Preparation and properties of degradable hydrogels as a temporary plugging agent used for acidizing treatments to enhance oil recovery

Abstract

Temporary plugging and diverting acidizing treatments have been proved to be a simple and effective method in stimulating the conventional/unconventional reservoirs. Importantly, the key of this technology lies in the temporary plugging agent (TPA). However, the existing particulate TPAs are of poor acid resistance, poor degradability and involved in complex removal process. Aiming at solving those problems, a novel degradable hydrogel ZDDA was prepared through aqueous radical polymerization in this study. The synthetic conditions of ZDDA were preferentially optimized by orthogonal experiment. The chemical composition, thermal stability and morphology were characterized. The degradable behavior of ZDDA in different media was investigated to understand its degradable mechanism. The results showed that the degradation rate of ZDDA is less than 6% in 2 h in 20% HCl solution. Besides, ZDDA can be completely degraded in solution of 3–20% HCl, 2–10% NaCl, 0.5–2.5% CaCl2, and water, respectively. The scanning electron microscopy (SEM) experiments demonstrated that the degradation process of ZDDA could be described as swelling from the initial water absorption to final degradation into linear polymers. Meanwhile, the degradation mechanism of ZDDA is accompanied by shifting the surface erosion mechanism to the decomposition of the molecular skeleton. Furthermore, the core displacement experiments revealed that the bearing capacity of ZDDA can reach 7.8 MPa. The plugging rate is more than 84%, and the core permeability recovery is more than 97%. Overall, ZDDA has proved to be a promising TPA in acidizing treatments.