®
Session 5: CASING DRILLING
Hydraulics
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
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.
Tesco CDE Software is Main
Engineering Calculation Tool
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.
Comparison of Casing to Drillpipe & Collars
7” Casing
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 2.812 drill collars
7460 ft of 4” Drill Pipe
DP & Collars
Annular Velocity for Casing is
High, but Constant
7” Casing
DP & Collars
0
1000
Casing
DP & Col
2000
Re = 2584
Depth, ft
3000
4000
Re = 3947
5000
All sections
in turbulent
flow
6000
7000
Re = 3268
8000
100
200
300
400
500
Annular velocity, ft/min
Inverted Pressure Profile (450 GPM)
7” Casing
1438 psi 2181 psi DP & Collars
0
1000
2000
Depth, ft
3000
4000
Casing
DP & Col
5000
6000
7000
ECD = 13.5 ppg
DPbit=487 psi
8000
ECD = 12.0 ppg
0
500
1000
1500
2000
Pressure, psi
2500
Re-designed Hydraulics for CASING DRILLING®
(DECREASE FLOW TO 300 GPM, MUD WT TO 10.8 PPG
& BIT JETS TO 11-11-11-11)
1042 psi
2181 psi
0
Casing
DP & Col
1000
2000
300 GPM
Depth, ft
3000
Casing
DP & Col
450 GPM
4000
Re = 1919
5000
6000
7000
8000
100
ECD = 11.9 ppg
7” Casing
200
300
400 0
Annular velocity, ft/min
1000
2000
Pressure, psi
3000
PUMP HORSEPOWER
HHP = P * Q / 1714
HHP = Hydraulic horsepower
P = pump pressure ,psi
Q = flow rate, gpm
Conventional
CASING DRILLING®
Flow Rate = 450 gpm
Delta P = 2,181 psi
HHP = 572 hp
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:
390 hp
$1300/day
40% fuel savings observed on TESCO CASING DRILLING® rigs.
Minimum ECD
ECD
 Increased flow rate reduces cuttings load in annulus.
 Increased flow rate increases friction in annulus.
Optimum
Flow Rate
Lower Flow Rate is Optimal
11.5
Drilling with 7” Casing
Drilling with 6 1/8” DC and 4” DP
Depth = 3,200 ft Mud Wt = 8.9
Conv, ROP = 200 ft/hr
Conv, ROP = 400 ft/hr
ECD. ppg
11
Conv, ROP = 600 ft/hr
CD, ROP = 200 ft/hr
10.5
CD, ROP = 400 ft/hr
10
9.5
9
100
Conventional operating range
Casing Drilling operating range
300
Flow Rate, gpm
500
Cuttings Transport
Cuttings Transport ratio
Annular velocity, ft/min
1

50
25
16.7
12.5
10
Typical Casing Drilling range
0.8
0.6
0.4
Lower limit set by
Sand in water
0.2
0
0
0.02
0.04
0.06
0.08
Inverse Annular velocity, min/ft
From Applied Drilling Engineering pp175
0.1
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:
Approximation:
de =
de =
Dhole2 + ODpipe2 –
Ln(Dhole / Odpipe)
0.816 * (Dhole - Odpipe)
Higher Transition Velocity for Narrow Annuli
Reynolds Number
5000
4000
3000
Turbulent
2000
7" casing
4-1/2" Drill Pipe
1000
0
0
100
200
300
Annular Velocity, Ft/Min
8.75 “ hole, 10 ppg mud, Pv = 10, YP = 5
400
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.
Eccentric Casing in Borehole Results
in Reduced ECD
30% reduction
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
Drag Force
 Better indicator in vertical wells.
Hydraulic Lift
Fluid Flow
End Force
Annular
Pressure
=
Fluid Drag
+
Annular DP times end area
+
DP from cuttings times end area
Hydraulic Lift Calculations
Drag Force
+
End Force
+
Cuttings Force
HL = p/4 * [Dh*Dc*Dpa +
0.052*Dc2* (re - rm ) ]
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
VAQUILLAS A1 198 Pump-Off Observed at 2074 ft
70000
60000
32,000 lb Pump-Off
50000
40000
HookLoad
30000
1500
1000
Fill Pipe
Pump Pressure
500
0
300
RPM
GPM
200
Note: Blocks were stationary
100
0
5
10
15
20
25
30
35
Time, seconds
40
45
50
Hydraulic Lift Helps Monitor
Condition of Hole
 Balling on casing
 Pack off on borehole wall
Balled Shale from shaker after working casing.
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.
Back-Reaming May Help Clean the Hole
Hydraulic Lift, lb.
30000
Trip
Pump-Off
25000
Trip
Predicted
20000
15000
10000
Backreamed each
connection
5000
0
1200
2200
3200
4200
Measured Depth, ft
ANB Cattle Co
5200
6200
Typical Lobo Hydraulic Lift
(without Back Reaming)
Hydraulic lift, lb
30,000
Measured
Predicted*
25,000
20,000
15,000
10,000
5,000
* Predicted before drilling, constant 320 gpm
0
500
2500
4500
Measured depth, ft
Walter Despain
6500
8500
Hydraulic Lift Warns of Lost Circulation
30000
25000
20000
15000
10000
Measured Pump-Off
Calculated Pump-off
5000
0
400
300
GPM
200
20
ECD from Pump-Off, ppg
15
10
5
500
1500
Vaquillas A1 198
2500
3500
4500
Depth, ft
5500
6500
7500
8500
Annular Pressure May Change as Joint is Drilled
1450
Pressure
1400
1350
1300
1250
15,000
WOB
WOB St Pt
Torque
10,000
5,000
0
400
RPM
ROP
300
200
100
0
3
BMT 179
6
Example 1585 ft
9
12
Time, minutes
15
Annular Pressure Changes While Drilling
1500
Pressure
1400
WOB Zero
1300
1200
14,000
WOB
WSP
Torque
"True" WOB
12,000
10,000
8,000
6,000
4,000
2,000
0
Harder
formation
350
300
Soft formation
Block Position
ROP
250
200
150
100
50
0
2
7
BMT 179 high speed data
12
17
Time, minutes
22
27
Example 2518 ft
Hydraulic Lift Affects Proper Bit Start After Connection
1. Start rotary (breaks gels).
2. Bring up mud pump.
3. After pressure stabilizes, zero WOB.
4. Set bit on bottom.
5. Adjust RPM & WOB.
Must be done each time flow rate is changed.
What Happens if flow Rate is Changed
with Bit on Bottom?
1. One-time change in WOB due to casing length
change.
2. Permanent change in hydraulic lift.
Must pick up off bottom to change flow rate and
re-zero WOB.
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
Hydraulic Lift, lb
20,000
15,000
Mud A - 300 gpm
Mud A - 250 gpm
Mud B - 300 gpm
10,000
5,000
0
1000
3000
5000
Measured depth, ft
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®.
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
Underreamer Activation Pressure
Type 5 Underreamer
P1
Spring
Force
d1
d2
P2
Internal Jet
d3
P3
Bit Jets
Pa
Size
Activation
Pressure
4-1/2”
5-1/2”
7”
9-5/8”
10-3/4”
13-3/8”
220 psi
110 psi
180 psi
120 psi
140 psi
125 psi
 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.
Underreamer pressures cannot be
determined accurately by surface flow test
due to cavitation at low back pressure.
Hydraulic Balancing
Mud Motor
Underreamer
Annulus
MWD
RSS
Bit
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
400 GPM
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
400 GPM
300 GPM
600 GPM
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
300 GPM
600 GPM
300 GPM
550 GPM
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
400 GPM
300 GPM
600 GPM
300 GPM
550 GPM
210 GPM
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
400 GPM
300 GPM
600 GPM
300 GPM
550 GPM
210 GPM
310 GPM (4 x 12)
Hydraulics Balancing (The Sum of the Parts)
180 GPM
400 GPM
300 GPM
600 GPM
300 GPM
550 GPM
210 GPM
310 GPM (4 x 12)
Minimum 310 GPM
Maximum 400 GPM
Operating Flow Range for CASING DRILLING™
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.