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Amphoteric Polymer as an Anti-calcium Contamination Fluid-Loss Additive in Water-Based Drilling Fluids

Liu, Fan, Jiang, Guancheng, Peng, Shuanglei, He, Yinbo, Wang, Jinxi
Energy & Fuels 2016 v.30 no.9 pp. 7221-7228
acrylamides, additives, bentonite, calcium, calcium chloride, drilling, energy-dispersive X-ray analysis, filtration, petroleum, polymers, shear stress, sodium, temperature, transmission electron microscopy, viscosity
Calcium ion contamination in water-based drilling fluids (WBDs) dramatically increases filtration volume loss and worsens rheological properties, especially in high-temperature bore holes. This study demonstrated two types of acrylamide polymers as anti-calcium contamination fluid-loss additives in WBDs, including an amphoteric polymer (ADD) synthesized by 2-acrylamide-2-methylpropanesulfonic acid (AMPS), acrylamide (AM), and diallyl dimethylammonium chloride (DMDAAC) and an anionic polymer (AD) synthesized by AMPS and AM. In transmission electron microscopy (TEM) of sodium bentonite (Na-BT)-based mud under 11.1% CaCl₂ contamination and 150 °C hot rolling, a typical “star-net” structure was observed between the ADD and Na-BT layers; however, polymer AD could not form such a net structure. Energy-dispersive spectrometry (EDS) analysis of the Na-BT layer indicated that ADD could greatly decrease the amount of Ca²⁺ on Na-BT layers in comparison to AD. Accordingly, in an American Petroleum Institute (API) filtration test and a rheological test of Na-BT-based mud with 11.1% CaCl₂ contamination after 150 °C hot rolling, Na-BT-based mud with 1.5% ADD could maintain an API filtration volume (FLAPI) as low as 9.6 mL, whereas Na-BT-based mud with 1.5% AD maintained a FLAPI of 36 mL. The rheological properties of Na-BT-based mud also showed that ADD could maintain higher viscosity and shear stress than AD, suggesting that amphoteric polymer ADD was suitable for making WBDs more resistant to calcium contamination and high temperature.