William L Power Baker Hughes - Reservoir Development Services*

Perth, Western Australia

*Current Address (June, 2016):

Power Geoscience Pty Ltd

bill@powergeoscience.com

Presented 18 May, 2011

Ho Chi Minh City, Vietnam

Geomechanical Model for the Rang Dong

Field - Off Shore Vietnam - Implications for

Development Strategy for Fractured

Basement Reservoirs

Acknowledgements to Japan Vietnam Petroleum

Corporation and partners for permission to present

these results

Special thanks to colleagues/collaborators

Toru Sano, Kiam Chai Ooi, Naoki Okawa,

Yusaku Konishi, & Huynh Ho Phuong

(JX Nippon Energy and JVPC)

David Castillo, Marian Magee, & Katharine Burgdorff

(Baker Hughes – Reservoir Development Services)

Scope of Work Our Studies at Rang Dong

Develop a geomechanical model

Apply to production and development

In this presentation

• Geomechanical Model

– Background/Field wide state of stress

– Anomalism near fault zones

• Optimum Drilling Direction

Developing the Geomechanical Model

Anomalous Stresses Near Faults

• Sv – Vertical Stress/Overburden

• Pp – Formation Pressure

• Shmin magnitude

• UCS – Unconfined Compressive Strength

• SHmax azimuth – orientation of SHmax

• SHmax magnitude

Increasing

Difficulty

Pp studies

Laos

Vietnam

Vung Tau

N

Geologic Setting

Reservoir:

Biotite-rich gneiss and tonalite

Faulted, Fractured, Weathered

Rang Dong

Study Wells

Data Used In This Study

Daily Drilling Reports and Drilling Experiences

Over 20 km of electrical/resistivity wellbore image data

RFT/MDT and DST

Testing Data

Production Data

Wireline Log Data

10 km

Well-1

Well-4

JVPC and partners have an

impressive array of data and a

large amount of practical

experience at Rang Dong.

This presentation shows details

from two wells.

Sv calculated by

integrating density

estimates over depth

Pressure/Stress Gradient (SG)

Sv

Cover

Basement dzgzgS rwwv

1 2 3

Density g/cm3 T

VD

(m

)

Seawater density

Smooth curve

Density estimated from sonic velocity Log

Density log data

Calculating Sv

Geotechnical density data

Seismic “Checkshot” data

Cover

Basement

1 2 3

Density g/cm3 T

VD

(m

) Pressure/Stress Gradient (SG)

Dep

th T

VD

MS

L (

m)

Sv

Sv

Sv Result

h

Pp from Drill Stem

Test Data

“hydrostatic” in

overburden ~1.03 SG

~1.13 SG in fractured

basement

Cover/Overburden

Basement

Pressure/Stress Gradient (SG) D

ep

th T

VD

MS

L (

m)

Sv

Pp

Pp

Cover

Basement

DST Tests

Formation

Pressure

SH

Shmin

Pressure/Stress Gradient (SG) D

ep

th T

VD

MS

L (

m)

Cover

Basement

Shmin estimated

using FIT and LOT

Shmin≈ 1.6 ± 0.1 SG

at reservoir depth

Sv

Pp

Shmin

Shmin

Least Compressive Stress

SH

Stress Polygon Constraint on Shmin

Rock is always faulted and

fractured

Stress cannot exceed the

strength of the faults and

fractures

Assume Mohr-Coulomb failure

Three cases:

1) S3=Sv Reverse Faulting

2) S2=Sv Strike-Slip Faulting

3) S1=Sv Normal Faulting

SH

max

Shmin

Reverse Strike-Slip

Normal

1

2

3

1

2

3

Shmin

The Stress Polygon For Rang Dong

Parameters used :

TVD = 3250 m

Sv = 2.26 SG

Pp = 1.13 SG

(Biot) = 1.0

(Poisson) = 0.25

i (internal Friction)= 1.0

Mohr-Coulomb Criterion

Shmin must be > 1.45-1.5 SG,

or normal faulting would be

expected

f = 0.6

f = 0.7 Reverse

Strike-Slip

Normal

Shmin

Typical BO and DITF Observations

Breakouts (BO)

Drilling

Induced

Tensile

Fractures

(DITF) 1 m

1

m

Azimuth

0 180 360

Azimuth

0 180 360

SHmax Azimuth

For

Breakout (BO)

Drilling Induced

Tensile Fracture

(DITF)

SHmax

N

Drilling Induced Failure

For a Vertical Well:

SHmax

Azimuth

Stress concentration ~4x

because rock is

“missing” in the wellbore

Shmin

For

BO

DITF

Pp

SHmax

Mud Weight and Temperature Effects

Mw Tformation

Tmud

Higher Mw DITF

Lower Mw BO

Mud heating the rock BO

Mud cooling the rock DITF

Well-1 Location and Details

N

0 10 km 0 10 km

Well-1

SHmax Azimuth

Well 1 drilled before production

Not in major fault or fracture zones

~ Vertical

Pp ≈ 1.13 SG

Mw ≈ 1.14-1.19 SG

TD ≈ 4200 m

Well-1 Failure Summary:

DITF and BO are pervasive

and consistent over 600 m

Conclusion:

SHmax azimuth ~ 148°N

200 m

Azimuth/Angle (deg)

M D

ep

th (

m)

20

0 m

SHmax Azimuth

SHmax Azimuth

150°

151°

165°

148°

148°

152°

154°

SHmax azimuth

Field-wide average 152°N ±10°

N

0 5 km

SHmax Azimuth

Well-1 :

~4200 TVD

Deviation=5°

Azimuth=262°

BO 062°N ± 4°

BO width ~30°

DITF 145°N ± 3°

200 m

Azimuth/Angle (deg)

M D

epth

(m

)

1 m

0 180 360

SHmax

Magnitude

Modelling

SHmax

Magnitude

Model BO with

minimum

mudweight,

smallest possible

temperature

contrast

Model DITF with

maximum

mudweight,

largest possible

temperature

contrast

200 m

Azimuth/Angle (deg)

M D

epth

(m

)

1 m

0 180 360

SHmax

Magnitude

Modelling

SHmax

Magnitude

Pre-production:

Strike-Slip Stress

Regime

SHmax > Sv > Shmin

Pressure/Stress Gradient (SG) D

epth

TV

D (

m)

Shmin

SHmax

Sv

Pp

SHmax

Magnitude

Geomechanical Model

Summary

Formation Pressure Change – Stress Path

Drill Stem Test Data Stresses if an isotropic

stress path is assumed

Sv

SHmax

Shmin

Pp

1994

2002

Well-4 Location and Details

N

0 10 km

Well-4

Well-4 Summary:

TD: 4420 MD, 3620 TVD

Deviation 2-90° to the W

Pp ~0.82 SG

Mw 1.03 SG (Seawater)

Near and through faults

Total Losses at 4000m MD

Well completed to 4420 MD with

no mud return

High temperature differential

Well-4 Failure Summary

3300-3700 m MD:

Some DITF are observed

DITF ~140-160°N

No BO Observed

Well Deviation

21°

30°

57°

10

0 m

Azimuth/Angle (deg) M

De

pth

(m

)

Wellbore enters faulted region

Lower hemisphere

stereoplots

Vertical Well

Horizontal well drilled to East

Well deviated 30° to South

Well-4 – Mw required to cause DITF

Required Mw for Tensile Failure

Lower hemisphere stereoplots

At Discovery (1994)

No tensile failure unless

Mw > ~1.4 SG

At Drilling (2001)

Tensile failure predicted for these

wellbore orientations

Well-4 – Mw required to cause DITF

Required Mw for Tensile Failure

DITF Observed,

Deviation

21°

30°

57°

Consideration of depletion was

required to explain the development

of DITF for deviated well-4.

Well-4 Location

N

0 10 km

Well-4

Well highly deviated to the West

Near an EW trending fault zone

Recall – total losses at 4000m MD

Well-4 Failure Summary

3600-4400 m MD

Variable Orientation DITF

are observed below

~3600 m

We infer these are related

to faulting/fracture zones

20

0 m

Azimuth/Angle (deg) M

De

pth

(m

)

Bottom Top Bottom

20

0 m

M

De

pth

(m

)

BOH TOH BOH

~90° rotation of DITF

orientation over 1-2 m

Fault/Fracture zone

DITF persist over a

distance of 12-20 m

along the wellbore,

then generally absent

1 m

Bottom Top Bottom

DITF Sides

DITF Top & Bottom

Faults and Fracture Complexity

Simple fault

Interaction

Slipped

fault/fracture with

open space

Stress concentration

~20-200 m

20-200 m

Stress Concentration at Contact Points

Mean Stress

Increase

De-stressed Area

Small fault or fracture

If we drill this: Bottom

Top

Bottom

Total loss of

circulation

High vertical Stress,

DITF top & bottom High horizontal Stress,

DITF on sides

Plan View of

Possible

Trajectory and

Fault zone

Many small, independent fractures, non-interacting

Anomalous stresses near major fractures/fault zones

Optimum Trajectory – Two Situations

For the fractured basement rock - If we know the fracture orientations,

we can optimize a trajectory

Example Fracture Distributions

Two sets Three sets

State of Stress, Fractures, & Best Well

Best well intersects the most critically stressed fractures

Best

Well

Best

Well

1 km

Major Fault Zones

1 km

Major fault zones may be 10-1000

times more permeable than

background fractured area

Major

Fault

Zones

Optimum Trajectory – A Balance

For fractured basement we must consider –

The best drilling orientation may a complex balance

1. Background flow in the fractured

reservoir distant from major faults –

If we optimize based on this alone -

potential problem: low production rate

2. Extremely permeable fault zone

“Freeways” for very easy flow –

If we optimize based on this alone -

potential problem: early water

breakthrough

Conclusions

Geomechanical model construction requires

Image data

Log data

Drilling experiences

Well test data

Geological inference

Geotechnical data

Seismic checkshot data

and More . . .

It is essential to integrate data from different sources

JVPC and partners have an extensive array of data that

made this study possible

Future – Fractured Basement Reservoirs

Continued (and better) integrative 3D work–

3D geological & geopysical modelling

3D Geological inference

3D production simulation

Extensive integration and interaction between disciplines

More complete use of all of the data

Geomechanical model knowledge needed

Image data will remain central

Microseismicity may be more widely used

Specially processed seismic data

Predictive geological inference – where are the fractures?

Summary – Uses of Geomechanics

Wellbore Stability

Injection

Sand Prediction

Fracture Perm

Fracture Stim

Compaction

Depletion

Subsidence

Casing Shear

Pore Pressure

Wellbore Stability

Sand Prediction

Subsidence

CO2 Storage

Fault Seal

Pore Pressure

Exploration Appraisal Development Harvest Abandonment

Geomechanical Model

With Geomechanics, Start early in the life of

the field, and collect as much data as possible!