In the acid stimulation of oil wells, slowing down the rate of the reaction between hydrochloric acid and carbonate rocks is a huge challenge, in order to increase the stimulation efficiency. In this work, acid solutions containing Nonylphenol nonionic surfactants of different degrees of ethoxylation were formulated to decrease the reaction rate of H⁺ ions with carbonate rocks. An experimental design plan was executed with a central compound design, showing that the reaction rate decreased up to 350 times (2.356 × 10⁻⁴ ± 0.133 grams of rock per second). It was possible to verify that the presence of the surfactant, in addition to reducing the surface tension and changing the wettability of the medium, also allowed an increase in the viscosity of the solution, which was the main factor for the delay of the reaction. Graphical Abstract