The study presents a numerical analysis of series of unanticipated events that took place upon the excavation of a landfill in a deep deposit of clayey soil in southwestern Ontario, Canada. During the excavation of a landfill cell to be used for waste disposal, unexpected lateral slope movements were observed followed by gas and water venting in several locations (while the excavation in low permeability clayey till was about 14m above the underlying aquifer). The clayey till is known to be underlain by permeable, natural gas bearing rock, and gas has been diffusing through the clayey deposit over about the last 13,000-15,000 years. Preliminary 2D and 3D elasto-plastic effective stress analyses using conventional soil mechanics –similar to what was used in design- are used to capture the general behaviour of the excavation. However, the analyses revealed the need for model modification to account for other governing factors (gassy soil and hydrofracturing) to be able to explain the mechanism that might have lead to the evolution of gas vents and upward water flow through the thick shale aquitard. The clayey deposit contains silty sand lenses at different elevations. The upward diffusion of methane and chloride from the bedrock aquifer through the clay till is modelled and the potential for chloride migration contributing to the exsolution of methane due to reduction in methane solubility is discussed. Two approaches to modelling the lenses are examined where gas exsolution either occurs prior to or during the excavation. The FE model is modified to account for hydrofacturing and gassy soil behaviour (for sand lenses). 2D and 3D forensic modelling studies are presented examining the potential causes for the unanticipated movements and the gas and water venting observed during the excavation. The model investigates the role of presence of gassy sand lenses and of the presence of a discontinuous weak sandy clayey silt layer between the bedrock and the low permeability till on the hydrofracturing path and gas venting. Finally, a parametric study is conducted to examine the effect of different parameters on the soil behaviour when excavated. Recommendations regarding further excavations within the same soil deposit are presented. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2012-08-23 16:33:05.062

Hydrocarbon production from mudrocks (“shales”) is vital to global economic growth and smooth transition to a clean energy infrastructure. The commercial development prospect of a shale play depends on its evolution history over millions of years. Economic hydrocarbon production from shale starts after hydraulic fracturing, that creates a multiscale fracture network leading to an increased overall permeability. The properties of the stimulated rock can be assessed via parameters at different scales (nano-, micro- and macro-scale). Better understanding of these parameters is the key to predicting well productivity and profitability. This work aims to deepen the understanding of the multiscale parameters that define effective hydraulic fracturing. To investigate permeability increase in shales, we start with a model of micro-capillary in contact with nanopores . We show that the nanopores that discharge gas into a fracture network in the source rock significantly increase and extend gas flow into the hydrofractured horizontal wells. We then use a fractal stimulated reservoir volume model to match production histories of 45 Barnett gas wells and to quantify connectivity between the nanopores and the fracture network. This model relies on a source term, ${s}$, and fracture permeability $k_f$ . Our analysis shows that the different degrees of coupling between ${s}$ and $k_f$ create distinctly different types of fracture networks after rock stimulation and impact the well production profiles. We then couple the fractal SRV model with universal scaling $τ − M$ model to simulate production history of 1000 wells each in the Barnett, Marcellus, Haynesville and Eagle Ford shale plays. The analysis shows the coupled effect of stimulated surface area $A$, fracture half-distance, $d$, and the fractal dimension ,$D$, on production and economics of gas production. These parameters define the key differences between different shale plays in the US. Finally, we simulate microfracturing associated with hydrocarbon expulsion in the Tuwaiq Mountain source rock, Saudi Arabia, and propose the pore/microchannel blocking by bitumen/pyrobitumen as a viable mechanism of sustaining the high pore pressure in the source rock for millions of years.