Large-scale geologic CO₂ storage is a technically feasible way to reduce anthropogenic emission of green house gas to atmosphere by human beings. In large-scale geologic CO₂ sequestration, high injection rate is required to satisfy economics and operational considerations. During the injection phase, temperature and pressure of the storage aquifers may vary significantly with the introduced CO₂. These changes would re-distribute the in-situ stresses in formations and induce fracture initiation or even propagation. If fractures are not permitted by regulators, then the injection operation strategies must be supervised and designed to prevent fracture initiation, and the storage formations should be screened for risk of fracturing. In more flexible regulatory environment, if fractures are allowed, fractures would strongly influence the CO₂ migration profile and storage site usage efficiency depending on fracture length and growth rate. In this dissertation, we built analytical heat transfer models for vertical and horizontal injection wells. The models account for the dependency of overall heat transfer coefficient on injection rate to more accurately predict the borehole temperature. Based on these models, we can calculate temperature change in formation surrounding wellbores and thus evaluate thermo-elastic stress around borehole as well as its impact on fracture initiation pressure. By considering the impact of thermo-elastic effect on fracturing pressure, we predicted maximum injection rate avoiding fracture initiation and provided injection and storage strategies to increase the maximum safe injection rate. The results show that thermo-elastic stress significantly limits maximum injection rate for no-fractured injection scenario, especially for horizontal injectors. To improve injection rate, partial perforation and pre-heating CO₂ before injection have been designed, and results shows that these strategies can strongly negate thermo-elastic influence for various injection scenarios. On the other hand, the model provides parametric analysis on geological and operational conditions of CO₂ storage project for site screening work. In the case of permitting fracture occurrence, a semi-analytical model was built to quantitatively describe fracture propagation and injected fluid migration profile of a fractured vertical injector for storage systems with various boundary conditions. We examined the correlation between fracture growth and CO₂ migration in various injection scenarios. Two-phase fractional flow model of Buckley-Leverett theory has been extended to account for the CO₂-brine three-region flow system (dry CO₂, CO₂-brine, and brine) from a fractured injector. In the sensitivity study, fracture growth and fluid migration greatly depend on Young's modulus of the formation rock and storage site boundary conditions. Consequently, the results show that fast growing, long fractures may yield a flooding pattern with large aspect ratio, as well as early breakthrough at the drainage boundary; in contrast, slow growing short fractures provides high injectivity without changing flooded area shape. We studied the physics for issues related to injection induced fractures in geologic CO₂ sequestration in saline aquifers, assessed risk associated to them and developed low cost and quick analytical models. These models could easily provide predictions on maximum injection rate in no-fracture regulation CO₂ storage projects as well as estimate fracture growth and injected fluid migration under fracture allowable scenarios. "Preferred storage aquifers" have following properties: larger permeability, deep formation, no over pressure, low Young's modulus and low Poisson's ratio and open boundaries. In many practical cases, however, injection strategies have to be designed if some properties of formation are out of ideal range. Besides applications in CO₂ storage, the approach and model we developed can also be applied into any injection induced fracture topics, namely water/CO₂ flooding and wasted water re-injection. / text

[pt] A ocorrência de eventos de perfuração em poços de óleo e gás é frequente, porém indesejada, uma vez que acarreta aumento no tempo e custo das operações. Sua ocorrência pode levar à perda de circulação do fluido, desmoronamento da parede do poço, restrição da sua funcionalidade, danos à plataforma, problemas ambientais e mesmo a perda de vidas humanas. Desta forma, o conhecimento das tensões é essencial para a estimativa da estabilidade do poço e aumento da segurança da perfuração. Existem diversos métodos para prever a tensão horizontal mínima, entretanto, para a máxima, ainda há dificuldades na sua determinação. No caso de poços inclinados, este cálculo se torna ainda mais complexo, uma vez que as tensões regionais não são alinhadas com o eixo do poço. Identificada essa necessidade, e partindo do princípio de que ao menos um poço já tenha sido perfurado em um campo e que este apresentou instabilidades do tipo colapso ou fraturamento induzido, esta dissertação trabalha na implementação de um algoritmo capaz de obter a magnitude da tensão horizontal máxima que levou ao surgimento dos mesmos. As fraturas Induzidas são falhas de tração, enquanto os Breakouts são gerados pelo colapso da parede do poço por falhas de compressão. Ambos devem ser devidamente identificados a partir de perfis de imagem. Os algoritmos implementados envolvem solução analítica, calculada através de métodos implícito e explícito. O procedimento para a rotação das tensões para poços inclinados é baseado em formulação presente na literatura, e os cálculos das tensões ao redor da parede do poço, nas equações de Kirsch. O fraturamento do material é avaliado de acordo com a tensão de cut-off, e o de ruptura, a partir do critério de Mohr-Coulomb ou Lade-Ewy. Os métodos desenvolvidos são comparados entre si, relatando suas vantagens e desvantagens. Aplicando uma vasta variação de inclinação e azimute do poço, os resultados alcançados apresentam uma diferença pequena com relação aos obtidos por meio de pacotes comerciais, sendo considerados satisfatórios. / [en] The occurrence of oil and gas well drilling events is common, but undesirable, once it increases time and cost of operations. Its occurence can lead to loss of fluid circulation, wellbore wall collapse, restriction of its functionality, platform damage, environmental issues and even the lost of human lives. stresses knowledge is essential to wellbore stability estimation and to the improvement of drilling safety. In fact, there are some methods and tests to compute the minimum horizontal stress, but there still exist difficulties on maximum horizontal stress determination. In the case of deviated wells, the calculations are even more complexes due to the lack of alignment between the regional stresses and well axis. Identified that problem, and considering that at least one wellbore has been drilled in a field and presented compressive or tensile instabilities, this dissertation works on the implementation of algorithms capable of obtaining the maximum horizontal stress magnitude that lead the appearance of breakout or induced fracture. The instability problems are identified and previously interpreted through image logs. The implemented algorithms involve an analytical solution, which is calculated by an explicit method and an implicit one, to the stated problem. The procedure to the stresses rotation on deviated wells used at this work is based on the formulation presented on technical literature, and the calculation of the stresses around the wellbore wall, on Kirsch s equation. The failure of the material is evaluated using a tensile cutoff for induced fractures and Mohr-Coulomb or Lade-Ewy criteria for breakouts. The developed methods are compared between each other, presenting the advantages and disadvantages of then. The results, applying a large variation on the wellbore inclination and azimuth, show that the values accomplished a low difference in relation to the obtained by using a commercial software, being considered as satisfactory.

Der vorliegende Beitrag befasst sich – motiviert vom Detail des monolithischen Anschlusspunktes der Stützen an den Überbau semi-integraler Brücken und den damit einhergehenden Besonderheiten für den Entwurf – mit der Thematik der verformungsinduzierten Rissbildung und ihren Einflussfaktoren. Anhand zweier Versuchsreihen wird der Einfluss der geometrischen Querschnittsparameter (Bewehrungsgrad, Bewehrungsumfang und Anzahl der Bewehrungslagen) auf die Rissbildung infolge Zwangsverformung untersucht.