Expandable and Contractable drill bit is a new concept in bits which will allow us to drill super wide boreholes with radii of our choice and at depth of our interest. It will allow us to drill increased diameter borehole, having passed through restricted casing and/or tubing diameter and can provide significant advantages. Among these is the ability to incorporate novel well construction techniques, using both solid and/or expandable tubular, as well as drilling with Casing possibilities, in which casing is run immediately behind the bit. The opportunity to incorporate these techniques can thus enhance well design to yield significant economic and well control gains. Current techniques for drilling such increased diameter holes, such as bi-centered bits and under-reamers, have limitations on their ability to expand, whilst at the same time compromising the cutting structure presented to the formation. Additional limitations include limited reaming and back-reaming capabilities, as well as non-directional response. One embodiment of the technique of Drilling with Casing requires a bit which can be retrieved through existing casing string. To achieve this and to maximize drilling performance requires a device with a formation cutting structure, indistinguishable from a standard PDC drill bit but capable of being withdrawn through a restriction significantly smaller than the borehole size just being drilled. This concept leads to the possibility that a viable solution to the task of drilling increased diameter holes could be a bit that offers substantial expansion and contraction while still presenting full cutting structure to the formation.
In this paper the authors will discuss the earlier problems and solutions and present a new approach with an "Expandable and Contractable Drill Bit". They will discuss the design concept of bit, working, advantages, challenges and finally will conclude that the use of an "Expandable and Contractable Drill Bit" will be a viable tool for variety of drilling applications.