Arab Formation Depositional Model

Report
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.
CONFIDENTIAL
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
Abu Dhabi Gas Development Company Ltd.
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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
Abu Dhabi Gas Development Company Ltd.
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
Abu Dhabi Gas Development Company Ltd.
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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
Abu Dhabi Gas Development Company Ltd.
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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
Abu Dhabi Gas Development Company Ltd.
CONFIDENTIAL
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
Abu Dhabi Gas Development Company Ltd.
A 4-1V
CONFIDENTIAL
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
Abu Dhabi Gas Development Company Ltd.
A 4-1V
CONFIDENTIAL
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
Abu Dhabi Gas Development Company Ltd.
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
Abu Dhabi Gas Development Company Ltd.
CONFIDENTIAL
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
Abu Dhabi Gas Development Company Ltd.
CONFIDENTIAL
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
Abu Dhabi Gas Development Company Ltd.
CONFIDENTIAL
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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CONFIDENTIAL
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.
Abu Dhabi Gas Development Company Ltd.
CONFIDENTIAL
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
Abu Dhabi Gas Development Company Ltd.
CONFIDENTIAL
Page 29

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