geomechanical model for the rang dong field - zohopowergeoscience.zohosites.com/files/spe vietnam...
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William L Power Baker Hughes - Reservoir Development Services*
Perth, Western Australia
*Current Address (June, 2016):
Power Geoscience Pty Ltd
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!