an introduction to dilution-based dual gradient …dgs+1015am...an introduction to dilution-based...
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An Introduction to Dilution-BasedDual Gradient (DBDG) Drilling
Presented at the 2011 IADC Dual Gradient Workshop, 5 May 2011
by Paul Boudreau, Dual Gradient Systems LLC
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• Heavier “downhole” mud weight is pumped down drillstring, through bit, and into annulus.
• At injection point (i.e., usually bottom of riser), a lighter density “dilution” mud is injected into annulus at a fixed dilution ratio.
• “Downhole” and “dilution” muds combine at injection point, resulting in column of “diluted” mud weight above injection point.
• “Diluted” mud is returned to rig and, in a continuous process, separated by specialized centrifuges back into “downhole” and “dilution” mud weight components.
How is a Dual Gradient Achieved with the DBDG Process?
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Simplified DBDG Circulating Process
CENTRIFUGE SEPARATION
SHAKERS
Downhole Mud
Dilution Mud
Diluted Mud
Light Weight Discharge
Heavy Weight Discharge
Injection Point
“Downhole”, “Dilution”, and “Diluted” muds are all the same fluid, only with
varying concentrations of barite. DrillstringAnnulus below
Wellhead
Riser
Surface
Boost Line
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How Do Dilution-based and Pump-based Dual Gradient Systems Differ?
Dilution-based Dual Gradient (DBDG)
Pump-based Dual Gradient (PBDG)
Well Design
Wellhead Hydrostatic Pressure
Diluted Riser Mud Hydrostatic
Usually Seawater Hydrostatic
Location of Inflection (Injection) Point
At seafloor, or potentially sub-mudline
At seafloor
Location of Complex Componentry At surface At seafloor
Fewer casing strings compared to single gradient design. Casing points may vary between DBDG
and PBDG based on respective pressure profiles.
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Basic Dual Gradient ConceptPressures and Gradients
To achieve 12.5ppg equivalent mud weight at 20,000ft, the PBDG system would require a 16.5ppg mud below the seabed (at 10,000ft), with seawater hydrostatic at the wellhead.
PBDG: Inflection point at seafloor
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Basic Dual Gradient ConceptPressures and Gradients
To achieve 12.5ppg equivalent mud weight at 20,000ft, the DBDG system could use a 14.5ppg mud below the wellhead (at 10,000ft), with a diluted 10.5ppg mud weight in the riser above the wellhead.
DBDG: Inflection (injection) point
at seafloor
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Dual Gradient Concept with Sub-Mudline InjectionPressures and Gradients
To achieve 12.5ppg equivalent mud weight at 20,000ft, the DBDG system could use a 16.5ppg mud below the sub-mudline injection point (at 13,300ft), with a diluted 10.5ppg mud weight above the injection point.
DBDG w/ SMLI: Inflection (injection) point moved, e.g., to surface casing shoe
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DBDG vs. Single Gradient Well Design
Well Design Considerations• Not all casing seats determined solely
by PP/FG/MW inter-relationship.• Isolation of stray hydrocarbon zones.• Maintaining adequate kick tolerance.• Maintaining multiple barriers between
reservoir and “the world”.• Contingency planning.• Completions design.
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DBDG vs. PBDG Well Design
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DBDG vs. PBDG Well Design
Depleted Sand
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DBDG w/ SMLI vs. DBDG Well Design
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DRILLSTRING
INJECTION STRING
MUD PITS
MUDPUMPS
DILUTION MUD = LIGHT WEIGHT DISCHARGE
FLOW STOP VALVE DOWNHOLE MUD = HEAVY WEIGHT DISCHARGE
DILUTED MUD = MIX MUD = FEED MUD
DEGASSERSHALE
SHAKERS
MUD PITSMUD PITS
CENTRIFUGES
DBDG Circulating System Using Surface BOP Stack (Not Shown)
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DRILLSTRING
BOOST LINE
MARINE RISER
KILLCHOKE LINE
LINE
MUD PITSSUBSEA BOP
MUDPUMPS
DILUTION MUD = LIGHT WEIGHT DISCHARGE
FLOW STOP VALVE DOWNHOLE MUD = HEAVY WEIGHT DISCHARGE
DILUTED MUD = RISER MIX MUD = FEED MUD
CENTRIFUGES
MUD PITSMUD PITS
DEGASSERSHALE
SHAKERS
DBDG Circulating System Using Subsea BOP Stack
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CAPM (Continuous Annular Pressure Management) System
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CAPM Circulating System
DRILLSTRING
CONVENTIONAL FLOWLINE
ROTATING CONTROL DEVICE
INNER RISER MANIFOLD
MARINE RISER
BOOSTER LINE
KILL LINECHOKE LINE
MUD PITS
SUBSEA BOP
MUDPUMPS
DILUTION MUD = LIGHT WEIGHT DISCHARGE
FLOW STOP VALVE DOWNHOLE MUD = HEAVY WEIGHT DISCHARGE
DILUTED MUD = RISER MIX MUD = FEED MUD
SHAKERS
CHOKEDRILLING
CENTRIFUGES
DEGASSERCORIOLIS FLOWMETER
MUD PITSMUD PITS
SHALE
PDP
PDIL
PPWD
PBOP
PRCD
PCHOKE
PRISER
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Customized DBDG Centrifuge
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Customized DBDG Centrifuge
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DGS / TO Centrifuge Testing
SOBM Drilling Fluid
G Force, in/sec2
Feed Rate, gpm
“Diluted” Feed MW,
ppg
“Downhole” Heavy MW,
ppg
“Dilution” Light MW,
ppg
Dilution Rate, QLight / QHeav y
Min - Ave - Max
90/10 OWR 220-1010 490-590 10.5-11.0 11.5-13.7 8.4-8.9 1.1 - 1.5 - 1.9
81/19 OWR, no LCM 500-1010 490-600 10.8-10.9 13.2-15.5 9.0-9.6 1.6 - 2.3 - 2.8
81/19 OWR, w/ LCM 500-780 490-500 10.9-11.1 14.8-15.4 9.3 2.4
Flottweg Centrifuge Testing Results
“Downhole”, “Dilution”, and “Diluted” muds are all the same fluid, only with varying concentrations of barite.
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DGS Flow Stop Valve
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Dual Gradient Drilling FSVU-Tube Arrested with Pumps Off
Upstream - Drillstringwith “Downhole” Mud
Downstream -BHA and Drill Bit
U-tube Pressure Resisted by Spring Forces
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Dual Gradient Drilling FSVBringing on Pumps Through Choke
Pump Pressure + U-Tube Overcome
Spring Force
Flow is Restricted to Provide Main Piston Opening Pressure
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Dual Gradient Drilling FSVMain Valve Opened for Normal Drilling
Choke is By-passed once Main
Valve Opens
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Dual Gradient Drilling FSVValve Closes Once Pumps Off
Upstream - Drillstringwith “Downhole” Mud
Downstream -BHA and Drill Bit
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Thank You