The Effect of the Polyoxyethylene Ether Group on the Adsorption Capacity of the Adsorption Acidification Retarding Agent on the Carbonate Rock Surface

Acidification is an important procedure to remove the plug and retard the acid–rock reaction to make acid reach deeper formations, which is beneficial for reservoir stimulation. The adsorption-type acidification retarding agent could form an adsorption film on the rock surface to isolate H+, resulting in a lower rate of the acid–rock reaction. In this study, the retarding agent AD-2 was synthesized by free radical polymerization using acrylamide (AM), octadecyl dimethyl allyl ammonium chloride (DMAAC-18), and allyloxypolyethylene glycol (APEG-2400) as raw materials, while AD-1 was synthesized from AM and DMAAC-18. The results of the Fourier transform infrared (FT-IR) spectrum and 1H nuclear magnetic resonance (1H NMR) indicated that the two retarding agents were successfully prepared. The adsorption behavior of AD-1 and AD-2 on the carbonate rock surface matched the Freundlich model and the adsorption capacity of AD-2 was about 3 times that of AD-1 at 70 °C and 9000 mg/L. Meanwhile, the higher the temperature, the greater the adsorption capacity of AD-2, but it was the opposite for AD-1. Furthermore, the introduction of the polyoxyethylene ether group was conducive to enhancing adhesion force and forming a dense adsorption film on the carbonate rock surface, which was evidenced by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The retarding rate of AD-2 and AD-1 was 90.1% and 78.3%, respectively, because the retarding agent AD-2 containing polyoxyethylene ether formed a much denser adsorption film on the rock surface. In addition, the viscosity of 9000 mg/L AD-2 retarding acid solution was as low as 12 mPa·s, compared with that of AD-1 retarding acid solution (42 mPa·s). This research could provide a reference for the design of an adsorption acidification retarding agent with low viscosity in reservoir stimulation.