The annular cement sheath plays a crucial role in ensuring well integrity by providing adequate zonal isolation, stabilizing the formation, and protecting the casing from corrosion. A majority of well integrity problems originate from oil well cement shrinkage and shrinkage-induced cracking, as well as cracking induced by other external stresses. The addition of expansive additives is a commonly used way to compensate for shrinkage. Compared to conventional ettringite-based and CaO-based expansive additives, MgO has many advantages including a thermally stable hydration product, relatively low water requirements for hydration, and designable expansion properties. These make MgO a promising candidate for delivering the desired expansion under the complex and variable underground wellbore environment. Self-healing materials which have the capability for autonomous crack repair are an attractive solution for addressing cracking problems in oil well cement. Engineered additions of healing agents for autonomic self-healing via a delivery system have been reported as effective ways to promote self-healing in cementitious materials. Microcapsules that can be easily added to cement pastes and dispersed through the cement matrix are considered particularly suitable for use in oil well cement. This research project investigates the efficacy of reactive MgO expansive additives to reduce shrinkage, and of sodium silicate microcapsules to improve the self-healing properties of oil well cement, and explores the feasibility of their combined use in a high temperature oil well environment. Three types of reactive MgOs from different reactivity grades, high reactivity N50, medium reactivity MAG-R, and low reactivity 92/200, were characterised in terms of their expansion characteristics in cement paste prisms cured in water, and further tested on their autogenous shrinkage reduction at 80oC. The highly reactive N50 could only partially compensate for autogenous shrinkage, while the less reactive MAG-R and 92/200 completely compensated for autogenous shrinkage. MAG-R and 92/200 also showed effective drying shrinkage reduction at 90% RH. The restrained expansion of MAG-R and 92/200 during an early age was found to significantly improve the cracking resistance of oil well cement. The free expansion of 92/200, with low reactivity, caused significant strength reduction, but under restrained conditions the effect was mitigated as its compressive strength was enhanced by confined expansion. The addition of MAG-R increased compressive strength under both free and restrained conditions. Two groups of sodium silicate microcapsules, T1 with rigid polyurea shells and T2 with rubbery polyurea shells, were characterised in terms of their thermal stability, alkalinity resistance and survivability during cement mixing, and the results verified their suitability for use in oil well cement at the high temperature of 80 oC. The effects of the two types of microcapsules on the self-healing performance of oil well cement at 80 oC were monitored using a variety of techniques. Oil well cement itself showed very little healing capability when cured at 80 oC, but the addition of microcapsules significantly promoted its self-healing performance, showing reduced crack width and crack depth, enhanced tightness recovery against gas permeability and water sorptivity, as well as strength recovery. Microstructure analyses of the cracking surface further verified the successful release of the sodium silicate core and its reaction with the cement matrix to form C-S-H healing products. Both groups of microcapsules showed comparable self-healing efficiency. Their different shell properties mainly influenced the strength of oil well cement, with rigid shell microcapsules causing less strength reduction than rubbery shell microcapsules. The overall performance of oil well cement containing both reactive MgO and microcapsules were evaluated. The combined addition of MgO MAG-R and T1 microcapsules showed similar expansion performance and self-healing efficiency compared to their individual use. The use of MgO MAG-R compensated for the strength reduction caused by the addition of microcapsules, achieving an overall improvement in the cement strength.

Made available in DSpace on 2014-12-17T14:07:03Z (GMT). No. of bitstreams: 1 AndrezaKC.pdf: 2477387 bytes, checksum: 5eafbea5e547e68eaf6513cad9b400ba (MD5) Previous issue date: 2009-10-29 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Primary cementing is one of the main operations in well drilling responsible for the mechanical stability and zonal isolation during the production of oil. However, the cement sheath is constantly under mechanical stresses and temperature variations caused by the recovery of heavy oil. In order to minimize fracture and wear of the cement sheath, new admixtures are developed to improve the properties of Portland cement slurries and avoid environmental contamination caused by leaking gas and oil. Polymers with the ability to form polymeric films are candidates to improve the properties of hardened cement slurries, especially their fracture energy. The present study aimed at evaluating the effect of the addition of a chitosan suspension on cement slurries in order to improve the properties of the cement and increase its performance on heavy oil recovery. Chitosan was dissolved in acetic ac id (0.25 M and 2 M) and added to the formulation of the slurries in different concentrations. SEM analyses confirmed the formation of polymeric films in the cementitious matrix. Strength tests showed higher fracture energy compared to slurries without the addition of chitosan. The formation of the polymeric films also reduced the permeability of the slurry. Therefore, chitosan suspensions can be potentially used as cementing admixtures for heavy oil well applications / A cimenta??o prim?ria ? uma das principais opera??es na perfura??o do po?o de petr?leo. A fixa??o do revestimento e o isolamento zonal garantir? seguran?a e diminui??o dos custos na fase de produ??o de ?leo. No entanto, ? constante a ocorr?ncia de problemas na bainha ciment?cia devido a esfor?os mec?nicos e a varia??o de temperatura, causada pela recupera??o de ?leos pesados. Visando minimizar as fraturas e desgaste da bainha, novas adi??es est?o sendo desenvolvidas para melhorar as propriedades do cimento Portland e evitar a contamina??o ambiental decorrente de vazamento de g?s e ?leo pelo anular. Pol?meros com a capacidade de formar filmes polim?ricos s?o op??es de adi??es, pois a poss?vel forma??o da teia polim?rica na matriz ciment?cia melhora as propriedades e a energia de fratura da pasta. O presente trabalho, tem como objetivo adicionar ?s pastas ciment?cias suspens?o de quitosana para melhorar as propriedades da pasta ciment?cia e aumentar seu desempenho em opera??es de recupera??o de ?leo pesado. A quitosana foi dilu?da em ?cido ac?tico (0,25 M e 2 M) e adicionada na formula??o das pastas em diferentes concentra??es. A an?lise do MEV confirmou a forma??o de redes polim?ricas na matriz ciment?cia e os testes deresist?ncia mec?nica comprovaram uma energia de fratura elevada em rela??o ? pasta sem adi??o do pol?mero. A forma??o da teia polim?rica tamb?m reduziu a permeabilidade da pasta. Com isso, a suspens?o de quitosana torna-se uma solu??o polim?rica com potencial para ser aplicado em cimenta??o de po?os de petr?leo

Made available in DSpace on 2014-12-17T14:07:06Z (GMT). No. of bitstreams: 1 BrunoLSC_DISSERT.pdf: 3848053 bytes, checksum: 28828821b0f45645fb6dc741dc2505bf (MD5) Previous issue date: 2013-09-28 / One of the great challenges at present time related with the materials area concerns of products and processes for use in petroleum industry, more precisely related to the Pre-salt area. Progresses were reached in the last years allowing the drilling of the salt layer, with the time reduction for drilling and larger success at the end. For the oil wells companies the preponderant factor is the technology, however, in spite of the progress, a series of challenges is still susceptible to solutions and one of them refers to the slurries preparation for cementing in those areas. Inside of this context, this study had for objective to analyze the influence of the salts NaCl, KCl, CaSO4 and MgSO4 in strength and chemical structure of the hydrated products. As methodology, they were prepared and analyzed cement slurries with varied concentrations of these salts that are commonly found in the saline formations. The salts concentrations used in formulations of the slurries were of 5%, 15% and 30%. The slurries were formulated with specific weight of 15,8 lb / gal and the cement used was Class G. Strength tests were accomplished in samples cured by 24 hours and 28 days. Also were realized crystallographic characterization (XRD) and morphologic (SEM). In agreement with the presented results, it is observed that the largest resistance values are attributed to the slurries with concentration of 15%. There was reduction of the strength values of the slurries formulated with concentration of 30%. Through the characterization microstructural it was possible to note the salts influence in the main cement hydrated products / Um dos grandes desafios da atualidade relacionado com a ?rea de materiais diz respeito ? produ??o de produtos e processos para uso na ind?stria do petr?leo, mais precisamente relacionado ? ?rea do Pr?-sal. Avan?os foram alcan?ados nos ?ltimos anos permitindo a perfura??o da camada de sal, com a redu??o do tempo para perfura??o dos po?os e maior ?xito ao final da opera??o. Apesar dos avan?os, uma s?rie de desafios ainda ? pass?vel de solu??es e um deles refere-se ? prepara??o de pastas para a cimenta??o de po?os nessas zonas com camadas evapor?ticas. Dentro deste contexto, este estudo teve por objetivo analisar a influ?ncia dos sais NaCl, KCl, CaSO4 e MgSO4 no comportamento mec?nico e estrutura qu?mica dos produtos hidratados. Como metodologia, foram preparadas e analisadas pastas de cimento com concentra??es variadas destes sais que s?o comumente encontrados nas forma??es salinas do reservat?rio do Pr?-sal. As concentra??es dos sais empregadas nas formula??es das pastas foram de 5%, 15% e 30%. As pastas foram formuladas com peso espec?fico de 15,8 lb/gal e o cimento utilizado na prepara??o das pastas foi o do tipo Portland Classe G. Foram realizados ensaios de resist?ncia ? compress?o em corpos de prova curados por 24 horas e 28 dias. Tamb?m foram realizados ensaios de caracteriza??o cristalogr?fica (DRX) e morfol?gica (MEV). De acordo com os resultados apresentados, observa-se que os maiores valores de resist?ncia s?o atribu?dos ?s pastas com concentra??o de 15 % para todos os sais. Houve, tamb?m, redu??o dos valores de resist?ncia das pastas formuladas com concentra??o de 30 % para todos os sais. Atrav?s das an?lises de caracteriza??o micro estrutural foi poss?vel observar a influ?ncia dos sais nos principais produtos hidratados do cimento Portland

Le processus de l’hydratation de ciment et la microstructure qui en résulte, dépendent de la formulation de la pâte et des conditions d’hydratation. Parmi différents facteurs, la température d’hydratation a un effet important sur la microstructure et les propriétés physiques et mécaniques des matériaux cimentaires. Ceci est particulièrement important pour l’étude du comportement des ciments pétroliers. En effet, dans un puits pétrolier, une gaine de ciment est coulée entre la roche réservoir et le cuvelage en acier pour assurer entre autre la stabilité et l’étanchéité du puits. En raison du gradient géothermique (environ 25°C par km), la gaine de ciment le long d'un puits est exposée à une température d'hydratation qui augmente avec la profondeur menant à une augmentation de perméabilité et une baisse de propriétés mécaniques le long du puits. L'objectif cette thèse est d'étudier l'effet de la température d'hydratation dans la gamme de 7°C à 90°C sur la microstructure d'une pâte de ciment (classe G) et d'établir le lien entre les modifications microstructurales et les propriétés élastiques du matériau. La caractérisation de la microstructure est faite en considérant une combinaison de plusieurs méthodes expérimentales, à savoir, la diffraction des rayons X & l’analyse Rietveld, l'analyse thermogravimétrique, porosimétrie par l'intrusion de mercure, l'évaluation de la porosité par lyophilisation ou par séchage à 11% HR, essais de sorption au Nitrogène et à la vapeur d'eau et finalement, la résonance magnétique nucléaire 1H. L’assemblage de masse des différentes phases de la microstructure a été évalué montrant une légère dépendance à la température d’hydratation. L’étude de la porosité a montré une augmentation de la porosité capillaire et une légère diminution de la porosité totale à 28 jours d’hydratation, ce qui résulte en une diminution de la porosité du gel de C-S-H en augmentant la température d'hydratation. Une méthode d'analyse a été proposée pour évaluer la densité saturée de C-S-H et sa composition chimique en termes des rapports molaires C/S et H/S pour un C-S-H sec et saturé. Les résultats montrent que la densité de C-S-H augmente avec la température d'hydratation expliquant ainsi l'augmentation observée de la porosité capillaire à températures élevées. Les rapports C/S et H/S diminuent avec l’augmentation de la température d’hydratation. La caractérisation de la microstructure a permis d’alimenter un modèle micromécanique destiné à prédire les propriétés élastiques de la pâte de ciment pour différentes températures d’hydratation. Des modèles d’homogénéisation auto-cohérents à deux et trois échelles ont montré que l’augmentation de la porosité capillaire ne suffit pas pour expliquer la baisse des propriétés mécaniques avec la température. En effet, l’augmentation de la densité de C-S-H avec la température d’hydratation annule l’effet de l’augmentation de la porosité capillaire sur les propriétés élastiques. La réduction des propriétés mécaniques pourrait être expliquée en considérant une distribution de porosité au sein de C-S-H sous forme de C-S-H basse densité LD et haute densité HD telle que proposée par Tennis et Jennings (2000). Cette possibilité est investiguée par une combinaison de techniques de porosimétrie : porosimétrie par l'intrusion de mercure, adsorption d'azote et désorption de vapeur d'eau et par un calcul inverse à l’aide de la modélisation micromécanique. Les résultats montrent que la porosité intrinsèque LD augmente légèrement tandis que la porosité intrinsèque HD diminue de manière significative avec l'augmentation de la température d'hydratation. La diminution des propriétés élastiques des matériaux cimentaires avec l’augmentation de la température d'hydratation s’avère être due à l’action combinée de l'augmentation de la porosité capillaire et des changements de porosités intrinsèques à l’intérieure de C-S-H / The cement hydration process and the resulting microstructure are highly dependent on the cement formulation and the hydration conditions. Particularly, the hydration temperature has a significant influence on the cement paste microstructure and its mechanical properties. This is for instance important for understanding the behaviour and properties of oil-well cements which are used to form a cement sheath between the casing and the surrounding formation for stability and sealing purposes. This cement sheath is hydrated under a progressively increasing temperature along the depth of a well due to the geothermal gradient (about 25°C/km). It results generally in a decrease of the mechanical properties and an increase of permeability along the well. The aim of the present thesis is to investigate the effect of the hydration temperature in the range of 7°C to 90°C on the microstructure of a class G cement paste and to establish the link between these temperature dependent microstructure and the elastic properties of the material. The microstructure characterization is done by combining various experimental methods, including X-Ray diffraction associated with the Rietveld analysis, thermogravimetric analysis, mercury intrusion porosimetry, porosity evaluation by freeze-drying or drying at 11% RH, Nitrogen and water vapour sorption experiments and finally 1H nuclear magnetic resonance. The mass assemblage of microstructure phases at different curing temperatures has been evaluated and showed a slight dependence on the hydration temperature. The porosity evaluations show an increase of the capillary porosity and a slight decrease of the total porosity at 28 days, resulting in a decrease of the gel porosity by increasing the hydration temperature. An analysis method has been proposed to evaluate the C-S-H saturated density and chemical composition in terms of H/S and C/S molar ratios. The C-S-H bulk density is increasing with increasing hydration temperature which explains the observed increase of the capillary porosity for higher curing temperatures. The C/S ratio and H/S ratio for both solid and saturated C-S-H are decreasing with increasing curing temperature. The provided quantitative characterization of cement paste microstructure is used in a micromechanical modelling for evaluation of the elastic properties at various hydration temperatures. Two and three-scale self-consistent micromechanical models have shown that the increase of capillary porosity with increasing hydration temperature cannot fully explain the drop of elastic properties. This is mainly due to the increased elastic properties of C-S-H being denser at higher temperature that cancel the effect of increasing capillary porosity on the overall elastic properties. Another way to fully account for the decrease of the mechanical properties of cement paste is to consider the porosity distribution inside the C-S-H in the form of two distinguished C-S-H types, High Density (HD) and Low Density (LD) C-S-H, as proposed by Tennis and Jennings (2000). This possibility is probed by a combination of various porosity evaluations: Mercury intrusion porosimetry, nitrogen adsorption and water vapour desorption and by a back calculation using micromechanical modelling. The results show that the LD intrinsic porosity is slightly increasing while the HD intrinsic porosity decreases significantly with increasing hydration temperature. The decrease of the elastic properties of cement based materials with increasing hydration temperature is therefore a combined action of the increase of capillary porosity and the changes of intrinsic C-S-H porosities