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Three probabilistic methods of different complexity for slope stability calculations are in this work evaluated with respect to a well-documented case study of slope failure in Lodalen, Norway. A finite element method considering spatial random fields of uncorrelated parameters cohesion and friction angle is taken as a reference for comparison with two simpler methods based on Taylor series expansion, known as first-order-second-moment methods. It is shown that the FOSM method enhanced by a reduction of variance of input parameters due to spatial averaging along the potential failure surface leads to a significant improvement in predictions. This method is computationally inexpensive and can be used in combination with any existing finite element code, it is thus a useful approximate probabilistic method for geotechnical practice. Several limitations of the extended method for calculating probability of a slope failure are identified. An advanced hypoplastic constitutive model is used in probabilistic analyses of a typical geotech- nical problem, strip footing. The model, including horizontal and vertical correlation lengths, was calibrated using a set of experimental data on sand from horizontally stratified deposit. Some parameters followed normal, whereas other followed lognormal distributions....

Since oil and gas production from conventional fields is decreasing, the produc-tion of unconventional hydrocarbon reservoirs is becoming imperative, where geo-mechanical responses play an important role. This research presents a methodology that starts exploring the inclusion of geomechanics in streamline simulations using a two-way explicit coupling approach between a reservoir and geomechanical simulators. This was done in an effort of conducting field-scale simulations considering the impact of geomechanical parame-ters on reservoir static properties, which affect ultimate recovery. Porosity, permeability, and porosity and permeability were used as the coupling parameters; the influence that they have on the process is problem-dependant as well. The results obtained from the two study cases presented, reveal that the per-formance of the approach is problem-dependent; the more complex the models are, the larger the geomechanical response is. One of the main aspects of this study was the limitations of the simulators. When software and hardware capacities improve, so will the results of the coupling ap-proach. Until then, more complex models should be tested, as well as more rigorous techniques, to improve the results presented here. / Petroleum Engineering

Hydraulic fracturing in tight gas and shale gas reservoirs is an essential stimulation technique for production enhancement. Often, hydraulic fracturing induces fracture patterns that are more complex than the planar geometry that has been assumed in the past models. These complex patterns arise as a result of the presence of planes of weakness, faults and/or natural fractures. In this thesis, two different 3D geomechanical models have been developed to simulate the interaction between the hydraulic fracture and the natural fractures, and to observe the impact of geomechanics on the potential microseismicity in these naturally fractured formations. Several cases were studied to observe the effects of natural fracture geometry, fracturing treatment, mechanical properties of the sealed fractures, etc. on the propagation path of the hydraulic fracture in these formations, and were found to be consistent with past experimental results. Moreover, the effects of several parameters including cohesiveness of the sealed natural fractures, mechanical properties of the formation, treatment parameters, etc. have been studied from the potential microseismicity standpoint. It is shown that the impact of geomechanics on potential microseismicity is significant and can influence the desired fracture spacing. In this thesis, the presented model quantifies the extent of potential microseismic volume (MSV) resulting from hydraulic fracturing in unconventional reservoirs. The model accounts for random geometries of the weak planes (with different dip and strike) observed in the field. The work presented here shows, for the first time, a fracture treatment can be designed to maximize the MSV, when the fractures form a complicated network of fractures, and in turn influence the desired fracture spacing in horizontal wells. Our work shows that by adjusting the fluid rheology and other treatment parameters, the spatial extent of MSV and the desired fracture spacing can be optimized for a given set of shale properties. / text

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Bibliography: pages 208-222. / The major objective of the work presented in this thesis was the development of a constitutive model for hard rock at high pressure. The model should capture the important features of material behaviour and should be soundly based on mechanical principles; furthermore it should be simple enough to permit implementation and use in large general purpose finite element codes. As a preliminary exercise, a state-of-the-art plasticity cap model was developed in order to provide a basis for comparison with the new model. Existing cap models were shown to exhibit certain inconsistencies associated with the suppression of a regime of potentially unstable behaviour; these inconsistencies were identified and eliminated in. the formulation which is presented in this thesis. The new rock model was based on internal damage concepts. The model is isotropic, and internal damage is measured by a scalar damage parameter. The properties of the material degrade as the damag~ parameter increases, and an evolution law governs the rate at which damage occurs. The damage model was calibrated against experimental results for Bushveld Norite, which is a very hard, brittle rock. The general form of the model, however, is suitable for application to soil and concrete. Both the plasticity cap model and the damage model were implemented into the finite element code NOSTRUM (developed by the Applied Mechanics Research Unit at the University of Cape Town). Solutions of a series of boundary value problems, including typical mining excavation problems, are presented to illustrate and compare the models.

The use of Discrete Fracture Networks (DFNs) is becoming increasingly common in geomechanical practice in addition to their continuing role in hydrogeology. These models can serve as useful tools for estimating interconnectedness of fractures, leading to estimates of probable block sizes and shapes for a set of input parameters. However, the development of these models is reliant on assumptions made about collected field data and while constructing the model themselves. The implications of these biases and assumptions are not well documented. This work investigates the variables involved in building a Discrete Fracture Network model in order to provide insight into the decisions and assumptions made during the modeling process. Select assumptions required within the FracMan DFN software pertaining to model selection and construction are evaluated; biases and assumptions relating to field data and how it is collected that may impact the development of DFN input parameters are investigated and limits of the effects of these models on block sizes are determined. The parameters determined to be critical in determining the overall geometry of the fracture network are ranked according to their relative importance in DFN modelling and according to the relative accuracy of each parameter. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2014-05-30 18:00:51.384