Bentonite slurries-zeta potential, yield stress, adsorbed additive and time-dependent behaviour
Bentonite slurries-zeta potential, yield stress, adsorbed additive and time-dependent behaviour
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DOI：
10.1007/s00397-010-0498-x
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发表时间：
2011-01-01
期刊：
影响因子：
2.3
通讯作者：
Lehane, Barry
中科院分区：
文献类型：
--
作者：
Goh, Raymond;Leong, Yee-Kwong;Lehane, Barry
膨润土是钻井泥浆的重要成分。钻井泥浆的时间依赖性和高剪切稀化屈服应力行为对于维持井眼稳定性以及清除钻屑、冷却和清洁钻头碎片至关重要。所制备的 3、5 和 7 wt.% 膨润土浆料表现出时间依赖性行为，其中屈服应力（快速搅拌后测量）随着静置时间而降低。 24小时后达到平衡值。尽管固体浓度较低，但屈服应力已经相对较高，并且在所有 pH 水平下均表现出来。屈服应力在 pH 值为 2 时最大，在 pH 值接近 7 时最小。该屈服应力是由于膨胀粘土颗粒形成凝胶结构所致。然而，添加磷酸盐添加剂如 (PO3)（19 -a 欧元千份）、（P3O10）（5 -a 欧元千份）和 (P2O7)（4 -a 欧元千份）在 pH 值高于 6 时完全分散了粘土浆料。在 pH 值低于 6 时，屈服应力仍然存在，但比纯膨润土浆料的屈服应力小 3 倍。使用磷酸盐添加剂时，完全分散 pH 值下的临界 zeta 电位大小约为 48 mV。然而，对于纯膨润土，浆料在 zeta 电位 > 50 mV 时仍保持絮凝状态。有趣的是，(P2O7)（千分之四欧元）阴离子在降低低 pH 值（类似于 2.0）下的屈服应力方面比其他两种磷酸盐添加剂更有效。
Bentonite clay is a vital ingredient of drilling mud. The time-dependent and high shear thinning yield stress behaviour of drilling mud is essential for maintaining wellbore stability and to remove cuttings, cool and clean the drill bit of debris. As-prepared 3, 5 and 7 wt.% bentonite clay slurries displayed time-dependent behaviour where the yield stress (measured after quick stirring) decreased with time of rest. An equilibrium value is reached after 24 h. Despite the low solids concentration, the yield stress is already relatively high and is displayed at all pH level. The yield stress is maximum at pH 2 and minimum at pH similar to 7. This yield stress is due to the formation of gel structure by the swelling clay particles. However the addition of phosphate additives such as (PO3)(19 -aEuro parts per thousand), (P3O10)(5 -aEuro parts per thousand) and (P2O7)(4 -aEuro parts per thousand) completely dispersed the clay slurries at pH above 6. At pH below 6, yield stress is still present but is 3-folds smaller than that of the pure bentonite slurry. With phosphate additives, the magnitude of the critical zeta potential at the complete dispersion pH is ca 48 mV. However for the pure bentonite, the slurry remained flocculated at zeta potential of > 50 mV in magnitude. Interestingly, (P2O7)(4 -aEuro parts per thousand) anions is more effective than the other two phosphate additives in reducing the yield stress at low pH, similar to 2.0.