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CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application Ser. No. 60/447,984, filed on Feb. 15, 2003, which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an automated control system for operating a drawworks or similar hoisting means during a back reaming operation. 
     BACKGROUND OF THE INVENTION 
     In the petroleum industry, the apparatus and machinery used to drill wells is commonly known as a drilling rig or a rig. On these rigs are means of rotating the drill pipe, the most popular and successful of which is a device known as a top drive system. The popularity and proliferation of top drive systems within the oilfield has greatly enhanced the capability of the industry&#39;s drillers and operators to handle drill pipe operations in safe and beneficial manners. 
     One such operation is “back reaming” wherein the operator hoists a drill pipe out of a borehole while simultaneous pumping drilling mud and rotating the drill pipe, thus avoiding the build-up of frictional forces between the drill pipe and the borehole that may lead to the drill pipe being jammed in the borehole. Until recently this back-reaming process has been done either completely manually or has involved the use of complicated controls within the hoisting equipment. 
     For example, in the manual process, the operator engages a hoisting means by engaging a clutch and then manually manipulating a hoisting throttle, either a hand or foot throttle, to slowly and carefully hoist the drill pipe out of the borehole. However, during this operation, the driller must simultaneously monitor the hookload, and the rotating torque or standpipe pressure (if using a downhole mud motor) for indications that the pipe is in danger of jamming in a lateral direction or a rotational direction, respectively. 
     Alternatively, in another process, the operator may be required to operate a control system that is connected to the hoisting means. In such a system, upon a command from the operator, the control system activates the hoisting means to slowly hoist the pipe out of the borehole. However, the driller must still monitor the hookload, the rotating torque and/or the standpipe pressure for indications of that the drill pipe may be in danger of jamming in the borehole. 
     In addition, a problem with both of these processes is that many hoisting systems cannot tolerate holding a drill pipe without movement for an extended period of time, a situation that can occur when a drill pipe does jam in the borehole. Thus, each of these processes relies on the operator&#39;s judgment to avoid equipment damage. Accordingly, a need exists for an improved control system that allows for greater control of the back reaming process while reducing operator burden. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a control system for the automated operation of a drawworks during a “back reaming” operation. In one embodiment the control system is connected to an operator control unit to allow a driller to enter maximum values to be reached during the reaming operation for one or more specified reaming parameters. During the reaming operation, the control system continuously monitors the specified reaming parameters and compares the measured values to the limits or maximum values input by the operator. When any of the maximum values are exceeded, a control signal is sent to the drawworks to reduce the speed of the hoisting. 
     In another embodiment, the specified reaming parameters may be selected from any or all of the pull on the drill bit (POB), the rate of hoisting (ROH), and the drilling torque. In still another embodiment, the speed of hoisting is controlled by the application of a drawworks brake assembly. 
     In one embodiment, the present invention is an automated method for controlling a back reaming operation of a drilling rig. The method includes providing a hoisting system that moves a drill pipe during a back reaming operation at a hoisting speed and a hoisting torque. The hoisting system includes at least one back reaming parameter sensor for measuring a corresponding at least one back reaming parameter. The method further includes comparing a predetermined value of the at least one back reaming parameter with the measured value for the at least one back reaming parameter; and initiating a braking assembly that resists the hoisting torque of the hoisting system when the measured value of the at least one back reaming parameter equals the predetermined value of the at least one back reaming parameter. 
     In another embodiment, the present invention is an automated method for controlling a back reaming operation of a drilling rig. The method includes providing a drawworks system that moves a drill pipe during a back reaming operation at a hoisting speed and a hoisting torque. The hoisting system comprises at least one back reaming parameter sensor for measuring a corresponding at least one back reaming parameter. The method further includes providing an operator control unit that allows an operator to input a predetermined value of the at least one back reaming parameter therein; and providing a control system that compares the predetermined value of the at least one back reaming parameter with the measured value for the at least one back reaming parameter, wherein the control system initiates a braking assembly that resists the hoisting torque of the drawworks system when the measured value of the at least one back reaming parameter equals the predetermined value of the at least one back reaming parameter. 
     In yet another embodiment, the present invention is a system that controls a back reaming operation of a drilling rig that includes a hoisting system that moves a drill pipe during a back reaming operation at a hoisting speed and a hoisting torque. The hoisting system comprises at least one back reaming parameter sensor for measuring a corresponding at least one back reaming parameter. An operator control unit allows an operator to input a predetermined value of the at least one back reaming parameter therein. A back reaming parameter sensor obtains the measured value of the at least one back reaming parameter. A control system monitors the at least one back reaming parameter. A braking assembly resists the hoisting torque of the drawworks system when the measured value of the at least one back reaming parameter equals the predetermined value of the at least one back reaming parameter. 
    
    
     
       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 representation of a drilling rig and a drawworks/brake control system according to the present invention; 
         FIG. 2  is a block diagram of the drawworks/brake control system of  FIG. 1  including a signal flow diagram; and 
         FIG. 3  is a schematic representation of the drawworks/brake control system of FIG.  1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in  FIGS. 1-3 , the invention is directed to a drawworks/brake control system  110  (hereinafter “control system  110 ”) for the automated operation of a drawworks  50  or similar hoisting means during a “back reaming” (hereinafter “reaming”) operation. 
     As shown in  FIG. 1 , in one embodiment of the current invention the control system  110  is connected to an operator control unit  115 . A driller or operator enters into the control unit  115  maximum values to be reached during the reaming operation for one or more specified reaming parameters. For example, the reaming parameters may include any or all of the pull on the drill bit (POB), the rate of hoisting (ROH), and the drilling torque. The operator then initiates the reaming operation. 
     During the reaming operation, the control system  110  continuously monitors the POB, ROH and/or the drilling torque through various sensors  90 ,  100  and  104 , and compares the measured values to the limits or maximum values input by the operator. When any of the maximum values are exceeded, a brake assembly  70  is activated via a control signal  109  from the control system  110  to reduce the speed of the hoisting. In such an embodiment, the brake assembly  70  modulates the speed of hoisting during the reaming operation by applying a braking torque that resists the hoisting torque of the drawworks  50  so as to maintain the limits set by the operator for POB, ROH and/or the drilling torque. 
       FIG. 1  shows a schematic representation of the control system  110  of the current invention interconnected to a conventional drilling rig. In the depicted embodiment, a derrick  10  supports, at an upper end thereof, a crown block  15 . A rope arrangement  17  connects the crown block  15  to a traveling block  20 , or load bearing part, for supporting a hook structure  25 . The hook structure  25  is connected to and supports a top drive assembly  12 , which in turn is connected to a drill string  13 . The drill string  13  includes one or more drill pipes and a drill bit  14  that produces a borehole  16  in a drilling operation upon rotation by the top drive assembly  12 . The drawworks  50  is then used to hoist the drill string  13  out of the borehole  16  during a reaming operation. 
     The drawworks  50  is attached to a hoisting line  30 , that assists the drawworks  50  in hoisting the drill string  13  during the reaming operation. The hoisting line  30  is securely fixed at one end to the ground by means of a dead line  35  and a dead line anchor  40 . The other end of the hoisting line  30  forms a fast line  45  that is attached to the drawworks  50 . 
     In the embodiment shown in  FIG. 1 , the drawworks  50  includes one or more motor(s)  55 , such as an electrical, diesel or other appropriate motor, and a transmission  60  connected to a cylindrical rotatable drum  65  for wrapping and unwrapping the fast line  45  as required for operation of the associated crown block  15  and traveling block  20  during drilling and reaming operations. In such an embodiment, the rotatable drum  65  is also referred to as a winding drum or a hoisting drum. Although one embodiment of a hoist system is shown in  FIG. 1  it should be understood that other hoist systems capable of controllably raising a drill pipe could be utilized with the automated reaming control system of the current invention. 
     As shown in  FIG. 1 , a plurality of positioning sensors, such as proximity switches  102  in the derrick  10  or an encoder  100  that is affixed to the drawworks drive shaft  85 , may be used to determine the position of the traveling block  20  for additional safety and control during the reaming process. In such an embodiment, an output control signal  107  or  105 , indicting the position of the traveling block  20  is sent from the proximity switches  102  or the encoder  100 , respectively, to the control system  110 . The actual speed and position of the traveling block  20  may then be used to ensure safe operation of the hoist during reaming. Although in one embodiment the positioning sensors are proximity switches  102 , it should be understood that other means for determining the position of the traveling block  20  could be utilized with the automated reaming control system of the current invention. 
     Although any brake capable of automated control may be utilized in the current invention, as shown in  FIG. 1 , the brake assembly  70  preferably includes a primary friction brake  80 , typically a band type brake or a caliper disk brake, an auxiliary brake  75 , such as an eddy current type brake or a friction plate brake, and an emergency brake  78 . The brake assembly  70  is connected to the drawworks  50  by a drive shaft  85  of the drawworks  50 . The brake assembly  70  is controlled by the control system  110 . Again, although any suitable actuator may be utilized in the current invention, typically the brake  70  of the current invention is actuated either hydraulically or pneumatically, using, for example, a pneumatic cylinder that is applied by rig air pressure that is modulated by control signals  109  issued by the control system  110  by way of, for example, an electronically controlled air valve. 
     As discussed above, to provide reaming monitoring signals to the control system  110 , a number of sensors may be utilized in the current invention. In the embodiment depicted in  FIG. 1 , a load sensing device  90 , such as a strain gage or a hydraulic load cell is affixed to the dead line  35 , and produces an output control signal  95  indicating the tension in the dead line  35  and consequently, the load carried by the traveling block  20  or POB. This POB measurement from the load sensing device  90  is provided sent from the strain gage  90  to the control system  110 . Various tension measuring devices may be employed to indicate the tension conditions on the line  35 . In one embodiment, as shown in  FIG. 1 , the actual hook load or POB is calculated using the load sensing device  90  input in conjunction with the number of lines strung and a calibration factor. Alternatively, a conventional load cell, hydraulic tension transducers or other load measuring device may be associated with the derrick  10  to provide the output control signal  95  representative of the load carried by the traveling block  20 . 
     Alternatively, or in addition, the system may also be provided with a sensor for monitoring the rate of hoisting. In such an embodiment, as shown in  FIG. 1 , a measuring device, such as an encoder  100 , for example, is affixed to the drawworks drive shaft  85 . In such an embodiment, an output control signal  105 , representative of the speed of rotation of the rotatable drum  65  as the drum  65  rotates to pull in or pay out the fast line  45  and as the traveling block  20  rises or descends, is sent from the encoder  100  to the control system  110 . Using such an encoder, the frequency of the signal may be used to measure the velocity of the traveling block  20  movement, typically, by calculating the actual drum  65  speed and ultimately the traveling block  20  speed based on lines strung, the diameter of the drum  65 , the number of line wraps and the line size. Alternatively, the velocity of the traveling block  20  movement may be calculated from the change in the vertical position of the traveling block  20 . In such a system, the ROH can be calculated from the velocity of the traveling block  20 . In addition, the proximity switches  102  may be utilized to confirm the measurements taken by the encoder  100 . 
     Finally, as shown in  FIG. 1 , alternatively, or in addition, the drilling torque may be monitored. The drilling torque may be measured by sensing the torque on the top drive or rotary table, such as by a torque sensor  104  or as reported by a top drive motor drive  112  or a rotary table drive  113 . In such an embodiment, an output control signal  108  indicating of the drilling torque is sent from the torque sensor  104  or from the drive  112  or  113  to the control system  110 . Alternatively, the drilling torque can be obtained by measuring the standpipe pressure when a downhole drilling motor is used. 
     Referring to  FIGS. 1-3 , the control system  110  is in signal connection with the brake assembly  70  to provide brake control signals  109 , and continuously receives output control signals  95 ,  105 , and  108  from the load sensing device  90 , the encoder  100 , and the torque sensor  104 , respectively, wherein each of the output control signals  95 ,  105 , and  108  is an electrical, digital or other appropriate signal. The control system  110  is also in signal communication with an operator control unit  115  located on or near the derrick  10  such that the operator can provide appropriate maximum values for the specified reaming parameters to be monitored. Alternatively, a separate workstation (not shown), located, for example, in an equipment room on or near the derrick  10 , can be connected to the control system  110  to provide an additional user interface and configuration signals. 
     In one embodiment, as depicted in  FIG. 2 , the operator control center  115  or man-machine interface preferably includes an industrial processor driven monitor  160  wherein the operator or driller can set and control the specified reaming parameters. For example, the operator can enter the maximum values to be reached during the reaming operation for any or all of the pull on the drill bit (POB), the rate of hoisting (ROH), and the drilling torque. 
     As shown in  FIG. 2 , the control system  110  includes a programmable controller (the drawworks PC  155 ), such as a programmable logic controller, a single board computer or an equivalent, to which are input the measured reaming values from the various sensors, and the respective operator defined maximum values from the operator control center  115 . The programmable controller  155  then compares the values and outputs appropriate control signals to the braking system and the drawworks that and are interfaced between the drive system  120  using, for example, a serial communication connection  150  such as, for example, an optical linkage and/or hard-wired linkage. 
     In the embodiment shown, two or more remote programmable controllers (PC) input/output (I/O) units  145  are used to control the brake assembly  70  (including, as shown in  FIG. 2  any or all of the disc brake  80 , the parking brake  75 , and the emergency brake  78 ) of the drawworks  50  and the drawworks processor  155 , although any suitable interface may be used. A processor  160  is also connected to the control system  110  for providing input and output of the operator values, operating parameters and calculated values during the performance of various drilling rig operations. 
     Although not necessary, the control system  110  may also be connected to the motor(s)  55  of the drawworks through the drive system  120 . The motor(s)  55  may be an alternating current (ac) motor or a direct current (dc) motor and the drive system  120  is an ac or a dc drive, respectively. The drive system  120  may further include, for example, a controller  125 , such as a programmable controller (PC) and one or more motor drives  130  connected to an ac bus  135  for providing control of the motor. 
     As discussed above, and shown in  FIG. 3 , the control system  110  of the current invention may includes an auto back reaming (ABR) mode that the operator initiates by engaging a drawworks clutch, i.e. a high  2 B or a low  2 A clutch. Engaging the clutch  2 A or  2 B while the ABR is enabled (such as while auto-drilling) commands the control system  110  to activate the drive system  120  and the brake assembly  70 . 
     During operation in the ABR mode, the control system  110  senses when the operator activates either the low or high clutch control, which in turn activates low and high clutch solenoids  7   g  or  7   e , respectively. Signals from the activated clutch solenoids  7   g  or  7   e  and/or pressure sensors  7 D on the low  2 A or a high  2 B are then communicated to the control system  110  CPU, which senses the operator&#39;s intent to back ream. 
     Once the drawworks clutch  2  is engaged, the control system  110  calculates the amount of torque needed to be supplied from the drawworks motor(s)  55 , and utilizes an output signal  7 F to control the torque command selector  9 , which in turn outputs a torque input  120 C to the drawworks drive  120 . The drawworks motor(s)  55  in turn produces torque, which exceeds that required to hold the load of the traveling block  20  stationary. The starting torque is calculated as the static hookload plus the operator entered maximum POB value. 
     The control system  110  then utilizes control signals from the various sensors  7 C to calculate and monitor the reaming parameters, and these values are compared versus the limits on those parameters input by the operator, to ensure that the back reaming operation is performed within the operator limits. If the measured values from the sensors match or exceed the limits input by the operator, the CPU sends a signal to the brake actuator, which in turn controls the braking system  70  to apply a torque to resist the hoisting torque of the drawworks motor(s)  55  and control the rate of hoisting of the drill string, to in turn maintain the limits input by the operator for ROH, POB, and/or the drilling torque. The CPU commands the braking system  70  to apply a torque that resists the hoisting torque of the drawworks motor(s)  55  such that the hoisting speed is reduced until the relevant maximum value is no longer exceeded, and then commands the brake actuator to reduce the resisting torque of the brake system  70  to allow the drawworks motor(s)  55  to increase the speed of hoisting. 
     For example, if while hoisting and back reaming, the top drive motor torque exceeds the limit input by the operator for drilling torque due to a tight hole condition, the CPU commands the brake actuator to control the brake assembly  70  to apply the brake to reduce the rate of hoisting to allow the drill motor torque to decrease as it drills through the tight area more slowly. This is possible because of the smooth proportional control of the brake assembly  70  and its sufficient capacity to produce more torque than the drawworks motor(s)  55  provides in this mode. 
     If stopping the drawworks motor(s)  55  completely is required to prevent the reaming system from exceeding one or more of the limits for the specified reaming parameters input by the operator, the control system  110  sends a torque command  7 F to the torque command selector  9 , which in turn sends a torque command  120 C from the drive system  120  to reduce the torque produced by the drawworks motor(s)  55  to zero. This prevents damage to the motor and allows safe operation. 
     When the control system  110  is not in the ABR mode, the drawworks torque command will come from a manual hand or foot throttle, or an equivalent device. 
     In an alternative embodiment other controls may be used by the operator to command hoisting torque while the braking system is still used for speed control of the hoisting. 
     As described above, the control system continuously monitors specified back reaming parameters and compares the measured values to the limits or maximum values input by the operator for the specified back reaming parameters. When any of the maximum values are meet or exceeded, a control signal is sent to the drawworks to reduce the speed of the hoisting. However, although the above description has focused on the monitoring of specific back reaming parameters, measured by specific back reaming parameter sensors, the monitored back reaming parameters can be any one or any combination of: weight on bit, hoisting torque, hoisting speed, drilling mud flow, drilling mud pressure, and formation cutting condition of mud screens within the drilling mud. These back reaming parameters can be measured by back reaming parameter sensors including any one or any combination of: strain gauges, proximity sensors/switches, cameras, gyroscopes, encoders, and magnetic pick ups/switches. 
     The preceding description has been presented with references to presently preferred 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, such as various changes in the size, shape, materials, components, circuit elements, wiring connections, as well as other details of the illustrated circuitry and construction. Accordingly, the foregoing description should not be read as pertaining only to the precise structures described and shown in the accompanying drawings, but rather should be read as consistent with and as support for the following claims, which are to have their fullest and fairest scope.

Summary:
A system that controls a back reaming operation of a drilling rig is provided that includes a hoisting system that moves a drill pipe during a back reaming operation at a hoisting speed and a hoisting torque. The hoisting system comprises at least one back reaming parameter sensor for measuring a corresponding at least one back reaming parameter. An operator control unit allows an operator to input a predetermined value of the at least one back reaming parameter therein. A back reaming parameter sensor obtains the measured value of the at least one back reaming parameter. A control system monitors the at least one back reaming parameter. A braking assembly resists the hoisting torque of the drawworks system when the measured value of the at least one back reaming parameter equals the predetermined value of the at least one back reaming parameter.