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Résumé -Étude théorique et expérimentale de la précipitation de sulfate de calcium en milieu poreux sur micromodèle de verre -Le mélange de deux eaux incompatibles lors d'injection d'eau donne habituellement lieu à précipitation et formation de dépôts minéraux dans les milieux poreux. Ces dépôts qui réduisent la porosité et surtout la perméabilité de la roche ont une influence considérable sur les performances des scénarios d'injection d'eau. Dans cette étude, une série d'expériences a permis d'étudier l'effet de différents paramètres sur la précipitation progressive de sulfate de calcium. Il s'agit notamment de la température, de la concentration des saumures mélangées, de la pression et du débit. En raison de sa transparence, un micromodèle de réseau représentatif d'un grès mouillable à l'eau a été utilisé comme support poreux et a permis d'observer facilement la formation et la distribution des dépôts minéraux. De plus, le suivi du déplacement des particules solides est largement facilité par le nouveau dispositif expérimental proposé. Les photos de coupes obtenues en microscopie montrent que le dépôt est initié sur les parois et les seuils des pores, qu'il se propage vers l'intérieur de ces pores, et que les cristaux solides ont une forme en crête de coq. Pour une meilleure compréhension de l'effet de chacun des paramètres mentionnés ci-dessus, il a été tracé une courbe de la réduction de perméabilité en fonction du volume de solution de saumure injectée dans les pores. Les résultats ont indiqué que l'augmentation de la température, de la concentration de saumure et du débit conduisent à une augmentation de la tendance au dépôt de minéraux. La pression n'a qu'un rôle mineur sur le développement du processus. Le dépôt de CaSO 4 se modélise comme une fonction de réduction de la perméabilité dépendante des différents paramètres. C'est pourquoi il a été proposé une fonction exponentielle (de corrélation) qui intègre sous une forme adimensionnelle tous les paramètres physiques ayant une influence sur le comportement du système. Le nombre de Reynolds, l'index de précipitation et l'écart par rapport aux conditions d'équilibre constituent le fondement de cette corrélation. Les exposants ajustables de l'équation ont été déterminés et optimisés au moyen d'un algorithme génétique. Cette corrélation significative peut également prédire, avec une précision raisonnable, les résultats issus d'expériences sur carottes. Abstract -Experimental and Theoretical Study of Calcium Sulphate Precipitation in Porous Media

The most commonly used technology for development of unconventional liquid-rich and light oil reservoirs is horizontal wells combined with large multi-stage hydraulic fracture treatments. However, even with these technological advancements, primary recovery factors are generally less than 10% (Shoaib and Hoffman, 2009) of the original oil in place (OOIP). Logically, operators have investigated the use of waterflooding to improve recovery in some tight oil reservoirs, but the success has been mixed. Low matrix permeability in some unconventional (tight) oil reservoirs will not allow effective displacement or movement of water through the reservoir. In some cases, even flooding with a gas will be a challenge, if matrix permeabilities are too low. This study investigates the feasibility of enhanced oil recovery (EOR) in a prominent tight oil reservoir in North America using cyclic solvent injection (CSI, sometimes referred to as "huff-n-puff") with carbon dioxide (CO2) as the solvent. CSI is a single well process, with the solvent remaining in the vicinity of the wellbore, as flow of the solvent through the reservoir to another well is not necessary. This type of process may be attractive from a capital cost point-of-view, as large expenditures on specialized facilities, in-field pipelines and well conversions are unnecessary. In this study, the success and profitability of huff-n-puff is evaluated for the Bakken tight oil reservoir. Knowledge gained from a parallel study (Kanfar and Clarkson, 2017) served to provide guidelines for optimizing the huff-n-puff process. Importantly, a genetic algorithm (GA) is utilized to find the optimum huff-n-puff program that maximizes net present value (NPV). Optimized parameters include: the number of cycles; duration of injection, soaking and production periods; and the start time of huff-n-puff operations. The target reservoir for evaluation is the US Bakken deep tight oil reservoir in North Dakota. The huff-n-puff EOR scheme was found to be successful, but only after the aforementioned operational parameters are optimized with GA. In particular, it is important to delay huff-n-puff until production rates decline and boundary-dominated flow (after fracture interference) is reached. Importantly, as with the parallel study (Kanfar and Clarkson 2017), the gridding scheme used in the simulation is found to have a profound impact on results of huff-n-puff.

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A study, entitled "Wabamun Lake Sequestration Project" or "WASP," was performed to evaluate large-scale CO 2 storage opportunities in the Wabamun area including potential risks. The project examined the feasibility of storing 20 megatons (Mt) of CO 2 per year over 50 years. This scale is one order of magnitude larger than the typical benchmark (1 Mt/year) used in academic research and commercial projects that are currently in place or under review. The study was conducted by a group of researchers from several universities as well as industry consultants. This study presents an overview of the reservoir modeling part of this study, which the authors were responsible for. The main objectives of the reservoir modeling for WASP project were as follows: (1) estimation of storage capacity (traditionally, this value is projected based on the available pore space, but we have an additional practical consideration: the maximum amount one can inject within short period of time [~50 years] and within a localized injection area [~30 km 9 90 km]); (2) investigation of CO 2 plume movement and pressure distribution during and after injection including the effect of formation dip angle on the plume shape and its migration; (3) investigation of the long-term fate of injection associated with free phase CO 2 (risks of leakage) and aquifer pressurization (possible geomechanical changes and related phenomena); (4) investigation of the phase behavior of H 2 S initially available and dissolved in brine during CO 2 sequestration process. The WASP reservoir modeling study mentioned above led to a few important findings. The most important one is that, when CO 2 is being injected into a sour aquifer, initially dissolved H 2 S will release into the expanding CO 2 plume and accumulate at the leading edge of the plume. Also, the large-scale injection scheme (20 Mt/ year), which requires multi well injectors, provides very different pressure response compared to a one well (1 Mt/year) scenario.

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