A salt-responsive amphoteric viscosifier for high-density solid-free completion fluids with high temperature resistance, strong solubility, and high viscosity enhancement

There is a lack of viscosity enhancers for high-temperature and high-density solid-free completion solutions in high-temperature and high-pressure oil and gas reservoirs. To address the problem of insufficient temperature resistance of biopolymers and poor performance of conventional viscosifiers in high-temperature and high-density solid-free completion fluids, an anti-temperature viscosifiers for high-density solid free completion fluids was synthesized using N,N-dimethylacrylamide(DMAA), diallyldimethylammonium chloride(DMDAAC) and the amphoteric ion [2-(Methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium Hydroxide(SBMA) as the main monomers. FPOD has salt-responsive properties. With the increase of brine concentration, the degree of stretching of FPOD molecular chain increased and formed a network structure through intermolecular forces, which provided a viscosity increasing effect on the solution. FPOD has good temperature resistance. The apparent viscosity of 1 wt% FPOD in 1.75 g/cm 3 CaBr 2 brine was 37 mPa·s, and after aging at 150 °C, the viscosity was still 32.5 mPa·s. The performance of FPOD before and after aging is better than other viscosifiers. FPOD is simple to prepare and has good viscosity enhancement effect in high density solid-free brines. Moreover, FPOD is well-compatible with other treatment agents for completion fluids, and the HTHP filtration loss of the completion fluid system with 2 wt% FPOD added at 150 °C is only 5 mL. FPOD could solve the problem of insufficient high temperature resistance and viscosity increasing performance of viscosifiers in high density brine completion fluids, and provide a new technical approach to drilling high-temperature and high-pressure oil and gas reservoirs.