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Dual Gradient Drilling Basic Technology
Dual Gradient Drilling Basic Technology
Lesson 2
Key Success Factors in DGD
Jerome J. Schubert
Hans C. Juvkam-Wold
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IntroductionIntroduction
Success Factors in EquipmentSuccess Factors in Drilling OperationsSuccess Factors in Well Control
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Success Factors in EquipmentSuccess Factors in Equipment
RiserReturn lineAchieving dual densityCuttings processing unit Isolation of mud from seawaterManaging the u-tube
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RiserRiser
No RiserConventional RiserOther
– Phantom riser– Super straw– Cork/Snapper– Holy riser– Top drum/tulip
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Return lineReturn line
RiserFree standingChoke & Kill lineBoost lineSeparate return line
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Achieving dual densityAchieving dual density
Gas liftGlass beadsWater-jet pumpCentrifugal pumpPositive displacement pump
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Positive displacement pumpsPositive displacement pumps
Progressive cavity pumpsReciprocating Piston or Plunger pumpsDiaphragm pumps
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Diaphragm pumpsDiaphragm pumps
Constant discharge rateHigh efficiencyLarge volume displacementGood HP ratingLow pressure surgesCan handle mud, gas, and solids
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Pump Design CriteriaPump Design Criteria
Maximum output GPMMaximum output HPMaximum pressureMaximum mud density
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Pump ControlsPump Controls
Match subsea pump rate with surface pump rate
Automatic pump operation vs. manual controls
Reaction time for start, stop, change in rateSubsea seawater pressure sensorSubsea mud reservoir level sensor
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Pump RedundancyPump Redundancy
What can be done if one or more of the pump chambers fails?
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Pump powerPump power
Hydraulic power– Electric motors to run hydraulic pumps– Hydraulic fluid pumped from the surface
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Solids processing unitSolids processing unit
System must handle solids in some wayPump okHow about plugging choke/kill and return
lines?
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Isolation of mud from seawaterIsolation of mud from seawater
How do we separate mud in the annulus from the seawater either in the riser or open ocean?
SRDPressure ratingActive for tripping, running casing, logging,
etc.
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Managing the u-tubeManaging 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?
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DSV design factorsDSV 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?
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Success Factors in Drilling OperationsSuccess Factors in Drilling Operations
Lower riser loadsLower deck loadsLower deck space requirementsDrill to TD with fewer casing strings
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Success Factors in Drilling OperationsSuccess 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
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What a Dual Gradient Drilling System Must Be Able To Do For Effective Well Control
ATM
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OutlineOutline
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?
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Understanding WC in DGDUnderstanding 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 . . .
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PUMP
U-Tubing in DGD
~SEAWATER HYDROSTATIC
PRESSURE
BOP
STATIC FLUID LEVEL
FLOATER
Even with a DSV there isstill a potential U-tube
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OutlineOutline
How can we educate ourselves and develop a detailed understanding?
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How can we Educate Ourselves?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
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OutlineOutline
What must an effective DGD well control system be able to accomplish?
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WC System must be able to: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
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Avoiding KicksAvoiding 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?
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Detecting Kicks EarlyDetecting 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?
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PUMPBOP
Dual Gradient Drilling System
SEAFLOOR
~SEAWATER HYDROSTATIC
PRESSURE
FLOATER
KICK
Surface PumpSeafloor Pump
How are yougoing to handle
this kick?
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Determining Kick SizeDetermining 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?
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Gas Kick BehaviorGas 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!
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OutlineOutline
What must an effective DGD system contain? - Essential Equipment?
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Which DGD System?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 controlwith all of these methods?
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Seafloor PumpBOP
Dual Gradient Drilling System
SEAFLOOR
~SEAWATER HYDROSTATIC
PRESSURE
FLOATER
KICK
Surface PumpTrip Tank(s)Mud Tanks, etc
Seafloor Pump- Power Transmission- Sensors- Controls
Seafloor Choke?- Backup?
Coordination between the pumps?- Instrumentation
Or gas or bead
injector
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In Summary ...In Summary ...
What are the Key Factors that will
ensure safe and efficient DGD
Drilling and Well Control?
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Key Success Factors for Well Control in DGD?
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
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Key Success Factors - cont’dKey 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
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Additional Success Factors Additional Success Factors
Tripping
Logging
Running Casing
Cementing Casing
Setting Cement Plugs, etc.
Handle Non-water Based Drilling Fluids…
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The EndThe EndThe EndThe End
Jerome J. Schubert
Hans C. Juvkam-Wold
Key Success Factors in DGD