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Understanding the strength and failure modes of overburdens and reservoirs is a critical component in safety assessments for oil sands surface mining and in situ thermal recovery operations. Currently, assumptions of homogeneity are often made for the geomechanical properties of oil sands in conventional slope stability analyses and reservoir simulation. The purpose of this work is to propose a numerical characterization workflow that helps predict the failure mode and shear strength of heterogeneous oil sands interbedded with shale beddings during thermal recovery. Heterogeneous models are generated through sequential indicator simulation with a calibrated constitutive model and geomechanical parameters for each lithology. Numerical simulations with boundary conditions reflecting in situ stress changes are conducted to study the impact of shale beddings on stress-strain response, failure modes, and shear strength of the sheared zone. The results show that shear failures of the weaker shale beddings play a significant role in the elastoplastic behavior and reduced shear strength of heterogeneous oil sands. The shear band and weak plane failures are found to be closely related to the volume fraction, variogram range ratio, and inclinations of shale beddings. The proposed numerical workflow allows for quantitative investigations of geomechanical response for rock mass with complex lithological heterogeneities. Key words: geomechanical characterization, heterogeneity, failure modes, shear strength, oil sands. La comprehension de la resistance et des modes de defaillance des morts-terrains et des reservoirs est un element essentiel des evaluations de la securite pour l'exploitation des sables bitumineux en surface et les operations de recuperation thermique in situ. Actuellement, des hypotheses d'homogeneite sont souvent formulees pour les proprietes geomecaniques des sables bitumineux dans les analyses classiques de stabilite des pentes et les simulations de reservoirs. L'objectif de ce travail est de proposer un flux de caracterisation numerique qui aide a predire le mode de defaillance et la resistance au cisaillement des sables bitumineux heterogenes interstratifies avec des couches de schiste pendant la recuperation thermique. Des modeles heterogenes sont generes par simulation d'indicateurs sequentiels avec un modele constitutif calibre et des parametres geomecaniques pour chaque lithologie. Des simulations numeriques avec des conditions limites refletant les changements de contraintes in situ sont realisees pour etudier l'impact des couches de schiste sur la reponse contraintedeformation, les modes de defaillance et la resistance au cisaillement de la zone cisaillee. Les resultats montrent que les ruptures de cisaillement des couches de schiste les plus faibles jouent un role important dans le comportement elastoplastique et la reduction de la resistance au cisaillement des sables bitumineux heterogenes. Il s'avere que la bande de cisaillement et les ruptures de plans faibles sont etroitement liees a la fraction volumique, au rapport de gamme des variogrammes et aux inclinaisons des couches de schiste. Le flux de travail numerique propose permet des etudes quantitatives de la reponse geomecanique pour des masses rocheuses presentant des heterogeneites lithologiques complexes. [Traduit par la Redaction] Mots-cles : caracterisation geomecanique, heterogeneite, modes de defaillance, resistance au cisaillement, sables bitumineux., 1. Introduction Oil sands are naturally occurring mixtures of sand, clay, water, and bitumen, estimated at 162.5 billion barrels occupying 96% of proven oil reserves in Canada (Natural Resources Canada [...]

Oil sand reservoirs and caprock undergo deformations triggered by pore pressure increases and thermal induced stresses during the steam-assisted-gravity-drainage (SAGD) processes. Geomechanical assessments are mandated by energy regulators to evaluate the caprock integrity and ensure the safe SAGD operations. Commercial reservoir simulation packages started to incorporate geomechanical effects when predicting flow response; however, these geomechanical modules are not able to correctly model the plastic deformations caused by thermal-hydraulic-mechanical (THM) interactions, which has a first order effect on predicting steam chamber propagation and evaluating caprock integrity. An integrated coupled THM modeling methodology is proposed here to improve the modeling of reservoir deformations and caprock integrity in a heterogeneous oil sand reservoir with interbedded shale barriers. The pressure and temperature front are found to propagate at different speed and that dominate the elastic and plastic deformations caused by changes of shear and mean effective stress. Therefore, four stages are divided in the SAGD process that can be interpretations of changes in stress paths including buildup of pore pressure, generation and dissipation of thermal induced stresses. The response surfaces of minimum factor of safety are introduced and computed to provide a conservative estimate for caprock integrity during SAGD of a heterogeneous reservoir with multiple layers of caprocks in Athabasca oil sands. [ABSTRACT FROM AUTHOR]

An efficient, numerical local upscaling technique for estimating elastic geomechanical properties in heterogeneous continua is proposed. The upscaled anisotropic elastic properties are solved locally with various boundary conditions and reproduce the anisotropic geomechanical response of fine-scale simulations of sand–shale sequence models with horizontal and inclined shale bedding planes. The algorithm is automated in a parallel program and can be used to determine optimum upscaling ratios in different regions of the reservoir. The successful application of the proposed upscaling method in a field-scale coupled reservoir–geomechanics simulation demonstrates an improvement in overall computational efficiency while maintaining accuracy in the geomechanical response and reservoir performance. [ABSTRACT FROM AUTHOR]

Large-scale mining methods are commonplace in the mining industry, and caving has become the preferred underground mining technique. The use of block caving has increased worldwide and is expected to grow because of high production rates, low mining costs, and low waste production. One key engineering consideration in block caving is the drawpoint spacing layout, which must be selected prior to production based on widely spaced exploration data; uncertainty is highest during this stage of mining; and selecting an appropriate extraction level and layout is important for economic and safety considerations. In the proposed methodology, uncertainty in the grade block model is assessed with sequential Gaussian simulation and an optimisation procedure is developed to maximise net present value over many realisations while being constrained by mining considerations. This novel approach generates one layout that is optimal over all realisations rather than consider optimisation on a single kriged model which is standard practice; in this way risk can be assessed and mitigated by selecting the layout that maximises profit but also minimises the variance of profit over all realisations. The methodology is demonstrated using a case study, and the proposed technique outperforms traditional optimisation based on a kriged model. [ABSTRACT FROM AUTHOR]