The aim of this work was to evaluate the influence of the chemical structure of carboxymethylcellulose (CMC) on the rheological performance and fluid loss of clay dispersions. The dispersions were prepared with a fixed content of bentonite clay (15 g/350 mL of water) and different concentrations of CMCs (0.5, 1.0, 2.0 g/350 mL of water). After aging for 24 h in ambient and static conditions, the dispersions were tested in a viscometer. Apparent and plastic viscosities, yield point and gel strength were obtained using the viscometer, according to Petrobras' standard (EP-1EP-00011-A). The filtrate volume was determined using the API filter press. The results showed that the addition of long chain, low degree of substitution and lower substitution uniformity of CMC contribute to the flocculation phenomenon. In addition, the different chemical characteristics of CMC only influence fluid loss when the ionic strength of the dispersion is set to any other value than zero.Este trabalho teve como objetivo avaliar a influência da estrutura química da carboximetilcelulose (CMC) no desempenho reológico e de perda de filtrado de dispersões de argila. As dispersões foram preparadas com concentração fixa de argila bentonítica (15 g/350 mL de água) e diferentes concentrações de CMCs (0,5, 1,0, 2,0 g/350 mL de água). Após repouso de 24 h, as dispersões foram testadas e com um viscosímetro foram calculadas as viscosidades aparente e plástica, o limite de escoamento e a força gel segundo norma da Petrobras (EP-1EP-00011-A) e o volume de filtrado foi determinado em filtro-prensa API. Os resultados evidenciaram que a adição de CMC com cadeia longa, baixo grau de substituição e menor uniformidade de substituição contribui para o fenômeno de floculação. Além disso, as diferentes características químicas do CMC somente influenciam a perda de filtrado quando a força iônica da dispersão é diferente de zero. Palavras-chave: carboximetilcelulose, desempenho, argila bentonítica, características químicas.

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This work aimed to correlate the reactivity and mineralogical composition of shales to their disintegration. To accomplish this, five samples of shale from Rio do Peixe Basin and Araripe Basin, located in the Brazilian States of Paraíba and Ceará, respectively, were characterized. A sample of industrialized bentonite clay was used as a reference to provide a comparison. Characterization was performed through cation exchange capacity, particle size analysis, X-ray fluorescence, and X-ray diffraction. Disintegration tests were performed according to the American Petroleum Institute standards in the presence of deionized water, aqueous potassium citrate solution, and drilling fluid. The results suggested that samples presenting no reactive clay mineral content may be unstable and the higher the reactivity of the samples to aqueous fluids does not necessarily imply a higher level of disintegration. This demonstrated that different mechanisms not associated with clay swelling may assume greater or lesser relevance on the instability of a formation.