Under-balanced Drilling Fluids

Candidate Selection

Harold Vance Department of Petroleum Engineering

Under-Balanced Fluids •Air (N2, Gas) •Mist •Gaseated •Foam •Oil •Water •Mud

Harold Vance Department of Petroleum Engineering

Subjects Covered • Candidate Selection • Flow Drilling • Aerated • Foam • Air/Gas/N2 • Completions Harold Vance Department of Petroleum Engineering

Reasons for UB Drilling 1. Limit lost circulation 2. Improve drilling rate 3. Avoid differential sticking 4. Protect reservoir Other benefits are not reasons. Harold Vance Department of Petroleum Engineering

Results Improve the rate of return on investment. (Broadened Scope)

Harold Vance Department of Petroleum Engineering

Candidate Selection Historical Perspective

Harold Vance Department of Petroleum Engineering

Cable Tools • The first underbalanced drillers. • No skin damage. • Great production. Harold Vance Department of Petroleum Engineering

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? Harold Vance Department of Petroleum Engineering

Underbalanced Drilling Areas 2000

Lost Circulation. Drilling Rate Reservoir Protection Geothermal

Harold Vance Department of Petroleum Engineering

Number of Underbalanced Wells in Canada 1500

Total Number of Wells

1600 1400 1200 1000 800

525

600

330

400 200 0

230 30 1992

120

1993

1994

1995

1996

Year Harold Vance Department of Petroleum Engineering

1997

New Subject

Underbalance Fluids Summary

Harold Vance Department of Petroleum Engineering

Drilling Fluid Densities 1.2

10.8 0 75

Weighted Mud (Barite)

t

Mist Air

Types Fluids and Relative Densities Types of of Drilling Fluids and Their TheirTheir Relative Densities Types ofDrilling Drilling Fluids and Relative Densities Harold Vance Department of Petroleum Engineering

2.0

Gallon

2 15 4 Poun ds P er C ubi 23 cF oo

12 . 90 6

s per und

.02 .3

11. 1 83

Po

re

Saturated Salt Water

ater

0.002

Fo am Ae wi rate th d M Ba ck ud Pr es Stable Foam su

nd W Gel a

.4

l Oi

0.5

52

ter Wa

6 6.9

4 8.3 .4 62

10.4 78

Native Cla y & Water s Beg in W eigh ted Mu d Ca Satu CL ra -W ted ate r

1.0

2.3

Categories of UB Drilling • Air and gas drilling. Mist drilling. • Foam drilling. • Gaseated drilling. • Flow drilling. Harold Vance Department of Petroleum Engineering

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

Harold Vance Department of Petroleum Engineering

Gas Drilling Common Drilling Gases • Air. • Natural gas. • Nitrogen. • Engine exhaust (Nitrogen). Harold Vance Department of Petroleum Engineering

Gas Drilling, Producing 3MM SCF/day

Harold Vance Department of Petroleum Engineering

Western Air Drilling, 1954

First Widespread use came with development of portable air compressors. Harold Vance Department of Petroleum Engineering

Advantages of Gas Drilling • Increase drilling rate. • No lost circulation* • No differential sticking. • Minimal reservoir damage. Harold Vance Department of Petroleum Engineering

Problems with Gas Drilling • Water. • Washouts, especially in coal. • Corrosion. • Downhole fires with air. • Crooked hole. Harold Vance Department of Petroleum Engineering

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). Harold Vance Department of Petroleum Engineering

Categories of UB Drilling • Air and gas drilling. • Foam drilling. • Gaseated drilling. • Flow drilling. Harold Vance Department of Petroleum Engineering

Foam Drilling

Harold Vance Department of Petroleum Engineering

FOAM Has the greatest potential of any of the “Light” fluids. Harold Vance Department of Petroleum Engineering

Advantages of Foam Drilling

• Great lifting capacity. • Controllable BHP. • Increase drilling rate. • No lost circulation* • No differential sticking. • Minimal reservoir damage. Harold Vance Department of Petroleum Engineering

Problems with Foam Drilling • Complex mixture-Hard to get a proper mixture and maintain it properly. • Disposal/Storage. • Cost. Harold Vance Department of Petroleum Engineering

Categories of UB Drilling • Air and gas drilling. • Foam drilling. • Gaseated drilling. • Flow drilling. Harold Vance Department of Petroleum Engineering

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). Harold Vance Department of Petroleum Engineering

Gaseated Separator

Harold Vance Department of Petroleum Engineering

Advantages of Gaseated Drilling • Increase drilling rate. • No lost circulation* • No differential sticking. • Minimal reservoir damage. Harold Vance Department of Petroleum Engineering

Problems with Gaseated Drilling • Surging (causing overpressures or caving). • Corrosion (not with nitrogen). • Hole caving. Harold Vance Department of Petroleum Engineering

Categories of UB Drilling • Air and gas drilling. • Foam drilling. • Gaseated drilling. • Flow drilling. Harold Vance Department of Petroleum Engineering

Flow Drilling

Harold Vance Department of Petroleum Engineering

Flow Drilling Conventional Mud Used in an Underbalanced Condition

Harold Vance Department of Petroleum Engineering

Advantages of Flow Drilling • Uses regular mud system. • Least expensive way of UB drilling. • No lost returns. • No differential sticking. • Improved ROP. Harold Vance Department of Petroleum Engineering

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. Harold Vance Department of Petroleum Engineering

All Good Ideas • All have problems. • Nothing works all the time. • UB does not improve production all of the time. Harold Vance Department of Petroleum Engineering

Candidate Selection COMMENTS!! Underbalanced Drilling Benefits

Harold Vance Department of Petroleum Engineering

Underbalanced Drilling • New processes involve risk. • Budget enough money. • Don’t promise too much. Harold Vance Department of Petroleum Engineering

Have at Least One Good Economic Reason or Technical Reason

Harold Vance Department of Petroleum Engineering

Remember the Learning Curve !!!!

Harold Vance Department of Petroleum Engineering

UB Drilling Applications

Harold Vance Department of Petroleum Engineering

UB Drilling Applications • Drilling. • Lost returns. • Drilling rate. • Differential pressure sticking. • Limited water. • Reservoir protection. Harold Vance Department of Petroleum Engineering

Lost Returns • Reduce the mud density. • Don’t add junk.

Harold Vance Department of Petroleum Engineering

Lost Circulation Candidates • Permeability > 1,000 md. • Large fractures (>100 micron opening). • Vugular porosity. • Overbalanced > 1,000 psi with conventional fluids. Harold Vance Department of Petroleum Engineering

Increased Drilling Rate Effect of Differential Pressure 7-7/8 TRICONE BIT 70

30,000 lbs. WOB 60 RPM

DRILLING RATE (ft/hr)

60

50

40

AUSTIN CHALK

p b

30

MANCOS SHALE 20

10

COLTON SANDSTONE

p p

0 0

1000

2000

3000

4000

DIFFERENTIAL PRESSURE (psi) Harold Vance Department of Petroleum Engineering

DRILLING RATE (ft/hr)

Drilling Rate-UB Effect of Differential Pressure Perfect Cleaning

p b

Bit Flounder

p p -500

0

+500

+1000

DIFFERENTIAL PRESSURE (psi) Harold Vance Department of Petroleum Engineering

Hard Rock & Crooked Hole • Air Hammer. • Pendulum.

Harold Vance Department of Petroleum Engineering

Differential Pressure Sticking DRILL PIPE

PH

FILTER CAKE

,K Pf PH > Pf DRILL COLLAR

Harold Vance Department of Petroleum Engineering

Limited Water Desert & Semi-Arid Regions Algeria South Yemen Libya SW United States Harold Vance Department of Petroleum Engineering

UB Drilling Applications (2) • Formation damage avoidance.  Skin

damage.  Fluid-fluid sensitivity.  Fluid-formation sensitivity.  Depleted zones. Harold Vance Department of Petroleum Engineering

Formation Damage

Harold Vance Department of Petroleum Engineering

Depleted Zones • Slow drilling rate. • Lost returns. • Differential pressure sticking. • Reservoir damage. Harold Vance Department of Petroleum Engineering

Skin Damage

Reservoir Core

Filter Cake

Harold Vance Department of Petroleum Engineering

Skin Damage Due to Filter Cake and Mud Solids Effective External Filtrate Seal

Internal Pluggin g

Ineffective External Seal for Small Fines & Filtrate

10u

10 micron pore throat 1-3 micron solids

10 micron pore throat 1 micron & smaller solids

10 micron pore throat 10 micron solids & some smaller solids Harold Vance Department of Petroleum Engineering

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

Harold Vance Department of Petroleum Engineering

Fluid Sensitivity

1. Fluid-Formation Reaction (Shale Instability) Instability 2.

Fluid-Fluid Reaction (Emulsions) Harold Vance Department of Petroleum Engineering

Mechanism for Formation Blocking (Bennion, 1995)

Non Wetting Phase Fines Case 1 Non-Wetting phase in motionminimal fines migration Case 2 Wetting phase in motion potential for fines migration

Wetting Phase Non Wetting Phase

Non Wettin g

Harold Vance Department of Petroleum Engineering

Formation Damage - Fractured Formations Fracture Plugging

Harold Vance Department of Petroleum Engineering

Mechanism for Formation Blocking (Bennion, 1995)

Fractured Formations High losses, minimal damage

Sealed Fracture, depth of invasion dependent on solids size distribution and overbalanced Poor Seal, potential continued leak-off of filtrate and small solids

Harold Vance Department of Petroleum Engineering

100 micron fracture 10 micron solids

100 micron fracture 10-100 micron solids

100 micron fracture 10-500 micron solids

UB Drilling in Fractured Reservoirs No Invasion of “Top” Fractures While Underbalanced

1

Drilling Fluid

Produced Fluid

Fluid Balance or Micro Fracture

2 Gravity Displacement

Harold Vance Department of Petroleum Engineering

Homogenous Sand-Clean Homogenous Sand-Dirty Laminated Sand-Clean Laminated Sand-Dirty Unconsolidated Sand Fractured Sand Perm-Matrix

Probable Unlikely

Possible

Harold Vance Department of Petroleum Engineering

Effect of High Overbalanced

Biological Damage

Fines Migration

Chemical Adsorption

Phase Trapping

Solids Invasion

Rock-Fluid Incompatibility

Damage Mechanism

Fluid-Fluid Incompatibility

Potential Formation Damage Mechanism in Different Sand Reservoir Types

Fractured Sand Low Perm Matrix Homogenous Carbonate Fractured Carbonate Impermeable Matrix Fractured Carbonate Permeable Matrix Vugular Carbonate

Probable Unlikely

Possible

Harold Vance Department of Petroleum Engineering

Effect of High Overbalanced

Biological Damage

Fines Migration

Chemical Adsorption

Phase Trapping

Solids Invasion

Rock-Fluid Incompatibility

Damage Mechanism

Fluid-Fluid Incompatibility

Potential Formation Damage Mechanism in Different Sand Reservoir Types

Candidate Selection Underbalanced Drilling Limitations

Harold Vance Department of Petroleum Engineering

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

fractured

Harold Vance Department of Petroleum Engineering

Underbalanced Problem ROTATING BOPs COMPRESSOR / N2 COST

SOLID/LIQUID/GAS SEPARATION

CORROSION HYDRAULIC CALCULATIONS VIBRATIONS CUTTINGS LIFTING FLUID INFLUX

HIGH TORQUE/ DRAG BOREHOLE STABILITY

FIRE/ EXPLOSION S

UNDERBALANCED COMPLETION

MWD TRANSMISSION

Harold Vance Department of Petroleum Engineering

If a reservoir will not produce without fracturing it is probably a poor UB prospect. Harold Vance Department of Petroleum Engineering

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

Harold Vance Department of Petroleum Engineering

The “Absolute” Rule for UB Operations …IT’S NOT WHAT YOU KNOW THAT HURTS YOU. …IT’S WHAT YOU KNOW THAT’S NOT TRUE!

Harold Vance Department of Petroleum Engineering

The No-Go Screen If the following occurs within the open hole section: DON’T DRILL UNDERBALANCED 1. Geopressured shales 2. Steeply dipping fractured formations 3. Thick broken coals 4. What about sands? - not sandstone Harold Vance Department of Petroleum Engineering

Primary Cause of Well Bore Collapse • NATURAL CAUSES Fractured or Faulted Zones High Pore Pressure (Geopressure) Weak, Low Strength Rocks High in Situ Stresses Harold Vance Department of Petroleum Engineering

Primary Causes of Well Bore Collapse 

INDUCED PROBLEMS  Pressure Surges  Wetted Shales Harold Vance Department of Petroleum Engineering

Compressive Failure Models Compressive Yielding and collapse

Naturally fractured rock

Friable Sandstone Brittle Shales Salt

Formation Breakdown and Lost Circulation

Induced hydraulic fracture

Convergence

Swelling Shales

Wellbore Pressure

Natural or Induced fractures Harold Vance Department of Petroleum Engineering

WELLSTAB - MEI Wellbore Stability Model Mechanical/Chemical Stability Design Multi-Depth Analysis Microsoft Office Report

Harold Vance Department of Petroleum Engineering

END

Harold Vance Department of Petroleum Engineering