1. Session 5: CASING DRILLING®
Hydraulics

2. ENGINEERING TOPICS FOR REVIEW
HYDRAULIC ISSUES
System comparison
Annular flow & ECD
Hydraulic lift
Hole cleaning
Underreamer activation
Mud selection
MECHANICAL ISSUES
Torque and Drag
Casing protection
Buckling
Fatigue
Wear
Vibration
Wireline Operations
DIRECTIONAL DRILLING
Motor selection
Directional performance

3. CHANGING PARADIGMS: CONVENTIONAL PRACTICE TO CASING DRILLING®
Our industry has a long history of developing “best practices” for conventional drilling.
Natural tendency is to transfer conventional “best practices” to CASING DRILLING®.
Often conventional “best practices” need to be adjusted for unique conditions of CASING DRILLING®.
The following sessions are aimed at helping sort through these issues.

4. Tesco CDE Software is Main Engineering Calculation Tool

5. Functions of the Hydraulic System
Transport drilled cuttings out of hole.
Control near wellbore fluid.
Support wellbore wall.
Lubricate bit and drillstring.
Power downhole motor (if used).
While avoiding:
Erosion of borehole wall.
Fracturing the formation.
Damage to production zone.

6. Comparison of Casing to Drillpipe & Collars
EXAMPLE
Hole Size = 8.75”
Bit depth = 8,000 ft
9-5/8” set at 500 ft
Flow rate = 450 gpm
Bit Jets = 14, 14, 14, 14
11.8 PPG MUD
PV = 14
Yp = 11
8,000 ft of 7” 23# Casing
COMPARED TO
540 ft 6.25 x drill collars
7460 ft of 4” Drill Pipe
DP & Collars

7. Annular Velocity for Casing is High, but Constant
DP & Collars
Re = 2584
Re = 3947
All sections in turbulent flow
Re = 3268

8. Inverted Pressure Profile (450 GPM)
1438 psi
2181 psi
7” Casing
DP & Collars
ECD = 13.5 ppg
ECD = 12.0 ppg
DPbit=487 psi

9. Re-designed Hydraulics for CASING DRILLING®
(DECREASE FLOW TO 300 GPM, MUD WT TO 10.8 PPG
& BIT JETS TO )
1042 psi
2181 psi
300 GPM
450 GPM
Re = 1919
ECD = 11.9 ppg
7” Casing

10. PUMP HORSEPOWER HHP = P * Q / 1714 Conventional CASING DRILLING®
HHP = Hydraulic horsepower
P = pump pressure ,psi
Q = flow rate, gpm
Conventional
Flow Rate = 450 gpm
Delta P = 2,181 psi
HHP = 572 hp
CASING DRILLING®
Flow Rate = 300 gpm
Delta P = 1,042 psi
HHP = 182 hp
Diesel => 145,000 BTU/gal
Assume 40% efficiency
Diesel cost => $4.00/gal
Savings: hp $1300/day
40% fuel savings observed on TESCO CASING DRILLING® rigs.

11. Minimum ECD ECD Friction Flow Rate
Increased flow rate reduces cuttings load in annulus.
Increased flow rate increases friction in annulus.
Optimum
ECD
Friction
Cuttings load
Flow Rate

12. Drilling with 6 1/8” DC and 4” DP
Lower Flow Rate is Optimal
Drilling with 7” Casing
Drilling with 6 1/8” DC and 4” DP
Depth = 3,200 ft Mud Wt = 8.9
Conventional operating range
Casing Drilling operating range

13. Cuttings Transport ¥ 50 25 12.5 16.7 10 Lower limit set by
Sand in water
Typical muds and cuttings
Annular velocity, ft/min
Typical Casing Drilling range
From Applied Drilling Engineering pp175

14. Is High Annular Velocity Detrimental?
Borehole erosion may be associated with
turbulent flow.
Turbulence typically begins at a Reynolds
Number of 2100 – 2500.
Re = 928 * r * Vel * de / m
r = mud density, ppg
Vel = fluid velocity, ft/sec
m = fluid viscosity, cp
de = equivalent hydraulic diameter
Dhole2 - ODpipe2
Best Estimate: de = Dhole2 + ODpipe2 –
Ln(Dhole / Odpipe)
Approximation: de = * (Dhole - Odpipe)

15. Higher Transition Velocity for Narrow Annuli
Turbulent
8.75 “ hole, 10 ppg mud, Pv = 10, YP = 5

16. Is high annular velocity a concern?
Observations:
Annular velocity is often higher for CASING DRILLING® than
around drill pipe for conventional drilling.
It is not unusual for the flow regime to be turbulent for CASING
DRILLING® applications.
No detrimental effect of turbulent flow has been observed
while drilling with casing (even at 475 ft/min with water).
Some publications indicate borehole wall damage once
thought to be from turbulent flow is actually caused by
drillstring vibration.
Designing flow rate based on ECD and hole cleaning will take
care of concerns about hole erosion.

17. Eccentric Casing in Borehole Results in Reduced ECD
30% reduction

18. Annular DP times end area DP from cuttings times end area
Hydraulic Lift
Flow in annulus lifts casing to
reduce WOB
Also occurs with drill pipe, but is
much less
Is a good monitor of hole cleaning
Better indicator in vertical wells.
Annular
Pressure
Drag Force
End Force
Fluid Flow
Hydraulic Lift =
Fluid Drag +
Annular DP times end area
DP from cuttings times end area

19. Hydraulic Lift Calculations
Drag Force +
End Force HL = p/4 * [Dh*Dc*Dpa +
*Dc2* (re - rm ) ]
Cuttings Force
HL = Hydraulic lift, lb
Dh = borehole diameter, in
Dc = casing OD, in
Dpa = annular pressure loss, psi
rm = clean mud density, ppg
re = effective mud density including cuttings, ppg

20. VAQUILLAS A1 198 Pump-Off Observed at 2074 ft
32,000 lb Pump-Off
Fill Pipe
Note: Blocks were stationary
Time, seconds

21. Hydraulic Lift Helps Monitor Condition of Hole
Balling on casing
Pack off on borehole wall
Balled Shale from shaker after working casing.

22. Procedure to Monitor Hydraulic Lift
Record hookload with bit off bottom, pumps off, and casing
rotating slowly.
Engage mud pump(s) and bring flow rate up to drilling speed
and record hookload.
Difference in hookload between having pumps on and off is
hydraulic lift.
Zero WOB
Begin drilling
In fast drilling formations, if ROP decreases while drilling joint
down, pick up an re-zero WOB to zero out cuttings loading
effect.

23. Back-Reaming May Help Clean the Hole
30000
Trip
Pump-Off
25000
Trip
Predicted
20000
Backreamed each connection
15000
Hydraulic Lift, lb.
10000
5000
1200
2200
3200
4200
5200
6200
Measured Depth, ft
ANB Cattle Co

24. Typical Lobo Hydraulic Lift
(without Back Reaming)
* Predicted before drilling, constant 320 gpm
Walter Despain

25. Hydraulic Lift Warns of Lost Circulation
Vaquillas A1 198

26. Annular Pressure May Change as Joint is Drilled
Time, minutes
BMT 179
Example 1585 ft

27. Annular Pressure Changes While Drilling
WOB Zero
Harder formation
Soft formation
BMT 179 high speed data
Time, minutes
Example 2518 ft

28. Hydraulic Lift Affects Proper Bit Start After Connection
Start rotary (breaks gels).
Bring up mud pump.
After pressure stabilizes, zero WOB.
Set bit on bottom.
Adjust RPM & WOB.
Must be done each time flow rate is changed.

29. What Happens if flow Rate is Changed with Bit on Bottom?
One-time change in WOB due to casing length change.
Permanent change in hydraulic lift.
Must pick up off bottom to change flow rate and re-zero WOB.

30. Thin Mud is Better than Reduced Flow Rate
Mud A – 9.25 ppg, 18 cp, 12lb/100 ft2
Mud B – 8.9 ppg, 12 cp, 5lb/100 ft2
5,000
10,000
15,000
20,000
1000
3000
5000
Measured depth, ft
Hydraulic Lift, lb
Mud A gpm
Mud A gpm
Mud B gpm

31. CASING DRILLING® Mud Selection
Conventional mud design uses chemistry and commercial mud products to develop fluid loss control.
Rheology designed for cuttings carrying capacity at low velocities.
Drilled solids and “Plastering Effect” with CASING DRILLING® provides superior fluid loss control.
Operator often wants to provide “Cadillac” mud on initial use of CASING DRILLING®.
Thin muds with slightly lower density are much superior for CASING DRILLING®.

32. CASING DRILLING® Pilot Bit Selection
Best bit for conventional drilling may not be best bit for drilling with casing.
Pilot bit is smaller.
Flow rate is less.
Nozzle size may be dictated by LCM.
Typically use fewer blades on PDC bit to better accommodate flow rate and limited nozzle size.
May use less aggressive bit than underreamer.
Matrix bit is best to control erosion
Flow may be high for bit size.
Erosion control on steel bit is less effective.
Erosion

33. Underreamer Activation Pressure
Type 5 Underreamer
Activation
Size Pressure
4-1/2” psi
5-1/2” psi
7” psi
9-5/8” psi
10-3/4” psi
13-3/8” psi P1
Spring
Force d1 d2 P2
Internal Jet
Required activation pressure depends on piston area, rod area, spring design.
Required activation pressure independent of mud properties and flow rate.
Delivered activation pressure depends on flow rate, mud weight, bit nozzles, and internal nozzle. d3 P3
Bit Jets Pa

34. Underreamer pressures cannot be determined accurately by surface flow test due to cavitation at low back pressure.

35. Hydraulic Balancing
Mud Motor
MWD
Underreamer
RSS
Bit
Annulus

36. Hydraulics Balancing (The Annulus)
Is the flow rate enough to clean the hole? 150 ft/min
Is the flow rate low enough that it will not break down
the formation? (2 ppg leakoff, 9.2 ppg mud)
What is the hydraulic lift?
180 GPM
Annulus
400 GPM

37. Hydraulics Balancing (MWD / RSS)
CASING DRILLING™ typically required less flow
than a conventional application for the size of
directional tools used.
What flow kits are available in the
Is there a pressure drop requirement for the RSS
180 GPM
Annulus
400 GPM
300 GPM
600 GPM
MWD / RSS

38. Hydraulics Balancing (The Mud Motor)
What are the options for a low flow motor.
7/8 power sections
What is the rev/gal. Does this limit the upper flow
range?
180 GPM
400 GPM
Annulus
300 GPM
MWD / RSS
600 GPM
300 GPM
Mud Motor
550 GPM

39. Hydraulics Balancing (The Underreamer)
Does the flow rate provide enough differential
pressure to open the Underreamer?
This is only an issue at very low flow rates
180 GPM
Annulus
400 GPM
300 GPM
MWD / RSS
600 GPM
300 GPM
Mud Motor
550 GPM
210 GPM
Underreamer

40. Hydraulics Balancing (The Bit)
What is the HHP? (>2.0)
How small can you run the jets?
(what is the LCM program?)
What’s the minimum pressure drop for RSS to operate.
180 GPM
Annulus
400 GPM
300 GPM
MWD / RSS
600 GPM
300 GPM
Mud Motor
550 GPM
210 GPM
Underreamer
310 GPM (4 x 12)
Bit

41. Operating Flow Range for CASING DRILLING™
Hydraulics Balancing (The Sum of the Parts)
180 GPM
Annulus
400 GPM
300 GPM
MWD / RSS
600 GPM
300 GPM
Mud Motor
550 GPM
210 GPM
Underreamer
310 GPM (4 x 12)
Bit
Minimum 310 GPM
Maximum 400 GPM
Operating Flow Range for CASING DRILLING™

42. Hydraulics Summary Higher AV is usually not a problem.
Higher ECD is manageable.
Fluid loss improved by mechanical plastering.
Hydraulic lift provides means of monitoring hole conditions.
Thin mud should be used as much as possible.
Pipe rotation increases pressure only slightly.
Discharge coefficient for bit nozzle should be 1.03.
CASING DRILLING® requires less horsepower resulting in fuel savings
Circulating pressures can be calculated adequately with conventional flow models.