The Origin of Matrix and Fracture Mega- Porosity in a Carbonate Bitumen Reservoir, Grosmont Formation, Saleski, Alberta T 85 R 19W4M

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1 The Origin of Matrix and Fracture Mega- Porosity in a Carbonate Bitumen Reservoir, Grosmont Formation, Saleski, Alberta T 85 R 19W4M Kent Barrett, Dr John Hopkins, Ken Wilde and Marnie Connelly Oct 2/07

2 Grosmont Bitumen Resource 2 Not all of Alberta s bitumen resource is in sands Significant bitumen reserves in Devonian subcrop underlying Cretaceous deposits Grosmont contains most significant Bitumen resource in carbonates 318 Billion barrels of bitumen resource in place Laricina has acquired a significant land position in the heart of the deposit and drilled 5 delineation wells last winter

3 What are Mega-Porosity Zones? 3 >25% High perm (>10 Darcies) Key factor in bitumen recovery

4 Grosmont Bitumen Resource 4 T100 T90 Saleski Net Bitumen Pay 6-12m 12-18m 18-24m Fifth Meridian T m Alberta Energy and Utilities Board, 1990 T70

5 W4 Grosmont Upper Devonian Grosmont D Direton Direton_ Pa y Dgrosmont Dgrsmnt_d1 Dgrsmnt_d2 Ireton 5 4 Subdivisions Dgrsmnt_d3 Shallowing upwards cycles Grosmont C Dgrsmnt_c Dgrsmnt_c1 Dgrsmnt_c2 Grosmont B Dgrsmnt_b Dgrsmnt_a Grosmont A

6 Upper Grosmont Petrophysics 6 Neutron-Density Porosity Resistivity Sonic >20% Ф >100Ω 300 μ sec D 50m C W4

7 Post Depositional Events 7 1. Dolomitization: probably during late Devonian or Mississippian 2. Uplift, Tilting and Erosion: Jurassic to Early Cretaceous related to the Larimide Orogeny 3. Oil Migration: Cretaceous to Oligocene 4. Oil Degradation to Bitumen: Tertiary

8 Caveats 8 Well logs and core examination Bitumen stain a problem Porosity development has obscured and commonly obliterated sedimentary textures Core analyses of high porosity zones are problematical

9 Direton Grosmont Facies Laminite Dgr osmont 325 Grosmont D Mixed Laminite Mixed >100Ω >20% Ф 350 Dgr smnt_c Grosmont C Laminite Vuggy Dolomite Argillaceous Dolomite Ф 375 Dgr smnt_b 400 Dgr smnt_a 9

10 Direton Argillaceous Dolomite Ireton Dgr osmont Lithology: bioturbated argillaceous dolomite Fossils: Vertical burrows, brachiopods Depositional Environment: Subtidal Non-Reservoir (locally vuggy) D Dgr smnt_c C Argillaceous Dolomite Dgr smnt_b B Dgr smnt_a 10

11 W4 Subvertical burrowing 11 Brachiopod beds

12 Direton W4 Ireton >20% Ф Dgr osmont 325 D 350 Dgr smnt_c Vuggy Dolomite Ф 375 C Dgr smnt_b B 400 Dgr smnt_a >100Ω 12

13 Facies 2- Vuggy Dolomite Massive carbonate Locally laminated Textures obscured/obliterated by vug development Fossils: some horizontal burrows, scattered corals Sedimentary Environment:? Sandwiched between tidal flat and subtidal unit Porosity: Excellent vuggy and fracture porosity, locally cavernous (can exceed 35% porosity/ 10 Darcy prem) W4 13

14 Bioturbation 14 CT Scan of Grosmont C at W4 Cretaceous outcrop analogue: Wabiskaw bioturbation Saleski W4 375m Cretaceous burrows

15 Facies 3- Laminated Dolomite Lithology: Laminated lime mudstones and grainstone. Occasional fenestral texture (U intertidal to supratidal indicator). Fossils: Occasional stromatolitic intervals (10-20 cm thick) Sedimentary Environment: Low Energy Tidal Flat (Tidal to Supratidal) Reservoir: Best matrix porosity. Typically intra-particle and intercrystalline porosity. Thick intraformational breccias with interbreccia clast porosity. Breccia Zones: 25-40% porosity/ 1-10 Darcy perm 15

16 Direton W4 Ireton >20% Ф Dgr osmont 325 D Laminated Dolomite 350 Dgr smnt_c C Ф 375 Dgr smnt_b B 400 Dgr smnt_a >100Ω 16

17 Dololaminite Textures Laminite Fenestral Fabric Stromatolite 17

18 Direton W4 Ireton >20% Ф Dgr osmont 325 D Mixed Lithology 350 Dgr smnt_c C Ф 375 Dgr smnt_b B 400 Dgr smnt_a >100Ω 18

19 Facies 4- Mixed Lithology Lithology: Green siliciclastic shale, dolomudstone and Amphipora floatstone. Sedimentary Structures: fenestral fabric, mud cracks, irregular bedding. Fossils: Occasional Amphipora beds (1-2m thick) Facies: Supratidal to lagoonal (Low energy with possible elevated salinities). Porosity and Permeability: Marginal reservoir (12-20%). Amphipora facies is generally vuggy (.1-.5 cm dia). Patchy intraparticle porosity. 19

20 20

21 Mud Cracks Profile 21 Top View

22 Amphipora Facies 22

23 23 Origin of Mega- Porosity Zones

24 Mega Porosity Zones High Porosity: 25 to >40% Found in Laminated and Vuggy Facies of Grosmont C & D Product of selective leaching of individual beds in Grosmont C & D Appearance: angular dolomite breccia clasts floating in bitumen 24

25 Brecciated Lower Grosmont D Laminite 25 Top Bottom W4

26 Closeup of brecciated Grosmont D 26

27 Evolution of a Mega Porosity Zone Grosmont C 350 Core

28 C Zone Breccia Zone Evolution Vuggy Reservoir Increased leaching and fracturing Vug collapsecrumble breccia Bitumen rich breccia zone Triple porosity system: Vugs, matrix and fractures 28

29 Chemistry of Carbonate Dissolution 29 Limestone solubility is highest at low temperature Limestone is most easily dissolved by fresh water Rain water is best (weakly acidic due to carbonic acid content) Solubility: Calcite (limestone) >>Dolomite

30 Grosmont Porosity Model 1. Early Dolomitization (5-10% porosity) 2. Fresh water leaching occurred during PreCretaceous erosional event Fresh water aggressively dissolved calcite Dolomitization is commonly incomplete Early dolomite provided rigid framework allowing preservation of cavernous porosity No cement: saturated brines discharged at surface? Laminite and Vuggy facies developed best porosity Some dolomite has been dissolved too 30

31 Fresh Water Diagenesis 31 Pre-McMurray Erosional Surface Fresh Water Flow

32 Evidence for Limestone Leaching Model Grosmont dolomites are calcite free: 1. High grain density: 2840kg/m3 (core & log data) 2. XRD data: absence of calcite/dominance of dolomite 3. Textural: dolomite rhomb micro-porosity 32

33 33 Calcite

34 Floating Dolomite Crystals- Evidence of Dissolution 34

35 35 SEM Photo: Corrosion of dolomite Xls due to fresh water leaching

36 Mega Porosity Zones Inter-breccia clast, vuggy and matrix porosity Found in Laminated and Vuggy Facies Laminated facies: Dissolution along bedding planes Vuggy Facies: Dissolution linked vugsvertical flow bias 36

37 37 What Role Does Karst Play?

38 Aspects of Karst Processes Vertical/not surface flow of groundwater Dissolution of limestone by fresh water Subterranean drainage system Caves/cave sediments/cave collapse Central France 38

39 Mega Porosity Reservoirs These are not caves This is good news Caves are narrow and unpredictable High porosity/permeability zones are regional stratigraphic layers Based on well control and seismic evidence 39

40 W4 D Mega Ф Zones C Mega Ф Zone Cross-section emphasising the stratigraphic nature of high perm zones

41 So What? Predictability High Porosities/Permeabilities Grosmont bitumen at Saleski is 100,000+ centipoise Unconventional means are needed for recovery Laricina feels that it can be exploited in a scalable manner using the right recovery method 41

42 Bitumen Covered Core Barrel W4 42

43 Acknowledgements I wish to thank the Management of Laricina and our partner, OSUM for permission to present this paper 43