The drilling of oil wells has traditionally been dangerous and labor intensive, due in part to the potential for blowouts. A "blowout", which is an uncontrolled eruption of gas and oil from a well, is caused by a massive influx of formation fluid into the well bore at extremely high pressure. In many cases, blowouts occur at pressures sufficiently high to damage rig equipment and injure rig personnel. Blowout preventers (BOP's) are valves placed on top of a well to prevent blowouts. U.S. Pat. No. 4,535,852 to Boyadjieff and Krasnov describes the use of a blowout preventer valve in a top drive drilling system and is incorporated by reference in its entirety into the present disclosure.
Top drive drilling systems (TDS's) rotate the upper end of a drill string directly by a drive system suspended from a traveling block, rather than using a traditional rotary table and kelly. U.S. Pat. No. 4,449,596 to Boyadjieff describes a TDS and is incorporated by reference in its entirety into the present disclosure. Two IBOP's (Inside Blowout Preventers) and a saver sub are typically threadedly connected to the drive shaft of a TDS. For example, often an upper IBOP can be threaded to the drive shaft, a lower IBOP can be threaded to the upper IBOP, and a saver sub can be threaded to the lower IBOP. The drill string is then threaded onto the saver sub. Thus, rotational motion is transferred from the drive shaft of the TDS, down through the upper IBOP, the lower IBOP and the saver sub, to the drill string.
The threaded connections between the drive shaft of a TDS, an upper IBOP, a lower IBOP, a saver sub and a drill string, must be torqued to a high level in order to survive the forces encountered in a conventional drilling operation, with the higher components being torqued significantly tighter than the lower components. Thus, these components are typically too tight to rely on the torque provided by a conventional TDS to break the connections. To provide the required high torques, U.S. Pat. No. 4,449,596 describes a special torque wrench, or "pipe handler", that provides additional force for making and breaking these tight connections. Such torque wrenches work well for "breaking out", or loosening, and "making up", or tightening, the connections between the upper IBOP, the lower IBOP, the saver sub and the drill string, but have not been able to be used for breaking out the upper IBOP. The problem is that the torque wrench has no way of reaching the main shaft of the TDS in order to keep it from rotating while applying torque to the upper IBOP.
In order to prevent blowouts, IBOP's are tested frequently to make sure they hold pressure. On average, a problem is found with an IBOP every two to three months, leading to its replacement. Traditionally, upper IBOP's have been removed manually using modified tong hangers which can weigh as much as 600 pounds. The hangers are taken off and the tongs are picked up with tugger lines. During this process, several strong people are required to hold the tongs level so they can bite into the upper IBOP and the main drive shaft of the TDS. Extreme lateral forces are exerted on the tongs, potentially causing them to break and injure the workers using them. This manual procedure takes an average of eight to ten hours of dangerous, difficult and frustrating labor. Clearly, it would greatly improve safety and efficiency if an automated method for replacing the upper IBOP could be provided.