Hydrophobically associating acid thickener for ultra-deep well acidizing: A ZnCl2-weighted system stable at 200 °C

Global ultra-deep oil and gas resources are abundant and possess tremendous development potential. However, ultra-deep reservoirs are characterized by ultra-high temperatures exceeding 200 °C and extremely high formation fracturing pressures, which pose significant challenges to reservoir stimulation. In this work, a novel hydrophobically associating acid thickener (PCHAP) with a viscosity-average molecular weight of 1.067 × 10 7 was synthesized via aqueous solution polymerization. PCHAP retains over 50% of its viscosity in ultra-high-salinity brine and maintains high phase angle and consistency factor under high shear, demonstrating excellent thickening and fluid-loss control that effectively reduces the acid–rock reaction rate. The weighted thickening acid, formulated with ZnCl 2 as a weighting agent, exhibits good shear resistance, corrosion inhibition, and compatibility at 200 °C, along with a low acid–rock reaction rate and a low H + mass transfer coefficient. The developed system meets the technical requirements for weighted pre-acidification in ultra-high temperature deep reservoirs, and has been successfully applied in an 8,900 m ultra-deep carbonate well in the Tarim Basin. This study provides reliable technical support for the safe and efficient development of ultra-deep oil and gas reservoirs.