Preparation of these workshop lectures on the broad topic of ‘clay in oil sands’ was motivated by two observations. The first was the growing interest in the effects of clay on oil-sands operations, in particular bitumen flotation and fine-tailings management. The second was the lack of a common basis of understanding, or even common vocabulary, among the various disciplines involved in investigating and managing those effects. The hope is that the contributions herein will summarize current knowledge about the effects of clay on oil-sands operations, while gently introducing basic theory, terminology, and methods that the authors and editors believe will facilitate further advances.

Depending on the context and discipline, the terms ‘clays’ or ‘clay’ may be used in three different ways: as a particle-size term, as a mineral term, and as a rock term ( Moore, 1996 ). The field of oil-sands research makes no exception and various uses can be encountered in the literature, including terms such as ‘clay-sized minerals,’ ‘fine clays,’ ‘ultrafine clays’ (or ‘ultrafines’), ‘estuarine clay,’ ‘marine clay,’ etc. In this chapter, an overview is given of: (1) the nomenclature associated with clays and clay minerals; (2) the structure and crystal chemistry of phyllosilicates; and (3) the geology and clay mineralogy of oil sands.

The oil-sand ores of northern Alberta provide a significant proportion of the overall energy portfolio for North America. Surprisingly, the presence of nano-sized clay minerals plays a defining role both in the extraction of bitumen and in tailings management. Although seemingly insignificant in size, naturally occurring clay minerals present in the oil sand ores of northern Alberta create significant challenges in all aspects of bitumen extraction and recovery, processing of oil sand ores, and management of tailings. Although a significant body of knowledge exists in relation to the characterization of ‘oil-sands clay minerals,’ much of this work has focused on the identification of the clay minerals present and not on their respective surface chemistries. This chapter focuses on some of the unique structural features of the clay minerals found in the oil sands and their respective surface chemistries.

Slurry colloidal and particle interaction theory is described and applied to clay mineral suspensions. Mechanisms which affect the colloidal properties of the dewatering behaviour of clay mineral suspensions are described, after which the processes of coagulation and flocculation are discussed. Finally, sedimentation and self-weight consolidation are discussed as the mechanisms by which a low-density slurry transitions to a high-density slurry or soil.

With the myriad of measurement techniques and definitions of clays, the first question generally asked is “how much clay is there” in a sample? This often refers to the magnitude of a clay attribute in the sample and the answer to this question may vary depending on the measurement method. Does the method measure the clay-mineral type, the size distribution or mean size, the surface area, cation exchange capacity (CEC), rheology, or plasticity? Clay mineral type, particle size, and surface area are commonly used in mining operations to optimize oil-sand ore blending. In bitumen extraction and tailings management, where slurry behavior contributes to the process performance, propertiess uch as rheology and plasticity are also used. The previous chapters in the volume have introduced the various properties of clay particles and clay minerals. The present chapter describes the common methods of measuring clays and clay minerals in oil sands.

The clay fundamentals explained in the preceding chapters affect the macroscale oil-sands processes discussed in the following chapters of this volume through a series of mesoscale phenomena. Each mesoscale phenomenon is itself the subject of a field of science, and applications to different fields of engineering have led to a confusion of terminology. Understanding the underlying physical processes helps to elucidate the positive and negative effects of clay in oil-sands processes.

The clay minerals present in the oil-sands ore are responsible for some of the most challenging (and intriguing) processing behavior experienced on a routine basis in oil-sands surface mining. In previous chapters, significant details have been provided on how specific clay properties can give rise to changes in slurry rheology and interface phenomena. Because the bitumen extraction process relies heavily on manipulation of interfacial effects to enhance separation, changes in clay content in the ore, not surprisingly, can have a dramatic impact on the ability to process the material. This chapter provides an overview of the extraction process, the influence of clay minerals on bitumen recovery, and the challenges in reacting to changes in the ore clay content in a typical operation. The chapters that follow focus on the larger issue of tailings treatment to create a reclaimed landscape at the end of mine life.

The particle-size distribution of oil-sands tailings has always figured prominently in the mine planning and overall operations and closure strategy in surface-mined oil sands. In oil-sands applications, the convention is to define the sand as the mineral components >44 μm in size and the fines as the mineral component which is <44 μm. The water-based extraction process uses 2 m 3 of water to extract the bitumen from 1 m 3 of oil sand, and as the bulk of this water is recycled, large containment areas are required to maintain a supply of extraction water. A significant proportion of water that is not recycled is retained in both the sand and fines components of the resulting tailings streams and the essence of tailings management comes down to separating and managing the water that can be recovered from the tailings. As the mining operations have become larger, and ore properties vary over wider ranges, the designation of sand and fines was simply inadequate in explaining the behavior of many of the tailings and a thorough understanding of the entire particle-size distribution became more important. Due in part to the upgrading and refinery operations often associated with bitumen production, the oil sands industry is relatively sophisticated in its approach to tailings characterization and tailings management. As a result, any discussion of clays can, and often does, include both a size and mineralogy component. In any case, there is no doubt about the importance of understanding and quantifying the clay component of any tailings stream when defining a dewatering or management strategy. Historically, it might have been argued that the strong correlation between clay content and fines content would be an adequate characterization and tailings-planning parameter. Although this is still largely true, the clay to fines correlations can sometimes be measurably different from operation to operation, resulting in varying tailings performance. In addition, some tailings-management options such as thickeners and centrifuges can separate the fines fraction and even the clay fraction in a fluid fine tailings stream. These upset operational modes can create what are known colloquially as Franken-Fines, a stream with a very disproportionately high clay content that can create an equally disproportionate tailings problem. The tailings strategies that will be discussed include composite/consolidated/non-segregating tailings, thickening, freeze-thaw processes, rim ditching, thin lift dewatering, and centrifugation. The present chapter outlines the evolution of many of these tailings-management strategies that have been tested extensively or are currently in use in the surface-mined oil-sands industry, with a particular emphasis on the importance of understanding the clay size and clay mineralogy in the evaluation and understanding of tailings dewatering performance.

The effects of clay on the geotechnical properties of oil-sands tailings deposits are discussed. The sources of fluid fine tailings are reviewed, and types of tailings deposits are described. The effects of clay on geotechnical index properties, hydraulic conductivity, compressibility, and shear strength are discussed, with example predictions for consolidation and strength gain in fines-enriched sand tailings and deep fines-dominated tailings deposits.

Abstract This CMS Workshop Lecture Series (WLS) volume is intended to give a summary of the current state-of-the-art of different spectroscopy and microscopy methods, as presented during a workshop held in conjunction with the EUROCLAY 2015 conference in Edinburgh, UK, on the 5th of July 2015. This workshop was initiated by the NEA Clay Club, The Clay Minerals Society, and the Euroclay conference series. This EUROCLAY 2015 workshop is a continuation of the very successful workshop “Clays under Nano- to Microscopic resolution” which took place from 6 th to the 8 th of September 2011 in Karlsruhe and documents new developments and the progress made over the past four years concerning research in low-permeability, clay-rich, geological formations. The workshop also provided an excellent opportunity for exchange of knowledge with research communities concerned with the safe long-term management of radioactive waste within argillaceous sediments, and with shale gas and oil exploration.

Abstract The application of ion-beam milling techniques to clays allows investigation of the porosity at nm resolution using scanning electron microscopy (SEM). Imaging of pores by SEM of surfaces prepared by broad ion beam (BIB) gives both qualitative and quantitative insights into the porosity and mineral fabrics in 2D representative cross-sections. The combination of cryogenic techniques with ion-beam milling preparation (BIB and FIB, focused ion beam) allows the study of pore fluids in preserved clay-rich samples. Characterization of the pore network is achieved, first, using X-ray computed tomography to provide insights into the largest pore bodies only, which are generally not connected at the resolution achieved. Secondly, access to 3D pore connectivity is achieved by FIB-SEM tomography and the results are compared with 2D porosity analysis (BIB-SEM) and correlated with bulk porosity measurements (e.g. mercury injection porosimetry, MIP). Effective pore connectivity was investigated with an analog of MIP based on Wood’s metal (WM), which is solid at room temperature and allows microstructural investigation of WM-filled pores with BIB-SEM after injection. Combination of these microstructural investigations at scales of <1 mm with conventional stress-strain data, and strain localization characterized by strain-fields measurement (DIC–digital image correlation) on the same sample offers a unique opportunity to answer the fundamental questions: (1) when, (2) where, and (3) how the sample was deformed in the laboratory. All the methods above were combined to study the microstructures in naturally and experimentally deformed argillites. Preliminary results are promising and leading toward better understanding of the deformation behavior displayed by argillites in the transition between rocks and soils.

Abstract Low-permeability (unconventional) reservoirs exhibit heterogeneities at multiple scales that affect flow. While macro-scale heterogeneities are typically evaluated using well-test or production-analysis techniques, core-scale (and finer) analyses are relied upon to evaluate micro-and nano-scale heterogeneities. Pore structure is a known control on flow at the core scale; for unconventional reservoirs, however, pore-size distributions, pore accessibility, and connectivity are challenging to evaluate. In the present study, a combination of neutron-scattering methods, fluid invasion, and imaging techniques were used to evaluate the degree of pore accessibility and connectivity in a tight oil reservoir within the Cardium Fm. of western Canada. In previous work, cm- to sub-cm scale variations in lithology (elementary lithological components, or ELCs) have been shown to affect flow at the core scale significantly and that reservoir quality varies with the ELCs. The fundamental controls on flow within these ELCs ( i.e. at the pore scale), however, are poorly understood. The aim of the present study was to gain insight into these controls. Small-angle and ultra-small angle neutron scattering (SANS/USANS) has revealed that while the Cardium samples exhibit a wide range in pore-size distribution, the accessibility of pores varies significantly with pore size. In particular, the large pore fraction seems to be less accessible than the small pore fraction, which is counter-intuitive. Mercury intrusion data partially support this finding. High-resolution scanning electron microscopy (SEM) imaging suggests that pores within mineral grains may indeed be disconnected/isolated. The SANS/USANS interpretations are based on a simple 2-component (pores + average mineral phase) model, however; detailed mineral mapping reveals that several components may affect significantly the scattering behavior which leads to the conclusion that a multi-phase model may be more appropriate, and that use of the conventional 2-phase model could lead to errors in calculated pore-size distributions and the percentage of disconnected porosity.

Abstract Grains within siliciclastic muds are deposited either as flocs, in which grains are generally <~10µm, or as single grains: “sortable silt,” generally > 10µm. When clay-size (<2µm diameter) particles form >30% of mudstones, pore-size distributions are controlled mainly by the interaction of phyllosilicates; these materials are ‘matrix-supported.’ Pores associated with clay-size particles are typically <20 nm, even at shallow burial. When clay-size particles comprise <~30% of the grain-size distribution, a second, much larger pore system is observed, controlled by the amount and size of sortable silt; these mudstones are ‘framework-supported.’ Compaction of these silt-rich materials occurs mainly by the loss of the largest pores, but large pores still exist up to high effective stresses in the absence of chemical compaction. Mercury injection porosimetry (MIP) gives information about pore-throat size and pore connectivity and thus provides useful data with which to estimate permeability. Models based on generally flat pore shapes can estimate the permeability of homogenous mudstones to ± a factor of 3 of the true value, but cannot be used for heterogeneous, laminated mudstones, which exhibit highly anisotropic permeabilities. As MIP gives information about pore throats and microscopy gives information about pore bodies, the two techniques generate different results. Both are required, along with other techniques such as small-angle neutron scattering and low-pressure gas sorption, in order to fully appreciate the complexity of mudstone pore systems.

Abstract Soils are highly heterogeneous entities in which organic and inorganic as well as living and non-living building blocks interact to form biogeochemical interfaces. While processes at these interfaces occur at the micrometer or submicrometer scale, they are thought to influence the behavior of soils at the global scale, e.g. soils as carbon sinks. Analytical methodologies with a high resolution are, therefore, required in order to investigate these processes with the final goal to understand biogeochemical-interface formation mechanistically. In the present study, sorption experiments of water-extractable organic matter on model minerals, such as boehmite and illite, were performed. Adsorption of organic matter on the minerals was quantified by conventional bulk-scale methods and compared with data from nanoSIMS measurements. From the data obtained, scaling factors have been developed which permit the quantification of organic matter in the secondary ion images provided by nanoSiMS.

Abstract The present study describes new instrumentation developments at the GSECARS 13-ID-E hard X-ray microprobe beamline at the Advanced Photon Source that allows for high-speed, coupled micro-beam X-ray diffractions/X-ray fluorescence/X-ray absorption fine structure mapping. These new methodologies provide Earth and environmental scientists with unique coupled tools for evaluating microscale mineralogical and chemical heterogeneities in fine-grained sediments, soils, shales, and mine tailings and associated secondary precipitates. In particular, new technologies and approaches for integrating fast µXRD mapping into routine X-ray microprobe beamline operations are described and several real-world examples are given of how this approach provides unique insights with regards to micrometer-scale heterogeneities in mineralogy and chemistry that are difficult to obtain by other methods. Examples described here include waste streams associated with mine tailings from the McClean Lake mining facility located on the eastern edge of the Athabasca Basin in northern Saskatchewan, Canada, and from mine-drainage waters from the epithermal Au-Ag-Cu deposits of the Lagunas Norte mine in the Peruvian Andes.

Abstract The development of complementary imaging techniques at beamline I18 at Diamond Light Source (Didcot, UK) to investigate the microstructure of inorganic materials is described. In particular, the use of X-ray micro-imaging techniques to understand the effect of alpha radiation on phyllosilicates, and the nature of individual catalytic particles are reported. Micro X-ray diffraction (µXRD) studies of the former materials have shown structural changes that will affect their adsorption properties, while the chemistry of the catalyst particles has been investigated using micro X-ray fluorescence, µXRD and µX-ray absorption near-edge structure mapping. The distribution of a Mopromoted Pt nitrobenzene hydrogenation catalyst has shown that some of the Pt penetrated to the core of the particle and has the same chemistry as the bulk of the Pt located on the outside of the particle. The phase distribution in an as-prepared Re-Ti-promoted Co Fischer-Tropsch catalyst is reported.