Browsing by Author "Wong, Ron C. K."

Now showing 1 - 7 of 7
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    A Conceptual Model for the Development and Persistence of Soap Holes (Unique Prairie Groundwater Discharge Features)
    (2019-04-25) Woods, Landon G.; Ryan, M. Cathryn; Lauer, Rachel M.; Karchewski, Brandon; Wong, Ron C. K.
    Soap holes manifest as localized areas of water-saturated, weak sediments which render farmland uncroppable and hazardous. The formation mechanisms and global distribution are largely unknown, despite being inferred as groundwater discharge phenomena on the Alberta prairies over 50 years ago. Here, the first conceptual model for soap hole development and persistence is created using time-series hydraulic and temperature data, electrical resistivity tomography, sediment analyses, and geochemical data (sediment and groundwater) from two locations in Alberta, Canada. The soap holes developed in smectite-rich, dominantly colloidal-size glacial sediments under strong flowing artesian conditions, resulting in quick conditions and liquefaction. Geoelectric and hydraulic conductivity contrasts (2-5 orders of magnitude), as well as groundwater geochemistry, suggest preferential groundwater flow of artesian aquifer provenance through a low permeability confining layer. In addition to natural occurrences, a proportion of soap holes may be the consequence of explosive-source seismic conducted for oil and gas exploration in Alberta.
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    Effect of Clay Fraction on Thermal-hydro-mechanical Responses of Soft Mudrocks
    (2015-09-24) Li, Biao; Wong, Ron C. K.
    Due to their low permeability, soft mudrocks often serve as geological seals for thermal recovery and nuclear waste disposal projects which are accompanied by thermal-hydro-mechanical (THM) coupled processes. The studies on the temperature, pore pressure, strain and stress developments in soft mudrock formations are the fundamentals of evaluating the risks such as wellbore collapse, casing failure and leakage through sealing rocks. Despite their importance, the variation in clay fraction and anisotropic nature of soft mudrocks has challenged the theoretical modeling and prediction of their THM responses. In this research, new approaches or models are proposed to investigate the effect of clay fraction on THM responses of soft mudrocks with emphasis on the micro-scale mechanisms. A cm-model is proposed to quantify structural states of soft mudrocks, which are dependent on clay fractions and porosities. Geomechanical properties and oriented fabric distributions are quantitatively related to structural states of soft mudrocks. Theoretical modelings on anisotropic hydraulic, static transversely isotropic (TI) elastic, and anisotropic thermal strain properties of soft mudrocks incorporating changes in the oriented fabric distribution are conducted. A modified Kozeny-Carman model is proposed to estimate the anisotropic permeability of soft mudrocks with different clay fractions. The directional tortuosity is directly linked to the fabric orientation distributions of soft mudrocks. For soft mudrocks with the similar mineralogy and porosity, logarithmic values of permeabilities decrease linearly with the increase of clay fraction. The static TI elastic properties of soft mudrocks are modeled using a differential effective-medium (DEM) approach. The elastic anisotropy is linked to the oriented fabric distribution by the Voigt approximation. A compositional thermal strain model is developed to interpret the anisotropic expansion or contraction behavior in soft mudrocks using cm-model. The compositional thermal strain model is validated by a series of experimental results. High clay fraction soft mudrocks are on the risk of having thermal contraction behavior which comes from clay dehydration or thermal plastic strain. Thermally induced tensile fracturing behavior in a high clay fraction soft mudrock is also investigated using analytical, experimental and numerical approaches. Above mentioned results are used in the comprehensive wellbore stability analysis of practical thermal recovery wells in Cold Lake area, Alberta.
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    In situ free phase gas production in initially saturated sediment
    (2019-04-24) Abboud, Jason M.; Ryan, M. Cathryn; Lauer, Rachel M.; Hayley, Jocelyn L. H.; Wong, Ron C. K.
    Free-phase gas (FPG) formation and migration in gas-saturated groundwater has geological and engineering implications. FPG has been implicated in geologic overpressurizing, and in remote earthquake triggering following FPG exsolution. FPG exsolution occurs when total dissolved gas pressure (PTDG) exceeds porewater pressure (PW) and capillary pressure (PCAP), forming FPG bodies. Existing soil-water characteristic curves show the relationship between desaturation and matric potential, but neglect desaturation that occurs as a consequence of in situ FPG formation. This research sought to observe and characterize FPG production in a previously saturated zone, and measure the responses of PTGD, PW, and water content during step-function unloading of dissolved gas-charged sediment in a loading cell filled with glass beads. A revised FPG characteristic curve showing FPG formation and consumption with respect to capillary pressure is proposed here. Future work can examine these processes with revised techniques to ensure accurate measurement of capillary pressure.
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    Mode I and Mode II Fracture Toughness of Montney Shale under Confining Pressure
    (2019-01-22) Chen, Qiang; Wong, Ron C. K.; Shrive, Nigel; Wan, Richard; Lines, Laurence R.; Martin, Charles Derek
    This thesis investigated the geomechanical properties of Montney shale using uniaxial compression, triaxial compression, Brazilian, semi-circular bending (SCB), straight-notched disk-bending (SNDB) and double shear (DS) tests. The volumetric strain method (VSM), crack volumetric strain method (CVSM), axial strain response method (ASR), and lateral strain response method (LSR) along with the crack axial and lateral strain method (CALSM) were employed to determine the crack closure and crack initiation stresses under uniaxial and triaxial compression. The LSR and ASR methods depend heavily on the initial portion of the stress-strain curve. Thus, at least two or three methods should be used when determining the crack stress thresholds. The Mode I fracture toughness under confining pressure was measured using SNDB samples with crack length to thickness ratios of about 0.2 and 0.4, respectively. The application of confining stress might induce tensile crack at the top of the SNDB sample with crack length to thickness ratio around 0.4. The tensile stresses achieved around the crack tip in confined SNDB tests under crack initiation load are close to the tensile strength of the sample and not affected by confining pressure. The Mode I fracture toughness of Montney shale is independent of confining pressure. The Mode II fracture toughness and shear fracture energy of Montney shale were measured using DS tests. The shear fracture energy values determined from post-peak portion of the axial force-displacement curve are always higher than those converted from the Mode II fracture toughness. However, with increasing confining pressure, the amount of difference decreases. Under confining pressures ranging from 0 MPa to 30 MPa, the Mode II fracture toughness and shear fracture energy increase with confining pressure. For confining pressure greater than 30 MPa, the double shear sample tends to behave ductile, evidenced by the multiple shear fractures branched out from the main shear fracture. Consequently, the double shear test is only suitable for determination of the Mode II fracture toughness of rock with confining pressure below 30 MPa.
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    Modeling Changes in Hydrate Stability Associated with Arctic Warming and its Impact on Slope
    (2018-12-17) Debnath, Khokan; Priest, Jeffrey A.; Hayley, Jocelyn L. H.; Wong, Ron C. K.
    If global warming continues at its current rate, widespread methane hydrate dissociation may occur leading to submarine slope instabilities. In this study, numerical models were developed to investigate the impact of different parameters, such as geothermal gradient, slope angle, rate of seafloor temperature rise, and hydrate saturation on the dissociated volume and potential for slope instabilities. It was found that the geothermal gradient impacts the shape of the hydrate stability zone and the pattern of hydrate dissociation. Slope stability analyses showed that steeper slopes fail earlier and produce lower dissociated hydrate volumes. Higher rate of seafloor temperature produces larger dissociated volume and leads to earlier slope failure. On the other hand, higher hydrate saturation leads to lower hydrate dissociated volume and causes to fail slope comparatively later than a slope with lower hydrate saturation.
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    Numerical Modeling of Pipe-Soil Interaction under Transverse Direction
    (2013-09-13) Farhadi Hikooei, Bahar; Wong, Ron C. K.
    Based on Winkler method, pipe can be simplified as a beam, while pipe-soil interaction can be represented by soil springs in the axial, horizontal and vertical direction. Pipe deflection and resultant forces are related to each other by coefficient K in the equation F=Kδ, where F is the resultant force and δ is the pipe displacement. This project studies pipe-soil interaction for pipelines buried in clay and sand subjected to pipeline displacement in oblique direction. The objective is to quantify the effect of soil parameters on coefficient K and maximum soil resistance. Pipe-soil behavior has been studied using the finite element software ABAQUS/CAE. There were totally 48 models with varying soil parameters, pipe burial depth and pipe-soil interaction friction to investigate the effect of each variable on pipe-soil behavior. The results have been presented in normalized force-displacement plots to identify the parameters which affect the soil resistance most. In addition they have been compared to the analytical results from ALA (2001) and proposed failure envelopes in previous studies. The results show that the maximum normal force per unit length depends on the type of soil surrounding the pipe. By comparing all the results pipe burial depth, soil cohesion, friction and dilation angles were found to have a significant effect on pipe-soil interaction and can considerably increase the maximum soil resistance.
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    A Study on Pile Setup of Driven Steel Pipe in Edmonton Till
    (2018-12-12) Ni, Jiachen; Wong, Ron C. K.; Priest, Jeffrey A.; Duncan, Neil A.
    As one of the major deep foundation types, driven steel pile (DSP) is widely used in all construction projects in Canada. Especially in rural northern Alberta areas where concrete supply is not accessible in a cost-effective manner, DSP foundation is highly preferred by heavy industrial development such as oil and gas related facilities. For driven steel pile set in the fine-grained soils, significant pile-soil setup (pile capacity gain) is expected due to excessive pore water pressure dissipation after the pile installations. In the field, pile appeared to have a much lower capacity at the end of the installation compared to long-term performance. In a fast-paced construction environment, the time cost to wait and verify the pile long-term capacity is not desired. To proceed the upper structure construction without any delay, a reasonable prediction of DSP setup is required. Extensive research has been conducted to explain the mechanism and magnitude of the pile-soil setup effect. However, very limited study has been done on the rate / time of pore water pressure dissipation in clayey soils. This study is aimed to provide a case study of the pile setup effect of DSP set in Edmonton clay till by using dynamic load testing, and wave equation analysis methods. A finite element numerical model is built to illustrate the pore water pressure dissipation and increase in radial effective stress, and allow geotechnical engineers to assess the pile setup behaviour with available soil testing results and reasonable assumptions.