Isolated Effect of pH on The Rheological, Filtration, and Lubricity Characteristics of Polymer-Free Bentonite Drilling Fluids

Adeolu Julius Alawode; Adeshina Toheeb Adeleke; Hussein Omeiza Aliu; Abass Akintunde Muhammed

doi:10.29017/scog.v49i2.2058

Authors

Adeolu Julius Alawode Department of Petroleum Engineering, University of Ibadan, Ibadan, Oyo State, Nigeria.
Adeshina Toheeb Adeleke Department of Petroleum Engineering, University of Ibadan, Ibadan, Nigeria https://orcid.org/0009-0005-4337-9027
Hussein Omeiza Aliu Department of Project and Contract Management, AUGJ Services Limited, Bonny Island, Rivers State, Nigeria. https://orcid.org/0000-0002-3268-2144
Abass Akintunde Muhammed Department of Petroleum Engineering, University of Ibadan, Ibadan, Oyo State, Nigeria. https://orcid.org/0009-0006-8229-1703

DOI:

https://doi.org/10.29017/scog.v49i2.2058

Keywords:

alkalinity control, bentonite dispersion, filtration, lubricity, rheology, viscosity

Abstract

Alkalinity is a key control parameter in water-based drilling muds (WBM), yet its intrinsic influence on bentonite systems independent of specialty additives remains poorly resolved. This study examines the effect of pH variation on the rheological, filtration, lubricity, and flow-modeling behavior of bentonite-based WBMs formulated at pH 7.5 (control), 8, 10, and 12 using potassium hydroxide as the pH modifier. All measurements were conducted in accordance with API RP 13B-1 standards. Results show that increasing alkalinity progressively disrupts mud structure, with plastic viscosity and yield point declining by approximately 50–67% between pH 7.5 and 12. Rheological modeling using Bingham Plastic, Power Law, and Herschel–Bulkley formulations confirms this trend, as yield stress parameters and model fidelity deteriorate at elevated pH, particularly at pH 12. Extreme alkalinity also adversely affected filtration behavior, increasing API fluid loss from 22.0 to 77.7 mL and producing thicker, more permeable filter cakes. In contrast, lubricity showed a modest improvement with increasing pH, with the lubricity coefficient decreasing from 0.49 to 0.43. The results highlight a clear performance trade-off, indicating that excessive alkalinity undermines rheological stability and fluid-loss control despite minor gains in lubricity, thereby supporting the use of moderate alkalinity for balanced WBM performance.

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