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a device with a formation cutting structure, indistinguishable from a standard PDC drill bit but capable of being withdrawn through a restriction significantly smaller than the borehole size just being drilled.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.


Current methods will never permit a single diameter bore hole to be drilled along its entire length, but new techniques have been recently developed which require a radical approach to the drilling process itself.

In situations where borehole stability is a concern, lining the hole at the same time as drilling removes some of the uncertainty from the operation and achieves reduced annular space when used with concentric casing strings. It may also be used with a mono-bore construction. Drilling with casing, however, also creates a whole set of challenges and requires a re-think of traditional drilling practices.

The width of a hole at every depth especially in the payzone is limited using the conventional drilling methods. This is because hole size is limited due to factors like cost of drilling a wide hole, rate of penetration, power requirements, size of BOP required, larger rigs required to handle more power and more weight, hence dramatically escalating the cost of the project.

Having large borehole at every depth or in the payzone is beneficial because it would:

  1. Enhance production

  2. Control the problem of sand production

  3. Accommodate a lot of down hole equipment

Expandable and Contractable bit allows us to enlarge the borehole radius up to the order of a few feet selectively in zones we choose. This is made possible by the EC bit, which uses rack and pinion mechanism with its unique clockwise and anticlockwise rotation to drill super wide borehole.

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