Geology and Bitumen Recovery Potential of the Grosmont Formation, Saleski, Alberta

Transcription

1 Geology and Bitumen Recovery Potential of the Grosmont Formation, Saleski, Alberta CHOA Technical Luncheon Reservoir & Production Nexen Conference Centre Ave SW, Plus 15 Level Kent Barrett & Mauro Cimolai Nov 10/08 1

2 Laricina: Who we are 2 Calgary-based Private Start-up founded in November 2005 Focus on in situ bitumen development High quality resource base of billion barrels of recoverable resource Well-advanced, resource focused development of innovative SAGD processes, solvent recovery methods and carbon sequestration Laricina s Positions in Four Key Oil Sands Formations 2

3 Grosmont: a resource looking for a solution 3 This is the number of barrels of bitumen resource assigned to the Grosmont Formation by the ERCB in

4 Grosmont Bitumen Resource 4 Not all of Alberta s bitumen resource is in sands Devonian subcrop has huge resource Grosmont has lion s share Laricina has acquired a significant land position in the heart of the deposit 2007: 5 delineation wells 2008: 15 wells + horizontal 4

5 Grosmont Bitumen Resource 5 T100 Net Bitumen Pay 6-12m 12-18m 18-24m 24-30m Alberta Energy and Utilities Board, 1990 Shell Fifth Meridian Husky T90 Laricina T80 T70 The Grosmont trend is a 240 km long NW to SE trend west of Ft McMurray. This Albert Energy and Utilities Board Map outlines the bitumen resource in the Grosmont Formation. This is a 6m interval contour map with a minimum of 6m of pay. >24m coloured red 5

6 6 LEL Lands Proposed Pilot 7-26 Type Well Cross-Section 2008 horizontal well Laricina s Saleski land block 6

7 7 50m Resistivity Grosmont C and D Each divided into 3 geological subdivisions. Different reservoir types coloured. >12% porosity shaded High Resistivity- oil wet Low Sonic Velocities= high bitumen content 7

8 Grosmont Geological History 8 1. Late Devonian shallow water marine deposit 2. Dolomitized: late Devonian or Mississippian 3. Uplift, Tilting and Erosion: Jurassic to Early Cretaceous Rocky Mtns 4. Karsting: Pre-McMurray Sandstone 5. Oil Migration: Cretaceous - Oligocene 6. Oil Degraded to Bitumen: Tertiary After deposition, the Grosmont underwent 5 steps that are important to their reservoir geology: dolomitization, uplift and erosion, karsting, oil migration and oil degradation to bitumen. 8

9 Chemistry of Karst 9 Karst- Surface water dissolution of carbonate rocks Limestone/dolomite solubility is highest at low temperature (i.e. near surface) Nature s Acid Job: Rain water is best (weakly acidic : carbonic acid content) 9

10 10 Grosmont exposed to erosion during pre-mcmurray exposure Fresh surface water flowed into Grosmont along pre-existing porosity trends and fractures 10

11 11 Grosmont buried by Cretaceous sediments Oil migrated into porosity during late Cretaceous to Oligocene and then was biodegradaded. 11

12 12 Middle Grosmont C Vuggy reservoir shaded green. 12

13 Vuggy Dolomite Massive vuggy dolomite Textures obscured/obliterated by vug development Fossils: burrows, scattered corals Environment: Intertidal - Upper Subtidal Excellent vuggy and fracture porosity Locally cavernous (can exceed 35% porosity/ 10 Darcy perm) W4 Most distinguishing characteristic of this facies is ubiquitous irregular cm dia vugs commonly connected by short, sub-vertical fractures. 13

14 14 Laminated grainstone reservoirs shaded blue. 14

15 Laminated Dolomite Lithology: Laminated grainstones. Fossils: Stromatolitic intervals (10-20 cm thick) Low Energy Tidal Flat - lamination due to variable tidal energy Best matrix porosity. Intra-particle and intercrystalline Thick breccias with inter-breccia clast porosity. Commonly 25-40% porosity/ 1-10 Darcy perm 15 15

16 Dololaminite Textures Laminite 16 Stromatolite When this facies has not been reduced to a breccia zone due to dissolution it is a laminated dolomite of tidal origin. 16

17 Breccia Facies: Cave Deposits Clast Supported 17 Matrix/Bitumen Supported Breccia Extremes Left: Clast supported Mosaic Breccia W4, 419.4m. Middle: Mosaic to matrix support (bitumen support?), W4, Core m Right: Matrix support (bitumen support?), W4, Core m 17

18 18 CD Marl Location of C-D Marl 18

19 C-D Marl Profile 19 Top View W4 CD Marl 361.1m May be a 1m barrier separating Grosmont C & D. More likely baffle or invisible. 19

20 Fear Not Heterogeneity! 20 Bulk of Saleski s Grosmont Resource >25% Ф High perm (>10 Darcies) Reservoir variability is not a problem with good permeability This is a core photo from a Grosmont D interval displaying Mega-Porosity. An unusual aspect of the Grosmont is the occurrence of thick intervals displaying porosities of 25 to +40% Permeabilities of 10 darcies or more These Mega-Porosity zones have huge bitumen storage capacity and are expected to play a key role in exploiting the resource. 20

21 W4 D Mega Ф Zones C Mega Ф Zone Cross-section emphasising the stratigraphic nature of high perm zones The C & D mega porosity zones are identified in yellow. The X -Section shows how the 3 mega-porosity zones can be correlated over 4.7 km across 3 well bores. It also shows that thicknesses of individual units do not vary significantly. Dissolution has not significantly affected isopach values- ie no evidence of collapse. 21

22 Fractures are our friends 22 Formed at shallow depth Open - high permeability Short: most < 10 cm long Commonly enlarged by dissolution Subvertical, irregular (non-planar) Uncemented No preferred direction- not tectonic Brittle rocks best Due to Compaction of Karst Cavities Provide vertical permeability 22

23 Analogue Wisconsin Caves 23 Silurian quarry Wisconsin- Caves on a stratigraphic horizon in dolomitic strata-photo from John Hopkins Zones with better permeability preferentially leached. Cavernous zones within the unit. Intervals between caves also have very good porosity and perm 23

24 24 Saleski breccia deposits could be found in caves. Inter-cave areas have good porosity too. 24

25 25 A horizontal well drilled through such a zone would encounter brecciated and nonbrecciated intervals. 25

26 Recovery Potential of the Grosmont Carbonate Why do we Really like this Reservoir? CHOA Luncheon Presentation November 10, This point of our presentation will focus on a portion of Laricina s laboratory test program in the Grosmont. 2. The key question we ll be addressing is: Why do we really like this reservoir? 3. Keeping in mind that in the order of 80% of North America s conventional oil is trapped in carbonate reservoirs, a corollary to our key question would be: What makes the Grosmont carbonate particularly suited to the recovery of bitumen? 26

27 Karstification Key to Grosmont Bitumen Recovery As highlighted in the geology overview, the karst development is perhaps the dominant diagenetic process within the Upper Grosmont. 2. The extensive regional karsting at Saleski provides a transformation of the bulk carbonate reservoir properties, which can be critical to the recovery of bitumen. 3. The slide provides an illustration of the karsted vuggy dolomite within the Grosmont C, with bitumen bleeding primarily from the developed vug/fracture network. 27

28 Dominant Grosmont Facies 28 Grosmont D Breccia Grosmont C Vuggy Dolomite Dr. TIPM Laboratories Nov A. 10, Kantzas, Computed tomography x-ray scanning of representative facies in core reveals essential differences between the Grosmont C and D zones. 2. The Grosmont D contains extensive breccia fill supported by a fine dolomite grainstone, with overlying layers of karsted laminite. The darker gray scale shading is indicative of a higher bitumen saturation. 3. While the Grosmont C also contains an upper laminite facies, it is more dominated by a lower saturation, highly fractured vuggy dolomite matrix. 28

29 Steam/Solvent Drainage Studies 29 Within Laricina s laboratory program, several core soak tests have been conducted including: 1. Steam soak of a Grosmont D breccia facies 2. Steam soak of a Grosmont C vuggy dolomite 3. Solvent soak of a Grosmont C vuggy dolomite These tests demonstrate a significant recovery potential within the Saleski project area. 1. As an emerging bitumen recovery target, Laricina has researched a range of Grosmont reservoir performance issues within our R & D program over the past two years. 2. An initial step in Laricina s Grosmont characterization program was to conduct a series of laboratory core soak tests. A primary objective of these tests was to study the degree of bitumen mobilization within the Grosmont karst to thermal and solvent recovery processes. 3. Within this presentation, we will illustrate why we believe the results of these tests demonstrate a significant recovery potential within the Saleski project area. 29

30 Grosmont D Steam Soak 30 TIPM Laboratories, Dr. A. Kantzas 1. An early question posed in the investigation of the Grosmont carbonate recovery potential, was whether bitumen would be mobilized beyond the open vug and fracture network. 2. As a first step in addressing this question, a simple steaming study was undertaken where a 1 meter length of Grosmont D breccia core was heated by circulating saturated steam around the outside of a vertically mounted sample. 3. Illustrated in the slide is the core holder and operation of this preliminary steam soak test. These experiments were conducted at the University of Calgary within Dr. Apostolos Kantzas Tomographic Imaging and Porous Media laboratory (TIPM). 30

31 Core Soak - Process Schematic C 1. In our first test, steam was injected in a side port 20 cm above the base of the core holder and circulated in the annular space around the vertically centered core to an exit port at the top of the assembly. Fluids were recovered and measured from the base of the core holder and exiting steam was concurrently condensed and measured. 2. The soak test consequently provides a very passive means to heat the core sample to steam temperature, while allowing the water vapour to distribute through the core following a gravity dominant bitumen drainage process. No essential pressure differential is created to affect the gravity drainage. 3. Reviewing the process schematic, what we effectively built might be more commonly recognized as a still, providing some further utility following the experiment. 31

32 W4 Grosmont D Breccia Illustrated are a section of tomographic density images from the steam soak core sample taken on a 1 cm spacing. 2. The slide demonstrates the rock framework for the extended breccia fill sections within the reservoir. The breccia forms a diverse agglomeration of carbonate clast material supported by progressively finer infilling rubble to dolomite grainstone sands. 3. This image sequence was scanned prior to steaming, such that the core was fully bitumen saturated. The comparative grey scaling provides an indication of bitumen saturation through the core. 32

33 Density Variance to Lithology The graph illustrates the comparative change in image density, and therefore bitumen drainage, resulting from the steam soak experiment. 2. In general, somewhat of a uniform density change is established over the core length, indicative of consistent depletion across the facies variations. 3. Interpretation of the drainage profile requires consideration of the similar density of both water and bitumen, plus the flow dynamics through the core sample. 33

34 Grosmont D Steam Distillation 29% Rf 34 Grosmont D Steam Soak Test 3 00 Cumulative Bitumen Production (g) Added bitumen from fittings g 205 g g Time (hours) Top Production Bottom Produc tion Total Production 1. This experiment yielded 39 g of 25 degree API oil carried with the exiting steam stream, 205 g of bitumen through the assembly bottom port and 12 g of residual oil recovered from the core holder fittings, representing a 29% recovery factor of the total oil collected following the final Dean Stark of the core sample. 2. The pronounced distillation of bitumen volatiles proved instructive in understanding the dynamics of thermal bitumen mobilization, which were consequently impaired within this experiment as a heavier residual was concentrated within the core. 3. The drainage profile within the graph demonstrates an initial flush production, with approximately a third of the recovery tailing over the remaining 80% of the experimental run. 34

35 Density Variance 35 Porosity Density Change (fraction) (kg/m3) 1. This slide provides an example of computed porosity and density change within the core following steaming. 2. From the images, it is readily apparent that bitumen mobilization has occurred throughout the core fabric in this experiment, within the clast matrix, the fractures and a network of supporting dolomitic grainstone with exceptional porosity, approaching 50%. 3. Karstification has restructured the reservoir continuity within the Grosmont, producing an enhanced hydraulic flow network beyond the depositional/diagenetic framework within more common carbonate reservoirs. 35

36 Grosmont D Steam Soak Summary 36 Significant bitumen is recoverable from Grosmont carbonate on steaming with a rapid early mobilization. 8 API native bitumen, 25 API distillate carried over top of assembly fractionation of bitumen. 29% weight recovery (31.5% by volume). Recovery impaired in this experiment due to distillation/depletion of volatiles. Bitumen drainage is demonstrated throughout the core facies. 1. Several findings from this initial steam soak test provide direct evidence of the thermal recovery potential within the Grosmont at Saleski. 2. With passive steaming, one third of the initial oil volume is demonstrated to be recovered largely by gravity drainage, indicating satistactory vertical continuity through the Grosmont breccia facies. 3. The 15 % recovery of distillates demonstrates that the Grosmont bitumen contains an acceptable level of vaporizable volatiles to form a useful solution gas drive component within a thermal recovery strategy. 36

37 W4 Grosmont C A second steam soak test was subsequently conducted on an alternate karst facies of a dominantly dissolution enhanced matrix rock within the Grosmont C unit. 2. Within this test, steam was inlet at the top of the core holder, with all fluid withdrawals taken from the bottom plate of the assembly. In this manner, all constituents were retained within the produced bitumen. 3. This slide illustrates a representative portion of the core sample, with the CT image scans again at 1 cm intervals. 37

38 Grosmont C Steam Soak 46% Rf 38 Grosmont C Steam Soak Test 350 Cumulative Bitumen Production (g) g 46% Recovery Factor Time (hours) 1. The Grosmont C core experiment yielded an abrupt flush production profile accounting for 75% of the ultimate recovery. 2. Despite the evident reduction of open fractures within this core sample, recovery improved to 46% within this test, to which the modified mechanical operation may have served as a factor. 3. Significant bitumen recovery is again demonstrated in a further Grosmont facies class. 38

39 Grosmont C Steam Soak 39 Grosmont C Steam Soak Test Bitumen Production Rate (g/hr) Time (hours) 1. An examination of the flush production of the Grosmont C steam soak is more readily illustrated in the log/log plot of the bitumen production rate. 2. Within the core heating over the second to fifth hour of the test, the bitumen recovery rate accelerated from 10 through 300 grams per hour. The test was interrupted following an abrupt drop in rate (initially, a line block was suspected) and subsequently continued at a substantially reduced sustained rate. 3. The steam soak experiments demonstrate potentially unique attributes to the rock-fluid physics in carbonates. 39

40 Grosmont C Bitumen Drainage Density Sg Before Steaming 0 1 Porosity Sg After Steaming 0 1. A helpful illustration of the bitumen drainage dynamics is presented in the calculated gas saturation change through the core sample. 2. This example illustrates that even within a lower porosity core section, a complex drainage pattern provides an evident recovery profile across the scan face. 3. Note that open porosity (vugs/fractures) are readily drained throughout the image, with areas of essentially minor porosity consistently demonstrating effectively little fluid movement. 40

41 Grosmont C Steam Soak Summary 41 The dissolution-enhanced karst matrix can demonstrate dramatic flush production. A complex depletion mechanism occurs within the rock matrix, but is effective through to low porosity rock. Recovery appears improved by retaining volatiles within produced fluids. 1. Several points of interest were demonstrated in the Grosmont C steam soak test, as itemized. 2. The apparent dual porosity nature of the Grosmont karst demonstrates a consistent flush production profile. 3. An enhanced recovery potential is suggested wherever formation karst development has been pronounced. 41

42 Grosmont C Solvent Soak In the final experiment presented, a bench solvent soak test was conducted at cold, or reservoir temperature, conditions with a Grosmont C vuggy dolomite facies core sample. 2. In this test, carbon dioxide is bubbled through liquid propane, producing a propane-saturated vapor circulated top down with a core sample mounted in the same configuration as the previous steam soak test. 3. The test is run with all fluids collected from the outlet port of the assembly bottom plate until the inlet and outlet gas compositions are identical. 42

43 W4 Grosmont C Solvent Soak An example section of the sample CT scan image set is illustrated at the 1 cm sample spacing. 2. Note the returned prominence of short scale open fractures, plus the enhanced development of vugs throughout the sample, demonstrating a range of interesting diagenetic features. 3. The vuggy dolomite facies prominent in the Grosmont C unit demonstrates a heterogeneous range of rock morphology. 43

44 Grosmont C Solvent Soak - >60% Rf 44 Grosmont C Solvent Soak Test 450 Cumulative Bitumen Production (g) g 326 g Time (hours) 1. The production profile for the solvent soak demonstrates a transitional drainage. 2. Direct bitumen recovery within this experiment was 54%. However, accounting for the oil that would have been otherwise present within depleted, or open vugs along the outside of the core sample, the vuggy dolomite recovery would have well exceeded 60%. 3. Note that the cold solvent vapor recovery in this experiment approaches some of the better recoveries that would be found within thermal operations in the clastics. 44

45 Grosmont C Solvent Soak Summary 45 At a core scale, cold solvent is readily dispersed throughout the rock fabric within the Grosmont karst. The kinetics of the solvent process is slower than the thermal response, but ultimately may prove a more effective recovery strategy. Solvent processes may be more uniquely effective within the karsted carbonate due to the high degree of open porosity. 1. Points of interest from the solvent soak experiment highlight the advantage that the open porosity in the Grosmont may provide in rapidly distributing solvent through the rock framework. 2. The consideration of solution gas drive in this non-thermal technique is removed, such that gravity drainage becomes the dominant reservoir drive mechanism. 3. Solvent processes may prove to be more effective within the Grosmont carbonate than possible within the clastics. 45

46 Soak Test Recoveries 46 Soak Test Recovery Factors Recovery Factor (fraction by weight) Time (hours) Grosmont D Steam Grosmont C Steam Grosmont C Solvent 1. The overlay of the soak test recovery profiles demonstrates that significant bitumen is recovered across all dominant Grosmont facies, inclusive of lower porosity reservoir rock where the karst-enhanced vertical drainage network is developed. 2. Although the solvent process has yielded the highest recovery, the flush production from the thermal technique provides a distinct potential advantage. 3. Curiously, each refinement that has been built from previous findings has achieved a marked response improvement in the soak test program. 46

47 Complex Reservoir Drainage In the application of our laboratory test results with Laricina s reservoir scale numerical simulation modeling, the Grosmont demonstrates distinctive features for the application of SAGD. 2. Illustrated in the slide is an element of symmetry of the steam chamber growth anticipated within the formation at Saleski, with the degree of varying fluid saturations developed as color scaled within the ternary diagram. 3. Note after 4 years the projected steam chamber carries a complex profile, reflective of the primary stratification as currently understood within the Grosmont. 47

48 Patented Production Strategy 48 ELITE-SAGD Production Profile Oil Production (m3/d) Time (days) Combi ned Zones Grosmont D Gr osm ont C 1. In turn, the development of effective production strategies for the Grosmont can be equally challenging. The slide illustrates one variation for an improved Saleski-specific production strategy, initially presented at the SPE Luncheon series on May 20, As an emerging development target, the carbonates will present specialized requirements for effective exploitation. 3. Laricina maintains an active carbonate research program, with relevant technology advancements specifically incorporated into patented production strategies. 48

49 Grosmont Bitumen Recovery Potential 49 Under passive treatment, significant bitumen is mobilized within the Grosmont carbonate karst. Open porosity within the Grosmont karst demonstrates flush production proving appreciable vertical continuity. Bitumen drainage is evidenced throughout the rock framework. A network of enhanced flow paths on a refined scale readily distribute steam and/or solvent within the karst. Extensive formation karsting provides a unique reservoir environment specifically advantaged for bitumen recovery. 1. Our final slide highlights some current thoughts addressing the opening question of: Why to we really like this reservoir? for the Grosmont. 2. The regional karstification forms a key development in providing a meaningful carbonate environment for bitumen production operations. 3. With continuing advances in our understanding of the Grosmont reservoir physics, Laricina believes that the Saleski area will sustain a significant operation, as carried within our current development program. 49