  using front plug  30 , and rear end cap  32  via threads. The rear end cap  32  is attached to the housing via threads  48 . As shown in  FIG. 7 , the rear end cap  32  comprises three geometric shaped holes  66  adapted to receive a correspondingly formed geometric tool used to rotate the rear end cap  32  to thread it into the cavity  18  to isolate the sonde  34  from the flow of fluid through the housing  17 . 
         [0032]    The front plug  30  remains in place sealing the front end opening  31  of the cavity  18  while the rear end cap  32  seals the rear end opening  33  of the cavity  18  and secures the sonde  34  in place within the non-magnetic housing  17 . By this means the sonde  34 , housing  17 , front plug  30 , and rear end cap  32 , rotate as a unit. 
         [0033]    While certain embodiments of the invention have been illustrated for the purposes of this disclosure, numerous changes in the method and apparatus of the invention presented herein may be made by those skilled in the art, such changes being embodied within the scope and spirit of the present invention as defined in the appended claims.