Hydraulic drilling rig

Details Hydraulic drilling rig Hydraulic drilling rig

2001-02-15

2002-02-05

Smith, Scott A. (Department: 3721)

Tool driving or impacting

Automatic control of power operated means

Tool advance causing or controlling means

C173S152000, C173S159000, C173S190000, C173S213000, C175S220000, C245S004000, C245S004000, C245S004000

Reexamination Certificate

active

06343662

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to drilling rigs, and in particular to rigs for drilling gas and oil wells, and rigs for servicing of existing wells. Even more particularly, the present invention relates to heavy-duty rigs for deep-water offshore drilling from drill ships or ocean-going drilling platforms.
BACKGROUND OF THE INVENTION
Drilling an oil or gas well involves two main operations: drilling and tripping. To commence the drilling procedure, a drill string terminating with a drill bit is positioned within a drilling rig and rotated such that the drill bit bores into the ground or into the seabed, in the case of offshore drilling, until it reaches a predetermined depth or penetrates a petroleum-bearing geological formation. The components of the drill string such as drill collars and drill pipe are threaded for interconnection. Depending on what type of drive system is being used, the uppermost length of drill pipe in the drill string is connected either to a kelly or to a top drive, both of which are further described hereinafter. As the drill bit advances and the top of the drill string approaches the working platform or drill floor of the drilling rig, additional lengths of drill pipe must be added to the drill string in order to advance the well further into the ground. This is accomplished by temporarily supporting the top of the drill string near the drill floor level (using devices called “slips”), disconnecting the kelly (or the top drive, as the case may be) from the top of the drill string, and then lifting a new section of drill pipe into position using the rig's elevating system and screwing it into the top of the drill string. The kelly (or the top drive) is then reconnected to the drill string, and drilling operations resume until it is again necessary to add drill pipe.
Perhaps the most common and well-known drive means for rotating a drill string is the rotary table, which is a rotating mechanism positioned on the drill floor, and which entails the use of a kelly, referred to previously. The kelly is essentially a heavy, four-sided or six-sided pipe, usually about 42 feet long or 57 feet long for offshore rigs. The rotary table has rotating bushings shaped to accommodate the kelly, plus roller bearings which allow the kelly to slide vertically through the bushings even as the rotary table is rotating. The kelly is suspended from the rig's main hoist, in conjunction with various accessories required for drilling operations such as swivel and pipe elevators. With the kelly connected to the top of the drill string, the hoist lowers the drill string until the lower end of the kelly is positioned within the bushings of the rotary table. The rotary table is then activated, rotating both the kelly and the drill string connected to it, thereby turning the drill bit at the bottom of the drill string and advancing the well to a greater depth. The process of turning the drill bit to advance the hole is referred to as “making hole”.
An increasingly common alternative to the rotary table is the top drive unit, which applies rotational drive at the top of the drill string, rather than at the drill floor as in the case of the rotary table. Top drive units are typically driven by either hydraulic or electric power. A significant advantage of the top drive is that a kelly is not required; instead, the drill string is connected directly to the top drive, as previously described. The top drive is supported by the rig's main hoist, and moves downward along with the drill string as drilling progresses. A rig using a top drive must provide some means for resisting or absorbing the torque generated by the top drive as it rotates the drill string, so that the top drive will be laterally and rotationally stable at all stages of drilling. This is typically accomplished by having the top drive travel along vertical guide rails built into the rig superstructure.
Tripping is a necessary but unproductive part of the overall drilling operation, and involves two basic procedures. The first procedure is extracting drill pipe from the well (referred to in the industry as “pulling out of hole” mode, or “POH”), and the second is replacing drill pipe in the well (“running in hole” mode, or “RIH”). Tripping may be necessary for several reasons, such as for replacement of worn drill bits, for recovery of damaged drill string components, or for installation of well casing.
In POH mode, the kelly (if there is one) is removed temporarily, the drill string is connected to the pipe elevators, and the drill string is then pulled partially out of the hole as far as the hoisting mechanism and geometry of the drilling rig will permit. The drill string is then supported by the slips so that the section or sections of the drill pipe exposed above the drill floor may be disconnected or “broken out” and moved away from the well. The elevators then reengage the top of the drill string so that more of the drill string may be pulled out of the hole. This process is repeated until the desired portion of the drill string has been extracted. The procedure for RIH mode is essentially the reverse of that for POH mode.
It is well known to use cable-and-winch mechanisms for hoisting and lowering the drill string and casing string during the drilling of gas and oil wells. In such mechanisms, a heavy wire-rope cable (or “drilling line”) runs upward from a winch (or “drawworks”) mounted at the drill floor, then is threaded through the sheaves of a “crown block” mounted high in the derrick or mast of the rig, and then down through the sheaves of a “travelling block”, which moves vertically with the load being hoisted. The entire weight of the drill string, which can be several hundred tons, is transferred via the travelling block, drilling line, and crown block to the rig's derrick, which accordingly must be designed and built to withstand such loads.
A significant disadvantage of cable-and-winch rigs is that the drilling line will deteriorate eventually, entailing complete removal and replacement. This may have to be done several times during the drilling of a single deep well. Drilling line cable, being commonly as large as two inches in diameter, is expensive, and it is not unusual for a rig to require a drilling line as up to 1500 feet long. Replacement of the drilling line due to wear accordingly entails a large direct expense. As well, the inspection, servicing, and replacement of drilling line typically results in a considerable loss of drilling time, and a corresponding increase in the overall cost of the drilling operation.
In hydraulic drilling rigs, hydraulic cylinders are used in various configurations to provide the required hoisting capability. Some hydraulic rigs also use cables and sheaves but have no winch; others eliminate the need for cables and sheaves altogether. A significant advantage of the latter arrangement is that vertical hoisting forces are not transferred to the mast, but rather are carried directly by the hydraulic cylinders. The mast therefore may be designed primarily for wind loads and other lateral stability forces only, and can be made much lighter and thus more economical than it might otherwise have been.
Whatever type of rig is being used, drilling operations require a convenient storage area for drill pipe that will be either added to or removed from the drill string during drilling or tripping. On many rigs, drill pipe is stored vertically, resting on the drill floor and held at the top in a rack known as a “fingerboard.” This system requires a “derrickman” working on a “monkey board” high up in the rig, to manipulate the top of the drill pipe as it is moved in and out of the fingerboard. Other rigs use a “pipe tub”, which is a sloping rack typically located adjacent to and extending below the drill floor. Drill ships and ocean-going drilling platforms often provide for vertical or near-vertical storage of drill pipe in a “Texas deck” located under the drill floor, with access being provided through a large opening in the drill floor.
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