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Previous issue date: 2008-10-28 / Oil wells subjected to cyclic steam injection present important challenges for the development of well cementing systems, mainly due to tensile stresses caused by
thermal gradients during its useful life. Cement sheath failures in wells using conventional high compressive strength systems lead to the use of cement systems that are more flexible and/or ductile, with emphasis on Portland cement systems with latex addition. Recent research efforts have presented geopolymeric systems as alternatives. These cementing systems are based on alkaline activation of amorphous aluminosilicates such as metakaolin or fly ash and display advantageous properties such as high compressive strength, fast setting and
thermal stability. Basic geopolymeric formulations can be found in the literature,
which meet basic oil industry specifications such as rheology, compressive strength and thickening time. In this work, new geopolymeric formulations were developed, based on metakaolin, potassium silicate, potassium hydroxide, silica fume and mineral fiber, using the state of the art in chemical composition, mixture modeling and additivation to optimize the most relevant properties for oil well
cementing. Starting from molar ratios considered ideal in the literature (SiO2/Al2O3 = 3.8 e K2O/Al2O3 = 1.0), a study of dry mixtures was performed,based on the compressive packing model, resulting in an optimal volume of 6% for the added solid material. This material (silica fume and mineral fiber) works both as an additional silica source (in the case of silica fume) and as mechanical
reinforcement, especially in the case of mineral fiber, which incremented the tensile strength. The first triaxial mechanical study of this class of materials was performed. For comparison, a mechanical study of conventional latex-based cementing systems was also carried out. Regardless of differences in the failure mode (brittle for geopolymers, ductile for latex-based systems), the superior uniaxial compressive strength (37 MPa for the geopolymeric slurry P5 versus 18 MPa for the conventional slurry P2), similar triaxial behavior (friction angle 21?
for P5 and P2) and lower stifness (in the elastic region 5.1 GPa for P5 versus 6.8 GPa for P2) of the geopolymeric systems allowed them to withstand a similar amount of mechanical energy (155 kJ/m3 for P5 versus 208 kJ/m3
for P2), noting that geopolymers work in the elastic regime, without the microcracking present in the case of latex-based systems. Therefore, the geopolymers studied on this work must be designed for application in the elastic region to avoid brittle failure. Finally, the tensile strength of geopolymers is originally poor (1.3 MPa for the
geopolymeric slurry P3) due to its brittle structure. However, after additivation with mineral fiber, the tensile strength became equivalent to that of latex-based systems (2.3 MPa for P5 and 2.1 MPa for P2). The technical viability of conventional and proposed formulations was evaluated for the whole well life, including stresses due to cyclic steam injection. This analysis was performed using finite element-based simulation software. It was verified that conventional slurries are viable up to 204?F (400?C) and geopolymeric slurries are viable above 500?F
(260?C) / Po?os sujeitos ? inje??o c?clica de vapor apresentam importantes desafios para desenvolvimento de pastas de cimenta??o, devido principalmente aos esfor?os de
tra??o causados pelos gradientes t?rmicos durante a sua vida ?til. Falhas em cimenta??es que empregaram pastas convencionais de elevada resist?ncia ? compress?o levaram ao emprego de pastas mais flex?veis e/ou d?cteis, com destaque para as pastas de cimento Portland com adi??o de l?tex. Recentes pesquisas t?m apresentado pastas geopolim?ricas como alternativa. Estas pastas cimentantes s?o baseadas na ativa??o alcalina de aluminosilicatos amorfos como
o metacaulim ou a cinza volante e possuem propriedades vantajosas como alta resist?ncia ? compress?o, r?pido endurecimento e estabilidade t?rmica. Encontram-se na literatura formula??es geopolim?ricas b?sicas que atendem ?s
especifica??es da ind?stria de petr?leo, incluindo reologia, resist?ncia ? compress?o e tempo de espessamento. Neste trabalho, desenvolveu-se novas formula??es geopolim?ricas ? base de metacaulim, silicato de pot?ssio, hidr?xido de pot?ssio, micross?lica e fibra mineral, utilizando o estado da arte em
composi??o qu?mica, modelagem de misturas e aditiva??o para otimizar as propriedades relevantes para a cimenta??o de po?os. Partindo de raz?es molares
consideradas ideais na literatura (SiO2/Al2O3 = 3,8 e K2O/Al2O3 = 1,0), realizou-se
um estudo de misturas secas baseado no modelo do empacotamento
compress?vel, obtendo-se um volume ?timo de 6% para o material s?lido
adicional. Este material (micross?lica e fibra mineral) serve tanto como fonte de s?lica adicional (no caso da micross?lica) quanto refor?o mec?nico, principalmente no caso da fibra mineral, a qual incrementou a resist?ncia ? tra??o. Realizou-se o
primeiro estudo mec?nico triaxial desta classe de pastas. Para efeito de compara??o, tamb?m foi realizado um estudo mec?nico de pastas convencionais ? base de l?tex. Apesar de diferen?as no modo de ruptura (fr?gil no caso dos geopol?meros, d?ctil no caso das pastas com l?tex), a superior resist?ncia compressiva uniaxial (37 MPa para a pasta geopolim?rica P5 versus 18 MPa para a pasta convencional P2), comportamento triaxial similar (?ngulo de atrito 21?
para P5 e P2) e menor rigidez (na regi?o el?stica 5,1 GPa para P5 versus 6,8 GPa para P2) das pastas geopolim?ricas permitiu uma capacidade de absor??o de energia (155 kJ/m3 para P5 versus 208 kJ/m3 para P2) compar?vel entre as duas, sendo que os geopol?meros atuam no regime el?stico, sem a
microfissura??o presente nas pastas com l?tex. Assim, os geopol?meros estudados neste trabalho devem ser dimensionados para aplica??es no regime el?stico para evitar fraturas fr?geis. Finalmente, a resist?ncia ? tra??o do
geopol?mero ? originalmente pobre (1,3 MPa para a pasta geopolim?rica P3) devido ? sua estrutura fr?gil. Entretanto, ap?s a aditiva??o desse sistema com fibra mineral, a resist?ncia ? tra??o do mesmo tornou-se equivalente (2,3 MPa
para P5 e 2,1 MPa para P2) ? das pastas com l?tex. A viabilidade t?cnica das formula??es convencionais e geopolim?ricas foi avaliada durante toda a vida ?til
do po?o, incluindo os esfor?os devidos ? inje??o c?clica de vapor. Esta an?lise foi feita utilizando um software de simula??o ? base de elementos finitos. Verificou-se que as pastas convencionais s?o vi?veis at? a temperatura de 204?C (400?F) e as geopolim?ricas acima de 260?C (500?F)
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufrn.br:123456789/12729 |
| Date | 28 October 2008 |
| Creators | Paiva, Maria das Dores Macedo |
| Contributors | CPF:06117988320, http://lattes.cnpq.br/3318871716111536, Melo, Marcus Ant?nio de Freitas, CPF:04514998320, http://lattes.cnpq.br/5840621182000517, Marinho, ?rika Pinto, CPF:02381892443, http://lattes.cnpq.br/1192938961586608, Martinelli, Ant?nio Eduardo, Toledo Filho, Romildo Dias, Melo, Dulce Maria de Ara?jo |
| Publisher | Universidade Federal do Rio Grande do Norte, Programa de P?s-Gradua??o em Ci?ncia e Engenharia de Materiais, UFRN, BR, Processamento de Materiais a partir do P?; Pol?meros e Comp?sitos; Processamento de Materiais a part |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/doctoralThesis |
| Format | application/pdf |
| Source | reponame:Repositório Institucional da UFRN, instname:Universidade Federal do Rio Grande do Norte, instacron:UFRN |
| Rights | info:eu-repo/semantics/openAccess |
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