Petrofísica e geoquímica de reservatório basáltico no município de Colômbia (SP): condicionantes para captura e armazenamento de CO2 na Formação Serra Geral
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2021-03-18
Autores
Navarro, Juan [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Nos últimos anos, os esforços para limitar o aumento da temperatura média global se intensificaram, principalmente pela redução das emissões de gases de efeito estufa, em especial o CO2. Diversas tecnologias para mitigação das emissões de CO2 vêm crescendo em importância, com especial destaque para a captura e armazenamento de carbono (Carbon Capture and Storage – CCS). Plantas-piloto de injeção de CO2 em derrames basálticos da Islândia e dos Estados Unidos demonstram que estas unidades geológicas são eficientes para promover a carbonatação in situ do CO2 injetado, aumentando a segurança do armazenamento. No Brasil, a Formação Serra Geral (FSG – Cretáceo da Bacia do Paraná) constitui um dos maiores derrames vulcânicos continentais do mundo, sendo composta predominantemente por litotipos basálticos, e está situada próxima a importantes zonas emissoras de CO2. Entretanto, estudos quanto ao aproveitamento desses basaltos para CCS são escassos. O presente trabalho, estudando derrames da FSG no município de Colômbia (SP), buscou avaliar se esta unidade possui uma estruturação que favoreça seu uso como reservatório para CCS e identificar os intervalos mais promissores para o armazenamento de carbono. Para caracterização petrofísica do arcabouço, empregou-se a análise de perfis geofísicos de poço (resistividade elétrica, sônico compensado e raios gama total), bem como equações empíricas relacionando velocidade de ondas sônicas, porosidade e permeabilidade em basaltos. Para caracterização geoquímica, utilizou-se análise química por fluorescência de raios-X portátil em amostras de calha dos poços perfilados. Também foi elaborado modelo conceitual para o reservatório e confeccionou-se modelo numérico sintético de fluxo para simulação de teste de bombeamento de vazão máxima. A interpretação dos perfis geofísicos e as estimativas de permo-porosidade revelaram a existência de quatro fácies distintas que se sucedem verticalmente: (I) basalto maciço, caracterizado por altos de resistividade elétrica e velocidades sônicas, e por baixa permo-porosidade; (II) basalto vesicular, caracterizado por baixos de resistividade elétrica e velocidades sônicas, e pelas maiores permo-porosidades; e (III) basalto alterado e (IV) horizonte argiloso, com características intermediárias entre as duas primeiras. As análises químicas demonstraram concentrações molares de Ca, Mg e Fe total relativamente homogêneas ao longo do perfil vertical, sem concentrações preferenciais em qualquer das fácies do derrame. O modelo conceitual apresentado aponta os intervalos de basalto vesicular como principais horizontes reservatórios e os horizontes de basalto maciço como selantes ao CO2, assumindo a possibilidade de lenta migração vertical por fraturas existentes nos níveis selantes. Este comportamento foi reforçado pelo modelo numérico de fluxo e pela análise da curva diagnóstica do teste de bombeamento simulado, os quais indicaram que o arcabouço se comporta como aquífero confinado drenante. Os resultados obtidos neste estudo apontam cenário favorável ao emprego de tecnologias de CCS na FSG. Indicam que os níveis vesiculares de topo dos derrames da unidade poderiam atuar como reservatórios de CO2 e possuem composição química que favorece as reações de carbonatação mineral, enquanto intervalos de basalto maciço promoveriam o trapeamento físico do CO2, aumentando a segurança do armazenamento e as taxas de retenção.
In recent years, efforts to limit the mean global temperature rising have been intensified, mainly through the greenhouse gases emission reduction, particularly the CO2. The importance of technologies to mitigate the CO2 emissions has increased, especially the carbon capture and storage (CCS) technologies. Pilot projects of CO2 injection in flood basalts from Iceland and United States prove these geological formations are efficient to promote in situ carbonation of the injected CO2, improving the storage security. In Brazil, the Serra Geral Formation (SGF – Cretaceous of the Paraná Basin) represents one of the largest continental igneous provinces worldwide and is predominantly composed of basaltic rocks and is located nearby important CO2 emission sources. However, there are few studies involving the use of SGF basalts for CCS. The present study, developed in Colômbia county, São Paulo State, aimed to assess the potential of SGF as CCS reservoir as well as to select the most promising intervals to carbon storage. The petrophysical characterization of the formation was carried using well log analysis (electrical resistivity, sonic velocity and total gamma-ray), as well as empirical equations correlating sonic velocities, porosity and permeability for basalts. The chemical analysis for geochemical characterization was performed on well cuttings by means of portable X-ray fluorescence spectrometer. A conceptual model of the reservoir was developed, and a synthetic groundwater flow model was built to simulate a constant-rate pumping test, to help diagnose pumping test results. The well log analysis and the porosity-permeability estimations identified four different facies in the flood basalt sequences: (I) massive basalt, denoted by higher values of resistivity and sonic velocities, and by lower porosity-permeability; (II) vesicular basalt, characterized by lower values of electrical resis-tivity and sonic velocities, and by higher porosity-permeability; (III) weathered basalt and (IV) clay intervals, which have intermediate characteristics between the first ones. The chemical analysis showed relatively homogeneous molar concentrations of Ca, Mg and total Fe along the vertical profile, without preferential distributions on the recognized facies. The conceptual model identifies the vesicular basalt intervals as the most promising reservoirs for the CO2 storage. The massive basalt acts as a caprock, although the possibility of slow vertical migration due to fractures in the internal flows is assumed. This behavior was endorsed by the results obtained from the numerical groundwater flow model and from the diagnostic plot analysis of the simulated pumping test, indicating that the formation behaves as a leaky confined aquifer. The results presented in this study point out a positive scenario for the use of CCS technologies in SGF. The top vesicular basalts intervals could be used as reservoirs for the CO2 storage and the chemical composition of these intervals could promote mineral carbonation reactions, while the interior massive basalts would act as caprocks, promoting the physical trapping of CO2 and enhancing the storage security and the retention taxes.
In recent years, efforts to limit the mean global temperature rising have been intensified, mainly through the greenhouse gases emission reduction, particularly the CO2. The importance of technologies to mitigate the CO2 emissions has increased, especially the carbon capture and storage (CCS) technologies. Pilot projects of CO2 injection in flood basalts from Iceland and United States prove these geological formations are efficient to promote in situ carbonation of the injected CO2, improving the storage security. In Brazil, the Serra Geral Formation (SGF – Cretaceous of the Paraná Basin) represents one of the largest continental igneous provinces worldwide and is predominantly composed of basaltic rocks and is located nearby important CO2 emission sources. However, there are few studies involving the use of SGF basalts for CCS. The present study, developed in Colômbia county, São Paulo State, aimed to assess the potential of SGF as CCS reservoir as well as to select the most promising intervals to carbon storage. The petrophysical characterization of the formation was carried using well log analysis (electrical resistivity, sonic velocity and total gamma-ray), as well as empirical equations correlating sonic velocities, porosity and permeability for basalts. The chemical analysis for geochemical characterization was performed on well cuttings by means of portable X-ray fluorescence spectrometer. A conceptual model of the reservoir was developed, and a synthetic groundwater flow model was built to simulate a constant-rate pumping test, to help diagnose pumping test results. The well log analysis and the porosity-permeability estimations identified four different facies in the flood basalt sequences: (I) massive basalt, denoted by higher values of resistivity and sonic velocities, and by lower porosity-permeability; (II) vesicular basalt, characterized by lower values of electrical resis-tivity and sonic velocities, and by higher porosity-permeability; (III) weathered basalt and (IV) clay intervals, which have intermediate characteristics between the first ones. The chemical analysis showed relatively homogeneous molar concentrations of Ca, Mg and total Fe along the vertical profile, without preferential distributions on the recognized facies. The conceptual model identifies the vesicular basalt intervals as the most promising reservoirs for the CO2 storage. The massive basalt acts as a caprock, although the possibility of slow vertical migration due to fractures in the internal flows is assumed. This behavior was endorsed by the results obtained from the numerical groundwater flow model and from the diagnostic plot analysis of the simulated pumping test, indicating that the formation behaves as a leaky confined aquifer. The results presented in this study point out a positive scenario for the use of CCS technologies in SGF. The top vesicular basalts intervals could be used as reservoirs for the CO2 storage and the chemical composition of these intervals could promote mineral carbonation reactions, while the interior massive basalts would act as caprocks, promoting the physical trapping of CO2 and enhancing the storage security and the retention taxes.
Descrição
Palavras-chave
Captura e armazenamento de carbono, Formação Serra Geral, Perfilagem geofísica, Fluorescência de raios-X, Modelagem numérica de fluxo, Análise de curva diagnóstica, Carbon capture and storage, Serra Geral Formation, Well logging, X-ray fluorescence, Numerical flow modeling, Diagnostic plot analysis