Transcript Arab Formation Depositional Model

Integrated Understanding of Enhanced Reservoir
Properties through Fracturing and Dissolution
Case Study from the Late Jurassic Arab Formation in a
Large Gas Field, Onshore UAE
Fatima Al Darmaki1, David A. Lawrence1, Richard P. Singleton1,
Budideti A. Reddy1, Georgeta Popa1, Pascal Cortes2
1
2
Al Hosn Gas, Abu Dhabi
Badley Ashton & Associates, Abu Dhabi
Abu Dhabi Gas Development Company Ltd.
CONFIDENTIAL
Page 1
Outline of Presentation
• Introduction & Field Overview
– Arab Formation Depositional Model
– Well Location Map and 2D Seismic Section
• Fracture Analysis in Arab Members
– Fracture Orientation Trends Within Arab Members
– Fracture Density Variations in Arab Members
•
•
•
•
Impact of Diagenesis & Dissolution in Arab Main Reservoirs
Porosity-Permeability Analysis in Arab Main Reservoirs
Layering Control on Fracturing in Arab Formation
Conclusions & Implications
Abu Dhabi Gas Development Company Ltd.
CONFIDENTIAL
Page 2
Outline of Presentation
• Introduction & Field Overview
– Arab Formation Depositional Model
– Well Location Map and 2D Seismic Section
• Fracture Analysis in Arab Members
– Fracture Orientation Trends Within Arab Members
– Fracture Density Variations in Arab Members
•
•
•
•
Impact of Diagenesis & Dissolution in Arab Main Reservoirs
Porosity-Permeability Analysis in Arab Main Reservoirs
Layering Control on Fracturing in Arab Formation
Conclusions & Implications
Abu Dhabi Gas Development Company Ltd.
CONFIDENTIAL
Page 3
Introduction & Field Overview
• SW of Abu Dhabi city
• Field discovered in 1966
• Oil production from Upper
Cretaceous
• Target: gas & condensate
from Late Jurassic Arab
Formation
• A total of 7 appraisal wells
drilled into Arab Reservoir
• Development drilling started
on NW flank
• Results from first
development wells showed
enhanced properties in the
main reservoirs
Abu Dhabi Gas Development Company Ltd.
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Page 4
Outline of Presentation
• Introduction & Field Overview
– Arab Formation Depositional Model
– Well Location Map and 2D Seismic Section
• Fracture Analysis in Arab Members
– Fracture Orientation Trends Within Arab Members
– Fracture Density Variations in Arab Members
•
•
•
•
Impact of Diagenesis & Dissolution in Arab Main Reservoirs
Porosity-Permeability Analysis in Arab Main Reservoirs
Layering Control on Fracturing in Arab Formation
Conclusions & Implications
Abu Dhabi Gas Development Company Ltd.
CONFIDENTIAL
Page 5
Arab Formation Depositional Model
Arab AB
• lime mudstones and anhydrites
• Dolomitic limestone
Arab C
Arab D
• Oolitic grainstone
SW
NE
•Marine lime-mudstone
•Minor Wackestone to Packstone
2 ft
0
2 km
Carbonate Ramp Setting
Main Field area Reservoir Data
Palaeo-environments of the
Arab Formation
• Reservoir
Ave Porosity
• U.Arab AB
10 -11%
1.0 – 2.0md
• L. Arab C
17-20 %
0.7 – 8.0 md
• L. Arab D
6-8%
0.05 – 1.0 md
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Ave Perm
Adapted from Azer and Peebles (1998)
Chronostratigraphic setting of the
Arab Formation
Page 6
Outline of Presentation
• Introduction & Field Overview
– Arab Formation Depositional Model
– Well Location Map and 2D Seismic Section
• Fracture Analysis in Arab Members
– Fracture Orientation Trends Within Arab Members
– Fracture Density Variations in Arab Members
•
•
•
•
Impact of Diagenesis & Dissolution in Arab Main Reservoirs
Porosity-Permeability Analysis in Arab Main Reservoirs
Layering Control on Fracturing in Arab Formation
Conclusions & Implications
Abu Dhabi Gas Development Company Ltd.
CONFIDENTIAL
Page 7
Well location Map and 2D Seismic Section
Arab C Structural Map
BHI Log
A 7-1V
A2-1V
A1-1V
0
1.25km
A2-1V
NW
SE
A1-1V
A5-1D
BHI Log
A 3-2S
Arab
A 6-1V
BHI Log
A 4-1V
0
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10 km
Vertical exaggeration: 2:1
CONFIDENTIAL
Page 8
Outline of Presentation
• Introduction & Field Overview
– Arab Formation Depositional Model
– Well Location Map and 2D Seismic Section
• Fracture Analysis in Arab Members
– Fracture Orientation Trends Within Arab Members
– Fracture Density Variations in Arab Members
•
•
•
•
Impact of Diagenesis & Dissolution in Arab Main Reservoirs
Porosity-Permeability Analysis in Arab Main Reservoirs
Layering Control on Fracturing in Arab Formation
Conclusions & Implications
Abu Dhabi Gas Development Company Ltd.
CONFIDENTIAL
Page 9
Fracture Analysis in Arab A/B Members
Gamma Ray
Resistivity
Conti. Conductive Frac.
Conti. Resistive Frac.
DisCont. Cond. Fra.
Neutron/
Density
DisCont. Resistive. Fra.
Mixed Fracture
Whole
Core
11.5 ft
Discontinuous
Resistive
Fractures
Fracture Analysis from Resistivity Image Data Correlated with other Open Hole Logs
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Page 10
Fracture Analysis in Arab C Member
Gamma Ray
Resistivity
Conti. Conductive Fracture
Conti. Resistive Fracture
DisCont. Cond. Fracture
Neutron/
Density
DisCont. Resistive. Fra.
Mixed Fracture
Whole
Core
5.5 ft
Discontinuous
Resistive
Fractures
Continuous
Resistive
Fractures
Fracture Analysis from Resistivity Image Data Correlated with Core Image and Open Hole Logs
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Page 11
Fracture Analysis in Arab D Member
Gamma Ray
Resistivity
Conti. Conductive Fracture
Conti. Resistive Fracture
DisCont. Cond. Fracture
Neutron/
Density
DisCont. Resistive. Fra.
Mixed Fracture
Whole
Core
6 ft
Discontinuous
Conductive Fractures
Continuous
Conductive Fractures
Fracture Analysis from Resistivity Image Data Correlated with Core Image and Open Hole Logs
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Page 12
Outline of Presentation
• Introduction & Field Overview
– Arab Formation Depositional Model
– Well Location Map and 2D Seismic Section
• Fracture Analysis in Arab Members
– Fracture Orientation Trends Within Arab Members
– Fracture Density Variations in Arab Members
•
•
•
•
Impact of Diagenesis & Dissolution in Arab Main Reservoirs
Porosity-Permeability Analysis in Arab Main Reservoirs
Layering Control on Fracturing in Arab Formation
Conclusions & Implications
Abu Dhabi Gas Development Company Ltd.
CONFIDENTIAL
Page 13
Fracture Trends in Arab A/B Members
• Few fractures are observed in Arab A/B
including conductive, resistive and mixed
features
• Varying strike orientations were
interpreted, mainly NNW-SSE and WNWESE
A 7-1V
No fractures
have been
interpreted
through Arab
AB Members
N= 22
A2-1V
A1-1V
A5-1D
N= 6
A 3-2S
Conti. Conductive Fracture
A 6-1V
Conti. Resistive Fracture
DisCont. Conductive Fracture
DisCont. Resistive Fracture
Mixed Fracture
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A 4-1V
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0
10 km
Page 14
Fracture Trends in Arab C Member
• The majority of the interpreted
fractures in Arab C were resistive
A 7-1V
• Few conductive and mixed fractures
were interpreted in the study wells
N= 6
• Several strike orientations were
interpreted in Arab C and show
dominant strikes along NNW-SSE and
WNW-ESE
• Subordinate trends in broadly NNE-SSW
and ENE-WSW directions and parallel
to the main fault trends
N= 50
A2-1V
A1-1V
A5-1D
N= 33
A 3-2S
Conti. Conductive Fracture
A 6-1V
Conti. Resistive Fracture
DisCont. Conductive Fracture
DisCont. Resistive Fracture
Mixed Fracture
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A 4-1V
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0
10 km
Page 15
Fracture Trends in Arab D Members
• Highest fracture intensity observed in
Arab D and most were continuous and
discontinuous conductive fractures
A 7-1V
N= 67
• Relatively few resistive fractures were
also interpreted in this interval.
• Strike orientations of fractures in Arab
D are dominantly NNW-SSE and WNWESE.
N= 544
A2-1V
• Subordinate trends in broadly NNESSW and ENE-WSW direction and
parallel to the main fault trends
A1-1V
A5-1D
N= 75
Conti. Conductive Fracture
A 3-2S
A 6-1V
Conti. Resistive Fracture
DisCont. Conductive Fracture
DisCont. Resistive Fracture
Mixed Fracture
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A 4-1V
CONFIDENTIAL
0
10 km
Page 16
Outline of Presentation
• Introduction & Field Overview
– Arab Formation Depositional Model
– Well Location Map and 2D Seismic Section
• Fracture Analysis in Arab Members
– Fracture Orientation Trends Within Arab Members
– Fracture Density Variations in Arab Members
•
•
•
•
Impact of Diagenesis & Dissolution in Arab Main Reservoirs
Porosity-Permeability Analysis in Arab Main Reservoirs
Layering Control on Fracturing in Arab Formation
Conclusions & Implications
Abu Dhabi Gas Development Company Ltd.
CONFIDENTIAL
Page 17
Fracture Density Variations in Arab Members
D1-1D
D2-1H
A7-1V
A 7-1V
D2-1H
D1-1D
A2-1V
A1-1V
A5-1D
A 6-1V
A 3-2S
A 4-1V
0
TD in Arab D
10 km
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Page 18
Outline of Presentation
• Introduction & Field Overview
– Arab Formation Depositional Model
– Well Location Map and 2D Seismic Section
• Fracture Analysis in Arab Members
– Fracture Orientation Trends Within Arab Members
– Fracture Density Variations in Arab Members
•
•
•
•
Impact of Diagenesis & Dissolution in Arab Main Reservoirs
Porosity-Permeability Analysis in Arab Main Reservoirs
Layering Control on Fracturing in Arab Formation
Conclusions & Implications
Abu Dhabi Gas Development Company Ltd.
CONFIDENTIAL
Page 19
Stylolitic bedding and Stylo-Fracture in Arab C Member
N
N
S
S
N
N
Nonmineralized
open
fractures
Partly
cemented
fractures
Stylofrac and
subparallel
stylolitic
bedding
Circumferential Core Photo
Borehole Image
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Page 20
Stylolitic bedding and Stylo-Fracture in Arab D Member
Circumferential N
Core Photo
Partly cemented
fractures
associated with
stylofrac
Bedding
S
N
N
S
N
Stylofrac
Bedding Mudstone
Borehole
Image
Non-mineralized
open fractures
associated with
stylofrac
Thin-section photomicrographs
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Page 21
Outline of Presentation
• Introduction & Field Overview
– Arab Formation Depositional Model
– Well Location Map and 2D Seismic Section
• Fracture Analysis in Arab Members
– Fracture Orientation Trends Within Arab Members
– Fracture Density Variations in Arab Members
•
•
•
•
Impact of Diagenesis & Dissolution in Arab Main Reservoirs
Porosity-Permeability Analysis in Arab Main Reservoirs
Layering Control on Fracturing in Arab Formation
Conclusions & Implications
Abu Dhabi Gas Development Company Ltd.
CONFIDENTIAL
Page 22
Porosity – Permeability Analysis in Arab C
1
‘Enhanced’ Trend
Por:24.6%
K: 41 mD
1
10143.30
2
‘Normal’ Trend
2
A6-1V
A2-1V
A4-1V
A5-1D
A7-1V
D1-1D
Por :23%
K: 2.4 mD
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Page 23
Porosity – Permeability Analysis in Arab D
1
Por :21%
K: 2.4 mD
Mostly plugs with
fractures &/or stylolites
+ some vugs
3
“Enhanced” K
Por :10%
K: 1.3 mD
3
2
2
Por :8.7%
K: 0. 1 mD
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1
A6-1V
A2-1V
A4-1V
A5-1D
A7-1V
D1-1D
Page 24
Outline of Presentation
• Introduction & Field Overview
– Arab Formation Depositional Model
– Well Location Map and 2D Seismic Section
• Fracture Analysis in Arab Members
– Fracture Orientation Trends Within Arab Members
– Fracture Density Variations in Arab Members
•
•
•
•
Impact of Diagenesis & Dissolution in Arab Main Reservoirs
Porosity-Permeability Analysis in Arab Main Reservoirs
Layering Control on Fracturing in Arab Formation
Conclusions & Implications
Abu Dhabi Gas Development Company Ltd.
CONFIDENTIAL
Page 25
Layering Control on Fracturing in Arab Formation
SW
Diffuse (layer-bound)
fracturing
Arab Formation
Jubaila
Arab D
Arab C
Arab AB
NE
faults / fractures
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Page 26
Layering Control on Fracturing in Arab Formation
SW
Arab Formation
Arab D
Arab C
Arab AB
NE
Cementation
‘Halo’ Around
Faults / Fractures
Diffuse (layer-bound)
fracturing
Jubaila
Dissolution in more
permeable layers &
along diffuse
fractures/ stylolites
faults / fractures
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Page 27
Conclusions & Implications
•
The first development wells encountered significantly enhanced reservoir properties in
both Arab C and D reservoirs.
•
Highest fracture intensity in Arab D followed by Arab C and A/B members.
•
Conductive fractures are observed mainly in Arab D, while the resistive fractures are
interpreted in Arab C member. Conductive fractures show two predominant strikes WNWESE & NNW-SSE whilst resistive fractures show various orientations.
•
Most fractures are layer-bound concentrating at mechanical contrasts, often associated
with stylolites.
•
Enhancement of reservoir properties is related to both dissolution along deep-rooted
faults/fracture corridors and bedding-parallel where the stylolites occurred.
•
Reservoir connectivity, well productivity and drainage area especially in the Arab D still
carry high uncertainties which are being reduced by focused continued data acquisition,
integration and modeling efforts.
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Page 28
ACKNOWLEDGEMENTS
Al Hosn Gas, ADNOC & Oxy Management for permission to
present
“Badley Ashton & Associates” support and “Baker Hughes” for
Borehole Image interpretation and support
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Page 29