Integrated Understanding of Enhanced Reservoir Properties through Fracturing and Dissolution

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 1 Al Hosn Gas, Abu Dhabi 2Badley Ashton & Associates, Abu Dhabi

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

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

Arab Formation Depositional Model Arab AB • lime mudstones and anhydrites • Dolomitic limestone Arab C Arab D • Ooliticgrainstone SW NE • Marine lime-mudstone • Minor Wackestone to Packstone Sabkha Intertidal Subtidal Inner Ramp Mid Ramp Outer Ramp SOGAS Arab Depositional Model 0 2 km 2 ft Carbonate Ramp Setting • 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 Palaeo-environments of the Arab Formation Adapted from Azer and Peebles (1998) Chronostratigraphic setting of the Arab Formation

Well location Map and 2D Seismic Section Arab C Structural Map BHI Log D4-1H D2-1H A 7-1V D3-1&2H A2-1V D1-1D IL 7300 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 Vertical exaggeration: 2:1 0 10 km

Fracture Analysis in Arab A/B Members Gamma Ray Resistivity Whole Core Conti. Conductive Frac. Conti. Resistive Frac. DisCont. Cond. Fra. DisCont. Resistive. Fra. Mixed Fracture Neutron/ Density Discontinuous Resistive Fractures 11.5 ft Fracture Analysis from Resistivity Image Data Correlated with other Open Hole Logs

Fracture Analysis in Arab C Member Gamma Ray Resistivity Whole Core Conti. Conductive Fracture Conti. Resistive Fracture DisCont. Cond. Fracture DisCont. Resistive. Fra. Mixed Fracture Neutron/ Density Discontinuous Resistive Fractures 5.5 ft Continuous Resistive Fractures Fracture Analysis from Resistivity Image Data Correlated with Core Image and Open Hole Logs

Fracture Analysis in Arab D Member Conti. Conductive Fracture Conti. Resistive Fracture DisCont. Cond. Fracture DisCont. Resistive. Fra. Mixed Fracture Gamma Ray Resistivity Whole Core Neutron/ Density Discontinuous Conductive Fractures 6 ft Continuous Conductive Fractures Fracture Analysis from Resistivity Image Data Correlated with Core Image and Open Hole Logs

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 WNW-ESE A 7-1V No fractures have been interpreted through Arab AB Members N= 22 D2-1H D4-1H D3-1&2H A2-1V D1-1D A1-1V Conti. Conductive Fracture Conti. Resistive Fracture DisCont. Conductive Fracture A5-1D N= 6 DisCont. Resistive Fracture Mixed Fracture A 3-2S A 6-1V A 4-1V 0 10 km

Fracture Trends in Arab C Member • 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 A 7-1V N= 6 N= 50 D2-1H D4-1H D3-1&2H A2-1V D1-1D A1-1V A5-1D N= 33 A 3-2S A 6-1V Conti. Conductive Fracture Conti. Resistive Fracture DisCont. Conductive Fracture DisCont. Resistive Fracture Mixed Fracture A 4-1V 0 10 km

Fracture Trends in Arab D Members • 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 A 7-1V N= 67 D2-1H N= 544 D4-1H D3-1&2H A2-1V D1-1D A1-1V A5-1D N= 75 A 3-2S A 6-1V Conti. Conductive Fracture Conti. Resistive Fracture DisCont. Conductive Fracture DisCont. Resistive Fracture Mixed Fracture A 4-1V 0 10 km

Fracture Density Variations in Arab Members D2-1H A7-1V D1-1D A 7-1V D2-1H D4-1H D3-1&2H A2-1V D1-1D A1-1V A5-1D A 6-1V A 3-2S A 4-1V TD in Arab D 0 10 km

Stylolitic bedding and Stylo-Fracture in Arab C Member Non-mineralized open fractures Partly cemented fractures Stylofrac and subparallel stylolitic bedding S N N N S N Circumferential Core Photo Borehole Image

Stylolitic bedding and Stylo-Fracture in Arab D Member Bedding Partly cemented fractures associated with stylofrac Stylofrac Non-mineralized open fractures associated with stylofrac N S N N S N Circumferential Core Photo Borehole Image Bedding Mudstone Thin-section photomicrographs

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

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 1 3 A6-1V A2-1V A4-1V A5-1D A7-1V D1-1D 2 2 Por :8.7% K: 0. 1 mD

Layering Control on Fracturing in Arab Formation SW NE Arab AB Arab C Arab Formation Arab D Jubaila Diffuse (layer-bound) fracturing faults / fractures

Layering Control on Fracturing in Arab Formation SW NE Arab AB Arab C Arab Formation Arab D Dissolution in more permeable layers & along diffuse fractures/ stylolites Cementation ‘Halo’ Around Faults / Fractures Jubaila Diffuse (layer-bound) fracturing faults / fractures

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.

ACKNOWLEDGEMENTS Al Hosn Gas, ADNOC & Oxy Management for permission to present “Badley Ashton & Associates” support and “Baker Hughes” for Borehole Image interpretation and support

Integrated Understanding of Enhanced Reservoir Properties through Fracturing and Dissolution