AIRMISTFOAM AND UNDERBALANCED DRILLING TECHNOLOGY

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Candidate Selection
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Under-Balanced Fluids

• Air (N2, Gas)
• Mist
• Gaseated
• Foam
• Oil
• Water
• Mud

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Subjects Covered

• Candidate Selection
• Flow Drilling
• Aerated
• Foam
• Air/Gas/N2
• Completions

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Reasons for UB Drilling

• 1. Limit lost circulation
• 2. Improve drilling rate
• 3. Avoid differential sticking
• 4. Protect reservoir

Other benefits are not reasons.
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Results

• Improve the rate of return on investment.

(Broadened Scope)
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Candidate Selection

• Historical Perspective

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Cable Tools

• The first underbalanced drillers.
• No skin damage.
• Great production.

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UB History

• 1938 - California Gas Drilling.
• 1948 - Aerated, Big Lake Texas.
• 1960 - AEC Foam, Nuclear Holes.
• 1965 - Aerated U.S.
• 1968 - Chevron Foam, California.
• 1986 - Aerated Canada.
• 192? - Russia, Where? What?

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Underbalanced Drilling Areas2000
Lost Circulation. Drilling Rate Reservoir
Protection Geothermal
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Number of Underbalanced Wellsin Canada
1500
1600
1400
1200
1000
Total Number of Wells
800
525
600
330
400
230
120
200
30
0
1992
1993
1994
1995
1996
1997
Year
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New SubjectUnderbalance Fluids Summary
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Drilling Fluid Densities
1.2
1.0
0
2.0
0.5
.4
2.3
0.002
Types of Drilling Fluids and Their Relative
Densities
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Categories of UB Drilling

• Air and gas drilling.
• Mist drilling.
• Foam drilling.
• Gaseated drilling.
• Flow drilling.

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Gas Drilling

• First commercial UB drilling was with gas in the
  U.S. (1940s)

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Gas DrillingCommon Drilling Gases

• Air.
• Natural gas.
• Nitrogen.
• Engine exhaust (Nitrogen).

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Gas Drilling, Producing 3MM SCF/day
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Western Air Drilling, 1954
First Widespread use came with development of
portable air compressors.
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Advantages of Gas Drilling

• Increase drilling rate.
• No lost circulation
• No differential sticking.
• Minimal reservoir damage.

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Problems with Gas Drilling

• Water.
• Washouts, especially in coal.
• Corrosion.
• Downhole fires with air.
• Crooked hole.

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Air/Mist Drilling

• Water detergent is added to air (or gas) when
  the hole becomes damp or when it is too washed
  out to lift the cuttings.
• Water added is normally between 5 bbl/hr to 10
  bbl/hr (0.8 m3/hr to 1.5 m3/hr).

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Categories of UB Drilling

• Air and gas drilling.
• Foam drilling.
• Gaseated drilling.
• Flow drilling.

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Foam Drilling
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FOAMHas the greatest potential of any of the
Light fluids.
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Advantages of Foam Drilling

• Great lifting capacity.
• Controllable BHP.
• Increase drilling rate.
• No lost circulation
• No differential sticking.
• Minimal reservoir damage.

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Problems with Foam Drilling

• Complex mixture-Hard to get a proper mixture and
  maintain it properly.
• Disposal/Storage.
• Cost.

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Categories of UB Drilling

• Air and gas drilling.
• Foam drilling.
• Gaseated drilling.
• Flow drilling.

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Gaseated Drilling

• Gaseated or aerated drilling uses a mixture of
  fluid and gas.
• Gas may generally be any gas.
• Fluid may be from oil to water to drilling mud.
• No binding agent is used (foamer).

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Gaseated Separator
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Advantages of Gaseated Drilling

• Increase drilling rate.
• No lost circulation
• No differential sticking.
• Minimal reservoir damage.

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Problems with Gaseated Drilling

• Surging (causing overpressures or caving).
• Corrosion (not with nitrogen).
• Hole caving.

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Categories of UB Drilling

• Air and gas drilling.
• Foam drilling.
• Gaseated drilling.
• Flow drilling.

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Flow Drilling
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Flow Drilling

• Conventional Mud Used in an Underbalanced
  Condition

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Advantages of Flow Drilling

• Uses regular mud system.
• Least expensive way of UB drilling.
• No lost returns.
• No differential sticking.
• Improved ROP.

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Problems with Flow Drilling

• Limited ability to reduce annular pressure below
  normal reservoir pressures.
• Drilling with a constant well flow or potential
  of well flow.

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All Good Ideas

• All have problems.
• Nothing works all the time.
• UB does not improve production all of the time.

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Candidate Selection

• COMMENTS!!
• Underbalanced Drilling Benefits

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Underbalanced Drilling

• New processes involve risk.
• Budget enough money.
• Dont promise too much.

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Have at Least One Good Economic Reason or
Technical Reason
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Remember the Learning Curve !!!!
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UB Drilling Applications
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UB Drilling Applications

• Drilling.
• Lost returns.
• Drilling rate.
• Differential pressure sticking.
• Limited water.
• Reservoir protection.

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Lost Returns

• Reduce the mud density.
• Dont add junk.

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Lost Circulation Candidates

• Permeability gt 1,000 md.
• Large fractures (gt100 micron opening).
• Vugular porosity.
• Overbalanced gt 1,000 psi with conventional fluids.

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Increased Drilling RateEffect of Differential
Pressure
70
7-7/8 TRICONE BIT 30,000 lbs. WOB 60 RPM
60
50
40
AUSTIN CHALK
DRILLING RATE (ft/hr)
p
b
30
MANCOS SHALE
20
10
COLTON SANDSTONE
p
p
0
0
1000
2000
3000
4000
DIFFERENTIAL PRESSURE (psi)
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Drilling Rate-UBEffect of Differential Pressure
Perfect Cleaning
DRILLING RATE (ft/hr)
p
b
Bit Flounder
p
p
-500
0
500
1000
DIFFERENTIAL PRESSURE (psi)
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Hard Rock Crooked Hole

• Air Hammer.
• Pendulum.

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Differential Pressure Sticking
DRILL PIPE
PH
FILTER CAKE
, K
Pf
PH gt Pf
DRILL COLLAR
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Limited Water

• Desert Semi-Arid Regions
• Algeria
• South Yemen
• Libya
• SW United States

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UB Drilling Applications (2)

• Formation damage avoidance.
• Skin damage.
• Fluid-fluid sensitivity.
• Fluid-formation sensitivity.
• Depleted zones.

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Formation Damage
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Depleted Zones

• Slow drilling rate.
• Lost returns.
• Differential pressure sticking.
• Reservoir damage.

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Skin Damage
Filter Cake
Reservoir Core
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Skin Damage Due to Filter Cake and Mud Solids
10 micron pore throat 1-3 micron solids
Effective External Filtrate Seal
10 micron pore throat 1 micron smaller solids
Internal Plugging
10 micron pore throat 10 micron solids
some smaller solids
Ineffective External Seal for Small Fines
Filtrate
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Skin Damage

• Avoidance Techniques
• UB Drilling
• Non-Invasive Mud Cake
• Ultra Clean Drill-in Fluid

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Fluid Sensitivity
1. Fluid-Formation Reaction (Shale Instability)
2.
Fluid-Fluid Reaction (Emulsions)
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Mechanism for Formation Blocking(Bennion, 1995)
Non Wetting Phase
Fines
Wetting Phase
Case 1 Non-Wetting phase in motion- minimal
fines migration
Non Wetting Phase
Case 2 Wetting phase in motion - potential for
fines migration
Non Wetting
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Formation Damage - Fractured Formations
Fracture Plugging
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Mechanism for Formation Blocking(Bennion,
1995)Fractured Formations
100 micron fracture 10 micron solids
High losses, minimal damage
100 micron fracture 10-100 micron solids
Sealed Fracture, depth of invasion dependent on
solids size distribution and overbalanced
100 micron fracture 10-500 micron solids
Poor Seal, potential continued leak-off of
filtrate and small solids
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UB Drilling in Fractured Reservoirs
No Invasion of Top Fractures While Underbalanced
Produced Fluid
Drilling Fluid
1
2
Fluid Balance or Micro Fracture
Gravity Displacement
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Potential Formation Damage Mechanism in
Different Sand Reservoir Types
Solids Invasion
Fines Migration
Biological Damage
Phase Trapping
Chemical Adsorption
Fluid-Fluid Incompatibility
Rock-Fluid Incompatibility
Effect of High Overbalanced
Damage Mechanism
Homogenous Sand-Clean
Homogenous Sand-Dirty
Laminated Sand-Clean
Laminated Sand-Dirty
Unconsolidated Sand
Fractured Sand Perm-Matrix
Probable Possible
Unlikely
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Potential Formation Damage Mechanism in
Different Sand Reservoir Types
Fluid-Fluid Incompatibility
Rock-Fluid Incompatibility
Effect of High Overbalanced
Chemical Adsorption
Fines Migration
Phase Trapping
Biological Damage
Solids Invasion
Damage Mechanism
Fractured Sand Low Perm Matrix
Homogenous Carbonate
Fractured Carbonate Impermeable Matrix
Fractured Carbonate Permeable Matrix
Vugular Carbonate
Probable Possible
Unlikely
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Candidate Selection

• Underbalanced Drilling Limitations

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UB Limits

• UB is not an enhancement technique.
• Mud column pressure is not a seal against
• Well kick.
• Broken or fractured formation.
• Weak formations.
• Heaving shale.

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Underbalanced Problem
ROTATING BOPs
COMPRESSOR / N2 COST
SOLID/LIQUID/GAS SEPARATION
CORROSION
HYDRAULIC CALCULATIONS
VIBRATIONS
CUTTINGS LIFTING
FLUID INFLUX
UNDERBALANCED COMPLETION
FIRE/ EXPLOSIONS
HIGH TORQUE/
DRAG
BOREHOLE STABILITY
MWD TRANSMISSION
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If a reservoir will not produce without
fracturing it is probably a poor UB prospect.
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Warning

• A poor prospect can prove failure. You must
  gamble with a well that can succeed.

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The Absolute Rule for UB Operations
ITS NOT WHAT YOU KNOW THAT HURTS YOU. ITS
WHAT YOU KNOW THATS NOT TRUE!
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The No-Go Screen

• If the following occurs within the open hole
  section
• DONT DRILL UNDERBALANCED
• 1. Geopressured shales
• 2. Steeply dipping fractured formations
• 3. Thick broken coals
• 4. What about sands? - not sandstone

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Primary Cause of Well Bore Collapse

• NATURAL CAUSES
• Fractured or Faulted Zones
• High Pore Pressure (Geopressure)
• Weak, Low Strength Rocks
• High in Situ Stresses

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Primary Causes of Well Bore Collapse

• INDUCED PROBLEMS
• Pressure Surges
• Wetted Shales

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Compressive Failure Models
Naturally fractured rock
Compressive Yielding and collapse
Friable Sandstone
Formation Breakdown and Lost Circulation
Brittle Shales
Induced hydraulic fracture
Salt
Convergence
Swelling Shales
Wellbore Pressure
Natural or Induced fractures
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WELLSTAB - MEI Wellbore Stability
Model Mechanical/Chemical Stability
Design Multi-Depth Analysis Microsoft Office
Report
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END
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