Esterification of Welan Gum With Polymaleic Anhydride‐1‐Octadecene for Enhanced Thermo‐Salt Tolerance in Harsh Oil Reservoirs

Most conventional oilfields in China have entered the dual‐high development stage, and high‐performance polymers are urgently needed in high‐temperature and high‐salinity (HTHS) reservoirs, Herein, welan gum (WG) was ester‐modified with polymaleic anhydride‐1‐octadecene (PMAO) to improve its property under ionic shielding and thermal degradation. Combibed with single‐factor experiments and Box–Behnken RSM, the optimal parameters were PMAO 0.91 wt% (45.6 mg/5 g WG), 87.3°C and 7.5 h. Wherein the viscosity of PMAO‐modified welan gum (PW) reached 256.16 ± 7.89 mPa·s at 85°C/50,000 mg/L NaCl. Structural characterization confirmed the successful grafting of PMAO onto WG, and the hydrophobicity and thermal stability of PW were significantly improved. Rheological and viscoelastic tests showed the HTHS resistance of PW was far superior to WG and partially hydrolyzed polyacrylamide. This was attributed to the synergy of ester bonding and hydrophobic association. This study provides a new strategy for WG modification, and PW is a promising polymer candidate in HTHS reservoirs.