Performance Evaluation on a Modified β-Cyclodextrin Crosslinking Acid System

Abstract

Maleic anhydride (MAH) and β-cyclodextrin (β-CD) were chosen to synthetize vinyl β-cyclodextrins monomer (MAH-β-CD) by alcoholysis reaction. A kind of thickener (PAADM) was synthesized with MAH-β-CD, AM, AMPS, and DMDAAC via free radical aqueous polymerization by adjusting the polymerization conditions through orthogonal method. The structure of the obtained quadripolymer was characterized by IR spectroscopy, ¹H NMR, and UV spectrum. Subsequently, its acid-soluble time was 100 min, not 120 min, and the apparent viscosity can be over 36 mPa s at the concentration of 0.8 wt %, which could meet the needs of on-site construction. Besides, the zirconium acetylacetonate was compounded with glutaraldehyde to be crosslinking agent for PAADM acid. When the concentration of hydrochloric acid was 20 wt %, the amount of thickening agent was 0.8 wt %, the crosslinking agent was 0.12 wt % (zirconium acetylacetonate and glutaraldehyde mass ratio of 1: 1), and when the crosslinking temperature was 70°C, the system could even reach 750 mPa s. Further, a series of performance evaluations were made on this crosslinked acid. The results showed crosslinked acid with good temperature resistance, retarding performance and compatibility. The core corrosion method showed that retardation rate could be enhanced to 60%, indicating the retarder performance of the crosslinked acid solution was significantly better than that of the thickening acid and the blank acid. The residual acid after breaking the gel kept a relatively low concentration of 2% at 60°C for 1 h, which could achieve the purpose of effective return of residual acid while the damage to the formation was smaller consequently, indicating great potential applications in petroleum and natural gas industry for unconventional reservoir recovery.