Browsing by Author "Priest, Jeffrey A."

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    Advances in Natural Fracture Characterization in Heterogeneous and Anisotropic Reservoirs
    (2020-05-05) Komaromi, Bram Alexander; Pedersen, Per Kent; MacKay, Paul A.; Ferrill, David A.; Enkelmann, Eva; Clarkson, Christopher R.; Priest, Jeffrey A.
    Natural fractures are the most common geologic structure in the Earth’s upper crust and have significant influence in a variety of geologic processes that affect many fields in geoscience and engineering related to hydrocarbon, geothermal, groundwater, and mineral resource exploration and production, carbon dioxide sequestration, waste disposal, and contaminant transport. This thesis addresses a number of problems involving natural fracture networks developed in anisotropic and heterogeneous unconventional reservoirs including: the controls on fracture stratigraphy, the relative timing and mode of natural fracturing, the variation in aperture along subsurface opening-mode fractures, and the scaling behavior of orientation dispersion. In order to address these challenges, a wide range of natural fracture datasets were collected and integrated from the subsurface and outcrop. Novel approaches to characterizing and quantifying fracture geometry are significant contributions of this thesis. Fracture characterization conducted in an organic-rich unconventional reservoir analog outcropping in the southern Alberta fold-and-thrust belt reveal that fracture stratigraphy is more strongly controlled by lithofacies characteristics than structural position, and that commonly applied scaling relationships are insufficient in describing fracture geometry. Detailed petrographic observation of the fracture-filling cements and fluid inclusion populations within the fractures reveal a complex geochemical and kinematic history among the different fracture sets. Textural evidence indicates differences in failure mode depending on lithofacies while fluid inclusion petrography and microthermometry indicate the fractures formed at depth and experienced a complex fluid migration history. Aperture measurements collected along opening-mode fractures exposed in a high-quality core of an unconventional reservoir correlate with lithology and show that previously established relationships between size and aperture are unreliable. Using a newly developed methodology, the scaling of orientation dispersion was quantified. High-resolution observations of fracture orientation, like those derived from well data, possess a large degree of variability that over-estimates the connectivity of fracture networks in reservoir-scale models. The research presented throughout this thesis serves to further the current understanding of natural fracture geometry in reservoirs characterized by heterogeneity and anisotropy. Furthermore, this thesis presents novel descriptions of natural fracture geometry and demonstrates newly developed approaches to quantifying the complexity of fracture geometry.
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    Geomechanical Characteristics of Hydrate-bearing Sands
    (2018-09-20) Abbas, Muhammad; Priest, Jeffrey A.; Hayley, Jocelyn L.; Clarkson, Christopher R.
    This thesis presents an experimental study on the geomechanical characteristics of lab-synthesized methane hydrate bearing sand. Sand was tested in four different states, namely, base sand (BS), frozen sand (FS), gas-saturated hydrate bearing sand (HS), and water-saturated hydrate bearing sand (WHS). Test specimens were evaluated for permeability, stiffness and triaxial strength. It was found that hydrate formation caused a reduction in permeability and a large increase in stiffness of sand. Triaxial test results indicate that both hydrate and ice increased the strength of sand and induced strain-softening behavior. However, HS showed higher peak strength than FS and exhibited different deformation characteristics. Stiffness and triaxial strength of WHS were lower than HS possibly due to marginal hydrate dissociation leading to a potential loss of cementation during water-saturation. The existence of inter-granular cementation in WHS was validated by analysis of experimental data using stress-dilatancy relationship for cohesive soils.
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    Geomechanical Properties of the Montney and Sulphur Mountain Formations
    (2017) McKean, Scott Harold; Priest, Jeffrey A.; Wong, Ron Chik-Kwong; Clarkson, Christopher R.
    Accurate modelling of hydraulic fracturing is critical for improving the cost efficiency and societal acceptance of unconventional hydrocarbon exploitation. This thesis investigates the geomechanical inputs required to improve hydraulic fracturing using X-Ray fluorescence, helium pyncnometry, microhardness, point load strength testing, unconfined compressive strength testing, Brazilian testing, multi-stage triaxial testing, and ultrasonic pulse transmission. The Montney Formation and its outcrop equivalent, the Sulphur Mountain Formation, are studied. Static and dynamic experimental results are interpreted and compared using a transversely isotropic framework. The Sulphur Mountain samples were more brittle and heterogeneous than Montney samples, which were harder and failed in a more stable fashion. Heterogeneity was a stronger control on failure, strength, and elastic constants than anisotropy caused by layering. Complex failure mechanisms were observed in Brazilian and triaxial tests and yielded insights into fracture propagation processes, inhomogeneity, and stress concentrations.
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    The impact of THF hydrate veins on the consolidation behavior of fine-grained soils
    (2021-01-26) Ma, Boning; Hayley, Jocelyn L. H.; Priest, Jeffrey A.; Wong, Ron Chik Kwong; Clarke, Matthew A.; Siemens, Greg A.
    Naturally occurring marine gas hydrates are ubiquitously found within sediments on continental slopes, where ongoing climate change or anthropogenic activities, such as hydrocarbon drilling and production, may dissociate the hydrates triggering slope instabilities. Large volumes of natural gas hydrate are contained within fine-grained marine sediments, observed as fracture filling veins, where these veins may hinder the sediment consolidation process resulting in weak, under-consolidated layers and possibly sea floor instability upon hydrate dissociation. Despite their potential impact, the behavior and properties of hydrates in fine-grained sediments remains poorly understood. To better understand the interaction between hydrate veins and consolidation, an experimental testing program was performed using cylindrical THF hydrate veins. Uni-axial compression tests, initially conducted on stand-alone THF hydrate specimens, indicated increasing specimen aspect ratio and reducing strain rate reduced compressive strength. Constant stress tests show the hydrate exhibits extensive plastic deformation as stresses approach failure conditions, with high aspect ratio specimens experiencing large out-of-plane deformations. Subsequent K0 consolidation tests on vein-bearing soil specimens, show considerable reduction in compressibility compared to those of the hydrate-free soils. Significant under consolidation of the soil occurs at high hydrate content and low to moderate confining stresses, although such effects are mitigated at higher confining stresses. These results indicate hydrate dissociation could lead to soil failure at low stress (i.e. shallow deltaic environments) and high hydrate content, and moderate to considerable volumetric deformation at high stresses (i.e. deeply buried sediments) and/or low hydrate content. Through this research, a better understanding of the impact of hydrate vein on the behavior of fine-grained soils has been achieved. This enables a more robust hypothesis to be developed for assessing the potential for submarine sea floor instabilities induced by hydrate dissociation through climate change. This may help evaluate the geohazard risk in marine environments and on coastal communities in these sensitive regions.
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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 Modelling using Finite Element Analysis with Advanced Soil Constitutive Models: Static and Quasi-static Approaches
    (2019-07-12) Bach, Thang Dinh; Wan, Richard; Priest, Jeffrey A.; Wong, Ron Chik Kwong
    The analysis of geostructures with failure as a central topic has been traditionally pursued through limit equilibrium methods in geotechnical engineering. In this thesis, the finite element approach together with advanced constitutive models encompassing micromechanics-based ingredients are used to examine discontinuous failure modes such as strain localization in a boundary value problem setting like in a plane-strain (biaxial) test on sand. The constitutive models used in the numerical simulations are: (1) a non-associated plasticity and fabric-based model, and (2) a micromechanically enriched model via multiscaling. These are implemented into a finite element solver following a time integration scheme that is either implicit or explicit. Under static conditions, an implicit scheme is typically adopted where a stiffness matrix needs to be inverted. Unfortunately, when a limit state, e.g. failure, is encountered, solution uniqueness is lost, thus leading to a bifurcation problem. The static problem can be alternatively formulated as a dynamic one involving velocity, acceleration and a properly chosen loading rate. This allows for an explicit time integration scheme in which the displacement field can be obtained without solving any system of equations -- so obviating the inversion of a stiffness matrix. This gives the method great potential in resolving difficulties encountered in a static simulation or in any numerical approach using the implicit scheme. To mimic the static problem in dynamic simulations, the loading rate is kept sufficiently small so that the response of the system can be quasi-static. Also, damping might be introduced to aid these simulations to converge properly toward the static equilibrium. Localized modes of failure are examined within bifurcation theory whereby there is a transition from an initially homogeneous deformation mode into one which involves localized deformations as a shear band. The anatomy of failure is examined and analyzed using the two constitutive models. It is shown that the micromechanically-enriched model gives important microstructural information such as coordination number and anisotropy at the particle level inside and outside the shear band to help understand the genesis of failure in soils.
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    Physical and Numerical Modelling of Pipelines in Elastic Visco-Plastic Soils Under Long-Term Ground Movements
    (2018-05-15) Wong, Chee Ken; Wan, Richard; Guo, Peijun; Priest, Jeffrey A.; Sudak, Leszek Jozef
    Pipelines have been constructed and designed to transport essential natural resources such as water, oil, and natural gas for the last 160 years. Many pipeline sections built are buried at shallow depths below the ground surface and through different geologic terrains. This includes complex terrains where permanent ground deformations can occur such as moving slopes/landslides, surface faulting, and ground subsidence. Pipeline sections subjected to such permanent ground deformations can yield because of large strain accumulation over time leading to large pipe stresses. The mode of pipe yielding promoted by permanent ground deformations is dependent on the pipeline axis orientation with respect to the ground movement direction. Longitudinal ground movements promote pipe buckling, transverse ground movements promote pipe bending, and complex ground movements promote a mix of pipe bending and buckling. This study introduces a set of numerical tools aimed at predicting the soil movement before a buried pipeline section reaches the onset of yielding. Various numerical tools are developed for pipelines buried in compacted clay soils such as Regina clay. Compacted clay soils are of specific interest as they exhibit significant time-dependent behavior such as creep, constant strain rate effect, and stress relaxation. The main benefit of the numerical tools developed in this thesis is for the pipeline industry to be able to continually assess pipeline performance in areas with unstable soil movements and to perform necessary remediation procedures such as pipe stress relief to prolong pipeline operation at the right time. The three phases of numerical tool development include: 1) Determination of constitutive models for compacted Regina clay and soil-pipe interface, 2) Validation of the longitudinal, transverse and vertical uplift soil resistances in existing buried pipeline guidelines through a series of physical soil-pipe prototype tests, and 3) Validation of the physical prototype test results through the creation of an Extended Finite Element Method (XFEM) numerical model. The physical prototype test results illustrate consistency with existing guidelines for transverse horizontal soil resistances, but a discrepancy for vertical uplift soil resistances. There also exists behavior discrepancy in the longitudinal soil resistances. The discrepancy in vertical pipe uplift results arises from neglecting the tensile failure mode of the soil in the guidelines. The behavior discrepancy in longitudinal loading is due to differences in adhesion factor estimation, also neglected in the guidelines. The final XFEM numerical model with cap (modified Drucker-Prager) plasticity coupled with Singh-Mitchell creep law for Regina clay demonstrate good predictions of soil-pipe interactions from physical prototype tests.
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    Stress Inversion and Damage Quantification in Tight Gas Shale with Application to Hydraulic Fracturing
    (2019-11) Jia, Suzie Qing; Wong, Ron; Eaton, David W.; Wan, Richard; Zhou, Qi; Wong, Teng-fong; Priest, Jeffrey A.
    This thesis aims to advance the quantitative analysis of stress and failure process in tight gas shale under hydraulic fracturing by integrating stress inversion, microseismic monitoring, acoustic emission and discrete element modeling techniques. With the introduction of a modified Bott hypothesis that allows for out-of-plane slip, a stress inversion algorithm is developed accounting for tensile components of the source mechanism. Synthetic test datasets are employed to quantify the error in stress determination that arises when the conventional stress inversion based on the original Bott hypothesis is applied in the presence of non-double-couple sources. The proposed method is evaluated using microseismic data collected from Barnett Shale in the Fort Worth Basin, Texas. Results show the modified method introduces a roughly 15 degree correction as compared with the inversion results from the conventional algorithm. With the same dataset, a case study is conducted to investigate the dynamic interactions between injected fluids and hydraulic fractures through the spatial-temporal analysis of microseismicity. Two types of triggering front expansion patterns are evident. With the presence of a dominant hydraulic fracture, the radius of the triggering front expands linearly with time, and the microseismic event cloud forms a planar shape with low tensile components. On the other hand, in the case of a complex fracture network with the absence of any major hydraulic fracture, the triggering front grows non-linearly with time, which can be treated as equivalent to a diffusion model. The microseismic events exhibit more tensile components and an equidimensional event cloud. Two stages of the microseismic dataset are analyzed and the derived fracture widths and fluid-loss coefficients fall into a realistic range of general observations. Two acoustic emission (AE) laboratory experiments are carried out to examine the failure behavior of Montney shale samples under conventional triaxial compression and fluid injection. Detailed analysis for the triaxial compression test includes deformation-induced velocity anisotropy, source hypocenter determinations, source mechanism analysis, and stress inversions. For the hydraulic fracturing test, the mechanical correlation with the AE activity is analyzed. The AE locations correlate reasonably well with the spatial distribution of shear fracture and hydraulic fracture imaged by X-ray computer tomography (CT) scanning. However, the signal-to-noise ratio of the AE waveform emitted from Montney shale sample is relatively low, especially for the hydraulic fracturing test, which makes the data processing quite challenging. Distinct characteristics of the AE activity in Montney shale are identified, which are different from those in granite, a type of rock that has been more extensively investigated in the past. These differences could arise from the different stress settings, the low brittleness and stiffness of shale. Additionally, the AE test under triaxial compression is simulated using dynamic micromechanical models based on the discrete element method, in which the transversely isotropic feature of Montney shale and moment tensor calculations are considered. Calibration and verification are conducted against the results of previous laboratory experiments in terms of the anisotropic behavior. The model results indicate some of the low energy AE signals might not be captured by the experimental recording system, and it further demonstrates that the shear fracture initiation contains high tensile failure components.
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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.
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    Thermal and Mechanical Modeling of Coastal Erosion Processes on Tuktoyaktuk Island, Northwest Territories
    (2021-09-16) Ouellette, Danika Sophie; Hayley, Jocelyn H.; Priest, Jeffrey A.; Moorman, Brian J.; Zhou, Qi
    Arctic coasts are particularly vulnerable to rapid and extreme erosion due to the presence of ice-rich permafrost sediment, with erosion rates varying anywhere from 1 to 20 m/yr in the region. Erosion is limited to the open-water season such that the factors controlling rates of erosion are warmer air temperatures and storm surges impacting the sensitive ice-rich permafrost coastal bluffs. Erosional processes in the Arctic are unique and consist of coupled thermal and mechanical mechanisms. The coastal community of Tuktoyaktuk, Northwest Territories, located along the Beaufort Sea coast in the western Canadian Arctic, has been dealing with the consequences of coastal erosion for many decades and will likely face displacement due to accelerating rates of erosion. In this study, a process-based thermal-mechanical erosion numerical model was developed for Tuktoyaktuk Island, which currently shelters the harbour and eastern shores of the community from wave impact, to investigate erosional processes commonly impacting ice-rich permafrost coasts including thermal denudation of the cliff face, and thermal abrasion and formation of thermoerosional niche at the base of the cliff under a storm surge to understand the impact of permafrost sediment properties on rates of erosion. It was found that erosion rates vary significantly between stratigraphic units, where sandy silt sediments have higher rates than ice rich clayey silt layers due to latent heat effects, and therefore should be considered on a site-specific scale for engineering purposes rather than the traditional cliff edge retreat method. The increased granularity improved our understanding of erosion rates on Tuktoyaktuk Island thus enabling future detailed consideration of mitigation strategies. It was concluded that massive block failure due to the formation of a thermoerosional niche under a storm surge is presently unlikely to occur on the island. For block failure to occur, either a storm of extreme duration or storm surge level is required. Lastly, it is expected that erosion rates will increase under climate-driven change such that the drivers of accelerated erosion are relative sea level rise, decrease in sea ice extent, and increase in surface air temperatures.
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    Water content of liquid acid gas and liquid propane in the presence of a hydrate phase
    (2020-12) Adeniyi, Kayode Israel; Marriott, Robert A.; Birss, Viola I.; Kusalik, Peter G.; Priest, Jeffrey A.; Chapoy, Antonin
    Natural gas coexists with water in subsurface reservoirs. Other impurities such as hydrogen sulfide (H2S) and carbon dioxide (CO2) can also be present depending on location and source. Many issues are associated with the presence of water and the acid gas (H2S and CO2) impurities during production, processing and transportation of natural gas such as solid hydrate blockage, corrosion and safety concerns. Before sale to consumers, water and the acid gas impurities are removed or reduced to meet sales and pipeline specifications. One of the viable strategies for managing the removed acid gas is injection (AGI) into underground formations either for sequestration, pressure maintenance or enhanced oil recovery. After acid gas removal, in some cases, natural gas liquid (NGL) are separated from the treated natural gas streams for use as a fuel or chemical feedstock. NGL are separated from the methane (CH4) in a cryogenic separation process, where the presence of water is highly undesirable because it can cause the formation of solid clathrate hydrates. Propane (C3H8) is a principal component of NGL and a sII hydrate former; hence, conditions at which its hydrate will form in the presence of saturated and unsaturated water are important to avoid their formation or determine how much dehydration is required. Because of the toxicity of H2S (100 ppm is the immediate dangerous to life and health concentration), there are limited dissociation data for its hydrate in the presence of water reported in the literature. Also, prior to this work, there were no water content data in equilibrium with only hydrate reported in the literature for H2S. On the other hand, hydrate formation/dissociation conditions for pure CO2 are well studied; however, analysis of the literature water content data at hydrate forming regions shows some variation regarding the pressure dependence of the measurements. These data are necessary to accurately calculate and prevent hydrate formation conditions in sour natural gas production, as well as to define the dehydration requirements for acid gas during transportation to injection facilities. In this work, the dissociation conditions for pure CO2 and pure H2S hydrates in the presence of water rich phase was measured using the phase boundary dissociation method. Also, the water content of pure CO2, pure H2S and pure C3H8 in equilibrium with their respective hydrate were measured using a tunable diode laser spectroscopy technique. These results were modelled using the reference quality Helmholtz energy equations of state for the fluid phases, and the van der Waal and Platteeuw model for the hydrate phases. The calculated results were compared to few available literature, where a good agreement was mostly observed. A thermodynamic model capable of calculating the water content and three phase loci independently using the same optimized parameters, was successfully developed for CO2. However, a single equilibrium model was not successfully found for H2S and C3H8 fluids, hence two different models were recommended for both the water content and three phase loci calculation. In conclusion, the pressure dependence of water content of these gases in equilibrium with their respective hydrates are very weak, but the water content increases as the temperature increases.