Browsing by Author "Priest, Jeffrey"
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Item Open Access A Modified Framework to Describe Stress-Strain Behavior and Volumetric Response of Hydrate-Bearing Sand(2023-09-19) Goharzay, Maral; Priest, Jeffrey; Wan, Richard; Karchewski, Brandon; Sudak, Les JozefGas hydrate-bearing sands (GHBS) contain a large volume of methane in the form of hydrate, which makes them an attractive source of energy. Hydrates exert a strong influence on the mechanical properties of sands, where increasing hydrate saturation (Sh) of the pore space leads to an increase in peak strength, post-peak strain softening, and dilation. Methane recovery from hydrates requires dissociation of the hydrate, which involves coupled and complex processes involving methane gas generation, increases in fluid pressure and reduction in effective stresses, along with changes in the mechanical behavior of GHBS, all of which may present potential geo-hazards and engineering challenges. Field-scale hydrate production tests have been carried out to evaluate the potential for methane recovery, however, these have sometimes ended abruptly due to technical failures. For this reason, numerical models are required to evaluate the long-term feasibility of hydrate production and reduce the risk of failure. Thus, the development of an appropriate constitutive geomechanical model is necessary in order to conduct realistic numerical analyses to assess the long-term response of the GHBS reservoir during hydrate production. Early attempts at modeling the geomechanical behavior of hydrate-bearing soils modified the Mohr-Coulomb (MC) model by incorporating a relationship between cohesion (𝑐) and hydrate Sh of the pore space. As the MC model did not capture the overall stress-strain, including volumetric, response of hydrate-bearing sands, recent models have considered Rowe's stress-dilatancy theory. In this model, the increase in strength is related to dilation of hydrate-bearing sand and assumes the impact of hydrate in the pore space to be kinematic in nature (function of soil friction) and ignores any 𝑐 component of the hydrate. Although modifications to Rowe’s theory have included a 𝑐 component, both soil friction (kinematic) and 𝑐 are considered to be constants, although recent laboratory studies suggest that 𝑐 is mobilized and subsequently lost during shearing. In this study, a stress-dilatancy model is developed to better describe stress-strain response of GHBS, including 𝑐 effects. The model includes extensions to the well-known equations for Rowe’s theory to incorporate functions that consider the unique hydrate characteristics, as well as soil density and 𝜎3. The developed model better represents the geomechanical stress dilatancy behavior applicable to GHBS that can easily be implemented in standard elastoplastic models for use in numerical simulations to assess the impact of hydrate, and its dissociation, on the long-term response of a GHBS reservoir.Item Open Access Advanced Failure Analysis in Geomaterials: Application to Reservoir Geomechanics(2017) Gong, Xu; Wan, Richard; Hicher, Pierre-Yves; Coombe, Dennis; Sudak, Les Jozef; Priest, Jeffrey; Wong, Ron Chik-KwongThe manifestation of failure in geomaterials and its proper analysis are constitutive aspects that geotechnical engineers are faced with routinely in design. In most instances, geostructures are examined at the ultimate plastic state where failure is deemed to occur along a slip surface where plastic deformations localize. This plasticity condition is classically analyzed with the Mohr-Coulomb failure criterion. However, other forms of failure also exist where the localization of deformations is totally absent such as in the case of static liquefaction. This distinct mode has been coined as ‘diffuse failure’ which has the peculiarity of occurring at stress levels well below the plastic limit, thus rendering a classic Mohr-Coulomb analysis insufficient. Hence, the signature of failure in geomaterials seems to be directly related to two principal modes by which it is manifested: one with localized slips, and another variant where deformations are diffused without any localization phenomena. In order to address the many subtle features of failure, a clear mathematical representation of the underlying physical phenomena is needed. In this thesis, failure is considered as an instability of homogeneous deformations, and as such the observed failuremode is a direct result of the underlying constitutive equations admitting bifurcations in solutions for the material response. Different failure criteria are derived, serving as failure indicators which signal the various modes that emerge during loading history following a certain hierarchy. To translate theory into engineering practice, the thesis endeavors to apply the above mathematical aspects of failure in the study of geomaterials undergoing multiphasic flow and thermal transport such as in the extraction of heavy oil from an oilsand reservoir in Alberta, Canada. Governing equations describing the physics of all phases (solid, water, gas and oil) involved are formulated within mixture theory using continuum mechanics principles. A special computational strategy is adopted to solve efficiently the coupled system of equations using both finite elements and finite differences. Finally, the developed computational model is tested in the context of an actual oil field case study implicating steam injection and oil production in an oilsand reservoir in Alberta, Canada. To close the loop, attention is obviously focused on material failure concepts developed in the first part of the thesis. Geomechanical properties that enter the computational model are obtained from a separate comprehensive laboratory testing of shales and oilsands at high temperature and pressure.Item Open Access Age of Soils: A Measure of Creep History(2017) Guo, Junwei; Wong, Ron Chik-Kwong; Wan, Richard; Priest, Jeffrey; Sudak, LesTime-dependent behaviors of soils are critical for engineering design. Results of one-dimensional (1-D) constant rate of strain (CRS) tests on clays show that there is an existence of unique relationship between current stress and strain state for a given constant strain rate, irrespective to previous stress-strain-time history. In the present study, this relationship is employed to estimate the creep rate during the CRS test. It is found that the creep rate is consistently related to distance from current stress-strain state to the instant compression line, which is the creep void ratio or creep history, termed age of soils. Based on the creep rate as a function of creep strain or age of soils, the stress relaxation rate function is derived through the correspondence principle. Age contours are iso-creep rate lines defining the creep rate field in stress-strain space. Creep Balanced State equation states that CRS path will converge to a iso-creep rate line. This equation is used to determine the CRS path and quantify the rate effect on preconsolidation pressure. Age- and pressure-dependent secondary compression coefficients are incorporated in the above framework.Item Open Access Characterization and Treatment of Oil Sands Blowdown Water(2016) Martez, Vitselle; Achari, Gopal; Langford, Cooper; Nowicki, Edwin; Priest, Jeffrey; Gay De Montella, Rafael; Singhal, AshokThe high concentrations of organic and inorganic impurities from the blowdown water of the Steam Assisted Gravity Drainage (SAGD) process in the oilsands operations cause significant operational and environmental issues. In this study the actual SAGD boiler and evaporator blowdown was investigated and found to contain complex mixtures of TSS, TOC and TDS. Further investigations were focused on SAGD boiler blowdown (BBD) water and included the screening of seven advanced oxidation processes (AOPs) which resulted in the selection of three O3/UV, H2O2/UV and O3/H2O2/UV AOP’s for testing TOC degradation in each sequence of the HCl-acidified, CaO-alkalized, CO2-neutralized and original BBD waters. O3/H2O2/UV irradiation showed effective degradation in the neutralized, alkalized, acidified and original BBD at 70%, 68.3%, 55.6% and 9.4% TOC removal. An unique, semi-batch treatment system was designed, integrated and evaluated using HCl-acidified, CaO-alkalized, CO2-neutralized BBD water in three stages; (1) Stage A; precipitation and centrifugation for TSS and TOC removal, (2) Stage B; O3/H2O2/UV for TOC degradation, and (3) Stage C; reverse osmosis filtration for the TDS and residual TOC removal. Stage A results showed that the HCl-acidified BBD at pH 4.2 achieved the highest TOC removal by 44.7% and TSS by 98.5% likely because the net reduction in the molecular electrical repulsion and neutralization of acid groups led to their aggregation and removal. Stage B results showed that the O3/H2O2/UV achieved the highest TOC removal of 68.0% in the CO2-neutralized BBD likely because interferences of the competing inorganic carbonate and bicarbonate species that scavenge hydroxyl radicals were minimized. Stage C results showed that reverse osmosis filtration purified all samples, but achieved the highest removal of 99.7% residual TOC and 98.8% TDS in the HCl-acidified BBD and the highest permeate recovery at 40.5% in the alkalized and neutralized BBD. Since there is a lack of published information on SAGD blowdown the result of this study is significant and a precursor to advancing future research solutions.Item Open Access Compression and Flow Behavior of Proppants in Hydraulically Induced Fracture(2016) Man, Shuai; Wong, Ron Chik-Kwong; Wan, Richard; Priest, Jeffrey; Dong, MingzheShort-term and long-term compression behavior of single proppant grains were thoroughly studied by diametrical compression tests and DEM/FEM simulations. Hydroprop showed the highest single grain crush-resistance while ceramic proppant grains with coarse surfaces were susceptible to creep behavior under load. One-dimensional compression tests under various stress levels and temporal conditions were systematically carried out to investigate the time-independent and time-dependent crushing behavior of proppant grain packs. Baylic Sand was the most crushing-prone whereas the OxSteel was the least. Most proppants showed creep behavior under long-term compression. Rock-proppant interaction tests were also performed which cast light on the proppant crushing and embedment under the field conditions. Pressure gradients of proppant-water slurries flowing through a small-diameter pipe were experimentally investigated and mimicked by DEM-CFD simulations. A generalized Darcy-Weisbach equation was proposed for the prediction of pressure gradients.Item Open Access Continuum Representation of the Micromechanics of Granular Materials via Homogenization and Statistical Approaches(2015-12-24) Pouragha, Mehdi; Wan, Richard; Wong, Ron C.K.; Priest, Jeffrey; Federico, Salvatore; Rothenburg, LeoGranular media display distinct constitutive features such as phase transition, dilatancy and localization that are difficult to analyze within traditional continuum mechanics. Such shortcoming has led to a paradigm shift from continuum to micromechanical approaches to highlight the discrete nature of granular media. Recent micromechanical studies have proven that most subtleties observed in granular mechanics can be clearly explained as a collective response of a large number of particles interacting through simple physics at the micro-/meso-scale. However, the emergence of an analytical constitutive model transcending the various scales highly relies on the extent to which statistical generalization methods are applicable to the problem at hand. From a statistical viewpoint, a continuum constitutive model can emerge from homogenizing discrete mechanisms if: (1) all the concerned parameters at the macroscopic level are expressed in terms of the same set of statistical descriptors, and (2) there exist enough internal consistencies among the statistical descriptors to ensure bijectivity of the formulation. Therefore, the current study sets out to first develop such a multiscale relation between strain and contact structure evolution through an investigation of the topology of the underlying Dirichlet tessellation network. A detailed study of the various mechanisms operating at the particle scale has resulted into an expression for macroscopic strain in terms of key micro-variables. These, together with the well-established ``Love-Weber'' formula for stress, satisfy the first above-mentioned requirement of having a common basis for statistical description. The second requirement about internal consistencies is addressed by exploring the interrelation between the evolution of the various micro-variables. For instance, changes in force network statistics enter an analytical scheme to describe the loss and gain of contacts during the initial stages of loading. On the other hand, post-yield microstructure characteristics have been studied by considering redundancy in the static equilibrium of the force network. Hence, a reference material state that unifies jamming and critical state concepts with the yielding properties of granular materials is proposed. Finally, a plastic potential naturally emerges from the proposed analytical framework which describes the stress-dilatancy relation of granular media with only a few material parameters, all micromechanical in nature.Item Open Access Experimental and Numerical Exploration of Electromagnetic-Induced Fracturing of Clay-Shale(2022-09) Chen, Xiaolin; Wan, Richard; Priest, Jeffrey; Wong, Ron; Okoniewski, Michal; Zhou, Qi; Chan, DaveThe rapid electromagnetic (EM) heating of saturated clays and shales offers a potential means of selectively fracturing interbedded shales, and thereby enhancing oil production while maintaining the caprock integrity of shaley oil sand reservoirs during thermal production process. It is hypothesized that fracturing will occur in an extremely low permeability porous medium due to a large increase in pore fluid pressure by electromagnetic wave heating. As opposed to classical resistive heating, the EM heating of saturated clays/shales is mainly achieved by the interaction between radiating electromagnetic waves and polar water molecules. The above provides the backdrop for the thesis which aims at understanding the underlying fracture and thermal stress mechanisms of EM heating in a geomaterial. As such, comprehensive laboratory experiments are conducted in a specially designed EM heating apparatus. Challenges of the experimental endeavor are highlighted, given the susceptibility of measurement sensors with electromagnetic radiation. Four scenarios of tests are performed on kaolinite clay samples, a surrogate for clay-shale, whose basic properties are measured prior to EM heating. The use of kaolinite samples allows for the conduct of repeatable tests and provides a benchmarking for future tests on actual clay-shale core samples. Results of undrained tests at different confining conditions show that the clay will lose its structural integrity when the thermally induced excess pore pressure in the sample is higher than its tensile strength plus confining pressure. Alongside with the above lab experiments, a two phase (water-steam) fully coupled Multiphysics (EM wave propagation/thermal/fluid/mechanics) model is developed to study the major mechanisms of rapid EM heating. The finite element method is employed with a segregated numerical strategy to solve this highly nonlinear problem using a commercial software COMSOL Multiphysics. The simulation results indicate that pore water pressures develop mainly due to the high contrast between the fluid and solid phase coefficients of thermal expansion. Numerically predicted zones of fracture initiations and patterns are verified against experimental observations using a Mohr-Coulomb failure envelope combined with a tension cutoff.Item Open Access Extended-FEM analysis of injection-induced slip on a fault with rate-and-state friction: Insights into parameters that control induced seismicity(Springer, 2023-03-09) Hosseini, Navid; Priest, Jeffrey; Eaton, DavidThe extended finite element method (X-FEM) is utilised to simulate the behavior of a heterogeneous fault characterized by rate-state frictional rheology, embedded within a poroelastic medium. The displacement and pore-pressure fields that are discontinuous across the fault are computed using X-FEM, by enriching the standard finite element approximation with additional degrees of freedom for elements intersected by the fault. We investigate a Mw 4.1 injection-induced earthquake in western Canada; this model incorporates depth-varying rate-slip behavior wherein a high-pressure zone due to hydraulic fracturing stimulation intersects the fault within a stable layer, producing aseismic slip that progressively loads an unstable fault region, thereby triggering dynamic rupture. Parametric studies using our numerical approach provide insights into the influence of rate-state parameters on fault activation, as well as hydraulic properties of a damage zone that surrounds the fault. Results confirm that aseismic slip near the injection zone propagates outwards to seismogenic unstable regions of the fault. The coseismic slip profile, seismic moment, and slip latency are determined by the difference a − b for rate-state parameters of the unstable fault regions. Hydraulic diffusivity in the damage zone controls the rate of pore-pressure diffusion along the fault, which affects timing of the initial seismic event and aftershock productivity.Item Open Access Influence of Particle Size Distribution on Mechanical Behavior of Hydrate-bearing Sands(2021-10-27) Zafar, Raheel; Priest, Jeffrey; Hayley, Jocelyn; Wong, Ron; Khoshnazar, RahilGas hydrates are natural ice-like, crystalline solid compounds that form in both permafrost and deep-water oceanic sediments. The large volumes of methane gas stored in hydrates make them an ideal resource for the world’s future energy demands. Hydrate-bearing coarse-grained sand sediments have great potential for commercial exploitation due to their high permeability and high hydrate content within pore space. The formation of hydrates significantly increases the strength and stiffness of host sediment and their dissociation directly impact host sediment stability. A recent study on natural hydrate-bearing sediments reported a significant correlation between sediment particle size and its strength and stiffness. Therefore, to ensure sustainable gas production activities, the effect of sediment particle size on the large-strain mechanical response of hydrate-bearing coarse-grained sediments needs to be investigated. This thesis reports on an experimental program that allowed the controlled and homogenous formation of gas hydrates within laboratory synthesized sand specimens and their subsequent laboratory testing to investigate the effect of particle size on their mechanical response. Specimens containing a different proportion of large particle sizes were prepared and their mechanical properties were investigated in two states: base sand (BS) and hydrate-bearing sand (HBS). Results show that the hydrate growth rate appears to be dependent on the particle size of sediment, with a decrease in sand particle size increasing the hydrate growth rate. Triaxial test results show that the strength and stiffness of HBS specimens strongly depend on particle size, hydrate saturation, and applied effective stress. The influence of particle size becomes evident at high hydrate saturations (> 46%). Increasing the proportion of large particles within the sediment matrix significantly increases the strength and stiffness of HBS specimens. The cohesion also exhibits dependency on particle size. An increase in the specific surface areas of sand grains reduces the cohesion of HBS specimens.Item Open Access Innovative Near-Surface Mounted Iron-Based Shape Memory Alloy for Strengthening Structures(2017) Rojob, Hothifa; El-Hacha, Raafat; Shrive, Nigel; Duncan, Neil; Priest, Jeffrey; Sudak, Leszek; Al-Mahaidi, RiadhA recent development of smart materials called Iron-based Shape Memory Alloys (Fe-SMA) envisages a new perspective in the rehabilitation of structures. SMAs are metallic alloys that recover their original shape through heating. Utilizing this interesting feature of SMAs to retrofit reinforced concrete (RC) beams is the main objective of the current research project. An innovative active self-prestressing technique using Near Surface Mounted (NSM) Fe-SMA bars/strips for flexural strengthening of RC beams is proposed. The pre-strained (elongated) Fe-SMA bar/strip is anchored in a pre-cut groove in the tension side of the RC beam; heating the bar/strip will then trigger the recovery of the induced strain (i.e. the bar/strip tendency to shorten). However, due to the restrained ends of the bar/strip, a tensile force develops instead (i.e. prestressing force). In this case, no jacking tools or special anchorage systems are required. The main objective of this study is to examine the potential capability of the newly developed Fe-SMA as an active retrofitting material for RC beams. Consequently, its contribution to the flexural performance enhancement of the RC beam at service and ultimate load conditions was investigated. In addition, the long-term performance of the strengthened beams subjected to freeze-thaw cycles and fatigue loading was studied. In total, 11 RC beams were tested; 7 beams with a length of 2 meters and 4 large-scale beams with a length of 5 meters. The experimental test results revealed the effectiveness of the proposed technique in enhancing the flexural capacity of the RC beams at the service and ultimate load conditions, while maintaining a ductile failure mode similar to the under-reinforced beams. The strengthened beams tested under severe freeze-thaw cycles and fatigue loading showed a good performance except for the bonding between the Fe-SMA bars and the grout which experienced a rapid deterioration and resulted in a rupture of the Fe-SMA bar at the anchorage location under fatigue loading.Item Open Access Integrated Simulation, Characterization and Enhanced Recovery Strategies For Shale/Tight Formations(2017) Kanfar, Mohammed; Clarkson, Christopher; Chen, Zhangxing; Gates, Ian; Hoffman, Todd; Priest, JeffreyThe recent economic downturn poses a challenge to the development of oil and gas prospects, especially unconventional or shale assets. As a result, it is prudent to improve well design and placement, and to investigate alternative hydrocarbon extraction methods. To help achieve this goal, this dissertation focuses on improving the following engineering approaches: rock and fracture characterization, and huff-n-puff design and model setup. Improved characterization is necessary for reservoir modeling which can then be used to find the optimum well design and placement. Huff-n-puff is an enhanced oil recovery technique that has been successfully applied to conventional reservoirs and may prove equally viable for unconventional assets. There are several approaches for rock and fracture characterization. One class of methods utilizes readily available production data to inverse model for reservoir parameters. If certain conditions are met, analytical methods can be used to determine reservoir parameters—such methods are referred to as rate transient analysis (RTA). On the other hand, if conditions are not met, sophisticated reservoir simulators are used to history match production data and thereby inverse model reservoir parameters. This dissertation improves existing analytical solutions that results in errors if applied to bilinear flow (a flow regime that is occasionally observed in shale/tight wells) in gas reservoirs. The improvement is incorporated as a correction factor applied to the bilinear flow analysis plot. In addition to this correction, this dissertation presents an innovative framework that utilizes compositional simulation, multi-objective genetic algorithms, and information theory to characterize reservoir parameters. In addition, the framework incorporates flowback data into the analysis to further improve the characterization results. This framework can be applied when conditions for RTA are not satisfied. The other engineering approach that is improved in this dissertation is huff-n-puff design and model setup. Although huff-n-puff has been successfully applied in conventional reservoirs, its success is yet to be established for unconventional reservoirs. A number of simulation and lab studies have been published to date. While lab studies agree that huff-n-puff is successful for unconventional reservoirs, simulation studies disagree. Consequently, this dissertation uses numerical simulation to investigate possible reasons for this conflict. In addition, this dissertation also endeavours to find key factors that influence huff-n-puff success. Finally, the feasibility of huff-n-puff is evaluated by utilizing genetic algorithms to find the optimum huff-n-puff design that maximizes net present value. In summary, this dissertation provides new methods for improved fracture and reservoir characterization and huff-n-puff design. A correction factor is derived that can be combined with existing analytical solutions to improve the characterization of fractures. A framework is also provided to characterize unconventional reservoirs; this framework can be used whenever RTA assumptions are violated. Moreover, this dissertation investigates huff-n-puff simulation, and finds that conflicts in the literature are probability caused by model setup, specifically grid refinement, and fracture pseudo-width. Furthermore, it concludes that higher fracture density, higher fracture complexity, presence of natural fractures, and delayed huff-n-puff can improve the ultimate recovery. Finally, the dissertation demonstrates that huff-n-puff can be economical if the huff-n-puff design is optimized. Two major design criteria are short injection, and longer soaking times. These findings can help operators improve reservoir characterization, and choose whether huff-n-puff is suitable for their respective wells. Importantly, these aspects can ultimately help reduce cost, a necessity in today’s economic climate.Item Open Access Micromechanical Analysis of Stresses and Instabilities in Wet Granular Materials: Homogenization and Discrete Element Approaches(2023-10-30) Farahnak Langroudi, Mojtaba; Wan, Richard; Nicot, Francois; Buscarnera, Giuseppe; Federico, Salvatore; Priest, Jeffrey; Jasso, MartinThis thesis presents the micromechanical analysis of wet granular material behavior within the pendular regime where particles are held by distinct liquid bridges through the action of capillarity and thin film adhesion. The presence of air and liquid phases within the pore space of solid particles significantly impacts the mechanical properties of wet geomaterials, and hence their failure behavior as a material instability phenomenon. The first question is how does the stress transport to the different phases (air, water, and solid) as a function of the internal microstructural construct and interfaces? An analytical expression of the internal stress partitioning between air, water and solid is formally derived via a homogenization scheme which upscales the interfacial surface tension physics at the pore scale to the macroscopic (specimen) scale. Focusing particularly on fine particles in the micrometer range, the study encompasses the two dominant mechanisms in wet conditions: adsorption and capillarity. These mechanisms consider the role of adsorbed liquid films governed by a disjoining pressure and liquid bridges arising from matric suction as a water potential. The final derivation reveals the tensorial nature of an adsorptive-capillary stress variable that is closely linked to the topology of the fluid partitions in the pore network, and is hence non-spherical. The next question is, among the various stress components, how does the contact (solid skeleton) stress tensor relate to the strain tensor to describe the constitutive behavior of wet granular materials? A multi-directional probing numerical experiment on a Representative Element Volume (REV) is implemented in Discrete Element Method (DEM) simulations to link increments of stresses to increments of strains through a bridging of grain/pore scale and the REV scale. Essentially, the incremental constitutive tangent operator is reconstructed through a perturbation analysis. This methodology also offers the possibility of micromechanically investigating bifurcation phenomena somewhat unexplored for partially saturated conditions. As a result, aspects of material instability, failure mechanisms, and shear band localization are examined by probing into the spectral characteristics of the micromechanically and hydromechanically informed tangent operator and the second-order work instability criterion for both dry and wet states.Item Open Access Multi-scale analysis of the influence of sedimentary fabric and composition on the geomechanical properties of organic-rich mudstones: a case study from the Duvernay Formation, Alberta, Canada(2021-06-24) Venieri, Marco; Pedersen, Per; Eaton, David; Ghanizadeh, Amin; Priest, Jeffrey; Wust, Raphael; Hart, BruceIn this research, the influence of sedimentary fabric and composition on the geomechanical properties of organic-rich mudstones has been investigated at the seismic, wireline log and core scale with resolution ranging from 50m- to the cm-scale. Our analysis reveals that a relationship is observable between composition, fabric, and elastic properties of the rock units at each scale of observation. Generally, carbonate-rich facies show the highest values of Young’s modulus (YM) and Poisson’s ratio (PR); clay-rich facies show the lowest YM and intermediate PR; biogenic silica-rich (“organic-rich”) facies show intermediate YM and the lowest PR. At the seismic scale, for which the resolution does not allow for assessment of intra-Duvernay mechanical heterogeneity characterization, significant difference in computed elastic moduli is observed between the organic-rich Duvernay Formation and its bounding strata which show different mineralogy. Analysis at the m- and cm-scale of compositional and geomechanical properties of the Duvernay Formation from outcrop samples reveals significant heterogeneity within the Duvernay Formation. Our research suggests that geological and geomechanical heterogeneity within the Duvernay Formation is facies-dependent. In fact, organic-rich mudstones show nearly twice as much variability in composition and mechanical hardness than carbonate-rich facies. This, in conjunction with our analysis of vertical and lateral geological heterogeneity within the Duvernay Formation from subsurface data, suggests that a cautionary approach should be adopted when using averaged or upscaled data for subsurface modeling which risk oversimplifying reservoir complexity. In this case, heterogeneity of rock properties should be included in reservoir models as a measure of uncertainty on the input data.Item Open Access Performance of Eccentrically Loaded Reinforced Concrete Columns Confined with Shape Memory Alloy Wires(2017-12-15) Abdelrahman, Khaled; El-Hacha, Raafat; Duncan, Neil; Shrive, Nigel; Priest, Jeffrey; Federico, Salvatore; Al-Mahaidi, RiadhSmart materials such as Shape Memory Alloys (SMA) are recently utilized for strengthening and repairing of concrete structures. The most common form of SMA wires used for concrete confinement applications is Nickle Titanium (NiTi) because it possesses unique thermo-mechanical properties such as the Shape Memory Effect (SME) along with high recovery stress (up to 600 MPa) and strain (up to 8 %). Initial investigations reported in the literature show that actively confining concrete columns with SMA wires can enhance the strength and significantly increase the ductility of concrete. To date, the vast majority of experiments on SMA-confined concrete have considered short, unreinforced, small-scale concrete cylinders subjected to concentric axial loading. The objective of this study is to present a systematic study of medium-size reinforced concrete circular columns, internally reinforced with longitudinal steel bars and transverse steel stirrups and externally confined with SMA wires, subjected to eccentric loading. Test data are compared against identical unconfined reinforced concrete (RC) columns, and confined RC columns strengthened passively using Carbon Fibre Reinforced Polymer (CFRP) wrap sheets, in order to quantify and verify the effectiveness of the active SMA-confinement method. In addition, an analytical model is presented to describe the behaviour of SMA-confined RC columns subjected to combined axial loads and bending moments. A parametric study was conducted to evaluate the effects of certain parameters on the overall response and the axial-flexural diagrams of the SMA-confined RC columns. The results of this study show that the RC columns confined with active SMA spirals exhibited significant enhancement in the strength and ductility compared to the unconfined RC columns subjected to varying load eccentricity. Additionally, the SMA-confined RC columns demonstrated superior overall performance when compared to the conventional passive CFRP-confined RC columns. The results of this study also show that the proposed analytical model conservatively predicted the axial load-bending moment response of the SMA-confined RC columns. The RC column confinement parameters investigated, namely the concrete compressive strength, the volumetric ratio of the SMA spirals, and the internal longitudinal steel reinforcement ratio, significantly influenced the load-moment interaction response of the SMA-confined RC columns.Item Open Access Rate and State Friction Analysis of the Upper Devonian Duvernay-Wabamun Interval and the Lower Triassic Montney Formation(2022-01-12) Hernandez Borbon, Jose Rogelio; Priest, Jeffrey; Shrive, Nigel; Clarkson, ChristopherProduction of unconventional hydrocarbon resources is an important activity for the economic prosperity of North America. To enhance productivity from unconventional reservoirs in the Western Canada Sedimentary Basin hydraulic fracturing (HF) is routinely employed, which involves the injection of highly pressurized fluids into the subsurface to generate multiple fractures within hydrocarbon reservoirs and increase overall permeability. Along with the increase in HF activities, there has been a parallel increase in induced seismic events in the vicinity of the injection wells. Fault reactivation is accepted as the triggering mechanism for induced seismicity. However, the underlying mechanism that leads to fault reactivation is still not very well understood. Recent studies have suggested that seismic slip of a fault, whose epicentre may be at some distance from HF activities, may arise due to loading from HF driven aseismic slip of the fault near the injection zone. The occurrence of aseismic or seismic slip is dependent on the rate and state frictional properties of the rock. To gain insights into the rate and state friction behavior of reservoir rocks that are typically subjected to HF stimulation, and surrounding formations, in Western Canada, a series of direct shear tests including velocity stepping and slide-hold-slide stages were conducted using a double direct shear assembly under a range of stress conditions to capture those that may occur in the subsurface. Simulated fault gouge material was obtained from samples belonging to the Perdrix, Shulphur Mountain, Ireton, Winterburn and Wabamun formations and groups, to assess the range of rate-state frictional behavior that might occur in the subsurface. Results show that frictional strength and slip stability of the rock samples were dependent on applied normal stress conditions and inherent rock mineralogy. For the majority of the rocks tested aseismic slip was the dominant response, although a small number of rock samples exhibited seismic slip at low normal stresses. Understanding of the rate-state behavior of rock formations will help in assessing the potential contribution of aseismic loading on earthquake nucleation in Western Canada, and lead to greater insights into the triggering of seismic events caused by hydraulic fracturing processes.Item Open Access The Influence of Tetrahydrofuran Hydrate Veins on Fine-Grained Soil Behaviour(2016) Smith, William; Grozic, Jocelyn; Priest, Jeffrey; Wong, Ron; Lauer, RachelGas hydrates are found in coarse-grained and fine-grained soil worldwide, within deepwater marine sediments and beneath permafrost. Natural gas hydrates can be formed within fine-grained marine sediments as sub-vertical complex fibrous vein structures. A better understanding is required of the geomechanical behaviour of fine-grained hydrate-bearing soil that resemble fracture-hosted natural deposits, as they have the potential to pose a significant geohazard. This thesis presents a simple, repeatable laboratory procedure for the formation of simplified, vertical, cylindrical, synthetic tetrahydrofuran hydrate veins centred within fine-grained soil. The geomechanical impact of the different-sized tetrahydrofuran hydrate veins was then determined by carrying out consolidated and unconsolidated undrained compression tests on specimens. These results were then used to develop relationships between the hydrate vein size and the strength and stiffness of the fine-grained specimens. The application of these relationships to natural fine-grained sediments hosting gas hydrate veins is then discussed.Item Open Access The Role of THF Hydrate Veins on the Geomechanical Behaviour of Hydrate-Bearing Fine Grained Soils(2016) Wu, Jiechun; Priest, Jeffrey; Grozic, Jocelyn; El-Hacha, Raafat; Clarke, MatthewNatural gas hydrate, which can form complex vein structures within fine-grained sediments, pose a significant geohazard if the hydrate were to dissociate. Therefore, understanding the role of hydrate veins on the geomechanical behavior of hydrate-bearing fine-grained sediments is essential for sediment stability assessment. This thesis presents the results of a laboratory study conducted to further understand the fine-grained soil behaviour with simplified cylindrical tetrahydrofuran (THF) hydrate veins within the soil. Compression tests were conducted on standalone THF hydrate veins of different diameters to determine their strength and stiffness. Subsequent consolidated undrained (CU) triaxial tests were conducted to determine the behaviour of fine-grained soils containing the same-size hydrate veins. Factors such as vein size and effective stress were considered to develop relationships between vein size and strength/stiffness of the hydrate-bearing soil. The results are used to consider the role that hydrates veins may have on natural sediments formed at different depths.