In the exploration of oil, gas and geothermal energy, drilling operations are used to create boreholes, or wells, in the earth. Modern drilling rigs may have two, three, or even four mast sections for sequential connection and raising above a substructure. The drilling rigs are transported to the locations where drilling activity is to be commenced. Once transported, large rig components are moved from a transport trailer into engagement with the other components located on the drilling pad.
Moving a full-size drilling rig requires significant disassembly and reassembly of the substructure, mast, and related component. Speed of disassembly and reassembly impacts profitability but safety is the primary concern. A reduction in disassembly reduces errors and delay in reassembly.
Transportation constraints and cost limit many of the design opportunities for building drilling rigs that can drill a well faster. Conventional drilling involves having a drill bit on the bottom of the well. A bottom-hole assembly is located immediately above the drill bit where directional sensors and communications equipment, batteries, mud motors, and stabilizing equipment are provided to help guide the drill bit to the desired subterranean target.
A set of drill collars are located above the bottom-hole assembly to provide a non-collapsible source of weight to help the drill bit crush the formation. Heavy weight drill pipe is located above the drill collars for safety. The remainder of the drill string is mostly drill pipe, designed to be under tension. Each drill pipe is roughly 30 feet long, but lengths vary based on the style. It is common to store lengths of drill pipe in “doubles” (two connected lengths) or “triples” (three connected lengths) or even “fourables” (four connected lengths). A “tubular stand” refers to connected sections of drill pipe, drill collars, or casing.
When the drill bit wears out, or when service, repairs or adjustments need to be made to the bottom-hole assembly, the drill string (drill pipe and other components) is removed from the wellbore and setback. When removing the entire drill string from the well, it is typically disconnected and setback in doubles or triples until the drill bit is retrieved and exchanged. This process of pulling everything out of the hole and running it all back in the hole is known as “tripping.”
Tripping is non-drilling time and, therefore, an expense. Efforts have long been made to devise ways to avoid it or at least speed it up. Running triples is faster than running doubles because it reduces the number of threaded connections to be disconnected and then reconnected. Triples are longer and therefore more difficult to handle due to their length and weight and the natural waveforms that occur when moving them around. Manually handling moving pipe in the derrick and at the drill floor level can be dangerous.
It is desirable to have a drilling rig with the capability to increase safety and reduce trip time. It is desirable to have a drilling rig with the capability of handing stands of drilling tubulars to devices alternative to conventional elevators and top drives. It is also desirable to have a system that includes redundancy, such that if an element of the system fails or requires servicing, the task performed by that unit can be taken-up by another unit on the drilling rig.
Most attempts to automate pipe handling are found offshore. However, solutions for pipe delivery on offshore drilling rigs are seldom transferable to onshore land rigs, due to the many differences in economic viability, size, weight, and transportation considerations.