5 - BHA and BHA Design

Drilling Engineering I BHA and BHA Design

© 2010 Weatherford. All rights reserved.

BHA and BHA Design • The BHA provides the following functions to the drilling operation p – Convey torque from surface at the rotary table to the bit – Transport drilling fluid to the bottom of the hole – Provide WOB – Control well bore direction

© 2010 Weatherford. All rights reserved.

BHA and BHA Design • The type of hole (ie. Vertical, directional, horizontal, extended-reach, etc.) that will be drilled will dictate the main design parameters of the BHA • However, other factors may also impose significant changes on the BHA design g – Formation geology and mechanical characteristics – Torque q & Drag, g Vibration – Axial, Torsional and Pressure loading – Buckling g and Fatigue g – Local Component Availability – Rig g Limitations – Operator Policies © 2010 Weatherford. All rights reserved.

BHA and BHA Design • A Bottom-Hole Assembly (BHA) consists of all components used in the drill string to drill the well – Bit – Collars Co a s – HWDP – Pipe – Jars and Shock Tools – Cross-over, Bit, Shock and Specialty Subs – Mud Motor / Rotary Steerable Tools – Stabilizers © 2010 Weatherford. All rights reserved.

BHA and BHA Design • Components – Bit • C Commonly l th the bit is i selected l t db by th the O Operator t b based d on experience, i pastt performance in the field, or on manufacturer’s specifications • The effects of the bit are usually unknown until after drilling begins • Common concerns with bits are: – ROP – Vibration – Torque – Durability – Steerability & stability (directional BHA)

• Usually a bit is selected per hole section, based on the formation lithologies that will be encountered in the hole section • An extremely wide range of bit types, cutting structures, shapes, designs, etc. are available leading to very complicated analysis – For simulation software, all the bit parameters must be entered, including g dimensioning

© 2010 Weatherford. All rights reserved.

BHA and BHA Design • Components – Tricone / Rock Bit / Roller Cone • C Creates t h hole l b by iimpacting ti th the formation with bit teeth mounted on rolling cones with bearing packs

– PDC (Polycristalline Diamond Carbide)) / Fixed Cutter • Creates hole by scraping or gouging the formation

• Usually used in softer formations

• Usually used in harder formations

• Less rotary torque

• More rotary torque

© 2010 Weatherford. All rights reserved.

BHA and BHA Design • Components – Drill Pipe • The Th mostt common BHA componentt b by quantity tit • Tool joints are upset at both ends for strength but are designed to fail before the pipe body • Classified by: – Size (OD) » 2 3/8” – 6 5/8” – Linear Weight (lb/ft) – Grade » ie. E, X, G, S, Z, V » Specify minimum yield strength – Class » Wall thickness / wear indicator » I – New >80% wall thickness » II - >70% wall thickness » III -