1 petroleum engineering 411 well drilling lesson 27 dual gradient drilling
TRANSCRIPT
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Petroleum Engineering 411Well Drilling
Lesson 27
Dual Gradient Drilling
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DESIGN PROJECTDESIGN PROJECT
Your PETE 411 Design Project will be assigned on Friday, November 15
The Project Report is Due in Dr. J-W’s Office by 5 p.m. on Monday, Dec. 9
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What is Dual Gradient Drilling?What is Dual Gradient Drilling? (DGD)? (DGD)?
In dual-gradient drilling the pressure profile in the annulus appears to have two distinct pressure gradients
An example would be a heavy mud below the mudline and a seawater gradient above the mud line
4ATM
Conventional Riser Drilling- Wellbore Pressures
SEAFLOOR
SEA WATER HYDROSTATIC
PRESSURE
DE
PT
H
MUD HYDROSTATIC BOP
FLOATER
DRILLING RISER
CHOKE LINE
5
Static Wellbore Pressures
SEA WATER HYDROSTATIC
PRESSUREPRESSURE
DE
PT
H
MUD HYDROSTATIC
PRESSURE DGD
MUD HYDROSTATIC
PRESSURE Conventional
BOP
FLOATER
RISER
CHOKE LINE
DGD
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Dual Gradient Drilling ProjectsDual Gradient Drilling Projects
Subsea Mudlift Drilling (SMD)
Hollow Glass Spheres
Deep Vision
Shell
Gas Lift
H.P. Riser
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Subsea Mudlift Drilling
( SMD )
Note Pump and Return
Line
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Subsea Mudlift Drilling
What is Subsea Mudlift Drilling? How does it work? Why do we need it? Pore pressures and fracture pressures Mud weights and casing programs What about connections and trips? What about kicks?
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1. “Riserless Drilling: Circumventing the Size/cost Cycle in Deepwater,” by Allen D. Gault. May 1996, Offshore, p.49
2. “Subsea Mudlift Drilling JIP: Achieving dual-gradient technology,” by K.L. Smith et al., World Oil - Deepwater Technology, August 1999, pp 21-28.
HW #15 (due 11-15-01)
References
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Current SMD Concepts
A water-filled drilling riser One or more separate small-diameter
mud return line(s) from seafloor to surface (e.g., two 4.5-in ID
lines)
A “dual mud density” system (DGD) Seawater gradient from surface to
seafloor Heavier drilling mud inside the wellbore
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Current SMD Concepts - cont’d
A seafloor mud pump to lift mud to surface
Pressure inside wellbore at seafloor is ~ the same as the pressure in the ocean at seafloor
Theoretically the well is always dead
Important in case of drive-off
Retains a Riser Margin
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Current Problems
Deeper water results in longer, larger diameter and heavier drilling risers
High pore pressures and low fracture pressures lead to more casing strings
This leads to larger wellheads, even larger and heavier risers, and finally to bigger and more
expensive rigs
Well control is more difficult - because of the pore pressure / fracture pressure proximity, and long
choke lines with high friction pressure drops
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Effect of Increasing Water Depth
Weight of drilling riser increaseswith depth. In 10,000 ft of water:
– 21-inch riser has an internal capacity of ~ 4,000 bbls! (value ~ $1 million)
– Weight of riser ~ 2 million lbs. Weight of 16 lb/gal mud inside
riser ~ 2.7 million lbs
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What About Subsea Mudlift Drilling?
Two 4.5” ID return lines with ~ 400 bbls capacity can do the job
Requires much less weight and volume for storage!
A smaller vessel can do the job A smaller vessel can easier be upgraded
to do the job
15ATM
SMD 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 two small - diameter pipes separate from the drillpipe (outside the main riser pipe)
A Mudlift system is used in the Return Line
What is Subsea Mudlift Drilling?
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Fig. 7.21 ADE
Pore pressure
gradient and fracture
gradient data for Jefferson Parish, LA.
Fracture Gradient
Pore Pressure Gradient
Equivalent Mud Density, ppg
0.5 ppg
0.5 ppg
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Pore Pressure
Frac Pressure
Max Mud Wt
Min Mud Wt
Equivalent Mud Wt, lb/gal
SEAFLOORConventional Casing Seat Selection
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Typical Overburden
Pressure grad.vs. Depth
Ref: “Fracture gradient prediction for the new generation,” by B.A. Eaton and T.L. Eaton. World Oil, October 1997.
17.3 ppg
11.5 ppg
19ATM
Conventional Riser Drilling- Wellbore Pressures
SEAFLOOR
SEA WATER HYDROSTATIC
PRESSURE
PRESSURE
DE
PT
HSTATIC PRESSURE
CIRCULATING PRESSURE
PBIT
BOP
FLOATER
Drill String
20ATM
Static Wellbore Pressures
SEAFLOOR
SEA WATER HYDROSTATIC
PRESSURE
PRESSURE
DEPTH
MUD HYDROSTATIC
PRESSURE SMD
MUD HYDROSTATIC
PRESSURE Conventional
21ATM
Example: Static Wellbore Pressures
At 30,000 ft, in 10,000 ft of water, the pore pressure is 21,000 psig.
For conventional drilling, what is the minimum mud weight that can control this pressure?
For SMD, what is the minimum mud weight that can control this pressure?
22ATM
Static Wellbore Pressures
P = 0.052 * MW * Depth
For conventional drilling, Minimum mud wt.
MWmin = 21,000/(0.052 * 30,000) = 13.5 lb/gal
Seafloor pressure = 0.052*8.6*10,000 = 4,472 psig
For SMD, Minimum mud weight = (21,000 - 4,472)/(0.052 * 20,000) = 15.9 lb/gal
23ATM
Solution: Static Wellbore Pressures
SEA WATER HYDROSTATIC
PRESSURE
8.6 lb/gal
4,472 psi
DEPTH
15.9 lb/gal SMD
13.5 lb/gal Conventional
21,000 psi
24ATM
Wellbore Pressures
SEAFLOOR
FRACTURE PRESSURE
PORE PRESSURE
SEA WATER HYDROSTATIC
PRESSURE
PRESSURE
DEPTH
MUD HYDROSTATIC
PRESSURE Conventional
25ATM
SEAFLOOR
FRACTURE PRESSURE
PORE PRESSURE
MUD HYDROSTATIC
PRESSURE
SMD
SEA WATER HYDROSTATIC
PRESSURE
PRESSURE
DEPTH
MUD HYDROSTATIC
PRESSURE Conventional
Wellbore Pressures
26ATM
Casing Requirements - Conventional
SEAFLOOR
FRACTURE PRESSURE
PORE PRESSURE
SEA WATER HYDROSTATIC
PRESSURE
PRESSURE
DEPTH
MUD HYDROSTATIC
PRESSURE Conventional
27ATM
Casing Requirements - SMD
SEAFLOOR
FRACTURE PRESSURE
PORE PRESSURE
MUD HYDROSTATIC
PRESSURE
SMD
SEA WATER HYDROSTATIC
PRESSURE
PRESSURE
DEPTH
28ATM
Pressure Considerations
SEAFLOOR
FRACTURE PRESSURE
PORE PRESSURE
MUD HYDROSTATIC
PRESSURE
SMD
SEA WATER HYDROSTATIC
PRESSURE
PRESSURE
DEPTH
MUD HYDROSTATIC
PRESSURE
ConventionalSMD
29ATM
Wellbore Pressures - Conventional
SEAFLOOR
SEA WATER HYDROSTATIC
PRESSURE
PRESSURE
DE
PT
H
STATIC PRESSURE
CIRCULATING PRESSURE
PBIT
BOP
FLOATER
30ATM
Static Pressures - SMD
SEAFLOOR
SEA WATER HYDROSTATIC
PRESSURE
PRESSURE
DE
PT
H
ANNULUS AND RETURN LINE
BOP
FLOATER
31ATM
Drillstring Circulating Pressures
SEAFLOOR
SEA WATER HYDROSTATIC
PRESSURE
PRESSURE
DEPTH
CONVENTIONAL
SMD
PBIT
32ATM
Annulus Circulating Pressures
SEAFLOOR
SEA WATER HYDROSTATIC
PRESSURE
PRESSURE
DEPTH
CONVENTIONAL (13.5 lb/gal)
SMD (15.9 lb/gal)
PPUMP
33ATM
Circulating Pressures - SMD
SEAFLOOR
SEA WATER HYDROSTATIC
PRESSURE
PRESSURE
DEPTH
ANNULUS AND RETURN LINE
DRILLSTRING PRESSURE
PBIT
PPUMP
34ATM
Circulating Pressures - SummaryP
RE
SS
UR
E
DISTANCE FROM STANDPIPE
CONVENTIONAL
SMD
PBIT
PML_PUMP
35ATM
Transient Behavior when Stopping Rig Pump
(U-tubing or Free-fall)
Why does the drillpipe fluid level fall? How fast does the Fluid Level in the
drillpipe drop?
How far does the Fluid Level drop?
Transients
36ATM
MUDLIFT
U-Tubing in SMD
~SEAWATER HYDROSTATIC
PRESSURE
BOP
STATIC FLUID LEVEL
FLOATER
Dri
llst
rin
g
An
nu
lus
37ATM
Static Pressures - SMD
SEAFLOOR
SEA WATER HYDROSTATIC
PRESSURE
PRESSURE
DEPTH
ANNULUS AND RETURN LINE
DRILLSTRING PRESSURE
Static Fluid Level in DP
38ATM
U-Tubing Rate vs. Time after Pump OFF
0
200
400
600
800
0 5 10 15 20 25 30
Elapsed Time, min
Mu
d F
low
Rate
, g
pm 3-in ID
4.276-in ID6-in ID
10,000 ft Water Depth
39ATM
Fluid Level vs. Time after Pump OFF
0
1,000
2,000
3,000
4,000
5,000
0 5 10 15 20 25 30
Elapsed Time, min
Flu
id L
evel i
n D
rillp
ipe, f
t
3-in ID 4.276-in ID6-in ID
10,000 ft Water Depth
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41ATM
How do you shut a well in after taking a kick?
With a DSV this is almost routine
Better still, it is not necessary to shut the well in. The wellbore pressures can be increased by temporarily slowing down the mudlift pump
Friction in the choke line is handled by the Mudlift Pump and is not seen by the weak formations
Well Control Considerations
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44ATM
General Summary
Dual Gradient Drilling is a method that offers potential for lowering drilling costs in very deep waters:
• Fewer casing strings• Smaller rigs • Less time on location
The method utilizes one or more small-diameter return lines from the seafloor to the surface. The drillpipe is separate from the return lines
45ATM
Summary - cont’d
A mudlift system (pump) is used to feed the return lines, thereby making a “dual-density” mud system possible
Wellhead pressure is maintained at seawater hydrostatic, so well is “dead” at all times
Well control is quite similar to that in conventional drilling with a riser, but offers a number of significant advantages
46ATM
THE END
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Gas Lift?Glass Beads?
How to HandleConnections?Trips?
Pumps?Gas Lift?Glass Beads?
Rotating BOP
Dual Gradient Alternatives
48ATM
MUDLIFTBOP
Advanced SMD System
SEAFLOOR
~SEAWATER HYDROSTATIC
PRESSURE
FLOATER
30,000’
10,000’
Circulation Rate 650 gpm
Drillpipe OD 6 5/8 in
Return Line ID 6 in
Hole Size 12 1/4 in