Multi-ring side groups copolymer as an effective filtration control additive for water-based drilling fluids under high temperature and salt contamination

Abstract

The control of filtration loss under high temperature and high salinity conditions has been a challenge in drilling fluid industry. In this study, a novel tetra-copolymer with multi-ring side groups was prepared with free radical polymerization as a filtration control additive. The copolymer consisting of N, N-dimethylacrylamide (DMAM) 2-acrylamide-2-methylpropanesulfonic acid (AMPS), N-acryloylmorpholine (ACMO), and sodium p-styrenesulfonate (SSS) was named DAAS. DAAS was analyzed for chemical structure and thermal stability, respectively. The rheological behavior and filtration performance of bentonite-based mud (BM) with DAAS addition was investigated under various temperatures and salt contamination (NaCl) conditions. The effect of DAAS on the dynamical stability of BM was analyzed by a multi-light scattering method. The relationship of DAAS absorption capacity on bentonite surface with concentration, absorption time, temperature and NaCl content was investigated in detail. The effect of DAAS on the chemical group, electrical properties, particle size of bentonite was studied to illuminate the mechanism. Based on the results, the DAAS maintained thermally stable up to 306 °C. DAAS enabled the BM to resist saturated salt contamination after aging at 200 °C with a filtration loss of 7.6 ml. DAAS with multiple ring groups absorbed on the bentonite by forming of hydrogen bond with bentonite. Even under saturated salt and high temperature conditions, the adsorption capacity of DAAS remained at a good level. The dispersion properties of BM were enhanced through decreasing the zeta potential and changing particle size of bentonite. One compact and low permeability filter cake was formed. The filtration loss of BM was finally controlled to a low volume.