Abstract:The rheological properties of self-diverting acid system with erucylamide betaine viscoelastic surfactant as main reagent were studied. By the experiments of steady shear flow, the constitutive equations of fresh and residual acid systems were obtained as follows: σ =0.0893γ0.803 (R2=0.967)and σ =6.30γ0.383(R2=0.983), which were in line with the power-laws equations for non-newtonian fluids. The viscosity of two acid systems reduced rapidly with increasing shear rate. Under shear rate of 100 s-1, the viscosity platform value of fresh acid was about 40 mPa·s, and that of residual acid was about 150 mPa·s at 400 s-1. The thixotropic experiment results of two acid systems showed that at low shear rate, the viscosity on downline of fresh acid system was higher than that on upline, which indicated the composite thixotropy. For residual system, the area of thixotropic loop was small which indicated good recovery of structure after shear. The small oscillation experiment results showed that in fresh acid system, storage modulus (G') was bigger than loss modulus (G''), and the curve of G'—G'' basically exhibited in beeline. However, in residual acid system, G'' was bigger than G', and the curve of G'—G'' was in line with Cole-Cole diagram of Maxwell model at low frequency, which suggested a linear viscoelastic behaviour with a single relaxation time. Whereas, under high frequency, the curve of G'—G'' showed linear trends, indicating a complex viscoelastic behaviour.