Patent Publication Number: US-7588099-B2

Title: Horizontal drilling system with oscillation control

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
   This application claims priority to U.S. Provisional Application No. 60/762,698, filed Jan. 27, 2006, the disclosure of which is incorporated herein by reference. 

   FIELD OF THE INVENTION 
   This invention relates to a horizontal drilling system having an automated oscillation control system, and more particularly to an oscillation control system that reverses directions when a torque limit is exceeded and/or a drilling motor stalls. 
   BACKGROUND OF THE INVENTION 
   A well-known phenomenon in directional drilling is that hole friction dramatically increases if a horizontal drilling segment is required. That is, static friction (drag) occurs between the mud motor, drill collars, and drill pipe, and the casing and/or open hole. This high friction is caused by the drill string bearing against the bottom side of the hole. Increases in frictional forces are also frequently observed when the drill string tool joints are pushed laterally through the hole. This static friction can cause misleading indications of weight on bit, string weight and down-hole torque making automated control of the drilling process difficult, if not impossible. 
   To reduce this misleading information, a drilling operator will vibrate or wiggle the drill string to cause it to slide within the hole. One way to vibrate the string is to rotate the drill string back and forth, a motion commonly referred to as oscillating the drill string. Oscillating the drill string causes the drill string to momentarily lift up in the hole thereby reducing the lateral friction. However, oscillating the drill string requires relatively rapid reversals of the drill string rotation. According to one method, such an oscillation of the drill string is done manually by the drilling operator using standard operator controls found on many conventional top drive systems. To perform the oscillation, the operator lowers the motor torque limit and rotates the drill string in a clockwise direction at a low RPM until the drill string stalls or winds-up. The direction of rotation is then changed causing the drill string to unwind and then stall or wind-up in the opposite direction. This procedure is repeated by the operator until the frictional forces are reduced. 
   However, this manual operation relies on the operator&#39;s skill and experience to set parameters and operate the controls correctly. Such a process is also relatively slow, and in some cases causes rapid wear on the motor brakes and drive components because of the non-automated nature of the process. Accordingly, a need exists for a horizontal drilling system having an improved and/or automated oscillation control system. 
   SUMMARY OF THE INVENTION 
   With the advent of top drive control systems (TDCS), AC motors, and variable frequency drives (VFD) the operator intensive procedure described above can be automated according to the present invention and enhanced to provide more accurate and smooth oscillation control during horizontal drilling with minimal machine wear. Utilizing the TDCS and VFD each unit can be programmed and/or parameterized to perform this function in a smooth and efficient manner. Using the system and method of the present invention, operational parameters can be monitored during operation, drill string stall can be detected, and string direction can be changed in a controlled manner. All of which will minimize drive component wear while enhancing the operation. 
   In one embodiment, the present invention is a horizontal drilling system that includes a top drive system having a motor that transmits a torque to a drill string to rotate the drill string. An automated controller is operably connected to the top drive to send at least one command signal to the top drive to initiate the rotation of the drill string. The top drive generates either a torque feedback signal indicating that a torque limit on the drill string is exceeded and/or a turn feedback signal indicating that the drill string is stalled. The controller receives the feedback signals and reverses the direction of the torque applied to the drill string when either the torque limit is exceeded or the drill string stalls. 
   In another embodiment, the top drive is an electric motor. In such an embodiment where the electric motor is a DC motor, the motor controller controls the speed of the electric motor by controlling the voltage applied, and regulates the amount of torque that can be applied by the electric motor by regulating the amount of current supplied to the electric motor. 
   In yet another embodiment, the electric motor is an AC motor. In such an embodiment, the controller regulates the torque and speed of the AC motor by regulating the frequency of the power supplied to the AC motor. 
   In still another embodiment, the controller sets the direction of rotation of the electric motor, through an appropriate means, such as a directional switch for reversing the direction of rotation of the electrical motor. 
   In still yet another embodiment, the torque feedback signal is determined by the electrical current flowing through the electric motor. 
   In still yet another embodiment, the electric motor may also be mechanically coupled to a turn encoder for monitoring the amount of rotation of the electric motor. In such an embodiment, a rotational feedback signal is generated when the turn indicator detects that the electric motor has ceased to rotate, or has “stalled.” 
   In still yet another embodiment, operational parameters may be input through a control station to set the programming instructions for the controller. In such an embodiment, the operator may input specific operating parameters for the controller to follow during an oscillation procedure, such as a torque limit for both the clockwise and counter-clockwise directions; and/or a rotation speed for both the clockwise and counter-clockwise directions. The torque limit may be the same in both the clockwise and counter-clockwise directions, or the torque limit may be different in the two directions. 
   In still yet another embodiment, the controller includes a processor having a central processing unit (CPU), a memory cache, and a bus interface. In such an embodiment, the bus interface is operatively coupled via a system bus to a main memory and an input/output (I/O) interface control unit. The I/O interface control unit is operatively coupled via I/O local bus to a storage controller, and an I/O interface for transmission and reception of signals to external devices. The storage controller is operatively coupled to a storage device for storage of the programming instructions. 
   In still yet another embodiment, the current invention is directed to a drill string oscillation procedure. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features and advantages of the present invention will be better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
       FIG. 1  is a schematic of a horizontal drilling system having a controller for controlling an oscillation procedure of a drill string in accordance with an exemplary embodiment of the present invention; 
       FIG. 2  is a schematic of portions of the horizontal drilling system of  FIG. 1 , shown enlarged; 
       FIG. 3  is a block diagram of the horizontal drilling system in accordance with an exemplary embodiment of the present invention; and 
       FIG. 4  is a block diagram of a controller in accordance with an exemplary embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   As shown in  FIGS. 1-4 , embodiments of the present invention are directed to a horizontal drilling system having a controller for controlling an oscillation procedure of a drill string, whereby the drill string is rotated in a back and forth motion. In one embodiment, the oscillation is controlled by reversing the direction of rotation of the drill string each time a torque limit is exceeded and/or when the drilling motor stalls. 
     FIG. 1  is a schematic view of a horizontal drilling system  10  in accordance with an exemplary embodiment of the present invention. As shown in  FIG. 2 , the horizontal drilling system  10  includes a top drive system  12 . The top drive system  12  is vertically movable along vertical supports  14  of a derrick  16 . The top drive system  12  includes a top drive motor  18 , which imparts translational and rotational forces to a drill string  20 . In one embodiment, the top drive system  12  is connected to a pipe running tool  22 , which in turn is connected to the drill string  20  to transfer the translational and rotational forces from the top drive system  12  to the drill string  20 . As shown in  FIG. 1 , the drill string  20  includes a horizontal segment  24  that produces a horizontal hole during a horizontal drilling operation. 
   As shown schematically in  FIG. 2 , the top drive system  12  is operably connected to a controller  26 . The controller  26  is used to control the top drive system  12  during both the drilling phases and the oscillation phases of a horizontal drilling procedure. As shown in  FIG. 2 , the top drive system  12  receives command signals  28  from the controller  26  and responds to the command signals  28  by generating a torque and a rotational speed that are applied to the drill string  20 . 
   During operation, the top drive system  12  generates feedback signals  30  that are transmitted to the controller  26 . The feedback signals  30  include a torque feed back signal and a rotational feed back signal. The controller  26  uses the feedback signals  30  to monitor the operation of the top drive system  12  during both drilling and oscillation procedures. The functions of the controller  26  are specified by a set of programming instructions  32  located in the controller  26 . 
     FIG. 3  is a block diagram of the horizontal drilling system  10  in accordance with an exemplary embodiment of the present invention. In such an embodiment, the horizontal drilling system  10  includes the top drive system  12  and the controller  26  as previously described. In addition, the horizontal drilling system  10  may include a motor controller  100  operatively connected to the top drive motor  18 , which in one embodiment is an electric motor. 
   In one such embodiment, using a DC motor, the motor controller  100  receives high voltage/high current AC power  106  from an AC power supply  108 , and transfers the AC power into regulated and controlled DC power for the electric motor  18 . The electric motor  18 , in turn, receives the DC power and supplies a torque to the top drive system  12 , which in turn, is transferred to the drill string  20 . 
   The motor controller  100  controls the speed of the electric motor  18  by controlling the voltage applied to the electric motor  18 , and regulates the amount of torque that can be applied by the electric motor  18  by regulating the amount of current supplied to the electric motor  18 . Although only a DC motor is described above an AC motor could also be used. In such an embodiment, the controller would regulate the torque and speed of the AC motor by regulating the frequency of the power supplied to the AC motor. 
   In one embodiment, the command signals  28  as described above include a directional command signal  110 , a torque limit signal  112  and a speed command signal  114 . In this embodiment, the motor controller  100  receives the directional command signal  110  transmitted by the controller  26  and responds to the directional command signal  110  by setting the direction of rotation of the electric motor  18 . The electrical motor  18  may also have a directional switch  104  for reversing the direction of rotation of the electrical motor  18 . 
   In this way, the controller  26  of this embodiment may control the rotational direction of the drill string  20  by generating a directional command signal  110  and transmitting the directional command signal  110  to the motor controller  100 . 
   In such an embodiment, the motor controller  100  may also receive the torque limit signal  112  transmitted by the controller  26 . The motor controller  100  of this embodiment uses the torque limit signal  112  to regulate the maximum amount of current supplied to the electric motor  18 . Since the maximum amount of current supplied to the electric motor  18  determines the maximum amount of torque that can be applied by the electric motor  18  to the drill string  20 , the controller  26  limits the amount of torque that can be applied by the electric motor  18  to the drill string  20 . 
   The motor controller  100  may also receive the speed command signal  114  transmitted by the system controller  26 . The motor controller  100  of such an embodiment uses the speed command signal  114  to regulate the voltage/frequency supplied to the electric motor  18 . Since the rotational speed of the electric motor  18  is determined by the voltage/frequency supplied to the electric motor  18 , the controller  26  determines the rotational speed that the electric motor  18  imparts of the drill string  20 . In one embodiment, the motor controller  100  may also include a Silicon Controlled Rectifier (SCR) independently regulating the current and voltage (or frequency) supplied to the electric motor  18 . 
   In one embodiment, the feedback signals  30  as described above include a torque feedback signal  116 . In this embodiment, the motor controller  100  generates the torque feedback signal  116  and transmits the signal to the system controller  26 . The torque feedback signal  116  is proportional to the electrical current flowing through the electric motor  18  and is thus proportional to the torque applied by the electric motor  18 . The controller  26  uses the torque feedback signal  116  to monitor the amount of torque applied to the drill string  20  by the electric motor  18 . 
   In one embodiment, the electric motor  18  may also be mechanically coupled to a turn encoder  118 . In such an embodiment the turn encoder  118  monitors the amount of rotation of the electric motor  18 , and sends a rotational feedback signal  120  to the controller  26  when the electric motor  18  has ceased to rotate, or has “stalled.” 
   In one embodiment, an operator inputs operational parameters into a control station (not shown) to set the programming instructions  32  of the controller  26 . For example, the operator may input specific operating parameters for the controller  26  to follow during an oscillation procedure, such as a torque limit for both the clockwise and counter-clockwise directions; and/or a rotation speed for both the clockwise and counter-clockwise directions. The torque limit may be the same in both the clockwise and counter-clockwise directions, or the torque limit may be different in the two directions. 
   With these parameters inputted, an oscillation procedure may be initiated. When the oscillation procedure is initiated, the controller  26  transmits command signals  28  to the top drive system  12  to initiate a rotation of the drill string  20  in an initial direction, for example the clockwise direction. During the rotation, the motor controller  100  monitors the torque applied to the drill string  20  and generates torque feedback signals  116  that are transmitted to the controller  26 ; and the turn encoder  118  monitors the amount of rotation of the drill string  20  and generates rotational feedback signals  120  that are transmitted to the controller  26 . 
   When either the torque feedback signal  116  transmits a signal signifying that the torque limit for the clockwise direction has been exceeded; or the rotational feedback signal  120  transmits a signal signifying that drill string  20  has ceased to rotate (i.e., the motor  18  has stalled), the direction of rotation of the drill string  20  is reversed to the counter-clockwise direction. 
   As with rotation in the clockwise direction, the controller  26  transmits command signals  28  to the top drive system  12  to initiate a rotation of the drill string  20  in the counter-clockwise direction. During rotation in the counter-clockwise direction, the motor controller  100  monitors the torque applied to the drill string  20  and generates torque feedback signals  116  that are transmitted to the controller  26 ; and the turn encoder  118  monitors the amount of rotation of the drill string  20  and generates rotational feedback signals  120  that are transmitted to the controller  26 . When either the torque feedback signal  116  transmits a signal signifying that the torque limit for the counter-clockwise direction has been exceeded; or the rotational feedback signal  120  transmits a signal signifying that drill string  20  has ceased to rotate, the direction of rotation of the drill string  20  is reversed back to the clockwise direction. This process may be repeated indefinitely. 
     FIG. 4  is a block diagram for the controller  26  in accordance with one embodiment of the present invention. In this embodiment, the controller  26  includes a processor  200 , having a central processing unit (CPU)  202 , a memory cache  204 , and a bus interface  206 . The bus interface  206  is operatively coupled via a system bus  208  to a main memory  210  and an input/output (I/O) interface control unit  212 . The I/O interface control unit  212  is operatively coupled via I/O local bus  214  to a storage controller  216 , and an I/O interface  218  for transmission and reception of signals to external devices. The storage controller  216  is operatively coupled to a storage device  22  for storage of the programming instructions  32 . 
   In operation, the processor  200  retrieves the programming instructions  32  and stores them in the main memory  210 . The processor  200  then executes the programming instructions  32  stored in the main memory  210 . The processor  200  uses the programming instructions  32  to generate the previously described command signals  28  and transmits the command signals  28  via the external I/O device  218  to the top drive system  12 . The top drive system  12  responds to the command signals  28  and generates the previously described feedback signals  30  that are transmitted back to the controller  26 . The processor  200  receives the feedback signals  30  via the external I/O device  218 . The processor  200  uses the feedback signals  30  and the programming instructions  32  to generate additional command signals, command signals  110 ,  112 , and  114 , for transmission to the top drive system  12  as previously described. 
   The preceding description has been presented with reference to various embodiments of the invention. Persons skilled in the art and technology to which this invention pertains will appreciate that alterations and changes in the described structures and methods of operation can be practiced without meaningfully departing from the principle, spirit and scope of this invention.