Abstract

Calcium halide-based fluids are often used in drilling and completion operations due to their high density, clay inhibition and low solid content. However, there is a lack of thickeners to promote gel strength, which improves the fluid's capacity to carry and suspend cuttings. To solve this problem, the branched polymer (hereafter abbreviated as PAD-B) was prepared by the copolymerization of N,N-dimethylacrylamide (DMAM) and 2-acrylamide-2-methylpropane sulfonic acid (AMPS), using polyethylenimine as a branching agent and cerium ammonium nitrate as the initiator. Compared with linear polymer (PAD-L), PAD-B has better shear strength at the same low viscosity. The experimental results indicated that the increase in shear strength of PAD-B is due to the interactions between branched PAD-B molecules, which lead to the formation of a network structure. The effect of calcium chloride (CaCl