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Rheological properties of magnesium bentonites and sepiolites at high temperature conditions

Athanasakis Nikolaos

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Summary

Clay minerals and mainly the smectite, the main components of bentonites, due to their crystalline structure and grain size, are able to form viscous suspensions. The rheological behavior of these suspensions, which differs significantly from that of Newtonian fluids, is related to the mineralogical characteristics of the clays. This property is used by the oil industry to produce drilling fluids, which cool and lubricate the cutting edges of the drilling machine and insulate the drilling. Due to the growing energy needs of the planet, hydrocarbon reservoirs have to be approached, which to date have remained unexploited due to their large depths. However, the deep depth causes a rise in temperature due to the friction of the cutting edges with the rock and the increase of the geothermal gradient. For this reason, there is a need to study the rheological properties of these suspensions in such extreme environments, which are poorly understood. In the present research, a study of five samples at the characterization level and at the level of rheological behavior at different temperatures is performed. Note that in order to better understand the mechanisms affecting the behavior of clay minerals, additional procedures are needed, which can be performed in future research. The samples included two sepiolites of Greek and Spanish origin, a stivensite, a hectorite and a saponite. The characterization included chemical and mineral analysis by XRF and XRD methods, respectively. The atomic absorption spectrometry method was also used to determine some cations in the filtrate and the thermogravimetry method to determine the dehydroxylation temperature. The characterization was completed by determining the ion exchange capacity of the samples (CEC). Rheological properties were determined in aqueous slurries of 5 wt.% in solid material, after dynamic aging at temperatures up to 230 oC. The procedures followed and the way they are conducted are proposed by the American Institute of Petroleum (API 13A). They included viscosity measurement on GRACE 3500 viscosimeter and study of filtrate properties, by using a low pressure, low temperature filter press (LTLP). The results showed significant changes in viscosity and other suspension parameters as the temperature increased.

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