Akpan, EU 
ORCID: https://orcid.org/0000-0001-5589-2462, Enyi, GC ORCID: https://orcid.org/0000-0003-1783-2420, Nasr, GG ORCID: https://orcid.org/0000-0001-7913-5802 and Yahaya, AA
2018,
'Stabilizing biopolymers in water-based drilling fluids at high temperature using antioxidants, a formate salt, and polyglycol'
, Journal of Engineering Technology, 7 (2)
, pp. 469-486.
Abstract
Biopolymers degrade in water-based drilling fluids when exposed to high temperatures for some time, thus leading to hole-cleaning problems such as stuck pipe. To stabilise biopolymers in drilling fluids, the mechanisms by which they degrade at elevated temperatures must be understood. The degradation mechanisms of thermally labile biopolymers, therefore, include acid-catalysed hydrolysis and oxidation-reduction (redox) reactions. In this paper, an attempt is, therefore, made to investigate whether the combination of anti-oxidants, formate salt, and polyglycol could stabilise biopolymers in water-based drilling fluids with pH 8 to 10 above 200°C. Novel clay-based drilling fluids were formulated with sodium carbonate, sodium bicarbonate, biopolymers, antioxidants, a formate salt, a defoamer and polyglycol. The rheological properties of the drilling fluid formulations were measured using Model 800 and Model 1100 viscometers before and after hot-rolling dynamically in a roller oven for sixteen hours to condition the fluids. Presented results showed that xanthan gum in bentonite-water suspension remained stable up to 1000°C, and konjac gum in bentonite-water suspension remained stable up to 65°C. Experimental data also indicated that after dynamic aging for 16 hours, the antioxidant, formate salt and polyglycol increased the stability temperatures of the biopolymers - konjac gum and xanthan gum – in water-based drilling fluid formulations above 200°C. The best additives package that increased the stability temperatures of the biopolymers was potassium formate, sodium erythorbate, and 0.7% polyethene glycol. This additive package also maintained the suspension capability of the drilling fluid formulations. These additives can, therefore, be used to stabilise water-based drilling fluids containing biopolymers in the 150-232°C temperature range without using expensive and formation damaging synthetic polymers.
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