Abstract: A method is disclosed for drilling a borehole through a production zone underlying an overburden of various earth formations. The method includes drilling the borehole through the overburden with at least one drill bit adapted to optimize at least one drilling performance parameter, and then drilling the borehole through at least part of the production zone with at least one drill bit adapted to optimize at least one production performance parameter.

Abstract: A roller cone drill bit having selected left hand walk is disclosed. The bit includes a bit body adapted to couple to a drill string, and a plurality of legs depending from the bit body. Each leg has a roller cone rotatably mounted thereon. Each cone includes a plurality of cutting elements thereon. At least one cone has a nose point of its profile displaced radially inward with respect to a nose point of the profile of the other cones. A roller cone drill bit having selected right hand walk is also disclosed. The bit include a bit body adapted to couple to a drill string, and a plurality of legs depending from the bit body. Each leg has a roller cone rotatably mounted thereon, each cone including a plurality of cutting elements thereon defining a profile. At least one cone has a nose point of the profile displaced radially outward with respect to a nose point of the profile of the other cones.