Patent Publication Number: US-7717193-B2

Title: AC powered service rig

Description:
FIELD OF THE INVENTION 
   Embodiments of the invention relate to service rigs for servicing wellbores and, more particularly, to an integrated power system for powering at least the propulsion, drawworks and sandline on a service rig. 
   BACKGROUND OF THE INVENTION 
   Oil wells typically require some servicing during the lifetime of the wellbore whether it be to increase production, such as by acidizing or fracturing the formation and the like, perform testing on the formation or the wellbore integrity, replace components such as sucker rods or production tubing or casing or to perform a variety of other operations as necessary. 
   Service rigs are typically designed to at least have the capacity to trip out or run in the production tubing and to run in and trip out a variety of downhole tools. Conventionally, the service rig generally comprises at least a drawworks for raising and lowering tubulars and the like and typically a sandline for raising and lowering downhole tools such as during swabbing operations. Each of the drawworks and sandline are typically powered by diesel motors to which they are mechanically connected. The conventional powering systems typically do not provide as fine a motor control of the drawworks and the sandline as is desired for servicing operations. AC motors are used in the drilling industry where weight is less of a limitation on design. 
   Production tubing typically cannot handle as much torque as a drill stem and therefore more control is required for tripping out and running in of production tubing as compared to drill pipe. Conventional positioning of components into or out of the wellbore for servicing therefore has required careful and continuous monitoring and management of at least the drawworks and sandline systems by the onsite driller to ensure safe operations. 
   Conventionally power has been provided for braking systems on the drawworks and the sandline drums through diesel motors and mechanical connections associated therewith. Similarly in conventional rigs, hydraulic motor systems are also provided to operate tongs and slips required to break or make sections of tubing from the tubing string as it removed from or inserted into the wellbore. 
   In many cases, where the formation is to be treated by chemicals, pumping units are brought onsite to provide specialized treatment fluids which are pumped into the wellbore. The pumping unit is typically provided with a separate power source onsite. 
   Service rigs are generally portable rigs which comprise a transportable platform mounted on an undercarriage and which are powered by a propulsion system for moving the rig from wellsite to wellsite. Conventionally propulsion systems for service rigs are separately powered and typically comprise at least a large diesel engine carried on the platform and mechanically connected to the transmission through a gear box. A plurality of axle/wheel configurations are typically available for the undercarriage so as to conform to Department of Transport regulations. Service rigs must be capable of carrying a significant amount of weight given the diverse equipment mounted thereon and must also be able to meet regulations governed by road bans to permit servicing of wellbores throughout the year and under a variety of environmental condition. This becomes a challenge for rig manufacturers who must balance the competing requirement of the industry for greater functionality of the rig while trying to reduce the weight to meet the road ban conditions. 
   Additionally, there are electrical requirements onsite to support servicing operations such as hotel loads, onsite lighting and other such requirements which are conventionally provided by one or more small generators separately provided. 
   There is a need to provide improved power systems for service rigs that are efficient, supply the needs of the operations at the wellsite and which do not add significantly to the problems associated with the weight of the rig so as to maintain maximum transportability. 
   SUMMARY OF THE INVENTION 
   A substantially electrically-powered service rig housed on a single mobile platform utilizes electrical power generated by an on-board engine-driven AC generator to power an electrical propulsion system, a drawworks system and a sandline system. Further, through use of electrical umbilical power requirements for separately transportable mud pumps systems and hotel loads may be met. In some embodiments, the prior art use of three generators can be reduced to one. 
   The system utilizes permanent magnet motors to drive a semi or fully automatic manual transmission and the driven shafts of the drawworks and sandline drums under the control of programmable logic controllers through variable frequency drives. Use of the permanent magnet motors, the electrical propulsion system and electric motor braking systems for the propulsion system and drawworks and sandline drums results in a significant weight reduction over the use of conventional induction motors enabling integration of the propulsion system, drawworks system and sandline system on a single mobile unit and which meets transport regulations. 
   In a broad aspect of the invention, an electrically-powered well service rig comprises: a mobile platform for transporting the service rig; an engine-driven generator carried by the platform for generating AC power; a propulsion system carried by the platform for transporting the mobile platform service rig having a collapsible mast thereon, the propulsion system having a permanent magnet propulsion motor for driving the platform, a propulsion variable frequency drive (VFD) connected between the generator and the propulsion motor; a drawworks system carried by the platform and having blocks adapted for raising and lowering a plurality of tubulars into and out of a wellbore, the drawworks system having at least a drawworks drum having drawworks cable wound thereon and rotatably driven by a permanent magnet drawworks motor; a drawworks VFD connected between the generator and the drawworks motor; a sandline system carried by the platform and adapted for raising and lowering a sandline tool into and out of a wellbore, the sandline system having at least a sandline drum having sandline cable wound thereon and rotatably driven by a permanent magnet sandline motor; a sandline VFD connected between the generator and the sandline motor; and one or more programmable logic controllers (PLC) carried by the platform for outputting speed setpoints to the propulsion VFD, the drawworks VFD; and the sandline VFD. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  is a perspective view of a substantially fully electrically-powered service rig according to an embodiment of the invention, a collapsible mast being shown in a folded transport position; 
       FIG. 1B  is a plan view schematic illustrating components of the rig according to  FIG. 1A ; 
       FIG. 2  is a right perspective rear view of the service rig of  FIG. 1 , the mast and railings removed for clarity; 
       FIG. 3  is a left perspective front view of the service rig of  FIG. 1 , the mast and railings removed for clarity; 
       FIG. 4  is a plan view according to  FIG. 2 ; 
       FIG. 5  is a bottom view according to  FIG. 2 , an engine, generator and differential removed for clarity; 
       FIG. 6  is a schematic illustrating an electrical power supply and control system for an embodiment according to  FIG. 1 ; 
       FIG. 7  is a schematic of an electrical power and control system for a propulsion system for an embodiment according to  FIG. 1 ; 
       FIG. 8  is a schematic of an electrical power and control system for a drawworks system for an embodiment according to  FIG. 1 ; 
       FIG. 9  is a schematic of an electrical power and control system for a sandline system for an embodiment according to  FIG. 1 ; 
       FIG. 10  is a side schematic view of a drawworks system for an embodiment according to  FIG. 1 , illustrating a control system for the drawworks drum and sensors for providing feedback to a drawworks PLC; 
       FIG. 11  is a schematic illustrating operational positions of the drawworks of  FIG. 10  wherein drawworks blocks are raised and lowered for positioning a tubing string at target locations and for positioning flagged collars of the tubulars a relative to at least some of the target locations; 
       FIG. 12  is a flowchart illustrating a calibration operation for the drawworks of  FIG. 10  and for subsequent raising and lowering of the blocks of the drawworks for tripping apparatus into and out of the wellbore; 
       FIG. 13  is a flowchart illustrating raising and lowering tubulars using the drawworks system of  FIG. 10  and for positioning collars of the tubulars at target locations relative to the rig and the wellbore; 
       FIGS. 14A-14C  are side schematic views of a sandline system for an embodiment according to  FIG. 1 , illustrating a control system for the sandline drum and sensors for providing feedback to a sandline PLC, more particularly 
       FIG. 14A  illustrates the sandline in a bottomhole position, a sandline cable payed out from the sandline drum for positioning apparatus connected thereto adjacent a bottom of a wellbore and illustrating a speed profile related to an entire depth from the rig to the bottom of the wellbore; 
       FIG. 14B  illustrates the sandline of  FIG. 14A , the sandline cable payed out from the sandline drum for positioning apparatus connected thereto intermediate the wellbore; and 
       FIG. 14C  illustrates the sandline system of  FIG. 14A , the sandline cable payed out from the sandline drum for positioning apparatus connected thereto adjacent a wellhead at a top of the wellbore; 
       FIG. 15  is a flowchart illustrating a process for running in or tripping out a swabbing tool from a wellbore using the sandline system of  FIGS. 14A-14C ; 
       FIG. 16  is a schematic illustrating a propulsion system according to an embodiment of the invention; and 
       FIG. 17  is a schematic illustrating connection of a mud pump system and, optionally, hotel loads to an embodiment of the invention through one or more electrical umbilicals. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Having reference to  FIGS. 1A-5 ,  8 ,  10  and  14 A- 14 C, a substantially electrically-powered well service rig  10  comprises an integrated AC power system for powering both propulsion for a mobile service rig platform  12  and the apparatus used for performing service operations. The well service rig  10  comprises a mast or collapsible mast  14 , and hoisting capability, such as a drawworks system  16 , sandline system  18  or both. The drawworks system  16  typically comprises multi-line blocks  20  supported from a crown  22  of the mast  14  which are raised and lowered in the mast  14  using drawworks cable  24  wound about a drawworks hoist drum  26 . Elevators supported from the blocks  20  handle apparatus such as lengths of tubing run into and tripped out of a well  28 . The well service rig  10  can further comprise the sandline system  18 . The sandline system  18  is raised and lowered through the mast  14  using a sandline cable  30  extending over a sheave  32  in the crown  22  and wound about a sandline drum  34 . Downhole apparatus or sandline tools  36  such as a swabbing tool  36   s  ( FIGS. 14A-14C ) are raised and lowered through the wellbore  28  connected to the sandline system  18 . 
   In an embodiment of the invention as shown in  FIGS. 1-5 , and in more detail, the service rig&#39;s mobile platform  12  comprises an undercarriage  60  for transport as a self-propelled portable unit, typically in a truck-type format. The undercarriage  60  may comprise a variety of wheel/axle formats as required to meet Department of Transport guidelines. Although not detailed in  FIG. 3 , engine  50  and generator  54  are generally located over the platform&#39;s front wheels. 
   Having reference as well to  FIGS. 10-15 , both the drawworks and sandline systems  16 ,  18  are operated for maximizing speed of running in and tripping out and for adjusting cable speeds when the moving apparatus reaches point of interest or target locations. More particularly, with reference to  FIGS. 10 ,  11  and  14 A- 14 C, it is desirable to carefully control the drawworks and sandline cable  24  and  30  speed at the extreme ranges of motion of the cables  24 ,  30  and at particular target locations in the well  28  or mast  14 . As shown in  FIG. 10 , when running tubing  44 , the passage of collars C through wellhead equipment  48 , a rig floor  38 , tubing tongs  40  and the crown  22  are examples of points of interest for each length of tubing. Further, arrival of an end  42  of the tubing string  44  of a plurality of lengths of tubing at a bottom of the well  46  can be a point of interest. As shown in  FIGS. 14A-14C , for the sandline system  18 , points of interest are more related to the starting and stopping of the sandline tool  36 , such as at the bottom of the well  46 , at the wellhead equipment at surface  48  and at the crown  22 . 
   As shown on  FIG. 6 , an electrical power system  49  comprises at least one diesel engine  50 , such as a diesel generator engine from CATERPILLAR™, USA which runs an AC generator  52  for generating AC electrical power. A plurality of variable frequency drives (VFDs)  54 , under the control of programmable logic controllers (PLC&#39;s)  56 , control a plurality of motors  58  for propulsion of the service rig  10  for transporting the rig from wellsite to wellsite and for controlling the drawworks system  16  and the sandline system  18  for raising and lowering apparatus into and out of the wellbore  28 . 
   With reference also to  FIGS. 1B-5  and  6 , the power system  49 , including at least the diesel engine  50 , the engine-driven generator  52  and the VFD&#39;s  54  and PLC&#39;s  56  as shown in  FIG. 6 , are mounted on the mobile platform  12 . The plurality of motors  58  are controlled by the VFD&#39;s  54 . Permanent magnet (PM) motors  58  are much lighter than conventional AC motors and their use permits integration of the systems into the service rig  10  which is transportable as a single mobile unit. For the same capability, a 1000 pound PM motor can replace a 6,000 to 10,000 pound induction motor. Further, PM motors  58  do not slip and can therefore provide maximum torque at zero revolutions to very low rpm which is useful for manipulating heavy equipment or adjacent target locations. The no-slip PM motors  58  enhance the rig&#39;s ability to accurately move apparatus connected to the drawworks and sandline systems  16 , 18  at the various points of interest. The use of PM motors  58  and implementing an electrical propulsion system enables, for the first time, an electrical service rig  10  and results in a considerable savings in weight of the mobile platform  12 , permitting transportability as a single mobile unit. In one embodiment, the motors  58  are DC brushless motors available from POWERTEC Industrial Motors, Rock Hill S.C. 29732, USA. 
   Also shown in  FIG. 6 , the braking capability of the lightweight PM motors  58  for the drawworks and sandline drums  26 ,  34  are supplemented with multi-disc wetted brakes  62 . A series of friction discs and separator discs are alternately stacked and the stacked discs are splined alternately between the drum shafts and stationary brake housings. The disc stack is compressed via springs or hydraulic pressure to actuate the brake. Wet multi-disc brakes run in fluid such as oil which dissipates the heat generated in use. A lightweight PM motor with a multi-disc wetted brake is about 20 to 30% the weight of an induction motor alone. 
   Having reference to  FIGS. 6 ,  7  and  16 , a propulsion system  70  comprises a transmission VFD  72  controlling a PM propulsion motor  74  connected to a transmission  76 . The transmission VFD  72  and propulsion motor  74  are controlled through a propulsion PLC  78  which is operatively connected to an operator control  80  for achieving required road speeds. The transmission  76  can be a semi-automatic or fully automatic manual transmission. Automated shifting manual transmissions have a weight advantage over automatic transmissions. Such transmissions incorporate transmission-specific controls such as a transmission PLC  82  for coordinating with the propulsion motor  74  such as during shifting and with ABS systems during braking. 
   Generally, the propulsion PLC  78  receives a desired road speed signal from the operator, such as through the operator control  80 . The propulsion PLC  78  communicates the desired road speed to the transmission PLC  82  for management of transmission specific control, such as gear selection and motor speed output. Ultimately, the transmission VFD  72  receives motor speed set points for operation of the propulsion motor  74 . In one embodiment, the transmission PLC  82  returns the motor speed set point to the propulsion PLC  78  for control of a propulsion VFD  84 . The transmission PLC  82  and propulsion PLC  78  act in concert to control shifting of the transmission in response to feedback from the operator. 
   In one embodiment, the transmission  76  has a plurality of gears to permit maximum gradeability. An example of such a semi-automatic transmission is an AS Tronic™ transmission (trademark of ZF Friedrichshafen AG, Germany, www.zf.com,) which implements a shift strategy using a non-synchronized three-stepped basic transmission with a synchronized range and splitter group and 12 pneumatically controlled gear steps. In particular the AS Tronic™ transmission already incorporates a sophisticated electronic interface between the transmission  76 , various power plant controllers, operator accelerator  80 , brake and ABS systems. 
   With reference to  FIGS. 3 ,  4  and  5 , the mobile platform  12  of the service rig  10  implements an electrical motor braking system  90  which, in embodiments of the invention, comprises a hybrid braking system for combining braking from the propulsion motor  74  with conventional braking, such as ABS brakes. In embodiments of the invention, dynamic braking and regenerative braking with electrical storage are implemented. When regenerative braking is not feasible, such as when the electrical storage such as capacitors is fully charged, dynamic braking utilizes a resistor bank  91  and cooling system  92  to dissipate braking energy. The propulsion PLC  78  controls how much regenerative braking  74   r  or dynamic braking is applied to supplement transmission range selection. The operator is typically provided with a selector switch which has an off, medium and high option and which is adaptive depending on the propulsion motor rpm. For example, as regenerative braking reaches maximum, the transmission  76  will automatically shift gears to lessen the regenerative or dynamic braking load. Further, the conventional anti-lock braking systems (ABS) provide signals to the propulsion PLC  78  when the ABS braking systems are operated. 
   The engine and generator  50 , 54  of the service rig  10  is capable of incorporating all the power needs for onboard propulsion, drawworks  16 , sandline  18  and further, for off-platform needs, including a mud pump system  100  and hotel loads. 
   Particularly advantageous is the ability to power the mud pump system  100 , which is necessarily separately transportable, having the mud pump motor  102  and mud tanks  104 . In an embodiment of the invention, the mobile platform generator  52  also powers the mud pump motor  102 . A power umbilical  108  or two, depending on the electrical cabling requirements, is releasably coupled with the mobile platform  12 . The mud system can utilize mud pumps driven by an asynchronous induction motor  102  and instrumentation can be directed back to the service rig  10  including mud levels, temperatures and motor temperatures. Mud pumps are typically positive displacement plunger pumps and a stroke counter can enable calculation of the volume of mud being pumped. Power can also be provided through one or more umbilicals  108  for hotel loads  106 , such as lighting, heating and the like. 
   A simple hydraulic power takeoff (not shown) from the engine  50  can provide auxiliary hydraulic power for lubricators, for the drawworks and sandline systems, power tongs, mast raising and telescoping hydraulics, leveling jacks and deck winches. 
   The collapsible mast  14  is typically mounted at a rear  15  of the platform  12  so as to be moveable between a lowered transport position over the rig&#39;s platform  12  and in a raised position, cantilevered over a wellhead connected to the wellbore  28  for performing a variety of servicing operations. The mast  14  is generally tilted through one or more hydraulic rams connected between the mast  14  and the platform  12  and powered by a hydraulic pump. 
   In an embodiment of the invention, as shown in  FIGS. 6 ,  8  and  10 - 13 , the drawworks system  16  comprises a drawworks VFD  110 , under the control of a drawworks PLC  112 , and a PM drawworks motor  114  operatively connected to the drawworks hoist drum  26 . The drawworks motor  114  is connected to the drawworks hoist drum  26  through a drawworks drum shaft  116  and includes a gear reducer, typically a three-speed gearbox. The drawworks hoist drum shaft  116  further includes an encoder  118  for providing position information for the hoist cable  24 . Additional instrumentation includes gearbox shift and brake controls and sensors for providing feedback regarding drawworks system health including temperature. 
   Having reference to  FIGS. 9 ,  14 A- 14 C and  15 , the sandline system  18  comprises a sandline VFD  120 , under the control of a sandline PLC  122  and a PM sandline motor  122  operatively connected to the sandline drum  34 . The sandline motor  122  is connected to the sandline drum  34  through a sandline drum shaft  124 . The sandline drum shaft  124  includes an encoder  126  for providing position information for the sandline cable  30 . Additional instrumentation includes brake controls and sensors for providing feedback regarding sandline system health, including temperature. 
   In an embodiment of the invention, the mast crown  22  includes encoders for additional position control of the drawworks and sandline cables  24 ,  30 . As shown in  FIGS. 9 and 10 , load sensor  130  enables adjustment for drawworks cable  24  or sandline cable  30  stretch and provides online calibration to better determine proximity to points of interest. Sandline cable  30  is particularly affected by load and stretch, largely due to the length of cable  30  payed out. Parameters required by the sandline PLC  122  are a load and a number of layers of sandline cable  30  on the sandline drum  34 . The sandline drum  34  typically has a fixed diameter and the length of sandline cable  30  wrapped about the first layer is readily calculated from the circumference and the rotation encoder  128 . However, the drum&#39;s effective diameter changes, each wrap or layer of cable  30  requiring adjustments in the length of cable  30  payed out or reeled in per revolution of the drum  34 . The cable diameter and the calibration process from crown  22  to rig floor  38  is typically input to the sandline PLC  122 . 
   As previously stated, the PM motors  58  are used for manipulating heavy equipment and embodiments of the invention are particularly suited for fine motor control for manipulating the apparatus adjacent points of interest or target locations. The target locations may or may not be on the service rig. Typically the target locations are fixed and are relative to either the well service rig  10  or the wellbore  28 . For example, the target locations relative to the wellbore  28  may be the bottom of the wellbore  46 , a wellhead or a lubricator  48  and the target locations relative to the rig  10  may be the rig floor  38 , power tongs  40 , and crown position  22 . 
   Additionally, conventional tubing logs are maintained to log the running in and out of the production string to maintain a relationship between a distal end  42  of production string  44  and bottom  46  of wellbore  28  in the overall operating system. As the service rig  10  operates, tubing section lengths are tallied as they are run into and out of the wellbore  28  for comparison with known target locations, like the bottom  46  of the wellbore  28 . The drawworks PLC&#39;s  112  is typically programmed with the known target locations, such as the well bottom  46 , which may be derived from previous tubing tallies or well logging tools. 
   Further as shown in FIGS.  11  and  14 A- 14 C, flag locations F are utilized to assist with running apparatus such as tubulars  44  or tools  36  into the wellbore  28  and are typically locations on the particular tool itself. The flag locations F are not fixed relative to the wellbore  28  or the rig  10  and move with the apparatus. Examples of flag locations F are the plurality of collars C between tubulars in a tubing string  44  or a top end  35  and bottom end  37  of a sandline tool  36 , such as a swabbing tool. 
   In embodiments of the invention, prior to performing a service on a wellbore  28 , a calibration is performed wherein calibration signals are sent to either or both of the drawworks PLC  112  and sandline PLC  122  as the apparatus is manipulated by the operator to the various target locations T. The calibration signal is sent by a switch to indicate correspondence between the target location T, such as the rig floor  38  and a flag location F, such as the tubing collar C, when a tubing collar C is aligned at the rig floor  38 . 
   In use, to minimize well servicing duration and cost, it is preferred to operate the drawworks and sandline systems  16 , 18  at a maximum speed whenever possible. However, the drawworks and sandline PLC&#39;s  112 , 122  act to control the speed of the drawworks and sandline PM motors  114 , 124  for reducing a maximum speed setpoint M to a slower speed when a flag location F is within a preset window distance of the target location T. In this way, the PLC&#39;s  112 , 122  control the operation for ensuring the apparatus is not bottomed out in the wellbore  28 , topped out in the crown  22  or pulled through wellhead equipment  48  at speeds which may result in damage to any of the equipment. As shown in  FIG. 14A , typically, the maximum speed setpoint M at which the sandline cable  30  is run in or tripped out is much faster than that of the drawworks blocks  20 . In accordance with the faster speeds, an appropriate window distance for the sandline system  18 , such as about either the bottom of the wellbore  46  or wellhead equipment  48 , may be as much as 60 feet. As shown in  FIG. 11 , the drawworks cable  24  is run at slower speeds and therefore an appropriate window for the drawworks system  18 , such as about the wellhead equipment  48  or at the rig floor  38 , power tongs  40  or crown  22 , may be about 2 feet. Speed of drawworks cable  24  deployment typically varies depending upon the weight of the tubing string  44  attached thereto and may be, for example, about 2 m/s for a 10,000 pound tubing string to about 1 m/s for tubing strings having a weight of about 100,000 pounds. 
   In embodiments of the invention, an operator utilizes a conventional appearing control panel which includes both a drawworks speed joystick and a sandline speed joystick. The drawworks and sandline PLC&#39;s  112 , 122  reduce the maximum speed setpoints by reducing the “gain” so that operator joystick maximum is reduced at target locations T from the higher or maximum speed setpoint used between target locations T. In other words, at the target locations T, the joystick maximum is set at the target location maximum for slowing the speed. 
   With reference to  FIGS. 10 and 14A , embodiments of the invention utilize a number of conventional sensors to provide feedback to the PLC&#39;s  56  regarding a variety of operational parameters which assist with controlling the rig systems. Rotation of the driven shafts  114 , 126  of the drawworks hoist drum  26  and sandline drum  34  are monitored using motor encoders  118 , 128 , typically dual output shaft encoders and resolvers, for monitoring motor  114 , 124  current draw, torque required to move the motor  114 , 124  and power utilized by the motor  114 , 124 . Feedback from the drawworks shaft encoder  118  coupled with the no-slip PM motor  114  permits accuracy of about ⅛″ of movement of a heavy tubing string  44  using the multiline blocks  20 . 
   Further as shown in  FIG. 10 , the drawworks deadline or block load sensor  130  provides feedback to the drawworks PLC  112  regarding the load on the drawworks system  16  for calculating alterations in tubing parameters, such as tubing stretch. Corrections to account for the alterations in tubing parameters can then be incorporated into the operational system, such as to adjust flag locations F relative to the tubing string  44 . 
   Further, as shown in  FIGS. 14A-14C , sandline sensors typically comprise at least the sandline shaft encoder  128  for providing positioning feedback to the sandline PLC  122  for determining positioning of apparatus, such as a swabbing tool  36   s , connected to the sandline cable  30  relative to the fixed target positions T and the flag positions F. 
   Dual output encoders are typically used to provide a redundancy in the signal to the various PLC&#39;s  56 . Two sets of internal electronics provide the redundancy and if, for some reason, the two signals do not agree, the PLC&#39;s  56  will automatically slow the speed of the driven drawworks or sandline shafts  116 , 126  from the maximum speed to the slower target location maximum or other minimum speed to permit verification of location. Further, resolvers may be added to the PM motors  58  as an additional redundancy to compare against encoder feedback to ensure accurate positioning. Once the position has been verified or the problem resolved, the PLC&#39;s  56  can then reset the speed to the maximum running speed. 
   Conventional switches can be used, as previously described, to permit calibration of the correspondence between a fixed target location T and a flag location F. The switches may be used in isolation to signal to the drawworks or sandline PLC  112 ,  122  the location of the relative target and flag positions T,F or can be used in at least a pair, for example the floor location  38  and the crown location  22 , for calculating drawworks or sandline cable  24 , 20  pay-out and reel-in distances for a particular drum. Additionally, cable diameter may be used to calculate variable correspondence between drum encoder  118 , 128  revolutions and actual distances payed out or reeled in. 
   Having reference to  FIGS. 10 ,  12  and  13 , the blocks  20  of the drawworks system  16  are raised and lowered by the drawworks cable between the rig floor  38 , the power tongs  40  and the crown  22  of the rig  10  for moving sections of tubulars  44  of fixed length into and out of the wellbore  28 . Said movement permits operators on the floor  38  of the rig  10  to make up the sections at the threaded collars C for running in or breaking out the sections at the threaded collars C when tripping out. 
   Having reference to  FIG. 12 , at block  200 , prior to running the tubulars  44 , the drawworks system  16  is first calibrated by moving the drawworks blocks  20  to each target locations T, being at block  201  the rig floor  38 , at block  202  the power tongs  40  and at block  203 , the crown  22 . The operator sets the location by pressing a switch and the location information is provided to the drawworks PLC  112  as previously described. The block  20  location is coordinated with the sections of tubulars  44  for locating collars C. 
   Once the system has been calibrated, the tubing string can be run in or tripped out. For ease of description, the process of running in is described, the process of tripping out being essentially a reverse operation. At block  204 , the drawworks maximum speed setpoint M is set to run in the tubing at the maximum block speed. At block  205 , the operator controls the joystick to run at up to the maximum speed. At blocks  206  and  207 , the drawworks PLC  112  is aware of the tubing string tally and monitors the location of the blocks  20  and flag locations F relative to the target locations T in the rig  10  through feedback from the encoders  118 ,  130 . As the blocks  20  approach the target locations T at block  206 , the drawworks PLC  112  automatically reduces the gain on the joystick at block  208  which reduces the setpoint M and slows the drawworks speed to ensure safe passage of the flag location F. As the blocks  20  leave the target location T, at block  207 , the drawworks PLC  112  sets the speed setpoint M to the maximum block speed, as shown at block  204 . The drawworks PLC  112  continues to operate at the maximum block speed until such time as the blocks  20  approach another target location T. 
   As shown in  FIG. 13 , when running tubulars, flag positions F, particularly the position of the tubing collars C, must be monitored to ensure the tubing collars C are not moved through the wellhead  48  at maximum speed. The drawworks PLC  112  is programmed with the average length of a tubular and the preset window distance so as to account for deviations in the length of the tubulars between collars C. The encoders  118  on the drawworks hoist drum shaft  116  and the drawworks motor  114  provide feedback to the drawworks PLC  112 . The data is corrected for any cable and tubing stretch through feedback from the block load sensor  130  to determine more precise flag locations F, in this case the location of the collars C. 
   As shown at block  210 , the drawworks PLC  112  sets the drawworks at maximum speed. At block  211 , the operator controls the joystick to run at the maximum speed during either running in or tripping out of the tubulars  44 , shown at block  212 . At block  213 , as the preset window distance approaches the target location T, the drawworks PLC  112  automatically reduces the speed setpoint M at block  214  from the maximum block speed by automatically reducing the gain for the joystick and runs the drawworks at the reduced target maximum speed until the preset window distance has passed the target location T as shown at block  215 . The drawworks PLC  112  then automatically increases the running block speed setpoint again to the maximum block speed at block  210  until the next preset window distance approaches the target location T. 
   Having reference to  FIGS. 14A-14C  and  15 , in a sandline operation, such as running in and tripping out a swabbing tool  36   s , target locations T for calibration, typically the rig floor  38  and the crown  22  are programmed into the sandline PCL  122 , much like the drawworks  16 , blocks  20  and tubing string  44  calibration. The operator presses a switch as the sandline cable  30  is deployed to each of the rig target positions  38 ,  22 . An optional mid-mast position may also be used for the calibration. Operational target locations T of the service rig  10 , such as the bottom of the wellbore  46  ( FIG. 14A ) and a top of the wellbore or wellhead  48  ( FIG. 14C ) are calculated and programmed into the sandline PLC  122 . The sandline PLC  122  is also programmed with preset slowdown windows of distance from the top of the wellbore or wellhead  48  and the bottom  46  of the wellbore  28 . 
   For ease of description, tripping out of the swabbing tool  36   s  is described, the running in being essentially a reverse operation. As shown in  FIG. 14A , as the sandline cable  30  is raised from the bottom  46  of the wellbore  28 , the sandline drum  34  is run at a set maximum speed. As the sandline-deployed swabbing tool  36   s  approaches the preset window distance from the top of the wellbore  48 , the sandline PLC  122  automatically reduces the speed of the sandline motor  124  and the sandline cable  30  and swabbing tool  36   s  are raised slowly to the surface to avoid pulling the swabbing tool  36   s  through the wellhead  48  at maximum speed. 
   Having reference to  FIG. 15  and for sandline system  1  operation, at block  300  the sandline PLC  122  sets the sandline motor  124  speed setpoint M at a maximum running speed. At block  301 , the operator controls the sandline motor  124  through a joystick which is also set at maximum speed for running a swabbing tool  36   s  into or out of the wellbore  28  ( FIG. 14B ) at block  302 . At block  303  as the swabbing tool  36   s  approaches a target location T ( FIGS. 14A and 14C ), the sandline PLC  122 , at block  304 , reduces the maximum sandline speed to a maximum target speed. At block  305 , once the swabbing tool  36   s  leaves the target location T, the sandline PLC  122 , increases the speed setpoint M once again to the maximum running speed ( FIG. 14B ).