PHYSICAL CONTROLS ON WATER MIGRATION IN ELEMENTAL SULPHUR

BLOCKS

A Thesis Submitted to the College of

Graduate Studies and Research

In Partial Fulfillment of the Requirements

For the Degree of Master of Science

In the Department of Geological Sciences

University of Saskatchewan

Saskatoon

By

KRISTIE L. BONSTROM

Keywords: elemental sulphur, fractured porous media, hydrophobic, water migration

© Copyright Kristie Leigh Bonstrom, April, 2007. All rights reserved.

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PERMISSION TO USE

In presenting this thesis in partial fulfillment of the requirements for a

Postgraduate degree from the University of Saskatchewan, I agree that the Libraries of

this University may make it freely available for inspection. I further agree that

permission for copying of this thesis in any manner, in whole or in part, for scholarly

purposes may be granted by the professor or professors who supervised my thesis work

or, in their absence, by the Head of the Department or the Dean of the College in which

my thesis work was done. It is understood that any copying or publication or use of this

thesis or parts thereof for financial gain shall not be allowed without my written

permission. It is also understood that due recognition shall be given to me and to the

University of Saskatchewan in any scholarly use which may be made of any material in

my thesis.

Requests for permission to copy or to make other use of material in this thesis in

whole or part should be addressed to:

Head of the Department of Geological Sciences

University of Saskatchewan

114 Science Place

Saskatoon, Saskatchewan

S7N 5E2

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ABSTRACT

Elemental sulphur (S0) is produced from processing bitumen from the oil sands

region, Alberta. Long term storage of this S0 is under consideration. The objective of the

current study was to determine the controls on water migration in variably saturated S0

blocks. Based on visual observations of S0 blocks, they were characterized as a

hydrophobic fractured porous media. Thus, measurements of the hydraulic

characteristics, including porosity (n) and hydraulic conductivity (K) of the matrix and

the fractured media, were undertaken. These data were used to create characteristic

relationships of unsaturated K (Kunsat) and volumetric moisture content (θ) change with

change in positive injection pressure (Ψ).

Analyses showed that the mean total matrix n (nm) was 0.094 ± 0.035 (n = 280),

the mean n available for water migration (na) was 0.065 ± 0.044 (n = 8) and the mean

(geometric) K for the matrix was 2.0 x 10-6 ± 2.1 x 10-6 ms-1. In the case of vertical

fractures, the aperture frequencies were measured to be 2.5, 10.0 and 21.0 m-1 for

fractures with apertures > 1.4, 1.4 to 0.6 and < 0.6 mm respectively while the frequency

of horizontal fractures, were measured to be 1.7 and 3.7 m-1 for with apertures > 1.4, and

< 1.4 mm respectively. The fracture n (nf) was determined to be 0.0135. θ – Ψ

relationships were determined for both the fractured and non fractured media. From

these plots, water entry values of 9 mm and 1 m were determined for the fracture pore

space and the matrix pore space, respectively.

Simulations of packer tests resulted in a bulk saturated K (Kb) values ranging

from 8.5 x 10-5 to 2 x 10-4 ms-1 above 9 m depth and 3 x 10-6 to 1.5 x 10-5 ms-1 below 9 m

depth. Coupled Kunsat – Ψ and θ – Ψ relationships were used to conceptually describe

iii

water migration in S0 blocks under different precipitation and mounding conditions.

These plots also showed that the Kb is dominated by the fractures.

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ACKNOWLEDGEMENTS

I would like to take this opportunity to acknowledge Drs M. Jim Hendry and S.

Lee Barbour for their guidance throughout my graduate studies. NSERC and Syncrude

generously funded an NSERC IPS 1 scholarship that also enabled me to have valuable

experience with industry. Also, I thank my husband Thorsten for personal and intellectual

support. Finally my parents have always been supportive in everything I have undertaken

and during my time in graduate studies this was especially true.

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TABLE OF CONTENTS

PERMISSION TO USE....................................................................................................... i

ABSTRACT........................................................................................................................ ii TABLE OF CONTENTS ……………………………………...………………………….v LIST OF FIGURES ……………………………………...……………………………..viii LIST OF TABLES……. ……………………………………...…………………...…….xii LIST OF ABBREVIATIONS………………………………...……………………...…xiii INTRODUCTION ...............................................................................................................1

1.1. Background.............................................................................................................. 3 BACKGROUND THEORY, LITERATURE REVIEW AND SITE DETAILS ................7

2.1. Introduction.............................................................................................................. 7 2.2. Elemental Sulphur.................................................................................................... 7 2.3. S0 Blocks.................................................................................................................. 8 2.4. Method of Block Placement................................................................................... 10 2.4. Fractured Porous Media......................................................................................... 12

2.4.1. Investigations of Water Flow in Variably Saturated Fractured Porous Media13 2.4.1.1. DNAPL Migration in Fractured Porous Media ....................................... 16

2.5. Hydrophobic Materials .......................................................................................... 17 2.6. Preliminary Hydrologic Studies of Sulphur Blocks............................................... 21 2.7. Statement of Problem............................................................................................. 22

MATERIALS AND METHODS.......................................................................................24

3.1. Introduction............................................................................................................ 24 3.2. Solids Sampling ..................................................................................................... 24 3.3. Visual Surveys of an Active Block, an Aged Block and Core Samples................ 27 3.4. Characterization of Matrix Properties.................................................................... 27

3.4.1. Matrix Porosity Measurements (nt and na)...................................................... 27 3.4.2. Matrix Hydraulic Conductivity (Km and Kp) .................................................. 32

3.5. Characterization of Fracture Properties ................................................................. 32 3.6. Field Scale Hydraulic Testing................................................................................ 33 3.7. Statistical Methods................................................................................................. 34

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3.7. Statistical Methods................................................................................................. 34 RESULTS AND DISCUSSION........................................................................................35

4.1. Solid Sampling Recovery ...................................................................................... 35 4.2. Visual Surveys ....................................................................................................... 35

4.2.1. Phase III Sulphur Block: A Visual Survey of an Active Block...................... 36 4.2.2. Phase I Sulphur Block: Visual Survey of an Aged (Phase I) Block ............... 38 4.2.3 Visual Survey of Core and Block Samples...................................................... 41

4.2.3.1. Core Samples ........................................................................................... 41 4.2.3.2. Block Sample ........................................................................................... 46

4.2.4. Identification of Physical Characteristic from Surveys .................................. 48 4.3. Hydraulic Characteristics of the Matrix................................................................. 48

4.3.1 Matrix Porosity ................................................................................................ 48 4.3.1.1. Total Matrix Porosity (nm) ....................................................................... 48 4.3.1.2. Available Matrix Porosity (na) ................................................................. 53

4.3.2. θ – Ψ Relationships for the Matrix ................................................................. 54 4.3.3. Saturated Hydraulic Conductivity of the Matrix ............................................ 56 4.3.4. Unsaturated Hydraulic Conductivity of the Matrix ........................................ 57

4.4. Hydraulic Characteristics of the Fractures............................................................. 60 4.4.1. Measurements of Fracture Properties ............................................................. 60 4.4.2. Fracture Porosity Measurements..................................................................... 64

4.4.2.1. Available Porosity of Fracture Pore Space .............................................. 64 4.4.2.2. θ – Ψ Relationship for the Fracture Network........................................... 65

4.4.3. Unsaturated Hydraulic Conductivity for the Fractures................................... 67 4.5. Saturated Bulk Hydraulic Conductivity (Kb)......................................................... 71

4.5.1. Packer Test Volumetric Fluid Flux Rates....................................................... 71 4.5.2. Formulation of SEEP/W ................................................................................. 72 4.5.3. Mesh Design and Boundary Conditions ......................................................... 73

4.5.4. Packer Test Results and Discussion............................................................ 75 4.6. Coupled θ – Ψ and Kunsat – Ψ relationships for Fractured Porous So Blocks......... 81

4.6.1. Coupled θ – Ψ Relationships .......................................................................... 81 4.6.2. Water Storage in S0 Blocks ............................................................................ 83 4.6.3. Coupled Kunsat – Ψ Relationships.................................................................... 84 4.6.4. Development of Krw/Kb Relationships from Packer Tests.............................. 85

4.7. S0 Block Compressibility....................................................................................... 87 4.8. Hydraulic Fracturing During Packer Testing......................................................... 89

CONCEPTUAL MODELS OF WATER DISTRIBUTION AND MIGRATION BASED

ON DEVELOPED HYDRAULIC FUNCTIONS .............................................................93

5.1. Introduction............................................................................................................ 93 5.2. Conceptual Model.................................................................................................. 94

5.2.1. Physical Characteristics That Control Flow in Fractured Porous S0 Blocks .. 94

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5.2.2. Matrix Component .......................................................................................... 95 5.2.3. Fracture Component........................................................................................ 96 5.2.4. The Fractured Porous System ......................................................................... 96

5.3. Water Infiltration into S0 Blocks during Precipitation Events............................... 97 5.5. Non-Linear Curve Fitting θ – Ψ Relationships.................................................... 102

5.5.1. Van Genuchten.............................................................................................. 103 5.5.2. Results of Non-Linear Curve Fitting θ – Ψ Relationships ........................... 103

5.6. Implications.......................................................................................................... 104 CONCLUSIONS AND RECOMMENDATIONS ..........................................................106

6.1. Introduction.......................................................................................................... 106 6.2. Conclusions.......................................................................................................... 106 6.3. Recommendations for Further Work ................................................................... 109

REFERENCES ................................................................................................................111 APPENDIX A. …...…………………………………………………………………… 116 APPENDIX B. ……………………………………………………………...………… 127 APPENDIX C. ………………………………………………………………...……… 136 APPENDIX D. …………………………………………………………...…………… 164 APPENDIX E. ……………………………………………...………………………… 183 APPENDIX F. ……………………………………………………………………...… 280 APPENDIX G. …………………………………………………………………...…… 316 APPENDIX H. ……………………………………………………………...………… 396

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LIST OF FIGURES

Figure 1-1. Photograph of the Phase I S0 block at Syncrude Canada Ltd’s Mildred Lake mine site, Fort McMurray, AB. The Phase I block is approximately 380 m long 170 m wide 16 m high. The Phase III block is located about 300 m to the west of the Phase II block. ……………………………………...………. 3 c

Figure 2-1. Site plan of the Phase I sulphur block at the Mildred Lake site. ….………. 9 c

Figure 2-2. Molten S0 pouring on the active Phase III block. Note the moveable aluminum forms around the perimeter of the block. Photo was taken in April, 2005. ……………………………………………………………….………. 11 c

Figure 2-3. Hydrophilic vs hydrophobic liquids in contact with a capillary tube (modified from (Hillel, 1998). …………………….………………………...…...…. 18 c

Figure 2-4. θ – Ψ relationship for hydrophilic porous media and a hypothesized θ – Ψ relationship for a hydrophobic porous media (hydrophilic θ – Ψ relationship adapted from Bear, (1972). ………………………………………..………. 19 c

Figure 3-1. Plan view of Phase I S0 block with locations of surface scanlines for fracture mapping and boreholes. ……………………...…………………...….……. 26 c

Figure 4-1. Molten S0 discharging from a spigot at the active Phase III block. …….…. 37 c

Figure 4-2. Phase III block surface (one day old). Note the polygonal fracturing (about 1 m in diameter) in massive S0 matrix. …………………………………...…. 37 c

Figure 4-3. Subhedral sulphur crystals on a one day old surface of the active Phase III block. ………………………………………………………...……...……... 38 c

Figure 4-4. Vertical polygonal fracturing on the upper surface of the Phase I block. …. 39 c

Figure 4-5. Horizontal and vertical fracturing on a side of the Phase I block. ………. 40 c

Figure 4-6. Non-wetting, ponded water on S0. ……………..…………..……...………. 40 c

Figure 4-7. Core sample 792C5 (60 mm diameter and 90 mm long) retained its original cylindrical (not crumbled) shape. The ends of this core sample are defined by lift interfaces. Note the massive texture of the matrix in this core sample... 42 c

Figure 4-8. A vertical fracture through core sample S845C5. Note the massive texture of the matrix media. ………………………………………………...………. 42 c

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Figure 4-9. Core hole C5 (9 – 15 m depth) containing 60 mm diameter core samples. Note the presence of horizontal fracturing (see arrows) and the crumbly texture of the core. ………………………………………………...………. 43 c

Figure 4-10. Massive to anhedral crystalline matrix with little visible pores in core sample 981E2. Note a lift interface at 20 mm. ……………………….……. 43 c

Figure 4-11. Visible pores (up to 2 mm in diameter) within a massive to anhedral crystalline matrix in core sample 1475C5. ………………………...………. 44 c

Figure 4-12. A vuggy horizon (located at 50 mm) with elongated pores (up to 10 mm in length) in core sample 904C5. The top of the sample is truncated at a lift interface. Another lift interface is present at 20 mm with wind blown sediment visible. Below 20 mm, the sample is massive with no visible pores. ……………………………………………………………………...………. 44 c

Figure 4-13. CT images of typical matrix textures of 60 mm diameter core samples. Clockwise from top left: massive matrix with no visible pores (core sample 883C5), massive matrix with visible pores (0.1 to 1 mm diameter; core sample 596A2), massive matrix with polygonal vertical fracturing (core sample 434E2), and vuggy horizon with pores up to 10 mm diameter (core sample 604A2). ……………………….…………………………...………. 46 c

Figure 4-14. The block-sample (~0.3 m high and ~0.2 m wide). The block is located on the CT table. Note lift interfaces evident on the side of the block (see arrows). ……………………………………...……………………….……. 47 c

Figure 4-15. CT images of block-sample from Phase I S0 block. The arrow on the left image shows the location of layers with visible pores (up to 5 mm diameter). The arrow on the right image shows the location of a lift interface (horizontal surface). The left image was approximately 0.21 m high x 0.19 m wide and the left block was 0.28 m high x 0.18 m wide. …………………..………. 47 c

Figure 4-16. Matrix porosity measurements on core samples vs. depth for all samples tested from boreholes A2, C5 and E2 (plot a). Samples selected for air permeability testing are also shown and the arithmetic mean nm of those samples is indicated. Plot b is a histogram of nm values showing a lower limit of 0.04. Tables of all nm values are provided in Appendix A. ……………. 51 c

Figure 4-17. θ – Ψ relationships measured on core samples of the matrix using water intrusion porosimetry: a) θ vs. psi measurements and b) θ normalized to degree of saturation (Se = 0 to 1) using nm vs. Ψ. …………………………. 55 c

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Figure 4-18. Plot a summarizes the Kp and Km results measured on the same samples... 56 c

Figure 4-19. Calculated Kunsat data for all core samples tested with water intrusion porosimetry: (a) Krw* Kp vs. Ψ, (b) the associated Kunsat - degree of saturation (Se) and (c) Krw*mean Kp vs. Se. …………………………………….……. 59 c

Figure 4-20. Rose diagrams of vertical fracture orientations for (a) set 1, (b) set 2, and (c) set 3 measured on the top of the Phase I S0 block. …………………...……. 61 c

Figure 4-21. Side of Phase I block showing differing step thickness. …………………. 64 c

Figure 4-22. (a)Estimated θ – Ψ relationship for the fracture network mapped on the Phase I S0 block. Crosses on curve represent estimated θ and Ψ values from fracture aperture and intensity. The near horizontal dashed line corresponds to a fracture pore space with aperture greater than 0.3 mm that were counted but the aperture was not measured. (b) Se vs. Ψ relationship for the fracture network. ……………………...…………………………….……...………. 66 c

Figure 4-23. Parallel plate fracture concept. S is the spacing of fracture set having aperture b (Bear, 1993). …………………………………………...………. 68 c

Figure 4-24. (a) Aperture distribution for vertical and horizontal fractures (crosses are measured aperture increments) and best fit power function. (b) Best fit frequency normalized to the sum of the best fit frequencies f(b) vs. b. ...…. 69 c

Figure 4-25. Estimated Kunsat vs. Ψ function for the fracture network. …………..……. 70 c

Figure 4-26. Example of Kw/Ksat– Ψ function used in SEEP/W simulations to determine Kb. The function shown corresponds to a simulation at 2.75 m depth below the surface of block at 1.43 m packer spacing. Crosses correspond to Kunsat, Ψ values input to the function. ………………………………..…...………. 74 c

Figure 4-27. 0.5 m packer spacing, upper 9 m of borehole (a), 0.5 m packer spacing, lower 9 to 14 m of borehole (b), 1.4 m packer spacing, upper 9 m of borehole (c), and 1.4 m packer spacing, bottom of borehole (d). Mean values for measured Q vs. gauge pressure are presented to aid in simplifying presentation of these data. ……..……………………...…………...………. 76 c

Figure 4-28. Kb vs. depth profiles measured using packer testing with 1.43 and 0.51 m packer spacings for packer test holes (a) SRD05-144A, (b) SRD05-143A and (c) SRD05-142A. ……………..…………………………………...………. 79 c

Figure 4-29. Estimate of range in coupled θ – Ψ relationships for block. …………..…. 83 c

Figure 4-30. Estimate of Kunsat – Ψ relationship (a) for fractured porous S0 blocks using matrix pore space estimations for sample 904C5. Plot b show Krw/Kb - Ψ

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relationship using Kb determine for the block above 9 m depth. ……….…. 86 c

Figure 4-31. Kb vs. depth profiles measured with packer testing and estimated using αsf. …………………………………………………………………………….... 89 c

Figure 4-32. Kb vs. depth profile measured using packer testing (1.43 m packer spacing) for hole SRD05-144A showing increase in measured Kb values measured at gauge pressures of 68.9 and 103.4 kPa below 9 m depth. ……………...…. 91 c

Figure 4-33. Pore pressure vs. depth profiles in the Phase I S0 block during packer tests at each gauge pressure and σv profile for the block. …………………………. 92 c

Figure 5-1. Physical characteristics of the pore space in a fractured porous bulk sulphur block that influence the flow system. ……………………………...………. 95 c

Figure 5-2. A typical precipitation event of 5 mmhr-1 at Fort McMurray AB would not result in immediate infiltration into the pore space. The plot shows the fracture pore space coupled with sample 904C5. ………………....……. 98 c

Figure 5-3. (a) θ and Kunsat values at the base of a S0 block where fractures are closed and only matrix contributed to water migration and storage and (b) where fractures remain open with 1 m mounding. ……………………...………. 100 c

Figure 5-4. Ponding depth required to invade fractures with apertures greater than the cut off aperture. …………………….………………………………...………. 101 c

Figure 5-5. Curve fitting results using the Van Genuchten model compared with observed results (904C5). ……………………………...…………………...………. 104 c

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LIST OF TABLES

Table 2-1. Summary of 2003 field investigation results (Syncrude, 2004). …...………. 21 c

Table 3-1. Summary of methods used to measure key hydrogeologic parameters. ….... 24 c

Table 3-2. Summary of test methods applied to core samples and measurement methods undertaken chronologically. Sample identification numbers denote the depth from surface at which the core was collected (in cm) and the borehole number. ……………………………...…………………...……………..…. 30 c

Table 3-3. X-Ray Computed Tomography settings for core sample and block sample scans. ……………………………...…………………...……………..……. 31 c

Table 4-1. Core sample recovery details of samples that were used for nm measurements. ……………………………...…………………...…………………….……. 35 c

Table 4-2. Total matrix porosity values measured using bulk density (BD) and x-ray computed tomography (CT) methods on the same core samples. ……...…. 53 c

Table 4-3. Summary of water intrusion porosimetry results on core samples. nm values are included to show that the na are equal to or less than with the exception of sample 757E2. ……………………………...…………………...………. 54 c

Table 4-4. Ksat and Km values for S0 core samples. ……………………………………. 60 c

Table 4-5a. Summary of fracture intensities mapped on the top of the Phase I S0 block for all scanlines. ……………………………...…………………..........………. 63 c

Table 4-5b. Summary of fracture intensities mapped on the top of the Phase I S0 block with 1 m scanline. ……………………………...………………….………. 63 c

Table 4-5c. Intensities for horizontal fractures mapped on the sides of the Phase I S0 block. ……………………………...…………………...……………..……. 63 c

Table 4-5d. Intensities for vertical fractures mapped on the sides of the Phase I S0 block. ……………………………...……………………………………....………. 64 c

Table 4-6. Details of drill holes used for packer testing. ………………………………. 71 c

Table 4-7. Measured Q and corresponding net injection pressures from packer testing.. 72 c

Table 4-8. Kb results from simulation of packer tests using SEEP/W. ………...………. 81

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LIST OF ABBREVIATIONS

Abbreviation page S0, Elemental Sulphur 1

θ, Volumetric Moisture Content 18

Ψ, Injection Pressure (L) 18

n, Porosity 20

na, Porosity available for water migration 24

nf, Fracture porosity 24

K, Hydraulic Conductivity (Lt-1) 24

Kunsat, Unsaturated Hydraulic Conductivity (Lt-1) 24

Ksat, Saturated Hydraulic Conductivity (Lt-1) 24

ρm, dry bulk density (ML-3) 27

vp, Pore Volume per gram of Sample (L3M-1) 30

vt, Total Sample Volume (L3) 30

Km, Kp, Saturated Hydraulic Conductivity of S0 Matrix (Mt-1) 32

b, Fracture Aperture (L) 33

Kb, Bulk Hydraulic Conductivity (Lt-1) 48

q, Water Flow in a Single Cylindrical Pore (L3t-1L2) 57

r, Pore Throat Radius (L) 57

Se, Degree of Saturation 58

f, Fracture Frequency (L-1) 64

γ, Surface Tension (Mt-2) 65

λ, Liquid - Solid Surface Contact Angle 65

ρ, Water Density (ML-3) 65

xiv

g, Gravitational Acceleration (Lt-2) 65

μ, Dynamic Viscosity (ML-1t-1) 67

S, Fracture Spacing (L) 67

k, Permeability (L2) 67

Q, Volumetric Fluid Flux (L3t-1) 71

Krw, Relative Hydraulic Conductivity 85

σv, Confining Pressure (P) 87

α, Compressibility (P-1) 87

μp, Pore Water Pressure (P) 90

σ', Effective Stress (P) 92

θr, Residual Volumetric Moisture Content 102

θs, Saturated Volumetric Moisture Content 102

1

CHAPTER 1 INTRODUCTION

Most anthropogenic sources of elemental sulphur (S0) in the world are derived

from the refinement of fossil fuels, with Canada and the US being the largest producers.

At the Syncrude Canada Limited (SCL) refinery north of Fort McMurray, S0 (99.8%

pure) is a by-product of the oil sand bitumen upgrading processes with approximately 7.5

kg of S0 produced per barrel of oil. Recent production levels of 212 000 barrels of oil per

day result in 1 590 000 kg (768 m3) of monoclinic S0 per day (Syncrude, 2004). As the

rate of oil production at SCL increases, the rate of S0 production will also increase.

The price of S0 in world-wide markets has been low as a result of overproduction

since 1969 (Ober, 2006). As a result, transporting S0 from SCL to any potential market

is not economical (Proce, 2006). Therefore, SCL has pursued the option of long-term,

on-site storage of S0 in above ground blocks.

During “blocking” of S0, molten sulphur is piped and poured as thin lifts (0.02 to

0.12 m thick) onto above ground storage areas lined with a clay or geo-synthetic liner.

These above ground storage blocks are typically 100 to 400 m long, 200 to 50 m wide

and up to 20 m high. Currently there are three phases of block development at the SCL

Mildred Lake site (Figure 1-1) with active pouring taking place at the Phase III block.

Storage facilities located throughout Alberta are constructed in the same manner as the S0

blocks at the Mildred Lake site (Syncrude, 2004).

The presence of low pH (typically

2

processes that govern the production of H2SO4 in the blocks and its migration from the

blocks are not understood. These processes must be quantified to assess the long-term

impact of above ground S0 blocks on the environment and to design future above-ground

storage facilities to minimize environmental impacts. Because existing above-ground

storage facilities require the long-term allocation of large tracts of valuable land and do

not control H2SO4 production, alternate methods of block storage, including underground

storage, are being explored.

A three-year, multidisciplinary project on the S0 blocks at SCL’s Mildred Lake

site near Fort McMurray, AB was initiated in June 2004 by researchers at the University

of Saskatchewan. The global objectives of this study are to: (1) identify and quantify the

hydraulic, geochemical, and biochemical mechanisms controlling the production of

H2SO4 in the blocks, and (2) quantify the effects of the H2SO4 on the geochemistry and

hydrogeology of the underlying geologic media and liner materials, including the fate and

transport of the H2SO4 in these clay media (Hendry, 2004).

3

Figure 1-1. Photograph of the Phase I S0 block at Syncrude Canada Ltd’s Mildred Lake mine site, Fort McMurray, AB. The Phase I block is approximately 380 m long 170 m wide 16 m high. The Phase III block is located about 300 m to the west of the Phase II block.

1.1. Background

A visual assessment of the Phase I S0 block (Figure 1-1) suggests that the S0

blocks can be described as a fractured porous medium. Evidence for this includes

extensive fracturing visible on the block top and sides as well as the presence of visible

porosity in the S0 matrix. Fracture systems develop in the blocks shortly after they are

poured as molten sulphur. These fractures form along horizontal planes which are lift

surfaces from pouring of the molten sulphur during block construction. Vertical

fracturing with undefined orientations also occurs when the molten sulphur cools.

Fractured porous media are often characterized by preferential flow in the fracture

network (1996; Dietrich, 2005; Hsich, 2001; Sauter, 2005; Silberhorn-Hemminger, 2005;

Wang, 1993). The hydraulic conductivity of the fractured network can be orders of

4

magnitude greater than in the matrix (Dietrich, 2005; Sauter, 2005). However, the water

storage capacity of the matrix pore space is generally much greater than that of the

fracture pore space (Dietrich, 2005; Sauter, 2005). Theories and methods used to

describe water migration in fractured porous media are commonly developed for

hydrophilic geologic materials (Wang and Narasimhan, 1985; Wang, 1993). In contrast,

S0 is a hydrophobic medium (Staszczuk, 1987) and, as a result, theories and methods

developed for hydrophilic media must be modified for use with S0 blocks. Given these

considerations, including the variably saturated nature of the above ground blocks, the

controls on water migration through this complex system must be identified and

quantified.

Characteristic curves describing the volumetric water content and hydraulic

conductivity as a function of pressure are required to describe water migration in variably

saturated conditions. In hydrophilic, variably saturated, media the pressures required to

reduce the water content and hydraulic conductivity to values less than those present at

saturation would require the application of negative water pressures (relative to

atmospheric pressure). This contrasts with hydrophobic media in that saturation will only

occur under positive water pressures.

1.2. Study Objectives

The objectives of this proposed research are to characterize and quantify the

physical controls on water migration in the above ground, hydrophobic, variably

saturated, fractured porous S0 blocks. The results of this study will help define the

hydraulic mechanisms controlling H2SO4 production in the blocks and the dominant

migration pathways for water and H2SO4 in the blocks.

5

The objectives of this research were attained using both laboratory and field

methods. S0 core samples extracted from the Phase I block were used to determine the

hydraulic conductivity and porosity of the matrix. Permeameter testing was used to

determine the hydraulic conductivity of the matrix. Water intrusion porosimetry testing

was conducted on core samples to measure changes in volumetric water content with

injection pressure, the maximum volumetric water content (i.e. porosity available for

water migration) and to quantify the distribution of pore sizes within the matrix (Jena and

Gupta, 2002). Bulk density values were determined on core and bulk samples of various

sizes (0.1 kg to a few kilograms) and images of fractures and matrix pores will be made

using x-ray computed tomography (Carlson, 2003). Field work also included in situ

hydraulic testing (packer testing) and fracture mapping (fracture aperture, spacing,

orientation and frequency) of the Phase I S0 block. From water intrusion porosimetry and

fracture mapping data, estimates of coupled characteristic relationships between

volumetric water content or unsaturated hydraulic conductivity and water pressure were

developed for the matrix and fractured pore space. From these, a model to estimate the

water content-pressure relationships for S0 blocks was determined. The water content-

pressure relationships measured for the S0 matrix were non-linear curve fit to

characteristic analytic forms of these relationships adapted from formulations in the

literature.

1.3. Thesis Format

Background theory, literature review and site information relevant to this study is

presented in Chapter 2. The rational and justification for parameter identification and

research methods used to obtain the objectives of this study are also presented and

6

discussed in this chapter. The materials and methods used in the thesis are presented in

Chapter 3. The results are presented and discussed in Chapter 4. Chapter 5 presents the

conceptual and qualitative models used to describe the distribution of water in the S0

block under various flow regimes. The analytic forms of the water content-pressure

relationships and the implications of the model results on water migration in S0 blocks

and closed form equations are also presented in Chapter 5. Conclusions and

recommendations are presented in Chapter 6. Measurements of total matrix porosity as

determined from core samples using specific gravity measurements are presented in

Appendix A and from x-ray computed tomography are presented in Appendix B. Water

intrusion porosimetry results are presented in Appendix C. Appendices D and E present

the results of hydraulic conductivity and pneumatic permeameter testing, respectively.

Results from fracture mapping are presented in Appendix F. Appendix G presents packer

test measurements conducted on the Phase I block and the finite element meshes and

boundary conditions used to simulate packer tests with SEEP/W (Geo-Slope, 2004). All

hydraulic functions predicted by the adapted Van Genuchten closed form equations (Van

Genuchten, 1980b) are presented in Appendix H.

7

CHAPTER 2 BACKGROUND THEORY, LITERATURE REVIEW AND SITE DETAILS

2.1. Introduction

This chapter reviews background knowledge and literature that is needed to

understand the characteristics of S0 that may influence water migration and storage in S0

blocks. These characteristics include the mineralogical and chemical properties of S0,

methods of S0 block construction and their influence on morphology and physical

features that may contribute to the flow system, water migration in fractured porous

media, DNAPL migration in fractured porous media, hydraulic properties of hydrophobic

materials and previous hydrologic investigations of S0 blocks.

2.2. Elemental Sulphur

S0 is a byproduct of the refining process of heavy oil to light sweet crude. Three

common forms of S0 exist in the current S0 blocks; molten, monoclinic crystalline and

orthorhombic crystalline. Monoclinic and orthorhombic S0 have melting points of 119oC

and 113oC, respectively and in the molten state the density of S0 is 1.82 gcm-3.

Monoclinic S0 is stable at 113 - 119oC and has a density of 1.96 gcm-3. Orthorhombic S0

is stable under normal atmospheric conditions and has a density of 2.07 gcm-3. S0 is

hydrophobic and virtually non soluble in water (Meyer, 1977) . S0 is a zero-valent native

mineral which is oxidized to S+6 during the production of H2S04. S0 oxidation to S+6 in

sulphuric acid is catalyzed by bacteria (Lawrence and Germida, 1991) and can be

represented by the simple stoichiometric equation (Meyer, 1977):

S8 + 8 H2O + 12 O2 ↔ 8 H2SO4 (2.1)

8

Low pH values of less than 1 were measured in run off from the Phase I block and

in the underlying clay rich and bitumen liner (Birkham, 2007). The source of these low

pH waters is acidic effluent from the block. The low pH effluent may cause the

dissolution of clay minerals, adversely impacting the structural stability of clay liner, and

may also mobilize metals contained in the liner (Shaw, 2006).

2.3. S0 Blocks

Much of SCL’s daily production of over 1 590 000 kg of S0 is stored in surface

blocks constructed by pouring molten sulphur in a series of lifts; a similar type of storage

as is used at many production sites within the province (Syncrude, 2004). There are

currently three phases of S0 block development at SCL (Figure 1-1). Pouring at Phases I

and II Blocks is considered complete while active pouring is taking place at the Phase III

Block. The current study was conducted on the Phase I S0 block at the Mildred Lake site.

This block is approximately 380 m long, 170 m wide and 16 m high (Figures 1-1 and 2-

1). It was selected for study because its top surface is accessible via a ramp.

Construction of the Phase I block began with the pouring of two sub-blocks between

1993 and 1998. The north-south trending alley between these two sub-blocks was

subsequently filled until it was level with the tops of the sub-blocks. Filling of the alley

between the sub-blocks was completed in 2002 (Figure 2-1). Since 2005, an additional

0.5 m of S0 was poured onto the surface of the Phase I block.

9

Figure 2-1. Site plan of the Phase I sulphur block at the Mildred Lake site.

Increased oil production at the SCL refinery has resulted in an increasing annual

volume of S0 production and has highlighted concerns over the long-term storage of S0

10

and the production of H2SO4. The above ground block may represent one end member of

the storage options available. Because these blocks are in direct contact with the

atmosphere (O2 and water) they can be considered the worst case end member for acid

production (see equation 2.1) and release to the geosphere and biosphere. Alternative

methods of S0 storage are also being investigated.

To minimize acid production and release in these designs, a rigorous

understanding of the mechanisms of H2SO4 production and redistribution must be

developed. The controls on water storage and migration within the blocks are central to

understanding the rates of H2SO4 production and release from the blocks. Parameters that

must be characterized to define the controls on gas and water migration in the Phase I

block should be applicable to S0 blocks developed using similar placement methods. In

addition, since S0 blocks at most sites in Alberta use similar placement methods and have

similar dimensions to the Phase I block (Syncrude, 2004), it is presumed that what can be

said about the Phase I block should apply to all other above ground S0 blocks as well.

2.4. Method of Block Placement

It is important to understand the method of S0 block construction because it

controls the final morphology and structure of the block which, in turn, controls the

pathways for water and gas migration. Block construction contributes to the

development of fracture patterns where, it is postulated, most of water migration takes

place.

Molten S0 at approximately 150oC is poured as 0.02 to 0.12 m lifts on a prepared

storage area, typically constructed with a clay-rich or geosynthetic liner. Lifts are poured

consecutively and the emplaced lift is allowed to cool and solidify typically for one day.

The lateral dimensions of the poured lift are controlled by moveable forms placed around

11

the perimeter of the storage area (Figure 2-2) (Syncrude, 2005). During cooling and

solidification at 119oC, the S0 changes from liquid to a monoclinic crystal structure and

undergoes volumetric shrinkage of approximately 7%, resulting in fracturing of the

block. A further shrinkage of approximately 5.5% occurs over approximately the next

month as the S0 crystal structure converts from monoclinic to the more stable

orthorhombic arrangement (Meyer, 1977).

Figure 2-2. Molten S0 pouring on the active Phase III block. Note the moveable aluminum forms around the perimeter of the block. Photo was taken in April, 2005.

The blocks also contains matrix porosity (Syncrude, 2004). This porosity is

postulated to be formed by trapped air pockets and vugs that form between large euhedral

crystals. Visible porosity is up to 10 mm in diameter however the majority of the visible

pores are 1 to 2 mm in diameter.

12

A component of the volume change that occurs during shrinkage is taken up

within fractures. This pore space, along with any matrix pore-space, is initially free of

water. Exposure to climatic precipitation will then allow some of this pore-space to

become water filled or at least water wet; however the hydrophobic nature of the S0 itself

will strongly control the ingress and storage of this water. The following literature

review describes pertinent background information on the behavior of systems similar to

the S0 blocks and also explores appropriate methods by which to characterize the S0

blocks.

2.4. Fractured Porous Media

The nature of water movement through a fractured porous media is well

documented (Dietrich, 2005; Evans, 2001; Sauter, 2005; Snow, 1969; Wang and

Narasimhan, 1985; Wang, 1993). These studies illustrate that water flows preferentially

through fracture networks in fractured porous media. The hydraulic conductivity and

porosity of the fracture system is vastly different from that of the matrix.

The fracture network commonly accounts for a small volume of the total pore

space. It can be as low as 0.1% of the total porosity as compared to the matrix pore space

which can have a total porosity ranging from 0.1% in granites to 44% in chalks

(Silberhorn-Hemminger, 2005). Because the matrix porosity may provide the majority of

the porosity within the media, it can contribute significantly more storage capacity to the

system than the fracture network.

This contrasts with the saturated hydraulic conductivity (K) which is often orders

of magnitude greater in the fracture network than in the matrix. Matrix K values can

range from as low as 10-12 ms-1 in granite to 10-5 ms-1 in limestone while fracture

network K can be as large as 10-1ms-1 (Silberhorn-Hemminger, 2005). Because there is a

13

large contrast in value of K between the fracture pore space and the matrix pore space,

the primary pathway for water migration under saturated conditions is typically in the

fracture network.

Early studies (Wang and Narasimhan, 1985) suggested that under variably

saturated conditions water migration takes place in the matrix pore space and fractures

with smaller relative apertures. This was not found to be the case in more recent

investigations (Dragila, 2000). Local variations in pressure have been shown to cause

preferential flow in fractures with larger relative apertures, even in variably saturated

systems (Indraratna et al., 2002; Pruess, 1998). Variably saturated conditions are

synonymous with unsaturated conditions (Therrien, 2005).

2.4.1. Investigations of Water Flow in Variably Saturated Fractured Porous Media

Because the two regions of pore space (fractures and matrix) exhibit different

properties, many studies have developed separate methods of testing for each of these

regions, depending on the scale of measurement and on the property of interest (Baraka-

Lokmane, 2005; Faybishenko, 2001).

Several studies have undertaken field and laboratory testing to characterize water

flow in variably saturated, hydrophilic, fractured porous media. Faybishenko et al.,

(2001) described a comprehensive study of a variably saturated, fractured basalt

(Snakebite Member, Idaho) at multiple spatial scales. They show the use of testing at

multiple scales is needed since multiple hydraulic parameters comprising fractured

porous media behave differently at different scales.

Elemental scale components were described as a single fracture or a block of

homogeneous matrix. These components were studied at the scale of core samples or as

single fracture models using a water dripping method to study flow in a single fracture.

14

Small scale components comprising one or a few fractures in the porous matrix were

studied using local field infiltration experiments. This was used to study fracture-matrix

interactions and small-scale flow rates and pressures. Intermediate scale components,

described as the representative elementary volume containing all heterogeneities

observed in a single basalt flow, were investigated using infiltration tests. These tests

were used to observe the migration of water in the interconnected fracture network. The

large scale component was described as the regional flow network that contained several

basalt flows and sedimentary inter-beds.

Dietrich et al. (2005) provided a comprehensive guide to scale dependent

experiments used to study fractured porous media. Using a case study in the

Stubensandstein Formation, a fractured sandstone in Germany, they divided fractured

porous media into three scales; core scale, bench scale and field-block scale. For each

scale typical methods of testing were described. The field-block scale was described as

the representative elementary volume that includes all heterogeneities. The core scale

was approximated as 0.1 m diameter samples of the porous media, or a sample containing

a single fracture, and was used to measure single fracture or matrix properties (Baraka-

Lokmane, 2005). Fracture geometry characterization experiments included resin casting,

micro-tomography and MRI experiments. Matrix hydraulic properties, including

saturated hydraulic conductivity, were measured on core samples using hydraulic

conductivity and pneumatic permeameters. The bench scale was identified as an

intermediate scale that linked the core and field-block scales. Bench scale samples were

recovered from the study site with one or more fractures and sample dimensions of

approximately 0.1 to 1 m. Water flow and transport experiments were conducted on

15

cylinders and blocks recovered from the Stubensandstein Formation. Cylindrical and

block samples were sealed and injected with water and tracers while pressure was

monitored with time at evenly spaced intervals to determine flow rates and preferential

flow paths. At the field-block scale, fracture length, spacing, density, aperture and

orientation were identified as key parameters that must be measured to adequately

quantify a fracture network. Fracture network characterization also included packer

testing and slug tests to quantify hydraulic properties. Witthuser et al., (2005)

recommended basic tests to distinguish between the fracture network and matrix. These

included measurement of basic fracture parameters at the field-block scale and the

analysis of the matrix parameters at the core scale including mercury porosimetry to

investigate the connected pore space and permeability measurements.

Wang and Narasimhan (1985) described the mechanisms governing flow in

fractures in a variably saturated fractured porous medium. The study developed a

conceptual model for variably saturated water flow in the Topogah Spring Member, a

fractured tuff at Yucca Mountain, Nevada. The model used capillary theory (Bear, 1972)

to identify the cut off aperture at which a fracture will desaturate and not transmit water

at a given matric suction. The K of the fracture system at a given pressure was limited by

the cut off aperture. Therefore, the K value at any given pressure was estimated using a

distribution of only the fractures with apertures less than that associated with the

specified pressure. The fracture distribution was described using a gamma function and

K was estimated using the cubic law (Snow, 1969). Wang and Narasimhan (1985) fit

fracture apertures and frequencies measured at the Yucca Mountain field site to two

gamma distributions (vertical and horizontal fractures) and estimated the K at a given

16

pressure. They derived water retention curves for the horizontal fracture set and vertical

fracture set and showed that the fractures should desaturate at low values of matric

suction (approximately 10-1 m of water for both fracture sets). Under field conditions at

Yucca mountain, fractures should not be saturated and matrix flow should dominate. The

conceptual model was tested using a numerical model that incorporated the estimated

water retention and K characteristic curves for the fracture network and using Van

Genucthen’s formulas to estimate the relationships for the matrix (Van Genuchten,

1980b). They simulated flow in different cases: with and without discrete fractures, with

porous matrix and with an impermeable matrix. They found representing the rock as a

porous media without discrete fractures was a good approximation of the flow system

under steady state, variably saturated, flow conditions. Under transient conditions in

which the system was draining from a saturated state, the flow was highly affected by the

presence of the fractures.

2.4.1.1. DNAPL Migration in Fractured Porous Media

A survey of the literature indicated that no studies have investigated water

migration in a hydrophobic fracture porous media under saturated or variably saturated

conditions. However, several studies investigated dense non-aqueous phase liquids

(DNAPL) migration in fractured porous media. DNAPLs are non-wetting fluids in most

geologic media including fractured clays and rocks. Kueper and McWhorter (1991)

studied the behavior of DNAPL migration in a water-saturated fractured porous clay.

Numerical simulations of DNAPL migration in a single fracture with a variable width

aperture (log-normally distributed) showed that the liquid entered the fracture at the

widest aperture. Positive injection pressures were required for the DNAPL to enter a

17

fracture and the entry pressure was shown to be inversely proportional to the fracture

aperture. DNAPL did not penetrate portions of the fracture where aperture was less than

the cutoff entry pressure simulated. As the DNAPL migrated into the fracture some areas

with smaller apertures were invaded if the Ψ was great enough (due to ponding at the

constricted aperture) to exceed the localized entry pressure. The localized entry pressure

corresponded to the injection pressure required to infiltrate the localized cut off aperture.

Also demonstrated by this experiment was that the ponding height of a pool of DNAPLs

is dependent on the aperture of the fracture over which it sits, the density of the DNAPL,

and the solid – liquid contact angle between the DNAPL and formation material.

Positive pressure was greater when DNAPLs fill a vertical fracture compared to the same

volume pooled in horizontal fractures. The presence of ponded conditions should

increase the downward movement of the DNAPL once it has entered a vertical fracture

and, due to a pressure increase, allow it to enter fractures with smaller apertures.

Ross and Lu (1999) simulated downward migration of a DNAPL in a 1D fracture

through a porous matrix. They showed that DNAPL movement into matrix pore space

from fracture pore space was inhibited when injection pressures were low. In simulations

of vertical fractures containing horizontal constrictions the DNAPL was shown to pool in

the fracture until sufficient pressure was developed to bypass the constriction via smaller

pathways.

2.5. Hydrophobic Materials

Water migration in the S0 blocks at Syncrude is affected by S0 - water

interactions. Materials with a solid - water contact angle of greater than 90o are

hydrophobic where water is a non-wetting liquid (Bear, 1972) (Figure 2-3). Based on

visual observations, S0 has a S0 - water contact angle greater that 90o suggesting that

18

positive injection pressure is necessary for water to infiltrate S0. Because S0 is

hydrophobic and the S0 blocks are variably saturated, the majority of water migration is

postulated to take place in the fracture networks and not through the matrix pore space,

similar DNAPL behavior. However, it is prudent to investigate the physical properties of

the matrix pore space because S0 oxidizing bacteria may occupy these pores. S0

oxidizing bacteria, when present in significant numbers can form a hydrophilic film on

the surface of the S0 matrix pore space due to bacteria being present (Personal

Communication with R.J. Lawrence,(2006)).

Figure 2-3. Hydrophilic vs hydrophobic liquids in contact with a capillary tube (modified from (Hillel, 1998).

Water retention curves describe the relationship between the volumetric moisture

content (θ) and the gauge water pressure (Ψ) within the fluid phase in variably saturated

materials (θ – Ψ relationship). The vast majority of literature and background

information on water retention curves are for hydrophilic materials. Hydrophilic

materials will remain saturated under zero or even negative water pressures, decreasing in

19

saturation as the water pressure is made increasingly negative (large suction)(Figure 2-4).

The degree of capillarity exhibited by the soil is a function of the contact angle of the

material with water and the pore-size distribution of the material. The combination of

contact angle and small pore-size allows pores to remain saturated even under negative

water pressures (Figure 2-4).

-8 -4 0 4 8

Ψ (m)

θ

Water Entry Value

HydrophobicHydrophilic

Air Entry ValueResidual Suction

Figure 2-4. θ – Ψ relationship for hydrophilic porous media and a hypothesized θ – Ψ relationship for a hydrophobic porous media (hydrophilic θ – Ψ relationship adapted from Bear, (1972).

A typical hydrophilic θ – Ψ relationship (Figure 2-4) contains distinct regions.

The air entry value corresponds to the matric suction at which the soil begins to drain and

become unsaturated and the residual suction is the suction value at which it becomes

increasingly difficult to reduce the water content of the soil by drainage alone. Pore size

distribution dictates the shape of a θ – Ψ relationship. Soils with a small range in pore

20

size (eg. a poorly graded sand) show a rapid change in volumetric water content with

increasing matric suction until the residual water content is reached while soils with a

wide pore size range (eg. a well graded sand) exhibit a gradual change in water content

and in some cases may not have a distinct residual water content or suction (Bear, 1972).

Hydrophobic media do not retain water under negative water pressures because

the contact angle is greater than 90o. As a result, the θ – Ψ relationship for a hydrophobic

porous media would have a similar shape to that for a hydrophilic porous media except

the pressure range would be shifted to positive pressures (Figure 2-4). The water entry

pressure will be the minimum positive pressure needed to start injecting water into the

pores of the media. The pore-size distribution will also affect the volume of water in the

media as a function of increasing pressure, in a similar manner to the decrease in water

storage in a hydrophilic media with increases in suction.

Bauters (2000) and Bauters et al., (1998) measured characteristic wetting and

drainage curves (θ – Ψ relationships) of soils with varying water repellence by packing

columns with treated water repellent soils. Water was injected through a needle into the

columns while the matric potential, moisture content and soil densities were measured at

intervals along the column. The resulting θ – Ψ relationships for the most repellent soils

showed distinctive ‘knees’ at the water entry values then a rapid increase in volumetric

water content with increasingly positive matric potential until saturation was reached.

The drying curves appeared similar to hydrophilic drying curves where increasingly

negative matric suctions were observed as the volumetric water content decreased. Field

studies of hydrophobic variably saturated sandy soils showed irregular infiltration,

preferential flow patterns and spatially variable volumetric moisture contents (Hendrickx,

21

2001). No studies were encountered which adapted existing analytic descriptions of θ –

Ψ relationships to hydrophobic soils or estimated the θ – Ψ relationships for fractured

networks in a hydrophobic matrix.

2.6. Preliminary Hydrologic Studies of Sulphur Blocks

A study conducted by SCL in 2003 and 2004 (Syncrude, 2004) characterized the

Phase I S0 block with fracture mapping (to determine fracture aperture, orientation and

frequency), percolation tests, packer tests and installation of monitoring piezometers.

This study resulted in the estimation of hydraulic conductivity values for the bulk

fractured porous block and open fracture porosity (Table 2-1). Packer tests were carried

out at several locations on the block, however, the apparatus used could not sustain

constant injection pressures when high injection rates were encountered. Because of this,

the study only reported minimum values for hydraulic conductivity using the Theis

equation (Royle, 2004).

Table 2-1. Summary of 2003 field investigation results (Syncrude, 2004). Method Mean Hydraulic

Conductivity (ms-1) Porosity (%)

Packer Test 10-5 - 10-6 Percolation Test 10-6 Fracture Mapping ~3

Fracture mapping was carried out for the SCL study along two trend lines (13 and

145 m in length) on the top of the Phase I S0 block as well as along a 7.95 m trend line on

the side of the S0 block. All fracture apertures greater than or equal to 1 mm and fracture

orientations were measured on the 13 m trend line while only fractures with an aperture

greater than or equal to 2 mm were measured on the 145 m trend line. All fractures

greater than or equal to 1 mm were measured on the trend line on the side of the block.

22

Fracture porosity was determined by the sum of all fracture apertures intersecting the

trend line divided by the total trend line length. The trend line on the top of the block

was used to determine vertical fracture porosity and the trend line on the side of the block

used to determine horizontal fracture porosity. The vertical fracture porosity was

doubled in this investigation since is it was assumed to be the porosity in a uniaxial

direction so the final fracture porosity stated was double the vertical fracture porosity and

the horizontal fracture porosity summed. However, this may be an over estimation since

the vertical fracture apertures encountered on the trend line should be accounted for only

once. A fracture in a 3D porous block accounts for a porosity of the aperture multiplied

by the length and width of the fracture. If the fracture is contained in a block of a unit

volume then the aperture must only be weighted by the frequency of fractures with the

given aperture.

2.7. Statement of Problem

Based on information gathered from the previous study of the Phase I block,

studies of DNAPL migration in fractured porous media and studies of the physical

properties controlling water migration in hydrophilic fractured porous media, a

preliminary conceptual model of water migration in a S0 block was developed.

Preferential flow is hypothesized to occur in the fractures with little flow in the

matrix during variably saturated conditions. However, the matrix is heterogeneous so in

some areas it may be more actively involved in water migration and storage than in other

areas. For instance vuggy horizons may contribute to flow if connected to a fracture

while a massive area with little visible porosity may have a negligible influence on flow

or storage. Preferential flow should be compounded by the hydrophobic nature of the S0.

23

The preliminary conceptual model must be refined to more adequately describe

water migration in a S0 block. To do so requires the determination of the controls that the

fractures have on the hydraulic conductivity under both saturated and variably saturated

conditions, how much the matrix influences the hydraulic conductivity in variably

saturated and saturated conditions, and what contribution the matrix and fractures make

to water storage in the system. Several parameters are needed to refine the conceptual

model of water flow through the variably saturated Phase I S0 block. These parameters

include: fracture porosity available for water migration and storage (nf), total matrix

porosity (nm), matrix porosity available for water migration and storage (na), fracture

aperture distribution (b and f(b)), matrix hydraulic conductivity (Km), bulk hydraulic

conductivity (Kb and Kp), and coupled θ - Ψ and unsaturated hydraulic conductivity

(Kunsat) - Ψ relationships of the matrix and the fracture network.

24

CHAPTER 3 MATERIALS AND METHODS

3.1. Introduction

The previous chapter described a preliminary conceptual model of water

movement within the S0 block developed from previous hydrologic studies and

background knowledge. Based on this knowledge, the hydrologic parameters and

methods of measurement needed to characterize the block were defined. These included

porosity, saturated hydraulic conductivity (K), fracture aperture and frequency (Table 3-

1). This chapter provides detailed descriptions of these methods.

Table 3-1. Summary of methods used to measure key hydrogeologic parameters Method Parameter

Specific Gravity

Pneumatic Permeameter

Hydraulic Conductivity Permeameter

Water Intrusion Porosimetry

X-ray Computed Tomography

Fracture Mapping

Packer Testing

Measured Porosity nm na nm nf Saturated Hydraulic Conductivity

Kp Km Kb

Aperture Distributions

b, f(b)

θ - Ψ Estimated θ - Ψ Kunsat - Ψ

3.2. Solids Sampling

Core samples were used to determine key matrix properties, including Km, Kp, nm,

na and θ – Ψ relationships. These data were obtained from core samples collected during

drilling programs conducted in 2003 (Syncrude, 2004) and 2005. In 2003, cores (0.06 m

diameter) were collected from 16 boreholes located at five sites (boreholes A to E; see

25

Figure 2-1, Table 3-1) using a Strata-Pack carbide bit. Water was used as a drilling fluid.

Three boreholes (approximately 13, 10 and 4 m below the surface of the S0 block) were

drilled at each location. A fourth borehole at location C was drilled through the block

and into the underlying geologic media to a total depth of 36 m.

In 2005, core samples (0.04 m diameter) were collected from four additional sites

(SRD05-142 to SRD05-145; Figure 3-1) using a similar drilling and coring approach to

that used in 2003; however, in the 2005 drilling, a diamond matrix face discharge bit and

a triple tube NQ wireline system with a split inner tube core barrel were used. Cores

were obtained to depths of 14 to 15 m below surface. Core samples from the 2003 drill

program were packed in core boxes, and shipped to the University of Saskatchewan for

storage and analysis. Core samples from the 2005 drill program were boxed and shipped

to the University of Saskatchewan in the same manner as the 2003 core samples. The

core profiles for A2, C5, E2 and SRD05-144A were measured and labelled with depth.

Core samples from the remaining core boxes were not labelled due the volume of

samples therefore core boxes representative of different locations and covering the entire

profile of the block were selected.

26

Figure 3-1. Plan view of Phase I S0 block with locations of surface scanlines for fracture mapping and boreholes.

27

3.3. Visual Surveys of an Active Block, an Aged Block and Core Samples

Qualitative descriptions of the block morphology were undertaken during two

walking tours of the top and sides of the Phase I block in April, 2005 and on the top of

the active Phase III block in April, 2005. Core samples were observed for qualitative

descriptions in March, 2005 and October, 2005 at the University of Saskatchewan.

Several general characteristics were observed during these field tours and core

examination and some specific quantitative data was obtained. These observations

included the distribution and extent of vertical and horizontal fracturing, characteristics

(i.e., estimation of visible porosity size and distribution and S0 crystal development and

size) of the matrix S0, dark zonations, evidence of hydrophobicity, and differing block

surface ages. The migration of molten S0 over a day-old pour block surface and the

development of matrix and fracture porosity was observed on the active Phase III block.

3.4. Characterization of Matrix Properties

3.4.1. Matrix Porosity Measurements (nt and na)

The dry bulk density (ρm) was measured on core samples from borehole A2 (0.90

to 9.73 m depth; n = 129), borehole C5 (4.27 to 15.13 m depth; n = 65), borehole E2

(1.32 to 9.90 m depth; n = 86), and borehole SRD05-144A (1.54 to 11.42 m depth; n =

103). These samples included broken and irregular cores as well as those that retained

the cylindrical shape of the core barrel. The mass of cores tested ranged from 510.3 to

82.4 g. The ρm was measured using the method specified by ASTM D 1188 – 96

(ASTM, 2002) with one key modification. Paraffin wax was determined to not be

suitable for use in this test because it was difficult to remove from the core samples after

testing, especially in the vuggy core samples, thus limiting the use of these samples for

additional testing. An alternate method of water-proofing the sample was developed

28

using plastic wrap and an air evacuation system. All recovered cylindrical samples (n =

383) were wrapped in plastic and were vacuum sealed using a FoodsaverTM 2000. The

density of the plastic wrap was determined and the mass of plastic wrap used on each

core measured separately. The method was verified using a cylinder of known volume

and density (ASTM, 2002). Total matrix porosity (nm) was calculated using:

⎟⎟⎠

⎞⎜⎜⎝

⎛−=

p

mmn ρ

ρ1 (3.1)

where ρm is the measured dry bulk density (ML3) and ρp is the particle density of the S0

(ML3) (2070 kgm-3) (Meyer, 1977). The variability in results from using the plastic wrap

method was tested by conducting duplicate tests on 26 samples to demonstrate its

repeatability. In these tests, the repeatability showed a range in relative standard

deviation from 6.43 to 0.09 % with a mean of 0.81 %.

Cylindrical core samples (n = 9; Table 3-2) that had been tested for specific

gravity were shipped to Porous Media Incorporated (PMI) (Ithaca, New York, USA) for

porosimetry analysis using a Water Intrusion Porosimeter (Table 3-2). The core samples

were selected from a range in depths from three core profiles, and included a range of ρm

values. The porosimetry method detailed in (ASTM, 2004a) was used. Water was used

in these tests as the non-wetting liquid instead of mercury because it is known to react

with S0. Core samples were cut into 50 mm lengths to fit into the sample chamber. Pore

diameter (L), cumulative pore volume (L3M-1) and cumulative surface area (L2M-1) were

measured at increasing injection pressure intervals from a minimum injection pressure of

0.07 kPa (0.01 m of water) to a maximum injection pressure of approximately 7584 kPa

(773 m of water). Cumulative pore volume measured at saturation (where pore volume

29

reaches a maximum value and did not increase with increasing pressure) and the ρm were

used to calculate na (ASTM, 2004a):

t

pe v

vn ∑= (3.2)

where vp is the pore volume (L3), and vt is the volume of the sample (mass of sample /

ρm)(L3). In addition, a θ – Ψ relationship for each sample was created by dividing the

volume of water injected at the corresponding Ψ by vt.

A HiSpeed CT/i Operating System (General Electric) was used to scan 12

samples at the Porous Media and Process Tomography Research Group, University of

Calgary. The CT (x-ray computed tomography) system was used to observe the visual

characteristics of a range of intact samples (13 cores and a 0.25 m x 0.20.m x 0.35 m

block) containing vertical fractures and matrix pores (massive, vuggy, crystalline). These

images were also used to characterize porosity (method presented in Section 3.3.1).

Ten core samples (Table 3-1) were scanned at 1 mm intervals and two core

samples were scanned at 1.5 mm intervals in a 0.1 m field of view with a 512 x 512 pixel

resolution. The field of view is the length in the x and y directions of the image produced

by the CT scanner. The z direction was defined as the axis of the core (cylinder) and was

the direction which the interval distance was measured. The block sample was scanned

at 5 mm intervals using a resolution of 512 x 512 pixels over a 0.36 m field of view.

Operating system parameters were set to optimize the resolution of the scanned images as

determined by Porous Media and Process Tomography Research Group technicians

(Table 3-3).

30

Table 3-2. Summary of test methods applied to core samples and measurement methods undertaken chronologically. Sample identification numbers denote the depth from surface at which the core was collected (in cm) and the borehole number. Bulk Density Pneumatic Permeameter Hydraulic

Conductivity Permeameter

Water Intrusion Porosimetery

X-Ray Computed Tomography

419A2 840C5 584A2 604A2 584A2 539A2 845C5 596A2 708A2 596A2

Borehole A2 129 samples

584A2 883C5 604A2 647C5 604A2 596A2 888C5 708A2 702C5 708A2 604A2 897C5 632C5 708C5 647C5

Borehole C5 65 samples

703A2 904C5 647C5 883C5 702C5 708A2 995C5 702C5 904C5 840C5 717A2 1022C5 708C5 1513C5 883C5

Borehole E2 86 samples

888A2 1262C5 840C5 757E2 1356C5 894A2 1268C5 845C5 1418C5 899A2 1277C5 883C5 1474C5

SRD05-144a 103 samples

955A2 1284C5 897C5 434E2 961A2 1356C5 904C5 427C5 1400C5 1418C5

492C5 1406C5 1474C5 500C5 1410C5 1513C5 510C5 1413C5 434E2

523C5 1418C5 757E2 536C5 1423C5 545C5 1474C5

613C5 1484C5 625C5 1492C5 632C5 1505C5

638C5 1508C5 647C5 1513C5 655C5 284E2

662C5 369E2 666C5 376E2 698C5 384E2

702C5 434E2 708C5 600E2 717C5 695E2

745C5 698E2 778C5 757E2 820C5 860E2

830C5 866E2 840C5 952E2 845C5 981E2

883C5

31

Table 3-3. X-Ray Computed Tomography settings for core sample and block sample scans. Parameter Value Parameter Value Field size 10 cm (core), 36 cm

(block) Voltage 120 kV

Image Matrix 512 x 512 Current 200 mA Scan Angle 360o Scan Time 0.8 s X-ray Filter 1 (beryllium) Thickness 1 mm Resolution

32

3.4.2. Matrix Hydraulic Conductivity (Km and Kp)

Matrix K was determined on core samples using both a pneumatic permeameter

and hydraulic conductivity permeameter technique. A pneumatic permeameter was used

to measure hydraulic conductivity (Kp) on 74 core samples using ASTM D 6539 – 00

(ASTM, 2005). The core samples tested were all cylindrical and collected from

boreholes A2, C5 and E2 (Table 3-2). The analyses were conducted with a confining

pressure of 60 kPa. This pressure was selected to ensure that the membrane sealed along

the sides of the sample without compromising the integrity of the S0. Duplicate

measurements were conducted on 18 core samples to assess the repeatability of the

method. Repeatability tests yielded a range in relative standard deviation from 20.16 to

0.09 % with a mean of 7.25 %.

Hydraulic conductivity permeameter measurements (Km) were conducted on 18 of

the core samples analyzed for Kp. These samples were selected to represent a range of

measured ρm and Kp values. MDH Engineered Solutions (MDH) measured the matrix

hydraulic conductivity (Kh) on the core samples using ASTM D 5084, (ASTM, 2004b).

Confining pressures during the analyses ranged from 15 to 20 kPa as determined by

MDH as adequate to seal the outside of the core with an impermeable membrane.

3.5. Characterization of Fracture Properties

Fracture frequency (number of fractures L-1), aperture (b), (L), and orientation

were measured using a circular scanline method (Mauldon et al., 2001) on both the

surface and sides of the Phase I block in April, 2005. Twenty scanlines were located

randomly across the top of the block. The scanline locations were determined by

drawing random locations on a plan view map of the Phase I S0 block and locating the

33

approximate area with a toss of a metal spike. The scanline locations and numbers are

shown in Figure 3-1.

Scanline radii of 1, 2 and/or 5 m were traced on the block surface at the random

locations. Vertical fractures that intersected the scanline were counted and fracture

apertures greater than 0.2 mm were measured using calipers. Practical limitations

prevented the measurements of aperture diameters less than 0.3 mm in the field using the

calipers. In these cases, fracture edges were often chipped, preventing accurate

measurements. Although the stated accuracy of the caliper used was ± 0.01 mm, the

accuracy of these measurements was considered to be ± 0.1 mm.

Safety constraints prevented the scanlines on the sides of the block from being

randomly located. Eight scanlines with either a 1.00 or 0.73 m radius were traced on

vertical faces at locations accessible to stable structures on the side of the block such as

areas with scaffolding or areas adjacent to the access ramp. Vertical and horizontal

fractures and lift interfaces were counted and fracture apertures measured on these

sections. Fracture porosity available for water migration and storage (nf), was estimated

using cumulative measured aperture / scanline radius for scanline data collected from the

block surface and side.

3.6. Field Scale Hydraulic Testing

Double packer tests were carried out at in boreholes located at sites SRD05-142A,

SRD05-143A and SRD05-144A (Figure 3-1) in September 2005 to determine Kb of the

block over a range in depths from 2.0 to 14.4 m below surface. Packer test methodology

is described by Royle (2004) and Brassington and Walthall (1985). Boreholes were

drilled (0.12 m diameter) using a wing-bit water rotary drill method and the hole was

allowed to remain open over night. Prior to testing, static water levels were measured to

34

confirm that all three holes were dry. Injection pressures of 34.5, 68.9 and 103.4 kPa

(3.5, 7.0 and 10.5 m of water) were used to inject water into the packed off interval

during the tests. Two continuous double packer test profiles were produced measured in

each borehole. In the first set of tests, a 1.43 m spacing double packer test profile was

measured starting at the bottom of the hole and moving up in 1.5 m increments. After the

completion of these tests, a 0.51 m spacing double packer test profile was measured,

again, starting at the bottom of the hole and moving up in 0.5 m increments. A total of 24

1.43 m double packer tests and 49 0.51 m double packer tests were conducted.

3.7. Statistical Methods

Student’s t-tests were used to compare the geometric mean of the log transformed

matrix porosity values for each borehole, the mean fracture intensities from different

fracture sets (based on aperture), and the geometric mean of pneumatic and hydraulic

conductivity permeameter results.

35

CHAPTER 4 RESULTS AND DISCUSSION

4.1. Solid Sampling Recovery

Core recovery from three of the holes drilled and cored in 2003 ranged from 62-

76 % (Table 4.1). The rock quality designation (RQD) method was used to determine the

degree of fracturing (Bieniawski, 1989). RQD is defined as the cumulative length of core

samples which are greater than 0.10 m in length divided by the total length of the cored

interval. Most samples collected during the 2003 and 2005 programs had RQD values of

zero because all but two samples were greater than 0.10 m in length. The two longer

samples were 0.11 and 0.12 m long. The low RQD values suggest that either the S0 block

was highly fractured or core breakage occurred during sample recovery (Syncrude,

2004).

Table 4-1. Core sample recovery details of samples that were used for nm measurements. Borehole Location on Phase I block

Date

Drilled Northing (m)

Easting (m) Depth from

Surface (m)

Surface Elevation

(masl)

Core recovery (%)

A2 2003 50973.5 50450.9 9.75 318.8* 76 C5 2003 50970.2 50525.0 15.24 319.3* 67 E2 2003 50976.8 50598.5 9.9 319.3* 62

SRD05-144C 09/2005 50906.5 50536.3 320.7 78 *Elevations reported from 2003, subsequent sulphur addition has increased the surface elevation to approximately 320.5 m and increased the depth from surface accordingly.

4.2. Visual Surveys

Visual surveys of the active block (Phase III), the aged block (Phase I) and core

samples were conducted to determine relevant characteristics that must be quantified to

36

describe water migration in S0 blocks. Visual surveys were used to determine the effects

of S0 placement on block morphology and texture. Visual assessment of core samples,

including the CT images of core samples, provided qualitative details on physical

characteristics observed at a smaller scale than those observed on the active and aged

blocks.

4.2.1. Phase III Sulphur Block: A Visual Survey of an Active Block

S0 pouring and solidification was observed on the active Phase III block. Molten

S0 was poured and its distribution controlled from one of three movable spigots (Figure

4-1) located at the western edge of the block. The molten S flowed in a non-permanent

channel to the eastern edge of the block. The temperature of the molten S0 was measured

with a thermal sensor. It ranged from 123 to 127 oC at the west side of the block near the

discharge spigot to approximately 100 oC at the eastern boundary of the active pour. The

flow of the molten S appeared to be more uniform when the temperature was greater and

slowed as the temperature decreased; exhibiting a ropy texture similar to that seen in

pahoehoe basalt flows (USGS, 2006).

A one-day-old solidified S0 surface was observed to have large polygonal

fracturing (1 to 10 m; Figure 4-2). These fractures appeared to be contiguous with

fractures in the underlying lifts. Most of the surface matrix appeared to be massive;

however large elongate (up to 20 mm long) subhedral crystals were also observed (Figure

4-3). These areas are assumed to be locations where vuggy horizons develop. The large

S crystals appeared to grow upward from the top of the lift and in some areas were

covered by laterally growing crystals.

37

Figure 4-1. Molten S0 discharging from a spigot at the active Phase III block.

Figure 4-2. Phase III block surface (one day old). Note the polygonal fracturing (about 1 m in diameter) in massive S0 matrix.

38

Figure 4-3. Subhedral sulphur crystals on a one day old surface of the active Phase III block.

4.2.2. Phase I Sulphur Block: Visual Survey of an Aged (Phase I) Block

Vertical and horizontal fractures observed on the S0 block created a fracture

network that appeared highly connected. Vertical fractures that intersected the upper

surface of the block exhibited a polygonal pattern roughly 0.1 to 10 m in diameter with

each fracture connecting to the next at no observed preferred orientation (Figure 4-4).

The block surface showed an increased frequency of fracturing and a decreased spacing