This research explores the efficacy of dually modified starch as a fluid loss controlling agent in drilling mud systems, aiming to optimize filtration properties for improved borehole stability and reservoir productivity. Filtrate loss and filter cake thickness (API and HPHT) were examined under varying conditions, focusing on the influence of degree of substitution (DS) of the starch, CMITS concentration, salt concentration, and temperature. The current findings reveal that DS 0.66 starch exhibited the highest reduction in filtrate volume and cake thickness, achieving an 81 decrease at 8 ppb concentration. Regression models accurately predicted filtration properties and were confirmed through additional experiments. Comparison with previous studies underscores the potential of modified starch as a cost-effective alternative for drilling mud additives. Furthermore, the correlation between viscosity and filtration properties was explored, highlighting its impact on improved filtration characteristics. Overall, this research contributes valuable insights into enhancing drilling efficiency and borehole stability, minimizing dependence on costly chemical additives. © 2024 Elsevier Ltd