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Effects of Organic Salts in the Physico-Chemical Properties of Shales

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Abstract

This paper present a study of changes in physic-chemical properties of preserved shale samples when immersed in organic salt solutions. The changes in the immersion fluid are also discussed. An offshore Brazilian shale was used throughout the study. the lab tests were conducted with three kinds of formate brimes. The obtained results indicated that the samples suffered reductions in water content and increased the ph of rock. Changes were observed in the chemical composition of rock pore fluid and in the cation exchange capacity as a function of preponderant ions in the organic salt solution. This immersion test shows great potential in understanding the interaction between drilling fluids and shales.
... It can alter the clay structure, weakling and destabilizing much more the formation near wellbore. To avoid or reduce these problems, many researchers suggest that the balance of water activity can adjust chemical potential between the drilling fluids and shales (Chenevert, 1970;Hale et al., 1992, Simpson andDearing, 2000;Rabe and Fontoura, 2003), through the addiction of salts to the water phase. ...
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Resumo Este trabalho apresenta os resultados de uma campanha de ensaios laboratoriais para obter a atividade química de folhelhos e do fluido dos poros originados de bacias sedimentares terrestres e marítimas. Os resultados das atividades químicas dos folhelhos estudados variaram de 0,754 a 0,923 e para os fluidos dos poros entre 0,940 a 0,987. Os resultados mostram que a atividade química medida através do equipamento no fluido dos poros pode ser quantificada em seis dias e 10 dias para a amostra de folhelho. O grau de saturação, teor de umidade, tipo e teor de argilominerais expansíveis e hidratáveis, porosidade total e interconectada, salinidade do fluido dos poros e pressões capilares das amostras dos folhelhos afetaram os resultados da atividade química. Abstract This paper presents a campaign of lab tests to obtain the water activity from shales and it's pore fluid originated from offshore and onshore basin. The results of water activity from shales indicate that the values rang from 0.754 to 0.923 and for the pore fluid are between 0.987 and 0.940. The results show that the water activity of interstitial water can be obtained in 6 days and the rock in 10 days using the thermohygrometer used. The degree of saturation, water content, kind and tenor of expansible and hydratable clay mineral, total and interconnected porosity, salinity of interstitial fluid and the capillary pressure of shale samples affected the results of water activity.
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