Influence of reactivity and mineralogical composition on instability due to the disintegration of shales from Paraíba and Ceará States, Brazil

Abstract

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.