1. Dual Gradient Drilling Basic Technology
Lesson 2
Key Success Factors in DGD
Jerome J. Schubert
Hans C. Juvkam-Wold

2. Introduction Success Factors in Equipment
Success Factors in Drilling Operations
Success Factors in Well Control

3. Success Factors in Equipment
Riser
Return line
Achieving dual density
Cuttings processing unit
Isolation of mud from seawater
Managing the u-tube

4. Riser No Riser Conventional Riser Other Phantom riser Super straw
Cork/Snapper
Holy riser
Top drum/tulip

5. Return line Riser Free standing Choke & Kill line Boost line
Separate return line

6. Achieving dual density
Gas lift
Glass beads
Water-jet pump
Centrifugal pump
Positive displacement pump

7. Positive displacement pumps
Progressive cavity pumps
Reciprocating Piston or Plunger pumps
Diaphragm pumps

8. Diaphragm pumps Constant discharge rate High efficiency
Large volume displacement
Good HP rating
Low pressure surges
Can handle mud, gas, and solids

9. Pump Design Criteria Maximum output GPM Maximum output HP
Maximum pressure
Maximum mud density
Need to get the pump rate, hp, pressure, etc of mlp

10. Pump Controls Match subsea pump rate with surface pump rate
Automatic pump operation vs. manual controls
Reaction time for start, stop, change in rate
Subsea seawater pressure sensor
Subsea mud reservoir level sensor

11. Pump Redundancy
What can be done if one or more of the pump chambers fails?

12. Pump power Hydraulic power Electric motors to run hydraulic pumps
Hydraulic fluid pumped from the surface

13. Solids processing unit
System must handle solids in some way
Pump ok
How about plugging choke/kill and return lines?

14. Isolation of mud from seawater
How do we separate mud in the annulus from the seawater either in the riser or open ocean?
SRD
Pressure rating
Active for tripping, running casing, logging, etc.

15. Managing the u-tube How will we handle the u-tube?
Write all procedures compensate for the active u-tube?
Build a DSV to manage it?

16. DSV design factors How is it going to open and close?
Will it have an adjustable opening pressure?
Will it pass MWD signals and LCM?
What will it do to circulating pressures?
Are the opening and circulating pressure repeatable?
Where will it be located in the drillstring?

17. Success Factors in Drilling Operations
Lower riser loads
Lower deck loads
Lower deck space requirements
Drill to TD with fewer casing strings

18. Success Factors in Drilling Operations
Balanced Cement Plug
Running Casing
Cementing
Check for Underbalance
Circulation
Connections
Dual to Single Density Conversion
Routine Drilling
Start-Stop Circulation
Tripping
Unplanned Shutdown
Fishing
Logging

19. What a Dual Gradient Drilling System Must Be Able To Do For Effective Well Control
ATM

20. Outline Understanding DGD Well Control - what is different ?
How can we educate ourselves and develop a detailed understanding?
What must an effective DGD well control system be able to accomplish?
What must an effective DGD system contain?

21. Understanding WC in DGD
Accept that DGD Well Control is not a simple task - it is different - and it is frequently neither intuitive nor obvious
for example U-tubing how does it affect kick detection? - how can we ensure that a constant bottom- hole pressure is being maintained? - what if power fails during WC operations?
More details later . . .

22. ~SEAWATER HYDROSTATIC PRESSURE
U-Tubing in DGD
FLOATER
~SEAWATER HYDROSTATIC PRESSURE
STATIC FLUID LEVEL
BOP
PUMP
Even with a DSV there is
still a potential U-tube
ATM 23

23. Outline
How can we educate ourselves and develop a detailed understanding?

24. How can we Educate Ourselves?
We have found that detailed hydraulics modeling is essential to understanding DGD
Study each aspect of the process in detail: - Four PhD and seven MS studies have been completed or are in progress at Texas A&M!
Detailed procedures had to be developed to cover all essential drilling and WC operations
Procedures are critically peer reviewed and tested against the hydraulics model

25. Outline
What must an effective DGD well control system be able to accomplish?

26. WC System must be able to:
Avoid kicks - as far as possible
Detect Kicks early - to minimize their size
Determine kick size and Intensity
Measure new formation pressure (“SI-BHP”)
Safely remove kick from hole
Maintain constant BHP
Detect equipment failures during WC operations
Provide contingencies for all potential failures

27. Avoiding Kicks Recognize the signs of increasing pore pressure? How?
Allow the recovery of cuttings of sufficient size to evaluate their characteristic shape and other properties?
Allow you to maintain satisfactory BHP during connections? While tripping? When cementing? When power fails?

28. Detecting Kicks Early Can you perform a conventional flow check?
How accurate is your pit gain indicator?
What other kick detection methods are available?
What is the smallest kick that can detect?
How quickly can you stop the influx? How?
How do you handle the U-tube to ensure that its effects are not confused with kick indicators?

29. ~SEAWATER HYDROSTATIC PRESSURE
Dual Gradient Drilling System
FLOATER
Surface Pump
Seafloor Pump
~SEAWATER HYDROSTATIC PRESSURE
SEAFLOOR
BOP
PUMP
How are you
going to handle
this kick?
KICK
ATM 27

30. Determining Kick Size
What is the initial size of the kick when its presence is first confirmed?
What is the size of the kick when influx stops?
How can you measure kick volume and intensity?
How can you maintain constant BHP - while circulating the kick out of the hole? - if you can’t circulate and kick is migrating?
What is the Expected Kick Fluid Behavior?

31. Gas Kick Behavior
As the gas kick moves up the hole the pressure generally decreases so we would expect the gas volume to expand - but how fast?
At the seafloor pump there is an increase in pressure - how does the volume behave?
Can we continue to assume that PV = const?
Or should we use PV = ZnRT?
We will take a closer look!

32. Outline
What must an effective DGD system contain? Essential Equipment?

33. Can we maintain safe well control with all of these methods?
Which DGD System?
There are basically two different methods we can use to Reduce annulus pressure at seafloor:
Install pump at seafloor
Inject a low density fluid in the return line
Gas (e.g. air or nitrogen)
Low density particles (e.g. hollow spheres)
Can we maintain safe well control
with all of these methods?

34. ~SEAWATER HYDROSTATIC PRESSURE
Dual Gradient Drilling System
FLOATER
Surface Pump
Trip Tank(s)
Mud Tanks, etc
~SEAWATER HYDROSTATIC PRESSURE
Or gas or bead injector
SEAFLOOR
BOP
Seafloor Pump
Seafloor Pump
- Power Transmission
- Sensors
- Controls
Seafloor Choke?
- Backup?
Coordination between the pumps?
- Instrumentation
KICK
ATM 27

35. In Summary ...
What are the Key Factors that will ensure safe and efficient DGD Drilling and Well Control?

36. Key Success Factors for Well Control in DGD?
Kick Detection
Kick Containment (stop flow into well)
Kick Removal (circulate kick out of hole?)
Determine New Pore Pressure (after kick)
Increase Mud Weight in hole (if necessary)
Perform Leak-off Test

37. Key Success Factors - cont’d
Manage the “U-tube”
Detect and Manage Trapped Pressure
Use Driller’s Method
Perform Volumetric Well Control
Manage Kick Expansion (pump very slowly)
Manage Loss of Pumping Capability
Understand the Behavior of Gas Kicks

38. Additional Success Factors
Tripping
Logging
Running Casing
Cementing Casing
Setting Cement Plugs, etc.
Handle Non-water Based Drilling Fluids…

39. Jerome J. Schubert Hans C. Juvkam-Wold Key Success Factors in DGD
The End
Jerome J. Schubert
Hans C. Juvkam-Wold
Key Success Factors in DGD