Assembly bottom design hole
When rotary drilling with roller cone bits , the type of bit makes very little difference to whether an assembly builds, holds or drops angle. Mainly because directional control is determined by the configuration of stabilizers and collars and by varying the drilling parameters. However, the type of bit has a significant influence on walk rates. Conventional tri-cone bits cause right-hand walk in normal rotary drilling. Generally speaking, long tooth bits drilling soft to medium hard formations give a greater right walk tendency than short tooth bits drilling a harder formation. This is because soft formation bits have a larger cone offset and cut the rock by a gouging action.
Bottom hole assembly
Bottom hole assembly (BHA) design for directional control - PetroWiki
Content of PetroWiki is intended for personal use only and to supplement, not replace, engineering judgment. SPE disclaims any and all liability for your use of such content. More information. The bottom hole assembly BHA is a portion of the drillstring that affects the trajectory of the bit and, consequently, of the wellbore. The BHA design objective for directional control is to provide the directional tendency that will match the planned trajectory of the well. The bit side force is the most important factor affecting the drilling tendency.
Bottom Hole Assembly 101
The Bottom Hole Assembly BHA is a key component of the drilling system, consisting of various components and tools including the drill bit itself which operate at the bottom of the wellbore and physically drill the rock. The BHA is connected to the drilling rig by the drill pipe, an extendable hollow tube which conveys the mechanical and hydraulic energy and movement from the surface rig systems to the bottom hole assembly. This complex arrangement of tools varies considerably depending on requirements, and can stack up to 1, ft long.
Because all packed assemblies will bend to some extent, however small the amount of deflection, it is not possible to make a perfectly vertical hole. The rate of hole angle change may be kept to a minimum for normal deviation but occasionally conditions will arise where the total hole deviation must be restricted to closer tolerances. When this condition occurs the pendulum technique is employed, however if it is anticipated that a packed hole assembly will be required after reduction of the hole angle, the packed pendulum technique is recommended.