Potential of the base-activated persulfate for polymer-plugging removal in low temperature reservoirs

Abstract

Conventional polymer-plugging removers perform badly in low temperature reservoirs and this has prompted researchers to look for more effective removers. In this work, base-activated sodium persulfate (PDS) was used to degrade polymer-plugging. The performance of the novel remover was first compared with that of conventional removers at 35 °C. Then, the degradation mechanism involved and factors of influence were investigated by carrying out radical scavenger and single-factor experiments, respectively. Finally, corrosion tests were performed and the ability of the new remover to remove plugging in porous media was investigated by carrying out flooding tests. The results show that the PDS/NaOH system is a much more potent remover at temperatures as low as 35 °C (giving a degradation efficiency of 100% compared to 10–70% using conventional removers). Furthermore, the radical scavenger experiments show that HO· is the predominant radical responsible for polymer gel degradation. The degradation efficiency is affected by the concentrations of the PDS and NaOH solutions, the temperature, and also by the salinity of the polymer gel. We also demonstrate that the polymer gel can be completely degraded when its salinity is 30,000 mg/L by optimizing the temperature and concentration of PDS and NaOH. The corrosion rate using PDS/NaOH was found to be 1.085 g m−2 h−1 which satisfies the requirements for entry well fluid. In addition, the static plugging degradation and dynamic plugging removal tests show that PDS/NaOH can degrade the plugging effectively and recover the permeability of the sandpack to over 65%. Our results suggest that the PDS/NaOH system is a highly promising plugging remover for use in low-temperature polymer flooding reservoirs and is a good replacement for the ones conventionally used.