You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus and methods for facilitating the connection of tubulars. More particularly, the invention relates to an interlock system for a top drive and a spider for use in assembling or disassembling tubulars. 
     2. Background of the Related Art 
     In the construction and completion of oil or gas wells, a drilling rig is constructed on the earth&#39;s surface to facilitate the insertion and removal of tubular strings into a wellbore. The drilling rig includes a platform and power tools such as an elevator and a spider to engage, assemble, and lower the tubulars into the wellbore. The elevator is suspended above the platform by a draw works that can raise or lower the elevator in relation to the floor of the rig. The spider is mounted in the platform floor. The elevator and spider both have slips that are capable of engaging and releasing a tubular, and are designed to work in tandem. Generally, the spider holds a tubular or tubular string that extends into the wellbore from the platform. The elevator engages a new tubular and aligns it over the tubular being held by the spider. A power tong and a spinner are then used to thread the upper and lower tubulars together. Once the tubulars are joined, the spider disengages the tubular string and the elevator lowers the tubular string through the spider until the elevator and spider are at a predetermined distance from each other. The spider then re-engages the tubular string and the elevator disengages the string and repeats the process. This sequence applies to assembling tubulars for the purpose of drilling, running casing or running wellbore components into the well. The sequence can be reversed to disassemble the tubular string. 
     During the drilling of a wellbore, a drill string is made up and is then necessarily rotated in order to drill. Historically, a drilling platform includes a rotary table and a gear to turn the table. In operation, the drill string is lowered by an elevator into the rotary table and held in place by a spider. A Kelly is then threaded to the string and the rotary table is rotated, causing the Kelly and the drill string to rotate. After thirty feet or so of drilling, the Kelly and a section of the string are lifted out of the wellbore, and additional drill string is added. 
     The process of drilling with a Kelly is expensive due to the amount of time required to remove the Kelly, add drill string, reengage the Kelly, and rotate the drill string. In order to address these problems, top drives were developed. 
     FIG. 1A is a side view of an upper portion of a drilling rig  100  having a top drive  200  and an elevator  120 . An upper end of a stack of tubulars  130  is shown on the rig  100 . The figure shows the elevator  120  engaged with a tubular  130 . The tubular  130  is placed in position below the top drive  200  by the elevator  120  in order for the top drive with its gripping means to engage the tubular. 
     FIG. 1B is a side view of a drilling rig  100  having a top drive  200 , an elevator  120 , and a spider  400 . The rig  100  is built at the surface  170  of the well. The rig  100  includes a travelling block  110  that is suspended by wires  150  from draw works  105  and holds the top drive  200 . The top drive  200  has a gripping means for engaging the inner wall of tubular  130  and a motor  240  to rotate the tubular  130 . The motor  240  rotates and threads the tubular  130  into the tubular string  210  extending into the wellbore  180 . The motor  240  can also rotate a drill string having a drill bit at an end, or for any other purposes requiring rotational movement of a tubular or a tubular string. Additionally, the top drive  200  is shown with elevator  120  and a railing system  140  coupled thereto. The railing system  140  prevents the top drive  200  from rotational movement during rotation of the tubular string  210 , but allows for vertical movement of the top drive under the travelling block  110 . 
     In FIG. 1B, the top drive  200  is shown engaged to tubular  130 . The tubular  130  is positioned above the tubular string  210  located therebelow. With the tubular  130  positioned over the tubular string  210 , the top drive  200  can lower and thread the tubular into the tubular string. Additionally, the spider  400 , disposed in the platform  160 , is shown engaged around a tubular string  210  that extends into wellbore  180 . 
     FIG. 2 illustrates a side view of a top drive engaged to a tubular, which has been lowered through a spider. As depicted in the Figure, the elevator  120  and the top drive  200  are connected to the travelling block  110  via a compensator  270 . The compensator  270  functions similar to a spring to compensate for vertical movement of the top drive  200  during threading of the tubular  130  to the tubular string  210 . In addition to its motor  240 , the top drive includes a counter  250  to measure rotation of the tubular  130  during the time tubular  130  is threaded to tubular string  210 . The top drive  200  also includes a torque sub  260  to measure the amount of torque placed on the threaded connection between the tubular  130  and the tubular string  210 . The counter  250  and the torque sub  260  transmit data about the threaded joint to a controller via data lines (not shown). The controller is preprogrammed with acceptable values for rotation and torque for a particular joint. The controller compares the rotation and the torque data to the stored acceptable values. 
     FIG. 2 also illustrates a spider  400  disposed in the platform  160 . The spider  400  comprises a slip assembly  440 , including a set of slips  410 , and piston  420 . The slips  410  are wedge-shaped and are constructed and arranged to slidably move along a slopped inner wall of the slip assembly  440 . The slips  410  are raised or lowered by piston  420 . When the slips  410  are in the lowered position, they close around the outer surface of the tubular string  210 . The weight of the tubular string  210  and the resulting friction between the tubular string  210  and the slips  410 , forces the slips downward and inward, thereby tightening the grip on the tubular string. When the slips  410  are in the raised position as shown, the slips are opened and the tubular string  210  is free to move axially in relation to the slips. 
     FIG. 3 is cross-sectional view of a top drive  200  and a tubular  130 . The top drive  200  includes a gripping means having a cylindrical body  300 , a wedge lock assembly  350 , and slips  340  with teeth (not shown). The wedge lock assembly  350  and the slips  340  are disposed around the outer surface of the cylindrical body  300 . The slips are constructed and arranged to mechanically grip the inside of the tubular  130 . The slips  340  are threaded to piston  370  located in a hydraulic cylinder  310 . The piston is actuated by pressurized hydraulic fluid injected through fluid ports  320 ,  330 . Additionally, springs  360  are located in the hydraulic cylinder  310  and are shown in a compressed state. When the piston  370  is actuated, the springs decompress and assist the piston in moving the slips  340 . The wedge lock assembly  350  is constructed and arranged to force the slips against the inner wall of the tubular  130  and moves with the cylindrical body  300 . 
     In operation, the slips  340 , and the wedge lock assembly  350  of top drive  200  are lowered inside tubular  130 . Once the slips  340  are in the desired position within the tubular  130 , pressurized fluid is injected into the piston through fluid port  320 . The fluid actuates the piston  370 , which forces the slips  340  towards the wedge lock assembly  350 . The wedge lock assembly  350  functions to bias the slips  340  outwardly as the slips are slidably forced along the outer surface of the assembly, thereby forcing the slips to engage the inner wall of the tubular  130 . 
     FIG. 4 illustrates a cross-sectional view of a top drive  200  engaged to a tubular  130 . The figure shows slips  340  engaged with the inner wall of the tubular  130  and a spring  360  in the decompressed state. In the event of a hydraulic fluid failure, the springs  360  can bias the piston  370  to keep the slips  340  in the engaged position, thereby providing an additional safety feature to prevent inadvertent release of the tubular string  210 . Once the slips  340  are engaged with the tubular  130 , the top drive  200  can be raised along with the cylindrical body  300 . By raising the body  300 , the wedge lock assembly  350  will further bias the slips  340 . With the tubular  130  engaged by the top drive  200 , the top drive can be relocated to align and thread the tubular with tubular string  210 . 
     In another embodiment (not shown), a top drive  200  includes a gripping means for engaging a tubular on the outer surface. For example, the slips can be arranged to grip on the outer surface of the tubular, preferably gripping under the collar  380  of the tubular  130 . In operation, the top drive is positioned over the desired tubular. The slips are then lowered by the top drive to engage the collar  380  of the tubular  130 . Once the slips are positioned beneath the collar  380 , the piston is actuated to cause the slips to grip the outer surface of the tubular  130 . Sensors may be placed in the slips to ensure proper engagement of the tubular. 
     FIG. 5 is a flow chart illustrating a typical operation of a string or casing assembly using a top drive and a spider. The flow chart relates to the operation of an apparatus generally illustrated in FIG.  1 B. At a first step  500 , a tubular string  210  is retained in a closed spider  400  and is thereby prevented from moving in a downward direction. At step  510 , top drive  200  is moved to engage a tubular  130  from a stack with the aid of an elevator  120 . The tubular  130  may be a single tubular or could typically be made up of three tubulars threaded together to form a stack. Engagement of the tubular by the top drive includes grasping the tubular and engaging the inner surface thereof. At step  520 , the top drive  200  moves the tubular  130  into position above the tubular string  210 . At step  530 , the top drive  200  threads the tubular  130  to tubular string  210 . At step  540 , the spider  400  is opened and disengages the tubular string  210 . At step  550 , the top drive  200  lowers the tubular string  210 , including tubular  130  through the opened spider  400 . At step  560  and the spider  400  is closed around the tubular string  210 . At step  570  the top drive  200  disengages the tubular string and can proceed to add another tubular  130  to the tubular string  210  as in step  510 . The above-described steps may be utilized in running drill string in a drilling operation or in running casing to reinforce the wellbore or for assembling strings to place wellbore components in the wellbore. The steps may also be reversed in order to disassemble the casing or tubular string. 
     Although the top drive is a good alternative to the Kelly and rotary table, the possibility of inadvertently dropping a tubular string into the wellbore exists. As noted above, a top drive and spider must work in tandem, that is, at least one of them must engage the tubular string at any given time during tubular assembly. Typically, an operator located on the platform controls the top drive and the spider with manually operated levers that control fluid power to the slips that cause the top drive and spider to retain a tubular string. At any given time, an operator can inadvertently drop the tubular string by moving the wrong lever. Conventional interlocking systems have been developed and used with elevator/spider systems to address this problem, but there remains a need for a workable interlock system usable with a top drive/spider system such as the one described herein. 
     There is a need therefore, for an interlock system for use with a top drive and spider to prevent inadvertent release of a tubular string. There is a further need for an interlock system to prevent the inadvertent dropping of a tubular or tubular string into a wellbore. There is also a need for an interlock system that prevents a spider or a top drive from disengaging a tubular string until the other component has engaged the tubular. 
     SUMMARY OF THE INVENTION 
     The present invention generally provides an apparatus and methods to prevent inadvertent release of a tubular or tubular string. In one aspect, the apparatus and methods disclosed herein ensure that either the top drive or the spider is engaged to the tubular before the other component is disengaged from the tubular. The interlock system is utilized with a spider and a top drive during assembly of a tubular string. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     So that the manner in which the above recited features, advantages and objects of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. 
     It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore, not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
     FIG. 1A is a side view of a drilling rig  100  having a top drive  200  and an elevator  120 . 
     FIG. 1B is a side view of a drilling rig  100  having a top drive  200 , an elevator  120 , and a spider  400 . 
     FIG. 2 illustrates a side view of a top drive engaged to a tubular, which has been lowered through a spider. 
     FIG. 3 is cross-sectional view of a top drive  200  and a tubular  130 . 
     FIG. 4 illustrates a cross-sectional view of a top drive  200  engaged to a tubular  130 . 
     FIG. 5 is a flow chart of a typical operation of tubular string or casing assembly using a top drive and a spider. 
     FIG. 6 shows a flow chart using an interlock system for a spider and a top drive. 
     FIG. 7 illustrates the mechanics of the interlock system in use with a spider, a top drive and a controller. 
     FIG. 8 illustrates a control plate for a spider lever and a top drive lever. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention is an interlock system for use with a top drive and a spider during assembly of a string of tubulars. The invention may be utilized to assemble tubulars for different purposes including drill strings, strings of liner and casing and run-in strings for wellbore components. 
     FIG. 6 is a flow chart illustrating the use of an interlock system of the present invention with a spider and a top drive and FIG. 7 illustrates the mechanics of the interlock system in use with a spider, a top drive and a controller. At step  500 , a tubular string  210  is retained in a closed spider  400  and prevented from moving in a downward direction. The spider includes a spider piston sensor located at a spider piston  420  to sense when the spider  400  is open or closed around the tubular string  210 . The sensor data  502  is relayed to a controller  900 . 
     A controller includes a programmable central processing unit that is operable with a memory, a mass storage device, an input control unit, and a display unit. Additionally, the controller includes well-known support circuits such as power supplies, clocks, cache, input/output circuits and the like. The controller is capable of receiving data from sensors and other devices and capable of controlling devices connected to it. 
     One of the functions of the controller  900  is to prevent opening of the spider. Preferably, the spider  400  is locked in the closed position by a solenoid valve  980  (FIG. 7) that is placed in the control line between the manually operated spider control lever  630  (FIG. 7) and the source of fluid power operating the spider. Specifically, the spider solenoid valve  980  controls the flow of fluid to the spider piston  420 . The solenoid valve  980  is operated by the controller  900  and the controller is programmed to keep the valve closed until certain conditions are met. While valve  980  is electrically powered in the embodiment described herein, the valve could be fluidly or pneumatically powered so long as it is controllable by the controller  900 . Typically, the valve  980  is closed and the spider  400  is locked until a tubular is successfully joined to the string and held by the top drive. 
     At step  510 , the top drive  200  is moved to engage a pre-assembled tubular  130  from a stack with the aid of an elevator  120 . A top drive sensor  995  (FIG. 7) is placed near a top drive piston  370  to sense when the top drive  200  is disengaged, or in this case engaged around the tubular  130 . The sensor data  512  is relayed to the controller  900 . At step  520 , the top drive  200  moves the tubular  130  into position and alignment above the tubular string  210 . At step  530 , the top drive  200  rotationally engages the tubular  130  to tubular string  210 , creating a threaded joint therebetween. Torque data  532  from a torque sub  260  and rotation data  534  from a counter  250  are sent to the controller  900 . 
     The controller  900  is preprogrammed with acceptable values for rotation and torque for a particular connection. The controller  900  compares the rotation data  534  and the torque data  532  from the actual connections and determines if they are within the accepted values. If not, then the spider  400  remains locked and closed, and the tubular  130  can be rethreaded or some other remedial action can take place by sending a signal to an operator. If the values are acceptable, the controller  900  locks the top drive  200  in the engaged position via a top drive solenoid valve  970  (FIG. 7) that prevents manual control of the top drive  200 . At step  540 , the controller  900  unlocks the spider  400  via the spider solenoid valve, and allows fluid to power the piston  420  to open the spider  400  and disengage it from the tubular string  210 . At step  550 , the top drive  200  lowers the tubular string  210 , including tubular  130  through the opened spider  400 . At step  560 , the spider  400  is closed around the tubular string  210 . The spider sensor  990  (FIG. 7) signals the controller  900  that the spider  400  is closed. If no signal is received, then the top drive  200  stays locked and engaged to tubular string  210 . If a signal is received confirming that the spider is closed, the controller locks the spider  400  in the closed position, and unlocks the top drive  200 . At step  570  the top drive  200  can disengage the tubular string  210  and proceed to add another tubular  130 . In this manner, at least the top drive or the spider is engaging the tubular string at all times. 
     Alternatively, or in addition to the foregoing, a compensator  270  (shown in FIG. 2) may be utilized to gather additional information about the joint formed between the tubular and the tubular string. The compensator  270 , in addition to allowing incremental movement of the top drive  200  during threading together of the tubulars, may be used to ensure that a threaded joint has been made and that the tubulars are mechanically connected together. For example, after a joint has been made between the tubular and the tubular string, the top drive may be raised or pulled up. If a joint has been formed between the tubular and the string, the compensator will “stoke out” completely, due the weight of the tubular string therebelow. If however, a joint has not been formed between the tubular and the string due to some malfunction of the top drive or misalignment between a tubular and a tubular string therebelow, the compensator will stroke out only a partial amount due to the relatively little weight applied thereto by the single tubular or tubular stack. A stretch sensor located adjacent the compensator, can sense the stretching of the compensator  270  and can relay the data to a controller  900 . Once the controller  900  processes the data and confirms that the top drive is engaged to a complete tubular string, the top drive  200  is locked in the engaged position, and the next step  540  can proceed. If no signal is received, then the spider  400  remains locked and a signal maybe transmitted by the controller to an operator. During this “stretching” step, the spider  400  is not required to be unlocked and opened. The spider  400  and the slips  410  are constructed and arranged to prevent downward movement of the string but allow the tubular string  210  to be lifted up and moved axially in a vertical direction even though the spider is closed. When closed, the spider  400  will not allow the tubular string  210  to fall through its slips  410  due to friction and the shaped of the teeth on the spider slips. 
     The interlock system  500  is illustrated in FIG. 7 with the spider  400 , the top drive  200 , and the controller  900  including various control, signal, hydraulic, and sensor lines. The top drive  200  is shown engaged to a tubular string  210  and is coupled to a railing system  140 . The railing system includes wheels  142  allowing the top drive to move axially. The spider  400  is shown disposed in the platform  160  and in the closed position around the tubular string  210 . The spider  400  and the top drive  200  may be pneumatically actuated, however the spider and top drive discussed herein are hydraulically activated. Hydraulic fluid is supplied to a spider piston  420  via a spider control valve  632 . The spider control valve  632  is a three-way valve and is operated by a spider lever  630 . 
     Also shown in FIG. 7 is a sensor assembly  690  with a piston  692  coupled to spider slips  410  to detect when the spider  400  is open or closed. The sensor assembly  690  is in communication with a locking assembly  660 , which along with a control plate  650  prevents the movement of the spider and top drive lever. The locking assembly  660  includes a piston  662  having a rod  664  at a first end. The rod  664  when extended, blocks the movement of the control plate  650  when the plate is in a first position. When the spider  400  is in the open position, the sensor assembly  690  communicates to the locking assembly  660  to move the rod  664  to block the control plate&#39;s  650  movement. When the spider  400  is in the closed position as shown, the rod  664  is retracted allowing the control plate  650  to move freely from the first to a second position. Additionally, the sensor assembly  660  can also be used with the top drive  200  as well in the same fashion. Similarly, hydraulic fluid is supplied to a top drive piston  370  via a top drive control valve  642  and hydraulic lines. The top drive control valve  642  is also a three-way valve and is operated by a top drive lever  640 . A pump  610  is used to circulate fluid to the respective pistons  370 ,  420 . A reservoir  620  is used to re-circulate hydraulic fluid and receive excess fluid. Excess gas in the reservoir  620  is vented  622 . 
     Further shown in FIG. 7, controller  900  collects data from a top drive sensor  995  regarding the engagement of the top drive to the tubular string  210 . Data regarding the position of the spider  400  is also provided to controller  900  from a spider sensor  990 . The controller  900  controls fluid power to the top drive  200  and spider  400  via solenoid valves  970 ,  980 , respectively. 
     In FIG. 7, the top drive  200  is engaged to tubular string  210  while the spider  400  is in the closed position around the same tubular string  210 . At this point, steps  500 ,  510 ,  520 , and  530  of FIG. 6 have occurred. Additionally, the controller  900  has determined through the data received from counter  250  and torque sub  260  that an acceptable threaded joint has been made between tubular  130  and tubular string  210 . In the alternative or in addition to the foregoing, a compensator  270  can also provide data to the controller  900  that a threaded joint has been made and that the tubular  130  and the tubular string  210  are mechanically connected together via a stretch sensor (not shown). The controller  900  then sends a signal to a solenoid valve  970  to lock and keep a top drive piston  370  in the engaged position within the tubular string  210 . Moving to step  540  (FIG.  6 ), the controller  900  can unlock the previously locked spider  400 , by sending a signal to a solenoid valve  980 . The spider  400  must be unlocked and opened in order for the top drive  200  to lower the tubular string  210  through the spider  400  and into a wellbore. An operator (not shown) can actuate a spider lever  630  that controls a spider valve  632 , to allow the spider  400  to open and disengage the tubular string  210 . When the spider lever  630  is actuated, the spider valve allows fluid to be flow to spider piston  420  causing spider slips  410  to open. With the spider  400  opened, a sensor assembly  690  in communication with a locking assembly  660  will cause a rod  664  to block the movement of a control plate  650 . Because the plate  650  will be blocked in the rightmost position, the top drive lever  640  is held in the locked position and will be unable to move to the open position. 
     As illustrated in FIG. 7, the interlock system when used with the top drive and the spider prevents the operator from inadvertently dropping the tubular string into the wellbore. As disclosed herein, the tubular string at all times is either engaged by the top drive or the spider. Additionally, the controller prevents operation of the top drive under certain, even if the top drive control lever is actuated. Further, the interlock system provides a control plate to control the physical movement of levers between an open and closed, thereby preventing the operator from inadvertently actuating the wrong lever. 
     FIG. 8 illustrates a control plate for a spider lever and a top drive lever that can be used with the interlock system of the present invention. The control plate  650  is generally rectangular in shape and is provided with a series of slots  656  to control the movement of the spider lever  630 , and the top drive lever  640 . Typically, the control plate  650  is slideably mounted within a box  652 . The slots  656  define the various positions in which the levers  630 ,  640  may be moved at various stages of the tubular assembly or disassembly. The levers  630 ,  640  can be moved in three positions: (1) a neutral position located in the center; (2) a closed position located at the top and causes the slips to close; and (3) an open position located at the bottom, which causes the slips to open. The control plate  650  can be moved from a first rightmost position to a second leftmost position with a knob  654 . However, both levers  630 ,  640  must be in the closed position before the control plate is moved from one position to another. The control plate  650  is shown in the first rightmost position with a rod  664  extending from a locking assembly  660  to block the movement of the control plate. In operation, in the first rightmost position of the control plate  650 , the spider lever  630  can be moved between the open and close positions, while the top drive lever  640  is kept in the closed position. In the second leftmost position, the top drive lever  640  can be moved between the open and close positions, while the spider lever  630  is kept in the closed position. A safety lock  658  is provided to allow the top drive or spider levers  630 ,  640  to open and override the control plate  650  when needed. 
     The interlock system may be any interlock system that allows a set of slips to disengage only when another set of slips is engaged to the tubular. The interlock system may be mechanically, electrically, hydraulically, pneumatically actuated systems. The spider may be any spider that functions to hold a tubular or a tubular string at the surface of the wellbore. A top drive may be any system that can grab a tubular by the inner or outer surface and can rotate the tubular. The top drive can also be hydraulically or pneumatically activated. 
     While the foregoing is directed to the preferred embodiment of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Summary:
An apparatus and methods to prevent an operator from inadvertently dropping a string into a wellbore during assembling and disassembling of tubulars. Additionally, the apparatus and methods can be used for running in casing, running in wellbore components or for a drill string.