In order to reduce the damage of adsorption and retention of traditional gelled acid in carbonate porous media

and reduce the damage to permeability of dense carbonate rock after stimulation. It is proposed that the quaternary ammonium cationic surfactant can be adsorbed on the rock surface for modification and then show retarding performance. Taking the carbonate rock in Majiagou Formation of Ordos Basin a

s the research object

based on the basic property tests

the adsorption capacity of cationic surfactant with different carbon chain length is determined

and the retarding mechanism of cationic surfactant is proposed by using molecular simulation technology combined with atomic force microscope and wetting angle observation. Then

the retarding performance and formation damage degree of cationic surfactant are studied by dynamic/static retarding performance test and damage evaluation experiment. The research results show that: ① Carbon chain length affects the interfacial adsorption effect by changing the adsorption form of surfactant molecules. C

14

TAC can form a vertical dense adsorption layer on the rock surface with the best wetting modification effect. ② The surface of rock is covered by cationic surfactant with interface adsorption

which can increase its hydrophobicity

prevent H

+

from contacting the rock surface

control the surface reaction rate

and achieve the purpose of retardation. ③ Compared with conventional acids

cation surfactants have good actionic and static slow performance

the kinetic parameters are reduced by 50 %~60 %

reducing the damage to the carbonate orifice throat. It is concluded that the quaternary ammonium salt cationic surfactant has the advantages of low molecular weight and strong interfacial adsorption ability

while maintaining the retarding ability

and effectively reducing the damage of thickened acid to the formation. This study is helpful to understand the rapid performance of the surfactant

improve the slow acid system

and improve the effect of carbonate reservoir reformation. They are all of positive significance.