Dual Gradient Drilling

5/24/2018 Dual Gradient Drilling

1/481

Petroleum Engineering 411

Well Drilling

Lesson 27

Dual Gradient Drilling


2/482

DESIGN PROJECT

Your PETE 411 Design Project will beassigned on Friday, November 16

The Project Report is Due in Dr. J-WsOffice by 5 p.m. on Monday, Dec. 3


3/48

3

What is Dual Gradient Drilling?

(DGD)?

In dual-gradient drilling the pressureprofile in the annulus has twodistinct pressure gradients

An example would be a heavy mudbelow the mudline and a

seawater gradient above the mudline


4/48

4AT

Conventional Riser Drilling - Wellbore Pressures

SEAFLOOR

SEA WATER

HYDROSTATIC

PRESSURE

DE

PTH

MUD HYDROSTATICBOP

FLOATER

DRILLING RISER

CHOKE LINE


5/48

5

Static Wellbore Pressures

SEA WATER

HYDROSTATIC PRESSURE PRESSURE

MUDHYDROSTATIC

PRESSURE

SMD

MUD

HYDROSTATIC

PRESSURE

Conventional

BOP

FLOATER

RISER

CHOKE

LINE

DGD


6/48

6

Dual Gradient Drilling Projects

Subsea Mudlift Drilling (SMD)

Hollow Glass Spheres

Deep Vision

Shell


7/48

7

SubseaMudliftDrilling

( SMD )

Note Pump

and ReturnLine


8/48

8

Subsea Mudlift Drilling

What is Subsea Mudlift Drilling?

How does it work?

Why do we need it? Pore pressures and fracture gradients

Mud weights and casing programs

What about connections and trips?

What about kicks?


9/48

9

1.Riserless Drilling: Circumventing the Size/costCycle 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 - DeepwaterTechnology, August 1999, pp 21-28.

HW #13 (due 11-2-01)

References


10/48

10

Current SMD Concepts

A water-filled drilling riser

One or more separate small-diametermud return line(s) from seafloor tosurface (e.g., two 4.5-in ID lines)

A dual mud density system (DGD)

Seawater gradient from surface toseafloor

Heavier drilling mud inside the wellbore


11/48

11

Current SMD Concepts - contd

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 deadImportant in case of drive-off

Retains a Riser Margin


12/48

12

Current Problems

Deeper water results in longer and heavier drillingrisers

High pore pressures and low fracture pressures

lead to more casing stringsThis leads to larger wellheads, even larger andheavier risers, and finally to bigger and more

expensive rigs

Well control is more difficult - because of the porepressure / fracture pressure proximity, and long

choke lines with high friction pressure drops


13/48

13

Effect of Increasing Water Depth

Weight of drilling riser increases

with depth. In 10,000 ft of water:

21-inch riser has an internal capacityof ~ 4,000 bbls! (value ~ $1 million)

Weight of riser ~ 2 million lbs.Weight of 16 lb/gal mud inside riser~ 2.7 million lbs


14/48

14

What About Subsea Mudlift Drilling?

Two 4.5 ID return lines with~ 400 bbls capacity can do the job

Requires much less weight and volumefor storage!

A smaller vessel can do the job A smaller vessel can easier be upgraded

to do the job


15/48

15ATM

SMD refers to drilling where mud returnsDO NOTgo through a conventional,large-diameter, drilling riser

Instead the returns move from the seafloorto 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?


16/48

16

Fig. 7.21 ADE

Porepressure

gradient and

fracture

gradient datafor Jefferson

Parish, LA.

Fracture

Gradient

Pore

Pressure

Gradient

Equivalent Mud Density, ppg

0.5 ppg

0.5 ppg


17/48

17

Pore Pressure

Frac Pressure

Max Mud Wt

Min Mud Wt

Equivalent Mud Wt, lb/gal

SEAFLOORConventional Casing Seat Selection


18/48

18

TypicalOverburden

Pressuregrad.vs. Depth

Ref: Fracture gradient

prediction for the newgeneration, by B.A.

Eaton and T.L. Eaton.

World Oil, October1997.

17.3 ppg

11.5 ppg


19/48

19ATM

Conventional Riser Drilling- Wellbore Pressures

SEAFLOOR

SEA WATER

HYDROSTATIC

PRESSURE

PRESSURE

DEPTH

STATIC PRESSURE

CIRCULATING PRESSURE

PBIT

BOP

FLOATER

Drill String


20/48

20ATM


SEAFLOOR

SEA WATERHYDROSTATIC

PRESSURE

PRESSURE

DEPTH

MUD

HYDROSTATICPRESSURE

SMD

MUD

HYDROSTATICPRESSURE

Conventional


21/48

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 theminimum mud weight that can control thispressure?

For SMD, what is the minimum mud weightthat can control this pressure?


22/48

22ATM


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


23/48

23ATM

Solution: Static Wellbore Pressures

SEA WATER

HYDROSTATIC

PRESSURE

4,472 psi

DEPTH

15.1 lb/galSMD

13.9 lb/galConventional

21,000 psi


24/48

24ATM

Wellbore Pressures

SEAFLOOR

FRACTURE

PRESSURE

PORE PRESSURE


PRESSURE

PRESSURE

DEPTH

MUD

HYDROSTATICPRESSURE

Conventional


25/48

25ATM

SEAFLOOR

FRACTURE

PRESSURE

PORE PRESSURE

MUD

HYDROSTATICPRESSURE

SMD


PRESSURE

PRESSURE

DEPTH

MUD

HYDROSTATICPRESSURE

Conventional

Wellbore Pressures


26/48

26ATM

Casing Requirements - Conventional

SEAFLOOR

FRACTURE

PRESSURE

PORE PRESSURE


PRESSURE

PRESSURE

DEPTH

MUD

HYDROSTATICPRESSURE

Conventional


27/48

27ATM

Casing Requirements - SMD

SEAFLOOR

FRACTURE

PRESSURE

PORE PRESSURE

MUD

HYDROSTATICPRESSURE

SMD

SEA WATER

HYDROSTATICPRESSURE

PRESSURE

DEPTH


28/48

28ATM

Pressure Considerations

SEAFLOOR

FRACTURE

PRESSURE

PORE PRESSURE

MUD

HYDROSTATICPRESSURE

SMD

SEA WATER

HYDROSTATIC

PRESSURE

PRESSURE

DEPTH

MUD

HYDROSTATICPRESSURE

Conventional

SMD


29/48

29ATM

Wellbore Pressures - Conventional

SEAFLOOR

SEA WATER

HYDROSTATIC

PRESSURE

PRESSURE

DEPTH

STATIC PRESSURE

CIRCULATING PRESSURE

PBIT

BOP

FLOATER


30/48

30ATM

Static Pressures - SMD

SEAFLOOR

SEA WATER

HYDROSTATICPRESSURE

PRESSURE

ANNULUS AND

RETURN LINE

BOP

FLOATER


31/48

31ATM

Drillstring Circulating Pressures

SEAFLOOR

SEA WATER

HYDROSTATIC

PRESSURE

PRESSURE

DEPTH

CONVENTIONALSMD

PBIT


32/48

32ATM

Annulus Circulating Pressures

SEAFLOOR

SEA WATER

HYDROSTATICPRESSURE

PRESSURE

DEPTH

CONVENTIONAL (13.5 lb/gal)

SMD (15.9 lb/gal)

PPUMP


33/48

33ATM

Circulating Pressures - SMD

SEAFLOOR

SEA WATER

HYDROSTATICPRESSURE

PRESSURE

DEPTH

ANNULUS AND RETURN LINEDRILLSTRING PRESSURE

PBIT

PPUMP


34/48

34ATM

Circulating Pressures - Summary

DISTANCE FROM STANDPIPE

CONVENTIONAL

SMD

PBIT

PML_PUMP


35/48

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 thedrillpipe drop?

How far does the Fluid Level drop?

Transients


36/48

36ATM

MUDLIFT

U-Tubing in SMD

~SEAWATER

HYDROSTATIC

PRESSURE

BOP

STATIC

FLUID

LEVEL

FLOATER


37/48

37ATM

Static Pressures - SMD

SEAFLOOR

SEA WATER

HYDROSTATICPRESSURE

PRESSURE

DEPTH

ANNULUS AND RETURN LINEDRILLSTRING PRESSURE


38/48

38ATM

U-Tub ing Rate vs. Time after Pump OFF

0

200

400

600

800

0 5 10 15 20 25 30

Elapsed Time, min

MudFlow

Rate,gpm 3-in ID

4.276-in ID

6-in ID

10,000 ft Water Depth


39/48

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

FluidLevelinDrillpipe,

ft

3-in ID

4.276-in ID

6-in ID

10,000 ft Water Depth


40/48

40


41/48

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 bytemporarily slowing down the mudlift pump

Friction in the choke line is handled by theMudlift Pump and is not seen by theweak formations

Well Control Considerations


42/48

42


43/48

43

G l S


44/48

44ATM

General Summary

Dual Gradient Drilling is a method that offerspotential for lowering drilling costs in very deepwaters:

Fewer casing stringsSmaller rigsLess time on location

The method utilizes one or more small-diameterreturn lines from the seafloor to the surface. Thedrillpipe is separate from the return lines


45/48

45ATM

Summary - contd

A mudlift system (pump) is used to feed thereturn lines, thereby making a dual-densitymud system possible

Wellhead pressure is maintained at seawaterhydrostatic, so well is dead at all times

Well control is quite similar to that inconventional drilling with a riser, but offers anumber of significant advantages


46/48

46ATM

THE END


47/48

47

Gas Lift?

Glass Beads?

How to Handle

Connections?

Trips?

Pumps?

Gas Lift?

Glass Beads?

Rotating BOP

Dual Gradient

Alternatives

Advanced SMD System


48/48

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

Documents

Dual Gradient Drilling