drilling bha

1. Bottom Hole Assembly
(BHA)

2. Contents
• Introduction
• Components & Functions
• Design
• Types
• Summary
• References

3. Introduction

4. Components
&
Functions

5. List of components:
• Drilling bits
• Drill collars
• HWDP
• Stabilizers
• Reamers
• Subs
• Thrusters
• Shock sub
• Jars
• Motors
• Turbines
Components & Functions

6. • Drilling bits
 Function
 Types
1) Rock-Bits
 According to cutters:
 Milled tooth bit
 Tungsten carbide insert bit
(TCI)
 According to no. of cones:
 Two cone bit
 Three cone bit
 Four cone bit
Components & Functions

7. • Drilling bits Types
2) Fixed Cutter
 PDC bit
 Impregnated bit
 Composite bit
Components & Functions

8. • Drilling bits
 Bit selection
 Formation type
 Mud type
 Well profile
 Drilling parameters
 Bit size
Components & Functions

9. • Drilling bits
 Hole opener
 Core bits
Components & Functions

10. • Drill collars
Description and Function
Types
1) Spiral
 Reduce possibility of differential wall stuck
2) Square
 Prevent deviation from existing hole
3) NMDC
 Shield directional survey instruments
Components & Functions

11. • HWDP
Description
Function
1)Transition between DC and DP is more
resistant to fatigue than DP
2) Recommended than DC for slim drilling
3)Recommended than DC for high angle
drilling
Components & Functions

12. • HWDP
Advantages
1) Permits high speed drilling with less torque
2)Reduces differential stuck and torque (less
contact area than DC)
3)Increases the buckling load (central upset
limit)
4) Acquires faster tripping
5) No loss of BOP control
Components & Functions

13. • Differece between HWDP & DP
Components & Functions

14. • Stabilizers
 Description
 Types
1) Sleeve
2) Replaceable blades
3) Integral
4) Long integral
5) Nipple with welded-on blades
Components & Functions

15. • Stabilizers Types
Components & Functions

16. • Stabilizers
 Role in
1) Directional drilling
2) BHA Centralizing
3) Prevention of buckling
4) Rock cutting
5) BHA Vibration
6) Pipe stuck
7) Torque and drag
Components & Functions

17. • Reamers
 Description
 Types of Rollers
1) Milled teeth roller
2) Tungsten carbide roller
3) Slick roller
Components & Functions

18. • Reamers
 Functions
1)Reduce torque by reducing the friction on
the BHA contact points
2) Cut gauge hole by the rollers
3) Reduce vibration
Components & Functions

19. • Subs
 Types
1) Crossover Sub
2) Float sub
 Advantages and
disadvantages
Components & Functions

20. • Subs
3) Circulating Sub
 Position
Above the MWD or the
motor in directional drilling
Above the bit in rotary
drilling
 Function
Used for LCM pumping
Used for fast hole cleaning
Types
Components & Functions

21. • Subs
4) Dart Sub
 Description
It is a landing sub for
drop in back pressure
valve
 Function
Used in Kick prevention
during POOH
Types
Components & Functions

22. • Subs
5) Bent Sub
 Description
Small collar provides an
offset (fixed angle 1-3° in
½° increment)
 Function
Used as a deflection tool
in the directional drilling
Types
Components & Functions

23. • Thrusters
 Description
 Applications
1)In difficult transfer of DC wt. to the bit
due to high drag
2) In high vibrations
3) In WOB control to optimize ROP
Components & Functions

24. • Shock Sub
 Function
 Choice constraints
 Spring rate should be such that the build
up of a tri-lobed bottom hole pattern is
prevented for the operated speed range.
 Should never be run fully closed or opened
but in its mid position.
Components & Functions

25. • Jar
Description
Operation & Function
Types
1) Drilling jar
2) Fishing jar
Components & Functions

26. • Mud motor
 Rotating the bit while the drill string is stationary
depends on rev/gallon (no. of loops).
Components & Functions

27. • Turbine motor
 Rotating the bit while
the drill string is
stationary depends on
rev/gallon (no. of
stages).
 Turbine motor gives
more rpm than the
mud motor.
Components & Functions

28. Design

29. Design
• Design involves determination of
1) Drill pipe length
2) Drill pipe weight
3) Drill pipe grade
• Design depends on
1) Hole depth and size
2) Mud weight
3) Safety factor (SF)
4) Drill collar length and weight

30. Design
• BHA design criteria are
1) Tension
2) Collapse
3) Shock Loading
4) Torsion

31. • Drill collars
Design
1) Buoyancy factor method
 ABW=BF * Wt.DC * SF
2) Pressure area method
BF1= - P A BF2= + PA
 ABW=BF1+BF2+ Wt.DC
Components & Functions

32. Design Design Criteria
1) Tension
• P= (Ldp * Wdp + Ldc * Wdc) * BF
where BF= (1- ρm/ρs)
• So the Dp strength expressed in
terms of yield strength should stand
this load. Dp
Dc
Bit
J J
P

33. Design Design Criteria
1) Tension
• Max. tensile design load (Pa) is 90%
of the theoretical yield strength (Pt).
Pa= Pt*0.9
• Margin of overpull (MOP)= Pa-P
• The design values of MOP ranges
from 50000-100000 lb
• SF= Pa/P
= Pt*0.9/ (Ldp * Wdp + Ldc * Wdc) * BF
• Ldp= [Pt*0.9/ SF*Wdp*BF]- Wdc*Ldc/Wdp
• Ldp= [(Pt*0.9-MOP)/Wdp*BF]-
Wdc*Ldc/Wdp
Dp
Dc
Bit
J J
P

34. Design Design Criteria
2) Collapse
• It is the external pressure required to
cause yielding of drillpipe or casing.
• This depends on the differential
pressure across the pipe body.
• The differential pressure Δp can be
expressed by the following equation
Δp= (L* ρ1/144)- [(L-Y)* ρ2/144]
Case 1: Empty pipe
Y=0 & ρ2=0
Δp=L* ρ1/144
Case 2: ρ1=ρ2=ρ
Δp=Y* ρ/144
Note: Length is in ft. and ρ is in pcf

35. Design Design Criteria
3) Shock Loading
• It arises whenever slips are set on moving
drillpipe and can contribute to parting of pipe in
marginal designs.
Fs= 3200 Wdp;
Wdp: weight per unit length in air

36. Design Design Criteria
4) Torsion
Case 1: Drillpipe
subjected to
pure torsion
Q=0.096167*J*
Y /D
Case 2: Drillpipe
subjected to both
torsion and tension
Qt=[0.096167*J/D]*(Ym
2-
P2/A2)
J= polar moment of inertia =0.098175*(D4-d4)
D= outside diameter (in), d= inside diameter (in)
Ym=yield strength (psi)
P= total load in tension (lb)
A= cross-sectional area (in2)
m
Where,
Q= torsional yield strength (lb-ft)
Qt= torsional yield strength (lb-ft)

37. Types

38. Types
1) Slick BHA
• defined as one in which no stabilizer is used.
• consists of bit, drill collars and drillpipe.
• is suitable only for mild crooked hole
formations.
• are seldom used except to drill to Kick-off point
in directional drilling.

39. Types
2) Pendulum BHA
• is used to reduce hole deviation as in the drop-
off section of an S-type directional well.
• is used to drill soft, unconsolidated formations.
Pendulum technique:
It relies on the principle that
the force of gravity may be
used to deflect the hole
back to vertical
F
θ

40. Types
2) Pendulum BHA
• Pendulum BHA consists of several drill
collars to provide the pendulum force.
• Maximum pendulum force can be
obtained by placing the first stabilizer as
high as possible. However, this exposes
the pendulum technique to failure.
• Main disadvantage is obtaining
misaligned hole difficult for running the
casing.
Solution: Min. drill collar OD
=2(csg coupling OD)- bit
OD

41. Types
3) Packed hole assembly
It relies on the principle that two points will contact
and follow a sharp curve, while three points will
follow a straight line.

42. Types
3) Packed hole assembly
It got three types depending on the severity of the crooked
hole tendencies.
Mild crooked hole
Packed BHA
Medium crooked hole
Packed BHA
Severe crooked hole
Packed BHA
stabilizer stabilizer
stabilizer
Stabilizer or
reamer
Stabilizer or
reamer
Vibration
dampener
Vibration
dampener
30 ft drill collar
30 ft drill collar
Zone III
Zone II
Zone I
Short drill collar
bit bit bit
Rest of string

43. Summary

44. Summary
• BHA main components are bits, DC, DP, HWDP,
stabilizers, reamers, subs, thrusters, jars,
motors and turbines.
• BHA design criteria are tension, collapse, shock
loading and torsion.
• BHA main types are Slick, Pendulum and
Packed.

45. References

46. References
• CH.3, Part 1, Section 6,Vol 2, Well engineering
knowledge, Shell round one
• Rabia, Hussain. Oil well Drilling Engineering.
1985

47. Thanks For Your Attention