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Dilution-Based Dual Gradient Well Control
Presented at the 2011 IADC Dual Gradient Workshop, 5 May 2011
by Paul Boudreau, Dual Gradient Systems LLC
• Review Dilution-based Dual Gradient (DBDG) well design, wellbore configuration, and well control equipment.
• Look at DBDG in conjunction with an MPD system; i.e., Transocean’s Continuous Annular Pressure Management (CAPM) system. (Any feature which does not apply to DBDG in absence of MPD will be highlighted.)
• Compare CAPM/DBDG and conventional single gradient well control.
• Have a quick look at the various well control options which may be employed within CAPM/DBDG.
In this very short presentation, we will…
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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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Single Gradient
DBDG
CAPM/DBDG 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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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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Conventional Single Gradient
CAPM / DBDG
Theory and Practice Conventional Unconventional and new to industry
Special Equipment None Flow Stop Valve required
Kick Detection Conventional, open system subject to heave-affected returns
Enhanced using Coreolis flowmeters and micro-influx detection on closed circulating system
Kick Volume Conventional, open system subject to heave-affected returns
Smaller due to enhanced detection
Determination of Bottom Hole
Pressure
Direct using SIDPP Drillstring normally overbalanced. BHP determined indirecly, by change in FSV crack-open pressure. (Direct after influx circulated above BOP pressure gauge)
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Conventional vs CAPM/DBDG Well Control
continued...
Conventional Single Gradient
CAPM / DBDG
Well Control Operations
Conventional More complex in that dilution must be maintained, but also offers more flexibility
Casing Shoe Pressures
Higher Lower shoe pressures due to heavier MW between kicking formation and shoe
Margin Between Wellbore Pressure
and Fracture
Lower Larger due to higher MW
Weight-up Strategy Weight up below BOP, then riser
Can kill well by raising Downhole MW, Riser MW, or both. May be able to kill well without increasing Riser MW.
Time to Kill Well Conventional, may even use both choke and kill lines
Increased due to having to dilute choke line returns. May be reduced in some cases by beginning circ through drilling choke.
Redundancy in C&K Lines
Yes No, must use one to inject dilution mud
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Conventional vs CAPM/DBDG Well Control...continued
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Conventional vs CAPM/DBDG Well ControlConventional Single Gradient CAPM / DBDG
Kick Detection
1. Return flowrate2. PWD 3. Pit gain (detection
problematic in very large circulating systems)
4. (ROP)5. (Hook load)6. (Standpipe pressure)
1. Delta flow in/out (using Coriolis flow meter on mud return line)
2. Subsea BOP and Riser pressures (due to more downhole mud flow into riser)
3. PWD4. (ROP)5. (Hook load)6. (Injection / boost line pressure)7. (Pit gain)
BottomholePressure Determination
1. SIDPP2. Shut in BOP pressure*3. SICP*
1. Flow Stop Valve crack-opening pressure2. Shut in BOP pressure (delta)*3. SICP** Especially once kick circulated above or out.
Kill Method Options
1. Wait-and-weight2. Driller’s method3. Riser Kill4. Bullheading
1. ‘Driller’s Method’ (no increase in MW for first circulation); through choke manifold and/or MPD drilling choke manifold
2. ‘Wait-and-weight’ (increase ‘Downhole’ MW)3. Riser Kill (increase ‘Riser’ MW)4. Bullheading
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CAPM/DBDG Well Control Flexibility
In this example, a kick is taken at 16,000ft at the section TD. Because there remains a wide margin between the mud hydrostatic and the fracpressure at the previous shoe (at 11,000ft), either the riser mud weight or the downhole mud weight may be increased to kill the well. The riser mud weight in this case is programmed to increase for the next hole section.
Note that the 12.85ppg pore pressure at TD exceeds the ~12.65ppg frac pressure at the shoe above (see dotted brown line); thus SG well control would not be possible with this casing design.
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CAPM/DBDG Well Control OptionsMethod Advantages Disadvantages
‘Wait-and-Weight’ (increasing Downhole MW)
1. Lower annular pressures compared to ‘Driller’s Method’ (well-specific).
2. Lower shoe pressures than with Riser Kill method.
1. Delay in circulation while building kill weight mud.
2. Complicates fluid management and calculations.
‘Driller’s Method’(no change to mud weights for first circulation)
1. Circulation can begin immediately.
2. Barite not required to begin circulating.
3. Can calculate BHP down annulus once kick is above BOP stack.
1. Requires additional circulation to kill well.2. Higher surface pressures than ‘W&W’ or
Riser Kill.3. Higher shoe pressures are possible.4. Requires both C&K lines (one to inject
dilution mud below closed BOP, one for well returns) when circulating out through the choke.
Riser Kill (increasing Riser or Choke Line MW by decreasing dilution ratio)
1. Can ‘kill’ formation quickly by displacing choke line and/or riser, even with kick still on bottom.
2. In certain situations; e.g., salt water kick, allows circulating up kick conventionally through open BOP.
3. No requirement to weight up mud on surface prior to commencing circulation.
1. Requires use of both choke and kill lines to inject dilution mud below closed BOP when circulating out through the choke.
2. Relies on properly functioning FSV to maintain constant BHP.
3. Increases shoe pressure compared to ‘W&W’ method.
Recommended