A High Temperature Comb and Zwitterionic Polymer Thinner

In deep and ultra-deep well drilling, high density water based drilling fluids are often faced with rheological problems of high viscosity and thickening at elevated temperatures. To solve these problems, a high temperature comb zwitterionic polymer thinner ZT-1 was developed with monomers including sodium p-styrene sulfonate, 2-acrylamido-2-methylpropane sulfonic acid, 2-allyl-2-methylammonium chloride and allyl polyoxyethylene ether. Characterization of the molecular structure of the thinner by IR spectrum shows that the synthesis of the comb zwitterionic polymer is successful. GTA characterization of the thinner demonstrates that ZT-1 has decomposition temperature of 250 ℃. Excellent properties of ZT-1 include high temperature stability and resistance to salt and calcium contamination; ZT-1 functions normally at temperatures up to 240 ℃, and it is resistant to salt contamination to saturation and to calcium contamination to 2% CaCl₂, respectively. A base mud treated with 0.3% ZT-1, after aging at 200 ℃, has its viscosity reduced by 77.7%. High density (2.4 g/cm³) drilling fluids can have their viscosity reduced by 33%, plastic viscosity reduced by 14% and yield point reduced by 67% with ZT-1. The performance of ZT-1 is better than that of the sulfonated tannin, XY-27 and ADS, the latter two being regular linear ionic zwitterionic polymers. This comb zwitterionic polymer thinner has good application in ultra-high density drilling fluids for ultra-high temperature drilling.