Slide 1 of 72

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Lesson 3
Dual Gradient DrillingBasic Technology
by Hans C. Juvkam-Wold

• Wellbore Pressures

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Contents

• Static Pressures in a conventional wellbore
• Circulating Press. in a conventional wellbore
• Static Pressures in an DGD wellbore
• Circulating Pressures in DGD wellbores, with and
  without Drillstring Valve (DSV)
• Pressure Profiles During a Connection
• Pressure Profiles when a Kick Occurs

3
Static Pressures in a Conventional Wellbore
0
Mud Weight 15 lb/gal Gradient 0.780 psi/ft
DEPTH, ft
Same inside and outside the wellbore
10,000
7,800
0
PRESSURE, psi
4
Static Pressures in a Conventional Wellbore
0
Depth Pressure ft psi 0
0 1 0.78 2 1.56 3
2.34 10 7.8 100
78 1,000 780 2,000 1,560
3,000 2,340 5,000 3,900 10,000
7,800
Mud Weight 15 lb/gal Gradient 0.780 psi/ft
DEPTH, ft
Same inside and outside the wellbore
10,000
7,800
0
PRESSURE, psi
5
Static Pressures in a Conventional Wellbore
(alternate view)
MW 15 lb/gal Gradient 0.780 psi/ft
7,800
PRESSURE, psi
Top of Drillpipe
Bottom of Hole
Top of Annulus
Annulus
Drillstring
0
0
10,000
20,000
Distance from Standpipe, ft
6
Circulating Pressures in a Conventional
Wellbore
SPP ?
0
Drillstring Friction 800 psi Pressure
Across bit 1,200 psi Annular Friction
200 psi Mud Weight 15 lb/gal
Drillstring Annulus Static
DEPTH, ft
Drillstring Circulating
Annulus Circulating
10,000
Bit
0
BHP ?
PRESSURE, psi
7
Circulating Pressures in a Conventional
Wellbore
SPP 2,200 psi
( 800 1,200 200 2,200 )
0
Drillstring Friction 800 psi Pressure
Across bit 1,200 psi Annular Friction (AFP)
200 psi Mud Weight 15 lb/gal
Static, DS Annulus
DEPTH, ft
Drillstring
Annulus
10,000
Circ. BHP DPHYDRO AFP
7,800 200 8,000 psi
7,800
8,000
9,200 psi
0
PRESSURE, psi
8
Circulating Pressures in a Conventional Wellbore
(alt. view)
MW 15 lb/gal
9,200 psi
Bit
Circ. BHP 8,000 psi
7,800
PRESSURE, psi
Static
2,200
Annulus
Drillstring
0
0
10,000
20,000
Distance from Standpipe, ft
9
Static Pressures - DGD
10
Static Pressures Conventional vs. DGD
11
Static Pressures - DGDNo DSV
12
U-tubing
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What is Delta MW (DMW)? Mud hydrostatic -
Seawater hydrostatic in the water column
Seawater Hydrostatic 0.052 8.6 10,000
4,472 psi
Mud Hydrostatic in the water column 0.052 15
10,000 7,800 psi
DMW Difference in Hydrostatic 7,800 - 4,472
3,328 psi
4,472 psi
DMW
Note that the U-Tube driving pressure is,
typically, DMW - 50 psi
3,328 psi
14
Static Pressures in an DGD Wellbore
0
SW Density 8.6 lb/gal Mud Weight 16 lb/gal
DEPTH, ft
10,000
What is the BHP ?
20,000
0
PRESSURE, psi
15
Example - Calculation

• Seawater hydrostatic
• 0.052 8.6 10,000 4,472 psi
• Mud Hydrostatic
• 0.052 16 10,000 8,320 psi
• BHP 4,472 8,320
• BHP 12,792 psi

16
Example 2
If the 20,000-ft well discussed in the previous
example were to be drilled conventionally, what
mud weight would you use in order to achieve the
same BHP?
Hint Use the same mud weight from top to
bottom.
p 12,792 psi
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Example 2 - Solution
BHP, p 0.052 MW Depth 12,792 0.052
MW 20,000 MW 12,792 / (0.052
20,000) MW 12.30 lb/gal
Note that (8.6 16.0) /2 12.30 any
comments?
p 12,792 psi
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Example 3
A new well is to be drilled using DGD. Water
depth is 8,000 ft. Depth BML is 19,000 ft. BHP is
expected to be 20,000 psi. What DGD Mud
weight will be required?
8,000
ML
19,000
p 20,000 psi
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Example 3 - Solution
At ML, p1 0.052 Density Depth p1
0.052 8.6 8,000 3,578 psi Hydrostatic
Pressure below the ML, p2 20,000 - 3,578
16,422 psi MW 16,422 / (0.052 19,000) MW
16.62 lb/gal
8,000
ML
19,000
p 20,000 psi
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Static Pressures - DGD (No DSV)
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Static Pressures in DGD Wellbore No DSV
(alternate view)
Drillstring
Annulus
BHP
Static Pressure across the Mudlift Pump
Static Fluid Level in DP
PRESSURE, psi
Bottom of the Hole
0
0
10,000
20,000
Distance from Standpipe, ft
22
Static Pressures - DGD (w / DSV)
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Circulating Pressures - DGD w / DSV
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Circ. Pressures in a Conventional Wellbore
(alternate view)
MW 15 lb/gal
Drillstring
Bit
AFP
7,800
PRESSURE, psi
Annulus
Static
0
0
10,000
20,000
Distance from Standpipe, ft
25
Circ. Pressures in an DGD Wellbore (alternate
view)
MW 15 lb/gal
MW 15 lb/gal
Drillstring
Bit
AFP
7,800
PRESSURE, psi
Annulus
Static Conventional
MLP
Drillstring
Annulus
0
0
10,000
20,000
Distance from Standpipe, ft
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Factors Affecting Pressure Profile in Wellbore

• Hydrostatics (mud, water, gas, cement slurry)
• Friction
• Drillpipe
• Annulus
• Area Change (nozzle, tool joint, MWD Sub, etc.)
• Kick
• Hydrostatics (kick density lower than mud
  density)
• Kick Intensity

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Effect of Hydrostatics on Wellbore Pressure
Profile
0
Depth, ft
Cement _at_ 16 lb/gal
Gas _at_ 1 lb/gal
Mud _at_ 12 lb/gal
Water _at_ 8.6 lb/gal
10,000
0
6,240
520
4,472
8,320
Pressure, psi
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Effect of Hydrostatics on Wellbore Pressure
Profile
Drillstring
Annulus
8,320
Mud _at_ 12 lb/gal
Cement _at_ 16 lb/gal
6,240
PRESSURE, psi
4,472
Water _at_ 8.6 lb/gal
520
Gas _at_ 1 lb/gal
0
0
10,000
20,000
Distance from Standpipe, ft
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Effect of Friction on Pressure Profile in
Conventional Wellbore
Bit
MW 15 lb/gal
High Circ. Rate
Higher circulation Rate means Higher Friction Loss
Medium Circ. Rate
PRESSURE, psi
Static
Drillstring
Annulus
0
0
10,000
20,000
Distance from Standpipe, ft
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Dynamic Shut-in of Kick(Stop Influx while
Circulating)

• When well kicks, MLP speeds up (pump is
  controlled by constant pump inlet pressure)
• Change pump from pressure control to rate
  control. Slow down MLP to pre-kick rate
• As a result the wellbore pressure increases until
  the influx stops (PWELLBORE PFORMATION)
• The kick is now under control
• SIDP can now be determined

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Subsea Mudlift Drilling System
FLOATER
Surface Pump Constant Rate Mudlift Pump Const.
Inlet Press.
SEAWATER HYDROSTATIC PRESSURE
10,000
SEAFLOOR
BOP
MUDLIFT
30,000
KICK
What next??
32
Kick Detection and Control
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Kick Detection and Control
Influx has stopped and pressures have stabilized
ATM
34
Kick Detection and Control
ATM
35
Dynamic Underbalance
Dynamic Underbalance required increase in
BHP to stop influx while circulating

• Total Underbalance (conventional) SIDP
• Dynamic Underbalance AFP
• AFP Annular Friction Pressure

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Pressure Profile in WellboreDuring a Connection
(w/DSV)

• Circulating - before connection
• During Connection - Rig Pump Stopped
• - Annular Friction Pressure (AFP) is lost
• During Connection - Rig Pump Stopped
• - Annular Friction Pressure (AFP) is
  applied at the MLP inlet
• Circulating - after connection

37
Circulating Pressures Before Connection
Return Line - Circulating
Annulus - Circulating
38
Static and Circulating Pressures in DGD
Return Line - Circulating
Static
Return Line Friction
Annulus - Circulating
Annulus - Static
AFP
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Static Pressures in DGD After Rig Pump is Stopped
for Connection
Static
Return Line Friction
Annulus - Static
AFP
40
Static Pressures in DGD After Rig Pump is
Stopped. AFP Applied at MLP to Avoid Chance of
Kick
Static
Return Line Friction
New Annulus - Static
Old Annulus - Static
AFP
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Circulating Pressures in DGD. Rig Pump is
Restarted. AFP is Removed
Return Line - Circulating
Static
Return Line Friction
New Annulus - Circulating
Old Annulus - Static
AFP
42
Pressure Profile in Wellbore- Changes when a
Kick Occurs

• Drilling - before kick begins
• Kick in progress - no action taken yet
• Influx is stopped - kick is still near bottom
• Kick moves up the hole
• Top of kick is at mudline
• Bottom of kick is at mudline
• Kill mud is filling annulus
• Kill mud all the way

43
Static and Circulating Pressures in DGD - no Kick
Return Line - Circulating
Static
MLP
Return Line Friction
Annulus - Circulating
Annulus - Static
AFP
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Circulating Pressures in DGD - Kick in Progress
- no Action
MLP Speeds Up - Automatically
Return Line - w/Kick
Return Line - Before Kick
Extra Return Line Friction
Annulus - Before Kick
Annulus - w/Kick
Kick, 2.5 ppg
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Slow Down MLP to Stop Influx- Kick Still Near
Bottom
Kick at Bottom - 2.5 lb/gal kick fluid
Kick
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Effect of Kick Intensity Wellbore Pressure
Profile - Small Kick
Kick Intensity 0.5 lb/gal 0.052 0.5 10,000
260 psi
8,000
18,000
47
Effect of Kick Size and Intensity on Wellbore
Pressures Profile
Kick still near Bottom - 2.5 lb/gal kick fluid
Return Line
Effect of Kick Intensity and Size
DEPTH
Annulus
Kick
PRESSURE
48
Effect of Kick Size and Intensity on Wellbore
Pressures Profile
Kick Halfway up Annulus - 2.2 lb/gal kick fluid
Effect of Kick Intensity and Large Kick
Kick
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Effect of Kick Size and Intensity on Wellbore
Pressures Profile
Top of Kick at Mudline
Kick 1.8 lb/gal
Effect of Kick Intensity
50
Effect of Kick Size and Intensity on Wellbore
Pressures Profile
Bottom of Kick at Mudline
Kick - 2.1 lb/gal
Effect of Kick Intensity
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Effect of Kick Size and Intensity on Wellbore
Pressures Profile
Kick is Out of Hole
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Effect of Kill Mud on Wellbore Pressures Profile
Kill Mud Totally Fills Hole
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Effect of Very Large Kick on Wellbore Pressures
Profile
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Pressure Profile in WellboreDuring SIDP
Measurement w/DSV

• Static Conditions
• DSV Set at Exact Balance
• DSV Set ONE or TWO lb/gal above balance
• Pressure Profile when DSV opens
• How to interpret the results and determine SIDP
  and Kick Intensity

55
Static Pressures - DGD (w / DSV)Exact Balance -
no Kick
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Static Pressures - DGD (w / DSV) - No Kick
0.052 1 10,000 520 psi 0.052 2 10,000
1,040 psi
Drillstring DSV in Balance DSV 1 lb/gal DSV 2
lb/gal
Return Line
10,000
Annulus
DSV
30,000
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Static Pressures - DGD (w / DSV) 0.5 lb/gal
Kick
0.052 0.5 20,000 520 psi
Drillstring DSV in Balance w/0.5 lb/gal kick
Return Line
10,000
Annulus
DSV
30,000
58
Static Pressures - DGD (w / DSV) 0.5 lb/gal
Kick
0.052 1 10,000 520 psi 0.052 0.6
20,000 624 psi
Drillstring DSV in Balance DSV _at_ 1 lb/gal DSV _at_ 1
lb/gal 0.6 lb/gal kick
Return Line
10,000
Annulus
DSV
30,000
59
Measuring SIDP w/DSV

• In the last example above, after a total shut-in,
  it takes 1,144 psi to open the DSV
• The DSV is set for 1 lb/gal above balance
• This accounts for 520 psi
• The remaining 624 psi corresponds to a kick
  intensity of 0.6 lb/gal
• Conclusion SIDP 1,144 - 520 624 psi
• Kick Intensity 0.6 lb/gal
• Increase mud weight by 0.6 lb/gal

0.052 1 10,000 520 psi
0.052 0.6 20,000 624 psi
60
Factors Affecting Pressure Profile in Wellbore

• Hydrostatics (mud weight) (Drillstring
  Ann.)
• Friction (circulation rate) (Drillstring
  Ann.)
• Changed MLP Inlet Pressure (Drillstring Ann.)
• Kick (Kick Intensity) (Drillstring
  Ann.
• Kick (Hydrostatics) (Annulus)
• Area Change (e.g., nozzles) (Drillstring)
• DSV Setting (Drillstring)

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SUMMARY of Wellbore Pressures - DGD (w / DSV)
Static
Circulating
Return Line
Drillstring
DEPTH
Annulus
PRESSURE
DSV
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Wellbore Pressures - Summary
Annulus
Drillstring
Return Line
Circulating Conventional
Circulating - DGD - No DSV
Pressure
Static - DGD
Static - Conventional
ML
ML
0
Distance from Standpipe
63
Questions?

• Static Pressures
• Circulating Pressures
• Kick Hydrostatic
• Kick Intensity
• Friction
• Delta MW (DMW) ?
• Dynamic Underbalance?

64
by Hans C. Juvkam-WoldNovember 2000The End
Subsea Mudlift DrillingBasic Technology
3. Wellbore Pressures