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 (Continuous Annular Pressure Management) DBDG System

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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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SG Well Control Kick Indicators

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CAPM/DBDG Well Control Kick Indicators

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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.

Thank You