schubert iadc wc conference

8/6/2019 Schubert IADC WC Conference

1/31

25-26 August 1999 Well Control Conference of theAmericas

Greater Kick Tolerance and

Fewer Casing Strings Make Dual

Gradient Drilling a WinnerSchubert, J. J., Seland, S.,

Johansen, T. J., Juvkam-Wold, H. C.


2/31


Houston, Texas

Introduction Problems Associated With Deepwater

Drilling

Single Gradient vs. Dual Gradient Concept

Methodology

Results

Conclusions


3/31


Houston, Texas

Problems Associated With

Deepwater Drilling Longer, heavier marine risers requires

Larger drilling vessels w/ greater storage

requirements

Large volume of mud just to fill the riser

Large forces imposed on the riser by currents

Large tension forces on the riser


4/31


Houston, Texas

Problems Associated With

Deepwater Drilling Narrowing of the Window between the Pore

Pressure and Fracture Pressure

Increase in number of casing strings

Near elimination of kick tolerance


5/31


Houston, Texas

Single vs. Dual Gradient Concept Single Gradient Wells

Wellbore contains a

single density fluid Single pressure

gradient

Dual Gradient Well

Wellbore feelsseawater gradient to

the seafloor, and mud

gradient to bottom

Pressure, psi

D

e

p

t

h

f

t

Seafloor @ 10,000

Seawater HSP

23,880 psi

@ 37,500

12.4 ppg mud

13.5 ppg mud


6/31


Houston, Texas

Dual Gradient Achieved by: Taking returns at the seafloor

Gas lift at the seafloor

Inject hollow gas spheres

Seafloor mud pumps


7/31


Houston, Texas

Assumptions Water depth of 10,000

Total depth of 37,500

For dual gradient drilling:

annulus pressure at the seafloor is kept equal to

seawater HSP during normal drilling operations

during kicks seafloor pressure adjusted to

control BHP equal to formation pressure


8/31


Houston, Texas

Pore and Fracture Gradients0

5000

10000

15000

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)

Depth(TVDs

s)

Dual Density:Pore Gradient

Fracture Gradient

Conventional:

ore Gradient

Fract re Gradient


9/31


Houston, Texas

Methodology Conventional Riser Drilling

Picked casing points graphically with with a 0.5

ppg stand off

Looked at the effect of 750 psi SIP

Looked at the effects of circulating pressures

for both: 0 bbls influx

50 bbls influx


10/31


Houston, Texas

Methodology Compared results to a dual gradient system:

Statically

Dynamically


11/31


Houston, Texas

Methodology Dual Gradient System, we picked casing

points:

Graphically (static wellbore pressures)

Dynamically:

0 bbl influx

50 bbl influx


12/31


Houston, Texas

Graphical Casing Seat Selection

0

5000

10000

15000

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


Depth(T

VD

s

30" 26"

20" 16"

13 3/8" 113/4"

9 5/8"

7 5/8"

5 1/2" to TD


13/31

25-26 August 1999 Well Control Conference of theAmericas Houston, Texas

Kick w/ 750 psi SIP

Pore Pressure

Fracture Pressure

Mud HSP (13.1 ppg)

Mud HSP + 750 psi

Formation has

fract red


14/31


Casing Seat Pressures

15000

15200

15400

15600

15800

16000

16200

16400

16600

010000200003000040000

Location of Bubble, ft. from Surface

Pressure,

psig

no gain

50 bbl gain

Fracture Pressure of 15,672 psi


15/31


Static Pressure - Dual Gradients

Pore Pressure

Fracture Pressure

Mud HSP (15.5 ppg)

Mud HSP = 750 psi


16/31


Choke Pressures1000 psi underbalanced, no pit gain

-1000

-800

-600

-400

-200

0

200

400

600

800

1000

1200

0500010000150002000025000300003500040000Location ofBubble, ft. from Surface

Pressure

,psig

Dual Density

ConventionalKill rate of 650 gpm

Indicates Choke is Wide Open

CLFP imposed downhole


17/31


Pressure at Casing Seat of22000 ft. (1000 psi SI, no pit gain)

14000

14500

15000

15500

16000

16500

17000

0500010000150002000025000300003500040000


Pressur

e,

psig

Dual Density

Conventional

Fracture Pressure of 15,672

Formation

has

Fractured


18/31


Bottom Hole Pressure, 1000 psi underbalanced, no gain

27200

27400

27600

27800

28000

28200

28400

28600

010000200003000040000


Pressure,

psig

Dual Density

Conventional

Formation Pressure


19/31


Graphical Casing Seat Selection -

Dual Density0

5000

10000

15000

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


Depth(TV

D

s

0.5 ppg trip and kick margin1.0 ppg trip and kick margin

11 3/4"

13 3/8"

16"

20"


20/31


Dynamic Casing Seat Selection

D

e

p

t

h

ft.

Pressure, psi

1.0 ppg kick

0 bbl influx volume


21/31


Dynamic Casing Seat Selection

1.0 ppg kick

50 bbl influx volume


22/31


Conclusions The narrow gap between pore pressure and

fracture pressure results in excess number

of casing strings for conventional riser

drilling.

The large number of casing strings mayresult in such a small production string that

high flow rates may not be possible.


23/31


Conclusions The narrow gap between pore pressure and

fracture pressure results in virtually no kick

tolerance for conventionally drilled wells.

The dual gradient system drastically reduces

the number of casing strings required toreach total depth.


24/31


Conclusions The dual gradient system widens the gap

between pore pressure and fracture pressure

resulting in a much higher kick tolerance.

The higher kick tolerance increases the

probability of a kick being killedsuccessfully.


25/31

25-26 August 1999 Well Control Conference of the

Americas

Houston, Texas

Conclusions The dual gradient system will increase the

probability of reaching the geologic

objective in ultra-deep water.

Dual gradient drilling will allow large

enough production casing to be able toinstall production tubing as large a 7 in

diameter.


26/31


Americas

Houston, Texas


27/31


Americas

Houston, Texas

6000 WDType Well 6000

Water Depth = 6000 feet0

5000

10000

15000

20000

25000

8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0 16.0 17.0 18.0 19.0 20.0 21.0


Depth(TVDs

s

Riserless Fracture Gradient

Riserless Pore Pressure

Conventional Fracture

GradientConventional Pore Pressure

20"


28/31


29/31


Americas

Houston, Texas

6000 WDSMDDrilling Type Well 6000WaterDepth = 6000 feet0

5000

10000

15000

20000

25000

8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0 16.0 17.0 18.0 19.0 20.0 21.0 22.0


Depth

(TVDs

s)

Conventional Fracture

GradientConventional Pore Pressure

.5 PPG Standoff FractureGradient1 PPG Standoff Fracture

Gradient

30"

117/8"

20"

16"

13 5/8"

9 7/8"

Full 1.0 PPG

Fracture Gradient

Margin


30/31


Americas

Houston, Texas

6000 WD

Kick Tolerance is Back

520 psi Underbalance from Kick

Formation

has Fractured

Formation

Intact

SMDCONVENTIONAL

15.5 PPG MUD

15.5 ppg mud + 520 psi

18.4 ppg mud

18.4 ppg mud + 520 psi


31/31


Americas

Houston, Texas

Kick Tolerance

30 @ 6300

20 @ 7000

16 @ 10,000

13 3/8 @ 16,500

11 3/4 @ 17,500

9 5/8 @ 20,000

0.5 ppg kick - 90 bbl gain




SMDConventional

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