Influência dos cátions lítio (Li + ), sódio (Na + ) e potássio (K + ) na reologia de bentonitas brasileiras para uso em fluidos de perfuração base aquosa

Abstract

ResumoOs cátions lítio (Li + ), sódio (Na + ) e potássio (K + ) encontram-se em primeiro lugar no plano de seletividade para a obtenção de bentonitas monocatiônicas a partir das policatiônicas, influenciando de forma específica o comportamento reológico dos fluidos de perfuração base água. O objetivo deste trabalho foi estudar a influência do Li + , Na + e K + na reologia de bentonitas do estado da Paraíba, Brasil, para uso em fluidos de perfuração à base de água. Os novos depósitos de bentonitas brasileiras foram comparados com base nas suas características químicas, físicas, mineralógicas, propriedades reológicas e de filtração. As amostras de bentonitas foram caracterizadas por meio da composição química através do método clássico, capacidade de troca de cátions, análise granulométrica por difração a laser, difração de raios X e análises térmicas. A reologia das dispersões foi estudada e determinadas as viscosidades aparente, viscosidade plástica e limite de escoamento com base nas normas da API e Petrobras, além dos estudos de inchamento em água e filtrado. Os resultados mostraram uma melhora significativa nas propriedades reológicas e de filtração das dispersões após a aditivação com os carbonatos de lítio e de sódio, nessa ordem, havendo presença de tixotropia nas curvas de fluxo das dispersões de argilas estudadas. Palavras-chave: bentonitas, carbonatos alcalinos, fluidos de perfuração. Abstract

Influence of Ca2+ in the rheological properties and filtration of bentonitic clay dispersions in aqueous drilling fluids

“…Table I presents the results of the chemical composition of the polycationic and monocationic (additive) samples A, B, C and D. It was observed that the results obtained presented SiO 2 contents in the range of 47%-51% and 18%-22% Al 2 O 3 , from the tetrahedral and octahedral sheets; 6%-8% Fe 2 O 3 and 2%-3% MgO, resulting from isomorphic substitutions occurring in the octahedral sheet; 3%-4% Na 2 O due to the process of additivation with the carbonate Na 2 CO 3 ; 1%-6% CaO and 0-1% K 2 O, among other oxides, where CaO was significant in samples B and D, confirming the results of XRD (Fig. 1), since different location extraction resulted in different chemical compositions [2,6]. The results presented are typical of the clays of the State of Paraíba [2,[6][7][8].…”

“…Using the mass of the sample (dry clay) used, the mass of sodium carbonate required to add to the clay was calculated [6]. Water was then added so that an ideal humidity of 30%-40% was reached and placed in closed bags during 5 days for curing so that the additive process was effective [2,6]. After the curing period, the rheological and filtration behaviors were studied.…”

“…The cation exchange reactions are selective, with a predominance of empirical data in the current context. Some preference orders are related, such as Li + , Na + , K + , Cs + , Mg 2+ , Ca 2+ , Fe 2+ [2,13]. It is thus observed that calcium clays, because they are not in the foreground of selectivity, lead to unsatisfactory rheological results [2,[13][14][15].…”

“…Some preference orders are related, such as Li + , Na + , K + , Cs + , Mg 2+ , Ca 2+ , Fe 2+ [2,13]. It is thus observed that calcium clays, because they are not in the foreground of selectivity, lead to unsatisfactory rheological results [2,[13][14][15]. Therefore, the existence of numerous limestone deposits is a challenge, requiring more and more studies that point out their characteristics for the most diverse industrial applications.…”

“…Their hexagonal plates carry a negative surface charge due to the isomorphic substitution in Al 3+ metal centers in the layers by lower valence metal ions, such as Fe 2+ and Mg 2+ , and is widely surrounded by exchangeable cations such as Na + , H + , K + and Ca 2+ , balancing the responsible network. In this sense, smectic clays can vary greatly in relation to their physical, chemical and mineralogical composition, where this variation depends on their geological formation, which can greatly compromise their industrial application [1][2][3][4][5].…”