#Drilling technology, #Directional drilling design #basic hole pattern

1. Directional
Drilling
Design

2. Definition
• The art and science
involving the intentional
deflection of a wellbore in
a specific direction in order
to reach a predetermined
objective below the
surface of the earth.

3. Purpose of Directional and Horizontal Drilling
• One of the primary uses of
directional drilling was to
sidetrack a well even if it was to
go around a stuck BHA

4. Purpose of Directional and Horizontal Drilling
• Sometimes multiple
sidetracks are used to
better understand geology
or to place the wellbore in a
more favorable portion of
the reservoir

5. Purpose of Directional and Horizontal Drilling
• Straight hole drilling is a special
application of directional drilling
– To keep from crossing lease lines
– To stay within the
specifications of a drilling
contract
– To stay within the well spacing
requirements of a developed field

6. Purpose of Directional and Horizontal Drilling
• Drilling multiple
wells from a
single structure
or pad
• Most offshore
development
would not be
possible without
directional drilling

7. Purpose of Directional and Horizontal Drilling
• Inaccessible surface
location
• Drilling in towns,
from land to offshore
and under
production facilities

8. Purpose of Directional and Horizontal Drilling
• Drilling around salt
domes
• Salt can cause significant
drilling problems and
directional drilling can be
used to drill under the
overhanging cap

9. Purpose of Directional and Horizontal Drilling
• Steeply dipping
sands can be drilled
with a single
wellbore

10. Purpose of Directional and Horizontal Drilling
• Fault drilling
• In hard rock, deviation
can be a problem
• Sometimes the bit can
track a fault
• Drilling at a higher
incident angle minimizes
the potential for
deflection of the bit

11. Purpose of Directional and Horizontal Drilling
• Relief well drilling
• Directional drilling into the
blowout when the surface
location is no longer
accessible
• Very small target and
takes specialized
equipment

12. Purpose of Directional and Horizontal Drilling
• Horizontal drilling
• Increasing exposure of the
reservoir to increase
productivity

13. Purpose of Directional and Horizontal Drilling
• Multilateral drilling
• Drilling more than
one wellbore from a
single parent
wellbore

14. Purpose of Directional and
Horizontal Drilling
• Extended reach wells are
characterized by high
inclinations and large
departures in the
horizontal plane

15. Purpose of Directional and Horizontal Drilling
• Extended reach wells are wellbores where the
horizontal departure HD is significantly higher
than the true vertical depth of the well TVD.
• Extended reach wells have been drilled with
greater HD/TVD ratios.

16. Purpose of Directional and Horizontal Drilling
• BP drilled a well at Wytch Farm with a measured depth of
34,967’ (10,658 m), a TVD of 5,266’ (1,605 m) and
horizontal departure of 33,181’ (10,114 m)

17. Basic Hole
Patterns

18. Basic hole Patterns
• There are 4 basic hole patterns
• Not all wells conform to the basic hole patterns and may
be a combination of patterns
• For simplicity, the basic hole patterns are defined as:

19. Basic hole Patterns
• Type I is a build and hold
– Drilled to a relatively
• shallow KOP
– Deflected to a maximum
inclination
– The inclination is held
relatively constant to TD

20. Basic hole Patterns
• Type II is a build, hold and
drop often termed an “S”
curve
– Multiple targets
– Around salt domes
– More torque and drag
for the same departure

21. Basic hole Patterns
• Type III is a continuous
build to target
– Deeper kickoff point
– Small horizontal
departure
– Less expensive

22. Basic hole Patterns
• Type IV is a horizontal
wellbore
– Build rates may be high
– Hold inclination is near
90 degrees

23. Deviation Control

24. Deviation Control
• If formation forces causes
the well to deviate,
directional drilling
techniques can be used to
help hit the target

25. Deviation Control
• Everyone agrees that deviation is caused by the
formations drilled
• Not everyone agrees as to how the formation causes
deviation
• Bed dip is a primary requirement for deviation
• If the formations are flat (no dip), deviation is usually not a
• problem

26. THEORIES OF CAUSES OF DEVIATED
HOLES
• Anisotropic theory is the
most widely believed
• – Bed dip causes the bit
to build inclination as
discussed in directional
drilling

27. Deviation Control
• Anisotropic theory

28. Deviation Control
• Formation drillability
theory
• – The harder formation
does not drill as fast as
the soft formation
causing deviation

29. Deviation Control
• Miniature whipstock
theory
• – The formation
fractures perpendicular
to the bedding plane
creating miniature
whipstocks on the low
side of the hole

30. Deviation Control
• Drill collar moment
theory
– The hard formation
causes a bending
moment at the bit
– Bit deviates up dip going
from soft to hard formation
– Bit deviates down dip
going from hard to soft
formation

31. Deviation Control
• Raymond Knapp
theory
• – The bit does not drill a
gage hole causing the
bit to deviate randomly

32. Deviation Control
• In the final analysis there is no one satisfactory
explanation for deviation.
• It appears to be related to geology.
• Deviation is never greater than bed dip.
• All theory and practice indicates that the maximum
deviation is perpendicular to or parallel to the formation
dip.
• In fact, Lubinski's model which is the most widely
accepted, suggests that total deviation will always be less
than formation dip.

33. Deviation Control
• The problems associated with deviation:
– Miss the target
– Keyseats
– Casing wear
– Rod and tubing wear
– Torque and drag

34. Deviation Control
• What are the causes of the
problem
– Miss the target
– Keyseats
– Casing wear
– Rod and tubing wear
– Torque and drag
Inclination
Dogleg severity
Dogleg severity
Dogleg severity
Dogleg severity

35. Deviation Control
• Methods to control
deviation
– Use a pendulum
assembly
– Reduce bit weight
– Works to reduce the
• inclination
– Does not reduce dogleg
severity

36. Deviation Control
• Other methods used to control deviation
– Woodpecker drill collar
– Two cone bit
– Hammer tool
– DM bit

37. Deviation Control
• – The woodpecker
drill collar had
some of the metal
removed from the
side of the drill collar
causing the center of
mass to be different
from the center of the
collar

38. Deviation Control
–As the collar was rotated,
the off center mass was
supposed to whip the low
side of the hole
–Unfortunately, it whips all
sides of the hole

39. Deviation Control
–The two cone bit has fewer inserts touching the bottom of
• the hole at any one time
–The bit would drill faster if the bit weight was the same

40. Deviation Control
–Hammer tool used in
air drilling operations
–The assumption is that the
inclination stays lower
since low bit weights are
required to drill at higher
penetration rates

41. Deviation Control
The DM bit was designed on a 39°
pin angle to drill a gage hole
(Raymond Knapp theory)

42. Deviation Control
• What is the real problem with
deviated wells?
– Miss the target
–Keyseats
–Casing wear
–Rod and tubing wear
–Torque and drag
Inclination
Dogleg severity
Dogleg severity
Dogleg severity
Dogleg severity

43. Deviation Control
• Inclination causes you to miss the target
• Dogleg severity causes everything else
• Don’t worry as much about inclination and worry about
controlling dogleg severity

44. Deviation Control
• Pendulum assemblies are designed to control inclination
but
• are not stiff and will not control dogleg severity
• Packed hole assemblies are designed to control
dogleg severity and will not minimize inclination

45. Deviation Control
• Packed hole assemblies will build inclination
• Running lower bit weight will not change the forces at the
bit

46. Deviation Control
• Effect of bit weight on
deviation tendency
• Increasing bit weight and
ROP changes the resultant
direction of the bit

47. Deviation Control
• Even if bit weight causes deviation, we must decide what is
• important
– Drill slow and minimize inclination
– Drill faster and minimize dogleg severity
• How much is inclination worth?

48. Deviation Control
• If you decide to drill slow,
the well costs more
• Offset the surface location
to drill faster and hit the
target

50. Problems caused by doglegs
– Torque and drag
– Keyseats and casing wear
– Fatigue

51. • Torque and drag are
caused by the friction
between the drill string
and the wall of the hole
• Higher tension and
doglegs result in higher
torque and drag

52. • Keyseats and casing
wear are caused by the
drill string being rotated
in a dogleg with higher
tension

53. • Fatigue is caused by
rotating the drill
• string in a bend
• The cyclic stresses cause
fatigue
• As the amount of tension
increases in a dogleg, the
amount of bending that can
be tolerated before causing
fatigue decreases