ADVANCED DRILLING USING A DUAL BIT SYSTEM

In conventional drilling a majority of drilling problems occur during tripping such as key seating and wall sticking. This leads to increase in rig time hence cost is unnecessarily high, especially in deep sea drilling.

Conventional drilling techniques use rotary drill bits which need to be replaced depending on the formations encountered. If the formation is very hard, the bit has to be replaced by a diamond bit. This change of bit requires unnecessary increase in trip time and hence rig cost. This trip time which can even take a day especially for deep wells and can be eliminated by using a novel method of a drill bit called a B_Piggy Back Dual BitB_ system.

This paper deals with the design and operation of such a novel Piggy Back Dual Bit system.

This new drill bit system has a tricone bit on the outside and a PDC or diamond studded bit inside. Both the tricone bit and PDC bit are expandable. When hard formations are encountered, the tricone bit is expanded by applied pressure to the mud which engages a latching mechanism in the BHA. By this action also the expandable PDC bit is forced out. The entire expansion mechanism is hydraulically actuated, by the pressure from fluid flowing through the bit. The drilling activity is now controlled by the PDC drill bit doing the drilling through the hard formation, while the tricone bit is now piggy back on the PDC drill bit doing no work at all, other than reaming a bigger hole.

Thus an entire hole can be drilled conveniently without frequent tripping operation to change the bit. Maximum efficiency can be achieved during drilling.

In petroleum industry rig time plays very vital role. By adopting such innovative method as mentioned above tripping time can be substantially reduced.