Post on 31-Mar-2015
Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL Page 1
Integrated Understanding of Enhanced Reservoir Properties through Fracturing and Dissolution
Fatima Al Darmaki1, David A. Lawrence1, Richard P. Singleton1, Budideti A. Reddy1, Georgeta Popa1, Pascal Cortes2
Case Study from the Late Jurassic Arab Formation in a Large Gas Field, Onshore UAE
1 Al Hosn Gas, Abu Dhabi 2 Badley Ashton & Associates, Abu Dhabi
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
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 4
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 5
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 6
Arab Formation Depositional Model
Chronostratigraphic setting of the Arab Formation
Adapted from Azer and Peebles (1998)
SW NE
Carbonate Ramp Setting
Arab DArab C
Arab AB
Palaeo-environments of the Arab Formation
• Oolitic grainstone
SOGAS Arab Depositional Model
• lime mudstones and anhydrites
• Dolomitic limestone
Main Field area Reservoir Data
• Reservoir Ave Porosity Ave Perm
• 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
Outer RampMid Ramp
SubtidalIntertidalSabkha
0 2 km2 ft
Inner Ramp
• Marine lime-mudstone• Minor Wackestone to
Packstone
Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL Page 7
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 8
Well location Map and 2D Seismic Section
A1-1V
A2-1V
D3-1&2H
D2-
1H D4-1H
D1-
1D
Arab C Structural Map
A1-1V
A 6-1V
A 3-2S
A 4-1V
A5-1D
A2-1V
A 7-1V
BHI Log
BHI Log
BHI Log
IL 7300
Vertical exaggeration: 2:1
Arab
NW SE
0 10 km
0 1.25km
Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL Page 9
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 10
Fracture Analysis in Arab A/B Members
Fracture Analysis from Resistivity Image Data Correlated with other Open Hole Logs
11.5
ft
Discontinuous Resistive Fractures
Gamma Ray Resistivity Neutron/ Density
Whole Core
Conti. Conductive Frac.Conti. Resistive Frac.DisCont. Cond. Fra.
DisCont. Resistive. Fra.
Mixed Fracture
Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL Page 11
Fracture Analysis in Arab C Member
Discontinuous Resistive Fractures
Continuous Resistive Fractures
5.5
ft
Fracture Analysis from Resistivity Image Data Correlated with Core Image and Open Hole Logs
Gamma Ray Resistivity Neutron/ Density
Conti. Conductive FractureConti. Resistive FractureDisCont. Cond. Fracture
DisCont. Resistive. Fra.
Mixed Fracture Whole Core
Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL Page 12
Fracture Analysis in Arab D Member
Fracture Analysis from Resistivity Image Data Correlated with Core Image and Open Hole Logs
Discontinuous Conductive Fractures
Continuous Conductive Fractures
6 ft
Whole Core
Conti. Conductive FractureConti. Resistive FractureDisCont. Cond. Fracture
DisCont. Resistive. Fra.
Mixed Fracture
Gamma Ray Resistivity Neutron/ Density
Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL Page 13
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 14
Fracture Trends in Arab A/B Members
A1-1V
A 6-1V
A 3-2S
A 4-1V
A5-1D
A2-1V
A 7-1V
D4-1H
D2-
1HD
1-1D
D3-1&2H
• Few fractures are observed in Arab A/B including conductive, resistive and mixed features
• Varying strike orientations were interpreted, mainly NNW-SSE and WNW-ESE
DisCont. Resistive Fracture
Mixed Fracture
Conti. Conductive Fracture
Conti. Resistive Fracture
DisCont. Conductive Fracture
No fractures have been interpreted through Arab AB Members
0 10 km
N= 22
N= 6
Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL Page 15
• The majority of the interpreted fractures in Arab C were resistive
• Few conductive and mixed fractures were interpreted in the study wells
• 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
Fracture Trends in Arab C Member
A1-1V
A 6-1V
A 3-2S
A 4-1V
A5-1D
A2-1V
A 7-1V
D4-1H
D2-
1HD
1-1D
D3-1&2H
0 10 km
DisCont. Resistive Fracture
Mixed Fracture
Conti. Conductive Fracture
Conti. Resistive Fracture
DisCont. Conductive Fracture
N= 50
N= 33
N= 6
Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL Page 16
• Highest fracture intensity observed in Arab D and most were continuous and discontinuous conductive fractures
• Relatively few resistive fractures were also interpreted in this interval.
• Strike orientations of fractures in Arab D are dominantly NNW-SSE and WNW-ESE.
• Subordinate trends in broadly NNE-SSW and ENE-WSW direction and parallel to the main fault trends
Fracture Trends in Arab D Members
A1-1V
A 6-1V
A 3-2S
A 4-1V
A5-1D
A2-1V
A 7-1V
D4-1H
D2-
1HD
1-1D
D3-1&2H
DisCont. Resistive Fracture
Mixed Fracture
Conti. Conductive Fracture
Conti. Resistive Fracture
DisCont. Conductive Fracture
0 10 km
N= 544
N= 75
N= 67
Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL Page 17
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 18
Fracture Density Variations in Arab Members
A1-1V
A 6-1V
A 3-2S
A 4-1V
A5-1D
A2-1V
A 7-1V
D1-1D
D2-1H
D3-1&2HD4-1H
0 10 km
D1-1D D2-1H A7-1V
TD in Arab D
Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL Page 19
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 20
Stylolitic bedding and Stylo-Fracture in Arab C Member
Circumferential Core PhotoBorehole Image
N S N
N NS
Non-mineralized
open fractures
Partly cemented fractures
Stylofrac and subparallel
stylolitic bedding
Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL Page 21
Circumferential Core Photo
Thin-section photomicrographs
S N
Borehole Image
Stylolitic bedding and Stylo-Fracture in Arab D MemberN NS
Bedding Mudstone
Bedding
StylofracPartly cemented fractures
associated with stylofrac
Non-mineralized open fractures associated with
stylofrac
N
Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL Page 22
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 23
Porosity – Permeability Analysis in Arab C
A6-1VA2-1VA4-1VA5-1DA7-1VD1-1D
2
‘Normal’ Trend
‘Enhanced’ Trend
110143.30
1
Por:24.6%K: 41 mD
Por :23%K: 2.4 mD
2
Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL Page 24
Porosity – Permeability Analysis in Arab D
Mostly plugs with fractures &/or stylolites
+ some vugs
“Enhanced” K
A6-1VA2-1VA4-1VA5-1DA7-1VD1-1D
Por :21%K: 2.4 mD
1
Por :10%K: 1.3 mD
3
Por :8.7%K: 0. 1 mD
2
13
2
Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL Page 25
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 26
Layering Control on Fracturing in Arab Formation
Diffuse (layer-bound) fracturing
faults / fractures
Jub
aila
Ara
b D
Ara
b C
Ara
b A
B
Ara
b F
orm
atio
n
SW NE
Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL Page 27
Layering Control on Fracturing in Arab Formation
Diffuse (layer-bound) fracturing
faults / fractures
SW
Jub
aila
Ara
b D
Ara
b C
Ara
b A
B
Ara
b F
orm
atio
n
NE
Cementation ‘Halo’ Around
Faults / Fractures
Dissolution in more permeable layers &
along diffuse fractures/ stylolites
Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL Page 28
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 WNW-ESE & 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 29
ACKNOWLEDGEMENTS
Al Hosn Gas, ADNOC & Oxy Management for permission to present
“Badley Ashton & Associates” support and “Baker Hughes” for Borehole Image interpretation and support