Shale gas buried deep in Weiyuan region in China's Sichuan province, the clay-free and water-base drilling fluid should have high density and high temperature resistant. Most viscosifiers such as XG (xanthan gum) could not meet the fluid requires, so a kind of well water-soluble hydrophobic polymer (SSZN) was synthesized and the clay-free drilling fluid meeting the requirements was laboratory formed.

Using acrylamide, AMPS (2-Acrylamido-2-Methyl Propane Sulfonic Acid), hydrophobic monomer and other acrylamide derivatives as monomers, the viscoelastic polymer was synthesized by the micellar polymerization. To get the optimal reaction conditions, the monomer ratio, initiator amount and reaction temperature were selected. With the electrostatic attraction between positive and negative charges and hydrophobic association between hydrophobic groups, the polymer had great viscoelasticity. With the polymer (SSZN) and other drilling fluid additives, a water-based and clay-free drilling fluid system with high density and high temperature resistant was formed.

First, the structure of the polymer was testified by FT-IR and 1H NMR spectrum. The reticular structure was seen by the TEM (transmission electron microscopy). Then, the viscosity of the polymer was tested by ZNN-D6 Viscometer. The polymer aqueous solution with the concentration of 1.5wt% had high viscosity and great temperature resistance. The apparent viscosity was beyond the range and the apparent viscosity was 0.07 Pa s after hot-rolling for 16 h at 130 °C. The viscoelasticity of the polymer was tested by the HAAKE Rheometer. At last, the water-based and clay-free drilling fluid with the density of 2.36 g/cm3 was formed, and after rolling for 16 hours at 150 °C the fluid had well rheological property.

The viscosifier (SSZN) had great viscoelasticity and high temperature resistant. With it a water-based and clay-free drilling fluid with high density and high temperature resistant was formed, which could meet the shale mining requirements in Sichuan Weiyuan region.

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