Transcript SubSea MudLift Drilling Basic Technology

Dual Gradient Drilling
Basic Technology
Lesson 1
Introduction to DGD
Jerome J. Schubert
11/6/00
Confidential to Subsea Mudlift Drilling JIP
DGD Template 1 of 64
Introduction

11/6/00
Current deepwater drilling problems
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DGD Template 2 of 64
Introduction, con’t

Brief history of DGD
– Phase I
– Phase II
– Phase III
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Introduction, con’t
Describe the DGD System
 How can DGD can solve the existing drilling
problems?
 Equipment overview

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Current Deepwater Drilling
Problems
Deeper water results in longer and heavier
drilling risers
 High pore pressures and low fracture
gradients leads to more casing strings

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Land Well
Riserless Drilling -A
Water Depth = 0 feet
0
5000
10000
2 strings of casing
Depth (TVD ss)
15000
after 20”
20000
25000
30000
35000
40000
8.0
9.0
10.0
11.0
12.0
13.0
14.0
15.0
16.0
17.0
18.0
19.0
Pressure Gradient (ppg)
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DGD Template 6 of 64
500’ Water Depth
Riserless Drilling -A
Water Depth = 500 feet
0
5000
10000
2 strings of casing
Depth (TVD ss)
15000
after 20”
20000
25000
30000
35000
40000
8.0
9.0
10.0
11.0
12.0
13.0
14.0
15.0
16.0
17.0
18.0
19.0
Pressure Gradient (ppg)
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DGD Template 7 of 64
1000’ Water Depth
Riserless Drilling -A
Water Depth = 1000 feet
0
5000
10000
2 strings of casing
Depth (TVD ss)
15000
after 20”
20000
25000
30000
35000
40000
8.0
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9.0
10.0
11.0
12.0
13.0
14.0
(ppg) JIP
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Subsea Gradient
Mudlift Drilling
15.0
16.0
17.0
18.0
19.0
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5000’ Water Depth
Riserless Drilling -A
Water Depth = 5000 feet
0
3 strings of casing
5000
after 20”
10000
Depth (TVD ss)
15000
20000
25000
30000
35000
40000
8.0
11/6/00
9.0
10.0
11.0
12.0
13.0
14.0
(ppg) JIP
Confidential toPressure
Subsea Gradient
Mudlift Drilling
15.0
16.0
17.0
18.0
19.0
DGD Template 9 of 64
10,000’ Water Depth
Riserless Drilling -A
Water Depth = 10000 feet
0
4 strings of casing
5000
after 20”
10000
with no kick or trip margins
Depth (TVD ss)
15000
20000
25000
30000
35000
40000
8.0
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9.0
10.0
11.0
12.0
13.0
14.0
Pressure Gradient (ppg)
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15.0
16.0
17.0
18.0
19.0
DGD Template 10 of 64
0.5 ppg Standoff
0
6 strings of casing
5000
Depth (TVD ss)
10000
30"
26"
20"
15000
after 20”
16"
13 3/8"
20000
113/4"
9 5/8"
7 5/8"
25000
30000
5 1/2" to TD
35000
40000
8.0
9.0
10.0
11.0
12.0
13.0
14.0
15.0
16.0
17.0
Pressure Gradient (ppg)
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Current Deepwater Drilling Problems

Too many shallow casing points
– May not reach TD
– No contingency casing available

11/6/00
This leads to larger wellheads, even larger
and heavier risers, and finally to bigger and
more expensive rigs
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Current Deepwater Drilling Problems

11/6/00
Well Control is more difficult - because of the
pore pressure/fracture proximity, and long
choke lines with high friction pressure drops
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Kick w/ 750 psi SIP
Mud HSP (13.1 ppg)
Mud HSP + 750
psi
Pore Pressure
Formation has
fractured
Fracture Pressure
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DGD Template 14 of 64
Current Deepwater Drilling Problems
Very high riser loads (current and weight)
 Weight of the drilling riser increases with
depth.

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Current Deepwater Drilling Problems

In 10,000’ of water
– 21-inch riser has an internal capacity of ~4000
bbls! (~$1 million)
– Weight of the riser itself is ~ 2million lbs
– Weight of 16 ppg mud inside the riser ~ 2.7
million lbs
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Current Deepwater Drilling Problems

Water depths beyond rig fleet
– New builds and major upgrades
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DGD Template 17 of 64
Current Deepwater Drilling Problems
Small wellbore at TD precludes large
production tubing - limiting production rates
 Began 2nd quarter of 2000

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Drilling’s Major Benefits
of DGD
11/6/00

Reduces drilling cost by $5-15 MM per well in young
depositional basins (4 casing strings)

Provides contingency casing for SWF’s, sub-salt
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Drilling’s Major Benefits
of DGD
11/6/00

Allows room for high rate completions

Expands capacity of existing rig fleet

Mitigates effects of high currents

Improves Well Control margin
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Describe the
DGD System
11/6/00

“DGD” Drilling, in the present context, refers to drilling
where mud returns DO NOT go through a conventional,
large-diameter, drilling riser.

Instead the returns move from the seafloor to the surface
through one or more small - diameter pipe(s) separate from
the drillpipe.

A Mudlift system is used in the Return Line

A Dual Gradient mud system is achieved.
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Single vs. Dual Gradient Concept

Single Gradient Wells
– Wellbore contains a
single density fluid
– Single pressure
gradient

Dual Gradient Well
– Wellbore feels seawater
gradient to the seafloor,
and mud gradient to
bottom
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Pressure, psi
D
e
p
t
h
Seawater HSP
Seafloor @ 10,000’
12.4 ppg mud
13.5 ppg mud
f
t
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23,880 psi
@ 37,500’
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Dual Gradient Achieved by:
Placing SRD on top of the BOP stack and
diverting the mud flow from the annulus to
the MLP
 The MLP then pumps mud back to the rig via
the return lines
 Suction pressure to the MLP is maintained at
Seawater HSP + ~20 to 50 psi

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Single vs. DualGradient Mud Systems
Conventional
Single
Mud
Weight
Dual Gradient
Heavier Mud w/
Seawater Above
Mudline
Same
Bottom Hole
Pressure
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From the perspective of the well, there is no mud
above the mudline
in a dual-gradient system!
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Figure 3
How can DGD can solve the
existing drilling problems?
By placing the MLP on the seafloor we can
reduce the pressure exerted on the shallow
weak formations and still maintain the
required pressure at the bottom of the hole to
control formation pressure
 Riser margin is back - emergency disconnect
and drive-off will not result in an automatic
kick.

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DGD Template 25 of 64
Pore and Fracture Gradients
0
Dual Density:
Pore Gradient
Fracture Gradient
5000
Depth (TVD ss)
10000
15000
20000
Conventional:
Pore Gradient
Fracture Gradient
30000
25000
35000
40000
8.0
9.0
10.0
11.0
12.0
13.0
14.0
15.0
16.0
17.0
18.0
19.0
Pressure Gradient (ppg)
11/6/00
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DGD Template 26 of 64
0
Graphical Casing Seat Selection Dual Density
0.5 ppg trip and kick margin
1.0 ppg trip and kick margin
5000
16"
10000
Depth (TVD ss)
13 3/8"
15000
20"
20000
11 3/4"
25000
30000
35000
40000
8.0
9.0
10.0
11.0
12.0
13.0
14.0
15.0
16.0
17.0
18.0
19.0
Pressure Gradient (ppg)
11/6/00
Confidential to Subsea Mudlift Drilling JIP
DGD Template 27 of 64
Dynamic Casing Seat Selection
Pressure, psi
D
e
p
t
h
1.0 ppg kick
Frac. Press.
0 bbl influx volume
ft.
11/6/00
Pore Press.
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DGD Template 28 of 64
Dynamic Casing Seat Selection
Frac. Press.
1.0 ppg kick
50 bbl influx volume
Pore Press.
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DGD Template 29 of 64
Kick Tolerance is Back
Conventional
DGD
16” @ 13,000’
0.5 ppg
standoff
13 3/8” @ 14,000’
no influx
20” @ 12,500’
11 3/4” @ 15,000’
20” @ 12,500’
16” @ 14,000’
1.0 ppg kick,
50 bbl influx
13 3/8” @ 17,000’
9 5/8” @ 17,500’
7 5/8” @20,000’
11 3/4” @ 22,800’
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5 1/2 “ @ TD
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9 5/8” @ TD
DGD Template
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Equipment overview
Marine Riser
 SRD - SubSea Rotating Diverter
 DSV - Drillstring Valve
 MLP - MudLift Pump
 Return Lines
 Manifolding
 Dual Trip Tanks

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DGD Template 31 of 64
SubSea MudLift Configuration
Seawater Pumps
(Existing Mud Pumps)
Mud Return and Pump
Return Line
Drillpipe
Seawater Power Line,
Control Umbilicals
Seawater Filled Marine Riser
Rotating Diverter
Seawater-Driven
MudLift Pump
Wellhead and BOP
BHA
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Drill String Valve
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DGD Template 32 of 64
Marine Riser

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Essentially a conventional riser filled with
seawater
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DGD Template 33 of 64
Wellbore Components
Riser
Adapter
Subsea Rotating
Diverter (SRD)
Return Outlets
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DGD Template 34 of 64
Drill String Valve (DSV)
Flow Nozzle
Closing Spring
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DGD Template 35 of 64
While
Mud
Displacing
Seawater
Enters
Seawater
the
the
Seawater
Driven
Pumped
Mud
Discharged
Diaphragm
Back
from
to the
to
the
MudLift
Pump
Pumps
Rig
Sea
Mud Inlet
Mud Outlet
Diaphragm Pump
Stroke Indicator
Magnet Assembly
Stroke Indicator
Sensor (Fixed)
Hydraulic Fluid
In/Out
Stroke Indicator
Tube (Moving)
Connection to
Diaphragm
Diaphragm
Mud In/Out
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DGD Template 37 of 64
Seawater Driven MudLift System
14’ x 17’ x 11’h
175,000 lbs
plus
Seawater Conduit
ROV-Style
Cables
Mud
B
C
K
H
Seawater
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DGD Template 38 of 64
Return Lines
Manifolding
Seawater Trip Tank
Mud Trip Tank
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DGD Template 39 of 64
The End
Jerome J. Schubert
Introduction to DGD
11/6/00
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