Appropriate selection of a bottom-hole assembly BHA is critical to the success of a drilling operation. In US Land drilling, these assemblies are often selected using local heuristics rather than rigorous analysis. These heuristics are frequently derived from the incentives of the directional contractor as opposed to incentives for the operator. Large motor bends enable more rotation though the curve and reduce the possibility of tripping for build rates. Unstabilized motors are believed to aid sliding and tool face control.
Bottom hole assembly (BHA) design for directional control
Bottom hole assembly (BHA) design for directional control - PetroWiki
The bottomhole assembly BHA is the component of the drill string located directly above the drill bit and below the drill pipe. The primary component of the BHA is the drill collar. Therefore, it has a signifi cant effect on drill bit performance. The other components of BHA are stabilizers, jars, reamers, crossovers, shocks, hole-openers, and various subs such as bit subs, shock subs Figure However, some classify the drill bit as a part of the BHA. It hangs below the drill pipe and provides weight to the drill bit to induce the teeth to penetrate the formation. The functions of BHA are i to protect the drill pipe in the drill string from excessive bending and torsional loads, ii to control direction and inclination in directional holes, iii to drill more vertical and straighter holes, iv to reduce severities of doglegs, key seats, and ledges, v to assure that casing can be run into a hole, vi to reduce rough drilling rig and drill string vibrations , and xi as a tool in fi shing, testing, and work over operations.
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A bottom hole assembly BHA is a component of a drilling rig. It is the lowest part of the drill string , extending from the bit to the drill pipe. The assembly can consist of drill collars, subs such as stabilisers, reamers, shocks, hole-openers, and the bit sub and bit.