GRI AGM ’99

TT00-03 1

Wellbore Stability Progress

GRI Exploration and Production

Advisory Group Meeting

William C. Maurer

Maurer Engineering Inc.

October 13-14, 1999, Houston, TX

GRI AGM ’99

TT00-03 2

Overview

• General

• Mechanical Aspects

• Physico-Chemical Aspects

- GRI Funded Groups

- Other Groups (Worldwide)

• MEI Wellbore Stability Model

• Summary of Mechanisms

• Recommendations for Future R&D

GRI AGM ’99

TT00-03 3

General

GRI AGM ’99

TT00-03 4

Cost of Wellbore Instability Problems

$500 million/year, before 1992G.M. Bol, SPE 24975

1992 SPE European Petroleum Conference

$92 million, BP 1997

$38 million, BP 1998 first quarterJ. Kijowski, BP-Amoco Downhole Talk, Issue 80

GRI AGM ’99

TT00-03 5

Wellbore Instability Problems

• High Torque and Drag

• Bridging and Fill

• Stuck Pipe

• Directional Control Problem

• Slow Penetration Rates

• High Mud Costs

• Cementing Failures and High Cost

• Difficulty in Running and Interpreting Logs

GRI AGM ’99

TT00-03 6

Wellbore Stability FundamentalStress vs Strength

Near Wellbore

Stresses

Formation

Strength

Near-Wellbore

Pore Pressure Mud ChemistryWell

Trajectory

In-SituStresses

FormationPressure

LithologyFabric

Cementation

Controllable Factors

Uncontrollable Factors

GRI AGM ’99

TT00-03 7

Mechanical Aspects

GRI AGM ’99

TT00-03 8

Typical Wellbore Problems(Aadnov and Chenevert, 1987)

Tight Hole

Borehole Enlargement

or Collapse

Vertical Fracture

Horizontal Fracture

Events which occur at

low wellbore pressures

Events which occur at

high wellbore pressures

GRI AGM ’99

TT00-03 9

Bore Hole Enlargement in Shale(Simpson et al., 1988)

GRI AGM ’99

TT00-03 10

Lost Circulation

• Naturally fractured

• Unconsolidated

• Highly permeable

• Cavernous or vugular

• Mechanically

induced fractures

GRI AGM ’99

TT00-03 11

Lost Circulation Material

• Granular - nut hulls,

asphalt, seeds, grains,

limestone, salt crystals, etc.

• Fibrous - wood fibers,

straw, mineral fibers, etc.

• Lamellar - mica,

cellophane, shredded

plastic, etc.

• Liquid - polymers, etc.

GRI AGM ’99

TT00-03 12

Compressive Failure (Collapse)

Collapse

σr

GRI AGM ’99

TT00-03 13

Effect of Borehole Pressures

GRI AGM ’99

TT00-03 14

Wellbore Failure MechanismsMAURY et al., 1987

INTERMEDIATE

INTERMEDIATE

HIGH

MED

BOREHOLEELONGATION

TOROIDALSPALLS

HYDRAULIC

FRACTURING

LOW

LOW

VERY HIGH

INTERMEDIATE STRESS

MED

HIGH

<D> EXTENSION

<B> SHEAR

MODE

<C> SHEAR

<A> SHEAR

MUD WT

GRI AGM ’99

TT00-03 15

Rock Failure

GRI AGM ’99

TT00-03 16

Rock Failure Mechanisms

PLASTICBRITTLE

GRI AGM ’99

TT00-03 17

Micro-fracture Pressure-Time CurveSoliman, et al, 1989

Breakdown Pressure

ReopeningPressure

ISIP

FCP

PumpingShut in

GRI AGM ’99

TT00-03 18

Rock Triaxial Stress TestMcLean & Addis, 1990

50

20

10Confining Pressure (MPA)

0

Axial Strain (%)

0 1.0 2.0 3.0 4.00

100

200

300

Devia

tor

Str

ess

σ1 -σ

3 (

MPa)

GRI AGM ’99

TT00-03 19

Effect of Pore Fluid Saturation

POROUS ROCKSOLID ROCK

Pf = Fluid Pressure

o=zo=z+pf

GRI AGM ’99

TT00-03 20

Effective Rock Stress

z= o - pf

o = Overburden Stress

z = Matrix Stress

pf = Pore Fluid Pressure

GRI AGM ’99

TT00-03 21

Change In Near-Wellbore Stresses

Caused by Drilling

V (overburden)

Hmin

Hmax Hmin

Hmax

Pw (hydrostatic)

Before DrillingIn-situ stress state

After DrillingLower stress within wellbore

GRI AGM ’99

TT00-03 22

Stress Concentration around

an Open Wellbore

Pw

Po

Hmin

Hmax

zq

q

r

z

r

r

GRI AGM ’99

TT00-03 23

Strength vs Stress

Identifying the Onset of Rock Yielding

Shear

Str

ess

r´

Effective Compressive Stress

Stable Stress State

q´

r´

Shear

Str

ess

r´

Effective Compressive Stress

Unstable Stress State

q´

r´

q´

MinStress

MaxStress

q´

GRI AGM ’99

TT00-03 24

Types of Yielding Occurring

around Wellbore

MINIMUM

STRESS

High shearstress zone

Limits ofdamagedregion

Extensional strain zone(usually single fracture)

BREAKOUTS

MAXIMUM STRESS

borehole

GRI AGM ’99

TT00-03 25

Rock Yielding around Wellbores

Laboratory TestsRawlings et al, 1993

Isotropic Stresses Anisotropic Stresses

GRI AGM ’99

TT00-03 26

Wellbore Radial Decrease

m = Poisson’s Ratio

R = Wellbore Radius

h = Original horizontal earth stress

Pw = Wellbore pressure

E = Young’s Modulus

r = (h-pw )(1+m )R / E

GRI AGM ’99

TT00-03 27

Borehole DeformationDunbar et al., 1985

GRI AGM ’99

TT00-03 28

Effect of PermeabilityHsiao, 1987

GRI AGM ’99

TT00-03 29

Wellbore Stable Condition

Collapse Failure

Fracture Failure

Stable

Mud Weight (ppg)

GRI AGM ’99

TT00-03 30

Physico-Chemical Aspects

GRI AGM ’99

TT00-03 31

Typical Occurrences of Wellbore

Instability in Shales

soft, swelling shale

brittle-plastic shale

brittle shale

naturally fractured shale

strong rock unit

GRI AGM ’99

TT00-03 32

Oil-Base Muds

BENEFITS

• Shale inhibition

• Formation fluid

compatible

• Lubricity

• Reduced hole

erosion

• Temperature,

corrosion , MWs...

LIMITATIONS

• Environmental/safety

• Base cost

• Emulsifiers’ reactivity

• Cement

incompatibility

• Water flows, losses...

• Operational

considerations

Basic Mud Types

GRI AGM ’99

TT00-03 33

Fresh Water-Base Muds

BENEFITS

• Base cost

• Environmental

/Handling

• Cement compatibility

• Water flow resilience

• Many types…

• Additives available to

achieve similar

characteristics as OBM

LIMITATIONS

• Shale reactivity

• Additives most properties

• Hole erosion at

high flow rates

• Formation fluid

incompatibility

• Temperature...

Basic Mud Types (continued)

GRI AGM ’99

TT00-03 34

Saline Water-Base Muds

BENEFITS

• Base cost

• Shale inhibition

• Cement compatibility

• Water flow resilience

• Many types…

• Additives available to

achieve similar

characteristics as OBM

LIMITATIONS

• Environmental &

disposal concerns

• Additives most

properties

• Hole erosion at

high flow rates

• Formation fluid

incompatibility

• Temperature...

Basic Mud Types (continued)

GRI AGM ’99

TT00-03 35

Low Density Fluids (Foam, Gas, Etc.)

BENEFITS

• Low density

• Reduced formation

damage

• Shale inhibition

• Many types...

LIMITATIONS

• Water flows

• Rheological properties

• Hole erosion at high flow rates

• Drillstring and casing

corrosion

• Pressure & temperature

• Operational considerations

• Surface equipment

requirements & costs

Basic Mud Types (continued)

GRI AGM ’99

TT00-03 36

Effect of Mud Type

Native

Fresh Water OBM

Fresh Water WBM

20% CaCl2 OBM

20% CaCl2 WBM

35% CaCl2 OBM

35% CaCl2 WBM

21000 0 62000 8 104

(1 - 3) psi Water Content, %

GRI AGM ’99

TT00-03 37

Check Water Fraction in Shales

GRI AGM ’99

TT00-03 38

Return Permeabilities

GRI AGM ’99

TT00-03 39

Return Permeabilities

GRI AGM ’99

TT00-03 40

Shale Borehole Stability TestsDarley, 1969

DIESELDISTILLED WATER

GRI AGM ’99

TT00-03 41

Montmorillonite Swelling PressurePowers, 1967

80,000

60,000

40,000

20,000

04th 3rd 2nd 1st

5000

4000

3000

2000

1000

0

SW

ELLIN

G P

RESSU

RE, psi

kg/c

m2

LAYERS OF CRYSTALLINE WATER

GRI AGM ’99

TT00-03 42

Shale Compaction TestsDarley, 1989

0.6

0.5

0.4

0.3

0.2

0.1

0

0 2500 5000 7500 10,000

WATER R

ETAIN

ED

g/g

OF D

RY C

LAY

EFFECTIVE LOAD, psi

CALCIUM BENTONITE

SODIUM BENTONITE

SHALE VENTURA CALIF.

GRI AGM ’99

TT00-03 43

Borehole Shale DeformationDarley, 1969

0

0.2

0.4

0.6

0.8

0 200 400 600 800 1000 1200

IMMEDIATELY AFTER DRILLING HOLE

RAD

IAL D

EFO

RM

ATIO

N, cc

MINUTES FROM DRILL OUT

GRI AGM ’99

TT00-03 44

Shale Water AdsorptionChenevert, 1970

0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00

5

4

3

2

1

0

WEIG

HT %

WATER

WATER ACTIVITY - aW

DESORPTION

ADSORPTION

GRI AGM ’99

TT00-03 45

Shale Swelling TestsChenevert, 1970

TIME - HOURS

LIN

EAR S

WELLIN

G -

%

.01 0.1 1.0 10

0.4

0.3

0.2

0.1

0

-0.1

1.00

0.910.880.840.75

0.25

Activity of Internal Phase

GRI AGM ’99

TT00-03 46

Effect of K+Ions on Shale SwellingBaroid, 1975

Ca ++

K+

K+

K+

Na+

Cs+

Na+

Ca++

Li+

K+

Rb+

Cs+

Na+

Mg++

Na+

10A°

Na+

--

--

-

--

-

-

-

-- -

-

-

GRI AGM ’99

TT00-03 47

Principle Mechanisms DrivingFlow of Water and Solute

Into/Out of ShalesForce

Flow

Fluid(water)

Solute(ions)

Hydraulic Gradient (Pw Po)Chemical Potential

Gradient (Amud Ashale)

HydraulicDiffusion

(Darcy´s Law)

Advection Diffusion(Fick´s Law)

ChemicalOsmosis

H2O

H2O H2O

H2Ot1

t2

t3

P

r

Other Driving Forces: Electrical Potential GradientTemperature Gradient

H2O H2O

H2O H2O

H2OH2O

H2O

+ -

-

-

+

+

+

-

GRI AGM ’99

TT00-03 48

Osmotic Flow of Water through

Ideal Semi-Permeable Membrane

Ideal Semipermeable Membrane- permeable to water- impermeable to dissolved

molecules or ions

Water flow directionHigh concentration

of dissolved moleculesor ions ( = Low Aw )

Low concentrationof dissolved molecules

or ions ( = High Aw )

GRI AGM ’99

TT00-03 49

Effect of Water Activitieson Transport of Water and Ions

under Downhole Conditions

Ideal Semi-Permeable Membrane(e.g. OBM-shale)

Mud Aw < Formation AwWater flows from formation to mud

Mud Aw > Formation AwWater flows from mud to formation

Mud Aw = Formation AwNo osmotic flow of water

GRI AGM ’99

TT00-03 50

Effect of Water Activitieson Transport of Water and Ions

under Downhole Conditions

Non-Ideal Semi-Permeable Membrane(e.g. WBM-shale)

Mud Aw < Formation AwWater flows from formation to mud

Ions diffuse from mud to formation

Mud Aw > Formation AwWater flows from mud to formation

Ions diffuse from formation to mud

Mud Aw = Formation AwNo osmotic flow of water

No ion movement (?)

GRI AGM ’99

TT00-03 51

Typical Scenarios for

Water and Solute Invasion of Shales

O/B, High Salt Conc., Low Perm.

O/B, Low Salt Conc., Ideal MembraneCapillary Threshold Pressure

WBM

OBMWBM

Ion Diffusion Front

Pressure Front

WBM

Pressure Front

Ion Diffusion Front

O/B, High Salt Conc., High Perm.

Pressure Front

O/B, Low Salt Conc., High Perm.

GRI AGM ’99

TT00-03 52

• Mud chemistry can affect near-wellbore

pore pressures

• Mud-shale interaction can affect shale

strength

• Mud-shale interaction can result in

swelling strains and/or hydrational

stresses

• Interfacial tension between immiscible

fluids can prevent mud penetration into

shale

Key Concepts

GRI AGM ’99

TT00-03 53

Effect of Osmotic Flow onNear-Wellbore Pore Pressure for a

Balanced Bottomhole Pressure Condition

Osmotic flow

from mud to

shale

Pore Pressure Increase

Osmotic

flow from

shale to

mud

r

amud< ashaleamud> ashale

P P

r

PW Pfm PW Pfm

Pore Pressure Decrease

GRI AGM ’99

TT00-03 54

Effective Stresses Partioningof Total Stress between

Mineral Grains and Pore Fluids

Po

´ = - a Po´ - effective stress

- total stressPo - pore pressure

a - Biot Coefficient

( 1 for weak, porous rocks)

GRI AGM ’99

TT00-03 55

Effect of Near-WellborePore Pressure Changeon Effective Stresses

Sh

ear

Str

ess

No Yield

Yield

Effective Compressive Stress

r´ q´r´ q´

Po increase

GRI AGM ’99

TT00-03 56

PW PW

max max

min min

High Support Pressure Low Support Pressure

Effect of Mud Support Pressure

on Rock Yielding

GRI AGM ’99

TT00-03 57

Effect of Filter-Cake onSupport Pressure

in Reservoir Rock and Shale

P

Effectivefilter-cake

r

Su

pp

ort

pre

ss

ure

Permeable Reservoir Rock

P

Ineffectivefilter-cake

r

Su

pp

ort

pre

ss

ure

Low Permeability Shale

rWrW

GRI AGM ’99

TT00-03 58

Mud Pressure Penetration and Damage

due to Yielding in Shales

Pw

Pw

minimalfilter-cake

Pfm

Shale

zone of no fluidpressure support

higher k (induced fractures due to yielding)

early time, before damage

steady-state, with damagedzone of higher ksteady-state,

no damage

P

r

GRI AGM ’99

TT00-03 59

Mechanism of Shale Support byCapillary Threshold Pressures

Dusseault and Gray, 1994

High efficiency due

to pressure drop

caused by capillary

effects

OBM

water-in-oilemulsion

native porepressure, Pfm

PW

borehole

capillary

immisciblefluids front

Pw - mudpressure

clay and siltwith small

pore throats

water-wetshale

GRI AGM ’99

TT00-03 60

Effect of Mud Pressure Penetration

on Wellbore StabilityS

he

ar

Str

es

s

No Yield

Yield

r´(2)

q ´(2)r´ (1)

q ´(1)

Effective Compressive Stress

No mud

pressure

penetration

Total mud

pressure

penetration

GRI AGM ’99

TT00-03 61

Bottomhole Pressure Regimes while

Overbalanced Drilling

Static OverbalanceBreakingCirculation

CirculationSolidsLoading

ReamingSpudding

SolidsLoading

SurgeSwab

Pistoning up Pistoning down

Formation Pressure Shock

pressure

INF

LU

X

MU

D L

OS

SE

S

FormationPore

PressurePw

Static

MinimumDynamic Pressure

MaximumDynamicPressure

BreakdownPressure

CollapsePressure

CO

LL

AP

SE

GRI AGM ’99

TT00-03 62

Effect of Strength Decrease on

Wellbore StabilityS

hear

Str

ess

No Yield

Yield

r´ q´

Effective Compressive Stress

GRI AGM ’99

TT00-03 63

Hydrational Stresses andSwelling Strains due to

Water Absorption into Shale

Before Drilling After Drillingz

r

z

r

hydrational stresses

H2O

Sand or silt grain

Clay particlecluster

Zo

Z1

ro

r1

eZ = Z1- Zo

Zo

er = r1-ro

ro

GRI AGM ’99

TT00-03 64

Factors Controlling

Swelling Behavior of Shales

• Clay percentage

• Type of clay minerals

• Pore water composition

• Porosity

• Initial water content

• Initial saturations

• Presence of gas phase

• Rock microfabric or structure

• Rock stress history

• Temperature

GRI AGM ’99

TT00-03 65

Effect of Hydrational Stresses on

Wellbore StabilityS

hear

Str

ess

No YieldYield

sq´sr´ sq´

hydrationalstress

Effective Compressive Stress

Most Likely Scenario for Stiff Shales

in High Stress Settings

GRI AGM ’99

TT00-03 66

Effect of Swelling Strains on

Wellbore Stability

Soft, Swelling ShaleHole Closure due to Swelling Strains

Most Likely Scenario for Soft

Reactive Shales in Low Stress Settings

GRI AGM ’99

TT00-03 67

Effect of Capillary Threshold Pressure

on Wellbore StabilityS

he

ar

Str

es

s

No Yield

Yield

r´ q´r´ q´

No mud pressurepenetration

Effective Compressive Stress

GRI AGM ’99

TT00-03 68

Membrane Efficiency

of Non-Ideal Semi-Permeable Membrane

PressureOsmoticlTheoretica

PressureOsmoticObservedEfficiencyMembrane

“Leaky” Membrane

Observed

Theoretical

Low Activity

Drilling Fluid

High Activity

Shale Formation

Osmotic Pressure

GRI AGM ’99

TT00-03 69

Research Progress

GRI AGM ’99

TT00-03 70

• OGS

• UT Austin (Chenevert)

• UT Austin (Morris)

GRI Funded Groups

GRI AGM ’99

TT00-03 71

OGS

GRI AGM ’99

TT00-03 72

Schematic of Downhole Simulation Cell

Mud Pump

Accumulator

Sample Vessel

Fluid Transfer

System

Flow Loop

GRI AGM ’99

TT00-03 73

Laboratory Measurement ofFlow Mechanisms at Downhole

Conditions

dataacquisition

boreholepressure

axial load

pore pressure

confiningpressuresystem

microbittable

triaxialdrillingcell withshalesample

mudhandling

Downhole Simulation Cell at OGS

GRI AGM ’99

TT00-03 74

Triaxial Drilling Cell Cross SectionGRI Funded Research at OGS

SHALE SAMPLE

JACKET

SAND PACK

DRILLING FLUID

CELL BODY

CONFINING FLUID

GRI AGM ’99

TT00-03 75

North Sea Speeton Shale SpecimenExposed at Zero P to Drilling Fluid

Drilling Fluid:

Ionic Water-Base

(CaCl2 Brine)

Activity = 0.78

GRI AGM ’99

TT00-03 76

North Sea Speeton Shale SpecimenExposed at Zero P to Drilling Fluid

Drilling Fluid:

Oil-Base Emulsion

(Oil with CaCl2 Brine)

Activity = 0.78

GRI AGM ’99

TT00-03 77

North Sea Speeton

Shale SpecimenExposed at Zero P to

Drilling Fluid

Drilling Fluid:

Non-Ionic Water-Base

(Methyl Glucoside in

Fresh Water)

Activity = 0.78

GRI AGM ’99

TT00-03 78

Effects of Drilling Fluid Activity andOverbalance Pressure on

Flow Into (or Out of) ShalesLaboratory Measurements, OGS, 1996

-8

-4

0

4

8

0 10 20 30 40 50 60

Flu

id T

ran

sp

ort

into

Sh

ale

(m

l)

Time (hr)

Fresh Wateradf = 1.00

DP = 400

CaCl2 brineadf = 0.78

DP = 400

Fresh Wateradf = 1.00DP = 0.00

Simulated Pore Fluidadf = 0.89

DP = 0.00CaCl2 brine

adf = 0.78

DP = 0.00

K Formate brineadf = 0.40

DP = 400

CaCl2 brineadf = .400

DP = 400CaCl2 brine

adf = 0.40

DP = 0.00

Note: pressure in psi

Ionic Water-Based Fluids and Fresh Water

GRI AGM ’99

TT00-03 79

Effects of Drilling Fluid Activity andOverbalance Pressure on

Flow Into (or Out of) ShalesLaboratory Measurements, OGS, 1996

-8

-4

0

4

8

0 10 20 30 40 50 60

Flu

id T

ran

sp

ort

into

Sh

ale

(m

l)

Time (hr)

Fresh Wateradf = 1.00

P = 400

Oil w/fresh wateradf = 0.99

P = 400

Fresh Wateradf = 1.00P = 0.00

Oil w/fresh wateradf = 0.99

DP = 0.00

Oil withCaCl2 brine

adf = 0.78

P = 400

Oil withCaCl2 brine

adf = 0.4

P = 400

Oil withCaCl2 brine

adf = 0.40

P = 0.00

Oil withCaCl2 brine

adf = 0.78

P = 0.00

Note: pressure in psi

Oil-Based Emulsion Fluids and Fresh Water

GRI AGM ’99

TT00-03 80

Effects of Drilling Fluid Activity andOverbalance Pressure on

Flow into (or out of) Shales

-8

-4

0

4

8

0 10 20 30 40 50 60

Flu

id T

ran

sp

ort

in

to S

ha

le (

ml)

Time (hr)

Fresh Wateradf = 1.00P = 400

Fresh Wateradf = 1.00P = 0.00

NaClbrine/MEG (30%)adf = 0.78P = 400

Note: pressure in psi

Fresh Water/Glyceroladf = 0.78P = 400 Fresh Water/ MEG (68%)

adf = 0.78P = 400

Fresh Water/ MEG (68%)adf = 0.78P = 0.00

Non-ionic Water-based Fluids

Laboratory Measurements, OGS, 1996

GRI AGM ’99

TT00-03 81

UT Austin (Chenevert)

GRI AGM ’99

TT00-03 82

Oven Shale Sample

Downhole Activity Cell DiagramUT Austin, Chenvert, 1998

GRI AGM ’99

TT00-03 83

A Critical Issue:

How Efficient Are Shale embranes ?Laboratory Measurements, Chenevert, 1998

Membrane Efficiency of Speeton Shale whenExposed to Various Water-based Fluids

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

de-ionized water

de-ionized water

de-ionized water

0.78 aw CaCl2

0.4 aw CaCl2

0.4 aw KCOOH

0.78 aw Glycerol

Osmotic Membrane Efficiency

GRI AGM ’99

TT00-03 84

Effect of Fluid/Shale Interaction

on Rock StrengthLaboratory Measurements, Chenevert, 1998

0 1000 2000 3000 4000 5000 6000 7000 8000

de-ionized water

de-ionized water

de-ionized water

0.78 aw CaCl2

0.4 aw CaCl2

0.4 aw KCOOH

0.78 aw Glycerol

0.78 aw MEG

0.78 aw NaCl/MEG

de-ionized water

simulated pore fluid

Deviatoric Stress at Failure (psi)

Strength of Speeton Shale after Exposure to Fluids

GRI AGM ’99

TT00-03 85

2500

2000

1500

1000

500

0

0 1000 2000 3000 4000 5000

a = 0.96mud

0.93

0.915

0.90

0.87

0.84

0.81

0.78

0.75

J (psi)1

J

2

½ (p

si)

Membrane Efficiency = 1

No Chemical Effect(a = a )mud shale

Effect of Mud Activity

on Stress State at Wellbore WallFonseca et al., 1996

GRI AGM ’99

TT00-03 86

Base Case

J1 (psi)

J

2

½ (p

si)

a

0.96mud =

0.915

0.870.84

0.810.78

0.750.90

0.93

2500

2000

1500

1000

500

00 2000 4000 6000 8000

a

a

= 0.20

= 0.96

a

0.96mud =

0.93

0.915

0.90

0.87

0.84

0.81

0.78

0.75

Effect of Biot’s Coefficient

on Stress State at Wellbore WallFonseca et al., 1996

GRI AGM ’99

TT00-03 87

12

10

8

6

4

2

0

0 1 2 3 4 5

Con

finin

g P

ress

ure

(ps

i)1

000

Time (hr)

Swelling Pressure History for Speeton Shale

Exposed to a 0.4 AW KCOOH SolutionChenevert, 1998

GRI AGM ’99

TT00-03 88

7.5

6.5

5.5

4.5

3.5

0 5 10 15 20

Time (hr)

Con

finin

g P

ress

ure

(psi

)

1000

Swelling Pressure History for Speeton Shale

Exposed to a 0.78 AW Glycerol SolutionChenevert, 1998

GRI AGM ’99

TT00-03 89

9

8

7

6

5

4

3

2

1

00 10 20 30 40 50 60

De-ionized Water Simlated Pore Fluid De-ionized

Water

Time (hr)

Con

fi nin

gPre

s su r

e(

100

0)

ps

iSwelling Pressure History for Speeton Shale

Exposed to Different FluidsChenevert, 1998

GRI AGM ’99

TT00-03 90

UT Austin (Morriss)

GRI AGM ’99

TT00-03 91

Velocity as a Function of Water Content for the Electro-Osmosis Test Samples

Davidson & Morriss, 1994

GRI AGM ’99

TT00-03 92

Magnitude of the Complex Reflection Coefficient as a Function of the Water Content

Davidson & Morriss, 1994

GRI AGM ’99

TT00-03 93

Velocity vs Water Content for theElectro-Osmosis Test Samples

Davidson & Morriss, 1994

GRI AGM ’99

TT00-03 94

Acoustic Reflection Coefficient for a Hydrating Sample of Wellington Shale

Davidson & Morriss, 1994

GRI AGM ’99

TT00-03 95

H3H2 H4 H5 H6 H8 H8 H9 H104

Sample slices

Wat

erc o

nten

t (%

wei

ght)

orBHN

BHN

Sample slices

Wat

erc o

nte n

t (%

wei

ght )

orBHN 8

9

7

6

5

Water %

Water Content and BHN of Pierre IAdisoemarta & Morriss, 1994

GRI AGM ’99

TT00-03 96

1211 13 14 15 16 17 18

9

8

7

6

5

4

Sample slices

Wat

erco

nten

t (%

wei

ght)

orBHN

Water %

BHN

3

Water Content and BHN of Pierre IIAdisoemarta & Morriss, 1994

GRI AGM ’99

TT00-03 97

H3H2 H4 H5 H6 H7 H8 H9

104

103

102

101

Sample slices

Dielec tric

Co n

s ta n

t

20 KHz

1.1 KHz

2 KHz

Electic-osmosis experiments (Pierre I Shale Sample)Cathode at Slice 1

100

Dielectric Constantat 3 Logging Tool Frequencies

Adisoemarta & Morriss, 1994

GRI AGM ’99

TT00-03 98

H3H2 H4 H5 H6 H7 H8 H9

100

10-1

10-2

Sample slices

Ele

ctr ic

alPro

pert i

es

Dissipation Factor

Conductivity

Susceptivity

Electic-osmosis experiments (Pierre I Shale Sample)

Cathode at Slice 1

10-3

Electrical Properties at 2 MHzAdisoemarta & Morriss, 1994

GRI AGM ’99

TT00-03 99

H3H2 H4 H5 H6 H7 H8 H9

0.9

0.8

0.3

Sample slices

El e

c tric

a lPro

per t i

es

Dissipation Factor

Conductivity

Susceptivity

Electic-osmosis experiments (Pierre I Shale Sample)

Cathode at Slice 1

H1

0.7

0.6

0.5

0.4

0.2

0.1

0.0

Electrical Properties at 1.1 GHzAdisoemarta & Morriss, 1994

GRI AGM ’99

TT00-03 100

105

106

107

108

109

1010

100

10-1

10-5

Frequency (Hz)

water content

water content

Ele

ctr

icalC

onductivity

(S/m

)

104

10-2

10-3

10-4

10-6

Effective Conductivity of a Pierre Shale Sample as a Function of Water Content

Davidson & Morriss, 1996

GRI AGM ’99

TT00-03 101

Change in the Calculated Velocityas the Shale Surface Rehydrates

Davidson & Morriss, 1996

GRI AGM ’99

TT00-03 102

Induced DC Potential (Wellington Shale)Davidson & Morriss, 1994

GRI AGM ’99

TT00-03 103

Induced DC for Various Materials

Davidson & Morriss, 1994

GRI AGM ’99

TT00-03 104

Induced DCfor a Thin Wellington Shale Sample

Davidson & Morriss, 1994

GRI AGM ’99

TT00-03 105

Induced DCfor a Thick Wellington Shale Sample

Davidson & Morriss, 1994

GRI AGM ’99

TT00-03 106

30 Minutes Water Loss for aReconstructed Wellington Sample

Davidson & Morriss, 1994

GRI AGM ’99

TT00-03 107

30 Minutes Water Loss for aNative Wellington Sample

Davidson & Morriss, 1994

GRI AGM ’99

TT00-03 108

Results of Immersion Tests for Various Mineral Oils for a Fractured Pierre Sample

Davidson & Morriss, 1994

GRI AGM ’99

TT00-03 109

Results of Immersion Tests for for an Undamaged Pierre Sample

Davidson & Morriss, 1994

GRI AGM ’99

TT00-03 110

Results of a Drying Experiment for aWelling Sample

Davidson & Morriss, 1994

GRI AGM ’99

TT00-03 111

P- and S-Wave Transmitter

P- and S-Wave Receiver

Load

Load

Sleeve

Oil Pressure

Core

Pore Pressure

Vented to the

Atmosphere

Configuration for the Triaxial Loading TestDavidson & Morriss, 1998

GRI AGM ’99

TT00-03 112

Compressional Wave Amplitudeas a Function of Strain

(North Sea Shale under Triaxial Loading)Davidson & Morriss, 1994

GRI AGM ’99

TT00-03 113

• CSIRO (Australia)

• Shell (Netherlands)

• Baroid

•AGIP (Italy)

•ELF Aquitaine (France)

•Exxon

•IKU (Norway)

•Schlumberger (UK)

•Institut Francais du Petrole (France)

•University of Calgary (Canada)

•University of Oklahoma

•University of Waterloo (Canada)

Other Groups (Worldwide)

GRI AGM ’99

TT00-03 114

Axial pressure

Confining pressure

Rubber sleeve withpressure ports

Triaxial core holder

Rock sample

Pressure tap ports

Mud Pressure Penetration Test CellCSIRO, 1998

GRI AGM ’99

TT00-03 115

Porous disk

Simulatedpore fluid

Axial pressure

Rubber jacket Confining pressure

Shale sample

Drilling fluidfiltrate

Chemical Potential Test Equipment

CSIRO, 1998

GRI AGM ’99

TT00-03 116

Jacket

LVDT(displacement

transducer)

Load cell

Sample

Radial strainguage

Swelling and

Hydrational

Stress Test Cell

CSIRO, 1998

GRI AGM ’99

TT00-03 117

Insulated electric lead

O-ring seals

Inner rubbermembrane

Outer rubber membrane

Pore fluid inletBorehole fluid inlet

Mud filtrate inlet

Rock Sample

Borehole gauge

Mud filtratecirculation path

Borehole Collapse Test DiagramCSIRO, 1998

GRI AGM ’99

TT00-03 118

ModeledMeasured 1.1 hrsMeasured 3.0 hrsMeasured 5.1 hrsMeasured 10.0 hrsMeasured 15.0 hrsMeasured 19.8 hrs

0 0.5 0.1 0.15 0.24.5

5.5

6.5

7.5

8.5

Distance From Elevated Pressure End (m)

Pre

ssu r

e(M

P a)

1.1 hrs

3.0 hrs

5.1 hrs10.0 hrs

15.0 hrs

19.8 hrs

Measured and Modeled Pore Pressurewithin a Shale Sample

(Mud Pressure Penetration Test)CSIRO, Tan, 1998

GRI AGM ’99

TT00-03 119

0 10 20 30 40 50 60 70

4.5

3.5

2.5

4

3

Dow

ns t

r eam

Pr e

ssur e

(MP

a)

Elapsed Time (hrs.)

MeasuredModeled

MeasuredModeled

MeasuredModeled

3́ = 9.5 MPa 3́ = 16.4 MPa 3´ = 26.6 MPa

9.5 MPa16.4 MPa

26.6 MPa

Pressure Response of a Shale Sample withOne End Exposed to Low-Activity NaCl Mud

CSIRO, Tan, 1998

GRI AGM ’99

TT00-03 120

J1 or Salt Content %

Invariant ShearStress Profile

Unstable

StableFailure envelope

Sh

ea

r S

tre

ss

J2

d½

Comparison of Failure Envelope withInvariant Stress Profile

Mudy & Hale, 1993

GRI AGM ’99

TT00-03 121

Osmotic Pressure between Mudand Pore Fluid Reservoirs

(Pressure Transmission Experiments)AGIP, Carminati et al, 1999

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0

Pre

ssu

re U

nd

erb

ala

nce

d (

Mp

a)

Glycol-1 does not have a cloud pointGlycol-2 has a cloud pointGlycol concentration = 5%K+ concentration = 0.67 mole/litre

GRI AGM ’99

TT00-03 122

predictedmeasured

120

100

80

60

40

20

00 10 20 30 40 50 60 70 80 90 100

Saturation (%)

Un

co

nfin

ed

Com

pre

ssiv

e S

tre

ng

th (

Mp

a)

Effect of Water Saturation on Unconfined Compressive Strength of Tournemire Shale

ELF, Schmitt et al, 1999

GRI AGM ’99

TT00-03 123

Mean Effective Stress

Surface Area

Shale

Str

ength

Typical Correlation Observed betweenSpecific Surface Area and

Compressive Strength of Shale

Exxon, Leung & Steiger, 1992

GRI AGM ’99

TT00-03 124

0 5 10 15 20 250

2

4

6

8

10

12

Axial Deformation (millistrain)

Referencelow KCl concentrationhigh KCl concentration

Diffe

rential S

tress (

MP

a)

Schematic Illustration of theEffect of KCL Fluid Exposure on

Constitutive Behavior of Shale

IKU, Horsrud et al., 1998

GRI AGM ’99

TT00-03 125

2.8 hrs14 hrs28 hrs

139 hrs

0.18

0.16

0.14

0.12

0.10

0.08

0.06

0.04

0.02

01 1.05 1.1 1.15 1.2

Radial Distance r/rw

Co

ncen

tra

tion

C

Calculated KCl Concentrationin the Shale Rock Mass around a Wellbore

IKU, Bostrom et al., 1998

GRI AGM ’99

TT00-03 126

without shrinkage 2.8 hrs 14 hrs 28 hrs139 hrs

15

10

5

0

-5

-10

1 1.2 1.4 1.6 1.8 2

Radial Distance r/rw

Vert

ica

l Effect

ive

Str

ess

(M

Pa

)

Vertical Stress Near a WellboreAffected by Shale Shrinkage

IKU, Bostrom et al., 1998

GRI AGM ’99

TT00-03 127

cracked coreradial samples

vertical samples

0 10 20 30 400

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Vertical Stress (MPa)

Bio

t C

oeffic

ient

Test Results Showing Effects of Stress and Sample Orientation on Biot’s Coefficient

Institut Francais du Petrole, Vincke et al., 1998

GRI AGM ’99

TT00-03 128

0

5

10

15

(R/r

) X10

0p

wl

0 0.2 0.4 0.6 0.8 1Time (hour)

WBM P - P = 5 MPaw fm

a = 0.95 a = 0.9shmud

WBM P - P = 5 MPawfm

a = ashmud

OBM P - P = 6 MPaw fm

Model Prediction of Plastic ZoneThickness (Rpl ) as a Function of

Mud Type, Mud Activity and Overbalance PressureIKU, Onaisi et al., 1994

GRI AGM ’99

TT00-03 129

Cross-Section of Failure around a Thick-Walled Cylinder Specimen (Bedding planes parallel to the drilled hole)

Schlumberger,

Okland & Cook, 1998

GRI AGM ’99

TT00-03 130

a b

qp

Pw

1 Yielded zone

2

Angular Extent of Yielded Zone (qp ) Predicted

by Analytical Elastioplastic ModelSchlumberger, Bradford et al., 1998

GRI AGM ’99

TT00-03 131

porous disk

radial

Upstream Reservoir

inlet outlet

capillary buret

pressurized sleeve

porous disk

radial

steel piston Downstream Reservoir

valve

pressure transducer

shalesample

axial axial

Experimental Apparatus Used for Pressure

Transmission and Osmosis TestsExxon, van Oort et al., 1996

GRI AGM ’99

TT00-03 132

Exchange to 35% CaCl2

Downstream Pressure

Upstream Pressure

600500400300200100Time (hrs)

00

0.5

1

1.5

2

2.5

3

3.5

Pre

s sur

e( M

Pa )

Pressure Transmission Test Results for

CaCl2 Drilling FluidExxon, van Oort et al., 1996

GRI AGM ’99

TT00-03 133

1

0.8

0.6

0.4

0.2

00 0.2 0.4 0.6 0.8 1

Dimensionless sample length

Ca contentBest fit to data

2+

Norm

aliz

ed C

atio

n C

once

ntr

atio

n(C

- C

)/(C

- C

)sh

df

sh

Ca2+ Ion Concentration as a Function of Invasion Depth in a Pierre Shale Sample after

Osmosis TestingExxon, van Oort et al., 1996

GRI AGM ’99

TT00-03 134

40030020010000.3

0.4

0.5

0.6

0.7

Time (min)

Pore Fluid

KCl/Polymer/Silicate Mud

Dow

nstr

em

Pre

ssure

(M

Pa)

Pressure Transmission Test Results for

KCl/Polymer/Sodium Silicate MudExxon, van Oort et al., 1996

GRI AGM ’99

TT00-03 135

normal

particle swelling stress swelling

low ionic concentration

high ionic concentration

Particle normal stress, normal

doublelayer

clay particle

--------------------------------------------+++++++++++++++++++++++++--------------------------------------------

Pa

rtic

le s

we

llin

g s

tra

in

Effect of Particle Confining Stress

and Pore Fluid Ionic Concentration

on Particle SwellingUniversity of Calgary, Wong & Wang, 1997

GRI AGM ’99

TT00-03 136

50 10 15 20 250

100

200

300

400

500

600

Pea

k C

ohes

ion

(kP

a)

Volumetic Swelling Strain (%)

best fit

data

Labiche Formation:Cretaceous clay-shaleNaCl Pore Fluid

700

Peak Cohesion Weakening

Caused by Shale Swelling

University of Calgary, Wong, 1998

GRI AGM ’99

TT00-03 137

+

+

+

waterOBMGel ChemTAMEPHPA

Angle

of S

hear

ing R

esist

ance

(deg

)

Time (days)

Variation of Shearing Resistance with Time

for Shale Fracture Surfaces Exposed to

Different Drilling FluidsUniversity of Calgary, Wang et al., 1997

GRI AGM ’99

TT00-03 138

a > a

a < a

a = a

mud sh

mud sh

mud sh

t = 4 min

1 2 3 4 5

r/r ( = 90)w q

Res

ulta

nt P

ore

Pre

ssur

e (M

Pa)

5

10

15

20

Calculated Pore Pressure around an Inclined

Borehole in Shale for Various Mud Activities

(after 4 minutes)University of Oklahoma, Ghassemi et al., 1998

GRI AGM ’99

TT00-03 139

t = 8 hrs

1 3 5 7 9r/r ( = 90)w q

R esu

l tant

P ore

P re s

sure

(MPa

)

5

10

15

20a = aa < aa > a

mudsh

mudsh

mudsh

Calculated Pore Pressure around an Inclined

Borehole in Shale for Various Mud Activities

(after 8 hours)University of Oklahoma, Ghassemi et al., 1998

GRI AGM ’99

TT00-03 140

Average activityOsmotic PressurePore Fluid Activity, c = 0.1 mole/litre

1.00

0.99

0.98

0.97

0.96

0.951E-9 1E-8 1E-7

-100

0

100

200

300

400

500

600

Wate

r A

ctiv

ity

Interparticle Distance (m)

Osm

otic

Pre

ssu

re (

kPa)

Predicted Effect of Clay Mineral Inter-Particle

Spacing on Shale Water Activity and Osmotic

Pressure (contacting a 1 mole/litre mud)University of Waterloo, Fam & Dusseault, 1998

GRI AGM ’99

TT00-03 141

Surface area =120 m /g2

Nor

mal

ized

She

ar S

treng

th

0.1 1 10

Reactivity Coefficient ( )

0.0

1.0

2.0

3.0

4.0

Predicted Correlation between Shale Reactivity

Coefficient and Shale Strength

(for a mono-minerallic clayey sediment)University of Waterloo, Fam & Dusseault, 1998

GRI AGM ’99

TT00-03 142

MEI Wellbore Stability Model

GRI AGM ’99

TT00-03 143

featuring

Shale/Mud Interaction

Mechanical/Chemical Stability Design

Multi-Depth Analysis

Microsoft Word/Excel Report

GRI AGM ’99

TT00-03 144

Mechanical/Chemical Property Input

GRI AGM ’99

TT00-03 145

Help Information as Clicking Question Mark

GRI AGM ’99

TT00-03 146

Pore Pressure Input/Predict

GRI AGM ’99

TT00-03 147

Pore Pressure Prediction via Log Data

GRI AGM ’99

TT00-03 148

In-Situ Stresses Input/Predict

GRI AGM ’99

TT00-03 149

Overburden Calculation via Log Data

GRI AGM ’99

TT00-03 150

Correlation to Determine Overburden

GRI AGM ’99

TT00-03 151

Output Windows

GRI AGM ’99

TT00-03 152

Safe Mud Weight vs Well Inclination

GRI AGM ’99

TT00-03 153

Near-Wellbore Stresses Distribution

GRI AGM ’99

TT00-03 154

Wellbore Stability Design

Too large inclination

GRI AGM ’99

TT00-03 155

Wellbore Stability Design (continued)

Decrease inclination

GRI AGM ’99

TT00-03 156

Wellbore Stability Design (continued)

Too high mud weight

GRI AGM ’99

TT00-03 157

Wellbore Stability Design (continued)

Increase mud weight

GRI AGM ’99

TT00-03 158

Not enough salinity

Wellbore Stability Design (continued)

GRI AGM ’99

TT00-03 159

Increase salinity

Wellbore Stability Design (continued)

GRI AGM ’99

TT00-03 160

Effect of Mud Salinity

GRI AGM ’99

TT00-03 161

Effect of Membrane Efficiency

GRI AGM ’99

TT00-03 162

Propagation of Swelling Pressure

GRI AGM ’99

TT00-03 163

Multi-Depth Data/Calculation Display

GRI AGM ’99

TT00-03 164

Microsoft Word Report

GRI AGM ’99

TT00-03 165

Summary of Important Wellbore

Stability Mechanisms in Shales

GRI AGM ’99

TT00-03 166

Osmosis

• Osmosis plays a significant role in

wellbore stability

• Drilling mud with low water activity can

draw water out of the shale

• The effectiveness of this mechanism

depends on the ability of the shale-mud

interface to form a semi-permeable

membrane (“membrane efficiency”)

• Osmotic pressure diminishes with time

GRI AGM ’99

TT00-03 167

Rock Strength

• Invasion of solute ions from mud into

shales affects rock strength

• Most results indicate that strength and

stiffness decrease with the invasion of

solute

• Methyl glucoside solutions has high

membrane efficiencies and are not

detrimental to North Sea Speeton shale

GRI AGM ’99

TT00-03 168

Hydration and Swelling

• The most controversial mechanism

• UT Austin and OGS observed shale

swelling in carefully preserved samples

• Need to standardize shale sampling and

handling techniques

GRI AGM ’99

TT00-03 169

Computer Models

• Many existing models are based on

poroelastic theory and include the effects

of osmosis, temperature and rock

anisotropy

• More sophisticated models require

numerical solution techniques

• Elastoplastic models have been developed

but are more difficult to use in practice

GRI AGM ’99

TT00-03 170

Recommendations for Future R&D

GRI AGM ’99

TT00-03 171

Essential Reasons

of Experimental Investigations of the

Mud-Shale Interaction Mechanisms

• For industry to develop more reliable

tools to predict and control wellbore

stability in shales

• A broader database of physico-chemical

properties is required to facilitate

wellbore stability design for analogue

shale formations

GRI AGM ’99

TT00-03 172

Recommendations

• The promising results obtained with non-

ionic water-based mud such as methyl

glucoside should be pursued

• Need to transfer the technical knowledge

to drilling and completions personnel in

operating and service companies

• Improvements in computer-based

modeling is strongly recommended

GRI AGM ’99

TT00-03 173

End of Presentation