Extendable Arm Drill Bit: A Novel Idea

Abstract In conventional vertical drilling, the drill string is tripped in, allowed to drill to the predetermined depth and tripped out so that a bit of a smaller diameter can be attached to continue drilling the hole. Extendable arm drill bit is essentially a rotary drill bit in which the roller cones can be extended so that the diameter of the bit corresponds to the required diameter of the hole to be drilled. This extension is done hydraulically by diverting some of the pressure of the circulating drilling mud to compress an assembly which would push down the roller cones, thus increasing the diameter. Now as drilling continues, the diameter of the bit can be adjusted by diverting a lesser amount of circulating pressure on the bit thereby "contracting" it to achieve a smaller diameter. It could be imagined like a tripod standing on its three legs. The idea behind this proposal is to save the time, power and the cost of tripping operations of the drill string to change the bit to a smaller diameter one, by reducing the frequency of tripping the string, if not completely eliminating the process. This would result in an increase in the overall rig efficiency, both in terms of time and mainly money. Thus, the time and money saved can be diverted, if required, towards problems arising due to unexpected hole problems and pipe stuck-ups. This paper gives the description of the most suitable design of such a drill bit and the possible modifications of this concept to be applicable in future developments.