Synthesis, characterization, and performance of carboxymethyl chitosan with different molecular weight as additive in water-based drilling fluid

摘要

With increasingly intensified energy demand and environmental pressure, it has been of great interest to develop high-performance and environmentally friendly drilling fluid additives, and natural-derived biopolymers are promising candidates. In this work, carboxymethyl chitosan (CM-CS) with different molecular weight, namely high- (CM-HMWCS), medium- (CM-MMWCS1, CM-MMWCS2) and low-molecular-weight (CM-LMWCS) CM-CS, were prepared and the structural factors including molecular weight (MW), degree of deacetylation (DD) and degree of substitution (DS) were determined. The impact of different CM-CS on rheological, filtration and inhibition properties of bentonite-based drilling fluid was evaluated, as well as the bentonite-polymer interactions. The experimental results showed that the lower the MW the higher the DS, while the DD seemed unaffected during reactions. All obtained CM-CS could effectively reduce the yield point of bentonite suspension before and after aging at 135 degrees C and 150 degrees C for 16 h, and the lower MW ones had better yield point-reducing effect and showed little influence on plastic viscosity. Besides, different CM-CS possessed the ability to control filtrate loss as well, which showed a high dependence on MW, the CM-HMWCS had the best filtration reduction performance. Meanwhile, all CM-CS had better inhibition properties to prevent clay swelling and shale disintegration than conventional inhibitors, in which the CM-MMWCS2 with medium MW and relatively higher DS exhibited the best inhibition. Therefore, the obtained different CM-CS was versatile and could perform thinning, filtration reduction and shale inhibition properties. These properties were dominated by their amphoteric molecular structures, and also related to the molecular weight. (C) 2020 Elsevier B.V. All rights reserved.