Desorption of hydrolyzed poly(AM/DMDAAC) from bentonite and its decomposition in saltwater under high temperatures

Under harsh conditions, the desorption of polyampholytes from bentonite (Bent) can affect the performance of drilling fluids. To study the desorption of polyampholyte from bentonite, partially hydrolyzed copolymers of acrylamide and diallyl dimethyl ammonium chloride (HPAD), containing carboxyl groups, quaternary ammonium groups and amide groups was synthesized via free radical copolymerization followed by hydrolyzation. The molecular structure of HPAD was characterized by H NMR and C NMR. The adsorption equilibrium of HPAD on Bent in the presence of 10 wt% NaCl was 106 mg·g . The adsorption-desorption behavior of HPAD on Bent was studied using a high pressure and high temperature (HPHT) filtration apparatus, to obtain the filtrate liquid and filter cakes. The content of HPAD in the filtration and the filter cakes was determined via UV and element analysis, respectively. As the temperature increased, the desorption of HPAD from Bent accelerated owing to molecular thermal motion and thermal degradation of the adsorptive groups. Notably, the decomposition rate of the amide group was more than twice that of the quaternary ammonium group. The critical temperature for HPAD desorption was 135°C, as the decomposition of the adsorptive groups became predominant over intensified molecular thermal motion at high temperatures.