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Surface chemistry and rheological properties of API bentonite drilling fluid: pH effect, yield stress, zeta potential and ageing behaviour

Authors :
Pek-Ing Au
Yee-Kwong Leong
Ting Chen
Xianhua Liu
Weian Huang
Zhengsong Qiu
Source :
Journal of Petroleum Science and Engineering. 146:561-569
Publication Year :
2016
Publisher :
Elsevier BV, 2016.

Abstract

API bentonite, a key ingredient of drilling muds, displayed a negative zeta potential across the whole pH range of 2.5–12.3. It contained two very rheological active ingredients, sodium montmorillonite or Na+Mt (40.4%) and needle-shape sepiolite (16%). Due to the interplay of these two ingredients, the rheological behaviour displayed by the API bentonite suspensions is quite different to other bentonite suspensions. The gel displayed a very low or no yield stress at low acidic pH and a maximum yield stress at pH 8–12. Magnesium leaching from sepiolite at low pH and its hydrolysis plays a role in affecting the rheological properties at high pH. Yield stress and ageing behaviour was observed in suspensions with at least 3 wt% solids. The Herschel-Bulkley (HB) model described the flow behaviour of these gels. Both the HB yield stress and viscosity at a fixed shear rate of the 7 wt% gel peaked at pH 8.5 and were smallest at pH 5.2. The ageing or structural recovery behaviour is most pronounced at high pH for the most concentrated gels. Both the Leong and Nguyen-Boger ageing models described the structural recovery behaviour well. The recovery of the recently discovered very open honeycomb structure formed by Na+MT gel, after breakdown by shear was invoked to explain the ageing behaviour.

Details

ISSN :
09204105
Volume :
146
Database :
OpenAIRE
Journal :
Journal of Petroleum Science and Engineering
Accession number :
edsair.doi...........c5c3134323f95accab9e4ab40714ab21
Full Text :
https://doi.org/10.1016/j.petrol.2016.07.016