Abstract:

The starch(St) graft sodium acrylate was synthesized by solvent method. It has a high viscosity and a strong shearresistance. The copolymerization was carried out using N,N′-methylene bisacrylamid as the crosslinker and ammonium persulfate as the initiator. Effects such as the amount of monomer, initiator and crosslinking agent, neutralization degree of the acrylic acid(AA), reaction time and temperature on the apparent viscosity were discussed. Through orthogonal experiment, the optimum graft copolymerization condition was obtained as the follows: the mass ratio of starch to acrylic acid is 1∶1.5, the mass fraction of alcohol is 80%, initiator is 1% and crosslinker is 0.6% on the basis of the mass of starch, the reaction time is 2.5 h, the reaction temperature is 55 ℃, and the neutralization degree of the acrylic acid is 70%. The experiments showed that the graft starch paste has an excellent thixotropy. When 14.0 g/L slurry was dissolved in 4% salt water and base fluid, the apparent viscosity of the slurry was 26 mPa·s and the filtration loss was 7.2 mL. When the dosage of slurry was added up to 23.5 g/L in saturated salt water and base fluid, the apparent viscosity of the slurry was 54.5 mPa·s and the filtration loss was 3.1 mL. Additionally, the apparent viscosity and the filtration loss of the slurry were essentially remained the same after the slurry was treated for 16 h at 80 ℃. The experimental results show that the graft starch copolymer has good capacities of increasing viscosity and depressing the filtration loss, and it has excellent properties of agingresistance and saltresistance.

Key words: Graft Starch, Apparent Viscosity, Thixotropy, Drilling Fluid