Dual Gradient Drilling Basic Technology

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

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
U-Tubing in DGD
FLOATER
SEAWATER HYDROSTATIC PRESSURE
STATIC FLUID LEVEL
PUMP
BOP
Even with a DSV there is still a potential U-tube
ATM
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 AM!
• 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
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
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
  cant 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
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
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
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 - contd

• Manage the U-tube
• Detect and Manage Trapped Pressure
• Use Drillers 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
The End

• Jerome J. Schubert
• Hans C. Juvkam-Wold
• Key Success Factors in DGD